Main Voltage Research Articles

Hybrid Equalization Topology for Battery Management Systems Applied to an Electric Vehicle Model

This paper presents a hybrid equalization (EQ) topology of lithium-ion batteries (LIB). Currently, LIBs are widely used for electric mobility due to their characteristics of high energy density and multiple recharge cycles. In an electric vehicle (EV), these batteries are connected in series and/or parallel until the engine reaches the voltage and energy capacity required. For LIBs to operate safely, a battery management system (BMS) is required. This system monitors and controls voltage, current, and temperature parameters. Among the various functions of a BMS, voltage equalization is of paramount importance for the safety and useful life of LIBs. There are two main voltage equalization techniques: passive and active. Passive equalization dissipates energy, and active equalization transfers energy between the LIBs. The passive has the advantage of being simple to implement; however, it has a longer equalization time and energy loss. Active is complex to implement but has fast equalization time and lower energy loss. This paper proposes the combination of these two techniques to implement simultaneously to control a pack of LIBs, equalizing voltage between stacks and at the cell level. For this purpose, a pack of LIBs was simulated with sixty-four cells connected in series and divided into eight stacks with eight battery cells each. The rated voltage of each cell is 3.7 V, with a capacity of 106 Ah. The total pack has a voltage of 236.8 V and 25 kW. Some LIBs were fitted with different SOC values to simulate an imbalance between cells. In the simulations, different topologies were evaluated: passive and active topology at the cell level and combined active and passive equalization at the pack level. Results are compared as a response time and state of charge (SOC) level. In addition, equalization topologies are applied in an EV model with the FTP75 conduction cycle. In this way, it is possible to evaluate the autonomy of each equalization technique simulated in this work. The hybrid topology active at the stack level and passive at the module level showed promising results in equalization time and autonomy compared with a purely active or passive equalization technique. This combination is a solution to achieve low EQ time and satisfactory SOC when compared to a strictly active or passive EQ.

Integration of Three-Phase LLC Resonant Converter and Full-Bridge Converter for Hybrid Modulated Multioutput Topology

A multioutput dc–dc topology based on hybrid modulation of pulse frequency modulation and the phase shift is proposed in this article. The proposed hybrid modulated multioutput converter is derived from the integration of a three-phase LLC resonant converter and the full-bridge converter. With the hybrid modulation, the multioutput is controlled independently free from cross-regulation and isolated from each other. With the three-phase interleaving operation, the resonant currents can be reduced, and thus, the efficiency will be improved. Furthermore, the output current ripple of the main output voltage is reduced; as a consequence, the lifetime of the output filter capacitor is extended, and the reliability is reinforced. What is more, the number of the power switches is reduced, and the zero-voltage switching of the power switches can be achieved within the entire load range by the proposed integrated topology. All the abovementioned features of the proposed converter will lead to a compact, efficient, and cost-effective design. Finally, a 1.4-kW triple-output laboratory prototype is built and tested to validate the feasibility and effectiveness of the proposed converter.

Novel Wind Power Grid-connection System Using Inductive Filtering Technology

Herein, a novel wind power grid-connection system based on inductive filtering is proposed to improve grid-connection compatibility, and is implemented in a 50-MW real system. First, the topology and wiring configuration of the proposed system are discussed. Thereafter, an equivalent circuit and mathematical model are established to reveal the filtering characteristics and resonance damping mechanism of the proposed system. Finally, a 50-MW wind farm-based experimental study, which is conducted to validate the effectiveness and availability of the system is discussed. The experimental results show that the main harmonics, power factor, voltage fluctuation, and flicker satisfy national standards.

A Voltage Balancing Method for Series-Connected Power Devices Based on Active Clamping in Voltage Source Converters

This article proposes a voltage balancing technique for series-connected power devices in voltage source converters (VSCs). Each main power device has an active clamping module (ACM), consisting of a capacitor and an auxiliary switch. The ACM can clamp the main power device voltage, and voltage sharing among series-connected power devices can be realized by balancing the ACM capacitor voltages. The balancing circuit does not affect the normal operation of the devices and the introduced power losses can be ignored. The possible charging and discharging principles of the ACM capacitors are summarized. Then, the control strategy to balance the ACM capacitor voltages is introduced. The operating principles of a VSC with series-connected devices and the proposed balancing circuits are presented, including charging stage, discharging stage, and steady voltage stage. A switching sequence of auxiliary switch and main power switch is proposed to ensure ZVS- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> of the auxiliary switch. Besides, design considerations of key parameters are presented. Finally, experimental results are provided to verify the effectiveness and feasibility of the proposed method. The voltage imbalance degree of the six series-connected devices is less than 3% under different operating conditions. The proposed method shows good balancing performance, good scalability, and low power losses.

Low Voltage Charging Technique for Electric Vehicles With 800 V Battery

It has been suggested that the main battery voltage of electric vehicles is increased from 400 to 800 V to improve the charging speed and driving distance. However, the secondary components in the dc/dc converter of the on-board charger have high voltage stresses due to the increased battery voltage. Therefore, this article proposes a low voltage charging technique. The previously designed and optimized dc/dc converter for 400 V battery is used to charge 800 V battery. The battery stack is divided into two modules. Dc/dc converter charges one of two modules alternatively using the battery selection circuit (BSC). Since the BSC has low voltage stresses, the proposed converter can have low voltage stresses on all the dc/dc and BSC parts. Moreover, the dc/dc converter and BSC can be decoupled by turning <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> the dc/dc converter while changing the charged battery. Therefore, the loss of BSC can be minimized by operating it with low frequency because the switching frequency of BSC can be independent of that of the dc/dc converter. The design process can also be simpler owing to decoupling operation. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter was adopted for dc/dc converter with 3.3 kW output to verify the proposed technique.

ELECTROMAGNETIC COMPATIBLE CURRENT SOURCES WITH RELAY CONTROL

The development of industry leads to an increase in nonlinear loads, which are generators of higher harmonics in the network. The quality indicators of voltage and current consumed from the network are established by international standards for the quality of electricity. The simplest method of filtering harmonics is passive filters, lack of low quality harmonic compensation. The use of active filters improves the quality of the current. But active filters have a complex control system. The use of active rectifiers as part of semiconductor power supplies solves the problem of generating higher harmonics in the network and provides a power factor equal to 1.&#x0D; Six variants of three-phase and single-phase power supplies have been developed. They operate as a current source. All circuits consist of two parts: an active rectifier and a DC-DC converter. The scope of use of such sources is different: a direct current electric drive, an electric power system of wind turbines, an electric system of aircraft. The control system of the relay converters provides the formation of current and the maximum speed in the processing of disturbances. &#x0D; Oscillograms of the current sources are obtained by digital modeling. They confirm the efficiency of the proposed sources, the electromagnetic compatibility of the power sources with the mains and the value of the power factor close to unity. Current sources are invarant to the action of disturbances: changes in load resistance, mains voltage. The study of electromagnetic processes made it possible to obtain analytical expressions for the maximum and minimum frequency of the relay mode, the capacitance of the capacitors and the operating conditions of the sources. &#x0D; The developed program allows you to get the parameters for choosing the power elements of the circuit: inductance, capacitance, switching frequency of transistors. &#x0D; The quality of the consumed current is analyzed by calculating the total harmonic distortion (THD). For all considered sources, the THD value is less than 5%, which meets the quality standards for the consumed current.

Determination of the input filter parameters of the active rectifier with a fixed modulation frequency

Goal. Development of a methodology for calculating the parameters of the active rectifier-voltage source input filter operating with a fixed modulation frequency to ensure electromagnetic compatibility with the supply network acceptable by standards at minimum values of the input inductance and checking its main characteristics on a mathematical model. Methodology. The authors have developed a methodology for calculating the parameters of the input filter of an active rectifier-voltage source. The calculation results are verified on the constructed mathematical model of a frequency converter, the scheme of which is an active rectifier and an autonomous voltage inverter. A series of experiments was carried out on a mathematical model to study the dependence of the total harmonic distortion of current and mains voltage on the value of the input inductance for various parameters of the input filter. Results. The structure and calculation procedure the input filter of an active rectifier operating with a fixed modulation frequency are proposed. The simulation results showed that the inclusion of a filter at the input of the active rectifier significantly improves its electromagnetic compatibility with the supply network in the entire range of variation of the input inductance of the circuit and makes it possible to achieve the values of the total harmonic distortion permissible by the norms. Originality. A structure and a calculation procedure the input filter of an active rectifier-voltage source operating with a fixed modulation frequency are proposed. Practical significance. The dependencies obtained in the article allow us to evaluate the relationship between the parameters of the filter elements and its characteristics among themselves and come to a compromise between them when designing a scheme for specific technical conditions.

A robust controller design procedure for LCL‐type grid‐tied proton exchange membrane fuel cell system in harmonics‐polluted network

AbstractProton exchange membrane fuel cell (PEMFC), due to its high efficiency and good stability, is one of the most efficient and effective sources of alternative renewable energy. The LCL filters are utilized to attenuate the harmonics caused by inverter‐based distributed power generation systems (DPGS). In this paper, a systematic robust control design is presented for an LCL‐type grid‐tied PEMFC inverter. The proposed nested control includes the capacitor current feedback and the outer grid current loops, considering the computational delays. The proposed control results in more accurate and realistic modeling to transfer the power of PEMFC and inject a high‐quality current into a weak and harmonics‐polluted network. Also, by utilizing the proposed method, the computational delays that affect the damping capability are eliminated, and the performance of the control system is improved. In addition, designing a virtual series and parallel impedances strengthens the phase and amplitude of the inverter output impedance. As a result, the robust operation of the inverter for significant changes in network impedance is improved, and the system well attenuates the mains voltage harmonics. The simulation results in Matlab/Simulink environment confirm the performance of the control system and the suitable quality of the injected current of the PEMFC system into the weak and harmonic‐polluted network.

Control of Solar PV Arrays Based Microgrid Intertied to a 3-Phase 4-Wire Distribution Network

This article presents a multiple solar photovoltaic (PV) array based microgrid (MG) integrated into a 3-phase 4-wire distribution network. The main voltage source converter (VSC) and ancillary VSC's dc links are assimilated to PV arrays with maximum power point tracking. The main VSC operates with current control in a grid interfaced mode. However, at grid interruption, voltage control is utilized in an autonomous mode as a grid forming inverter, which sustains frequency and voltage across point of common coupling (PCC) for continuous power to loads. The ancillary VSC operates in current control. The feed-forward powers of PV arrays in VSCs current control improve MG dynamic behavior. MG's satisfactory behavior is achieved for changes in solar insolation and load, load unbalances, and neutral current compensation in MATLAB, and is authenticated in hardware in loop via a real-time controller, i.e., OPAL-RT (OP4510) with RT-LAB environment. The MG has the capability to sustain islanding and its mode transitions operation is seamless. The grid current total harmonics distortion (THD) and autonomous mode's PCC voltages THD are found to adhere to standard IEEE-519-2014.

Static Analysis and Optimization of Voltage and Reactive Power Regulation Systems in the HV/MV Substation with Electronic Transformer Tap-Changers

The quality of electricity is a very important indicator. The durability and reliable operation of all connected devices depend on the quality of the network voltage. Rapid changes in loads, changes in network connections and the presence of uncontrolled energy sources require the development of new voltage regulation systems. This requires voltage regulation systems capable of responding quickly to sudden voltage changes. In substations with control transformers, it is possible thanks to the use of semiconductor tap changers. Moreover, voltage regulation and reactive power compensation systems should be built as one system. This is due to the close dependence of voltage and reactive power in the network node. Therefore, it was proposed to use artificial intelligence methods to build a new voltage regulation and reactive power compensation system using all measurement voltages of network nodes. In the first stage of the research, active and reactive powers, as well as the voltage of the reference node, were selected for 6420 periods of the mains voltage. The simulation results were compared for the classic voltage regulation system with semiconductor tap changers and the evolution algorithm based on voltage measurements from the entire MV network. A significant improvement in the quality of voltage regulation with the use of an evolutionary algorithm was demonstrated. Then, a second set of input data with increased values of reactive power was generated. The results of the evolutionary algorithm after the application of the classic, independent reactive power compensation system and two-criteria optimization were compared. It has been shown that only the two-criteria optimization algorithm keeps both |tgφ| within the acceptable range and the quality of voltage regulation is the best. The article compares different working algorithms for semiconductor tap changers.

DOWNHOLE THERMOELECTRIC MODULE SYSTEM TO EXPAND THE APPLICATION AND INCREASE THE EFFICIENCY OF THE STEAM GRAVITATION INFLUENCE METHOD

The article discusses the existing technologies for thermal insulation of tubing (tubing) when using thermal methods of influencing an oil reservoir with high-viscosity oil, inherent in the fields of Kazakhstan. An urgent problem in the use of steam cycle treatment (CSS), steam gravity treatment (SAGD) and in situ combustion is significant heat loss with increasing well depth, which imposes restrictions on the use of these enhanced oil recovery methods. The large depth of occurrence of productive formations with high viscosity of fluids causes this problem of delivering the coolant to the productive formation with a given steam temperature, since the main indicator of the effectiveness of the use of thermal methods is the temperature of the coolant, in connection with which the solution of the issue of reducing heat losses in the process of delivering the coolant through the tubing string to a productive reservoir is an important technical problem, the solution of which with minimal costs of material resources will increase the interest of mining companies in the application of these methods, namely the SAGD technology. The paper carried out a comparative analysis and recommended a technology that improves the efficiency of the SAGD method for the fields of Kazakhstan. Currently, there are two main technologies for thermal insulation of the tubing string using the SAGD method, in high-viscosity oil fields - vacuum insulated tubing (Vacuum Insulated Tubing-VIT); - heat-insulated tubing. This article proposes a new method based on the conversion of electricity into heat by placing a borehole thermoelectric module in the tubing string. The proposed downhole thermoelectric module system makes it possible to maintain the coolant temperature along the entire length of the wellbore, which makes it possible to apply the SAGD method to depths of 1500 meters or more. The design of the downhole thermoelectric module system is simple, technologically advanced, reliable in operation and easily replicable. The downhole thermoelectric module system, placed in the tubing string, provides the possibility of increasing the depth of wells using the SAGD method and is characterized by a significantly lower cost compared to vacuum insulated tubing (VIT) and heatinsulated tubing systems. Modern heat cables of the SAMREG 40-2CR type, manufactured in South Korea, provide power up to 40 W / m, which is quite enough to maintain the desired temperature of the coolant. The cable is characterized as a self-regulating, heating, heating, shielded cable (braided), operates from a mains voltage of 220-240 V, with a frequency of 50 Hz.

A review of voltage sag control measures and equipment in power systems

In recent years, voltage sags are one of the most critical research issues in the field of power quality. With the all-embracing study of voltage sag mitigation measures and equipment, the classification of voltage sag mitigation measures and equipment is becoming more and more necessary. Reasonable classification methods not only can guide users to choose appropriate control measures and equipment, but also provide basis and research direction for new voltage sag control measures and equipment. Firstly, this study performs a detailed analysis of the current stage of voltage sag control measures and equipment, and proposes a classification method that divides the voltage sag control measures into three categories: the power supply side, the customer side and the equipment manufacturing company. Secondly, due to the difference between single power supply and dual power supply in voltage sag control equipment, this study proposes a classification method for voltage sag control equipment based on the number and type of power supply. Finally, in order to help users to select the voltage sag control equipment suitable for the actual situation, this paper summarizes the prevention and control ability of the main voltage sag control equipment.

ПРИСТРІЙ ДЛЯ КОРИГУВАННЯ ФОРМИ НАПРУГИ МЕРЕЖІ, ЯКА ЖИВИТЬ ПОТУЖНИЙ КЕРОВАНИЙ ВИПРЯМЛЯЧ

A circuit solution of a device for correcting the waveform of the mains voltage, which feeds a controlled semiconductor rectifier of comparable power, is proposed. The sags and swells in the mains phase voltage, which occur during current switching from one phase to another, are compensated by correction pulses, which are transformed into these phases from the phase, which is not involved in switching, using transformers. The mains phase voltage correction circuit, which generates the correction pulses, is connected to the rectifier by four groups of gates in each phase. These groups contain two counter-parallel controlled thyristors, which connect the rectifier to the network phases and its neutral conductor. An algorithm for controlling the controlled thyristors is described. Ref. 8, fig. 2.

РОЗРОБКА МОДЕЛІ СТРУМОВОГО РЕЛЕЙНОГО ЗАХИСТУ В ПАКЕТІ MATLAB/SIMULINK

Based on MATLAB / SIMULINK, a model of a radial network with one-way power supply and three radial lines with a complex load at the end of each line is built. The model allows you to study the relationship of processes in the network in the case of normal operation, and in the case of possible damage at different distances from the power supply. The proposed model of the current protection device consists of a three-phase current meter, a switching element and a display. In the dialog box of the device, the primary current of the transformer current, the mains voltage frequency, the multiplicity of the protection tripping current and the tripping time multiplier are set, and the type of the standard curve of the protection tripping time characteristic is selected. A protection device with inverse time delay characteristics measures the RMS value of three-phase AC. The switch-off signal is given from the output of the relay protection device, depending on the time delay. The display shows the operating time of the device, primary and secondary currents and setpoint multiplicity. The performance of the device was evaluated by a three-phase short circuit. As a result of research it is established that the offered model of the relay protection device confirms correct behavior of the relay of the maximum current in various operating modes of a network. The behavior of the protection device indicates that the proposed model can be used in further work to develop algorithms for current protection of lines. To improve the model of the device, it is necessary to investigate the influence of simulation parameters, such as data on power sources, power lines, load and type of damage on the parameters of the protection device. The scientific novelty is the the developed models of the electric network and the device of the maximum current protection with all inverse characteristics of endurance of time provided by the ANSI / IEEE and IEC standards. The practical significance of the work is the possibility of using the model to test the selectivity and sensitivity of protection in the event of changes in network parameters in a wide range and in the case of research in the development and improvement of relay protection devices and training.

Voltage Sag Mitigation with DVR optimized in DFIG based Wind Energy System

One of the most serious power quality problems in electrical networks is voltage drops. The DVR is known as the most common special power devices used in solving these power quality problems. In this study, optimization is made with WCA algorithm in DVR’S control circuit under wind energy system for fast and reliable detection of mains voltage disruptions, voltage drops and voltage spikes, Its performances were evaluated according to conventional PI controller. These control methods can instantly extract the amplitude and phase information of the mains voltage to detect voltage changes quickly and accurately and with the help of this information, The voltage that needs to be injected into the connection point can be obtained. In the simulation study, the tensions produced by DVR in DFIG based wind energy system and injected into the system were also presented using these two different control methods. The superiority of WCA-based PI controller is clearly seen in the results.

Reduction in Circulating Current With Improved Secondary Side Modulation in Isolated Current-Fed Half Bridge AC–DC Converter

Current-fed half bridge converter with bidirectional switches on ac side and a full bridge converter on dc side of a high frequency transformer is an optimal topology for single stage galvanically isolated ac-dc converter for onboard vehicle charging application. AC side switches are actively commutated to achieve zero current switching (ZCS) using single phase shift modulation (SPSM) and discontinuous current phase shift modulation (DCPSM). Furthermore, zero voltage turn-on (ZVS) is achieved for dc side switches. Compared to SPSM, DCPSM maintains a constant peak current in the converter throughout the grid cycle of ac mains voltage. However, constant peak current contributes to a high circulating current near the zero crossings of ac mains voltage and also at light load conditions.This paper proposes an improved discontinuous current phase shift modulation (IDCPSM) to increase the efficiency of the converter across different loading conditions. A dual control variable is adopted to actively reduce the circulating current while maintaining soft switching of both ac and dc side switches across the grid cycle of ac mains voltage. A 1.5 kW laboratory prototype has been developed to experimentally validate the analysis, design and improvement in performance for different loading conditions.

Design of energy-saving driver circuit for 80 Watt LED using Flyback Converter

Due to numerous features such as compact size, longevity, mercury-free start, and higher color rendering index, the introduction of light-emitting diode (LED) lights has changed residential and commercial lighting systems worldwide. There are two main types of LED driver configurations: single-stage (SS) and double-stage (DS). Low-power systems employ SS configuration converters, while high-power commercial systems use DS configuration converters. This study presented a discontinuous conduction mode (DCM) flyback converter with a PI controller for LED lighting, replacing double-stage converter systems. The proposed DCM-based flyback AC-DC converter includes fewer components, lower total harmonic distortions (THD), improved power factor, and high efficiency. The hardware prototype was created and tested at various AC main voltages to ensure the feasibility of the proposed model. At rated voltage 230 V, system THD is 5.2 %, power factor is 0.995, and efficiency is 92.1 %. The whole system efficiency meets the Energy Star standards.

Development of Medium Power High Efficiency Multi-Level Buck-Boost DC-DC Converter

Power DC/DC converters or regulators form the backbone of different portable electronic devices like cellular phones, laptops, portable electronic devices which are using batteries as their power supply. Portable devices usually comprise of several sub-circuits that should be supplied with different voltage levels, which are not the same as battery’s voltage level which is the main supply voltage. A new approach of buck-boost converter is presented in this paper, that automatically detects the zero-inductor current &amp; compels the convertor to deliberately switch from Continuous Conduction Mode (CCM) to Discontinuous Conduction Mode (DCM), once the inductor current attempts towards negative values, restricting the inductor current to approach towards negative value, and thus enhancing the convertor's performance and efficiency at low load conditions. The converter steps down 200 V input voltage to 187 V and steps up to 211 V simultaneously at 100 Ω load resistance using PSIM software at switching frequency of 100 KHz. The comprehensive analysis of the topology is carried out and the simulated results are compared with the earlier designs at variable loads to verify the performance of the converter.

DC-link Voltage Equalization and Output Voltage Stabilization Control of the Medium Voltage High Power Cascaded Converter Source

Nowadays, H-bridge cascaded converter is widely adopted in the field of ship’s shore power supply in ports and quays, new energy grid connection, et al. This paper focuses on the design and key technology of cascaded inverter. According to the design requirements of medium voltage shore power supply, the main circuit voltage, current and other parameters were calculated firstly, and overall design scheme of cascaded H-bridge type converter power supply is designed. And then the specific realization process of the carrier phase-shifted control of each H-bridge module in the cascaded connection converter was analyzed. To solve the problems of unequal capacitor voltages and unstable output voltages caused by power grid fluctuation and variable load, the DC-link voltages equalization and output voltages stabilization control method of the converter power supply without output voltage sensors was proposed. Furthermore, a sliding window iterative DFT algorithm was used to detect current feedback rapidly. Based on the design parameters, the system simulation was built, and the principle prototype was completed. Finally, the simulation and experimental results are compared to verify the design and control method. And the results indicate that the system design scheme proposed in this paper can basically meet the requirements of design indexes, and realize the control of DC-link voltage equalization and output voltage stabilization at the same time. All those certify the control method is correct and effective.

The Role of Hybrid Battery–SMES Energy Storage in Enriching the Permanence of PV–Wind DC Microgrids: A Case Study

The superior access to renewable sources in modern power systems increases the fluctuations in system voltage and power. Additionally, the central dilemmas in using renewable energy sources (RESs) are the intermittent nature of and dependence on wind speed and solar irradiance for wind and photovoltaic (PV) systems, respectively. Therefore, utilizing a vigorous and effective energy storage system (ESS) with RESs is crucial to overcoming such challenges and dilemmas. This paper describes the impacts of using a battery storage system (BSS) and superconducting magnetic energy storage (SMES) system on a DC bus microgrid-integrated hybrid solar–wind system. The proposed method employs a combination of BSS and SMES to improve the microgrid stability during different events, such as wind variation, shadow, wind turbine (WT) connection, and sudden PV outage events. Distinct control approaches are proposed to control the system’s different components in order to increase overall system stability and power exchange. Both the PV and wind systems are further equipped with unique maximum power point tracking (MPPT) controllers. Additionally, each of the ESSs is controlled using a proposed control method to supervise the interchange of the active power within the system and to keep the DC bus voltage constant during the different examined instabilities. Furthermore, to maintain the load voltage /frequency constant, the prime inverter is controlled using the proposed inverter control unit. The simulation results performed with Matlab/Simulink show that the hybrid BSS + SMES system successfully achieves the main targets, i.e., DC voltage, interchange power, and load voltage/frequency are improved and smoothed out. Moreover, a comparison among three case studies is presented, namely without using ESSs, using the BSS only, and once more using both BSS and SMES systems. The findings prove the efficacy of the proposed control method based on the hybrid BSS + SMES approach over BSS only in preserving the modern power system’s stability and reliability during the variable events.