Low Frequency Inter-area Oscillations Research Articles

Adaptive optimal wide‐area controller for multi‐area power system using phasor measurement unit measurements

A neural network-based adaptive optimal controller for the damping of inter-area low-frequency electromechanical oscillations inherent to multi-area power systems is proposed. The controller is designed based on the linear quadratic regulator, which is usually designed based on the linear model obtained about an operating point (OP). As the power system is non-linear and dynamic, the optimal condition will only be satisfied at the designed OP. This proposed controller utilises an adaptive structure so that the controller can effectively act in all operating conditions. The phasor measurement unit measurements provide the remote feedback input to the controller. The generator states are estimated using the unbiased minimum variance filter so that the estimation can be done in the absence of generator input measurements. The performance of the proposed structure under various operating conditions and dynamic conditions are analysed in this study.

Power oscillations damping using wide-area-based solar plant considering adaptive time-delay compensation

The aim of this paper is to investigate the use of the ever increasing penetration of renewable energy into the power grid to solve challenging problems such as inter area power oscillations without the use of expensive power electronic devices and power system stabilizers. The increase in size of interconnected power systems, energy demand, and installation of remote renewable energies with relatively weak tie-lines has witnessed different stability problems such as low-frequency inter-area oscillations. Inter-area oscillation reduces system stability and transmission capacity. Without effective damping control mechanism, these oscillations could prolong and threaten the security of the system. This paper proposes a supplementary controller from a photovoltaic (PV) solar plant for damping inter-area oscillations. Due to its strong correlation to active power flow and monitoring system stress, area phase-angle difference is employed for the remote signal input of the controller. The signal can be obtained from phasor measurement unit (PMU) through wide-area measurements systems (WAMS). To deal with a wide range of variable delay in the signal input, an adaptive compensator is designed to reduce the impact of the communication latency using neuro-fuzzy inference system. A two-area four-machine test system is used and simulated with a Simulink-based package developed for the work of this study. The time-domain simulations, modal and frequency response analysis demonstrate the capability of the proposed controller to effectively damp inter-area oscillations, under a small- and large-scale disturbances and against a wide range of time delays.

A delay-dependent anti-windup compensator for wide-area power systems with time-varying delays and actuator saturation

In this paper, a delay-dependent anti-windup compensator is designed for wide-area power systems to enhance the damping of inter-area low-frequency oscillations in the presence of time-varying delays and actuator saturation using an indirect approach. In this approach, first, a conventional wide-area damping controller is designed by using H&#x221E output feedback with regional pole placement approach without considering time-varying delays and actuator saturation. Then to mitigate the effect of both time-varying delays and actuator saturation, an add-on delay-dependent anti-windup compensator is designed. Based on generalized sector conditions, less conservative delay-dependent sufficient conditions are derived in the form of a linear matrix inequality &#x0028 LMI &#x0029 to guarantee the asymptotic stability of the closed-loop system in the presence of time-varying delays and actuator saturation by using Lyapunov-Krasovskii functional and Jensen integral inequality. Based on sufficient conditions, the LMI-based optimization problem is formulated and solved to obtain the compensator gain which maximizes the estimation of the region of attraction and minimizes the upper bound of L2-gain. Nonlinear simulations are performed first using MATLAB &#x002F Simulink on a two-area four-machine power system to evaluate the performance of the proposed controller for two operating conditions, e.g., 3-phase to ground fault and generator 1 terminal voltage variation. Then the proposed controller is implemented in real-time on an OPAL-RT digital simulator. From the results obtained it is verified that the proposed controller provides sufficient damping to the inter-area oscillations in the presence of time-varying delays and actuator saturation and maximizes the estimation of the region of attraction.

Electromagnetic torque analysis‐based method for performance evaluation and optimisation of closed‐loop CPS regarding small signal stability

Low frequency oscillation occurs frequently in the smart grid, which threatens the security and stability of the physical system. Wide-area damping controller (WADC), which belongs to cyber system, can effectively suppress inter-area low frequency oscillations and improve the small signal stability of the closed-loop cyber-physical system (CPS). However, with the introduction of global signals, time delays of communication are inevitable. Considering that, this paper deduces the general mathematics expression among electromagnetic torque coefficients, WADC control parameters and time delays, which makes it possible to analyse the influence mechanism of time delay on small signal stability. Based on these analysis, on the one hand, the time-delay small signal stability region is established to evaluate the operation state of closed-loop CPS, on the other hand, if small signal stability is not achieved due to the measured time delays, optimisation scheme is proposed to carry out WADC control parameters coordination to optimise small signal stability of the closed-loop system. Finally, taking two time delays as example, this study verifies the effectiveness and advantages of the proposed method by comparing the closed-loop system performance considering two time delays with the cases of considering singe time delay and without time delay.

Wide-Area-Based Adaptive Neuro-Fuzzy SVC Controller for Damping Interarea Oscillations

Low-frequency interarea oscillation is a major problem in interconnected power systems with weak tie-lines that causes several stability problems if not damped. Fuzzy logic controller can generate human knowledge-based control rules to solve complex nonlinear problems. Unlike a neural network, fuzzy systems cannot learn from data, and it takes a long time to modify the membership functions. The adaptive neuro-fuzzy inference system (ANFIS) is a robust and intelligent system that integrates the capabilities of fuzzy logic and neural networks with several advantages such as adaptability, robustness, rapidity, and flexibility. In this paper, an ANFIS-based controller is proposed for controlling the reactive power provided by static var compensator to damp interarea oscillations. The controller input is a remote signal provided by a wide-area measurement system, and it is calculated as the center-of-inertia difference of generator rotor speed deviations. Moreover, a proportional-plus-derivative time-delay compensator with adaptive parameters is added to the controller to reduce the influence of time delay. A two-area four-machine test system is used and simulated with a Simulink-based package developed for the work of this paper. The time-domain simulations and frequency response analysis demonstrate the capability of the proposed controller to effectively damp interarea oscillations, under a small- and large-scale disturbances and against a wide range of time delays and load uncertainty.

Damping Inter-Area Oscillations With Large-Scale PV Plant by Modified Multiple-Model Adaptive Control Strategy

Studies suggest that inter-area low-frequency oscillations can be damped with supplementary damping control of large-scale photovoltaic (PV) plants. Multiple-model adaptive control (MMAC) is applied as the damping strategy to deal with uncertain variations of the postdisturbance operating conditions. To reduce the scales of the model bank and the damper bank, K-means clustering algorithm is used taking inter-area modes as features for operating condition clustering, and a common damper is designed for each cluster. Based on the deviation between the output dynamic responses of the actual system and models, Bayesian approach is employed to calculate the probability of each model representing the actual system in real time, followed by updating weights of each damper's output. The weighted average of the individual damper's outputs is attached to the reactive power control of the PV plant. A new continuous form of probability calculation with an inertial link is proposed to smooth weight fluctuation caused by discrete calculation in conventional MMAC and ease stress of power regulation of the PV plant. The nonlinear simulation results demonstrate that the proposed control strategy is able to sufficiently damp the inter-area modes of interest in unexpected operating conditions without any prior knowledge about the postdisturbance state.

The design of delay-dependent wide-area DOFC with prescribed degree of stability α for damping inter-area low-frequency oscillations in power system

In this paper, the delay-dependent wide-area dynamic output feedback controller (DOFC) with prescribed degree of stability is proposed for interconnected power system to damp inter-area low-frequency oscillations. Here, the prescribed degree of stability α is used to maintain all the poles on the left of s=−α in the s-plane. Firstly, residue approach is adopted to select input-output control signals and the schur balanced truncation model reduction method is utilized to obtain the reduced power system model. Secondly, based on Lyapunov stability theory and transformation operation in complex plane, the sufficient condition of asymptotic stability for closed-loop power system with prescribed degree of stability α is derived. Then, a novel method based on linear matrix inequalities (LMIs) is presented to obtain the parameters of DOFC and calculate delay margin of the closed-loop system considering the prescribed degree of stability α. Finally, case studies are carried out on the two-area four-machine system, which is controlled by classical wide-area power system stabilizer (WAPSS) in reported reference and our proposed DOFC respectively. The effectiveness and advantages of the proposed method are verified by the simulation results under different operating conditions.

Improved model‐free adaptive wide‐area coordination damping controller for multiple‐input–multiple‐output power systems

Wide-area power system stabiliser (WAPSS) has been proved to be an effective method to damp inter-area low-frequency oscillations by using synchronised-phasor measurements. However, negative interactions among the WAPSSs may happen when they are designed separately. The conventional model-based coordination design methods are difficult to get good damping performance because model identification of the high-order, non-linear and time-varying power system is difficult. In this study, an improved model-free adaptive control (MFAC) algorithm is proposed for WAPSS coordination design. With the consideration of the interactions among the controllers and system noises, a novel decoupled multiple-input–multiple-output power system description for WAPSS coordination design are given. The MFAC control law and adaption law for each subsystem are improved to satisfy the controller coordination design requirements. The closed-loop system stability and parameter settings of the improved MFAC algorithm are also analysed from a global perspective. Compared with model-based methods, the proposed MFAC algorithm can ensure the controllers cooperate with each other and perform well under various operating conditions without tedious system modelling. The effectiveness of the proposed controllers is tested on an interconnected large-scale power system in China. An MFAC-WAPSS control system for field application is also presented in this study to validate its practicality.

EFFICIENT POWER OSCILLATION DAMPING CONTROL BY ADAPTIVE NEURO FUZZY CONTROLLER BASED POWER SYSTEM STABILIZER

Low frequency Inter-area oscillations are undesirable which affects the goals of maximum power transfer and optimal power flow. Power system stabilizers can be added to the automatic voltage regulators on the generators to reduce the effect of low frequency inter area oscillation. Different types of power system stabilizers are developed to reduce low frequency inter area oscillations inter but the area is still open for the efficient power stabilizer, for handling the power oscillations without increasing the system controller complexity. This paper presents a way to improve the dynamic stability of interconnected power systems by damping of inter area oscillations in two area four machine power system by designing of Adaptive Neuro Fuzzy Inference System based controller. The implementation is done with the Simulink of MATLAB 2012(b).The obtained results shows that ANIFS-PSS is capable of damping power oscillations in multi area system.

Wide area adaptive hybrid fuzzy STATCOM controller for dynamic stability enhancement

Purpose The purpose of this paper is to develop an adaptive fuzzy controller for STATCOM to damp low-frequency inter-area oscillation over wide operating range using wide area signals in multimachine power system. Design/methodology/approach In this paper tuneable fuzzy model is proposed where the parameters of the fuzzy inference system are tuned by using the adaptive characteristic of the artificial neural network. Based on back propagation algorithm and method of least square estimation, the fuzzy inference rule base is tweaked according to the data from which they are modelled. The wide area control signals, for the proposed controller, available in the power system are selected on the basis of eigenvalue sensitivity defined in terms of participation factor. Findings The effectiveness of the proposed controller with wide area signals is tested on two test cases, namely, two area network and IEEE 12 bus benchmark system. The comparative analysis of the proposed adaptive fuzzy controller is carried out with conventional STATCOM controller along with fuzzy-and neural-based supplementary controller all using selected wide area signals. The results show that neural network tuned fuzzy controller leads to better system identification and have enhanced damping characteristics over wide operating range. Originality/value In the available literature, numerous researchers have indicated the use of fuzzy logic controller and neural controller along with their hybrid schemes as STATCOM controller for improving the dynamics of the multimachine power system using local signals. The main contribution of the paper is in using the hybrid intelligent control scheme for STATCOM using wide area signals. The advantage of proposed scheme is that the performance of well-designed fuzzy system can be enhanced with the same training data that are used for designing a neural controller thus giving enhanced performance in comparison to individual intelligent control scheme.

Coordination of PSSs and SVC Damping Controller to Improve Probabilistic Small-Signal Stability of Power System With Wind Farm Integration

A modified fruit fly optimization algorithm (MFOA) combined with a probabilistic approach are proposed in this paper to coordinate and optimize the parameters of power system stabilizers (PSSs) and static VAR compensator (SVC) damping controller for improving the probabilistic small-signal stability of power systems with large-scale wind generation, taking into consideration the stochastic uncertainty of system operating conditions. It is generally accepted that there is a threat to the stability of power system with penetration of wind farm. In addition, the stochastic fluctuations of wind generation make PSSs tuning more difficult. In this paper, PSSs and SVC damping controller are employed for suppressing local and inter-area low frequency oscillation. In order to eliminate the adverse effect between PSSs and SVC damping controller, the MFOA based on the probabilistic eigenvalue is applied to coordinate and optimize their parameters. The effectiveness of the proposed approach is verified on two test systems.

Load following mechanism and power flow algorithm under generator rotor angle control mode

Recently, a new strategy that controls generator rotor angle has appeared. The new control strategy can suppress inter-area low-frequency oscillations effectively without the help of any remote signal. It can also improve transient stability. This paper investigates the load balancing mechanism after rotor angle controllers are deployed. Analysis shows that the primary frequency control and automatic generation control currently used can be fulfilled in a new manner under this new control strategy. The generators can follow load demands quickly and precisely without the intervention of a dispatching centre. Consequently, the task of frequency control may be separated from the dispatching centre since the new control strategy is essentially decentralised and autonomous. Moreover, a load variation will be distributed to all generators that run in fix angle mode according to their distance from the load. Though power flow calculation is not needed during this process, it can be used to obtain generator outputs for any set of rotor angle aim values after loads change. Since generator rotor angle and the terminal bus voltage are given as inputs, the traditional Newton–Raphson method must be modified before it can be used. Those modifications and some extra steps with generator output limits are also given.

Wind power converters improving the power system stability

This study analyses the coordinated actions of modern wind power plants for improving the transient and small-signal stability in power systems. Supplementary controls on wind farms are considered, and specific modifications on the controllers are tailored to increase the grid-support services. The proposal is analysed and validated in a practical power system based on the Argentine electrical network. The wind farm supplementary controls use active and reactive power control loops as well as local and remote measurements. Local controls can rapidly respond decelerating the system frequency in the first instants of a fault, consequently reducing the transient angle separations and improving the first-swing stability. On the other hand, remote controls using global information are able to increase the damping of low-frequency inter-area oscillations. Structures combining centralised and decentralised control approaches will become more common in the near future. With this aim, the integration of fast local controls with remote controls is thoroughly studied using non-linear time-domain simulations and eigenvalue analyses. A robustness evaluation is also performed to validate the proposal over a wide range of operating conditions.

Research on coordination optimization of DC modulation controller in multi-infeed transmission system based on improved Prony and chaos cloud particle swarm algorithm

The application of DC power modulation of DC transmission lines can effectively suppress the phenomenon of inter-area low frequency oscillation between AC and DC interconnected grids. But in multi-infeed AC/DC transmission power system, the role of DC modulation is weakened due to the lack of mutua l coordination. In order to improve the stability of the operation of the overall interconnected system, in this paper a control strategy is proposed to apply the improved Prony algorithm to identify the electromechanical mode of low frequency oscillation in interconnected power systems, and then chaos particle swarm algorithm combined with the cloud model of adaptive adjustment of inertia weight coefficient is adopted to coordinate and optimize the parameters of each DC modulation controller. In this method, multi-signal is firstly introduced into traditional Prony algorithm to combinationally identify low frequency oscillations in AC/DC hybrid systems, and then the mutual influence between the DC modulators are identified and simplified, which is used as the basis of the coordination and optimization model. On the basis of it, we use the chaos cloud particle swarm optimization algorithm with high precision and rapid convergence to optimize the parameters of each DC modulation controller. Through simulation in eight-generator three-region multi-infeed AC/DC power transmission system, and the results show that DC modulation controllers based on improved Prony with its parameters optimized by chaos cloud particle swarm algorithm attached to system can maximize regional power oscillation damping, and enhance the system operation stability, and possess quite good control effects.

Decentralised wide‐area fractional order damping controller for a large‐scale power system

This study presents the design of wide-area fractional order damping controller for low frequency inter-area oscillations in Western Electricity Coordinating Council (WECC) system. The developed wide-area damping control scheme is implemented in a decentralised manner by examining the entire system through decentralised identification at the level of each generator bus and FACTS devices in large-scale system. The decentralised identification is done by applying n4sid (Subspace State Space System Identification) algorithm to the time-domain simulated response of WECC system. The main features of the proposed approach are: (a) measurement-based control which does not require complete model of WECC; (b) minimise the communicating signals required for damping controller and incorporate practical method of time-delay compensator (TDC) design to reduce the effect of time-varying delay. The performance of wide-area control (WAC) scheme is tested on the practical WECC system and verified by non-linear time-domain simulation. The proposed decentralised WAC scheme is compared with local and centralised control scheme, which enhances the damping of inter-area oscillation effectively compared to local control scheme and more reliable compared to centralised control scheme and its robustness is verified over a wide-range of operating conditions.

Oscillation Energy Analysis of Inter-Area Low-Frequency Oscillations in Power Systems

Low-frequency inter-area oscillation is a potentially dangerous phenomenon in power systems involving exchange of power among generators in different areas. In this paper, we study the characteristics of inter-area oscillation by analyzing the distribution of the oscillation energy. First, we introduce equations for the kinetic energy of generators and the potential energy of network branches, derived from the linearization of system dynamic equations. Then, we study the mode composition and the distribution of the generators' kinetic energy during low-frequency oscillations. A modal kinetic energy participation factor is proposed for evaluating the participation of each generator in the oscillation. The relationships among electromagnetic power oscillation distribution, rotor speed deviation, and generator kinetic energy are analyzed and compared to their modal parameter left eigenvectors, right eigenvectors, and linear participation factors, respectively. The bus voltage angle deviation, active power oscillation, and branch potential energy are calculated using the right eigenvector from modal analysis. The distribution characteristics of voltage angle oscillation and branch potential energy in inter-area oscillation is developed. The simulation results for a four-generator two-area system and the New England 10-machine 39-bus system illustrate the feasibility and validity of the proposed theory and method for analysis of inter-area oscillations.

Identification of dominant low‐frequency modes in ring‐down oscillations using multiple Prony models

This study presents a simple approach to modify the Prony algorithm to extract dominant low-frequency modes present in ring-down oscillations in power systems. The proposed approach is based on the observation that true modes present in the ring-down oscillations appear consistently, irrespective of the order of the Prony model. It is shown that the consistently appearing modes can be extracted using a sorting method. The improved Prony algorithm which has the feature of extracting only the true modes present in the input signal is utilised to propose an oscillation monitoring algorithm in this study. The suitability of the proposed oscillation monitoring algorithm for real-time monitoring of low-frequency inter-area oscillations is demonstrated using synthetic signals and simulated signals of different test systems.

Wide‐area power system stabiliser based on model‐free adaptive control

The interconnection of regional power grids has resulted in inter-area low-frequency oscillation, which has become a serious problem that threatens the security of power systems. Wide-area power system stabiliser (WAPSS) is an effective device to damp this oscillation. Given that the interconnected multi-machine power system is a strongly non-linear and complex system with time-varying structure and operating conditions, satisfactory control performance of WAPSS is difficult to obtain by using conventional model-based control methods. In this study, a data-driven control method called model-free adaptive control (MFAC) is introduced to WAPSS design. The MFAC algorithm is improved to meet the wide-area damping control requirements in consideration of system disturbances. The stability of the closed-loop system with the improved MFAC-WAPSS is also analysed, and the parameter settings of the improved MFAC algorithm are provided in detail. The improved MFAC-WAPSS can adjust its parameters adaptively only based on the input and output data and avoid the complex system modelling process. The proposed adaptive WAPSS is evaluated on a simplified New England power system. Simulation results show the effectiveness of this new technique.

Design and implementation of an identifier system for inter-area power oscillations

Identifying inter-area oscillations can be a challenge for interconnected grids. Two identifier algorithms (FBMSWA and TBR-EMD) proposed to detect these oscillations are comparatively tested in this research. FBMSWA is implemented with T-STATCOM to damp out 0.15Hz low-frequency inter-area oscillation after interconnection Turkey with ENTSO-E. Developed TBR-EMD algorithm has certain achievements, e.g. admissible for real time, handling intermittency problem of EMD, proved by real data.

A new wide area damping controller design method considering signal transmission delay to damp interarea oscillations in power system

Wide area damping controller (WADC) is usually utilized to damp interarea low frequency oscillation in power system. However, conventional WADC design method neglects the influence of signal transmission delay and damping performance of WADC designed by the conventional method may deteriorate or even has no effect when signal transmission delay is beyond delay margin, an index that denotes delay endurance degree of power system. Therefore, a new design method for WADC under the condition of expected damping factor and required signal transmission delay is presented in this work. An improved delay margin with less conservatism is derived by adopting a new Lyapunov-Krasovskii function and more compact bounding technique on the derivative of Lyapunov-Krasovskii functional. The improved delay margin, which constructs the correlation of damping factor and signal transmission delay, can be used to design WADC. WADC designed by the proposed method can ensure that power system satisfies expected damping factor when WADC input signal is delayed within delay margin. Satisfactory test results demonstrate the effectiveness of the proposed method.