Feedforward of grid line-to-line voltages for grid-connected inverter under the weak grid condition

Feedforward control is reliable for rejecting fast and dynamic voltage disturbances in the grid. Mainly this scheme is implemented based on phase voltages of the wye connected configuration. Under unbalanced and distorted grid-condition, the online conversion of line-to-line values into the phase values is unworkable. In order to exploit full advantages of feedforward controller, an appropriate modulator is needed. In this paper the feedforward of grid line-to-line voltages is used in lieu of phase voltages. The introduced feedforward method is implemented with implicit zero-sequence discontinuous pulse width modulation (IZDPWM) technique that is compatible for grid-connected inverters. Regardless the grid topology, IZDPWM exactly copies the distorting harmonics of the grid voltage. Hence, a sinusoidal current is injected to the grid. Moreover, for measuring the grid line-to-line voltages two sensors are required; hence overall system cost is reduced and control system reliability is increased.