Research On Some Key Technologies For High Quality Operation Of Microgrid

Although the high penetration of distributed generation has many advantages,it brings a great challenge to the security and effective operation of the power grid.In order to make better use of distributed generation,microgrid takes a system approach to use a set of microsource and related load as a single controllable system.Microgrid is a controlled unit to meet the needs of the power system,and it can meet the special needs of power customers as well as reduce the cost of small scale distributed generation system.Microgrid is easy to realize the high penetration of distributed generation and can become an important part of the smart grid,so it has broad prospects for development.The power sharing ratio,PCC voltage quality and power exchange capacity are the important indicators of the high quality operation of microgrid.So operation control of microgrid is studied in this dissertation from three aspects of power sharing,voltage quality and power exchange,the main research achievements are as follows:The power sharing ratio between the parallel microsources is difficult to stable if these microsources use traditional droop control when lines does not match.This dissertation compensates the voltage drop and phase angle difference caused by line to the traditional droop control,so a power sharing method for parallel microsources based on the droop control including line compensation is proposed.When the parallel structure microgrid operates in island mode with line mismatch,this method can ensure stable power sharing ratio between the microsources under the condition of balanced load or unbalanced load change.The simulation results verify the effectiveness of the proposed method.The unbalanced load within the islanded microgrid can cause the PCC line voltage unbalance and reduce the PCC voltage quality.This dissertation connects the cascade STATCOM with delta configuration to the PCC of the islanded microgrid,so a negative sequence current compensation method for microgrid based on cascade STATCOM is proposed.The cascade STATCOM with delta configuration compensates the negative sequence current component of the unbalanced load,the microsources only need to provide the positive sequence current component in order to ensure the balance of the PCC line voltage and the microsources output line currents.The simulation results verify the feasibility and effectiveness of the proposed method.Grid-connected microgrid through the transformer limits the power exchange capacity between microgrid and distribution network.This dissertation connects the input side of the MMC matrix converter to the distribution network and the output side to the PCC of microgrid,so a grid-connected access method for microgrid based on MMC matrix converter is proposed.This method can realize asynchronous connection and power bidirectional transmission between the microgrid and distribution network,effectively reduce the influence of the distributed energy randomness and intermittent within the microgrid on the distribution network stability,and the power exchange between the microgrid and distribution network does not change the desired power sharing result of parallel microsources.The simulation results verify the feasibility and effectiveness of the proposed method.