Stability improvement method for follow-on hybrid power station based on adaptive hybrid damping

Abstract

This invention discloses a method for improving the stability of a hybrid power station based on adaptive hybrid damping. The method includes online monitoring of the total harmonic distortion (THD) at the common ground point. When the THD does not meet grid-connected stability requirements, a mapping table is searched offline based on the grid-connected output power value to obtain virtual impedance parameters matching the grid-connected output power. The mapping table is pre-constructed under the constraint boundary conditions of virtual impedance values ​​in the grid-connected energy storage system. After eliminating low-frequency instability risks using the virtual impedance parameters, if the THD still does not meet grid-connected stability requirements, an enhanced admittance strategy control loop is added to the grid-connected control loop. The real-time resonant frequency of the hybrid power station is calculated online based on the voltage and current at the common ground point. This real-time resonant frequency is input into the equivalent expression of the control loop, and iterative cycles are performed until an effective enhanced admittance control parameter that meets grid-connected stability requirements is obtained to eliminate mid-frequency instability risks.

Description

Technical Field

[0001] This invention relates to the field of grid connection stability technology for new energy power plants and grid-connected energy storage, specifically to a method for improving the stability of grid-connected / grid-connected hybrid power plants based on adaptive hybrid damping. Background Technology

[0002] New power systems are gradually developing "high-voltage and high-efficiency" characteristics. Currently, the control method for grid-connected units in new energy power plants mainly adopts grid-following (GFL) mode, using a phase-locked loop (PLL) to synchronize with the grid voltage phase. This leads to frequent power oscillation accidents caused by the interaction between the PLL and grid impedance under weak grid conditions. Adding grid-forming (GFM) energy storage to improve the stability of new energy power plants has become one of the important damping methods. However, most current research focuses on local frequency instability problems such as sub-synchronous / supersynchronous oscillations in hybrid GFL / GFM power plants, neglecting the combined improvement of the wide-range stability of hybrid GFL / GFM power plants.

[0003] For broadband oscillations in hybrid power plants connected to the grid, impedance modeling is currently widely used for stability analysis. GFMs exhibit negative resistivity-capacitance characteristics at low frequencies, leading to low-frequency instability risks associated with GFM energy storage. The most practical method in current engineering projects is to add virtual impedance to dampen this instability risk. GFLs have a "negative resistance + capacitance" impedance characteristic in the mid-frequency range, while GFMs have a "positive resistance + inductance" impedance characteristic at low frequencies. Due to their complementary impedance characteristics, GFM energy storage can be used to suppress broadband oscillations caused by GFLs. The technical approaches can be broadly divided into two directions:

[0004] 1) Increase the configuration ratio of GFM energy storage units to increase the dominance of GFM in the equivalent grid impedance, thereby improving the grid impedance characteristics and preventing interaction with GFL impedance. This approach is simple to implement, but in practical engineering, the cost of installing GFM energy storage needs to be considered, and the parallel stability problem between multiple GFM energy storage units needs to be solved.

[0005] 2) An optimization strategy is added to the GFM control loop to reshape the GFM impedance characteristics in the wide-band oscillation range, enabling GFM energy storage to suppress wide-band oscillations in the grid-connected voltage and current of hybrid power plants. This approach only adds an optimization control strategy without increasing the equipment cost of the power plant. However, in actual engineering, GFM energy storage generally already incorporates virtual impedance to improve its grid-connected stability. The virtual impedance will interact with the newly added optimization control strategy, affecting the strategy's ability to improve the GFM energy storage's ability to suppress wide-band oscillations. Furthermore, the output power of new energy power plants is intermittent and fluctuating. When the operating conditions of hybrid power plants change, the optimization control strategy needs to have the ability to adjust control parameters online to improve the wide-range stability of hybrid power plants. In related technologies, the paper "Analysis and Improvement Stability of Grid-connected Energy Storage Converter in New Energy Access Scenarios, Wu Jiajie et al., Proceedings of the CSEE" utilizes a current loop structure while neglecting the influence of the voltage outer loop on impedance characteristics, establishing an active damping strategy equivalent to RLC impedance. This strategy can dampen resonances in the tens to hundreds of Hz range. However, it only considers the stabilization capability of the grid-connected converter on the grid-connected converter (mid-frequency band), without considering the stability improvement of the grid-connected converter itself (low-frequency band). The paper "Suppression Method of Subsynchronous Oscillation between Wind Farm and Weak Grid Based on Grid-connected Energy Storage, Wu Shuangxi et al., Power Construction" connects a bandpass filter in series in the voltage circuit loop, but this has no equivalent physical meaning and lacks adaptive adjustment capability, only damping subsynchronous oscillations at specific frequencies. The literature "Adaptability Analysis and Improvement of Wide Short-Circuit Ratio Range of Grid-Type Converters, Liu Long et al., Automation of Electric Power Systems" constructs a hybrid damping strategy using virtual impedance and virtual admittance, which basically eliminates the low-frequency oscillation risk of grid-type converters. However, it excessively enhances the amplitude-frequency characteristics of the grid-type impedance, resulting in a decrease in the influence of the grid-type impedance after the grid-type converter is connected in parallel with the grid-type converter. Using this method will increase the instability risk in the mid-frequency range of the hybrid power plant. Summary of the Invention

[0006] The technical problem to be solved by this invention is how to achieve a synergistic improvement in the stability of low-frequency and mid-frequency bands of hybrid power plants.

[0007] The present invention solves the above-mentioned technical problems through the following technical means: A method for improving the stability of a hybrid hydroelectric power station based on adaptive hybrid damping is proposed, the method comprising: The total harmonic distortion (THD) result of the common grounding point is monitored online. When the THD result does not meet the grid-connected stability requirements, the mapping relationship table is searched offline based on the grid output power value to obtain the virtual impedance parameter that matches the grid output power. The mapping relationship table is pre-constructed under the constraint boundary conditions of the virtual impedance value of grid-connected energy storage. If the total harmonic distortion result still does not meet the grid connection stability requirements after eliminating the risk of instability in the low-frequency band using virtual impedance parameters, then an enhanced admittance strategy control loop is added to the grid control loop. The real-time resonant frequency of the hybrid power station is calculated online based on the voltage and current at the common grounding point. The real-time resonant frequency is then input into the equivalent expression of the control loop and iterated until an effective enhanced admittance control parameter that meets the grid connection stability requirements is obtained to eliminate the risk of instability in the mid-frequency band.

[0008] Furthermore, before obtaining the virtual impedance parameter matching the grid output power by offline lookup of the mapping table based on the grid output power value, the method further includes: Based on the stability criteria from the perspective of grid-connected power, a virtual impedance constraint boundary is established for grid-connected energy storage in hybrid power plants under different output power conditions. Under the constraint boundary conditions of virtual impedance value, a mapping relationship table between grid output power and virtual impedance parameters is formed.

[0009] Furthermore, the stability criterion from the perspective of the network structure is:

[0010] In the formula, For phase margin, Port line impedance from a network perspective. The network impedance transfer function is... To keep up with grid power fluctuations phase curve, for phase curve, For the impedance transfer function of the grid, j It is the basic unit of imaginary numbers. Angular frequency, For virtual impedance parameters, To accommodate the grid connection impedance of the hybrid power station, Indicates a parallel relationship. Here is the frequency domain expression for the impedance of the grid-connected line of the hybrid power station. This is the frequency domain expression for the port line impedance from a network perspective. The output power of the grid.

[0011] Furthermore, the constraint boundary for the virtual impedance value is:

[0012] In the formula, This is the negative RC boundary angular frequency of the mesh-type impedance. Angular frequency, For network impedance transfer function phase curve, For the network impedance under the negative RC boundary angular frequency condition, The line impedance of the network port under different grid output powers under the negative RC boundary angular frequency condition is given, where the variable is the output power under the grid condition. j It is the basic unit of imaginary numbers. For virtual impedance parameters, To match the output power of the grid, The symbol is '|', and the separator is '|'.

[0013] Furthermore, taking the overall impedance of the hybrid power station as the criterion, the formula for calculating the overall impedance of the hybrid power station is as follows:

[0014]

[0015]

[0016] In the formula, Indicates the overall impedance of the hybrid power station. This indicates the overall impedance of the network. This represents the overall impedance of the network. Indicates a parallel relationship; Represents the negative-sequence component of the line impedance. , , , These are the positive-sequence self-impedance, negative-sequence self-impedance, positive-negative-sequence coupling impedance, and negative-positive-sequence coupling impedance of the grid-connected converter, respectively. , , , These are the positive-sequence self-impedance, negative-sequence self-impedance, positive-negative-sequence coupling impedance, and negative-positive-sequence coupling impedance of the grid-type converter, respectively. This represents the positive-sequence disturbance voltage of the network configuration. This represents the positive-sequence response voltage of the network type. This indicates the positive sequence disturbance voltage of the network type. This indicates the positive sequence response voltage of the grid.

[0017] Furthermore, the grid connection stability criterion for the aforementioned hybrid power station is:

[0018] In the formula, For phase margin, To determine the line impedance between the common grounding point of the hybrid power plant and the power grid, To determine the overall impedance of the hybrid power station, for phase curve, for The phase curve.

[0019] Furthermore, the online calculation of the real-time resonant frequency of the hybrid power station based on the voltage and current of the common grounding point includes: The voltage and current at the common grounding point are decomposed online using Fast Fourier Transform to obtain the real-time resonant frequency of the hybrid power station.

[0020] Furthermore, the transfer function of the enhanced admittance strategy is:

[0021] In the formula, This indicates a simplified impedance configuration for the mid-frequency band with an enhanced admittance strategy. This represents the second-order bandpass control element of the admittance enhancement strategy. This represents the compensation gain stage of the admittance enhancement strategy; For the center frequency, This is the gain coefficient. For quality factor; This represents the proportionality coefficient of the current loop. This represents the voltage loop proportionality coefficient. Indicates the voltage loop integral coefficient; Indicates the fundamental angular frequency. This indicates a mesh filter inductor. Represents angular frequency. Represents virtual impedance. Represents the variables in the complex field. j The basic unit representing imaginary numbers.

[0022] Furthermore, the method also includes: The enhanced admittance strategy is equivalent to connecting an RLC branch in parallel with the network impedance. The equivalent expression of the control loop is the relationship between the parameters of the enhanced admittance control loop corresponding to the various impedance components of the RLC branch and the corresponding relationship between the resonant frequency and resonant bandwidth generated by it, as follows:

[0023] In the formula, R e This indicates an increase in the admittance resistive component. L e This indicates an increase in the perceptual component of admittance. C e This indicates an enhanced admittance capacitive component. Indicates the resonant bandwidth; To enhance the resonant center frequency generated by the admittance strategy, This is the gain coefficient. This is the quality factor.

[0024] Furthermore, the step of inputting the real-time resonant frequency into the equivalent expression of the control loop and performing iterative iterations until effective enhanced admittance control parameters that meet grid-connected stability requirements are obtained includes: The resonant center frequency generated by the enhanced admittance strategy is set to equal the real-time resonant frequency, and this resonant center frequency is input into the equivalent expression of the control loop for iterative iteration to increase the gain coefficient. This reduces the amplitude of the positive resistance component in the enhanced admittance, and also lowers the quality factor. This expands the resonant bandwidth until an effective enhanced admittance control parameter that meets the grid-connected stability requirements is obtained.

[0025] Furthermore, this invention also proposes a stability enhancement system for a hybrid hydroelectric power station based on adaptive hybrid damping, the system comprising: The virtual impedance parameter adjustment module is used to monitor the total harmonic distortion result of the common grounding point online. When the total harmonic distortion result does not meet the grid connection stability requirements, it searches the mapping relationship table offline based on the grid output power value to obtain the virtual impedance parameter that matches the grid output power. The mapping relationship table is pre-constructed under the constraint boundary conditions of the virtual impedance value of grid-connected energy storage. The enhanced admittance module is used to add a control loop of the enhanced admittance strategy to the grid control loop if the total harmonic distortion result still does not meet the grid stability requirements after eliminating the risk of instability in the low-frequency band using virtual impedance parameters. The enhanced admittance control parameter adjustment module is used to calculate the real-time resonant frequency of the hybrid power station online based on the voltage and current of the common grounding point. The real-time resonant frequency is input into the equivalent expression of the control loop and iterated until an effective enhanced admittance control parameter that meets the grid connection stability requirements is obtained to eliminate the risk of instability in the mid-frequency band.

[0026] Furthermore, the present invention also proposes a GFM control device, including a memory and a processor, characterized in that the processor reads executable program code stored in the memory to run a program corresponding to the executable program code, so as to implement the above-described method for improving the stability of a hybrid power plant based on adaptive hybrid damping.

[0027] The advantages of this invention are: By pre-constructing a mapping table between grid-connected output power and virtual impedance parameters under the constraint boundary conditions of virtual impedance values ​​in the hybrid power plant, a virtual impedance parameter matching the currently acquired grid-connected output power can be obtained by offline lookup of the mapping table. This forms an adaptive control strategy for the virtual impedance parameter, preventing excessively large virtual impedance parameters from further affecting the mid-frequency stability of the hybrid power plant. Furthermore, by adding an enhanced admittance control loop to the grid-connected control loop containing virtual impedance, the phase of the hybrid power plant in the instability frequency band is specifically raised, eliminating the risk of instability in the low-frequency band. The addition of the enhanced admittance control loop to the grid-connected control loop introduces a resonant frequency and bandwidth to the GFM impedance. Therefore, this invention achieves online monitoring of the grid-connected output power. The voltage and current waveform quality is assessed by calculating the real-time resonant frequency of the hybrid power station online based on the voltage and current at the grid-connected common grounding point. The enhanced admittance resonant center frequency is then input into the expression of the control parameters (including the resonant frequency and resonant bandwidth). This process is iterated until the enhanced admittance resonant center frequency equals the real-time resonant frequency and the total harmonic distortion meets the grid-connected stability requirements. This results in effective enhanced admittance control parameters, which can raise the phase of the impedance of the hybrid power station and expand the effective range of the strategy, eliminating the risk of instability in the mid-frequency band. Therefore, this invention achieves a synergistic improvement in the low-frequency and mid-frequency wide-range stability of the hybrid power station by adaptively adjusting the control parameters through real-time detection of the output power status and grid-connected output voltage and current waveform quality of the hybrid power station.

[0028] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0029] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0030] Figure 1 This is a block diagram of the overall control principle of a hybrid power plant according to one embodiment of the present invention; Figure 2 This is a schematic diagram of the impedance structure of a hybrid power station in one embodiment of the present invention; Figure 3 This is a schematic diagram of the impedance characteristics of a hybrid power station in one embodiment of the present invention; Figure 4 This is a schematic diagram of port line impedance from a network perspective in one embodiment of the present invention; Figure 5 This is a schematic diagram of the constraint boundary for virtual impedance values ​​in one embodiment of the present invention; Figure 6 This is a schematic diagram of a hybrid damping control strategy in one embodiment of the present invention; Figure 7 This is a schematic diagram of the reshaping / construction of the hybrid power station impedance using a hybrid damping control strategy in one embodiment of the present invention; Figure 8 This is a flowchart illustrating a method for improving the stability of a hybrid power station based on adaptive hybrid damping, as proposed in an embodiment of the present invention. Figure 9 This is an overall control flowchart of adaptive hybrid damping in one embodiment of the present invention; Figure 10 This is a diagram showing the relationship between power and virtual impedance in one embodiment of the present invention; Figure 11 This is a waveform diagram of grid-connected voltage and current of a hybrid power station with integrated grid and cross-grid structure, which exhibits broadband oscillation in one embodiment of the present invention. Figure 12 This is a grid-connected voltage and current waveform diagram of adaptive hybrid damping suppressing broadband oscillation in one embodiment of the present invention; Figure 13 This is a schematic diagram of a stability enhancement system for a hybrid power station based on adaptive hybrid damping, proposed in an embodiment of the present invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, 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.

[0032] In this embodiment, to address the problem of insufficient wide-range damping capacity in hybrid power plants with grid connection and substation, which exhibit instability risks in both low and mid-frequency bands, this invention proposes a stability improvement method for hybrid power plants with grid connection and substation based on adaptive hybrid damping. This method proposes a virtual impedance value constraint boundary for the hybrid power plant with grid connection and substation, and constructs a mapping table between grid connection output power and virtual impedance parameters under this constraint. An offline lookup table method is used to form an adaptive control strategy for the virtual impedance parameters, which is used to improve the low-frequency stability of the hybrid power plant. Simultaneously, an enhanced admittance control strategy is proposed to reshape the impedance characteristics of the mid-frequency hybrid power plant, improving its mid-frequency stability. The control block diagram is shown below. Figure 1 As shown.

[0033] Because the output power of new energy power plants is intermittent and fluctuating, in order to address the problem of real-time changes in power oscillation risk caused by variations in the operating conditions of hybrid power plants, this invention combines an adaptive control strategy for virtual impedance parameters with an enhanced admittance control strategy to form an adaptive hybrid damping strategy: For different grid-connected output power, an offline lookup table method is used to form an adaptive control strategy for virtual impedance parameters to eliminate the risk of instability in the low-frequency band; based on the real-time oscillation frequency of the hybrid power plant obtained online, the parameters of the enhanced admittance control loop are adaptively adjusted to eliminate the risk of instability in the mid-frequency band. This achieves a synergistic improvement in the stability of hybrid power plants across a wide range of low and mid-frequency bands.

[0034] This embodiment quantifies the broadband oscillation risk of hybrid power plants connected to the grid, obtains the broadband oscillation frequency, and proposes the aforementioned optimization strategies accordingly. (1) Establish impedance models for grid-following (GFL) and grid-connecting (GFM) types, and then establish an overall impedance model for the GFL / GFM hybrid power station based on the topology of the GFL / GFM hybrid power station. Specifically, the GFM impedance model and the GFL impedance model are constructed as follows: (1) (2) In the formula, This indicates the overall impedance of the network. Indicates the overall impedance of the network; This represents the positive-sequence disturbance voltage of the network configuration. This represents the positive-sequence response voltage of the network type. This indicates the positive sequence disturbance voltage of the network type. Indicates the positive sequence response voltage of the grid type; Represents the negative-sequence component of the line impedance; , , , These are the positive-sequence self-impedance, negative-sequence self-impedance, positive-negative-sequence coupling impedance, and negative-positive-sequence coupling impedance of the grid-connected converter, respectively. , , , These are the positive-sequence self-impedance, negative-sequence self-impedance, positive-negative-sequence coupling impedance, and negative-positive-sequence coupling impedance of the grid-type converter.

[0035] like Figures 2 to 3 As shown, with the point of common coupling (PCC) as the reference, the overall impedance of the hybrid power station is equivalent to the GFL impedance and GFM impedance in parallel. The equivalent grid impedance model is expressed by equation (3): (3) In the formula, Indicates the overall impedance of the hybrid power station. It indicates a parallel relationship.

[0036] (2) Determine the stability criterion from the perspective of grid-type, and based on the stability criterion, design the virtual impedance value constraint boundary of GFM energy storage in the hybrid power station under different output power conditions of GFL; Specifically, using the impedance model of the hybrid power station based on equation (3) and the Nyuist stability criterion, a stability criterion for the hybrid power station based on equation (4) was constructed: (4) In the formula, For phase margin, To determine the line impedance between the common grounding point of the hybrid power plant and the power grid, To determine the overall impedance of the hybrid power station, for phase curve, for phase curve, j It is the basic unit of imaginary numbers. ω is the angular frequency.

[0037] And a stability criterion from the perspective of network structure was constructed as follows: (5) In the formula, For phase margin, Port line impedance from a network perspective (e.g.) Figure 4 (as shown) The network impedance transfer function is... To keep up with grid power fluctuations phase curve, for phase curve, For the impedance transfer function of the grid, j It is the basic unit of imaginary numbers. Angular frequency, For virtual impedance parameters, To accommodate the grid connection impedance of the hybrid power station, Indicates a parallel relationship. Here is the frequency domain expression for the impedance of the grid-connected line of the hybrid power station. This is the frequency domain expression for the port line impedance from a network perspective. The output power of the grid.

[0038] It should be noted that, since the grid-connected inverter is a current-source inverter, the increase in grid-connected output power leads to a decrease in the amplitude of the grid-connected impedance, which in turn leads to a decrease in the amplitude of the equivalent impedance obtained by connecting the grid-connected inverter in parallel with the grid connection point line impedance. Therefore, in equation (5), the intersection point of the port line impedance and the grid-connected impedance from the grid-connected perspective is more biased towards the fundamental frequency. The fundamental frequency is the frequency band where the phase of the grid-connected impedance is the lowest, and the positive damping is insufficient, which makes it easy to generate oscillations. After adding virtual impedance, the port line impedance from the grid-connected perspective increases, and its intersection point with the grid-connected impedance is far away from the fundamental frequency. Therefore, the phase margin is improved. If PM>0, it will definitely be stable; otherwise, the virtual impedance is insufficient, leading to instability.

[0039] Further, based on the stability criteria from the perspective of grid structure, the virtual impedance value constraint boundary for GFM energy storage in the hybrid power station with and without grid structure is established under different output power conditions of GFL (the output power of the grid structure affects the magnitude of the grid impedance), as shown in equation (6): (6) In the formula, This is the negative RC boundary angular frequency of the mesh-type impedance. Angular frequency, For network impedance transfer function phase curve, For the network impedance under the negative RC boundary angular frequency condition, The line impedance of the network port under different grid output powers under the negative RC boundary angular frequency condition is given, where the variable is the output power under the grid condition. j It is the basic unit of imaginary numbers. For virtual impedance parameters, To match the output power of the grid, The symbol is '|', and the separator is '|'.

[0040] According to equation (6), the expression for the value of the virtual impedance can be obtained as shown in equation (7): (7) It should be noted that, using formula (7), the virtual impedance under the following network power conditions is calculated based on the amplitude difference between the network impedance and the port line impedance from the perspective of the network.

[0041] It should be noted that, as Figure 5 As shown, the negative RC boundary angular frequency of the network impedance is determined. Subsequently, due to the large output power of the network, the port line impedance from the perspective of the network configuration increased. The network impedance produces an impedance intersection point that does not satisfy equation (5). At this time, after calculating the value of the virtual impedance according to equation (7), a suitable virtual impedance parameter is added to shift the intersection point to the left, which just satisfies the condition PM=0 in equation (5). Therefore, the virtual impedance parameter is the virtual impedance boundary value under the network output power.

[0042] (3) Construct a reduced-order GFM impedance model. By analyzing the reduced-order model, the control loop of the dominant GFM impedance characteristics in the mid-frequency band is determined to be the voltage-current loop. Specifically, since virtual impedance cannot specifically dampen the instability risk in the mid-frequency band, this embodiment introduces an enhanced damping control loop into the GFM control structure. However, the GFM control structure is complex. Based on the bandwidth of each control loop: the current loop bandwidth is generally 1 / 30 to 1 / 10 of the switching frequency, and the voltage loop bandwidth is 1 / 30 to 1 / 150 of the switching frequency, the control loop that dominates the GFM impedance characteristics in the mid-frequency band is determined to be the voltage and current loops. A reduced-order GFM impedance model is constructed as shown in equation (8): (8) In the formula, This represents the GFM voltage loop command voltage in the dq coordinate system. This represents the voltage feedback of the GFM filter capacitor in the dq coordinate system. This represents the feedback current of the GFM filter inductor in the dq coordinate system. Indicates the GFM filter inductor. This represents the proportionality coefficient of the current loop. This represents the voltage loop proportionality coefficient. Indicates the voltage loop integral coefficient. This represents the virtual impedance of the GFM. Indicates the fundamental angular frequency. Represents a variable in the complex field.

[0043] (4) Based on the voltage and current loop structure of GFM, an enhanced admittance control strategy is proposed to specifically improve the impedance phase of the hybrid power station in a specific frequency band, so that the phase margin of the intersection point between the impedance of the hybrid power station and the impedance of the power grid line meets the requirements of the stability criterion. Specifically, connecting an RLC branch in parallel with the GFM impedance can increase the GFM impedance amplitude at the LC resonant frequency. To reduce circuit energy loss, such as... Figure 6The control strategy should be added to the control loop of the GFM to make it equivalent to an RLC branch connected in parallel with the GFM impedance. Since the voltage loop input is a voltage difference signal and the current closed loop output is an inductor current signal, the forward channel transfer function of this part can be regarded as an admittance transfer function. Taking its reciprocal, the impedance transfer function of the voltage and current loops can be obtained. After adding the above-mentioned enhanced admittance control link, the reduced GFM impedance is shown in equation (9): (9) In the formula, This indicates a simplified impedance configuration for the mid-frequency band with an enhanced admittance strategy. This represents the second-order bandpass control element of the admittance enhancement strategy. This represents the compensation gain stage of the admittance enhancement strategy; For the center frequency, This is the gain coefficient. For quality factor; This refers to a mesh-type filter inductor.

[0044] Furthermore, due to The presence of a differential term, when the target frequency band is the mid-frequency band, may amplify the high-frequency components of the output current, affecting the system control accuracy. Therefore, subsequent... It can be simplified to .

[0045] It should be noted that this embodiment uses an actual RLC circuit connected in parallel with the network impedance. The positive damping within the resonant bandwidth of this circuit can counteract mid-frequency oscillations. However, this increases circuit power loss. Therefore, an active damping method is used to connect a bandpass filter in parallel with the voltage-current loop impedance covering the mid-frequency band. This filter has the same effect as the RLC and does not increase circuit power loss. However, since the compensation point of this bandpass filter is at the inductor current, it cannot be implemented in actual control. Therefore, the compensation point is moved forward to the current loop output signal. Consequently, the transfer function of the bandpass filter will be multiplied by [a factor not specified in the original text]. The expression (this is due to the control block diagram transformation).

[0046] Since this enhanced admittance control strategy is equivalent to an RLC branch connected in parallel across the GFM impedance in the actual physical circuit, the expression for this RLC branch can be expressed using equation (10): (10) Because the RLC branch has a resonant frequency, it indirectly causes the impedance of the hybrid power station to have a certain bandwidth of resonance. Equation (11) can be used to express the resonant frequency and resonant bandwidth caused by the GFM impedance of the RLC branch: (11) exist f <f e Within the frequency band, this RLC branch mainly exhibits positive resistivity and capacitance characteristics. f > f e Within the frequency band, this RLC branch mainly exhibits positive resistive-inductive characteristics. f = f e At this time, the RLC branch exhibits positive resistance characteristics. f e The RLC branch is the transition frequency from capacitive to inductive, therefore in f e The phase of the RLC increases significantly. Since the enhanced admittance strategy is physically equivalent to paralleling this RLC branch across the GFM impedance, it can further increase the impedance Z of the hybrid power station. HPP exist f e The phase rise at this point increases the phase margin of the hybrid power station in this frequency band, thereby satisfying the stability criterion of equation (4).

[0047] The resonant characteristics of the RLC branch and the resistive component of equation (10) R e and BW e Related to, with K E The increase, R e It will decrease because of the resonant frequency Z. HPP Given the negative resistance characteristic, the resonant frequency can be obtained based on the parallel connection relationship. f e The impedance relationship at that point is: (12) in <0, with R e Decrease The overall value is greater than 0, eliminating the risk of instability caused by negative resistance characteristics.

[0048] And reduce Q e improve BW e This can extend the effective frequency band of the enhanced admittance strategy. Therefore, this embodiment can increase... K E Simultaneously reduce Q e This will raise the Z-band to a wider range. HPP Phase, the final effect is as follows Figure 7 As shown, it can satisfy the stability criterion of the hybrid power plant shown in equation (4).

[0049] Furthermore, the relationships between the various impedance components of this RLC branch and the parameters of the enhanced admittance control loop, as well as the corresponding resonant frequencies and bandwidths, are expressed as follows: (13) In the formula, R e This indicates an increase in the admittance resistive component. L e This indicates an increase in the perceptual component of admittance. C e This indicates an enhanced admittance capacitive component. Indicates the resonant bandwidth; To enhance the resonant center frequency generated by the admittance strategy, This is the gain coefficient. This is the quality factor.

[0050] Based on the above analysis, due to the intermittent and fluctuating output power of new energy power plants, the operating conditions of hybrid power plants change in real time. Therefore, the instability frequency of hybrid power plants will vary. To cope with the wide range of oscillating conditions, the first embodiment of this invention establishes a stability improvement method for hybrid power plants based on adaptive hybrid damping, such as... Figures 8 to 9 As shown, the method includes the following steps: S10. Monitor the total harmonic distortion result of the common grounding point online. When the total harmonic distortion result does not meet the grid connection stability requirements, look up the mapping relationship table offline based on the grid output power value to obtain the virtual impedance parameter that matches the grid output power. The mapping relationship table is pre-constructed under the constraint boundary conditions of the virtual impedance value of grid-connected energy storage. It should be noted that if the total harmonic distortion result of the common grounding point monitored online meets the grid connection stability requirements, then there is no need to change the virtual impedance parameters, nor is it necessary to introduce a control loop with enhanced admittance strategy into the grid control loop.

[0051] S20. If the total harmonic distortion result still does not meet the grid connection stability requirements after eliminating the risk of instability in the low-frequency band using virtual impedance parameters, then add a control loop with enhanced admittance strategy to the grid construction control loop. It should be noted that if the total harmonic distortion result meets the grid connection stability requirements after eliminating the low-frequency instability risk through virtual impedance parameter control, the current operation will be exited directly. If the total harmonic distortion result still does not meet the grid connection stability requirements, an enhanced admittance strategy control loop will be added to the grid construction control loop. This enhanced admittance strategy is determined by the impedance angle of the hybrid power station and can be equivalent to connecting an RLC branch in parallel on the grid construction impedance.

[0052] S30. Calculate the real-time resonant frequency of the hybrid power station online based on the voltage and current of the common grounding point, input the real-time resonant frequency into the equivalent expression of the control loop, and perform iterative looping until an effective enhanced admittance control parameter that meets the grid connection stability requirements is obtained to eliminate the risk of instability in the mid-frequency band.

[0053] Specifically, by setting the resonant center frequency generated by the enhanced admittance strategy Equal to the real-time resonant frequency of the hybrid power station The resonant center frequency is input into the equivalent expression of the control loop, and the loop is iterated until the iteration termination condition is met to obtain the effective enhanced admittance control parameters. The mid-frequency instability risk is eliminated based on the effective enhanced admittance control parameters. The termination condition is that the total harmonic distortion result meets the grid-connected stability requirements.

[0054] As a further preferred technical solution, in step S10, before obtaining the virtual impedance parameter matching the grid output power by offline lookup of the mapping relationship table based on the grid output power value, the method further includes the following steps: S1. Based on the stability criterion under the grid-type perspective as shown in Equation (5), establish the virtual impedance value constraint boundary of grid-type energy storage in the hybrid power station under different output power conditions as shown in Equation (6). S2. Under the constraint of virtual impedance values, form a mapping table between the grid output power and the virtual impedance parameters, such as... Figure 10 As shown.

[0055] As a further preferred technical solution, step S30 involves calculating the real-time resonant frequency of the hybrid power station online based on the voltage and current of the common grounding point, specifically including the following steps: Online fast Fourier decomposition of the voltage and current at the common grounding point yields the real-time resonant frequency of the hybrid power station. .

[0056] Specifically, this embodiment monitors the total harmonic distortion (THD) of the point of common ground (PCC) online. When the THD result does not meet the grid-connected stability requirements, the resonant frequency of the hybrid power station is obtained based on the Fast Fourier Transform (FFT) results of the PCC point voltage and current. .

[0057] As a further preferred technical solution, step S30: inputting the real-time resonant frequency into the equivalent expression of the control loop, and performing iterative iterations until an effective enhanced admittance control parameter that meets the grid-connected stability requirements is obtained to eliminate the risk of mid-frequency instability, specifically including: Let the resonant center frequency generated by the enhanced admittance strategy Equal to real-time resonant frequency and the resonant center frequency That is, the real-time resonant frequency The input is fed into the equivalent expression of the control loop, and iterative loops are performed to increase the gain coefficient. This reduces the amplitude of the positive resistance component in the enhanced admittance, and also lowers the quality factor. This expands the resonant bandwidth until an effective enhanced admittance control parameter that meets the grid-connected stability requirements is obtained.

[0058] It should be noted that in this embodiment, the enhanced admittance resonant center frequency is input into the expression (13) of the control parameter, and the gain coefficient k is increased through iterative iteration. E This reduces the amplitude of the positive resistance component in the enhanced admittance, thus strengthening the dominance of the positive resistance in the parallel structure and canceling out the negative resistance characteristic at the resonant frequency; simultaneously, it reduces the quality factor Q. E Expanding the resonant bandwidth allows the positive resistance characteristic to cover a wider frequency range until the iteration termination condition is met (THD of the voltage and current at the PCC point is less than 5%), at which point effective enhanced admittance control parameters are obtained. Effective enhanced admittance control parameters include... , , Effectively enhancing admittance control parameters can raise the phase of the impedance of hybrid power plants and extend the effective range of the strategy, eliminating the risk of instability in the mid-frequency band.

[0059] It should be noted that this embodiment determines the virtual impedance parameters from the perspective of the grid-type impedance and determines the enhanced admittance strategy from the perspective of the hybrid power station impedance. Then, an adaptive hybrid damping strategy is constructed by combining the virtual impedance and the enhanced admittance: for different output power of GFL, an adaptive control strategy for the virtual impedance parameters is formed by offline table lookup to eliminate the risk of instability in the low-frequency band; at the same time, the real-time wide-range oscillation frequency of the grid-type / grid-type hybrid power station is obtained by online fast Fourier transform (FFT) to determine the frequency of mid-frequency instability risk, and then the enhanced admittance control parameters are adaptively adjusted to eliminate the risk of mid-frequency instability.

[0060] The following are the main parameters in this embodiment: Table 1 Main Parameters

[0061] It should be noted that virtual impedance is generally added to hybrid power plants connected to the grid to improve the grid-connected stability of GFM energy storage. However, virtual impedance only addresses the risk of instability in the low-frequency band. As the output power of the GFL increases, hybrid power plants connected to the grid face the risk of broadband oscillations, as shown in the voltage and current waveforms at the PCC point. Figure 11As shown in the waveform, it can be seen that there is a certain frequency resonance in the voltage and current, which causes severe distortion.

[0062] In this embodiment, the voltage and current waveforms after applying the stability improvement method proposed in this invention are as follows: Figure 12 As shown, it can be seen that after the voltage and current THD at the PCC point do not meet the grid connection stability requirements, the controller adaptively adjusts the hybrid damping control parameters according to the FFT results of the voltage and current at the PCC point, so that the impedance of the hybrid power station is reshaped and the risk of broadband oscillation is eliminated, and finally the voltage and current waveform at the PCC point returns to a stable state.

[0063] In addition, such as Figure 13 As shown, the second embodiment of the present invention also proposes a stability improvement system for a hybrid hydroelectric power station based on adaptive hybrid damping, the system comprising: The virtual impedance parameter adjustment module 10 is used to monitor the total harmonic distortion result of the common grounding point online. When the total harmonic distortion result does not meet the grid connection stability requirements, it searches the mapping relationship table offline based on the grid output power value to obtain the virtual impedance parameter that matches the grid output power. The mapping relationship table is pre-constructed under the constraint boundary conditions of the virtual impedance value of grid-connected energy storage. The enhanced admittance module 20 is used to add a control loop of the enhanced admittance strategy to the grid control loop if the total harmonic distortion result still does not meet the grid stability requirements after eliminating the risk of instability in the low-frequency band using virtual impedance parameters. The enhanced admittance control parameter adjustment module 30 is used to calculate the real-time resonant frequency of the hybrid power station online based on the voltage and current of the common grounding point, input the real-time resonant frequency into the equivalent expression of the control loop, and perform iterative cycles until an effective enhanced admittance control parameter that meets the grid connection stability requirements is obtained to eliminate the risk of instability in the mid-frequency band.

[0064] Furthermore, the third embodiment of the present invention also proposes a GFM control device, including a memory and a processor. The processor reads executable program code stored in the memory to run a program corresponding to the executable program code, so as to implement the stability improvement method of the root / structure hybrid power station based on adaptive hybrid damping as described in the first embodiment above.

[0065] It should be noted that other embodiments or specific implementation methods of the adaptive hybrid damping-based root / structure hybrid power station stability improvement system and GFM control equipment described in this invention can refer to the above-mentioned method embodiments, and will not be repeated here.

[0066] It should be noted that the computer-readable medium disclosed in this embodiment may be a computer-readable signal medium or a computer-readable storage medium, or any combination thereof. A computer-readable storage medium may 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 a computer-readable storage medium may include, but are not limited to: 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, and portable compact disk read-only memory (CD-ROM). ROM, optical storage devices, magnetic storage devices, or any suitable combination thereof. In this disclosure, a computer-readable storage medium can be any tangible medium containing or storing a program that can be used by or in connection with an instruction execution system, apparatus, or device. In this disclosure, a computer-readable signal medium can include a data signal propagated in baseband or as part of a carrier wave, carrying computer-readable program code. Such propagated data signals can take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof. A computer-readable signal medium can also be any computer-readable medium other than a computer-readable storage medium, which can send, propagate, or transmit a program for use by or in connection with an instruction execution system, apparatus, or device. The program code contained on the computer-readable medium can be transmitted using any suitable medium, including but not limited to: wires, optical fibers, RF (radio frequency), etc., or any suitable combination thereof.

[0067] The aforementioned computer-readable medium may be included in the aforementioned electronic device; or it may exist independently and not assembled into the electronic device. The aforementioned computer-readable medium carries one or more programs, which, when executed by the electronic device, cause the electronic device to perform a zero-sample image anomaly detection method according to the above embodiments.

[0068] Computer program code for performing the operations of this disclosure can be written in one or more programming languages ​​or a combination thereof, including object-oriented programming languages ​​such as Java, Smalltalk, and C++, and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The program code can be executed entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server.

[0069] In cases involving remote computers, the remote computer can be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN), or it can be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0070] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0071] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," 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 the invention. 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.

[0072] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" or "several" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0073] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for improving the stability of a hybrid hydropower station based on adaptive hybrid damping, characterized in that, include: The total harmonic distortion (THD) result of the common grounding point is monitored online. When the THD result does not meet the grid-connected stability requirements, the mapping relationship table is searched offline based on the grid output power value to obtain the virtual impedance parameter that matches the grid output power. The mapping relationship table is pre-constructed under the constraint boundary conditions of the virtual impedance value of grid-connected energy storage. If the total harmonic distortion result still does not meet the grid connection stability requirements after eliminating the risk of instability in the low-frequency band using virtual impedance parameters, then an enhanced admittance strategy control loop is added to the grid control loop. The real-time resonant frequency of the hybrid power station is calculated online based on the voltage and current at the common grounding point. The real-time resonant frequency is then input into the equivalent expression of the control loop and iterated until an effective enhanced admittance control parameter that meets the grid connection stability requirements is obtained to eliminate the risk of instability in the mid-frequency band.

2. The method for improving the stability of a hybrid power station based on adaptive hybrid damping as described in claim 1, characterized in that, Before obtaining the virtual impedance parameter matching the grid output power by offline lookup of the mapping table based on the grid output power value, the method further includes: Based on the stability criteria from the perspective of grid-connected power, a virtual impedance constraint boundary is established for grid-connected energy storage in hybrid power plants under different output power conditions. Under the constraint boundary conditions of virtual impedance value, a mapping relationship table between grid output power and virtual impedance parameters is formed.

3. The method for improving the stability of a hybrid power station based on adaptive hybrid damping as described in claim 2, characterized in that, The stability criterion from the perspective of network structure is: In the formula, For phase margin, Port line impedance from a network perspective. The network impedance transfer function is... To keep up with grid power fluctuations phase curve, for phase curve, To be related to the impedance transfer function, j It is the basic unit of imaginary numbers. Angular frequency, For virtual impedance parameters, To accommodate the grid connection impedance of the hybrid power station, Indicates a parallel relationship. Here is the frequency domain expression for the impedance of the grid-connected line of the hybrid power station. This is the frequency domain expression for the port line impedance from a network perspective. The output power of the grid.

4. The method for improving the stability of a hybrid power station based on adaptive hybrid damping as described in claim 2, characterized in that, The constraint boundary for the virtual impedance value is: In the formula, This is the negative RC boundary angular frequency of the mesh-type impedance. Angular frequency, For network impedance transfer function phase curve, For the network impedance under the negative RC boundary angular frequency condition, The line impedance of the network port under different grid output powers under the negative RC boundary angular frequency condition is given, where the variable is the output power under the grid condition. j It is the basic unit of imaginary numbers. For virtual impedance parameters, To match the output power of the grid, The symbol is '|', and the separator is '|'.

5. The method for improving the stability of a hybrid power station based on adaptive hybrid damping as described in claim 3, characterized in that, Taking the overall impedance of a hybrid power station as the criterion, the formula for calculating the overall impedance of a hybrid power station is as follows: In the formula, Indicates the overall impedance of the hybrid power station. This indicates the overall impedance of the network. This represents the overall impedance of the network. Indicates a parallel relationship; Represents the negative-sequence component of the line impedance. , , , These are the positive-sequence self-impedance, negative-sequence self-impedance, positive-negative-sequence coupling impedance, and negative-positive-sequence coupling impedance of the grid-connected converter, respectively. , , , These are the positive-sequence self-impedance, negative-sequence self-impedance, positive-negative-sequence coupling impedance, and negative-positive-sequence coupling impedance of the grid-type converter, respectively. This represents the positive-sequence disturbance voltage of the network configuration. This represents the positive-sequence response voltage of the network type. This indicates the positive sequence disturbance voltage of the network type. This indicates the positive sequence response voltage of the grid.

6. The method for improving the stability of a hybrid power station based on adaptive hybrid damping as described in claim 1, characterized in that, The grid connection stability criterion for the aforementioned hybrid power station is: In the formula, For phase margin, To determine the line impedance between the common grounding point of the hybrid power plant and the power grid, To determine the overall impedance of the hybrid power station, for phase curve, for The phase curve.

7. The method for improving the stability of a hybrid power station based on adaptive hybrid damping as described in claim 1, characterized in that, The online calculation of the real-time resonant frequency of the hybrid power station based on the voltage and current of the common grounding point includes: The voltage and current at the common grounding point are decomposed online using Fast Fourier Transform to obtain the real-time resonant frequency of the hybrid power station.

8. The method for improving the stability of a hybrid power station based on adaptive hybrid damping as described in claim 1, characterized in that, The transfer function of the enhanced admittance strategy is: In the formula, This indicates a simplified impedance configuration for the mid-frequency band with an enhanced admittance strategy. This represents the second-order bandpass control element of the admittance enhancement strategy. This represents the compensation gain stage of the admittance enhancement strategy; For the center frequency, This is the gain coefficient. For quality factor; This represents the proportionality coefficient of the current loop. This represents the voltage loop proportionality coefficient. Indicates the voltage loop integral coefficient; Indicates the fundamental angular frequency. This indicates a mesh filter inductor. Represents angular frequency. Represents virtual impedance. Represents the variables in the complex field. j The basic unit representing imaginary numbers.

9. The method for improving the stability of a hybrid power station based on adaptive hybrid damping as described in claim 1, characterized in that, The method further includes: The enhanced admittance strategy is equivalent to connecting an RLC branch in parallel with the network impedance. The equivalent expression of the control loop is the relationship between the various impedance components of the RLC branch and the parameters of the enhanced admittance control loop, and the corresponding resonant frequency and resonant bandwidth, which are as follows: In the formula, R e This indicates an increase in the admittance resistive component. L e This indicates an increase in the perceptual component of admittance. C e This indicates an enhanced admittance capacitive component. Indicates the resonant bandwidth; To enhance the resonant center frequency generated by the admittance strategy, This is the gain coefficient. This is the quality factor.

10. The method for improving the stability of a hybrid power station based on adaptive hybrid damping as described in claim 9, characterized in that, The step of inputting the real-time resonant frequency into the equivalent expression of the control loop and performing iterative iterations until effective enhanced admittance control parameters that meet grid-connected stability requirements are obtained includes: The resonant center frequency generated by the enhanced admittance strategy is set to equal the real-time resonant frequency, and this resonant center frequency is input into the equivalent expression of the control loop for iterative iteration to increase the gain coefficient. This reduces the amplitude of the positive resistance component in the enhanced admittance, and also lowers the quality factor. This expands the resonant bandwidth until an effective enhanced admittance control parameter that meets the grid-connected stability requirements is obtained.

11. A stability enhancement system for a hybrid power station based on adaptive hybrid damping, characterized in that, include: The virtual impedance parameter adjustment module is used to monitor the total harmonic distortion result of the common grounding point online. When the total harmonic distortion result does not meet the grid connection stability requirements, it searches the mapping relationship table offline based on the grid output power value to obtain the virtual impedance parameter that matches the grid output power. The mapping relationship table is pre-constructed under the constraint boundary conditions of the virtual impedance value of grid-connected energy storage. The enhanced admittance module is used to add a control loop of the enhanced admittance strategy to the grid control loop if the total harmonic distortion result still does not meet the grid stability requirements after eliminating the risk of instability in the low-frequency band using virtual impedance parameters. The enhanced admittance control parameter adjustment module is used to calculate the real-time resonant frequency of the hybrid power station online based on the voltage and current of the common grounding point. The real-time resonant frequency is input into the equivalent expression of the control loop and iterated until an effective enhanced admittance control parameter that meets the grid connection stability requirements is obtained to eliminate the risk of instability in the mid-frequency band.

12. A GFM control device, comprising a memory and a processor, characterized in that, The processor reads the executable program code stored in the memory to run the program corresponding to the executable program code, so as to implement the method for improving the stability of the root / structure hybrid power station based on adaptive hybrid damping as described in any one of claims 1-10.

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