## 4 Discussion
Voltage sag and flicker reduction using a hysteresis fuzzy control that drove the EES showed superior voltage stability in simulations than in a scenario without the control system [103]. The authors of [72] developed a self-tuned fuzzy-PI controller for a DVR and demonstrated through simulations that the proposed method better mitigated severe voltage sag. Decreasing harmonic distortions of voltages and currents is solved using APFs, which in many cases are upgraded by FSCs to better serve their purpose. This situation is found in [88], where the authors designed a thyristor-controlled LC-coupling hybrid APF and used a hysteresis FLC to adjust the parameters of the filter for THD reduction in medium voltage-level systems. The results showed a switch loss decrease of 38% compared to using hysteresis control with a fixed band. In [84], the authors proposed an auto-tuning scheme based on an FLC to automatically calibrate the APF's control coefficient and maintain the voltage's THD within the standard limits in wind farms. Furthermore, an adaptive fuzzy method with a supervisory compensator for a three-phase APF is described in detail in [95]; more specifically, the authors use a Sugeno FLC, an adaptive law and supervisory controller, to reduce the THD from 24.71% to 1.72%. The efficacy assessment was performed using both simulations and experiments from [73; 76; 96; 123]. The researchers in [73] used a hybrid FCS that contained a Takagi-Sugeno type-1 fuzzy controller to automatically switch between a PI and fractional-order PI controller. This approach gave greater results than employing only a PI controller, as the THD reduced from 55.8% to 2.4% and 5%. An adaptive hysteresis FLC has proven to give superior outcomes than a PI controller under various scenarios [75]. The implementation of a modified FLC on a microcontroller to control a shunt APF is described in [96]. The authors of [76] upgraded a repetitive controller with fuzzy logic, obtaining an adaptive version that showed better performance than the fixed repetitive version. This was clear, as the harmonic distortion factor decreased from 35.1% to 3.1%. The authors of [123] describe a modified adaptive FLC--more specifically, a Lyapunov-based fuzzy control. The authors compare the proposed controller with two methods from the literature through simulations. Additionally, they built a prototype that was tested in the laboratory. All tests showed that the proposed method was better, reducing the THD from 26.04% to 4.14%. Reactive power control plays a crucial role in maintaining voltage control and power system stability. Hence, researchers often associate reactive power regulation with voltage variations and develop control systems that solve both issues simultaneously. This is the situation in [83], where the authors used a type-1 FLC to control the reactive power produced by distributed generation units. Similarly [144] describes the use of a type-1 fuzzy to adjust the SVC's capacitance for better control of reactive power and voltage control. In [145], a fuzzy self-tuning PI control together with two other regulation methods performed a three-layer coordinated reactive power compensation, and the results showed the better stability of reactive power variations than a PI-based control strategy. The reactive power control in power systems with wind generators is reflected in [93; 133]. A fuzzy-PID where two FLCs give the \(k\) parameters of the PID controller plus a modulated hysteresis method is proposed in [133], and the authors show that the proposed method gave a 50.23% reduction in reactive power ripples in comparison to the conventional approach. A type -1 fuzzy with three inputs and one output is described in [93] to reduce the ripples of reactive power. All these studies used simulations to demonstrate the efficacy of the proposed methods and compared the FLCs with conventional approaches, i.e., the sensitivity method [83], no control [144], PI control [73], and conventional control [146].