Reactive power control of wind farm made up with doubly fed induction generators in distribution system

In recent years, the number of small size wind farm made up with doubly fed induction generators (DFIG) located within the distribution system is rapidly increasing. DFIG can be utilized as the continuous reactive power source to support system voltage control by taking advantage of their reactive power control capability. In this paper, considering both reactive power control and distribution network reconfiguration can be used to reduce power losses and improve voltage profile, a joint optimization algorithm of combining reactive power control of wind farm and network reconfiguration is proposed to obtain the optimal reactive power output of wind farm and network structure simultaneously. The proposed algorithm has been successfully implemented on the 16 bus distribution network and the results obtained demonstrate the efficiency of the algorithm.     

Robust control of an isolated hybrid wind-diesel power system using Linear Quadratic Gaussian approach

This paper presents the application of the Linear Quadratic Gaussian (LQG) controller for voltage and frequency regulation of an isolated hybrid wind-diesel scheme. The scheme essentially consists of a vertical axis wind turbine driving a self-excited induction generator connected via an asynchronous (AC-DC-AC) link to a synchronous generator driven by a diesel engine. The synchronous generator is equipped with a voltage regulator and a static exciter. The wind generator and the synchronous generator together cater for the local load and power requirement. However, the load bus voltage and frequency are governed by the synchronous generator. The control objective aims to regulate the load voltage and frequency. This is accomplished via controlling the field voltage and rotational speed of the synchronous generator. The complete nonlinear dynamic model of the system has been described and linearized around an operating point. The standard Kalman filter technique has been employed to estimate the full states of the system. The computational burden has been minimized to a great extent by computing the optimal state feedback gains and the Kalman state space model off-line. The proposed controller has the advantages of robustness, fast response and good performance. The hybrid wind diesel energy scheme with the proposed controller has been tested through a step change in both wind speed and load impedance. Simulation results show that accurate tracking performance of the proposed hybrid wind diesel energy system has been achieved.     

Chaotic ant swarm optimization for fuzzy-based tuning of power system stabilizer

In this paper, chaotic ant swarm optimization (CASO) is utilized to tune the parameters of both single-input and dual-input power system stabilizers (PSSs). This algorithm explores the chaotic and self-organization behavior of ants in the foraging process. A novel concept, like craziness, is introduced in the CASO to achieve improved performance of the algorithm. While comparing CASO with either particle swarm optimization or genetic algorithm, it is revealed that CASO is more effective than the others in finding the optimal transient performance of a PSS and automatic voltage regulator equipped single-machine-infinite-bus system. Conventional PSS (CPSS) and the three dual-input IEEE PSSs (PSS2B, PSS3B, and PSS4B) are optimally tuned to obtain the optimal transient performances. It is revealed that the transient performance of dual-input PSS is better than single-input PSS. It is, further, explored that among dual-input PSSs, PSS3B offers superior transient performance. Takagi Sugeno fuzzy logic (SFL) based approach is adopted for on-line, off-nominal operating conditions. On real time measurements of system operating conditions, SFL adaptively and very fast yields on-line, off-nominal optimal stabilizer variables.     

考虑频率安全约束及风电综合惯性控制的电力系统机组组合

随着风电渗透率上升,电力系统惯性响应和一次调频能力下降,频率安全问题凸显,有必要在机组日前发电计划安排中考虑频率安全约束。依据电力系统频率安全要求,提出了考虑频率跌落最低值的频率安全约束构造方法。同时引入风电综合惯性控制使风电机组参与一次调频,在此基础上建立了考虑频率安全约束及风电综合惯性控制的机组组合模型。运用M语言动态控制多机频率响应模型进行Simulink仿真,并将其嵌入到改进粒子群优化算法中迭代求解。含风电的IEEE39节点系统算例结果表明,所提模型和方法能有效提升系统频率响应能力,保证系统安全运行。     

Small signal stability enhancement of DFIG based wind power system using optimized controllers parameters

This paper presents the state space modelling of doubly fed induction generator (DFIG) for small signal stability assessment. The gains of PI controller in torque and voltage control loop of rotor-side converter (RSC) are optimized by particle swarm optimization (PSO) to improve the dynamic performance of DFIG. These optimized parameters results in improved damping of DFIG and minimizes the oscillations in rotor currents and electromagnetic torque. The nature of modes of oscillations for DFIG integrated to infinite bus are analysed under different operating conditions such as varying wind speed and grid strength. The transient analysis with optimized parameters shows the enhancement in LVRT capability during voltage sag and three phase fault as desired by grid codes.     

Optimal power flow by a fuzzy based hybrid particle swarm optimization approach

This paper presents a fuzzy based hybrid particle swarm optimization (PSO) approach for solving the optimal power flow (OPF) problem with uncertainties. Wind energy systems are being considered in the study power systems. OPF is an optimization problem which minimizes the total thermal unit fuel cost, total emission, and total real power loss while satisfying physical and technical constraints on the network. When performing the OPF problem in conventional methods, the load demand and wind speed must be forecasted to prevent errors. However, actually there are always errors in these forecasted values. A characteristic feature of the proposed fuzzy based hybrid PSO method is that the forecast load demand and wind speed errors can be taken into account using fuzzy sets. Fuzzy set notations in the load demand, wind speed, total fuel cost, total emission, and total real power loss are developed to obtain the optimal setting under an uncertain environment. To demonstrate the effectiveness of the proposed method, the OPF problem is performed on the IEEE 30- and 118-Bus test systems.     

An active power control strategy for a DFIG-based wind farm to depress the subsynchronous resonance of a power system

This study presents a novel auxiliary damping control strategy to depress subsynchronous resonance (SSR) oscillations in nearby turbine generators. In the proposed control strategy, SSR damping is achieved by adding turbine generator speed as a supplementary signal at the active power loop of the rotor-side converter (RSC) of doubly-fed induction generator (DFIG)-based wind farms. To design the SSR auxiliary damping controller, a transfer function between turbine generator speed and the output active power of the wind farms was introduced to derive the analytical expression of the damping coefficient. Then the damping effect of the active power of the DFIG-based wind farms was analyzed, and the phase range to obtain positive damping was determined. Next, the PID phase compensation parameters of the auxiliary damping controller were optimized by genetic algorithm to obtain the optimum damping in the entire subsynchronous frequency band. The last, the validity and effectiveness of the proposed auxiliary damping control were demonstrated on a modified version of the IEEE first benchmark model by time domain simulation analysis with the use of DigSILENT/PowerFactory.     

Cascade controller based modeling of a four area thermal: gas AGC system with dependency of wind turbine generator and PEVs under restructured environment

This paper investigates automatic generation control (AGC) of a realistic hybrid four-control area system with a distinct arrangement of thermal units, gas units and additional power generation. A proportional-integral-double derivative cascaded with proportional-integral (PIDD-PI) controller is employed as secondary controller in each control area for robust restructured AGC considering bilateral transactions and contract violations. The Harris Hawks algorithm is used to determine the optimal controller gains and system parameters under several scenarios. Electric vehicle (EV) aggregators are employed in each area to participate fully along with thermal and gas units to compensate for the unscheduled system demand in the local area. A comparison of non-cascaded controllers such as PI-PD, PD-PID and the proposed PIDD-PI proves the superiority of the last. The effect of the decline in inertia is closely examined because of the sudden outage of a generating unit while at the same time considering the change in area frequency response characteristics and area control error. EV fleets make significant contributions to improving the system dynamics during system inertia loss. The use of EVs in the presence of a wind energy-supported grid can provide a stable efficacy to the power grid. Numerous simulations with higher load demands, stochastic communication delays in presence of the WTG plant, and violations in system loadings and changes in gas turbine time constants in the absence of WTG demonstrate the robustness of the proposed control approach.     

Advanced control of a doubly-fed induction generator for wind energy conversion

The aim of this paper is to propose a control method for a doubly-fed induction generator used in wind energy conversion systems. First, stator active and reactive powers are regulated by controlling the machine inverter with three different controllers: proportional–integral, polynomial RST based on pole placement theory and Linear Quadratic Gaussian. The machine is tested in association with a wind-turbine emulator. Secondly a control strategy for the grid-converter is proposed. Simulations results are presented and discussed for each converter control and for the whole system.     

Sliding mode controller design for frequency regulation in an interconnected power system

In this paper, a Sliding mode controller design method for frequency regulation in an interconnected power system is presented. A sliding surface having four parameters has been selected for the load frequency control (LFC) system model. In order to achieve an optimal result, the parameter of the controller is obtained by grey wolf optimization (GWO) and particle swarm optimization (PSO) techniques. The objective function for optimization has been considered as the integral of square of error of deviation in frequency and tie-line power exchange. The method has been validated through simulation of a single area as well as a multi-area power system. The performance of the Sliding mode controller has also been analyzed for parametric variation and random loading patterns. The performance of the proposed method is better than recently reported methods. The performance of the proposed Sliding mode controller via GWO has 88.91% improvement in peak value of frequency deviation over the method of Anwar and Pan in case study 1 and similar improvement has been observed over different case studies taken from the literature.     

直驱永磁风力发电系统仿真与优化控制

分析了直驱永磁风力发电系统的基本原理及各模块的控制策略,在Matlab/Simulink中搭建风电系统及其控制器的仿真模型,仿真验证了模型的正确性。在发电机精确模型的基础上,忽略发电机定子暂态得到实用模型,并对两种模型的适用性进行讨论。仿真分析表明:当分析发电机本身的动态问题时,可采用精确模型;当进行并网计算时,实用模型和精确模型均可以准确描述。最后利用粒子群算法对直驱永磁风力发电系统中的控制器参数进行优化,提高了系统的动态特性,实验结果验证了该直驱永磁风力发电系统控制器参数优化方法的有效性和可行性。     

考虑风电消纳多向量流系统的遗传优化方法

随着全球能源短缺问题的加剧,风电的大规模消纳显得十分重要。为了克服风电大规模消纳困难的问题,提出一种多矢量储氢发电系统的遗传优化方法。分别研究分析风力风电、氢储能系统、储气罐中的等效荷电状态的数学模型,建立以风电本地消纳最大化为目标的联合优化模型,结合多种约束条件,通过遗传算法实现能量流最优解的求取。以东北某地区的实际测量数据为基础,进行了案例分析。通过对系统在运行过程中的风电消纳效果进行比较,验证了所提方法能够有效减少交互电量,实现了风电本地消纳最大化。     

基于风电场景概率的电热混合储能优化配置

本文提出一种考虑风电典型场景概率的电热混合储能优化配置方案,以提高风电入网的经济性和可行性。首先通过场景分析,利用k-means聚类法将大量风机历史出力数据简化为6个典型出力场景,确定各场景发生的概率,其中聚类数目由肘部曲线法和Dunn指数法综合确定;其次提出电热混合储能系统控制策略,建立适用于多场景的风储联合系统模型;最后,以经济性成本最低与弃风量最小为目标,建立包含电、热负荷综合响应的容量配置优化模型,并将场景概率以权值的形式加入到目标函数中,利用粒子群算法对模型进行求解。通过仿真分析和与其他储能配置场景对比,我们发现所提出的配置策略能够提高风电利用率约11.04%,同时减少系统综合成本约44.52%,验证所提策略的合理性和有效性。     

Modelling,simulation and optimisation of robust PV based micro grid for mitigation of reactive power and voltage instability

This paper proposes a robust H-infinity STATCOM controller for compensating reactive power in stand-alone micro grid consisting of a PV–Wind–Diesel hybrid system. In order to carry out MATLAB based simulation, a small signal linear model of the stand-alone hybrid power system is considered, comprising of a photo voltaic cell, a DFIG based wind turbine and a diesel generator. Synchronous generator based DG acts as a backup for the hybrid system. Generally these standalone systems experience frequent variation of loads, wind power input and solar radiation, which affect the vital system parameters like reactive power, terminal voltage and frequency to a great extent. These variations of system parameters with variation of load inputs are studied and its impact on overall system stability and reactive power compensation is properly monitored. Furthermore the system performance is improved and the robustness of the controller is enhanced with the incorporation of GA and PSO.     

Modeling and control of PMSG-based variable-speed wind turbine

This paper presents a control scheme of a variable-speed wind turbine with a permanent-magnetic synchronous generator (PMSG) and full-scale back-to-back voltage source converter. A comprehensive dynamical model of the PMSG wind turbine and its control scheme is presented. The control scheme comprises both the wind-turbine control itself and the power-converter control. In addition, since the PMSG wind turbine is able to support actively the grid due to its capability to control independently active and reactive power production to the imposed set-values with taking into account its operating state and limits, this paper presents the supervisory reactive power control scheme in order to regulate/contribute the voltage at a remote location. The ability of the control scheme is assessed and discussed by means of simulations, based on a candidate site of the offshore wind farm in Jeju, Korea.     

Multi objective load frequency control using hybrid bacterial foraging and particle swarm optimized PI controller

Excessive load demand with reliability in power availability, demands for interconnection of large number of generating units over existing tie lines. Due to sudden change in demand, the power transfer over existing tie lines working close to their thermal limits results in low frequency power oscillations. Thus, in modern power systems the study of mitigation of these frequency oscillations is more involved and formulates the area of Load Frequency Control (LFC). Many conventional and heuristic control techniques have been recently applied to address the issue of LFC. This paper investigates load frequency control of large interconnected power system consisting of conventional and renewable energy sources, using hybrid heuristic approach. The proposed strategy is shown to result in improved system damping resulting in faster mitigation of low frequency oscillations.     

A fuzzy logic supervisor for active and reactive power control of a fixed speed wind energy conversion system

In this paper, we present the design of a fuzzy logic supervisor for the control of active and reactive power which is generated by fixed speed wind energy conversion systems (WECS). First, the modelling of a three-phase induction generator driven by a horizontal axis wind turbine is described. An adjustable capacitor bank is plugged at the connection point with a Static Var Compensator (SVC), which is controlled to regulate the rms voltage. The obtained model is reduced by taking into consideration the dynamics of the system. A fuzzy logic-based supervisor is proposed in order to minimize variations of the generated active power and the stator voltage. The regulation of the rms voltage is performed while imposing a reactive power reference. The pitch angle of the turbine blades is set to obtain the maximum wind power. The obtained performances of the proposed supervisor are then presented.     

Grasshopper optimization algorithm optimized multistage controller for automatic generation control of a power system with FACTS devices

This paper uses a Grasshopper Optimization Algorithm (GOA) optimized PDF plus (1+ PI) controller for Automatic generation control (AGC) of a power system with Flexible AC Transmission system (FACTS) devices. Three differently rated reheat turbine operated thermal units with appropriate generation rate constraint (GRC) are considered along with different FACTS devices. A new multistage controller design structure of a PDF plus (1 + PI) is introduced in the FACTS empowered power system for AGC while the controller gains are tuned by the GOA. The superiority of the proposed algorithm over the Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) algorithms is demonstrated. The dynamic responses of GOA optimized PDF plus (1+ PI) are compared with PIDF, PID and PI controllers on the same system. It is demonstrated that GOA optimized PDF plus (1+ PI) controller provides optimum responses in terms of settling time and peak deviations compared to other controllers. In addition, a GOA-tuned PDF plus (1 + PI) controller with Interline Power Flow Controller (IPFC) exhibits optimal results compared to other FACTS devices. The sturdiness of the projected controller is validated using sensitivity analysis with numerous load patterns and a wide variation of parameterization. To further validate the real-time feasibility of the proposed method, experiments using OPAL-RT OP5700 RCP/HIL and FPGA based real-time simulations are carried out.     

A combination of genetic algorithm and particle swarm optimization for optimal DG location and sizing in distribution systems

Distributed generation (DG) sources are becoming more prominent in distribution systems due to the incremental demands for electrical energy. Locations and capacities of DG sources have profoundly impacted on the system losses in a distribution network. In this paper, a novel combined genetic algorithm (GA)/particle swarm optimization (PSO) is presented for optimal location and sizing of DG on distribution systems. The objective is to minimize network power losses, better voltage regulation and improve the voltage stability within the frame-work of system operation and security constraints in radial distribution systems. A detailed performance analysis is carried out on 33 and 69 bus systems to demonstrate the effectiveness of the proposed methodology.     

A new two-degree of freedom combined PID controller for automatic generation control of a wind integrated interconnected power system

Frequency control of an interconnected power system in the presence of wind integration is complex since wind speed/power variations also affect system frequency in addition to load perturbations. Therefore, improving existing control schemes is necessary to maintain a stable frequency in such complex power system scenarios. In this paper, a new 2-degree of freedom combined proportional-integral and derivative control scheme is applied to a wind integrated interconnected power system. In designing the controller, several inputs used for a secondary frequency control loop are considered along with the merits of the existing controllers. The combined controller provides better control action than existing controllers in the presence of wind as is evidenced by the wide variety of results pre sented. For tuning of the controller gains, a crow search optimization algorithm (CRSOA) is used. Results are obtained via the MATLAB/Simulink software.