# US 2021/0281183 A1 · High-voltage dc transformation apparatus and power system and control method thereof

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- Number: US 2021/0281183 A1
- Document ID: US20210281183A1
- Status: Published application
- Kind: A1
- Application number: 17/190,718
- Filed: 2021-03-03
- Published: 2021-09-09
- Earliest claimed: 2020-03-09
- Assignees: Delta Electronics (Shanghai) Co., Ltd.
- Applicants: Delta Electronics (Shanghai) Co., Ltd.
- Inventors: Li Chen; Changyong Wang; Yansong Lu; Aibin Qiu
- Web page: https://patentgrep.com/patent/US20210281183A1

## CPC

- H02J 3/36: Arrangements for transfer of electric power between AC networks via high-voltage DC [HVDC] links; Arrangements for transfer of electric power between generators and networks via HVDC links
- H02M 7/483: Converters with outputs that each can have more than two voltages levels
- H02J 3/381: {Dispersed generators}
- H02M 1/007: {Plural converter units in cascade (push-pull DC/DC converters with pre-regulator H02M3/3374; DC-AC converters following a DC-DC stage including a high frequency transformer H02M7/4807; DC-AC converters following a DC-DC conversion stage generating periodically varying voltages H02M7/4826)}
- H02M 3/33569: {having several active switching elements (H02M3/3353 takes precedence)}
- H02M 7/4835: {comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage}
- H02J 3/388: Arrangements for the handling of islanding, e.g. for disconnection or for avoiding the disconnection of power
- H02J 2101/28: Wind energy
- H02J 2105/16: being internal to power sources or power generation plants
- H02M 1/0074: {Plural converter units whose inputs are connected in series}
- Y02E 60/60: Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
- H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P)
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION

## Abstract

A high-voltage DC transformation apparatus, a power system and a control method of the power system. The high-voltage DC transformation apparatus is electrically connected to at least one high-voltage DC power generator. The high-voltage DC transformation apparatus includes at least one bidirectional AC/DC conversion module, at least one first transformer and at least one unidirectional rectifier module. A DC terminal of the bidirectional AC/DC conversion module is electrically connected to the corresponding high-voltage DC power generator. The first transformer includes a first transmission terminal and a second transmission terminal. The first transmission terminal is electrically connected to an AC terminal of the corresponding bidirectional AC/DC conversion module. The unidirectional rectifier module includes an input terminal and an output terminal. The input terminal is electrically connected to the second transmission terminal of the corresponding first transformer, and the output terminal is electrically connected to a high-voltage grid.

## Claims

### Claim 1

A high-voltage DC transformation apparatus, electrically connected to at least one high-voltage DC power generator, comprising:
at least one bidirectional AC/DC conversion module, wherein a DC terminal of the bidirectional AC/DC conversion module is electrically connected to the corresponding high-voltage DC power generator;
at least one first transformer each of that comprises a first transmission terminal and a second transmission terminal, wherein the first transmission terminal is electrically connected to an AC terminal of the corresponding bidirectional AC/DC conversion module; and
at least one unidirectional rectifier module each of that comprises an input terminal and an output terminal, wherein the input terminal is electrically connected to the second transmission terminal of the corresponding first transformer, and the output terminal is electrically connected to a high-voltage grid.

### Claim 2 (depends on 1)

The high-voltage DC transformation apparatus according to claim 1, wherein an operating frequency of the first transformer is larger than 50 Hz.

### Claim 3 (depends on 1)

The high-voltage DC transformation apparatus according to claim 1, wherein the high-voltage DC transformation apparatus comprises a plurality of said bidirectional AC/DC conversion modules and a plurality of said first transformers, the DC terminal of each of the plurality of bidirectional AC/DC conversion modules is electrically connected to the corresponding high-voltage DC power generator, the AC terminal of each of the plurality of bidirectional AC/DC conversion modules is electrically connected to the first transmission terminal of the corresponding first transformer, and the second transmission terminals of the plurality of first transformers are electrically connected together in parallel and then electrically connected to the unidirectional rectifier module.

### Claim 4 (depends on 1)

The high-voltage DC transformation apparatus according to claim 1, wherein the high-voltage DC transformation apparatus comprises a plurality of said bidirectional AC/DC conversion modules, the DC terminal of each of the plurality of bidirectional AC/DC conversion modules is electrically connected to the corresponding high-voltage DC power generator, the AC terminals of the plurality of bidirectional AC/DC conversion modules are electrically connected together in parallel and then electrically connected to the first transmission terminal of the first transformer, and the second transmission terminal of the first transformer is electrically connected to the input terminal of the unidirectional rectifier module.

### Claim 5 (depends on 1)

The high-voltage DC transformation apparatus according to claim 1, wherein the high-voltage DC transformation apparatus comprises a plurality of said bidirectional AC/DC conversion modules, the DC terminal of each of the plurality of bidirectional AC/DC conversion modules is electrically connected to the corresponding high-voltage DC power generator, the first transmission terminal of the first transformer comprises a plurality of windings, each of the plurality of windings is electrically connected to the AC terminal of the corresponding unidirectional rectifier module, and the second transmission terminal of the first transformer is electrically connected to the input terminal of the unidirectional rectifier module.

### Claim 6 (depends on 1)

The high-voltage DC transformation apparatus according to claim 1, wherein the high-voltage DC transformation apparatus comprises a plurality of said bidirectional AC/DC conversion modules, a plurality of said first transformers and a plurality of said unidirectional rectifier modules, the DC terminal of each of the plurality of bidirectional AC/DC conversion modules is electrically connected to the corresponding high-voltage DC power generator, the AC terminal of each of the plurality of bidirectional AC/DC conversion modules is electrically connected to the first transmission terminal of the corresponding first transformer, the second transmission terminal of each of the plurality of first transformers is electrically connected to the input terminal of the corresponding unidirectional rectifier module, and the output terminals of the plurality of unidirectional rectifier modules are electrically connected together in parallel.

### Claim 7 (depends on 1)

The high-voltage DC transformation apparatus according to claim 1, wherein the first transmission terminal of the first transformer comprises a plurality of windings, the bidirectional AC/DC conversion module comprises a plurality of bidirectional AC/DC converters connected in series, each of the plurality of windings is electrically connected to the corresponding bidirectional AC/DC converter, and each of the plurality of bidirectional AC/DC converters comprises a switch circuit and a first controller for controlling the switching operation of the switch circuit to adjust a voltage on a DC side of the bidirectional AC/DC converter.

### Claim 8 (depends on 7)

The high-voltage DC transformation apparatus according to claim 7, wherein the first controller performs a control method comprising steps of:
(a) adjusting the voltage on the DC side of the bidirectional AC/DC converter according to a set voltage value on the DC side of the bidirectional AC/DC converter, and generating a first current command;
(b) adjusting a current on the corresponding winding of the first transmission terminal of the first transformer according to the first current command, and generating a first control signal; and
(c) generating a first PWM signal according to the first control signal, and controlling the switching operation of the switch circuit according to the first PWM signal.

### Claim 9 (depends on 1)

The high-voltage DC transformation apparatus according to claim 1, wherein the bidirectional AC/DC conversion module comprises a multilevel converter and a first controller, and the first controller is electrically connected to the multilevel converter for controlling the switching operation of the multilevel converter, thereby adjusting a voltage on the DC terminal of the bidirectional AC/DC conversion module.

### Claim 10 (depends on 9)

The high-voltage DC transformation apparatus according to claim 9, wherein the first controller performs a control method comprising steps of:
(a) adjusting the voltage on the DC terminal of the bidirectional AC/DC conversion module according to a set voltage value on the DC terminal of the bidirectional AC/DC conversion module, and generating a first current command;
(b) adjusting a current on the AC terminal of the bidirectional AC/DC conversion module according to the first current command, and generating a first control signal; and
(c) generating a first PWM signal according to the first control signal, and controlling the switching operation of the multilevel converter according to the first PWM signal.

### Claim 11 (depends on 9)

The high-voltage DC transformation apparatus according to claim 9, wherein the first controller performs a control method comprising steps of:
(a) adjusting the voltage on the DC terminal of the bidirectional AC/DC conversion module according to a set voltage value on the DC terminal of the bidirectional AC/DC conversion module, and generating a first current command;
(b) adjusting a current on the output terminal of the unidirectional rectifier module according to the first current command, and generating a first control signal; and
(c) generating a first PWM signal according to the first control signal, and controlling the switching operation of the multilevel converter according to the first PWM signal.

### Claim 12 (depends on 9)

The high-voltage DC transformation apparatus according to claim 9, wherein the unidirectional rectifier module comprises a Vienna rectifier and a second controller, and the second controller is electrically connected to the Vienna rectifier for controlling the switching operation of the Vienna rectifier, thereby adjusting a voltage on the input terminal of the unidirectional rectifier module.

### Claim 13 (depends on 12)

The high-voltage DC transformation apparatus according to claim 12, wherein the second controller performs a control method comprising steps of:
(a) adjusting the voltage on the input terminal of the unidirectional rectifier module according to a set voltage value on the input terminal of the unidirectional rectifier module, and generating a second current command;
(b) adjusting a current on the input terminal of the unidirectional rectifier module according to the second current command, and generating a second control signal; and
(c) generating a second PWM signal according to the second control signal, and controlling the switching operation of the Vienna rectifier according to the second PWM signal.

### Claim 14 (depends on 1)

The high-voltage DC transformation apparatus according to claim 1, wherein when the high-voltage DC power generator generates power, the high-voltage DC transformation apparatus enters a grid-connected mode, and when the high-voltage DC power generator stops generating power, the high-voltage DC transformation apparatus enters an off-grid mode.

### Claim 15 (depends on 14)

The high-voltage DC transformation apparatus according to claim 14, further comprising at least one energy storage device electrically connected to the input terminal of the unidirectional rectifier module, wherein when the high-voltage DC transformation apparatus enters the off-grid mode, the at least one energy storage device provides an auxiliary power required by the high-voltage DC power generator.

### Claim 16 (depends on 15)

The high-voltage DC transformation apparatus according to claim 15, wherein the energy storage device comprises at least one energy storage element, at least one bidirectional inverter module and at least one second transformer, a DC terminal of the bidirectional inverter module is electrically connected to the corresponding energy storage element, a first transmission terminal of the second transformer is electrically connected to an AC terminal of the corresponding bidirectional inverter module, and a second transmission terminal of the second transformer is electrically connected to the input terminal of the unidirectional rectifier module;
wherein an operating frequency of the second transformer is the same as an operating frequency of the first transformer.

### Claim 17 (depends on 16)

The high-voltage DC transformation apparatus according to claim 16, wherein the energy storage device comprises a plurality of said energy storage elements and a plurality of said bidirectional inverter modules, the DC terminal of each of the plurality of bidirectional inverter modules is electrically connected to the corresponding energy storage element, the AC terminals of the plurality of bidirectional inverter modules are electrically connected together in parallel and then electrically connected to the first transmission terminal of the second transformer, and the second transmission terminal of the second transformer is electrically connected to the input terminal of the unidirectional rectifier module.

### Claim 18 (depends on 16)

The high-voltage DC transformation apparatus according to claim 16, wherein the energy storage device comprises a plurality of said energy storage elements and a plurality of said bidirectional inverter modules, the DC terminal of each of the plurality of bidirectional inverter modules is electrically connected to the corresponding energy storage element, the first transmission terminal of the second transformer comprises a plurality of windings, each of the plurality of windings is electrically connected to the AC terminal of the corresponding bidirectional inverter module, and the second transmission terminal of the second transformer is electrically connected to the input terminal of the unidirectional rectifier module.

### Claim 19 (depends on 16)

The high-voltage DC transformation apparatus according to claim 16, wherein the bidirectional inverter module further comprises a third controller and an inverter, and when the high-voltage DC transformation apparatus enters the grid-connected mode, the third controller controls the switching operation of the inverter so as to adjust a conversion power of the bidirectional inverter module, and when the high-voltage DC transformation apparatus enters the off-grid mode, the third controller controls the switching operation of the inverter so as to adjust a voltage on the first transmission terminal of the second transformer.

### Claim 20 (depends on 19)

The high-voltage DC transformation apparatus according to claim 19, wherein when the high-voltage DC transformation apparatus enters the grid-connected mode, the third controller performs a control method comprising steps of:
(a) adjusting the conversion power of the bidirectional inverter module according to a target power of the bidirectional inverter module, and generating a third current command;
(b) adjusting a current on the AC terminal of the bidirectional inverter module according to the third current command, and generating a third control signal; and
(c) generating a third PWM signal according to the third control signal, and controlling the switching operation of the inverter according to the third PWM signal.

### Claim 21 (depends on 19)

The high-voltage DC transformation apparatus according to claim 19, wherein when the high-voltage DC transformation apparatus enters the off-grid mode, the third controller performs a control method comprising steps of:
(a) adjusting the voltage on the first transmission terminal of the second transformer according to a set voltage value on the first transmission terminal of the second transformer, and generating a third current command;
(b) adjusting a current on the AC terminal of the bidirectional inverter module according to the third current command, and generating a third control signal; and
(c) generating a third PWM signal according to the third control signal, and controlling the switching operation of the inverter according to the third PWM signal.

### Claim 22 (depends on 19)

The high-voltage DC transformation apparatus according to claim 19, wherein the unidirectional rectifier module further comprises a Vienna rectifier and a second controller, and the second controller is electrically connected to the Vienna rectifier for controlling the switching operation of the Vienna rectifier, thereby adjusting a voltage on the output terminal of the unidirectional rectifier module.

### Claim 23 (depends on 22)

The high-voltage DC transformation apparatus according to claim 22, wherein when the high-voltage DC transformation apparatus enters the off-grid mode, the second controller performs a control method comprising steps of:
(a) adjusting the voltage on the output terminal of the unidirectional rectifier module according to a set voltage value on the output terminal of the unidirectional rectifier module, and generating a second current command;
(b) adjusting a current on the input terminal of the unidirectional rectifier module according to the second current command, and generating a second control signal; and
(c) generating a second PWM signal according to the second control signal, and controlling the switching operation of the Vienna rectifier according to the second PWM signal.

### Claim 24

A power system, comprising:
at least one high-voltage DC power generator; and
a high-voltage DC transformation apparatus, electrically connected to the at least one high-voltage DC power generator, comprising:
at least one bidirectional AC/DC conversion module, wherein a DC terminal of the bidirectional AC/DC conversion module is electrically connected to the corresponding high-voltage DC power generator;
at least one first transformer each of that comprises a first transmission terminal and a second transmission terminal, wherein the first transmission terminal is electrically connected to an AC terminal of the corresponding bidirectional AC/DC conversion module; and
at least one unidirectional rectifier module each of that comprises an input terminal and an output terminal, wherein the input terminal is electrically connected to the second transmission terminal of the corresponding first transformer, and the output terminal is electrically connected to a high-voltage grid.

### Claim 25

A control method for a power system, wherein the power system comprises at least one high-voltage DC power generator and a high-voltage DC transformation apparatus electrically connected to the at least one high-voltage DC power generator, the high-voltage DC transformation apparatus comprises at least one bidirectional AC/DC conversion module, at least one first transformer and at least one unidirectional rectifier module, a DC terminal of the bidirectional AC/DC conversion module is electrically connected to the corresponding high-voltage DC power generator, each of the at least one first transformer comprises a first transmission terminal and a second transmission terminal, the first transmission terminal is electrically connected to an AC terminal of the corresponding bidirectional AC/DC conversion module, each of the at least one unidirectional rectifier module comprises an input terminal and an output terminal, the input terminal is electrically connected to the second transmission terminal of the corresponding first transformer, the output terminal is electrically connected to a high-voltage grid, and the control method comprises steps of:
(a) converting a first DC voltage outputted by the high-voltage DC power generator into a first AC voltage by the bidirectional AC/DC conversion module;
(b) boosting the first AC voltage to a second AC voltage by the first transformer; and
(c) rectifying the second AC voltage by the unidirectional rectifier module to generate a second DC voltage.

### Claim 26 (depends on 25)

The control method according to claim 25, wherein the high-voltage DC transformation apparatus comprises at least one energy storage device electrically connected to the input terminal of the unidirectional rectifier module, the energy storage device comprise an energy storage element, a bidirectional inverter module and a second transformer, and the control method further comprises steps of:
(S1) determining an operating mode of the high-voltage DC transformation apparatus;
(S2) when the high-voltage DC transformation apparatus operating in a grid-connected mode, utilizing the energy storage device to adjust an electric energy outputted by the high-voltage DC power generator;
(S3) when the high-voltage DC transformation apparatus operating in an off-grid mode, utilizing the energy storage device to provide an auxiliary power for the high-voltage DC power generator.

### Claim 27 (depends on 26)

The control method according to claim 26, wherein the step (S2) comprises substeps of:
(S21) determining whether the electric energy provided by the high-voltage DC power generator is larger than an electric energy needed by the high-voltage grid, performing substeps (S22), (S23) and (S24) if the determining result is not satisfied, and performing substeps (S25) and (S26) if the determining result is satisfied;
(S22) converting an energy storage voltage provided by the energy storage element into a third AC voltage by the bidirectional inverter module;
(S23) boosting the third AC voltage to the second AC voltage by the second transformer;
(S24) converting the second AC voltage into a DC voltage by the unidirectional rectifier module, and feeding the DC voltage into the high-voltage grid;
(S25) decreasing the second AC voltage outputted by the first transformer to the third AC voltage by the second transformer; and
(S26) converting the third AC voltage into a charging voltage by the bidirectional inverter module, and charging the energy storage element by the charging voltage,
wherein the step (S3) comprises substeps of:
(S31) converting an energy storage voltage provided by the energy storage element into a third AC voltage by the bidirectional inverter module;
(S32) boosting the third AC voltage the second AC voltage by the second transformer;
(S33) decreasing the second AC voltage to the first AC voltage by the first transformer; and
(S34) converting the first AC voltage into the first DC voltage by the bidirectional AC/DC conversion module, and feeding the first DC voltage into the high-voltage DC transmission grid.