Characters of the invented circuit are that each single-phase inverter includes following parts: voltage measuring apparatus for measuring voltage between two ends of capacitance at DC side of inverter; evaluator of minimum capacity voltage for determining minimum value among capacity voltages at DC side of each inverter, and the minimum value being as reference voltage of pulse width regulator; the pulse width regulator carrying out error adjusting between signal of measured capacity voltage at DC side and reference voltage; pulse amplifier for magnifying signal of pulse width modulation and adjusting voltage between two ends of capacitance at DC side of inverter. The invented circuit can compensate unbalanced voltage at DC side of reactive generating device, making equipment operate normally.