The coordinated control strategy of DC microgrid based on multiple energy storage units

Abstract

Recently, the DC microgrid (MG) has caught people’s attention because of its simpler control system than the AC microgrid. In this paper, the bus voltage layering control method based on droop control is used for DC microgrid coordination control. According to the working characteristics of the DC bus, the voltage of the DC bus is divided into five sections, corresponding to 5 operating modes respectively. Inside the DC microgrid, each unit converts the operation mode by local control according to voltage amplitude. The photovoltaic power generation unit adopts MPPT control and constant voltage control to adjust the running point tracking, so as to realize changing-over smoothly between voltage regulator mode and MPPT. The battery system adopts a hierarchical operation control method of several batteries on the basis of the state of charge (SOC). To realize the target, which means getting rational active power allocation and SOC equilibrium of each battery unit, as well as different batteries changing-over the charge and discharge modes on the basis of SOC size, so as to adjust the droop curve according to the power size. Finally, the balance between the three objectives of the highest photovoltaic energy utilization rate, energy storage SOC balance, and stable bus voltage is achieved.