Parallel Inverters using a DC Common Mode PWM Filter with an AC Differential Mode PWM Filter

An inductor filter arrangement is assessed that filters the high-frequency PWM common mode, CM, and differential mode, DM, PWM voltages experience between two 180° interleaved 2-level voltage source converters (VSCs) connected to the same dc-link voltage. A 3-limb coupled inductor, CI, connecting the two inverters presents a large inductance for filtering DM PWM voltages between the two inverters, and a CM dc choke that presents a high inductance for the CM PWM voltage between the two inverters is used as a CM PWM filter. However, the dc-choke has a low inductance for current drawn by the inverters to supply the load. Likewise, the 3-limb CI has a low inductance to the flow of fundamental currents to the load. The size and weight of the filter arrangement are compared with separate CIs used in each phase, which can cope with both CM and DM PWM voltages without saturating and are shown to be 20% smaller in comparison. A PWM scheme is demonstrated to produce high-quality 3-level phase and 5-level PWM line voltages. The system described is suitable for medium voltage high power drives and high-speed machines with application in aerospace, electric vehicles, and utility connected rectifiers. The performance of the system is demonstrated with PLECS simulation and experimental results of an 8 kW (300V, 208 V/22A) laboratory prototype operating with a fundamental voltage of 60 Hz and 1.1 kHz.