Control method for AC motor with LC filter

Abstract

The invention relates to the technical field of AC motor control, and discloses a control method for an AC motor with an LC filter, and the method comprises the steps: obtaining an instruction voltage vector and a current vector of an inverter end; estimating the voltage vector and the current vector of the motor end under the estimation coordinate system according to the instruction voltage vector and the current vector of the inverter end; and calculating a difference value between the corresponding stator flux linkage vectors according to the voltage vector and the current vector of the motor end under the estimation coordinate system, and estimating the position and the rotating speed of the motor rotor according to the calculated difference value. According to the invention, only the current vector at the inverter end needs to be measured, and the sensorless control of the AC motor with the LC filter can be realized without designing a high-order observer or a high-order controller.

Description

Technical Field

[0001] The invention relates to the technical field of AC motor control, and in particular to an AC motor control method with an LC filter. Background Art

[0002] In some applications involving long-line drive or high-speed motor drive, in order to reduce the voltage harmonics and current harmonics at the motor end to reduce system losses and extend the life of the motor, an LC filter is usually installed between the inverter and the motor. Due to the presence of the LC filter, the model order of the control object of the drive system increases, making the conventional motor current controller and position observer no longer applicable.

[0003] In order to solve this problem, some solutions have been proposed to achieve effective control of the motor current and correct estimation of the motor rotor position by simultaneously sampling the phase current at the motor end and the phase current at the inverter end. However, for general motor drives, such solutions require more current sensors, resulting in higher system costs. In addition, such solutions require redesign of the current control loop of the conventional vector control solution. In addition, high-order observers are required to estimate the motor rotor position, which increases the complexity of implementing such solutions and the difficulty of debugging. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides an AC motor control method with an LC filter.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0006] A method for controlling an AC motor with an LC filter comprises the following steps:

[0007] Obtaining the command voltage vector and current vector at the inverter end;

[0008] The voltage vector and the current vector at the motor end in the estimation coordinate system are estimated according to the command voltage vector and the current vector at the inverter end;

[0009] The difference between the corresponding stator flux vectors is calculated according to the voltage vector and the current vector at the motor end in the estimated coordinate system, and the position and speed of the motor rotor are estimated according to the calculated difference.

[0010] Preferably, estimating the voltage vector and current vector of the motor end in the coordinate system according to the command voltage vector and current vector of the inverter end includes:

[0011] The voltage vector at the motor end in the estimation coordinate system is estimated according to the command voltage vector and current vector at the inverter end;

[0012] The current vector at the motor terminal in the estimated coordinate system is estimated according to the voltage vector at the motor terminal in the estimated coordinate system.

[0013] Preferably, the voltage vector at the motor end in the estimation coordinate system is estimated according to the command voltage vector and current vector at the inverter end, specifically:

[0014] ud_m=ud-id_i×Lf×w_e-id_i×Rf

[0015] uq_m=uq-iq_i×Lf×w_e-iq_i×Rf

[0016] Among them, ud_m and uq_m are the direct-axis component and quadrature-axis component of the voltage vector at the motor end in the estimated coordinate system, ud and uq are the direct-axis component and quadrature-axis component of the voltage vector at the inverter end in the estimated coordinate system, id_i and iq_i are the direct-axis component and quadrature-axis component of the current vector at the inverter end in the estimated coordinate system, w_e is the estimated speed of the motor, Lf and Rf are the inductance and resistance of the LC filter, respectively.

[0017] Preferably, the current vector at the motor end in the estimated coordinate system is estimated according to the voltage vector at the motor end in the estimated coordinate system, specifically:

[0018] id_m=id_i-ud_m×s×C

[0019] iq_m=iq_i-uq_m×s×C

[0020] Among them, id_m and iq_m are the direct-axis component and quadrature-axis component of the current vector at the motor end in the estimated coordinate system, id_i and iq_i are the direct-axis component and quadrature-axis component of the current vector at the inverter end in the estimated coordinate system, ud_m and uq_m are the direct-axis component and quadrature-axis component of the voltage vector at the motor end in the estimated coordinate system, s is the differential operator in the frequency domain, and C is the capacitance of the LC filter.

[0021] Preferably, a high-pass filter is used to filter the current vector at the motor end in the estimated coordinate system according to the voltage vector at the motor end in the estimated coordinate system, specifically:

[0022]

[0023] Among them, id_m and iq_m are the direct-axis component and quadrature-axis component of the current vector at the motor end in the estimated coordinate system, id_i and iq_i are the direct-axis component and quadrature-axis component of the current vector at the inverter end in the estimated coordinate system, ud_m and uq_m are the direct-axis component and quadrature-axis component of the voltage vector at the motor end in the estimated coordinate system, s is the differential operator in the frequency domain, a is the filter coefficient of the high-pass filter, and C is the capacitance of the LC filter.

[0024] Preferably, calculating the difference between the corresponding stator flux vectors according to the voltage vector and the current vector at the motor end in the estimated coordinate system, and estimating the position and speed of the motor rotor according to the calculated difference includes:

[0025] The stator flux equation is established according to the voltage vector and current vector at the motor end in the estimated coordinate system;

[0026] A low-pass filter is used to filter the stator flux equation, a voltage model of the motor in the estimated coordinate system is established, and the stator flux vector of the motor is estimated to obtain the voltage model-stator flux vector in the estimated coordinate system;

[0027] According to the current vector at the motor end in the estimated coordinate system, a current model of the motor in the estimated coordinate system is established and the stator flux vector of the motor is estimated to obtain the current model-stator flux vector in the estimated coordinate system;

[0028] The position and speed of the motor rotor are estimated based on the difference between the voltage model-stator flux vector and the current model-stator flux vector in the estimated coordinate system.

[0029] Preferably, estimating the position and speed of the motor rotor according to the difference between the voltage model-stator flux vector and the current model-stator flux vector in the estimated coordinate system includes:

[0030] The rotor position angle estimation error is calculated according to the difference between the voltage model-stator flux vector and the current model-stator flux vector in the estimation coordinate system;

[0031] estimating the rotation speed of the motor rotor according to the rotor position angle estimation error;

[0032] The position angle of the motor rotor is estimated according to the rotation speed of the motor rotor.

[0033] Preferably, the rotor position angle estimation error is calculated according to the difference between the voltage model-stator flux vector and the current model-stator flux vector in the estimation coordinate system, specifically:

[0034]

[0035] Among them, △theta is the rotor position angle estimation error, atan is the inverse tangent function, sin is the sine function, cos is the cosine function, fd and fq are the direct-axis component and quadrature-axis component of the voltage model-stator flux vector in the estimated coordinate system, fdc and fqc are the direct-axis component and quadrature-axis component of the current model-stator flux vector in the estimated coordinate system, theta_a is the actual rotor position angle, and theta_e is the estimated rotor position angle.

[0036] Preferably, the speed of the motor rotor is estimated according to the rotor position angle estimation error, specifically:

[0037]

[0038] Among them, w_e is the estimated motor rotor speed, △theta is the rotor position angle estimation error, k is the integral gain coefficient, and s is the differential operator in the frequency domain.

[0039] Preferably, the position angle of the motor rotor is estimated according to the rotation speed of the motor rotor, specifically:

[0040]

[0041] Among them, theta_e is the estimated position angle of the motor rotor, w_e is the estimated speed of the motor rotor, and s is the differential operator in the frequency domain.

[0042] The present invention has the following beneficial effects:

[0043] The present invention first estimates the voltage vector and current vector at the motor end using the command voltage vector at the inverter end and the current vector at the inverter end, and then estimates the motor rotor position and speed based on the difference between the two stator flux vectors in the estimated coordinate system. The present invention does not need to measure the phase current on the motor side, but only needs to measure the phase current on the inverter side; in addition, the present invention uses a voltage model and a current model based on vector control to estimate the motor stator flux vector in the estimated coordinate system, and then estimates the motor rotor position and speed based on the difference between the two stator flux vectors, that is, the present invention does not need to design a high-order observer or a high-order controller, and its calculation amount is small, and there are fewer adjustable parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a flow chart of a method for controlling an AC motor with an LC filter;

[0045] Figure 2 This is a schematic diagram of the principle of an AC motor control system with an LC filter. DETAILED DESCRIPTION

[0046] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0047] like Figure 1 As shown, an AC motor control method with an LC filter provided by an embodiment of the present invention includes the following steps S1 to S3:

[0048] S1, obtaining the command voltage vector and current vector at the inverter end;

[0049] S2, estimating the voltage vector and current vector at the motor end in the estimation coordinate system according to the command voltage vector and current vector at the inverter end;

[0050] S3. Calculate the difference between the corresponding stator flux vectors according to the voltage vector and the current vector at the motor end in the estimated coordinate system, and estimate the position and speed of the motor rotor according to the calculated difference.

[0051] like Figure 2 As shown in the figure, it is the control block diagram of AC motor control system with LC filter. Based on motor vector control, Figure 2 In the figure, idq_ref is the command current vector of the inverter in vector control, idq_i is the feedback current vector of the inverter in vector control, udq is the command voltage vector of the inverter in vector control, idq_m and udq_m are the current vector and voltage vector of the motor, respectively, and theta_e and w_e are the estimated motor rotor position and speed. The voltage vector or current vector mentioned above all represents that the vector is a vector in the estimated coordinate system. For example, the feedback current vector idq_i can be obtained by transforming the three-phase current of the inverter in combination with the estimated rotor position theta_e.

[0052] In this embodiment, the voltage vector and current vector of the motor end in the coordinate system are estimated according to the command voltage vector and current vector of the inverter end, including:

[0053] The voltage vector at the motor end in the estimation coordinate system is estimated according to the command voltage vector and current vector at the inverter end;

[0054] The current vector at the motor terminal in the estimated coordinate system is estimated according to the voltage vector at the motor terminal in the estimated coordinate system.

[0055] In this embodiment, the voltage vector at the motor end is first estimated according to the command voltage vector at the inverter end in the vector control, and the estimation process is:

[0056] ud_m=ud-id_i×Lf×w_e-id_i×Rf

[0057] uq_m=uq-iq_i×Lf×w_e-iq_i×Rf

[0058] Among them, ud_m and uq_m are the direct-axis component and quadrature-axis component of the voltage vector at the motor end in the estimated coordinate system, ud and uq are the direct-axis component and quadrature-axis component of the voltage vector at the inverter end in the estimated coordinate system, id_i and iq_i are the direct-axis component and quadrature-axis component of the current vector at the inverter end in the estimated coordinate system, w_e is the estimated speed of the motor, Lf and Rf are the inductance and resistance of the LC filter, respectively.

[0059] The current vector on the motor side can be further obtained based on the voltage vector on the motor side. The estimation process is:

[0060] id_m=id_i-ud_m×s×C

[0061] iq_m=iq_i-uq_m×s×C

[0062] Among them, id_m and iq_m are the direct-axis component and quadrature-axis component of the current vector at the motor end in the estimated coordinate system, id_i and iq_i are the direct-axis component and quadrature-axis component of the current vector at the inverter end in the estimated coordinate system, ud_m and uq_m are the direct-axis component and quadrature-axis component of the voltage vector at the motor end in the estimated coordinate system, s is the differential operator in the frequency domain, and C is the capacitance of the LC filter.

[0063] This embodiment uses a high-pass filter to approximate the actual differential calculation result, so the above formula can be rewritten as:

[0064]

[0065] Among them, id_m and iq_m are the direct-axis component and quadrature-axis component of the current vector at the motor end in the estimated coordinate system, id_i and iq_i are the direct-axis component and quadrature-axis component of the current vector at the inverter end in the estimated coordinate system, ud_m and uq_m are the direct-axis component and quadrature-axis component of the voltage vector at the motor end in the estimated coordinate system, s is the differential operator in the frequency domain, a is the filter coefficient of the high-pass filter, and C is the capacitance of the LC filter.

[0066] In this embodiment, the voltage vector at the motor end is substituted into the above formula to obtain the complete expression of the estimated value of the current vector at the motor end:

[0067]

[0068] It can be seen from the above formula that the current vector on the motor side can be estimated by the voltage vector on the inverter side (that is, the voltage command vector of the vector control).

[0069] In this embodiment, the difference between the corresponding stator flux vectors is calculated based on the voltage vector and the current vector at the motor end in the estimated coordinate system, and the position and speed of the motor rotor are estimated based on the calculated difference, including:

[0070] The stator flux equation is established according to the voltage vector and current vector at the motor end in the estimated coordinate system;

[0071] A low-pass filter is used to filter the stator flux equation, a voltage model of the motor in the estimated coordinate system is established, and the stator flux vector of the motor is estimated to obtain the voltage model-stator flux vector in the estimated coordinate system;

[0072] According to the current vector at the motor end in the estimated coordinate system, a current model of the motor in the estimated coordinate system is established and the stator flux vector of the motor is estimated to obtain the current model-stator flux vector in the estimated coordinate system;

[0073] The position and speed of the motor rotor are estimated based on the difference between the voltage model-stator flux vector and the current model-stator flux vector in the estimated coordinate system.

[0074] In this embodiment, the motor stator flux equation can be obtained based on the motor voltage equation:

[0075] fd=∫(ud_m-R×id_m+w×fq)dt

[0076] fq=∫(uq_m-R×iq_m-w×fd)dt

[0077] Among them, fd and fq are the direct-axis component and quadrature-axis component of the voltage model-stator flux vector in the estimated coordinate system, respectively.

[0078] In order to avoid the influence of the DC bias measured by the system on the integral operation in the above formula, this embodiment uses a low-pass filter to replace the integral operation in the above formula, and rewrites the above formula as follows:

[0079]

[0080] The above formula is the voltage model of the motor in the estimated coordinate system, and the voltage model in the estimated coordinate system can be used to perform real-time estimation of the motor stator flux vector.

[0081] At the same time, the estimated current vector on the motor side can be combined with the current model of the motor in the estimated coordinate system to estimate the stator flux vector. The specific estimation process is as follows:

[0082] fdc=id_m×L+ff

[0083] fqc=iq_m×L

[0084] Among them, fdc and fqc are the direct-axis component and quadrature-axis component of the current model-stator flux vector in the estimated coordinate system, ff is the motor rotor flux amplitude, and L is the motor stator inductance.

[0085] It can be seen from the above formula that fdq is the stator flux vector calculated by the voltage model in the estimated coordinate system, recorded as the voltage model-stator flux vector; fdqc is the stator flux vector calculated by the current model in the estimated coordinate system, recorded as the current model-stator flux vector. When there is an error between the voltage model-stator flux vector and the current model-stator flux vector, it means that there is also an error between the estimated rotor position and the actual rotor position, that is, the difference between the two stator flux vectors is a function of the angle error, and the angle error can be directly calculated based on this vector difference. Compared with the traditional phase-locked loop solution, this method does not need to assume that the sinusoidal value of the angle error is approximately equal to the angle error, and can adapt to a wider range of angle error changes. Especially when the initial position of the synchronous machine is inaccurate, it can still ensure the convergence of the observer's estimated position, reducing the observer's sensitivity to the initial position error. The process of calculating the rotor position angle estimation error based on the difference between the two stator flux vectors is:

[0086]

[0087] Among them, △theta is the rotor position angle estimation error, atan is the inverse tangent function, sin is the sine function, cos is the cosine function, fd and fq are the direct-axis component and quadrature-axis component of the voltage model-stator flux vector in the estimated coordinate system, fdc and fqc are the direct-axis component and quadrature-axis component of the current model-stator flux vector in the estimated coordinate system, theta_a is the actual rotor position angle, and theta_e is the estimated rotor position angle.

[0088] The speed can be estimated directly based on the rotor position angle estimation error △theta, and the estimation process is:

[0089]

[0090] Among them, w_e is the estimated motor rotor speed, △theta is the rotor position angle estimation error, k is the integral gain coefficient, and s is the differential operator in the frequency domain.

[0091] The estimated rotor position angle can be obtained by directly integrating the estimated motor speed w_e. The estimation process is:

[0092]

[0093] Among them, theta_e is the estimated position angle of the motor rotor, w_e is the estimated speed of the motor rotor, and s is the differential operator in the frequency domain.

[0094] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0095] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0096] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0097] The present invention uses specific embodiments to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

[0098] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. A method for controlling an AC motor with an LC filter, characterized in that: The following steps are involved: Obtaining the command voltage vector and current vector at the inverter end; The voltage vector and the current vector at the motor end in the estimation coordinate system are estimated according to the command voltage vector and the current vector at the inverter end; The difference between the corresponding stator flux vectors is calculated according to the voltage vector and the current vector at the motor end in the estimated coordinate system, and the position and speed of the motor rotor are estimated according to the calculated difference.

2. The AC motor control method with LC filter according to claim 1, characterized in that: According to the command voltage vector and current vector of the inverter end, the voltage vector and current vector of the motor end in the estimated coordinate system include: The voltage vector at the motor end in the estimation coordinate system is estimated according to the command voltage vector and current vector at the inverter end; The current vector at the motor terminal in the estimated coordinate system is estimated according to the voltage vector at the motor terminal in the estimated coordinate system.

3. The AC motor control method with LC filter according to claim 2, characterized in that: The voltage vector at the motor end in the estimation coordinate system is estimated according to the command voltage vector and current vector at the inverter end, specifically: ud_m=ud-id_i×Lf×w_e-id_i×Rf uq_m=uq-iq_i×Lf×w_e-iq_i×Rf Among them, ud_m and uq_m are the direct-axis component and quadrature-axis component of the voltage vector at the motor end in the estimated coordinate system, ud and uq are the direct-axis component and quadrature-axis component of the voltage vector at the inverter end in the estimated coordinate system, id_i and iq_i are the direct-axis component and quadrature-axis component of the current vector at the inverter end in the estimated coordinate system, w_e is the estimated speed of the motor, Lf and Rf are the inductance and resistance of the LC filter, respectively.

4. The AC motor control method with LC filter according to claim 2, characterized in that: The current vector at the motor end in the estimated coordinate system is estimated according to the voltage vector at the motor end in the estimated coordinate system, specifically: id_m=id_i-ud_m×s×C iq_m=iq_i-uq_m×s×C Among them, id_m and iq_m are the direct-axis component and quadrature-axis component of the current vector at the motor end in the estimated coordinate system, id_i and iq_i are the direct-axis component and quadrature-axis component of the current vector at the inverter end in the estimated coordinate system, ud_m and uq_m are the direct-axis component and quadrature-axis component of the voltage vector at the motor end in the estimated coordinate system, s is the differential operator in the frequency domain, and C is the capacitance of the LC filter.

5. The AC motor control method with LC filter according to claim 4, characterized in that: When estimating the current vector at the motor end in the estimated coordinate system according to the voltage vector at the motor end in the estimated coordinate system, a high-pass filter is used for filtering, specifically: Among them, id_m and iq_m are the direct-axis component and quadrature-axis component of the current vector at the motor end in the estimated coordinate system, id_i and iq_i are the direct-axis component and quadrature-axis component of the current vector at the inverter end in the estimated coordinate system, ud_m and uq_m are the direct-axis component and quadrature-axis component of the voltage vector at the motor end in the estimated coordinate system, s is the differential operator in the frequency domain, a is the filter coefficient of the high-pass filter, and C is the capacitance of the LC filter.

6. The AC motor control method with LC filter according to claim 1, characterized in that: Calculating the difference between the corresponding stator flux vectors according to the voltage vector and the current vector at the motor end in the estimated coordinate system, and estimating the position and speed of the motor rotor according to the calculated difference includes: The stator flux equation is established according to the voltage vector and current vector at the motor end in the estimated coordinate system; A low-pass filter is used to filter the stator flux equation, a voltage model of the motor in the estimated coordinate system is established, and the stator flux vector of the motor is estimated to obtain the voltage model-stator flux vector in the estimated coordinate system; According to the current vector at the motor end in the estimated coordinate system, a current model of the motor in the estimated coordinate system is established and the stator flux vector of the motor is estimated to obtain the current model-stator flux vector in the estimated coordinate system; The position and speed of the motor rotor are estimated based on the difference between the voltage model-stator flux vector and the current model-stator flux vector in the estimated coordinate system.

7. The AC motor control method with LC filter according to claim 6, characterized in that: Estimating the position and speed of the motor rotor based on the difference between the voltage model-stator flux vector and the current model-stator flux vector in the estimated coordinate system includes: The rotor position angle estimation error is calculated according to the difference between the voltage model-stator flux vector and the current model-stator flux vector in the estimation coordinate system; estimating the rotation speed of the motor rotor according to the rotor position angle estimation error; The position angle of the motor rotor is estimated according to the rotation speed of the motor rotor.

8. The AC motor control method with LC filter according to claim 7, characterized in that: The rotor position angle estimation error is calculated based on the difference between the voltage model-stator flux vector and the current model-stator flux vector in the estimated coordinate system, specifically: Among them, △theta is the rotor position angle estimation error, atan is the inverse tangent function, sin is the sine function, cos is the cosine function, fd and fq are the direct-axis component and quadrature-axis component of the voltage model-stator flux vector in the estimated coordinate system, fdc and fqc are the direct-axis component and quadrature-axis component of the current model-stator flux vector in the estimated coordinate system, theta_a is the actual rotor position angle, and theta_e is the estimated rotor position angle.

9. The AC motor control method with LC filter according to claim 7, characterized in that: The motor rotor speed is estimated based on the rotor position angle estimation error, specifically: Among them, w_e is the estimated motor rotor speed, △theta is the rotor position angle estimation error, k is the integral gain coefficient, and s is the differential operator in the frequency domain.

10. The AC motor control method with LC filter according to claim 7, characterized in that: The position angle of the motor rotor is estimated according to the rotation speed of the motor rotor, specifically: Among them, theta_e is the estimated position angle of the motor rotor, w_e is the estimated speed of the motor rotor, and s is the differential operator in the frequency domain.

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