Coordinated Control Strategies For Distributed Generators In A Microgrid

As an important way to realize the large-scale utilization of distributed generators(DGs),microgrids offer a new idea for the consumption of new energy in power grids.However,DGs in microgrids are varied in form and performance.In order to give full play to the potential advantages of microgrids,the coordinated control of DGs is very important.In this context,the coordinated control of DGs is explored in this paper and the main findings can be summarized as follows:1.A centralized coordinated control strategy for DGs is proposed for the microgrid which can operate in both grid-connected and islanded mode.The proposed control strategy includes the coordinated control of renewable energy sources(RESs)and energy storage systems(ESSs)and the coordinated control of multiple ESSs.The coordinated control of RESs and ESSs has two functions:1)A large charge/discharge margin of ESSs is maintained by the cooperation of microgrid's multiple operation modes for the purpose of improving a microgrid's schedulability in grid-connected mode and dynamic stability performance in islanded mode;2)When a microgrid is in the normal operation mode,the loads will be shared by RESs with first priority,i.e.,the power deficiency will be compensated by ESSs when the sum of RESs' maximum output power is less than the capacity of total loads to reduce the loss of ESSs.At the same time,the charge/discharge power of ESSs would be dynamically adjusted with the variation of SOC deviation by the coordinated control of multiple ESSs to realize state of charge(SOC)balance smoothly.2.A distributed coordinated control strategy for DGs without the central controller is proposed for islanded microgrids.The proposed control strategy includes the primary linear droop control,the secondary frequency recovery control and the tertiary SOC-based droop control.The primary control is used to achieve well-performed fast dynamics for microgrid within seconds;the secondary control is used to maintain the microgrid's frequency in the permitted range;the tertiary control is used to realize multiple EESs' SOC balance so that the microgrid can maintain long-term-stable operation and all its ESSs can be jointly operated with other droop-control DGs.