Method and arrangement for heating a vehicle battery of a motor vehicle

Abstract

The invention relates to a method and an arrangement (1) for heating a vehicle battery (51) of a motor vehicle (50), wherein the arrangement (1) comprises a pulse inverter (2) with a control unit (3), wherein the pulse inverter (2) is connected to the vehicle battery (51) and an electric machine (52), wherein a torque (T) and a speed (n) of the electric machine (52) are specified to the control unit (3), wherein the control unit (3) is configured to heat the vehicle battery (51) during driving operation by means of an additional current without changing the torque (T), wherein the control unit (3) is configured such that a magnetic flux (ψ) is assigned to the speed (n) by means of an assignment rule (4), wherein a current (i) and a phase angle (α) are assigned to the magnetic flux (ψ) and the torque (T) by means of assignment rules (5, 6).which is set by the pulse inverter (2), wherein a periodic additional flux (ψ, ) is added to the magnetic flux (ψ, Z ) is imprinted.

Description

[0001] The invention relates to a method and an arrangement for heating a vehicle battery of a motor vehicle.

[0002] Battery cells in vehicle batteries exhibit significantly reduced discharge and charge performance at low temperatures of the internal active material. Consequently, the driving and charging performance of electric vehicles is very low when the vehicle battery, especially the high-voltage battery, has cooled down, for example, after a long period of inactivity. While externally mounted heating elements or devices can provide some relief, they initially only heat the battery or cell casing. The temperature of the internal active material of the cells, on the other hand, only begins to rise after a time lag following the heating of the battery and cell casing. Furthermore, heating is inefficient due to heat losses during the warming of the cell casing, resulting in an overall insufficient heating effect.

[0003] From DE 10 2019 117 944 A1, a method and a device for charging a vehicle battery are known, wherein a control unit is configured to influence a charging process of the vehicle battery, wherein the device comprises a switching device, and wherein the switching device is configured to transmit a signal to the control unit in response to an actuation of the switching device, in particular by a user, wherein the control unit is configured to influence the vehicle battery before the charging process in response to the receipt of the signal depending on at least one target state for the charging process.

[0004] From DE 10 2018 208 358 A1, an electrical on-board network, a means of transport and an electrical circuit are known.The electrical circuit comprises an input terminal for a battery with an internal resistance and an inductance, a capacitor connected with its first terminal to the input terminal and with its second terminal to an electrical ground, a first switch connected with its first terminal to the input terminal and with its second terminal to an electrical ground, and an evaluation unit which, in response to a need to heat the battery, closes the first switch so that a current flows through the inductor, storing energy in the inductor, and then opens the first switch so that the energy causes a current to flow into the capacitor, and subsequently the voltage across the capacitor causes a current to flow back into the battery.The battery is therefore heated by thermal losses at an internal resistance of the battery.

[0005] A generic method is known from DE 10 2022 207 314 A1. The additional current is designed and applied in such a way that it does not impair the vehicle's drive; that is, the additional current does not cause any change in the speed of an electric machine powered by the drive current, nor does it produce any additional torque, but is instead converted into heat. It is stated that the additional current is generated by applying at least one harmonic.

[0006] From the subsequently published DE 10 2023 206 499 A1, a method for heating a vehicle battery of a vehicle with an electric machine is known, wherein during a journey of the vehicle, the drive current is selected by the pulse inverter from a drive current provided by the pulse inverter, wherein the drive current is selected as a function of a predetermined torque and by specifying an energy stored in a magnetic field of the electric machine such that the stored energy in the magnetic field is varied and thus a pulsating heating current is generated between the vehicle battery and the electric machine without changing the torque.

[0007] From the subsequently published DE 10 2023 004 191 A1, a method for heating a motor vehicle with an electric motor as a traction motor is known, which is controlled by means of "Deadbeat direct torque control / control and flux control" (DB DTFC), wherein the torque and the magnetic flux are controlled in a decoupled manner and losses are generated with the AC currents to produce heat.

[0008] The invention addresses the technical problem of improving a generic method in such a way that it can be easily integrated into an existing control system for a pulse inverter. A further technical problem is the creation of a suitable arrangement.

[0009] The solution to the technical problem is achieved by a method having the features of claim 1 and an arrangement having the features of claim 7. Further advantageous embodiments of the invention are set forth in the dependent claims.

[0010] In this method for heating a vehicle battery, an additional current is superimposed on the drive current supplied by a pulse inverter during vehicle operation. This is achieved by controlling the pulse inverter in such a way that the discharge current from the vehicle battery is increased. The torque of an electric motor remains unchanged. A magnetic flux is assigned to the rotational speed using a mapping rule, whereby a current and a phase angle are assigned to the magnetic flux and the torque by mapping rules, and these are set by the pulse inverter. A periodic additional flux is superimposed on the magnetic flux. Visually, the current vector pulsates along an isoline of the torque, thus generating high heating power at the internal resistance of the vehicle battery. The current and the phase angle represent the phasor diagram of a dq current control.Pulsating the current is considerably more efficient than a constant increase in current, since the heat loss in the latter case is primarily generated in the electric machine. The electric machine can, in principle, be an asynchronous machine, a permanent magnet synchronous machine, or a separately excited synchronous machine.

[0011] Preferably, the periodic additional flow is mean-free, so that on average the additional flow has no effect on the rotational speed.

[0012] In another embodiment, the additional flow has a triangular function.

[0013] In an alternative embodiment, the additional flow has at least one sine function. Different sine functions can also be superimposed. The advantage of the sine function is that it has no discontinuities in the gradient. However, a triangular function is very easy to implement in software.

[0014] In another embodiment, a maximum current for the electric machine is specified, whereby the current determined by the assignment rule from the torque and the magnetic flux is limited to this maximum current. This prevents the electric machine from being subjected to excessive thermal stress during heating operation. The maximum current can, for example, be determined empirically beforehand.

[0015] In another embodiment, the frequency of the periodic additional flux is greater than 500 Hz. Due to this high frequency, combined with the fact that the additional flux is free of averaging flux, it has no influence on the rotational speed, since the rotational speed cannot react quickly enough to the magnetic flux due to the inertia of the electric machine. Preferably, the frequency of the additional flux is greater than or equal to 1 kHz.

[0016] Regarding the details of the order, full reference is made to the preceding explanations of the procedure.

[0017] The invention is explained in more detail below with reference to a preferred embodiment. The figures show: Fig. 1 a schematic representation of an arrangement for heating a vehicle battery of a motor vehicle and Fig. 2 a combined representation of normalized iso-torque and flux characteristics of an electric machine with a control for determining the current and phase angle.

[0018] In the Fig. Figure 1 schematically depicts an arrangement 1 for heating a vehicle battery 51 of a motor vehicle 50, enabling the vehicle battery 51 to be heated even while driving. For this purpose, the arrangement 1 includes a pulse inverter 2 and a control unit 3 for controlling the pulse inverter 2. An electric motor 52, connected to the pulse inverter 2, is also shown. At least one temperature sensor 51-1 is assigned to the vehicle battery 51, and the control unit 3 receives either the temperature of the vehicle battery 51 or a signal indicating that the temperature of the vehicle battery 51 is below a threshold value. When the vehicle is stationary, the vehicle battery 51 can be preheated, for example, as described in DE 10 2022 207 314 A1, with the subsequent heating during driving now being controlled by... Fig. 2 will be explained in more detail.

[0019] The left side shows normalized iso-torque and flux characteristics, where the circle represents the maximum current i. max of the electric machine 52. The cross current i is... q above the longitudinal flow i d The control unit 3 receives a speed n and a torque T or drive torque as input from an engine control unit (not shown).

[0020] Using a mapping rule 4, the rotational speed n is transformed into a magnetic flux ψ. Mapping rule 4 can be a lookup table or an analytical mapping (formula). Using further mapping rules 5 and 6, a current i and a phase angle φ are then determined from the magnetic flux ψ and the torque T. Mapping rules 5 and 6 can also be lookup tables or analytical mappings. Alternatively, one of the mapping rules 5 and 6 can be an analytical mapping rule and the other a lookup table. The current i then passes through a limiter 7 to ensure that the current i is limited to the maximum current i. max is limited. The current i and the phase angle φ represent the phasor representation of the longitudinal current i. d and the crossflow i qThis represents the current waveforms, which can then be transformed, after a known transformation, into the three current waveforms for the three phases of the electric machine 52. Without a heating function, for example, a current i and a phase angle φ would be set, as shown on the left in the normalized iso-torque and flux characteristics. According to the invention, a periodic additional flux ψ is now applied. Z The additional flux ψ is added to the magnetic flux ψ due to the rotational speed n. Z is mean-free, i.e., the integral is zero. The frequency of the additional flux ψ Z is preferably greater than or equal to 1 kHz. Due to the additional flux ψ Z The current vector i runs from the indicated position along an isometric characteristic curve of the torque T to the right until the maximum current i is reached. max and then back to the left until the maximum current is reached again. max is reached. The two turning points are on the circle of i. maxThis is shown. This generates a pulsating current that flows through the internal resistance of the vehicle battery 51 and heats it due to the heat loss, without changing the torque T. Since the additional flux ψ Z is mean-free and the frequency of the additional flux ψ Z Since the rotational speed n remains constant, the rotational speed n is considerably larger than the inertia of the electric machine 52. Reference symbol list 1. Arrangement 2 pulse inverters 3 Control unit 4 Assignment rule 5 Assignment rule 6 Assignment rule 7 limiters 50 motor vehicles 51 Vehicle battery 51-1 Temperature sensor 52 Electric machine i electricity i max Maximum current i d longitudinal current i q Crossflow n rotational speed T torque φ Phase angle ψ magnetic flux ψ Z Additional flow

Claims

[1] Method for heating a vehicle battery (51) of a motor vehicle (50), wherein during a journey the motor vehicle (50) is subjected to an additional current by controlling the pulse inverter (2) in such a way that a discharge current from the vehicle battery (51) is increased, wherein a torque (T) of an electric machine (52) is not changed by the additional current, characterized by , that a magnetic flux (ψ) is assigned to a rotational speed (n) of the electric machine (52) by means of an assignment rule (4), wherein a current (i) and a phase angle (α) are assigned to the magnetic flux (ψ) and the torque (T) by means of assignment rules (5, 6), which are set by the pulse inverter (2), wherein a periodic additional flux (ψ) is added to the magnetic flux (ψ). Z ) is imprinted. [2] Method according to claim 1, characterized by , that the periodic additional flow (ψ Z) is free of mean values. [3] Method according to claim 1 or 2, characterized by , that the additional flow (ψ Z ) has a triangular function. [4] Method according to claim 1 or 2, characterized by , that the additional flow (ψ Z ) has at least one sine function. [5] Method according to any of the preceding claims, characterized by , that a maximum current (i max ) for the electric machine (52) is specified, wherein the current (i) determined by the assignment rule (5) from the torque (T) and the magnetic flux (ψ) is applied to the maximum current (i max ) is limited. [6] Method according to any of the preceding claims, characterized by , that the frequency of the periodic additional flux (ψ Z ) greater than 500 Hz. [7] Arrangement (1) for heating a vehicle battery (51) of a motor vehicle (50), wherein the arrangement (1) comprises a pulse inverter (2) with a control unit (3), wherein the pulse inverter (2) is connected to the vehicle battery (51) and an electric machine (52), wherein the control unit (3) is provided with a torque (T) and a speed (n) of the electric machine (52), wherein the control unit (3) is configured to heat the vehicle battery (51) during driving operation by means of an additional current without changing the torque (T), characterized by, that the control device (3) is designed such that a magnetic flux (ψ) is assigned to the rotational speed (n) by means of an assignment rule (4), wherein a current (i) and a phase angle (φ) are assigned to the magnetic flux (ψ) and the torque (T) by means of assignment rules (5, 6), which is set by the pulse inverter (2), wherein a periodic additional flux (ψ) is added to the magnetic flux (ψ). Z ) is imprinted. [8] Arrangement according to claim 7, characterized by , that the periodic additional flow (ψ Z ) is free of mean values. [9] Arrangement according to claim 7 or 8, characterized by , that the additional flow (ψ Z ) has a triangular function or at least a sine function. [10] Arrangement according to any one of claims 7 to 9, characterized by , that the frequency of the periodic additional flux (ψ Z ) greater than 500 Hz.

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