Patent ID: 7872887

Claim:
A power converting apparatus comprising: two capacitors that are connected in series between a positive electrode and a negative electrode of a direct-current power generation facility so as to equally bear a direct-current voltage output from the direct-current power generation facility, wherein a point of connection between the two capacitors is connected to a grounded wire of a single-phase commercial power system, the commercial power system having two lines via which power is distributed to consumers, with one of said lines being the grounded wire; an inverter unit including two series connected switching elements connected between an output terminal and a positive electrode side of the series circuit of the two capacitors, and two series connected switching elements connected between said output terminal and a negative electrode side of the series circuit of the two capacitors, and a point of connection between the two switching elements at the positive electrode side and a point of connection between the two capacitors being connected to each other by a first clamp diode, and a point of connection between the two switching elements at the negative electrode side and a point of connection between the two capacitors being connected to each other by a second clamp diode; a smoothing circuit that connects the output terminal of the inverter unit to the ungrounded power supply line from the commercial power system; a current detector that detects an alternate current flowing through one of the ungrounded power supply line and the grounded wire, or a system voltage detector that directly detects an alternate voltage at the grounded wire; and an operation controller that controls the generation of a pulse-width-modulation signal applied to the four switching elements of the inverter so as to minimize a difference between a current value detected by the current detector and a target current value, or minimize a difference between a voltage value detected by the system voltage detector and a target voltage value, in the process of on/off controlling the four switching elements in a predetermined order and outputting alternate-current power corresponding to a frequency and a voltage of the commercial power system from the inverter output terminal; wherein in stopping the operation in the control of the inverter unit, the operation controller controls the switching elements connected to both the positive electrode side and the negative electrode side to an off-operation state, and controls the switching elements connected to the inverter output terminal such that the switching element at the positive electrode side is set to an on-operation state and the switching element at the negative electrode side is set to an off-operation state, in a positive half cycle of the system, respectively, and the switching element at the positive electrode side is set to an off-operation state and the switching element at the negative electrode side is set to an on-operation state, in a negative half cycle of the system, respectively.