Inertia Emulation Control Research Articles

Application of inertia emulation control strategy with energy storage system in multi-area hydro -thermal system using a novel metaheuristic optimized tilt controller

This article presents the application of a novel artificial hummingbirds’ algorithm (AHA) based tilt-integral second order of double-derivative controller (TIDD2) in a three-area hydro-thermal power system. Also, the inertia emulation control strategy has been incorporated using various energy storage systems (ESS) to established the frequency in interconnected power system. The supremacy of the proposed controller is established by comparing the system dynamic response with some existing controllers, such as proportional-integral-derivative (PID), tilt-integral-derivative (TID) and cascade of IDD - PID controllers. The fruitfulness of proposed AHA has also been evaluated with system dynamic and convergence characteristics comparison over some of existing metaheuristic optimization techniques such as harris hawk's optimization (HHO) and bird swarm algorithm (BSA). Further, effect of random load pattern (RLP), communication time delay (CTD) and variable CTD on the system dynamic is analyzed. The study of inertia emulation control strategy in a multi-area interconnected power system revealed that, when inertia is emulated with superconducting magnetic energy storage (SMES), the system dynamic exhibits better performance over battery energy storage (BES) and ultra-capacitor (UC). Furthermore, the proposed systems are validated in a real-time environment using OPAL-RT lab software. Also, the scalability of the proposed method is evaluated by using eigenvalue analysis.

Inertia Emulation Control Strategy of an Accurate Model of HVDC Link in a Multi-area Automatic Generation Control System Integrated Precise Wind Turbine System

Inertia Emulation Control Strategy of an Accurate Model of HVDC Link in a Multi-area Automatic Generation Control System Integrated Precise Wind Turbine System

Development of Virtual Inertia Control with State-of-Charge Recovery Strategy Using Coordinated Secondary Frequency Control for Optimized Battery Capacity in Isolated Low Inertia Grid

Integrating renewable energy through inverter-based generators has decreased the power system’s inertia. Reduced inertia may lead to frequency instability during power imbalance disturbances, particularly in an isolated power system with limited inertia. The Battery Energy Storage System (BESS) and a virtual inertia (VI) emulation control system have become popular to mitigate this issue. Nonetheless, the BESS utilization for VI emulation is highly dependent on the availability of BESS capacity, which may affect the energy cost. Therefore, developing a VI emulation control strategy that requires less energy and can recover the state of charge (SoC) to a desired level to optimize BESS utilization is required. This paper proposes a VI control with an SoC recovery strategy through coordination with the generators’ secondary frequency control. Instead of relying on the frequency, such as in the conventional approach, the controlled signal of the generators’ secondary frequency control also includes the VI power and BESS SoC. Hence, the generators can contribute to lowering the VI required energy and recovering the BESS SoC. The results show that the proposed method outperforms the conventional method by requiring around 36% lower energy and the ability to maintain the BESS SoC.

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.

FPGA Implementation of an Inertia Emulation Control Strategy for a DC Microgrid

FPGA Implementation of an Inertia Emulation Control Strategy for a DC Microgrid

Performance of fast responding ultracapacitor energy storage for virtual inertia emulation control

AbstractThis paper proposes a black widow optimization (BWO) algorithm‐based derivative‐type control for optimized virtual inertia (VI) emulation using fast responding ultracapacitor (UC) as energy storage system for frequency regulation in a two‐area deregulated power system composed of thermal and hydro units with high penetration of solar photovoltaic. The parameters of the system have been controlled by using newly formulated BWO and their performance have been compared for virtual inertial emulation efficacy with other algorithms under different contract obligations. The impact of the coordinated action of BWO‐based proportional‐integral (PI) controller with VI emulation has been validated on the area frequency, tie‐line power, and generated power of different units. The eigenvalue approach has been applied to verify the performance and effect of VI emulation control using fast acting UC on system stability. The proposed VI emulation control studies have been evaluated under nonlinear environment of deregulated power system. The comparative studies show that BWO optimized PI‐based VI emulation using fast responding UC provides superior dynamic responsiveness in all competitive electricity market scenarios tested under different operating conditions.

Primary frequency regulation scheme applicable to LCC – VSC series hybrid HVDC considering AC voltage stability at receiving end

The penetration of high proportion renewable energy generation in the load center reduces the inertia of the power system and causes frequency stability problems. Series hybrid HVDC (e.g., BaiHeTan-JiangSu) with landing point at load center should play an important role in primary frequency regulation. Thus, this paper proposes a control scheme that coordinates line-commutated converter (LCC) and voltage-source converter (VSC) operation of the series hybrid HVDC (SHHVDC) and couples inertia emulation control with droop control (CIEDC). The CIEDC absorbs or releases the energy stored in the augmented capacitor of VSC for inertia emulation through regulating DC voltage. Then the DC voltage of LCC is coupled with the DC voltage of VSC through the voltage distribution coefficient. Meanwhile, the DC voltage of the inverter side is used to transmit the frequency information to the rectifier side to change the DC current order value without communication-based. Next, The equivalent DC input resistance based on communication-free is introduced to obtain the reactive power variation caused by LCC, which is transmitted to the reactive power control link in VSC to suppress the AC side converter bus voltage fluctuation. Finally, The CIEDC control scheme is verified by case studies in the event of slight AC fault and step load variation compared with the Fixed-Inertia Emulation Control Scheme (FIEC) and conventional droop control (CDC) in AC bus voltage stability, frequency deviation, rate of change of frequency (RoCoF).

External Inertia Emulation Controller for Grid-Following Power Converter

The advent of renewable energy has posed difficulties in the operation of power systems whose net inertia is becoming critically low. To face such challenges, grid-forming power has been one of the potential solutions pursued by the industry and research community. Although promising, grid-forming power converters are still immature for mass deployment in power systems. In the meanwhile, an enormous amount of grid-following power converters has been underexploited when it comes to grid-supporting functionalities. Therefore, this article proposes an external inertia emulation controller (eIEC) for grid-following power converter to provide frequency support to the grid. For the purpose of minimizing installation efforts and resources, the controller is designed in such a way that it can be implemented in an external controller communicating with the grid-following power converter via an industrial communication link. This article also investigates the effect of communication delay on the stability performance of the proposed controller. In addition to the detailed analysis, hardware-in-the-loop experiments are also carried out to validate the proposed eIEC.

Coordinated frequency regulation among asynchronous AC grids with an MTDC system

With the increasing penetration level of renewable power, the power systems’ inertias are decreasing. To ensure that the frequency is above the threshold of the under frequency load shedding, one effective way is to share the spinning reserves among asynchronous AC grids through HVDC systems. In this paper, a coordinated frequency regulation scheme that enables spinning reserves sharing is proposed for such hybrid AC/DC grids. This scheme is a communication-free method that consists of the droop control, the inertia emulation control and the frequency safety control. The combined response of the three controls can increase not only the frequency nadir but also the settled frequency of the disturbed grid. In addition, the hysteresis comparators and the power injection limits are adopted in the frequency regulation scheme to reduce the coupling effect among AC grids. Thus, under small and harmless disturbance, the frequency regulation scheme will be inactive; the disturbance in strong AC grids would not affect the weak AC systems. The frequency regulation scheme coordinates well with the automatic generation control of the grids. The feasibility and effectiveness of the proposed frequency regulation scheme are verified through simulation studies.

Adaptive inertia emulation control for high‐speed flywheel energy storage systems

Low-inertia power systems suffer from a high rate of change of frequency (ROCOF) during a sudden imbalance in supply and demand. Inertia emulation techniques using storage systems, such as flywheel energy storage systems (FESSs), can help to reduce the ROCOF by rapidly providing the needed power to balance the grid. In this work, a new adaptive controller for inertia emulation using high-speed FESS is proposed. The controller inertia and damping coefficients vary using a combination of bang–bang control approaches and self-adaptive ones, to simultaneously improve both the ROCOF and the frequency nadir. The performance of the proposed adaptive controller has been initially validated and compared with several existing adaptive controllers by means of offline simulations, and then validated with experimental results. The proposed controller has been implemented on a real 60 kW high-speed FESS, and its performance has been evaluated by means of power hardware-in-the-loop (PHIL) testing of the FESS in realistic grid conditions. Both simulations and PHIL testing results confirm that the proposed inertia emulation control for the FESS outperforms several previously reported controllers, in terms of reducing the maximum ROCOF and improving the frequency nadir during large disturbances.

Inertia and Droop Controller for a Modern Variable Speed Wind Turbine to Provide Frequency Control in a Microgrid

The increasing penetration of modern Variable Speed Wind Turbines (VSWTs) in microgrids creates the problem of frequency stabilization due to reduced inertia of the power system. To emulate the Inertia Response of the conventional synchronous machines, wind turbines can be provided with an inertia emulation controller. The modelling presented in this paper aims at equipping the modern Type D wind turbine with inertia response and primary frequency control (PFC) capabilities. Two controllers — inertial and droop, are implemented and their frequency control capabilities are compared in an isolated power system which consists of a conventional steam turbine generator and a wind farm. The results suggest that proposed controllers help in better frequency control performance in the microgrid

PIDF(1+FOD) controller for load frequency control with SSSC and AC–DC tie‐line in deregulated environment

In this study, a maiden application of cascade proportional–integral–derivative with filter (PIDF) and one plus fractional-order derivative (1+FOD), i.e. PIDF(1+FOD) controller is proposed for the load frequency control mechanism. The main purpose of the cascade and fractional order controller is to increase the degree of freedom and reject the disturbances faster. A novel attempt has also been made to model a static synchronous series compensator (SSSC) with AC tie-line and HVDC tie-line. Here SSSC and HVDC tie-line are used to regulate and increase the power transfer capabilities between interconnected areas. Furthermore stored energy in the HVDC tie-line is utilised to improve the system dynamics by inertia emulation control strategy. An evolutionary salp swarm algorithm-based optimisation technique is adopted to optimise control parameters. The performance of the proposed controller is tested on a two-area hydro-thermal interconnected power system in deregulated environment. First, the effectiveness AC–DC-SSSC tie line is shown over AC-SSSC and alone AC tie-line with proposed PIDF(1+FOD) controller followed by the supremacy of proposed PIDF(1+FOD) over classical controllers. Finally, sensitivity is analysed by variation in system parameters, which shows the robustness of the proposed controller.

Inertia emulation control technique based frequency control of grid‐connected single‐phase rooftop photovoltaic system with battery and supercapacitor

With the increasing penetration of renewable energy sources in the power system, the power electronic inverters are widely used to interface with the grid, which will reduce the inertia of the power system. This study proposes ancillary inertial service from single-phase rooftop solar photovoltaic (PV) based inverter to the grid. The inertia emulation control technique transforms the behaviour of inverter like a synchronous generator under power imbalances. A hybrid energy storage system consisting of battery and supercapacitor (SC) has been connected at the DC bus to take care of the variability in PV output power and load fluctuations. The SC absorbs/injects the fast-varying power and provides the inertial response to arrest the frequency deviation and battery charges/discharges to bring back the frequency to the nominal value. Real-time simulation is carried out to test the system behaviour for different operating conditions using OPAL-RT 5700.

Integrated multi-area power system with HVDC tie-line to enhance load frequency control and automatic generation control

In this paper, a high-voltage direct current (HVDC) tie-line has been accurately modeled and proposed for multi-area interconnected power system to enhance load frequency control and automatic generation control (AGC). HVDC tie-line has been modeled based on a simple first-order transfer function for AGC system. Time constant of this transfer function indicates the required time by HVDC to set DC current because of load perturbation in multi-area interconnected power systems. It is worth mentioning that the inexact and very simple model of HVDC-line cannot yield a reliable and correct response. Hence, an accurate and interpretable model is proposed for HVDC-link to control the AGC system. To verify the accuracy of the proposed model, it has been analytically compared with the conventional HVDC model. The integrated multi-area power system has also implemented the inertia emulation controller technique which enables AGC system to tackle the accumulated energy in HVDC-line’s capacitance.

Decoupling Control Scheme for VSG-WPPs to Participate in Grid Frequency Response

By adopting the virtual synchronous generator (VSG) scheme with the inertia emulation controller and droop controller, wind power plants (WPPs) can participate in inertial response (IR) and primary frequency regulation (PFR). According to the analysis in this article, besides the well-known dynamic coupling between the wind turbine operating point (WTOP) controller and the inertia emulation controller, there is a static coupling between the WTOP controller and the droop controller. These couplings would impair the IR and PFR characteristics of the VSG controlled WPPs (VSG-WPPs). The equivalent droop coefficient of the VSG-WPPs is no longer equal to the setting value and changes under different operation conditions. To eliminate these adverse impacts, a decoupling control scheme is proposed. According to the MATLAB simulations and real-time hardware-in-loop testing results provided in this article, under the same power disturbance, the frequency response characteristics of the WPPs with the proposed scheme are much better than the WPPs with the original scheme.

Equivalent Modeling and Comprehensive Evaluation of Inertia Emulation Control Strategy for DFIG Wind Turbine Generator

With the increasing penetration of renewable energy in power grid, many inertia emulation control strategies have been proposed to provide extra support to the power grid in system disturbances. To explain the physical resemblance and relations among all kinds of inertia emulation strategies, a proper double-fed induction generator (DFIG) model is proposed based on equivalent electromotive force $\text{E}_{\boldsymbol{r}}^{\mathrm {eq}}$ and equivalent power angle $\delta _{\mathrm {eq}}$ . A co-simulation research platform is also designed based on a real-time digital simulator (RTDS) and GH Bladed simulation software, and the detailed comparisons are made in terms of inertia response performance, weak grid operation stability, secondary frequency drop, and wind tower fatigue load. Research results point out that different control schemes are similar in inertia response while virtual synchronous generator (VSG) control and inertial synchronization control (ISynC) can improve weak grid operation stability, the VSG strategy is also effective in reducing frequency secondary drop and wind tower fatigue load, and the combination of the VSG for RSC and the ISynC for GSC can achieve the best control performance in all evaluation indexes.

Dynamic control strategy for the participation of variable speed wind turbine generators in primary frequency regulation

This paper introduces a novel strategy for the participation of variable speed wind turbine generators in primary frequency regulation. The proposed strategy is based on modifying the droop and inertia emulation control loops in such a way to help the wind turbine provide a secure frequency response throughout the dynamic control of the turbine tip-speed ratio and de-loading percentage. The proposed control does not directly act on the active power reference such as classical droop and inertia controls but on adjusting the rotor speed set-point and the pitch angle directly in response to the frequency deviation. The wind turbine is assumed to operate at 10% de-loading percentage under normal conditions. The over-speed, pitch control, and de-rated control are combined together to provide a power reserve. The control strategy is valid for all the wind speed ranges and does not require any direct wind measurements as a control input. The simulation results confirm that the proposed frequency response strategy improves effectively the frequency stabilization of the power system and has the ability to provide transient and steady-state power-sharing within the stable and secure limits.

Primary Frequency Response Enhancement for Future Low Inertia Power Systems Using Hybrid Control Technique

Maintaining the stability of a conventional power system during under frequency events is partially dominated by a natural behavior called inertial response. Although a variable speed wind turbine (VSWT) is fundamentally deprived from such behavior, it was shown recently that it can virtually emulate this response, hence increasing its output power given to the grid to sustain the power balance. This paper reviews and analyzes the performance of four primary frequency control structures, and provides comparison between these controllers in terms of security indices. The results reflect the superiority of the inertia emulation controller and the droop control type in low and high wind speed respectively. To enhance the system frequency control response and take any inherent advantage of each controller, this paper proposes two novel controllers based on combination (hybridization) strategy between the four controllers. The results show that the combination between the inertia emulation controller and the de-loading controller will lead to reducing the rate of change of frequency (ROCOF) and raising the frequency nadir (FN) values. Finally, the role of each discussed controller in determining the correlations among ROCOF, FN and wind power penetration level are explored.

ESO-Based Inertia Emulation and Rotor Speed Recovery Control for DFIGs

In recent years, with the ever increasing penetration of wind generation, great concerns have been raised since the constantly decline of system's inertia may considerably deteriorate the frequency stability of power system. In this regard, an inertial response control technique is proposed to enable wind generators to provide the power system with controlled inertia in need via releasing energy to or absorbing energy from the system. In this paper, an extended state observer (ESO)-based inertia emulation controller (InEC) is proposed for doubly-fed induction generators (DFIGs), which is shown to be robust to measurement noise and changing working conditions. In addition, to mitigate potential adverse impacts of rotor speed recovery control (RSRC) of DFIGs on system frequency, an ESO-based RSRC is derived, allowing a schedulable dynamic of speed recovery. Experiments carried out on a power hardware-in-loop testbed manifest that the proposed controllers outperform the traditional proportional-differential type InEC and proportional-integral type RSRC in performance and robustness.

ドライブトレインベンチの低慣性化制御技術と実路走行負荷模擬制御への応用

Drivetrain bench system is utilized to test powertrain components of a vehicle such as transmission, torque converter, etc. Conventional drivetrain bench system emulates the moment of inertia of a vehicle body. In order to simulate real road loads of the powertrain components, it is necessary that the dynamometer of the drivetrain bench emulates the moment of inertia of a tire. The moment of inertia of the tire is lower than the moment of inertia of the dynamometer. So, the dynamometer needs low inertia emulation control. The drivetrain bench is mechanical vibration system. The principal factor of the vibraion is stiffness of a drive shaft. In this paper, we propose a low inertia emulation control method for vibration system and its application to simulating real road loads. Basic idea of the proposed low inertia emulation control method is feedforward of torque that is necessary for accelerating emulated inertia. By numerical simulations, it is shown that real road loads tests can be implemented with the proposed control method.