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<front>
<journal-meta>
<journal-id journal-id-type="publisher-id">Front. Energy Res.</journal-id>
<journal-title>Frontiers in Energy Research</journal-title>
<abbrev-journal-title abbrev-type="pubmed">Front. Energy Res.</abbrev-journal-title>
<issn pub-type="epub">2296-598X</issn>
<publisher>
<publisher-name>Frontiers Media S.A.</publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="publisher-id">1488234</article-id>
<article-id pub-id-type="doi">10.3389/fenrg.2024.1488234</article-id>
<article-categories>
<subj-group subj-group-type="heading">
<subject>Energy Research</subject>
<subj-group>
<subject>Original Research</subject>
</subj-group>
</subj-group>
</article-categories>
<title-group>
<article-title>Battery swapping scheduling for electric vehicles: a non-cooperative game approach</article-title>
<alt-title alt-title-type="left-running-head">Zhang et al.</alt-title>
<alt-title alt-title-type="right-running-head">
<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.3389/fenrg.2024.1488234">10.3389/fenrg.2024.1488234</ext-link>
</alt-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname>Zhang</surname>
<given-names>Yu</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<role content-type="https://credit.niso.org/contributor-roles/writing-original-draft/"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Han</surname>
<given-names>Tao</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<role content-type="https://credit.niso.org/contributor-roles/writing-original-draft/"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname>He</surname>
<given-names>Wei</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<role content-type="https://credit.niso.org/contributor-roles/Writing - review &#x26; editing/"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Xia</surname>
<given-names>Jianhua</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<role content-type="https://credit.niso.org/contributor-roles/Writing - review &#x26; editing/"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Cui</surname>
<given-names>Lichao</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<role content-type="https://credit.niso.org/contributor-roles/Writing - review &#x26; editing/"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Ma</surname>
<given-names>Zuofu</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<role content-type="https://credit.niso.org/contributor-roles/Writing - review &#x26; editing/"/>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Liu</surname>
<given-names>Shiwei</given-names>
</name>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
<xref ref-type="corresp" rid="c001">&#x2a;</xref>
<uri xlink:href="https://loop.frontiersin.org/people/2758758/overview"/>
<role content-type="https://credit.niso.org/contributor-roles/writing-original-draft/"/>
<role content-type="https://credit.niso.org/contributor-roles/Writing - review &#x26; editing/"/>
</contrib>
</contrib-group>
<aff id="aff1">
<sup>1</sup>
<institution>Three Gorges Electric Power Co., Ltd.</institution>, <addr-line>Wuhan</addr-line>, <country>China</country>
</aff>
<aff id="aff2">
<sup>2</sup>
<institution>China Yangtze Power Co., Ltd.</institution>, <addr-line>Beijing</addr-line>, <country>China</country>
</aff>
<aff id="aff3">
<sup>3</sup>
<institution>School of Artificial Intelligence and Automation</institution>, <institution>Huazhong University of Science and Technology</institution>, <addr-line>Wuhan</addr-line>, <country>China</country>
</aff>
<author-notes>
<fn fn-type="edited-by">
<p>
<bold>Edited by:</bold> <ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/1973685/overview">Chao Deng</ext-link>, Nanjing University of Posts and Telecommunications, China</p>
</fn>
<fn fn-type="edited-by">
<p>
<bold>Reviewed by:</bold> <ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/2172225/overview">Kaishun Xiahou</ext-link>, South China University of Technology, China</p>
<p>
<ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/1909941/overview">Runjia Sun</ext-link>, Shandong University, China</p>
<p>
<ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/2231549/overview">Weiji Han</ext-link>, Shanghai Jiao Tong University, China</p>
</fn>
<corresp id="c001">&#x2a;Correspondence: Shiwei Liu, <email>m202373546@hust.edu.cn</email>
</corresp>
</author-notes>
<pub-date pub-type="epub">
<day>02</day>
<month>12</month>
<year>2024</year>
</pub-date>
<pub-date pub-type="collection">
<year>2024</year>
</pub-date>
<volume>12</volume>
<elocation-id>1488234</elocation-id>
<history>
<date date-type="received">
<day>29</day>
<month>08</month>
<year>2024</year>
</date>
<date date-type="accepted">
<day>01</day>
<month>11</month>
<year>2024</year>
</date>
</history>
<permissions>
<copyright-statement>Copyright &#xa9; 2024 Zhang, Han, He, Xia, Cui, Ma and Liu.</copyright-statement>
<copyright-year>2024</copyright-year>
<copyright-holder>Zhang, Han, He, Xia, Cui, Ma and Liu</copyright-holder>
<license xlink:href="http://creativecommons.org/licenses/by/4.0/">
<p>This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.</p>
</license>
</permissions>
<abstract>
<p>In recent years, electric vehicle (EV) battery-swapping technology has rapidly evolved and is expected to become widely prevalent shortly. Therefore, it is crucial to develop efficient battery-swapping scheduling algorithms to optimize the operations of battery-swapping systems. This paper proposes a non-cooperative game approach for the battery-swapping scheduling of EVs. To reduce the waiting time for battery swapping and improve the scheduling efficiency of EVs, a swapping process model inspired by the job-shop scheduling problem is proposed, and the cost function of each EV comprehensively considers the travel time, waiting time, and battery swapping price. To capture the competitive relationship among EVs, a non-cooperative game model for battery swapping scheduling is established considering the finite quantities of batteries and swapping grippers. To find the pure strategy Nash equilibrium, an iterative best response algorithm is developed, satisfying constraints including those couple decisions of different EVs. Case studies demonstrate the fairness and scheduling efficiency of the proposed approach.</p>
</abstract>
<kwd-group>
<kwd>battery swapping</kwd>
<kwd>electric vehicle</kwd>
<kwd>integer programming</kwd>
<kwd>non-cooperative game</kwd>
<kwd>transportation electrification</kwd>
</kwd-group>
<custom-meta-wrap>
<custom-meta>
<meta-name>section-at-acceptance</meta-name>
<meta-value>Smart Grids</meta-value>
</custom-meta>
</custom-meta-wrap>
</article-meta>
</front>
<body>
<sec id="s1">
<title>1 Introduction</title>
<p>In recent years, the rapid growth of electric vehicles (EVs) has been considered an effective method to address environmental and energy crises (<xref ref-type="bibr" rid="B7">Kocer et al., 2022</xref>; <xref ref-type="bibr" rid="B24">Yu et al., 2024</xref>). Replacing internal combustion engine vehicles with EVs can reduce greenhouse gas emissions (<xref ref-type="bibr" rid="B2">Cui et al., 2023</xref>) and significantly improve air quality. As an industry encouraged by the government, EVs have been widely promoted in many cities (<xref ref-type="bibr" rid="B30">Zhao et al., 2024</xref>). In the logistics sector, given that the external costs of logistics are primarily associated with air pollution and noise, many logistics companies have already introduced electric trucks for operations (<xref ref-type="bibr" rid="B5">Jie et al., 2019</xref>). However, the widespread adoption of EVs is limited by-long charging times (<xref ref-type="bibr" rid="B27">Zhang et al., 2017</xref>; <xref ref-type="bibr" rid="B25">Zeng et al., 2023</xref>) as well as the increased peak-to-valley difference of the power grid caused by the simultaneous charging of a large number of EVs (<xref ref-type="bibr" rid="B20">Yong et al., 2023</xref>). To address these issues, battery swapping stations (BSSs) have been developed as a new method to provide energy to EVs. When EVs arrive at a swapping station, they can replace exhausted batteries with fully charged ones in several minutes (<xref ref-type="bibr" rid="B17">Yang et al., 2023</xref>). Moreover, swapping stations can centrally manage batteries that need recharging, thus avoiding adverse impacts on the grid (<xref ref-type="bibr" rid="B6">Ko et al., 2020</xref>).</p>
<p>Because of the immense potential of the battery-swapping model, research in this area has been rapidly expanding in recent years. Studies have focused on various aspects such as pricing and charging strategies (<xref ref-type="bibr" rid="B8">Liang and Zhang, 2018</xref>), operational models of swapping stations (<xref ref-type="bibr" rid="B11">Sarker et al., 2014</xref>), evaluation of the service capacity of a swapping station (<xref ref-type="bibr" rid="B28">Zhang et al., 2018</xref>), swapping demand forecasting (<xref ref-type="bibr" rid="B14">Wang et al., 2023</xref>), and construction planning for swapping stations (<xref ref-type="bibr" rid="B26">Zhang F. et al., 2024</xref>; <xref ref-type="bibr" rid="B29">Zhang Y. et al., 2024</xref>). With the widespread proliferation of EVs and swapping stations, allowing EVs to approach swapping stations without coordination may lead to congestion and queues at some stations while others remain underutilized (<xref ref-type="bibr" rid="B23">You et al., 2020</xref>). Therefore, the battery swapping scheduling for EVs plays a crucial role in enhancing the operational efficiency of swapping stations. Centralized (<xref ref-type="bibr" rid="B21">You et al., 2017a</xref>) and distributed (<xref ref-type="bibr" rid="B22">You et al., 2017b</xref>) swapping scheduling methods for electric vehicles were proposed, taking into account constraints related to EVs and power grid operations. An online station allocation algorithm was developed to reduce costs for EVs and alleviate congestion at swapping stations (<xref ref-type="bibr" rid="B23">You et al., 2020</xref>). Recently, a swapping station recommendation method based on game theory was presented (<xref ref-type="bibr" rid="B9">Ran et al., 2023</xref>).</p>
<p>Existing research on battery swapping scheduling has two main limitations. First, exiting swapping scheduling models ignored the waiting time of EVs caused by a finite number of swapping grippers. A similar issue of waiting time resulting from the occupation of charging equipment was studied in previous works on electric vehicle charging (<xref ref-type="bibr" rid="B4">Guo et al., 2017</xref>; <xref ref-type="bibr" rid="B19">Yang et al., 2018</xref>), where linear expressions of queue length were used to roughly estimate waiting times affected by variable charging times of vehicles. However, in the context of swapping processes, the swapping time is roughly constant, typically about 5 min (<xref ref-type="bibr" rid="B18">Yang et al., 2014</xref>). Furthermore, the approach in (<xref ref-type="bibr" rid="B4">Guo et al., 2017</xref>; <xref ref-type="bibr" rid="B19">Yang et al., 2018</xref>) overlooked the coupled relationship between waiting time and vehicle arrival time, and might thus lead to inaccurate scheduling results.</p>
<p>Second, few studies consider the complex competitive relationships among EVs in the context of swapping scheduling. EVs may belong to different entities, and battery swapping decisions of an EV not only impact its own swapping efficiency and costs but also potentially influence the decisions of others. Consequently, vehicle owners might not comply with centralized scheduling results. So far, only (<xref ref-type="bibr" rid="B9">Ran et al., 2023</xref>) utilized game theory to analyze this issue, where the swapping station with the lowest total cost was recommended for EVs with a pricing function designed to adjust swapping prices. In addition, it is difficult to directly apply game theory-based methods from the related electric vehicle charging scheduling problem (<xref ref-type="bibr" rid="B4">Guo et al., 2017</xref>; <xref ref-type="bibr" rid="B16">Yang et al., 2015</xref>; <xref ref-type="bibr" rid="B1">Chen and Leung, 2019</xref>; <xref ref-type="bibr" rid="B13">Wan et al., 2020</xref>) to battery swapping scheduling, since the availability of batteries was not considered. Therefore, it is necessary to develop a new game theory-based method specifically tailored to address the swapping scheduling problem to enhance overall operational efficiency at swapping stations and improve the swapping experience for vehicle owners.</p>
<p>To overcome the above limitations, this paper proposes a non-cooperative game approach for the battery swapping scheduling of EVs. The main contributions are threefold:<list list-type="simple">
<list-item>
<p>1) To reduce the waiting time for battery swapping and improve the scheduling efficiency of EVs, a swapping process model inspired by the job-shop scheduling problem is proposed, and the cost function of each EV comprehensively considers the travel time, waiting time, and battery swapping price.</p>
</list-item>
<list-item>
<p>2) To capture the competitive relationship among EVs, a non-cooperative game model for battery swapping scheduling is established considering the finite quantities of batteries and swapping grippers.</p>
</list-item>
<list-item>
<p>3) To find the pure strategy Nash equilibrium, an iterative best response algorithm is developed satisfying constraints including those couple decisions of different EVs.</p>
</list-item>
</list>
</p>
<p>The remainder of this paper is organized as follows. <xref ref-type="sec" rid="s2">Section 2</xref> formulates the problem. <xref ref-type="sec" rid="s3">Section 3</xref> develops the solution methodology. <xref ref-type="sec" rid="s4">Section 4</xref> presents the numerical results. Finally, <xref ref-type="sec" rid="s5">Section 5</xref> concludes the study.</p>
</sec>
<sec id="s2">
<title>2 Problem formulation</title>
<p>As illustrated in <xref ref-type="fig" rid="F1">Figure 1</xref>, the battery-swapping system consists of EVs, a cloud platform, and BSSs. The cloud platform collects relevant information from BSSs and EVs, runs the scheduling algorithm, and then distributes the results to all EVs and BSSs.</p>
<fig id="F1" position="float">
<label>FIGURE 1</label>
<caption>
<p>Battery swapping system.</p>
</caption>
<graphic xlink:href="fenrg-12-1488234-g001.tif"/>
</fig>
<sec id="s2-1">
<title>2.1 Operation constraints</title>
<p>This paper focuses on a single scheduling period (<xref ref-type="bibr" rid="B9">Ran et al., 2023</xref>; <xref ref-type="bibr" rid="B4">Guo et al., 2017</xref>). Let <inline-formula id="inf1">
<mml:math id="m1">
<mml:mrow>
<mml:mi mathvariant="double-struck">I</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>,</mml:mo>
<mml:mi>I</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula> denote the set of EVs requesting battery swapping indexed by <italic>i</italic>, and <inline-formula id="inf2">
<mml:math id="m2">
<mml:mrow>
<mml:mi mathvariant="double-struck">K</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>,</mml:mo>
<mml:mi>K</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula> represent the set of BSSs indexed by <italic>k</italic>. Let <inline-formula id="inf3">
<mml:math id="m3">
<mml:mrow>
<mml:mi mathvariant="double-struck">T</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>,</mml:mo>
<mml:mi>T</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula> denote the set of minutes (sufficient) to complete battery swapping actions, indexed by <italic>t</italic>, determined in this scheduling period. The number of minutes <italic>T</italic> should be sufficiently large to ensure that all vehicles can complete the battery-swapping process within the time interval from 0 to <italic>T</italic>. In the worst case, <italic>T</italic> can be calculated as the latest arrival time among all EVs, plus the product of the average swapping time and the number of EVs. The swapping system administrator can also set the value of <italic>T</italic> based on his/her experience. It is assumed that the total number of available batteries is greater than or equal to the number of EVs requesting swapping.<list list-type="simple">
<list-item>
<p>1) Decision variables: For each EV <italic>i</italic>, integer variables <italic>b</italic>
<sub>
<italic>i</italic>
</sub> and <italic>c</italic>
<sub>
<italic>i</italic>
</sub> represent the beginning time and completion time of the battery swapping process, respectively. Binary decision variables, <italic>u</italic>
<sub>
<italic>i,k</italic>
</sub>, represent the assignment relationship between EVs and BSSs: If EV <italic>i</italic> is assigned to BSS <italic>k</italic> for battery swapping, then <italic>u</italic>
<sub>
<italic>i,k</italic>
</sub> &#x3d; 1; otherwise, <italic>u</italic>
<sub>
<italic>i,k</italic>
</sub> &#x3d; 0. The assignment vector of EV <italic>i</italic> is represented as <bold>
<italic>u</italic>
</bold>
<sub>
<italic>i</italic>
</sub> &#x3d; (<italic>u</italic>
<sub>
<italic>i,</italic>1</sub>, <italic>u</italic>
<sub>
<italic>i,</italic>2</sub>, &#x2026; , <italic>u</italic>
<sub>
<italic>i,k</italic>
</sub>
<italic>,</italic> &#x2026; , <italic>u</italic>
<sub>
<italic>i,K</italic>
</sub>). To further capture the status of EV <italic>i</italic> at time <italic>t</italic>, binary decision variables, <italic>x</italic>
<sub>
<italic>i,k,t</italic>
</sub>, are used: If EV <italic>i</italic> is engaged in battery swapping at BSS <italic>k</italic> at time <italic>t</italic>, then <italic>x</italic>
<sub>
<italic>i,k,t</italic>
</sub> &#x3d; 1; otherwise, <italic>x</italic>
<sub>
<italic>i,k,t</italic>
</sub> &#x3d; 0. The swapping matrix of EV <italic>i</italic> is represented as <inline-formula id="inf4">
<mml:math id="m4">
<mml:mrow>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mfenced open="[" close="]" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mrow>
<mml:mi>k</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">K</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>t</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">T</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> In addition, the decision variables of EV <italic>i</italic> are summarized as <inline-formula id="inf5">
<mml:math id="m5">
<mml:mrow>
<mml:msub>
<mml:mi mathvariant="bold-italic">v</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>b</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>c</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi mathvariant="bold-italic">u</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi mathvariant="bold-italic">x</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>.</p>
</list-item>
<list-item>
<p>2) BSS selection constraints: Each EV <italic>i</italic> chooses one BSS for swapping, i.e.,</p>
</list-item>
</list>
<disp-formula id="e1">
<mml:math id="m6">
<mml:mrow>
<mml:mstyle displaystyle="true">
<mml:munder>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>k</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">K</mml:mi>
</mml:mrow>
</mml:munder>
</mml:mstyle>
<mml:msub>
<mml:mi>u</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>&#x2003;</mml:mo>
<mml:mo>&#x2200;</mml:mo>
<mml:mi>i</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">I</mml:mi>
<mml:mo>,</mml:mo>
</mml:mrow>
</mml:math>
<label>(1)</label>
</disp-formula>
<list list-type="simple">
<list-item>
<p>3) Travel distance constraints: The assigned BSS should be within the driving distance of the EV given its initial states of charge (SoC), i.e.,</p>
</list-item>
</list>
<disp-formula id="e2">
<mml:math id="m7">
<mml:mrow>
<mml:msub>
<mml:mi>u</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
<mml:msub>
<mml:mi>s</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2264;</mml:mo>
<mml:mi>&#x3b3;</mml:mi>
<mml:msub>
<mml:mi>q</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mo>&#x2200;</mml:mo>
<mml:mi>i</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">I</mml:mi>
<mml:mo>,</mml:mo>
<mml:mo>&#x2003;</mml:mo>
<mml:mo mathvariant="double-struck">&#x2200;</mml:mo>
<mml:mi>k</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">K</mml:mi>
<mml:mo>,</mml:mo>
</mml:mrow>
</mml:math>
<label>(2)</label>
</disp-formula>where <inline-formula id="inf6">
<mml:math id="m8">
<mml:mrow>
<mml:msub>
<mml:mi>s</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> denotes the distance between EV <italic>i</italic> and BSS <italic>k</italic>, <inline-formula id="inf7">
<mml:math id="m9">
<mml:mrow>
<mml:mi>&#x3b3;</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> denotes the electric energy consumption per kilometer, and <inline-formula id="inf8">
<mml:math id="m10">
<mml:mrow>
<mml:msub>
<mml:mi>q</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> denotes the initial SoC of EV <italic>i</italic>.<list list-type="simple">
<list-item>
<p>4) Swapping process model: Inspired by the processing time model of the job shop scheduling problem (<xref ref-type="bibr" rid="B15">Yan et al., 2021</xref>), the swapping process is modeled as follows. The battery swapping time is roughly constant (typically about 5 min), and the average swapping time is denoted by <inline-formula id="inf9">
<mml:math id="m11">
<mml:mrow>
<mml:mi>&#x3bb;</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>. The swapping process is non-preemptive, meaning that the end time is equal to the start time plus the required swapping time (minus 1), i.e.,</p>
</list-item>
</list>
<disp-formula id="e3">
<mml:math id="m12">
<mml:mrow>
<mml:msub>
<mml:mi>c</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi>b</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mi>&#x3bb;</mml:mi>
<mml:mo>&#x2212;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>&#x2200;</mml:mo>
<mml:mi>i</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">I</mml:mi>
<mml:mo>,</mml:mo>
<mml:mo>&#x2003;</mml:mo>
<mml:mo mathvariant="double-struck">&#x2200;</mml:mo>
<mml:mi>t</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">T</mml:mi>
<mml:mo>,</mml:mo>
</mml:mrow>
</mml:math>
<label>(3)</label>
</disp-formula>
<disp-formula id="e4">
<mml:math id="m13">
<mml:mrow>
<mml:mn>0</mml:mn>
<mml:mo>&#x2264;</mml:mo>
<mml:msub>
<mml:mi>b</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>c</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x2264;</mml:mo>
<mml:mi>T</mml:mi>
<mml:mo>,</mml:mo>
<mml:mo>&#x2003;</mml:mo>
<mml:mo>&#x2200;</mml:mo>
<mml:mi>i</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">I</mml:mi>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
<label>(4)</label>
</disp-formula>
</p>
<p>If EV <italic>i</italic> is assigned to BSS <italic>k</italic>, the time interval [<italic>b</italic>
<sub>
<italic>i</italic>
</sub>, <italic>c</italic>
<sub>
<italic>i</italic>
</sub>] represents the duration when the swapping occurs. According to the definition of binary variables <italic>x</italic>
<sub>
<italic>i,k,t</italic>
</sub>, the following constraint should be satisfied:<disp-formula id="e5">
<mml:math id="m14">
<mml:mrow>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mrow>
<mml:mfenced open="{" close="" separators="|">
<mml:mrow>
<mml:mtable columnalign="left">
<mml:mtr>
<mml:mtd>
<mml:mrow>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>&#x2003;</mml:mo>
<mml:mtext>if&#x2009;</mml:mtext>
<mml:msub>
<mml:mi>b</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x2264;</mml:mo>
<mml:mi>t</mml:mi>
<mml:mo>&#x2264;</mml:mo>
<mml:msub>
<mml:mi>c</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mtext>&#x2009;and&#x2009;</mml:mtext>
<mml:msub>
<mml:mi>u</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
</mml:mrow>
</mml:mtd>
</mml:mtr>
<mml:mtr>
<mml:mtd>
<mml:mrow>
<mml:mn>0</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>&#x2003;</mml:mo>
<mml:mtext>otherwise</mml:mtext>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:mtd>
</mml:mtr>
</mml:mtable>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
<label>(5)</label>
</disp-formula>
</p>
<p>This logical relationship is linearized through the big-M method:<disp-formula id="e6">
<mml:math id="m15">
<mml:mrow>
<mml:mi>t</mml:mi>
<mml:mo>&#x2265;</mml:mo>
<mml:msub>
<mml:mi>b</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x2212;</mml:mo>
<mml:mi>M</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mn>1</mml:mn>
<mml:mo>&#x2212;</mml:mo>
<mml:mstyle displaystyle="true">
<mml:munder>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>k</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">K</mml:mi>
</mml:mrow>
</mml:munder>
</mml:mstyle>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>,</mml:mo>
<mml:mo>&#x2003;</mml:mo>
<mml:mo>&#x2200;</mml:mo>
<mml:mi>i</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">I</mml:mi>
<mml:mo>,</mml:mo>
<mml:mo mathvariant="double-struck">&#x2200;</mml:mo>
<mml:mi>t</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">T</mml:mi>
<mml:mo>,</mml:mo>
</mml:mrow>
</mml:math>
<label>(6)</label>
</disp-formula>
<disp-formula id="e7">
<mml:math id="m16">
<mml:mrow>
<mml:mi>t</mml:mi>
<mml:mo>&#x2264;</mml:mo>
<mml:msub>
<mml:mi>c</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mi>M</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mn>1</mml:mn>
<mml:mo>&#x2212;</mml:mo>
<mml:mstyle displaystyle="true">
<mml:munder>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>k</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">K</mml:mi>
</mml:mrow>
</mml:munder>
</mml:mstyle>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>,</mml:mo>
<mml:mo>&#x2003;</mml:mo>
<mml:mo>&#x2200;</mml:mo>
<mml:mi>i</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">I</mml:mi>
<mml:mo>,</mml:mo>
<mml:mo mathvariant="double-struck">&#x2200;</mml:mo>
<mml:mi>t</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">T</mml:mi>
<mml:mo>,</mml:mo>
</mml:mrow>
</mml:math>
<label>(7)</label>
</disp-formula>
<disp-formula id="e8">
<mml:math id="m17">
<mml:mrow>
<mml:mstyle displaystyle="true">
<mml:munder>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>t</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">T</mml:mi>
</mml:mrow>
</mml:munder>
</mml:mstyle>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi>u</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mi>&#x3bb;</mml:mi>
<mml:mo>,</mml:mo>
<mml:mo>&#x2200;</mml:mo>
<mml:mi>i</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">I</mml:mi>
<mml:mo>,</mml:mo>
<mml:mo>&#x2003;</mml:mo>
<mml:mo mathvariant="double-struck">&#x2200;</mml:mo>
<mml:mi>k</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">K</mml:mi>
<mml:mo>,</mml:mo>
</mml:mrow>
</mml:math>
<label>(8)</label>
</disp-formula>where <italic>M</italic> is a big number.</p>
<p>Based on the distance from EV <italic>i</italic> to BSS <italic>k</italic>, the corresponding arrival time can be calculated and is denoted by <italic>a</italic>
<sub>
<italic>i,k</italic>
</sub>. The start time for the battery swap should not be earlier than this arrival time, i.e.,<disp-formula id="e9">
<mml:math id="m18">
<mml:mrow>
<mml:msub>
<mml:mi>b</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x2265;</mml:mo>
<mml:mstyle displaystyle="true">
<mml:munder>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>k</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">K</mml:mi>
</mml:mrow>
</mml:munder>
</mml:mstyle>
<mml:msub>
<mml:mi>u</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mo>&#x2003;</mml:mo>
<mml:mo>&#x2200;</mml:mo>
<mml:mi>i</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">I</mml:mi>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
<label>(9)</label>
</disp-formula>
<list list-type="simple">
<list-item>
<p>5) Capacity constraints: Each BSS <italic>k</italic> has a finite number of swapping grippers (typically 1 or 2), denoted by <inline-formula id="inf10">
<mml:math id="m19">
<mml:mrow>
<mml:msubsup>
<mml:mi>n</mml:mi>
<mml:mi>k</mml:mi>
<mml:mi>G</mml:mi>
</mml:msubsup>
</mml:mrow>
</mml:math>
</inline-formula>, constraining the maximum number of swaps that can be conducted simultaneously at that BSS, i.e.,</p>
</list-item>
</list>
<disp-formula id="e10">
<mml:math id="m20">
<mml:mrow>
<mml:mstyle displaystyle="true">
<mml:munder>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">I</mml:mi>
</mml:mrow>
</mml:munder>
</mml:mstyle>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2264;</mml:mo>
<mml:msubsup>
<mml:mi>n</mml:mi>
<mml:mi>k</mml:mi>
<mml:mi>G</mml:mi>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:mo>&#x2003;</mml:mo>
<mml:mo>&#x2200;</mml:mo>
<mml:mi>k</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">K</mml:mi>
<mml:mo>,</mml:mo>
<mml:mo>&#x2003;</mml:mo>
<mml:mo mathvariant="double-struck">&#x2200;</mml:mo>
<mml:mi>t</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">T</mml:mi>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
<label>(10)</label>
</disp-formula>
</p>
<p>Each BSS <italic>k</italic>, has a finite number of batteries available for swaps, denoted by <inline-formula id="inf11">
<mml:math id="m21">
<mml:mrow>
<mml:msubsup>
<mml:mi>n</mml:mi>
<mml:mi>k</mml:mi>
<mml:mi>B</mml:mi>
</mml:msubsup>
</mml:mrow>
</mml:math>
</inline-formula>, representing the maximum number of swapping services that BSS can support for the scheduling period, i.e.,<disp-formula id="e11">
<mml:math id="m22">
<mml:mrow>
<mml:mstyle displaystyle="true">
<mml:munder>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">I</mml:mi>
</mml:mrow>
</mml:munder>
</mml:mstyle>
<mml:msub>
<mml:mi>u</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2264;</mml:mo>
<mml:msubsup>
<mml:mi>n</mml:mi>
<mml:mi>k</mml:mi>
<mml:mi>B</mml:mi>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:mo>&#x2003;</mml:mo>
<mml:mo>&#x2200;</mml:mo>
<mml:mi>k</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">K</mml:mi>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
<label>(11)</label>
</disp-formula>
</p>
</sec>
<sec id="s2-2">
<title>2.2 Game model</title>
<p>It is assumed that each EV acts selfishly, aiming to minimize its own cost. It is evident from <xref ref-type="disp-formula" rid="e10">Equations 10</xref>, <xref ref-type="disp-formula" rid="e11">11</xref> that the BSS selection strategies of individual EVs are interdependent. Therefore, the cost for each EV is not only determined by its own decisions but also influenced by the decisions of others. To describe the strategic interactions among EVs, a non-cooperative game model is proposed to ensure fairness in BSS matching. This game <italic>Q</italic> is defined as follows:<disp-formula id="e12">
<mml:math id="m23">
<mml:mrow>
<mml:mi>Q</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:mi mathvariant="double-struck">I</mml:mi>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">I</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mo>&#x220f;</mml:mo>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">I</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
<label>(12)</label>
</disp-formula>
<list list-type="simple">
<list-item>
<p>&#x2022; Player set <inline-formula id="inf12">
<mml:math id="m24">
<mml:mrow>
<mml:mi mathvariant="double-struck">I</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>: The EVs that request for battery swapping.</p>
</list-item>
<list-item>
<p>&#x2022; Strategy set <inline-formula id="inf13">
<mml:math id="m25">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>: The nonempty, compact, and discrete set of feasible decisions for each EV <italic>i.</italic>
</p>
</list-item>
<list-item>
<p>&#x2022; Cost function <inline-formula id="inf14">
<mml:math id="m26">
<mml:mrow>
<mml:msub>
<mml:mo>&#x220f;</mml:mo>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>: For each EV <italic>i</italic>, the cost is a weighted sum of the swapping start time and the battery swapping price.</p>
</list-item>
</list>
<disp-formula id="e13">
<mml:math id="m27">
<mml:mrow>
<mml:msub>
<mml:mo>&#x220f;</mml:mo>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi mathvariant="bold-italic">v</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi mathvariant="bold-italic">v</mml:mi>
<mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mi>i</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi>f</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>&#x3b1;</mml:mi>
<mml:msub>
<mml:mi>b</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mstyle displaystyle="true">
<mml:munder>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>k</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">K</mml:mi>
</mml:mrow>
</mml:munder>
</mml:mstyle>
<mml:msub>
<mml:mi>p</mml:mi>
<mml:mi>k</mml:mi>
</mml:msub>
<mml:msub>
<mml:mi>u</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
<label>(13)</label>
</disp-formula>where <bold>
<italic>v</italic>
</bold>
<sub>
<italic>-i</italic>
</sub> &#x3d; (<bold>
<italic>v</italic>
</bold> <sub>
<italic>1</italic>
</sub>, &#x2026; , <bold>
<italic>v</italic>
</bold> <sub>
<italic>i-1</italic>
</sub>, <bold>
<italic>v</italic>
</bold> <sub>
<italic>i&#x2b;1</italic>
</sub>, &#x2026; , <bold>
<italic>v</italic>
</bold> <sub>
<italic>I</italic>
</sub>) is the strategies of all EVs except for that of <italic>i</italic>, <inline-formula id="inf15">
<mml:math id="m28">
<mml:mrow>
<mml:mi>&#x3b1;</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> is a coefficient to convert time into cost, and <italic>p</italic>
<sub>
<italic>k</italic>
</sub> denotes the swapping price at BSS <italic>k</italic>. According to <xref ref-type="disp-formula" rid="e3">Equation 3</xref>, considering the swapping start time <italic>b</italic>
<sub>
<italic>i</italic>
</sub> in <xref ref-type="disp-formula" rid="e13">Equation 13</xref> is equivalent to considering the swapping end time <italic>c</italic>
<sub>
<italic>i</italic>
</sub>. Moreover, the travel time (counted in the arrival time <italic>a</italic>
<sub>
<italic>i,k</italic>
</sub>) and waiting time for battery swapping are considered in <italic>b</italic>
<sub>
<italic>i</italic>
</sub> based on the swapping process model <xref ref-type="disp-formula" rid="e3">Equations 3</xref>&#x2013;<xref ref-type="disp-formula" rid="e9">9</xref>.</p>
<p>
<statement content-type="definition" id="Definition_1">
<label>Definition 1</label>
<p>Consider the game <italic>Q</italic>, a vector <inline-formula id="inf16">
<mml:math id="m29">
<mml:mrow>
<mml:mi mathvariant="bold-italic">v</mml:mi>
<mml:mo>&#x2a;</mml:mo>
<mml:mo>&#x3d;</mml:mo>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi mathvariant="bold-italic">v</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mspace width="-0.2em"/>
<mml:mo>&#x2a;</mml:mo>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi mathvariant="bold-italic">v</mml:mi>
<mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mi>i</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mspace width="-0.5em"/>
<mml:mo>&#x2a;</mml:mo>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2208;</mml:mo>
<mml:mi>V</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> is called a generalized Nash equilibrium if no player can reduce its cost by unilaterally changing his decisions (<xref ref-type="bibr" rid="B3">Facchinei and Kanzow, 2010</xref>), i.e., <inline-formula id="inf17">
<mml:math id="m30">
<mml:mrow>
<mml:msub>
<mml:mo>&#x220f;</mml:mo>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi mathvariant="bold-italic">v</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mspace width="-0.2em"/>
<mml:mo>&#x2a;</mml:mo>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi mathvariant="bold-italic">v</mml:mi>
<mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mi>i</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mspace width="-0.7em"/>
<mml:mo>&#x2a;</mml:mo>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2264;</mml:mo>
<mml:msub>
<mml:mo>&#x220f;</mml:mo>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi mathvariant="bold-italic">v</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi mathvariant="bold-italic">v</mml:mi>
<mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mi>i</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mspace width="-0.7em"/>
<mml:mo>&#x2a;</mml:mo>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>,</mml:mo>
<mml:mo>&#x2200;</mml:mo>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi mathvariant="bold-italic">v</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi mathvariant="bold-italic">v</mml:mi>
<mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mi>i</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mspace width="-0.7em"/>
<mml:mo>&#x2a;</mml:mo>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2208;</mml:mo>
<mml:mi>V</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> holds for all <inline-formula id="inf18">
<mml:math id="m31">
<mml:mrow>
<mml:mo>&#x2200;</mml:mo>
<mml:mi>i</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">I</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>.</p>
<p>The existence of the Nash equilibrium in game <italic>Q</italic> is discussed in Theorem 1.</p>
</statement>
</p>
<p>
<statement content-type="theorem" id="Theorem_1">
<label>Theorem 1</label>
<p>For the battery swapping scheduling game <inline-formula id="inf19">
<mml:math id="m32">
<mml:mrow>
<mml:mi>Q</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:mi mathvariant="double-struck">I</mml:mi>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">I</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mo>&#x220f;</mml:mo>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">I</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>, the pure strategy Nash equilibrium always exists.</p>
<p>Similar to the proof of Theorem 1 in (<xref ref-type="bibr" rid="B9">Ran et al., 2023</xref>), Theorem 1 here can be proven based on Theorem 3.1 in (<xref ref-type="bibr" rid="B12">Tian 2015</xref>).</p>
</statement>
</p>
</sec>
</sec>
<sec id="s3">
<title>3 Solution methodology</title>
<p>To find the pure strategy Nash equilibrium, this section presents a best response algorithm that extends a Jacobi-type algorithm (<xref ref-type="bibr" rid="B10">Sagratella, 2016</xref>) to suit for the generalized Nash equilibrium game <italic>Q</italic>.</p>
<p>The difficulty is to preserve the satisfaction of constraints <xref ref-type="disp-formula" rid="e1">Equations 1</xref>&#x2013;<xref ref-type="disp-formula" rid="e4">4</xref> and <xref ref-type="disp-formula" rid="e6">Equations 6</xref>&#x2013;<xref ref-type="disp-formula" rid="e11">11</xref> during the iterative solution process, especially constraints <xref ref-type="disp-formula" rid="e10">Equations 10</xref>, <xref ref-type="disp-formula" rid="e11">11</xref> that couple different EVs. When updating the decisions of EV <italic>i</italic>, the original Jacobi-type method that fixes the strategies of all EVs except for EV <italic>i</italic> cannot be directly applied. To overcome this difficulty, our idea is that decisions of EVs arriving before <italic>i</italic> should still be kept unchanged, while those of EVs arriving after <italic>i</italic> should be adjusted properly.</p>
<p>Let <inline-formula id="inf20">
<mml:math id="m33">
<mml:mrow>
<mml:msub>
<mml:mi mathvariant="double-struck">J</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo mathvariant="double-struck">&#x2286;</mml:mo>
<mml:mi mathvariant="double-struck">I</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> represent the set of EVs that arrived before it, when EV <italic>i</italic> is updating its decisions. Constraints <xref ref-type="disp-formula" rid="e10">Equation 10</xref> become <xref ref-type="disp-formula" rid="e14">Equation 14</xref>,<disp-formula id="e14">
<mml:math id="m34">
<mml:mrow>
<mml:mstyle displaystyle="true">
<mml:munder>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x2208;</mml:mo>
<mml:msub>
<mml:mi mathvariant="double-struck">J</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:munder>
</mml:mstyle>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2264;</mml:mo>
<mml:msubsup>
<mml:mi>n</mml:mi>
<mml:mi>k</mml:mi>
<mml:mi>G</mml:mi>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:mo>&#x2200;</mml:mo>
<mml:mi>k</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">K</mml:mi>
<mml:mo>,</mml:mo>
<mml:mo mathvariant="double-struck">&#x2200;</mml:mo>
<mml:mi>t</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">T</mml:mi>
<mml:mo>,</mml:mo>
</mml:mrow>
</mml:math>
<label>(14)</label>
</disp-formula>where <inline-formula id="inf21">
<mml:math id="m35">
<mml:mrow>
<mml:mstyle displaystyle="true">
<mml:munder>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x2208;</mml:mo>
<mml:msub>
<mml:mi mathvariant="double-struck">J</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:munder>
</mml:mstyle>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> is fixed as input data, while <inline-formula id="inf22">
<mml:math id="m36">
<mml:mrow>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> are decision variables.</p>
<p>Similarly, <xref ref-type="disp-formula" rid="e11">Equation 11</xref> becomes <xref ref-type="disp-formula" rid="e15">Equation 15</xref>,<disp-formula id="e15">
<mml:math id="m37">
<mml:mrow>
<mml:mstyle displaystyle="true">
<mml:munder>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x2208;</mml:mo>
<mml:msub>
<mml:mi mathvariant="double-struck">J</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:munder>
</mml:mstyle>
<mml:msub>
<mml:mi>u</mml:mi>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:msub>
<mml:mi>u</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2264;</mml:mo>
<mml:msubsup>
<mml:mi>n</mml:mi>
<mml:mi>k</mml:mi>
<mml:mi>B</mml:mi>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:mo>&#x2003;</mml:mo>
<mml:mo>&#x2200;</mml:mo>
<mml:mi>k</mml:mi>
<mml:mo mathvariant="double-struck">&#x2208;</mml:mo>
<mml:mi mathvariant="double-struck">K</mml:mi>
<mml:mo>,</mml:mo>
</mml:mrow>
</mml:math>
<label>(15)</label>
</disp-formula>where <inline-formula id="inf23">
<mml:math id="m38">
<mml:mrow>
<mml:mstyle displaystyle="true">
<mml:munder>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x2208;</mml:mo>
<mml:msub>
<mml:mi mathvariant="double-struck">J</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:munder>
</mml:mstyle>
<mml:msub>
<mml:mi>u</mml:mi>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> is fixed as input data, while <inline-formula id="inf24">
<mml:math id="m39">
<mml:mrow>
<mml:msub>
<mml:mi>u</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> are decision variables.</p>
<p>For EV <italic>i</italic>, its response at an iteration is obtained by solving problem <italic>P</italic>
<sub>
<italic>i</italic>
</sub> as follows:<disp-formula id="e16">
<mml:math id="m40">
<mml:mrow>
<mml:mfenced open="{" close="" separators="|">
<mml:mrow>
<mml:mtable columnalign="left">
<mml:mtr>
<mml:mtd>
<mml:mrow>
<mml:munder>
<mml:mi>min</mml:mi>
<mml:mrow>
<mml:msub>
<mml:mi>u</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>k</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>b</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
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<label>(16)</label>
</disp-formula>
</p>
<p>EV <italic>i</italic> selects its target BSS by solving problem <italic>P</italic>
<sub>
<italic>i</italic>
</sub> (<xref ref-type="disp-formula" rid="e16">Equation 16</xref>) in order to minimize its cost iteratively in <xref ref-type="statement" rid="Algorithm_1">Algorithm 1</xref>. EVs that were originally scheduled to arrive after EV <italic>i</italic> may need to adjust their schedules to reflect shifts in their timings in line 7. If EV <italic>i</italic> was scheduled to BSS <italic>k</italic>
<sub>1</sub> (in the previous iteration) and is updated to BSS <italic>k</italic>
<sub>2</sub>, EVs that would arrive at <italic>k</italic>
<sub>1</sub> will be moved forward in time, while those that would arrive at <italic>k</italic>
<sub>2</sub> will be moved backward. As illustrated in <xref ref-type="fig" rid="F2">Figure 2</xref>, if EV 3 was originally scheduled to BSS <italic>k</italic>
<sub>1</sub> in iteration <italic>m</italic>-1 and is then updated to BSS <italic>k</italic>
<sub>2</sub> (in line 5) in iteration <italic>m</italic>, the schedules of EVs 4, 6 and 7 will be adjusted. EV 4 will be moved forward in the queue at BSS <italic>k</italic>
<sub>1</sub>, while EVs 6 and 7, will be moved backward in the queue at BSS <italic>k</italic>
<sub>2</sub>. The algorithm iterates until no EV deviates from its decisions, i.e., a Nash equilibrium has been found.</p>
<fig id="F2" position="float">
<label>FIGURE 2</label>
<caption>
<p>Illustration of EV schedule update in an iteration.</p>
</caption>
<graphic xlink:href="fenrg-12-1488234-g002.tif"/>
</fig>
<p>
<statement content-type="algorithm" id="Algorithm_1">
<label>Algorithm 1</label>
<p>Extended Jacobi-type method.<list list-type="simple">
<list-item>
<p>
<bold>Input:</bold> Initial SoC, distance to BSS, arrival time at the BSS, swapping price;</p>
</list-item>
<list-item>
<p>
<bold>Output:</bold> Scheduling results <bold>
<italic>v</italic>
</bold>
</p>
</list-item>
<list-item>
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</mml:mrow>
</mml:math>
</inline-formula> and set <italic>m</italic>: &#x3d; 1, <italic>i</italic>: &#x3d; 1;</p>
</list-item>
<list-item>
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</mml:math>
</inline-formula> is not a solution of the Nash equilibrium <bold>do</bold>
</p>
</list-item>
<list-item>
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</p>
</list-item>
<list-item>
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</inline-formula>;</p>
</list-item>
<list-item>
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</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula> by solving <italic>P</italic>
<sub>
<italic>i</italic>
</sub> (<xref ref-type="disp-formula" rid="e16">Equation 16</xref>);</p>
</list-item>
<list-item>
<p>6:&#x2003;&#x2003;<bold>for</bold> <inline-formula id="inf30">
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</p>
</list-item>
<list-item>
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</list-item>
<list-item>
<p>8:&#x2003;&#x2003;<bold>end</bold>
</p>
</list-item>
<list-item>
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</list-item>
<list-item>
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</p>
</list-item>
<list-item>
<p>12:&#x2003;&#x2003;<bold>end if</bold>
</p>
</list-item>
<list-item>
<p>13:&#x2003;<bold>end</bold>
</p>
</list-item>
</list>
</p>
</statement>
</p>
</sec>
<sec id="s4">
<title>4 Case studies</title>
<p>The proposed battery-swapping scheduling approach is tested in two cases. In Case 1, a smaller size example is tested to demonstrate the fairness and reduced waiting time of our approach. In Case 2, a larger size example is tested to demonstrate the advantages of our approach on the swapping success rate and average cost compared with the shortest arrival time approach. Both cases demonstrate the computational efficiency of the proposed algorithm.</p>
<p>Testing is conducted on a system with an Intel Core i5-13500H CPU, 32 GB of RAM, using Python 3.11 in PyCharm and Gurobi 10.0.1.</p>
<sec id="s4-1">
<title>4.1 Case 1</title>
<p>In this example, we consider an area with 3 BSSs and 10 EVs requesting battery swapping. Each EV&#x2019;s location and initial SoC are generated randomly, with an average driving speed of 24 km/h. All batteries are of the same specification, allowing a battery-swapped EV to travel up to 230 km. The swapping prices and the number of batteries at each BSS are also generated randomly. Input data of EVs and BSSs are presented in <xref ref-type="table" rid="T1">Tables 1</xref>, <xref ref-type="table" rid="T2">2</xref>, respectively. The number of minutes <italic>T</italic> is set to 70.</p>
<table-wrap id="T1" position="float">
<label>TABLE 1</label>
<caption>
<p>Initial SOCs of EVs in case 1.</p>
</caption>
<table>
<thead valign="top">
<tr>
<th align="center">EV</th>
<th align="center">Initial SoC (%)</th>
<th align="center">EV</th>
<th align="center">Initial SoC (%)</th>
</tr>
</thead>
<tbody valign="top">
<tr>
<td align="center">1</td>
<td align="center">32</td>
<td align="center">6</td>
<td align="center">34</td>
</tr>
<tr>
<td align="center">2</td>
<td align="center">34</td>
<td align="center">7</td>
<td align="center">35</td>
</tr>
<tr>
<td align="center">3</td>
<td align="center">32</td>
<td align="center">8</td>
<td align="center">36</td>
</tr>
<tr>
<td align="center">4</td>
<td align="center">39</td>
<td align="center">9</td>
<td align="center">37</td>
</tr>
<tr>
<td align="center">5</td>
<td align="center">31</td>
<td align="center">10</td>
<td align="center">37</td>
</tr>
</tbody>
</table>
</table-wrap>
<table-wrap id="T2" position="float">
<label>TABLE 2</label>
<caption>
<p>Input data of BSSs in Case 1.</p>
</caption>
<table>
<thead valign="top">
<tr>
<th align="center">BSS</th>
<th align="center">Swapping price ($)</th>
<th align="center">Number of batteries</th>
</tr>
</thead>
<tbody valign="top">
<tr>
<td align="center">A</td>
<td align="center">49</td>
<td align="center">10</td>
</tr>
<tr>
<td align="center">B</td>
<td align="center">21</td>
<td align="center">6</td>
</tr>
<tr>
<td align="center">C</td>
<td align="center">42</td>
<td align="center">8</td>
</tr>
</tbody>
</table>
</table-wrap>
<p>
<xref ref-type="fig" rid="F3">Figure 3</xref> illustrates the results using a centralized optimization approach that minimizes the total cost of all EVs. In the scheduling results, two EVs highlighted in the green box have tendencies to change their target BSSs. EV 6 prefers to switch its target from BSS B to BSS C, reducing its cost from $54.4 to $49.8, and EV 9 prefers to switch from BSS C to BSS B, lowering its cost from $63.4 to $48.6. This indicates that the centralized optimization method lacks fairness.</p>
<fig id="F3" position="float">
<label>FIGURE 3</label>
<caption>
<p>Scheduling results of centralized optimization.</p>
</caption>
<graphic xlink:href="fenrg-12-1488234-g003.tif"/>
</fig>
<p>
<xref ref-type="fig" rid="F4">Figure 4</xref> displays the results using the proposed non-cooperative game approach. The results compose a schedule where no EV can reduce its cost by unilaterally changing its decisions, i.e., a Nash equilibrium.</p>
<fig id="F4" position="float">
<label>FIGURE 4</label>
<caption>
<p>Scheduling results of our approach in Case 1.</p>
</caption>
<graphic xlink:href="fenrg-12-1488234-g004.tif"/>
</fig>
<p>To demonstrate <xref ref-type="statement" rid="Algorithm_1">Algorithm 1</xref>&#x2019;s performance, iteration results are illustrated in <xref ref-type="fig" rid="F5">Figure 5</xref>. After 15 iterations, each EV&#x2019;s cost becomes a stable value (and then examined in the last 9 iterations), confirming that the algorithm successfully converges to a pure strategy Nash equilibrium. The solution time of 24 iterations is 1.01 s.</p>
<fig id="F5" position="float">
<label>FIGURE 5</label>
<caption>
<p>Total costs of EVs over iterations in Case 1.</p>
</caption>
<graphic xlink:href="fenrg-12-1488234-g005.tif"/>
</fig>
<p>To demonstrate the benefits of our swapping process model, the following battery swapping waiting time is calculated from the scheduling results, according to <xref ref-type="disp-formula" rid="e17">Equation 17</xref>
<disp-formula id="e17">
<mml:math id="m52">
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<mml:mi>w</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
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<mml:msub>
<mml:mi>b</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x2212;</mml:mo>
<mml:mstyle displaystyle="true">
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</mml:mrow>
</mml:munder>
</mml:mstyle>
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<mml:mrow>
<mml:mi>i</mml:mi>
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</mml:mrow>
</mml:msub>
<mml:msub>
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</mml:mrow>
</mml:math>
<label>(17)</label>
</disp-formula>
</p>
<p>For comparison purposes, our non-cooperative game approach is also tested without considering the waiting time, i.e., the swapping process model is omitted and the swapping start time in <xref ref-type="disp-formula" rid="e13">Equation 13</xref> is substituted by the arrival time. The average waiting times of all EVs with and without considering the waiting time are compared in <xref ref-type="table" rid="T3">Table 3</xref>. The results demonstrate that modeling the waiting time in the scheduling formulation can significantly reduce the average waiting time.</p>
<table-wrap id="T3" position="float">
<label>TABLE 3</label>
<caption>
<p>Comparison of average waiting times between two models.</p>
</caption>
<table>
<thead valign="top">
<tr>
<th align="center">Model</th>
<th align="center">Waiting time (min)</th>
</tr>
</thead>
<tbody valign="top">
<tr>
<td align="center">Without considering waiting time</td>
<td align="center">14.2</td>
</tr>
<tr>
<td align="center">With considering waiting time</td>
<td align="center">4.8</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s4-2">
<title>4.2 Case 2</title>
<p>In Case 2, we increase the number of BSSs to 5 and the number of EVs to 30. Input data of EVs and BSSs are presented in <xref ref-type="table" rid="T4">Tables 4</xref>, <xref ref-type="table" rid="T5">5</xref>, respectively. The number of minutes <italic>T</italic> is set to 100.</p>
<table-wrap id="T4" position="float">
<label>TABLE 4</label>
<caption>
<p>Initial SOCs of EVs in case 2.</p>
</caption>
<table>
<thead valign="top">
<tr>
<th align="center">EV</th>
<th align="center">Initial SoC (%)</th>
<th align="center">EV</th>
<th align="center">Initial SoC (%)</th>
</tr>
</thead>
<tbody valign="top">
<tr>
<td align="center">1</td>
<td align="center">32</td>
<td align="center">16</td>
<td align="center">34</td>
</tr>
<tr>
<td align="center">2</td>
<td align="center">30</td>
<td align="center">17</td>
<td align="center">31</td>
</tr>
<tr>
<td align="center">3</td>
<td align="center">30</td>
<td align="center">18</td>
<td align="center">38</td>
</tr>
<tr>
<td align="center">4</td>
<td align="center">39</td>
<td align="center">19</td>
<td align="center">30</td>
</tr>
<tr>
<td align="center">5</td>
<td align="center">30</td>
<td align="center">20</td>
<td align="center">39</td>
</tr>
<tr>
<td align="center">6</td>
<td align="center">35</td>
<td align="center">21</td>
<td align="center">38</td>
</tr>
<tr>
<td align="center">7</td>
<td align="center">38</td>
<td align="center">22</td>
<td align="center">36</td>
</tr>
<tr>
<td align="center">8</td>
<td align="center">38</td>
<td align="center">23</td>
<td align="center">31</td>
</tr>
<tr>
<td align="center">9</td>
<td align="center">39</td>
<td align="center">24</td>
<td align="center">32</td>
</tr>
<tr>
<td align="center">10</td>
<td align="center">31</td>
<td align="center">25</td>
<td align="center">30</td>
</tr>
<tr>
<td align="center">11</td>
<td align="center">38</td>
<td align="center">26</td>
<td align="center">30</td>
</tr>
<tr>
<td align="center">12</td>
<td align="center">37</td>
<td align="center">27</td>
<td align="center">32</td>
</tr>
<tr>
<td align="center">13</td>
<td align="center">33</td>
<td align="center">28</td>
<td align="center">38</td>
</tr>
<tr>
<td align="center">14</td>
<td align="center">30</td>
<td align="center">29</td>
<td align="center">37</td>
</tr>
<tr>
<td align="center">15</td>
<td align="center">33</td>
<td align="center">30</td>
<td align="center">33</td>
</tr>
</tbody>
</table>
</table-wrap>
<table-wrap id="T5" position="float">
<label>TABLE 5</label>
<caption>
<p>Input data of BSSs in Case 2.</p>
</caption>
<table>
<thead valign="top">
<tr>
<th align="center">BSS</th>
<th align="center">Swapping price ($)</th>
<th align="center">Number of batteries</th>
</tr>
</thead>
<tbody valign="top">
<tr>
<td align="center">A</td>
<td align="center">35</td>
<td align="center">7</td>
</tr>
<tr>
<td align="center">B</td>
<td align="center">35</td>
<td align="center">5</td>
</tr>
<tr>
<td align="center">C</td>
<td align="center">34</td>
<td align="center">8</td>
</tr>
<tr>
<td align="center">D</td>
<td align="center">35</td>
<td align="center">6</td>
</tr>
<tr>
<td align="center">E</td>
<td align="center">34</td>
<td align="center">7</td>
</tr>
</tbody>
</table>
</table-wrap>
<p>
<xref ref-type="fig" rid="F6">Figure 6</xref> presents the scheduling results using the shortest arrival time approach. BSS A is assigned 9 EVs despite having only 7 batteries, and BSS D is assigned 8 EVs despite having only 6 batteries. Although each EV reaches the nearest BSS, 4 EVs failed to swap their batteries.</p>
<fig id="F6" position="float">
<label>FIGURE 6</label>
<caption>
<p>Scheduling results of shortest arrival time.</p>
</caption>
<graphic xlink:href="fenrg-12-1488234-g006.tif"/>
</fig>
<p>
<xref ref-type="fig" rid="F7">Figure 7</xref> illustrates the scheduling results using our method. The iterative process of the algorithm is shown in <xref ref-type="fig" rid="F8">Figure 8</xref>, where <xref ref-type="statement" rid="Algorithm_1">Algorithm 1</xref> converges after 128 (&#x3d; 99 &#x2b; 29) iterations. The solution time is 8.24 s, demonstrating the computational efficiency of our method.</p>
<fig id="F7" position="float">
<label>FIGURE 7</label>
<caption>
<p>Scheduling results of our approach in Case 2.</p>
</caption>
<graphic xlink:href="fenrg-12-1488234-g007.tif"/>
</fig>
<fig id="F8" position="float">
<label>FIGURE 8</label>
<caption>
<p>Total costs of EVs over iterations in Case 2.</p>
</caption>
<graphic xlink:href="fenrg-12-1488234-g008.tif"/>
</fig>
<p>For better comparison, <xref ref-type="table" rid="T6">Table 6</xref> summarizes the swapping success rates and average total costs using these two approaches. It appears that the swapping success rate of the shortest arrival approach is only 86.7%, while that of our approach is 100%. Furthermore, the average cost of all EVs is reduced from $81.7 using the shortest arrival time approach to $62.8 using our approach, by 23.1%. Note that for a convenient comparison of the average cost, the number of batteries in BSS A is increased to 9, and that in BSS D is increased to 8 to avoid EVs from unsuccessful battery swapping. These results demonstrate that the non-cooperative game approach increases the swapping success rate while reducing the average cost of EVs.</p>
<table-wrap id="T6" position="float">
<label>TABLE 6</label>
<caption>
<p>Comparison of results.</p>
</caption>
<table>
<thead valign="top">
<tr>
<th align="center">
<break/>Approach</th>
<th align="center">Swapping success rate (%)</th>
<th align="center">Average cost ($)</th>
</tr>
</thead>
<tbody valign="top">
<tr>
<td align="center">Shortest arrival time</td>
<td align="center">86.7%</td>
<td align="center">81.7</td>
</tr>
<tr>
<td align="center">Non-cooperative game</td>
<td align="center">100%</td>
<td align="center">62.8</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
</sec>
<sec sec-type="conclusion" id="s5">
<title>5 Conclusion</title>
<p>This paper proposes a non-cooperative game approach for the battery-swapping scheduling of EVs. A swapping process model inspired by the job-shop scheduling problem is proposed, and the cost function of each EV comprehensively considers the travel time, waiting time, and battery swapping price. A non-cooperative game model for battery swapping scheduling is established considering the finite quantities of batteries and swapping grippers. An iterative best response algorithm is developed satisfying constraints including those couple decisions of different EVs. Two cases are tested. In Case 1, a smaller size example is tested to demonstrate the fairness and reduced waiting time of our approach. In Case 2, a larger size example is tested to demonstrate the advantages of our approach on the swapping success rate and average cost compared with the shortest arrival time approach. Both cases demonstrate the computational efficiency of the proposed algorithm.</p>
</sec>
</body>
<back>
<sec sec-type="data-availability" id="s6">
<title>Data availability statement</title>
<p>The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.</p>
</sec>
<sec sec-type="author-contributions" id="s7">
<title>Author contributions</title>
<p>YZ: Writing&#x2013;original draft. TH: Writing&#x2013;original draft. WH: Writing&#x2013;review and editing. JX: Writing&#x2013;review and editing. LC: Writing&#x2013;review and editing. ZM: Writing&#x2013;review and editing. SL: Writing&#x2013;original draft, Writing&#x2013;review and editing.</p>
</sec>
<sec sec-type="funding-information" id="s8">
<title>Funding</title>
<p>The author(s) declare that financial support was received for the research, authorship, and/or publication of this article. This work was supported by the research project of China Yangtze Power Co., Ltd., under Grant Z412302053.</p>
</sec>
<sec sec-type="COI-statement" id="s9">
<title>Conflict of interest</title>
<p>Authors YZ, TH, and WH were employed by Three Gorges Electric Power Co., Ltd. Authors JX, LC, and ZM were employed by China Yangtze Power Co., Ltd.</p>
<p>The remaining author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.</p>
<p>The authors declare that this study received funding from China Yangtze Power Co., Ltd. The funder had the following involvement in the study: study design, analysis of data, the writing of this article, and the decision to submit it for publication.</p>
</sec>
<sec sec-type="disclaimer" id="s10">
<title>Publisher&#x2019;s note</title>
<p>All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.</p>
</sec>
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