System Frequency Fluctuation Research Articles

Adaptive load control of electrolytic aluminum for power system frequency regulation based on the aluminum production operation state

The national ”double carbon” plan promotes the reform of the power system, and large-scale distributed energy is connected to the power system. It is difficult to control the fluctuation of new energy only by the reserve of thermal power units. Therefore, it is urgent to excavate new auxiliary service subjects and increase the flexibility of power grid frequency control. Taking electrolytic aluminum as an example, the traditional high load capacity load has large capacity continuous regulation ability, but it is seldom used in frequency stability control of power grid. Thus this paper proposes the precise coordinated frequency modulation control strategy of electrolytic aluminum load in the case of large N-1 failure. By means of updating the running status of electrolytic aluminum load regularly and calculating the load damping coefficient adaptively, this strategy can realize the rapid response to the system frequency change and ensure that the system frequency fluctuation does not exceed the limit. Finally, we built the regional power grid of Wenshan in Yunnan province and the results verify the feasibility of the effectiveness of the proposed strategy in dealing with DC locking.

Smoothing of Wind Power Output Fluctuations by Particle Filter

Wind power generation is a renewable energy source that has been gradually introduced in a variety of applications. However, this power is generated by the wind, and thus it is variable power source that fluctuates according to wind speed variations. This may cause frequency fluctuations in power systems, which can adversely affect the power grid operations. In this study, a method using a particle filter to predict the expected value of fluctuating wind power is proposed. The effect of the proposed method on suppressing grid system frequency fluctuations is evaluated by simulation analysis for a grid system with permanent magnet synchronous generator (PMSG) based wind turbines under natural wind speed fluctuations.

Efficient Model for Accurate Assessment of Frequency Support by Large Populations of Plug-in Electric Vehicles

In recent years, plug-in electric vehicles (PEVs) have gained immense popularity and are on a trajectory of constant growth. As a result, power systems are confronted with new issues and challenges, threatening their safety and reliability. PEVs are currently treated as simple loads due to their low penetration. However, as their numbers are growing, PEVs could potentially be exploited as distributed energy storage devices providing ancillary services to the network. Batteries used in PEVs are developed to deliver instantaneously active power, making them an excellent solution for system frequency support. This paper proposes a detailed dynamic model that is able to simulate frequency support capability from a large number of PEVs, using an innovative aggregate battery model that takes into account the most significant constraints at PEV and aggregate battery levels. The cost optimization algorithm, which is the most time-consuming process of the problem, is executed only at the aggregate battery level, thereby reducing the computational requirements of the model without compromising the obtained accuracy. The proposed method is applied to the power system of Crete exploiting detailed statistical data of EV mobility. It is proven that PEVs can effectively support power system frequency fluctuations without any significant deviation from their optimal operation.

Research on Direct Power Control Strategy Based on Voltage Controlled Virtual Synchronous Generator

To support the “carbon peak and carbon neutrality” goal, new energy is poised to explode, and new energy power generation converter is simultaneously facing new challenges. The conventional current-controlled new energy converter can quickly transmit active power on the DC bus to the power grid. However, for the weak grid, the stability margin of the converter grid-connected system is reduced on the one hand, which can easily cause resonance oscillation; on the other hand, the current controlled converter cannot actively respond to system frequency and voltage fluctuation to offer support. The voltage controlled virtual synchronous generator (VVSG) is used to improve system small signal stability and frequency stability; however, its power response speed is too slow to meet the requirements of fast following power command. Although a voltage/current dual-mode switching control scheme is put forward to achieve characteristics complementary of current controlled converter and voltage-controlled converter, the control structure switching and intermediate variable following is required to realize mode switching, which is prone to large power shocks and switching failures. In view of the problem, a direct power control strategy based on VVSG is proposed. The control structure is raised based on a conventional VVSG outer active power control loop, and the output active power and frequency characteristics are analyzed. Compared with the voltage and current dual-mode control, VVSG with direct power control can perform large inertia characteristic in the weak grid and fast power following characteristics in the strong grid by adjusting λ, and without control structure switching and intermediate variable following. Moreover, the two characteristics can be smoothly transited. In addition, the active support ability of voltage source can be maintained under both characteristics. Finally, the effectiveness of the proposed control strategy is verified through simulation results.

Primary Frequency Regulation of Intelligent Building-type Virtual Power Plant

In order to cope with the impact of intelligent building-type virtual power plant on system frequency, this paper proposes a primary frequency control strategy. Firstly, a typical demand-side resource model of intelligent building-type virtual power plant is established, which considers the travel uncertainty of electric vehicles and resident’s comfort preference. Secondly, the control parameters of electric vehicles and air-conditioning loads are designed respectively, and a control strategy based on variable coefficient droop control is proposed. Finally, a simulation example verifies the effectiveness of the primary frequency regulation strategy, which can effectively reduce system frequency fluctuations while ensuring user demand.

A new synthetic inertia system based on electric vehicles to support the frequency stability of low-inertia modern power grids

The increasing share of renewables into modern power systems has resulted in lower levels of existing rotational inertia accompanied by conventional generation units. This issue results in an increase in system frequency fluctuations, which leads to system deterioration and instability. To overcome the ever-decreasing issue of inertia, several endeavors in inertia emulation have been provided based on external sources of energy (e.g., energy storage systems (ESSs)). However, the high capital and running costs associated with the adoption of these sources for inertia enhancement significantly deter their wide applications. Hence, to tackle these issues, this study proposes a new synthetic inertia control (SIC) system that relies on electric vehicles (EVs) as a pre-existing energy source in low-inertia modern power grids to expand inertial emulation capability and support frequency stability. In this way, the power system inertia can be imitated by exploiting the surplus stored energy in already existing system resources (e.g., EVs) without changing system hardware, thus decreasing the ESS’s required capacity. The proposed SIC is constructed based on the derivative control technique, where it is utilized to estimate the rate of change of frequency (RoCoF) to add adequate inertia power to the power grid set-point during contingencies, thereby improving frequency stability of low-inertia systems. The usability and superiority of the suggested SIC system based on EVs are validated by comparison with the traditional frequency control system against variant load/renewables disruptions, uncertainties, and physical constraints. The simulation results verified that the suggested SIC system exhibits ameliorated system performance and reliability, which could greatly support low-inertia modern power grids against contingencies.

Cyber Attack Detection Scheme for a Load Frequency Control System Based on Dual-Source Data of Compromised Variables

Cyber attacks bring key challenges to the system reliability of load frequency control (LFC) systems. Attackers can compromise the measured data of critical variables of the LFC system, making the data received by the defender unreliable and resulting in system frequency fluctuation or even collapse. In this paper, to detect potential attacks on measured data, we propose a novel attack detection scheme using the dual-source data (DSD) of compromised variables. First, we study the characteristics of the compromised LFC system considering potentially vulnerable variables and different types of attack templates. Second, by designing a variable observer, the relationship between the known security variables and the variables which are at risk of being compromised in the LFC system is established. The features of the data obtained by the observer can reflect those of the true data. Third, a Siamese network (SN) is designed to quantify the distance between the characteristics of measured data and that of observed data. Finally, an attack detection scheme is designed by analyzing the similarity of the DSD. Simulation results verify the feasibility of the detection scheme studied in this paper.

1-cycle RMS를 이용한 독립계통용 디젤발전기의 자동전압제어장치 성능 개선에 관한 연구

Since the power system in an island area is generally small-scale and not connected to the main land, it should be able to operate independently. And the power is mainly supplied by diesel generators. Under these circumstances, the frequency variation occurs easily when a variable load with a large capacity is operated during the diesel generator start-up or stand-alone operation. So, AVR(Automatic Voltage Regulator) unit generally used in the main land, which is based on 60 Hz fundamental frequency DFT(Discrete Fourier Transform) algorithm, cannot control the voltage reliably and immediately due to the error of voltage effective value caused by the system frequency fluctuation. In this study, the performance of the AVR unit with 1-cycle RMS(Root Mean Square) algorithm, which enables stable voltage control despite frequency variation, was developed and demonstrated through field application tests.

A new optimal robust controller for frequency stability of interconnected hybrid microgrids considering non-inertia sources and uncertainties

In this paper, a virtual inertia control based on a new optimal robust controller is proposed to improve the frequency stability of modern power systems considering renewables, nonlinearities, and frequency measurement effects. In applying the virtual inertia control technique, a phase-locked loop (PLL) is required to obtain the estimation of the system frequency data. However, the use of PLL can lead to greater system frequency fluctuation, and thus this problem will be aggravated with a lack of inertia in microgrids, which leads to system degradation and instability. Therefore, the proposed robust control technique is implemented based on a coefficient diagram method (CDM), which is designed optimally by a novel metaheuristic algorithm named chaotic crow search algorithm (CCSA). Where this proposed algorithm results from adding chaotic behavior to the crow search algorithm (CSA) in order to avoid suboptimal solutions and increase the convergence rate. Moreover, this study seeks to keep pace with smart future power systems by presenting a two-area interconnected hybrid microgrid (HMG) considering high penetration levels of renewable energy sources (RESs). Each HMG contains a thermal power plant, solar and wind power, electric vehicles (EVs), energy storage system (ESS), and customer loads. The superiority of the proposed control strategy (i.e., virtual inertia control based on the optimal robust CDM controller) is validated by comparing its performance with; conventional load frequency control (LFC) (i.e., integral controller), and virtual inertia control technique-based derivative control with/without the PLL. Moreover, the simulation results proved that the proposed control strategy could substantially endorse low-inertia multi-HMG for several contingencies.

Frequency regulation strategy of photovoltaic system based on system identification

The large-scale grid connection of photovoltaic power generation results in the power system frequency fluctuation and frequency regulation capacity decline, which endangers the dynamic security of power grid frequency. In order to reduce the frequency deviation of power grid and tap the potential of photovoltaic power generation participating in frequency regulation, a control method of photovoltaic power participating in frequency regulation of power grid is proposed in this paper. The maximum allowable power of photovoltaic power is predicted through system identification, and the load shedding rate is determined based on this, and the output power is corrected according to the system frequency deviation to participate in frequency regulation of power grid. The model based on MATLAB Simulation results shows the effectiveness of the proposed method.

Simulation analyses of stabilization control of power system frequency fluctuations resulting from wind farm output by gas turbine thermal power plant

AbstractThis paper presents a basic study about the control ability of LNG thermal power plant driven by Motor‐assisting Gas Turbine (MGT) for frequency stabilization of power grid system. An analytical model of the regulation system with assisting motor and gas turbine is developed, and its performance for frequency stabilization under fluctuating power due to renewable energy sources is investigated by numerical simulation analyses.

MVO optimized hybrid FOFPID-LQG controller for load frequency control of an AC micro-grid system

Purpose This paper aims to implement a maiden methodology for load frequency control of an AC multi micro-grid (MG) by using hybrid fractional order fuzzy PID (FOFPID) controller and linear quadratic Gaussian (LQG). Design/methodology/approach The multi MG system considered is consisting of photovoltaic, wind turbine and a synchronous generator. Different energy storage devices i.e. battery energy storage system and flywheel energy storage system are also integrated to the system. The renewable energy sources suffer from uncertainty and fluctuation from their nominal values, which results in fluctuation of system frequency. Inspired by this difficulty in MG control, this research paper proposes a hybridized FOFPID and LQG controller under random and stochastic environments. Again to confer viability of proposed controller its performances are compared with PID, fuzzy PID and fuzzy PID-LQG controllers. A comparative study among all implemented techniques i.e. proposed multi-verse optimization (MVO) algorithm, particle swarm optimization and genetic algorithm has been done to justify the supremacy of MVO algorithm. To check the robustness of the controller sensitivity analysis is done. Findings The merged concept of fractional calculus and state feedback theory is found to be efficient. The designed controller is found to be capable of rejecting the effect of disturbances present in the system. Originality/value From the study, the authors observed that the proposed hybrid FOPID and LQG controller is robust hence, there is no need to reset the controller parameters with a large change in network parameters.

Simulation Analyses of Stabilization Control of Power System Frequency Fluctuations Resulting from Wind Farm Output by Gas Turbine Thermal Power Plant

Simulation Analyses of Stabilization Control of Power System Frequency Fluctuations Resulting from Wind Farm Output by Gas Turbine Thermal Power Plant

Enhanced Nature-Inspired Meta-Heuristic Algorithm for Microgrid Performance Improvement

In this article, a new selection technique based on Enhanced Nature-Inspired Meta-Heuristic (ENIMH) optimization algorithm is presented to improve the Microgrid (MG) dynamic performance. Interconnected microgrids have the ability to provide a clean and sustainable energy during normal and emergency operating conditions. The concerned microgrid includes hybrid renewable energy sources (RES) and energy storages systems (ESS). MG achieves a reduced dependency on the electric grid and provides flexible and adaptive energy supply. This paper develops a new selection technique based on ENIMH optimization that distinguishes the degrees of resemblance between the best individual and other individuals of current population. This technique proposes a binary coding of individuals, and is compared to conventional techniques; it allows each individual to occupy a section of the modified roulette wheel selection for the calculated degree of resemblance. This enhanced optimization technique tunes the dynamic PID parameters of microgrid closed loop system. The designed strategy is dependably to locate the arrangement of enhanced parameters to minimize the system frequency fluctuations in the microgrid and to provide the improved dynamic performance by being sensitive to variations for closed loop response under various power and load conditions. The proposed technique has been demonstrated using Matlab/Simulink simulation on the underlined microgrid, where the achieved results confirm the effectiveness of proposed selection method for the reproduction of best individuals to show the improved performance. The proposed technique achieved satisfactory performance for PID-controllers, and provided a good closed loop performance, minimum overshoot and minimum fitness index, in comparison with other well-established methods. The results emphasize that ENIMH optimization algorithm has the exploration and exploitation capability of population best individuals to accomplish the best solutions.

Frequency Stability and Economic Operation of Transactive Multi-Microgrid Systems with Variable Interconnection Configurations

With the progressive addition of microgrids at the distribution level, complex networks of interconnected microgrids and the utility grid are likely to emerge. In such a scenario, advanced microgrid controllers are required to achieve operational stability objectives while maintaining a cost-effective operation. This paper investigates the control strategies, trading mechanisms, and interconnection configurations of a multi-microgrid and utility grid system for frequency stability analysis and operational cost optimization. The analysis is performed on a model of two interconnected microgrids and the utility grid, all possible interconnection configurations are tested. A robust controller is designed and the control parameters are later optimized to ensure that the frequency stability of the system is maintained under normal operating conditions and under various disturbances. A new control element based on switching between interconnection configurations is introduced to handle the power that flows between microgrids, aiming to minimize inter-microgrid energy trading cost while maintaining the system frequency fluctuations within tolerance levels. The effectiveness of the designed controller is demonstrated in this work. This work is expected to provide new insights in the field of multi-microgrid system design.

Fractional order cascaded controller for AGC study in power system with PV and diesel generating units

This paper emphases on automatic generation control (AGC) of a two-area power system comprising of different diversified sources such as hydro, thermal, wind, photo voltaic (PV), and diesel. Integration of a PV unit brings the intricacy in the system frequency and tie-line power fluctuation due to lack of damping under normal and severe load change. To overcome this problem a novel three degrees of freedom cascade controller incorporated with derivative filter (N) (3DOF-FOPIDN-FOPDN) controller is designed by endorsing a maiden application of WGA (Wild Goat Algorithm) algorithm to reach out an improved dynamic performance. The proficiency of 3DOF-FOPIDN-FOPDN controller against a random load perturbation as well as power fluctuation in PV unit, stands tall which ensures the robustness of the controller.

Optimal Guaranteed Cost Event-triggered Control of Smart Grid Against Time Delay Switch Attack

This paper mainly studies the optimal robust guaranteed cost load frequency control (LFC) problem for a class of uncertain power system under time delay switch (TDS) attack. The closed-loop power system is modelled as time delay system when an event-triggered communication scheme is adopted to reduce bandwidth consumption. In order to obtain less conservative stability criteria of the system with additive time delays, a novel Lyapunov-Krasovskii (L-K) functional is proposed and some latest integral inequalities are applied as well. Then, an optimal guaranteed cost controller is designed to eliminate the system uncertainty and frequency fluctuation, and the minimum upper bound of the performance index can be obtained by solving a convex optimization problem.

Wind power grid-connected frequency regulation strategy based on ESO control and PI control

Frequency fluctuation of wind power grid-connected system is difficult to adjust, aiming at this problem, this paper proposed a control strategy based on the combination of inner loop control and outer loop to restrain frequency fluctuation. extended state observer (ESO) is used as the outer loop. The error and disturbance which cannot be reflected directly in the system structure are estimated by linearization. The inner loop PI controller is designed through the parameters of proportional link and integral link to realize the reasonable allocation of internal model poles and achieve better damping effect. Simulation show that the control strategy can effectively suppress the system frequency fluctuation caused by load fluctuation and maintain frequency stable. The research results can be used to guide engineering practice.

A Virtual Filter Approach for Wind Energy Conversion Systems for Mitigating Power System Frequency Fluctuations

The increasing penetration of wind power may deteriorate power system frequency performance. This paper proposes a novel virtual filter (VF) approach for a grid-connected wind energy conversion system to mitigate power system frequency fluctuations. The principle is to modify the traditional wind power controller to emulate a physical energy storage system to smooth the wind power output. The VF proposed in this paper is tuned as a band-stop filter to selectively reject the power system frequency-sensitive components in wind power output. Therefore, the power system frequency fluctuations can be correspondingly reduced with only a small amount loss of wind energy. The advantages of the proposed VF are: 1) no need for a physical deployment of energy storage system, 2) no need for power system frequency signal and communication channel, and 3) ability to selectively filter the power system frequency sensitive components. Simulation results verified the outstanding performance of the proposed VF in system frequency fluctuation mitigation, while with less wind energy loss comparing with existing method.

A fuzzy logic-based frequency control scheme for an isolated AC coupled PV-wind-battery hybrid system

ABSTRACT The power generation from a renewable energy system has a fluctuating nature due to the intermittent sources. Mismatch between power generation and load demand causes a deviation from the desired frequency in power supply. A frequency control scheme for an isolated PV-wind-battery hybrid energy system is proposed by using fuzzy logic control for automatically select the frequency deviation suppressing element without communications among the different operational controllers. That said, the scheme proposed in this paper requires fewer measuring instruments. The proposed control scheme requires two parameters – system frequency and battery state of charge measurement in order to execute the following tasks. The first task includes – selection of proper frequency balancing element (i.e. battery or a dump load or a primary variable load) that depends on the frequency deviation and battery state of charge. The second task is to address the control operation of the selected element from battery, dump load and primary load. Here, we have demonstrated that by the control scheme, fluctuation of system frequency can be suppressed within an allowable limit owing to effective power management of the hybrid system. The scheme presented here simplifies the integration of renewable energy systems to an existing hybrid power system.