Digital control of a four leg inverter for standalone photovoltaic systems with unbalanced load

Three leg inverters for photovoltaic systems have a lot of disadvantages, especially when the load is unbalanced. These disadvantages are for example, small utilisation of the DC link voltage, the dependency of the modulation factor of the load current and the superposition of a DC component with the output AC voltage. In this paper a three dimensional space vector modulation of a four leg inverter for standalone photovoltaic systems is presented to solve these problems. A digital control strategy based on a load current observer is introduced to control the whole system with a microcontroller. Simulation and experimental results are presented to verify the performance of the proposed system