CN-122001221-A - DC transformer, control method thereof and DC power grid system

Abstract

The application provides a direct-current transformer, a control method thereof and a direct-current power grid system. The direct current transformer comprises an inversion module, a transformation module and a rectification module. The inverter module comprises a current source type converter and a voltage source type converter which are connected in parallel. The current source type converter is used for converting the first direct current into the first alternating current. The voltage source type converter is used for stabilizing the first alternating current. The transformation module is used for transforming the voltage class of the first alternating current to obtain a second alternating current. The rectification module is used for converting the second alternating current into the second direct current and outputting the second direct current. Compared with a direct-current transformer with an inverter module fully adopting a voltage source type converter, the direct-current transformer provided by the application has the advantages of simple topological structure and low cost. The direct-current transformer provided by the application can be used for renewable energy collection and delivery scenes, and can meet the technical requirements of high transformation ratio, high voltage and large capacity.

Inventors

• GAO CHONG
• WEI CHENYANG
• WU YILIN
• LIN ZHIGUANG
• CHEN KAILONG
• TANG GUANGFU

Assignees

• 中国电力科学研究院有限公司
• 国网智能电网研究院有限公司

Dates

Publication Date

20260508

Application Date

20241101

Claims (15)

1. 1. The direct current transformer is characterized by comprising an inversion module, a transformation module and a rectification module, wherein the inversion module comprises a current source type converter and a voltage source type converter which are connected in parallel; the current source type converter is used for converting a first direct current into a first alternating current; The voltage source type converter is used for stabilizing the first alternating current; The transformation module is used for transforming the voltage level of the first alternating current to obtain a second alternating current; the rectification module is used for converting the second alternating current into a second direct current and outputting the second direct current.
2. 2. The direct current transformer according to claim 1, wherein the inverter module comprises one or more current source type converters, the current source type converters being three-phase current source type converters.
3. 3. The direct current transformer according to claim 1, wherein the inverter module comprises 3N current source type converters, each of the 3N current source type converters being a single-phase current source type converter.
4. 4. The dc transformer of claim 2 wherein the three-phase current source converter employs a three-phase H-bridge topology.
5. 5. The dc transformer of claim 4, wherein each leg in the three-phase current source converter is a series leg or a hybrid leg.
6. 6. A dc transformer according to claim 3, characterized in that the single-phase current source converter comprises a single-phase H-bridge topology.
7. 7. The dc transformer of claim 6, wherein each leg in the single-phase current source converter is a series leg or a hybrid leg.
8. 8. The dc transformer of claim 5 or 7, wherein the series leg comprises a plurality of series connected gate commutated thyristors.
9. 9. The direct current transformer according to claim 5 or 7, characterized in that the hybrid leg comprises a main leg, an auxiliary leg and a lightning arrester in parallel.
10. 10. The direct current transformer of claim 9, wherein the main bridge arm comprises a controllable reactor, a first branch and a single-phase full bridge unit which are sequentially connected in series, wherein the first branch comprises a plurality of thyristors which are connected in series, the single-phase full bridge unit comprises a first insulated gate bipolar transistor, a second insulated gate bipolar transistor, a third insulated gate bipolar transistor, a fourth insulated gate bipolar transistor and a commutation capacitor, the collectors of the first insulated gate bipolar transistor and the third insulated gate bipolar transistor are connected with the first branch, the emitters of the first insulated gate bipolar transistor and the collectors of the second insulated gate bipolar transistor are connected with the positive electrode of the commutation capacitor, the emitters of the third insulated gate bipolar transistor and the collectors of the fourth insulated gate bipolar transistor are connected with the negative electrode of the commutation capacitor, and the emitters of the second insulated gate bipolar transistor and the fourth insulated gate bipolar transistor are connected with the negative electrode of the commutation capacitor.
11. 11. The direct current transformer of claim 9 or 10, wherein the auxiliary leg comprises a second leg and a third leg in series, wherein the second leg comprises a plurality of fifth insulated gate bipolar transistors in series, and the third leg comprises a plurality of first diodes in series.
12. 12. A dc transformer according to claim 3, characterized in that the dc transformer comprises three transformation modules; The first windings of the three voltage transformation modules are connected in a star shape and are all connected with the voltage source type converter; the second windings of the three voltage transformation modules are respectively correspondingly connected with a first current source type converter, a second current source type converter and a third current source type converter in the 3N current source type converters; and the third windings of the three voltage transformation modules are connected in a star shape and are connected with the rectification modules.
13. 13. The direct current transformer of claim 1, wherein the rectifying module adopts a three-phase six-pulse topology, and wherein each leg of the three-phase six-pulse topology comprises a plurality of second diodes connected in series.
14. 14. A direct current network system comprising a direct current transformer according to any one of claims 1 to 13.
15. 15. A control method of a dc transformer, comprising: The method comprises the steps of controlling a current source type converter in a constant direct current voltage control mode to enable the current source type converter to convert first direct current into first alternating current; Controlling a voltage source type converter in a voltage-frequency control mode to enable the voltage source type converter to stabilize the first alternating current; transforming the voltage level of the first alternating current through a transformation module to obtain a second alternating current; And converting the second alternating current into a second direct current through a rectifying module and outputting the second direct current.

Description

DC transformer, control method thereof and DC power grid system Technical Field The application relates to the technical field of direct current power grids, in particular to a direct current transformer, a control method thereof and a direct current power grid system. Background Compared with the traditional alternating current transmission, the direct current power grid and the direct current transmission technology have the advantages of long transmission distance, large transmission capacity and the like. The voltage source type converter is used as core equipment of a direct current power grid system, and has the advantages of being flexible and controllable and adapting to a weak power grid. Therefore, the voltage source type converter plays an important role in renewable energy grid-connected and output scenes. In a large-scale renewable energy farm aggregate delivery scenario, a direct current grid system may transmit the renewable energy farm's electrical energy to the grid (i.e., forward transmission of power). In situations where grid feeding is required for renewable energy sites, load balancing, etc., the dc grid system may also transfer power from the grid to the renewable energy sites (i.e., reverse transfer of power). The direct current transformer is used as a key power control device in a renewable energy station collecting and sending scene, and the technical requirement of high-power transmission exists. However, in the dc transformer provided in the related art, the inverter module employs a voltage source type converter (voltage source converter, VSC). Because of the large number of all-control devices in the VSC, the whole DC transformer has a complex topological structure and high cost. Disclosure of Invention In order to solve the problems of complex topological structure and high cost in the prior art, the application provides a direct current transformer which can comprise an inversion module, a transformation module and a rectification module. The inverter module comprises a current source type converter and a voltage source type converter which are connected in parallel. The current source type converter is used for converting the first direct current into the first alternating current. The voltage source type converter is used for stabilizing the first alternating current. The transformation module is used for transforming the voltage class of the first alternating current to obtain the second alternating current. The rectification module is used for converting the second alternating current into the second direct current and outputting the second direct current. In some possible implementations, the inverter module includes one or more current source converters. The current source type converter is a three-phase current source type converter. In other possible implementations, the inverter module includes 3N current source converters. Each of the 3N current source converters is a single-phase current source converter. In one example, a three-phase current source converter employs a three-phase H-bridge topology. Each bridge arm in the three-phase current source type converter adopts a series bridge arm or a mixed bridge arm. Optionally, the single-phase current source converter comprises a single-phase H-bridge topology. Each bridge arm in the single-phase current source type converter adopts a series bridge arm or a mixed bridge arm. Illustratively, the series leg includes a plurality of series connected gate commutated thyristors. The hybrid bridge arm comprises a main bridge arm, an auxiliary bridge arm and a lightning arrester which are connected in parallel. The main bridge arm comprises a controllable reactor, a first branch and a single-phase full-bridge unit which are sequentially connected in series. Wherein the first branch comprises a plurality of thyristors connected in series. The single-phase full-bridge unit comprises a first insulated gate bipolar transistor, a second insulated gate bipolar transistor, a third insulated gate bipolar transistor, a fourth insulated gate bipolar transistor and a commutation capacitor. The collectors of the first insulated gate bipolar transistor and the third insulated gate bipolar transistor are connected with the first branch, the emitter of the first insulated gate bipolar transistor and the collector of the second insulated gate bipolar transistor are connected with the positive electrode of the phase-change capacitor, the emitter of the third insulated gate bipolar transistor and the collector of the fourth insulated gate bipolar transistor are connected with the negative electrode of the phase-change capacitor, and the emitters of the second insulated gate bipolar transistor and the fourth insulated gate bipolar transistor are connected. The auxiliary bridge arm comprises a second branch and a third branch which are connected in series. The second branch comprises a plurality of fifth insulated gate bipolar transistors conne