A Multi-level Active Power Filter for Common-Mode Voltage Attenuation in Multi-level Inverters

This paper proposes a multi-level active power filter (APF) for common-mode voltage (CMV) attenuation in multi-level inverter systems. The proposed system is composed of a multi-level inverter and an additional fourth leg as the APF. The same 5-level Active-neutral-point-clamped (ANPC) II type inverter architecture is used for both the inverter and APF as an example of multi-level inverters in this paper. For CMV attention in the system, the APF has to generate and inject the voltage equal to the CMV generated by the inverter. Therefore, the APF requires a CMV prediction algorithm and PWM technique for the APF voltage generation. The CMV generated by the inverter has multi-level and more complex forms than the output voltages of the inverter. Thus, a unique PWM technique is required for the APF instead of conventional carrier-based PWM methods to generate the same voltage as the CMV. Through the APF PWM generation using the proposed CMV prediction algorithm and APF PWM, the APF can generate and inject the APF voltage equal to the CMV. As a result, the proposed APF can significantly attenuate the CMV of the system. Simulation and experimental results have verified the validity of the proposed method.