The location of wind-generated electricity generating depends on wind energy. High-voltage (HV) transmission lines are usually far from these facilities (Xie and Sun, 2022). If the facility has medium power, medium voltage (MV) distribution wires will link the WF. The most distinguishing characteristic of these connections is an improved voltage control sensitivity to load variations (Huang et al., 2021). Therefore, the capability of the scheme to normalize potential at the PCC, which is the point at which the electrical system and the WF are coupled, is an essential factor in the proper operation of the WF. In addition, it is common knowledge that wind farms produce variable amounts of electric power due to the unpredictable nature of wind resources. These variations harm the consistency and quality of the electricity provided by the electric power systems (Song et al., 2023).

Additionally, SCIG-used wind turbines have been in use since the beginning of energy extraction from wind resources. The supply mains or capacitor banks supply the required reactive power with SCIG (Yang et al., 2024). There are fluctuations in the rotor speed. For example, the power grid’s injected (demanded) WF active (reactive) power will fluctuate due to wind disturbances. This will produce variations in the WF terminal potential and the system’s impedance. Electrical power turbulences will eventually find their way into the power system (Zhang et al., 2023), which may result in a spectacle known as a “flicker,” which is characterised by oscillations in the level of illumination caused by voltage variations. Additionally, the regular operation of the WF is hampered by these disturbances. The effect is significantly more significant when “weak grids” (WG) are specifically considered.

Several potential methods have been proposed in demand to reduce the possible electric variations that can result in a “flicker” at the WF terminals. Updating the electrical grid by raising the power level at short circuits at the PCC is the most popular solution. This decreases system sensitivity to power fluctuations and voltage control issues (Liu et al., 2023).

Electronic equipment for electric power systems has become widespread due to high-power electronics technology. This device reacts faster than line frequency. FACTS and devices give these active compensators tremendous flexibility for controlling power flow in gearbox systems employing Custom Power System (CUPS) devices (Liu et al., 2023). This type of active compensator increased wind energy assimilation in weak systems, as researched (Miaofen et al., 2023).

We propose and test a UPQC-based compensation approach for a SCIG-based WF connected to a weak distribution power grid. This system is based on a study (Li et al., 2022a). The potential at the WF terminal can be controlled and the PCC experiences fewer voltage swings due to the management of the UPQC. These fluctuations are caused by changes in the system load and the pulsating power provided by the WF, respectively. Inoculating the voltage “in phase” with the PCC potential, the series converter with UPQC controls the electrical potential at the WF terminal (Miaofen et al., 2023). This is achieved through voltage injection. Similarly, the parallel converter is utilised to screen the power created by the WF to prevent voltage swings. This function requires the ability to actively and reactively handle electricity. The standard DC link takes active power distribution among various converters (Chen et al., 2022). Simulations were carried out to demonstrate how successful the proposed compensatory strategy not only for UPQC and also verified with fuzzy logic controller.

The electrical system being looked at in this research can be seen in Figure 1. The WF comprises 36 wind turbines utilising squirrel cage induction generators, producing 21.6 MW of electrical power. Each turbine is coupled to an electrical grid of a 630 kVA 0.69/33 kV transformer and features attached fixed reactive compensation capacitor banks with a rating of 175kVAr. Based on reference (Liu et al., 2018), this system depicts a real-life scenario.

The indication of the “connection weakness” based on the power ratio during a quick circuit to the power-valued WF. Consequently, while taking into consideration the fact that the short circuit power in MV6 is S _SC > 120 MV A, so this ratio can be calculated with (1). r = S S C P W F ≅ 5.5 (1)

Any value of r < 20 is regarded as having a “weak grid” linkage (Nie et al., 2022).

The following expression determines the amount of electricity obtained from a WT: P = 1 2   .   ρ   .   π   .   R 2   .   v 3   .   C P (2)

Where ρ is the air density, R is the radius of the swept area, v is wind speed, and C _P is the power coefficient.

For the considered turbines (600 kW), the values are R = 31.2 m,ρ= 1.225 kg/m ³ and C _P calculation is taken from (Damchi and Eivazi, 2022).

The power from the turbines is then combined to create a comprehensive model of the WF, showing that the entire WF is represented by a single corresponding turbine producing electrical potential from wind power, which is the same as the mean totality of the power provided by each turbine is expressed in (3): P T = ∑ i = 1 , 2 , 3 … . . 36 P i (3)

In addition, disruptions in the wind flow can cause the wind speed v in (2) to fluctuate about its usual value. The first is determined by an irregularity in the stream of air that is “seen” from the blades of the turbine because of “tower shadow” and/or edge coat of the atmosphere, and the second is caused by erratic changes that are referred to as “turbulence.” Both of these factors can affect the energy produced using the wind turbine. Consider disruption to the airflow induced by the support structure (tower) as part of our analysis. When applied to the mid value of v, the disruption is viewed as a sinusoidal modulation. This modulation has a frequency of N _rotor for the three-bladed WT, and the breadth depends on the tower’s design. An amplitude modulation of 15% and an average 12 m/s wind speed is used (Rao et al., 2023).

In most situations, the effect of the edge coat of the atmosphere is disregarded in favour of the results provided by the shadow effect produced by the tower (Yang et al., 2015). Note that the total of perturbations can occur if the entire turbines operate in the same sequence and in phase, which has the most significant impression on the electrical grid (worst case scenario) because the pulsation of power has the most significant peak in this situation. Therefore, the turbine combination method is acceptable.

The model used for the SCIG is the one that is included in the Matlab/Simulink, Sim Power Systems package (Venkata Govardhan Rao et al., 2022). Dynamic voltage fluctuations are accounted for by supplying the MV6 (PCC) bus bar with potential in series and active reactive power. This is accomplished with a unified type compensator, a UPQC (Ray et al., 2021). The general layout of this compensator can be seen in Figure 2A, while Figure 1 should be used as a reference for the bus bar and impedance numbering.

The process involves utilising VSI or CSI electrical converters to create three-phase voltages. As for its lower loss of DC link and quicker system response, the VSI converter is preferred over the CSI converter (Srikanth et al., 2023). The UPQC’s shunt converter is accountable for injecting current at PCC, as explained in Figure 2B, while the series converter produces electric potential for PCC and UI. The vital theme of the compensator is that the series and shunt VSIs operate using the same DC bus. Thanks to this functionality, the two different types of converters can actively transfer power.

The converters are manufactured using ideal regulated voltage sources since the switching control of the converters is outside the purview of this work, and the higher-order harmonics produced by VSI converters are outside the bandwidth of importance in the simulation analysis. It is completed since the switching converter control is not involved in this task. Figure 3 displays the finalized model of the UPQC system’s power side. T = 2 3 sin ϴ sin   ϴ − 2 π 3 sin   ϴ + 2 π 3 cos   ϴ cos   ϴ − 2 π 3 cos   ϴ + 2 π 3 1 2 1 2 1 2 (4) f d f q f 0 = T   .   f a f b f c (5)

Where fi = a,b,c represents either the phase voltage or current, and fi = d,q,0 represents that magnitude transformed to the dqo space. The controlling of UPQC, with rotating frames using a park’s transformation is mentioned in (4) & (5).

It enables the position of a reference frame of the rotating body in the positive direction of the PCC potential space vector. A PLL mechanism determines a reference angle synchronism with the PCC positive sequence fundamental voltage space vector. This makes it possible to get the desired outcome. This study has a PLL that is examined using the “instantaneous power theory”.

Under balanced and equilibrium conditions, the synchronous reference frame’s electric potential and current vectors do not change. This quality is advantageous for study and detached control.

The WF terminal voltage is maintained at its nominal level by managing the UPQC serial converter (as in Figure 3), which makes up for variations in the PCC voltage. If this is done, the grid-generated voltage disturbances will not be able to reach the WF facilities. If voltage dips occur at the WF terminals due to this control action, it may have the unexpected impact of increasing the LVRT capacity.

Figure 4A explains the series converter controller block diagram. The PCC electric potential is subtracted from the reference electric potential to produce the injected electric potential, which is aligned in phase with the PCC electric potential. The voltage is injected as a result. On the other hand, the UPQC uses its shunt converter to mesh the pulsations of active and reactive power components, which WF causes. As a result, there will not be any pulsations in the electricity that the WF compensator set injects into the grid. Pulsations cause voltage fluctuations that may propagate throughout the system. This action can be finished with the correct electrical current injection into the PCC. Additionally, this converter has been able to normalize the voltage on the DC bus.

The block architecture of the shunt converter controller is displayed in Figure 4B. The voltage instructions of E _{d_shuC*} and E _{q_shuC*} are produced in this way, depending on the variations ΔP and ΔQ, respectively. The deviations are computed by deducting the mean power from the instantaneous power measured in PCC. Filing by low pass filter calculates the expected values of the active and reactive power components. These filters’ bandwidths are altered such that, by the IEC61000-4-15 standard, the fluctuation components for power are chosen as they lie in the flicker band and accept compensation.

Additionally, the control action for the DC–bus voltage loop is contained within E _{d_shuC} *since its components operate at a frequency that is lower than that of the flicker–band.

In the rotating reference frame, the powers P _shuC and Q _shuC are computed as follows in (6): P s h u C t = 3 2   .   V d P C C t   .   I d s h u C t Q s h u C t = − 3 2   .   V d P C C t   .   I d s h u C t (6)

The equations other than PCC voltage variation, can be expressed as follows in (7): P s h u C t = k p ′   .   I d   _   s h u C t Q s h u C t = k q ′   .   I q   _   s h u C t (7)

Given that the shunt converter is built around a VSI, we must produce sufficient voltage to attain the currents in (6). It is possible by the model of VSI, which is discussed in (Song et al., 2022a), which leads to a linear relationship between the power output and the controlled voltages. Following are the resultant equation in (8): P s h u C t = k p ″   .   E d * _ t s h u C Q s h u C t = k q ″   .   E d   * _ t s h u C (8)

Proportional controllers have examples of P and Q control loops, whereas the DC–bus loop is an example of a PI controller.

In a nutshell, UPQC is considered a “power buffer” in the suggested strategy, which helps to equalise the power inoculated into the power system grid. This style of operation is conceptually represented by a schematic, which may be found in Figure 5.

It is crucial to remember that the storage element installed on the bus containing UPQC must uphold its mean power at zero because the bus lacks an external DC supply. This is the situation to protect the system’s integrity. To do this, a well-designed DC voltage controller is essential.

The concept of power buffer may not be executed with a DVR; however, it is possible to do so with a DSTATCOM. A DVR device is more appropriate in this situation than DSTATCOM’s solution since voltage regulation during moderately significant disturbances cannot be effectively managed with just DSTATCOM’s reactive power.

The enormous potential of fuzzy set theory for effectively addressing the problem’s uncertainty is evident (Raju and Rao, 2015). It is an outstanding mathematical tool for handling ambiguity-related uncertainties. The concept of fuzzification and de-fuzzification is explained in Figure 6A, and the membership functions of fuzzy controller are depicted in Figure 6B.

Matlab/Simulink software was used to create the prototypical view of the power system scheme depicted in Figure 1. The controllers and the control strategy described in Section III are included in this model. Numerical simulations were carried out to determine and compensate for the voltage fluctuation brought on by variations in wind power and voltage regulation difficulties brought on by a sudden load hook-up.

The UPQC and fuzzy logic controller results clearly illustrate the power demand potential of the PCC series and shunt compensators’ injected power. However, here, we proposed a fuzzy logic controller implementation to the same system; with this, we are maintaining all the parameters are the same, but the THD value of the Fuzzy system with the PI controller is meagre, i.e., 2.81% in comparison to the UPQC system of 5.13%. Shown in Figure 22A,B, the outcomes of the simulations demonstrate that the proposed compensation technique is beneficial in improving the Quality of power and stability in WF.

The article presents a newfangled compensation stratagem built by a UPQC compensator to link SCIG wind farms to feeble power grids. The recommended compensating technique raises the system’s power quality by utilizing the wholly DC energy storage and the active power sharing across UPQC converters. The DVR and DSTATCOM compensators do not include these features. The THD of the fuzzy controller improved the UPQC controller. The simulation’s outcomes explain that it is possible to regulate the voltage induced by an unexpected load connection and reject the power fluctuations caused by the “tower shadow effect” with satisfactory results. The research example thus shows that the suggested compensation scheme accomplishes its objectives. The performance levels of the various types of compensators will be compared in future research.