一种改进的PWM整流器滑模控制方法

Research on an improved sliding mode control method for PWM rectifier

传统的三相两电平脉宽调制(PWM)整流器在PI控制下的启动运行瞬间会产生较大冲击电流,易损坏电路器件,影响系统的动、稳态性能,为此,提出了一种利用指数趋近律的改进滑模变结构双闭环控制策略。首先建立PWM整流器交流侧的离散化数学模型公式,分析影响启动冲击电流的参数变量关系。对PWM整流器进行预充电,以降低启动冲击电流。同时进行电流前馈补偿,以加快系统动态响应。其次通过采用可变边界层进行滑模控制的改进,削弱系统抖动影响。通过仿真实验,验证了改进滑模控制启动比传统PI控制输出波形更平滑;当负载改变时其动态响应时间也减少。改进后的滑模变结构输出波形的抖振得到了抑制,稳定状态时期望参数变量在滑模面上的波动幅值降低,避免了控制器的高频切换。系统的动、稳态性能更好。

For the traditional three-phase two-level pulse width modulation(PWM)rectifier under PI control,the start-up operation of the rectifier under PI control generates a large impulse current instantly,which is easy to damage the circuit components and affect the dynamic and steady-state performance of the system.A double closed-loop control strategy for sliding mode variable structure using exponential approximation law is proposed.First,the study has established the discrete mathematical model formula for the AC side of the PWM rectifier,and analyzed the relationship between parameter variables that affect the inrush current during startup.The PWM rectifier is pre-charged to reduce the start-up impulse current,and the current feedforward compensation is carried out to accelerate the dynamic response of the system.Then,by using a variable boundary layer for improved sliding mode control,the impact of system chattering is mitigated.Through simulation experiments,it was verified that the improved sliding mode control produces a smoother output waveform at startup compared to traditional PI control;the dynamic response time is also reduced when the load changes.The chattering of the output waveform in the improved sliding mode variable structure is suppressed,and the fluctuation amplitude of the desired parameter variables on the sliding mode surface during steady-state is reduced,avoiding high-frequency switching of the controller.The dynamic and steady-state performance of the system is significantly better.