不平衡电网下无锁相环三相并网逆变器控制策略

Control Strategies of Three-phase Grid-connected Inverters Without Phase-lock Loop Under Unbalanced Grids

在并网发电系统中,快速准确的相位同步检测是有效控制的前提条件。该文分析了不平衡电压对常规锁相环下三相逆变器的影响。当电网电压存在不平衡时,电压的检测和锁相角计算过程中会产生误差,从而影响逆变器控制精度。因此,提出两种并网逆变器的无锁相环控制策略:直接功率和直接电流控制,并且建立数学模型验证其可行性。这两种控制策略分别在dq坐标系和αβ坐标系下进行电网电压的正序分量分离。将无锁相环控制与常规有锁相环控制在电压不平衡时进行对比,同时在两种无锁相环控制策略之间进行总结与对比。仿真和实验结果表明,与锁相环相比,无锁相环控制策略能够快速精确地从不平衡的电网电压中分离出正序分量,在动态响应上直接电流控制策略更胜一筹。

Ingrid-connected power generation systems, the rapid and accurate phase synchronization detection is the foundation for control. The paper analyzes the effect of unbalanced grids on three-phase inverters with the traditional phase locked loop （PLL）. When the grid voltage unbalance exists, the detection of grid voltage and the calculation of phase angles have errors, which would influence the control precision. Hence, the paper proposes two space vector pulse width module （SVPWM） control strategies without PLL for three-phase grid-connected inverters： direct power control strategy and direct current control strategy, and builds the mathematical models to verify the feasibility. The two strategies separate the positive sequence voltage component from the rotating synchronousdq frame and theαβ frame respectively. The paper also compares non-PLL strategies with traditional PLL strategy under unbalanced grid voltages and summarized and compares the two non-PLL strategies. The simulation and experimental results show that the non-PLL strategies can accurately and rapidly extract the positive sequences from unbalanced grid voltages compared with PLL. What’s more, the dynamic response of direct current control strategy is even better than that of direct power control strategy.