具有中点电位非对称控制的VSVPWM技术

在降低NPC式三电平逆变器中点电位波动问题时,传统的VSVPWM算法未考虑直流侧电容电压非对称情况。为此,需从理论上探讨对称时的虚拟矢量形式是否适用于非对称状态下的各虚拟矢量。提出了具有中点电位非对称控制的VSVPWM技术,并在引入中点电位不平衡度的基础上通过改进零矢量的持续作用时间实现直流侧电容电压非对称控制。该方法具有较宽的调制比适用范围,并能够精确地控制直流侧电容电压,提高线电压质量,有效降低中点电位波动幅度。仿真和实验结果验证了该方法的有效性和优越性。

A VSVPWM Strategy on Asymmetrical Neutral-point Potential Control

The traditional virtual space vector pulse width modulation(VSVPWM)algorithm for neutral point clamped(NPC)three-level inverter has been adopted to solve the neutral-point potential fluctuation without considering DC side capacitors voltage asymmetry.So it is necessary to improve theoretically that the expressions of traditional VSVPWM virtual vectors in the symmetric state are applicable to virtual vectors in the asymmetric state.A VSVPWM strategy on a symmetrical neutral-point potential control was proposed,and on the basis of neutralpoint potential unbalance degree,the control of asymmetrical DC side capacitors voltage was realized by regulating zero vector continuous action time.The proposed method could meet the requirement of a wide range of modulation ratio,and control the DC side capacitor voltage accurately so that the quality of the line voltage was improved and neutral-point potential fluctuation range was reduced greatly.The effectiveness and superiority of the proposed method were tested and verified by simulation and experiments.