Frequency Regulation Strategy Research Articles

Global hydraulic stability analysis for dynamic regulation in multi-zone variable air volume air-conditioning system

Variable air volume air-conditioning system (VAV system) has multiple control loops that interfered with each other, which has serious impacts on its actual operation effect. To solve this problem, the index of global hydraulic stability, which takes the physical quantity of the pipe network pressure and the air flow rate as reference, is proposed based on Graph theory, and a pipe network model for the hydraulic calculation is built. Then, the simulation study based on the actual operation data is carried out in MATLAB. The distribution of the pressure and the air flow in the pipe network is obtained, and the action interferences among adjacent terminal boxes are analyzed based on global hydraulic stability under damper position regulation strategy (DP strategy) and fan frequency regulation strategy (FF strategy). Results indicate that the FF strategy can decrease the total change distance of the damper position compared with the DP strategy, and then the fluctuation of the pressure and the air flow can be reduced. The contribution of this study is to provide an evaluation index of global hydraulic stability, which can also be used in other air-conditioning systems with multiple terminals and multiple control loops.

Warp-Aware Adaptive Energy Efficiency Calibration for Multi-GPU Systems

Massive GPU acceleration processors have been used in high-performance computing systems. The Dennard-scaling has led to power and thermal constraints limiting the performance of such systems. The demand for both increased performance and energy-efficiency is highly desired. This paper presents a multi-layer low-power optimisation method for warps and tasks parallelisms. We present a dynamic frequency regulation scheme for performance parameters in terms of load balance and load imbalance. The method monitors the energy parameters in runtime and adjusts adaptively the voltage level to ensure the performance efficiency with energy reduction. The experimental results show that the multi-layer low-power optimisation with dynamic frequency regulation can achieve 40% energy consumption reduction with only 1.6% performance degradation, thus reducing 59% maximum energy consumption. It can further save about 30% energy consumption in comparison with the single-layer energy optimisation.

Research and implementation of frequency control strategy of islanded microgrids rich in grid-connected small hydropower

Due to the weak network architecture of mountainous power grid rich in grid-connected small hydropower, once the small hydropower units operate independently as a network when the upper power grid fails and loses power, the reliability of the power supply could be effectively improved. To cope with the problem of insufficient frequency regulation capacity of small hydropower units and the large risk of separation fault, this paper proposes a piecewise variable coefficient PID control strategy which improves the speed regulation control strategy of hydropower units, and a joint frequency regulation strategy of hydropower energy storage is designed to optimize the system operation state. Based on the MATLAB simulation platform, a hydropower energy storage microgrid model of mountainous power grid was built to verify the effectiveness of the segmented variable parameter control strategy. Using the proposed control strategy, the hydropower intelligent control terminal was developed and put into application in a certain area of Guangdong. Through simulation analysis and engineering applications, the practicality of the application of device engineering is verified to have good application and promotion value for a multi-hydropower mountainous power grid.

Frequency Regulation Strategy of Two-Area Microgrid System with Electric Vehicle Support Using Novel Fuzzy-Based Dual-Stage Controller and Modified Dragonfly Algorithm

Energy in microgrids (MGs) can now be generated from a variety of renewable sources, but their effective and sustainable use is dependent on electrical energy storage (EES) systems. Consequently, the expansion of MGs is greatly reliant on EES systems. The high infiltration of electric vehicles (EVs) causes some problems for the smooth functioning of the electric power system. However, EVs are also able to offer ancillary services, such as energy storage, to power systems. The research presented in this paper aims to develop a novel frequency regulation (FR) approach for biogas diesel engines (wind), the organic Rankine cycle (ORC), and solar-based two-area islanded microgrids with EVs in both areas. This article discusses the introduction of a fuzzy logic controller (FLC) for FR with scaled factors configured as proportional integral (PI) and proportional derivative with filter (PDF), i.e., a FLC-SF-PI-PDF controller. A recently created modified dragonfly algorithm is used to determine the best values for the controller parameters. To justify the effectiveness of the proposed controller with the presence of EVs, the execution of the proposed controller is associated with and without the presence of EVs. This research also looks at the different uncertain conditions, non-linearities, and eigenvalue stability analysis to validate the supremacy of the proposed approach.

Optimal Strategy of Primary Frequency Regulation for Wind-Storage System Considering Adaptive Parameter Control

For the problem that the power system has different demands on the frequency response characteristics in different segments of dynamic frequency response, this paper proposes an optimal primary frequency regulation strategy for the wind-storage system considering adaptive parameter control. Firstly, the dynamic frequency response processes of the system under single, continuous disturbances are analyzed to obtain the frequency regulation demand of the system in different segments. Secondly, the frequency response model of the power system is established to obtain the transfer function of the system’s primary frequency regulation. Finally, the adaptive parameter adjustment strategy of the wind-storage system is proposed, and the optimal primary regulation strategy of the wind-storage system is established. The result of the case study indicates that the proposed optimal primary frequency regulation strategy can effectively improve the performance of the power system in the dynamic frequency response process, especially when a continuous disturbance occurs.

Primary Frequency Regulation Strategy of PMSG-Based Wind Turbines Integrated Inertia Control

Direct-drive permanent magnet synchronous wind turbine-generator (PMSG) generally operates in maximum power point tracking (MPPT) mode. PMSG cannot provide additional active power support when the grid frequency fluctuates.The gradual increase of wind power penetration leads to greater frequency regulation pressure, which brings hidden dangers to the power grid. This paper focuses on the grid connection of direct-drive PMSG, proposing a primary frequency regulation strategy integrated with inertia control. The proposed strategy controls the rotor kinetic energy to simulate inertia of synchronous units by adding the support power of the response frequency variation. It concludes with variable power tracking control and energy storage system control. Compared with the traditional strategy retains active power, this proposed strategy increases wind energy utilization. Adopting variable power tracking control combined with energy storage can overcome secondary frequency drop and reduce energy storage configuration capacity.

Improvement of Frequency Support for a DFIG Using a Virtual Synchronous Generator Strategy at Large Power Angles

The frequency regulation rate and operation stability of a doubly fed induction generator (DFIG) based on a virtual synchronous generator (VSG) strategy decreases under large-power-angle conditions, which reduces the grid frequency support capacity. This paper proposes the compound adaptive parameter (CAP) and coordinated primary frequency regulation (CPFR) strategies to improve the grid frequency support capacity in terms of multiple dimensions of the transient properties, operation condition range, and regulation duration. Mathematical and small signal models of the DFIG-VSG system are constructed. The effect of large-power-angle conditions on the transient properties under grid frequency perturbations is analyzed based on these models, and the CAP strategy for excitation control and virtual damping is formulated. The constraints of the rotor kinetic energy and the load increase capacity of the grid-side converter are analyzed, and the CPFR strategy is formulated based on this. Finally, the effectiveness of the proposed strategies is verified via simulations of single-machine and wind farm scenarios under grid frequency perturbation.

Frequency Regulation of Electric Vehicle Aggregator Considering User Requirements with Limited Data Collection

High penetration of renewable energy in the power grid causes serious frequency deviations. Large-scale integrations of electric vehicles (EVs) in the power grid provide considerable vehicle-to-grid potential for frequency regulation. Existing frequency regulation strategies with aggregated EVs realize accurate power control that relies on complete information interaction between the EV aggregator and individual EVs. However, the data collection for all EV parameters is not applicable due to privacy protection and the limited communication environment. Considering the limited data collection from grid-connected EVs, this paper provides a novel frequency regulation strategy and tends to address the uncertain influence from EV users’ charging requirements, the EV aggregator’s power regulation, and the frequency regulation performance. Firstly, considering the influence of the limited data collection by EVs on the users’ requirement of traveling and regulation preference, a probabilistic evaluation model for the available regulation capacity of the EV aggregator and the probabilistic control method for EVs are developed. Then, a frequency regulation strategy with error correction control and progressive regulation recovery is developed to simultaneously guarantee the system frequency regulation performance and the regulation requirements of EV users. Finally, case studies are carried out to validate the effectiveness of frequency regulation strategy for decreasing the uncertain influence from the limited data collection, ensuring the EV users’ requirements, and improving the system frequency stability.

Research on primary frequency regulation strategies for ancillary wind power inertia based on the rotor kinetic energy

The additional frequency control of wind turbines is an effective method to solve the problem of low inertia in power systems with high proportions of new energy. The primary frequency regulation of auxiliary wind power inertia systems based on rotor kinetic energy can not only make the wind turbine run at the maximum power point but also has the lowest cost and better economy of the auxiliary frequency regulation module. The wind power inertia output control scheme based on rotor kinetic energy control is constructed by considering the frequency response characteristics of synchronous generator sets and loads. The calculation model of the minimum inertia demand of the power system is established using the rate of change of frequency and the maximum frequency offset as constraints. Combined with the real-time operating conditions of the wind turbine, the speed regulation limit of the wind turbine rotor kinetic energy control is obtained to avoid wind turbine off-grid due to excessive frequency regulation. To prevent frequency secondary drop of the system during the speed recovery process, the steady speed recovery of the wind turbine is controlled by setting the rate of speed change. The feasibility of the strategy for the regulation of the auxiliary primary frequency proposed in this study was verified in an example based on a two-region, four-machine system. When a disturbance sets the sudden load power to 150 MW, under the kinetic energy control of the wind turbine rotor, the system frequency change rate and the maximum frequency offset are increased; in particular, the maximum frequency offset is reduced by 0.348 Hz, which further illustrates the flexibility and plasticity of the rotor kinetic energy control of the wind turbines. The results of this study provide a theoretical basis for adding additional frequency control to existing wind turbines.

Reliability Assessment of Interconnected Power Systems with HVDC Links Considering Frequency Regulation Process

With various components and complex topologies, the applications of high-voltage direct current (HVDC) links bring new challenges to the interconnected power systems in the aspect of frequency security, which further influence their reliability performances. Consequently, this paper presents an approach to evaluate the impacts of the HVDC link outage on the reliability of interconnected power system considering the frequency regulation process during system contingencies. Firstly, a multi-state model of an HVDC link with different available loading rates (ALRs) is established based on its reliability network. Then, dynamic frequency response models of the inter- connected power system are presented and integrated with a novel frequency regulation scheme enabled by the HVDC link. The proposed scheme exploits the temporary overload capability of normal converters to compensate for the imbalanced power during system contingencies. Moreover, it offers frequency support that enables the frequency regulation reserves of the sending-end and receiving-end power systems to be mutually available. Several indices are established to measure the system reliability based on the given models in terms of abnormal frequency duration, frequency deviation, and energy losses of the frequency regulation process during system contingencies. Finally, a modified two-area reliability test system (RTS) with an HVDC link is adopted to verify the proposed approach.

Research on the Frequency Regulation Strategy of Large-Scale Battery Energy Storage in the Power Grid System

Driven by the carbon peaking and carbon neutrality target, the large-scale grid-connected of renewable energy such as wind and solar has increased, and the volatility and randomness have posed new challenges to the stability of the power grid frequency. In this case, battery energy storage is a grid auxiliary resource with fast response and adjustable parameters, which can provide frequency support for the grid system in a short period. This paper studies the frequency regulation strategy of large-scale battery energy storage in the power grid system from the perspectives of battery energy storage, battery energy storage station, and battery energy storage system, respectively. First of all, the droop control based on logistic function and the virtual inertia control based on piecewise function are proposed for battery energy storage frequency regulation, which improves the performance of battery energy storage power output effectively. Second, the weighting factor is set according to the current battery charge to achieve the most optimal distribution of frequency regulation power for each battery pack in the battery energy storage station. In the end, a control framework for large-scale battery energy storage systems jointly with thermal power units to participate in system frequency regulation is constructed, and the proposed frequency regulation strategy is studied and analyzed in the EPRI-36 node model. The results of the study show that the proposed battery frequency regulation control strategies can quickly respond to system frequency changes at the beginning of grid system frequency fluctuations, which improves the stability of the new power system frequency including battery energy storage. In addition, this paper also provides a certain reference for the construction of the new power system dispatching that integrates “Generation-Grid-Load-Storage” in the future.

An Improved Adaptive Load Shedding Control Strategy for Primary Frequency Regulation of Wind Power Generation System

With the continuous improvement of the proportion of wind power generation, the volatility and uncertainty of wind power pose a serious threat to the stable operation of the power system. However, the traditional primary frequency regulation strategy does not fully consider the influence of wind turbine inertia. In addition, it may cause the secondary frequency drop if the instantaneous power of the wind turbine drops too much during the speed recovery. To solve this problem, this paper proposes an adaptive primary frequency regulation strategy for the mobile load shedding power tracking curve. Under this strategy, by controlling the output active power reference value, the kinetic energy stored in the rotor is fully released to support the grid frequency for a short time. Then, in the process of rotor speed recovery, the frequency secondary drop can be alleviated by moving the load-shedding power tracking curve. Finally, the simulation results in MATLAB/Simulink verify the rationality of the proposed adaptive load-shedding control strategy.

Reactive power assisted frequency regulation scheme for large-scale solar-PV plants

Due to reduction in power system inertia and frequency regulation reserve with high penetration of power-electronic converter (PEC) interfaced renewable sources, advanced control strategies must be developed to exploit the full potential of solar-photovoltaic (PV) systems to improve the frequency stability. In this paper, a new frequency regulation approach is proposed based on reactive-power control (i.e., frequency regulation via reactive-power control (FRQC) scheme) for solar-PV systems, which manipulates the active power demand as a function of the system frequency deviation by varying network voltages via reactive power control. The feasibility of the proposed control scheme is investigated using both theoretical analysis and simulation studies following a loss of a major generation source. Frequency and voltage deadbands, and time delays are added to the FRQC scheme to activate and deactivate the control scheme, and hence it maximises the frequency support without affecting the voltage stability. The reliability and voltage stability (RVS) test system is used to demonstrate the effectiveness of the proposed FRQC scheme under different gains of the controller, PV loading levels, and different PV penetration levels. The comparative results show that the proposed FRQC scheme improves the post-fault frequency trajectory, and hence the system frequency stability.

An active primary frequency regulation strategy for grid integrated wind farms based on model predictive control

The increasing penetration level of wind power can reduce the dependency on fossil fuels, but it is accompanied with challenges such as the jeopardized dynamic stability of the frequency of power grid. As an effective method to improve frequency dynamic stability, primary frequency regulation (PFR) is conventionally based on the feedback of measured frequency, by which means it is conducted through analyzing historical information. By taking the predictive information into account, this paper introduces an active PFR (APFR) strategy for grid integrated wind farms (WFs) to enhance control performance of PFR. According to small-signal models of power system integrated with WFs based on conventional PFR and APFR, the state-space predictive models are established to obtain the predictive states. Then, to take active measures to deal with the electrical load disturbance, the predicted frequency is optimized in a receding horizon period by adjusting the PFR power reference of WFs flexibly. Moreover, a finite terminal weighting matrix based Lyapunov​ function is presented to prove the asymptotic stability of the closed-loop model predictive control system. Finally, extensive case studies based on the standard test systems are performed to validate the effectiveness of the theoretical analysis and the superiority of APFR strategy.

A control strategy for a grid-connected virtual synchronous generator with virtual impedance

Virtual synchronous generator (VSG) can simulate synchronous generator turning and damping characteristics, which can further improve the penetration rate of renewable energy in the grid. However, the output impedance of virtual synchronous generator in medium and low voltage microgrids is dominated by resistance, which leads to the coupling of active/reactive power and affects the grid integration control effect, and the phase of VSG and grid voltage will be biased in the absence of a pre-synchronization link. For this purpose, a strategy of grid-connected control of VSG with virtual impedance is proposed. Firstly, the VSG mathematical model is established and virtual impedance is introduced into the VSG electrical portion to improve the grid-connected inverter output characteristics. Secondly, a secondary frequency and voltage regulation strategy to improve VSG control is proposed to restore the frequency and voltage of the VSG, and the SOGI phase-locked loop collects the grid voltage phase to complete the grid-connected pre-synchronization design. Finally, the effectiveness and correctness of the proposed strategy were verified by the simulation results based on MATLAB/ Simulink.

A Frequency Regulation Strategy for Dynamic Process Noise Suppression in LCC-S WPT Systems

This article proposed a frequency regulation strategy (FRS) to realize zero voltage switching (ZVS) in the dynamic process of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCC</i> -S wireless power transfer systems, which aims at suppressing serious switching noise in the starting-up phase of the inverter. By detecting the magnitude and direction of the output current of the inverter, a delayed turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> signal is timely applied to ensure that the inverter can achieve ZVS in all operating conditions. The origins of the mechanism of switching noise are presented, and the closed-loop stability of the system under the proposed control strategy is analyzed. The correctness of the theoretical analysis and the effectiveness of the control strategy is verified by both simulation and experiment results. This control strategy is technically effective for all resonant converters in the switching noise suppression. Finally, the method is verified in a 1.5 kW, 85 kHz, 310V <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCC</i> -S WPT system, and the experimental results show that the FRS can reduce electromagnetic interference by 13 dB in one dynamic starting-up cycle.

A comprehensive control strategy for photovoltaic virtual synchronous generator considering frequency regulation capability

The existing photovoltaic frequency regulation strategies do not take into account the differences in the frequency regulation capability. So they cannot fully exploit the support capacity to the grid frequency. For the purpose of improving the control precision and regulation effect of PV, a comprehensive control strategy for photovoltaic virtual synchronous generator (PV-VSG) is proposed, which accurately considers the frequency regulation capability. First, the inertia regulation margin, power regulation speed and power regulation margin are taken as the evaluation index of frequency regulation capability of PV. Then, the frequent deviation-free control strategy with integral link and the multiple control modes switching strategy are proposed, whose control parameters are designed according to the frequency regulation capability. In the simulation verification, the proposed method reduces the frequency deviation by 0.11 Hz compared to existing strategies, and can quickly recover to the normal value. At the same time, the frequency regulation utilizes the capability of the PVs, which also validates the effectiveness of the proposed strategy.

Design of a maiden synthetic inertia controller using super-capacitor energy storages and electric vehicles and real-time validation of the performance of the controller

Large-scale integration of renewable power (RP) into a power system (PS) decreases the inertia of the PS which generates a high rate of change of frequency (ROCOF) and frequency instability in the PS. A multi-area PS integrating RP has to overcome even more complex frequency instability issues while delivering power to the load. The frequency control mechanism of such inertia-less or low-inertia multi-area systems is supported by additional synthetic inertia (SI) control scheme for enhancement of system inertia and maintenance of frequency stability. In this paper, super-capacitor (SC) energy storages and electric vehicles (EV) have been used to support the frequency regulation of a multi-area PS with high renewable RP penetration. The proposed SI control scheme includes two SI control loops - an SC bank forms the SC control loop and charging/discharging EVs forms the EV control loop. The designed fractional order (FO) controllers along with both inertia and damping properties have been considered in the SI control loops. Genetic algorithm (GA) has been used for optimising the parameters of the proposed SI control system. The performance of the proposed 2-loop (SC + EV) SI control strategy has been compared to other SI control techniques for different weather conditions and variation in load. The robustness of the proposed frequency regulation scheme has been verified by comparing the dynamic response of the multi-area PS for different controllers for randomly varying loads and weather conditions, changing system parameters, and different operating conditions. The efficiency of the proposed SI control technique has also been verified in real-time using Opal-RT.

Improved Frequency Control Strategy for Offshore Wind Farm Integration via VSC-HVDC

Voltage source converter based high voltage DC system (VSC-HVDC) has become a very promising solution to integrate offshore wind farm. However, the equivalent inertia of the modern power system with large renewable energy integration becomes small, which will arouse some frequency stability problems. To tackle this problem, this paper proposes an improved frequency regulation strategy for VSC-HVDC integrated offshore wind farm. Firstly, in the frequency decrease stage, the rotor kinetic energy of wind turbines (WTs) is used to suppress the decrease of the frequency, and the control parameters are determined to make full use of the mechanical power and rotor kinetic energy of WTs, the frequency nadir is improved. Secondly, in the rotor speed recovery stage, the DC capacitors of VSC-HVDC are used to release power to compensate the deficiency value of wind farm output power and avoid the secondary frequency drop (SFD) problem. Lastly, the simulation is conducted in PSCAD/EMTDC to validate the effectiveness of the proposed coordinated frequency control strategy.

Short-term frequency regulation of power systems based on DFIG wind generation

Short-term frequency regulation is important for the safety and efficiency of power systems based on wind generation units. However, unmodeled dynamics and stochastic disturbances in wind speed and load present a challenge for frequency regulation. This paper offers a frequency regulation scheme that caters for doubly fed induction generator-based wind power units requiring short-term frequency regulation. To this end, a data-driven additive controller is cast into a stochastic framework. Since the survival information potential (SIP) of a random variable has some advantages over information potential, the SIP of frequency deviation is presented in order to simultaneously evaluate droop control and inertial control. Thereafter, the optimal additive control coefficient can be obtained using a particle swarm optimization technique and an arithmetic mean filter. Finally, simulation results demonstrate the effectiveness of the proposed approach over traditional additive control strategies.