Power balancing device and control method thereof

Abstract

The present application discloses a power balancing device and a control method thereof, belonging to the field of high-power power electronics technology. The power balancing device includes a converter and a control system. The converter includes three phase units, each phase unit includes a filter unit and a submodule connected in series, the submodule includes a power transmission unit, an active balancing unit and a submodule control unit, the power transmission unit and the active balancing unit are connected in parallel; the control system is connected to the submodule control unit in communication. The device adopts a modular design concept, and the active balancing unit and the power transmission unit are integrated and installed in the same submodule, which does not occupy additional space and has a high degree of equipment integration. At the same time, a filter unit is set in each phase unit of the converter, and no additional filter branch is required, which further reduces the equipment footprint and equipment investment, improves utilization, and improves the economy of the system.

Description

Technical Field

[0001] The present application belongs to the field of high-power power electronics technology, and specifically relates to a power balancing device and a control method thereof. Background Art

[0002] When the active power at the load end of the power grid is suddenly lost or the reactive power suddenly changes, the power supply end needs to adjust its power output. Once the power change exceeds the adjustment capability of the power supply end, it will cause the power angle of the power supply end to be unbalanced, and then the frequency and voltage of the power grid will increase, endangering the safety of electrical equipment. In serious cases, it may cause power disconnection, grid decoupling, equipment overvoltage damage and other accidents, causing significant economic losses. In addition, the black start function of the isolated grid also requires a certain amount of adjustable load to cooperate with the power supply to achieve. Therefore, power balancing equipment is usually used in the power grid to achieve active and reactive power regulation to achieve the purpose of power balance.

[0003] Existing power balancing equipment usually uses a combination of active balancing equipment and reactive balancing equipment to achieve decoupling control of active power and reactive power. Among them, active balancing equipment will only be put into short-term use when the active load of the power grid changes suddenly. In order to reduce losses, the equipment is in a locked or shut down state most of the time, and the utilization rate of the equipment is not high; reactive balancing equipment not only needs to compensate for the reactive power and harmonics of the power grid, but also needs to control the reactive power and harmonics brought by the active balancing equipment when it is working. Therefore, the existing power balancing equipment has problems such as multiple electrical branches, high coupling degree of active and reactive control functions, large capacity of reactive compensation equipment and large footprint. Summary of the invention

[0004] Purpose of the invention: The purpose of the present application is to provide a power balancing device to overcome the technical problems existing in the power balancing device of the prior art, such as too many electrical branches, low equipment utilization, high coupling degree between active and reactive control functions, large capacity of reactive compensation equipment and large floor space; another purpose of the present application is to provide a control method for the above-mentioned power balancing device.

[0005] Technical solution: A power balancing device described in this application includes:

[0006] A converter, wherein the converter comprises three phase units, each phase unit comprises a filter unit and a submodule connected in series, the submodule comprises a power transmission unit, an active power balancing unit and a submodule control unit, and the power transmission unit and the active power balancing unit are connected in parallel;

[0007] A control system is communicatively connected with the submodule control unit.

[0008] In some embodiments, the power transmission unit includes a switching device and a DC side capacitor, and the DC side capacitor is connected to the DC side of the full-bridge and / or half-bridge circuit composed of the switching device; the active power balancing unit is connected in parallel with the DC side capacitor.

[0009] In some embodiments, the active power balancing unit includes a resistance unit and a switch unit connected in series.

[0010] In some embodiments, the resistance unit is selected from one or more of a resistor, an electric boiler, and a battery.

[0011] In some embodiments, the switch unit is selected from at least one of a mechanical switch and a power electronic switch.

[0012] In some embodiments, the power electronic switch uses one or more power semiconductor devices with a turn-off function.

[0013] In some embodiments, the filtering unit includes a reactor.

[0014] In some embodiments, the converter is a two-level converter or a multi-level converter.

[0015] In some embodiments, the inverter is equipped with a cooling device; the control system is connected to the submodule control unit via optical fiber communication.

[0016] In some embodiments, the submodule control unit is disposed in the power transmission unit and / or in the active power balancing unit.

[0017] Accordingly, the present application provides a control method for the power balancing device described above, comprising:

[0018] Controlling the DC side capacitor voltage of the power transmission unit to a target value;

[0019] According to the control target of active power or grid frequency, controlling the power balancing device to achieve active power regulation;

[0020] According to any one or more control targets of reactive power, grid voltage, power factor, and harmonics, the power balancing device is controlled to achieve reactive power regulation.

[0021] In some embodiments, the active power regulation is achieved by controlling the on or off of a switch unit of the active balancing unit; or, the active power regulation is achieved by adjusting a target value of the DC link capacitor voltage.

[0022] In some embodiments, the reactive power regulation is achieved by controlling a switching device of the power transmission unit.

[0023] In some embodiments, the converter is started by the control system, and a control command is issued by the control system to achieve:

[0024] The DC side capacitor voltage of the power transmission unit is controlled at a target value, the active power is regulated, and the reactive power is regulated.

[0025] Beneficial effects: Compared with the prior art, the power balancing device of the present application includes a converter and a control system. The converter includes three phase units, each phase unit includes a filter unit and a submodule connected in series, the submodule includes a power transmission unit, an active balancing unit and a submodule control unit, the power transmission unit and the active balancing unit are connected in parallel; the control system is communicatively connected with the submodule control unit. It can be understood that the power balancing device adopts a modular design concept, and the active balancing unit and the power transmission unit are integrated and installed in the same submodule, which does not occupy additional space and has a high degree of equipment integration. At the same time, a filter unit is set in each phase unit of the converter, and no additional filter branch is required, which further reduces the equipment footprint and equipment investment, improves utilization, and improves the economy of the system.

[0026] Compared with the prior art, the control method of the power balancing device of the present application includes controlling the DC side capacitor voltage of the power transmission unit at a target value; controlling the power balancing device to achieve active power regulation according to the control target of active power or grid frequency; and controlling the power balancing device to achieve reactive power regulation according to any one or more control targets of reactive power, grid voltage, power factor, and harmonics. It can be understood that the control method can quickly and effectively achieve independent decoupling control of active power and reactive power and achieve smooth control with small harmonics, reduce coupling, and achieve grid frequency and voltage regulation, power oscillation suppression, reactive compensation, harmonic suppression and other functions, effectively solve the problem of power imbalance in the grid, improve the stability of the power system and improve the quality of power. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 The structural intention of the power balancing device provided in the embodiment of the present application;

[0029] Figure 2 Schematic diagram of the unit structure of a power balancing device using power electronic switches and resistors in an embodiment of the present application. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0031] Since electric energy is produced and consumed immediately and cannot be stored on a large scale, the power grid needs to maintain a real-time balance between active power and reactive power. The problem of power balance will be more prominent due to the weak power supply capacity and large load fluctuations of power grids or isolated grids located in remote areas. At the same time, with the continuous increase in the transmission capacity of offshore wind power through flexible direct current transmission, once wind power fluctuations or wind turbines are disconnected from the grid, the power balance of the system must be maintained to ensure the safety of the entire regional power grid. The applicant found that the existing power balancing equipment has multiple electrical branches, high coupling between active and reactive control functions, large capacity of reactive compensation equipment and large footprint.

[0032] In view of this, an embodiment of the present application provides a power balancing device, which includes a converter and a control system. The converter includes three phase units, and each phase unit can be composed of a filter unit and at least one submodule connected in series. The filter unit includes at least one reactor, and the submodule includes a power transmission unit, an active balancing unit and a submodule control unit. The power transmission unit is composed of a switching device and a DC side capacitor. At least one active balancing unit is connected in parallel at both ends of the DC side capacitor of the power transmission unit. The active balancing unit includes a resistor unit and a switch unit, and the active balancing unit is composed of at least one resistor unit and at least one switch unit connected in series.

[0033] For details, please refer to Figure 1 As shown, Figure 1 The preferred embodiment structure of the present application is shown in the figure. In this embodiment, the power balancing device includes a three-phase modular multilevel converter M1 and a control system M2. The converter M1 includes three phase units, each of which includes a bridge arm, which is composed of three bridge arms in total and is star-connected. Each bridge arm is composed of a filter reactor L and N sub-modules SM in series. Each sub-module SM includes a power transmission unit X1, an active balancing unit X2 and a sub-module control unit X3, wherein the power transmission unit X1 includes switching devices S1, S2, S3, S4 and a DC side capacitor C1, the switching devices S1, S2, S3, S4 form a full-bridge circuit, the DC side capacitor C1 is connected to the DC side of the full-bridge circuit, and the active balancing unit X2 includes a resistor unit R1, a switching device S5 and a diode D5, please refer to Figure 2The switch device S5 and the diode D5 shown in the figure form a switch unit, and the active power balancing unit X2 is connected in parallel to both ends of the DC side capacitor C1 of the power transmission unit X1.

[0034] In this embodiment, the converter may be a two-level converter in addition to a multi-level converter.

[0035] Please combine Figure 2 As shown, the active balancing unit includes a resistor R, a switch tube S and a diode D. One end of the switch tube S is connected to the positive electrode of the DC side capacitor of the power transmission unit in the submodule, the other end of the switch tube S is connected to one end of the resistor R, and the other end of the resistor R is connected to the negative electrode of the DC side capacitor of the power transmission unit in the submodule.

[0036] In this embodiment, the filter unit may be a filter reactor L, or may be a cascade of multiple filter reactors L, or may be a series-parallel combination of a filter reactor L and a capacitor.

[0037] In this embodiment, the resistance unit R1 is selected from one or more of a resistor, an electric boiler, and a battery, and the resistance unit R1 can be a resistor, or multiple resistors, electric boilers including resistors, electric boilers, and batteries connected in series, in parallel, or in a series-parallel combination cascade manner, and is not limited to an actual resistor.

[0038] In this embodiment, the switch unit composed of the switch device S5 and the diode D5 can be formed by any one of a mechanical switch and a power electronic switch, or a combination of the two.

[0039] Among them, for power electronic switches, one or more power semiconductor devices with a turn-off function can be used, such as: IGBT (Insulated Gate Bipolar Transistor), IGCT (Integrated Gate-Commutated Thyristor), GTO (Gate Turn-Off Switch), MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), etc.

[0040] Similarly, in this embodiment, the switch unit may be a switch tube and a diode, or may be a plurality of mechanical switches or power electronic switches connected in series, in parallel, or in a cascaded manner.

[0041] In this embodiment, a certain current will flow through the power semiconductor device of the power balancing device, so a corresponding cooling device needs to be configured. Preferably, water cooling can be used for heat dissipation.

[0042] In this embodiment, the control system M1 of the power balancing device communicates with the submodule control unit X3 centrally arranged in the power transmission unit X1 through optical fiber to transmit control command signals and status monitoring signals.

[0043] In addition, the submodule control unit X3 may also be arranged in the power transmission unit X1 and the active power balancing unit X2 respectively, or may be centrally arranged in the active power balancing unit X2.

[0044] In the embodiment of the present application, the parallel connection of the active balancing unit belongs to the parallel connection on the DC side of the submodule of the converter. Such beneficial effects are: (1) The power balancing device can adopt a modular design concept, and the active balancing unit is directly integrated with the power transmission unit and installed in the same submodule, without occupying additional space. This advantage is crucial in certain occasions where space is tight. (2) The active balancing unit does not need to obtain energy independently. The control circuit of the mechanical switch or switch tube therein can share the energy circuit with the power transmission unit in the submodule, and can directly obtain energy from the DC side capacitor of the power transmission unit. (3) The active balancing unit does not need to be equipped with an independent cooling device, and can share the cooling device with the submodule, further reducing the size and cost.

[0045] Accordingly, the embodiment of the present application further provides a control method for the above-mentioned power balancing device, and the control method may include the following steps:

[0046] (1) The converter of the power balancing device is started by the control system, and the DC side capacitor voltage u of each sub-module power transmission unit is set to dc Controlled at target value u dcref .

[0047] (2) The control system is based on the active power control target P ref Or the control target of the grid frequency f ref , active power regulation is achieved by sending control commands through optical fiber.

[0048] (3) The control system is based on the reactive power control target Q ref Or the control target of the grid voltage U acref Or the control target of power factor P Fref Or the control target of harmonics I href , U href , reactive power regulation is achieved by sending control commands through optical fiber.

[0049] Furthermore, in step (2), active power regulation can be achieved by controlling the closing and opening of a mechanical switch in the active balancing unit, or by controlling the opening and closing of a power electronic switch in the active balancing unit, or by controlling the target voltage value u of the DC side capacitor of the power transmission unit. dcref Realize active power regulation.

[0050] Furthermore, in step (3), reactive power regulation can be achieved by controlling the on and off of the switch devices S1, S2, S3, and S4 of the power transmission unit.

[0051] It should be further explained that, in the description of the embodiments of the present application, the so-called cascade includes connection modes such as series connection, parallel connection and combination of series and parallel connection.

[0052] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0053] The power balancing device and the control method thereof provided in the embodiments of the present application are introduced in detail above, and the principles and implementation methods of the present application are explained by using specific examples. The description of the above embodiments is only used to help understand the technical solution and core idea of ​​the present application; ordinary technicians in this field should understand that: they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some of the technical features therein with equivalents; and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solution of the embodiments of the present application.

Claims

1. A power balancing device, characterized in that: include: A converter, wherein the converter comprises three phase units, each phase unit comprises a filter unit and a submodule connected in series, the submodule comprises a power transmission unit, an active power balancing unit and a submodule control unit, the power transmission unit and the active power balancing unit are connected in parallel; the power transmission unit comprises a DC side capacitor, the active power balancing unit is connected in parallel with the DC side capacitor, and the active power balancing unit comprises a resistance unit and a switch unit connected in series; A control system, wherein the control system is communicatively connected with the submodule control unit, and the control system is configured to achieve active power regulation by controlling the on or off of the switch unit of the active balancing unit, or to achieve the active power regulation by adjusting the target value of the DC side capacitor voltage.

2. The power balancing device according to claim 1, characterized in that: The power transmission unit further comprises a switching device, and the DC side capacitor is connected to the DC side of a full-bridge or half-bridge circuit formed by the switching device.

3. The power balancing device according to claim 1, characterized in that: The resistance unit is selected from one or more of a resistor, an electric boiler, and a battery.

4. The power balancing device according to claim 1, characterized in that: The switch unit is selected from at least one of a mechanical switch and a power electronic switch.

5. The power balancing device according to claim 4, characterized in that: The power electronic switch adopts one or more power semiconductor devices with a turn-off function.

6. The power balancing device according to claim 1, characterized in that: The filtering unit includes a reactor.

7. The power balancing device according to claim 1, characterized in that: The converter is a two-level converter or a multi-level converter.

8. The power balancing device according to claim 1, characterized in that: The inverter is equipped with a cooling device; the control system is connected to the submodule control unit via optical fiber communication.

9. The power balancing device according to claim 1, characterized in that: The submodule control unit is arranged in the power transmission unit and / or in the active power balancing unit.

10. A control method for a power balancing device according to any one of claims 1 to 9, characterized in that: include: Controlling the DC side capacitor voltage of the power transmission unit to a target value; According to the control target of active power or grid frequency, controlling the power balancing device to achieve active power regulation; According to any one or more control targets of reactive power, grid voltage, power factor, and harmonics, the power balancing device is controlled to achieve reactive power regulation.

11. The control method of the power balancing device according to claim 10, characterized in that: The active power regulation is achieved by controlling the on or off of the switch unit of the active balancing unit; or, the active power regulation is achieved by adjusting the target value of the DC link capacitor voltage.

12. The control method of the power balancing device according to claim 10, characterized in that: The reactive power regulation is achieved by controlling the switching devices of the power transmission unit.

13. The control method of the power balancing device according to claim 10, characterized in that: The converter is started by the control system, and a control command is issued by the control system to achieve: The DC side capacitor voltage of the power transmission unit is controlled at a target value, the active power is regulated, and the reactive power is regulated.

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