电网电压不平衡时两级式三相光伏并网系统控制策略研究

Research on Control Strategy for Two-stage Three-phase PV Grid-connected System Under Unbalanced Voltage Conditions

在实际运行中,电网可能会出现不平衡状况。根据光伏阵列输出特性和逆变器并网要求,对两级式光伏并网逆变系统进行研究,建立不平衡情况下的数学模型来实现前级Boost电路和后级逆变系统的独立控制。为了抑制负序分量,采用基于二阶广义积分(SOGI)的正交信号发生器进行正负序分量分离并完成对电网电压的锁相,同时,提出一种基于dq同步旋转坐标系下的抑制负序电流的控制策略。最后通过建立光伏并网系统的仿真模型,验证了所提出的控制策略在电网电压不平衡情况下的有效性。

In actual operation,voltage imbalance may occur.According to output characteristics of photovoltaic array and the requirement of grid-connected inverter,two-stage PV grid-connected system is studied,and the mathematical model of unbalanced grid is established to independently control the Boost chopper and the inverter system.In order to restrain the negative sequence component,orthogonal signal generator based on second-order generalized integrator（SOGI）is used to separate the positive-negative sequence component and realize the phase locking of grid voltage.At the same time,a control strategy of suppressing the negative sequence current in dq synchronous rotation reference frame is proposed.In the end,simulation model of PV grid-connected system is established to verify the validity of proposed strategy under the unbalanced grid voltage conditions.