Resonant frequency tracking control method and device for linear compressor based on linear superspiral sliding mode

Abstract

The invention discloses a linear compressor resonant frequency tracking control method and device based on a linear super-spiral sliding mode, and belongs to the technical field of linear compressor sensorless resonant frequency tracking control, and the method comprises the steps: constructing a linear super-spiral sliding mode observer to observe a motor back electromotive force signal, and calculating a speed observation signal; a third-order generalized integrator is adopted to carry out filtering processing on the observed speed signal, and a discretization implementation mode of the third-order generalized integrator is designed based on a forward Euler method; a filtered stroke signal is directly obtained by using an orthogonal filtering characteristic of a third-order generalized integrator; and carrying out product calculation on the obtained stroke signal and the obtained current signal, carrying out filtering processing on the product value by adopting a low-pass filter to obtain a direct-current component containing stroke current phase difference information, and further controlling the direct-current component to be 0 by adopting a P controller, so that the stroke current phase difference is always 90 degrees, and resonant frequency tracking control is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of position sensorless resonant frequency tracking control of linear compressors, and in particular relates to a linear compressor resonant frequency tracking control method and device based on a linear super-helical sliding mode. Background Art

[0002] The compressor is the heart of the refrigeration (heat) system and is widely used in people's production and life. Compared with the traditional rotary compressor with a crank-connecting rod mechanism, the linear compressor uses a linear oscillation motor to directly drive the piston to perform linear reciprocating motion. It has the advantages of small size, high efficiency, and adjustable piston stroke. For linear compressors, if precise piston stroke control is to be implemented to achieve the required exhaust volume, it is necessary to obtain the piston mover position information in real time to achieve stroke closed-loop control. Considering that the piston and cylinder inside the linear compressor system are highly integrated, installing a position sensor will cause maintenance difficulties, increased volume, and reduced system reliability. For this reason, implementing position sensorless control is a necessary means to improve the performance of the linear compressor control system.

[0003] At present, there are relatively few studies on the position sensorless control of linear compressors, mainly focusing on the back-EMF integration method and sliding mode observer. The core idea of ​​these two methods is to obtain the back-EMF signal based on the voltage equation, and then use the proportional relationship between the back-EMF and the piston running speed to obtain the speed signal, and finally integrate the speed to obtain the stroke signal. Among them, the back-EMF integration method directly calculates the back-EMF based on the voltage equation, and then uses a pure integrator to integrate the back-EMF to obtain the piston stroke. The use of a pure integrator will continuously accumulate the DC component in the voltage and current signals, leading to the pure integral saturation problem. Compared with the back-EMF integration method, the sliding mode observer has the advantages of strong parameter robustness and high observation accuracy, and has attracted the attention of many scholars. However, the traditional sliding mode observer has serious sliding mode chattering problems, and the pure integral saturation problem has not been solved. To this end, it is necessary to study a higher-performance stroke observation method to improve the stroke observation accuracy and achieve efficient control of the linear compressor.

[0004] In addition, the linear compressor has a system resonant frequency point. Only when the system operates at the resonant frequency point can the maximum efficiency be obtained. Therefore, it is necessary to implement resonant frequency tracking control on the linear compressor. The traditional method often uses a search method, that is, directly searching for the maximum efficiency point to obtain the system resonant frequency. The present invention designs a resonant frequency tracking control method based on the characteristic that when the linear compressor operates at the system resonant frequency point, the current and stroke phase difference is 90°, and combines it with a stroke observer to realize position sensorless resonant frequency tracking control, so as to greatly improve the control system performance. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a linear compressor resonant frequency tracking control method based on linear super-helical sliding mode, which aims to solve the problems of inaccurate stroke observation, serious pure integral saturation, low resonant frequency tracking accuracy, etc. in the existing methods.

[0006] To achieve the above object, the present invention adopts the following technical solution: a linear compressor resonant frequency tracking control method based on linear super-helical sliding mode, comprising the following steps: Step S1. According to the voltage equation of the linear compressor, the current state equation is obtained, and a linear super-helical sliding mode observer is constructed to reconstruct the motor back electromotive force signal; Step S2. Calculate the piston speed observation signal according to the relationship that the back electromotive force is proportional to the piston speed; Step S3. Using a third-order generalized integrator to filter the piston speed observation signal, and discretizing the state equation of the third-order generalized integrator based on the forward Euler method, giving a discretized implementation form, and using the orthogonal property of the third-order generalized integrator to obtain the piston stroke observation signal; Step S4. Calculate the product of the piston stroke observation signal and the current signal to obtain a product value, and filter the product value with a low-pass filter to obtain a DC component containing a stroke current phase difference; Step S5. Use a P controller to control the DC component to zero, ensure that the phase difference of the stroke current is 90°, and realize resonant frequency tracking control; at the same time, use a PI controller to control the stroke observation signal to the stroke given value to realize position sensorless stroke closed-loop control.

[0007] The present invention also provides a linear compressor resonant frequency tracking control device based on linear super-helical sliding mode, comprising: a computer-readable storage medium and a processor; The computer-readable storage medium is used to store executable instructions; The processor is used to read the executable instructions stored in the computer-readable storage medium to execute the above-mentioned linear compressor resonant frequency tracking control method based on linear super-helical sliding mode of the present invention.

[0008] In general, compared with the prior art, the above technical solutions conceived by the present invention have the following beneficial effects: The linear compressor stroke observation method provided by the present invention has higher stroke observation accuracy than the existing method, and can further improve the position sensorless control performance; the constructed linear super-helical sliding mode observer can significantly reduce the sliding mode chattering and improve the observation accuracy; the third-order generalized integrator is used instead of the pure integrator, which can eliminate the influence of the DC component and improve the filter performance; the third-order generalized integrator is discretized based on the forward Euler method, which has the advantages of simple calculation and easy implementation; the stroke observer is combined with the resonant frequency tracking control method to realize position sensorless resonant frequency tracking control. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a structural block diagram of the linear compressor resonant frequency tracking control based on the super-helical sliding mode observer of the present invention; Figure 2 is a structural block diagram of a third-order generalized integrator of the present invention; Figure 3 It is a travel observation result using different filters provided by an embodiment of the present invention; Figure 4 It is a stroke observation result using different sliding mode observers provided in an embodiment of the present invention; Figure 5 This is the control result of the present invention combining the linear super-helical sliding mode observer with the designed resonant frequency tracking. DETAILED DESCRIPTION

[0010] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0011] The present invention provides a linear compressor resonant frequency tracking control method based on a super-helical sliding mode observer, and the control system structure block diagram is as follows: Figure 1 As shown in the figure To observe the travel signal, and are the amplitudes of the stroke reference value and the stroke observation signal, respectively, and SPWM is sinusoidal pulse width modulation. The overall control of the linear oscillation motor can be briefly described as follows: first, a linear super-helical sliding mode observer is constructed based on the voltage equation to obtain the motor back electromotive force signal; the speed observation signal is calculated using the proportional relationship between the back electromotive force and the speed; a third-order generalized integrator is used to filter the observed speed signal, such as Figure 2As shown, the orthogonal signal is output, which is the piston stroke signal. Then, the piston stroke signal is multiplied with the current signal, and the DC component of the product value is obtained by a low-pass filter. The P controller is used to control it to 0, which can ensure that the phase difference of the stroke current is 90°. In addition, the amplitude of the piston stroke signal is calculated, and it is subtracted from the stroke reference value. The PI controller is used to adjust the stroke error. The PI output value is the voltage signal required for the linear oscillation motor to operate. The voltage signal output by the PI controller and the frequency signal output by the P controller are used to implement SPWM signal modulation, thereby realizing the amplitude and frequency adjustment of the motor operating voltage.

[0012] Specifically, the method comprises the following steps: Step S1. According to the voltage equation of the linear compressor, the current state equation is obtained, and a linear super-helical sliding mode observer is constructed to reconstruct the motor back electromotive force signal; Specifically, the voltage equation of the linear compressor is: ; in, , , , They are stator resistance, stator inductance, armature current and armature voltage respectively. is the motor back electromotive force, and t is the time.

[0013] According to the voltage equation, the current state equation can be obtained as: ; The linear super-helical sliding mode observer can be constructed from the current state equation as follows; ; in, is the current observation signal, is the current observation error, , is the gain coefficient, is the switch function.

[0014] Thus, the reconstructed back EMF signal can be obtained for: ; S2. Calculate the piston speed observation signal according to the proportional relationship between the back electromotive force and the piston speed; Specifically, the linear oscillation motor back electromotive force observation signal With piston speed observation signal The relationship is: ; in, Electromagnetic thrust.

[0015] S3. A third-order generalized integrator is used to filter the piston speed observation signal, and the state equation of the third-order generalized integrator is discretized based on the forward Euler method, and a discretization implementation form is given; according to the orthogonal property of the third-order generalized integrator, the piston stroke observation signal can be obtained; Specifically, the transfer function of the third-order generalized integrator is: ; ; Among them, a is an independent state variable, and are the forward transfer function and the quadrature transfer function respectively. is the input signal of the filter, is the positive output signal, is the quadrature output signal, and is the gain coefficient, is the center frequency of the filter.

[0016] Therefore, the state equation can be obtained as: ; ; in, , , Represent the three state variables of the third-order generalized integrator, , , are the first-order derivatives of the three state variables respectively; and are the filtering output variable and the orthogonal output variable of the third-order generalized integrator respectively; is the output variable matrix of the third-order generalized integrator; Specifically, the discretization form of the forward Euler method is: ; Where T is the sampling period, Represents the moment, is the state variable of the forward Euler method The first derivative of ; Specifically, the discretization implementation form of the third-order generalized integrator is: ; ; Solving the above equation, we can get the piston observation stroke signal: for .

[0017] S4. Calculate the product of the stroke observation signal and the current signal, filter the product value with a low-pass filter, and obtain a DC component containing a stroke current phase difference; Specifically, the sinusoidal expressions of the travel observation signal and the current signal are: ; ; in, is the current amplitude, is the motor frequency, is the stroke amplitude, It is the phase difference between stroke and current action.

[0018] Therefore, the product of the travel observation signal and the current signal is: ; The low-pass filter is: ; in, is the cut-off frequency, is the complex variable of the transfer function. After filtering by a low-pass filter, the DC component containing the phase difference of the stroke current can be obtained. .

[0019] S5. Use the P controller to control the DC component to zero, ensure that the phase difference of the stroke current is 90°, and realize resonant frequency tracking control; at the same time, use the PI controller to control the stroke observation signal to the stroke given value to realize position sensorless stroke closed-loop control.

[0020] Example This embodiment takes a 120W linear compressor as an example to simulate and verify the above method. The motor stator resistance is 18.4Ω, the stator inductance is 0.755H, the thrust coefficient is 30N / A, and the mover piston mass is 1.03kg.

[0021] The system operating frequency is set to 22Hz, the DC components of current and voltage are 0.1A and 0.1V respectively, and the travel observation results of the motor with two different filters are as follows under open-loop operation: Figure 3 As shown. It can be seen that the travel observation method based on the second-order generalized integrator is greatly affected by the DC component and has the problem of integral drift, while the travel observation method using the third-order generalized integrator can completely eliminate the influence of the DC component. The system operating frequency is set to 23.48Hz, the travel reference amplitude is 5mm, and the third-order generalized integrator is selected instead of the pure integrator. The traditional sliding mode observer and the proposed sliding mode observer are used for travel observation respectively. The results are shown in Figure 4As shown in Figure 2, it can be seen that compared with the traditional sliding mode observer, the designed linear super-helical sliding mode observer has higher stroke observation accuracy. The observed stroke signal is used for resonant frequency tracking control, and the results are shown in Figure 2. Figure 5 Obviously, the proposed method can control the phase difference between stroke and current to 90°, and realize position sensorless resonant frequency tracking control.

[0022] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A resonant frequency tracking control method for a linear compressor based on linear super-helical sliding mode. It is characterized in that The following steps are involved: Step S1. According to the voltage equation of the linear compressor, the current state equation is obtained, and a linear super-helical sliding mode observer is constructed to reconstruct the motor back electromotive force signal; Step S2. Calculate the piston speed observation signal according to the relationship that the back electromotive force is proportional to the piston speed; Step S3. Using a third-order generalized integrator to filter the piston speed observation signal, and discretizing the state equation of the third-order generalized integrator based on the forward Euler method, giving a discretized implementation form, and using the orthogonal property of the third-order generalized integrator to obtain the piston stroke observation signal; Step S4. Calculate the product of the piston stroke observation signal and the current signal to obtain a product value, and filter the product value with a low-pass filter to obtain a DC component containing a stroke current phase difference; Step S5. Use a P controller to control the DC component to zero, ensure that the phase difference of the stroke current is 90°, and realize resonant frequency tracking control; at the same time, use a PI controller to control the stroke observation signal to the stroke given value to realize position sensorless stroke closed-loop control.

2. According to claim 1, the linear compressor resonant frequency tracking control method based on linear super-helical sliding mode, It is characterized in that The voltage equation of the linear compressor in step S1 is: ； in, , , , They are stator resistance, stator inductance, armature current, and armature voltage, respectively. is the motor back electromotive force, t is the time; According to the voltage equation, the current state equation is: ； The linear super-helical sliding mode observer is constructed from the current state equation: ； in, is the current observation signal, is the current observation error, , is the gain coefficient, is the switch function; Thus, the reconstructed back electromotive force signal is obtained for: 。 3. The linear compressor resonant frequency tracking control method based on linear super-helical sliding mode according to claim 2, It is characterized in that In step S2, the motor back electromotive force observation signal With piston speed observation signal The relationship is: ； in, Electromagnetic thrust.

4. The linear compressor resonant frequency tracking control method based on linear super-helical sliding mode according to claim 3, It is characterized in that In step S3, the transfer function of the third-order generalized integrator is: ； ； Among them, a is an independent state variable, and are the forward transfer function and the orthogonal transfer function respectively, is the input signal of the filter, is the positive output signal, is the quadrature output signal, and is the gain coefficient, is the center frequency of the filter; The state equation of the third-order generalized integrator is: ； ； in, , , Represent the three state variables of the third-order generalized integrator, , , are the first-order derivatives of the three state variables respectively; and are the filtering output variable and the orthogonal output variable of the third-order generalized integrator respectively; is the output variable matrix of the third-order generalized integrator; The discretization form of the forward Euler method is: ； Where T is the sampling period, Represents the moment, is the state variable of the forward Euler method The first derivative of ; The discretization implementation form of the third-order generalized integrator is: ； ； Solve the above equation to get the piston observation stroke signal: for .

5. The linear compressor resonant frequency tracking control method based on linear super-helical sliding mode according to claim 1, It is characterized in that In step S4, the sinusoidal expressions of the observed travel signal and the current signal are: ； ； in, is the current amplitude, is the stroke amplitude, is the motor frequency, It is the phase difference between stroke and current action; Therefore, the product of the stroke and the current signal is: ； The low-pass filter is: ； in, is the cut-off frequency, is the complex variable of the transfer function; after filtering by a low-pass filter, the DC component containing the phase difference of the stroke current is obtained .

6. The linear compressor resonant frequency tracking control method based on linear super-helical sliding mode according to claim 1, It is characterized in that In step S5, the P controller is used to control the DC component to zero to ensure that the phase difference of the stroke current is 90°; the PI controller can The amplitude Control is the stroke given value .

7. A linear compressor resonant frequency tracking control device based on linear super-helical sliding mode, It is characterized in that comprising a computer readable storage medium and a processor; The computer-readable storage medium is used to store executable instructions; The processor is used to read the executable instructions stored in the computer-readable storage medium to execute the linear compressor resonant frequency tracking control method based on linear super-helical sliding mode according to any one of claims 1 to 6.

Images