The invention relates to a power inverter circuit for coupling a power station to a power supply system. The invention addresses the problem to reduce the risk of damages to components of the power station and the power supply system in the course of coupling action by providing a power inverter circuit for adjusting symmetry of the AC voltage before coupling the inverter output to a load, comprising: first switching means for selectively connecting a positive voltage to the inverter circuit output, second switching means for selectively connecting a negative voltage to the inverter output, and ohmic resistance means coupled in parallel to the inverter output, a controller for selectively switching the first and second switching means with a switching frequency to produce an AC voltage from the positive and negative voltage, wherein the controller is adapted to alter the duty ratio of the switching frequency to adjust the symmetry of the AC voltage produced by the inverter.