Static reactive power regulation system based on direct-series compensation interface and control method

Abstract

The invention discloses a static var adjusting system based on a direct-series compensation interface, and discloses a control method corresponding to the static var adjusting system based on the direct-series compensation interface, and the static var adjusting system keeps the physical architecture of a standard SVG, sampling modulation, control and protection and other original schemes basically unchanged. Under the condition of not changing the volume size and the operation burden of the commutation chain, the direct-series compensation interface is coupled, and the integration level of the system is improved; the equivalent grid-connected inductance of the system is dynamically adjustable, the adjustment freedom degree of equipment is increased, and the system has the grid-connected point interface impedance matching capability; the resistance value of a direct-series compensation interface of the system is reduced, and the equipment can better realize grid-side harmonic elimination and has better dynamic response capability; and the resistance value of the direct-series compensation interface of the system is increased, so that the equipment can obtain a more stable steady-state operation effect.

Description

Technical Field

[0001] The present invention relates to the technical field of reactive power compensation devices for power systems, and particularly relates to a static reactive power regulation system and a control method based on a series compensation interface. Background Art

[0002] With the construction of a new power system, the grid connection of a large number of new energy sources and the access of power electronic equipment have caused great changes in the operating conditions of conventional reactive power compensation devices in the power grid. Voltage flicker and fluctuations caused by insufficient reactive power capacity in the system can lead to large-scale chain disconnection of various clean energy sources, posing a serious threat to the stable operation of the power system. To ensure the economic and stable operation of the system, rapid and effective compensation of reactive power has become crucial.

[0003] With the development of power electronic technology, cascaded static synchronous compensators (SVG) have been widely used in China's power grid projects in recent years due to their superior performance. SVG devices with flexible reactive power regulation capabilities have achieved engineering substitution of a large number of fixed shunt capacitors, mainly including most grid-connected SVGs and a small number of grid-forming SVGs.

[0004] In the system, grid-connected SVGs can be equivalent to current source structures, thus having better dynamic performance and response capabilities. However, the negative resistance frequency band in the amplitude-frequency and phase-frequency characteristic curves of this type of SVG is extremely likely to cause system oscillations and then induce malignant accidents. For this reason, grid-forming SVGs with better stability and support performance have received more attention. However, there are still many difficulties in aspects such as the physical characteristics, frequency domain characteristics, and control strategies of existing grid-forming SVG devices.

[0005] In terms of physical characteristics, the operating mode of grid-forming SVGs is similar to that of synchronous machines. By exchanging power with the power grid to simulate inertia and damping characteristics, adjusting the reference voltage and output frequency to achieve synchronization with the power grid, it generally shows voltage source characteristics externally. Although the control strategy of grid-forming SVGs simulates the external characteristics of traditional synchronous machines, there are essential differences between the physical structures of converters and synchronous machines. Existing strategies are difficult to simulate the magnetic flux characteristics of synchronous machines, and it is difficult to balance their steady-state, transient, and super-transient characteristics. There is a contradiction between steady-state power flexible regulation and transient voltage support.

[0006] In terms of frequency domain characteristics, in the new power system, the access of large-scale power electronic devices has changed the frequency domain characteristics of the system, and the stability requirement extends from the fundamental wave to a wider frequency band. The salient-pole structure of the synchronous generator forms an alternating air-gap permeance, and the few main magnetic field harmonic components generated have an important impact on the output characteristics of the motor. Although existing grid-following / grid-forming SVG both have harmonic matching capabilities, there are problems of harmonic blocking in the fixed reactor, and it is necessary to increase the length of the converter chain to increase the harmonic output capacity, and it can usually only handle low-range harmonics such as the 5th and 7th harmonics. Therefore, it usually only operates in the fundamental wave regulation mode on site.

[0007] In terms of control strategies, grid-forming SVG usually adopts the virtual synchronous generator method to achieve transient voltage support. In order to take into account the advantages of both grid-forming and grid-following modes at the same time, researchers have carried out research including grid-following / grid-forming hybrid control strategies, etc., all of which are implemented based on the standard SVG topology. However, during the control process, the fundamental wave differential equation of the underlying inner loop is dual to the hardware structure, and it is not easy to balance the dynamic response ability of the fundamental wave reactive power and the harmonic frequency domain stability. The cross-coupling terms of the inner and outer loop AC / DC paths further restrict the value of the inductor. Summary of the Invention

[0008] The present invention aims to solve at least one of the technical problems existing in the prior art. For this reason, the present invention proposes a static var regulation system based on a series compensation interface, which can keep the original schemes such as the physical architecture, sampling modulation, and control and protection of the standard SVG basically unchanged, and couple the series compensation interface without changing the volume size and operation burden of the converter chain, thereby improving the integration of the system; at the same time, the equivalent grid-connected inductance of the system is dynamically adjustable, increasing the adjustment freedom of the device and having the ability to match the interface impedance at the grid connection point; the resistance value of the series compensation interface of the system is reduced, and the device can better eliminate harmonics on the grid side and has better dynamic response ability; when the resistance value of the series compensation interface of the system increases, the device can instead obtain a more stable steady-state operation effect.

[0009] The present invention also proposes a control method for a static var regulation system with a series compensation interface.

[0010] The static var regulation system based on the series compensation interface according to the first aspect embodiment of the present invention is characterized in that it includes a single-phase structure topology, and the single-phase structure topology includes:

[0011] A disconnecting switch (S0), one end of which is connected to the line, and the other end is sequentially connected to an overvoltage protection arrester (R1), an earthing switch (S1), a starting resistor (R2), and a starting bypass switch (S2);

[0012] The front-end connecting reactor (L0) has one end connected to the starting resistor (R2) and the starting bypass switch (S2), and the other end connected to the bypass reactor (L1) and the back-end connecting reactor (L2);

[0013] The cascaded unit group (H1 - H n ), where one end of the cascaded unit (H1) is connected to the back-end connecting reactor (L2) and the bypass reactor (L1), and the subsequent cascaded units are connected in series in turn;

[0014] The cascaded unit (H1), the front-end connecting reactor (L0), the bypass reactor (L1), and the back-end connecting reactor (L2) form a direct series compensation interface structure;

[0015] During system operation, the cascaded unit (H1) is in a direct series compensation operation state, and the remaining cascaded units (H2 - H n ) are in a grid-forming or grid-following SVG reactive power compensation operation state, and the reactive power dynamic regulation and harmonic suppression are realized by adjusting the equivalent impedance parameters of the direct series compensation interface.

[0016] According to the static var regulation system based on the direct series compensation interface of the embodiments of the present invention, it can realize the flexible regulation of reactive power and the fast response to harmonics from both the structural and control aspects. While keeping the original schemes such as the physical architecture, sampling modulation, and control protection of the standard SVG basically unchanged, without changing the volume size and operation burden of the converter chain, the direct series compensation interface is coupled to improve the system integration; at the same time, the equivalent grid-connected inductance of the system is dynamically adjustable, increasing the adjustment freedom of the equipment and having the ability to match the interface impedance of the connection point; the resistance value of the system direct series compensation interface is reduced, and the equipment can better eliminate the grid-side harmonics and has better dynamic response capabilities; when the resistance value of the system direct series compensation interface increases, the equipment can obtain a more stable steady-state operation effect instead.

[0017] According to some embodiments of the present invention, the cascaded unit includes an H-bridge unit or an MMC half-bridge unit.

[0018] According to some embodiments of the present invention, the single-phase structure topology adopts a Y-type connection or a Δ-type connection.

[0019] According to some embodiments of the present invention, the control strategy of the direct series compensation interface structure is: controlling the cascaded unit (H1) to inject a series voltage with an adjustable amplitude and a phase angle of 90° with the current into the line, equivalently changing the grid-connected impedance parameters of the reactive power compensation device.

[0020] According to some embodiments of the present invention, one or a combination of the following functions is realized by adjusting the resistance value of the direct series compensation interface:

[0021] When the resistance value is reduced, the grid-side harmonic elimination ability and the dynamic response speed are enhanced;

[0022] Improve the steady-state operation stability of the system when increasing the resistance value.

[0023] A control method for a static var regulation system based on a series-parallel compensation interface according to an embodiment of the second aspect of the present invention is characterized by comprising the following steps:

[0024] Control the cascaded unit (H1) to output a series compensation voltage with a 90° phase difference from the line current;

[0025] Dynamically adjust the amplitude of the series compensation voltage to change the equivalent grid connection impedance parameters;

[0026] Switch the resistance value mode of the series-parallel compensation interface according to system requirements to achieve the dynamic balance of harmonic suppression and steady-state operation.

[0027] According to some embodiments of the present invention, the amplitude adjustment of the series compensation voltage is based on real-time grid operating condition data and is achieved through a closed-loop control algorithm.

[0028] According to some embodiments of the present invention, the closed-loop control algorithm includes the coordinated control of a voltage outer loop and a current inner loop, and decouples the coupling terms of the AC / DC axis channels to optimize the inductor parameters.

[0029] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, wherein:

[0031] Figure 1 It is a schematic diagram of the Y-type connection topology of a static var regulation system based on a series-parallel compensation interface according to an embodiment of the present invention;

[0032] Figure 2 It is a schematic diagram of the Δ-type connection topology of a static var regulation system based on a series-parallel compensation interface according to an embodiment of the present invention;

[0033] Figure 3 It is a control block diagram of a static var regulation system based on a series-parallel compensation interface according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] Embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary only for explaining the present invention and should not be construed as limiting the present invention.

[0035] In the description of the present invention, it should be understood that for the orientation description, such as the orientation or positional relationship indicated by up, down, front, back, left, right, etc., it is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention.

[0036] In the description of the present invention, the meaning of several is one or more, the meaning of multiple is more than two, greater than, less than, exceeding, etc. are understood as not including the present number, above, below, within, etc. are understood as including the present number. If the first and second are described only for the purpose of distinguishing technical features, they should not be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or the sequence relationship of the indicated technical features.

[0037] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installation, connection, etc. should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above terms in the present invention in combination with the specific content of the technical solution.

[0038] Embodiment 1

[0039] To meet the needs of the prior art, the present invention provides a static var regulation system based on a series compensation interface. The topology of the single-phase structure of the static var regulation system mainly includes:

[0040] Disconnecting switch S0, overvoltage protection arrester R1, earthing switch S1, starting resistor R2, starting bypass switch S2, front-end connecting reactor L0, bypass reactor L1, back-end connecting reactor L2, cascade units H1 - H n , where n is the number of cascade units. The cascade units include, but are not limited to, H-bridge units, MMC half-bridge units, etc. The Y-connected topology is as shown in the appendix Figure 1 shown, and its Δ-connected topology is as shown in the appendix Figure 2 shown.

[0041] The single-phase structure of the static var regulation system is taken as the basic unit. In the topology: one end of the disconnecting switch S0 is connected to the line, and the other end is connected to one end of the overvoltage protection arrester R1, the earthing switch S1, the starting resistor R2, and the starting bypass switch S2. The other ends of the overvoltage protection arrester R1 and the earthing switch S1 are grounded. The other ends of the starting resistor R2 and the starting bypass switch S2 are connected to the front-end connecting reactor L0. The other end of the front-end connecting reactor L0 is connected to one end of the bypass reactor L1 and the rear-end connecting reactor L2. The other end of the rear-end connecting reactor L2 is connected to one end of the cascaded unit H1. The other end of the bypass reactor L1 is connected to one end of the cascaded unit H1 and is connected to one end of the cascaded unit H2 until the cascaded unit H n .

[0042] In the static var regulation system, the cascaded unit H1, the front-end connecting reactor L0, the bypass reactor L1, and the rear-end connecting reactor L2 form the series compensation interface structure. During the operation of the system, the cascaded unit H1 is in the series compensation operation state, and the cascaded units H2 - H n are in the standard grid-forming or grid-following SVG reactive power compensation operation state.

[0043] Embodiment 2:

[0044] Based on the static var regulation system with a series compensation interface provided in Embodiment 1, a corresponding control method is provided for the influence.

[0045] The basic working principle of the series compensation interface structure is similar to that of the standard static synchronous series compensator (SSSC). The control strategy is to control the cascaded unit H1 to inject a series voltage with an adjustable amplitude and a phase angle of 90° with the current into the line. Here, it is equivalent to connecting a controllable impedance in series at the standard SVG connection port, which can change the equivalent grid-connected impedance parameters of the reactive power compensation device, so as to realize the regulation of the impedance parameters of the SVG reactive power compensation interface and achieve the static var regulation system and control based on the series compensation interface. The control block diagram of the static var regulation system based on the series compensation interface is as shown in the appendix Figure 3 .

[0046] Dynamically adjust the amplitude of the series compensation voltage to change the equivalent grid-connected impedance parameters;

[0047] According to the system requirements, switch the resistance value mode of the series compensation interface to achieve the dynamic balance between harmonic suppression and steady-state operation.

[0048] The device embodiments described above are only illustrative. The units described as separate components may or may not be physically separated, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0049] Those of ordinary skill in the art will understand that all or some of the steps and systems disclosed in the above methods can be implemented as software, firmware, hardware, and their appropriate combinations. Some physical components or all physical components can be implemented as software executed by a processor, such as a central processing unit, a digital signal processor, or a microprocessor, or can be implemented as hardware, or can be implemented as an integrated circuit, such as an application specific integrated circuit. Such software can be distributed on a computer-readable medium, which can include a computer storage medium (or non-transitory medium) and a communication medium (or transitory medium). As is well known to those of ordinary skill in the art, the term computer storage medium includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information, such as computer-readable instructions, data structures, program modules, or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technologies, CD-ROM, digital versatile disk (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and can be accessed by a computer. In addition, as is well known to those of ordinary skill in the art, communication media typically includes computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transmission mechanism, and can include any information delivery medium.

[0050] The above is a specific description of the preferred embodiments of the present application, but the present application is not limited to the above embodiments. Those skilled in the art can also make various equivalent deformations or substitutions without departing from the spirit of the present application, and these equivalent deformations or substitutions are all included within the scope defined by the claims of the present application.

Claims

1. A static var regulation system based on a series compensation interface, characterized in that, Including a single-phase structure topology, the single-phase structure topology includes: A disconnector (S0), one end of which is connected to a line, and the other end is sequentially connected to a lightning arrester for overvoltage protection (R1), an earthing switch (S1), a starting resistor (R2), and a starting bypass switch (S2); A front-end connecting reactor (L0), one end of which is connected to the starting resistor (R2) and the starting bypass switch (S2), and the other end is connected to a bypass reactor (L1) and a back-end connecting reactor (L2); Cascade unit group (H1 - H n ), one end of the cascade unit (H1) is connected to the backend connecting reactor (L2) and the bypass reactor (L1), and the subsequent cascade units are connected in series in turn; The cascaded unit (H1), the front-end connecting reactor (L0), the bypass reactor (L1), and the back-end connecting reactor (L2) form a series compensation interface structure; When the system is running, the cascaded unit (H1) is in the series compensation operation state, and the remaining cascaded units (H2 - H n ) are in the grid-forming or grid-following SVG reactive power compensation operation state, and the reactive power dynamic regulation and harmonic suppression are realized by adjusting the equivalent impedance parameters of the series compensation interface.

2. The static var regulation system according to claim 1, wherein The cascaded unit includes an H-bridge unit or an MMC half-bridge unit.

3. The static var regulation system according to claim 1, characterized in that The single-phase structure topology adopts a Y-connection or a Δ-connection.

4. The static var regulation system according to claim 1, characterized in that, The control strategy of the series compensation interface structure is: controlling the cascaded unit (H1) to inject a series voltage with an adjustable amplitude and a phase angle of 90° with respect to the current into the line, equivalently changing the grid-connected impedance parameters of the reactive power compensation device.

5. The control strategy according to claim 4, wherein One or a combination of the following functions is achieved by adjusting the resistance value of the series compensation interface: Enhancing the grid-side harmonic elimination ability and dynamic response speed when reducing the resistance value; Improving the steady-state operation stability of the system when increasing the resistance value.

6. A control method for a static var regulation system based on a series compensation interface, characterized in that, Including the following steps: Controlling the cascaded unit (H1) to output a series compensation voltage with a phase difference of 90° from the line current; Dynamically adjusting the amplitude of the series compensation voltage to change the equivalent grid-connected impedance parameters; Switching the resistance value mode of the series compensation interface according to system requirements to achieve a dynamic balance between harmonic suppression and steady-state operation.

7. The control method according to claim 6, wherein The amplitude adjustment of the series compensation voltage is based on real-time grid operating condition data and is achieved through a closed-loop control algorithm.

8. The control method according to claim 7, characterized in that The closed-loop control algorithm includes the coordinated control of a voltage outer loop and a current inner loop, and decouples the coupling terms of the AC / DC axis channels to optimize the inductor parameters.

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