Built-in permanent magnet synchronous motor control method

Abstract

The invention relates to the technical field of motor control, and particularly discloses a built-in permanent magnet synchronous motor control method, which is used for solving the problem of slow dynamic response in the prior art. Comprising the following steps of 1, establishing a dq-axis voltage model and an electromagnetic torque equation of the built-in permanent magnet synchronous motor; step 2, according to the dq-axis voltage model deformation in the step 1, substituting the dq-axis voltage model deformation into an electromagnetic torque equation to obtain an equivalent torque equation; 3, a current vector angle beta is defined, and dq-axis current components are defined according to the relation between the current vector angle beta and the stator current amplitude. According to the method, a new MTPA criterion extraction mode is adopted, and sin (omega ht) and # imgabs0 # are directly multiplied to perform signal demodulation, so that the use of a band-pass filter is omitted, the dynamic response of the system is accelerated, high-order terms of two or more than two times of Taylor expansion are eliminated, and the precision of the algorithm is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of motor control, and in particular to a method for controlling a built-in permanent magnet synchronous motor. Background Art

[0002] At present, the main methods for studying MTPA control include: direct formula calculation method, online parameter identification method, table lookup method, online search method, etc.

[0003] Direct formula calculation method based on motor parameters, that is, the MTPA point is derived directly through the motor state model and mechanical formula, where the formula includes d-axis inductance, q-axis inductance, permanent magnet flux ψ f , stator resistance R s By checking the parameters on the motor nameplate, you can get the factory nominal values ​​of these electrical parameters. However, these electrical parameters will change during the operation of the motor. For example, after the motor temperature rises, the value of the permanent magnet flux of the motor will decrease, and the q-axis inductance will increase with i due to magnetic saturation. q Therefore, calculating the MTPA point using the value on the motor nameplate is obviously not suitable for all working conditions. Therefore, the MTPA point calculated using the direct formula based on motor parameters is often not accurate enough.

[0004] The electrical parameter online identification method monitors the changes of various electrical parameters in real time and then updates the MTPA point according to the changed values. However, this method increases the amount of online calculations because each electrical parameter needs to be calculated in real time, making the entire system more complicated.

[0005] The table lookup method is to test the electrical parameters of the motor under various working conditions when the motor is offline, and then make a table of the parameters obtained by the test. When the motor is running, it will query the corresponding electrical parameter values ​​in the table when it runs into different working conditions, and update the MTPA point based on this. This method will occupy certain hardware resources and has great limitations. When using different motors or different brands of drivers, you need to make a new table;

[0006] The virtual injection method is more commonly used in the online search method. This method tracks the MTPA trajectory by injecting a high-frequency auxiliary small signal on the current vector angle. When the system works at the MTPA point, it is equivalent to the minimum ratio of torque to stator current. From a mathematical point of view, under the condition of a given load torque, it means that there is a minimum value of the stator current amplitude at this time, that is, there is an extreme point. Therefore, the information that the MTPA point is the extreme point is used as the MTPA criterion information. By injecting a high-frequency auxiliary signal into the system and then building a corresponding torque model, the high-frequency signal will cause the torque model to generate a corresponding high-frequency response signal. Then, the MTPA criterion information contained in the high-frequency response signal is extracted through the extraction process of the high-frequency response signal. The criterion information is then integrated to obtain the optimal current vector angle. This type of method has good control accuracy and stability due to the high frequency of the injected signal and is robust to the motor parameters. The disadvantage is that it requires a complex coordinate transformation process. During the signal injection process, it is necessary to transform from the dq axis coordinate system to the polar coordinate system, and then from the polar coordinate system back to the dq axis coordinate system, which requires a large amount of calculation. In Taylor expansion, higher-order terms above the second order are ignored, resulting in a partial loss of accuracy. In the signal extraction process, the cascade of bandpass filters and low-pass filters is also involved, resulting in a slower dynamic response.

[0007] Based on this, a control method for a built-in permanent magnet synchronous motor is now provided, which can eliminate the disadvantages of existing devices. Summary of the invention

[0008] The purpose of the present invention is to provide a control method for a built-in permanent magnet synchronous motor, which solves the problem of slow dynamic response in the prior art.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] A control method for a built-in permanent magnet synchronous motor, step 1: establishing a dq axis voltage model (1) and an electromagnetic torque equation (2) of the built-in permanent magnet synchronous motor;

[0011] Step 2: According to the deformation of the dq axis voltage model in step 1, substitute it into the electromagnetic torque equation (2) to obtain the equivalent torque equation (3);

[0012] Step 3: Define the current vector angle β, and use its relationship with the stator current amplitude to define the dq axis current components (4);

[0013] Step 4: According to the current angle β in step 3, modify the signal injection method and establish the dq axis current equation (5) containing high frequency components;

[0014] Step 5: Based on the torque equation in step 2, establish the torque equation (6) containing high-frequency components;

[0015] Step 6: Since the injection method of the virtual signal is modified, the criterion formula of MTPA is re-derived to obtain formula (7);

[0016] Step 7: Perform Taylor expansion at β=0 on the torque equation containing high-frequency components in step 5 to obtain equation (8);

[0017] Step 8: Substitute the dq axis current equation containing high frequency components in step 4 into the torque equation containing high frequency components in step 5 T e h At the same time, T e h exist Taylor expansion can be performed to obtain formula (9);

[0018] Step 9: According to the torque equation in step 8, modify the signal extraction method and use sin(ω h t) and Directly multiply to demodulate the signal and get the demodulated signal T edem ;

[0019] Step 10: Pass the demodulated signal in step 9 through a low-pass filter with a cutoff frequency much lower than the injection frequency to extract the MTPA criterion T elpf ;

[0020] Step 11: Send the MTPA criterion information obtained in step 10 to the integrator, and the output of the integrator is the optimal current vector angle β MTPA ;

[0021] Step 12: Optimal current vector angle β according to step 11 MTPA And the equation in step 4 redistributes the dq axis current value i d 、i q Given as dq axis current.

[0022] On the basis of the above technical solution, the present invention also provides the following optional technical solution:

[0023] In an optional solution, the direct-axis and quadrature-axis voltage equations (1) and (2) are:

[0024]

[0025] where u d 、u q Respectively represent the dq axis voltage, i d 、i q They are respectively represented as dq axis current, L d , L q is the dq axis inductance, ψ f is the permanent magnet flux, ω eis the rotor electrical angular velocity, and P is the number of motor pole pairs.

[0026] In an optional solution: the equivalent torque equation (3) is:

[0027]

[0028] In an optional solution: the dq axis current component (4) is:

[0029]

[0030] In the optional scheme: Since the injection angle does not exceed 5°, the value of the amplitude A is very small, so sinΔβ≈Δβ, cosΔβ≈1, and the dq axis current equation (5) containing high-frequency components is established:

[0031]

[0032] In the alternative solution: establish the torque equation (6) containing high frequency components:

[0033]

[0034] The criterion formula is re-derived as (7):

[0035]

[0036] The torque equation of the high-frequency component is Taylor expanded at β = 0 to obtain equation (8):

[0037]

[0038] In the optional scheme: the dq axis current equation containing high frequency components in step 4 is substituted into the torque equation containing high frequency components in step 5. At the same time, according to the electromagnetic torque equation in step 1, The formula (9) is obtained as:

[0039]

[0040] It is worth noting that T e h It does not contain partial derivatives above the second order, thus avoiding the errors caused by ignoring high-order partial derivatives in the traditional virtual injection method.

[0041] In an optional solution, the demodulated signal in step nine is passed through a low-pass filter with a cutoff frequency much lower than the injection frequency to extract the MTPA criterion T elpf :

[0042]

[0043] The MTPA criterion information obtained in step 10 is sent to the integrator, and the output of the integrator is the optimal current vector angle β MTPA ;

[0044] Redistribute the dq axis current values ​​as dq axis current given:

[0045]

[0046] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0047] The present invention proposes an improved algorithm based on the existing traditional virtual signal injection method, and improves on its shortcomings of large computational complexity and poor dynamic response, so that more accurate MTPA control can be achieved under different load conditions. Compared with the existing traditional virtual signal injection method, the present invention simplifies the injection signal method and speeds up the dynamic response of the control system by modifying the injection method of the current angle and the signal extraction method. It does not require the main parameters of the motor to be obtained in advance, and the implementation process is simpler. In addition, the quadratic and higher-order terms of the Taylor expansion are eliminated in this process, so the implementation accuracy is improved compared with the existing method. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 Schematic diagram of the definition of current vector angle in the dq axis coordinate system.

[0049] Figure 2 It is a schematic diagram of a traditional virtual signal injection module of the present invention.

[0050] Figure 3 This is a block diagram of the improved virtual injection control of the present invention.

[0051] Figure 4 It is a schematic diagram of a permanent magnet synchronous motor drive control system based on an improved virtual injection method of the present invention. DETAILED DESCRIPTION

[0052] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0053] like Figure 1-Figure 4 As shown, the embodiment of the present invention provides a control method for a built-in permanent magnet synchronous motor, specifically:

[0054] The dq axis voltage model (1) of the interior permanent magnet synchronous motor is established as:

[0055]

[0056] The electromagnetic torque equation (2) is:

[0057]

[0058] where u d 、u q Respectively represent the dq axis voltage, i d 、i q They are respectively represented as dq axis current, L d , L q is the dq axis inductance, ψ f is the permanent magnet flux, ω e is the rotor electrical angular velocity, P is the number of motor pole pairs;

[0059] After removing the differential term from equation (1), we get the steady-state voltage equation (3) in the dq coordinate system:

[0060] U d =Ri d -ω e L q i q

[0061] U q =Ri q +ω e L d i d +ω e ψ f

[0062] Arrange and transpose the terms to get equation (4):

[0063] U d -Ri d =-ω e L q i q

[0064] U q -Ri q =ω e L d i d +ω e ψ f

[0065] Substituting formula (4) into formula (2), we get formula (5):

[0066]

[0067] The dq axis current components (6) are defined as:

[0068]

[0069] Establish the dq axis current equation (7) containing high frequency components:

[0070]

[0071] Establish the torque equation (8) containing high-frequency components:

[0072]

[0073] The values ​​of the parameters in the above formula are obtained by sampling the d-axis voltage U d , q-axis voltage U q , d-axis current i d , q-axis current i q 、Motor speedω m These quantities are processed by a low-pass filter to eliminate unnecessary switching noise.

[0074] The criterion formula of MTPA is re-derived as (9):

[0075]

[0076] The torque equation containing high-frequency components is Taylor expanded at β = 0 to obtain equation (10):

[0077]

[0078] Substitute the dq axis current equation containing high frequency components in equation (7) into the torque equation containing high frequency components in equation (8). At the same time, according to the electromagnetic torque equation in equation (2), we know that: The formula (11) is:

[0079]

[0080] It is worth noting that T e h It does not contain partial derivatives above the second order, thus avoiding the errors caused by ignoring high-order partial derivatives in the traditional virtual injection method.

[0081] Modify the signal extraction method, omit the use of bandpass filter, and use sin(ω h t) and Direct multiplication for signal demodulation yields equation (12):

[0082]

[0083] It can be seen that the demodulated signal T edem The constant term of contains the MTPA criterion information. The demodulated signal is passed through a low-pass filter with a cutoff frequency much lower than the injection frequency to extract the MTPA criterion T elpf :

[0084]

[0085] The obtained MTPA criterion information is sent to the integrator, and the output of the integrator is the optimal current vector angle β MTPA . Redistribute the dq axis current value i d 、i q Given as dq axis current:

[0086]

[0087] The injected sinusoidal signal Δβ is defined as Asin(ωht). Since the injection angle does not exceed 5°, the amplitude A is very small, and its range is 0<A≤0.08. In this implementation case, A is 0.08. The injected sinusoidal signal frequency f h Set to 500Hz, the cutoff frequency of the low-pass filter ω c Set to 10rad / s, which can effectively eliminate all harmonics close to the signal frequency. Therefore, the proposed control scheme based on the improved virtual injection method is also robust to voltage and current harmonics and other electrical noises.

[0088] The traditional signal injection method of the virtual injection method is to first obtain the dq axis current i after sampling and filtering. d 、i q , through

[0089]

[0090] Calculate the stator current i s and the current vector angle β, and then mathematically add a small high-frequency signal Δβ to the current vector angle β, and then convert it back to the dq coordinate system by calculation to obtain The operation process involves square root, which is redundant. In the subsequent signal processing, a band-pass filter and a low-pass filter are cascaded, resulting in poor dynamic response of the system.

[0091] Improvements are made to the shortcomings of the traditional virtual injection method, such as large amount of calculation and poor dynamic response, to achieve more accurate MTPA control under different load conditions. Compared with the existing traditional virtual signal injection method, the present invention simplifies the injection signal method and speeds up the dynamic response of the control system by modifying the injection method of the current angle and the signal extraction method. It does not require the main parameters of the motor to be obtained in advance, and the implementation process is simpler. In addition, the quadratic and higher-order terms of the Taylor expansion are eliminated in this process, so the implementation accuracy is improved compared with the existing method.

[0092] 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, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A control method for a built-in permanent magnet synchronous motor, characterized in that: The following steps are involved: Step 1: Establish the dq axis voltage model (1) and electromagnetic torque equation (2) of the interior permanent magnet synchronous motor; Step 2: According to the deformation of the dq axis voltage model in step 1, substitute it into the electromagnetic torque equation (2) to obtain the equivalent torque equation (3); Step 3: Define the current vector angle β, and use its relationship with the stator current amplitude to define the dq axis current components (4); Step 4: According to the current angle β in step 3, modify the signal injection method and establish the dq axis current equation (5) containing high frequency components; Step 5: Based on the torque equation in step 2, establish the torque equation (6) containing high-frequency components; Step 6: Since the injection method of the virtual signal is modified, the criterion formula of MTPA is re-derived to obtain formula (7); Step 7: Perform Taylor expansion at β=0 on the torque equation containing high-frequency components in step 5 to obtain equation (8); Step 8: Substitute the dq axis current equation containing high frequency components in step 4 into the torque equation containing high frequency components in step 5 At the same time, exist Taylor expansion can be performed to obtain equation (9); Step 9: According to the torque equation in step 8, modify the signal extraction method and use sin(ω h t) and Directly multiply to demodulate the signal and get the demodulated signal T edem ; Step 10: Pass the demodulated signal in step 9 through a low-pass filter with a cutoff frequency much lower than the injection frequency to extract the MTPA criterion T elpf ; Step 11: Send the MTPA criterion information obtained in step 10 to the integrator, and the output of the integrator is the optimal current vector angle β MTPA ; Step 12: Optimal current vector angle β according to step 11 MTPA And the equation in step 4 redistributes the dq axis current value i d 、i q Given as dq axis current.

2. The method for controlling an interior permanent magnet synchronous motor according to claim 1, characterized in that: The direct-axis and quadrature-axis voltage equations (1) and (2) are: where u d 、u q Respectively represent the dq axis voltage, i d 、i q They are respectively represented as dq axis current, L d , L q is the dq axis inductance, ψ f is the permanent magnet flux, ω e is the rotor electrical angular velocity, and P is the number of motor pole pairs.

3. The method for controlling an interior permanent magnet synchronous motor according to claim 1, characterized in that: The equivalent torque equation (3) is:

4. The method for controlling an interior permanent magnet synchronous motor according to claim 1, characterized in that: The dq axis current component (4) is:

5. The method for controlling an interior permanent magnet synchronous motor according to claim 1, characterized in that: Since the injection angle does not exceed 5°, the amplitude A is very small, so sinΔβ≈Δβ, cosΔβ≈1, and the dq axis current equation (5) containing high frequency components is established:

6. The method for controlling an interior permanent magnet synchronous motor according to claim 1, characterized in that: Establish the torque equation (6) containing high-frequency components: The criterion formula is re-derived as (7): The torque equation of the high-frequency component is Taylor expanded at β = 0 to obtain equation (8):

7. The method for controlling an interior permanent magnet synchronous motor according to claim 5, characterized in that: Substitute the dq axis current equation containing high frequency components in step 4 into the torque equation containing high frequency components in step 5. At the same time, according to the electromagnetic torque equation in step 1, The formula (9) is obtained as: It is worth noting that the improved virtual injection method It does not contain partial derivatives above the second order, thus avoiding the errors caused by ignoring high-order partial derivatives in the traditional virtual injection method.

8. The method for controlling an interior permanent magnet synchronous motor according to claim 1, characterized in that: The demodulated signal in step nine is passed through a low-pass filter with a cutoff frequency much lower than the injection frequency to extract the MTPA criterion T elpf : The MTPA criterion information obtained in step 10 is sent to the integrator, and the output of the integrator is the optimal current vector angle β MTPA ; Redistribute the dq axis current values ​​as dq axis current given:

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