A primary frequency regulation method and system for a doubly-fed wind turbine generator system based on a variable speed coefficient

Abstract

The present invention provides a method and system for primary frequency regulation of a doubly-fed wind turbine generator set based on a variable speed coefficient, comprising the following steps: first, the difference between the actual value and the set value of the power grid frequency is calculated based on real-time monitoring of the power grid frequency change, and it is determined whether the power grid is in a frequency regulation demand. If so, the doubly-fed wind turbine generator set enters the speed coefficient adaptive adjustment stage and starts primary frequency regulation; secondly, the initial moment of the speed coefficient adaptive stage is recorded as t0, and the speed coefficient is adaptively adjusted according to the frequency deviation until the speed coefficient recovery stage is entered at time t1; finally, the speed coefficient is given according to a pre-set recovery curve, and the speed coefficient is gradually restored to 1. At this moment, the speed coefficient recovery stage ends, and the doubly-fed wind turbine generator set enters the maximum power operation stage, and its participation in the primary frequency regulation of the power grid ends. The present invention increases the lowest point of the frequency drop, and also solves the problem of secondary frequency drop caused by direct speed recovery.

Description

Technical Field

[0001] The present invention relates to the field of new energy access and control technology, and in particular to a primary frequency regulation method and system for a doubly-fed wind turbine generator set based on a variable speed coefficient. Background Art

[0002] With the global shift in energy mix and the widespread promotion of clean energy, wind power, as a renewable energy source, is increasingly playing a vital role in electricity generation. As the core equipment for wind energy conversion, the operational efficiency and stability of wind turbines are crucial for the safe and economical operation of power systems. Doubly-fed wind turbines are the mainstream type of wind power generator. Because the rotor of a doubly-fed wind turbine is connected to the grid via a converter, the turbine's rotor speed is completely decoupled from system frequency, making it unable to respond to changes in system frequency. Therefore, the integration of large-scale wind power into the grid may weaken the system's frequency regulation capabilities, impacting system stability.

[0003] Doubly-fed wind turbines have abundant rotational inertia and a wide speed adjustment range, and are often used to support system frequency stability. However, during the speed recovery phase of the frequency support process using the rotor kinetic energy of the doubly-fed wind turbine, electromagnetic power needs to be absorbed from the power grid, resulting in secondary disturbances in frequency recovery. In other words, when participating in grid frequency regulation, the prior art doubly-fed wind turbines often ignore the smoothness of the speed recovery process, which can easily cause unnecessary mechanical stress and electrical shock to the turbine itself, and may also cause secondary shocks to the system frequency stability. Therefore, the present invention provides a primary frequency regulation method and system for doubly-fed wind turbines based on a variable speed coefficient. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a primary frequency regulation method and system for a doubly fed wind turbine generator set based on a variable speed coefficient to solve the problems raised in the above background technology. The present invention takes the grid frequency deviation as the criterion and realizes the active power calculation of the wind turbine generator set at different stages by flexibly adjusting the speed coefficient, thereby improving the primary frequency regulation capability of the doubly fed wind turbine generator set, solving the problem of secondary drop in system frequency that may be caused during the speed recovery process, achieving the technical effect of improving the wind power support capability for the grid frequency, and providing technical support for the operation of a high-proportion new energy power grid.

[0005] In order to achieve the above object, the present invention is implemented through the following technical solution: a primary frequency regulation method of a doubly-fed wind turbine generator system based on a variable speed coefficient, comprising the following steps:

[0006] S1: Obtain the speed of the doubly-fed wind turbine generator set and the frequency of the grid to which it is connected, calculate the grid frequency deviation value, and set the frequency regulation dead zone and speed upper and lower limits of the doubly-fed wind turbine generator set;

[0007] S2: When the grid frequency deviation exceeds the frequency regulation dead zone, the grid is judged to be in a frequency regulation demand state. At this time, the speed coefficient of the doubly fed wind turbine enters the adaptive adjustment stage, and the doubly fed wind turbine begins to enter the frequency regulation mode; otherwise, the doubly fed wind turbine maintains the current control mode unchanged;

[0008] S3: In the speed coefficient adaptive adjustment stage, the initial time of entering this stage is first recorded as t0, and the speed coefficient is adaptively adjusted according to the frequency deviation until time t1, when it enters the speed coefficient recovery stage;

[0009] S4: In the speed coefficient recovery stage, the speed coefficient is given according to the pre-set speed coefficient recovery curve until the speed coefficient is restored to 1 at time t2, and the speed coefficient recovery stage ends;

[0010] S5: After the speed coefficient recovery phase ends, due to inertia, the wind turbine speed gradually recovers to the speed value before frequency regulation and enters the maximum power operation phase. The process of the doubly fed wind turbine participating in the primary frequency regulation of the power grid ends.

[0011] Furthermore, the grid frequency deviation Δf in step S1 e , satisfying the following relational expressions:

[0012] Δf e =f e -f n

[0013] Where, f e is the actual measured frequency of the power grid, f n is the rated frequency of the power grid; the frequency regulation dead zone of the doubly fed wind turbine generator set in step S1 is ±0.05Hz.

[0014] Furthermore, the speed coefficient in step S2 refers to the proportional coefficient k of the actual speed of the doubly fed wind turbine. The actual speed value is multiplied by the speed coefficient to obtain the equivalent value of the actual speed. The actual speed equivalent value is subtracted from the speed reference value and PI adjustment is performed to finally obtain the active reference value P of the doubly fed wind turbine. ref ; The speed reference value ω ref From the stator power P s It is actually the speed command function of the doubly-fed wind turbine operating in the maximum power point tracking (MPPT) state.

[0015] ω ref =aP s 2 +bP s +c

[0016] Where a, b, and c are constants. Generally, a is -0.67, b is 1.42, and c is 0.51.

[0017] Furthermore, the adaptive adjustment phase in step S3 is from time t0 to time t1. In the adaptive adjustment phase, the speed coefficient k is calculated online according to the frequency deviation:

[0018]

[0019] Where α and β are constants, which are determined according to the application scenario; ω0 is the speed at the initial moment, ω min is the lower limit of speed, Δf e (t) is the time-varying frequency deviation.

[0020] Furthermore, the value of the time t1 is determined according to the adaptively adjusted duration Δt u Sure,

[0021] t1=t0+Δt u

[0022] The duration of adaptive adjustment Δt u Depends on the application scenario.

[0023] Furthermore, the speed coefficient recovery phase in step S4 refers to the period from time t1 to time t2, and the recovery curve refers to the curve of the speed coefficient recovering from k(t1) at time t1 to 1. In this phase, the speed coefficient is:

[0024]

[0025] Where k(t1) refers to the k value at time t1, which can be obtained by the calculation formula described in claim 4

[0026] Furthermore, the value of the time t2 is determined according to the duration Δt of the speed coefficient recovery curve. r Determine, t2 can be determined by the following formula

[0027] t2=t1+Δt r

[0028] The speed coefficient recovery time Δt r Depends on the application scenario.

[0029] A frequency modulation system used in the above frequency modulation method includes a measurement module, a time determination module, a speed coefficient determination module, and a power reference value determination module.

[0030] Furthermore, the measurement module is used to measure the speed of the doubly fed wind turbine generator set and the frequency of access to the power grid; the time determination module is used to determine the duration of the rising curve, the duration of the adaptive adjustment, and the duration of the speed coefficient recovery; the speed coefficient determination module calculates the time-varying speed coefficient k online in real time; the power reference value determination module calculates the active power reference value of the doubly fed wind turbine generator set based on the speed coefficient, real-time speed, and speed reference value.

[0031] Beneficial effects of the present invention:

[0032] 1. This method of primary frequency regulation of doubly-fed wind turbines based on variable speed coefficient takes the grid frequency deviation as the criterion and flexibly adjusts the speed coefficient to realize the active power calculation of wind turbines at different stages, thereby improving the primary frequency regulation capability of doubly-fed wind turbines.

[0033] 2. The present invention monitors the frequency changes of the power grid in real time, calculates the difference between the actual value of the power grid frequency and the set value, and determines whether the power grid is in a frequency regulation demand. It effectively increases the lowest point of the frequency drop and solves the problem of secondary frequency drop caused by direct speed recovery. It achieves the technical effect of improving the wind power support capacity for the power grid frequency and provides technical support for the operation of a high proportion of new energy power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the speed control principle diagram of the doubly-fed wind turbine generator system based on maximum power point tracking;

[0035] Figure 2 It is a power tracking control method based on variable speed coefficient;

[0036] Figure 3 Flowchart for calculating the speed coefficient of doubly-fed wind turbines in different stages of frequency regulation;

[0037] Figure 4 Schematic diagram of the control curve of the speed coefficient k. DETAILED DESCRIPTION

[0038] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific implementation methods.

[0039] See also Figures 1 to 4 The present invention provides the following technical solution: a method and system for primary frequency regulation of a doubly-fed wind turbine generator system based on a variable speed coefficient. The specific solution is as follows:

[0040] First, based on the real-time monitoring of grid frequency changes, the difference between the actual grid frequency and the set value is calculated to determine whether the grid is in frequency regulation demand. If so, the doubly fed wind turbine enters the speed coefficient adaptive adjustment stage and starts a frequency regulation; secondly, the initial moment of the speed coefficient adaptive stage is recorded as t0, and the speed coefficient is adaptively adjusted according to the frequency deviation until the speed coefficient recovery stage is entered at moment t1; finally, the speed coefficient is given according to the recovery curve, and the speed coefficient gradually recovers to 1. At this moment, the speed coefficient recovery stage ends, the doubly fed wind turbine enters the maximum power operation stage, and its participation in the grid primary frequency regulation ends.

[0041] In order to better understand the above technical solution, the above technical solution will be described in detail below with reference to the accompanying drawings and specific implementation methods.

[0042] See also Figure 1 、 Figure 2 and Figure 3 The embodiment of the present invention provides a primary frequency regulation method of a doubly-fed wind turbine generator system based on a variable speed coefficient, which specifically includes the following steps:

[0043] S1: Obtain the speed of the doubly-fed wind turbine generator set and the frequency of the grid to which it is connected, calculate the grid frequency deviation value, and set the frequency regulation dead zone and speed upper and lower limits of the doubly-fed wind turbine generator set;

[0044] This step is explained in detail. Based on the measured grid frequency value and the rated frequency value, the grid frequency deviation Δf is calculated. e :

[0045] Δf e =f e -f n

[0046] Where, f e is the actual measured frequency of the power grid, f n is the rated frequency of the grid.

[0047] The frequency regulation dead zone f of the doubly fed wind turbine db ±0.05Hz.

[0048] S2: When the grid frequency deviation exceeds the frequency regulation dead zone, it is determined that the grid is in a frequency regulation demand state. At this time, the speed coefficient of the doubly fed wind turbine enters the adaptive adjustment stage, and the doubly fed wind turbine begins to enter the frequency regulation mode. Otherwise, the doubly fed wind turbine maintains the current control mode unchanged;

[0049] Specifically, refer to the attached Figure 2The speed coefficient refers to the proportional coefficient k of the actual speed of the doubly fed wind turbine. The actual speed value is multiplied by the speed coefficient to obtain the equivalent value of the actual speed. The actual speed equivalent value is subtracted from the speed reference value and PI adjustment is performed to finally obtain the active reference value P of the doubly fed wind turbine. ref .

[0050] The speed reference value ω ref From the stator power P s It is confirmed that it is actually the speed command function of the doubly-fed wind turbine generator set operating in the maximum power point tracking (MPPT) state.

[0051] ω ref =aP s 2 +bP s +c

[0052] Wherein, a, b, and c are constants. In this embodiment, a is -0.67, b is 1.42, and c is 0.51.

[0053] S3: In the speed coefficient adaptive adjustment stage, the initial time of entering this stage is first recorded as t0, and the speed coefficient is adaptively adjusted according to the frequency deviation until time t1, when it enters the speed coefficient recovery stage;

[0054] Specifically, see Figure 3 The adaptive adjustment phase is from time t0 to time t1, during which the speed coefficient k is calculated online according to the frequency deviation:

[0055]

[0056] Where α and β are constants, which are determined according to the application scenario; ω0 is the speed at the initial moment, ω min is the lower limit of speed, Δf e (t) is the time-varying frequency deviation.

[0057] The value of the time t1 is determined by the adaptively adjusted duration Δt u Sure,

[0058] t1=t0+Δt u

[0059] The duration of adaptive adjustment Δt u Depends on the application scenario.

[0060] The speed coefficient change curve of this stage is shown in Figure 4 .

[0061] S4: In the speed coefficient recovery stage, the speed coefficient is given according to a pre-set speed coefficient recovery curve until the speed coefficient is restored to 1 at time t2, and the speed coefficient recovery stage ends.

[0062] Specifically, see Figure 3 The speed coefficient recovery phase is from time t1 to time t2, and the recovery curve is the curve of the speed coefficient recovering from k(t1) at time t1 to 1. In this phase, the speed coefficient is:

[0063]

[0064] Where k(t1) refers to the k value at time t1, which can be calculated as follows:

[0065]

[0066] The value of the time t2 is determined according to the duration Δt of the speed coefficient recovery curve. r Determine, t2 can be determined by the following formula

[0067] t2=t1+Δt r

[0068] The speed coefficient recovery time Δt r Depends on the application scenario.

[0069] The speed coefficient change curve of this stage is shown in Figure 4 .

[0070] S5: After the speed coefficient recovery phase ends, due to inertia, the wind turbine speed gradually recovers to the speed value before frequency regulation and enters the maximum power operation phase. The process of the doubly fed wind turbine participating in the primary frequency regulation of the power grid ends.

[0071] The basic principles, main features and advantages of the present invention are shown and described above. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention.

[0072] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A primary frequency modulation method for a doubly-fed wind turbine generator system based on a variable speed coefficient, characterized in that: The following steps are involved: S1: Obtain the speed of the doubly-fed wind turbine generator set and the frequency of the connected power grid, calculate the power grid frequency deviation value, and set the frequency regulation dead zone and speed upper and lower limits of the doubly-fed wind turbine generator set; S2: When the grid frequency deviation exceeds the frequency regulation dead zone, it is judged that the grid is in a frequency regulation demand state. At this time, the speed coefficient of the doubly fed wind turbine unit enters the adaptive adjustment stage, and the doubly fed wind turbine unit begins to enter the frequency regulation mode; otherwise, the doubly fed wind turbine unit maintains the current control mode unchanged; S3: In the speed coefficient adaptive adjustment stage, the initial time of entering the speed coefficient adaptive adjustment stage is first recorded as t0, and the speed coefficient is adaptively adjusted according to the frequency deviation until the speed coefficient recovery stage is entered at time t1; S4: In the speed coefficient recovery stage, the speed coefficient is given according to the preset speed coefficient recovery curve until the speed coefficient is restored to 1 at time t2, and the speed coefficient recovery stage ends; S5: After the speed coefficient recovery phase is over, due to inertia, the speed of the wind turbine gradually recovers to the speed value before frequency regulation and enters the maximum power operation phase. The process of the doubly-fed wind turbine participating in the primary frequency regulation of the power grid ends; The adaptive adjustment phase in step S3 refers to the period from time t0 to time t1. In the adaptive adjustment phase, the speed coefficient k is calculated online according to the frequency deviation: In the formula, α and β are constants, which are determined according to the application scenario; ω0 is the speed at the initial moment, ω min is the lower speed limit, Δf e (t) is the time-varying frequency deviation; The value of the time t1 is determined according to the adaptively adjusted duration Δt u Sure, t1=t0+Δt u The duration of adaptive adjustment Δt u Depends on the application scenario; The speed coefficient recovery stage in step S4 refers to the period from time t1 to time t2, and the recovery curve refers to the curve of the speed coefficient recovering from time t1 k(t1) to 1. In this stage, the speed coefficient is: Where k(t1) refers to the k value at time t1.

2. A primary frequency modulation method for a doubly-fed wind turbine generator system based on a variable speed coefficient according to claim 1, characterized in that: The grid frequency deviation Δf in step S1 e , satisfying the following relational expressions: Δf e =f e -f n In the formula, f e is the actual measured frequency of the power grid, f n is the rated frequency of the power grid; the frequency regulation dead zone of the doubly-fed wind turbine generator set in step S1 is ±0.05 Hz.

3. The primary frequency modulation method of a doubly-fed wind turbine generator system based on a variable speed coefficient according to claim 1, characterized in that: The speed coefficient in step S2 refers to the proportional coefficient k of the actual speed of the doubly fed wind turbine. The actual speed value is multiplied by the speed coefficient to obtain the equivalent value of the actual speed. The actual speed equivalent value is subtracted from the speed reference value and PI is adjusted to finally obtain the active reference value P of the doubly fed wind turbine. ref ; The speed reference value ω ref From the stator power P s It is actually the speed command function of the doubly-fed wind turbine generator set operating in the maximum power point tracking (MPPT) state. Where a, b, and c are constants.

4. The primary frequency modulation method of a doubly-fed wind turbine generator system based on a variable speed coefficient according to claim 1, characterized in that: The value of the time t2 is based on the speed coefficient recovery duration Δt r Determine, t2 is determined by the following formula, t2=t1+Δt r The speed coefficient recovery duration Δt r Depends on the application scenario.

5. A frequency modulation system used in the frequency modulation method according to claim 1, characterized in that: It includes a measuring module, a time determining module, a speed coefficient determining module, and a power reference value determining module.

6. The frequency modulation system according to claim 5, characterized in that: The measuring module is used to measure the speed of the doubly-fed wind turbine and the frequency of access to the power grid; the time determination module is used to determine the duration of the rising curve, the duration of the adaptive adjustment, and the duration of the speed coefficient recovery; The speed coefficient determination module calculates the time-varying speed coefficient k online in real time; the power reference value determination module calculates the active power reference value of the doubly-fed wind turbine generator set according to the speed coefficient, the real-time speed and the speed reference value.

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