Power conversion system
A power conversion system includes a first capacitor, an isolated type converter circuit, and a control circuit. The first capacitor is connected to the direct-current power supply via an inrush current prevention circuit. The inrush current prevention circuit is switchable at least between a high-impedance state and a low-impedance state. The converter circuit includes a transformer, and the first capacitor is connected to a primary winding wire of the transformer. The control circuit controls the inrush current prevention circuit and the converter circuit to cause the converter circuit to start operating, and then, the control circuit switches the inrush current prevention circuit from the high-impedance state to the low-impedance state.
1. A power conversion system configured to unidirectionally or bidirectionally transfer electric power between a direct-current power supply and any one of an alternating-current grid, an alternating-current load, or a direct-current load, the power conversion system comprising:
a capacitor connected to the direct-current power supply via an inrush current prevention circuit which is switchable at least between a high-impedance state where impedance is relatively high and a low-impedance state where the impedance is relatively low; and
a converter circuit which is an isolated type converter circuit, the converter circuit including a transformer, the transformer having a primary winding wire and a secondary winding wire, the capacitor being connected to the primary winding wire;
a control circuit configured to control the inrush current prevention circuit and the converter circuit,
the control circuit being configured to cause the converter circuit to start operating and then switch the inrush current prevention circuit from the high-impedance state to the low-impedance state.
2. The power conversion system of claim 1 , wherein
the inrush current prevention circuit includes
a first openable/closable unit having one end connected to the direct-current power supply and the other end connected to the capacitor, the first openable/closable unit being configured to bring the inrush current prevention circuit into the low-impedance state by making an electrical path between the direct-current power supply and the capacitor, and
a second openable/closable unit which is, between the direct-current power supply and the capacitor, connected in parallel to the first openable/closable unit, the second openable/closable unit being configured to bring the inrush current prevention circuit into the high-impedance state by making an electrical path between the direct-current power supply and the capacitor.
3. The power conversion system of claim 1 , wherein
the control circuit is configured to cause the converter circuit to operate when the inrush current prevention circuit is in the high-impedance state.
4. The power conversion system of claim 1 , wherein
the converter circuit has a first frequency which is a drive frequency when the inrush current prevention circuit is in the high-impedance state, the first frequency being higher than a second frequency which is a drive frequency of the converter circuit at a steady state.
5. The power conversion system of claim 4 , wherein
the control circuit is configured to stop the converter circuit or reduce a duty cycle of the converter circuit before the drive frequency of the converter circuit is switched from the first frequency to the second frequency.
6. The power conversion system of claim 1 , further comprising a snubber circuit connected to the secondary winding wire.
7. The power conversion system of claim 6 , wherein
the snubber circuit includes a second capacitor which is different from a first capacitor serving as the capacitor and which is connected to the secondary winding wire,
the control circuit is configured to switch the inrush current prevention circuit to the low-impedance state when at least one of a voltage across the first capacitor or a voltage across the second capacitor has reached a specified voltage since operation of the converter circuit was started or at a lapse of a specified time since starting of the operation of the converter circuit.
8. The power conversion system of claim 1 , wherein
the inrush current prevention circuit is switchable among the high-impedance state, the low-impedance state, and an off-state where the direct-current power supply and the capacitor are electrically disconnected from each other, and
the control circuit is configured to cause the converter circuit to start operating at a switching timing at which the inrush current prevention circuit is switched from the off-state to the high-impedance state or before the switching timing.
9. The power conversion system of claim 1 , further comprising the inrush current prevention circuit.