低压微电网逆变器并离网平滑切换控制

分布式能源通过电力电子变换器与本地负载、储能设备等相结合构成微电网;并实现在并网、离网及并离网相互切换模式下的稳定运行。采用下垂控制实现微电网离网运行时逆变器输出电压和频率的稳定、并网运行时输出功率的恒定,并且不改变控制方式实现并离网的平滑切换控制。由于传统下垂控制在离网运行时,逆变器输出电压与频率存在一定的偏差;并且为了使逆变器输出阻抗呈阻性以减小控制参数对输出阻抗的影响,采用一种改进的下垂控制策略;并在逆变器双闭环控制中加入虚拟阻抗。仿真结果验证了改进下垂控制策略在离网、并网以及并离网相互切换运行时的有效性,以及相比于传统下垂控制策略的优越性。

Smooth Switching Control of Inverter between Off-grid and Grid-connected Modes in Low Voltage Micro-grid

Using power electronics converters, distributed energy can be connected with local load, energy storage device and so on and thus micro-grid can be achieved. Micro-grid should operate steadily in both grid-connected and off-grid modes, and achieve smooth switching between these two modes. Droop control can be used to achieve stable inverter output voltage and frequency in island mode, constant power in grid-connected mode, and smooth switching between them without changing control scheme. However, using traditional droop control, deviations between desired and real values for output voltage and frequency still exist in off-grid mode. Therefore, this paper proposes an improved droop control and adds virtual impedance in double control loop of inverter, making the output impedance of the inverter be resistive with reduced influence from control parameters. Simulation results show the effectiveness of the improved droop control in grid-connected, off-grid, and switching modes between them and its advantageous compared with traditional droop control.