VSG frequency control method based on power correction, and device and storage medium

Abstract

A VSG frequency control method based on power correction, and a device and a storage medium, which belong to the technical field of power electronics, and solve the problem of how to suppress VSG output power oscillation. In the technical solution of the present invention, an output power Pe(s) is corrected, and a corrected value is then fed back to a control circuit, so as to achieve the effect of suppressing power oscillation. The expression of G(s) in a power correction stage is flexible, appropriate parameters may be set on the basis of a phase margin of a system, and a parameter selection principle is provided for correction coefficients τ1 and τ2, such that adjustment coefficients in the power correction stage and the values of τ1 and τ2 do not affect the effect of a steady-state gain in a transient process. The present invention can suppress VSG output power oscillation, and can also provide greater inertia support, thereby improving the stability of a VSG system. Moreover, compared with a VSG system without correction, the system with correction has a significantly improved anti-interference performance and a significantly enhanced overshoot suppression capability.

Description

VSG frequency control method, device and storage medium based on power correction Technical Field

[0001] The present invention belongs to the technical field of power electronics and relates to a VSG frequency control method, device and storage medium based on power correction. Background Art

[0002] Virtual Synchronous Generator (VSG) technology is a new power generation technology based on power electronics. Its emergence provides new insights and development directions for power system development. By applying VSG technology, power system generation and operation can be made more flexible and efficient. Currently, VSG technology has been widely used in fields such as renewable energy generation, ultra-high voltage transmission, and market-based power trading. In the future, VSG technology will continue to leverage its advantages and bring new opportunities and challenges to the power industry.

[0003] The new energy industry is booming, and the amount of renewable energy generated by power electronics is increasing year by year. However, the grid-connected nature of most converters leads to a reduction in power system inertia, which can easily lead to system instability. To address this widespread reduction in inertia in new power systems, virtual synchronous generator technology is being widely used in distributed systems.

[0004] The virtual synchronous generator (VSG) simulates the rotor motion equations of a synchronous generator (SG), imbuing the inverter with virtual inertia and damping characteristics, which helps increase the system's inertia and frequency stability. However, the introduction of the rotor swing equation also imparts oscillation characteristics similar to those of the SG. Improper settings of parameters such as the virtual inertia and damping coefficient can cause the VSG to exhibit "electromechanical-like" power oscillations.

[0005] Summary of the Invention

[0006] The present invention is used to solve the problem of how to suppress VSG output power oscillation.

[0007] The present invention solves the above technical problems through the following technical solutions:

[0008] A VSG frequency control method based on power correction includes the following steps:

[0009] S1. In the VSG control loop, obtain the output power P e (s) and multiplied by the correction link transfer function G(s) and then fed back to the frequency generation link of the active power-frequency control loop, where P e(s) refers to the output power of the VSG grid connection point, which is calculated after sampling;

[0010] S2. Obtain the frequency ω according to the active power-frequency control link in the VSG control loop, and compensate the frequency generation link in step S1 into the control loop to obtain the compensated frequency ω. * ;

[0011] S3. Based on the power correction link transfer function G(s) and the phase margin requirement of the system open-loop transfer function, the coefficients τ1 and τ2 in the power correction link transfer function G(s) are parameterized.

[0012] Furthermore, the output power P e The calculation formula for (s) is:

[0013] Where, e d 、e q 、i d 、i q are the d-axis component and q-axis component of the voltage and current at the sampling PCC after abc / dq0 transformation, and s is the transformation parameter in the Laplace transform.

[0014] Furthermore, the frequency ω is expressed as:

[0015] Where, J is the virtual inertia coefficient, D p is the damping coefficient, P ref (s) is the reference power, and ω0 is the rated angular frequency of the power grid.

[0016] Furthermore, the compensated frequency ω * The expression is:

[0017] Among them, G(s) is the transfer function of the correction link.

[0018] Furthermore, the transfer function of the correction link is expressed as:

[0019] Where τ1 and τ2 are the adjustment coefficients of the power correction link, G2(s) is the conversion from the angular frequency △ω to the output power P in the VSG small signal model. e The transfer function of (s).

[0020] Furthermore, the angular frequency Δω to output power P in the VSG small signal model e The expression of the transfer function G2(s) of (s) is as follows:

[0021] Where, L Xis the filter inductor L f and the transmission line inductance L g The sum, R X is the sum of the resistances of the transmission line, E is the VSG output voltage amplitude, U g is the grid side voltage.

[0022] Furthermore, the open-loop transfer function of the system is expressed as:

[0023] At this time, the phase margin of the system is expressed as: PM=180°+∠[G open (s)] (7)

[0024] Taking the phase margin of the system as an indicator, the adjustment coefficients τ1 and τ2 of the power correction link are designed.

[0025] Furthermore, the process of parameter design of the adjustment coefficients τ1 and τ2 of the power correction link is as follows:

[0026] The power correction link is equivalent to the lead-lag link, and its characteristics are expressed as:

[0027] Where, φ(ω m ) is the maximum lead angle provided by the power correction link, ω m is the angular frequency corresponding to the maximum lead angle;

[0028] According to formula (6), the cutoff frequency and phase margin expressions of the system are shown in formula (9):

[0029] Where, ω c is the cutoff frequency of the VSG system after adding power correction, φ(ω c ) is the phase angle corresponding to the cutoff frequency after adding power correction, and the specific expression is:

[0030] Setting ω c =ω m , Substituting equations (8) and (10) into equation (9), we can obtain the binary equations of τ1 and τ2 as shown in equations (11) and (12):

[0031] Select the phase margin γ and use equations (11) and (12) together to find the specific values ​​of parameters τ1 and τ2.

[0032] An electronic device includes a memory and a processor, wherein the memory is used to store a program that supports the processor to execute the above-mentioned VSG frequency control method based on power correction, and the processor is configured to execute the program stored in the memory.

[0033] A storage medium stores a computer program, which, when executed by a processor, executes the steps of the above-mentioned VSG frequency control method based on power correction.

[0034] The advantages of the present invention are:

[0035] The technical solution of the present invention is to adjust the output power P e (s) is corrected, and then the corrected value is fed back to the control loop to achieve the effect of suppressing power oscillation. The expression of the power correction link G(s) is flexible, and appropriate parameters can be set according to the phase margin of its own system. At the same time, the principle of parameter selection is given for the correction coefficients τ1 and τ2. The adjustment coefficients of the power correction link and the values ​​of τ1 and τ2 will not affect the steady-state gain in the transient process. The present invention can not only suppress the VSG output power oscillation, but also provide a larger inertia support, thereby improving the stability of the VSG system. Compared with the VSG system without correction, the anti-interference performance of the system is significantly improved after correction, and the overshoot suppression capability is significantly enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG1 is a flow chart of a VSG frequency control method based on power correction;

[0037] Figure 2 shows the VSG main circuit topology and control structure;

[0038] Figure 3 shows the uncorrected VSG active power-frequency control link;

[0039] Figure 4 shows the VSG active power-frequency control link with the addition of a power correction link;

[0040] Figure 5 shows the main circuit topology and control structure of the VSG with power correction added;

[0041] Figure 6(a) is the operating diagram of the reference power shock;

[0042] Figure 6(b) is the operating diagram for the reference power step;

[0043] Figure 6(c) is the operating diagram of the grid angular frequency step;

[0044] Figure 7(a) shows the VSG output power response when the reference power is impacted;

[0045] Figure 7(b) shows the VSG output angular frequency response during the reference power shock;

[0046] Figure 8(a) shows the VSG output power response when the reference power step is applied;

[0047] Figure 8(b) shows the VSG output angular frequency response when the reference power step is applied;

[0048] Figure 9(a) shows the VSG output power response when the grid angular frequency steps;

[0049] Figure 9(b) shows the VSG output angular frequency response when the grid angular frequency steps. DETAILED DESCRIPTION

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0051] The technical solution of the present invention is further described below with reference to the accompanying drawings and specific embodiments:

[0052] Example 1

[0053] As shown in FIG1 , the VSG frequency control method based on power correction according to an embodiment of the present invention includes the following steps:

[0054] Step 1: In the VSG control loop, obtain the output power P e (s) is multiplied by the correction link transfer function G(s) and then fed back to the frequency generation link of the active power-frequency control loop, thereby suppressing power oscillation and increasing system robustness. e (s) refers to the output power of the VSG grid connection point, which is calculated after sampling;

[0055] Step 2: Obtain the frequency ω according to the active power-frequency control link in the VSG control loop, and compensate the frequency generation link in step 1 into the control loop to obtain the compensated frequency ω. * ;

[0056] Step 3: Based on the power correction link transfer function G(s) and the phase margin requirement of the system open-loop transfer function, the coefficients τ1 and τ2 in the power correction link transfer function G(s) are designed.

[0057] FIG2 shows the main circuit topology and control structure based on the VSG power correction strategy in an embodiment of the present invention, wherein the sampled output power P e The calculation formula of (s) is shown in formula (1):

[0058] Where, e d 、e q 、i d 、i q are the d-axis component and q-axis component of the voltage and current at the sampling PCC after abc / dq0 transformation, and s is the transformation parameter in the Laplace transform.

[0059] Figure 3 shows the small signal model of VSG. According to the active power-frequency control link in the VSG small signal model, the expression of frequency ω can be obtained as shown in formula (2):

[0060] Where, J is the virtual inertia coefficient, D p is the damping coefficient, P ref (s) is the reference power, and ω0 is the rated angular frequency of the power grid.

[0061] Add the frequency generation link of the active power-frequency control loop mentioned in step 1 to the VSG control loop to obtain the VSG active power-frequency control link shown in Figure 4. At this time, the corresponding compensated frequency ω is obtained. * The expression of is shown in formula (3):

[0062] The corresponding VSG main circuit topology and control structure are shown in Figure 5.

[0063] The expression of the correction link transfer function G(s) in step 3 is:

[0064] Where τ1 and τ2 are the adjustment coefficients of the power correction link, G2(s) is the conversion from the angular frequency △ω to the output power P in the VSG small signal model. e The transfer function of (s) is expressed as follows:

[0065] Where, L X is the filter inductor L f and the transmission line inductance L g R is the sum of the resistances of the transmission lines, ω0 is the rated angular frequency of the grid, E is the output voltage amplitude of the VSG, and U g is the grid side voltage.

[0066] After adding the frequency generation link, according to Figure 4, combined with equations (4) and (5), it can be seen that the open-loop transfer function of the system can be expressed by equation (6):

[0067] At this time, the phase margin of the system can be expressed as: PM=180°+∠[G open(s)] (12)

[0068] It can be seen from formula (7) that the system phase margin PM can be used as an indicator to perform parameter design on the adjustment coefficients τ1 and τ2 of the power correction link in formula (6).

[0069] The design process of the coefficients τ1 and τ2 in the correction link G(s) is as follows:

[0070] The correction strategy based on power correction feedback mentioned in the present invention can be equivalent to a lead-lag link, and its characteristics can be expressed as follows:

[0071] Where, φ(ω m ) is the maximum lead angle provided by the power correction link, ω m is the angular frequency corresponding to the maximum lead angle

[0072] According to formula (6), the cutoff frequency and phase margin expressions of the system can be obtained as shown in formula (9):

[0073] Where, ω c is the cutoff frequency of the VSG system after adding active power correction, φ(ω c ) is the phase angle corresponding to the cutoff frequency after adding power correction, and the specific expression is:

[0074] In order to make full use of the maximum lead angle provided by the power correction link, set ω c =ω m Substituting equations (8) and (10) into equation (9) yields the binary equations for τ1 and τ2 as shown in equations (11) and (12):

[0075] Generally speaking, the larger the phase margin of the system, the more stable the system. However, too large a phase margin will slow down the response speed of the system. Therefore, after comprehensive consideration, the present invention selects a phase margin γ = 35°. The specific values ​​of parameters τ1 and τ2 can be obtained by combining equations (11) and (12).

[0076] To verify the effectiveness of the method of the present invention, the main circuit topology and control structure model of the VSG system as shown in Figure 5 was built in Matlab / Simulink, and the given system parameters are shown in Table 1.

[0077] Table 1 Specific parameters of VSG system

[0078] Two control experiments were set up, one without correction and the other with the correction strategy of the method of the present invention. The transient response of the VSG output was observed when the grid frequency and the reference power were disturbed, and the frequency domain analysis was performed based on the indicators of the system response performance.

[0079] Figures 6(a), 6(b), and 6(c) are the operating condition diagrams of the reference power impact, reference power step, and grid angular frequency step in the method of the present invention; Figures 7(a) and 7(b) are the output power and output angular frequency responses of the VSG during the reference power impact in the method of the present invention, respectively; Figures 8(a) and 8(b) are the output power and output angular frequency responses of the VSG during the reference power step in the method of the present invention, respectively; Figures 9(a) and 9(b) are the output power and output angular frequency responses of the VSG during the grid angular frequency step in the method of the present invention, respectively. Figures 7(a), 7(b), 8(a), and 8(b) show that regardless of the reference power impact or the reference power step, after the correction control strategy of the method of the present invention is added, the output power of the VSG system, the overshoot of the angular frequency, and the adjustment time are all reduced, which illustrates the correctness of the control strategy of the present invention; Figures 9(a) and 9(b) show that although the peak value of the output power decreases at the moment of disturbance and the inertia response capability of the system is reduced, the amplitude is not large and is almost negligible compared to the advantage brought by the large attenuation of the system's oscillation degree, indicating that the correction strategy can also demonstrate good support capabilities when the grid frequency is disturbed.

[0080] In summary, the experimental results verify the correctness of the method of the present invention. Therefore, when the VSG output power oscillates, the system can be dynamically corrected to maintain the stable performance of the system and obtain a larger inertia support.

[0081] In the VSG control loop, the present invention obtains the output power P e(s) is multiplied by the correction link G(s) and then fed back to the frequency generation link of the active power-frequency control loop, thereby suppressing power oscillation and increasing the robustness of the system; according to the active power-frequency control link in the VSG control loop, the expression of the frequency ω is obtained, and the added frequency generation link is compensated to the control loop, thereby obtaining a new expression of ω*; the specific expression of the power correction link G(s) is determined, and the coefficients τ1 and τ2 in the power correction link G(s) are parameterized in combination with the phase margin requirements of the system open-loop transfer function; the correctness of the proposed correction strategy is verified by experiments; the present invention can enhance the anti-interference ability of VSG by adding structures such as power correction to the VSG control loop, which provides a new idea for enhancing the stability of the VSG system. The expression of its power correction link G(s) is flexible, and appropriate parameters can be set according to the phase margin of its own system. The adjustment coefficient of the power correction link and the values ​​of τ1 and τ2 will not affect the steady-state gain during the transient process; it can suppress the VSG output power oscillation while increasing the system's inertia support capacity. Compared with the uncorrected VSG system, the anti-interference performance of the system is significantly improved after correction, and the overshoot suppression capability is significantly enhanced.

[0082] Example 2

[0083] An electronic device includes a memory and a processor, wherein the memory is used to store a program that supports the processor to execute the VSG frequency control method based on power correction in embodiment 1, and the processor is configured to execute the program stored in the memory.

[0084] Example 3

[0085] A storage medium stores a computer program, which, when executed by a processor, executes the steps of the VSG frequency control method based on power correction in embodiment 1.

[0086] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A VSG frequency control method based on power correction, characterized in that: The following steps are involved: S1. In the VSG control loop, obtain the output power P e (s) and multiplied by the correction link transfer function G(s) and then fed back to the frequency generation link of the active power-frequency control loop, where P e (s) refers to the output power of the VSG grid connection point, which is calculated after sampling; S2, according to the active power-frequency control link in the VSG control loop, the frequency ω is obtained, and the frequency generation link in step S1 is compensated to the control loop, thereby obtaining the compensated frequency ω * ; S3. According to the power correction link transfer function G(s), combined with the phase margin requirement of the system open-loop transfer function, the coefficients τ1 and τ2 in the power correction link transfer function G(s) are designed.

2. The VSG frequency control method based on power correction according to claim 1, characterized in that: The output power P e The calculation formula of (s) is: In the formula, e d 、e q 、i d 、i q are the d-axis component and q-axis component of the voltage and current at the sampling PCC after abc / dq0 transformation, and s is the transformation parameter in the Laplace transform.

3. The VSG frequency control method based on power correction according to claim 1, characterized in that: The expression of the frequency ω is: Where J is the virtual inertia coefficient, D p is the damping coefficient, P ref (s) is the reference power, and ω0 is the rated angular frequency of the power grid.

4. The VSG frequency control method based on power correction according to claim 3, characterized in that: The compensated frequency ω * The expression is: Among them, G(s) is the transfer function of the correction link.

5. The VSG frequency control method based on power correction according to claim 4, characterized in that: The expression of the transfer function of the correction link is: Where τ1 and τ2 are the adjustment coefficients of the power correction link, and G2(s) is the angular frequency △ω in the VSG small signal model. To output power P e (s) transfer function.

6. The VSG frequency control method based on power correction according to claim 5, characterized in that: The VSG small signal model is used to calculate the angular frequency △ω to the output power P e The expression of the transfer function G2(s) of (s) is as follows: Where, L X is the filter inductor L f and the transmission line inductance L g The sum, R X is the sum of the resistances of the transmission line, E is the VSG output voltage amplitude, U g is the grid side voltage.

7. The VSG frequency control method based on power correction according to claim 6, characterized in that: The open-loop transfer function of the system is expressed as: At this time, the phase margin of the system is expressed as: PM=180°+∠[G open (s)] (7) Taking the phase margin of the system as an indicator, the adjustment coefficients τ1 and τ2 of the power correction link are designed.

8. The VSG frequency control method based on power correction according to claim 7, characterized in that: The process of parameter design of the adjustment coefficients τ1 and τ2 of the power correction link is as follows: The power correction link is equivalent to a lead-lag link, and its characteristics are expressed as: In the formula, φ(ω m ) is the maximum lead angle provided by the power correction link, ω m is the angular frequency corresponding to the maximum lead angle; According to formula (6), the cutoff frequency and phase margin expressions of the system are shown in formula (9): In the formula, ω c is the cutoff frequency of the VSG system after adding active power correction, φ(ω c ) is the phase angle corresponding to the cutoff frequency after adding power correction. The specific expression is: Setting c =ω m , Substituting equations (8) and (10) into equation (9), we get the binary equations of τ1 and τ2 as shown in equations (11) and (12): Select the phase margin γ and combine equations (11) and (12) to find the specific values ​​of parameters τ1 and τ2.

9. An electronic device, comprising a memory and a processor, characterized in that: The memory is used to store a program that supports the processor to execute the VSG frequency control method based on power correction according to any one of claims 1 to 8, and the processor is configured to execute the program stored in the memory.

10. A storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the VSG frequency control method based on power correction according to any one of claims 1 to 8 are executed.

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