Single-Phase Transformerless PV Inverter with Reactive Power Compensation

The transformer-less grid-tied PV inverter system has been more adopted nowadays due to its high efficiency, lightweight and low cost, etc. There has been an increasing interest among researchers due to the same reasons. Therefore, many novel topologies and control techniques have been proposed and put in use focusing on active power injection without leakage current issues. Recently more and more distributed energy sources are tied to the grid injecting active power. But the reactive power requirement is still high which can cause grid instability. According to some recent codes PV inverters have to inject reactive power into utility for the grid support. This paper is focusing on reactive power injection along with active power injection. A two-stage PV inverter topology is employed for the same. The two-stage inverter topology consists of a dc-dc boost converter stage used to increase the wide range of input voltage while lowering the inverter's needed kilovolt ampere rating. Furthermore, it acts as the MPPT block for maximum power tracking. The NPC inverter was used as the inverter which kept the common-mode voltage constant and result in a low leakage current. The voltage balancing of the capacitors of the NPC inverter is achieved by injecting a dc current into the reference current depending on the unbalance.