Optimal LCL Filter Design for a Regenerative Cascaded H-Bridge (CHB) Motor Drive

This paper proposes an optimal passive damping LCL filter design scheme for regenerative Cascaded H-Bridge (CHB) motor drives. To obtain full regeneration ability for the conventional CHB drive system, the three-phase diode rectifier in each cell is needed to be replaced with an active front-end rectifier/inverters. To satisfy grid harmonic code IEEE STD-519 2014, a suitable filter is required to be designed. However, with the existence of the phase-shifting transformer in CHB drives, the existing filter design methods cannot be applied directly. To tackle this problem, an LCL filter design framework using genetic algorithm (GA) optimization is proposed based on the Simulink model. Unlike the conventional design procedures based on the mathematical model, the CHB Simulink model can take DC voltage constraint, PLL performance, transformer factors, and harmonics profile into consideration while designing the LCL filters. With the proposed filter design framework, the designed LCL filter can guarantee both the harmonic performance and the system performance with minimum passive component size, which cannot be achieved through the existing methods. Finally, the proposed method is validated on a seven-level CHB inverter with simulation.