Supplementary Damping Controller Research Articles

Supplementary damping controller design for FACTS devices using the Fuzzy Elman Wavelet Neural Network

AbstractThe occurrence of inter‐area oscillations in a power system is challenging to prevent. Thus, it is imperative to dampen inter‐area oscillations due to their potential to cause various instability problems. In this study, the Fuzzy Elman Wavelet Neural Network (FEWNN) was created as a novel neuro‐fuzzy network that combines the beneficial features of the Wavelet Neural Network (WNN), Takagi‐Sugeno‐Kang (TSK) fuzzy model, and cross‐coupled feedbacks inspired by the Elman Neural Network (ENN). Compared to alternative fuzzy wavelet networks, the representations of high‐order nonlinear dynamic systems in the proposed novel FEWNN are more effective, the training speed and computational power are greater, and interval type‐2 fuzzy membership functions are able to manage uncertainties in the power system. This paper uses FEWNN to develop a novel method for damping inter‐area oscillations caused by flexible alternating current transmission systems (FACTS) employing a supplementary damping controller (SDC) based on direct adaptive control theory (DACT). The proposed SDC is integrated into a Static Synchronous Series Compensator (SSSC) in a two‐machine two‐area power system and Kundor's four‐machine two‐area power system, as well as a Unified Power Flow Controller (UPFC) in Kundor's four‐machine two‐area power system. In conclusion, the damping power of the system is compared to that of other SDCs presented in recent studies. The MATLAB/SIMULINK environment was used to conduct all simulations for this work.

Improved methodology for damping sub‐synchronous oscillation in a series‐compensated DFIG‐based wind farm

AbstractThe interaction between the wind farm and the series‐compensated transmission line may lead to the sub‐synchronous oscillation (SSO) phenomenon which affects the system stability and equipment safety. Among the presented methods for damping the SSO phenomenon, the supplementary damping controller (SDC) is the most prevalent method because of its low cost, effectiveness, and simplicity. In all previous studies, one input control signal is fed to the SDC for mitigating the SSO. Here, two input control signals (active power and reactive power deviation) are applied to the SDC for enhancing the system stability and damping the SSO quickly. The ability of the proposed method for damping the SSO has not been investigated before. The proposed SDC is embedded into the q‐axis of the rotor‐side converter (RSC) inner current loop. The modified IEEE first benchmark model (FBM) is used to analyze the performance of the proposed method under different compensation levels, variable wind speeds, and sub‐synchronous control interaction (SSCI). Small‐signal stability using the eigenvalue approach is carried out, where the impact of the proposed method on sub‐synchronous mode, and super‐synchronous mode is investigated. The results successfully prove the superiority of the proposed method for damping the SSO under various operating conditions compared to some previous methods, where the least overshoot and faster convergence have been achieved by the proposed method in all studied cases.

A Supplementary Damping Control for MMC-HVDC System to Mitigate the Low-Frequency Oscillation Under Low Inertia Condition

With the increasing penetration of renewable energy, the inertia of AC system gradually decreases. When modular multilevel converter (MMC) based high voltage DC transmission (HVDC) system is connected to a low inertia AC system, the low-frequency oscillation may occur due to the interaction between MMC and synchronous generator (SG). To investigate this issue, a detailed small-signal model considering the dynamics of MMC and SG is developed and the corresponding eigenvalue analysis is conducted. Based on the developed model, the impact of the inertia on the low-frequency oscillation of MMC-HVDC system is studied, and the dominant low-frequency mode is investigated by participation factor and control parameter sensitivity analysis. From the results, it is found out that there exists close control interaction between SG and MMC under low inertia condition. To damp the low-frequency oscillation of MMC-HVDC system under low inertia condition, a supplementary damping control (SDC) approach is proposed, the parameters of the SDC approach are tuned by pole-assignment approach. Finally, the damping effect of the SDC approach is validated by theoretical analysis and simulation study in PSCAD.

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).

Multimachine stability improvement with hybrid renewable energy systems using a superconducting magnetic energy storage in power systems

Energy storage systems (ESS) have played a vital role in modern power systems to improve system stability and reliability in recent years. This paper describes the role of SMES in improving the power system stability of a multimachine interconnected with hybrid renewable energy systems (RES) such as wind and solar PV. It studies the transient stability of the system by creating a symmetrical fault in a multimachine system at various locations. The hybrid RES simulates an equivalent aggregated 75 MW photovoltaic array and a wind turbine with a capacity of 300 MW PMSG (permanent magnet synchronous generator). It couples a common DC link via a voltage source and dc/dc boost converters. A voltage source inverter connected with a step-up transformer and transmission line coupled to a multimachine system. The voltage source converter and inverter use a model predictive controller (MPC) for a better output voltage profile and to improve the system stability. A SMES is connected through a dc/dc converter with PID-SDC (Proportional Integrating Derivative Supplementary Damping Controller). It effectively suppresses power oscillations and smoothening during generation fluctuations. It reduces the low-frequency oscillations at the multimachine side during three-phase fault conditions at various locations in the system. The system's stability is improved by 3.36 s after clearing the fault. The effectiveness of the entire system is studied in the time domain simulations using MATLAB/SIMULINK software.

Influence evaluation of signal transmission delay on supplementary damping controller for SVC in power system

Supplementary damping controller (SDC) for static var compensator (SVC) can be used to damp interarea low-frequency oscillations, but the influence of signal transmission delay on damping performance is generally neglected in the previous research. Because the delay may deteriorate damping performance or even cause instability for power system, this work intensively investigates the influence of signal transmission delay on input signal selection and parameter setting in SDC design. A novel evaluation method based on delay-dependent stability criterion and model order reduction is proposed to obtain the tradeoff between damping performance and delay margin for the SDC to be designed. Delay margin, determined by the proposed method, is taken as a critical index to evaluate the delay influence on SDC design. Case studies are carried out on two-area four-generator power system. Results show that for input signals with higher mode observability by residue method, such as current magnitude and active power of transmission line, delay margin decreases with the increase of SDC gain or delay variation ratio, which indicates that appropriately setting the gain can ensure SDC with better damping performance and larger delay margin.

Adaptive Damping Control Scheme for Wind Grid-Connected Power Systems With Virtual Inertia Control

With the large-scale wind power integration into the power system, the inertia and damping characteristics of the system have been weakened, which is not conducive to fulfill the grid-friendly operation of wind power. Aiming at this, an adaptive control scheme combining virtual inertia control (VIC) and supplementary damping controller (SDC) is proposed in this paper. Firstly, the mathematical model of wind grid-connected power system with VIC is established. Secondly, the polytopic linear parameter varying (LPV) system is built to describe the uncertainty of system operating points, and the gap metric-based nonlinear evaluation method is used for polytope vertex configuration. Next, Youla-Kucera parametrization are extended to polytopic LPV system to design an adaptive damping control, in which VIC and SDC are coordinated to provide damping and virtual inertia simultaneously. Finally, the proposed adaptive control scheme is compared with several existing control techniques to validate its effectiveness and advantages in suppressing system oscillation in the modified IEEE 39-bus system integrated with 2 wind turbines.

Sub‐synchronous interaction damping controller for a series‐compensated DFIG‐based wind farm

Sub-synchronous interaction (SSI) phenomenon is one of the dynamic system problems that have an adverse influence on the safety and stability of the system.The use of supplementary damping controllers (SDCs) in the double-fed induction generator (DFIG) converter controllers is quite promising due to their simplicity,low costs, effectiveness, and easiness of tuning. This paper presents a new effective input control signal, rotor voltage, to the SDC for damping SSI in a series-compensated DFIG-based wind farm. The proposed SDC is embedded into both the q-axis and d-axis of the rotor-side converter inner current loops. Particle swarm optimization algorithm is used to identify the optimum parameters of the SDC which maintain the system stability at various operation conditions. Both eigenvalue analysis and time-domain simulations have been carried out to demonstrate the capability of the proposed SDC for enhancing the system stability and damping SSI. Compared to the conventional SDC, the proposed SDC has the best performance where it can quickly and robustly damp the SSI at different compensation levels, different wind speeds, and sub-synchronous control interaction.

Robust Power Designing of Supplementary Damping Controller in VSC HVDC System to Improve Energy Conversion Efficiency of Wind Turbine and Power System Stability

Because of low losses and voltage drop, fast control of power, limitless connection distance, and isolation issues, using high-voltage direct-current (HVDC) transmission system is recommended to transfer power in the power systems, including wind farms. This paper aims to propose a supplementary damping controller (SDC) based on the HVDC to improve not only power system dynamic stability but also energy conversion efficiency and torsional vibration damping in the wind power plants (WPPs). When the WPPs are working in power control mode, the active power is set to its reference value, which is extracted from power-speed curve. This paper shows that torsional oscillations associated with the poorly torsional modes can be affected by different operating regions of the power-speed curve of WPP. Therefore, it is essential to employ an SDC to have the optimum energy conversion efficiency in the wind turbine and the most dynamic stability margin in the power system. The SDC is designed using a fractional-order PID controller (FOPID) based on the multiobjective bat-genetic algorithm (MOBGA). The simulation results show that the proposed control strategy effectively works in minimizing the torsional and electromechanical oscillations in power system and optimizing the energy conversion efficiency in the wind turbine.

Damping forced oscillations in power system via interline power flow controller with additional repetitive control

With the continuous expansion of power systems and the application of power electronic equipment, forced oscillation has become one of the key problems in terms of system safety and stability. In this paper, an interline power flow controller (IPFC) is used as a power suppression carrier and its mechanism is analyzed using the linearized state-space method to improve the system damping ratio. It is shown that although the IPFC can suppress forced oscillation with well-designed parameters, its capability of improving the system damping ratio is limited. Thus, combined with the repetitive control method, an additional repetitive controller (ARC) is proposed to further dampen the forced power oscillation. The ARC control scheme is characterized by outstanding tracking performance to a system steady reference value, and the main IPFC controller with the ARC can provide higher damping, and further reduce the amplitude of oscillations to zero compared with a supplementary damping controller (SDC). Simulation results show that the IPFC with an ARC can not only greatly reduce the oscillation amplitude, but also actively output the compensation power according to the reference value of the ARC tracking system.

Mitigating inter-area oscillation of an interconnected power system considering time-varying delay and actuator saturation

A wide area damping controller (WADC) is designed in this paper to mitigate the frequency deviation of interconnected power system. The effect of time delay during wide area measurement system (WAMS) and saturation of the actuator is also considered in this work while designing the WADC. The effect of communication delay along with the saturation of a actuator can make the interconnected power system unstable. This paper focuses on finding a stabilization criterion of the power system connected with a WADC. The WADC is designed taking the effect of time-varying delay in the WAMS and saturation of the actuator into consideration. The saturation of the actuator is modelled with the help of dead zone type non-linearity. In this paper, a Lyapunov–Krasovskii functional is used to design a state feedback control law based on linear matrix inequality (LMI) taking time-varying delay and the actuator saturation into consideration. A thyristor controlled series capacitor (TCSC) is used as an actuator. A supplementary damping controller (SDC) is used as the WADC in this paper to provide sufficient damping. Simulation study on four machine 11 bus power system and New England 39 bus power system is performed to understand the performance of the designed controller. The results are also verified in real-time using OPAL-RT.

Controller design for output constrained thyristor controlled series capacitor (TCSC) of time-delayed power system

Abstract Thyristor Controlled Series Capacitor (TCSC) is employed as actuator in an interconnected power system using Supplementary Damping Controller (SDC) to enhance the power transfer capabilities between areas as well as damp out the Inter-Area Low-Frequency (IALF) oscillations by varying the impedance of transmission lines. The time-varying delays in the feedback loop and asymmetric saturation limits at the output of TCSC may reduce the performance of the designed controller and lead to closed-loop instability if these are not considered in the process of controller design. Usually, a Minimum Absolute Saturation Bound technique (MASB) is used to convert asymmetric saturation limits into symmetric one. However, such consideration provides an apparent conservative and degrades the performance of the control system. To reduce the conservative in the control design process, a Normalized Saturation Bound (NSB) technique is used in this paper to convert asymmetric saturation limits of TCSC of time-delayed power system. The L-K functional and generalized sector conditions are utilized in the proposed controller design process to compensate the effect of time-varying delay and converted symmetric saturation limits. Sufficient conditions required for controller design are formulated in LMI form. 2-area 4-machine power model is used to verify the performance of the designed controller. From the simulation results, it is observed that the designed controller is giving superior performance in the present of time-varying delays and asymmetric saturation as compared to the designed controller using MASB technique.

Coordinated Damping Control Design for Power System With Multiple Virtual Synchronous Generators Based on Prony Method

With more renewables integrated into power grids, the systems are being transformed into low inertia power electronic dominated systems. In this situation, the virtual synchronous generator (VSG) control strategy was proposed to deal with insufficient inertia challenge caused by the reduction of synchronous generation. However, as the VSG control method emulates the dynamic behavior of traditional synchronous machines, the interaction between multiple VSG controllers and synchronous generators (SGs) may cause low-frequency oscillation similar to that caused by the interaction between multiple SGs. This paper reveals that the system low-frequency oscillatory modes are affected by multiple VSGs. Then Prony analysis is utilized to extract the system mode information which will be subsequently used for VSG controller design, and a decentralized sequential coordinated method is proposed to design the supplementary damping controller (SDC) for multiple VSGs. The system low-frequency oscillation is first analyzed based on a modified two-area system with a linearized state-space model, and a further case study based on a revised New England 10-machine 39-bus system is used to demonstrate the effectiveness of the proposed coordinated method for multiple VSGs.

Coordinated Wide-Area Control of Multiple Controllers in a Power System Embedded With HVDC Lines

This paper develops a coordinated wide-area control of power system stabilizers (PSSs), static VAr compensators (SVCs), and supplementary damping controllers (SDCs) for damping low frequency oscillations (LFOs) in a power system embedded with multiple high voltage DC (HVDC) lines. The improved damping is achieved by designing a coordinated wide-area damping controller (CWADC) that employs partial state feedback. The design methodology uses a linear matrix inequality (LMI)-based mixed H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> robust control for multiple operating scenarios. To reduce the high computational burden, an enhanced version of selective modal analysis (SMA) is employed that not only reduces the number of required wide-area feedback signals, but also identifies alternate feedback signals, in case of failure of the primary signals. Additionally, the impact of delays on the performance of the control design is investigated. The studies are performed on a 29 machine, 127 bus equivalent model of the Western Electricity Coordinating Council (WECC) system-embedded with three HVDC lines and two wind farms.

Mitigation of Subsynchronous Control Interactions Using Multi-Terminal DC Systems

This article presents a control strategy to mitigate subsynchronous control interactions in doubly-fed induction generator (DFIG)-based wind farms. The strategy makes use of a multi-terminal dc (MTDC) system to damp subsynchronous oscillations (SSOs) by adding a supplementary damping control (SDC) to MTDC grid converters. The SDC is focused on stations with modular multilevel converters. This converter topology currently allows the integration of several high-voltage and high-power MTDC applications into modern power systems. Additionally, the case in which SDCs are added to both MTDC grid converters and DFIG converters is analyzed. The SDC is designed using an identified model of the system. The identification method injects probing signals from the converter terminals and obtains an identified model by measuring the response of the system. This method facilitates the control tuning and implementation of the SDC in practical systems in which either the equations and parameters of some equipment can be difficult to know precisely or the model of commercial equipment is not available.

Mitigation of forced oscillations using VSC-HVDC supplementary damping control

Forced oscillation has become one of the main power grid dynamic stability problems, which can cause high amplitude oscillation of the active power in the tie line. The supplementary damping controller (SDC) of the voltage source converter based high voltage direct current (VSCHVDC) has demonstrated its effectiveness in suppressing inter-area modal oscillation, but its role in mitigating forced oscillation has not been studied in the literature. In this paper, an active disturbance rejection control (ADRC) based SDC of the VSCHVDC is designed to mitigate forced oscillations. The mitigation effect of the ADRC based SDC on forced oscillation is compared to the traditional one under different scenarios. Simulation results of four-machine two-area AC-DC hybrid system indicate that the traditional SDC is sensitive to the frequency of the disturbance source, and the reactance between the disturbance source and the VSCHVDC, whereas the ADRC based SDC can effectively mitigate the forced oscillation whatever the frequency of disturbance source is near or far from the inter-area natural frequency, and its mitigating effect is almost not affected by the reactance between the disturbance source and the VSCHVDC.

Integrations of Neural Networks and Transient Energy Functions for Designing Supplementary Damping Control of UPFC

This article presents an integrated scheme for supplementary damping control of unified power flow controllers (UPFCs) in order to mitigate low-frequency oscillations in power systems. The entire control system consists of the primary control and the supplementary control. In the primary control, the passivity-based control is considered in the current control loop of two converters for achieving more prompt and accurate dynamical responses. In the supplementary control, the transient energy function (TEF) approach will be explored first for designing the damping control of UPFCs. This control action can be considered as an extension of droop control used in the synchronous generator. In order to further cope with unmodeled dynamics of power systems and provide the online dynamic adaptation ability, neural networks approximated control actions are designated for online weight adjustments of the TEF-based supplementary control. Numerical simulations on three benchmark systems have been performed to validate the proposed control method for providing the extra damping and suppressing power swings even under severe operating conditions.

Anti‐windup compensator design for power system subjected to time‐delay and actuator saturation

In this study, a delay-dependent anti-windup compensator (AWC) is designed for supplementary damping control (SDC) of flexible AC transmission system (FACTS) device to enhance the damping of inter-area oscillations of the power system subjected to time-delay and actuator saturation. By employing global signal measurements, an SDC of FACTS device is designed without considering the effect of time-delay and actuator saturation to stabilise the power system using a robust output feedback controller with pole placement approach. Then, based on the generalised sector condition and Lyapunov–Krasovskii functional, an add-on delay-dependent AWC is designed to mitigate the adverse effect of time-delay and actuator saturation non-linearity. For the design of delay-dependent AWC, sufficient conditions guarantee the asymptotic stability of the closed-loop power system are formulated in the form of linear matrix inequalities (LMIs). These conditions are cast into the LMI-based convex optimisation problem to compute the AWC gains. To evaluate the effectiveness of the proposed controller, non-linear simulations were performed first using MATLAB/Simulink. Then, the authors implemented the proposed controller in real-time using the Opal-RT digital simulator. From the obtained results, it is observed that the proposed controller enhances the damping of inter-area oscillations by compensating the effect of time delay and actuator saturation.

PSS AND IPFC POD controllers coordinated tuning by an Adaptive Genetic Algorithm with Hyper-mutation

Flexible AC transmission systems (FACTS) are a modern technology to increase controllability in power systems. This work presents an analysis of Interline Power Flow Controller (IPFC) which is a FACTS device. This device control and manage power flow in transmission lines. Supplementary damping controller is installed on IPFC Proportional Integral (PI) control. Power Oscillation Damping (POD) and Power System Stabilizers (PSS) contribute to power system stability. This works represents the electric power system and Interline Power Flow Controller FACTS device by a current sensitivity model (CSM). This work focuses on small-signal stability studies using an Adaptive Genetic Algorithm and Hyper-mutation (AGAH) to design simultaneously controller parameters. Adaptive Genetic Algorithm aims to find optimal controller parameters to enhance greatly stability of the power system. This paper considers two areas 14 bus symmetrical system in order to assess proposed algorithm. Simulations are carried out in MatLab platform in order to compare genetic algorithm with proposed algorithm performance. Results show AGAH outweighed AG by time convergence and accuracy.

Coordinated Supplementary Damping Control of DFIG and PSS to Suppress Inter-Area Oscillations With Optimally Controlled Plant Dynamics

This paper proposes a design method to coordinate dual-channel supplementary damping controllers (SDCs) of doubly-fed induction generators (DFIGs) and power system stabilizers (PSSs) for suppression of inter-area power oscillations. A dynamic performance index is introduced to measure the dynamics of the conventional synchronous generator and DFIG during the damping control process. Hence, the proposed method designing the PSS and SDC is formulated as an optimization problem with the objective function being the sum of weighted performance indexes and the constraints indicating the requirements on the damping of the inter-area modes. Solving the optimization problem can obtain the optimal SDC and PSS, which can meet the required damping results as well as optimize dynamics of the controlled plants. Moreover, by adjusting weights in the objective function, the damping control burden can be flexibly and feasibly allocated between active and reactive power channels of DFIGs or among the damping controllers. Simulations with the modified New England and New York interconnected system prove that the proposed optimization based tuning method can not only robustly coordinate the PSS and SDC to effectively damp inter-area oscillations but also improve the dynamics of controlled plants during the damping control process over different operating conditions.