Presynchronization Control for Grid-Connected Inverters Without Grid Voltage Sensors

The grid voltage sensorless control for grid-connected inverters samples the line current to estimate the voltage at the point-of-common-coupling and achieve grid synchronization. The sensorless control tends to enlarge in-rush currents and fails to connect to the grid. For addressing this issue, this letter proposes a presynchronization control strategy to achieve a fast and reliable connection to the grid. By applying periodic pulses with a designed duty cycle, the converter operates in the rectifier mode with unit power factor before being connected to the ac grid as an inverter. The initial phase of the ac grid can thereby be estimated by the sampled current, where a synchronous reference frame phase-locked loop is applied to obtain the current phase. The proposed strategy is validated by experimental tests.