Rotor rotating speed protection and recovery control method based on virtual synchronous machine

Abstract

The invention provides a rotor rotating speed protection and recovery control method based on a virtual synchronous machine, which comprises the following steps of: firstly, acquiring a real-time system frequency deviation, judging whether the system frequency deviation is greater than a frequency deviation threshold value, if so, judging that a fan is in a frequency drop state due to disturbance, and acquiring a real-time rotor rotating speed; comparing the rotor rotating speed with a rotor rotating speed threshold value and a rotating shaft rotating speed lower limit value, and dynamically adjusting a power reference value of the fan according to different modes such as a frequency support mode, a first protection mode and a second protection mode, so that a stable intersection point exists between the output power of the fan and a mechanical dynamic curve; it is ensured that the rotating speed of the draught fan is not too low due to too large output power in the frequency supporting process, and therefore instability is avoided; meanwhile, after disturbance, the mode is switched to a recovery mode, the output power is adjusted by adjusting the power reference value, the rotating speed of the rotor is recovered to the optimal rotating speed, and the capture power of the draught fan and the system frequency stability are improved.

Description

Technical Field

[0001] This application relates to the technical field of rotor speed protection and recovery of fans, and particularly relates to a control method for rotor speed protection and recovery based on a virtual synchronous machine. Background Technique

[0002] Traditional grid-following virtual inertia control fans generally achieve rotor speed protection and recovery through adjustment coefficients. The traditional grid-following control method realizes synchronization with the power grid by using a phase-locked loop (PLL) to collect the AC voltage at the point of common coupling (PCC). However, the premise of this method is that the voltage at the point of common coupling is stable; since large-scale wind power bases are usually located in areas with rich wind resources but far from the main power grid, using PLL in a weak power grid environment will cause oscillation problems. To address this challenge, a grid-forming control method is proposed, that is, a grid-forming virtual synchronous machine (VSG) is used to control the fan.

[0003] VSG control achieves the same frequency support ability as virtual inertia through adjustment coefficients and does not require the aid of PLL. However, the parameters of VSG control are coupled with its damping characteristics and there is an adjustment range; when the VSG-controlled fan experiences a wind speed drop or a large system frequency fluctuation during the frequency support process, the intersection point between the fan output power and the mechanical dynamic curve becomes unstable, causing the rotor speed to continuously drop or even become unstable and trip out of the grid; in addition, after the disturbance, the rotor speed cannot be effectively restored to the optimal value, resulting in a decrease in the captured power of the fan and insufficient system frequency stability. Summary of the Invention

[0004] The purpose of this application is to address the above problems and provide a control method for rotor speed protection and recovery based on a virtual synchronous machine.

[0005] This application provides a control method for rotor speed protection and recovery based on a virtual synchronous machine, including the following steps: S1: Obtain the real-time system frequency deviation , and judge whether the system frequency deviation is greater than the frequency deviation threshold ; S2: When the system frequency deviation is greater than the frequency deviation threshold , it is determined that the fan is in a frequency drop state due to disturbance; compare the real-time rotor speed with the rotor speed threshold and the lower limit value of the rotor speed , and dynamically adjust the power reference value respectively according to the frequency support mode, the first protection mode, and the second protection mode, so that the output power P of the fan has an intersection point with the mechanical dynamic curve; S3: After the disturbance ends, switch to the recovery mode and adjust the power reference value to make the rotor speed return to the optimal speed.

[0006] According to the technical solution provided by the present application, before step S2, the following steps are further included: S11: When the system frequency deviation is less than or equal to the frequency deviation threshold , it is determined that the fan is in the normal operation state, trigger the start of the MPPT mode, and track the power at the maximum power point to adjust the power reference value . .

[0007] According to the technical solution provided by the present application, step S2 includes the following steps: S21: When the rotor speed is greater than the rotor speed threshold , trigger the start of the frequency support mode, and track the power at the maximum power point to adjust the power reference value . .

[0008] According to the technical solution provided by the present application, step S2 further includes the following steps: S22: When the rotor speed is less than or equal to the rotor speed threshold and greater than the lower limit value of the rotor speed , trigger the start of the first protection mode, and adjust the power reference value using formula one ; Formula one; wherein, is the optimal power coefficient, is the power value at the start time of the first protection mode, is the droop coefficient.

[0009] According to the technical solution provided by the present application, step S2 further includes the following steps: S23: When the rotor speed is less than or equal to the lower limit value of the rotor speed , trigger the start of the second protection mode, and track the power at the maximum power point to adjust the power reference value . .

[0010] According to the technical solution provided by the present application, the maximum power point tracking power is calculated using formula two ; Formula Two.

[0011] According to the technical solution provided by the present application, based on the power reference value , droop coefficient , and the real-time system frequency deviation , the output power is calculated using Formula Three P ; Formula Three.

[0012] According to the technical solution provided by the present application, step S3 includes the following steps: S31: After the perturbation ends, the recovery mode is started at time, and the first power reference value at time is recorded ; S32: Based on the logistic regression function curve, the preliminary power reference calculation value is obtained; S33: According to the preliminary power reference calculation value, the actual power reference value is obtained using Formula Four; Formula Four.

[0013] According to the technical solution provided by the present application, the preliminary power reference calculation value is calculated using Formula Five and Formula Six; Formula Five; Formula Six; where: is the basic gain of the virtual synchronous machine; is the mapping factor of the logistic regression function curve; is the translation factor of the logistic regression function curve; is the frequency change rate; is the power integral increment.

[0014] Compared with the prior art, the beneficial effects of the present application are: The present application provides a rotor speed protection and recovery control method based on a virtual synchronous machine, including the following steps: First, obtain the real-time system frequency deviation, and determine whether the system frequency deviation is greater than the frequency deviation threshold. When the system frequency deviation is greater than the frequency deviation threshold, it is determined that the wind turbine is in a frequency drop state due to disturbance. At this time, obtain the real-time rotor speed, compare the rotor speed with the rotor speed threshold and the lower limit value of the shaft speed, and dynamically adjust the power reference value according to different modes such as the frequency support mode, the first protection mode, and the second protection mode, so that there is a stable intersection between the output power of the wind turbine and the mechanical dynamic curve, ensuring that the wind turbine will not have too low a speed due to excessive output power during the frequency support process, thereby avoiding instability; at the same time, after the disturbance, switch to the recovery mode, and adjust the output power by adjusting the power reference value to restore the rotor speed to the optimal speed, improving the capture power of the wind turbine and the system frequency stability.

[0015] It should be understood that the description of technical features, technical solutions, beneficial effects or similar languages in the present application does not imply that all features and advantages can be achieved in any single embodiment. On the contrary, it can be understood that the description of features or beneficial effects means that at least one embodiment includes specific technical features, technical solutions or beneficial effects. Therefore, the description of technical features, technical solutions or beneficial effects in this specification does not necessarily refer to the same embodiment. Furthermore, the technical features, technical solutions and beneficial effects described in this embodiment can be combined in any appropriate manner. Those skilled in the art will understand that an embodiment can be implemented without one or more specific technical features, technical solutions or beneficial effects of a specific embodiment. In other embodiments, additional technical features and beneficial effects can also be identified in specific embodiments that do not embody all embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in this embodiment, the following will briefly introduce the drawings required for the description of the embodiment. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0017] Figure 1 It is a flowchart of a rotor speed protection and recovery control method based on a virtual synchronous machine provided by an embodiment of the present application; Figure 2 It is a process and principle diagram of a rotor speed protection and recovery control based on a virtual synchronous machine provided by the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] To enable those skilled in the art to better understand the technical solution of this application, the technical solution in the embodiments of this application will be clearly and completely described below in conjunction with the accompanying drawings. The description in this part is only exemplary and explanatory, and should not have any restrictive effect on the protection scope of this application. Specifically, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without creative efforts should fall within the protection scope of this application.

[0019] It should be noted that similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0020] To make the technical solution of this application clearer and easier to understand, a rotor speed protection and recovery control method based on a virtual synchronous machine provided in the embodiments of this application will be introduced below.

[0021] It should be noted that this method can be executed by a virtual synchronous machine (VSG) controller. For the convenience of understanding, this method will be introduced from the perspective of a control device below.

[0022] As Figure 1 shown, this figure is a flowchart of a rotor speed protection and recovery control method based on a virtual synchronous machine provided in this embodiment. This method includes the following steps: S1: Obtain the real-time system frequency deviation , and judge whether the system frequency deviation is greater than the frequency deviation threshold ; S2: When the system frequency deviation is greater than the frequency deviation threshold , it is determined that the fan is in a frequency drop state due to disturbances; compare the real-time rotor speed with the rotor speed threshold and the lower limit value of the rotor speed , and dynamically adjust the power reference value respectively according to the frequency support mode, the first protection mode and the second protection mode, so that the output power P of the fan has an intersection with the mechanical dynamic curve; S3: After the disturbance ends, switch to the recovery mode and adjust the power reference value , so that the rotor speed returns to the optimal speed.

[0023] Specifically, the output power of the VSG controller can be divided into inertial power and droop power. The magnitude of the inertial power is related to the virtual inertia time constant and the rate of change of the angular velocity with time ; while tends to 0 when the frequency is stable, so this part of the power will not affect the steady-state power; in the actual system, the instability of the VSG-WT (Virtual Synchronous Generator Wind Turbine) is mainly due to the VSG droop loop; From Equation Three it can be seen that the output power of the VSG controller is related to the power reference value , the droop coefficient and the system frequency deviation ; since the adjustment range of the VSG controller droop coefficient is narrow and the system frequency deviation is uncontrollable, only the power reference value can be controlled to achieve the protection and recovery functions of the VSG-WT; Working principle: This application compares the real-time rotor speed with the rotor speed threshold and the lower limit of the shaft speed, and dynamically adjusts the power reference value according to different modes such as the frequency support mode, the first protection mode, and the second protection mode, so that the output power of the fan has a stable intersection with the mechanical dynamic curve (i.e., the wind speed), ensuring that the fan will not have too low a speed due to excessive output power during the frequency support process, thus avoiding instability; at the same time, after the disturbance, switch to the recovery mode, adjust the output power by adjusting the power reference value, so that the rotor speed returns to the optimal speed, improving the capture power of the fan and the system frequency stability.

[0024] In some embodiments, the following steps are further included before step S2: S11: When the system frequency deviation is less than or equal to the frequency deviation threshold , it is determined that the fan is in the normal operation state, trigger the start of the MPPT mode, and adjust the power reference value according to the maximum power point tracking power .

[0025] Specifically, when , that is, at this time the system frequency deviation is within the operating range and there is no disturbance in the system, it is determined that the fan is in the normal operation state. At this time, the VSG-WT does not participate in the frequency support, that is, adjust the power reference value of the fan according to the maximum power point tracking power ​ , therefore .

[0026] In some embodiments, step S2 includes the following steps: S21: When the rotor speed is greater than the rotor speed threshold , trigger the start of the frequency support mode, and track the power according to the maximum power point to adjust the power reference value .

[0027] In this embodiment, due to disturbances and other sudden increases in load, the system causes a large frequency drop, such that when, the system is in a frequency drop state, and at the same time the rotor speed is greater than the rotor speed threshold , the VSG controller switches to the frequency support mode. In this mode, the rotor speed is relatively high, with sufficient kinetic energy reserve. The wind turbine releases the rotor kinetic energy by reducing the rotor speed, converts it into electromagnetic power and outputs it to the grid, and can support the grid frequency without endangering its own stability; In the frequency support mode, the power reference value of the wind turbine remains the maximum power point tracking power ; at the same time, the wind turbine increases the active power through the frequency support mode (where the increase is determined by the droop coefficient and the frequency deviation), simulates the inertial response of the synchronous generator, and slows down the frequency drop speed. At this time, the output power ; in this mode, the wind speed is maintained at V1, and the relationship between the power reference value of the VSG controller and the output power P is shown in Figure 2 curves AB and curve A'B'. The change curve of the output power P has an intersection with the wind speed V1.

[0028] In some embodiments, step S2 further includes the following steps: S22: When the rotor speed is less than or equal to the rotor speed threshold and greater than the lower limit value of the rotor speed , trigger the start of the first protection mode, and adjust the power reference value using formula one ; Formula one; where is the optimal power coefficient, is the power value at the start time of the first protection mode, is the droop coefficient; Specifically, when the external environment changes severely and the rotor speed continuously decreases, when the rotor speed drops to the rotor speed threshold Below and greater than the lower limit value of the rotor speed When this occurs, the first protection mode is triggered to start; in the first protection mode, the power reference value is dynamically adjusted through linear interpolation , and the formula is: ; where is the optimal power coefficient, is the power value at the start time of the first protection mode, is the droop coefficient, is the system frequency deviation; when the power reference value is reduced, the output power is reduced simultaneously to avoid further decline in the rotor speed and prevent the wind turbine from becoming unstable; when in the first protection mode, by dynamically adjusting the power reference value, the rotor speed is finally stabilized within the range , to ensure that the wind turbine operates within a safe range and at the same time maintain the frequency stability of the system; at the same time, in this mode, the wind speed drops from V1 to V2, and the change of the power reference value of the VSG controller and the output power P are shown in Figure 2 curves BC and B'C', and the change curve of the output power P has an intersection point C' with the wind speed V2.

[0029] In some embodiments, step S2 further includes the following steps: S23: When the rotor speed is less than or equal to the lower limit value of the rotor speed , the second protection mode is triggered to start, and the power reference value is adjusted according to the maximum power point tracking power . .

[0030] Specifically, if the wind speed further drops and the rotor speed drops below the lower limit value of the rotor speed , at this time the rotor speed is too low, and the wind turbine may become unstable due to releasing too much rotor kinetic energy; therefore, at this time the wind turbine no longer participates in frequency support and is forced to operate in the MPPT mode to ensure its stable operation; In the second protection mode, the power reference value is forcibly set to the maximum power point tracking power , and the formula is: , where is the optimal power coefficient; since the power reference value is reduced, the output power also decreases accordingly, ensuring that the wind turbine operates in the MPPT mode; In this mode, the change of the power reference value of the VSG controller and the output power P are shown in Figure 2 curves EF and E'F'.

[0031] In some embodiments, step S3 includes the following steps: S31: After the disturbance ends, at start the recovery mode, and record the first power reference value at ; S32: Based on the logistic regression function curve, obtain the preliminary power reference calculation value ; S33: According to the preliminary power reference calculation value, use Equation Four to obtain the actual power reference value ; Equation Four.

[0032] In some embodiments, the preliminary power reference calculation value is calculated using Equation Five and Equation Six ; Equation Five; Equation Six; Where: is the base gain of the virtual synchronous generator; is the mapping factor of the logistic regression function curve; is the translation factor of the logistic regression function curve; is the frequency change rate; is the power integral increment.

[0033] Specifically, after traditional VSG-WT performs frequency support, the rotational speed will deviate from the optimal rotational speed, thus causing a part of power loss. Therefore, this application sets a recovery mode to make the rotor speed of the fan return to the optimal rotational speed after stabilization, which not only further improves the stability of the fan and captures power, but also improves the steady-state frequency of the system after disturbance. There are many conditions for starting the recovery mode, such as based on the system frequency change rate and the rotor speed deviation. However, in the actual system, due to the random change of the wind speed, the system frequency and the rotor speed fluctuate, which may cause mis-start. Therefore, this application adopts the method of manually starting the recovery mode; In this embodiment, after the disturbance ends, at start the recovery mode, and record the first power reference value at ; Subsequently, based on the logistic regression function curve, obtain the preliminary power reference calculation value ; The formula is:

[0034] ; Where: is the base gain of the virtual synchronous generator; is the mapping factor of the logistic regression function curve; is the translation factor of the logistic regression function curve; is the frequency change rate; is the power integral increment; when the frequency change rate is too small, the power integral increment increases and decreases, slowing down the frequency drop; According to Equation 5, the preliminary power reference calculation value will continue to decrease before the rotor speed reaches This will cause the system frequency to drop; the core of the recovery mode control is to return the wind turbine to the MPPT mode control. Therefore, the actual power reference value in the recovery mode is: ; At this stage, the power reference value of the VSG controller and the change of the output power P are shown in Figure 2 Curves CD and C'D'. It can be seen that the recovery mode control makes the rotor speed return to the optimal speed at wind speed V2, improving the output power of the wind turbine.

[0035] In this article, specific examples are used to elaborate on the principle and implementation manner of this application. The description of the above embodiments is only used to help understand the method and its core idea of this application. The above are only the preferred implementation manners of this application. It should be noted that due to the limitation of literal expression and objectively there are infinite specific structures. For those of ordinary skill in the art in this technical field, without departing from the principle of this application, several improvements, refinements or changes can be made, or the above technical features can be combined in an appropriate manner; these improvements, refinements, changes or combinations, or directly applying the inventive concept and technical solution to other occasions without improvement, should all be regarded as the protection scope of this application.

Claims

1. A rotor speed protection and recovery control method based on a virtual synchronous machine, characterized in that: The steps include: S1: Get real-time system frequency deviation , determine the system frequency deviation Is it greater than the frequency deviation threshold? ; S2: When the system frequency deviates Greater than the frequency deviation threshold When the fan is in a frequency drop state due to disturbance, the real-time rotor speed is compared. and rotor speed threshold And the lower limit of rotor speed The power reference value is dynamically adjusted according to the frequency support mode, the first protection mode and the second protection mode. , so that the output power of the fan P There is an intersection with the mechanical dynamic curve; S3: After the disturbance ends, switch to recovery mode and adjust the power reference value , so that the rotor speed Restore to optimal speed.

2. The rotor speed protection and recovery control based on a virtual synchronous machine according to claim 1, characterized in that: After step S1 and before step S2, the following steps are also included: S11: When the system frequency deviates Less than or equal to the frequency deviation threshold When the wind turbine is in normal operation, the MPPT mode is triggered to start, and the power is tracked according to the maximum power point. Adjust the power reference value .

3. A rotor speed protection and recovery control method based on a virtual synchronous machine according to claim 2, characterized in that: Step S2 includes the following steps: S21: When the rotor speed Greater than the rotor speed threshold When the frequency support mode is triggered, the power is tracked according to the maximum power point Adjust the power reference value .

4. The rotor speed protection and recovery control method based on a virtual synchronous machine according to claim 3 is characterized in that: Step S2 also includes the following steps: S22: When the rotor speed Less than or equal to the rotor speed threshold and is greater than the lower limit of the rotor speed When the first protection mode is triggered, the power reference value is adjusted using formula 1. ; Formula 1; in, is the optimal power factor, is the power value at the time of starting the first protection mode, is the droop coefficient.

5. A rotor speed protection and recovery control method based on a virtual synchronous machine according to claim 4, characterized in that: Step S2 also includes the following steps: S23: When the rotor speed Less than or equal to the lower limit of the rotor speed When the second protection mode is triggered, the power is tracked according to the maximum power point. Adjust the power reference value .

6. A rotor speed protection and recovery control method based on a virtual synchronous machine according to claim 5, characterized in that: Use formula 2 to calculate the maximum power point tracking power ; Formula 2.

7. The rotor speed protection and recovery control method based on a virtual synchronous machine according to claim 1, characterized in that: According to the power reference value , droop coefficient and real-time system frequency deviation , use formula 3 to calculate the output power P ; Formula three.

8. The rotor speed protection and recovery control method based on a virtual synchronous machine according to claim 1, characterized in that: Step S3 includes the following steps: S31: After the disturbance ends, Always start recovery mode and record The first power reference value at the moment ; S32: Based on the logistic regression function curve, obtain the preliminary power reference calculation value ; S33: Based on the preliminary power reference calculation value, the actual power reference value is obtained using formula 4 ; Formula 4.

9. A rotor speed protection and recovery control method based on a virtual synchronous machine according to claim 8, characterized in that: Use formula 5 and formula 6 to calculate the preliminary power reference value ; Formula 5; Formula 6; in: is the base gain of the virtual synchronous machine; is the mapping factor of the logistic regression function curve; is the translation factor of the logistic regression function curve; is the frequency change rate; is the power integral increment.

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