内蕴电压平衡控制的飞跨电容逆变器的PWM方法

Flying Capacitor Multilevel Inverter Pwm Method with Intrinsic Voltage Balancing Control

采用多电平结构是逆变器实现高电压大容量化的有效途径。飞跨电容逆变器因为只需要一个独立直流供电电源、电平数易扩展、控制灵活等优点而备受青睐,但是电容电压的平衡问题却制约其推广应用。针对此问题,该文提出一种内蕴电压平衡控制的PWM方法,该方法由直接PWM算法和基于最大单元电压偏差抑制的开关状态选择法则组成,前者是由给定的ABC坐标系下的参考电压来确定逆变器所需输出的电平电压、相应的作用时间及作用顺序;后者是确定逆变器的开关状态以产生已确定的电平电压,同时控制电容电压的平衡。该PWM方法理论上适用于任意电平的飞跨电容逆变器,它不但能够有效控制电容电压的平衡,而且还能够保证功率开关频率的均衡、便于数字化实现。该文给出了该方法的数字化实现原理。最后,基于飞跨电容五电平变频器对所提出的PWM方法,做了详尽的仿真分析和大量的实验验证。

Multilevel inverters have been considered as overall effective approach for inverter to achieve high capacity and high output voltage conversion. Using only single-supply DC voltage, scalable in terms of voltage levels and control flexibility, flying capacitor inverter has being attracted wide industrial interests recently. But, it needs to ensure balancing flying capacitor voltages under all operation conditions. A novel PWM method with intrinsic voltage balancing control is proposed for flying capacitor multilevel inverter. The method consists of direct PWM algorithm and maximum voltage variation suppression oriented switching selection. The direct PWM algorithm is used to determine the voltage levels needed and corresponding dwelling times and their generating sequences according to the given reference signal under A, B, C coordinates, The maximum voltage variation suppression oriented switching selection rules are used to determine the status of the switches to generate the voltage levels, which are determined by direct PWM algorithm, and to control voltage balancing simultaneously. Principles of digital control are also proposed. Extensive simulations and experimental results are demonstrated using a five-level flying capacitor inverter based frequency converter.