Method for analyzing frequency modulation capability of double-fed wind turbine based on adaptive cubic speed feedforward compensation

Abstract

The application provides a double-fed fan frequency modulation capacity analysis method based on adaptive third-order rotational speed feedforward compensation, a double-fed fan rotor motion disturbance equation is established, a variation of an active power instruction determined by a third-order rotor mechanical rotational speed feedforward amount is obtained, mechanical power variation caused by rotational speed drop in a frequency modulation process is offset, an offset effect of MPPT control on constant additional power instructions is eliminated, complete tracking of constant additional power instructions by stator grid-connected power is realized, an accurate expression of double-fed fan frequency modulation capacity and frequency modulation duration are determined, and an influence mechanism of frequency modulation duration on frequency modulation capacity is accurately obtained, accurate data support is provided for subsequent active power distribution and rotational speed coordination, and grid frequency stability is ensured.

Description

Technical Field

[0001] This invention relates to a method for analyzing the frequency regulation capability of wind turbines, and more particularly to a method for analyzing the frequency regulation capability of doubly fed wind turbines based on adaptive triple speed feedforward compensation. Background Technology

[0002] Doubly-fed induction generator (DFIG) wind turbines are widely used in wind power systems due to their mature technology and high cost-effectiveness. In DFIG grid-connected operation, maximum power point tracking (MPPT) control is the core technology for ensuring efficient wind energy utilization. However, under the classic MPPT control structure and system parameters, the stator reference power output by the MPPT decreases significantly with decreasing speed, offsetting the superimposed constant additional power command value. Therefore, the stator grid-connected power of the DFIG wind turbine cannot increase the power according to the constant additional power command value, resulting in the unit's inability to effectively utilize its frequency regulation capability and affecting the frequency regulation effect.

[0003] In existing technologies, frequency regulation capability is generally defined as the energy actually fed into the system when the rotor speed decreases. This energy is related to the constant additional power value and the frequency regulation duration. However, due to the complexity of the expression for mechanical power, its integral over time is difficult to obtain, making it impossible to obtain a specific analytical expression for frequency regulation capability. Consequently, it is impossible to determine the frequency regulation capability and the frequency regulation duration, and thus impossible to accurately obtain the mechanism by which the frequency regulation duration affects the frequency regulation effect. It is also impossible to accurately analyze the frequency regulation capability of doubly-fed induction generators, let alone analyze the optimal solution for active power distribution and speed coordination based on the frequency regulation capability. This leads to increased grid frequency fluctuations and affects the stable operation of the grid.

[0004] Therefore, in order to solve the above-mentioned technical problems, it is urgent to propose a new technical approach. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for analyzing the frequency regulation capability of doubly-fed induction generator (DFIG) wind turbines based on adaptive triple speed feedforward compensation. By establishing the rotor motion disturbance equation of the DFIG wind turbine, the change in active power command determined by the triple rotor mechanical speed feedforward is factored in, thereby offsetting the mechanical power change caused by the decrease in speed during frequency regulation, eliminating the offsetting effect of MPPT control on the constant additional power command, and achieving complete tracking of the constant additional power command by the stator grid-connected power. Furthermore, the accurate expression of the frequency regulation capability of the DFIG wind turbine and the frequency regulation duration are determined, thereby accurately obtaining the influence mechanism of the frequency regulation duration on the frequency regulation capability, providing accurate data support for subsequent active power allocation, speed coordination, etc., and ensuring the stability of the power grid frequency.

[0006] This invention provides a method for analyzing the frequency regulation capability of a doubly-fed wind turbine based on adaptive triple speed feedforward compensation, comprising the following steps:

[0007] S1. Obtain the operating parameters of the doubly-fed wind turbine, including the additional power command value P. add And the moment of inertia J of the doubly fed wind turbine;

[0008] S2. Construct the rotor motion disturbance equation of the doubly-fed induction generator (DFIG) based on the operating parameters of the DFIG:

[0009] (1);

[0010] Where: ω m0 Δω represents the rotor mechanical angular velocity at the initial moment of frequency modulation of the doubly-fed wind turbine. m (t) represents the change in the rotor's mechanical angular velocity at time t, δ temp Denotes the transient correction coefficient, ΔP m and ΔP r These are the changes in mechanical power and the changes in slip power, respectively.

[0011] S3. Construct an adaptive cubic speed feedforward compensation term model to determine the change in active power command P. fd And make P fd +ΔP m =0;

[0012] S4. Solve for the change in rotor mechanical angular velocity Δω at time t based on formula (1). m (t);

[0013] S5. Based on the change in rotor mechanical angular velocity Δω at time t m (t) determines the frequency regulation capability of the doubly fed fan.

[0014] Furthermore, the adaptive three-stage speed feedforward compensation model is specifically as follows:

[0015] ;

[0016] Where: k opt It is the maximum power point tracking coefficient, ω m This refers to the rotor mechanical angular velocity of the doubly fed wind turbine.

[0017] Furthermore, the change in mechanical power ΔP is determined using the following method. m :

[0018] .

[0019] Furthermore, the slip power change ΔP is determined using the following method. r :

[0020] ;

[0021] k1=(kopt ω1(ω m0 ) 2 +2P add ) / ω1; where: ω1 represents the synchronous angular velocity of the doubly fed fan.

[0022] Furthermore, based on the change in rotor mechanical angular velocity Δω at time t m (t) The specific frequency regulation capability of the doubly fed wind turbine is determined as follows:

[0023] ; where: E cap This indicates the frequency regulation capability of the doubly fed fan, where ΔT is the frequency regulation duration.

[0024] k1=(k opt ω1(ω m0 ) 2 +2P add ) / ω1; where: ω1 represents the synchronous angular velocity of the doubly fed fan.

[0025] Furthermore, the frequency modulation duration ΔT is determined using the following method:

[0026] ;

[0027] k1=(k opt ω1(ω m0 ) 2 +2P add ) / ω1;

[0028] Where: ω min ω1 represents the minimum permissible speed of the doubly-fed wind turbine, and ω1 represents the synchronous angular velocity of the doubly-fed wind turbine.

[0029] Furthermore, the maximum power point tracking coefficient k is determined using the following method. opt :

[0030] k opt =0.5πρR 5 C p_opt / (Nλ opt ) 3 ;

[0031] Where: ρ is the air density, λ opt and C p_opt R represents the optimal tip speed ratio and the optimal wind energy utilization coefficient, and N represents the impeller radius of the doubly-fed wind turbine and the gearbox transmission ratio of the doubly-fed wind turbine.

[0032] The beneficial effects of this invention are as follows: By establishing the rotor motion disturbance equation of the doubly-fed induction generator (DFIG) wind turbine, the change in active power command determined by the third rotor mechanical speed feedforward is factored in, thereby offsetting the mechanical power change caused by the decrease in speed during frequency regulation, eliminating the offsetting effect of MPPT control on the constant additional power command, and achieving complete tracking of the stator grid-connected power to the constant additional power command; and determining the accurate expression of the frequency regulation capability of the DFIG wind turbine and the frequency regulation duration, thereby accurately obtaining the influence mechanism of the frequency regulation duration on the frequency regulation capability, providing accurate data support for subsequent active power distribution, speed coordination, etc., and ensuring the stability of the power grid frequency. Attached Figure Description

[0033] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0034] Figure 1 This is a schematic diagram of the process of the present invention.

[0035] Figure 2 This is a schematic diagram of the doubly fed fan control structure with tertiary rotor mechanical speed feedforward control according to the present invention.

[0036] Figure 3 This invention relates to the frequency regulation capability of a doubly fed wind turbine generator set under different initial rotor mechanical angular velocities and constant additional power. Detailed Implementation

[0037] The present invention will be further described in detail below:

[0038] This invention provides a method for analyzing the frequency regulation capability of a doubly-fed wind turbine based on adaptive triple speed feedforward compensation, comprising the following steps:

[0039] S1. Obtain the operating parameters of the doubly-fed wind turbine, including the additional power command value P. add And the moment of inertia J of the doubly fed wind turbine;

[0040] S2. Construct the rotor motion disturbance equation of the doubly-fed induction generator (DFIG) based on the operating parameters of the DFIG:

[0041] (1);

[0042] Where: ω m0 Δω represents the rotor mechanical angular velocity at the initial moment of frequency modulation of the doubly-fed wind turbine. m (t) represents the change in the rotor's mechanical angular velocity at time t, δ temp Denotes the transient correction coefficient, ΔP m and ΔP r These are the changes in mechanical power and the changes in slip power, respectively.

[0043] S3. Construct an adaptive cubic speed feedforward compensation term model to determine the change in active power command P. fd And make P fd +ΔP m =0;

[0044] S4. Solve for the change in rotor mechanical angular velocity Δω at time t based on formula (1). m (t);

[0045] S5. Based on the change in rotor mechanical angular velocity Δω at time t m (t) The frequency regulation capability of the doubly-fed induction generator (DFIG) wind turbine is determined. Using the above method, by establishing the rotor motion disturbance equation of the DFIG wind turbine, the change in active power command determined by the third rotor mechanical speed feedforward is factored in. This offsets the mechanical power change caused by the decrease in rotor speed during frequency regulation, eliminating the offsetting effect of MPPT control on the constant additional power command, and achieving complete tracking of the constant additional power command by the stator grid-connected power. Furthermore, the accurate expression for the frequency regulation capability of the DFIG wind turbine and the frequency regulation duration are determined, thus accurately obtaining the influence mechanism of the frequency regulation duration on the frequency regulation capability. This provides accurate data support for subsequent active power allocation, speed coordination, etc., ensuring grid frequency stability.

[0046] like Figure 2 As shown: In Figure 2 In the middle, the lowest value has the change in active power command P. fd The branch is the one that incorporates three-stage rotor mechanical speed feedforward control in this invention. Figure 2 Chinese: ω w Let ω be the angular velocity of the wind turbine. r ω1 and ω2 are the rotor electrical angular velocity and synchronous angular velocity, respectively; p is the number of pole pairs of the motor; and N is the gearbox transmission ratio. add The constant additional power command received by the doubly-fed wind turbine from the station's frequency regulation control system; P MPPT The electromagnetic power output for maximum power point tracking (MPPT).

[0047] Specifically: the adaptive three-stage speed feedforward compensation model is as follows:

[0048] (2);

[0049] Where: k opt It is the maximum power point tracking coefficient, ω m This refers to the rotor mechanical angular velocity of the doubly fed wind turbine.

[0050] The change in mechanical power ΔP is determined using the following method. m :

[0051] (3).

[0052] The slip power change ΔP is determined using the following method. r :

[0053] (4);

[0054] k1=(k opt ω1(ω m0 ) 2 +2P add ) / ω1; where: ω1 represents the synchronous angular velocity of the doubly fed fan.

[0055] Based on the change in rotor mechanical angular velocity Δω at time t m (t) The specific frequency regulation capability of the doubly fed wind turbine is determined as follows:

[0056] (5); where: E cap This indicates the frequency regulation capability of the doubly-fed induction generator (DFIG), where ΔT is the frequency regulation duration. The frequency regulation capability is defined as: from the start of frequency regulation until the speed drops to the lowest permissible speed ω of the fan. min At that time, the total energy released by the unit to the system.

[0057] k1=(k opt ω1(ω m0 ) 2 +2P add ) / ω1; where: ω1 represents the synchronous angular velocity of the doubly fed fan.

[0058] The frequency modulation duration ΔT is determined using the following method:

[0059] (6);

[0060] k1=(k opt ω1(ω m0 ) 2 +2P add ) / ω1;

[0061] Where: ω min ω1 represents the minimum permissible speed of the doubly-fed wind turbine, and ω1 represents the synchronous angular velocity of the doubly-fed wind turbine.

[0062] The maximum power point tracking coefficient k is determined using the following method. opt :

[0063] k opt =0.5πρR 5 C p_opt / (Nλ opt ) 3 ;

[0064] Where: ρ is the air density, λopt and C p_opt R represents the optimal tip speed ratio and the optimal wind energy utilization coefficient, and N represents the impeller radius of the doubly-fed wind turbine and the gearbox transmission ratio of the doubly-fed wind turbine.

[0065] Formulas (5) and (6) directly reflect the influence of the FM duration on the FM capability, and by adjusting ω... m0 Parameters such as ω at different frequency modulation start times m0 They are different, thus changing the duration and capability of frequency modulation.

[0066] like Figure 3 As shown: Under the same constant additional power, the lower the initial speed of the doubly-fed induction generator (DFIG) wind turbine, the greater its frequency regulation capability. However, when the constant additional power value is large, the speed is prone to exceeding the limit and exiting frequency regulation. This means that the frequency regulation capability of DFIG wind turbines with lower initial speeds is relatively limited, essentially because they store less kinetic energy. Conversely, for DFIG wind turbines with higher initial speeds, although their frequency regulation capability under the same constant additional power is smaller than that of turbines with lower initial speeds, the constant additional power command they can accept is larger, implying that they have greater frequency regulation potential. Furthermore, from... Figure 3 It can also be seen that the frequency regulation capability of doubly-fed induction generator (DFIG) wind turbines has a maximum value, corresponding to the maximum energy released to the system. After this moment, the rotor of the unit continues to release kinetic energy, but the energy released to the system begins to decrease. Furthermore, under different constant additional power conditions, the maximum frequency regulation capability of DFIG wind turbines occurs almost simultaneously, showing relatively little influence from constant additional power commands. It is also noteworthy that the moment of the maximum frequency regulation capability is negatively correlated with the initial speed of the wind turbine; that is, the higher the initial speed of the DFIG wind turbine, the earlier the maximum frequency regulation capability occurs.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for analyzing the frequency regulation capability of a doubly-fed wind turbine based on adaptive triple speed feedforward compensation, characterized in that: Includes the following steps: S1. Obtain the operating parameters of the doubly-fed wind turbine, including the additional power command value P. add And the moment of inertia J of the doubly fed wind turbine; S2. Construct the rotor motion disturbance equation of the doubly-fed induction generator (DFIG) based on the operating parameters of the DFIG: (1)； Where: ω m0 Δω represents the rotor mechanical angular velocity at the initial moment of frequency modulation of the doubly-fed wind turbine. m (t) represents the change in the rotor's mechanical angular velocity at time t, δ temp Denotes the transient correction coefficient, ΔP m and ΔP r These are the changes in mechanical power and the changes in slip power, respectively. S3. Construct an adaptive cubic speed feedforward compensation term model to determine the change in active power command P. fd And make P fd +ΔP m =0; The adaptive cubic speed feedforward compensation term model is as follows: ； Where: k opt It is the maximum power point tracking coefficient, ω m This refers to the rotor mechanical angular velocity of the doubly-fed wind turbine. S4. Solve for the change in rotor mechanical angular velocity Δω at time t based on formula (1). m (t); S5. Based on the change in rotor mechanical angular velocity Δω at time t m (t) determines the frequency regulation capability of the doubly fed fan.

2. The method for analyzing the frequency regulation capability of a doubly-fed wind turbine based on adaptive triple speed feedforward compensation according to claim 1, characterized in that: The change in mechanical power ΔP is determined using the following method. m : 。 3. The method for analyzing the frequency regulation capability of a doubly-fed wind turbine based on adaptive triple speed feedforward compensation according to claim 1, characterized in that: The slip power change ΔP is determined using the following method. r : ； k1=(k opt ω1(ω m0 ) 2 +2P add ) / ω1; where: ω1 represents the synchronous angular velocity of the doubly fed fan.

4. The method for analyzing the frequency regulation capability of a doubly-fed wind turbine based on adaptive triple speed feedforward compensation according to claim 1, characterized in that: Based on the change in rotor mechanical angular velocity Δω at time t m (t) The specific frequency regulation capability of the doubly fed wind turbine is determined as follows: ； Among them: E cap This indicates the frequency regulation capability of the doubly fed fan, where ΔT is the frequency regulation duration. k1=(k opt ω1(ω m0 ) 2 +2P add ) / ω1; where: ω1 represents the synchronous angular velocity of the doubly fed fan.

5. The method for analyzing the frequency regulation capability of a doubly-fed wind turbine based on adaptive triple speed feedforward compensation according to claim 4, characterized in that: The frequency modulation duration ΔT is determined using the following method: ； k1=(k opt ω1(ω m0 ) 2 +2P add ) / ω1; Where: ω min ω1 represents the minimum permissible speed of the doubly-fed wind turbine, and ω1 represents the synchronous angular velocity of the doubly-fed wind turbine.

6. The method for analyzing the frequency regulation capability of a doubly-fed wind turbine based on adaptive triple speed feedforward compensation according to any one of claims 2-5, characterized in that: The maximum power point tracking coefficient k is determined using the following method. opt : k opt =0.5prR 5 C p_opt / (Nλ opt ) 3 ; Where: ρ is the air density, λ opt and C p_opt R represents the optimal tip speed ratio and the optimal wind energy utilization coefficient, and N represents the impeller radius of the doubly-fed wind turbine and the gearbox transmission ratio of the doubly-fed wind turbine.

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