Power conversion device
Each phase arm of a power conversion device includes at least one converter cell connected in series. For each converter cell, an element driving unit is provided which turns on one switching element in the converter cell as a startup element. The element driving unit is supplied with power from a DC capacitor, and when voltage of the DC capacitor exceeds startup voltage Vsh, turns on the startup element. Thus, at the time of startup of the power conversion device, the DC capacitor in each converter cell is initially charged to desired voltage.
1. A power conversion device for performing power conversion between plural-phase AC and DC, the power conversion device comprising a plurality of leg circuits each including a positive arm and a negative arm connected in series, the leg circuits being connected in parallel between positive and negative DC buses, wherein
each of the positive arm and the negative arm in each leg circuit includes at least one first converter cell connected in series, and
each first converter cell includes: two series units connected in parallel and each composed of two semiconductor switching elements connected in series to each other; and a DC capacitor connected in parallel to the series units, wherein one of connection portions between the two semiconductor switching elements in each series unit is used as an output end,
the power conversion device further comprising a charge control unit for controlling initial charging of the DC capacitor in each first converter cell, wherein
the charge control unit includes, for each first converter cell, an element driving unit for driving, as a startup element, one of four semiconductor switching elements in the two series units of the first converter cell, the element driving unit turning on only the startup element and having the other three semiconductor switching elements kept off when the DC capacitor is initially charged.
2. The power conversion device according to claim 1 , wherein
each of the positive arm and the negative arm further includes at least one second converter cell connected in series to the first converter cell,
each second converter cell includes: a series unit composed of a plurality of semiconductor switching elements connected in series to each other; and a DC capacitor connected in parallel to the series unit, wherein two connection portions of the plurality of semiconductor switching elements are used as output ends, and
when the charge control unit controls initial charging of the DC capacitor in each first converter cell, the DC capacitor in each second converter cell is initially charged in a state in which all the plurality of semiconductor switching elements in the second converter cell are OFF.
3. The power conversion device according to claim 1 , wherein
the plural-phase AC is three-phase AC, and
the charge control unit includes, only for two phases of the three phases, the element driving unit for driving the startup element in each first converter cell.
4. The power conversion device according to claim 1 , wherein
each leg is connected to an AC circuit, and
a charge current from the AC circuit flows via two phases of a same polarity arms to charge each DC capacitor in one of the two phases and bypass each DC capacitor in the other phase when the start-up element of each first converter is turned on.
5. The power conversion device according to claim 1 , wherein
each element driving unit is supplied with power from the DC capacitor in the corresponding first converter cell.
6. The power conversion device according to claim 5 , wherein
each element driving unit starts ON control for the corresponding startup element on the basis of voltage of the corresponding DC capacitor.
7. The power conversion device according to claim 5 , wherein
the charge control unit includes a central control unit for outputting a turn-on command to start ON control for each startup element simultaneously, to all the element driving units.
8. The power conversion device according to claim 7 , wherein
the central control unit outputs the turn-on command to all the element driving units after a set time has elapsed since initial charging of the DC capacitors has been started.
9. The power conversion device according to claim 7 , wherein
the central control unit monitors voltage of the DC capacitor in each first converter cell, and based on the monitored voltages, outputs the turn-on command to all the element driving units.
10. A power conversion device for performing power conversion between plural-phase AC and DC, the power conversion device comprising a plurality of leg circuits each including a positive arm and a negative arm connected in series, the leg circuits being connected in parallel between positive and negative DC buses, wherein
each of the positive arm and the negative arm in each leg circuit includes at least one first converter cell and at least one second converter cell connected in series, and
each first converter cell includes: two series units connected in parallel and each composed of a plurality of semiconductor switching elements connected in series to each other; and a DC capacitor connected in parallel to the series units, wherein one of connection portions between the plurality of semiconductor switching elements in each series unit is used as an output end,
each second converter cell includes: a series unit composed of a plurality of semiconductor switching elements connected in series to each other; and a DC capacitor connected in parallel to the series unit, wherein two connection portions of the plurality of semiconductor switching elements are used as output ends,
the power conversion device further comprising a charge control unit for controlling initial charging of the DC capacitor in each first converter cell, wherein
the charge control unit includes, for each first converter cell, an element driving unit for driving, as a startup element, one of the plurality of semiconductor switching elements in the first converter cell, the element driving unit turning on the startup element when the DC capacitor in each first converter cell is initially charged, and
when the charge control unit controls initial charging of the DC capacitor in each first converter cell, the DC capacitor in each second converter cell is initially charged in a state in which all the plurality of semiconductor switching elements in the second converter cell are OFF.
11. The power conversion device according to claim 10 , wherein
the plural-phase AC is three-phase AC, and
the charge control unit includes, only for two phases of the three phases, the element driving unit for driving the startup element in each first converter cell.
12. The power conversion device according to claim 10 , wherein
each element driving unit is supplied with power from the DC capacitor in the corresponding first converter cell.
13. The power conversion device according to claim 12 , wherein
each element driving unit starts ON control for the corresponding startup element on the basis of voltage of the corresponding DC capacitor.
14. The power conversion device according to claim 12 , wherein
the charge control unit includes a central control unit for outputting a turn-on command to start ON control for each startup element simultaneously, to all the element driving units.
15. The power conversion device according to claim 14 , wherein
the central control unit outputs the turn-on command to all the element driving units after a set time has elapsed since initial charging of the DC capacitors has been started.
16. The power conversion device according to claim 14 , wherein
the central control unit monitors voltage of the DC capacitor in each first converter cell, and based on the monitored voltages, outputs the turn-on command to all the element driving units.