A Scheme Of Connecting Microgird To AC Grid Via Flexible Power Electronics Interface

In order to realize the emerging potential of distributed generation, microgrid technologies are gaining widespread attention. Study on integrated operation mode of microgrids and related problems is worth probing further to meet the requirements of higher quality and higher stability of microgrid. After deeply analyzing the voltage source converter (VSC) technology, this paper presents a new scheme of connecting microgird to AC grid via flexible power electronics interface, which separates the microgrid from the AC grid, prevents harmonic component transmitting from one side to the other side and precisely control the active power flowing bidirectionally between microgrid and main grid, as well as in charge of reactive power compensation and keeping the microgrid voltage stable. A storage interface is reserved, making allowance for the condition that the connection was cut off when main grid fault occurs. The main contributions of the paper are:On the base of theory analysis of synthetic control of microgrid, this paper presents two control schemes for connecting interface. Aiming at the conditions of synthetic control of microgrid based on Grid-Forming control strategy, the consumer side converter is designed to adopt constant frequency and AC voltage control strategy. When inverters in microgirds mainly adopt Grid-Following control strategy, the consumer side converter should adopt constant AC voltage control strategy.In view of asymmetrical fault, two additional fault control modules are proposed based on positive and negative sequence detecting technology. One is based on negative sequence voltage compensation, and the other is based on oscillating active power elimination.After analysis of hybrid energy storage based on high-capacity batteries and supercapacitors, two types of DC/DC interface of storage system were presented and comparative Analysis were carried out.A microgrid study system and electrical-magnetic model of connecting interface were established in PSCAD/EMTDC. Tests are made to verify its performance of active power control and reactive power compensation.