Bidirectional unisolated DC-DC converter based on cascaded cells

摘要

A DC-DC converter (200) comprising a first (201) and a second (202) variable voltage source, a capacitor (203), an alternating current filter (204), and controlling means (205), is provided. A first DC voltage (UDC1) is provided over a series-connection of the first and the second voltage source, and a second DC voltage (UDC2), being lower in magnitude than (UDC1), is provided over the second voltage source. The conversion between (UDC1) and (UDC2) is effected by circulating an alternating current within a circuit comprising the two voltage sources and the capacitor, thereby exchanging power between the two voltage sources. The alternating current is driven by AC voltage components provided by the first and the second voltage source. The controlling means is arranged for controlling the first and the second voltage source so as to maintain a phase difference between the AC components to be close to π.

主权项

1. A DC-DC converter for high voltage direct current (HVDC) power transmission and distribution and for converting a first DC voltage into a second DC voltage or vice versa and comprising:
a first phase leg having a first, a second, and a third connection terminal, the first phase leg comprising:
a first variable voltage source and a second variable voltage source being arranged for providing a first voltage (U1(t)) and a second voltage (U2(t)), respectively, each voltage having an AC voltage component and a DC voltage component, each variable voltage source having a first pole and a second pole, the first pole of the first variable voltage source being connected to the first terminal of the first phase leg, the second pole of the first variable voltage source being connected to the first pole of the second variable voltage source, and the second pole of the second variable voltage source being connected to the second terminal of the first phase leg, wherein the first DC voltage (UDC1) is provided between the first terminal and the second terminal of the first phase leg, and the second DC voltage (UDC2) is provided between the third terminal and the second terminal of the first phase leg,a first capacitor being connected between the first terminal and the second terminal of the first phase leg, and being arranged between an input end of the first phase leg of the DC-DC converter and an output end of the first phase leg of the DC-DC converter, wherein the input end of the first phase leg is provided with the first DC voltage (UDC1) and the output end of the first phase leg of the DC-DC converter is provided with the second DC voltage (UDC2), andan alternating current, AC, filter being connected between the first pole of the second variable voltage source and third terminal of the first phase leg,and
a control unit configured to control the first variable voltage source and the second variable voltage source of the first phase leg so as to circulate an AC current (IAC(t)) within a loop of the first capacitor, the first variable voltage source, and the second variable voltage source, of the first phase leg.