一种适用于低压微电网的改进型下垂控制器

Improved droop controller for low-voltage microgrid

针对低压微电网中采用传统下垂控制器多微源之间功率分配精度不高和非线性负载影响的问题,通过虚拟阻抗的设计,将等效线路阻抗设计为在工频附近呈现阻性,满足低压微电网的线路阻抗特点,同时降低了微源逆变器功率均分控制对输出线路阻抗的敏感性;等效线路阻抗在高频谐波段呈感性,有效抑制非线性负载造成的高频谐波。同时改进了功率控制环,避免了较大的阻性等效输出阻抗造成电压降低的问题,加入的并网自动跟踪相角控制器在计划并网前自动调整微源输出电压相角,保证并网过程平滑过渡。仿真结果验证了提出的改进下垂控制器可以消除微源之间的环流,同时抑制高频谐波,输出电压与设定值无静差且并网过程平滑无冲击;基于DSP的样机实验结果也验证了该方法的正确性和可靠性。

Aiming at the low accuracy of power distribution among multiple micro-sources and the effect of nonlinear load existing in the low-voltage microgrid with traditional droop controller,a virtual impedance is designed for the equivalent line output impedance,which is resistive near power frequency to meet the line impedance characteristics of low-voltage microgrid and reduce the sensitivity of inverter output power distribution control on the line impedance,but which is inductive in high frequency bands to effectively suppress the high-frequency harmonics induced by nonlinear loads. The power control loop is improved to avoid the voltage drop caused by the larger resistive equivalent output impedance and an auto-tracking phase-angle controller is added to automatically regulate the phase angle of output voltage for the smooth transition during the grid-connection operation. The simulative results prove that,with the proposed droop controller,the circulating current between micro-sources is eliminated,the high frequency harmonics are suppressed,zero static error of output voltage is realized,and smooth grid-connection operation is accomplished. The experimental results of DSP-based prototype show the correctness and reliability of the proposed method.