Inertia Control Research Articles

Virtual Inertia Control in Autonomous Microgrids via a Cascaded Controller for Battery Energy Storage Optimized by Firefly Algorithm and a Comparison Study with GA, PSO, ABC, and GWO

Modern (micro) grids host inverter-based generation units for utilizing renewable and sustainable energy resources. Due to the lack of physical inertia and, thus, the low inertia level of inverter-interfaced energy resources, the frequency dynamic is adversely affected, which critically impacts the stability of autonomous microgrids. The idea of virtual inertia control (VIC), assisted by battery energy storage systems (BESSs), has been presented to improve the frequency dynamic in islanded microgrids. This study presents the PD-FOPID cascaded controller for the BESS, a unique method for enhancing the performance of VIC in islanded microgrids. Using the firefly algorithm (FA), the settings of this controller are optimally tuned. This approach is robust to disruptions due to uncertainties in islanded microgrids. In several scenarios, the performance of the suggested approach is compared with those of other control techniques, such as VIC based on an MPC controller, VIC based on a robust H-infinite controller, adaptive VIC, and VIC based on an optimized PI controller. The simulation results in MATLAB show that the suggested methodology in the area of VIC is better than previous methods.

Modified Differential Evolution Algorithm for Governing Virtual Inertia of an Isolated Microgrid Integrating Electric Vehicles

In modern power systems, there is a greater penetration of renewable sources, resulting in the expansion of microgrid. By implementing RES instead of conventional synchronous machines, the system’s overall inertia is significantly reduced. Modern and future power systems must reduce system inertia and keep the frequency at its nominal value since frequency oscillation impacts on the functionality, stability, and resilience of the system. Therefore, creating a stable, scalable, and reliable virtual inertia control system is crucial to effectively minimize the deviations during significant contingencies. Consequently, taking into account the probable issues, the foremost objective of this research work is to improve the dynamic security of an island microgrid through the implementation of a frequency control concept based on virtual inertia control. In the research study, the proposed microgrid system comprises of photovoltaics, wind-generating units, thermal power units, storage units, electric vehicles (EVs), and loads. A cascaded PIDFN controller is optimally designed using a novel metaheuristic modified differential evolution (MDE) algorithm that regulates the frequency based on virtual inertia control. In the MATLAB®/SIMULINK environment, various operating situations such as load variations, RES, and EVs disconnection are investigated, and the performance of the VIC-based MDE controller was compared to that of other controllers based on evolutionary optimization algorithms such as DE and TLBO. The results validate that the recommended virtual inertia control strategy enhances the reliability of the system.

Configuration and control strategy for an integrated system of wind turbine generator and supercapacitor to provide frequency support

Wind turbine generators (WTGs) can provide fast frequency support to power systems through inertial control via the release of kinetic energy stored in rotating masses. However, because the kinetic energy is limited, the frequency support from WTGs based on inertial control cannot last until the system frequency recovers to the nominal value. Thus, it must be terminated during system frequency control, which results in adverse effects on the system frequency response. To guarantee sufficient energy and fast response for the frequency support of a permanent magnet synchronous generator based WTG, this study proposed the integration of a DC/DC converter-interfaced supercapacitor (SC) at the DC link of the WTG and consequently formed an integrated system of WTG and SC (WTG-SC system). First, the configuration of the SC was proposed based on the evaluation of the energy consumption of the WTG-SC system for frequency support and the available kinetic energy of the WTG. Second, a control structure that coordinates the machine-side converter (MSC), grid-side converter (GSC), and DC/DC converter of the SC was proposed. Finally, a “dual-droop” frequency support control scheme for the WTG was proposed to enhance the WTG-SC system’s frequency support capability and the efficiency of energy utilisation during frequency support. The efficacy of the proposed approach was validated using a modified IEEE 39 bus system with a wind farm comprising 100 WTG-SC systems under different operating conditions.

The Doubly-fed Wind Power Generator Virtual Synchronous Control

Given the high proportion of wind power frequency/voltage stability problems, the power system based on synchronized coordinates (DFIG) mathematical model of doubly-fed motor, studies a current source containing inertial link type wind turbine virtual synchronous control strategy, and the virtual synchronous control loop and the current control design of the inner ring. Established in the Matlab/Simulink simulation model of doubly-fed wind power generator, the virtual synchronous generator realized virtual synchronous generator inertia. Simulation results confirm the validity of the theoretical analysis and the effectiveness of the proposed control strategy.

Virtual Inertia Control for CHB-STATCOM in a Power Electronics Dominated Grid

Integration of renewable energy sources (RESs) leads the power system to be a low inertia system, resulting in frequency deviation in the grid. This paper presents a cascaded H-bridge (CHB) converter-based static synchronous compensator (STATCOM) providing virtual synchronous inertial support. This topology achieves two functionalities. 1. It reduces the system frequency deviation in a power electronics dominated grid (PEDG) following the updated grid codes. 2. Without disturbing the normal operation of CHB-STATCOM, it provides reactive power support. This topology uses the cumulative stored energy in the distributed DC-bus capacitors of CHB-STATCOM to improve the frequency nadir/zenith and the rate of change of frequency (RoCoF), preventing frequency instability. A closed- loop control algorithm is developed, which injects an adequate amount of stored energy to prevent frequency variation. It also facilitates re-energizing the capacitors in a smooth fashion, so that subsequent frequency events can be taken care of. For this, a high-pass-filter (HPF) is designed for autonomous DC- link voltage restoration for CHB converter. Relationship between frequency variation and inertial energy support by CHB is analyzed in depth. Finally, the viability of the proposed theory is verified in OPAL-RT test bench for step-up and step-down load change.

Inertia control method of direct drive permanent magnet wind turbine under high wind power permeability

Direct-drive permanent magnet wind turbine has high power generation efficiency, especially in low wind speed environment, and is widely used for wind power generation. Direct-driven permanent magnet wind turbines show no inertia response to the system through the grid connection of full-power converters, resulting in increased frequency fluctuation, poor response effect and reduced stability time of the system under sudden load and sudden wind speed conditions. Based on this, an inertia control method of direct-drive permanent magnet wind turbine under high wind power penetration is proposed, and the model of direct-drive permanent magnet wind turbine is built by designing functional modules to improve the synchronous control effect under high wind power penetration. The vector control calculation method is used to design the virtual inertia control parameters, and the decoupling quantity is introduced to decouple the parameters with filter inductance, so as to improve the supporting capacity of power grid frequency fluctuation. The simulation results show that the proposed method has a fast frequency response under sudden load change, and it drops to the lowest value of 49.16 Hz at 12.14 s. Under the condition of sudden change of wind speed, the system frequency rises to the highest value of 50.38 Hz at 12.94 s. It is proved that the proposed method has a certain suppression effect on the amplitude of frequency change, effectively shortens the time for the system frequency to return to steady state, and thus has more advantages.

Stability Analysis: Two-Area Power System with Wind Power Integration

This paper focuses on a comprehensive stability study of a two-area power system with wind power integration and synthetic inertia control in each area, considering the effects of varying the interconnection link. Normally, synthetic inertia proposals are analyzed in one-area systems, in which stability is tested without considering transmission system phenomena, such as coherency. As modern power systems are progressively becoming interconnected, the possibility of forming two or more non-coherent areas is likely, which poses a challenge to synthetic inertia control techniques that use system frequency as a main feedback signal. In this context, this work addresses a crucial gap in the existing literature and provides a valuable starting point for studying more complex interconnected power systems with wind power integration. Simulations were performed in Matlab-Simulink considering a data-driven frequency dynamics model of the Chilean Electric System, and a wind power model with synthetic inertia control H2 norm minimization in each area. The results showed that it is possible to find local optimal feedback gains, preserving the stability of the global system under significant variations in the interconnection link. RoCoF and Nadir indicators are provided, highlighting the benefits of synthetic inertia control, particularly in low-inertia situations.

Mountain gazelle optimisation‐based 3DOF‐FOPID‐virtual inertia controller for frequency control of low inertia microgrid

AbstractThe primary objective of the authors is to design a new robust and improved virtual inertia controller (VIC) for renewable energy dominated inverter interfaced low inertia microgrid (LIMG). Increasing penetration of inertia‐less renewable generation in microgrid leads to increased frequency deviation during and after a disturbance. To improve the frequency response of the LIMG, conventional VIC added with different second stage and third stage controllers are proposed in existing works. Higher degree‐of‐freedom (DOF) PID controller synchronised with fractional‐order (FO) operators are used with conventional VIC controllers. These controllers work in addition with conventional VIC and the multi‐stage controllers make the system more complex. To reduce the number of controller stages and, subsequently, reduce cost and complexity of the system, a single stage 3DOF‐FOPID controller is proposed to mitigate the frequency deviation after a disturbance in a LIMG. Performance of the proposed single stage controller is compared with that of the existing controllers to establish the advantages of the proposed controller. The parameters of the proposed 3DOF‐FOPID controller are optimised by Mountain Gazelle Optimsation. The robustness of this controller is also tested for random load fluctuation and renewable power variations in presence of system non‐linearities.

INFLUENCE OF THE SYNTHETIC INERTIA REGULATOR ON FREQUENCY CHANGES OF ELECTRIC POWER SYSTEMS IN TRANSIENT MODES

The article is devoted to the use of wind power plants as sources of synthetic inertia in order to increase the stability margins and damping frequency fluctuations. The purpose of this study is to establish the possibility of using the synthetic inertia controller of wind turbines to reduce the amplitudes of frequency fluctuations in transient conditions. One consequence of integrating a large number of wind farms is to reduce the amount of kinetic energy (inertia) available to operate the system. If the system inertia becomes too low, it can compromise frequency stability when large generating units fail. The smaller the moment of inertia in the system, the greater the frequency fluctuations occur after the active power balance is disturbed. A regulator of synthetic inertia of a wind power plant has been obtained, which makes it possible to reduce frequency dips during transient conditions. Recommendations are made regarding the choice of gain factors for the inertia controller. A control model for wind turbines with a synthetic inertia controller is presented. On the example of a test circuit of an electric power system, modeling of disturbances in the form of a load surge and a short circuit was carried out. As a result, the characteristics of the change in the frequency of the electric power system in the absence and presence of a wind power plant are given.

Damping control of polodes, inertia and natural frequencies: Theory and application to automotive suspensions

This paper shows how tunable dampers can help control the instant centre of rotation of a 2D rigid body and its polode in planar motion, which in turn implies that the inertia tensor can also be controlled. For mechanisms equipped with some elasticity the results show that damping can also control their natural frequencies. The foundation of a general theory to control the polode is presented, exploring the chance of an optimal control formulation of the problem via a variational control principle, approached by the LQR (Linear Quadratic Regulator) method, after a suitable linearization. Application to automotive suspension linkages is presented that demonstrates the control of the instant roll centre and axis and consequently its instant roll vibration frequency to optimize the response, when excited by lateral inertia forces.

Small-Signal Modeling and Stability Analysis of a Grid-Following Inverter with Inertia Emulation

Power-converter-based energy-harvesting and storage systems are becoming more prevalent in the electrical grid, replacing conventional synchronous generators. Consequently, grid inertia is diminishing, and to address this, inverter-based energy conversion systems are required by grid codes to provide frequency control support to the main grid. This is undertaken to increase the equivalent inertia of the system and reduce frequency variations. This type of control is necessary and designed for handling large system transients. However, it also impacts the small-signal stability of the grid-connected converters. To investigate this issue, this paper addresses the influence of synthetic inertia control on the output admittance of a grid-following inverter and its interaction with the grid equivalent impedance. A synchronous reference frame dynamic model of the grid-following inverter closed-loop system is obtained and linearized at an operating point to analyze the small-signal stability of the low-switching frequency inverter. The models are validated through numerical simulations. The analysis verifies the interactions of the internal control loops, such as the AC current control with voltage feedforward, DC-link voltage control with power-feedforward, phase-locked loop, and AC voltage control with inertial control. Additionally, the interactions between the output admittance of the inverter and the grid impedance are verified using the generalized Nyquist criterion. The stability regions are validated through simulations, and the results show that the system gain margin is reduced for increasing values of synthetic inertia gain and lower grid short-circuit ratios. Furthermore, there is a limit in the voltage and power-feedforward bandwidth to avoid degrading the system stability when utilizing the synthetic inertia control.

A virtual inertial control strategy for bidirectional interface converters in hybrid microgrid

Insufficient inertia is one of the urgent problems to be solved in the stability of AC-DC hybrid microgrid. In order to improve AC bus frequency and DC bus voltage inertia in hybrid microgrid, a virtual inertia control strategy for bidirectional interface converter (BIC) based on virtual synchronous generator (VSG) is proposed. The virtual inertia equations on both sides of the AC and DC are used to slow down the variation of the DC voltage and the AC frequency. When the load fluctuates, the dynamic response of the DC voltage, the AC frequency and the power transmission between the AC and DC subnets is improved, thus improving the stability of the system. This control strategy enables BICs to share active power equally under stable conditions, prevents circulating power, and achieves accurate power sharing among parallel BICs. The small signal model of BIC under virtual inertia control is established, the dynamic characteristics of the system under different control parameters are analyzed, and the influence of the control parameters on the system is discussed. The simulation model is established in PSCAD/EMTDC software to verify the correctness of the proposed control strategy.

Inertia Evaluation of Wind Farm Under Overspeed Power Shedding Control

As the penetration rate of wind power generation gradually increases in most grids, it is necessary to evaluate wind farms’ inertia to provide inertia information for electric grids and boost grid stability. This paper firstly models the inertia control mode of overspeed power shedding, which can realize the inertia control under the operation of different blade tip speed ratios, so that the wind turbine has a high inertia support capability. Then the energy change process in the inertia control process is analyzed, and the virtual inertia time constant is derived to evaluate a single unit’s inertia. Finally, a simple wind condition and the wind farm’s inertia control requirements in a day are simulated using an equivalent model, and the inertia level of the wind farm is calculated. The proposed research approach can alleviate the sophistication of inertia evaluation which also effectively consider the influence of inertia control.

Parameter Optimization for Temporary Primary Frequency Control of Wind Turbines Based on Analytical Derivation

DFIG has the capability to participate in power system frequency modulation through inertial control by returning the energy stored in the rotating mass of the generator that is delivered to the grid. When frequency modulation occurs, the primary frequency drop can lead to a reduction in the rotor kinetic energy stored in the DFIG, which is subsequently used to produce extra active power to sustain the system frequency. However, once the available rotor kinetic energy is released, the output power of the DFIG abruptly drops to restore the rotor speed. To reduce the extent of the secondary frequency deviation caused by the inertial control of DFIGs, this paper applies an analytically derived approach to optimize the parameters of temporary primary frequency control during rotor speed recovery. Specifically, the parameters optimized include termination time and active power Simulation results conducted using DIGSILENT simulation software have demonstrated that the optimized temporary primary frequency control strategy is capable of effectively reducing the secondary frequency drop that may occur when the DFIG is removed from frequency control. Moreover, setting the optimal termination time and controlling the active power output while the rotor speed is being restored are crucial to prevent excessive mechanical wear and fatigue that may be induced by a too-rapid recovery of rotor speed.

Multi-Mode Active Inertia Support Strategy for MMC-HVDC Systems Considering the Constraint of DC Voltage Fluctuations

The Modular Multilevel Converter based High Voltage Direct Current Transmission (MMC-HVDC) systems can provide active inertia support for the connected ac grid for fast frequency recovery. However, the submodule (SM) capacitance voltages will be affected by the transient power flow and there exist dc voltage fluctuation issues during the active inertia support process. This paper proposes a multi-mode active inertia support strategy for MMC-HVDC systems considering the constraint of dc voltage fluctuations. The analytical relationship of dc voltage fluctuations and ac frequency variations when MMC adopts the virtual inertia control is firstly established, and then different inertia support operation modes are divided according to the allowable dc voltage fluctuation ranges. Next, the multi-mode active inertia support strategy for MMC-HVDC is proposed, which can provide flexible active inertia support on the premise of reasonable dc voltage fluctuations according to different frequency variations and recovery requirements. Besides, the inertia support process of MMC is equivalent to the zero-input response of first-order circuit to calculate the maximum sustainable supporting time, which ensures that the dc voltage fluctuation constraint can be well satisfied in different operation modes. Finally, several simulation results verify the effectiveness of the proposed control strategy.

Adaptive virtual inertia controller based on machine learning for superconducting magnetic energy storage for dynamic response enhanced

The goal of this paper was to create an adaptive virtual inertia controller (VIC) for superconducting magnetic energy storage (SMES). An adaptive virtual inertia controller is designed using an extreme learning machine (ELM). The test system is a 25-bus interconnected Java Indonesian power grid. Time domain simulation is used to evaluate the effectiveness of the proposed controller method. To simulate the case study, the MATLAB/Simulink environment is used. According to the simulation results, an extreme learning machine can be used to make the virtual inertia controller adaptable to system variation. It has also been discovered that designing virtual inertia based on an extreme learning machine not only makes the VIC adaptive to any change in the system but also provides better dynamics performance when compared to other scenarios (the overshoot value of adaptive VIC is less than -5×10-5).

Control technique for power quality improvement of isolated wind power generation system

Power quality (PQ) problems for renewable energy system (RES) is major challenge for using these systems. Amplitude, frequency, and waveform is important PQ parameters especially for standalone or isolated systems. In this paper we propose RES with wind turbine (WT) and permanent magnet synchronous generator (PMSG) to feed different loads (liner, non-liner) through AC-DC-AC converter. The PMSG operate with fuzzy logic inertia controller, to convert turbine torque form PU to Nm. The inverter stage in the converter operate according to proportional integral derivative (PID) controller with 3rd harmonic injection pulse width modulation (PWM) to regulate the AC voltage in load side. For the same case study and operating condition, we compared the result for system parameters when using ordinary PWM and using PID with 3rd harmonic injection. Voltages total harmonics distortion (THD) was less than 2% with liner loads, and 3.5% with non-liner load and the same was for current load, the voltage amplitude was between (1-1.03) PU under different wind speed by using the proposed controller.

Control technique for power quality improvement of isolated wind power generation system

Power quality (PQ) problems for renewable energy system (RES) is major challenge for using these systems. Amplitude, frequency, and waveform is important PQ parameters especially for standalone or isolated systems. In this paper we propose RES with wind turbine (WT) and permanent magnet synchronous generator (PMSG) to feed different loads (liner, non-liner) through AC-DC-AC converter. The PMSG operate with fuzzy logic inertia controller, to convert turbine torque form PU to Nm. The inverter stage in the converter operate according to proportional integral derivative (PID) controller with 3rd harmonic injection pulse width modulation (PWM) to regulate the AC voltage in load side. For the same case study and operating condition, we compared the result for system parameters when using ordinary PWM and using PID with 3rd harmonic injection. Voltages total harmonics distortion (THD) was less than 2% with liner loads, and 3.5% with non-liner load and the same was for current load, the voltage amplitude was between (1-1.03) PU under different wind speed by using the proposed controller.

Adaptive Control of Mini Space Robot Based on Linear Separation of Inertial Parameters

Space robots exhibit a strong dynamic coupling between the manipulator and the base spacecraft, with this phenomenon being particularly pronounced in mini space robots. The uncertainty surrounding the inertial parameters of space robots often renders dynamics-based controllers ineffective, and identifying these parameters in an on-orbit environment poses significant challenges. In this paper, we propose an adaptive controller for dynamic approximation that is specifically designed for mini space robots. This controller employs a linear separation of inertial parameters and utilizes recursive least-squares and Lyapunov methods to update the inertial parameter vectors. Simulation results validate the effectiveness of this adaptive controller in enabling mini space robots to accurately track predefined trajectories. Additionally, we compare the effects of the two parameter update methods on the controller stability under varying prior inertial parameter errors. The proposed inertial parameter separation adaptive controller significantly approximates the dynamics of mini space robots and facilitates precise on-orbit control, thereby offering considerable potential for advancing space exploration, satellite missions, and robotic operations.

Coupling stability analysis of synchronous generator and virtual synchronous generator in parallel under large disturbance

With the development of virtual synchronous generators (VSG), microgrids can choose a synchronous generator (SG) or a virtual synchronous generator (VSG) as the main power supply of an isolated island system. The governor of a synchronous generator and the active power control loop of a virtual synchronous generator may cause the transient power angle instability of the system, while the excitation device and reactive power control loop may cause the transient voltage instability. At present, there have been many studies on these two aspects. However, when a synchronous generator and a virtual synchronous generator are used as the main power sources to supply power to the isolated island system, the mutual coupling between the synchronous generator and the virtual synchronous generator may cause transient power angle and voltage instability. At present, there is little research in this field. Therefore, this paper focuses on the influence of the parallel mutual coupling of synchronous generator and virtual synchronous generator on the system stability, derives the mutual coupling model of a parallel system, it is also revealed that the coupling relationship between the SG and VSG parallel systems will produce a positive feedback mechanism that will be constantly amplified, which will greatly affect the system's stability. At the same time, the influence of coupling on the stability of a parallel system is carefully analyzed using large signal analysis, and the corresponding coupling suppression strategy and adaptive inertia control (AIC) is proposed. Finally, the correctness and feasibility of the proposed method are verified by time-domain simulation, and the experimental results are analyzed.