Traversal-based weak magnetic working point calculation method of permanent magnet synchronous motor

Abstract

The invention discloses a traversing-based weak magnetic working point calculation method of a permanent magnet synchronous motor, and relates to a weak magnetic working point calculation method of the permanent magnet synchronous motor. According to the method, the problem that calculation is not converged under certain working conditions in a traditional Newton iteration method is solved. A flux weakening working point function is constructed, and the influence of torque, rotating speed and voltage on the position of a working point is considered at the same time. The weak magnetic working point function has the characteristic that the derivative is positive in the involved interval, so that monotonicity can be adopted to carry out traversal calculation to solve the working point. According to the method, the working point calculation process is given in detail, and the calculated working points can be used in a lookup table to provide reference for field weakening control of the permanent magnet synchronous motor. The invention belongs to the technical field of permanent magnet synchronous motor flux weakening.

Description

Technical Field

[0001] The invention relates to a method for calculating a weak magnetic field operating point of a permanent magnet synchronous motor, and belongs to the technical field of weak magnetic field of permanent magnet synchronous motors. Background Art

[0002] The lookup table method is a control method widely used in industry. It directly gives the control quantity by looking up the table. It is also an open-loop control method. It realizes fast target current distribution by pre-calculating and storing the operating parameters of the motor, avoiding the slow response and nonlinear problems in traditional closed-loop control. The method of controlling permanent magnet synchronous motors by the lookup table method is widely used in the field of electric vehicle control. The classic lookup table method searches for the required current according to the torque and speed to solve the problems of slow current distribution speed and torque-current nonlinearity in the deep weak magnetic field control in the traditional negative d-axis current weak magnetic field control. The methods for obtaining the lookup table are generally divided into test methods and calculation methods. The present invention discusses the problems in the calculation method, such as when calculating the weak magnetic field operating point of the permanent magnet synchronous motor, the traditional Newton iteration method has the problem of non-convergence of calculation under certain working conditions, which needs to be solved urgently. Summary of the invention

[0003] The present invention solves the problem that the traditional iterative method has deficiencies in calculating the weakening magnetic working point, and further proposes a method for calculating the weakening magnetic working point of a permanent magnet synchronous motor based on traversal.

[0004] The technical solution adopted by the present invention to solve the above-mentioned problem is: the steps of the present invention include:

[0005] Step 1, analyzing the weakening magnetic field operation point of the permanent magnet synchronous motor;

[0006] Step 2: construct an operating point function with a constant positive derivative;

[0007] Step 3: Use the ergodic method to calculate the field weakening operating point.

[0008] Furthermore, in step 1, the stator flux ψ is defined s for:

[0009]

[0010] In formula (1), ω e represents the electrical angular velocity, u s represents the stator voltage amplitude, ψ d represents the d-axis magnetic flux, ψ q represents the q-axis magnetic flux, where:

[0011]

[0012] In formula (2), ψ f represents the permanent magnet flux, L dIndicates the d-axis inductance, L q represents the q-axis inductance, i d represents d current, i q represents the q-axis current.

[0013] Furthermore, step 2 specifically includes:

[0014] Step 201: Construct about i d The MTPA function f MTPA (i d ):

[0015]

[0016] In formula (3), T e Indicates the torque of the motor, which is equal to the load torque in steady state, p n Indicates the number of pole pairs of the motor;

[0017] Step 202: Construct about i d The field weakening function f FW (i d ):

[0018]

[0019] In formula (4), ω e Indicates the motor electrical angular velocity, u FW Indicates the voltage limit of the inverter, which is also the voltage amplitude during field weakening;

[0020] All operating points that satisfy formula (3) are on the MTPA curve, and its derivative satisfies:

[0021]

[0022] All operating points that satisfy formula (4) are the intersection points of the flux linkage ellipse and the torque curve in the field weakening operation area, and their derivatives satisfy:

[0023]

[0024] According to the monotonicity of formulas (3) and (4), the required i is obtained by traversal calculation d .

[0025] The beneficial effects of the present invention are:

[0026] 1. The present invention avoids the divergence of the calculation process on the one hand; on the other hand, it simplifies the calculation process, and the calculation result of the working point can be obtained by traversing and calculating a simple function;

[0027] 2. The present invention adopts Newton's method to calculate the divergence of calculation when calculating certain weak magnetic working points;

[0028] 3. The monotonicity of the present invention ensures the accuracy of traversal calculations, and can greatly improve the calculation accuracy if the computing power allows;

[0029] 4. The present invention constructs an MTPA function and a magnetic weakening function, and calculates the magnetic weakening operating point using a traversal method based on their monotonicity. The magnetic weakening operating point calculation method of the present invention can be used in a lookup table to provide a reference for the magnetic weakening control of a permanent magnet synchronous motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the analysis of the working point of the weak magnetic operation on the current plane;

[0031] Figure 2 is a flow chart for calculating the operating point lookup table;

[0032] Figure 3 is a schematic diagram of the expected value of current on the working plane;

[0033] Figure 4 It is a schematic diagram of the expected voltage value on the working plane. DETAILED DESCRIPTION

[0034] Specific implementation method 1: Figure 1 As shown, a method for calculating the weakening magnetic working point of a permanent magnet synchronous motor based on traversal, the specific steps include:

[0035] Step 1, analyzing the weakening magnetic field operation point of the permanent magnet synchronous motor;

[0036] Define the stator flux ψ s for:

[0037]

[0038] In formula (1), ω e represents the electrical angular velocity, u s represents the stator voltage amplitude, ψ d represents the d-axis magnetic flux, ψ q represents the q-axis magnetic flux, where:

[0039]

[0040] In formula (2), ψ f represents the permanent magnet flux, L d Indicates the d-axis inductance, L q represents the q-axis inductance, i d represents d current, i q represents the q-axis current.

[0041] Step 2: construct an operating point function with a constant positive derivative; the specific steps include:

[0042] Step 201: Construct about i d The MTPA function f MTPA (i d ):

[0043]

[0044] In formula (3), T e Indicates the torque of the motor, which is equal to the load torque in steady state, p n Indicates the number of pole pairs of the motor;

[0045] Step 202: Construct about i d The field weakening function f FW (i d ):

[0046]

[0047] In formula (4), ω e Indicates the motor electrical angular velocity, u FW Indicates the voltage limit of the inverter, which is also the voltage amplitude during field weakening;

[0048] All operating points that satisfy formula (3) are on the MTPA curve, and its derivative satisfies:

[0049]

[0050] All operating points that satisfy formula (4) are the intersection points of the flux linkage ellipse and the torque curve in the field weakening operation area, and their derivatives satisfy:

[0051]

[0052] According to the monotonicity of formulas (3) and (4), the required i is obtained by traversal calculation d ;

[0053] Step 3, use the ergodic method to calculate the weak magnetic working point;

[0054] The calculation process of the ergodic method is as follows Figure 2 As shown; given i d The initial value is 0 and then decreases until f is satisfied FW (i d )<0, and then perform MTPA limiting on it, calculate the operating points under various working conditions in turn and store them in the lookup table.

[0055] like Figure 2 As shown, the core is the traversal method, given i d The initial value is 0 and then decreases until f is satisfied FW (i d)<0, and then perform MTPA limiting on it;

[0056] Assume Δi d , Δω e , ΔT e Respectively represent the desired accuracy of current, speed and torque, [ω e,min ,ω e,max ] is the required speed range, [T e,min ,T e,max ] is the required torque range;

[0057] Assume that the size of the lookup table to be calculated is m max ×n max , and m max and n max They are all artificially set positive integers.

[0058] In addition, the calculation and storage operations are completed in the program initialization, while in actual operation, it is necessary to extract the values ​​of adjacent nodes according to the torque and speed information for two-dimensional linear interpolation to obtain the required i in real time. d .

[0059] Calculation results

[0060] like Figure 3 and Figure 4 As shown, the result takes into account both the MTPA working area and the weak magnetic working area: in the MTPA working area, the required current is determined only by the torque requirement, while in the weak magnetic working area, it is determined by both the torque and speed requirements. The parameters of the permanent magnet synchronous motor used in the calculation are: rated power 2.2kW, d-axis inductance 9mH, q-axis inductance 18.5mH, permanent magnet flux 0.249Wb.

[0061] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement made to the above embodiments without departing from the content of the technical solution of the present invention, based on the technical essence of the present invention, within the spirit and principles of the present invention, still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for calculating the weakening magnetic working point of a permanent magnet synchronous motor based on traversal, characterized in that: The specific steps include: Step 1, analyzing the weakening magnetic field operation point of the permanent magnet synchronous motor; Step 2: construct an operating point function with a constant positive derivative; Step 3: Use the ergodic method to calculate the field weakening operating point.

2. The method for calculating the weakening magnetic working point of a permanent magnet synchronous motor based on traversal according to claim 1, characterized in that: In step 1, the stator flux ψ is defined s for: In formula (1), ω e represents the electrical angular velocity, u s represents the stator voltage amplitude, ψ d represents the d-axis magnetic flux, ψ q represents the q-axis magnetic flux, where: In formula (2), ψ f represents the permanent magnet flux, L d Indicates the d-axis inductance, L q represents the q-axis inductance, i d represents d current, i q represents the q-axis current.

3. The method for calculating the weakening magnetic field operating point of a permanent magnet synchronous motor based on traversal according to claim 1, characterized in that: Step 2 specifically includes: Step 201: Construct about i d The MTPA function f MTPA (i d ): In formula (3), T e Indicates the torque of the motor, which is equal to the load torque in steady state, p n Indicates the number of pole pairs of the motor; Step 202: Construct about i d The field weakening function f FW (i d ): In formula (4), ω e Indicates the motor electrical angular velocity, u FW Indicates the voltage limit of the inverter, which is also the voltage amplitude during field weakening; All operating points that satisfy formula (3) are on the MTPA curve, and its derivative satisfies: All operating points that satisfy formula (4) are the intersection points of the flux linkage ellipse and the torque curve in the field weakening operation area, and their derivatives satisfy: According to the monotonicity of formulas (3) and (4), the required i is obtained by traversal calculation d .

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