Electric power conversion apparatus and electric power conversion system

1. An electric power conversion apparatus comprising:

an electric power conversion circuit that includes a DC terminal and an AC terminal, allows the DC terminal to be connected to a DC power source via a DC bus line, and performs at least any one of converting DC power of the DC power source into AC power and outputting the AC power from the AC terminal, and converting AC power into DC power and outputting the DC power from the DC terminal;

a DC switch that is provided between the DC power source and the electric power conversion circuit, and is turned on when the electric power conversion circuit performs electric power conversion;

an AC switch that is provided on a side of the AC terminal, and is turned on when the electric power conversion circuit performs the electric power conversion;

a DC voltmeter that measures a potential at a predetermined portion which has been determined beforehand, on a side of the DC terminal;

a ground connection portion for connecting the DC bus line with a ground potential; and

a control circuit that is connected to the electric power conversion circuit, the DC switch, the AC switch and the DC voltmeter, wherein

the control circuit is structured so as to

detect whether or not a DC ground fault voltage has been generated on the basis of a measurement value of the DC voltmeter, while the electric power conversion circuit performs the electric power conversion;

when the DC ground fault voltage has been generated, execute AC-side opening control of opening the AC switch in a state in which the DC switch is turned on,

when the DC ground fault voltage has been restored in response to the AC-side opening control, determine that the DC ground fault is not occurring on a side of the DC terminal, and

when the DC ground fault voltage is not restored in response to the AC-side opening control, determine that the DC ground fault has occurred on the side of the DC terminal.

2. The electric power conversion apparatus according to claim 1 , further comprising:

a positive electrode DC bus line and a negative electrode DC bus line that each connect the DC power source with the DC terminal, wherein

the ground connection portion comprises a ground resistor for connecting the negative electrode DC bus line with the ground potential.

3. The electric power conversion apparatus according to claim 1 , further comprising:

a positive electrode DC bus line and a negative electrode DC bus line that each connect the DC power source with the DC terminal, wherein

the ground connection portion comprises a voltage dividing resistance circuit that contains a plurality of resistors connected in series,

one end of the voltage dividing resistance circuit is connected to the positive electrode DC bus line, the other end of the voltage dividing resistance circuit is connected to the negative electrode DC bus line, and

an intermediate connection point between the plurality of resistors included in the voltage dividing resistance circuit is connected to the ground potential.

4. An electric power conversion system comprising a plurality of the electric power conversion apparatuses according to claim 1 , wherein

the AC terminals of the plurality of electric power conversion apparatuses are connected to each other at a parallel connection point without being connected via a transformer.

5. An electric power conversion apparatus comprising:

an electric power conversion circuit that includes a DC terminal and an AC terminal, allows the DC terminal to be connected to a DC power source via a DC bus line, converts DC power of the DC power source into AC power, and outputs the AC power from the AC terminal;

a DC switch that is provided between the DC power source and the electric power conversion circuit, and is turned on when the electric power conversion circuit performs electric power conversion;

a DC voltmeter that is provided on a side closer to the DC power source than the DC switch;

a ground connection portion for connecting the DC bus line with a ground potential on a side closer to the DC power source than the DC switch; and

a control circuit that is connected to the electric power conversion circuit, the DC switch and the DC voltmeter, wherein

the control circuit is structured so as to

detect whether or not a DC ground fault voltage has been generated on the basis of a measurement value of the DC voltmeter, while the electric power conversion circuit performs the electric power conversion;

when the DC ground fault voltage has been generated, execute DC-side opening control of opening the DC switch,

when the DC ground fault voltage has been restored in response to the DC-side opening control, determine that the DC ground fault is not occurring on a side closer to the DC power source than the DC switch, and

when the DC ground fault voltage is not restored in response to the DC-side opening control, determine that the DC ground fault has occurred on a side closer to the DC power source than the DC switch.

6. The electric power conversion apparatus according to claim 5 , wherein

the DC power source comprises a converter that converts AC power into DC power, and

in the ground connection portion, one of a ground resistor provided in the converter and a voltage dividing resistance circuit that is provided in the converter and of which an intermediate connection point is grounded is shared by the converter and the electric power conversion circuit.

7. An electric power conversion system comprising a plurality of the electric power conversion apparatuses according to claim 5 , wherein

the AC terminals of the plurality of electric power conversion apparatuses are connected to each other at a parallel connection point without being connected via a transformer.