Power quality device, power system and power quality compensation method

Abstract

The invention relates to a power quality device, a power system and a power quality compensation method. The power quality device comprises a converter module, wherein the alternating current side of the converter module is connected with a power grid; the transformer comprises a primary winding and a secondary winding, the first end of the primary winding is connected with a power grid, the second end of the primary winding is grounded through a load, the first end of the secondary winding is connected with the alternating current side of the converter module, and the second end of the secondary winding is grounded; a bypass switch connected in parallel with the primary winding; and the control module is respectively connected with the bypass switch and the converter module and is used for controlling the on-off state of the bypass switch according to the working condition of the power grid and controlling the converter module to provide reactive power or compensation voltage for the power grid according to the electrical parameters of the power grid, the electrical parameters of the converter module and the on-off state of the bypass switch. The switching of the power quality device between providing reactive power or compensating voltage for the power grid is realized by multiplexing the bypass switch, the structure is simple, and the cost is low.

Description

Technical Field

[0001] The present application relates to the technical field of electric power, and particularly to a power quality device, a power system, and a power quality compensation method. Background Art

[0002] With the increasing proportion of new energy and non-linear loads in the distribution network, power quality problems such as reactive power shortage, voltage sag, and harmonics in the active power grid are becoming increasingly severe. To improve the overall power quality of the active power grid, typical shunt power quality devices (such as active power filters, static var compensators, etc.) and series power quality devices (such as dynamic voltage compensators, etc.) are widely connected to the power grid. Although connecting shunt power quality devices and series power quality devices to the power grid realizes reactive power compensation and voltage compensation for the power grid, the number of connected modules is large and the cost is high. Summary of the Invention

[0003] Based on this, it is necessary to provide a power quality device, a power system, and a power quality compensation method.

[0004] In a first aspect, the present application provides a power quality device, including:

[0005] A converter module, the AC side of the converter module is connected to the power grid;

[0006] A transformer, including a primary winding and a secondary winding, the first end of the primary winding is connected to the power grid, the second end of the primary winding is grounded through a load, the first end of the secondary winding is connected to the AC side of the converter module, and the second end of the secondary winding is grounded;

[0007] A bypass switch, connected in parallel with the primary winding;

[0008] A control module, respectively connected to the bypass switch and the converter module, for controlling the on-off state of the bypass switch according to the operating conditions of the power grid, and controlling the converter module to provide reactive power or compensate voltage for the power grid according to the electrical parameters of the power grid, the electrical parameters of the converter module, and the on-off state of the bypass switch.

[0009] In one embodiment, the operating conditions include a normal operating condition and a voltage sag condition;

[0010] The control module is further configured to control the bypass switch to be in a conducting state when the operating condition is the normal operating condition, and to control the converter module to provide reactive power for the power grid according to the electrical parameters of the power grid and the electrical parameters of the converter module when the bypass switch is in a conducting state;

[0011] The control module is further configured to control the bypass switch to be in an open state when the operating condition is the voltage dip condition, and when the bypass switch is in the open state, control the converter module to provide a compensation voltage for the power grid according to the electrical parameters of the power grid and the electrical parameters of the converter module.

[0012] In one embodiment, the electrical parameters of the converter module at least include one of the DC-side voltage, the AC-side current, and the AC-side voltage; the electrical parameters of the power grid at least include one of the grid voltage and the load current;

[0013] The control module includes:

[0014] A first control unit, connected to the converter module and the load, is configured to control the converter module to provide reactive power for the power grid according to the DC-side voltage, the AC-side current, and the load current when the bypass switch is in a conducting state;

[0015] A second control unit, connected to the converter module and the load, is configured to control the converter module to provide a compensation voltage for the power grid according to the grid voltage, the AC-side voltage, and the AC-side current when the bypass switch is in an open state.

[0016] In one embodiment, the first control unit includes:

[0017] A coordinate system positive transformation sub-unit, configured to convert the AC-side current into an active current component and a reactive current component;

[0018] An active control sub-unit, configured to obtain an active current reference value according to the DC-side voltage and the DC-side voltage reference value, and determine the d-axis component of the first modulation signal according to the active current reference value and the active current component;

[0019] A reactive control sub-unit, configured to obtain the reactive current reference value of the converter module according to the load current, and determine the q-axis component of the first modulation signal according to the reactive current reference value and the reactive current component;

[0020] A coordinate system inverse transformation sub-unit, configured to convert the d-axis component and the q-axis component of the first modulation signal into the first modulation signal;

[0021] A first PWM generator, configured to generate a first control signal according to the first modulation signal and send the first control signal to the converter module to instruct the converter module to provide reactive power for the power grid.

[0022] In one embodiment, the active control sub-unit includes:

[0023] A first subtractor for obtaining the difference between the DC terminal voltage and the DC terminal voltage reference value;

[0024] A first PI regulator for determining the reference value of the active current according to the difference between the DC terminal voltage and the DC terminal voltage reference value;

[0025] A second subtractor for obtaining the difference between the reference value of the active current and the active current component;

[0026] A second PI regulator for determining the d-axis component of the first modulation signal according to the difference between the reference value of the active current and the active current component;

[0027] The reactive power control sub-unit includes:

[0028] A coordinate system positive converter module for obtaining the reference value of the reactive current of the converter module according to the load current;

[0029] A third subtractor for obtaining the difference between the reference value of the reactive current and the reactive current component;

[0030] A third PI regulator for determining the q-axis component of the first modulation signal according to the difference between the reference value of the reactive current and the reactive current component.

[0031] In one embodiment, the second control unit includes:

[0032] A modulation wave generation sub-unit for determining the reference value of the AC terminal voltage according to the grid voltage and the load voltage reference value, determining the reference value of the AC terminal current according to the reference value of the AC terminal voltage and the AC terminal voltage, and generating a second modulation signal according to the reference value of the AC terminal current and the AC terminal current;

[0033] A second PWM generator for generating a second control signal according to the second modulation signal and sending the second control signal to the converter module to instruct the converter module to provide a compensation voltage for the grid.

[0034] In one embodiment, the modulation wave generation sub-unit includes:

[0035] A fourth subtractor for determining the reference value of the AC terminal voltage according to the grid voltage and the load voltage reference value;

[0036] A fifth subtractor for obtaining the difference between the reference value of the AC terminal voltage and the AC terminal voltage;

[0037] A fourth PI regulator, configured to determine the reference value of the AC terminal current according to the difference between the reference value of the AC terminal voltage and the AC terminal voltage;

[0038] A sixth subtractor, configured to obtain the difference between the reference value of the AC terminal current and the AC terminal current;

[0039] A fifth PI regulator, configured to generate the second modulation signal according to the difference between the reference value of the AC terminal current and the AC terminal current.

[0040] In a second aspect, the present application provides a power system, including a power grid and the power quality device provided in any one of the above embodiments.

[0041] In a third aspect, the present application provides a power quality compensation method, the method including:

[0042] Controlling the on / off state of the bypass switch according to the operating conditions of the power grid;

[0043] Controlling the converter module to provide reactive power or compensate voltage for the power grid according to the electrical parameters of the power grid, the electrical parameters of the converter module, and the on / off state of the bypass switch.

[0044] In one embodiment, the electrical parameters of the converter module at least include one of the DC terminal voltage, the AC terminal current, and the AC terminal voltage; the electrical parameters of the power grid at least include one of the power grid voltage and the load current;

[0045] The controlling the converter module to provide reactive power or compensate voltage for the power grid according to the electrical parameters of the power grid, the electrical parameters of the converter module, and the on / off state of the bypass switch includes:

[0046] When the bypass switch is in the on state, controlling the converter module to provide reactive power for the power grid according to the electrical parameters of the power grid and the electrical parameters of the converter module;

[0047] When the bypass switch is in the off state, controlling the converter module to provide compensation voltage for the power grid according to the electrical parameters of the power grid and the electrical parameters of the converter module.

[0048] In the above power quality device, power system, and power quality compensation method, the power quality device includes a converter module, a transformer, a bypass switch, and a control module. Among them, the AC side of the converter module is connected to the power grid, and the primary winding of the transformer is connected to the power grid and is connected in parallel with the bypass switch. The control module can control the on-off state of the bypass switch according to the operating conditions of the power grid, change the connection relationship between the transformer and the power grid, and thus indirectly change the circuit connection relationship between the converter module and the power grid, enabling the converter module to provide reactive power or compensate for voltage to the power grid under different operating conditions of the power grid. The structure is simple and the cost is low. Further, the control module can also adjust the output voltage and output current on the AC side of the converter module according to the electrical parameters of the power grid and the electrical parameters of the converter module, so that the converter module can accurately provide the required reactive power or compensate for voltage to the power grid, ensuring the normal operation of the load. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the technical solutions in the embodiments of the present application or in the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0050] Figure 1 Schematic structural diagram of a power quality device provided for an embodiment;

[0051] Figure 2 Circuit diagram of the power quality device provided for an embodiment when the bypass switch is in the on state;

[0052] Figure 3 Circuit diagram of the power quality device provided for an embodiment when the bypass switch is in the off state;

[0053] Figure 4 Schematic structural diagram of the control module provided for an embodiment;

[0054] Figure 5 Schematic structural diagram of the first control unit provided for an embodiment;

[0055] Figure 6 Schematic structural diagram of the second control unit provided for an embodiment;

[0056] Figure 7 Schematic structural diagram of the power quality device provided for another embodiment;

[0057] Figure 8 Flowchart of the power quality compensation method provided for an embodiment;

[0058] Figure 9Flowchart for providing reactive power to the power grid for an embodiment;

[0059] Figure 10 Flowchart for providing compensation voltage to the power grid for an embodiment. Detailed implementation manners

[0060] To facilitate the understanding of this application, the following will describe this application more comprehensively with reference to the relevant drawings. Embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of this application more thorough and comprehensive.

[0061] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the description of this application herein are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0062] It can be understood that the terms "first", "second", etc. used in this application can be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish the first element from another element. For example, without departing from the scope of this application, the first PI regulator can be referred to as the second PI regulator, and similarly, the second PI regulator can be referred to as the first PI regulator. Both the first PI regulator and the second PI regulator are PI regulators, but they are not the same PI regulator.

[0063] It can be understood that "connection" in the following embodiments should be understood as "electrical connection", "communication connection", etc. if there is an electrical signal or data transfer between the connected circuits, modules, units, etc.

[0064] It can be understood that "at least one" means one or more, and "a plurality" means two or more. "At least part of an element" means part or all of the element.

[0065] As used herein, the singular forms "a", "an" and "the" may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms "comprise / include" or "have" etc. specify the presence of the stated features, wholes, steps, operations, components, parts or combinations thereof, but do not exclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts or combinations thereof. At the same time, the term "and / or" used in this specification includes any and all combinations of the related listed items.

[0066] In one embodiment, this application provides a power quality device, such asFigure 1 As shown in the figure, it includes a converter module 100, a transformer 200, a bypass switch 300, and a control module 400. Among them, the AC side of the converter module 100 is connected to the power grid 500. The transformer 200 includes a primary winding and a secondary winding. The first end of the primary winding is connected to the power grid 500, the second end of the primary winding is grounded through a load 600, the first end of the secondary winding is connected to the AC side of the converter module 100, and the second end of the secondary winding is grounded. The bypass switch 300 is connected in parallel with the primary winding. The control module 400 is respectively connected to the bypass switch 300 and the converter module 100.

[0067] The converter module 100 can be used to convert a DC signal into an AC signal and output the AC signal to the power grid. A DC signal can be provided for the DC side of the converter module 100 through an energy storage unit, such as an energy storage inductor, an energy storage capacitor, or a battery. Under normal circumstances, the load not only obtains active power from the power grid but also obtains reactive power from the power grid. If the reactive power in the power grid is in short supply, the load does not have enough reactive power to establish a normal electromagnetic field, and the terminal voltage of the load will drop, thus affecting the normal operation of the load. Therefore, the converter module 100 is provided to supply the reactive power required for the load to operate at the rated working condition to the power grid. When the power grid voltage drops, the terminal voltage of the load drops, affecting the normal operation of the load. Therefore, the converter module 100 can be set to supply a compensation voltage to the power grid so that the terminal voltage of the load can be maintained at the rated working voltage.

[0068] The control module 400 can control the on-off state of the bypass switch 300 according to the working condition of the power grid 500, and control the converter module 100 to supply reactive power or compensation voltage to the power grid according to the electrical parameters of the power grid, the electrical parameters of the converter module, and the on-off state of the bypass switch 300. The electrical parameters of the converter module 100 at least include one of the DC terminal voltage, the AC terminal current, and the AC terminal voltage. The electrical parameters of the power grid at least include one of the power grid voltage and the load current. The control module 400 can control the on-off state of the bypass switch 300 according to the working condition of the power grid, change the connection relationship between the transformer 200 and the power grid, and thus indirectly change the circuit connection relationship between the converter module 100 and the power grid, so that the converter module 100 can supply the required reactive power or compensation voltage to the power grid under different working conditions of the power grid, ensuring the normal operation of the load.

[0069] In an embodiment of the present application, the power quality device includes a converter module 100, a transformer 200, a bypass switch 300, and a control module 400. Among them, the AC side of the converter module 100 is connected to the power grid, and the primary winding of the transformer 200 is connected to the power grid and is connected in parallel with the bypass switch 300. The control module 400 can control the on-off state of the bypass switch 300 according to the operating conditions of the power grid, change the connection relationship between the transformer 200 and the power grid, and thus can indirectly change the circuit connection relationship between the converter module 100 and the power grid, so that the converter module 100 can provide reactive power or compensate for voltage for the power grid under different operating conditions of the power grid. Further, the control module 400 can also adjust the output voltage and output current of the AC side of the converter module 100 according to the electrical parameters of the power grid 500 and the electrical parameters of the converter module 100, so that the converter module 100 can accurately provide the required reactive power or compensate for voltage for the power grid, ensuring the normal operation of the load.

[0070] In one embodiment, the operating conditions of the power grid 500 include normal operating conditions and voltage sag conditions. Among them, the voltage sag condition refers to the effective value of the power grid voltage rapidly dropping between 90% and 10% of the rated voltage.

[0071] The control module 400 is further configured to control the bypass switch 300 to be in the on state when the operating condition is the normal operating condition, and when the bypass switch 300 is in the on state, control the converter module 100 to provide reactive power for the power grid according to the electrical parameters of the power grid 500 and the electrical parameters of the converter module 100. As Figure 2 shown, when the bypass switch 300 is in the on state, the primary winding of the transformer 200 is short-circuited by the bypass switch 300, and only the secondary winding of the transformer 200 is connected to the entire circuit. At this time, the power quality device operates in the reactive power compensation mode and can provide the reactive power required for the normal operation of the load for the power grid.

[0072] The control module 400 is further configured to control the bypass switch 300 to be in the off state when the operating condition is the voltage sag condition, and when the bypass switch 300 is in the off state, control the converter module 100 to provide compensation voltage for the power grid according to the electrical parameters of the power grid 500 and the electrical parameters of the converter module 100. As Figure 3 shown, when the bypass switch 300 is in the off state, both the primary winding and the secondary winding of the transformer 200 are connected to the entire circuit. At this time, the power quality device operates in the voltage compensation mode and can provide the compensation voltage required for the normal operation of the load for the power grid.

[0073] Further, as Figure 4As shown in the figure, the control module 400 includes a first control unit 410 and a second control unit 420. The first control unit 410 is connected to the converter module 100 and the load, and is configured to control the converter module 100 to provide reactive power to the power grid according to the DC-side voltage, the AC-side current, and the load current when the bypass switch 300 is in the on state. The second control unit 420 is connected to the converter module and the load, and is configured to control the converter module 100 to provide a compensation voltage to the power grid according to the grid voltage, the AC-side voltage, and the AC-side current when the bypass switch 300 is in the off state.

[0074] As Figure 4 shown, the first control unit 410 may include a coordinate system positive transformation subunit 411, an active power control subunit 412, a reactive power control subunit 413, a coordinate system inverse transformation subunit 414, and a first PWM generator 415.

[0075] The coordinate system positive transformation subunit 411 is configured to convert the AC-side current into an active current component and a reactive current component. The AC-side current of the converter module 100 is generally represented in a three-phase stationary coordinate system. The coordinate system positive transformation subunit can perform a coordinate transformation on the AC-side current, converting it from a three-phase stationary coordinate system to a dq-axis coordinate system. The d-axis component of the AC-side current can represent the active current component, and the q-axis component of the AC-side current can represent the reactive current component.

[0076] The active power control subunit 412 is configured to obtain an active current reference value according to the DC-side voltage and the DC-side voltage reference value, and determine the d-axis component of the first modulation signal according to the active current reference value and the active current component. The DC-side voltage reference value is the same as or close to the grid voltage. The active power in the converter module 100 is mainly provided by the energy storage unit on the DC side. Therefore, the active power control subunit 412 can obtain an active current reference value according to the DC-side voltage and the preset DC-side voltage reference value, and determine the d-axis component of the first modulation signal according to the active current reference value and the active current component.

[0077] Specifically, as Figure 5 shown, the active power control subunit 412 includes a first subtractor, a first PI regulator, a second subtractor, and a second PI regulator. The first subtractor is configured to obtain the difference between the DC-side voltage and the DC-side voltage reference value. The first PI regulator is configured to determine the active current reference value according to the difference between the DC-side voltage and the DC-side voltage reference value. The input of the first PI regulator is the difference between the DC-side voltage and the DC-side voltage reference value, and after integral, differential, and proportional linear combination, it outputs the active current reference value. The second subtractor is configured to obtain the difference between the active current reference value and the active current component. The second PI regulator is configured to determine the d-axis component of the first modulation signal according to the difference between the active current reference value and the active current component.

[0078] The reactive power control sub-unit 413 is used to obtain the reactive current reference value of the converter module according to the load current, and determine the q-axis component of the first modulation signal according to the reactive current reference value and the reactive current component. Under the normal operating condition of the power grid, it is expected that all the reactive power required for load operation is provided by the power quality device, and the power grid only provides active power for the load. Therefore, the load current can be subjected to coordinate transformation, transformed from the three-phase stationary coordinate system to the dq-axis coordinate system, and the q-axis component of the load current is used as the reactive current reference value. Further, the q-axis component of the first modulation signal is determined according to the reactive current reference value and the reactive current component.

[0079] Specifically, as Figure 5 shown, the reactive power control sub-unit 413 includes a coordinate system positive converter, a third subtractor, and a third PI regulator. The coordinate system positive converter is used to obtain the reactive current reference value of the converter module 100 according to the load current. The third subtractor is used to obtain the difference between the reactive current reference value and the reactive current component. The third PI regulator is used to determine the q-axis component of the first modulation signal according to the difference between the reactive current reference value and the reactive current component.

[0080] The coordinate system inverse transformation sub-unit 414 is used to convert the d-axis component and the q-axis component of the first modulation signal into the first modulation signal. The coordinate system inverse transformation sub-unit 414 can perform coordinate inverse transformation on the first modulation signal, transforming from the dq-axis coordinate system to the three-phase stationary coordinate system.

[0081] The first PWM generator 415 is used to generate a first control signal according to the first modulation signal, and send the first control signal to the converter module 100 to instruct the converter module 100 to provide reactive power for the power grid. The first PWM generator can perform modulation processing on the first modulation signal, generate the first control signal, send the first control signal to the converter module 100, adjust the duty cycle of each power transistor in the converter module 100, so as to realize the regulation of the AC terminal current of the converter module 100, and enable the converter module 100 to provide the required reactive power for the power grid.

[0082] In one embodiment, as Figure 4 shown, the second control unit 420 includes a modulation wave generation sub-unit 421 and a second PWM generator 422.

[0083] The modulation wave generation sub-unit 421 is used to determine the AC terminal voltage reference value according to the grid voltage and the load voltage reference value, determine the AC terminal current reference value according to the AC terminal voltage reference value and the AC terminal voltage, and generate a second modulation signal according to the AC terminal current reference value and the AC terminal current.

[0084] Refer to Figure 3 , in the case where the operating condition of the power grid is a voltage sag condition, the grid voltage is US, according to Kirchhoff's voltage law:

[0085] U L = U S + U tr1 ;

[0086] U S = U C + U tr2 ;

[0087] Wherein, U L represents the load voltage, U S represents the grid voltage, U tr1 represents the voltage of the primary winding of transformer 200, U tr2 represents the voltage of the secondary winding of transformer 200, U C represents the AC terminal voltage of the converter module 100.

[0088] Assume that the turns ratio of transformer 200 is 1, that is, U tr1 = U tr1 ,

[0089] Then, U C = 2U S - U L .

[0090] Therefore, the modulation wave generation sub-unit 421 can determine the AC terminal voltage reference value according to the grid voltage and the preset load voltage reference value. Then, according to the AC terminal voltage reference value and the AC terminal voltage, it determines the AC terminal current reference value, and generates the second modulation signal according to the AC terminal current reference value and the AC terminal current.

[0091] Specifically, as Figure 6 shown, the modulation wave generation sub-unit 421 includes a fourth subtractor, a fifth subtractor, a fourth PI regulator, a sixth subtractor and a fifth PI regulator. The fourth subtractor is used to determine the AC terminal voltage reference value according to the grid voltage and the load voltage reference value. The fifth subtractor is used to obtain the difference between the AC terminal voltage reference value and the AC terminal voltage. The fourth PI regulator is used to determine the AC terminal current reference value according to the difference between the AC terminal voltage reference value and the AC terminal voltage. The sixth subtractor is used to obtain the difference between the AC terminal current reference value and the AC terminal current. The fifth PI regulator is used to generate the second modulation signal according to the difference between the AC terminal current reference value and the AC terminal current.

[0092] The second PWM generator is used to generate the second control signal according to the second modulation signal and send the second control signal to the converter module 100 to instruct the converter module 100 to provide a compensation voltage for the grid.

[0093] In one embodiment, the first control unit and the second control unit can share a PWM generator.

[0094] In one embodiment, as Figure 7 shown, the converter module 100 includes a DC capacitor C and an inverter. The inverter includes two full-bridge arms, and each full-bridge arm includes two insulated gate bipolar transistors. Transistors T1 and T2 form the first full-bridge arm, and transistors T3 and T4 form the second full-bridge arm. The DC capacitor C serves as the energy storage unit of the converter module 100.

[0095] In one embodiment, the power quality device further includes a filtering module. As Figure 7 shown, the filtering module includes a capacitor Cf and an inductor Lf.

[0096] In one embodiment, the present application further provides a power system, which includes a power grid and the power quality device provided in any of the above embodiments.

[0097] Based on the same inventive concept, the present application further provides a power quality compensation method, which can be applied to the power quality device provided in any of the above embodiments. For the definitions of the steps in the following methods, reference is made to the definitions of the above power quality device.

[0098] In one embodiment, as Figure 8 shown, the power quality compensation method includes steps S802 - S804.

[0099] S802, controlling the on / off state of the bypass switch according to the operating conditions of the power grid.

[0100] S804, controlling the converter module to provide reactive power or compensate voltage for the power grid according to the electrical parameters of the power grid, the electrical parameters of the converter module, and the on / off state of the bypass switch.

[0101] In the embodiments of the present application, by controlling the on / off state of the bypass switch according to the operating conditions of the power grid, the connection relationship between the transformer and the power grid is changed, so that the circuit connection relationship between the converter module and the power grid can be indirectly changed, enabling the converter module to provide reactive power or compensate voltage for the power grid under different operating conditions of the power grid. Further, the control module can also adjust the output voltage and output current on the AC side of the converter module according to the electrical parameters of the power grid and the electrical parameters of the converter module, so that the converter module can accurately provide the required reactive power or compensate voltage for the power grid, ensuring the normal operation of the load.

[0102] In one embodiment, controlling the on / off state of the bypass switch according to the operating conditions of the power grid includes the steps of controlling the bypass switch to be in the on state when the operating condition is the normal operating condition, and controlling the bypass switch to be in the off state when the operating condition is the voltage sag condition.

[0103] In one embodiment, according to the electrical parameters of the power grid, the electrical parameters of the converter module, and the on / off state of the bypass switch, controlling the converter module to provide reactive power or compensating voltage for the power grid includes, when the bypass switch is in the on state, controlling the converter module to provide reactive power for the power grid according to the electrical parameters of the power grid and the electrical parameters of the converter module, and when the bypass switch is in the off state, controlling the converter module to provide compensating voltage for the power grid according to the electrical parameters of the power grid and the electrical parameters of the converter module.

[0104] In one embodiment, as Figure 9 shown, controlling the converter module to provide reactive power for the power grid according to the electrical parameters of the power grid and the electrical parameters of the converter module includes steps S902 - S914.

[0105] S902, converting the AC terminal current into an active current component and a reactive current component.

[0106] S904, obtaining the active current reference value according to the DC terminal voltage and the DC terminal voltage reference value.

[0107] S906, determining the d-axis component of the first modulation signal according to the active current reference value and the active current component.

[0108] S908, obtaining the reactive current reference value of the converter module according to the load current.

[0109] S910, determining the q-axis component of the first modulation signal according to the reactive current reference value and the reactive current component.

[0110] S912, converting the d-axis component and the q-axis component of the first modulation signal into the first modulation signal.

[0111] S914, generating a first control signal according to the first modulation signal and sending the first control signal to the converter module to instruct the converter module to provide reactive power for the power grid.

[0112] In one embodiment, as Figure 10 shown, controlling the converter module to provide compensating voltage for the power grid according to the electrical parameters of the power grid and the electrical parameters of the converter module includes steps S1002 - S1008.

[0113] S1002, determining the AC terminal voltage reference value according to the power grid voltage and the load voltage reference value.

[0114] S1004, determining the AC terminal current reference value according to the AC terminal voltage reference value and the AC terminal voltage.

[0115] S1006. Generate a second modulation signal based on the AC terminal current reference value and the AC terminal current.

[0116] S1008. Generate a second control signal according to the second modulation signal, and send the second control signal to the converter module to instruct the converter module to provide a compensation voltage for the power grid.

[0117] In the description of this specification, the descriptions referring to the terms "some embodiments", "other embodiments", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example.

[0118] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0119] The above-described embodiments only represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A power quality device, characterized in that: include: A converter module, wherein the AC side of the converter module is connected to a power grid; A transformer, comprising a primary winding and a secondary winding, wherein a first end of the primary winding is connected to a power grid, a second end of the primary winding is grounded through a load, a first end of the secondary winding is connected to an AC side of the converter module, and a second end of the secondary winding is grounded; a bypass switch connected in parallel with the primary winding; The control module is connected to the bypass switch and the converter module respectively, and is used to control the on-off state of the bypass switch according to the working condition of the power grid, and control the converter module to provide reactive power or compensation voltage for the power grid according to the electrical parameters of the power grid, the electrical parameters of the converter module and the on-off state of the bypass switch.

2. The power quality device according to claim 1, characterized in that: The operating conditions include normal operating conditions and voltage drop conditions; The control module is further used for controlling the bypass switch to be in an on state when the operating condition is the normal operating condition, and controlling the converter module to provide reactive power for the power grid according to the electrical parameters of the power grid and the electrical parameters of the converter module when the bypass switch is in the on state; The control module is also used to control the bypass switch to be in an off state when the operating condition is the voltage drop condition, and when the bypass switch is in the off state, control the converter module to provide a compensation voltage for the power grid according to the electrical parameters of the power grid and the electrical parameters of the converter module.

3. The power quality device according to claim 2, characterized in that: The electrical parameters of the converter module include at least one of the DC terminal voltage, the AC terminal current and the AC terminal voltage; the electrical parameters of the power grid include at least one of the power grid voltage and the load current; The control module comprises: a first control unit connected to the converter module and the load, and configured to control the converter module to provide reactive power for the power grid according to the DC terminal voltage, the AC terminal current and the load current when the bypass switch is in an on state; A second control unit is connected to the converter module and the load, and is used to control the converter module to provide a compensation voltage for the grid according to the grid voltage, the AC end voltage and the AC end current when the bypass switch is in an off state.

4. The power quality device according to claim 3, characterized in that: The first control unit comprises: A coordinate system forward transformation subunit, used for converting the AC terminal current into an active current component and a reactive current component; an active power control subunit, configured to obtain an active current reference value according to the DC terminal voltage and the DC terminal voltage reference value, and determine a d-axis component of the first modulation signal according to the active current reference value and the active current component; a reactive power control subunit, configured to obtain a reactive current reference value of the converter module according to the load current, and determine a q-axis component of the first modulation signal according to the reactive current reference value and the reactive current component; A coordinate system inverse transformation subunit, used to transform the d-axis component and the q-axis component of the first modulated signal into the first modulated signal; The first PWM generator is used to generate a first control signal according to the first modulation signal, and send the first control signal to the converter module to instruct the converter module to provide reactive power for the power grid.

5. The power quality device according to claim 4, characterized in that: The active power control subunit comprises: A first subtractor, used for obtaining a difference between the DC terminal voltage and the DC terminal voltage reference value; a first PI regulator, configured to determine the active current reference value according to a difference between the DC terminal voltage and the DC terminal voltage reference value; a second subtractor, configured to obtain a difference between the active current reference value and the active current component; a second PI regulator, configured to determine a d-axis component of the first modulation signal according to a difference between the active current reference value and the active current component; The reactive power control subunit comprises: A coordinate system positive converter module, used for obtaining a reactive current reference value of the converter module according to the load current; a third subtractor, configured to obtain a difference between the reactive current reference value and the reactive current component; The third PI regulator is used to determine the q-axis component of the first modulation signal according to the difference between the reactive current reference value and the reactive current component.

6. The power quality device according to claim 3, characterized in that: The second control unit comprises: a modulation wave generating subunit, configured to determine an AC terminal voltage reference value according to the grid voltage and the load voltage reference value, determine the AC terminal current reference value according to the AC terminal voltage reference value and the AC terminal voltage, and generate a second modulation signal according to the AC terminal current reference value and the AC terminal current; The second PWM generator is used to generate a second control signal according to the second modulation signal, and send the second control signal to the converter module to instruct the converter module to provide a compensation voltage for the power grid.

7. The power quality device according to claim 6, characterized in that: The modulation wave generating subunit comprises: a fourth subtractor, configured to determine an AC terminal voltage reference value according to the grid voltage and the load voltage reference value; a fifth subtractor, configured to obtain a difference between the AC terminal voltage reference value and the AC terminal voltage; a fourth PI regulator, configured to determine the AC-end current reference value according to the AC-end voltage reference value and a difference between the AC-end voltage; a sixth subtractor, configured to obtain a difference between the AC end current reference value and the AC end current; A fifth PI regulator is used to generate the second modulation signal according to the difference between the AC end current reference value and the AC end current.

8. A power system, characterized in that: The invention comprises a power grid and a power quality device as claimed in any one of claims 1 to 7.

9. A method for compensating power quality, characterized in that: The method comprises: Control the on / off state of the bypass switch according to the working conditions of the power grid; According to the electrical parameters of the power grid, the electrical parameters of the converter module and the on / off state of the bypass switch, the converter module is controlled to provide reactive power or compensation voltage for the power grid.

10. The method according to claim 9, characterized in that The electrical parameters of the converter module include at least one of the DC terminal voltage, the AC terminal current and the AC terminal voltage; the electrical parameters of the power grid include at least one of the power grid voltage and the load current; The controlling the converter module to provide reactive power or compensation voltage for the power grid according to the electrical parameters of the power grid, the electrical parameters of the converter module and the on / off state of the bypass switch comprises: When the bypass switch is in an on state, according to the electrical parameters of the power grid and the electrical parameters of the converter module, controlling the converter module to provide reactive power for the power grid; When the bypass switch is in an off state, the converter module is controlled to provide a compensation voltage for the grid according to electrical parameters of the grid and electrical parameters of the converter module.

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