Permanent magnet synchronous fan sliding mode control method based on novel index control law

Abstract

The invention discloses a permanent magnet synchronous fan sliding mode control method based on a novel index control law, belongs to the field of fan sliding mode control, and is used for speed loop control of a permanent magnet synchronous generator so as to realize stable tracking of the optimal rotating speed of a fan. According to the scheme, a novel terminal sliding mode function based on exponential convergence is constructed, a controller is designed so as to effectively cope with the nonlinear characteristic of a system, and the characteristics of high-precision reference signal tracking and buffeting suppression can be achieved while rapid convergence is achieved; the problem of singularity of a conventional terminal sliding mode is avoided by avoiding the processing of differentiating an exponential function in equivalent control. The invention has the characteristics of simple structure, high control precision, fast convergence speed, small buffeting, strong anti-interference capability and the like.

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 a novel 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 a new 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: A sliding mode control method for a permanent magnet synchronous fan based on a new exponential control law adopts a fast terminal sliding mode function based on exponential convergence and a jitter-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 jitter. The new exponential sliding mode controller includes a new exponential sliding surface design, an equivalent control term and a switching term design.

[0006] Further, 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 the 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 the interference of the external environment, such as wind speed fluctuations, air turbulence, etc.; i q is the q-axis component of the stator current; J is the moment of inertia of the rotating main shaft; B is the transmission damping coefficient; P n is the number of generator pole pairs; 2) Take the optimal speed value of the fan ω ref and the actual speed value ω m As the input of the speed loop controller, a new exponential sliding mode controller is designed, and the output is the q-axis current reference value ; d-axis current reference value Calculated based on reactive power demand; 3) , and the actual dq axis current i d、 i q As the input signal of the current loop controller, the output voltage reference value , ; 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.

[0007] Furthermore, in 2), the design process of the new 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)=-D0(t), u is the control quantity ; 2.2) Design of new 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.

[0008] Furthermore, the step 2) further comprises the following steps: 2.3) Construct equivalent control term u eq With switch item u sw , and calculate the expected value of the quadrature-axis current , (5); Where 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.

[0009] Preferably, the step 2) further comprises 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.

[0010] 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

[0011] Figure 1 The figure is a structural diagram of a permanent magnet synchronous wind power generation system based on a new exponential sliding mode speed controller, where wind is the natural wind and Grid is the power grid.

[0012] Figure 2This is the structural block diagram of the new exponential sliding mode speed controller.

[0013] 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.

[0014] Figure 4 It is a curve diagram comparing the q-axis current jitter suppression of a fan using the present invention and using full-order sliding mode control.

[0015] Figure 5 The optimal rotation speed tracking situation is achieved by using the present invention and full-order sliding mode control in a random wind environment.

[0016] Figure 6 It is the power output curve of PMSG using the present invention and using full-order sliding mode control in a random wind environment.

[0017] 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

[0018] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0019] Figure 1 The overall structure of the permanent magnet synchronous wind power generation system is shown in Figure 2. 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 a new 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.

[0020] A sliding mode control method for a permanent magnet synchronous fan based on a new exponential control law adopts a fast terminal sliding mode function based on exponential convergence and a jitter-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 jitter. The new exponential sliding mode controller includes a new exponential sliding surface design, an equivalent control term and a switching term design.

[0021] Further, 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 the 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 the interference of the external environment, such as wind speed fluctuations, air turbulence, etc.; i q is the q-axis component of the stator current; J is the moment of inertia of the rotating main shaft; B is the transmission damping coefficient; P n is the number of generator pole pairs; 2) Take the optimal speed value of the fan ω ref and the actual speed value ω m As the input of the speed loop controller, a new exponential sliding mode controller is designed, and the output is the q-axis current reference value ; d-axis current reference value Calculated based on reactive power demand, usually taken as 0; In the sliding mode control method of the permanent magnet synchronous fan based on the novel exponential control law, the novel exponential sliding mode controller takes the optimal speed value ω of the fan as ref and the actual speed value ω m As the input of the speed loop controller, the output is the q-axis current reference value ; It includes the design of new exponential sliding surface, equivalent control term and switching term design, which is implemented in the following steps: 2.1) Define the generator speed error, (2); Taking the derivative of equation (2) and substituting it into equation (1), we get: (3); In the formula , D(t)=-D0(t), u is the control quantity ; 2.2) Design of a new exponential sliding mode function s ω , (4); 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; 2.3) Construct equivalent control term u eq With switch item u sw , (5); In the formula ; 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.

[0022] 2.4) Verify the stability of the system and define the Lyapunov function. (7); Combining equations (4)-(7), we get: (8) 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 new exponential sliding mode controller is shown in Figure 2 shown.

[0023] In this embodiment, the motor reference speed is set to a constant speed of 400rpm, the wind speed is suddenly reduced from a constant wind speed of 6m / s to 4.8m / s, and then suddenly increased to 8m / s after the system is stable. The controller parameters are set to: c=120, k=850, and 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, From the output, it can be seen that compared with the full-order sliding mode control, the current jitter of the q-axis 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.

[0024] 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 a new exponential control law, characterized in that: A fast terminal sliding mode function based on exponential convergence and a chattering-free control law are used to obtain a smooth and continuous control signal. This 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 the reference signal and suppressing chattering. The new exponential sliding mode controller includes a new exponential sliding surface design, equivalent control term and switching term design.

2. The sliding mode control method for a permanent magnet synchronous fan based on a novel exponential control law according to claim 1 is characterized in that: 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 the 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 q-axis component of the stator current; J is the moment of inertia of the rotating main shaft; B is the transmission damping coefficient; P n is the number of generator pole pairs; 2) Take the optimal speed value of the fan ω ref and the actual speed value ω m As the input of the speed loop controller, a new exponential sliding mode controller is designed, and the output is the q-axis current reference value ; d-axis current reference value Calculated based on reactive power demand; 3) , and the actual dq axis current i d、 i q As the input signal of the current loop controller, the output voltage reference value , ; 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.

3. The sliding mode control method for a permanent magnet synchronous fan based on a novel exponential control law as claimed in claim 2 is characterized in that: In 2), the design process of the new 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)=-D0(t), u is the control quantity ; 2.2) Design of new 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.

4. The sliding mode control method for a permanent magnet synchronous fan based on a novel exponential control law as claimed in claim 3 is characterized in that: The above 2) also includes the following steps: 2.3) Construct equivalent control term u eq With switch item u sw as follows, （5）； Where 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.

5. The sliding mode control method for a permanent magnet synchronous fan based on a novel exponential control law as claimed in claim 4 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.

Images