Impedance reshaping type VSG current harmonic suppression method based on current negative feedforward
By introducing a bandpass filter and an active suppression branch into the VSG system, current negative feedforward is used to reshape the equivalent harmonic output impedance of the VSG, which solves the problems of cumbersome current harmonic control solutions and poor stability in the existing technology. , achieving efficient current harmonic suppression and power quality improvement.
Patent Information
- Application Number
- CN202411543086.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-22
- Publication Date
- 2025-01-21
AI Technical Summary
The VSG current harmonic management solution under distorted power grid is relatively cumbersome and difficult to achieve stability. The value of the virtual impedance will cause the system to be instable, and the value of the too small will cause the suppression performance of the current harmonics.
The impedance-reshaping VSG current harmonic suppression method based on current negative feedforward is used to extract the harmonic component of the grid-side current through the band-pass filter, and the compensation amount of the VSG harmonic voltage is generated through the active suppression branch to achieve the Reshaping of VSG equivalent harmonic output impedance.
It achieves the harmonic suppression effect of the maximum virtual impedance, greatly improves the power quality of the grid-side current, simplifies the implementation process, and reduces the amount of calculation.
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Figure CN119341003A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of power quality control, and in particular to an impedance reshaping type VSG current harmonic suppression method based on current negative feedforward. Background Art
[0002] Virtual synchronous generator (VSG) technology is friendly to distributed energy access to the grid. At the fundamental frequency, VSG can provide the grid with the necessary voltage and frequency support. However, when it is connected to a distorted grid, the grid-side current will be directly affected by the background harmonics of the grid, causing different degrees of distortion, and the power quality of the output current will deteriorate sharply. Since the line impedance and grid-side impedance are small in value, the equivalent harmonic output impedance of VSG directly determines the content of grid-side current harmonics.
[0003] In the prior art, the control scheme for VSG current harmonics in distorted power grids mostly uses a control method based on virtual impedance, and its control block diagram is as follows: Figure 5 As shown in the figure, this scheme subtracts the voltage drop at a virtual impedance from the voltage reference value output by the VSG to generate a new voltage reference value to simulate the influence of the real impedance, thereby equivalently adding an actual impedance of the same size as the virtual impedance. This method theoretically increases the size of the total output impedance of the inverter in each frequency band and suppresses the harmonics in the grid-side current. It is worth noting that the larger the value of the virtual impedance, the stronger the ability to suppress current harmonics. However, as the value of the virtual impedance increases, the system tends to be unstable, and as the value decreases, the suppression performance of current harmonics is poor. In addition, the implementation process of the virtual impedance method includes steps such as harmonic decoupling, positive and negative sequence separation, and voltage calculation at the virtual impedance, and the implementation process is relatively cumbersome.
[0004] Therefore, in order to improve the power quality of current when VSG is connected to the distorted grid, it is urgent to design a simple and effective current harmonic control solution. Summary of the invention
[0005] The present invention provides an impedance reshaping type VSG current harmonic suppression method based on current negative feedforward, which can achieve the harmonic suppression effect of maximum virtual impedance, greatly improve the power quality of grid-side current, and has a simpler implementation process.
[0006] This application provides the following technical solutions:
[0007] The impedance reshaping type VSG current harmonic suppression method based on current negative feedforward includes the following steps:
[0008] S1. Establish the impedance model of VSG, analyze the mechanism of VSG output current distortion under distorted grid and the shortcomings of traditional virtual impedance method
[0009] S2. According to the analysis results of S1, an active suppression branch including a bandpass filter is designed; the bandpass filter is used to extract the harmonic components of the grid-side current; the active suppression branch performs negative feedforward on the extracted grid-side current harmonic components to generate compensation for the VSG harmonic voltage, thereby reshaping the VSG equivalent harmonic output impedance.
[0010] Technical principle: Through the frequency selectivity of the bandpass filter, harmonic components of a specific order can be accurately selected for extraction, and the extracted harmonic components of a specific order are used to generate compensation for the harmonic voltage through the current negative feedback front path, which can accurately control the reshaping of the equivalent harmonic output impedance.
[0011] Beneficial effect: Since the line impedance and grid-side impedance are small in value, the equivalent harmonic output impedance of the VSG directly determines the content of grid-side current harmonics. When the equivalent harmonic output impedance is accurately reshaped, a better harmonic suppression effect can be obtained.
[0012] At the same time, compared with the traditional virtual impedance solution, the present invention does not need to perform two steps of positive and negative sequence separation and harmonic voltage calculation, which reduces the amount of calculation and is easier to implement.
[0013] Furthermore, the transfer function of the bandpass filter is:
[0014]
[0015] Where h represents the order of the extracted current harmonics, ω c represents the bandwidth of the bandpass filter, ω h Indicates the angular frequency of the main harmonic.
[0016] Beneficial effects: The use of a bandpass filter can accurately extract signals within a specific frequency range, and at the same time, the structure is simple, the cost is low, and the adjustment of parameters is relatively convenient.
[0017] Furthermore, the bandwidth of the bandpass filter is 10-20 rad / s.
[0018] Beneficial effects: Considering that the harmonic components that have a greater impact on the power quality in the power grid mainly include the 5th, 7th, 11th, and 13th harmonic components, and the harmonic components fluctuate within a certain frequency range. Therefore, in order to improve the anti-frequency interference ability of the bandpass filter, the bandwidth should be as large as possible. The anti-frequency interference ability of 20rad / s is stronger, while that of 10rad / s is weaker. Setting its bandwidth to 20rad / s can effectively complete the extraction of the above harmonic components.
[0019] Furthermore, after the active suppression branch is introduced, the closed-loop transfer function of the capacitor voltage is:
[0020]
[0021] Where, T ur (s) is the voltage reference gain, is the reference value of the capacitor voltage, Z out (s) is the equivalent output impedance of VSG, i g (s) is the grid-side current, -m is the feedforward coefficient of harmonic current, T h (s) represents the gain of VSG harmonic voltage compensation, i gh (s) represents the harmonic component of the grid-side current.
[0022] Beneficial effect: The current negative feedforward branch method does not need to perform two steps of positive and negative sequence separation and harmonic voltage calculation, which reduces the amount of calculation and is easier to implement.
[0023] Furthermore, the value of m is 130-180.
[0024] Beneficial effect: The optimal harmonic compensation voltage is obtained by reasonably selecting the feedforward coefficient, and the stable operation of the system is ensured while increasing the harmonic equivalent output impedance as much as possible.
[0025] The larger the value of m is, the greater the harmonic output impedance of the reshaped VSG is, and the better the suppression effect of current harmonics is. When m is in the range of 130-180, the suppression effect of current harmonics is better. When m is greater than 180, there is a risk of overmodulation in the system, and when it is less than 130, the harmonic suppression effect is poor.
[0026] Furthermore, it also includes S3, building a hardware-in-the-loop experimental platform to verify the effectiveness of the current harmonic suppression method.
[0027] Beneficial effects: Through the constructed hardware-in-the-loop experimental platform, harmonic injection can be easily completed, various parameters such as frequency, amplitude, phase, etc. of harmonic components can be adjusted, and the grid voltage, grid current, active power, and reactive power of the power quality output on the grid side can be measured to quickly verify and adjust the harmonic suppression strategy.
[0028] Further, the S3 includes:
[0029] S31. Comparison of harmonic suppression performance with traditional VSG control and virtual impedance-based methods under variable line impedance conditions;
[0030] S32. Verify the current harmonic suppression performance during dynamic power changes.
[0031] Beneficial effects: The current harmonic suppression performance is evaluated under the conditions of variable line impedance and dynamic power changes, which can more comprehensively reflect the difference in the effects of current harmonic suppression methods. BRIEF DESCRIPTION OF THE DRAWINGS
[0032] Figure 1 It is the control block diagram of the traditional VSG algorithm;
[0033] Figure 2 It is the fundamental wave equivalent circuit and harmonic domain equivalent circuit diagram of the VSG-based grid-connected system;
[0034] Figure 3 for i gh / u gh Schematic diagram of the relationship with the equivalent harmonic output impedance of VSG;
[0035] Figure 4 It is the Bode diagram of the total output impedance of the inverter under the traditional VSG control method;
[0036] Figure 5 It is a control block diagram of the existing virtual impedance method;
[0037] Figure 6 is an equivalent circuit diagram based on the existing virtual impedance method;
[0038] Figure 7 The Bode diagram of the total output impedance of the inverter before and after the virtual impedance method is adopted;
[0039] Figure 8 It is the overall control block diagram of the impedance reshaping current harmonic suppression solution based on current negative feedforward;
[0040] Fig. 9 is the Bode diagram of the harmonic extractor;
[0041] Fig.10 The equivalent circuit diagram of the VSG grid-connected system using the harmonic suppression method of the present invention;
[0042] Fig.11 The traditional VSG control, virtual impedance scheme and harmonic suppression method of the present invention are shown in Figure 2. total Bode diagram of
[0043] Fig.12 This is the structural diagram of the hardware-in-the-loop experimental platform;
[0044] Fig.13 Z line = Schematic diagram of experimental results of grid-side current when 200μH;
[0045] Fig.14 Z line = Schematic diagram of experimental results of grid-side current when 600μH;
[0046] Fig.15 Z line = Schematic diagram of experimental results of grid-side current when 1000μH;
[0047] Fig.16 It is a schematic diagram of the experimental results of the grid-side current when the active power changes suddenly;
[0048] Fig.17 Schematic diagram of experimental results of grid-side current when reactive power changes suddenly. DETAILED DESCRIPTION
[0049] In order to solve the problem of grid-side current distortion when VSG is connected to a distorted grid, the current harmonic control solution based on virtual impedance subtracts the voltage drop at a virtual impedance from the voltage reference value output by VSG to generate a new voltage reference value to simulate the influence of real impedance, thereby equivalently adding an actual impedance of the same size as the virtual impedance. This method theoretically increases the total output impedance of inverters in each frequency band and suppresses harmonics in the grid-side current.
[0050] However, as the virtual impedance increases, the system will tend to be unstable. In addition, the implementation process of the virtual impedance method includes steps such as harmonic decoupling, positive and negative sequence separation, and voltage calculation at the virtual impedance, and the implementation process is relatively cumbersome. Therefore, in order to improve the power quality of the current when the VSG is connected to the distorted power grid, the present invention provides a simple and effective current harmonic control method. The following is further explained in detail through specific implementation methods:
[0051] Embodiment 1
[0052] The impedance reshaping type VSG current harmonic suppression method based on current negative feedforward of the present invention comprises the following steps:
[0053] S1. Establish the impedance model of VSG, analyze the mechanism of VSG output current distortion under distorted power grid and the shortcomings of traditional virtual impedance method.
[0054] The overall control block diagram of the inverter using the traditional VSG algorithm is as follows Figure 1 As shown. Among them, U dc is the DC side voltage, L f and C f are the inverter side inductor and filter capacitor respectively, i L and i g Indicates the inverter side current and grid side current, Z line , Z g is the line impedance between VSG and the grid and the grid impedance, Z g (s)=sL g , Z line (s)=sL line ,u c represents the capacitor voltage, u PCC represents the voltage at the common coupling point, u g Indicates the grid voltage.
[0055] The control link first calculates the instantaneous active and reactive power by collecting capacitor voltage and inverter-side current, and provides the calculated instantaneous power to the power loop of VSG. The active-frequency control loop provides inertia and damping for the system to achieve primary frequency modulation of the power grid; the reactive-voltage control loop can achieve primary voltage regulation of the power grid while adjusting the reactive output. In addition, the power loop of VSG also provides a reference value for the capacitor voltage for the voltage closed-loop control. Since the control link operates in a two-phase stationary coordinate system, the voltage closed-loop uses a quasi-proportional resonant controller (QPR) to accurately track the fundamental voltage command value output by the VSG. The transfer function of the controller is expressed by G u Indicates; the current closed loop uses P controller for closed loop control, and G i Finally, the control signal of the inverter is generated through SVPWM, thereby realizing the friendly grid connection of the voltage source inverter.
[0056] analyze Figure 1 It can be seen that the closed-loop transfer function of the capacitor voltage is:
[0057]
[0058] In the formula, is the reference value of the capacitor voltage, T ur (s) represents the voltage reference gain, Z out (s) is the equivalent output impedance of VSG, T ur (s) and Z out The expression of (s) is as follows:
[0059]
[0060] In formula (2) and (3), Z Cf =1 / sC f , defined as the equivalent impedance of the filter capacitor; Z Lf =sL f , defined as the equivalent impedance of the inverter side inductor; K pwm Represents the equivalent gain of the inverter. According to formula (1), the fundamental wave equivalent circuit and harmonic domain equivalent circuit of the VSG-based grid-connected system can be derived, as follows: Figure 2 (a) and (b). Z outf , Z linef , Z gf 、u gf They represent the capacitor voltage reference value, VSG equivalent output impedance, line impedance, grid impedance and fundamental component of grid voltage respectively. Z outh , Z lineh , Z gh 、u ghThen it represents their respective harmonic components.
[0061] The expression of the grid-side current in the fundamental domain is shown in equation (4), and the expression in the harmonic domain is shown in equation (5).
[0062]
[0063]
[0064] The grid-side current expression can be obtained by superimposing the fundamental component and the harmonic component, as shown in equation (6):
[0065] i g (s) = i gf (s)+i gh (s) (6)
[0066] Since the output of the VSG power loop is only the fundamental voltage amplitude and phase information that can ensure normal power transmission, the capacitor voltage reference value output by the VSG only contains the fundamental component. In other words, in the harmonic domain, the voltage and current of the VSG are both open-loop controlled, that is, Therefore, the expression of the grid-side current in the harmonic domain can be further expressed as equation (7). Therefore, at the fundamental frequency, although the VSG can provide the necessary voltage and frequency support for the grid, when it is connected to the distorted grid, the grid-side current will be directly affected by the background harmonics of the grid and will be distorted to varying degrees. To facilitate the following analysis, let Z total =Z out +Z line +Z g , represents the total output impedance of the inverter.
[0067]
[0068] From the analysis of formula (7), it can be seen that the harmonic content of the grid-side current depends on the total output impedance of the inverter. However, since the line impedance and the grid-side impedance are small, the equivalent harmonic output impedance of the VSG directly determines the harmonic content of the grid-side current. Figure 3 Showing i gh / u gh The equivalent harmonic output impedance Z of VSG outh From the relationship between , it can be seen that the direct way to reduce the harmonic content in the grid-side current is to increase the VSG equivalent harmonic impedance. Figure 4 The bode diagram of the total output impedance of the inverter under traditional VSG control is shown. It can be seen that the total output impedance of the inverter under traditional VSG control is small in all frequency bands. Therefore, when VSG is connected to the distorted grid, it becomes a harmonic source, causing the harmonic content in the grid-side current to increase sharply.
[0069] Figure 5 The control block diagram of the current harmonic control solution based on virtual impedance is shown, where R v and L v Represent virtual resistance and virtual inductance respectively. This solution subtracts the voltage drop at a virtual impedance from the voltage reference value output by the VSG to generate a new voltage reference value to simulate the influence of the real impedance, thereby equivalently adding an actual impedance of the same size as the virtual impedance. This method theoretically increases the total output impedance of the inverter in each frequency band and suppresses the harmonics in the grid-side current. Its equivalent circuit diagram is shown in the figure below. Figure 6 As shown in the figure, the total output impedance of the inverter is increased by a virtual impedance Z v The actual impedance of the same size. Assuming that the background harmonics of the grid voltage are mainly 5, 7, 11 and 13, the Bode diagram of the total output impedance of the inverter before and after the virtual impedance method is used is as follows: Figure 7 shown.
[0070] However, as the virtual impedance increases, the system will tend to be unstable. In addition, the implementation process of the virtual impedance method includes steps such as harmonic decoupling, positive and negative sequence separation, and voltage calculation at the virtual impedance, and the implementation process is relatively cumbersome.
[0071] S2. Based on the analysis results of S1, an active suppression branch including a harmonic extractor is designed.
[0072] After the above analysis, the present invention introduces an active suppression branch on the basis of the original traditional VSG control. In the active suppression branch, the harmonic components of the grid-side current are first extracted, and then the current harmonic components are used to generate the compensation amount of the VSG harmonic voltage through a suitable negative feedforward branch to reshape the equivalent harmonic impedance of the VSG. At the fundamental frequency, the proposed scheme does not change the structure of the original VSG control, and retains its support for the grid inertia and frequency; and in the harmonic domain, the added active suppression branch realizes the closed-loop control of the VSG for the harmonic current.
[0073] The overall control block diagram of the impedance reshaping current harmonic suppression solution based on current negative feedforward is as follows: Figure 8 shown.
[0074] In order to ensure the accurate extraction of the grid-side harmonic components in the active suppression branch, the harmonic extractor adopts a bandpass filter, and its transfer function is shown in equation (8):
[0075]
[0076] Where h represents the order of the extracted current harmonics, ω c represents the bandwidth of the bandpass filter, ω hIndicates the angular frequency of the main harmonic. Since the current harmonic components to be extracted fluctuate within a certain frequency range. Therefore, in order to improve the anti-frequency interference ability of the bandpass filter, the bandwidth should be as large as possible. The anti-frequency interference ability of 20rad / s is stronger, while that of 10rad / s is weaker. In this embodiment, ω c =20rad / s. According to formula (8), the Bode diagram of the harmonic extractor can be drawn, as shown in Fig. 9 shown.
[0077] After adding the current harmonic suppression method described in this application, the closed-loop transfer function of the capacitor voltage is shown in formula (9):
[0078]
[0079] In formula (9),
[0080]
[0081] Indicates the compensation amount of VSG harmonic voltage.
[0082] It is not difficult to find that the closed-loop transfer function of the capacitor voltage reference gain is consistent with that when the proposed current harmonic suppression strategy is not added. This is because the addition of the active suppression branch only changes the control structure in the harmonic domain, and does not change the control loop at its fundamental frequency. Since the compensation amount of the VSG harmonic voltage is generated by the current harmonic component through negative feedforward, its expression is shown in formula (12):
[0083]
[0084] Therefore, formula (9) can be further expressed as formula (13):
[0085]
[0086] Where, T ur (s) is the voltage reference gain, is the reference value of the capacitor voltage, Z out (s) is the equivalent output impedance of VSG, i g (s) is the grid-side current, T h (s) represents the gain of VSG harmonic voltage compensation, i gh (s) represents the harmonic component of the grid current. gh The feedforward coefficient represents negative feedforward, which is used to output and increase the compensation amount of the VSG harmonic voltage, thereby equivalently increasing the harmonic output impedance of the VSG.
[0087] The larger the value of m is, the greater the harmonic output impedance of the reshaped VSG is, and the better the suppression effect of current harmonics is. When m is in the range of 130-180, the suppression effect of current harmonics is better. When m is greater than 180, there is a risk of overmodulation in the system, and when it is less than 130, the harmonic suppression effect is poor. In this embodiment, m is taken as 180.
[0088] According to formula (13), the equivalent circuit of the VSG-based grid-connected system in the fundamental frequency and harmonic domain can be further obtained, as follows: Fig.10 (a) and (b). It can be seen that the proposed strategy does not change the components of the traditional VSG at the fundamental frequency. By analyzing its equivalent circuit in the harmonic domain, the expression of the grid-side current in the harmonic domain after adding the proposed scheme can be obtained, as shown in formula (14):
[0089]
[0090] from Fig.10 It is not difficult to see from (b) and equation (14) that after adopting the current harmonic control scheme, on the basis of traditional VSG control, the equivalent harmonic output impedance Z of VSG is outh Added a new item mG e T h (s), forming a new harmonic output impedance Z outvh , realizing the reshaping of VSG equivalent harmonic output impedance.
[0091] Fig.11 The Bode diagram of the total output impedance of the inverter under different schemes is shown, where the value of the virtual impedance in the virtual impedance method is the maximum virtual impedance value (L v =15mH), further increasing the value of virtual impedance will cause system instability. Fig.11 It can be seen that compared with the traditional VSG control Z total , Z after adopting the harmonic suppression method of the present invention total It has a higher amplitude gain at the corresponding harmonic frequency. In other words, the method of the present invention is equivalent to increasing the harmonic output impedance of the inverter. In addition, compared with the traditional virtual impedance method, the method of this invention is more effective in Z total The corresponding harmonic frequencies of also have higher amplitude gains. Figure 3 The mechanism shown is that the larger the inverter output harmonic impedance, the less the grid-side current is affected by the background harmonics of the power grid. In theory, the method of the present invention has better harmonic suppression effect than the traditional virtual impedance scheme, and greatly improves the quality of VSG output current under distorted power grid.
[0092] At the same time, compared Figure 8 and Figure 5Control block diagram of two harmonic control methods. The method of the present invention can generate the compensation amount of VSG harmonic voltage through appropriate negative feedforward after current harmonic extraction, while the traditional virtual impedance solution still needs to perform two steps of positive and negative sequence separation and harmonic voltage calculation. Therefore, the method of the present invention has a simpler implementation process in practical applications.
[0093] S3. Build a hardware-in-the-loop experimental platform to verify the effectiveness of the current harmonic suppression method.
[0094] In order to verify the effectiveness and reliability of the harmonic control method proposed in the present invention, the inventors constructed a hardware in the loop (HIL) experimental platform. Fig.12 The structure diagram of the hardware-in-the-loop experimental platform. The hardware-in-the-loop simulator uses a real-time simulator to simulate the main circuit. Rapid control prototyping (RCP) is essentially a controller that can be quickly reused to quickly test and adjust the VSG control algorithm and harmonic suppression strategy. To simulate the impact of background harmonics in the power grid, 6V 5th, 7th, 11th, and 13th harmonics are uniformly injected into the power grid voltage.
[0095] S31. Comparison of harmonic suppression performance with traditional VSG control and virtual impedance-based methods under variable line impedance conditions;
[0096] In order to verify the effectiveness and reliability of the harmonic suppression method of the present invention, comparative experiments were carried out under different line impedance conditions. Fig.13 , 14 and 15 are Z line =200μH, 600μH and 1000μH using the traditional VSG control, the method based on virtual impedance and the method of the present invention. Comparing the experimental results, it can be seen that compared with the traditional VSG control, the total harmonic distortion (THD) of the grid-side current is reduced from 8.52% to 1.17% after the harmonic suppression scheme of the present invention is adopted, and the power quality is significantly improved. This is because the equivalent harmonic output impedance of the VSG is greatly improved after the scheme proposed by the present invention is adopted.
[0097] Longitudinal observation Fig.13 , 14 From 15, we can see that in Z line =200μH, 600μH and 1000μH, the THD of the grid-side current after the scheme proposed in the present invention is adopted is 1.72%, 1.40% and 1.17% respectively. It is not difficult to find that compared with the method based on virtual impedance, the scheme of the present invention has better harmonic suppression effect because it provides higher gain at the corresponding harmonic frequency of the VSG equivalent output impedance.
[0098] In addition, it is worth noting that with the continuous increase of line impedance, the power quality of grid-side current using the virtual impedance method is constantly deteriorating. This is because the virtual impedance in the experiment is already the maximum virtual impedance value that can be selected, and increasing the value of the virtual impedance will cause the system to become unstable. However, increasing the line impedance is actually the same as increasing the virtual impedance, so the increase in line impedance under this method will cause the system to become unstable. At the same time, it can be found that compared with the method based on virtual impedance, the scheme proposed in the present invention is less affected by changes in line impedance. In summary, the scheme proposed in the present invention is effective and superior for improving the power quality of grid-side current when VSG is connected to a distorted power grid.
[0099] S32. Verify the current harmonic suppression performance during the dynamic power change process;
[0100] In order to verify the harmonic suppression capability of the proposed method on the grid-side current during the dynamic change of VSG output power, the active power command value was increased from 5kW to 7kW, and the reactive power command value was increased from 0kVar to 2kVar in the experiment. Fig.16 and 17 They are the experimental results of grid-side current when active and reactive power suddenly change.
[0101] from Fig.16 and 17 It can be seen that the grid-side current under traditional VSG control contains a high content of harmonics during transient changes, and the current harmonics are suppressed to a certain extent after the virtual impedance method is adopted. After the scheme of the present invention is adopted, the grid-side current has a higher sinusoidality during transient changes, which is due to the fact that the scheme of the present invention can provide a higher gain at the corresponding harmonic frequency of the VSG equivalent output impedance.
[0102] In summary, the impedance reshaping current harmonic suppression method based on current negative feedforward proposed in the present invention has better harmonic suppression performance in both transient and steady-state processes.
[0103] The above are only embodiments of the present invention. The invention is not limited to the field involved in this implementation case. The common knowledge such as the known specific structure and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.
Claims
1. The impedance reshaping VSG current harmonic suppression method based on current negative feedforward is characterized in that: The steps include: S1. Establish the impedance model of VSG, analyze the mechanism of VSG output current distortion under distorted power grid and the shortcomings of traditional virtual impedance method; S2. According to the analysis results of S1, an active suppression branch including a bandpass filter is designed; the bandpass filter is used to extract the harmonic components of the grid-side current; the active suppression branch performs negative feedforward on the extracted grid-side current harmonic components to generate compensation for the VSG harmonic voltage, thereby reshaping the VSG equivalent harmonic output impedance.
2. The impedance reshaping type VSG current harmonic suppression method based on current negative feedforward according to claim 1 is characterized in that: The transfer function of the bandpass filter is: Where h represents the order of the extracted current harmonics, ω c represents the bandwidth of the bandpass filter, ω h Indicates the angular frequency of the main harmonic.
3. The impedance reshaping type VSG current harmonic suppression method based on current negative feedforward according to claim 2 is characterized in that: The bandwidth of the bandpass filter is 10-20 rad / s.
4. The impedance reshaping type VSG current harmonic suppression method based on current negative feedforward according to claim 3 is characterized in that: The closed-loop transfer function of the capacitor voltage after the active suppression branch is introduced is: Where, T ur (s) is the voltage reference gain, u * VSG (s) is the reference value of the capacitor voltage, Z out (s) is the equivalent output impedance of VSG, i g (s) is the grid-side current, -m is the feedforward coefficient of harmonic current, T h (s) represents the gain of VSG harmonic voltage compensation, i gh (s) represents the harmonic component of the grid-side current.
5. The impedance reshaping type VSG current harmonic suppression method based on current negative feedforward according to claim 4 is characterized in that: The value range of m is 130-180.
6. The impedance reshaping type VSG current harmonic suppression method based on current negative feedforward according to claim 5 is characterized in that: Also includes: S3. Build a hardware-in-the-loop experimental platform to verify the effectiveness of the current harmonic suppression method.
7. The impedance reshaping type VSG current harmonic suppression method based on current negative feedforward according to claim 6 is characterized in that: The S3 includes: S31. Comparison of harmonic suppression performance with traditional VSG control and virtual impedance-based methods under variable line impedance conditions; S32. Verify the current harmonic suppression performance during dynamic power changes.