不对称故障下低电压穿越的多目标解耦控制策略

Multi-objective decoupling control strategy for low voltage ride through under asymmetrical faults

在传统不对称故障低电压穿越控制中,由于控制自由度有限,并网逆变器控制存在无法同时实现输出电流负序分量和直流侧电压二倍频波动抑制的问题。对此,文中提出一种不对称故障下两级式光伏并网系统低电压穿越的多目标解耦控制策略。该策略将逆变器的控制目标设置为输出电流负序分量抑制,给出了综合考虑逆变器输出电流限幅和无功输出需求的逆变器电流内环控制参考值计算方法;通过双向Buck-Boost变换器将超级电容接入直流母线电容两端维持其电压稳定,并将直流侧电压二倍频波动转移至超级电容输入侧进行抑制。仿真结果表明,相比传统控制方法,所提控制策略有效降低了逆变器三相间的不平衡度,改善了输出电流畸变,减小了直流侧电压二倍频波动。

For the traditional low voltage ride through control under asymmetrical faults,due to the limited control degrees of freedom,the grid-connected inverter control suffers from the problem of not being able to simultaneously realize the output current negative-sequence component suppression and the DC side voltage double-frequency fluctuation suppression.In this regard,a multiple-objective decoupling control strategy is proposed for low voltage ride through of two-stage grid-connected photovoltaic system under asymmetrical faults.The strategy sets the control objective of the inverter as the negative-sequence component suppression of the output current and gives a reference value calculation method for the inner current loop considering the inverter output current limit and reactive power output demand.The super-capacitor is connected to both ends of the DC bus capacitor through the bidirectional Buck-Boost converter to maintain its voltage stability,and the DC side voltage double-frequency fluctuation is transferred to the super-capacitor side.The simulation results show that under the proposed control strategy,the unbalance between three phases of the inverter is reduced and the output current distortion is improved.The double frequency fluctuation of the DC side voltage is reduced significantly compared with the traditional control method.