Gate-controlled Series Capacitor Research Articles

Coordination of time delay and GCSC for frequency stabilization of dual‐area interlinked microgrid using non‐integer controller optimization

AbstractThis study presents a novel frequency regulation solution for renewables (wind‐solar tower)‐bio (biodiesel‐biogas) cogenerated independent dual‐area interlinked microgrid power system (IµPS) with collective effect of time delay and flexible gate‐controlled series capacitor (GCSC). As a component, a non‐integer proportional fractional integral fractional derivative (PFIFD) controller is introduced whose dynamic responses is compared with integer order PID (IOPID) and fractional order PI (FOPI) controllers. The findings demonstrate that the suggested non‐integer PFIFD controller performs better than IOPID and FOPI at giving superior dynamic properties, such as different decision parameters and minimum error function (J). Subsequently, to obtain the optimally tuned controllers’ parameters, a recently developed yellow saddle goatfish technique (YSGA) is leveraged. In this study, the comparative effect of time delay, interline power flow controller (IPFC) and GCSC scheme have been analyzed under real time wind data in IµPS. Further, a meticulous sensitivity assessment of YSGA tuned PFIFD controller is performed under different uncertainties. The improved results show that the recommended YSGA‐based PFIFD controller offers a wonderful improvement in system frequency stability under a variety of situations, including system uncertainties, physical constraints, and significant renewables penetration. Finally, real‐time hardware‐in‐the‐loop (HIL) simulation platform is utilized to validate the proposed control approach.

Gate‐controlled series capacitor: A new methodology for mitigating sub‐synchronous resonance in a series‐compensated DFIG‐based wind farm

AbstractSeries‐compensated transmission lines can lead to a sub‐synchronous resonance (SSR) phenomenon at high compensation levels, where the system lacks stability. Gate‐controlled series capacitor (GCSC) is widely used to damp the SSR. Here, an effective and new methodology for damping the SSR is presented. The proposed method aims to alleviate the SSR phenomenon based on estimating both the frequency and the maximum value of the voltage magnitude signal rather than using the Proportional Integral controller. The appropriate turn‐off angle corresponding to the maximum value of the voltage magnitude signal is applied to the GCSC on the condition that the estimated frequency of the voltage magnitude signal is within the range of the SSR frequency. If the estimated frequency of the voltage magnitude signal is out of the range of the SSR frequency, the steady‐state turn‐off angle (1130) is applied to the GCSC. The capability of the proposed method for damping the SSR under various compensation levels, various wind speeds, and sub‐synchronous control interaction (SSCI) is validated by time‐domain simulation and eigenvalue analysis. Compared to the presented latest method for SSR damping using GCSC, all the obtained results demonstrate that the oscillations converge faster when the proposed method is activated.

Mitigation of AGC Problem of the RES Integrated Hydro-Thermal System Using FACTS and INEC Based AHVDC with ESS Considering the 3DOF-TIDN Controller

This article highlights the mitigation of automatic generation control (AGC) problem considering various FACTS devices and inertia emulation control (INEC) strategies based accurate model of HVDC links using various energy storage systems (ESS). The proposed system comprises a three-area hydro-thermal system integrated with renewable energy sources (RES) such as a realistic dish-Stirling solar thermal system (RDSTS) and a precise wind turbine system (PWTS). A maiden effort has been made to design a novel secondary controller called three degrees of freedom tilt-integral-derivative with filter coefficient (3DOF-TIDN) for the proposed system, and their parameters are successfully optimized by the bird swarm algorithm (BSA). The comparative analysis of system dynamics corresponding to the proposed 3DOF-TIDN controller exhibits betters dynamics over 3DOF-PID and 2DOF-PID controllers. The system dynamic performances are also evaluated considering RDSTS and PWTS in all the areas, and it has been evident that the incorporation of RDSTS and PWTS improves system dynamics. The system with AHVDC link shows quickly damped out the system oscillation. Moreover, the study on inertia emulation using various ESS such as redox flow battery (RFB), ultra-capacitor (UC) and battery energy storage (BES) systems inferred that the system’s initial response with RFB is better than others. Furthermore, the integration of various FACTS devices such as thyristor control phase shifter (TCPS), static synchronous series capacitor (SSSC) and Gate-Controlled Series Capacitor (GCSC) revealed that the system dynamics marginally enhanced with GCSC than TCPS and SSSC.

Adaptive Fuzzy Supplementary Controller for SSR Damping in a Series-Compensated DFIG-Based Wind Farm

Although using a series compensation technique in a long transmission line effectively increases the transmittable power; it may cause a sub-synchronous resonance (SSR) phenomenon. Gate-controlled series capacitor (GCSC) is an effective method for SSR damping by controlling the turn-off angle. In the previous studies, a constant supplementary damping controller (SDC) was used for controlling the turn-off angle, which can mitigate the SSR phenomenon. However, these methods can not capture the maximum transmittable power at different operating points. In this paper, a fuzzy logic controller (FLC) is proposed to compute the gain of SDC based on the wind speed and the error between the measured and reference line currents for transferring as much power as possible and damping the SSR phenomenon simultaneously. Using the MATLAB/SIMULINK program, the proposed method is tested at different operating points to validate its effectiveness and robustness. Compared to the traditional method (constant SDC), the maximum transmittable power, as well as SSR damping, is achieved in all studied cases by the proposed method (variable SDC).

SMES-GCSC Coordination for Frequency and Voltage Regulation in a Multi-Area and Multi-Source Power System with Penetration of Electric Vehicles and Renewable Energy Sources

Frequency, tie-line power, and the terminal voltages of synchronized generators must all be kept within prescribed limits to ensure the stability of an interconnected power grid through combined automatic generation control (AGC) and automatic voltage regulator (AVR) loops. Thermal power plants, electric vehicles, and renewable energy sources—including solar and wind, geothermal, and solar thermal power plants—form the two-area integrated power system in present research. A new cascade controller named the cascaded proportional integral derivative (PID) and fractional-order PID (CPID-FOPID) controller is proposed for the first time, whose performance is compared with the PID and FOPID controller. The results show that the proposed cascade controller outperforms PID and FOPID in delivering superior dynamic characteristics, including short settling times and low oscillation amplitudes. A new metaheuristic algorithm named the coot algorithm was applied to optimize the parameters of these controllers. The suggested controller outperforms FOPID in the combined AGC and AVR problem under uncertain conditions (random load disturbance, variable input of solar irradiation, and wind power). Robustness of the controller is tested with significant variation in the turbine time constant of the thermal and geothermal power plant. In this study, authors also investigated the best possible coordination between the superconducting magnetic energy storage (SMES) and gate-controlled series capacitor (GCSC) devices to control both voltage and frequency simultaneously. The effect of communication time to the power system is analyzed in this study. Additionally, the obtained results are satisfactorily validated using OPAL-RT real-time digital simulator.

A multi-model multi-objective robust damping control of GCSC for hybrid power system with offshore/onshore wind farm

In the recent decade, the power network has experienced a remarkable energy transition due to the large-scale integration of wind energy resources, especially converter-interfaced modern wind turbines. The increasing/decreasing wind penetration, on the other hand, unexpectedly affects the low frequency oscillations of the modern power grid. In this context, the proposed work adopts a multi-model multi-objective robust control framework to design a supplementary damping controller for the gate-controlled series capacitor (GCSC) to stabilize the hybrid power system with a permanent magnet synchronous generator (PMSG)-based off-shore wind farm (OSWF) and a doubly-fed induction generator (DFIG)-based onshore wind farm (ONWF). A bilinear matrix inequality (BMI) optimization problem, formulated as multi-objective synthesis considering H2/H∞ performance along with pre-defined pole placement, is presented for the GCSC control design, which is solved by a two-step linear matrix inequality (LMI) approach. In addition, all LMI constraints are constructed based on the multi-model control framework to incorporate multiple operating conditions. Afterward, the significant improvement in the damping characteristics of the closed-loop system, covering a wide operating range, is confirmed using eigenvalue analysis. The effectiveness of the scheme is validated using two case studies based on the hybrid power system, subject to various disturbances and uncertainties. The simulation results show the robustness and higher damping performance of the proposed multi-model strategy, compared to a conventional and a robust damping controller, for mitigating power system oscillations alongside voltage fluctuations of the wind farms.

Modelling and control of static synchronous series compensator interfaced with DFIG-based wind farm using PSO for SSR alleviation

Subsynchronous resonance (SSR) in wind turbine generators interfaced with series compensated transmission line has been explored in recent few years. Instead of torsional interaction (TI), the induction generation effect (IGE) prompts SSR in such systems. The mitigation of SSR using flexible ac transmission system (FACTS) devices like a thyristor-controlled series capacitor (TCSC), gate-controlled series capacitor (GCSC), static var compensator (SVC) and static synchronous compensator (STATCOM) has been researched in the literature. However, in wind turbine generators, the efficacy of static synchronous series compensator (SSSC) to mitigate SSR is relatively less explored. This paper presents mathematical modelling of SSSC and a study of hybrid series compensation of transmission line using SSSC and fixed series capacitor (FSC) to diminish the SSR effect in doubly-fed induction generator (DFIG)-based wind farm. The values of controller parameters of SSSC for SSR mitigation are identified using particle swarm optimisation (PSO) and compared with the Ziegler and Nichols (Z–N) method. Results obtained through PSO are more precise and finer than the conventional approach. The eigenvalue analysis and fast Fourier transform (FFT) analysis are shown to demonstrate the damping offered by SSSC to SSR oscillations along with transient simulations. The impact of SSR at different compensation levels and wind speed is examined, and the effectiveness of SSSC for SSR mitigation is illustrated using the hybrid compensation method. The risk of SSR is high at low wind speeds and a high compensation level. In such instances, it is shown that SSSC is capable of effectively alleviating SSR.

Robust Model Predictive Control of Gate-Controlled Series Capacitor for LFC of Power Systems

In this article, a robust model predictive control (MPC) is proposed for the gate-controlled series capacitor (GCSC) to contribute to load frequency control. The proposed control model consists of a two-layer MPC in which a nominal MPC produces an initial control signal together with a prediction of system frequency response in a nominal system without uncertainty. An ancillary MPC then produces a control command for the actual system with uncertainty based on measurements, and signals provided by the nominal system. The control signals are provided in such a way that the error in the frequency response of the actual system is minimized with respect to that of the nominal system. Optimization procedures are also conducted to attain optimal values of weighting coefficients associated with the input, and output in the objective functions. Constraints associated with system, and GCSC control are also taken in providing the control signals into consideration. A linear model is presented to formulate the contribution of GCSC control to the power flow of tie-line. The effectiveness of the proposed method in dealing with uncertainties is compared with a conventional MPC, a scheme with proportional-integral controllers, and a system without GCSC. The method robustness is also illustrated by case studies with load uncertainty, and wind power fluctuations, and also uncertainty of parameters. The impact of the delay in communication links on the performance of the control scheme is also evaluated.

Contribution of GCSC to regulate the frequency in multi-area power systems considering time delays: A new control outline based on fractional order controllers

This paper addresses the application of the gate controlled series capacitor (GCSC) in coordination with automatic generation control (AGC) for providing better dynamic responses in interconnected multi-area power systems. A novel controller scheme called Hybrid controller for modeling the GCSC is proposed. The proposed control model consists of a fractional-order proportional-integral-derivative (FOPID) controller and a tilt-integral-derivative (TID) one. Optimized coefficients of the controllers are obtained by applying the Sine-Cosine algorithm (SCA). The delay in communication links as a common feature in wide area control of power systems may cause instability problem. So, a robust stability criterion is presented to estimate the maximum delay time which allows an AGC scheme embedded with the GCSC damping controller to retain stable. Comprehensive discussions are presented on a deregulated two-area power system and a traditional three-area one. Simulation results confirm that the proposed Hybrid controller is capable to achieve better dynamic responses and provide better coordination between the GCSC and AGC in comparison to the other coordinated controllers including PID-based GCSC-AGC, TID-based GCSC-AGC, and FOPID-based GCSC-AGC ones. Eventually, the sensitivity analysis is accomplished to assess the robustness property of the proposed controller against the variations of the parameters.

Efficiency improvement of high‐frequency inverter for wireless power transfer system using series compensator

AbstractThis paper proposes a wireless power transfer system using a series compensator GCSC (gate‐controlled series capacitor) as a primary side capacitor. The GCSC is a circuit module that functions as a series variable capacitor by controlling semiconductor switches. The advantage of applying the GCSC to the primary side capacitor is that it provides controllability of the output power factor for a high‐frequency inverter. Therefore, optimum operation of the high‐frequency inverter can be achieved irrespective of the coil parameters by controlling the output power factor. Experimental results with a 1 kW laboratory prototype confirmed that the proposed system can achieve optimum operation and high efficiencies of the high‐frequency inverter.

An intelligent coordinator design for GCSC and AGC in a two-area hybrid power system

This study addresses the design procedure of an optimized fuzzy fine-tuning (OFFT) approach as an intelligent coordinator for gate controlled series capacitors (GCSC) and automatic generation control (AGC) in hybrid multi-area power system. To do so, a detailed mathematical formulation for the participation of GCSC in tie-line power flow exchange is presented. The proposed OFFT approach is intended for valid adjustment of proportional–integral controller gains in GCSC structure and integral gain of secondary control loop in the AGC structure. Unlike the conventional classic controllers with constant gains that are generally designed for fixed operating conditions, the outlined approach demonstrates robust performance in load disturbances with adapting the gains of classic controllers. The parameters are adjusted in an online manner via the fuzzy logic method in which the sine cosine algorithm subjoined to optimize the fuzzy logic. To prove the scalability of the proposed approach, the design has also been implemented on a hybrid interconnected two-area power system with nonlinearity effect of governor dead band and generation rate constraint. Success of the proposed OFFT approach is established in three scenarios by comparing the dynamic performance of concerned power system with several optimization algorithms including artificial bee colony algorithm, genetic algorithm, improved particle swarm optimization algorithm, ant colony optimization algorithm and sine cosine algorithm.

Load frequency control of a multi‐area system incorporating distributed generation resources, gate controlled series capacitor along with high‐voltage direct current link using hybrid ALO‐pattern search optimised fractional order controller

The power output from the wind turbine in distributed generation (DG) resources is intermittent in nature, which adversely affects the system frequency in an interconnected system. Hence, it is important to study the system dynamic performance when DG resources are connected to the existing power system. This study presents the load frequency control of the three-area thermal-thermal-hydro system with DG resources in area 1. Proportional integral fractional derivative (PID μ ) controller is proposed as a secondary controller. System dynamics are compared among integral, proportional integral (PI), PI derivative (PID), fractional order PID (PI λ D μ ) and PID μ controllers whose parameters are optimised simultaneously using nature inspired ant lion optimiser (ALO) technique. The analysis shows the competitive performance of PI λ D μ and PID μ controllers. Furthermore, the PID μ controller parameters are optimised using hybrid ALO-pattern search technique, which outperforms the ALO optimised PID μ controller. A flexible AC transmission system device called gate controlled series capacitor performs better than an interline power flow controller. The studies show that the gate controlled series capacitor placed in all lines is its optimal location. The system dynamics are improved considerably with the incorporation of high voltage direct current link, the transient droop of the hydro governor. The PID μ controller effectively handles the parametric variations, random load and wind power profiles.

Comprehensive review of gate‐controlled series capacitor and applications in electrical systems

Flexible AC transmission system series compensation, such as series switched capacitors including gate-controlled series capacitor (GCSC) plays an important role to enhance grid system transfer power, stability, power quality and loss reduction. GCSC devices are implemented using fixed or switched capacitor in parallel with a pair of anti-parallel gate-commuted switches. They are connected in series of transmission and distribution lines and are commonly used to control the power flow on congested transmission lines. This study presents a review of GCSC devices and future perspectives.

MGSO optimised TID‐based GCSC damping controller in coordination with AGC for diverse‐GENCOs multi‐DISCOs power system with considering GDB and GRC non‐linearity effects

This study presents automatic generation control (AGC) in the presence of a gate controlled series capacitor (GCSC) to provide an effective frequency control ancillary service for a two-area diverse-GENCOs multi-DISCOs power system. First, the contribution of the GCSC in tie-line power exchange is formulated mathematically and then a tilt-integral-derivative (TID)-based damping controller is proposed. The effectiveness of the proposed TID-based GCSC-AGC coordinated controller is compared with just AGC, proportional-integral-derivative-based GCSC-AGC, thyristor controlled series capacitor-AGC, static synchronous series compensator-AGC, and thyristor controlled phase shifter-AGC. A modified group search optimisation (MGSO) algorithm is employed to adjust the considered controllers. Physical limitations of generation rate constraint (GRC) non-linearity and governor dead-band (GDB) effect are taken into account in the evaluations to obtain realistic results. Bilateral contracts and pool-co transactions are considered concurrently for the realisation of a competitive environment. Simulations reveal that the proposed controller outperforms the other controllers in providing better dynamic responses. Additional evaluations are performed under the un-contracted step, sinusoidal and random load demands seen as contract violations to demonstrate the superiority of the proposed controller over other controllers. Sensitivity analyses are performed for different uncertainty scenarios to show the robustness of the proposed control approach.

SSR Damping in Fixed-Speed Wind Farms Using Series FACTS Controllers

Subsynchronous resonance (SSR) damping in fixed-speed wind turbine generator systems (FSWTGS) by using two series flexible ac transmission system (FACTS) devices, the thyristor-controlled series capacitor (TCSC), and gate-controlled series capacitor (GCSC) are studied in this paper. The former is a commercially available series FACTS device, and the latter is the second generation of series FACTS devices using gate turnoff (GTO) or other gate-commuted switches. The GCSC is characterized by a fixed capacitor in parallel with a pair of antiparallel gate-commuted switches enabling rapid control of series impedance of a transmission line. It is shown that the SSR damping with a GCSC is limited to changing the resonance frequency, in comparison with a fixed capacitor, which may not be adequate to damp out the SSR. Therefore, a supplementary SSR damping controller (SSRDC) is designed for the GCSC. Moreover, it is proven that the GCSC equipped with a well-designed SSRDC can effectively damp the SSR in FSWTGS. In order to verify the effectiveness of the GCSC in SSR damping, its performance is compared with the TCSC, which is an existing series FACTS device. In addition, time-frequency analysis (TFA) is employed in order to evaluate and compare the SSR time-varying frequency characteristics of the GCSC and TCSC. The IEEE first benchmark model on SSR is adapted with an integrated FSWTGS to perform studies, and extensive simulations are carried out using PSCAD/EMTDC to validate the result.

Symmetrical and asymmetrical low‐voltage ride through of doubly‐fed induction generator wind turbines using gate controlled series capacitor

This study proposes a new method to improve low-voltage ride through of the doubly-fed induction generator (DFIG) wind turbines (WTs) using gate-controlled series capacitor (GCSC) in series with the generator rotor. Using GCSC, as soon as a voltage dip occurs at the generator's terminals, the GCSC inserts its capacitor in series with the rotor, increasing the voltage seen by the rotor winding. Consequently, the rotor over-current is limited and transmission of the inrush energy to the rotor side converter is reduced. Moreover, by this method, the chopper is not required for protecting the DC-link capacitor. Unlike the Crowbar method, which control of the generator is lost during the fault, the proposed method in this study avoids the loss of control during the grid faults. To validate the effectiveness of the proposed method, extensive time-domain simulation is performed using MATLAB/SIMULINK on a 1.5 MW DFIG-based WT.

Modeling and Control of Gate-Controlled Series Capacitor Interfaced With a DFIG-Based Wind Farm

This paper presents application and control of the gate-controlled series capacitor (GCSC) for series compensation and subsynchronous resonance (SSR) damping in doubly-fed induction generator (DFIG)-based wind farms. The GCSC is a new series FACTS device composed of a fixed capacitor in parallel with a pair of antiparallel gate-commuted switches. The study considers a DFIG-based wind farm, which is connected to a series-compensated transmission line whose parameters are derived from the IEEE first benchmark model for computer simulation of the SSR. The small-signal stability analysis of the system is presented, and the eigenvalues of the system are obtained. Using both modal analysis and time-domain simulation, it is shown that the system is potentially unstable due to the SSR mode. Therefore, the wind farm is equipped with a GCSC to solve the instability of the wind farm resulting from the SSR mode, and an SSR damping controller (SSRDC) is designed for this device using residue-based analysis and root locus diagrams. Using residue-based analysis, the optimal input control signal to the SSRDC is identified, which can damp the SSR mode without destabilizing other modes, and using root-locus analysis, the required gain for the SSRDC is determined. MATLAB/Simulink is used as a tool for modeling, design, and time-domain simulations.

Analysis of sub‐synchronous resonance in doubly‐fed induction generator‐based wind farms interfaced with gate – controlled series capacitor

This paper first presents a step-by-step tutorial on modal analysis of a doubly-fed induction generator (DFIG)-based series compensated wind farm. The model of the system includes a wind turbine aerodynamics, a sixth-order order induction generator, a second-order two-mass shaft system, a fourth-order order series compensated transmission line, an eighth-order rotor-side converter (RSC) and grid-side converter (GSC) controllers, and a first-order DC-link model. Then, using modal analysis and time-domain simulations, it is shown that a fixed-series compensated DFIG is highly unstable due to the sub-synchronous resonance (SSR) mode. In order to damp the SSR mode, the wind farm is interfaced with the gate-controlled series capacitor (GCSC) - which is a new series flexible AC transmission system (FACTS) device. A SSR damping controller (SSRDC) is designed for the GCSC using residue-based analysis and root locus diagrams, and an effective input control signal (ICS) to the SSRDC is identified in order to simultaneously increase damping of both the SSR and super-synchronous (SupSR) modes. The IEEE first benchmark model on SSR is adapted with an integrated DFIG-based wind farm to perform studies. Matlab/Simulink is used as a tool for designing process, and PSCAD/EMTDC is used for time-domain simulations.

Low voltage ride-through enhancement of fixed-speed wind farms using series FACTS controllers

This paper studies the application and control of three series flexible AC transmission system (FACTS) devices namely, the gate-controlled series capacitor (GCSC), the thyristor controlled series capacitor (TCSC), and series braking resistor (SBR), in order to enhance the low voltage ride-through (LVRT) in fixed-speed wind turbine generator systems (FSWTGS). Modeling and simulations are carried out in order to investigate and compare the performance of these devices, considering (1) successful reclosing of circuit breakers (CBs), (2) unsuccessful reclosing of CBs, and (3) connection of a dynamic load to the point of common coupling (PCC). Simulation results exhibit significantly enhanced transient stability of FSWTGS due to the employment of the GCSC. Furthermore, the GCSC is competitive with the TCSC and the SBR, and it requires less power rating to stabilize the wind generator system. Therefore, the proposed GCSC can be considered an effective tool to improve the LVRT of FSWTGS.

A Novel SSR Mitigation Method Based on GCSC in DFIG with Series Connected Compensator

This paper presents a novel study for SSR mitigating in the wind power systems based on DFIG using GCSC (Gate controlled series capacitor). The GCSC is composed of three pairs of anti-parallel GTO Thyristors (Gate Turn- off) connected in parallel with a fixed capacitor. The GCSC is applied to reduce inrush current in capacitor compensator during the transient operation by executing a proper firing angle control of thyristor gates. In order to realize SSR oscillation when the transient operation occurred, the DFIG turbine is connected through the shaft turbine model. The simulation results shown that the GCSC device is suitable and reasonable for suppressing SSR caused by torsional interaction (TI) and torque amplification (TA) and also damping the subsynchronous oscillation as well. The transient simulations have been carried out using PSCAD/EMTDC program to demonstrate the capability of the GCSC device in mitigating SSR.