A comprehensive power quality management system and control method

Abstract

The present invention discloses a comprehensive power quality management system, comprising a first and a second AC bus, wherein the first AC bus is connected to a first power supply, and the system further comprises a power supply unit, an inverter unit and a switching unit; the DC output side of the power supply unit is connected to the DC input side of the inverter unit, and the AC output side of the inverter unit is connected to the second AC bus; the second AC bus is connected to a second power supply through the switching unit; the power supply unit provides active power to the inverter unit; the inverter unit converts DC into AC; the present invention also provides a control method for the system.

Description

Technical Field

[0001] The present invention relates to the field of power electronic power conversion, and in particular to a comprehensive power quality management system and a control method. Background Art

[0002] Voltage sag is a power quality issue that is receiving more and more attention. Some important sensitive loads will be greatly affected when voltage sag occurs, such as chip production lines. The economic loss caused by a voltage sag can reach millions or even tens of millions. The voltage sag compensation system 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 points: (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 compensation when the grid voltage drops deeply. The energy storage compensation device occupies a large area and has high cost. It is difficult to install it decentralized on the user load side. (3) There are usually several power quality problems in the distribution network system at the same time, and the power quality needs to be comprehensively managed. Existing compensation devices are difficult to meet the needs. Summary of the invention

[0003] In view of the above technical problems, the technical problem to be solved by the present invention is to provide a low-cost comprehensive power quality management system. The system is applied to a dual-power supply system. The inverter units and fast switching switches are distributed and installed on the AC busbars of two substations or switch stations. In the event of a single power supply failure, fast power transfer can be achieved to ensure continuous operation of the load carried by the faulty busbar; at the same time, it has the functions of reactive power compensation and flow regulation.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] A comprehensive power quality management system includes a first and a second AC bus, wherein the first AC bus is connected to a first power supply, and the system also includes a power supply unit, an inverter unit and a switching unit; the DC output side of the power supply unit is connected to the DC input side of the inverter unit, and the AC output side of the inverter unit is connected to the second AC bus; the second AC bus is connected to a second power supply through the switching unit; the power supply unit provides active power to the inverter unit; the inverter unit converts DC into AC; and the switching unit has the function of rapid separation or power flow regulation.

[0006] In a further preferred embodiment, the input side of the energy supply unit is connected to the first AC bus to convert AC into DC.

[0007] In a further preferred embodiment, the energy supply unit is composed of an energy storage unit, and the energy storage unit is a battery or a super capacitor.

[0008] In a further preferred embodiment, the system further comprises a connecting switch, wherein the connecting switch connects the input side of the energy supply unit with the first AC bus.

[0009] In a further preferred embodiment, the inverter unit includes three commutation chains, each commutation chain includes N inverter unit submodules connected in series, and N is an integer greater than or equal to 2; the submodule is a bridge circuit composed of a DC capacitor and a fully controlled power semiconductor device; one end of the three commutation chains are connected together, and the other end is respectively connected to the ABC three-phase of the second AC bus to form a star connection; or the three commutation chains are interconnected head to tail, and the three connection points are connected to the ABC three-phase of the second AC bus to form a delta connection.

[0010] In a further preferred embodiment, the energy supply unit is composed of a multi-winding transformer and 3N rectifier modules, and the rectifier module is a bridge circuit composed of diodes or fully-controlled power semiconductor devices; the primary side of the multi-winding transformer serves as the input side of the energy supply unit, and the secondary side includes 3N windings, which are connected to the input side of the 3N rectifier modules, and the output side of the rectifier module is connected one-to-one with the positive and negative poles of the DC capacitor of the inverter unit sub-module of the inverter unit.

[0011] In a further preferred embodiment, the inverter unit is a two-level or three-level power electronic conversion circuit composed of a DC capacitor and a fully controlled power semiconductor device.

[0012] In a further preferred embodiment, the switching unit is a solid-state switch or a mechanical switch composed of a power semiconductor device; the power semiconductor device is a fully controlled power semiconductor device or a half-controlled power semiconductor device; and the switching unit has the ability to bidirectionally block current or voltage.

[0013] In a further preferred embodiment, the switching unit is composed of switching submodules connected in series, and the switching submodules include a DC capacitor and four groups of power semiconductor devices to form an H-bridge circuit.

[0014] In a further preferred embodiment, the system further comprises a bus tie switch, one end of the bus tie switch is connected to the first AC bus, and the other end of the bus tie switch is connected to the second AC bus.

[0015] In a further preferred embodiment, the system further comprises an output transformer, wherein the output transformer is connected between the inverter unit and the second AC bus.

[0016] The present invention also proposes a control method for the above-mentioned comprehensive power quality management system, including the following three modes:

[0017] (1) The inverter unit operates in a reactive power compensation mode, and the control method comprises the following steps:

[0018] Step 1: The energy supply unit stops working;

[0019] Step 2: The inverter unit generates reactive power according to the target command to control the power quality of the second AC bus grid connection point, including power factor, AC bus voltage, harmonic compensation, and imbalance compensation.

[0020] In a preferred solution, when there is a connecting switch between the input side of the energy supply unit of the system and the first AC bus, after step 1, it also includes disconnecting the connecting switch.

[0021] (2) When the second AC bus fails or the voltage sags, the energy supply unit is put into operation, and the inverter unit and the switching unit jointly operate in the voltage sag compensation mode. The control method includes the following steps:

[0022] Step 1: The system detects that the voltage of the second AC bus decreases;

[0023] Step 2: When the switching unit is a semi-controlled power semiconductor device, the inverter unit outputs and adjusts the output voltage so that the current flowing through the semi-controlled power semiconductor device quickly passes through zero; otherwise, directly execute step 3;

[0024] Step 3: Quickly separate the switching unit;

[0025] Step 4: The inverter unit adjusts the output AC voltage based on the pre-fault voltage as a reference;

[0026] Step 5: The energy supply unit provides active power to the inverter unit to meet the power demand of the load carried by the second AC bus.

[0027] (3) The energy supply unit is put into operation, and the inverter unit and the switching unit jointly operate in a unified power flow control mode. The control method includes the following steps:

[0028] Step 1: The system detects the voltage of the second AC bus and the current flowing through the switching unit as feedback;

[0029] Step 2: According to the power flow control target, the switching submodule fully controlled power semiconductor devices in the switching unit are controlled to turn on and off, the voltage across the switching unit is controlled, and the current flowing through the switching unit is indirectly adjusted;

[0030] Step 3: The inverter unit takes reactive power as the control target, injects reactive power into the system, and cooperates with the switching unit until the target of power flow control is achieved.

[0031] Compared with the prior art, the power quality comprehensive management system and control method described in the present invention have the following technical effects:

[0032] 1) The inverter unit and the fast switching switch are distributed and installed on the AC busbars of two substations or switch stations, and can be flexibly arranged. The switching unit is connected between the busbar and the AC power supply. When the AC power supply fails, the fault can be completely isolated through the switching unit, and the voltage required for normal operation is provided by the inverter unit. The required active power is provided by the energy supply unit, which can be taken from another power supply system. Therefore, this system can achieve rapid power transfer under single power failure, ensuring that the load terminal voltage carried by the faulty busbar is maintained within the normal range, and achieving continuous operation;

[0033] 2) The system of the present invention can support the entire bus voltage in the event of a fault, ensuring the power supply reliability of the load carried by the bus. It is a centralized compensation solution that avoids the problem of decentralized compensation, is easy to install, and is convenient for operation and maintenance. It does not need to be configured with an energy storage unit, and power can be transferred from another bus, which is low-cost.

[0034] 3) Under normal operating conditions, the inverter unit can switch the operating mode and have the function of a static VAR compensator (SVG) to control the AC bus power factor and stabilize the AC bus voltage.

[0035] 4) When the system can enter the power flow control mode, it is achieved by controlling the switching unit to switch the power semiconductor devices in the sub-module on and off. The system also has multiple power quality compensation functions, which greatly improves the equipment utilization rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic diagram of one embodiment of a comprehensive power quality management system provided by the present invention;

[0037] Figure 2 This is a schematic diagram of a second embodiment of a comprehensive power quality management system provided by the present invention;

[0038] Figure 3 It is a schematic diagram of one embodiment of the energy supply unit and the inverter unit provided by the present invention.

[0039] Figure 4 It is a schematic diagram of the second embodiment of the energy supply unit and the inverter unit provided by the present invention.

[0040] Figure 5 This is an embodiment of the energy supply submodule and the inverter unit submodule provided by the present invention.

[0041] Figure 6 It is one of the embodiments of the switching unit provided by the present invention.

[0042] Figure 7 This is the second embodiment of the switching unit provided by the present invention.

[0043] Figure 8 This is a flow chart of one embodiment of a comprehensive power quality management system control method provided by the present invention

[0044] Fig. 9 This is a flow chart of the second embodiment of a comprehensive power quality management system control method provided by the present invention

[0045] Fig.10 This is a flow chart of the third embodiment of a comprehensive power quality management system control method provided by the present invention

[0046] Fig.11 This is a flow chart of a fourth embodiment of a power quality comprehensive management system control method provided by the present invention

[0047] Description of the numbers in the figure:

[0048] 1. Inverter unit; 2. Energy supply unit; 3. Switching unit; 4. Connecting switch; 5. Multi-winding transformer; 6. Inverter unit submodule; 7. Energy supply submodule; 8. Energy storage unit; S1-S4 fully controlled power semiconductor devices; K, bypass switch; L1, first AC bus; L2, second AC bus. DETAILED DESCRIPTION

[0049] The specific implementation modes of the present invention will be further described in detail below in conjunction with the accompanying drawings.

[0050] The present invention discloses a comprehensive power quality management system, comprising a first AC bus L1 and a second AC bus L2, such as Figure 1 As shown, the first AC bus is connected to a first power supply, and the system further includes an energy supply unit 2, an inverter unit 1 and a switching unit 3; the DC output side of the energy supply unit is connected to the DC input side of the inverter unit, and the AC output side of the inverter unit is connected to the second AC bus; the second AC bus is connected to a second power supply through a switching unit; the energy supply unit provides active power to the inverter unit; the inverter unit converts DC into AC; and the switching unit has the function of fast separation or power flow regulation.

[0051] The input side of the energy supply unit is connected to the first AC bus to convert AC into DC.

[0052] Among them, Figure 2 As shown, the energy supply unit is composed of an energy storage unit, and the energy storage unit is a battery or a super capacitor and does not need to be connected to the first AC bus.

[0053] Among them, Figure 1 As shown, the system further comprises a connecting switch 4, which connects the input side of the energy supply unit with the first AC bus.

[0054] Among them, Figure 3 As shown, the inverter unit includes three commutation chains, each commutation chain includes N inverter unit submodules 6 connected in series, and N is an integer greater than or equal to 2; the submodule is a bridge circuit composed of a DC capacitor and a fully controlled power semiconductor device; one end of the three commutation chains is connected together, and the other end is respectively connected to the ABC three-phase of the second AC bus to form a star connection.

[0055] In a preferred embodiment, it is also possible to Figure 3 The star connection in the circuit is replaced by three commutation chains connected end to end, and the three connection points are respectively connected to the ABC three-phases of the second AC bus to form a delta connection.

[0056] like Figure 3 As shown, the energy supply unit is composed of a multi-winding transformer 5 and 3N rectifier modules, and the rectifier module 7 is a bridge circuit composed of a diode or a fully controlled power semiconductor device; the primary side of the multi-winding transformer serves as the input side of the energy supply unit, and the secondary side includes 3N windings, which are connected to the input side of the 3N rectifier modules, and the output side of the rectifier module is connected to the positive and negative poles of the DC capacitor of the inverter unit submodule of the inverter unit in a one-to-one correspondence.

[0057] like Figure 4 The energy supply unit is composed of an energy storage unit, and the DC side of the energy storage unit is connected to the positive and negative electrodes of the DC capacitor of the inverter unit submodule in a one-to-one correspondence.

[0058] like Figure 5 As shown, an embodiment of connecting a rectifier module to an inverter unit submodule is shown, wherein the rectifier module is a three-phase uncontrolled rectifier bridge composed of diodes, the DC side of the rectifier bridge is correspondingly connected to the positive and negative poles of the DC capacitor of the inverter unit submodule, and the inverter unit submodule is an H-type bridge circuit composed of a DC capacitor and four groups of IGBTs with anti-parallel diodes, and the four groups of IGBTs are S1, S2, S3, and S4 in the figure respectively; in order to increase reliability, the output side of the inverter unit submodule also includes a bypass switch K.

[0059] In another preferred embodiment, the inverter unit is a two-level or three-level power electronic conversion circuit composed of a DC capacitor and a fully controlled power semiconductor device.

[0060] Wherein, the switching unit is a solid-state switch or a mechanical switch composed of a power semiconductor device; the power semiconductor device is a fully controlled power semiconductor device or a semi-controlled power semiconductor device; and the switching unit has the ability to bidirectionally block current or voltage. Figure 6 As shown, a switching unit is formed by two groups of series thyristors connected in reverse parallel.

[0061] Among them, Figure 7As shown, the switching unit is composed of switching submodules connected in series, and the switching submodules include a DC capacitor and four groups of power semiconductor devices to form an H-bridge circuit.

[0062] The system further comprises a bus tie switch, one end of which is connected to the first AC bus, and the other end of which is connected to the second AC bus.

[0063] The system further comprises an output transformer connected between the inverter unit and the second AC bus. When the output voltage of the inverter unit does not match the voltage of the second AC bus, the output transformer can be used to perform voltage conversion.

[0064] The present invention also provides a control method for the comprehensive power quality management system, including the following three modes:

[0065] (1) Disconnect the energy supply unit and the inverter unit operates in reactive power compensation mode, such as Figure 8 The control method shown comprises the following steps:

[0066] Step 1: The energy supply unit stops working;

[0067] Step 2: The inverter unit generates reactive power according to the target command to control the power quality of the second AC bus grid connection point, including power factor, AC bus voltage, harmonic compensation, and imbalance compensation.

[0068] If the system in question has a connection switch, such as Fig. 9 As shown in the control flow, after step 1, the connection switch is disconnected.

[0069] (2) When the second AC bus fails or the voltage sags, the energy supply unit is put into operation, and the inverter unit and the switching unit jointly operate in the voltage sag compensation mode. The control method includes the following steps:

[0070] Step 1: The system detects that the voltage of the second AC bus decreases;

[0071] Step 2: When the switching unit is a semi-controlled power semiconductor device, the inverter unit outputs and adjusts the output voltage so that the current flowing through the semi-controlled power semiconductor device quickly passes through zero; otherwise, directly execute step 3;

[0072] Step 3: Quickly separate the switching unit;

[0073] Step 4: The inverter unit adjusts the output AC voltage based on the pre-fault voltage as a reference;

[0074] Step 5: The energy supply unit provides active power to the inverter unit to meet the power demand of the load carried by the second AC bus.

[0075] Control process such as Fig.10 shown.

[0076] (3) The energy supply unit is put into operation, and the inverter unit and the switching unit jointly operate in a unified power flow control mode. The control method includes the following steps:

[0077] Step 1: The system detects the voltage of the second AC bus and the current flowing through the switching unit as feedback;

[0078] Step 2: According to the power flow control target, the switching submodule fully controlled power semiconductor devices in the switching unit are controlled to turn on and off, the voltage across the switching unit is controlled, and the current flowing through the switching unit is indirectly adjusted;

[0079] Step 3: The inverter unit takes reactive power as the control target, injects reactive power into the system, and cooperates with the switching unit until the target of power flow control is achieved.

[0080] Control process such as Fig.11 shown.

[0081] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A comprehensive power quality management system, comprising a first AC bus and a second AC bus, wherein the first AC bus is connected to a first power supply, characterized in that: The system also includes an energy supply unit, an inverter unit and a switching unit; the DC output side of the energy supply unit is connected to the DC input side of the inverter unit, and the AC output side of the inverter unit is connected to the second AC bus; the second AC bus is connected to the second power supply through the switching unit; the energy supply unit provides active power to the inverter unit; the inverter unit converts DC into AC; the switching unit has the function of fast separation or power flow regulation; The inverter unit includes three commutation chains, each of which includes N inverter unit submodules connected in series, where N is an integer greater than or equal to 2; the submodule is a bridge circuit composed of a DC capacitor and a fully controlled power semiconductor device; one end of the three commutation chains are connected together, and the other end is respectively connected to the ABC three-phase of the second AC bus to form a star connection; or the three commutation chains are interconnected head to tail, and three connection points are connected to the ABC three-phase of the second AC bus to form a delta connection.

2. The comprehensive power quality management system according to claim 1 is characterized in that: The input side of the energy supply unit is connected to the first AC bus to convert AC into DC.

3. The comprehensive power quality management system according to claim 1 is characterized in that: The energy supply unit is composed of an energy storage unit, and the energy storage unit is a battery or a super capacitor.

4. The comprehensive power quality management system according to claim 2 is characterized in that: The system further comprises a connecting switch, wherein the connecting switch connects the input side of the energy supply unit and the first AC bus.

5. The comprehensive power quality management system according to claim 1 is characterized in that: The energy supply unit is composed of a multi-winding transformer and 3N rectifier modules, and the rectifier module is a bridge circuit composed of diodes or fully-controlled power semiconductor devices; the primary side of the multi-winding transformer serves as the input side of the energy supply unit, and the secondary side includes 3N windings, which are connected to the input sides of the 3N rectifier modules, and the output side of the rectifier module is connected to the positive and negative poles of the DC capacitor of the inverter unit submodule of the inverter unit in a one-to-one correspondence.

6. The comprehensive power quality management system according to claim 1 is characterized in that: The inverter unit is a two-level or three-level power electronic conversion circuit composed of a DC capacitor and a fully controlled power semiconductor device.

7. The comprehensive power quality management system according to claim 1 is characterized by: The switching unit is a solid-state switch or a mechanical switch composed of a power semiconductor device; the power semiconductor device is a fully controlled power semiconductor device or a half-controlled power semiconductor device; the switching unit has the ability to bidirectionally block current or voltage.

8. The comprehensive power quality management system according to claim 1 is characterized by: The switching unit is composed of switching submodules connected in series, and the switching submodules include a DC capacitor and four groups of power semiconductor devices to form an H-type bridge circuit.

9. The comprehensive power quality management system according to claim 1 is characterized in that: The system further comprises a bus tie switch, one end of which is connected to the first AC bus and the other end of which is connected to the second AC bus.

10. The comprehensive power quality management system according to claim 1, characterized in that: The system further includes an output transformer connected between the inverter unit and the second AC bus.

11. A control method based on the comprehensive power quality management system according to any one of claims 1 to 6, characterized in that: The inverter unit operates in a reactive power compensation mode, and the control method comprises the following steps: Step 1: The energy supply unit stops working; Step 2: The inverter unit generates reactive power according to the target command to control the power quality of the second AC bus grid connection point, including power factor, AC bus voltage, harmonic compensation, and imbalance compensation.

12. The control method according to claim 11, characterized in that: When there is a connection switch between the input side of the energy supply unit of the system and the first AC bus, after step 1, the method further includes disconnecting the connection switch.

13. A control method based on the comprehensive power quality management system according to any one of claims 1 to 8, characterized in that: When the second AC bus fails or the voltage sags, the energy supply unit is put into operation, and the inverter unit and the switching unit jointly operate in the voltage sag compensation mode. The control method includes the following steps: Step 1: The system detects that the voltage of the second AC bus decreases; Step 2: When the switching unit is a semi-controlled power semiconductor device, the inverter unit outputs and adjusts the output voltage so that the current flowing through the semi-controlled power semiconductor device quickly passes through zero; otherwise, directly execute step 3; Step 3: Quickly separate the switching unit; Step 4: The inverter unit adjusts the output AC voltage based on the pre-fault voltage as a reference; Step 5: The energy supply unit provides active power to the inverter unit to meet the power demand of the load carried by the second AC bus.

14. A control method based on the comprehensive power quality management system according to any one of claims 1 to 6 or 8, characterized in that: The energy supply unit is put into operation, and the inverter unit and the switching unit jointly operate in a unified power flow control mode. The control method includes the following steps: Step 1: The system detects the voltage of the second AC bus and the current flowing through the switching unit as feedback; Step 2: According to the power flow control target, the switching submodule fully controlled power semiconductor devices in the switching unit are controlled to turn on and off, the voltage across the switching unit is controlled, and the current flowing through the switching unit is indirectly adjusted; Step 3: The inverter unit takes reactive power as the control target, injects reactive power into the system, and cooperates with the switching unit until the target of power flow control is achieved.

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