DC bus splitting voltage feedforward injection method for virtually-grounded three-phase inverter

The virtually-grounded grid-connected voltage-source three-phase inverter has been proven to be more effective in alleviating the common-mode noise than the one without the virtual ground and in extending the utilization of DC bus voltage, as compared to the four-wire configuration. However, similar to the four-wire configuration, such virtually-grounded configuration would have DC bus unbalance, which would cause modulation saturation and output current distortion. Typically, two splitting capacitor voltages are measured and compared to produce a common-mode DC bias voltage to the output voltage of the inverter and thereby eliminate such effect. To reduce the number of sensors, a DC voltage feedforward injection method, which utilizes the intra-cycle average value of the duty cycles of the gate signals, is proposed to mitigate possible modulation saturation and output current distortion under the unbalanced condition of DC splitting voltage. A 3kW prototype has been built and evaluated to investigate the effectiveness of the proposed method.