Varying phase-shift carriers pulse-width modulation for cascaded H-bridges with improved line-to-line voltage

Cascaded H-bridges has been proven to be a suitable topology for high-power drives applications. The modular structure and high output power quality make the topology appealing in various applications, especially in medium voltage drives. This paper introduces an improved phase-shifted carriers pulse-width modulation (PWM) method that is able to produce enhanced line-to-line voltage waveform over the conventional phase-shifted carriers PWM. The proposed method uses interleaving among the H-bridge cells, which allows symmetric loading and increased apparent switching frequency. The proposed method varies the phase-shift of the carriers based on the voltage reference, allowing a smooth line-to-line voltage waveform. The modulation method is simulated with a 2.3 kV five-level cascaded H-bridge inverter.