有源前端型三电平逆变器中点电位平衡的一种控制策略

A Strategy for Balancing Neutral-Point Potential of Three-Level AFE-Inverter

由三电平有源前端(AFE)和三电平逆变器构成的中高压变频器在能量再生,功率因数,输入和输出谐波方面具有良好的性能.在这种变频器中,为了实现直流侧中点电位平衡控制(NPB),以往的方法都要对逆变控制采用的SVPWM算法进行调整,这不可避免地会增加逆变输出谐波.本文提出一种无需调整SVPWM算法而只在变频器前端解决NPB问题的策略,避免了逆变输出谐波的增加,使负载电机旋转磁场具有较为理想的圆度.文中介绍了这种NPB的基本原理,对在前端控制与在逆变侧控制的输入和输出性能进行了比较分析.仿真实验研究结果证明了该控制策略的正确性和有效性.

The medium and high voltage three-level inverter fed by a three-level active front end shows high performance in terms of power regeneration, power factor, input and output harmonics distortion. SVPWM, a common used algorithm for controlling inverter, must be modified for balancing dc bus neutral-point potential in the inverter. In this case, output harmonics will inevitably increase. In order to overcome this drawback, a neutral-point potential balancing （NPB） strategy which is implemented at the front end is presented. Because this strategy does not modify SVPWM algorithm, the output harmonics of the inverter is low and load motor＇s rotating magnetic field is more dose to round in shape. The basic principle of the proposed NPB is introduced and input and output performance comparisons of the converter are made between the NPB strategies implemented at the AFE and at the inverter respectively. Simulation results show that the proposed control strategy is correct and effective.