CN110190794A - Calculation method and device for current given value of built-in permanent magnet synchronous motor - Google Patents

Abstract

The embodiment of the present invention discloses a method and device for calculating a given current value of a built-in permanent magnet synchronous motor. The method includes: when the bus voltage is the rated voltage of the motor, the torque is calibrated to obtain a current lookup table , the current lookup table contains the corresponding relationship between different torques and different rotational speeds and current values under the rated bus voltage; according to the current rotational speed and given torque, the given values of d and q axis currents are calculated.

Description

Calculation method and device for current given value of built-in permanent magnet synchronous motor

technical field

The invention relates to a control technology of a built-in permanent magnet synchronous motor for an electric vehicle, in particular to a torque control method and device for a built-in permanent magnet synchronous motor based on a look-up table method.

Background technique

Interior Permanent Magnet Synchronous Motor (IPMSM) has become the motor of choice for electric vehicle drive systems due to its high power density and small size. IPMSM AC and D-axis inductance are different, and the operation is limited by the output voltage and output current of the inverter, the torque control strategy is more complicated, usually using the maximum torque current ratio (MTPA, Maximum Torque Per Ampere) control and field weakening control Combined control strategy. Theoretical calculations of MTPA and field weakening control are very cumbersome and difficult to use in real-time control. In actual use, a two-dimensional lookup table is usually established by calibration to record the d and q axis current values corresponding to different rotational speeds and different torques. The controller calculates the d and q axis current given values through two-dimensional interpolation according to the torque command and the current speed value. The current output range of the motor is affected by the voltage limit circle and the current limit circle, as shown in Figure 1. The lookup table corresponds to a certain bus voltage. Under different bus voltages, the d and q axis current values corresponding to the same speed and torque point may be different. Assuming that the bus voltage when calibrating the table is Udc, when the bus voltage is higher than Udc, the voltage limit circle expands, and the current given value calculated according to the original query table will inevitably fall within the new voltage limit circle, indicating that the current given value is Achievable; when the bus voltage is lower than Udc, the voltage limit circle will shrink, and the current given value calculated according to the original query table may fall outside the new voltage limit circle, and the current value at this time exceeds the motor's The current output range is unrealizable, and the motor cannot output the required torque.

It can be seen that the current look-up table can only correspond to a bus voltage, and when the bus voltage becomes low, the current given value calculated according to the look-up table may be incorrect. If the look-up tables are designed according to different bus voltage values, the difficulty of design will be greatly increased. Therefore, it is necessary to design a torque table and d, q-axis current calculation method that can adapt to bus voltage changes and is easy to implement.

Contents of the invention

In view of this, the embodiments of the present invention provide a method and device for calculating a given current value of an internal permanent magnet synchronous motor, which can ensure the validity of the output current and the correctness of the output torque.

A method for calculating a current given value of a built-in permanent magnet synchronous motor, comprising:

When the bus voltage is the rated voltage of the motor, the torque is calibrated to obtain a current look-up table, the current look-up table includes the corresponding relationship between different torques and different speeds and current values under the rated bus voltage;

According to the current speed and given torque, calculate d, q axis current given value.

The step of calculating the d and q axis current given values according to the current speed and given torque includes:

Judging the bus voltage value;

When the bus voltage value is greater than or equal to the rated voltage, according to the current lookup table, the current speed value is used as the table lookup speed value, and the table lookup calculation is performed;

When the bus voltage is lower than the rated voltage, the current speed is increased in the same proportion as the bus voltage value drops to generate a table look-up speed value; according to the current look-up table, the table look-up calculation is performed according to the speed value used for table look-up .

The step of increasing the current speed in the same proportion as the bus voltage value drops, and generating the table look-up speed value is as follows:

ω _T ＝ωU _dc /U _Ndc , where, ω _T is the speed value of the look-up table; ω is the actual speed value; U _Ndc is the rated voltage; U _dc is the bus voltage.

The steps for performing table look-up calculation are specifically:

According to the look-up table speed value ω _T , determine the speed range [ω _k ,ω _k+1 ] to which it belongs;

Find the interval [T _k,n ^* ,T _k,n+1 ^* ] of the torque T _e ^* in the table corresponding to ω _k , and use linear interpolation to calculate the current value i _d,k corresponding to the torque under ω _k ^* and i _{q, k} ^* ; then obtain the current value i _{d, k+1} ^* and i _{q, k+1} ^* corresponding to the torque under the rotational speed ω _k+1 ;

Perform linear interpolation again on i _d,k ^* , i _q,k ^* and i _d,k+1 ^* , i _q,k+1 ^* according to the speed interval to obtain the current given value i _d ^* corresponding to the speed ω _T , _iq ^* .

A calculation device for a given current value of a built-in permanent magnet synchronous motor, comprising:

The table building unit, when the bus voltage is the rated voltage of the motor, calibrates the torque to obtain a current lookup table, the current lookup table includes the correspondence between different torques and different speeds and current values under the rated bus voltage relation;

The calculation unit calculates the d and q axis current given values according to the current speed and given torque.

The computing unit includes:

Judging module, judging the bus voltage value;

The first query module, when the bus voltage value is greater than or equal to the rated voltage, according to the current look-up table, perform table look-up calculation according to the current speed value;

The second query module, when the bus voltage is lower than the rated voltage, the current speed is increased in the same proportion as the bus voltage value drops; according to the current look-up table, the table look-up calculation is performed according to the increased speed value .

In the practice of the present invention, when performing torque control on the built-in permanent magnet synchronous motor, it is only necessary to establish a current lookup table under the rated bus voltage. When the bus voltage decreases, the validity of the output current and the correctness of the output torque are guaranteed through the calculation of the speed-up look-up table.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is a voltage limit circle and a current limit circle in the prior art;

Fig. 2 is the schematic flow chart diagram of the calculation method of the built-in permanent magnet synchronous motor current given value of the present invention;

Fig. 3 is the current look-up form when the rated bus voltage among the present invention;

Fig. 4 is a flow chart of calculating a given current value in the present invention.

Fig. 5 is a connection schematic diagram of a calculation device for a given current value of an interior permanent magnet synchronous motor according to the present invention.

Detailed ways

Embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

It should be clear that the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

The purpose of the present invention is to provide a built-in permanent magnet synchronous motor current look-up table design and current given value calculation method. In this method, the design of the look-up table only needs to correspond to a certain bus voltage value, but it can adapt to the change of the bus voltage during the calculation process of the current given value.

As shown in Figure 2, it is a calculation method of a built-in permanent magnet synchronous motor current given value according to the present invention, including:

Step 101, when the bus voltage is the rated voltage of the motor, the torque is calibrated to obtain a current lookup table, which contains the corresponding relationship between different torques and different speeds and current values under the rated bus voltage ,As shown in Figure 3;

Step 102, according to the current rotational speed and the given torque, calculate the given values of the d-axis and the q-axis current.

The step 102 includes:

Judging the bus voltage value;

When the bus voltage value is greater than or equal to the rated voltage, according to the current lookup table, the current speed value is used as the table lookup speed value, and the table lookup calculation is performed;

When the bus voltage is lower than the rated voltage, the current speed is increased in the same proportion as the bus voltage value drops to generate a table look-up speed value; according to the current look-up table, the table look-up calculation is performed according to the speed value used for table look-up .

The step of increasing the current speed in the same proportion as the bus voltage value drops, and generating the table look-up speed value is as follows:

ω _T ＝ωU _dc /U _Ndc , where, ω _T is the speed value of the look-up table; ω is the actual speed value; U _Ndc is the rated voltage; U _dc is the bus voltage.

The step of performing table look-up calculation is specifically as follows: according to the look-up table speed value ω _T , determine the speed range [ω _k , ω _k+1 ] to which it belongs;

Find the interval [T _k,n ^* ,T _k,n+1 ^* ] of the torque T _e ^* in the table corresponding to ω _k , and use linear interpolation to calculate the current value i _d,k corresponding to the torque under ω _k ^* and i _{q, k} ^* ; then obtain the current value i _{d, k+1} ^* and i _{q, k+1} ^* corresponding to the torque under the rotational speed ω _k+1 ;

Perform linear interpolation again on i _d,k ^* , i _q,k ^* and i _d,k+1 ^* , i _q,k+1 ^* according to the speed interval to obtain the current given value i _d ^* corresponding to the speed ω _T , _iq ^* .

Embodiment 1 of the present invention is described below, and the method includes:

Step 1) Calibrate the torque when the bus voltage is the rated voltage of the motor, and obtain the current lookup table at this time. The table is a two-dimensional table, which corresponds to the current values under different torques and different speeds under the rated bus voltage.

Step 2), calculate d and q axis current given values according to the current speed and given torque. In the calculation process, first judge the bus voltage value. When the bus voltage is greater than or equal to the rated voltage, the table look-up calculation is performed according to the current speed value. When the bus voltage is lower than the rated voltage, the current speed is increased in the same proportion as the bus voltage drops, and the table look-up calculation is performed according to the increased speed value. Assuming that the bus voltage during calibration is U _Ndc , according to the voltage limit circle equation

In the formula, L _d is the d-axis inductance; L _q is the q-axis inductance; Ψ _f is the flux amplitude of the permanent magnet, ω is the speed, and U _dc is the bus voltage.

When the bus voltage becomes αU _Ndc (α<1), the voltage limit circle with speed ω ₁ is consistent with the voltage limit circle with bus voltage U _Ndc and speed ω ₁ /α. Therefore, when the bus voltage decreases, the current given value calculated by looking up the table by increasing the speed in the same proportion will inevitably fall within the current voltage limit circle, ensuring that the output current is within a reasonable range.

Embodiment 2 of the present invention is described below.

Step 1), under the rated bus voltage, the motor torque is calibrated through the bench test, and the d-axis and q-axis current query tables corresponding to different speeds and torques satisfying MTPA control and field weakening control are obtained, as shown in Figure 3 .

Step 2), the calculation process of the current given value is shown in Figure 4. When the controller receives the torque command T _e ^* to calculate the current given value, it first determines the rotational speed value ω _T for looking up the table according to the bus voltage value. When the bus voltage U _dc is greater than or equal to the rated voltage U _Ndc , ω _T is equal to the current speed ω, when the bus voltage U _dc is lower than the rated voltage U _Ndc , ω _T rises to ω U _dc /U _Ndc .

Step 3), according to the look-up table speed value ω _T , determine the speed range [ω _k , ω _k+1 ] to which it belongs.

Step 4), find the interval [T _k,n ^* ,T _k,n+1 ^* ] of the torque T _e ^* in the table corresponding to ω _k , and use linear interpolation to calculate the current value corresponding to the torque under ω _k i _d,k ^* and i _q,k ^* . Then use the same method to obtain the current values id _,k+1 ^* and i _q,k+1 ^* corresponding to the torque at the rotational speed ω _k+1 .

Step 5), perform linear interpolation again on i _d,k ^* , i _q,k ^* and i _d,k+1 ^* , i _q,k+1 ^* according to the speed range, and obtain the current given value corresponding to the speed ω _T i _d ^* , i _q ^* .

As shown in Figure 5, it is a calculation device for a given value of the built-in permanent magnet synchronous motor current according to the present invention, including:

The table building unit 51, when the bus voltage is the rated voltage of the motor, calibrates the torque to obtain a current lookup table. The current lookup table contains the difference between different torques and different speeds and current values under the rated bus voltage. Correspondence;

The calculation unit 52 calculates the given values of the d-axis and the q-axis current according to the current rotational speed and the given torque.

The computing unit 52 includes:

Judging module, judging the bus voltage value;

The first query module, when the bus voltage value is greater than or equal to the rated voltage, according to the current look-up table, perform table look-up calculation according to the current speed value;

The second query module, when the bus voltage is lower than the rated voltage, the current speed is increased in the same proportion as the bus voltage value drops; according to the current look-up table, the table look-up calculation is performed according to the increased speed value .

The present invention has the following beneficial effects:

When performing torque control on the built-in permanent magnet synchronous motor, it is only necessary to establish a current lookup table at the rated bus voltage. When the bus voltage decreases, the validity of the output current and the correctness of the output torque are guaranteed through the calculation of the speed-up look-up table.

Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be implemented through computer programs to instruct related hardware, and the programs can be stored in a computer-readable storage medium. During execution, it may include the processes of the embodiments of the above-mentioned methods. Wherein, the storage medium may be a magnetic disk, an optical disk, a read-only memory (Read-Only Memory, ROM) or a random access memory (Random Access Memory, RAM) and the like.

The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Anyone skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present invention. All should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (6)

1. A calculation method of a built-in permanent magnet synchronous motor current given value is characterized in that, comprising: When the bus voltage is the rated voltage of the motor, the torque is calibrated to obtain a current look-up table, the current look-up table includes the corresponding relationship between different torques and different speeds and current values under the rated bus voltage; According to the current speed and given torque, calculate d, q axis current given value. 2. The method according to claim 1, wherein the step of calculating the given values of d and q axis currents according to the current rotational speed and given torque comprises: Judging the bus voltage value; When the bus voltage value is greater than or equal to the rated voltage, according to the current lookup table, the current speed value is used as the table lookup speed value, and the table lookup calculation is performed; When the bus voltage is lower than the rated voltage, the current speed is increased in the same proportion as the bus voltage value drops to generate a table look-up speed value; according to the current look-up table, the table look-up calculation is performed according to the speed value used for table look-up . 3. The method according to claim 2, characterized in that, the step of raising the current rotational speed in the same proportion as the bus voltage value drops, and generating the table look-up rotational speed value is specifically: ω _T ＝ωU _dc /U _Ndc , where, ω _T is the speed value of the look-up table; ω is the actual speed value; U _Ndc is the rated voltage; U _dc is the bus voltage. 4. The method according to claim 3, characterized in that, the step of performing table look-up calculation is specifically: According to the look-up table speed value ω _T, determine the speed range [ω _k, ω _k+1 ] to which it belongs; Find the interval [T _k,n ^* ,T _k,n+1 ^* ] of the torque T _e ^* in the table corresponding to ω _k , and use linear interpolation to calculate the current value i _d,k corresponding to the torque under ω _k ^* and i _{q, k} ^* ; then obtain the current value i _{d, k+1} ^* and i _{q, k+1} ^* corresponding to the torque under the rotational speed ω _k+1 ; Perform linear interpolation again on i _d,k ^* , i _q,k ^* and i _d,k+1 ^* , i _q,k+1 ^* according to the speed interval to obtain the current given value i _d ^* corresponding to the speed ω _T , _iq ^* . 5. A calculation device for a built-in permanent magnet synchronous motor current given value, characterized in that it comprises: The table building unit, when the bus voltage is the rated voltage of the motor, calibrates the torque to obtain a current lookup table, the current lookup table includes the correspondence between different torques and different speeds and current values under the rated bus voltage relation; The calculation unit calculates the d and q axis current given values according to the current speed and given torque. 6. The device according to claim 5, wherein the computing unit comprises: Judging module, judging the bus voltage value; The first query module, when the bus voltage value is greater than or equal to the rated voltage, according to the current lookup table, the current speed value is used as the table lookup speed value, and the table lookup calculation is performed; The second query module, when the bus voltage is lower than the rated voltage, the current speed is increased in the same proportion as the bus voltage value drops, and the table look-up speed value is generated; according to the current look-up table, according to the table look-up speed The value is calculated in the look-up table.