Suppression of Common-Mode Voltage Using a Multicentral Photovoltaic Inverter Topology With Synchronized PWM

This paper describes an optimal configuration for multicentral inverters in a medium-voltage (MV) grid, which is suitable for large-scale photovoltaic (PV) power plants. We theoretically analyze a proposed common-mode equivalent model for problems associated with multicentral transformerless-type three-phase full bridge (3FB) PV inverters employing two-winding MV transformers. We propose a synchronized pulse width modulation (PWM) control strategy to effectively reduce the common-mode voltages that may simultaneously occur. In addition, we propose that the existing 3FB topology may also have the configuration of a multicentral inverter with a two-winding MV transformer by making a simple circuit modification. Simulation and experimental results of three 350 kW PV inverters in a multicentral configuration verify the effectiveness of the proposed synchronization control strategy. The modified transformerless-type 3FB topology for a multicentral PV inverter configuration is verified using an experimental prototype of a 100 kW PV inverter.