电网不平衡工况下三电平直接矩阵变换器反步滑模控制策略

Back-stepping sliding-mode control strategy for a three-level direct matrix converter in unbalanced grid conditions

三电平直接矩阵变换器(three-level direct matrix converter, TLDMC)因具有高功率密度、高效率、共模电压较小等特点,在电机驱动、分布式发电、可再生能源等领域受到广泛关注。但在电网电压不平衡工况下,TLDMC输入侧的电流畸变会影响功率因数和输出侧的电能质量,降低系统的可靠性。现有的TLDMC输入闭环控制策略不能兼顾高动态响应和强鲁棒性的要求。为此,提出适用于平衡和不平衡电网电压,且无需正负序分离的TLDMC反步滑模控制策略(back-stepping sliding-mode control, BS-SMC)。采用动态调制系数抑制不平衡工况下的有功功率2倍频波动,再通过消除Lyapunov导函数中的非线性项并引入滑模面作为虚拟误差来控制输入无功。经过理论和实验分析比较,结果表明所提方法相较于传统控制策略,响应速度和电能质量均得到提高。所提方法为矩阵变换器的输入控制策略提供了一种参考。

The three-level direct matrix converter(TLDMC)has attracted wide attention in the fields of motor drive,distributed power generation,and renewable energy because of its advantages of high power density,high efficiency,and low common mode voltage.However,in unbalanced grid voltage conditions,the current distortion on the input side of the TLDMC will affect the power factor and power quality of the output side,and reduce the reliability of the system.The existing TLDMC input closed-loop control strategy cannot meet the requirements of high dynamic response and robustness.To this end,a TLDMC nonlinear control strategy is proposed based on back-stepping sliding-mode control(BS-SMC)which is suitable for balanced and unbalanced grid voltage conditions without positive and negative sequence separation.A dynamic modulation index is used to suppress the ripple of the active power double frequency in unbalanced conditions.The input reactive power is controlled by eliminating the nonlinear term in the Lyapunov derivative function and applying a sliding mode surface as a virtual error.After theoretical analysis and comparative experiments,the results show that compared with the traditional control strategies,the response speed of the back-stepping sliding-mode control is increased,and the THD is reduced.The method proposed provides a reference for the input control strategy of matrix converters.