Method for field-oriented control of a synchronous machine, control unit and electric drive train

Abstract

Method for field-oriented control of a synchronous machine, in particular a permanent magnet synchronous machine, of a vehicle in which additional losses (P loss_tgt ) in the synchronous machine for heating at least one further component of the vehicle with the resulting waste heat, characterized in that one of the additional losses (P loss_tgt ) corresponding loss current (I amp_tgt ) is calculated, a device for determining d-current (I d_tgt_LUT ) and q-current (I q_tgt_LUT) used target flow (ψ Max ) according to the loss current (I amp_tgt ) is reduced, the reduction of the target flow (ψ Max ) on one for a target torque (Trq tgt ) required minimum flow (ψ Min ) is limited and an excess flow (ψ corr_overflow ) when limiting the target flow (ψ Max ) is determined, and the d-current (Id_tgt_LUT ) and the q-current (I q_tgt_LUT) corresponding to the excess flow (ψ corr_overflow ) are corrected in such a way that the target torque (Trg tgt ) is issued.

Description

[0001] The present invention relates to a method for field-oriented control of a synchronous machine, in particular a permanent magnet synchronous machine, of a vehicle, in which additional losses in the synchronous machine are generated for heating at least one further component of the vehicle, resulting in waste heat. The invention further relates to a control unit configured and programmed to execute the method, and to an electric drive train comprising a power electronics unit, a synchronous machine, and the control unit.

[0002] Prior art methods for controlling a synchronous machine are known in which additional losses are generated to produce additional heat. This heat can then be used to warm another component of the vehicle. This method of generating additional heat is intended to replace the vehicle's heating system in order to reduce costs.

[0003] Such procedures 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.

[0004] DE 10 2021 201 765 A1 discloses an electric motor-driven compressor for an air conditioning system in a vehicle. The electric motor is driven by an inverter which has a heat-generating current setpoint section configured to increase the temperature of the electric motor by changing the d-current setpoint and the q-current setpoint.

[0005] Existing methods (in particular EP 2 540 552 B1, which discloses a traction motor control with dissipation mode in an electric vehicle) are indeed capable of introducing inefficient stator currents without affecting torque accuracy. However, these methods have limitations, as the losses are generated by adding a so-called inefficient flux. Therefore, for any given torque, there is a minimum flux that can be achieved. When reducing the flux to increase the current, the current that can flow through the motor is limited at certain operating points.

[0006] The object of the present invention is therefore to provide a technology 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 problem is solved by the articles with the features according to the independent claims. Advantageous embodiments are the subject of the dependent claims.

[0008] A method for field-oriented control of a synchronous machine, in particular a permanent magnet synchronous machine, of a vehicle is disclosed, in which additional losses in the synchronous machine are used to heat at least one other component of the vehicle, resulting in waste heat. This other component of the vehicle can be a battery, a fluid circuit, and / or the vehicle interior. First, a loss current corresponding to the additional losses is calculated. Then, a target flow used to determine the d-current and q-current is reduced according to the loss current. The reduction of the target flow is limited to the minimum flow required for a given target torque. Any excess flow resulting from this reduction is determined, and the d-current and q-current are corrected accordingly to ensure that the target torque is still achieved.

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

[0010] When calculating the loss current, losses in the stator windings of the synchronous machine can be taken into account. This allows for a more precise determination of a new d-current and a new q-current.

[0011] The loss current of the previous control cycle can be subtracted from the calculated loss current to calculate a loss current error.

[0012] The leakage current error can then be entered into a PI controller to determine a current correction value.

[0013] The target flow rate can then be reduced according to the current correction value. Therefore, an appropriate reduction of the target flow rate is possible.

[0014] The d-current and q-current can initially be calculated using a lookup table into which the reduced target flux, a target torque, and preferably a temperature of the synchronous machine are entered. Therefore, a standard lookup table can be used for the initial determination of the currents. Subsequently, the currents can be adjusted by a respective correction value.

[0015] The d-current correction value can be calculated from the excess flow using a scaling factor. This takes the excess flow into account.

[0016] The d-current correction value can be limited according to the difference between the voltage across the stator windings and a nominal voltage, or by using a dedicated PI controller. This ensures that a voltage limit is not reached.

[0017] 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.

[0018] Also disclosed is a control unit that is designed and programmed to execute the procedure 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 activate them according to a calculation result. The procedure 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.

[0019] Also revealed is an electric drive train with a power electronics unit, a synchronous machine and the control unit.

[0020] The present invention is described in detail below with reference to the figures. These show: Fig. 1 a block diagram of a control unit according to an embodiment of the present invention; Fig. 2 a block diagram of a fault current calculation unit that is present in an energy harvesting control unit; Fig. 3. A block diagram of a unit for calculating the d-current correction value, which is present in an energy harvesting control unit; and Fig. 4 a d-current / q-current diagram in which a characteristic map for determining a d-current and a q-current, an MTPA line, a line for the minimum flux, torque hyperbolas and flux lines are plotted.

[0021] The present invention is described below with reference to preferred embodiments and the figures. However, this description of embodiments should not be considered exhaustive.

[0022] Fig. Figure 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 control 2, an energy harvesting control 4, a look-up table 6, and a unit 8 for correcting the d-current and the q-current.

[0023] A method known from the prior art can be used as field weakening control 2, with which a corresponding flux ψ can be controlled. Max is determined.

[0024] The flux ψ determined by the field weakening control 2 Max is together with a desired power loss P loss_tgt , a stator resistor R S , a current I amp_last_iter a previous control cycle, a maximum current I amp_max , a target torque Trq tgt and a temperature T Mot The synchronous machine is entered into the energy harvesting control 4. Additionally, a power loss P can be specified. loss_ironin the stator windings to allow for a more precise determination.

[0025] The energy harvesting control 4 then determines an adapted flow ψ tgt_output and a d-current correction value I d_Offset The adapted flow ψ tgt_output is together with the target torque Trq tgt and possibly the temperature T Mot The synchronous machine is entered into look-up table 6 to obtain a d-current I. d_tgt_LUT and a q-current I q_tgt_LUT to determine initially.

[0026] The d-current I d_tgt_LUT and the q-current I q_tgt_LUT are then combined with the d-current correction value I d_Offset entered into unit 8 to correct the d-current and the q-current to create a new d-current I d_tgt_new and a new q-current I q_tgt_new to determine which are then impressed into the stator windings of the synchronous machine.

[0027] Therefore, an additional power loss P will be imprinted. loss_tgt caused by the energy harvesting control 6, which is added to a known field weakening control 2. The structure of the energy harvesting control 4 is described below with reference to the Fig. 2 and Fig. 3 described.

[0028] First, a fault current calculation unit 10 is used, into which the desired power loss P is entered. loss_tgt is entered based on Fig. 2 described. Additionally, a power loss P can also occur. loss_iron input into the stator windings and in the adder 12 of the desired power loss P loss_tgt to be subtracted. The resulting power loss P loss_tgt_CopperThe result 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 taken to obtain the 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 limited. Finally, the loss current I amp_tgt the loss current I amp_last_iter a previous control cycle is subtracted in the adder 22 to determine the fault current I amp_err to obtain.

[0029] The fault current I obtained in this way amp_err will be in a Fig. Unit 24, as shown, is used to calculate the d-current correction value. First, the fault current is input into a PI controller 26 to determine a current correction value I. amp_correction to obtain the current correction value I amp_correctionThe result is then multiplied in a multiplier 28 by a scaling factor I_to_ψ_scale_factor to obtain a flow correction value ψ. correction to obtain the one in the adder 30 from the river ψ Max The value obtained from field weakening control 2 is subtracted. A resulting corrected flux ψ corrected The value is then entered into limiter 32, which limits the flow to a range between a minimum flow ψ. Min and the flux ψ supplied by the field weakening control 2 Max is done.

[0030] The minimum flux ψ Min The minimum flux is determined by a unit 34. This unit 34 is provided by a lookup table. The rationale is that for each torque, a specific minimum flux ψ is required. Min is necessary. As soon as this minimum flow ψ MinOnce this limit is reached, a further reduction in flow would also result in a reduction in output torque.

[0031] This relationship is demonstrated using Fig. Figure 4 explains this by showing a d-current / q-current diagram. This diagram includes 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. As is known, 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 chosen that lies as far away as possible from the MTPA line 44, in the direction of a lower flux, along the same torque hyperbola. However, as mentioned earlier, the flux cannot be reduced beyond a certain limit, as this would result in a reduction of torque. This limit is shown in Figure 4. Fig. 4 is represented by line 44 for the minimum flow. This line is now subtracted in unit 34 to represent the minimum flow ψ. Min , which is for a specific torque Trq tgt is necessary to be able to determine.

[0032] The flow ψ output by the limiter 32 tgt_output will then, as in Fig. 1 shown, entered into look-up table 6 to find the currents I d_tgt_LUT and I q_tgt_LUT to determine.

[0033] In an adder 36, the flow ψ output by the limiter 32 is used. tgt_output then the corrected flux ψ corrected subtracted to obtain an excess flow ψ corr_overflow to calculate. The excess flow ψ corr_overflow is multiplied in a multiplier 38 with the scaling factor 1 / I_to_ψ_scale_factor to obtain a d-current correction value I d_Offset to obtain.

[0034] The d-current correction value I d_OffsetThe current is then limited in a limiter 40 to a range between a minimum d-current correction value and 0 to prevent the energy harvesting control 4 from influencing the field weakening control 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 limit can be achieved by taking into account a saturation proportional to the distance to the system's voltage limit or with a special PI controller.

[0035] As in Fig. Figure 1 shows the d-current correction value I d_Offset Entered into unit 8 to correct the d-current and the q-current. The new d-current I d_tgt_new is easily calculated by adding the d-current I d_tgt_LUT from look-up table 6 with the d-current correction value I d_Offset reached: Id_tgt_new=Id_tgt_LUT+Id_Offset

[0036] Since a mere change in the d-current would alter the output torque, the new q-current I must be q_tgt_new with a q-current correction value Iq_Offset be adapted: Iq_tgt_new=Iq_tgt_LUT+Iq_Offset

[0037] The q-current correction value I q_Offset can be calculated, for example, by approximating the torque hyperbola: Iq_Offset=[Id_Offset*Trqtgt*(Ld−Lq)] / (−1.5*Motor_pole_pairs*[(Ld−Lq)*Id_tgt_new+PsiPM]2)

[0038] These new current values ​​I d_tgt_new and I q_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. Reference symbol list 1 control unit 2 Field weakening control 4 Energy Harvesting Control 6 Look-Up Table Unit 8 for correcting the d-current and the q-current 10 Fault current calculation unit 12 Adders 14 Multipliers 16 Multipliers 18th root 20 limiters 22 Adders 24 units for calculating the d-current correction value 26 PI controllers 28 Multipliers 30 Adders 32 limiters 34 Unit for determining a minimum flow 36 Adders 38 multipliers 40 limiters 42 Unit for determining a limit value for the d-current correction value 44 MTPA characteristic curve 46 lines for minimum flow

Claims

[1] Method for field-oriented control of a synchronous machine, in particular a permanent magnet synchronous machine, of a vehicle in which additional losses (P loss_tgt ) in the synchronous machine for heating at least one other component of the vehicle, generating waste heat as a result, characterized by , that one of the additional losses (P loss_tgt ) corresponding loss current (I amp_tgt ) is calculated, a device for determining d-current (I d_tgt_LUT ) and q-current (I q_tgt_LUT) used target flow (ψ Max ) according to the loss current (I amp_tgt ) is reduced, the reduction of the target flow (ψ Max ) on one for a target torque (Trq tgt ) required minimum flow (ψ Min ) is limited and an excess flow (ψ corr_overflow ) when limiting the target flow (ψ Max ) is determined, and the d-current (I d_tgt_LUT) and the q-current (I q_tgt_LUT) corresponding to the excess flow (ψ corr_overflow ) are corrected in such a way that the target torque (Trg tgt ) is issued. [2] Method according to claim 1, characterized by , that when calculating the loss current (I amp_tgt ) a loss (P loss_iron ) is taken into account in the stator windings of the synchronous machine. [3] Method according to claim 1 or 2, characterized by , that the loss current (I amp_last_iter ) of the previous control cycle from the calculated loss current (I amp_tgt ) to calculate a leakage current error (I amp_err ) is subtracted. [4] Method according to claim 3, characterized by , that the leakage current error (I amp_err ) into a PI controller (26) to determine a current correction value (I amp_correction ) will be entered. [5] Method according to claim 4, characterized by , that the target flow (ψ Max ) according to the current correction value (I amp_correction) is reduced. [6] Method according to any one of claims 1 to 5, characterized by , that the d-current (I d_tgt_LUT ) and the q-current (I q_tgt_LUT ) first using a look-up table (6) into which the reduced target flow (ψ) tgt_output ), a target torque (Trg tgt ) and preferably a temperature (T Mot ) of the synchronous machine is entered, calculated, and then adjusted by a respective correction value (I d_Offset , I q_Offset ) will be adjusted. [7] Method according to claim 6, characterized by , that the d-current correction value (I d_Offset ) from the excess flow (ψ corr_overflow ) is calculated using a scaling factor. [8] Method according to one of claims 6 or 7, characterized by , that the q-current correction value (I d_Offset ) is determined taking into account a torque hyperbola in a d-current / q-current diagram. [9] Control unit (1) which is configured and programmed to execute the method according to any 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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