Method and system for suppressing power oscillation of grid-constructing / grid-following converter parallel system under limited capacity

Abstract

The invention discloses a method and a system for suppressing power oscillation of a grid-constructing / grid-following converter parallel system under limited capacity, and the method comprises the steps: introducing a transient current compensation branch circuit related to a q-axis output voltage, a d-axis output voltage and a q-axis current reference value into a grid-constructing / grid-following converter; the method can effectively reduce the interaction between the network construction type converter and the network construction type / following network type converter under the condition that the extra parameters of the network construction type energy storage converter and the AC bus are not required to be detected and no extra control information is required, inhibits the power oscillation of the network construction type / following network type converter parallel system, and improves the reliability of the network construction type / following network type converter parallel system. And the anti-interference capability and the operation stability of the system under the dynamic working condition are enhanced.

Description

Technical Field

[0001] The present invention relates to the field of microgrid operation and stability control, and in particular to a method and system for suppressing power oscillation of a parallel system of grid-forming / grid-following converters under limited capacity. Background Art

[0002] With the development of new energy technologies, new energy microgrids based on grid-forming converters and grid-forming / following converters have been widely used and researched. However, compared with traditional power grids, the overall power support capability of these systems is weaker, and the dynamic interaction between grid-forming converters and grid-forming / following converters is more complex, which can easily cause power oscillations during load disturbances, affecting system stability and power supply quality.

[0003] In such systems, the grid-forming converter regulates the grid frequency and voltage by simulating the inertia and damping characteristics of synchronous generators, while the grid-forming / following converters employ AC current control strategies to track the system voltage, ensuring stable grid-connected operation. However, the parallel system's power supply capacity is limited, and the switching of high-power loads causes dynamic fluctuations in the system voltage and frequency, exacerbating the interaction between the grid-forming converter and the grid-forming / following converters, leading to power oscillations.

[0004] At present, research on oscillations in grid-connected / grid-following converter parallel systems is mainly focused on the subsynchronous oscillation problem in grid-connected scenarios. CN118739347A discloses a method and system for suppressing subsynchronous oscillations in a grid-connected / grid-following new energy hybrid parallel system. By adding a damping compensation controller to the voltage control link of the grid-connected new energy grid-connected inverter, the impedance of the hybrid parallel system is reshaped to weaken its negative damping characteristics. This method can effectively improve the operating stability of the grid-connected / grid-following new energy hybrid parallel system and suppress the subsynchronous oscillation of the system caused by wide-range changes in grid strength. The above method mainly solves the problem of voltage subsynchronous oscillation that occurs when the grid-following / grid-connecting converter is connected to the grid. However, when the grid-following / grid-connecting converter parallel system operates in off-grid mode, the system power supply capacity is limited, and the power oscillation problem caused by load power shock has not been effectively solved. In addition, with the expansion of the scale of parallel systems and the influence of non-ideal factors such as dynamic load shocks, traditional oscillation suppression methods based on centralized controllers are difficult to balance fast response and engineering feasibility. There is an urgent need for a new distributed power oscillation suppression strategy that does not require additional measurement of virtual synchronous machine side parameters and can directly perform compensation control on the grid-forming / grid-following converter side to improve the dynamic stability and power supply reliability of the grid-forming / grid-following converter parallel system under limited capacity. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of existing technologies and provide a method and system for suppressing power oscillations in a parallel system of grid-connected / grid-following converters under limited capacity. This method and system achieve rapid suppression of power oscillations in the parallel system without the need to detect virtual synchronous machines and AC bus parameters and without requiring the system to provide any additional control information, while retaining the distributed control characteristics of the virtual synchronous machines and grid-connected / grid-following converters. This method solves the power oscillation problem caused by the interaction between virtual synchronous machines and parallel grid-connected / grid-following converters when the parallel system power supply capacity is limited, thereby ensuring the safe and reliable operation of the parallel grid-connected / grid-following converter system.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is: a method for suppressing power oscillations in a parallel system of grid-connected / grid-following converters under limited capacity, comprising the following steps:

[0007] The three-phase output voltage and three-phase output current of the grid-forming / grid-following converter are sampled, and the d-axis voltage component u of the grid-forming / grid-following converter is obtained by Park transformation using the three-phase output voltage. 2d and the q-axis voltage component u 2q , the d-axis current component i of the grid-forming / grid-following converter is obtained by Park transformation of the three-phase output current. 2d and the q-axis current component i 2q ;

[0008] According to the q-axis voltage component u of the grid-forming / grid-following converter 2q Calculate the current phase θ GFI , according to the d-axis component u of the output voltage of the grid-forming / grid-following converter 2d and the q-axis component u 2q Introduce the transient current compensation branch and calculate the transient current compensation component I c ;

[0009] According to the d-axis voltage component u of the grid-forming / grid-following converter 2d , q-axis voltage component u 2q , d-axis current component i 2d and the q-axis current component i 2q , and the current phase θ GFI , calculate the d-axis electromotive force e of the terminal voltage of the grid-following converter 2d and q-axis electromotive force e 2q ;

[0010] d-axis electromotive force e 2d and q-axis electromotive force e 2q Perform inverse Park transformation to obtain the output three-phase electromotive force of the grid-forming / grid-following converter. GFI And output three-phase electromotive force e2abc Perform PWM modulation on the grid-forming / grid-following converter to obtain the switch tube driving signal K of the grid-forming / grid-following converter PWM2 .

[0011] The present invention introduces a transient current compensation component related to the q-axis voltage component, d-axis voltage component and q-axis reference current into the current control inner loop of the grid-forming / grid-following converter, effectively reducing the interaction between the grid-forming converter and the grid-forming / grid-following converter, and suppressing the power oscillation of the grid-forming / grid-following converter parallel system.

[0012] Current phase θ GFI The calculation formula is:

[0013] θ GFI =∫(K kp u 2q +K ip ∫u 2q dt)dt;

[0014] Among them, K kp and K ip are the phase proportional coefficient and phase integral coefficient respectively.

[0015] Transient current compensation component I c The calculation formula is:

[0016] I c =I 2qn ·arctan(u 2q / u 2d );

[0017] Among them, I 2qn It is the q-axis reference current of the grid-forming / grid-following converter.

[0018] d-axis electromotive force e 2d and q-axis electromotive force e 2q The calculation formula is:

[0019]

[0020] Among them, I 2dn Indicates the d-axis reference current of the grid-forming / grid-following converter, K p2 and K i2 Represents the current control proportional coefficient and current control integral coefficient respectively, L f2 and ω n They represent the output filter inductance and rated angular frequency of the grid-forming / grid-following converters respectively.

[0021] As an inventive concept, the present invention also provides a power oscillation suppression system for a grid-type / grid-following converter parallel system under limited capacity, comprising one or more processors and a memory; one or more programs are stored on the memory, and when the one or more programs are executed by the one or more processors, the one or more processors implement the steps of the above method.

[0022] As an inventive concept, the present invention also provides a computer-readable storage medium having a computer program / instruction stored thereon; the computer program / instruction implements the steps of the above method when executed by a processor.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention introduces a transient current compensation component related to the q-axis voltage component, d-axis voltage component and q-axis reference current of the grid-forming / grid-following converter into the current control inner loop, effectively reducing the interaction between the grid-forming converter and the grid-forming / grid-following converter, suppressing the power oscillation of the grid-forming / grid-following converter parallel system, and improving the dynamic stability and power supply reliability of the grid-forming / grid-following converter parallel system under limited capacity.

[0025] 2. The voltage and current data used in the present invention can be directly detected by the voltage and current data acquisition module and processed in real time by the control chip, which is simple to implement and has low operational complexity. In addition, the present invention can detect additional parameters of the network-forming converter and the AC bus, and does not require the system to provide any additional control information. Therefore, there is no need to set up interconnection communication between units, and there is no need to consider potential data loss and transmission delay issues during the interconnection communication between units.

[0026] 3. Due to the q-axis voltage component u 2q The steady-state value of is 0, so the transient current compensation component I 2c The steady-state value of is also 0, so the present invention does not affect the steady-state output power of the grid-forming / grid-following converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the structure of a parallel system of grid-forming / grid-following converters under limited capacity in an embodiment of the present invention;

[0028] Figure 2 This is a control block diagram of the dq decoupling control of the grid-forming / grid-following converter in an embodiment of the present invention;

[0029] Figure 3 The output power waveform of the grid-type / grid-following converter parallel system is constructed before and after the power oscillation suppression method proposed in the embodiment of the present invention is introduced. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0031] Example 1

[0032] like Figure 1 As shown, the parallel system structure of the grid-forming / grid-following converters in an embodiment of the present invention includes at least one grid-forming converter controlled by a virtual synchronous generator and at least one grid-forming / grid-following converter controlled by a dq decoupling. Both the grid-forming converter and the grid-forming / grid-following converter are connected to loads through a bus, and the loads include steady-state loads and dynamic loads.

[0033] exist Figure 1 In, L f1 and L f2 are the output filter inductors of the grid-forming converter and the grid-forming / grid-following converter respectively; C f1 and C f2 are the output filter capacitors of the grid-forming converter and the grid-forming / grid-following converter respectively; L 1line 、L 2line 、R 1line and R 2line are the line inductance and line resistance of the virtual synchronous machine and the grid-forming / grid-following converter connected to the AC bus respectively; u 1abc and u 2abc are the three-phase voltages output by the grid-forming converter and the grid-forming / grid-following converter respectively; i 1abc and i 2abc are the three-phase currents output by the grid-forming converter and the grid-forming / grid-following converter respectively; K PWM1 and K PWM2 The output electromotive force effective values are for the grid-forming converter and the grid-forming / grid-following converter respectively.

[0034] like Figure 2 As shown, the power oscillation suppression method and system of the grid-connected / grid-following converter parallel system under limited capacity in the embodiment of the present invention specifically include the following steps:

[0035] Step 1: Sampling and coordinate transformation

[0036] Sampling the output three-phase voltage u of the grid-forming / grid-following converter 2abc And the output three-phase current i 2abc, using the output three-phase voltage u 2abc Perform Park transformation to obtain the d-axis voltage component u of the grid-forming / grid-following converter 2d and the q-axis voltage component u 2q , using the output three-phase current i 2abc Perform Park transformation to obtain the d-axis current component i of the grid-forming / grid-following converter 2d and the q-axis current component i 2q .

[0037] Step 2: Current phase calculation

[0038] The q-axis voltage component u of the grid-forming / grid-following converter calculated according to step 1 2q Calculate the current phase θ GFI , the specific formula is

[0039] θ GFI =∫(K kp u 2q +K ip ∫u 2q dt)dt

[0040] Among them, K kp and K ip are the phase proportional coefficient and phase integral coefficient respectively.

[0041] Step 3: Generate transient current compensation component

[0042] The d-axis component u of the output voltage of the grid-forming / grid-following converter calculated in step 1 is 2d and the q-axis component u 2q The transient current compensation branch is introduced, and then the transient current compensation component I is calculated. c , the specific formula is:

[0043] I c =I 2qn ·arctan(u 2q / u 2d )

[0044] Among them, I 2qn It is the q-axis reference current of the grid-forming / grid-following converter.

[0045] Step 4: Modulation voltage generation

[0046] The d-axis voltage component u of the grid-forming / grid-following converter calculated in step 1 2d , q-axis voltage component u 2q , d-axis current component i 2d and the q-axis current component i 2q , and the current phase θ calculated in step 2 GFI, calculate the d-axis electromotive force e of the terminal voltage of the grid-following converter 2d and q-axis electromotive force e 2q , the specific formula is:

[0047]

[0048] Among them, I 2dn Represents the d-axis reference current of the grid-forming / grid-following converter; K p2 and K i2 Respectively represent the current control proportional coefficient and current control integral coefficient; L f2 and ω n They represent the output filter inductance and rated angular frequency of the grid-forming / grid-following converters respectively.

[0049] Step 5: Generate drive signal

[0050] The d-axis electromotive force e calculated in step 4 2d and q-axis electromotive force e 2q Perform inverse Park transformation to obtain the output three-phase electromotive force of the grid-forming / grid-following converter. GFI And output three-phase electromotive force e 2abc Perform PWM modulation on the grid-forming / grid-following converter to obtain the switch tube driving signal K of the grid-forming / grid-following converter PWM2 .

[0051] like Figure 3 As shown in the figure, the output power waveforms of the parallel system of grid-type / grid-type converters before and after the introduction of the proposed power oscillation suppression method in the embodiment of the present invention are shown. At 1 second, the system is connected to a 30kW dynamic load. At this time, the grid-type converter quickly responds to the dynamic load power change. However, due to the limited system capacity, there is a serious interaction between the grid-type converter and the grid-type / grid-type converter, causing the output power of the grid-type / grid-type converter to fluctuate violently, with the peak-to-valley difference in power fluctuation reaching 11.29kW, seriously affecting the stable operation of the system. 2 seconds later, the power oscillation suppression method proposed in the embodiment of the present invention is introduced. At this time, the grid-type converter responds to the dynamic load power change, while the grid-type / grid-type converter maintains the rated power output. At this time, the peak-to-valley difference in power fluctuation of the grid-type / grid-type converter is 1.25kW, and the power oscillation is reduced by 88.93%. The power oscillation is effectively suppressed, indicating that the embodiment of the present invention can effectively suppress the power oscillation of the parallel system of grid-type / grid-type converters and achieve stable operation of the parallel system of grid-type / grid-type converters.

[0052] Example 2

[0053] Embodiment 2 of the present invention further provides a grid-forming / grid-following converter parallel control system corresponding to the above-mentioned embodiment 1, comprising: one or more processors, a memory and one or more programs stored thereon, wherein when the one or more programs are executed by the one or more processors, the one or more processors implement the steps of the power oscillation suppression method of the diesel-storage parallel power supply system of the above-mentioned embodiment 1 of the present invention. In some implementations, the memory may be a high-speed random access memory (RAM), and may also include a non-volatile memory (NonVolatileMemory), such as at least one disk storage. In other implementations, the processor may be various types of general-purpose processors such as a central processing unit (CPU), a digital signal processor (DSP), etc., which are not limited here.

[0054] The grid-connected control based on the virtual synchronous machine included in the embodiment of the present invention is applicable to both off-grid operation mode and grid-connected operation mode.

[0055] In some implementations, the memory may be a high-speed random access memory (RAM), and may also include a non-volatile memory, such as at least one disk storage.

[0056] In other implementations, the processor may be a central processing unit (CPU), a digital signal processor (DSP), or other general-purpose processors, which are not limited herein.

[0057] Example 3

[0058] Embodiment 3 of the present invention provides a computer-readable storage medium corresponding to the above-mentioned embodiment 1, on which a computer program / instruction is stored. When the computer program / instruction is executed by a processor, the steps of the method of the above-mentioned embodiment 1 are implemented.

[0059] Computer readable storage media can be tangible devices that hold and store instructions used by instruction execution devices. Computer readable storage media can be, for example, but not limited to, electronic storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any combination thereof.

[0060] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code. The scheme in the embodiment of the present application can be implemented in various computer languages, for example, object-oriented programming language Java and literal translation scripting language JavaScript, etc.

[0061] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0062] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0063] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

[0064] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A method for suppressing power oscillations in a parallel system of grid-connected / grid-following converters under limited capacity, characterized in that: The following steps are involved: The three-phase output voltage and three-phase output current of the grid-forming / grid-following converter are sampled, and the d-axis voltage component u of the grid-forming / grid-following converter is obtained by Park transformation using the three-phase output voltage. 2d and the q-axis voltage component u 2q , the d-axis current component i of the grid-forming / grid-following converter is obtained by Park transformation of the three-phase output current. 2d and the q-axis current component i 2q ; According to the q-axis voltage component u of the grid-forming / grid-following converter 2q Calculate the current phase θ GFI , according to the d-axis component u of the output voltage of the grid-forming / grid-following converter 2d and the q-axis component u 2q Introduce the transient current compensation branch and calculate the transient current compensation component I c ; According to the d-axis voltage component u of the grid-forming / grid-following converter 2d , q-axis voltage component u 2q , d-axis current component i 2d and the q-axis current component i 2q , and the current phase θ GFI , calculate the terminal voltage of the grid-type converter d-axis electromotive force e 2d and q-axis electromotive force e 2q ; d-axis electromotive force e 2d and q-axis electromotive force e 2q Perform inverse Park transformation to obtain the output three-phase electromotive force of the grid-forming / grid-following converter. GFI And output three-phase electromotive force e 2abc Perform PWM modulation on the grid-forming / grid-following converter to obtain the switch tube driving signal K of the grid-forming / grid-following converter PWM2 .

2. The method for suppressing power oscillations of a parallel system of grid-connected / grid-following converters under limited capacity according to claim 1, characterized in that: Current phase θ GFI The calculation formula is: θ GFI =∫(K kp u 2q +K ip ∫u 2q dt)dt; Among them, K kp and K ip are the phase proportional coefficient and phase integral coefficient respectively.

3. The method for suppressing power oscillation of a parallel system of grid-connected / grid-following converters under limited capacity according to claim 1, characterized in that: Transient current compensation component I c The calculation formula is: I c =I 2qn ·arctan(u 2q / u 2d ); Among them, I 2qn It is the q-axis reference current of the grid-forming / grid-following converter.

4. The method for suppressing power oscillation of a parallel system of grid-connected / grid-following converters under limited capacity according to claim 1, characterized in that: d-axis electromotive force e 2d and q-axis electromotive force e 2q The calculation formula is: Among them, I 2dn Indicates the d-axis reference current of the grid-forming / grid-following converter, K p2 and K i2 Represents the current control proportional coefficient and current control integral coefficient respectively, L f2 and ω n They represent the output filter inductance and rated angular frequency of the grid-forming / grid-following converters respectively.

5. A power oscillation suppression system for a grid-connected / grid-following converter parallel system under limited capacity, characterized in that: The method comprises one or more processors and a memory; the memory stores one or more programs, and when the one or more programs are executed by the one or more processors, the one or more processors implement the steps of the method according to any one of claims 1 to 4.

6. A computer-readable storage medium, characterized in that A computer program / instruction is stored thereon; it is characterized in that when the computer program / instruction is executed by a processor, the steps of the method according to one of claims 1 to 4 are implemented.

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