Circulating Current Suppression of Parallel Photovoltaic Grid-Connected Converters

The photovoltaic (PV) grid-connected converter (GCC) is a critical interface between solar energy and the power grid. Improved efficiency is possible if several PV GCCs have a common array bus. However, the dc side shunt causes the circulation of a zero-sequence current, which will distort the GCC or even damage semiconductor devices. The zero-sequence current includes high- and low-frequency components. A novel passive filter is proposed to increase the order of the zero-sequence circulating current transfer function to reduce the high-frequency component without increasing the cost. Furthermore, an advanced finite-time controller is introduced to mitigate the low-frequency component with fast regulation performance and strong disturbance rejection. The test results for two 10-kW GCCs are presented to confirm the performance of the method.