AC/DC-DC/AC级联变流器DC与AC双侧双向交互稳定性分析及协调优化控制

Bidirectional Interactive Stability Analysis of DC and AC Sides for AC/DC-DC/AC Cascade Converter and Coordinative Optimization Control

AC/DC-DC/AC级联变流器系统面临双向功率流动时,若不切换变流器控制策略,直流侧与交流侧的稳定性在正向功率与反向功率之间存在明显的差异,即双向功率稳定性差异,这种稳定性差异可能会导致系统发生振荡。针对这一问题,对直流侧和交流侧变流器阻抗进行了小信号建模,对比分析了各端口变流器阻抗在正反向功率下的阻抗特性差异,并提出了一种协调优化控制策略,发生扰动时,使其同时优化AC环节与DC环节在双向功率下的稳定性。通过阻抗稳定判据以及奈奎斯特稳定性判据,分别对比分析了交、直流侧优化前后正向功率与反向功率下稳定性的变化。研究结果表明:采用协调优化控制后,交流侧和直流侧电压在双向功率流动的情况下都能保持较好的稳定性,双向功率稳定性差异被大大减小。最后所提出控制策略的有效性通过Matlab/Simulink仿真和实验进行了验证。

When bidirectional power flow occurs in AC/DC-DC/AC cascade converter system,there is a significant stability difference between forward power and reverse power on both DC and AC sides if the control strategy between converters is not switched,that is,there is difference in the bidirectional power stability,which will cause the system to oscillate.To solve this problem,firstly,the small-signal modeling of the converter impedances on the AC and DC sides are performed.Then,the impedance characteristic difference between forward and reverse power flow of each port impedance is compared and analyzed.In addition,a coordinative optimization control strategy is proposed.When disturbances occur,the control strategy is adopted to optimize the bidirectional power stability on AC and DC sides.Moreover,combined with the impedance stability criterion and Nyquist stability criterion,the stability variations before and after optimization on the AC and DC sides are compared and analyzed.The results show that,after the coordinative optimization control is adopted,the AC-side and DC-side voltages can maintain excellent stability under a bidirectional power flow,and the bidirectional power stability difference is significantly reduced.Finally,the effectiveness of the proposed control strategy is verified by Matlab/Simulink simulations and experiments.