并网光伏系统中3L-T-type QZSI参与电网电压不平衡控制

针对传统逆变器在不平衡网压情况下工作时较难抑制输入电网有功功率振荡分量的问题,提出一种基于三电平T型准阻抗源逆变器(Three Level T-Type Quasi-Z Source Inverter,3L-T-type QZSI)抑制有功功率振荡分量的控制策略。文中从功率理论推导得到其并网的参考电流,实现并网有功功率恒定且以单位功率因数为目标的控制策略。即:使用二阶广义积分器(Second-order Generalized Integrator,SOGI)完成电压的正负序分离;再结合基于载波的电平位移调制(Level-Shifted PWM,LS-PWM)技术,用以调节功率开关直通状态的占空比和叠加的平衡分量,实现直流侧电压控制和中点电压平衡。最后,在Simulink平台上模拟了电网电压不平衡情况,对间歇性能源不同出力情况进行了仿真,仿真结果表明,该策略可有效抑制间歇性能源的有功功率二倍频波动,有利于实现中点电位平衡和间歇性能源并网稳定运行。

Study of 3L-T-type QZSI participation in grid voltage imbalance control in grid-connected photovoltaic systems

Aiming at the problem that traditional inverters cannot suppress the input active power oscillation component when working under unbalanced network voltage, a control strategy based on a Three Level T-Type Quasi-Z Source Inverter (3L-T-type QZSI) to suppress the active power oscillation component is proposed. The reference current for grid-connected QZSI was derived from power theory in the paper, achieving a control strategy with constant grid-connected active power and unit power factor as the goal for grid connection. That is, a second-order generalized integrator (SOGI) was used to complete the positive and negative sequence separation of the voltage; and then the carrier-based level-shift modulation (LS-PWM) technique was combined to regulate the duty cycle of the power switch through state and the superimposed balance component to realize the DC-side voltage control and midpoint voltage balance. Finally, the voltage imbalance of the power grid was simulated on the Simulink platform, and the simulation results show that the strategy can effectively suppress the active power diabatic fluctuations of intermittent energy sources, which is conducive to the midpoint potential balance and the stable operation of intermittent energy sources on the grid.