An active damper control method based on oscillation risk assessment

Abstract

The application discloses an active damper control method based on oscillation risk assessment, and relates to the technical field of new energy power generation systems.The control method comprises four parts: an inverter conventional control part, an oscillation risk assessment part, a stability margin improvement part and an oscillation monitoring and instability recovery control part.The inverter conventional control part is the basis of the active damper control and runs through the whole control stage, and the other three control parts cyclically act in sequence to ensure the stable operation of the inverter system, assess the oscillation risk of the system through current relation, and thus do not need voltage information, thereby reducing the calculation burden of the controller, improving the stability margin of the system before the system is unstable, and improving the stability margin to a set value.

Description

Technical Field

[0001] This invention relates to the field of new energy power generation system technology, specifically an active damper control method based on oscillation risk assessment. Background Technology

[0002] With the transformation of the global energy structure, the power system is facing tremendous changes. More and more distributed generation units and energy storage devices are being installed in the power system, resulting in non-negligible impedance within the power grid and the power grid increasingly exhibiting weak grid characteristics.

[0003] Traditional grid-connected inverters are typically designed for operation under strong grid conditions. Therefore, even if they operate stably under strong grid conditions, the system may still become unstable and oscillate under weak grid conditions due to the interaction between the inverter and the weak grid, and between inverters themselves.

[0004] Currently, to address the instability issue of multiple inverters operating in parallel under weak grid conditions, system stability can be improved by modifying the control parameters of the grid-connected inverters or designing oscillation suppression strategies. Alternatively, system stability can be restored by connecting active dampers in series or parallel with the PCC (Power Control Controller). Current research on active dampers requires waiting until the system experiences instability and oscillations before sampling the system's harmonic current or voltage information to generate corresponding active damping—a process of "instability first, suppression later." Furthermore, it's impossible to determine the degree of stability improvement after adding active damping, i.e., the extent to which the system's stability margin is enhanced is unclear. Summary of the Invention

[0005] To address the shortcomings mentioned in the background art, the present invention aims to provide an active damper control method based on oscillation risk assessment, which improves the stability margin of the system before system instability and can increase the stability margin to a set value.

[0006] The objective of this invention can be achieved through the following technical solution: an active damper control method based on oscillation risk assessment, the method comprising the following steps:

[0007] The method comprises four parts: inverter conventional control, oscillation risk assessment, stability margin enhancement, and oscillation monitoring and instability recovery control. The inverter conventional control is the foundation for the normal operation of the active damper, and the entire control process is implemented based on this. In the oscillation risk assessment, the system's oscillation and instability risk is assessed based on the disturbance response in the inverter system using a disturbance injection method, and the oscillation-prone frequency points are obtained. In the stability margin enhancement, based on the oscillation-prone frequency points obtained in the oscillation risk assessment, disturbances are continuously injected at these frequencies to obtain real-time system stability information. This stability information is then used as a characteristic quantity for feedback adjustment to improve the inverter system's stability. Both the oscillation risk assessment and stability margin enhancement sections require the inverter system to operate stably. Therefore, when the inverter system has already become unstable and oscillated, the oscillation monitoring and instability recovery control section is needed to ensure the inverter system returns to stability.

[0008] Preferably, the conventional control section of the inverter adopts an AC current inner loop and a DC voltage outer loop control.

[0009] Preferably, the oscillation risk assessment section performs discrete Fourier transform on the disturbance currents flowing into the power grid and the inverter system to calculate the amplitude ratio and phase angle difference of the two disturbance currents, assesses the VPM or VGM of the inverter system, evaluates the oscillation risk of the inverter system, and identifies one or more oscillation-prone frequency bands of the inverter system without performing discrete Fourier transform on the PCC point voltage.

[0010] Preferably, the oscillation risk assessment section does not require discrete Fourier transform calculation of the PCC point voltage, thereby reducing the computational burden on the controller.

[0011] Preferably, the stability margin enhancement section targets the frequency band with the smallest VPM or VGM, continuously injects disturbance current at a fixed frequency, acquires the changes in VPM or VGM within the frequency band in real time, and adjusts the magnitude of the active damping to stabilize the inverter system's VPM or VGM near the set value, ensuring that the system's stability margin is enhanced before the inverter system becomes unstable.

[0012] Preferably, the oscillation monitoring and instability recovery control section is responsible for monitoring the magnitude of harmonic voltage in the inverter system in real time.

[0013] Preferably, when the inverter system has become unstable, the oscillation monitoring and instability recovery control section generates active damping, thereby restoring the inverter system to stability.

[0014] Preferably, when the inverter system is running stably, the risk oscillation assessment and control and stability margin enhancement section is responsible for increasing the stability margin of the inverter system before it becomes unstable. Depending on actual needs, it performs one round every tens of minutes or hours, with each round lasting several seconds or tens of seconds. During other time periods or when the inverter system has already become unstable and oscillated, the oscillation monitoring and instability recovery control section takes effect to restore the inverter system to stability.

[0015] Preferably, an apparatus includes:

[0016] One or more processors;

[0017] Memory, used to store one or more programs;

[0018] When one or more of the programs are executed by one or more of the processors, the one or more of the processors implement an active damper control method based on oscillation risk assessment as described above.

[0019] Preferably, a storage medium containing computer-executable instructions, which, when executed by a computer processor, are used to perform an active damper control method based on oscillation risk assessment as described above.

[0020] The beneficial effects of this invention are:

[0021] This invention assesses the oscillation risk of a system solely through current relationships, without requiring voltage information, thus reducing the computational burden on the controller. It can improve the system's stability margin before instability occurs and can increase the stability margin to a set value. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 The connection method between the active damper topology and the original system is shown in the diagram.

[0024] Figure 2 This is a block diagram of the active damper control strategy of the present invention;

[0025] Figure 3 This is a block diagram of the perturbation injection amplitude adaptive algorithm of the present invention;

[0026] Figure 4 This is a voltage and current waveform diagram of the present invention;

[0027] Figure 5These are waveform diagrams of key parameters for the three control stages of this invention;

[0028] Figure 6 This is a VPM waveform diagram for the stability margin improvement stage of this invention.

[0029] Figure 7 This is a curve showing the change in virtual conductance during the stability margin improvement stage of this invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] like Figure 1 As shown, an active damper control method based on oscillation risk assessment is presented, the method comprising the following steps:

[0032] The method comprises four parts: inverter conventional control, oscillation risk assessment, stability margin enhancement, and oscillation monitoring and instability recovery control. The inverter conventional control is the foundation for the normal operation of the active damper, and the entire control process is implemented based on this. In the oscillation risk assessment, the system's oscillation and instability risk is assessed based on the disturbance response in the inverter system using a disturbance injection method, and the oscillation-prone frequency points are obtained. In the stability margin enhancement, based on the oscillation-prone frequency points obtained in the oscillation risk assessment, disturbances are continuously injected at these frequencies to obtain real-time system stability information. This stability information is then used as a characteristic quantity for feedback adjustment to improve the inverter system's stability. Both the oscillation risk assessment and stability margin enhancement sections require the inverter system to operate stably. Therefore, when the inverter system has already become unstable and oscillated, the oscillation monitoring and instability recovery control section is needed to ensure the inverter system returns to stability.

[0033] The inverter's conventional control section employs an inner loop for AC current and an outer loop for DC voltage control.

[0034] The oscillation risk assessment section performs discrete Fourier transform on the disturbance currents flowing into the power grid and the inverter system to calculate the amplitude ratio and phase angle difference of the two disturbance currents, assesses the VPM or VGM of the inverter system, evaluates the oscillation risk of the inverter system, and identifies one or more oscillation-prone frequency bands of the inverter system without performing discrete Fourier transform on the PCC point voltage.

[0035] The oscillation risk assessment section does not require discrete Fourier transform calculations on the PCC point voltage, thus reducing the computational burden on the controller.

[0036] The stability margin enhancement section targets the frequency band with the lowest VPM or VGM, continuously injecting disturbance current at a fixed frequency, acquiring changes in VPM or VGM within the frequency band in real time, and adjusting the magnitude of the active damping to stabilize the inverter system's VPM or VGM near the set value, ensuring that the system's stability margin is enhanced before the inverter system becomes unstable.

[0037] The oscillation monitoring and instability recovery control section is responsible for monitoring the magnitude of harmonic voltage in the inverter system in real time.

[0038] When the inverter system has become unstable, the oscillation monitoring and instability recovery control section generates active damping, which restores the inverter system to stability.

[0039] When the inverter system is running stably, the risk oscillation assessment and control and stability margin enhancement section is responsible for increasing the stability margin of the inverter system before it becomes unstable. Depending on actual needs, it performs one round every tens of minutes or hours, with each round lasting several seconds or tens of seconds. At other times or when the inverter system has already become unstable and oscillated, the oscillation monitoring and instability recovery control section takes effect to restore the inverter system to stability.

[0040] It needs further explanation that, in the specific implementation process, such as Figure 2 As shown, the conventional control section of the inverter employs an inner loop for AC current and an outer loop for DC voltage control. This control is an existing control strategy, and the active damping control described above is based on this strategy.

[0041] When the oscillation risk assessment and control section is activated, a disturbance current i is injected into the system through sinusoidal frequency sweep. ADh Disturbance current i ADh Partial flow into the power grid i gh Part of the flow flows into the inverter power generation unit i invh And generate a disturbance voltage response u in the PCC. pcch . to i gh and i invh By performing discrete Fourier transforms on each, the amplitude and phase angle of the disturbance current can be obtained, denoted as . and u pcc It can also be expressed as According to the impedance stability criterion, the stability of the system can be determined by the internal impedance Z of the power grid. g and inverter output impedance Z inv The ratio G=Z g / Z invDetermine the system's stability. The system is stable when G satisfies the nyquist criterion; it is unstable when G does not satisfy the nyquist criterion. Clearly,

[0042]

[0043] That is, it can be determined solely by the ratio of the current amplitude to I. invh / I gh and phase angle difference To determine the stability of the system. According to the Nyquist criterion, when I... invh / I gh =1 and If the system is unstable, it will become unstable; otherwise, it will remain stable.

[0044] Define virtual phase margin VPM or virtual gain margin VGM. VPM refers to the virtual gain margin at any logarithmic amplitude-frequency response. When the logarithmic amplitude-frequency characteristic curve crosses zero, VPM has the same meaning as the traditional PM. VGM refers to any phase frequency characteristic, VGM = 1 / |Gop(jw)|. When the logarithmic phase frequency curve crosses ±180°, VGM has the same meaning as the traditional GM. Taking VPM as an example, when the current amplitude ratio is close to 1 and VPM is very small or even negative, the system is considered to have low stability margin and a large risk of oscillation; when the current amplitude ratio is less than 1 or much greater than 1, or when the current amplitude ratio is close to 1 but VPM is large, the system is considered to have high stability margin and a low risk of oscillation. The purpose of oscillation risk assessment and control is to use frequency sweeping to assess the stability of the system. gh and i invh By continuously performing discrete Fourier transform operations, I is calculated. invh / I gh and Find I invh / I gh Close to 1 and Frequency bands that are close to or less than 0 are prone to unstable oscillations.

[0045] like Figure 2 As shown, when the frequency sweep of the oscillation risk assessment section is completed, the frequency point f most prone to oscillation in the original system is obtained. osc At this point, the stability margin improvement plays a role. For the frequency band with the minimum VPM or VGM, a fixed frequency f is used. osc Continuous injection of current disturbance, sampling to obtain i gh and i invh . to i gh and i invh +i GrefA Discrete Fourier Transform (DFT) is performed to obtain the VPM or VGM of the system in this frequency band in real time. Based on this, the magnitude of the active damper is adjusted to stabilize the system's VPM or VGM near a set value. The damping generated by the active damper is not only effective at easily oscillating frequencies, but is applicable to all frequencies except the fundamental frequency band. Therefore, the damping conductance G is generated as follows:

[0046] G = G ref G NF

[0047] Because the frequency of the oscillation point may be high and the bandwidth of the current controller is insufficient, a compensation circuit G was designed. c ,

[0048] Among them G NF For a notch filter at the fundamental frequency, G LPF Let L1 and L2 be the transfer function of the low-pass filter, and k be the filter inductance of the active damper. cp This is the proportional gain of the current loop controller.

[0049] like Figure 2 As shown, the oscillation risk assessment phase and the stability margin enhancement phase can be executed every tens of minutes or hours, with each phase lasting several seconds or tens of seconds, depending on actual needs. During other time periods, the oscillation monitoring and instability recovery control components take over. During this control phase, u is monitored in real time. pcch When the amplitude exceeds a certain set value, the system is considered to be unstable, and at this time, U... pcch The feedback signal is used to generate active damping through a PI controller to suppress oscillations and restore system stability.

[0050] like Figure 3 As shown, when the system sweeps to a frequency point prone to oscillation, resonance within the system may amplify the disturbance current excitation or disturbance voltage response, interfering with the stable operation of the system. Therefore, it is necessary to adaptively change the set value of the disturbance current amplitude according to the disturbance current amplitude. The disturbance current amplitude setting value is adaptively scaled proportionally to the amount by which it exceeds the maximum allowable value.

[0051] The table below shows the parameters of the active damper in this example.

[0052] parameter numerical values parameter numerical values <![CDATA[Filter inductor L1]]> 0.4mH <![CDATA[Current controller coefficient k cp > 10 <![CDATA[Filter inductor L2]]> 0.3mH Voltage controller PI parameters 1+50 / s <![CDATA[Filter capacitor C f > 5uF Active damping controller PI parameters 0.0004+0.01 / s <![CDATA[DC capacitor C dc > 2.5mF <![CDATA[VPM set value VPM ref > 40° <![CDATA[Grid voltage U g > 220V The ratio of current disturbance to rated current 10％ <![CDATA[DC capacitor voltage U dc > 500V Frequency sweep range 500Hz~2kHz Switching frequency 20kHz Discrete Fourier Transform Sampling Frequency 50kHz

[0053] Based on the same inventive concept, this invention also provides a computer device, comprising: one or more processors, and a memory for storing one or more computer programs; the programs include program instructions, and the processor executes the program instructions stored in the memory. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, used to implement one or more instructions, specifically for loading and executing one or more instructions stored in a computer storage medium to implement the above-described method.

[0054] It should be further explained that, based on the same inventive concept, the present invention also provides a computer storage medium storing a computer program, which, when executed by a processor, performs the above-described method. This storage medium can be any combination of one or more computer-readable media. The computer-readable medium can be a computer-readable signal medium or a computer-readable storage medium. The computer-readable storage medium can be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples of computer-readable storage media (a non-exhaustive list) include: an electrical connection having one or more wires, a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof. In the present invention, the computer-readable storage medium can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device.

[0055] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0056] The foregoing has shown and described the basic principles, main features, and advantages of this disclosure. Those skilled in the art should understand that this disclosure is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this disclosure. Various changes and modifications can be made to this disclosure without departing from its spirit and scope, and all such changes and modifications fall within the scope of this disclosure as claimed.

Claims

1. An active damper control method based on oscillation risk assessment, characterized in that, The method includes the following steps: The method consists of four parts: inverter conventional control, oscillation risk assessment, stability margin enhancement, and oscillation monitoring and instability recovery control. The conventional control section of the inverter is the foundation for the normal operation of the active damper, and the entire control process is implemented based on the conventional control section. In the oscillation risk assessment section, the oscillation and instability risk of the system is assessed based on the disturbance response in the inverter system through disturbance injection, and the oscillation frequency points are obtained. In the stability margin enhancement section, based on the oscillation frequency points obtained in the oscillation risk assessment section, disturbances are continuously injected at the oscillation frequency to obtain system stability information in real time. The stability information is used as a characteristic quantity for feedback adjustment to improve the stability of the inverter system. The stability information includes VPM or VGM, where VPM is the virtual phase angle margin and VGM is the virtual gain margin. Both the oscillation risk assessment section and the stability margin enhancement section can only work under the premise that the inverter system is operating stably. Therefore, when the inverter system has become unstable and oscillating, the oscillation monitoring and instability recovery control section is required to ensure that the inverter system returns to stability.

2. The active damper control method based on oscillation risk assessment according to claim 1, characterized in that, The inverter's conventional control section employs an inner loop for AC current and an outer loop for DC voltage control.

3. The active damper control method based on oscillation risk assessment according to claim 1, characterized in that, The oscillation risk assessment section performs discrete Fourier transform on the disturbance currents flowing into the power grid and the inverter system to calculate the amplitude ratio and phase angle difference of the two disturbance currents, assesses the VPM or VGM of the inverter system, evaluates the oscillation risk of the inverter system, and identifies one or more oscillation-prone frequency bands of the inverter system.

4. The active damper control method based on oscillation risk assessment according to claim 3, characterized in that, The oscillation risk assessment section does not require discrete Fourier transform calculations on the PCC point voltage, thus reducing the computational burden on the controller.

5. The active damper control method based on oscillation risk assessment according to claim 1, characterized in that, The stability margin enhancement section targets the frequency band with the lowest VPM or VGM, continuously injecting disturbance current at a fixed frequency, acquiring changes in VPM or VGM within the frequency band in real time, and adjusting the magnitude of the active damping to stabilize the inverter system's VPM or VGM near the set value, ensuring that the system's stability margin is enhanced before the inverter system becomes unstable.

6. The active damper control method based on oscillation risk assessment according to claim 1, characterized in that, The oscillation monitoring and instability recovery control section is responsible for monitoring the magnitude of harmonic voltage in the inverter system in real time.

7. The active damper control method based on oscillation risk assessment according to claim 6, characterized in that, When the inverter system has become unstable, the oscillation monitoring and instability recovery control section generates active damping, which restores the inverter system to stability.

8. The active damper control method based on oscillation risk assessment according to claim 7, characterized in that, When the inverter system is running stably, the risk oscillation assessment and control and stability margin enhancement section is responsible for increasing the stability margin of the inverter system before it becomes unstable. Depending on actual needs, it performs one round every tens of minutes or hours, with each round lasting several seconds or tens of seconds. At other times or when the inverter system has already become unstable and oscillated, the oscillation monitoring and instability recovery control section takes effect to restore the inverter system to stability.

9. A device, characterized in that, include: One or more processors; Memory, used to store one or more programs; When one or more of the programs are executed by one or more of the processors, the one or more of the processors implement an active damper control method based on oscillation risk assessment as described in any one of claims 1-8.

10. A storage medium containing computer-executable instructions, characterized in that, The computer-executable instructions, when executed by a computer processor, are used to perform an active damper control method based on oscillation risk assessment as described in any one of claims 1-8.

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