A Voltage Sensor-Less and PLL-Less Inner-Loop Control Method for Grid-Tied Inverter-Based Resources

This paper presented a voltage sensor-less inner-loop control method without a Phase-Locked Loop (PLL) circuit. Only the inverter output current is fed back to the controller from the current sensors. Grid-tied inverters typically employ a synchronization method that depends on the sensed grid voltage for phase estimation. However, this method may be unreliable under weak grid conditions where large grid impedance can compromise the stability and robustness of the control system. To overcome this limitation, we proposed this control method that makes the inverter synchronize with the grid without relying on grid voltage information. This method avoids the degradation of robustness caused by grid impedance uncertainty. Moreover, the proposed inner-loop current control possesses fast dynamic responses under step command changes and maintains good steady-state performance. Finally, the use of virtual resistance in the control loop damps the oscillation caused by grid disturbances.