Quasi 2N+1 Level Modulation Based on Steps Construction for Long-Cable-Fed CHB Motor Drives

The overvoltage oscillation (ringing) in long-cable-fed motor drives is caused by the mismatch between motor surge impedance and cable characteristic impedance, which increases the insulation stress of motor winding while also exacerbating electromagnetic interference (EMI). Passive filters can effectively suppress overvoltage, but the drawbacks of high losses, large size, and additional costs limit their application in high-power scenarios. This brief proposes a quasi 2N+1 level modulation method for cascade H-bridge (CHB) inverters in medium-voltage motor drives. The suppression principle is to construct two or 2N steps with predetermined width during each PWM transition by changing the carrier phase shift angles within and between submodules of CHB inverter to make traveling waves cancel out in pairs on the cable. Theoretical derivation of motor terminal voltage s-domain expression with proposed method and detailed explanation of traveling waves counterbalanced were provided, the experimental results also proved its correctness and effectiveness.