Research On Three-Phase Inverters And Microgrid Control Methdos By Extremal Optimization

Nowadays the energy crisis and environmental crisis prompte the rapid development of renewable energy generation technology,Microgrids,distributed generation(DG)technology.As a power conversion interface between Microgrids and the DG units,three-phase inverter is the key equipment in Microgrids.Meanwhile,for different work mode and enviroment,the control strategies of Microgrids and the three-phase inverter become more and more complicated.Then,a multiple closed loop,multi-level and mutual coupling control topological structures are proposed based on single closed-loop PID or PI control topology.The performance of these control topological structuredepends on the tuning parameters of the controllers.As one of well-known traditional empirical tuning methods,Z-N method has been widely used by design controller parameters for PID or PI.But it seriously relies on the empirical rules of the designers and hard to apply in the three-phase inverter and Microgrids.So how to design a tuning method for PID or PI controller in the three-phase inverter and Microgrids is a huge challenge.This paper presents a novel controller design method based on the binary-coded extremal optimization for the three-phase inverters under different modes and Microgrids,which aim to obtain satisfied quality of output voltage waveform for three-phase inverters,power sharing and system stabilith of microgrids.The main work of this paper is as follows:(1)In order to improve the waveform quality of output voltage form the three-phase inverter,and the robustness under variable loads conditions,this paper presents a novel double closed-loop PI controller design method for the three-phase inverter based on binary-coded extremal optimization(BCEO).The basic idea behind the proposed method consists of two steps.Firstly,formulating the design problem of double closed-loop PI controller for the three-phase inverter as a typical constrained optimization problem,where the total harmonic distortion(THD)and the integral of time weighted absolute error(ITAE)of output voltage waveform are weighted as the optimization objective function.Secondly,the BCEO algorithms are designed to solve this formulated problem.The transient and steady-state indices of the system are satisfied,which is demonstrated by both simulation and experimental results.(2)The modeling method of a disturbuted generation in droop control mode is designed by studying the working mechanism of droop control.The modeling method of droop control are studied.A novel droop controller design method for the disturbuted generation by the adaptive population extremal optimization(APEO)is proposed.This method implements a decoupling control algor ithm between the voltage performance and power sharing for disturbuted generation.In order to improve the robustness of the output voltage's amplitude,frequency,and power sharing performance,the THD and ITAE of output voltage waveform,and the THD of output current waveform are weighted as the optimization objective function.The superiority of the proposed method compared to genetic algorithm,particle swarm optimization is verified by both simulation and experimental results.The above work enriches the droop control theory.(3)In order to improve the accuracy and dynamic stability of reactive power sharing for distributed generation,a reactive power compensator is designed.To ensure the state optimization of control parameters,a noval P-Q controller for the three-phase inverter under APEO is proposed in this paper.The main idea of the method also consists of two steps.Firstly,formulating the design problem of P-Q controller for distributed generation as a typical constrained optimization problem.six parameters of P-Q controller are encoded as decision variable,where the ITAE of active power and reactive power are weighted as the optimization objective function.Secondly,an APEO algorithm is designed to solve this formulated problem.Finally,the effectiveness of the proposed method is verified by both simulation and experimental results.(4)The control system of three-phase inverters for mode transfer faces many problems,such as too many modes,too many control parameters and hard to tuning.So a noval seamless transfer controller for disturbuted generation based on APEO is designed to solve these problems.The model of the system with transient current feed forward is designed.Then,the design problem of transfer controller for the three-phase inverter is formulated as a typical constrained optimization problem,and an APEO algorithm is designed to solve this formulated problem.The validity and effectiveness of the method are verified by simulation results.The transient voltage shock is reduced.Microgrids and significant loads work steadly under this method.(5)In order to improve the steady-state characteristics of frequency controller in islanded microgrid,this paper presents an effective Fractional order PID frequency controllers for islanded Microgrids by using a Multi-objective extremal optimization(MOEO)algorithm.A frequency controller based on small-signal model of FOPID for an islanded microgrid is builded.Then the frequency deviation and the controller output signal,which conflict each other,are weighted as the optimization objective function,Finally,a MOEO algorithm is used to optimize the parameters.The designed method's superiority to nondominated sorting genetic algorithm-II(NSGA-II)based FOPID/PID controllers and other recently reported single-objective evolutionary algorithms such as Kriging-based surrogate modeling and real-coded population extremal optimization-based FOPID controllers is demonstrated by the simulation studies on a typical islanded microgrid in ter ms of the control performance including frequency deviation,deficit grid power,controller output signal and robustness.This paper presents a novel controller design method for the three-phase inverters under different modes and Microgrids.The problem o f parameters tuning for the three-phase inverters and Microgrids is done based on extremal optimization(EO),which obtain high-quality performances such as high stability,satisfied transient and steady-state indices,low total harmonic distortion and strong robustness.These works expand the application area of EO,and also supply reference to the optimal designing of other power systems.