A potential induced degradation suppression method for photovoltaic systems

Potential induced degradation (PID) is regarded as one of leading causes of photovoltaic (PV) module degradation. A PID suppression method is proposed in this paper, in which a PID suppression unit is added between DC negative bus and ground. The idea is to regulate the output voltage of the added power supply, and then correspondingly raise the voltage of the PV module to the ground to suppress the PID effect. A high-value resistor is added in the proposed PID suppression unit for the safety of preventing electric shock. To determine the value of the high-value resistor, detailed analysis for PV module positive or negative terminals shorted to the ground is performed. The design of the added power supply is investigated, including topology selection, voltage setting, and close-loop control. Furthermore, detailed voltage analysis for the added power supply is implemented for the systems with front-end boost DC/DC converters and 3-level boost DC/DC converters, respectively. Additionally, in the proposed solution, a switch is used to control whether the PID suppression unit is connected to the system. Three requirements are explained, as well as the corresponding control for the switch. Finally, experimental results are presented to validate the proposed theory.