CND controller-based rotor speed protection and recovery control method

Abstract

The invention provides a CND controller-based rotor rotating speed protection and recovery control method, 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 or not, and judging that a fan is in a frequency drop state due to disturbance when the system frequency deviation is greater than the frequency deviation threshold value; at the moment, the real-time rotor rotating speed is obtained, the rotor rotating speed is compared with a rotor rotating speed threshold value and a rotating shaft rotating speed lower limit value, and the droop coefficient is dynamically adjusted according to different modes such as a frequency supporting mode, a first protection mode and a second protection mode so that the output power of the draught fan and the mechanical dynamic curve can have a stable intersection point; 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; and after disturbance, switching to a recovery mode is carried out, and the output power is adjusted by adjusting the droop coefficient, so that the rotating speed of the rotor is recovered to the optimal rotating speed, and the capture power of the 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 to a rotor speed protection and recovery control method based on a CND controller. Background Art

[0002] Traditional grid-following virtual inertia control fans generally achieve rotor speed protection and recovery through adjustment coefficients. The traditional grid-following control method uses a phase-locked loop (PLL) to collect the AC voltage at the point of common coupling (PCC) to achieve synchronization with the power grid. 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 a PLL in a weak power grid environment will cause oscillation problems. To address this challenge, a grid-forming control method, i.e., using a grid-forming virtual synchronous generator (VSG) to control the fan, has been proposed.

[0003] VSG control achieves the same frequency support ability as virtual inertia through adjustment coefficients and does not require the use of a 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, leading to continuous rotor speed drop and even instability and disconnection from the grid; in addition, after a disturbance, the rotor speed cannot be effectively restored to the optimal value, resulting in a decrease in the power captured by 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 rotor speed protection and recovery control method based on a CND controller.

[0005] This application provides a rotor speed protection and recovery control method based on a CND controller, including the following steps: S1: Obtain the real-time system frequency deviation , and determine 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 a 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 droop coefficient 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 droop coefficient 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 adjust the droop coefficient according to the initial droop coefficient .

[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 adjust the droop coefficient according to the initial droop coefficient .

[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 droop coefficient using formula one ; Formula one; wherein, is the initial droop coefficient, is the rotor speed, is the rotor speed threshold, is the lower limit value of the rotor speed.

[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 adjust the droop coefficient according to the initial droop coefficient .

[0010] According to the technical solution provided by the present application, according to the power reference value , droop coefficient and the real-time system frequency deviation , the output power is calculated using Equation 3 P ; Equation 3

[0011] According to the technical solution provided by the present application, step S3 includes the following steps: S31: After the disturbance ends, start the recovery mode at time, and record the first power droop coefficient at time ; S32: Modulate the droop coefficient using Equation 4 ; Equation 4

[0012] Compared with the prior art, the beneficial effects of the present application are as follows: The present application provides a rotor speed protection and recovery control method based on a CND controller, 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 fan is in a frequency drop state due to a 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 droop coefficient 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 fan and the mechanical dynamic curve, ensuring that the fan 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 droop coefficient to restore the rotor speed to the optimal speed, improving the capture power of the fan and the system frequency stability.

[0013] 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. Description of the Drawings

[0014] 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 drawings in the following description 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.

[0015] Figure 1 It is a flowchart of a rotor speed protection and recovery control method based on a CND controller provided by an embodiment of the present application; Figure 2 It is a process and schematic diagram of rotor speed protection and recovery control based on a CND controller provided by the present application; Figure 3 It is a schematic structural diagram of the CND controller provided by the present application; Figure 4 It is an active power control loop diagram of the CND controller provided by the present application. Specific embodiments

[0016] To enable those skilled in the art to better understand the technical solutions of the present application, the following will clearly and completely describe the technical solutions in the embodiments of the present application in conjunction with the drawings. The description in this part is only exemplary and explanatory, and should not have any restrictive effect on the protection scope of the present application. Specifically, the described embodiments are only some embodiments of the present application, rather than all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts should fall within the protection scope of the present application.

[0017] It should be noted that similar reference numerals and letters represent 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 "include" and "have" 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 clearly listed steps or units, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or devices.

[0018] To make the technical solutions of the present application clearer and easier to understand, the following introduces a rotor speed protection and recovery control method based on a CND controller provided by an embodiment of the present application.

[0019] It should be noted that this method can be executed by a CND (Configurable Natural Droop) controller. For the sake of easy understanding, the following will introduce this method from the perspective of the control device.

[0020] As shown Figure 1 in the figure, this is a flowchart of a rotor speed protection and recovery control method based on a CND controller provided by this embodiment. The method includes the following steps: S1: Obtain the real-time system frequency deviation , and determine 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 droop coefficient 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 (i.e., wind speed); S3: After the disturbance ends, switch to the recovery mode and adjust the droop coefficient to make the rotor speed return to the optimal speed.

[0021] Specifically, in order to solve the problem that the droop coefficient of the VSG controller is coupled with the damping characteristic and cannot be freely adjusted, a configurable natural droop controller is proposed; the structure of the CND controller is as Figure 3 shown. The input of this controller is the reference value of the active power and the deviation of the active power, and the output is the virtual angular velocity. , and are adjustable parameters respectively; on the basis of realizing the SG swing equation, this structure adds a droop loop to control the droop slope of P-f at steady state; compared with the traditional VSG controller, the CND controller provides an additional degree of freedom without increasing the order of the transfer function, and can independently configure the inertia constant, the damping characteristic and the droop characteristic; specifically as follows: The output characteristic of the CND controller is the same as that of the VSG controller, as shown in the following formula: , where and are the inertia time constant and the droop coefficient of the CND controller respectively, is the rated angular frequency, is the change rate of the angular velocity with time; The transfer function of the CND controller is: ; where: , and are adjustable parameters respectively, is the Laplace operator; The active power control loop diagram of the CND controller is as shown in Figure 4 where is the grid attack angle, is the difference between the virtual attack angle output by the inverter and the grid attack angle; When the system impedance is approximately inductive, can be expressed as: , in the formula, E and V are the effective values of the inverter output voltage and the grid voltage respectively, X is the system impedance; Substituting the formula into the transfer function of Figure 4 , the closed-loop transfer function formula of the active power can be obtained as , and the P-f characteristic formula ; where is the damping coefficient, is the natural frequency; From the formula , the formula and the formula it can be obtained that , and have the following relationships with the damping coefficient , the inertia time constant and the droop coefficient of the system: ; ; ; In the formula, represents the rated capacity of the inverter, represents the synchronous angular frequency; First, determine the values of the parameters damping coefficient , the inertia time constant and the droop coefficient according to the system, and then calculate the values of , and through the above formulas and input them into the CND controller, thereby realizing the independent configuration of the inertia time constant, damping characteristics and droop coefficient; Therefore, this application adjusts the droop coefficient in different modes based on the CND controller according to the rotor speed; Working principle: This application compares the rotor speed with the rotor speed threshold and the lower limit value of the shaft speed, and dynamically adjusts the droop coefficient 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 point between the output power of the fan and the mechanical dynamic curve, 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, it switches to the recovery mode, adjusts the output power by adjusting the droop coefficient, and makes the rotor speed return to the optimal speed, improving the capture power of the fan and the system frequency stability.

[0022] In some embodiments, after step S1 and 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, triggering the start of the MPPT mode, and adjusting the droop coefficient according to the initial droop coefficient .

[0023] Specifically, in this embodiment, the output power , where: is the power reference value; under the control of the CND controller, is always set to the maximum power point tracking power, that is, ; 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 CND-WT (Configurable Natural Droop Wind Turbine) does not participate in frequency support, that is, the initial droop coefficient adjusts the droop coefficient of the fan , so .

[0024] 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 adjust the droop coefficient according to the initial droop coefficient .

[0025] In this embodiment, due to disturbances such as sudden load addition in the system, a large-scale frequency drop occurs, making , the system is in the frequency drop state, and at the same time the rotor speed is greater than the rotor speed threshold , the CND 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 power grid, and can support the grid frequency without endangering its own stability; In the frequency support mode, the droop coefficient of the wind turbine remains the initial droop coefficient ; in this mode, the wind speed is maintained at V1. The variation of the output power P of the CND controller is shown in Figure 2 Curve BC. The variation curve of the output power P intersects with the wind speed V1.

[0026] 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 droop coefficient using Formula 1 ; Formula 1; wherein, is the initial droop coefficient, is the rotor speed, is the rotor speed threshold, is the lower limit value of the rotor speed.

[0027] Specifically, when the external environment changes severely and the rotor speed continues to decrease, when the rotor speed drops below the rotor speed threshold and is greater than the lower limit value of the rotor speed , trigger the start of the first protection mode; assume the moment when the first protection mode starts is , record the rotor speed at moment as ; in the first protection mode, couple the droop coefficient with the rotor speed through the formula ; when reducing the droop coefficient, the output power decreases simultaneously, avoiding further decline of the rotor speed and preventing the wind turbine from becoming unstable; in the first protection mode, by dynamically adjusting the droop coefficient, finally make the rotor speed stable in the interval Figure 2 , to ensure that the wind turbine operates within a safe range and maintain the frequency stability of the system; meanwhile, in this mode, the wind speed drops from V1 to V2. The variation of the output power P of the CND controller is shown in

[0028] 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 , trigger the start of the second protection mode, and adjust the droop coefficient according to the initial droop coefficient .

[0029] 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, set the droop coefficient to zero, so that the CND controller no longer provides droop power; in this mode, the change of the output power P of the CND controller is shown in Figure 2 curve FG.

[0030] In some embodiments, step S3 includes the following steps: S31: After the disturbance ends, start the recovery mode at time, and record the first power droop coefficient at ; S32: Modulate the droop coefficient using Equation Four ; Equation Four.

[0031] Specifically, after the traditional VSG-WT performs frequency support, the rotational speed will deviate from the optimal rotational speed, so a part of power loss will be caused. Therefore, this application sets a recovery mode to make the rotor speed of the wind turbine return to the optimal rotational speed after stabilization, which not only further improves the stability of the wind turbine and captures power, but also improves the steady-state frequency of the system after disturbance; In this embodiment, after the disturbance ends, start the recovery mode at time, and record the first power droop coefficient at ; then adjust the droop coefficient based on Equation . During the recovery process, the droop coefficient gradually decreases due to the deviation between and , so the output power gradually decreases and the rotor accelerates; when the droop coefficient decreases to zero, the output power , which means that the wind turbine returns to the MPPT mode control operation. During this stage, the change of the output power P of the CND controller is shown in Figure 2As shown by curve DE, it can be seen that the recovery mode control returns the rotor speed to the optimal speed at wind speed V2, improving the output power of the wind turbine.

[0032] In this article, specific examples are used to elaborate on the principles and implementation methods 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 modes of this application. It should be noted that due to the limited nature of written expression and the objectively infinite specific structures, for those of ordinary skill in the art, without departing from the principles 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 CND controller, 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 droop coefficient is adjusted dynamically 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 the recovery mode and adjust the droop coefficient , 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 fan is judged to be in normal operation, the MPPT mode is triggered to start according to the initial droop coefficient Adjust the droop factor .

3. A rotor speed protection and recovery control method based on CND controller 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 initial droop coefficient Adjust the droop factor .

4. The rotor speed protection and recovery control method based on CND controller 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 droop coefficient is adjusted using formula 1. ; Formula 1; in, is the initial droop coefficient, is the rotor speed, is the rotor speed threshold, is the lower limit of rotor speed.

5. A rotor speed protection and recovery control method based on CND controller 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 initial droop coefficient Adjust the droop factor .

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

7. The rotor speed protection and recovery control method based on CND controller according to claim 1 is characterized in that: Step S3 includes the following steps: S31: After the disturbance ends, Always start recovery mode and record The first work droop coefficient at time ; S32: Modulation droop coefficient using formula four ; Formula 4.

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