A hybrid least square-fuzzy bacterial foraging strategy for harmonic estimation

Harmonic estimation for a signal distorted with additive noise has been an area of interest for researchers in many disciplines of science and engineering. This work presents a new algorithm based on the foraging behavior of E. coli bacteria in our intestine to estimate the harmonic components present in power system voltage/current waveforms. The basic foraging strategy is made adaptive, through a Takagi-Sugeno fuzzy scheme, depending on the operating condition to make the convergence faster. Besides, the harmonic estimation is linear in amplitude and nonlinear in phase. As the proposed algorithm does not rely on Newton-like gradient descent methods, this is used for phase estimation whereas the linear least square scheme estimates the amplitude, thereby presenting the hybrid method. The improvement in %error, as well as the processing time compared with the conventional discrete Fourier transform and genetic algorithm method is demonstrated in this paper. Besides, the performance is quite acceptable even in the presence of decaying dc component as well as to change in amplitude and phase angle of harmonic components.     

Development of a Fuzzy Rule-Based Multi-Objective Hybrid Controller for Static Synchronous Compensator

Static synchronous compensator (Statcom) is a powerful new device for power systems, which can be used for various purposes. The multi-objective demands are quite different in nature, e.g. continuous linear control for voltage maintaining, and discrete bang-bang control for oscillation damping. Unfortunately, they often conflict with each other. In this respect, a supplementary damping control together with an independent voltage control is normally used. However, inevitable small disturbance and uncertainties will cause problems in the coordination of the two functions. To overcome such difficulties, a fuzzy rule-based hybrid controller is proposed in this paper, which incorporates conventional linear voltage control along with the fuzzy rule-based supplementary power damping control to form a unified global controller for Statcom. Because only simple fuzzy rules and a few input signals are involved, it is very easy to implement in a practical power system. The simulation performed on a Single- Machine-Infinite-Bus (SMIB) power system and an actual large power system demonstrates the effectiveness of the proposed approach.     

Bacterial foraging optimization and adaptive version for economically optimum sitting,sizing and harmonic tuning orders setting of LC harmonic passive power filters in radial distribution systems with linear and nonlinear loads

This paper presents bacterial foraging optimization (BFO) algorithm and its adaptive version to optimize the planning of passive harmonic filters (PHFs).The important problem of using PHFs is determining location, size and harmonic tuning orders of them, which is reach standard levels of harmonic distortion with applying minimum cost of passive filters.In this study to optimize the PHFs location, size and setting the harmonic tuning orders in the distribution system, considered objective function includes the reduction of power loss and investment cost of PHFs. At the same time, constraints include voltage limits, number/size of installed PHFs, limit candidate buses for PHFs installation and the voltage total harmonic distortion (THDv) in all buses. The harmonic levels of system are obtained by current injections method and the load flow is solved by the iterative method of power sum, which is suitable for the accuracy requirements of this type of study. It is shown that through an economical placement and sizing of PHFs the total voltage harmonic distortion and active power loss could be minimized simultaneously.The considered objective function is of highly non-convex manner, and also has several constraints. On the other hand due to significant computational time reduction and faster convergence of BFO in comparison with other intelligent optimization approach such as genetic algorithm (GA), particle swarm optimization (PSO) and artificial bee colony (ABC) the simple version of BFO has been implemented. Of course other versions of BFO such as Adaptive BFO and combination of BFO with other method due to complexity of harmonic optimization problem have not considered in this research.The simulation results for small scale test system with 10 buses, showed the significant computational time reduction and faster convergence of BFO in comparison with GA, PSO and ABC. Therefore in large scale radial system with 34 buses, the proposed method is solved using BFO.The simulation results for a 10-bus system as a small scale and 34-bus radial system as a large scale show that the proposed method is efficient for solving the presented problem.     

Design of output filter for inverters using fuzzy logic

This paper proposes a design method to improve the harmonic of output voltage of a single phase inverter with an L-C output filter using fuzzy logic controller (FLC). In practice, the harmonic characteristics of circuits are complicated and entangled. There are two kinds of harmonic sources that cause inverter output voltage waveform distortion: One is the PWM switching of inverter and the other is the nonlinear characteristics of the load. In general, PI feedback control by coefficient diagram method (CDM) is used to design the output voltage filter. The relation between the L-C value and the system time constant are described with the closed form and the filter values must be calculated repeatedly to satisfy the prescribed voltage total harmonic distortion (THD) of the system. Therefore, the MATLAB Fuzzy Logic Toolbox for the fuzzy logic control algorithm is proposed. The L-C value of the filter can be set to a fixed range in the nonlinear characteristic of the practical condition, to improve the harmonic of output voltage more effectively and to avoid repeated calculation.     

带分布式电源的有源滤波器的模糊自适应控制

由于分布式电源逆变并网发电与有源电力滤波器(active power filter,APF)在结构功能上具有相似性,本文提出了结合绿色分布式电源的有源电力滤波器拓扑结构,这种结构使APF除了能够滤除谐波外,还可以向负载供能,拓展了APF的应用范围,有利于电网的绿化和供能的多元化.分布式电源通过逆变升压整流来维持APF直流侧的电容电压的稳定,而不需要消耗电网中的能量.针对畸变电压的工况,设计了自适应dq检测算法;在APF控制上采用了自适应模糊控制的策略,不仅能快速跟踪谐波电流,而且具有较强的鲁棒性.仿真结果验证了该系统设计的可行性和可靠性,证明了本文所提算法的有效性和正确性.     

Approximated fuzzy logic controlled shunt active power filter for improved power quality

Shunt active power filters have been widely used for power quality improvement. With the advancement in artificial intelligence techniques, the applications of fuzzy logic‐based control systems have increased manifolds. This paper proposes a reduced rule fuzzy logic controller (FLC) in the voltage control loop of a shunt active power filter (APF), which is approximating a conventional large rule FLC. The difference between the controlled outputs of two controllers is compensated by proposed compensating factors. The dynamic response and harmonic compensation performance of proposed 4‐rule approximated fuzzy logic controller (AFLC) is compared with 25‐rule FLC. A three‐phase shunt APF is used for harmonic and reactive power compensation. The proposed scheme is tested with randomly varying single and multiple non‐linear loads. The simulation results presented under transient and steady‐state conditions confirm that the proposed 4‐rule AFLC efficiently approximates the 25‐rule FLC. The proposed control methodology takes less computational time and computational memory as the numbers of rules are reduced significantly.     

Selective compensation of voltage harmonics in grid-connected microgrids

In this paper, a novel approach is proposed for selective compensation of main voltage harmonics in a grid-connected microgrid. The aim of compensation is to provide a high voltage quality at the point of common coupling (PCC). PCC voltage quality is of great importance due to sensitive loads that may be connected. It is assumed that the voltage harmonics are originated from distortion in grid voltage as well as the harmonic current of the nonlinear loads. Harmonic compensation is achieved through proper control of distributed generators (DGs) interface converters. The compensation effort of each harmonic is shared considering the respective current harmonic supplied by the DGs. The control system of each DG comprises harmonic compensator, fundamental power controllers, voltage and current proportional-resonant controller and virtual impedance loop. Virtual impedance is considered at fundamental frequency to enhance power control and also at harmonic frequencies to improve the nonlinear load sharing among DGs. The control system design is discussed in detail. The presented simulation results demonstrate the effectiveness of the proposed method in compensation of the voltage harmonics to an acceptable level.     

有源电力滤波器谐波检测的新型SRF-PLL设计研究

针对有源电力滤波器中基于同步坐标系的锁相环(synchronous reference frame PLL,SRF-PLL)在三相电网电压不平衡且有畸变时,负序基频分量和高频谐波电流对SRF-PLL的影响。文章采用在基于同步坐标系的锁相环中加入自适应陷波器(adaptive notch filter,ANF)和自适应滤波器(adaptive filter)的技术。利用自适应陷波器的两个相互正交的输出量抵消同频负序分量导致的2倍工频波动,并采用自适应滤波器的最小均方算法(Least Mean Square,LMS)滤除高频谐波分量,从而准确的提取基波电压的幅值与相位。文章以单独加入自适应滤波器或自适应陷波器作比较,通过仿真分析验证文中方法能更加准确的提取电网电压频率,正余弦函数曲线更加平滑,具有良好的动态性能和稳定性。     

BFO optimized RLS algorithm for power system harmonics estimation

In this paper a new estimation approach combining both Recursive Least Square (RLS) and Bacterial Foraging Optimization (BFO) is developed for accurate estimation of harmonics in distorted power system signals. The proposed RLS–BFO hybrid technique has been employed for estimating the fundamental as well as harmonic components present in power system voltage/current waveforms. The basic foraging strategy is made adaptive by using RLS that sequentially updates the unknown parameters of the signal. Simulation and experimental studies are included justifying the improvement in performance of this new estimation algorithm.     

Parallel Distributed Fuzzy Sliding Mode Control for Nonlinear Mismatched Uncertain Systems

A new design approach of a parallel distributed fuzzy sliding mode controller for nonlinear systems with mismatched time varying uncertainties is presented in this paper. The nonlinear system is approximated by the Takagi–Sugeno fuzzy linear model. The approximation error between the nonlinear system and the fuzzy linear model is considered as one part of the uncertainty in the uncertain nonlinear system. The time varying uncertainties are assumed to have the format which enables the design of the coefficient matrix of the sliding function to satisfy a sliding coefficient matching condition. With the sliding coefficient matching condition satisfied, a parallel distributed fuzzy sliding mode controller (PDFSC) is designed. The stability and the sliding mode of the fuzzy sliding control system are guaranteed. Also, the nonlinear system is shown to be invariant on the sliding surface. Moreover, the chattering around the sliding surface in the sliding mode control can be reduced by the proposed design approach. Simulation results are included to illustrate the effectiveness of the proposed fuzzy sliding mode controller. This work is partly supported by the the R.O.C. National Science Council through Grant NSC93-2213-E-197-004.     

Practical frequency response analysis of non-linear time-delayed differential or difference equation models

A systematic algorithm for generating the polyharmonic balance equations for any system within a broad class of time-delayed differential, or non-linear difference equation models, is presented. The method, which is readily automated, enables the balance equations to be written down directly in terms of the coefficients of the governing equation, and the complex amplitudes of a general harmonic waveform. The system frequency response or amplitude dependent describing function is then readily computed. The method is illustrated by means of examples including both a time-delayed differential system example and a discrete time NARX model application. The results are validated against detailed numeric simulation which confirms the accuracy and efficacy of the approach.     

基于ETAP的海上风电场接入对电能质量的评估分析

由于海上风资源的多变性,以及风力发电机中存在较多的电力电子元器件,海上风电场并网后会产生电能质量问题。本文选取某海上风电场作为研究对象,基于风电场实际运行数据,参考国标规定,对该风电场的电能质量（电压偏差、电压闪变、电压波动、谐波）进行求解。基于风机的无功特性,本文对某海上风电场接入电网公用变电站的无功补偿容量进行研究。在电能质量计算与分析方面,参考相关规程规定,完成电压偏差、电压闪变、电压波动部分指标的限值与实际值计算,并进行对比;通过ETAP软件中的谐波分析模块,进行谐波模拟仿真,得到谐波指标的实际值,并与理论计算的限值对比。当谐波电流超出国家标准的时候,通过在母线接入单调谐滤波器的方法,进行谐波治理,达到电能质量相关要求。     

H∞ switching fuzzy control of solar power generation systems with asymmetric input constraint

This paper aims at presenting a maximum power point tracking (MPPT) controller for photovoltaic (PV) systems subject to asymmetric input constraint. Indeed, the output voltage of the DC‐DC converter used for adjusting the photovoltaic output power can be controlled by means of variation of duty ratio limited between 1 and 0. The control design goal is to improve the efficiency of PV systems under asymmetric saturation of duty ratio. To achieve this goal, first, a Takagi‐Sugeno (T‐S) fuzzy model is used to represent the nonlinear behavior of the PV system. A T–S reference model is employed to give the ideal state direction which must be followed. To achieve a good steady state tracking, the integral of the state tracking error is used to define an extended system state vector. Second, the input characteristic is partitioned into several regions. In each region, the asymmetric saturation function can be considered as a symmetric saturation function. Furthermore, H∞ stabilization conditions for the resulting switching fuzzy control of the PV system under actuator saturation are formulated in term of linear matrix inequalities (LMI) using the Lyapunov approach. Simulation results are exhibited to demonstrate the effectiveness of the proposed design method.     

Reactive power planning using a new hybrid technique

Voltage deviation and stability constrained VAr planning or reactive power planning (RPP) is an important challenging issue in power systems. This paper presents a new hybrid technique for modeling and solving RPP problem taking into account the static voltage stability constraint. First, the uncertain fuzzy clustering theory is employed to select new candidate VAr source locations. Then, modified gray code is applied and used to represent a series of non-uniform VAr capacity intervals at different candidate buses. Based on the new ordering of the VAr capacity intervals, a simplified piecewise linear function between the total transfer capability and new VAr capacity is derived and applied as static voltage stability constraint in RPP problem. Last, the RPP optimization problem is solved by a self adaptive fuzzy chaotic interactive honey bee mating optimization (FCIHBMO) technique taking advantage of the modified gray code. In the FCIHBMO algorithm, a modified definition of the updating factors on generation solution is proposed. In the case study, uncertain fuzzy clustering mechanism, the modified gray code, and the modified HBMO are applied to the IEEE 118-bus and IEEE 300-bus systems. Test results conclude that the proposed hybrid technique is a simplified and effective approach for voltage stability constrained VAr planning with contingency considered.     

Robust Constrained Model Predictive Control for Discrete‐Time Uncertain System in Takagi‐Sugeno's Form

In this paper, we investigate a robust constrained model predictive control synthesis approach for discrete‐time Takagi‐Sugeno's (T‐S) fuzzy system with structured uncertainty. The key idea is to determine, at each sampling time, a state feedback fuzzy predictive controller that minimizes the performance objective function in the infinite time horizon by solving a class of linear matrix inequalities (LMIs) optimization problem. To do this, the fuzzy predictive controller is designed on the basis of non‐parallel distributed compensation (non‐PDC) control law, relaxed stability conditions of the closed‐loop fuzzy system are developed by employing an extended nonquadratic Lyapunov function and introducing additional slack and collection matrices. In addition, the presented approach is capable of ensuring the robust asymptotic stability as well as the recursive feasibility of the closed‐loop fuzzy system. Simulations on a highly nonlinear continuous stirred tank reactor (CSTR) are eventually presented to demonstrate the effectiveness of the developed theoretical approach.     

基于自适应逆控制的有源滤波器的检测算法

提出一种新的并联型电力有源滤波器的检测方法,通过控制有源滤波器直流电容电压来确定电网电流所需的基波有功分量的幅值,首次将自适应逆控制用于电力有源滤波器.将系统的主电路部分及有源滤波器看作广义有源滤波器,通过自适应逆控制方式控制直流电容电压,使其输出跟随参考输入,最终达到抑制谐波和补偿无功的目的.此检测算法简单有效,稳态和暂态的仿真结果均证实了该算法的可行性.     

单相电力电子变压器整流级新型直接功率控制策略

针对传统dq电流解耦双闭环控制的单相级联H桥整流器受系统电感参数变化的影响,同时为避免系统频率偏移的干扰,提出了一种无需电感参数和系统角频率的新型直接功率解耦控制器,实现了有功、无功功率的独立控制.并利用级联延时信号消除算法提取基波正序分量,消除谐波信号带来的影响.在MATLAB/Simulink中搭建了三级联H桥整流...     

微电网HHT谐波检测与时频分析方法

为解决微电网谐波、突变等复杂非平稳信号的精确检测问题,提出一种基于Hilbert-Huang变换（HHT）的微电网谐波检测与时频分析方法。该方法采用保形分段三次埃尔米特插值法拟合极值点曲线,对谐波信号进行经验模态分解（EMD）,得到有限个固有模态分量（IMF）并进行Hilbert变换,最终计算各个IMF分量的瞬时频率和瞬时幅值,实现微电网谐波等非平稳电能信号的时频特性精确检测。仿真结果表明,该方法能够快速、准确地获取谐波信号频率成分、幅度及电压突变时刻。相对于FFT变换及传统HHT方法具有较高的精度和时域区分特性,可满足微电网谐波微机检测的工程应用需求。     

有源电力滤波器多内模复合控制策略控制分析

为消除单一通过矢量谐振(VR)进行控制时面临的缺陷,采用重复控制(RC)并合理设置校正因子,设计了多内模控制器,通过对RC进行充分控制的方式达到跟踪与控制谐波分量的作用.采用MATLAB软件建立了上述系统模型并完成仿真测试.研究结果表明:电压与电流总谐波失真(THD)都低于1％,并没有发生明显畸变,呈现正弦波的特征.以...