Virtual Inertia Control Research Articles

Multi-segment droop control and optimal parameter setting strategy of wind turbine for frequency regulation

Traditionally, virtual inertia is used as the control strategy for wind turbines when participating in frequency regulation. However, it has inherent defects in measurement error amplification due to the frequency differential. Also, when control delay of wind turbines is taken into consideration, virtual inertia is essentially a fast power response, just the same as droop control. Hence, considering the adaptability of droop control, it is valuable to explore a novel droop control method without virtual inertia, as the frequency response model of wind turbines. For this reason, a multi-segment droop control strategy is proposed to provide a reliable frequency regulation model for wind turbines that can be broadly applied to other inverter-based power sources. Firstly, based on the extended system frequency response model, a differential equation including piecewise time-varying coefficients is established, and the analytical expression of the frequency response is obtained using the impulse function balancing principle and the integration by parts algorithm. Subsequently, based on analytical expression, the performance of the presented strategy is theoretically analyzed via comparison with virtual inertia control, and the conclusion that the presented multi-segment droop control has better frequency regulation performance can be got. Furthermore, to achieve optimal frequency regulation performance, a Lagrangian function is established to determine the optimal parameters of the proposed control strategy. Finally, the performance of the proposed strategy was verified in a two-area system model constructed on MATLAB/Simulink. Results show that the proposed multi-segment droop control has better frequency regulation performance.

Coordinated control of wind-storage combined with primary frequency regulation and variable coefficient based on wind speed and SOC

The increase of wind power penetration rate will cause the power system to face the problems of lower inertia level and insufficient primary frequency regulation capability, which will seriously affect the system frequency security. Wind turbine generally operate in MPPT mode, and the primary frequency regulation capability is realized through additional control, but when the wind turbine uses the kinetic energy of the rotor to participate in the primary frequency regulation of the system, it will cause a secondary drop in the system frequency. Participating in the primary frequency regulation of the system with the energy storage auxiliary wind turbine can further reduce the depth of the system frequency drop and improve the secondary drop of the system frequency. However, after the energy storage participates in the system frequency regulation, the State of Charge (SOC) will decrease, which will affect the frequency regulation capability of the subsequent energy storage. In view of the above problems, a control strategy of wind and storage participating in the primary frequency regulation of the power system is proposed considering the energy storage recovery strategy. During the primary frequency regulation, the joint output of the wind turbine using virtual inertia control and the Energy storage battery using droop control can effectively suppress the system frequency drop; During frequency regulation, the Energy storage battery is charged using a recovery strategy to ensure that the SOC of the Energy storage battery is in the state of maximum frequency regulation capacity. The three-machine and nine-node model of the wind and storage system is built through RTLAB. The real-time simulation verifies that the joint output of the wind and storage system under the step disturbance increases the minimum value of the power grid frequency drop and increases the minimum value of the frequency secondary drop. It can also be used under continuous disturbances. Realize the recovery of energy storage SOC.

Adaptive Virtual Inertial Control and Virtual Droop Control Coordinated Control Strategy for Hybrid Energy Storage Taking into Account State of Charge Optimization

For energy-storage-assisting conventional units to participate in the primary frequency regulation of a power system, firstly, based on the frequency regulation mechanism of virtual inertial control (VIC) and virtual droop control (VDC) of energy storage, we analyze the effect of the action timing of energy storage on the frequency deviation of the grid under two control methods and put forward a reasonable combination of the two control methods; on this basis, we also put forward hybrid energy storage adaptive VIC and VDC based on the demand of VIC and VDC on the power and capacity of energy storage. On this basis, based on the demand of VIC and VDC on the power and capacity of energy storage, a hybrid energy storage adaptive VIC and VDC coordinated control strategy based on supercapacitor–lithium batteries is proposed, whereby a high-power storage supercapacitor responds to inertial control signals to rapidly suppress a drop in frequency, and the high-capacity lithium battery responds to droop control signals to perform long-time droop control. The high-capacity lithium battery responds to the sagging control signal and is used to perform a long-time sagging power response; finally, in order to avoid the state of charge (SOC) of energy storage falling into a low/high working condition and losing the subsequent frequency regulation ability, an adaptive power control strategy of energy storage based on the improved logistic function is proposed. The simulation results show that under typical load disturbance, the SOC level of the proposed strategy increases by 19.17% and 30.16%, respectively, compared with that of the single-lithium strategy and no energy storage, and the SOC level of the supercapacitor and lithium battery increases by 29.4% and 2.1%, respectively, compared with that of logistic optimization.

Integrated bus voltage control method for DC microgrids based on adaptive virtual inertia control

Integrated bus voltage control method for DC microgrids based on adaptive virtual inertia control

Reinforcement-Learning-Based Virtual Inertia Controller for Frequency Support in Islanded Microgrids

As the world grapples with the energy crisis, integrating renewable energy sources into the power grid has become increasingly crucial. Microgrids have emerged as a vital solution to this challenge. However, the reliance on renewable energy sources in microgrids often leads to low inertia. Renewable energy sources interfaced with the network through interlinking converters lack the inertia of conventional synchronous generators, and hence, need to provide frequency support through virtual inertia techniques. This paper presents a new control algorithm that utilizes the reinforcement learning agents Twin Delayed Deep Deterministic Policy Gradient (TD3) and Deep Deterministic Policy Gradient (DDPG) to support the frequency in low-inertia microgrids. The RL agents are trained using the system-linearized model and then extended to the nonlinear model to reduce the computational burden. The proposed system consists of an AC–DC microgrid comprising a renewable energy source on the DC microgrid, along with constant and resistive loads. On the AC microgrid side, a synchronous generator is utilized to represent the low inertia of the grid, which is accompanied by dynamic and static loads. The model of the system is developed and verified using Matlab/Simulink and the reinforcement learning toolbox. The system performance with the proposed AI-based methods is compared to conventional low-pass and high-pass filter (LPF and HPF) controllers.

Role Determination of Impedance Coupling in GCC With DC-Link Virtual Inertia Control

Role Determination of Impedance Coupling in GCC With DC-Link Virtual Inertia Control

Load frequency control of a two-area using virtual inertia and a PSO-PID controller with integrated electric vehicles

The increasing penetration level of converter-based renewable energy sources in the grid causes low inertia, which leads to grid frequency variation. To deal with this problem, virtual inertia (VI) control with particle swarm optimisation (PSO)-based PID controller has been applied to a two-area power system with multi-generating units. This improves the frequency variation and response time. In this paper, a derivative control technique has been used to emulate the VI, which controls the active power of the energy storage device which provides the inertia support to the power system. The integral time absolute error (ITAE) has been used as the performance index for PSO. Furthermore, the primary frequency control is augmented by integrating electric vehicles as vehicle-to-grid resources. Finally, various cases of disturbance and a comparative analysis have been performed between the VI with PSO-PID control and conventional control (PI). The simulation has been performed using MATLAB/Simulink, which demonstrates the superior performance of the VI with PSO-PID over a conventional controller by improving the settling by 45.84% in Area 1 and 39.77% in Area 2 for the almost same overshoot of frequency deviation. These simulation results have also been validated by performing hardware-in-loop (HIL) experiments utilising the OPAL-RT real-time simulator.

Adaptive distributed MPC based load frequency control with dynamic virtual inertia of offshore wind farms

AbstractThe penetration of offshore wind farms (OWFs) in city‐close power systems is rapidly increasing. System inertia will be further reduced. Active frequency support of wind power is essential to solve the load frequency control (LFC) problem. Here, the dynamic virtual inertia control (VIC) method is employed to enhance frequency stability within the permitted operating states of OWFs. An adaptive distributed model predictive control (DMPC) method is proposed and applied to an interconnected power system. The dynamic VIC‐based LFC model is derived and used to construct the predictive model of DMPC. To expand the adaptation of the analytical linearized model of OWFs in different operating points, the adaptive law is further designed to dynamically adjust the parameters of DMPC. The simulation results demonstrate the effectiveness of the proposed control method. The frequency fluctuations can be well‐restrained under different disturbances.

Coordinated frequency support strategy for VSC-HVDC integrated offshore wind farm system

The large-scale offshore wind power integrated into the onshore power grid through voltage source converter-based high voltage direct current (VSC-HVDC) system is unable to provide inertia response and frequency support to the onshore power grid. To improve the frequency characteristics of the receiving-end power grid, a coordinated frequency control strategy combining VSC-HVDC and offshore wind power is proposed. The onshore converter adopts virtual inertia control, which uses DC capacitors to absorb or release energy for inertia support after the receiving-end grid is disturbed. Wind-farm-side VSC (WFVSC) obtains the frequency signal of the receiving-end power grid by detecting the local DC voltage. The offshore wind farm (OWF) transfers the frequency deviation into an additional power signal and sends it to the power controller to adjust the output, thereby performing inertia and primary frequency response. In addition, a secondary frequency regulation strategy for wind farms has been designed to achieve non-difference frequency regulation of the receiving-end power grid. Finally, a simulation model of VSC-HVDC integrated OWF system is constructed to demonstrate the proposed coordinated frequency control strategy for VSC-HVDC and OWF. The results indicate that the proposed control strategy can effectively enhance the frequency support capability of the receiving-end power grid.

An adaptive virtual inertia control design for energy storage devices using interval type-2 fuzzy logic and fractional order PI controller

This research paper introduces a novel methodology, referred to as the Optimal Self- Tuning Interval Type-2 Fuzzy-Fractional Order Proportional Integral (OSTIT2F-FOPI) controller for inverter-based energy storage system (ESS) to regulate the input and output power of ESSs, aimed at enhancing the frequency control of microgrids (MGs) with varying levels of renewable energy sources (RESs) integration. The proposed method entails the integration of a self-tuner interval type-2 fuzzy logic controller (IT2FLC) and FOPI controller within a virtual inertia (VI) control loop. Within the OSTIT2F-FOPI control framework, the IT2FLC block tunes the parameters of the FOPI controller in an online method to deal with problems associated with fixed gains of the FOPI controller. Consequently, the VI control unit can emulate varying degrees of inertia and damping based on the integrated levels of RESs or load variations. The self-tuning capability of the proposed method enables real-time performance improvement of the system, resulting in enhanced frequency stabilization and improved control efficiency, particularly in low-inertia MGs. Moreover, a different control methodology, referred to as EO-FOPI-based VI, is developed to compare and assess the results achieved by the suggested OSTIT2F-FOPI control framework. This alternative method incorporates Equilibrium Optimization (EO) to adjust VI and FOPI parameters and provide a comparative analysis of the obtained outcomes.

Integrated control strategy of BESS in primary frequency modulation considering SOC recovery

AbstractThis paper proposes a comprehensive control strategy for a battery energy storage system (BESS) participating in primary frequency modulation (FM) while considering the state of charge (SOC) recovery. On the one hand, when the frequency fluctuations are outside the dead zone of the FM, variable coefficient virtual sag control and variable coefficient virtual inertia control are coordinated for more accurate primary FM. Also, an assisted FM strategy is proposed, where the temporal alignment of assisted FM is determined by the regional segmentation of the frequency deviation and SOC, and it enables the BESS to recover SOC concurrently during its involvement in primary FM. On the other hand, when the frequency fluctuations are inside the dead zone of the FM, typical S‐type functions are deployed to dynamically establish the mutual constraints relationships of SOC recovery demand coefficient and frequency deviation. Subsequently, the recovery control coefficients are derived, and accordingly, a SOC recovery strategy is proposed. Finally, simulation results verify the efficacy of the proposed control strategy in the grid primary FM system and demonstrate that the strategy expedites the SOC recovery and concurrently diminishes the conventional unit output.

Research on primary frequency regulation hybrid control strategy of battery energy storage system in new type power system

The integration of a significant amount of renewable energy into the power system brings uncertainties in terms of source-side output and the balance between source and load supply and demand. This increase in uncertainty, following system disturbances, poses challenges for frequency regulation and stable operation. This paper presents a primary frequency control strategy with energy storage assistance. It employs a combination of droop control and virtual inertia control to effectively modulate the frequency. The strategy utilizes energy storage system monitoring of the power grid’s operating state. In cases of significant disturbances, it employs a combination of droop control and virtual inertia control to mitigate frequency decline and assist in the recovery of system frequency. For minor disturbances, it directly utilizes droop control to maintain system frequency stability. Simulation experiments were conducted on the enhanced IEEE 9-bus system model using Matlab/Simulink. The results demonstrate that the proposed algorithm maintains system frequency stability under different circumstances.

Active Power Allocation Method of Doubly Fed Induction Generators Based on Rotor Speed

The integration of wind power into a grid on a large scale results in a reduction of the system’s inertia level, causing an impact on the stability of the system frequency. Doubly fed induction generators (DFIG) can optimize active output but lack inertia support under maximum power point tracking control. To make the wind turbine improve the inertia support ability of the system based on virtual inertia control, a method for active power allocation based on the rotor speed of DFIG is proposed. Firstly, the minimum system inertia requirement based on the frequency change rate of the system is established. Active power allocation assumes that the wind farm inertia meets the minimum system inertia requirement. Secondly, the objective is to enhance the inertia support capability and overall active power output of the wind farm, considering the constraint of the minimum system inertia requirement. Based on the rotor speed to establish the inertia allocation weight factor, the weight of the power command is assigned to a single machine to achieve the wind farm active power allocation. Finally, it is verified that the system’s equivalent inertia meets the minimum inertia requirement of the system. Simulations show that the proposed allocation method can adequately elevate the inertia support capability of DFIGs to the system and the rotor kinetic energy utilization.

Enhancing Virtual Inertia Control in Microgrids: A Novel Frequency Response Model Based on Storage Systems

The integration of renewable resources in isolated systems can produce instability in the electrical grid due to its intermintency. In today’s microgrids, which lack synchronous generation, physical inertia is substituted for inertia emulation. To date, the most effective approach remains the frequency derivative control technique. Nevertheless, within this method, the ability to provide virtual drooping is often disregarded in its design, potentially leading to inadequate development in systems featuring high renewable penetration and low damping. To address this issue, this paper introduces an innovative design and analysis of virtual inertia control to simultaneously mimic droop and inertia characteristics in microgrids. The dynamic frequency response without and with renewable energy sources penetration is comparatively analyzed by simulation. The proposed virtual inertia control employs a derivative technique to measure the rate of change of frequency slope during inertia emulation. Sensitivity mapping is conducted to scrutinize its impact on dynamic frequency response. Finally, the physical battery storage system of the University of Cuenca microgrid is used as a case study under operating conditions.

Design of Power System Stabilizer for DFIG-based Wind Energy Integrated Power Systems Under Combined Influence of PLL and Virtual Inertia Controller

Design of Power System Stabilizer for DFIG-based Wind Energy Integrated Power Systems Under Combined Influence of PLL and Virtual Inertia Controller

Influence of Wind-Turbine-Generator Power Control on the Performance of a Virtual Synchronous Machine

Implementation of renewable energy sources (RESs) in power systems can reduce the dependence on fossil-fuel-based thermal power generation systems. At the same time, however, the system inertia decreases as synchronous generators decrease; this is crucial for maintaining the stability of the power system. Virtual inertia control (VIC) can regulate the output of an inverter-based resource (IBR) by increasing the inertia. For a wind turbine generator (WTG), output control factors such as pitch angle control and maximum power point tracking (MPPT) significantly affect the performance of the VIC. This paper theoretically clarifies that the pitch angle control contributes to improvements in the performance of the VIC and helps avoid a loss of operation of the WTG in frequency drop events by analyzing the movement of the operational point of the WTG based on the physical characteristic of the WTG and control characteristics of the pitch angle control and MPPT; an electromagnetic transient (EMT) simulation, performed to verify the analysis, is also presented.

A Bidirectional Virtual Inertia Control Strategy for the Interconnected Converter of Standalone AC/DC Hybrid Microgrids

The interconnected converter (IC) links the ac and dc microgrids (MGs) and exchanges powers to maintain the hybrid system stability. However, inertia stored in the ac or dc side cannot be transferred through IC to support each other flexibly according to demand. This paper proposes a novel bidirectional virtual inertia (BVI) control strategy for the IC with an inertia transferring mechanism. IC actively transfers the inertial power to balance the transient performance of both sides of the interconnected MGs. The adaptive strategy is proposed for coefficients of the BVI control to change the inertial power flexibly according to the inertia gap caused by disturbances. Experimental results demonstrate that the proposed strategy of transferring inertia strikes a transient balance between the dc voltage and ac frequency and hence, enhance the transient stability of the hybrid system.

Hierarchical Control Strategy for Effective Virtual Frequency Responses of Multiple WPPs

When renewable energy-based generations are increasing, they are subject to cause frequency stability problems in a power system. To solve this problem, various virtual inertial control methods (VICMs) have been recently developed. However, they all have dealt not with the steady-state frequency stability, but only with dynamic frequency stability issues. In particular, the wind power plants (WPPs) operated by these VICMs can only provide a similar inertial response (IR) to that by conventional synchronous generators without providing the primary frequency response (PFR). This results in lowering the settling frequency (SF) below the maximum steady-state frequency deviation (MSSD) band.This paper proposes the new hierarchical control strategy for the WPPs, which are operated by three virtual frequency response control methods (VFRCMs) to provide both IR and PFR. Firstly, the VFRCM-1 provides virtual IR. Next, the VFRCM-2 increases the output power from the WPPs to prevent the frequency drop, which can occur after the frequency nadir is arrested. Finally, the VFRCM-3 makes the WPPs possible to raise the SF above the MSSD band by providing the virtual PFR. The effectiveness of proposed hierarchical control strategy is verified by several case studies on the IEEE 39-bus test system with the high penetration of renewables.

Optimal Tuning of Virtual Inertia Control for Frequency Regulation of Microgrid

Optimal Tuning of Virtual Inertia Control for Frequency Regulation of Microgrid

A Hybrid Sparrow Search Optimized Fractional Virtual Inertia Control for Frequency Regulation of Multi-Microgrid System

A Hybrid Sparrow Search Optimized Fractional Virtual Inertia Control for Frequency Regulation of Multi-Microgrid System