Hybrid SVPWM Strategy for Diode-clamped 3H-bridge Inverter

The paper presents a novel space vector modulation strategy for a single phase three-level neutral-point-clamped(NPC) inverter. Based on the operating principle of NPC inverter, this strategy overcomes one of the main problems of this inverter, which is the DC-link capacitors voltage unbalancing problem that appears in the neutral point under some operating conditions. The algorithm is a hybrid pulse-width modulation strategy, which based on traditional space vector pulse-width modulation (SVPWM) and virtual SVPWM (VSVPWM). The criterion is made according to the change of reference voltage, which is transited between the traditional SVPWM and the VSVPWM method. A strategy for balancing the voltages on the dc-link capacitors is also proposed and designed, which is based on a neutral point voltage balancing factor. So that the output voltage waveform is improved not only, but also the distortion of capacitor voltages is decreased. Simulation and experimental results are given to verify the correctness and validity of the proposed method.