A method for determining the cost function of low switching frequency for permanent magnet synchronous wind turbines

Abstract

The present invention discloses a method for giving a low switching frequency cost function of a permanent magnet synchronous wind turbine generator, which specifically comprises the following steps: collecting real-time data of the generator, calculating the mechanical angular velocity ω of the generator rotor at time k m (k); predict the rotor mechanical angular velocity ω at time k+1 mb (k+1); Taking into account the prediction error, mb (k+1) performs error compensation, and the predicted value of the rotor mechanical angular velocity at time k+1 after compensation is ω mp (k+1); calculate the speed prediction reference trajectory; give a low switching frequency cost function. The present invention can effectively reduce the number of system switches and improve the robustness and efficiency of the system.

Description

Technical Field

[0001] The invention belongs to the field of wind power generation conversion control, and in particular relates to a method for giving a low switching frequency cost function of a permanent magnet synchronous wind generator. Background Art

[0002] Direct-drive permanent magnet wind turbines have been widely used due to their advantages of eliminating gearboxes, high power density, and high efficiency. Too high switching frequency of the converter will lead to increased losses, and the speed response speed and control accuracy determine the reliability and stability of the system. Therefore, it is necessary to design a method for determining the optimal voltage vector of a permanent magnet synchronous wind turbine. Summary of the invention

[0003] In view of the defects or shortcomings described in the background technology, the present invention provides a method for determining an optimal voltage vector of a permanent magnet synchronous wind turbine generator, thereby improving the robustness and efficiency of the system.

[0004] A method for giving a low switching frequency cost function of a permanent magnet synchronous wind turbine generator, comprising the following steps:

[0005] (1) Collect real-time data of the generator and calculate the mechanical angular velocity ω of the generator rotor at time k m (k);

[0006] (2) Calculate the predicted value ω of the rotor mechanical angular velocity at time k+1 mb (k+1);

[0007] (3) Taking into account the prediction error, mb (k+1) performs error compensation and calculates the predicted value of the rotor mechanical angular velocity ω at time k+1 after compensation mp (k+1);

[0008] (4) Calculate the speed prediction reference trajectory y m (k+1);

[0009] (5) When ω m (k) When the generator speed is less than or equal to 1 / 2 times the rated speed, the cost function g1 = [ω mp (k+1)-y m (k+1)] 2 +[Δi q (k)] 2 ;

[0010] (6) When ω m (k) When it is greater than 1 / 2 times the rated speed of the generator, construct the cost function

[0011] In step (1), the mechanical angular velocity ω of the generator rotor at time k mThe calculation formula of (k) is as follows:

[0012]

[0013] Where J is the moment of inertia; B is the friction coefficient; T L (k-1) is the load torque at time k-1; P n is the pole pair number; ψ f is the permanent magnet flux; T s is the sampling time; i q (k-1) is the q-axis component of the stator current sampling value at time k-1.

[0014] The predicted value ω of the rotor mechanical angular velocity at time k+1 in step (2) is mb The calculation formula for (k+1) is as follows:

[0015]

[0016] In the formula Δi q (k) is the q-axis current increment at the current moment.

[0017] The predicted value of the rotor mechanical angular velocity ω at time k+1 after compensation in step (3) mp The calculation formula for (k+1) is as follows:

[0018] ω mp (k+1)=ω mb (k+1)+e(k) (3)

[0019] Where prediction error e(k) = ω m (k) = ω mb (k).

[0020] The speed prediction reference trajectory y in step (4) m The calculation formula for (k+1) is as follows:

[0021] y m (k+1)=0.3ω m (k)+0.7ω mef (k) (4)

[0022] Where ω mef (k) is the given value of the rotor mechanical angular velocity at time k.

[0023] In step (5), the cost function g1=[ω mp (k+1)-y m (k+1)] 2 +[Δi q (k)] 2 The optimal control rate can be obtained when it is minimum.

[0024] The cost function in step (6) is The optimal control rate can be obtained when it is maximum.

[0025] The benefits of the present invention compared with the prior art are:

[0026] (1) This method constructs cost functions in the low speed range and high speed range of the permanent magnet synchronous wind turbine generator, respectively, so that the system has a smaller switching frequency.

[0027] (2) This method reduces the speed static error and jitter, and has higher control accuracy and robustness. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention is a flowchart of the method for implementing the present invention. DETAILED DESCRIPTION

[0029] In order to describe the present invention more specifically, the present invention is further described below in conjunction with the accompanying drawings and implementation modes.

[0030] like Figure 1 As shown, a method for giving a low switching frequency cost function of a permanent magnet synchronous wind turbine generator comprises the following steps:

[0031] (1) Collect real-time data of the generator and calculate the mechanical angular velocity ω of the generator rotor at time k m (k);

[0032] (2) Calculate the predicted value ω of the rotor mechanical angular velocity at time k+1 mb (k+1);

[0033] (3) Taking into account the prediction error, mb (k+1) performs error compensation and calculates the predicted value of the rotor mechanical angular velocity ω at time k+1 after compensation mp (k+1);

[0034] (4) Calculate the speed prediction reference trajectory y m (k+1);

[0035] (5) When ω m (k) When the generator speed is less than or equal to 1 / 2 times the rated speed, the cost function g1 = [ω mp (k+1)-y m (k+1)] 2 +[Δi q (k)] 2 ;

[0036] (6) When ω m (k) When it is greater than 1 / 2 times the rated speed of the generator, construct the cost function

[0037] The mechanical angular velocity ω of the generator rotor at time k in step (1) m The calculation formula of (k) is as follows:

[0038]

[0039] Where J is the moment of inertia; B is the friction coefficient; T L (k-1) is the load torque at time k-1; P n is the pole pair number; ψ f is the permanent magnet flux; T s is the sampling time; i q (k-1) is the q-axis component of the stator current sampling value at time k-1.

[0040] The predicted value of the rotor mechanical angular velocity at time k+1 in step (2) is ω mb The calculation formula for (k+1) is as follows:

[0041]

[0042] In the formula Δi q (k) is the q-axis current increment at the current moment.

[0043] The predicted value of the rotor mechanical angular velocity ω at time k+1 after compensation in step (3) mp The calculation formula for (k+1) is as follows:

[0044] ω mp (k+1)=ω mb (k+1)+e(k) (3)

[0045] Where prediction error e(k) = ω m (k)-ω mb (k).

[0046] The speed prediction reference trajectory y in step (4) m The calculation formula for (k+1) is as follows:

[0047] y m (k+1)=0.3ω m (k)+0.7ω mef (k) (4)

[0048] Where ω mef (k) is the given value of the rotor mechanical angular velocity at time k.

[0049] In step (5), the cost function g1 = [ω mp (k+1)-y m (k+1)]2 +[Δi q (k)] 2 The optimal control rate can be obtained when it is minimum.

[0050] The cost function in step (6) The optimal control rate can be obtained when it is maximum.

[0051] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention. All modifications and improvements based on the ideas and principles of the present invention belong to the protection scope of the present invention.

Claims

1. A method for determining a low switching frequency cost function of a permanent magnet synchronous wind turbine, characterized in that the steps include: (1) Collect real-time data of the generator and calculate the mechanical angular velocity ω of the generator rotor at time k m (k); (2) Calculate the predicted value ω of the rotor mechanical angular velocity at time k+1 mb (k+1); (3) Taking into account the prediction error, mb (k+1) performs error compensation and calculates the predicted value of the rotor mechanical angular velocity ω at time k+1 after compensation mp (k+1); (4) Calculate the speed prediction reference trajectory y m (k+1); (5) When ω m (k) When the generator speed is less than or equal to 1 / 2 times the rated speed, the cost function g1 = [ω mp (k+1)-y m (k+1)] 2 +[Δi q (k)] 2 ; (6) When ω m (k) When it is greater than 1 / 2 times the rated speed of the generator, construct the cost function The mechanical angular velocity ω of the generator rotor at time k in step (1) m The calculation formula of (k) is as follows: Where J is the moment of inertia; B is the friction coefficient; T L (k-1) is the load torque at time k-1; P n is the pole pair number; ψ f is the permanent magnet flux; T s is the sampling time; i q (k-1) is the q-axis component of the stator current sampling value at time k-1; The predicted value ω of the rotor mechanical angular velocity at time k+1 in step (2) is mb The calculation formula for (k+1) is as follows: In the formula Δi q (k) is the q-axis current increment at the current moment; The predicted value of the rotor mechanical angular velocity ω at time k+1 after compensation in step (3) mp The calculation formula for (k+1) is as follows: oh mp (k+1)=ω mb (k+1)+e(k) (3) Where prediction error e(k) = ω m (k)-ω mb (k).

2. A method for giving a low switching frequency cost function of a permanent magnet synchronous wind turbine according to claim 1, characterized in that: The speed prediction reference trajectory y in step (4) m The calculation formula for (k+1) is as follows: y m (k+1)=0.3ω m (k)+0.7h mef (k) (4) Where ω mef (k) is the given value of the rotor mechanical angular velocity at time k.

3. A method for determining a low switching frequency cost function of a permanent magnet synchronous wind turbine according to claim 1, characterized in that: In step (5), the cost function g1=[ω mp (k+1)-y m (k+1)] 2 +[Δi q (k)] 2 The optimal control rate can be obtained when it is minimum.

4. A method for determining a low switching frequency cost function of a permanent magnet synchronous wind turbine according to claim 1, characterized in that: The cost function in step (6) is The optimal control rate can be obtained when it is maximum.

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