Energy storage device and power system and control method thereof

Patent metadata

Field	Value
Publication number	US-11239663-B2
Application number	US-202117190288-A
Country	US
Kind code	B2
Filing date	Mar 2, 2021
Priority date	Mar 9, 2020
Publication date	Feb 1, 2022
Grant date	Feb 1, 2022

Abstract

An energy storage device for a power system is provided. The energy storage device is electrically connected with a high voltage DC transmission grid. The energy storage device includes at least one energy storage element, at least one bidirectional inverter module, at least one medium frequency transformer and at least one bidirectional AC/DC conversion module. A DC terminal of each bidirectional inverter module is electrically connected with the corresponding energy storage element. A first transmission terminal of each medium frequency transformer is electrically connected with an AC terminal of the corresponding bidirectional inverter module. An AC terminal of each bidirectional AC/DC conversion module is electrically connected with a second transmission terminal of the corresponding medium frequency transformer. A DC terminal of each bidirectional AC/DC conversion module is electrically connected with the high voltage DC transmission grid.

First claim

What is claimed is:

1. An energy storage device for a power system, the energy storage device being electrically connected with a high voltage DC transmission grid, the energy storage device comprising:
at least one energy storage element;
at least one bidirectional inverter module, wherein a DC terminal of each bidirectional inverter module is electrically connected with the corresponding energy storage element;
at least one medium frequency transformer, wherein a first transmission terminal of each medium frequency transformer is electrically connected with an AC terminal of the corresponding bidirectional inverter module; and
at least one bidirectional AC/DC conversion module, wherein an AC terminal of each bidirectional AC/DC conversion module is electrically connected with a second transmission terminal of the corresponding medium frequency transformer, and a DC terminal of each bidirectional AC/DC conversion module is electrically connected with the high voltage DC transmission grid.

2. The energy storage device according to claim 1 , wherein a working frequency of each medium frequency transformer is 400 Hz.

3. The energy storage device according to claim 1 , wherein the power system further comprises a power generator, and the power generator is electrically connected with the high voltage DC transmission grid, wherein when the power generator generates electric energy, the energy storage device is operated in a grid-connected mode, and when the power generator does not generate electric energy, the energy storage device is operated in an off-grid mode and provides auxiliary electric energy to the power generator.

4. The energy storage device according to claim 3 , wherein each bidirectional AC/DC conversion module comprises a modular multilevel converter and a first controller electrically connected with the modular multilevel converter;
wherein when the energy storage device is operated in the grid-connected mode, the first controller controls a switching operation of the modular multilevel converter to adjust a voltage on the second transmission terminal of the medium frequency transformer to a medium frequency high AC voltage, and when the energy storage device is operated in the off-grid mode, the first controller controls the switching operation of the modular multilevel converter to adjust a voltage on a DC terminal of the modular multilevel converter;
wherein a frequency of the medium frequency high AC voltage is equal to a working frequency of the medium frequency transformer.

5. The energy storage device according to claim 4 , wherein when the energy storage device is operated in the grid-connected mode, the first controller performs a control method, which comprises steps of:
(a) adjusting the voltage on the second transmission terminal of the medium frequency transformer according to a set voltage value on the second transmission terminal of the medium frequency transformer, thereby generating a current command;
(b) adjusting a current on the second transmission terminal of the medium frequency transformer according to the current command, thereby generating a control signal; and
(c) generating a pulse width modulation signal according to the control signal, and controlling the switching operation of the modular multilevel converter according to the pulse width modulation signal.

6. The energy storage device according to claim 4 , wherein when the energy storage device is operated in the off-grid mode, the first controller performs a control method, which comprises steps of:
(a) adjusting the voltage on the DC terminal of the modular multilevel converter according to a rated voltage of the high voltage DC transmission grid, thereby generating a current command;
(b) adjusting a current on an AC terminal of the modular multilevel converter according to the current command, thereby generating a control signal; and
(c) generating a pulse width modulation signal according to the control signal, and controlling the switching operation of the modular multilevel converter according to the pulse width modulation signal.

7. The energy storage device according to claim 4 , wherein each bidirectional inverter module comprises an inverter and a second controller electrically connected with the inverter, wherein when the energy storage device is operated in the grid-connected mode, the second controller controls a switching operation of the inverter to adjust a conversion power of the bidirectional inverter module, and when the energy storage device is operated in the off-grid mode, the second controller controls the switching operation of the inverter to adjust a voltage on the AC terminal of the bidirectional inverter module;
wherein a frequency of the voltage on the AC terminal of the bidirectional inverter module is equal to a working frequency of the medium frequency transformer.

8. The energy storage device according to claim 7 , wherein when the energy storage device is operated in the grid-connected mode, the second controller performs a control method, which comprises steps of:
(a) adjusting the conversion power of the bidirectional inverter module according to a target power of the bidirectional inverter module, thereby generating a current command;
(b) adjusting a current on the AC terminal of the bidirectional inverter module according to the current command, thereby generating a control signal; and
(c) generating a pulse width modulation signal according to the control signal, and controlling the switching operation of the inverter according to the pulse width modulation signal.

9. The energy storage device according to claim 7 , wherein when the energy storage device is operated in the off-grid mode, the second controller performs a control method, which comprises steps of:
(a) adjusting the voltage on the AC terminal of the bidirectional inverter module according to a set voltage value on the AC terminal of the bidirectional inverter module, thereby generating a current command;
(b) adjusting a current on the AC terminal of the bidirectional inverter module according to the current command, thereby generating a control signal; and
(c) generating a pulse width modulation signal according to the control signal, and controlling the switching operation of the inverter according to the pulse width modulation signal.

10. The energy storage device according to claim 3 , wherein the second transmission terminal of each medium frequency transformer comprises a plurality of windings, and each bidirectional AC/DC conversion module comprises a plurality of serially-connected converters;
wherein each of the plurality of windings is electrically connected with the corresponding converter, and each of the plurality of converters comprises a switch circuit and a first controller electrically connected with the corresponding switch circuit;
wherein when the energy storage device is operated in the grid-connected mode, each first controller controls a switching operation of the corresponding switch circuit to adjust a power on the corresponding winding of the second transmission terminal of the medium frequency transformer, and when the energy storage device is operated in the off-grid mode, the each first controller controls the switching operation of the corresponding switch circuit to adjust a voltage on a DC side of the corresponding converter.

11. The energy storage device according to claim 10 , wherein when the energy storage device is operated in the grid-connected mode, the each first controller performs a control method, which comprises steps of:
(a) adjusting the power on the corresponding winding of the second transmission terminal of the medium frequency transfor

Assignees

• Delta Electronics Shanghai Co

Inventors

• Chen Li
• Wang Changyong
• Lu Yansong
• Qiu Aibin

Classifications

• H02J7/865

  Battery or charger load switching, e.g. concurrent charging and load supply (H02J7/50 takes precedence) · CPC title

• H02J2101/28

  Wind energy · CPC title

• H02J7/02

  for charging batteries from AC mains by converters · CPC title

• H02J7/34

  Parallel operation in networks using both storage and other DC sources, e.g. providing buffering (H02J7/14 takes precedence) · CPC title

• H02J3/32 Primary

  using batteries or super capacitors with converting means · CPC title