级联H桥光伏并网逆变器的无锁相环控制策略

CONTROL STRATEGY FOR CASCADED H-BRIDGE GRID-CONNECTED PHOTOVOLTAIC INVERTER WITHOUT PHASE-LOCKED LOOP

级联H桥光伏并网系统采用多电平调制方法和各模块独立的MPPT控制,具有较高的效率,但是系统控制性能受锁相环影响较大,当电网电压畸变时锁相环的测量准确度会受到严重影响,使系统控制性能下降,尤其是在功率不平衡的情况下会出现过调制,导致系统不稳定。为此,提出一种应用在级联H桥光伏并网逆变器的无锁相环控制策略。该策略在基于无功补偿的级联H桥光伏并网逆变器控制策略的基础上,采用电网电压基波同步信号算法,在电网电压畸变时无需锁相环即可获取与电网电压基波同频同相的正、余弦信号,较好地满足了系统在功率平衡、功率不平衡2种工作状态下的控制要求。仿真结果和实验结果都验证了所提控制策略的有效性。

The cascaded H-bridge grid-connected photovoltaic inverter has high efficiency when it adopts multi-level modulation method and independent MPPT control of each module. However,its control performance is greatly affected by the PLL(phase-locked loop). When the grid voltage is distorted,the measurement accuracy of the PLL is seriously affected. Especially in the case of power imbalance,overmodulation may occur which causes system instability. For this reason,a non-PLL control strategy is proposed for the cascaded H-bridge grid-connected photovoltaic inverter. Based on the control method of cascaded H-bridge grid-connected photovoltaic inverter with reactive power compensation,this strategy adopts the grid voltage fundamental wave synchronous signal algorithm. When the grid voltage is distorted,the sine and cosine signals synchronized with the grid voltage fundamental wave can be obtained without PLL,which satisfies the control requirements of the system under power balance and power imbalance. The simulation results and experimental results verify the effectiveness of the proposed control strategy.