Permanent magnet synchronous motor control method and system of improved sliding mode observer

Abstract

The invention provides an improved sliding-mode observer for permanent magnet synchronous motor position sensorless control. A traditional sliding-mode observer can cause a jitter phenomenon of observation information in motor control. According to the method, the control equation of the sliding-mode observer is redesigned, the adaptive rate is combined, and a low-pass filter is replaced, so that the estimation precision of the back electromotive force is improved. A hyperbolic tangent function is used to replace a sign function to alleviate the jitter problem of the observer, and a phase-locked loop technology is used to replace an arc tangent function to reduce estimation errors and phase delay. The feasibility of the control system is verified by building a system simulation model based on a static coordinate system in MATLAB / Simulink. A simulation result shows that the control system reduces the rotor speed error and the rotor position error, so that the control performance and the stability of the permanent magnet synchronous motor are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of motor control, and in particular to a permanent magnet synchronous motor control method and system with an improved sliding mode observer. Background Art

[0002] Permanent magnet synchronous motors are widely used in fields that require high control accuracy and reliability, such as high-precision CNC machines, electric vehicles, and robot manufacturing, due to their simple structure, light weight, small size, durable and reliable operation, high power factor, and high torque / weight ratio. These features make them easy to dissipate heat and maintain. In recent years, with the reduction in the price of rare earth materials, the replacement of power electronic devices and special motor control chips, and the continuous innovation in the field of permanent magnet synchronous motor control, permanent magnet synchronous motor speed control systems have been widely recognized and applied in more and more fields.

[0003] The speed and current dual closed-loop vector control strategy has become a hot topic in the research and application of high-performance speed control systems for permanent magnet synchronous motors in recent years. The core idea is to convert the three-phase stator current into a rotating coordinate system through vector transformation, decouple it into torque component current and excitation component current, and directly control these two currents to achieve direct control of the motor torque. This method makes the speed regulation performance of AC motors close to that of separately excited DC motors, bringing torque response, speed control accuracy and speed regulation range comparable to those of DC motors. In order to achieve speed and current dual closed-loop vector control, it is necessary to accurately and real-timely obtain the motor speed and rotor position information.

[0004] In the traditional permanent magnet synchronous motor speed control system, mechanical sensors such as tachometer generators and photoelectric encoders are usually installed on the rotor shaft to detect the speed and rotor position. However, this method will bring a series of problems: the system cost increases, the circuit between the motor and the controller is more susceptible to interference, the system reliability is reduced, and the use of sensors has strict requirements on the installation location, ambient temperature and humidity, which limits the promotion and application of permanent magnet synchronous motor speed control systems. In order to solve these problems, position sensorless can be applied to vector control strategies. This method abandons the traditional mechanical sensors, detects physical quantities such as the three-phase stator current and three-phase voltage of the motor, and uses a specific rotor position estimation algorithm to extract the speed and rotor position information for the feedback of the double closed-loop vector control. This solves all the disadvantages of mechanical sensors, reduces system costs, improves system reliability, and reduces the requirements for the installation environment, making the application of permanent magnet synchronous motor speed control systems more extensive. Summary of the invention

[0005] The purpose of the present invention is to provide a permanent magnet synchronous motor control method and system with an improved sliding mode observer, wherein the method has better observation accuracy and smaller jitter than a traditional sliding mode observer.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0007] The permanent magnet synchronous motor control method and system of the improved sliding mode observer of the present invention comprises the following steps:

[0008] (1) The back EMF is estimated by using an improved sliding mode observer combined with a designed adaptive rate;

[0009] (2) The obtained back electromotive force is used to calculate the rotor position information and speed information through a phase-locked loop.

[0010] Furthermore, the step (1) includes the following steps:

[0011] Build a mathematical model of the motor:

[0012] The permanent magnet synchronous motor is a highly coupled and complex nonlinear system. Different mathematical models are usually used for different control algorithms. According to the difference in the position of the permanent magnet on the rotor, the current permanent magnet synchronous motors can be divided into two categories: one is to install the permanent magnet on the outer surface of the rotor, so that the d-axis and q-axis inductances of the motor are equal. This structure is simple and has low manufacturing cost, and is called a surface mounted permanent magnet synchronous motor; the other is to embed the permanent magnet inside the rotor, so that the d-axis and q-axis inductances of the motor are unequal. This structure has higher power density and dynamic performance, and is called an internal permanent magnet synchronous motor.

[0013] In order to simplify the analysis, the permanent magnet synchronous motor is assumed to be an ideal motor. The three-phase voltage equation of the surface-mounted permanent magnet synchronous motor in the natural coordinate system is transformed into the stationary coordinate system commonly used by the sliding mode observer through Clark transformation.

[0014] Under α-β, we can get:

[0015]

[0016] In order to facilitate the design of the sliding mode observer, the equation can be rewritten as follows:

[0017] d s / dt=Ai s +Bv s +K E e s

[0018] Where: i s =[i α i β ] T ;

[0019] e s =[e sα e sβ ] T =[-ψ f ω e sinθ e ψ f ω e cosθ e ] T is the stator back electromotive force, ψ f ,ω e ,θ e are permanent magnet flux, motor electrical angular velocity, and electrical angle respectively; v s =[v α v β ] T ;

[0020] Create a sliding mode observer:

[0021] First, define the sliding surface function Construct the sliding mode observation equation:

[0022]

[0023] in: are the estimated values ​​of the corresponding variables, k is the sliding mode gain and is a negative constant, tanh(s) is the hyperbolic tangent function;

[0024] In order to verify whether the constructed sliding mode observer converges, the Lyapunov function is taken

[0025] when The observer converges, that is

[0026] It can be deduced that:

[0027] It is worth mentioning that the selection of sliding mode gain k can be achieved by building a PMSM control model including a position sensor in Simulink. By using the real feedback value, the appropriate k value can be determined. This method can ensure the convergence and stability of the sliding mode observer;

[0028]

[0029] After the system enters the sliding surface, the observed value will jitter in a small range on the sliding surface, so it can be considered that the observed value is equal to the actual value, that is, We can get:

[0030]

[0031] It can be seen that the back EMF value obtained is a high-frequency switching signal;

[0032] To establish the adaptive rate:

[0033] In PMSM, the electrical time constant is very small, and it can be considered that the speed does not change in one cycle, that is, dw / dt = 0. s Differentiating it gives:

[0034]

[0035] Establish the adaptive rate for rotor position and speed estimation:

[0036]

[0037] Select the Lyapunov function, It can be deduced that:

[0038]

[0039] Substituting the formula into the selected Lyapunov function, we can get:

[0040]

[0041] It can be concluded from the formula that as long as f takes a positive constant That is, the designed adaptation rate is stable.

[0042] Furthermore, the implementation process of step (2) is as follows:

[0043] Since sliding mode control is accompanied by high-frequency jitter in sliding mode, if this back-EMF with high-frequency jitter is introduced into the rotor position estimation method of the inverse tangent function, the high-frequency jitter error will be amplified, resulting in a large angle error. This paper uses a phase-locked loop to calculate the position and speed information of the motor in the back-EMF;

[0044]

[0045] if It can be considered Then the estimated electrical angle can be expressed as:

[0046]

[0047] According to formula (11), we can get θ e arrive The transfer function of .

[0048]

[0049] Comparing the standard transfer function of the second-order system, we can see that:

[0050]

[0051] Further, based on the above-mentioned inventive concept, this paper proposes a permanent magnet synchronous motor control method and system with an improved sliding mode observer, characterized in that it includes: a speed loop PI controller, a q-axis current loop PI controller, an inverse Park transformation module, an SVPWM module, an inverter circuit, a current and voltage detection circuit, a permanent magnet synchronous motor, an adaptive sliding mode observer module, a phase-locked loop module, and a d-axis current loop PI controller;

[0052] After the permanent magnet synchronous motor is started, the voltage and current of the rotor are obtained through the detection circuit, and the voltage and current information are converted from the free coordinate system to the α-β coordinate system through Clark transformation;

[0053] The adaptive sliding mode observer calculates the back electromotive force containing the rotor speed and position information based on the converted voltage and current information, and finally extracts the rotor speed and position information from the back electromotive force through a phase-locked loop.

[0054] The beneficial effects of the present invention are as follows:

[0055] The present invention proposes a permanent magnet synchronous motor control method and system with an improved sliding mode observer, which improves the estimation accuracy of back electromotive force by rewriting the control equation of the traditional sliding mode observer and combining the designed adaptive rate to replace the low-pass filter. In addition, the hyperbolic tangent function is used to replace the sign function to alleviate the jitter problem of the sliding mode observer, and the phase-locked loop technology is used to replace the inverse tangent function to reduce the estimation error and phase delay. Finally, a system simulation model based on a stationary coordinate system is built in MATLAB / Simulink to verify the feasibility of the control system. The simulation results show that the control system reduces the rotor speed error by 33% and the rotor position error by 50%. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0057] Figure 1 Block diagram of the phase-locked loop for rotor position and speed estimation.

[0058] Figure 2 This is the block diagram of the permanent magnet synchronous motor position sensorless control.

[0059] Figure 3 The waveforms are simulated for the actual and estimated speed values.

[0060] Figure 4 To improve the speed error of the sliding mode observer.

[0061] Figure 5 is the speed error of the traditional sliding mode observer.

[0062] Figure 6 are the estimated and actual values ​​of the rotor position.

[0063] Figure 7 To improve the rotor position error of the sliding mode observer.

[0064] Figure 8 is the rotor position error of the sliding mode observer. DETAILED DESCRIPTION

[0065] The following describes the implementation methods of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific implementation methods, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the following embodiments and the features in the embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present application.

[0066] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on the present application, it should be understood by those skilled in the art that an aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number and aspect described herein can be used to implement the device and / or practice the method. In addition, other structures and / or functionalities other than one or more of the aspects described herein can be used to implement this device and / or practice this method.

[0067] It should also be noted that the diagrams provided in the following embodiments are only schematic illustrations of the basic concept of the present application, and the diagrams only show components related to the present application, rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component can be changed at will, and the component layout type may also be more complicated.

[0068] Additionally, in the following description, specific details are provided to facilitate a thorough understanding of the examples. However, it will be understood by those skilled in the art that the embodiments may be practiced without these specific details.

[0069] The present invention is further described in detail below with reference to the accompanying drawings.

[0070] Since sliding mode control is accompanied by high-frequency jitter in sliding mode, if this back-EMF with high-frequency jitter is introduced into the rotor position estimation method of the inverse tangent function, the high-frequency jitter error will be amplified, resulting in a large angle error. This paper uses a phase-locked loop to calculate the position and speed information of the motor in the back-EMF. Its principle block diagram is shown in the figure. Figure 1 shown.

[0071] Among them, the phase-locked loop is an electronic feedback system used to synchronize the frequency and phase of a signal. In motor control, it stabilizes the motor speed and position estimation by synchronizing the back electromotive force phase, thereby reducing the interference of high-frequency noise on the estimation accuracy.

[0072] like Figure 2 As shown in the figure, a Simulink model of a position sensorless control system of a permanent magnet synchronous motor is shown. The entire control system is a closed-loop control system that uses a sliding mode observer to estimate the rotor position and speed, thereby realizing position sensorless control of the permanent magnet synchronous motor.

[0073] The system mainly includes speed control, dq axis current control, SVPWM generation, inverter, permanent magnet synchronous motor, current and voltage observer and other parts.

[0074] Speed ​​Controller: First, the user provides a target speed (TL1). The speed controller part receives the target speed and the actual speed (Wm) and calculates the error between the two. This error signal is input to a proportional integral (PI) controller, which generates a target q-axis current (iq*). This target q-axis current is the key quantity used to control the motor torque.

[0075] dq axis current control: The dq axis current controller receives the target d axis current (id*) and the target q axis current (iq*), as well as the actual d axis current (id) and q axis current (iq). The d axis and q axis currents are controlled by two PI controllers respectively to generate the target d axis voltage (Vd*) and the target q axis voltage (Vq*). The d axis current here is usually set to zero to maximize the torque efficiency of the motor.

[0076] dq to α-β transformation: The generated target d-axis voltage (Vd*) and target q-axis voltage (Vq*) are converted into α-β axis voltages (Valpha and Vbeta) through the Anti-Park module. The purpose of this step is to adapt to the input requirements of the SVPWM (space vector pulse width modulation) algorithm.

[0077] SVPWM generation: The SVPWM generation module receives the α-β axis voltage (Valpha and Vbeta) and generates a pulse signal (pulse) for driving the inverter. SVPWM is a common technology used to control three-phase inverters. It can efficiently convert DC to AC while reducing harmonic distortion.

[0078] Inverter: The inverter module receives the pulse signal (pulse) and DC voltage (Vdc) generated by SVPWM and converts the DC voltage into a three-phase AC voltage (Uabc). This three-phase AC voltage is used to drive the permanent magnet synchronous motor to run.

[0079] Permanent magnet synchronous motor: It operates according to the input three-phase AC voltage (Uabc) and generates corresponding torque (Te), speed (Wm) and rotor position (The). These outputs are the key physical quantities of the system, among which the speed and rotor position are the feedback signals of the control system. Current and voltage observer: The current and voltage observer monitors the three-phase voltage (Uabc) and three-phase current (Iabc) in real time, and estimates the α-β axis voltage and current (Ealpha, Ebeta). These estimated values ​​are used for further rotor position and speed estimation.

[0080] Sliding Mode Observer: The sliding mode observer uses the estimated α-β axis voltage and current (Ealpha, Ebeta) to estimate the rotor position (theta_est) and speed (we_est). The sliding mode observer is a robust state estimator that is particularly suitable for environments with large uncertainties and disturbances in motor control systems.

[0081] Feedback and calculation part: The system feeds back the estimated rotor position and speed to the controller for closed-loop control, adjusting the output to meet the target speed and position. The feedback signal is used to adjust the output of the PI controller to reduce errors and improve the dynamic response and steady-state accuracy of the system.

[0082] Figure 3 The simulation waveforms of the actual and estimated speed values ​​obtained by the improved sliding mode observer are shown. The dotted line represents the actual value and the solid line represents the estimated value. It can be seen that the difference between the actual value and the estimated value is very small. It can be seen from the figure that the speed can reach the set value twice in a very short time. When the torque changes, the system can still adjust quickly and reach the set speed. The stability of the control system is verified.

[0083] Figure 4 The error between the estimated speed and the actual speed of the improved sliding mode observer is shown. As can be seen from the figure, the maximum speed error occurs when the motor starts, which is -71r / min. When the set speed changes suddenly, the maximum speed error is -70r / min. When the motor is running steadily, the maximum speed error is 5r / min.

[0084] Figure 5 The speed error diagram of the traditional sliding mode observer is shown. In contrast, the maximum speed error when the motor starts is , when the set speed changes suddenly, the maximum speed error is , and the maximum speed error when the motor is running steadily is . From the above analysis, it can be seen that the improved sliding mode observer can estimate the speed information with a smaller error when the motor starts and the speed is stable.

[0085] Figure 6 The waveforms of the estimated and actual rotor position values ​​obtained by the improved sliding mode observation are shown. It can be seen from the figure that the estimated rotor position and the actual rotor position basically coincide with each other, and there is basically no phase lag.

[0086] Figure 7 is the rotor position error of the improved sliding mode observer. The maximum rotor position estimation error is 0.028 rad, and the maximum error is 0.021 rad when the motor is stable.

[0087] Figure 8 is the rotor position error of the sliding mode observer. The maximum rotor position estimation error is 0.046 rad, and the maximum error is 0.042 rad when the motor is stable.

[0088] It should be noted that the terms "first", "second", "third", "fourth", etc. (if any) in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein.

[0089] The same or similar parts between the various embodiments in this specification can be referred to each other, and each embodiment focuses on the differences from other embodiments. Especially for the product embodiment described later, since it corresponds to the method, the description is relatively simple, and the relevant parts can be referred to the partial description of the system embodiment.

[0090] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A permanent magnet synchronous motor control method and system with an improved sliding mode observer, characterized in that: The following steps are involved: (1) The back EMF is estimated by using an improved sliding mode observer combined with a designed adaptive rate; (2) The obtained back electromotive force is used to calculate the rotor position information and speed information through a phase-locked loop.

2. The permanent magnet synchronous motor control method and system of the improved sliding mode observer according to claim 1, characterized in that: The step (1) comprises the following steps: Build a mathematical model of the motor: In order to facilitate the design of the sliding mode observer, the equation can be rewritten as formula (2): d s / dt=Ai s +Bv s +K E e s (Formula 2) Among them: i s =[i α i β ] T ; e s =[e sα e sβ ] T =[-ψ f ω e sinθ e ψ f ω e cosθ e ] T is the stator back electromotive force, ψ f ,ω e ,θ e are permanent magnet flux, motor electrical angular velocity, and electrical angle respectively; v s =[v α v β ] T ; Create a sliding mode observer: First, define the sliding surface function At the same time, the sliding mode observation equation is constructed according to formula (II): in: are the estimated values ​​of the corresponding variables, k is the sliding mode gain and a negative constant, tanh(s) is the hyperbolic tangent function; to verify whether the constructed sliding mode observer converges, the difference between formula (3) and formula (2) is obtained: After the system enters the sliding surface, the observed value will jitter in a small range on the sliding surface, so it can be considered that the observed value is equal to the actual value, that is, From formula (IV), we can get: From formula (5), we can know that the back electromotive force value obtained is a high-frequency switching signal; To establish the adaptive rate: In PMSM, the electrical time constant is very small, and it can be considered that the speed does not change in one cycle, that is, dw / dt = 0; s Differentiating it gives: The adaptive rate of rotor position and speed estimation is established according to formula (VI): Select the Lyapunov function, According to formula (VII), we can deduce: Substituting formula (8) into the selected Lyapunov function, we can obtain: From formula (IX), we can conclude that as long as f is a positive constant That is, the designed adaptation rate is stable.

3. The permanent magnet synchronous motor control method and system with improved sliding mode observer according to claim 1, characterized in that: The step (2) comprises the following steps: Since sliding mode control is accompanied by high-frequency jitter in sliding mode, if this back-electromotive force with high-frequency jitter is introduced into the rotor position estimation method of the inverse tangent function, the high-frequency jitter error will be amplified, thereby causing a large angle error; the present application adopts a phase-locked loop to calculate the position and speed information of the motor in the back-electromotive force; the principle of the present application is as follows: if It can be considered Then the estimated electrical angle can be expressed as: According to formula (XI), θ e arrive The transfer function of Comparing the standard transfer function of the second-order system, we can see that:

4. A permanent magnet synchronous motor control method and system using the improved sliding mode observer of the method of claims 1-3, characterized in that: include: Speed ​​loop PI controller, q-axis current loop PI controller, inverse Park transformation module, SVPWM module, inverter circuit, current and voltage detection circuit, permanent magnet synchronous motor, adaptive sliding mode observer module, phase-locked loop module, d-axis current loop PI controller; After the permanent magnet synchronous motor is started, the voltage and current of the rotor are obtained through the detection circuit, and the voltage and current information are converted from the free coordinate system to the α-β coordinate system through Clark transformation; The adaptive sliding mode observer calculates the back electromotive force containing the rotor speed and position information based on the converted voltage and current information, and finally extracts the rotor speed and position information from the back electromotive force through a phase-locked loop.

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