Power conversion device
A power conversion device includes a conversion circuit constituted of a plurality of arm circuits and a bypass circuit. The bypass circuit includes a full-wave rectification circuit, a positive-side connection arm, and a negative-side connection arm. The full-wave rectification circuit is connected between a plurality of AC connections, a positive-side intermediate node, and a negative-side intermediate node, and configured to convert AC voltages generated at the plurality of AC connections into a DC voltage across the positive-side intermediate node and the negative-side intermediate node and output the DC voltage. The positive-side connection arm blocks a current in a direction from a positive-side DC terminal toward the positive-side intermediate node. The negative-side connection arm is connected between the negative-side intermediate node and a negative-side DC terminal and blocks a current in a direction from the negative-side intermediate node toward a negative-side DC terminal.
1. A power conversion device to convert power between an AC circuit and a DC circuit, the power conversion device comprising:
a plurality of positive-side arm circuits connected between a plurality of AC connections connected to the AC circuit and a positive-side DC terminal connected to the DC circuit;
a plurality of negative-side arm circuits connected between the plurality of AC connections and a negative-side DC terminal connected to the DC circuit; and
a bypass circuit,
each of the positive-side arm circuits and each of the negative-side arm circuits each including a plurality of converter cells connected in series,
each of the converter cells including:
an energy storage; and
a bridge circuit to switch connection between the energy storage and outside, the bypass circuit including:
a full-wave rectification circuit connected between the plurality of AC connections, a positive-side intermediate node, and a negative-side intermediate node to convert AC voltages generated at the plurality of AC connections into a DC voltage across the positive-side intermediate node and the negative-side intermediate node and output the DC voltage;
a positive-side connection arm connected between the positive-side intermediate node and the positive-side DC terminal, the positive-side connection arm blocking a current in a direction from the positive-side DC terminal toward the positive-side intermediate node; and
a negative-side connection arm connected between the negative-side intermediate node and the negative-side DC terminal, the negative-side connection arm blocking a current in a direction from the negative-side intermediate node toward the negative-side DC terminal.
2. The power conversion device according to claim 1 , wherein
each arm constituting the full-wave rectification circuit includes a plurality of diode elements connected in series such that a direction from the negative-side intermediate node toward the positive-side intermediate node is defined as a forward direction,
the positive-side connection arm includes a plurality of diode elements connected in series such that a direction from the positive-side intermediate node toward the positive-side DC terminal is defined as the forward direction, and
the negative-side connection arm includes a plurality of diode elements connected in series such that a direction from the negative-side DC terminal toward the negative-side intermediate node is defined as the forward direction.
3. The power conversion device according to claim 2 , wherein
each of the positive-side connection arm and the negative-side connection arm further includes a switching element connected in series to the plurality of diode elements.
4. The power conversion device according to claim 3 , wherein
the switching element has such a non-linear current and voltage characteristic that when a voltage not lower than a first threshold value is applied, a current flows through the switching element and a voltage across terminals is lowered.
5. The power conversion device according to claim 4 , wherein
each of the positive-side connection arm and the negative-side connection arm further includes a non-linear element connected in parallel to the switching element,
the non-linear element has such a non-linear current and voltage characteristic that when a voltage not lower than a second threshold value is applied, a current flows through the non-linear element and a voltage across terminals is lowered, and
the second threshold value is smaller than the first threshold value.
6. The power conversion device according to claim 3 , wherein
each of the positive-side connection arm and the negative-side connection arm further includes a first resistive element connected in parallel to the switching element.
7. The power conversion device according to claim 2 , wherein
each diode element included in arms constituting the full-wave rectification circuit, the positive-side connection arm, and the negative-side connection arm is an avalanche diode.
8. The power conversion device according to claim 2 , wherein
each of arms constituting the full-wave rectification circuit, the positive-side connection arm, and the negative-side connection arm further includes a plurality of second resistive elements connected in parallel to the plurality of diode elements.
9. The power conversion device according to claim 3 , wherein
the power conversion device has a first operation mode and a second operation mode,
in the first operation mode, the switching element is controlled to turn off,
in the second operation mode, the switching element is controlled to turn on, and
when a short-circuiting failure of the DC circuit is detected, the operation mode of the power conversion device is switched from the first operation mode to the second operation mode.
10. The power conversion device according to claim 1 , wherein
the bridge circuit included in each of the converter cells is of a half-bridge configuration.
11. The power conversion device according to claim 10 , wherein
the positive-side connection arm of the bypass circuit is connected to a second positive-side DC terminal provided on a DC line between the positive-side DC terminal and the DC circuit,
the negative-side connection arm of the bypass circuit is connected to a second negative-side DC terminal provided on a DC line between the negative-side DC terminal and the DC circuit, and
the power conversion device further comprises:
a positive-side switch connected between the positive-side DC terminal and the second positive-side DC terminal, the positive-side switch being capable of switching between conduction and non-conduction between the positive-side DC terminal and the second positive-side DC terminal; and
a negative-side switch connected between the negative-side DC terminal and the second negative-side DC terminal, the negative-side switch being capable of switching between conduction and non-conduction between the negative-side DC terminal and the second negative-side DC terminal.
12. The power conversion device according to claim 11 , wherein
the power conversion device has a first operation mode and a second operation mode,
in the first operation mode, the positive-side switch and the negative-side switch are controlled to turn on,
in the second operation mode, the positive-side switch and the negative-side switch are controlled to turn off, and
when a short-circuiting failure of the DC circuit is detected, the operation mode of the power conversion device is switched from the first operation mode to the second operation mode.
13. The power conversion device according to claim 1 , wherein
each of the positive-side arm circuits and each of the negative-side arm circuits each include at least one first converter cell including a full-bridge or hybrid bridge circuit and at least one second converter cell including a half-bridge bridge circuit.
14. The power conversion device according to claim 13 , wherein
the energy storage is a capacitor, and
the capacitor provided in each first converter cell is higher in capacity than the capacitor provided in each second converter cell.
15. The power conversion device according to claim 13 , wherein
each first converter cell includes a starting circuit,
the starting circuit is a low-voltage circuit started up by a charging voltage of the energy storage, and
after the starting circuit is started, the starting circuit controls any one semiconductor switching element constituting the bridge circuit to turn on and controls a remaining semiconductor switching element to turn off.
16. The power conversion device according to claim 15 , wherein
when the charging voltage of the energy storage reaches a defined voltage, the starting circuit turns on two semiconductor switching elements provided on two arms connected to an identical terminal of the energy storage.
17. The power conversion device according to claim 13 , wherein
each first converter cell includes a starting circuit,
the starting circuit is a low-voltage circuit started up by a charging voltage of the energy storage, and
after the starting circuit is started, the starting circuit alternately repeats a first control state and a second control state each for a certain time period,
in the first control state, any one semiconductor switching element constituting the bridge circuit is controlled to turn on, and
in the second control state, two semiconductor switching elements provided on two arms connected to an identical terminal of the energy storage among four arms constituting the bridge circuit are controlled to turn on.
18. The power conversion device according to claim 13 , wherein
each first converter cell includes a normally closed switch connected in parallel to any one semiconductor switching element constituting a full bridge or a hybrid bridge.
19. A power conversion device to convert power between an AC circuit and a DC circuit, the power conversion device comprising:
a plurality of positive-side arm circuits connected between a plurality of AC connections connected to the AC circuit and a positive-side DC terminal connected to the DC circuit;
a plurality of negative-side arm circuits connected between the plurality of AC connections and a negative-side DC terminal connected to the DC circuit; and
a bypass circuit,
each of the positive-side arm circuits and each of the negative-side arm circuits each including a plurality of converter cells connected in series,
each of the converter cells including:
an energy storage; and
a bridge circuit to switch connection between the energy storage and outside, the bypass circuit including;
a full-wave rectification circuit connected between the plurality of AC connections, a positive-side intermediate node, and a negative-side intermediate node to convert AC voltages generated at the plurality of AC connections into a DC voltage across the positive-side intermediate node and the negative-side intermediate node and output the DC voltage;
a positive-side switch connected between the positive-side intermediate node and the positive-side DC terminal, the positive-side switch being capable of switching between conduction and non-conduction between the positive-side intermediate node and the positive-side DC terminal; and
a negative-side switch connected between the negative-side intermediate node and the negative-side DC terminal, the negative-side switch being capable of switching between conduction and non-conduction between the negative-side DC terminal and the negative-side intermediate node.
20. The power conversion device according to claim 19 , wherein
the power conversion device has a first operation mode and a second operation mode,
in the first operation mode, the positive-side switch and the negative-side switch are controlled to turn off,
in the second operation mode, the positive-side switch and the negative-side switch are controlled to turn on, and
when a short-circuiting failure of the DC circuit is detected, the operation mode of the power conversion device is switched from the first operation mode to the second operation mode.