Field-oriented open-loop / closed-loop control of a synchronous machine

Abstract

The invention relates to a method for field-oriented open-loop / closed-loop control of a synchronous machine of a vehicle, in which additional losses (Ploss_tgt) are generated in the synchronous machine for the purpose of heating at least one further component of the vehicle using resulting waste heat. For this purpose, a leakage current (lamp_tgt) corresponding to the additional losses (Ploss_tgt) is calculated, a target flux (ΨMax) used for determining d current (ld_tgt_LUT) and q current (lq_tgt_LUT) is reduced in accordance with the leakage current (lamp_tgt), the reduction of the target flux (ΨMax) is limited to a minimum flux (ΨMin) required for a target torque (Trgtgt), and an excess flux (Ψcorr_overflow) is ascertained during the limitation of the target flux (ΨMax). The d-current (ld_tgt_LUT) and the q-current (lq_tgt_LUT) are subsequently corrected in accordance with the excess flux (Ψcorr_overflow) in such a way that the target torque (Trgtgt) is output. The invention also relates to a control unit (1) and to an electric drivetrain having a power electronics unit, a synchronous machine and the control unit.

Description

[0001] Description

[0002] FIELD-ORIENTED CONTROL OF A SYNCHRONOUS MACHINE

[0003] The present invention relates to a method for the field-oriented control / regulation of a synchronous machine, in particular a permanent magnet synchronous machine, of a vehicle, in which additional losses are generated in the synchronous machine for heating at least one other component of the vehicle with the resulting waste heat. The invention also relates to a control unit configured and programmed to carry out the method, and to an electric drive train comprising a power electronics unit, a synchronous machine, and the control unit.

[0004] Methods for controlling a synchronous machine are known in the prior art, in which additional losses are generated to generate additional heat. This heat can then be used to heat another component of the vehicle. This method of generating additional heat is intended to replace heaters in the vehicle in order to reduce costs.

[0005] Such methods are known, for example, from US 2018 / 0 083 509 A1 , WO 2017 / 214 234 A1 , EP 2 540 552 B1 , US 10 183 580 B2 and DE 10 2019 133 634 A1.

[0006] Existing methods (in particular EP 2 540 552 B1) are capable of injecting inefficient stator currents without compromising torque accuracy. However, these methods have limitations because the losses are generated by adding a so-called inefficient flux. Therefore, for each torque there is a minimum flux that can be achieved. With the method of reducing the flux in order to increase the current, the current that can flow through the motor is limited at certain operating points. It is therefore the object of the present invention to provide a technique that is more advanced than the prior art. In particular, the amplitude of a leakage current should be adjustable to a desired value. Furthermore, the desired torque should be maintained and the voltage limits of the system should be observed.

[0007] This object is achieved by the subject matter having the features according to the independent claims. Advantageous embodiments are the subject matter of the dependent claims.

[0008] Disclosed is a method for the field-oriented control / regulation of a synchronous machine, in particular a permanent magnet synchronous machine, of a vehicle, in which additional losses are generated in the synchronous machine for heating at least one other component of the vehicle with the resulting waste heat. The other component of the vehicle can be a battery, a fluid circuit, and / or a vehicle interior. For this purpose, a loss current corresponding to the additional losses is first calculated. Subsequently, a target flux used to determine the d-current and q-current is reduced according to the loss current. The reduction in the target flux is limited to a minimum flux required for a target torque. Any excess flux when limiting the target flux is determined, and the d-current and the q-current are corrected according to the excess flux such that the target torque continues to be output.

[0009] As a result, the additional losses can be set to a desired value. When the minimum flux limit is reached at the given target torque, the excess flux is used to correct the d-current and q-current so that the target torque can be maintained even while generating losses.

[0010] When calculating the leakage current, a loss in the stator windings of the synchronous machine can be taken into account. This allows for a more accurate determination of a new d-current and a new q-current. The leakage current of the previous control cycle can be subtracted from the calculated leakage current to calculate a leakage current error.

[0011] The leakage current error can then be entered into a PI controller to determine a current correction value.

[0012] The target flow can then be reduced according to the current correction value. Accordingly, an appropriate reduction in the target flow is possible.

[0013] The d-current and q-current can first be calculated using a look-up table, into which the reduced target flux, a target torque, and preferably a temperature of the synchronous machine are entered. Thus, a standard look-up table can be used to initially determine the currents. The currents can then be adjusted by a respective correction value.

[0014] The d-current correction value can be calculated from the excess flow using a scaling factor. Thus, the excess flow is taken into account.

[0015] The d-current correction value can be limited according to the voltage difference between the stator windings and the nominal voltage, or by using a dedicated PI controller. This ensures that voltage limitation is not reached.

[0016] The q-current correction value can be determined by considering a torque hyperbola in a d-current / q-current diagram. The q-current is then adjusted accordingly so that the target torque can be maintained.

[0017] Also disclosed is a control unit configured and programmed to execute the method according to one of the above aspects. The control unit has inputs for acquiring measurement signals and outputs for controlling power electronics in order to actuate them according to a calculation result. The method is stored in the control unit in the form of program code, which can be executed by a central processing unit of the control unit.

[0018] Also disclosed is an electric drive train with a power electronics unit, a synchronous machine and the control unit.

[0019] The present invention is described in detail below with reference to the figures. They show:

[0020] Fig. 1 is a block diagram of a control unit according to an embodiment of the present invention;

[0021] Fig. 2 is a block diagram of a fault current calculation unit present in an energy harvesting controller of the control unit;

[0022] Fig. 3 is a block diagram of a unit for calculating the d-current correction value, which is present in an energy harvesting controller of the control unit; and

[0023] Fig. 4 is a d-current / q-current diagram in which a map for determining a d-current and a q-current, an MTPA line, a minimum flux line, torque hyperbolas and flux lines are plotted.

[0024] The present invention will be described below using preferred embodiments with reference to the figures. However, the description of the embodiments should not be considered exhaustive.

[0025] Fig. 1 shows a block diagram of a control unit 1 according to an embodiment of the present invention. The control unit 1 comprises a field weakening controller 2, an energy harvesting controller 4, a look-up table 6, and a unit 8 for correcting the d-current and the q-current. A method known from the prior art can be used as the field weakening controller 2, with which a corresponding flux i Max is determined.

[0026] The flux i Max determined by the field weakening control 2 is used together with a desired power loss Piossjgt, a stator resistance Rs, a current lampjast ter of a previous control cycle, a maximum current lam P_max, a target torque Trqtgt, and a temperature TMot of the synchronous machine are entered into the energy harvesting control 4. In addition, a power loss Pioss ron in the stator windings can be entered to enable a more precise determination.

[0027] The energy harvesting controller 4 then determines an adjusted flux i tgt_output and a d-current correction value lejottset. The adjusted flux i tgt_output is entered into the look-up table 6 together with the target torque Trqtgt and, if applicable, the temperature TMot of the synchronous machine to determine a d-current ld_t g t_LUT and a q-current lq_t g t_i_uT to be determined initially.

[0028] The d-current ld_tgt_LUT and the q-current lq_t g t_i_uT are then input together with the d-current correction value ld_otrset into the unit 8 for correcting the d-current and the q-current to obtain a new d-current ld_t g t_new and a new q-current lq_t gt_new, which are then impressed into the stator windings of the synchronous machine.

[0029] Consequently, an additional power loss Piossjgt is caused by the energy harvesting controller 6, which is added to a known field weakening controller 2. The structure of the energy harvesting controller 4 is described below with reference to Figures 2 and 3.

[0030] First, a fault current calculation unit 10, into which the desired power loss Piossjgt is input, is described with reference to Fig. 2. Additionally, a power loss Piossjron in the stator windings can also be input and subtracted from the desired power loss Piossjgt in the adder 12. The resulting power loss Piossj gt_copper is multiplied by 2 / 3 in a multiplier 14 and then divided by the stator resistance Rs in a multiplier 16. The square root 18 is then extracted to obtain a desired leakage current. This leakage current is then limited by the limiter 20 to a value between 0 and the maximum current I amp_max. Finally, the leakage current lampjgt of a previous control cycle is subtracted from the leakage current lampjast ter in the adder 22 to obtain the error current I amp_err.

[0031] The resulting fault current lam P_err is input to a unit 24 shown in Fig. 2 for calculating the d-current correction value. First, the error current is input to a PI controller 26 to obtain a current correction value I amp_correction . The current correction value I amp_correction is then multiplied by a scaling factor l_to_i _scale_factor in a multiplier 28 to obtain a flux correction value jcorrection, which is subtracted in the adder 30 from the flux i Max obtained from the field weakening controller 2. The obtained corrected flux i corrected is then input to the limiter 32, where the flux is limited to a range between a minimum flux i Min and the flux i Max supplied by the field weakening controller 2.

[0032] The minimum flow i min is determined by a unit 34 for determining a minimum flow. Unit 34 is provided by a look-up table. The reason for this is that a certain minimum flow i min is required for each torque. Once this minimum flow i min is reached, a further reduction in the flow would also result in a reduction in the output torque.

[0033] This relationship is explained using Fig. 4, which shows a d-current / q-current diagram in which a characteristic map for determining a d-current and a q-current, an MTPA line 44, a line 46 for the minimum flux, torque hyperbolas and flux lines are plotted. As is known, the losses are optimized near the MTPA (maximum torque per ampere) line 44. To generate additional losses, a combination of d-current and q-current must be selected that is as far away as possible from the MTPA line 44 in the direction of a lower flux on the same torque hyperbola. As already mentioned, the flux cannot be reduced beyond a certain limit, as this would result in a reduction in torque. This limit is represented in Fig. 4 by the line 44 for the minimum flux.This line is now stored in unit 34 in order to determine the minimum flow i Min required for a specific torque Trqtgt.

[0034] The flow output by the limiter 32 is g t_output is then entered into the look-up table 6 as shown in Fig. 1 to obtain the currents ld_tgt_LUT and lq_t g t_LUT to determine.

[0035] In an adder 36, the corrected flow i corrected is then subtracted from the flow i tgt_output output by the limiter 32 to calculate an excess flow i corr_overflow. The excess flow i C orr_overfiow is multiplied by the scaling factor 1 / l_to_i _scale_factor in a multiplier 38 to obtain a d-current correction value ld_offeet.

[0036] The d-current correction value ld_offeet is then limited in a limiter 40 to a range between a minimum d-current correction value and 0 to prevent the energy harvesting controller 4 from influencing the field weakening controller 2. The minimum d-current correction value is determined by a unit 42 for determining a limit value for the d-current correction value. The limitation can be achieved by taking into account a saturation that is proportional to the distance from the system's voltage limit or with a special PI controller.

[0037] As shown in Fig. 1, the d-current correction value ld_offeet is input to the d-current and q-current correction unit 8. The new d-current ld_t g t_new is simply calculated by adding the d-current ld_t gt_LUT from the look-up table 6 with the d-current correction value ld_offeet is achieved: ld_tgt_new — ld_tgt_LUT + ld_Offset Since a mere change of the d-current would change the output torque, the new q-current lq_t g t_new can be adjusted with a q-current correction value iq_offeet: lq_tgt_new = lq_tgt_LUT + lq_Offset

[0038] The q-current correction value lq_offeet can be calculated, for example, by approximating the torque hyperbola: l q _offset = [ld_offset * Trqtgt * (Ld - L q )] / (-1 .5 * Motor_pole_pairs * [(Ld - Lq) * ld_tgt_new + PsiPM ] 2 )

[0039] These new current values ​​Id. _tgt_new and lq. _tgt_new are then used for the further operation of the synchronous machine and generate the same output torque while simultaneously generating the desired power loss.

[0040] List of reference symbols

[0041] 1 control unit

[0042] 2 Field weakening control

[0043] 4 Energy Harvesting Control

[0044] 6 Look-up table

[0045] 8 Unit for correcting the d-current and the q-current

[0046] 10 Residual current calculation unit

[0047] 12 adders

[0048] 14 multipliers

[0049] 16 multipliers

[0050] 18 root

[0051] 20 limiters

[0052] 22 adders

[0053] 24 Unit for calculating the d-current correction value

[0054] 26 PI controllers

[0055] 28 multipliers

[0056] 30 adders

[0057] 32 limiters

[0058] 34 Unit for determining a minimum flow

[0059] 36 adders

[0060] 38 multipliers

[0061] 40 limiters

[0062] 42 Unit for determining a limit value for the d-current correction value

[0063] 44 MTPA characteristic curve

[0064] 46 Line for the minimum flow

Claims

Claims 1. Method for the field-oriented control / regulation of a synchronous machine, in particular a permanent magnet synchronous machine, of a vehicle, in which additional losses (Piossjgt) are generated in the synchronous machine for heating at least one further component of the vehicle with the resulting heat loss, characterized in that a loss current (lampjgt) corresponding to the additional losses (Piossjgt) is calculated, a target flux (i Max) used to determine the d-current (ldjgtj_uT) and the q-current (Iqjgtj-UT) is reduced according to the loss current (lampjgt), the reduction of the target flux (i Max) is limited to a minimum flux (i Min) required for a target torque (Trqtgt), and an excess flux (i corr_overflow) is determined when limiting the target flux (i Max), and the d-current (ldjgtj_uT) and the q-current (Iqjgtj-UT) are reduced according to the excess flux (4Jcorr_overfiow) be corrected in such a way,that the target torque (Trgtgt) is output., 2. Method according to claim 1, characterized in that when calculating the leakage current (lampjgt) a loss (Piossjron) in stator windings of the synchronous machine is taken into account.

3. Method according to claim 1 or 2, characterized in that the leakage current (lampjastjter) of the previous control cycle is subtracted from the calculating leakage current (lampjgt) to calculate a leakage current error (lamp_err).

4. Method according to claim 3, characterized in that the leakage current error (lam P _err) into a PI controller (26) for determining a current correction value (lam P _correction).

5. Method according to claim 4, characterized in that the target flow (i Max) according to the current correction value (lam P _correction) is reduced.

6. Method according to one of claims 1 to 5, characterized in that the d-current (ld_t g t_LUT) and the q-current (lq_tgt_i_uT) are initially calculated using a look-up table (6) into which the reduced target flow (i tgt_out P ut), a target torque (Trgtgt) and preferably a temperature (TMot) of the synchronous machine are entered, is calculated, and then adjusted by a respective correction value (IdjDffeet, lq_offset).

7. The method according to claim 6, characterized in that the d-current correction value (ld_offset) is calculated from the excess flow (i corr_overfiow) using a scaling factor.

8. Method according to one of claims 6 or 7, characterized in that the q-current correction value (ld_offeet) is determined taking into account a torque hyperbola in a d-current / q-current diagram.

9. Control unit (1) which is designed and programmed to carry out the method according to one of claims 1 to 8.

10. Electric drive train with a power electronics unit and a synchronous machine, characterized by the control unit (1) according to claim 9.

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