Flexible loop closing device with voltage sag treatment function and control method

Abstract

The invention discloses a flexible loop closing device with a voltage sag treatment function and a control method, the flexible loop closing device comprises a series connection of a three-phase current conversion chain and a three-phase high-speed switch, one end of the series connection is connected with a first alternating current system, and the other end is connected with a second alternating current system; wherein a connection load is led out from a connection point of the three-phase commutation chain and the three-phase high-speed switch; each phase of current conversion chain in the three-phase current conversion chain comprises N sub-modules, and the alternating current ends of the N sub-modules are connected in series; the energy supply unit provides energy for the sub-modules; the three-phase high-speed switch is a mechanical switch or a solid-state switch composed of a power semiconductor device. The system is applied to a dual-power-supply hand-in-hand power supply mode, the device can adjust the power flow when the power grid voltage is normal, and the device can be switched to a load power supply mode when the power grid voltage drops; the system has the functions of voltage sag and power flow regulation, and is low in cost and flexible in configuration.

Description

Technical Field

[0001] The invention belongs to the field of power electronic power conversion, and in particular relates to a flexible loop closing device with voltage sag control function and a control method. Background Art

[0002] The voltage sag problem is an increasingly concerned power quality problem. The existing distribution network system adopts a hand-in-hand power supply method, which can avoid complete power outage of the load to a certain extent. However, when the system voltage sags, the voltage-sensitive load will still be affected. To fundamentally solve this problem, it is necessary to add a voltage sag compensation device. The compensation device is connected in series between the power supply and the load to ensure the reliability of the user's power supply. When a voltage sag occurs, the voltage of the sensitive load is maintained unchanged during the fault. The existing disadvantages of traditional compensation devices mainly include the following: (1) The compensation device is usually installed close to the load and adopts a decentralized installation method. When the sensitive load is decentralized, the installation is difficult and the operation and maintenance are difficult; (2) The current voltage sag compensation device is divided into two types: with energy storage and without energy storage. The non-energy storage method is small in size and low in cost, but it cannot achieve the compensation effect when the grid voltage drops deeply. The energy storage compensation device occupies a large area, has high cost, and is difficult to be decentralized and installed on the user load side. On the other hand, in the prior art, a flexible loop device is used to connect the power supplies on both sides. By adjusting the output voltage of the device, power transmission control can be achieved. This solution can achieve power flow regulation, but cannot achieve voltage sag control.

[0003] Therefore, it is necessary to study low-cost comprehensive power quality management solutions that can achieve power flow control and voltage sag management without adding high-cost energy storage units. Summary of the invention

[0004] In response to the above technical problems, the technical problem to be solved by the present invention is to provide a low-cost flexible closed-loop device system with voltage sag control function, which is applied to the hand-in-hand power supply mode of dual power supply. When the grid voltage is normal, the device can adjust the power flow. When the grid voltage drops, it can switch to the load power supply mode; at the same time, it has the functions of voltage sag and power flow regulation.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] On the one hand, the present invention discloses a flexible loop closing device with voltage sag control function;

[0007] The flexible loop closing device comprises a series connection of a three-phase commutation chain and a three-phase high-speed switch, one end of the series connection is connected to a first AC system, and the other end is connected to a second AC system, wherein a connection load is led out from a connection point between the three-phase commutation chain and the three-phase high-speed switch;

[0008] Each phase of the three-phase commutation chain includes N sub-modules, the AC ends of the N sub-modules are connected in series, and N is an integer greater than or equal to 1; the sub-module is an H-bridge circuit composed of four groups of power semiconductor devices and a DC capacitor; the DC capacitor of the sub-module is connected to an energy supply unit, and the energy supply unit provides energy for the sub-module.

[0009] More preferably,

[0010] The three-phase high-speed switch is a mechanical switch or a solid-state switch composed of power semiconductor devices.

[0011] More preferably,

[0012] The solid-state switch is composed of a reverse-parallel thyristor valve string, and the thyristor valve string includes at least one pair of reverse-parallel thyristors.

[0013] More preferably,

[0014] The energy supply unit includes a multi-winding transformer and 3N rectifier units, the primary side of the multi-winding transformer is connected to the first AC system or the second AC system; the multi-winding transformer includes a 3-phase primary winding and 3N secondary windings, each secondary winding is connected to the two ends of the DC capacitor of the corresponding sub-module through a rectifier unit, the secondary winding is connected to the input end of the rectifier unit, and the output DC end of the rectifier unit is connected to the DC capacitor of the sub-module.

[0015] More preferably,

[0016] The rectifier unit is a three-phase half-bridge rectifier circuit composed of 6 groups of power semiconductor devices or a full-bridge rectifier circuit composed of 4 groups of power semiconductor devices.

[0017] More preferably,

[0018] The load is a sensitive load, and the sensitive load will operate abnormally when the voltage temporarily drops.

[0019] More preferably,

[0020] A bypass switch is also connected in parallel to the AC end of each submodule.

[0021] More preferably,

[0022] The three-phase commutation chain is also connected in series with a three-phase reactor.

[0023] On the other hand, the present invention further discloses an interconnection mode control method based on the flexible loop closing device with voltage sag control function, and the interconnection mode control method comprises the following steps:

[0024] Step 1: When it is detected that the voltage of the first AC system and the voltage of the second AC system are both within the voltage and phase angle range that meet the closing loop requirements, close the three-phase high-speed switch;

[0025] Step 2: Start the energy supply unit to charge the DC capacitor of the submodule;

[0026] Step 3: Unlock the power semiconductor devices in the three-phase commutation chain module;

[0027] Step 4: According to the interconnection mode power command, adjust the output voltage of the three-phase commutation chain so that the power flowing through the flexible closing device follows the command value, completing the closing operation of the two-terminal AC system.

[0028] Further preferably, the control method further comprises:

[0029] Step 5: Real-time detection of the AC system voltage at both ends of the closing device. When it is detected that the AC system voltage connected to the three-phase high-speed switch drops, the process proceeds to step 6; when it is detected that the AC system voltage connected to the three-phase commutation chain drops, the process proceeds to step 9;

[0030] Step 6: Lock the power semiconductor devices in the three-phase commutation chain module and disconnect the three-phase high-speed switch;

[0031] Step 7: Re-unlock the power semiconductor devices in the three-phase commutation chain module;

[0032] Step 8: Adjust the output voltage of the three-phase commutation chain to stabilize the voltage on the load side;

[0033] Step 9: Keep the three-phase high-speed switch in a closed state and lock the power semiconductor devices in the three-phase commutation chain module.

[0034] Compared with the prior art, the flexible loop closing device and control method with voltage sag control function described in the present invention have the following technical effects:

[0035] 1) The technical solution proposed in the present invention can be applied to the hand-in-hand ring network power supply method widely used in the distribution network system: "Hand-in-hand" ring network power supply refers to the two or more feedback lines of different busbars in different substations or the same substation, which are connected to each other into a loop for power supply. The device of the present invention is installed in series between two different power sources, which can be a feeder or a bus tie. The device of the present invention provides three ports, two ends of which are connected to different power sources, and one end is connected to an important load. The device contains two parts, a three-phase commutation chain and a high-speed switch. The loads arranged between the two can be included in the protection range, and the configuration method is flexible.

[0036] 2) When the grid voltage is normal, the device of the present invention can act as a flexible loop closing device to maintain the high-speed switch in a closed state, and use the three-phase commutation chain to adjust the power flow, which can be used to balance the load between two substations.

[0037] 3) The device of the present invention utilizes dual power supplies to support each other, eliminating the need for energy storage devices, taking up little space, and having low costs. The three-phase commutation chain and the high-speed switch are mutually redundant, and a single unit failure will not cause the load to lose power. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the structure of the flexible loop closing device with voltage sag control function of the present invention;

[0039] Figure 2 is a schematic diagram of a solid-state switch composed of a thyristor valve string;

[0040] Figure 3 Schematic diagram of the functional unit structure of the submodules and corresponding connections. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without creative work are all within the scope of protection of the present invention.

[0042] like Figure 1 As shown, the present invention provides a flexible loop-closing device with voltage sag control function. The flexible loop-closing device includes a series connection of a three-phase commutation chain 1 and a three-phase high-speed switch 2, one end of the series connection is connected to a first AC system S1, and the other end is connected to a second AC system S2, wherein a connection load 3 is led out from a connection point between the three-phase commutation chain and the three-phase high-speed switch; each phase commutation chain in the three-phase commutation chain includes N submodules 4, and the AC ends of the N submodules are connected in series, where N is an integer greater than or equal to 1; the submodule is an H-bridge circuit composed of four groups of power semiconductor devices and DC capacitors; the DC capacitor of the submodule is connected to an energy supply unit, and the energy supply unit provides energy for the submodule; the three-phase high-speed switch 2 is a mechanical switch or a solid-state switch composed of power semiconductor devices.

[0043] Among them: Figure 2 As shown, the solid-state switch is composed of a reverse-parallel thyristor valve string, and the thyristor valve string includes at least one thyristor.

[0044] Wherein: the energy supply unit includes a multi-winding transformer 5 and 3N rectifier units 6, the primary side of the multi-winding transformer is connected to the first AC system or the second AC system, and includes 3N secondary windings, the secondary windings are connected to the input end of the rectifier unit, and the output DC end of the rectifier unit is connected to the DC capacitor of the sub-module.

[0045] Wherein, the rectifier unit is a three-phase half-bridge rectifier circuit composed of 6 groups of power semiconductor devices or a full-bridge rectifier circuit composed of 4 groups of power semiconductor devices. Figure 3 The embodiment is a three-phase half-bridge rectifier current composed of 6 groups of diodes.

[0046] The load is a sensitive load, which will operate abnormally when the voltage drops temporarily.

[0047] Wherein, the AC end of the submodule is also connected in parallel with a bypass switch 7, such as Figure 3 shown.

[0048] Among them: Figure 1 As shown, the three-phase commutation chain is also connected in series with a three-phase reactor 8.

[0049] The embodiment of the present invention further provides an interconnection mode control method of the flexible loop closing device with voltage sag control function, and the interconnection mode control method comprises the following steps:

[0050] Step 1: When it is detected that the voltage of the first AC system and the voltage of the second AC system are both within the voltage and phase angle range that meet the closing loop requirements, close the three-phase high-speed switch;

[0051] Step 2: Start the energy supply unit to charge the DC capacitor of the submodule;

[0052] Step 3: Unlock the power semiconductor devices in the three-phase commutation chain module;

[0053] Step 4: According to the interconnection mode power command, the output voltage of the three-phase commutation chain is adjusted so that the power flowing through the flexible closing device follows the command value, thereby completing the closing operation of the AC system at both ends;

[0054] Step 5: Real-time detection of the AC system voltage at both ends of the closing device. When it is detected that the AC system voltage connected to the three-phase high-speed switch drops, the process proceeds to step 6; when it is detected that the AC system voltage connected to the three-phase commutation chain drops, the process proceeds to step 9;

[0055] Step 6: Lock the power semiconductor devices in the three-phase commutation chain module and disconnect the three-phase high-speed switch;

[0056] Step 7: Re-unlock the power semiconductor devices in the three-phase commutation chain module;

[0057] Step 8: Adjust the output voltage of the three-phase commutation chain to stabilize the voltage on the load side;

[0058] Step 9: Keep the three-phase high-speed switch in a closed state and lock the power semiconductor devices in the three-phase commutation chain module.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A flexible loop closing device with voltage sag control function, characterized in that: The flexible loop closing device comprises a series connection of a three-phase commutation chain and a three-phase high-speed switch, one end of the series connection is connected to a first AC system, and the other end is connected to a second AC system, wherein a connection load is led out from a connection point between the three-phase commutation chain and the three-phase high-speed switch; Each phase of the three-phase commutation chain includes N sub-modules, the AC ends of the N sub-modules are connected in series, and N is an integer greater than or equal to 1; the sub-module is an H-bridge circuit composed of four groups of power semiconductor devices and a DC capacitor; the DC capacitor of the sub-module is connected to an energy supply unit, and the energy supply unit provides energy for the sub-module.

2. The flexible loop closing device with voltage sag control function according to claim 1 is characterized in that: The three-phase high-speed switch is a mechanical switch or a solid-state switch composed of power semiconductor devices.

3. The flexible loop closing device with voltage sag control function according to claim 2 is characterized in that: The solid-state switch is composed of a reverse-parallel thyristor valve string, and the thyristor valve string includes at least one pair of reverse-parallel thyristors.

4. The flexible loop closing device with voltage sag control function according to claim 1 is characterized in that: The energy supply unit includes a multi-winding transformer and 3N rectifier units, the primary side of the multi-winding transformer is connected to the first AC system or the second AC system; the multi-winding transformer includes a 3-phase primary winding and 3N secondary windings, each secondary winding is connected to the two ends of the DC capacitor of the corresponding sub-module through a rectifier unit, the secondary winding is connected to the input end of the rectifier unit, and the output DC end of the rectifier unit is connected to the DC capacitor of the sub-module.

5. The flexible loop closing device with voltage sag control function according to claim 4 is characterized in that: The rectifier unit is a three-phase half-bridge rectifier circuit composed of 6 groups of power semiconductor devices or a full-bridge rectifier circuit composed of 4 groups of power semiconductor devices.

6. The flexible loop closing device with voltage sag control function according to claim 1 is characterized in that: The load is a sensitive load, and the sensitive load will operate abnormally when the voltage temporarily drops.

7. The flexible loop closing device with voltage sag control function according to claim 1 is characterized in that: A bypass switch is also connected in parallel to the AC end of each submodule.

8. The flexible loop closing device with voltage sag control function according to claim 1 is characterized in that: The three-phase commutation chain is also connected in series with a three-phase reactor.

9. A method for controlling interconnection modes of a flexible loop-closing device with voltage sag control function according to any one of claims 1 to 8, characterized in that: The interconnection mode control method comprises the following steps: Step 1: When it is detected that the voltage of the first AC system and the voltage of the second AC system are both within the voltage and phase angle range that meet the closing loop requirements, close the three-phase high-speed switch; Step 2: Start the energy supply unit to charge the DC capacitor of the submodule; Step 3: Unlock the power semiconductor devices in the three-phase commutation chain module; Step 4: According to the interconnection mode power command, adjust the output voltage of the three-phase commutation chain so that the power flowing through the flexible closing device follows the command value, completing the closing operation of the two-terminal AC system.

10. The control method according to claim 9, characterized in that: After completing the loop closing operation of the two-terminal AC system, the control method further includes: Step 5: Real-time detection of the AC system voltage at both ends of the closing device. When it is detected that the AC system voltage connected to the three-phase high-speed switch drops, the process proceeds to step 6; when it is detected that the AC system voltage connected to the three-phase commutation chain drops, the process proceeds to step 9; Step 6: Lock the power semiconductor devices in the three-phase commutation chain module and disconnect the three-phase high-speed switch; Step 7: Re-unlock the power semiconductor devices in the three-phase commutation chain module; Step 8: Adjust the output voltage of the three-phase commutation chain to stabilize the voltage on the load side; Step 9: Keep the three-phase high-speed switch in a closed state and lock the power semiconductor devices in the three-phase commutation chain module.

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