Research Of Control Strategies For Microgrid Inverter

With higher penetration of distributed generation, the negative effects ofdistributed generation to the grid cannot be ignored anymore. As an effective wayto integrate all kinds of distributed generation and to reduce their negative effects,microgrid has a promising future. As energy storage units play a key role inmaintaining the microgrid’s voltage stability and frequency stability, this paperfocus on the control of energy storage unit in a microgrid. According to thecharacteristics and the control strategy of synchronous generator, this paperdesigned energy storage unit to mimic them, and had a research of thecharacteristics and stability issues of the virtual synchronous generator underdifferent operation modes of microgrid. The main contents of this paper are asfollowed:First of all, the characteristics and development of microgrid were introduced;The control requirements of microgrid were analysised, and control strategies weresummarized.Secondly, the implemental method to design a inverter to mimic a synchronousgenerator and the algorithm of the virtual synchronous generator were provided.The digital speed governor and excitation controller were designed, extracting fromthe essence of excitation controller of synchronous generator, also, the synchronouscontroller were designed. The virtual synchronous generator has the samepower-frequency characteristic and voltage regulating characteristic assynchronous generator set, and the parameters can be changed neatly.Thirdly, the behavior of virtual synchronous generator under differentoperation modes of microgrid were analysised, selectively analysised thecharacteristics of the power output under grid-connected operation and powersharing under island parallel operation.Fourthly, the small-signal models of grid-connected operation system andisland parallel operation system were established, and the stability and dynamiccharacteristics were analysised.Finally, the simulation platform and experiment platform of grid-connectedoperation system and island parallel operation system were built, and verifications were done, the final simulation results and experiment results showed the validityof analysises and feasibility of the scheme.