DC/DC converter for flexible direct current transmission and its control method

Abstract

A DC / DC converter for flexible direct current transmission and a control method thereof belong to the field of flexible direct current transmission, and solve the problems of large device stress, large system loss and large volume in existing non-isolated high-voltage DC / DC converters. Converter: the diode string D1 and the diode string D2 are connected in series between the positive pole of the DC low voltage side and the positive pole of the DC high voltage side, and the diode string D3 and the diode string D4 are connected in series between the positive pole and the negative pole of the DC low voltage side. Switch S1 and switch S2 are connected in parallel with diode string D2 and diode string D4 respectively. The half-bridge sub-module string and the inductor L are connected in series between the common end of the diode string D1 and the diode string D2 and the common end of the diode string D3 and the diode string D4. Control method: set the on-off state of switch S1 and switch S2 according to the power transmission direction between the DC low-voltage side and the DC high-voltage side; control the charge and discharge states of the half-bridge sub-module strings, and then maintain energy balance when power transmission occurs .

Description

technical field

[0001] The invention relates to a DC / DC converter and belongs to the field of flexible direct current transmission. Background technique

[0002] In recent years, with the development of flexible DC transmission technology, DC transmission projects are changing from multi-terminal DC transmission systems to DC grids with mesh. Just as transformers are to AC grids, DC / DC converters play a vital role in the development of DC grids. At present, there are a large number of DC / DC converter topologies in medium and low voltage applications. However, these topologies cannot be extended to hundreds of kilovolts due to constraints such as device stress, loss, cost, voltage change rate, and filter volume and weight. , hundreds of megawatts.

[0003] Aiming at high-voltage and large-capacity DC / DC power conversion, there have been many reports in recent years. Among them, the isolated DC / DC converter represented by the "face-to-face" modular multilevel DC / DC converte...

Examples

Embodiment

[0037] Embodiment: combine below Figure 1 to Figure 5 This embodiment will be described in detail.

[0038] refer to figure 1 and figure 2 , the DC / DC converter for flexible direct current transmission described in this embodiment includes a diode string D1 to a diode string D4, a half-bridge sub-module string, an inductor L, a switch S1, and a switch S2;

[0039] The circuit structures of the diode strings D1 to D4 are the same, and each diode string includes a plurality of diodes connected in series in forward direction;

[0040] The half-bridge sub-module string includes half-bridge sub-module SM1~half-bridge sub-module SMN, and the circuit structure of the half-bridge sub-module SM1~half-bridge sub-module SMN is the same. For the half-bridge sub-module SM1~half-bridge sub-module SMN, the former The current output terminals are in turn connected to the current input terminals of the latter;

[0041] The anode of the diode string D1 is connected to the anode of the DC ...

technical field

[0001] The invention relates to a DC / DC converter and belongs to the field of flexible direct current transmission. Background technique

[0002] In recent years, with the development of flexible DC transmission technology, DC transmission projects are changing from multi-terminal DC transmission systems to DC grids with mesh. Just as transformers are to AC grids, DC / DC converters play a vital role in the development of DC grids. At present, there are a large number of DC / DC converter topologies in medium and low voltage applications. However, these topologies cannot be extended to hundreds of kilovolts due to constraints such as device stress, loss, cost, voltage change rate, and filter volume and weight. , hundreds of megawatts.

[0003] Aiming at high-voltage and large-capacity DC / DC power conversion, there have been many reports in recent years. Among them, the isolated DC / DC converter represented by the "face-to-face" modular multilevel DC / DC converte...

Examples

Embodiment

[0037] Embodiment: combine below Figure 1 to Figure 5 This embodiment will be described in detail.

[0038] refer to figure 1 and figure 2 , the DC / DC converter for flexible direct current transmission described in this embodiment includes a diode string D1 to a diode string D4, a half-bridge sub-module string, an inductor L, a switch S1, and a switch S2;

[0039] The circuit structures of the diode strings D1 to D4 are the same, and each diode string includes a plurality of diodes connected in series in forward direction;

[0040] The half-bridge sub-module string includes half-bridge sub-module SM1~half-bridge sub-module SMN, and the circuit structure of the half-bridge sub-module SM1~half-bridge sub-module SMN is the same. For the half-bridge sub-module SM1~half-bridge sub-module SMN, the former The current output terminals are in turn connected to the current input terminals of the latter;

[0041] The anode of the diode string D1 is connected to the anode of the DC ...

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