Maximum torque-to-current ratio control method for permanent magnet synchronous motor considering thermal effect

Abstract

The present invention relates to a method for controlling the maximum torque current ratio of a permanent magnet synchronous motor considering thermal effects, comprising: step S1: receiving a dynamic reference torque, and obtaining a reference AC-DC axis current and a reference current vector angle of a nominal MTPA operating point based on the received reference torque combined with the nominal parameters of the motor and the electrical parameters of the inverter; step S2: when the motor is in a stable operating state, calculating the tangent vector of the nominal electromagnetic torque and the corresponding current increment vector, and calculating the inner product value of the tangent vector and the current increment vector, and determining the compensation direction of the current vector angle based on the inner product value obtained, and adjusting the compensation amount through a linear gain; step S3: based on the compensation direction and compensation amount of the obtained current vector angle, combined with the current vector angle, obtaining the current vector angle and the corresponding current distribution value updated at the next moment. Compared with the prior art, the present invention has the advantages of being able to accurately compensate for the MTPA angle deviation caused by parameter perturbation in real time, and not needing to estimate parameters such as AC-DC axis inductance and permanent magnet flux linkage.

Description

Technical Field

[0001] The invention relates to the field of maximum torque current ratio control of permanent magnet synchronous motors, and in particular to a maximum torque current ratio control method of permanent magnet synchronous motors taking thermal effects into consideration. Background Art

[0002] Permanent magnet synchronous motor (PMSM) has the advantages of small size, high efficiency, high power density, etc. The closed-loop speed regulation system composed of permanent magnet synchronous motor can achieve excellent dynamic performance, high precision and a wide speed regulation range, so it is widely used in the field of new energy electric vehicle motor drive. With the continuous development of high speed, high power density and high integration of new energy electric vehicle electric drive system, the resulting thermal effect has a significant impact on the operating performance and service life of the motor. It is necessary to further study the control method of permanent magnet synchronous motor under thermal effect.

[0003] New energy electric vehicle drive motors all use embedded permanent magnet synchronous motors (IPMSM). Compared with surface-mounted permanent magnet synchronous motors, they have the advantages of permanent magnets not easy to fall off and output reluctance torque, so that the motor can run under high-speed conditions and output high electromagnetic torque. In order to further improve the efficiency of IPMSM, make full use of reluctance torque, reduce copper loss generated during operation, and obtain excellent control effect, it is required to output the maximum electromagnetic torque under the condition of minimum current, that is, maximum torque to current ratio control (MTPA).

[0004] The existing MTPA control is mainly divided into two types. One is the method based on model parameters, including direct formula method, table lookup method, curve fitting method and parameter identification method. However, these methods all rely on the accuracy of model parameters. When the external environment changes (such as temperature rise and fall, magnetic saturation, etc.), the actual operating parameters of the motor, such as inductance, permanent magnet flux, stator resistance, etc., will inevitably change, which will cause the MTPA control based on motor parameters to deviate from the optimal point and fail to achieve the expected effect.

[0005] The other control method is not based on the motor model parameters, which mainly includes high-frequency signal injection method and search method. The core of the high-frequency signal injection method is to inject a high-frequency current or voltage signal with a small amplitude into the vector control system to extract the torque response and track the optimal vector angle. The high-frequency signal injection method includes actual signal injection and virtual signal injection. The method based on actual signal injection will introduce new interference signals, resulting in the output of high-frequency pulsating torque, affecting the stability of the drive system. The method of virtual signal injection is to extract the virtual output power, analyze the virtual torque response through a bandpass filter, and realize the compensation of the MTPA angle. However, the cutoff frequency of the bandpass filter is difficult to determine, and the feedback signal also needs to be filtered. It is difficult to set the pass frequency of all filters to the optimal level, and it is rarely used in engineering. As for the search method, a fixed-step search method is usually adopted, but its search speed is slow and it is very sensitive to load changes. Summary of the invention

[0006] The purpose of the present invention is to provide a method for controlling the maximum torque-to-current ratio of a permanent magnet synchronous motor taking thermal effects into consideration.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A method for controlling a maximum torque current ratio of a permanent magnet synchronous motor considering thermal effects, comprising:

[0009] Step S1: receiving a dynamic reference torque, and obtaining a reference quadrature and direct-axis current and a reference current vector angle of a nominal MTPA operating point based on the received reference torque combined with the motor nominal parameters and the inverter electrical parameters;

[0010] Step S2: when the motor is in a stable operating state, the tangent vector of the nominal electromagnetic torque and the corresponding current increment vector are calculated, and the inner product value of the tangent vector and the current increment vector is calculated, and the compensation direction of the current vector angle is determined based on the obtained inner product value, and the compensation amount is adjusted by the linear gain;

[0011] Step S3: Based on the obtained compensation direction and compensation amount of the current vector angle and in combination with the current vector angle, the updated current vector angle and the corresponding current distribution value at the next moment are obtained.

[0012] The step S1 is specifically as follows:

[0013] Receive the dynamic reference torque and determine whether the absolute value of the reference torque is less than the absolute value of the maximum torque. If so, combine the motor nominal parameters and inverter electrical parameters to obtain the nominal MTPA working point reference AC and DC axis current and reference current vector angle. Otherwise, feedback corrects the reference torque.

[0014] The nominal parameters of the motor include the nominal permanent magnet flux linkage, the nominal direct-axis inductance and the nominal quadrature-axis inductance, and the electrical parameters of the inverter include the maximum phase current of the inverter;

[0015] The maximum torque is:

[0016] T emax =1.5Pi qmax (ψ m0 +(L d0 -L q0 )i dmax )

[0017]

[0018] Where: T emax is the maximum torque, i qmax is the quadrature axis current at maximum torque, ψ m0 is the nominal permanent magnet flux, L d0 is the nominal direct-axis inductance, L q0 is the nominal quadrature-axis inductance, i dmax is the quadrature axis current at maximum torque, I smax is the maximum phase current of the inverter.

[0019] The process of determining the reference AC and DC axis currents and the reference current vector angle at the nominal MTPA operating point includes:

[0020] Solve for the direct-axis current i that satisfies the MTPA condition d The quartic polynomial equation of the direct axis current i is obtained d , where the quartic polynomial equation is:

[0021]

[0022] Among them, A, B, C, D are polynomial coefficients, and P is the number of permanent magnet pole pairs;

[0023] Based on the direct axis current i d Get the reference direct-axis current of the MTPA operating point

[0024] Based on the obtained reference direct-axis current of the MTPA operating point, the reference quadrature-axis current and reference current vector angle of the MTPA operating point are calculated as follows:

[0025]

[0026] in: is the quadrature axis current at the MTPA operating point, is the current vector angle of the MTPA operating point, T eref is the reference torque.

[0027] In step S2, the process of determining whether the motor is in a stable operating state specifically includes:

[0028] Get the time series sampling data of motor speed;

[0029] Calculate the root mean square error of the time series sampling data of the motor speed, and determine whether the calculated root mean square error is less than a preconfigured error threshold. If so, determine that the motor is in a stable operating state.

[0030] The root mean square error is specifically:

[0031]

[0032] Where: n is the number of sampling times, ω i is the sampling value of the i-th speed, is the average speed.

[0033] In step S2, the process of obtaining the compensation direction and compensation amount includes:

[0034] Get the real-time quadrature-axis current and direct-axis current, and calculate the tangent vector of the nominal electromagnetic torque and the corresponding current increment vector respectively:

[0035]

[0036] in: is the tangent vector of the nominal electromagnetic torque, is the current increment vector, i q is the quadrature axis current;

[0037] Calculate the inner product of the tangent vector and the current increment vector:

[0038]

[0039] in: is the inner product value, χ tex is the x-component of the tangent vector of the torque curve, χ tey is the y component of the tangent vector of the torque curve;

[0040] Determine the deviation direction of the current vector angle based on the obtained inner product value and the deviation from 0;

[0041] Adjust the compensation amount by linear gain:

[0042]

[0043] Among them: Δβ is the adjusted compensation amount, and γ is the compensation gain.

[0044] The deviation direction of the current vector angle is determined based on the obtained inner product value and the deviation from 0, specifically:

[0045] When the inner product value is greater than 0, the output of the current vector angle at the next moment needs to be reduced, and the compensation direction is negative;

[0046] When the inner product value is less than 0, it is necessary to increase the output of the current vector angle at the next moment, and the compensation direction is positive.

[0047] In step S3, the updated current vector angle is:

[0048]

[0049] Where: β MTPA is the updated current vector angle;

[0050] The updated current distribution values ​​are:

[0051]

[0052] i qref =i dref tanβ MTPA

[0053] Where: i dref To compensate for the updated MTPA operating point direct-axis current distribution value, i qref To compensate for the updated MTPA operating point quadrature-axis current distribution value.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] 1. The inner product value of the tangent vector and the current increment vector is used as the basis for the compensation amount and direction. The influence of nonlinear factors such as parameter perturbations caused by core magnetic saturation and temperature changes on the unit inner product value of the motor electromagnetic torque increment vector and the phase current increment vector is fully considered. The MTPA angle deviation caused by parameter perturbations can be compensated in real time and accurately, without the need to estimate parameters such as the AC and DC axis inductance and permanent magnet flux.

[0056] 2. The MTPA angle is compensated based on the real-time unit inner product value of the nominal torque tangent vector and the phase current increment vector. The real-time unit inner product value is used as the observation object. The disturbance judgment is made by comparing the difference between the real-time unit inner product value and the ideal unit inner product value of 0. The MTPA angle output at the next moment is compensated according to the disturbance deviation, thereby determining the current correction strategy, so that the disturbance compensation step size is updated adaptively, and the step size is changed in real time with the current operating status of the system, solving the problem of poor accuracy of fixed step size.

[0057] 3. The MTPA angle compensation algorithm is operated in a steady-state intervention mode, which solves the problem of large angle fluctuation caused by intervening the MTPA angle search algorithm when the system has not reached steady-state operation, thereby avoiding large disturbances in the current command distribution and improving the stability of the entire control system. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is a schematic flow chart of the main steps of the method of the present invention;

[0059] Figure 2 This is a comparison chart of the actual MTPA angle of the motor;

[0060] Figure 3 This is a comparison chart of the actual MTPA control efficiency of the motor. DETAILED DESCRIPTION

[0061] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0062] A maximum torque-to-current ratio control method for permanent magnet synchronous motor considering thermal effect, such as Figure 1 As shown, including:

[0063] Step S1: receiving a dynamic reference torque, and obtaining a reference AC-DC axis current and a reference current vector angle of a nominal MTPA operating point based on the received reference torque combined with the motor nominal parameters and the inverter electrical parameters, specifically:

[0064] Receive the dynamic reference torque and determine whether the absolute value of the reference torque is less than the absolute value of the maximum torque. If so, combine the motor nominal parameters and inverter electrical parameters to obtain the nominal MTPA working point reference AC and DC axis current and reference current vector angle. Otherwise, feedback corrects the reference torque.

[0065] Based on the nominal parameters of the motor, a mathematical model of the permanent magnet synchronous motor under the nominal parameters can be constructed, and the nominal MTPA current distribution strategy under the reference torque command can be derived under the nominal model, so as to obtain the reference AC and DC axis current and reference current vector angle of the nominal MTPA working point in real time.

[0066] Among them, the nominal parameters of the motor include the nominal permanent magnet flux, the nominal direct-axis inductance and the nominal quadrature-axis inductance, and the electrical parameters of the inverter include the maximum phase current of the inverter;

[0067] In this embodiment, the maximum torque is:

[0068] T emax =1.5Pi qmax (ψ m0+(L d0 -L q0 )i dmax )

[0069]

[0070] Where: T emax is the maximum torque, i qmax is the quadrature axis current at maximum torque, ψ m0 is the nominal permanent magnet flux, L d0 is the nominal direct-axis inductance, L q0 is the nominal quadrature-axis inductance, i dmax is the direct-axis current at maximum torque, I smax is the maximum phase current of the inverter.

[0071] The process of determining the reference AC and DC axis currents and the reference current vector angle at the nominal MTPA operating point includes:

[0072] Solve for the direct-axis current i that satisfies the MTPA condition d The quartic polynomial equation of the direct axis current i is obtained d , where the quartic polynomial equation is:

[0073]

[0074] Among them, A, B, C, D are polynomial coefficients, and P is the number of permanent magnet pole pairs;

[0075] Based on the direct axis current i d Get the reference direct-axis current of the MTPA operating point In some embodiments, the process can be solved using Newton's iteration method;

[0076] Based on the obtained reference direct-axis current of the MTPA operating point, the reference quadrature-axis current and reference current vector angle of the MTPA operating point are calculated as follows:

[0077]

[0078] in: is the quadrature axis current at the MTPA operating point, is the current vector angle of the MTPA operating point, T eref is the reference torque.

[0079] Step S2: when the motor is in a stable operating state, the tangent vector of the nominal electromagnetic torque and the corresponding current increment vector are calculated, and the inner product value of the tangent vector and the current increment vector is calculated, and the compensation direction of the current vector angle is determined based on the obtained inner product value, and the compensation amount is adjusted by the linear gain;

[0080] In step S2, the process of determining whether the motor is in a stable operating state specifically includes:

[0081] Get the time series sampling data of motor speed;

[0082] Calculate the root mean square error of the time series sampling data of the motor speed, and determine whether the calculated root mean square error is less than a preconfigured error threshold. If so, determine that the motor is in a stable operating state.

[0083] The current limit circle is centered at the origin and the maximum phase current I smax The circle with radius is , according to the torque curve and the current limit circle, two vectors of the working point on the MTPA curve can be determined, one is the tangent vector of the point along the torque curve One is the direction vector of the phase current increment at this point When the parameters are not perturbed, the tangent vector With the increment direction vector They are perpendicular to each other, that is, their inner product value is 0. Therefore, in step S2, the process of obtaining the compensation direction and the compensation amount includes:

[0084] Get the real-time quadrature-axis current and direct-axis current, and calculate the tangent vector of the nominal electromagnetic torque and the corresponding current increment vector respectively:

[0085]

[0086] in: is the tangent vector of the nominal electromagnetic torque, is the current increment vector, i q is the quadrature axis current;

[0087] Calculate the inner product of the tangent vector and the current increment vector:

[0088]

[0089] in: is the inner product value, χ tex is the x component of the torque curve tangent vector, χ tey is the y component of the tangent vector of the torque curve;

[0090] Determine the deviation direction of the current vector angle based on the obtained inner product value and the deviation from 0;

[0091] Adjust the compensation amount by linear gain:

[0092]

[0093] Among them: Δβ is the adjusted compensation amount, and γ is the compensation gain.

[0094] Generally, at the MTPA operating point, the inner product value should be 0.

[0095] The deviation direction of the current vector angle is determined based on the obtained inner product value and the deviation from 0, specifically:

[0096] When the inner product value is greater than 0, the output of the current vector angle at the next moment needs to be reduced, and the compensation direction is negative;

[0097] When the inner product value is less than 0, it is necessary to increase the output of the current vector angle at the next moment, and the compensation direction is positive.

[0098] Step S3: Based on the obtained compensation direction and compensation amount of the current vector angle and in combination with the current vector angle, the updated current vector angle and the corresponding current distribution value at the next moment are obtained.

[0099] Among them, the updated current vector angle is:

[0100]

[0101] Where: β MTPA is the updated current vector angle;

[0102] The updated current distribution values ​​are:

[0103]

[0104] i qref =i dref tanβ MTPA

[0105] Where: i dref To compensate for the updated MTPA operating point direct-axis current distribution value, i qref To compensate for the updated MTPA operating point quadrature-axis current distribution value.

[0106] like Figure 2 As shown, it is a comparison chart of the actual MTPA angle of the motor obtained by the traditional formula method + ideal parameter variable calculation, the traditional calculation formula calculation and the MTPA angle compensation calculation. At 0.5s, the motor parameter ψ m Reduce by 50 percent;

[0107] like Figure 3 As shown, it is a comparison chart of the actual MTPA control efficiency of the motor obtained by the traditional formula method + ideal parameter variable calculation, the traditional calculation formula calculation and the MTPA angle compensation calculation. At 0.5s, the motor parameter ψ m Reduce by 50 percent.

Claims

1. A method for controlling the maximum torque current ratio of a permanent magnet synchronous motor considering thermal effects, characterized in that: include: Step S1: receiving a dynamic reference torque, and obtaining a reference quadrature and direct-axis current and a reference current vector angle of a nominal MTPA operating point based on the received reference torque combined with the motor nominal parameters and the inverter electrical parameters; Step S2: when the motor is in a stable operating state, the tangent vector of the nominal electromagnetic torque and the corresponding current increment vector are calculated, and the inner product value of the tangent vector and the current increment vector is calculated, and the compensation direction of the current vector angle is determined based on the obtained inner product value, and the compensation amount is adjusted by the linear gain; Step S3: Based on the obtained compensation direction and compensation amount of the current vector angle, combined with the current vector angle, the updated current vector angle and the corresponding current distribution value at the next moment are obtained; The step S1 is specifically as follows: Receive the dynamic reference torque, and determine whether the absolute value of the reference torque is less than the absolute value of the maximum torque. If so, obtain the reference AC and DC axis current and the reference current vector angle of the nominal MTPA working point by combining the nominal parameters of the motor and the electrical parameters of the inverter. Otherwise, feedback the corrected reference torque; The process of determining the reference AC and DC axis currents and the reference current vector angle at the nominal MTPA operating point includes: Solve for the direct-axis current i that satisfies the MTPA condition d The quartic polynomial equation of the direct axis current i is obtained d , where the quartic polynomial equation is: Among them, A, B, C, D are polynomial coefficients, P is the number of permanent magnet poles, ψ m0 is the nominal permanent magnet flux, L d0 is the nominal direct-axis inductance, L q0 is the nominal quadrature-axis inductance; Based on the direct axis current i d Get the reference direct-axis current of the MTPA operating point Based on the obtained reference direct-axis current of the MTPA operating point, the reference quadrature-axis current and reference current vector angle of the MTPA operating point are calculated as follows: in: is the quadrature axis current at the MTPA operating point, is the current vector angle of the MTPA operating point, T eref is the reference torque; In step S2, the process of obtaining the compensation direction and compensation amount includes: Get the real-time quadrature-axis current and direct-axis current, and calculate the tangent vector of the nominal electromagnetic torque and the corresponding current increment vector respectively: in: is the tangent vector of the nominal electromagnetic torque, is the current increment vector, i q is the quadrature axis current; Calculate the inner product of the tangent vector and the current increment vector: in: is the inner product value, χ tex is the x-component of the tangent vector of the torque curve, χ tey is the y component of the tangent vector of the torque curve; Determine the deviation direction of the current vector angle based on the obtained inner product value and the deviation from 0; Adjust the compensation amount by linear gain: Among them: Δβ is the adjusted compensation amount, and γ is the compensation gain.

2. A method for controlling the maximum torque current ratio of a permanent magnet synchronous motor considering thermal effects according to claim 1, characterized in that: The nominal parameters of the motor include the nominal permanent magnet flux linkage, the nominal direct-axis inductance and the nominal quadrature-axis inductance, and the electrical parameters of the inverter include the maximum phase current of the inverter; The maximum torque is: T emax =1.5Pi qmax (ψ m0 +(L d0 -L q0 )i dmax ) Where: T emax is the maximum torque, i qmax is the quadrature axis current at maximum torque, i dmax is the direct-axis current at maximum torque, I smax is the maximum phase current of the inverter.

3. The method for controlling the maximum torque current ratio of a permanent magnet synchronous motor considering thermal effects according to claim 1, characterized in that: In step S2, the process of determining whether the motor is in a stable operating state specifically includes: Get the time series sampling data of motor speed; Calculate the root mean square error of the time series sampling data of the motor speed, and determine whether the calculated root mean square error is less than a preconfigured error threshold. If so, determine that the motor is in a stable operating state.

4. The method for controlling the maximum torque current ratio of a permanent magnet synchronous motor considering thermal effects according to claim 1, characterized in that: The deviation direction of the current vector angle is determined based on the obtained inner product value and the deviation from 0, specifically: When the inner product value is greater than 0, the output of the current vector angle at the next moment needs to be reduced, and the compensation direction is negative; When the inner product value is less than 0, the output of the current vector angle at the next moment needs to be increased, and the compensation direction is positive.

5. The method for controlling the maximum torque-to-current ratio of a permanent magnet synchronous motor considering thermal effects according to claim 1, characterized in that: In step S3, the updated current vector angle is: Where: β MTPA is the updated current vector angle; The updated current distribution values ​​are: i qref =i dref ·tanβ MTPA Where: i dref To compensate for the updated MTPA operating point direct-axis current distribution value, i qref To compensate for the updated MTPA operating point quadrature-axis current distribution value.

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