单周期控制的三相三电平VIENNA整流器输出中点电位分析及控制方法研究

Study and Analysis of Neutral-point Potential and Control Methods for One-cycle Controlled Three-phase Three-level VIENNA Rectifiers

三相三电平VIENNA整流器作为三电平Boost型中点箝位(neutral point clamped,NPC)结构变换器一种,具有电路结构简单、开关电压应力小、输入电流谐波含量低、可实现输入单位功率因数校正等优点,适合应用于高压中大功率场合。同时,三相功率因数校正(power factor correction,PFC)整流器的单周期控制方案因其控制简单,无需乘法器及采用输入电压受到广泛研究。输出中点电位波动是NPC结构变换器的一个固有问题,以基于单周期控制的三相三电平VIENNA整流器为研究对象,详细地分析整流器输出中点电位波动机理,根据单周期控制方案的特点,提出在三相输入电流采样中注入三次谐波电流分量,同时分析三次谐波电流注入后对整流器输出中点电位的影响,给出三次谐波电流最佳注入系数。在此基础之上,向传统单周期控制系统中继续引入均压环路,使得最终改进后的三相三电平VIENNA整流器单周期控制系统一方面可以提高整流器直流母线电压利用率,另一方面可以有效抑制中点电位的直流和交流波动。仿真与实验验证了所提出的改进单周期控制策略对于整流器输出中点电位平衡控制的有效性。

As one kind of three level Boost-type neutral- point-clamped （NPC） structure rectifiers, the three-phase three-level VIENNA rectifier has many advantages such as simple circuit structure, low voltage stress of switch, low total harmonic distortion （THD） of input currents and input power factor correction, and it is very suitable for application in high voltage and power occasion. The one-cycle control （OCC） strategy used in the PFC circuit is widely researched because of the simple circuits and without the need of multiplier and sampling input voltages. The fluctuation in the neutral-point -potential （NPP） is a significant problem with NPC three-level rectifiers. With the OCC based three-phase three-level VIENNA rectifier as the research object, a detailed analysis of fluctuation mechanism of NPP was shown in this paper. According to the characteristic of OCC strategy, the three times harmonic of input currents was proposed to inject into the three phase sampled currents. The influence of three times harmonic injection to NPP was also analyzed, and the optimization inject coefficient was also discussed. Based on the above, the equalizing voltage ring was proposed to introduce in the traditional OCC strategy. At last, the modified OCC strategy not only could improve the utilization of the DC bus, but also could restrain the fluctuation of NPP. The effectiveness of the proposed new control strategy to balance the NPP was verified by simulation and experimental results.