A New Control Scheme for Voltage Source Inverter without DC-Link Capacitor under Abnormal Input Voltage Conditions

As the conventional voltage source inverter has the drawback of low power density and high input current distortion because of large electrolytic capacitor on the dc link. A novel voltage source inverter without electrolytic capacitor is investigated. Replacing the electrolytic capacitor by a small snubber capacitor the input current quality is improved but the output current are easy distorted by abnormal input voltage,The input currents is also easy distorted by output currents due to the power balance between the input and output. A new control scheme, which combines feed-forward compensation control with dc link voltage measurement to closed-loop output current control, is proposed. The feed forward control makes sure that the perfectly sinusoidal local average output voltage can still be achieved under abnormal input voltage by implementing a time-varying modulation index, the closed-loop control remove the output current low order harmonics produced from loads. Thus, high quality input and output currents could be achieved using proposed control scheme under normal and abnormal input voltage conditions, Furthermore, it is easy to implement and doesn´t require complicated computing. Finally the validity and feasibility of proposed control scheme is verified by simulation and experimental results.