Grid-side current and direct-current voltage-based synchronous control method for grid-forming converter

Abstract

The invention relates to the technical field of converter control, in particular to a synchronous control method for a grid-forming converter based on grid-side current and direct-current voltage, and the method comprises the steps: obtaining the direct-current capacitor voltage on a direct-current bus and the output current of a grid-connected converter; according to the DC capacitor voltage on the DC bus and the output current of the grid-connected converter, working frequency required by the grid-connected converter is calculated; and integrating the working frequency required by the grid-connected converter to obtain a working phase for synchronously controlling the converter, and controlling the grid-connected converter by using the working phase information. The method is simple to control and can ensure the stability of the system.

Description

Technical Field

[0001] The invention relates to the technical field of converter control, and in particular to a synchronous control method of a grid-type converter based on grid-side current and direct current voltage. Background Art

[0002] With the continuous advancement of the transformation of energy and power systems, photovoltaic, wind power and other new energy power generation sites are gradually being connected to the power grid on a large scale. As the core grid-connected interface, power electronic converters are also profoundly affecting the stable operation mechanism and dynamic response characteristics of the current power system, and bringing difficulties and challenges that are very different from traditional power systems. According to the different control architectures and operation mechanisms, the current types of grid-connected converters are mainly classified into: grid-following (GFL) and grid-forming (GFM). The grid-following converter has current source characteristics and "following" characteristics to the external power grid as a whole, and it is difficult to provide active voltage support. It relies on the voltage of the external power grid for grid-connected synchronization, and cannot operate stably when the power grid strength is weak or the line impedance is large. The grid-forming converter mainly presents voltage source characteristics to the outside, relies on its own active power flow to achieve grid-connected synchronization, and has the ability to actively build voltage and support frequency under multiple time scales. It is one of the important guarantees for the safe and stable operation of the new power system, and is also a hot direction and frontier issue in current research. Traditional grid-type control methods (such as active power-frequency droop control, virtual synchronous machine control, etc.) require the DC side to be a constant DC voltage source, while the matching control method based on DC capacitor voltage synchronization does not need to be so. Through the equivalent simulation of the synchronous generator rotor inertia, the matching control can achieve DC voltage stability control and AC frequency stability control by itself. Therefore, matching control can be widely used in a variety of non-ideal constant voltage DC bus scenarios without additional energy storage, such as photovoltaic power generation, wind power generation, static VAR compensation, flexible DC transmission, etc., and has important research value and application potential.

[0003] Among the related matching control methods, directly sampling the DC capacitor voltage and then scaling it to obtain the operating frequency of the converter is the simplest and most well-known control method. However, it is worth noting that the above control only simulates the rotation dynamics of the synchronous machine rotor, and does not further simulate the synchronous damping effect of the synchronous machine damping winding. For the synchronous generator, when its own damping effect is insufficient, the small signal stability of the system cannot be guaranteed. At this time, the synchronous machine will be prone to low-frequency oscillation and shaft torsional vibration problems, which may cause damage to the rotor shaft system and cause system instability removal. At this time, through analogy speculation and test verification, it can be known that, similar to the synchronous machine, the above-mentioned simplest and most basic matching control method will also have low-frequency oscillation problems caused by insufficient self-damping. Therefore, in general, in the current matching control synchronization method based on DC capacitor voltage, there is still a lack of an improved control method with a simple control structure and which can effectively enhance the system's synchronous damping effect and ensure the stability of the system's small signal. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a synchronous control method of a grid-type converter based on grid-side current and DC voltage in view of the deficiencies in the above-mentioned prior art, so as to solve the technical problem that the current control method is complex and prone to low-frequency oscillation.

[0005] The objective of the present invention is achieved by the following technical solutions: In a first aspect, the present invention provides a method for synchronously controlling a grid-type converter based on grid-side current and DC voltage, comprising: Obtaining the DC capacitor voltage on the DC bus and the output current of the grid-connected converter; The required operating frequency of the grid-connected converter is calculated according to the DC capacitor voltage on the DC bus and the output current of the grid-connected converter; The working frequency required by the grid-connected converter is integrated to obtain a working phase for synchronously controlling the converter, and the grid-connected converter is controlled using the working phase information. As a further improvement of the present invention, obtaining the DC capacitor voltage on the DC bus and the output current of the grid-connected converter specifically includes: After the output current of the grid-connected converter is obtained, the output current of the grid-connected converter is subjected to coordinate transformation to obtain the d-axis component of the output current.

[0006] As a further improvement of the present invention, the operation frequency required by the grid-connected converter is calculated based on the DC capacitor voltage on the DC bus and the output current of the grid-connected converter, specifically including: According to the DC bus voltage reference value, the DC capacitor voltage on the DC bus and the proportionally processed output current d-axis component are calculated to obtain a first result; The output of the first result after the second proportional control is calculated with the grid frequency reference value to obtain the operating frequency required by the grid-connected converter.

[0007] As a further improvement of the present invention, according to the DC bus voltage reference value, the DC capacitor voltage on the DC bus and the proportionally processed output current d-axis component are calculated to obtain a first result, which specifically includes: After the output current d-axis component of the grid-connected converter is subjected to a first proportional control, a first output quantity is obtained; The first result is obtained by subtracting the first output value from the difference between the DC capacitor voltage on the DC bus and the DC bus voltage reference value.

[0008] As a further improvement of the present invention, the output amount of the first result after the second proportional control is calculated with the grid frequency reference value to obtain the operating frequency required by the grid-connected converter, specifically including: After performing a second proportional control on the first result, a second output is obtained; The second output quantity is added to the grid frequency reference value to obtain the required operating frequency of the grid-connected converter.

[0009] As a further improvement of the present invention, the first proportional control process adopts a proportional coefficient of proportional control link; the second proportional control process adopts the proportional control link with proportional coefficient N.

[0010] As a further improvement of the present invention, the working phase information is used to adopt The modulation method is used to generate a PWM wave control signal for the semiconductor switching device of the grid-connected converter.

[0011] As a further improvement of the present invention, the grid-connected converter adopts a two-level three-phase full-bridge topology structure.

[0012] As a further improvement of the present invention, after obtaining the working phase for synchronously controlling the converter, it also includes obtaining a voltage amplitude control instruction and performing coordinated control according to the voltage amplitude control instruction.

[0013] As a further improvement of the present invention, the voltage amplitude control instruction is obtained according to open-loop voltage control, voltage-current dual inner loop or reactive power-voltage droop control.

[0014] In a second aspect, the present invention provides a synchronous control system for a grid-type converter based on a grid-side current and a DC voltage, which is used to implement the above-mentioned synchronous control method for a grid-type converter based on a grid-side current and a DC voltage, comprising: A data acquisition module, used to acquire the DC capacitor voltage on the DC bus and the output current of the grid-connected converter; A data processing module, used for calculating the required operating frequency of the grid-connected converter according to the DC capacitor voltage on the DC bus and the output current of the grid-connected converter; The synchronous control module is used to integrate the working frequency required by the grid-connected converter to obtain the working phase for synchronously controlling the converter, and use the working phase information to control the grid-connected converter.

[0015] As a further improvement of the present invention, the control system is also used to coordinate with the voltage amplitude control system to control the grid-connected AC device.

[0016] In a third aspect, the present invention provides a computer-readable storage medium storing one or more programs, wherein the one or more programs include instructions, which, when executed by a computing device, enable the computing device to execute the above-mentioned method for synchronous control of a grid-type converter based on grid-side current and DC voltage.

[0017] In a fourth aspect, the present invention provides a computing device, comprising: One or more processors, a memory and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include steps for executing the above-mentioned method for synchronous control of a grid-type converter based on grid-side current and DC voltage.

[0018] The beneficial effects of the present invention are as follows: the synchronous control method of the grid-connected converter based on the grid-side current and DC voltage provided by the present invention has a very simple control structure and only needs to sample two electrical quantities as input quantities. The control link is simple and easy to implement, and compared with other matching controls based on DC voltage, the proposed synchronous control introduces the grid-side output current as the input quantity, thereby improving the damping effect of the system itself, thereby improving the system stability margin and ensuring the small signal stability of the system. The operating frequency and phase of the grid-connected converter are controlled based on accurate DC capacitor voltage and output current feedback, which can stabilize the grid voltage and frequency. The converter operates according to the appropriate operating frequency and phase calculated, which can compensate for the fluctuation of the grid voltage and adjust the frequency deviation to a certain extent.

[0019] Furthermore, by controlling the ratio of the DC capacitor voltage and the d-axis current component, the fluctuation of voltage and current can be effectively suppressed and the stability of the system can be improved. At the same time, by controlling the d-axis current component, the power factor of the converter can be optimized and the loss of reactive power can be reduced. Through the second proportional control, the operating frequency of the grid-connected converter can be accurately adjusted to keep it consistent with the grid frequency, thereby enhancing the synchronization and stability of the system. By accurately controlling the voltage and current, energy loss is reduced and the overall efficiency of the system is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 The present invention is applicable to a grid-type converter system circuit diagram and a simplified control block diagram taking into account non-ideal constant voltage DC conditions.

[0022] Figure 2 The invention provides a block diagram of synchronous control of a grid-type converter based on grid-side current and DC voltage.

[0023] Figure 3 In the test of the single-machine grid-connected system, when the grid-side power grid frequency first drops and then recovers, the converter output frequency , DC side voltage , output active Waveform change diagram.

[0024] Figure 4 The synchronous control method proposed in the present invention is used in the single-machine grid-connected system test, when the output power of the current machine side is When it first decreases and then increases, the inverter output frequency , DC side voltage , output active Waveform change diagram.

[0025] Figure 5 It is a schematic diagram of the structure of an electronic device of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose and technical solution of the present invention clearer and easier to understand, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0027] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, wherein the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0028] Example 1 like Figure 2-Figure 4As shown, this embodiment provides a synchronous control method for a grid-type converter based on grid-side current and DC voltage, which is suitable for the case where the front-stage system has a constant power input, and can effectively improve the damping effect of the system itself, thereby simultaneously ensuring the stability of the DC side voltage and the AC side frequency. The following is a specific implementation method.

[0029] First, obtain the DC capacitor voltage on the DC bus and the output current of the grid-connected converter .

[0030] Among them, the output current of the grid-connected converter is obtained After that, the output current of the grid-connected converter is transformed to obtain the d-axis component of the output current The current output by the grid-type converter is a three-phase current.

[0031] Secondly, the required operating frequency of the grid-connected converter is calculated according to the DC capacitor voltage on the DC bus and the output current of the grid-connected converter.

[0032] According to the DC bus voltage reference value , the DC capacitor voltage on the DC bus and the proportionally processed output current d-axis component are calculated to obtain a first result. Specifically, after the output current d-axis component of the grid-connected converter is subjected to the first proportional control, a first output quantity is obtained; the difference between the DC capacitor voltage on the DC bus and the DC bus voltage reference value is subtracted from the first output quantity to obtain the first result. In this embodiment, the first proportional control process uses a proportional coefficient of Proportional control link. Proportional coefficient It is a constant and is set according to the actual control situation.

[0033] The output after the second proportional control is performed on the first result, and the grid frequency reference value is calculated to obtain the operating frequency required by the grid-connected converter. Specifically, after the second proportional control is performed on the first result, the second output is obtained; the second output is calculated with the grid frequency reference value. Add them together to get the working frequency ω required by the grid-connected converter. Among them, the second proportional control process adopts a proportional control link with a proportional coefficient of N. Proportional coefficient It is a constant and is set according to the actual control situation.

[0034] Among them, the DC bus voltage reference value of this embodiment is And the grid frequency reference value It is a fixed constant set according to the grid standard.

[0035] Finally, the required operating frequency of the grid-connected converter is integrated to obtain the operating phase for synchronous control of the converter. , using the working phase information to control the grid-connected converter.

[0036] In this embodiment, the converter control system adopts the classic Modulation to generate a PWM wave control signal for the converter semiconductor switching device.

[0037] like Figure 3 The figure shows a constant power input single-machine grid-connected system model built in MATLAB / Simulink software. The synchronous control method proposed in the present invention is adopted. When the grid-side power grid frequency is disturbed, the output frequency of the converter corresponding to , DC side voltage , Active Power Waveform diagram. At 0.2s, the grid frequency is reduced from 1 pu to 0.99 pu, and the converter output frequency and DC voltage will also decrease, and the active power output The frequency of the power grid remains basically unchanged, and the overall system can achieve a stable transition under small disturbances; and the grid frequency is restored to 1 pu in 1s, and the overall converter system can also ensure stability.

[0038] like Figure 4 The figure shows the output frequency of the converter when the power output of the previous stage is disturbed. , DC side voltage , Active Power The waveform diagram shows that the current stage outputs a constant active power of When the inverter output frequency decreases from 1 pu to 0.75 pu in 0.2s, and DC voltage Can ensure stability and output active power Input active power The corresponding is consistent; at 1s, the previous stage input active power When it returns to 1 pu again, the overall converter system can also ensure stability.

[0039] Example 2 This embodiment provides a synchronous control system of a grid-type converter based on a grid-side current and a DC voltage, which is used to implement the synchronous control method of a grid-type converter based on a grid-side current and a DC voltage in Embodiment 1, including: A data acquisition module, used to acquire the DC capacitor voltage on the DC bus and the output current of the grid-connected converter; A data processing module, used for calculating the required operating frequency of the grid-connected converter according to the DC capacitor voltage on the DC bus and the output current of the grid-connected converter; The synchronous control module is used to integrate the working frequency required by the grid-connected converter to obtain the working phase for synchronously controlling the converter, and use the working phase information to control the grid-connected converter.

[0040] The single-machine grid-connected converter system architecture studied in this embodiment is as follows Figure 1 As shown in the figure, the leftmost box in the system circuit topology represents the front-stage power generation equivalent system. The front-stage power generation equivalent system can actually be a photovoltaic generator set, a wind turbine generator set, etc. Under this condition, the power output of the front-stage system It can be approximately regarded as a constant power output within a certain time scale. The DC bus is hung with an equivalent DC filter stabilizing capacitor The grid-connected converter is a classic two-level three-phase full-bridge topology, and the filter circuit and line impedance are uniformly converted to the inductive line impedance ( and ), among which The output current of the converter is three-phase AC, and the external equivalent power grid is In the system control architecture of this embodiment, it is also used to coordinate with the voltage amplitude control system to control the grid-connected AC device. Indicates the voltage amplitude control instruction. The voltage loop control method can be arbitrarily customized, such as open-loop voltage control, voltage and current dual inner loop, reactive power-voltage droop control, etc.

[0041] The synchronous control method proposed in this embodiment has two input quantities and one output quantity. The two input quantities are the DC capacitor voltage on the DC bus. , and the converter output current of Axis Component The output of the proposed synchronous control is the working phase of the converter The converter control system adopts the classic Modulation to generate a PWM wave control signal for the converter semiconductor switching device.

[0042] Example 3 In another embodiment of the present invention, the present invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a terminal device for storing programs and data. It is understandable that the computer-readable storage medium here can include both the built-in storage medium in the terminal device and the extended storage medium supported by the terminal device, and can be any tangible medium containing or storing a program, which can be used by an instruction execution system, device or device or used in combination with it. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that more specific examples (non-exhaustive list) of the computer-readable storage medium here include: an electrical connection with one or more wires, a portable disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above.

[0043] Computer readable storage media also include data signals propagated in baseband or as part of a carrier wave, which carry readable program codes. Such propagated data signals can take a variety of forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination of the above. The readable storage medium can also be any readable medium other than a readable storage medium, which can send, propagate, or transmit a program for use by or in conjunction with an instruction execution system, device, or device. The program code contained on the readable storage medium can be transmitted using any appropriate medium, including but not limited to wireless, wired, optical cable, RF, etc., or any suitable combination of the above.

[0044] Program code for performing the operations of the present invention may be written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Java, C++, etc., and conventional procedural programming languages ​​such as "C" or similar programming languages. The program code may be executed entirely on the user computing device, partially on the user device, as a separate software package, partially on the user computing device and partially on a remote computing device, or entirely on a remote computing device or server. In the case of a remote computing device, the remote computing device may be connected to the user computing device through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computing device (e.g., through the Internet using an Internet service provider).

[0045] One or more instructions stored in a computer-readable storage medium may be loaded and executed by a processor to implement the corresponding steps of the method for synchronous control of a grid-type converter based on grid-side current and DC voltage in the above embodiment; one or more instructions in the computer-readable storage medium are loaded and executed by the processor as follows: Obtaining the DC capacitor voltage on the DC bus and the output current of the grid-connected converter; The required operating frequency of the grid-connected converter is calculated according to the DC capacitor voltage on the DC bus and the output current of the grid-connected converter; The working frequency required by the grid-connected converter is integrated to obtain a working phase for synchronously controlling the converter, and the grid-connected converter is controlled using the working phase information.

[0046] Example 4 See also Figure 5 , the terminal device is a computer device, and the computer device 60 of this embodiment includes: a processor 61, a memory 62, and a computer program 63 stored in the memory 62 and executable on the processor 61. When the computer program 63 is executed by the processor 61, the synchronous control method of the grid-type converter based on the grid-side current and DC voltage in the embodiment is implemented. To avoid repetition, it is not described one by one here. Alternatively, when the computer program 63 is executed by the processor 61, the functions of each model / unit in the computing system composed of the synchronous control method of the grid-type converter based on the grid-side current and DC voltage are implemented. To avoid repetition, it is not described one by one here.

[0047] The computer device 60 may be a computing device such as a desktop computer, a notebook, a PDA, or a cloud server. The computer device 60 may include, but is not limited to, a processor 61 and a memory 62. Those skilled in the art will appreciate that Figure 5 This is only an example of the computer device 60 and does not constitute a limitation of the computer device 60. It may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, the computer device may also include input and output devices, network access devices, buses, etc.

[0048] The processor 61 may be a central processing unit (CPU), or other general-purpose processors, central processing units, graphics processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, data processing logic based on quantum computing, discrete hardware components, etc. A general-purpose processor may be a microprocessor or the processor may be any conventional processor, etc.

[0049] The memory 62 may be an internal storage unit of the computer device 60, such as a hard disk or memory of the computer device 60. The memory 62 may also be an external storage device of the computer device 60, such as a plug-in hard disk, a smart memory card (SmartMediaCard, SMC), a secure digital (SecureDigital, SD) card, a flash card (FlashCard), etc. equipped on the computer device 60.

[0050] Furthermore, the memory 62 may include both an internal storage unit of the computer device 60 and an external storage device. The memory 62 is used to store computer programs and other programs and data required by the computer device. The memory 62 may also be used to temporarily store data that has been output or is to be output.

[0051] Any reference to a memory, database or other medium used in the embodiments provided in this application may include at least one of a non-volatile and a volatile memory. Non-volatile memory may include a read-only memory (ROM), a magnetic tape, a floppy disk, a flash memory, an optical memory, a high-density embedded non-volatile memory, a resistive random access memory (ReRAM), a magnetic random access memory (MRAM), a ferroelectric random access memory (FRAM), a phase change memory (PCM), a graphene memory, etc. Volatile memory may include a random access memory (RAM) or an external cache memory, etc. As an illustration and not limitation, RAM may be in various forms, such as a static random access memory (SRAM) or a dynamic random access memory (DRAM), etc.

[0052] The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. The non-relational database may include a distributed database based on blockchain, etc., but is not limited thereto. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but is not limited thereto.

Claims

1. A synchronous control method for a grid-type converter based on grid-side current and DC voltage, characterized in that: include: Obtaining the DC capacitor voltage on the DC bus and the output current of the grid-connected converter; The required operating frequency of the grid-connected converter is calculated according to the DC capacitor voltage on the DC bus and the output current of the grid-connected converter; The working frequency required by the grid-connected converter is integrated to obtain a working phase for synchronously controlling the converter, and the grid-connected converter is controlled using the working phase information.

2. The method for synchronous control of a grid-type converter based on grid-side current and DC voltage according to claim 1, characterized in that: Obtaining the DC capacitor voltage on the DC bus and the output current of the grid-connected converter includes: After the output current of the grid-connected converter is obtained, the output current of the grid-connected converter is subjected to coordinate transformation to obtain the d-axis component of the output current.

3. The synchronous control method of a grid-type converter based on grid-side current and DC voltage according to claim 2, characterized in that: The step of calculating the required operating frequency of the grid-connected converter according to the DC capacitor voltage on the DC bus and the output current of the grid-connected converter specifically includes: According to the DC bus voltage reference value, the DC capacitor voltage on the DC bus and the proportionally processed output current d-axis component are calculated to obtain a first result; The output of the first result after the second proportional control is calculated with the grid frequency reference value to obtain the operating frequency required by the grid-connected converter.

4. The synchronous control method of a grid-type converter based on grid-side current and DC voltage according to claim 3, characterized in that: According to the DC bus voltage reference value, the DC capacitor voltage on the DC bus and the proportionally processed output current d-axis component are calculated to obtain a first result, which specifically includes: After the output current d-axis component of the grid-connected converter is subjected to a first proportional control, a first output quantity is obtained; The first result is obtained by subtracting the first output value from the difference between the DC capacitor voltage on the DC bus and the DC bus voltage reference value.

5. The synchronous control method of a grid-type converter based on grid-side current and DC voltage according to claim 3, characterized in that: The output amount after the second proportional control of the first result is calculated with the grid frequency reference value to obtain the required operating frequency of the grid-connected converter, specifically including: After performing a second proportional control on the first result, a second output is obtained; The second output quantity is added to the grid frequency reference value to obtain the required operating frequency of the grid-connected converter.

6. The method for synchronous control of a grid-type converter based on grid-side current and DC voltage according to claim 4 or 5, characterized in that: The first proportional control process uses a proportional coefficient of proportional control link; the second proportional control process adopts the proportional control link with proportional coefficient N.

7. The method for synchronous control of a grid-type converter based on grid-side current and DC voltage according to claim 1, characterized in that: Using the working phase information The modulation method is used to generate a PWM wave control signal for the semiconductor switching device of the grid-connected converter.

8. The method for synchronous control of a grid-type converter based on grid-side current and DC voltage according to claim 7, characterized in that: The grid-connected converter adopts a two-level three-phase full-bridge topology.

9. The method for synchronous control of a grid-type converter based on grid-side current and DC voltage according to claim 7, characterized in that: After obtaining the working phase for synchronously controlling the converter, it also includes obtaining a voltage amplitude control instruction and performing coordinated control according to the voltage amplitude control instruction.

10. The method for synchronous control of a grid-connected converter based on grid-side current and DC voltage according to claim 9, characterized in that: The voltage amplitude control command is obtained according to open-loop voltage control, voltage-current dual inner loop or reactive-voltage droop control.

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