Power inverter circuit for adjusting symmetry of the AC-voltage without load-coupling

Power inverter circuit that produces an AC voltage at an inverter output and that adjusts a symmetry of the AC voltage before coupling the inverter output to a load, the symmetry being the amount of positive voltage in the AC voltage in relation to the amount of negative voltage in the AC voltage, the power inverter circuit comprising:

• first switching means (50) for selectively connecting a positive AC voltage to the inverter output (61),
• second switching means (51) for selectively connecting a negative AC voltage to the inverter output,
• ohmic resistance means (80) coupled in parallel to the inverter output via third switching means (90), wherein that the ohmic resistance means functions as a substitute for the load of the power inverter during times when the power inverter output is disconnected from the load to allow the symmetry of the AC voltage output from the power inverter to be matched to the AC voltage of the load using the ohmic resistance means before coupling the power inverter output to the load,
• fourth switching means (60,63) arranged between the ohmic resistance means and the inverter output for selectively coupling the inverter output to the load,
• a controller for selectively switching the first and second switching means with a switching frequency and with respective amounts of on-time to produce an AC voltage from the positive and negative voltage,
• wherein the controller is adapted to adjust the symmetry of the AC voltage produced by the inverter by altering the respective amounts of on-time of the first and second switching means.