A State-Space Approach to the Modelling and Control of the Neutral Leg of a Four Legs, Three-Phase Inverter

In this article, a novel approach to determine the model of an independently controlled neutral leg is proposed. Based on this model, a cascaded control method is developed to provide a steady neutral point connection for a three-phase four-wire inverter and to balance the two dc capacitors voltages of a split dc-bus. Validation of the model is realised by simulations and the control has been tested by experiments. Results have shown good performance even with a high level of neutral current, which demonstrate the ability of the system to work within an unbalanced load or grid.