Power System Frequency Research Articles

A unified power flow controller-based robust damping controller considering time delay in electrical power systems

Nowadays, different power systems are connected to each other due to technical and economic reasons and form a complex developed network. Such networks measure and send system data to decision-making centers for control and protection. This information transmission is accompanied by a delay and causes the performance of the system’s damping controllers to be affected. To improve power system dynamic stability, the supplementary controller in flexible alternating current transmission system (FACTS) devices is designed to account for information transmission delays. In these methods, to increase the controllability and observability of the inter-area mode, the remote signals extracted from the wide area measurement system (WAMS) are used as the input of the modulator. WAMS systems’ time delay reduces power system stability and even causes instability, so it’s crucial to find the maximum delay margin that ensures stability. Therefore, it is necessary to carefully study the role of FACTS tools in stabilizing the power system and damping interregional fluctuations, considering the delay. This research shows that supplementary controller design can dampen frequency and load angle fluctuations in multi-zone power systems despite information transmission delays. The method works in power system analysis toolbox (PSAT) simulation and MATLAB programming.

Research on Control Strategy of Hybrid Energy Storage System Participating in Primary Frequency Regulation of Power Grid

With the ongoing development of China’s power system, there is a gradual increase in the proportion of new energy power generation. However, the randomness and volatility associated with new energy power generation can lead to increased frequency fluctuations in the power grid, posing a significant challenge to power system frequency regulation. In this paper, we investigate the control strategy of a hybrid energy storage system (HESS) that participates in the primary frequency modulation of the system. We analyze the advantages and disadvantages of various types of new energy storage from both technical and economic perspectives and perform an applicability analysis system to select lithium batteries and supercapacitor energy storage for forming a HESS. We propose a virtual droop control strategy to regulate the output of the HESS in the primary frequency regulation of the system. Finally, we build a simulation model that includes the HESS and power grid on the MATLAB/Simulink simulation platform and conduct a simulation analysis. The results show that the proposed strategy is superior and effective in controlling the HESS’s output when participating in the primary frequency modulation of the system.

Load Frequency Control With Renewable Energy Sources Using Practical Swarm Optimization Based On PID

Future competitive solutions for the production of electricity may be provided by emerging renewable energy sources (RESs) technologies as wind, solar photovoltaic, and solar thermal power systems. In this study, simulation tests have been conducted on autonomous hybrid generating systems(HGSs) made up of diesel engine generators (Degs), fuel cells (FCs), wind turbine generators (Wpg), solar photovoltaic generators (Pvpg), battery energy storage systems (Bess), and flywheels (Fess). The abrupt fluctuations in load, generation, or both cause the power system's frequency to vary. PID controller tuning using particle swarm optimization (PSO) is used for the optimization of controllers’ gains of the proposed hybrid systems. The proposed method is compared with a genetic algorithm (GA) and a traditional PID controller. To test the proposed controller, three different scenarios were used: first, changing the load's value with a fixed value over a set period of time; second, changing the load's value with variable values; and third, changing the load's value with a variable value while changing the system parameters. The simulation results reveal that the suggested controller performs better and is more resilient against load and generational disruptions by reducing the maximum overshoot value and settling time by 70% and 65%, respectively, and by 14.2% and 5% when compared to a GA-PID control.

A robustness-enhanced frequency regulation scheme for power system against multiple cyber and physical emergency events

Emergency events, e.g., accidental generator outages and abrupt steeps in electric load in physical layer, and unexpected communication time delays in cyber layer, are raising increasing concerns in modern power systems, and can cause system frequency deterioration, thus threatening power energy security. However, currently there is few discussions on dealing with multiple emergency events in power system comprehensively and simultaneously. In order to counter the adverse effects caused by these various emergency events and maintain the system frequency, a robustness-enhanced frequency regulation scheme is proposed in this article based on the coordinate transformation technique and Lyapunov theorem. First, to analyze the dynamic process of the power system in contingency conditions, the model of the power system frequency regulation is reconstructed considering multiple emergency events. Furthermore, to guarantee the power system frequency stability, a virtual auxiliary surface is constructed based on the coordinate transformation technique, which can provide the control reference for frequency regulation. On this basis, a robust controller is developed to drive the system’s trajectory to the proposed virtual auxiliary surface, thus guaranteeing the robustness of power system frequency, e.g., minor frequency deviation and faster recovery speed, even with emergency events. In addition, the stability of the system with the proposed controller is rigorously proved by Lyapunov theorem. Finally, the effectiveness of the proposed scheme is verified by case studies. The results show that by using the proposed scheme, the maximum frequency deviation and recovery time can be improved to about 61.11% and 46.40% of the original value under multiple emergency events, respectively. Therefore, the proposed scheme can counter well against emergency events and contribute to the power system’s frequency regulation and energy security.

Age-of-information-aware PI controller for load frequency control

Open communication system in modern power systems brings concern about information staleness which may cause power system frequency instability. The information staleness is often characterized by communication delay. However, communication delay is a packet-centered metric and cannot reflect the requirement of information freshness for load frequency control (LFC). This paper introduces the age of information (AoI), which is more comprehensive and informative than the conventional communication delay modeling method. An LFC controller and communication are integrated into the design for LFC performance improvement. An AoI-aware LFC model is formulated first, and considering each allowable update period of the smart sensor, different AoI-aware PI controllers are then designed according to the exponential decay rate. The right AoI-aware controller and update period are selected according to the degree of frequency fluctuation of the power system. Case studies are carried out on one-area and two-area power systems. The results show the superior performance of the AoI-aware controllers in comparison to the delay-dependent controllers.

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

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

A fast and robust DOBC based frequency and voltage regulation scheme for future power systems with high renewable penetration

AbstractThis paper proposes a disturbance‐observer‐based control (DOBC) scheme for frequency and voltage regulation in modern power systems with high renewable energy sources (RES) penetration. The proposed approach acts as a feed‐forward control that improves the dynamic performance of the conventional proportional‐integral‐derivative (PID) controller. The proposed voltage and frequency control has been validated through hardware‐in‐loop (HIL) implementation on OPAL‐RT, and testing on laboratory‐scale experimental test setup. The robustness of the proposed control scheme has been validated through simulations under worst‐case and stochastic uncertainties to mitigate real‐time variability in RES output and load. Real‐time simulation results depict superior performance of the proposed control strategy in comparison to several well‐established techniques under practical operating conditions, in the presence of communication delay and white noise. To validate the proposed control on laboratory‐scale experimental setup, the digital twin of the physical plant transfer function has been designed. Results reveal that the proposed DOBC control scheme drastically improves the system performance without rendering much computational burden under practical operation scenarios.

FOPTID+1 controller with capacitive energy storage for AGC performance enrichment of multi-source electric power systems

The demand for power increases during the peak hours and the power supply can't exceed its limitations. This results into mismatch between the supplied and demanded powers causing fluctuations in the frequency. Extreme power-frequency deviations may cause power system blackouts. To maintain the constant frequency of power system, automatic generation control (AGC) should be embedded with a reliable controller. In this paper, a fractional order proportional tilt integral derivative plus one (FOPTID+1) controller is introduced in the design of AGC to retain frequency constancy. This controller has the ability to regulate the frequency hastily during load disruptions. The controller parameters are optimized by exploiting global neighbourhood algorithm (GNA). Firstly, the investigation is directed on a one-area multi-source thermal-hydro-gas generating system. To authenticate the expandability of the method, the study is then extended to multi-source interconnected two-area thermal-hydro-gas power system without/with nonlinearities. The dominance of the suggested controller is recognized over various recently published results of I/PI/PID/TID/FOTID and GNA tuned PID/FOPID controllers. Inspection of results authorizes the worthier performance of FOPTID+1 over other controllers regarding least overshoot/undershoot/settling time of frequency/tie-line power change and error criteria at disturbances. To further advance the system performance, capacitive energy storage (CES) units are incorporated to compensate the power demanded by the load disturbances. The obtained results demonstrate that CES is capable to improve system performance effectively. With CES, FOPTID+1 produces less cost function value for both one-area (9.52%) and two-area (8.97% for linear and 11.38% for nonlinear) systems. The control system stability is verified by the study of bode diagram. The resilience behaviour of the controller is confirmed by the stout conduct of controller under ±25% variation of system parameters and tie-line outages.

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

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

Rotor Winding Design and Standalone Operation Research of High Natural Synchronous Speed Brushless Doubly-Fed Generator Based on Differential Modulation

Differential Modulation Brushless Doubly-fed Machine (DMBDFM) can achieve smaller equivalent pole-pair number, which broaden the operating range and application of Brushless Doubly-fed Machine (BDFM). However, the existing basic theory of BDFM can not be directly applied to DMBDFM, and the design method of the modulated rotor with different combination of pole-pair numbers (PPN) is not complete. Therefore, in order to achieve the highest natural synchronous speed(<i>n</i>_s) of BDFM at power system frequency, the rotor winding of 3&#x002F;2 pole pairs is designed in this paper. Then the test prototype is developed with the designed rotor scheme and the relevant parameters are given. The validity of the rotor design scheme is verified by finite element simulation and test results.

Augmented Complex Least Lncosh Algorithm for Adaptive Frequency Estimation

In this paper, an augmented complex least mean lncosh (ACLlncosh) algorithm is proposed to estimate the frequency of the three-phase unbalanced power system in impulsive noise environment. By introducing the Clarke’s αβ transformation and widely linear (WL) model into the Llncosh cost function, and using CR Calculus, the ACLlncosh algorithm is derived. Moreover, a variable parameter method is proposed to improve the performance of ACLlncosh. The mean and mean-square stability of the proposed ACLlncosh algorithm are analyzed, and the corresponding stable step size ranges are also given. Computer simulations under some typical power system operating situations verify the superiority of the proposed ACLlncosh algorithm than the complex least mean lncosh (CLlncosh) and augmented complex least mean square (ACLMS) algorithms in power system frequency estimation.

Frequency Domain Analysis of Load Frequency Control Using PIDTune Model Standard

The load frequency control system aims to regulate the frequency in the electric power system at a normal value with a predetermined tolerance limit. In practice, the load frequency control system does not always operate optimally, therefore a controller is needed to be added to the load frequency control system. The controller designed is a variation of the combination of Proportional-Integral-Differential (PID) controllers with the standard model PIDTune method consisting of proportional (P) controller, proportional integral (PI) controller, proportional differential (PD) controller, Proportional Integral Differential (PID) controller, Proportional Differential controller with first-order filter on differential section (PDF), and Proportional Integral Differential controller with first-order filter on differential section (PIDF). This study is aiming to carry out simulation and analysis in the frequency domain and then analyze the robustness of the reheat type power frequency control system and then design a PID controller for the reheat type power frequency control system in basic configuration, filter configuration, feedback configuration, feedforward configuration, and cascade configuration using PIDtune Model Standard on Matlab software. From the results of simulation and analysis, the controller that complies the design criteria and can make the reheat type of load frequency control system work optimally based on frequency domain analysis and robustness analysis is a proportional-integral (PI) controller in a feedback configuration with gain margin (Kg) equals to 38.11 dB, phase margin equals to 59.6°, infinity bandwidth, peak resonance value (Mr) equals to 1.19, maximum sensitivity peak value (MS) equals to 1.24, and complementary maximum sensitivity peak value (MT) equals to 1,17.

Frequency Control of Power System with Distributed Sources by Adaptive Type 2 Fuzzy PID Controller

The unpredictability of solar and wind energy sources affects contemporary power networks and adds frequency variations. An appropriate intelligent controller is necessary to balance electricity between generation and demand. As a result, in this research, we present a sine-cosine adaptive improved equilibrium optimization (SCaIEO) method tuned to Adaptive Type 2 Fuzzy PID Controller (AT2FPID) for frequency management of cutting-edge power systems. The efficiency of the SCaIEO approach is assessed by comparing it to the original equilibrium optimization (EO) and other comparable algorithms for the test function. Moreover, engineering applications of the SCaIEO technique are carried out by constructing an AT2FPID controller to manage the frequency of power systems that include renewable energy and dispersed sources. First, we show that SCaIEO outperforms EO, Particle Swarm Optimization, Genetic Algorithm, Moth Flame Optimization, and Gravitational Search Algorithm in the PID controller (Gravity Search Algorithm). The AT2FPID is next evaluated, and the SCaIEO AT2FPID controller’s dominance is proven by equating the outcome to the original, PID Type 1 Fuzzy PID, Type 2 Fuzzy PID controller.

Power system frequency profile improvement using satin bowerbird optimized tilt fractional cascade controller with reduced data based cost function

The objectives of the automatic generation control (AGC) are attained via secondary control mechanism with optimal controller gains. The best solutions of these gains are identified by population search-based algorithms with the help of performance metrices. The controller design issues of AGC treat these performance metrics as a cost function. This paper introduces a new performance measure implemented with dominated samples information extracted from the frequency and tie line power changes. This new integral square error (NISE) is incorporated in fitness function and tested on isolated and multi area interconnected power system scenarios with satin bowerbird optimizer to tune the controller gains. Additionally, integral-tilt proportional-fractional order derivative controller is proposed in this paper and comparisons are made with popular controllers to show the merits in terms of AGC specifications. Optimal gain parameters of all controllers are achieved with existing integral square error and the proposed NISE cost functions and extensive simulations are carried out to illustrate the merits of the work. Studies are also expanded to nonlinear systems in order to evaluate the adaptability, performance improvement, and effectiveness of the suggested cost function, controller, and tuning method.

Improved Combined Inertial Control of Wind Turbine Based on CAE and DNN for Temporary Frequency Support

With the continuous and large-scale development of renewable energy, there is a prominent decrease in the level of inertia in new power systems. This decrease leads to the weakening of the system’s capability to provide inertia support and frequency regulation during disturbance events. The wind turbines (WT), as the main representatives of renewable energy generation, should be more efficiently involved in the power system frequency regulation dynamics. However, optimal frequency regulation is difficult to achieve through the combined inertial control strategy of wind turbines because it greatly depends on control parameters and fluctuates in different scenarios. To cope with disturbance efficiently and quickly in different scenarios and obtain the optimal frequency regulation results, this paper presents an improved combined inertial intelligent control strategy of WT based on contractive autoencoder (CAE) and deep neural network (DNN). This method obtains the optimal parameters for combined inertial control using the particle swarm optimization (PSO) algorithm, then effectively extracts features from actual data using CAE followed by building a network model to predict the optimal combined inertial control parameters online. To verify and test the proposed method, it is applied in the IEEE 9-bus test system. The simulation results show that the method can obtain optimal control parameters with a faster computational time, good prediction accuracy, and generalization capability.

Proactive Frequency Stability Scheme: A Distributed Framework Based on Particle Filters and Synchrophasors

The reactive nature of traditional under-frequency load shedding schemes can lead to delayed response and unnecessary loss of load. This work presents a proactive framework for power system frequency stability. Bayesian filters and synchrophasors are leveraged to produce predictions after disturbances are detected. By being able to estimate the future state of frequency corrective actions can be taken before the system reaches a critical condition. This proactive approach makes it possible to optimize the response to a disturbance, which results in a decrease in the amount of compensation utilized. The framework is tested via Matlab simulations based on Kundur’s Two-Area System, and the IEEE 14-Bus System. Performance metrics are provided and evaluated against other contemporary solutions found in literature. During testing this framework outperformed other solutions by drastically reducing the amount of load dropped during compensation.

Multi-Area Load Frequency Control in Power System Integrated With Wind Farms Using Fuzzy Generalized Predictive Control Method

Frequency security is critical for the power systems&#x2019; stability and reliability. The integration of renewable energy resources brings new challenges to the frequency security of power systems. To provide a more robust control method for controlling the frequency and tie-line power flow of an interconnected power system integrated with wind farms (IPSWF), a load frequency control (LFC) controller of generalized predictive control (GPC) based on the Takagi-Sugeno (T&#x2013;S) fuzzy model (fuzzy-GPC) is proposed in this paper. First, the T&#x2013;S fuzzy model of the IPSWF is constructed. Then, the GPC is used to design the controller. Lastly, to validate the proposed scheme, an LFC strategy is established for a two-area interconnected power system integrated with a wind farm in power systems computer aided design (PSCAD). The control performance of proportional-integral, GPC, and fuzzy-GPC controller are compared under two faulty operating conditions. The simulation results show that the performance indicators and the dynamic behavior when the fuzzy-GPC controller is used are better than the performance when the PI controller and GPC controller are used. The proposed fuzzy-GPC used in the LFC of the IPSWF can regulate the frequency deviation and tie-line power deviation adaptively and achieve minimum frequency deviation and tie-line power deviation in a multi-area IPSWF.

Augmented Complex Minimization of Error Entropy With Fiducial Points for Power System Frequency Estimation

Frequency estimation plays an important role in ensuring the stability of the power system. The augmented complex minimum error entropy (ACMEE) algorithm has achieved better performance in frequency estimation under impulsive noise environments. However, it has the problem of unknown error probability density function (PDF) in frequency tracking, the improved algorithms called the complex minimization of error entropy with fiducial points (CMEEF) and the augmented CMEEF (ACMEEF) are proposed in this paper. The ACMEEF algorithm based on widely linear modeling uses second-order statistical information to process the non-circular signal through the complex voltage signal. At the same time, it incorporates a location-sensitive cost into minimum error entropy (MEE) to automatically locate the peak of the error PDF at the origin, which can accurately estimate the grid frequency under the unbalanced system and interference of noise. The stability of the proposed algorithm and the computational complexity are analyzed. Finally, the enhanced frequency estimation performance of the proposed ACMEEF algorithm is verified through simulation results of different synthetic signals and real-world data.

Resnet-based power system frequency security assessment considering frequency spatiotemporal distribution characteristics

Under the background of the accelerated transformation of the modern power system, renewable energy will gradually replace the role of traditional energy in the power system. Because of the randomness, uncertainty, and low inertia of renewable energy, the power system frequency security assessment is becoming a serious issue under the influence of large-scale renewable energy integrations. To achieve the rapid assessment of power system frequency security, a resnet-based frequency security assessment method considering frequency spatiotemporal distribution characteristics is proposed. In this paper, to provide more comprehensive frequency response information, the spatiotemporal characteristics of frequency are introduced and integrated into the input feature set. At the same time, the Resnet network and multi-task-learning framework are applied to construct a frequency security assessment model. Based on the experimental results on the modified IEEE39 bus system, the assessment accuracy is higher than 99%, which shows the excellent assessment performance of the proposed model.

Examination of fast frequency response capacity requirements considering frequency ride-through capabilities in distributed generators with legacy inverters

Given the rapid increase in inverter-based distributed generators (IBDGs), their response and subsequent impacts on power system stability during abnormal power system conditions are becoming important. Recent events have shown that an unexpected loss of IBDGs triggered by their outdated frequency ride-through (FRT) capability can occur, which in turn can lead to a power system frequency below the secure operation region. As FRT characteristics of IBDGs are dependent on their time of installation and capability to update FRT parameters, IBDGs with different ride-through characteristics are mixed within the power system. In this study, the potential impacts of FRT capabilities of IBDGs with legacy inverters have been investigated. The analysis was conducted considering the penetration level of IBDGs and complying with FRT characteristics. Furthermore, the required amount of fast frequency response resources, which are generally provided by battery energy storage systems, was evaluated along with the secure operating envelope that can aid in future power system planning. Case studies on modified New England 10-machine test system and Korean power system were conducted to validate the effectiveness of the analysis.