Power Quality Control Of Island-based Microgrid Based On Virtual Sychronous Generator

With the development of society and the growth of population,energy consumption is becoming more and more serious.Since the 21 st century,countries in the world have been studying the multi-energy complementary integrated system of renewable energy.Took a new direction.Due to the decentralized and random nature of distributed power generation,it affects the safe and stable operation of access to large power grids.The birth of microgrid technology has solved the shortcomings of distributed power generation and provided a new direction for the development of power systems.The microgrid system is connected to the distributed generation unit through different converters,and adopts appropriate control strategies for the converters to maintain the stability of the system.There are two main ways of micro-grid operation: island operation and grid-connected operation.This thesis mainly studies the power quality of island micro-grid.This subject has certain practical application value on the basis of domestic and foreign research.The research mainly includes the following aspects:(1)Under the operating conditions of island microgrid,the virtual synchronous generator control technology(VSG)is adopted for the inverter.The virtual synchronous generator technology used in this thesis simulates the second-order mathematical model of the synchronous generator.The virtual synchronous generator has inertial and damping characteristics,which can enhance the anti-interference ability of the system.(2)The small-signal modeling of the virtual synchronous generator control system,the output power is calculated through the equivalent schematic diagram of the inverter,combined with the VSG control,the decoupled VSG small-signal model is calculated.According to the decoupled VSG small signal model,the transfer function of the active and reactive loops is calculated,the root locus and Bode plot are drawn,and the two parameters of rotational inertia J and damping coefficient D are analyzed to stabilize the system under different values To determine the appropriate parameter value range.(3)When the system is connected to a non-linear load,power quality problems such as current waveform distortion will occur.Aiming at this problem,the thesis adopts a comprehensive strategy based on the VSG control method.First,a third-order generalized integral cross-cancellation feedback network is used to separate the harmonic current of the system output current,and the fundamental current and corresponding harmonic current are extracted.Then construct a variable virtual impedance,combine the fundamental impedance and harmonic impedance with the fundamental current and harmonic current,respectively,to construct a harmonic compensation voltage.Finally,multiple PR control strategies are used in the voltage and current double loop to suppress harmonics of the output voltage.(4)The Matlab / Simulink simulation software and d SPACE(DS1104)experimental platform are used to simulate and verify the control strategy mentioned in the thesis.The simulation part mainly builds and analyzes the VSG part of the simulation model,as well as a single inverter and two In the case of parallel connection of load,the change of system power and frequency,and the power of two inverters in parallel are divided equally.In the experimental part of d SPACE,when the system adopts droop control and VSG control to switch the load,the influence of the main parameter changes on the stability of the system.And the harmonic distortion analysis of the harmonic current separation method of the third-order generalized integrator cross-cancellation feedback network.