Frequency improvement in power system by Synchronization Inverter-based distributed generators

Owing to the growth in penetration of DGs (distributed generators), inverters installed together with the DGs have been increasing rapidly. In general, these grid-connected inverters need a dedicated synchronization unit such as a phase locked loop (PLL), which receives voltage phase, frequency, and amplitude of the grid voltage as reference from power grids. As the installation of inverters keeps growing at this rate, synchronizing power in the main power grids will become insufficient, and thus there is a possibility that the power grids will be unstable condition. This is because the inverter frequency is controlled just to follow frequency determined by the other synchronous generators. Therefore, it is necessary to improve the power grid stability considering the DGs penetration. In this paper, the authors employ an inverter named “Synchronization Inverter”, which consists of a governor function and, calculation functions of the swing equation and the power equation, to deal with massive installation of DGs. With the intention of verifying the effectiveness of a Synchronization Inverter, the authors evaluated the stability of power grid frequency in an isolated power grid simulator and compared its performance with a typical conventional inverter. Through the evaluation, we conclude that introduction of Synchronization Inverter improves the power grid stabilization even if the DGs are increased.