微网系统稳定运行及模式平滑切换研究

提出了一种基于对等结构的控制策略,实现微网系统在并网和孤岛两种模式下的稳定运行和平滑切换。稳定运行时的多环控制策略包含电压-相角下垂控制、虚拟阻抗控制和电压电流双环控制,可按逆变器额定容量之比精确分配负荷功率,保持系统电压幅值、频率的稳定。并网时采用基于双二阶广义积分器及锁频环的电压同步策略,使微网的电压幅值、相角快速向主网同步,从而平滑并网。解列时设计了功率同步策略,通过降低微网与主网间的交互功率,抑制切换时的功率冲击。仿真结果表明,所提控制策略能够保证微网系统的稳定运行,同时在过渡模式下,减小网络冲击,稳定系统频率,实现模式平滑切换。

Study on stable operation and mode smooth transition of microgrid

A control strategy based on peer-to-peer structure is proposed, so as to realize stable operation and smooth transition between grid-connected and islanding modes of microgrid. In stable operation mode, the multiloop control strategy includes voltage-phase droop control, virtual impedance control and voltage-current dual loop control. According to the ratio of the rated capacity of the inverters, the load power can be precisely distributed. Also, it can maintain the voltage amplitude and frequency of the system. In grid connecting transition mode, a voltage synchronization strategy is proposed. It is based on dual second-order generalized integrator and frequency locked loop, which synchronizes the voltage amplitude and phase of microgrid with the main grid in a short time, so that it can be connected to the main grid smoothly. In grid disconnecting transition mode, a power synchronization strategy is proposed. The overshoot of power is suppressed by reducing the interaction power between the microgrid and the main grid. The simulation results show that the proposed control strategy can maintain the stable operation of the microgrid. Also, when modes switching, it can reduce the overshoot in the grid and control the frequency of the system, so as to realize mode smooth transition. This work is supported by National Science and Technology Support Project of China (No. 2015BAG19B02) and Project of Shanghai Committee of Science and Technology (No. 13DZ1200403).