A sliding mode control method for permanent magnet synchronous fan based on exponential control law

Abstract

A sliding mode control method for a permanent magnet synchronous fan based on an exponential control law belongs to the field of sliding mode control for fans and is used for speed loop control of a permanent magnet synchronous generator to achieve stable tracking of the optimal speed of the fan. The scheme constructs a terminal sliding mode function based on exponential convergence and designs a controller to effectively deal with the nonlinear characteristics of the system, and can have the characteristics of high-precision tracking of reference signals and suppression of jitter while converging quickly. By avoiding the differential processing of the exponential function in the equivalent control, the singularity problem of the conventional terminal sliding mode is avoided. The invention has the characteristics of simple structure, high control accuracy, fast convergence speed, small jitter and strong anti-interference ability.

Description

Technical Field

[0001] The invention belongs to the technical field of permanent magnet synchronous wind power generation system control, and in particular relates to an exponential sliding mode control method for a permanent magnet synchronous generator. Background Art

[0002] Direct-drive permanent magnet synchronous wind turbines have the advantages of high energy transfer efficiency, high reliability, and low maintenance costs. With the rapid development of rare earth permanent magnet materials, direct-drive permanent magnet synchronous wind turbines are becoming the mainstream choice and future trend for large-capacity wind turbines.

[0003] The permanent magnet synchronous wind power generation system is a complex system with highly nonlinear, strong coupling and multivariable characteristics. By controlling the rotor speed, the generator can achieve the best energy conversion efficiency at different wind speeds to ensure the stability of the power grid. Due to the randomness of wind speed and the uncertainty of the external environment, traditional control methods may be difficult to meet the control requirements and affect the power output of the wind power generation system. Therefore, advanced control strategies are needed to improve the power output efficiency and anti-disturbance ability of the system. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the present invention proposes a sliding mode control method for a permanent magnet synchronous fan based on an exponential control law, which is used for the speed loop control of a permanent magnet synchronous generator, aiming to achieve stable tracking of the optimal speed of the fan and improve the power generation efficiency of the fan.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A sliding mode control method for a permanent magnet synchronous fan based on an exponential control law adopts a fast terminal sliding mode function based on exponential convergence and a chattering-free control law to obtain a smooth and continuous control signal. The control law can effectively cope with the nonlinear characteristics of the system and can converge within a limited time while having high-precision tracking of reference signals and suppressing chattering. The exponential sliding mode controller includes an exponential sliding surface design, an equivalent control term and a switching term design.

[0007] Further, the method comprises the following steps:

[0008] 1) Collect the stator three-phase current signal of the synchronous motor in the three-phase stationary coordinate system , , , and the rotor electrical angle signal θ e and mechanical angular velocity signal ω m, and construct the mathematical model of the permanent magnet synchronous generator in the dq rotating coordinate system; considering that the permanent magnet synchronous wind turbine model will be affected by the changes in internal parameters and external disturbances, the electromechanical coupling kinematic equation of the wind power generation system is expressed as,

[0009] (1);

[0010] In the formula, , , M is a constant greater than zero; is the impeller torque of the fan, is the rotor flux of the generator; , , They are the uncertain parts caused by the measurement error of the fan impeller torque, the rotor flux disturbance and the change of the damping coefficient; is the torque including disturbance; Indicates interference from the external environment, such as fluctuations in wind speed, turbulence in airflow, etc.; i q is the stator current q Axis component; J is the moment of inertia of the rotating spindle; B is the transmission damping coefficient; P n is the number of generator pole pairs;

[0011] 2) The optimal speed of the fan ω ref The actual speed value ω m As the input of the speed loop controller, an exponential sliding mode controller is designed, and the output is q Shaft current reference value ; d Shaft current reference value Calculated based on reactive power demand, usually taken as 0;

[0012] 3) , and actual dq Shaft current i d、 i q As the input signal of the current loop controller, the output voltage reference value , ; d Shaft current reference value Calculated based on reactive power demand;

[0013] 4) , Coordinate transformation is performed and space pulse vector modulation technology is used to output PWM signals to control the operation of the machine-side converter.

[0014] Furthermore, in 2), the design process of the exponential sliding surface in the speed loop controller is as follows:

[0015] 2.1) Define the generator speed error,

[0016] (2);

[0017] Taking the derivative of equation (2) and substituting it into equation (1) in 1), we get:

[0018] (3);

[0019] In the formula, , D(t) =- D 0(t), u For control ;

[0020] 2.2) Design of exponential sliding surface s ω The expression is as follows,

[0021] (4);

[0022] In the formula, , used to control the convergence speed of the system state, is the hyperbolic tangent function, , which determines the speed and accuracy at which the system state approaches its limit.

[0023] Furthermore, the step 2) further comprises the following steps:

[0024] 2.3) Construct equivalent control items u eq With switch item u sw , and calculate the expected value of the quadrature-axis current ,

[0025] (5);

[0026] In the formula k is the integral control gain, ;

[0027] Combined with formula (1), the expected value of the quadrature axis current is calculated: , which is the output of the controller,

[0028] (6);

[0029] Finally, the formula (6) And the actual q-axis current i q As the input signal of the current loop controller to achieve precise current control.

[0030] Preferably, the step 2) further comprises the following steps:

[0031] 2.4) Verify the stability of the system and define the Lyapunov function.

[0032] (7)

[0033] Combining equations (4)-(7), we get:

[0034] (8);

[0035] It can be seen from formula (8) that the system tracking error can converge to 0 in a finite time, and the system can operate stably.

[0036] Compared with the prior art, the beneficial effects of the present invention are: a fast terminal sliding mode surface based on exponential convergence and a jitter-free control law are designed to obtain a smooth and continuous control signal. The control law can effectively deal with the nonlinear characteristics of the system, and can converge in a finite time while having the characteristics of high-precision tracking of reference signals and suppressing jitter. In addition, by avoiding the differential processing of the exponential function in the equivalent control, the singularity problem of the conventional terminal sliding mode is circumvented. Compared with the traditional sliding mode controller, it has faster convergence speed, smaller jitter and stronger anti-disturbance performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The structure diagram of a permanent magnet synchronous wind power generation system based on an exponential sliding mode speed controller is shown in the figure, where wind is the natural wind and Grid is the power grid.

[0038] Figure 2 This is the structural block diagram of the exponential sliding mode speed controller.

[0039] Figure 3 It is a speed comparison curve diagram of the fan under the condition of sudden wind speed change when using the present invention and when using full-order sliding mode control.

[0040] Figure 4 It is a comparison curve diagram of the q-axis current jitter suppression of the fan using the present invention and using full-order sliding mode control.

[0041] Figure 5 The optimal rotation speed tracking is performed using the present invention and full-order sliding mode control in a random wind environment.

[0042] Figure 6It is the power output curve of PMSG using the present invention and using full-order sliding mode control in a random wind environment.

[0043] Figure 7 It is the energy release curve of PMSG using the present invention and using full-order sliding mode control in a random wind environment. DETAILED DESCRIPTION

[0044] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0045] Figure 1 The overall structure of the permanent magnet synchronous wind power generation system is shown in Figure 1. The generator stator is connected to the grid through a full-power converter. By controlling the converters on the generator side and the grid side, the wind power generation system can achieve stable power generation. The generator-side converter and the grid-side converter each have an independent control system. The generator-side converter uses a rotor magnetic field oriented vector control strategy to control the electromagnetic torque and speed. The optimal speed ω ref The output is MPPT, the speed outer loop adopts exponential sliding film control strategy, and the current inner loop adopts PI control. and Through coordinate transformation and the use of space pulse vector modulation technology (SVPWM), the PWM signal is output to control the machine-side converter and put the wind power system in a maximum tracking working state.

[0046] A sliding mode control method for a permanent magnet synchronous fan based on an exponential control law adopts a fast terminal sliding mode function based on exponential convergence and a chattering-free control law to obtain a smooth and continuous control signal. The control law can effectively cope with the nonlinear characteristics of the system and can converge within a limited time while having high-precision tracking of reference signals and suppressing chattering. The exponential sliding mode controller includes an exponential sliding surface design, an equivalent control term and a switching term design.

[0047] Further, the method comprises the following steps:

[0048] 1) Collect the stator three-phase current signal of the synchronous motor in the three-phase stationary coordinate system , , , and the rotor electrical angle signal θ e and mechanical angular velocity signal ω m , and construct the mathematical model of the permanent magnet synchronous generator in the dq rotating coordinate system; considering that the permanent magnet synchronous wind turbine model will be affected by the changes in internal parameters and external disturbances, the electromechanical coupling kinematic equation of the wind power generation system is expressed as,

[0049] (1);

[0050] In the formula, , , M is a constant greater than zero; is the impeller torque of the fan, is the rotor flux of the generator; , , They are the uncertain parts caused by the measurement error of the fan impeller torque, the rotor flux disturbance and the change of the damping coefficient; is the torque including disturbance; Indicates interference from the external environment, such as fluctuations in wind speed, turbulence in airflow, etc.; i q is the stator current q Axis component; J is the moment of inertia of the rotating spindle; B is the transmission damping coefficient; P n is the number of generator pole pairs;

[0051] 2) The optimal speed of the fan ω ref The actual speed value ω m As the input of the speed loop controller, an exponential sliding mode controller is designed, and the output is q Shaft current reference value ; d Shaft current reference value Calculated based on reactive power demand, usually taken as 0;

[0052] In the above sliding mode control method of permanent magnet synchronous fan based on exponential control law, the exponential sliding mode controller is based on the optimal speed value of the fan. ω ref The actual speed value ω m As the input of the speed loop controller, the output is q Shaft current reference value ; It includes exponential sliding surface design, equivalent control term and switching term design, which is implemented in the following steps:

[0053] 2.1) Define the generator speed error,

[0054] (2);

[0055] Taking the derivative of equation (2) and substituting it into equation (1), we get:

[0056] (3);

[0057] In the formula , D(t) =- D 0(t), u For control ;

[0058] 2.2) Design of exponential sliding mode function s ω ,

[0059] (4);

[0060] In the formula, , used to control the convergence speed of the system state, is the hyperbolic tangent function, , determines the speed and accuracy at which the system state approaches the limit;

[0061] 2.3) Construct equivalent control items u eq With switch item u sw ,

[0062] (5);

[0063] In the formula ;

[0064] Combined with formula (1), the expected value of the quadrature axis current is calculated: , which is the output of the controller,

[0065] (6);

[0066] Finally, the formula (6) And the actual q-axis current i q As the input signal of the current loop controller to achieve precise current control.

[0067] 2.4) Verify the stability of the system and define the Lyapunov function.

[0068] (7);

[0069] Combining equations (4)-(7), we get:

[0070] (8)

[0071] From equation (8), we can see that the system tracking error can converge to 0 in a finite time, and the system can operate stably. The structural block diagram of the exponential sliding mode controller is as follows: Figure 2 shown.

[0072] In this embodiment, the motor reference speed is set to a constant speed of 400 rpm, the wind speed is constant from 6 m / s It suddenly dropped to 4.8 m / s , and then increase to 8 after the system stabilizes m / s , the controller parameters are set to: c =120, k =850, its speed response curve is as follows Figure 3 As shown. It can be seen that compared with the full-order sliding mode control method, this method has a faster response speed and no overshoot during the startup process, and when the wind speed changes suddenly, this method has a smaller speed fluctuation, which proves that this method has better anti-interference ability. Figure 4 In this method and full-order sliding mode control, Output situation, it can be seen that compared with the full-order sliding mode control, q The current jitter of the shaft current under the control of this method will be smaller. Figure 5 and Figure 6 As shown, compared with full-order sliding mode control, this method has higher optimal speed tracking accuracy and generates more electric power. Figure 7 The energy curves of the fan under the two control methods within 800s are shown. It can be seen that within these 800s, the fan using this method produced 4900J more energy than the fan using the full-order sliding mode control method.

[0073] The contents described in the embodiments of this specification are merely enumerations of implementation forms of the inventive concept and are for illustrative purposes only. The protection scope of the present invention should not be considered to be limited to the specific forms described in this embodiment, and the protection scope of the present invention also extends to equivalent technical means that can be thought of by ordinary technicians in this field based on the inventive concept.

Claims

1. A sliding mode control method for a permanent magnet synchronous fan based on an exponential control law, characterized in that: The fast terminal sliding mode function based on exponential convergence and the chatter-free control law are used to obtain a smooth and continuous control signal. The control law can effectively deal with the nonlinear characteristics of the system, and can converge within a limited time while having high-precision tracking of the reference signal and suppressing chattering; the exponential sliding mode controller includes the design of the exponential sliding mode surface, the design of the equivalent control term and the switching term; The method comprises the following steps: 1) Collect the stator three-phase current signal of the synchronous motor in the three-phase stationary coordinate system , , , and the rotor electrical angle signal θ e and mechanical angular velocity signal ω m , and construct the mathematical model of the permanent magnet synchronous generator in the dq rotating coordinate system; considering that the permanent magnet synchronous wind turbine model will be affected by the changes in internal parameters and external disturbances, the electromechanical coupling kinematic equation of the wind power generation system is expressed as, （1）； In the formula, , , M is a constant greater than zero; is the impeller torque of the fan, is the rotor flux of the generator; , , They are the uncertain parts caused by the measurement error of the fan impeller torque, the rotor flux disturbance and the change of the damping coefficient; is the torque including disturbance; Indicates interference from the external environment; i q is the stator current q Axis component; J is the moment of inertia of the rotating spindle; B is the transmission damping coefficient; P n is the number of generator pole pairs; 2) The optimal speed of the fan ω ref The actual speed value ω m As the input of the speed loop controller, an exponential sliding mode controller is designed, and the output is q Shaft current reference value ; d Shaft current reference value Calculated based on reactive power demand; 3) , and actual dq Shaft current i d、 i q As the input signal of the current loop controller, the output voltage reference value , ; 4) , Perform coordinate transformation and use space pulse vector modulation technology to output PWM signals to control the operation of the machine-side converter; In 2), the design process of the exponential sliding surface in the speed loop controller is as follows: 2.1) Define the generator speed error, （2）； Taking the derivative of equation (2) and substituting it into equation (1) in 1), we get: （3）； In the formula, , D(t) =- D 0(t), u For control ; 2.2) Design of exponential sliding surface s ω The expression is as follows, （4）； In the formula, , used to control the convergence speed of the system state, is the hyperbolic tangent function, , which determines the speed and accuracy at which the system state approaches its limit.

2. The sliding mode control method for a permanent magnet synchronous fan based on an exponential control law according to claim 1, characterized in that: The above 2) also includes the following steps: 2.3) Construct equivalent control items u eq With switch item u sw as follows, （5）； In the formula, k is the integral control gain, ; Combined with formula (1), the expected value of the quadrature axis current is calculated: , which is the output of the controller, （6）； Finally, the formula (6) And the actual q-axis current i q As the input signal of the current loop controller to achieve precise current control.

3. The sliding mode control method for a permanent magnet synchronous fan based on an exponential control law according to claim 2 is characterized in that: The above 2) also includes the following steps: 2.4) Verify the stability of the system and define the Lyapunov function. （7） Combining equations (4)-(7), we get: （8）； It can be seen from formula (8) that the system tracking error can converge to 0 in a finite time, and the system can operate stably.

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