Sensorless resonant frequency control method and system for linear compressor based on double SOGI

Abstract

The application discloses a kind of based on double SOGI linear compressor sensorless resonant frequency control method and system, belong to linear compressor resonant frequency tracking control technical field, the method according to linear compressor work in system resonant frequency point when piston stroke and current phase difference is 90 ° characteristics, using SOGI combines second-order low-pass filter to calculate the phase difference between stroke and current, and utilize P controller to control the phase difference to 90 °, to realize resonant frequency tracking;Sliding mode observer is constructed to observe motor back electromotive force information, and estimated back electromotive force signal is filtered using SOGI, to obtain almost no amplitude and phase shift piston stroke signal.The method proposed in the application can accurately track system resonant frequency, with small amount of calculation, simple operation, tracking precision and the like advantages.

Description

Technical Field

[0001] This invention belongs to the field of linear compressor resonant frequency tracking control technology, and more specifically, relates to a sensorless resonant frequency control method for linear compressors based on dual SOGI (second-order generalized integrator). Background Technology

[0002] Linear compressors are a new type of compressor that directly converts electromagnetic force into linear motion, and they have broad application prospects in cryogenic refrigeration, gasification and liquefaction, and other fields. Compared with traditional rotary motor-driven compressor systems, linear compressors eliminate the crank-connecting rod device, resulting in advantages such as simple structure, low noise, and adjustable stroke.

[0003] Linear compressors have a resonant frequency point; when the system operates at this resonant frequency, it achieves maximum output efficiency. Since the phase difference between the piston stroke and the current is exactly 90° when the linear compressor operates at the system's resonant point, some researchers have used this characteristic to achieve frequency tracking by controlling the phase difference between the motor's back EMF and the winding current. However, this method suffers from errors caused by zero-crossing detection during phase angle detection. To effectively avoid the detection errors caused by zero-crossing detection in phase angle detection, and to reduce periodic error interference in sampling, some researchers have achieved compressor resonant frequency tracking control by controlling the average value of the product of piston stroke and current to be zero. However, because the frequency constantly changes during the control process, calculating the average value of the definite integral is extremely difficult, resulting in severe oscillations and a large computational burden.

[0004] As is known from existing resonant frequency tracking control methods, the piston stroke signal is crucial for tracking the system's resonant frequency. Furthermore, since the piston stroke of a linear compressor is unrestricted, excessive voltage can cause the piston stroke to exceed the maximum allowable range, leading to piston collision. Therefore, closed-loop control of the piston stroke is necessary. While position sensors can provide accurate piston stroke signals, this method suffers from difficulties in sensor installation and maintenance, high cost, and increased system size. Consequently, researchers have explored sensorless control of linear compressors. Currently, the most common method is to directly calculate the motor's back electromotive force (EMF) based on the voltage equation, and then calculate the piston speed signal based on the proportional relationship between the back EMF and piston speed. Finally, the piston speed signal is integrated to obtain the piston stroke signal. However, this method is an open-loop calculation, and its estimation accuracy is easily affected by motor parameters, requiring improvement. In summary, existing resonant frequency tracking methods heavily rely on the piston stroke signal, resulting in severe oscillations and low tracking accuracy. Moreover, sensorless methods exhibit poor parameter robustness, and the accuracy of stroke observation needs further improvement. Summary of the Invention

[0005] To address the shortcomings and improvement needs of existing technologies, this invention provides a sensorless resonant frequency control method and system for a linear compressor based on dual SOGI, aiming to improve the accuracy of resonant frequency estimation while achieving resonant frequency tracking and sensorless piston stroke closed-loop control.

[0006] To achieve the above objectives, the present invention provides a sensorless resonant frequency control method for a linear compressor based on dual SOGI, comprising the following steps:

[0007] S1. The SOGI method is used to orthogonalize the current signal of the linear compressor to obtain an orthogonal current signal;

[0008] S2. Multiply the linear compressor piston stroke signal with the current signal and the current quadrature signal respectively, and filter them respectively to obtain two sets of DC components;

[0009] S3. Calculate the ratio of the two DC components to obtain the cotangent value of the phase difference of the stroke current; use the P controller to adjust the cotangent value to 0 to ensure that the phase difference between the piston stroke and the current signal is 90°; add the frequency change during the adjustment process to the original operating frequency of the motor to realize the system resonant frequency tracking control.

[0010] S4. Based on the motor voltage equation, design a sliding mode observer to observe the motor back electromotive force signal;

[0011] S5. Obtain the piston speed signal based on the back electromotive force signal observed by the sliding mode observer, and use SOGI to filter and integrate the piston signal to obtain the estimated piston stroke signal.

[0012] S6. The estimated piston stroke signal is used for product calculation of the resonant frequency tracking method and piston stroke closed-loop control, thereby realizing sensorless resonant frequency tracking control.

[0013] Further, the method described in step S1 includes:

[0014] The transfer function used for SOGI is:

[0015]

[0016]

[0017] in Forward transfer function, It is an orthogonal transfer function. For the independent variables of the transfer function, For input signal, This is the filtered output signal. The quadrature signals of the filtered output signal are... Here is the filter constant. The center frequency.

[0018] Furthermore, the expression for the linear compressor current signal is:

[0019]

[0020] Furthermore, the expression for the current orthogonal signal after SOGI orthogonalization is:

[0021]

[0022] in, This represents the peak current.

[0023] Further, the method described in step S2 includes:

[0024] The expression for the piston stroke signal is:

[0025]

[0026] The product of the piston stroke signal and the current signal is calculated as follows:

[0027]

[0028] The product of the piston stroke signal and the orthogonal current signal is calculated as follows:

[0029]

[0030] The transfer function of the second-order low-pass filter used is:

[0031]

[0032] in, For cutoff filtering, is the filter constant.

[0033] Furthermore, by filtering the stroke-galvanometer stroke-current quadrature signals separately using a second-order low-pass filter, two sets of DC components are obtained:

[0034]

[0035]

[0036] in, It is an abbreviation for low-pass filter.

[0037] Further, the method described in step S3 includes:

[0038] The cotangent of the phase difference of the travel current is obtained by comparing the DC components filtered by the second-order low-pass filter.

[0039]

[0040] Furthermore, by using a P controller to adjust the cotangent value to 0, it can be ensured that the phase difference between the piston stroke and the current signal is 90°. By accumulating the frequency change controlled by the P controller to the original operating frequency of the motor, the system resonant frequency can be obtained, thus achieving resonant frequency tracking control.

[0041] Further, the method described in step S4 includes:

[0042] The voltage equation for a linear compressor is:

[0043]

[0044] in, For resistance, For inductance, For output voltage, For sampling current, This is the back electromotive force of the motor.

[0045] Furthermore, the voltage equation can be rewritten as a current state equation:

[0046]

[0047] Furthermore, the sliding mode observer is designed based on the current state equation as follows:

[0048]

[0049] in, To observe the current, To switch the gain, It is a saturation function. To observe the current.

[0050] Further, the method described in step S5 includes:

[0051] The back electromotive force information obtained using a sliding mode observer is as follows:

[0052]

[0053] in, The observed back electromotive force.

[0054] Furthermore, based on the relationship between the motor's back electromotive force and its speed, the estimated piston speed signal is obtained as follows:

[0055]

[0056] Furthermore, by filtering and integrating the estimated speed signal using SOGI, the piston stroke estimation signal can be obtained. .

[0057] Furthermore, the stroke estimation signal obtained using the sliding mode observer and SOGI in step S6 is used not only for the product calculation of the resonant frequency tracking method, but also for the piston stroke closed-loop control. Therefore, the method proposed in this paper can realize sensorless resonant frequency tracking control of a linear compressor.

[0058] The present invention also provides a sensorless resonant frequency control system for a linear compressor based on dual SOGI, comprising: a computer-readable storage medium and a processor;

[0059] The computer-readable storage medium is used to store executable instructions;

[0060] The processor is used to read the executable instructions stored in the computer-readable storage medium and execute the above-described sensorless resonant frequency control method for a linear compressor based on dual SOGI.

[0061] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art:

[0062] (1) Compared with existing methods, the linear compressor resonant frequency tracking control method provided by the present invention has strong parameter robustness of the sliding mode observer based on saturation function, which can greatly improve the accuracy of stroke estimation. The proposed dual SOGI resonant frequency tracking method is not affected by piston stroke changes, which significantly improves the anti-interference ability of the algorithm.

[0063] (2) Compared with the traditional open-loop back EMF integration method, the piston stroke signal is observed by a sliding mode observer, which greatly improves the parameter robustness of the algorithm and the stroke estimation accuracy is high.

[0064] (3) A dual SOGI structure is adopted, in which one SOGI is used in the resonant frequency tracking method to generate current quadrature signals, and the other SOGI is used as a sliding mode observer to replace the pure integrator to obtain the piston stroke signal accurately.

[0065] (4) By combining the sliding mode observer with the resonant frequency tracking method, the sensorless resonant frequency tracking control of the high-performance linear compressor can be realized. Attached Figure Description

[0066] Figure 1 Block diagram of a sensorless resonant frequency control method for a linear compressor based on dual SOGI;

[0067] Figure 2Block diagram of resonant frequency tracking control method based on piston stroke-current phase difference

[0068] Figure 3 Piston stroke estimation results based on sliding mode observer combined with SOGI;

[0069] Figure 4 Resonant frequency tracking results;

[0070] Figure 5 The relationship between piston stroke and current phase under steady state. Detailed Implementation

[0071] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0072] This invention provides a sensorless resonant frequency control method for a linear compressor based on dual SOGI, and its control system structure block diagram is shown below. Figure 1 As shown, it includes the following steps:

[0073] S1. The SOGI method is used to orthogonalize the current signal of the linear compressor to obtain an orthogonal current signal;

[0074] Specifically, the transfer function for SOGI is:

[0075]

[0076]

[0077] The expression for the current signal of a linear compressor is:

[0078]

[0079] The expression for the current orthogonal signal after SOGI orthogonalization is:

[0080]

[0081] S2. The linear compressor piston stroke signal is multiplied by the current signal and the current orthogonal signal respectively, and then filtered by a second-order low-pass filter to obtain two sets of DC components.

[0082] Specifically, the expression for the piston stroke signal is:

[0083]

[0084] The product of the piston stroke signal and the current signal is calculated as follows:

[0085]

[0086] The product of the piston stroke signal and the orthogonal current signal is calculated as follows:

[0087]

[0088] The transfer function of the second-order low-pass filter used is:

[0089]

[0090] The stroke-current quadrature signals from the galvanometer and the travel meter are filtered separately using a second-order low-pass filter, resulting in two sets of DC components:

[0091]

[0092]

[0093] S3. Calculate the ratio of the two DC signals to obtain the cotangent value of the phase difference of the stroke current; use the P controller to adjust the cotangent value to 0 to ensure that the phase difference between the piston stroke and the current signal is 90°; add the frequency change during the adjustment process to the original operating frequency of the motor to achieve resonant frequency tracking control.

[0094] Specifically, by comparing the DC components filtered by the second-order low-pass filter, the cotangent value of the phase difference of the travel current is obtained as follows:

[0095]

[0096] The structural block diagram of the resonant frequency tracking control method constructed by S2-S3 is as follows: Figure 2 As shown.

[0097] S4. Based on the motor voltage equation, design a sliding mode observer to observe the motor back electromotive force signal;

[0098] Specifically, the voltage equation for the linear compressor is:

[0099]

[0100] Rewrite the voltage equation as a current state equation:

[0101]

[0102] The sliding mode observer is designed based on the current state equation as follows:

[0103]

[0104] S5. Obtain the piston speed signal based on the back electromotive force signal observed by the sliding mode observer, and use SOGI to filter and integrate the piston signal to obtain a piston stroke signal with almost no amplitude and phase shift.

[0105] Specifically, the back electromotive force information obtained using the sliding mode observer is as follows:

[0106]

[0107] The relationship between the back electromotive force of the motor and its speed is as follows:

[0108]

[0109] Based on the observed back electromotive force The estimated velocity signal is:

[0110]

[0111] S6. The estimated piston stroke signal is used for product calculation of the resonant frequency tracking method and piston stroke closed-loop control, thereby realizing sensorless resonant frequency tracking control.

[0112] Example:

[0113] This embodiment takes a linear compressor driven by a linear oscillating motor as an example to simulate and verify the above method. The rated power is set to 120W, the system resonant frequency is 23.41Hz, the stator resistance is 18.4Ω, the stator inductance is 0.755H, the thrust coefficient is 30N / A, and the mass of the mover piston is 1.03kg.

[0114] The piston stroke reference amplitude is set to 5mm, and the initial operating frequency is 21Hz. For example... Figure 3 As shown, the proposed sliding mode observer can accurately estimate the piston stroke signal. Figure 4 As shown, the proposed resonant frequency tracking method can accurately track the system's resonant frequency. Figure 5 As shown, once the control system stabilizes, the phase difference between the piston stroke and the current is 90°, which verifies the effectiveness of the resonant frequency tracking method.

[0115] Those skilled in the art will readily understand that the above description is merely 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 within the scope of protection of the present invention.

Claims

1. A sensorless resonant frequency control method for a linear compressor based on dual SOGI, characterized in that, Includes the following steps: S1. The SOGI method is used to orthogonalize the current signal of the linear compressor to obtain an orthogonal current signal; S2. Multiply the linear compressor piston stroke signal with the current signal and the current quadrature signal respectively, and filter them respectively to obtain two sets of DC components; S3. Calculate the ratio of the two DC components to obtain the cotangent value of the phase difference of the stroke current; use the P controller to adjust the cotangent value to 0 to ensure that the phase difference between the piston stroke and the current signal is 90°; add the frequency change during the adjustment process to the original operating frequency of the motor to achieve resonant frequency tracking control. S4. Based on the motor voltage equation, design a sliding mode observer to observe the motor back electromotive force signal; S5. Obtain the piston speed signal based on the back electromotive force signal observed by the sliding mode observer, and use SOGI to filter and integrate the piston signal to obtain the estimated piston stroke signal. S6. The estimated piston stroke signal is used for product calculation of the resonant frequency tracking method and piston stroke closed-loop control, thereby realizing sensorless resonant frequency tracking control.

2. The control method according to claim 1, characterized in that, The transfer function of SOGI in step S1 is: in Forward transfer function, It is an orthogonal transfer function. For the independent variables of the transfer function, For input signal, This is the filtered output signal. The quadrature signals of the filtered output signal are... Here is the filter constant. The center frequency; The expression for the linear compressor current signal is: The expression for the current orthogonal signal after SOGI orthogonalization is: in, This represents the peak current.

3. The control method according to claim 2, characterized in that, Step S2 includes: The expression for the piston stroke signal is: The product of the piston stroke signal and the current signal is calculated as follows: The product of the piston stroke signal and the orthogonal current signal is calculated as follows: in, This represents the stroke amplitude.

4. The control method according to claim 3, characterized in that, The transfer function of the second-order low-pass filter used for filtering is: in, For cutoff filtering, Here is the filter constant; By filtering the product of the travel signal and the current signal, and the product of the travel signal and the current quadrature signal, using a second-order low-pass filter, two sets of DC components are obtained: in, It is an abbreviation for low-pass filter.

5. The control method according to claim 3, characterized in that, Step S3 includes: The cotangent of the phase difference of the travel current is obtained by comparing the DC components filtered by the second-order low-pass filter. By using a P controller to adjust the cotangent value to 0, it can be ensured that the phase difference between the piston stroke and the current signal is 90°. By accumulating the frequency change controlled by the P controller to the original operating frequency of the motor, the system resonant frequency can be obtained, thus realizing resonant frequency tracking control.

6. The control method according to claim 1, characterized in that, The voltage equation in step S4 is: in, For resistance, For inductance, For output voltage, For sampling current, This is the back electromotive force of the motor; Rewrite the voltage equation as a current state equation: The sliding mode observer is designed based on the current state equation as follows: in, To observe the current, To switch the gain, It is a saturation function. To observe the current.

7. The control method according to claim 6, characterized in that, Step S5 includes: The back electromotive force information obtained using a sliding mode observer is as follows: in, For the observed back electromotive force; The relationship between the back electromotive force of the motor and its speed is as follows: in, This is the thrust coefficient; Based on the observed back electromotive force The estimated velocity signal is: By using SOGI to filter the speed signal, a piston stroke estimation signal can be obtained. .

8. The control method according to claim 1, characterized in that, The stroke signal obtained in step S5 can be used for product calculation and piston stroke closed-loop control during the resonant frequency tracking process, thereby realizing sensorless resonant frequency tracking control.

9. A sensorless resonant frequency control system for a linear compressor based on dual SOGI, characterized in that, include: Computer-readable storage media and processors; The computer-readable storage medium is used to store executable instructions; The processor is used to read executable instructions stored in the computer-readable storage medium and execute the sensorless resonant frequency control method for a linear compressor based on dual SOGI as described in any one of claims 1 to 8.

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