Method for heating a motor vehicle

Abstract

Method for heating components of an electric vehicle when the electric vehicle is stationary comprising: using an inverter 3 to supply only a direct (d) current (no / zero quadrature (q) current) to an

Description

Method for heating a motor vehicle The invention relates to a method for heating a motor vehicle. Motor vehicles comprising an internal combustion engine generate enough waste heat, when the internal combustion engine is running, to be able to heat the passenger compartment and / or the vehicle battery. These possibilities are not available in motor vehicles comprising an electric motor as traction motor. However, the electric motor and the associated power electronics can also generate waste heat, which can be used to heat the passenger compartment and / or the vehicle battery via a coolant circuit. This heat source is thus not available when the motor vehicle is stationary since, when the electric motor is at a standstill, it accordingly does not generate any heat. The present invention seeks to provide a method for heating a motor vehicle comprising an electric motor as traction motor, which method allows the passenger compartment and / or the vehicle battery to be heated even when the motor vehicle is stationary. This may be achieved by the features of claim 1. One exemplary embodiment of the invention relates to a method for heating a motor vehicle comprising a three-phase electric motor as traction motor, wherein a pulse- controlled inverter is provided for supplying power to the electric motor, wherein a coolant circuit is provided for cooling the electric motor and the pulse-controlled inverter using coolant, said coolant circuit using the coolant to supply heat to a heat exchanger for heating the passenger compartment and / or to the vehicle battery, wherein when the electric motor is stationary, a positive d current and / or negative d current is controlled in the d-axis, with the result that heat loss is generated, said heat loss being introduced into the coolant. As a result, current can be fed to the electric motor without a motor vehicle drive torque which propels the motor vehicle being produced. The current feed nonetheless results in heat loss being generated, said heat loss being introduced into a coolant which can be used for heating. Thus, the provided electric motor can be used as a heat source by using a targeted current feed even though the electric motor is not propelling the motor vehicle in this operating mode. In one exemplary embodiment, it is also advantageous for the electric motor to be supplied with the d current in the d-axis and to generate heat loss, which is used as waste heat, both in the electric motor and in the pulse-controlled inverter, wherein the g current in the g-axis is equal to zero. Propulsion occurs only as a result of generating a torque on the basis of a q current. The d current without any q current therefore does not propel the motor vehicle and nonetheless generates heat loss. The terms “d current” and “q current” derive from consideration in terms of d / q coordinates in order to describe a three-phase electric motor on the basis of a d / q transformation. The d / q transformation generally serves to transfer three-phase values as in the case of a three-phase electric motor, also known as a three-phase machine, with the axes U, V, W to a two-axis coordinate system with the axes d and q. In a further exemplary embodiment, it is expedient if as a result of the d current being set, no torque that could propel the motor vehicle is applied to the wheels of the motor vehicle. Power loss is thus induced without the motor vehicle having to be moved. It is also advantageous for the heat loss from the electric motor to be generated as power losses from the winding of the electric motor and / or as eddy current losses in laminations and / or for the heat loss in the pulse-controlled inverter to be generated as on-state losses from the power switches and freewheeling diodes and / or as switching losses when the power switches are switched and / or line losses and / or losses in the DC-link capacitor during operation of the power switches. Furthermore, it is also advantageous for the pulse-controlled inverter to have an electronic circuit comprising power switches and freewheeling diodes, wherein the current through the power switches and the freewheeling diodes is modulated. The desired d current can thus be temporally modulated in order to achieve suitable heating and not to damage the electric motor. It is also advantageous for the pulse-controlled inverter to have high-side power transistors, low-side power transistors, low-side diodes and high-side diodes, wherein the current through the high-side power transistors and the low-side diodes is controlled in a modulated manner and / or wherein the current through the low-side power transistors and the high-side diodes is controlled in a modulated manner. This respective modulation allows heating to be achieved with a defined current feed, without the electric motor being damaged. It is preferable for the current through the power transistors and diodes to be pulse- modulated, in particular with a square-wave signal having a constant amplitude or a modulated amplitude. This respective modulation allows heating to be achieved with a defined current feed, without the electric motor being damaged. Embodiments of the invention will be discussed in detail below on the basis of an exemplary embodiment and with reference to the drawings. In the drawings: fig. 1 shows a schematic depiction of an interconnection of an electric motor with a pulse-controlled inverter for illustrating the method according to an embodiment of the invention, fig. 2 shows a schematic depiction regarding operation of the electric motor to generate heat loss when the electric motor is at a standstill, fig. 3 shows a schematic depiction regarding operation of the electric motor in an alternative manner to generate heat loss when the electric motor is at a standstill, fig. 4 shows a schematic depiction regarding operation of the electric motor in an alternative manner to generate heat loss when the electric motor is at a standstill, and fig. 5 shows a schematic depiction regarding operation of the electric motor in an alternative manner to generate heat loss when the electric motor is at a standstill. Figure 1 schematically shows an electric motor 1 as a three-phase machine, which is supplied with current by a high-voltage vehicle electrical system 2 and a pulse- controlled inverter 3. For this purpose, the three individual phases of the electric motor 1 can be supplied with current | in a separately controlled manner. In this case, the electric motor 1 has resistive components which can be inductive or ohmic; see reference signs 4 and 5. The current through the electric motor 1 with its three phases can be depicted in a three-dimensional coordinate system, such that the currents ly, lv and lw can be depicted. A d / q transformation also makes it possible to employ a depiction with currents lq and lq. The pulse-controlled inverter 3 has power switch modules 6, which are equipped with high-side power switches 7, low-side power switches 8, high-side diodes 9 and low-side diodes 10. In this case, the power switches may be in the form of MOSFET power switches or, as shown in figure 1, IGBT power switches 11. In this case, the diode is integrated into the IGBT power switch 11. A power switch module 6 can consist herein of two IGBT power switches 11. In this case, the torque M of the electric motor 1 has a plurality of terms. In one term, the respective torque component of M is proportional to ls * lq, and in the other term, the torque component is proportional to lg. This means that when Iq = 0, no torque M is transmitted. However, in this case, ls may be non-zero, with the result that heat loss is induced. M~A*lg*lg+B*lq where the factors A and B are proportional to the number of pole pairs p, the flux F of the permanent magnets and / or the secant inductance S in the d / g-axis, with A=3 / 2*p*Ssd— Ssq) and B = 3 / 2*p*F. Accordingly, heating while the motor vehicle is at a standstill can be used at operating points at which lq = 0. Therefore, the method according to an embodiment of the invention for heating a motor vehicle comprising a three-phase electric motor 1 as traction motor provides the following approach, wherein a pulse-controlled inverter 3 is provided for supplying power to the electric motor 1, wherein a coolant circuit 12 is provided for cooling the electric motor 1 and the pulse-controlled inverter 3 using coolant, said coolant circuit using the coolant to supply heat to a heat exchanger for heating the passenger compartment and / or to the vehicle battery 13. In this case, the vehicle battery 13 is part of the high-voltage vehicle electrical system 2. When the electric motor 1 is stationary, a positive d current and / or negative d current is controlled in the d-axis, with the result that heat loss is generated, said heat loss being introduced into the coolant. This then allows the vehicle battery 13 and / or the passenger compartment to be heated. In this case, the electric motor 1 is supplied with the d current in the d-axis and heat loss, which is used as waste heat, is generated both in the electric motor and in the pulse-controlled inverter, wherein the q current in the g-axis is equal to zero. In this case, setting the d current to zero ensures that no torque that could propel the motor vehicle is applied to the wheels of the motor vehicle. The heat loss from the electric motor 1 occurs as power losses from the winding of the electric motor 1 and / or as eddy current losses in laminations and / or the heat loss in the pulse-controlled inverter 3 occurs as on-state losses from the power switches 7, 8 and freewheeling diodes and / or as switching losses when the power switches 7, 8 are switched and / or line losses and / or losses in the DC-link capacitor during operation of the power switches 7, 8. According to figure 1, the pulse-controlled inverter 3 has an electronic circuit comprising power switches 7, 8 and freewheeling diodes 9, 10, wherein the current through the power switches 7, 8 and the freewheeling diodes 9, 10 is modulated. In the exemplary embodiment shown, the pulse-controlled inverter 3 has high-side power transistors 7, low-side power transistors 8, high-side diodes 9 and low-side diodes 10, wherein the current through the high-side power transistors 7 and the low-side diodes 10 is controlled in a modulated manner and / or wherein the current through the low-side power transistors 8 and the high-side diodes 9 is controlled in a modulated manner. In this case, the current through the power transistors 7, 8 and diodes 9, 10 can be pulse-modulated, in particular with a square-wave signal having a constant amplitude or a modulated amplitude. Figures 2 to 4 show examples of such a modulation of the currents. In figure 2, the high-side power transistor current is modulated in alternation with the low-side diode current as a square-wave signal, such that Iq = 0 and Id is, for example, equal to 644 A. The currents lpn, lpn and lpnw of the phases U, V, W are correspondingly also shown. In this case, lpn is constantly positive at around 644 A, and the currents len and lenw are constant and negative at approximately -180 A and approximately -450 A, such that Ig = 0 as a result, and lq is 644 A. In figure 3, the low-side power transistor current is modulated in alternation with the high-side diode current as a square-wave signal, such that Iq = 0 and Id is, for example, equal to -644 A. The currents lpn, pv and lpyw of the phases U, V, W are correspondingly also shown. In this case, lpn u is constantly negative at around - 644 A, and the currents Ipu,v and lpu,w are constant and positive at approximately 180 A and approximately 450 A, such that lq = 0 as a result, and lq is -644 A. In figure 4, the low-side power transistor current is modulated in alternation with the high-side diode current as a higher-frequency square-wave signal, and this is effected in alternation with the high-side power transistor current being modulated in alternation with the low-side diode current as a higher-frequency square-wave signal, such that lg = 0 and lq alternates between +400 A and -400 A as a square- wave signal. The currents lpnu, lpHv and Ipnw of the phases U, V, W are correspondingly also shown. Said currents are also in the form of corresponding square-wave signals, such that lq = 0 as a result, and ls jumps between +400 A and - 400 A. In figure 5, the low-side power transistor current is modulated in alternation with the high-side diode current as a higher-frequency signal with a sinusoidal amplitude, and this is effected in alternation with the high-side power transistor current being modulated in alternation with the low-side diode current as a higher-frequency signal with a sinusoidal amplitude, such that lg = 0 and lq alternates between +400 A and - 400 A as a sine-wave signal. The currents lpn u, lpr and Ipnw of the phases U, V, W are correspondingly also shown. Said currents are also in the form of corresponding sine-wave signals, such that I = 0 as a result, and lq alternates sinusoidally between +400 A and 400 A. List of reference signs Electric motor High-voltage vehicle electrical system Pulse-controlled inverter Resistive component Resistive component Power switch module High-side power switches / high-side power transistors Low-side power switches / low-side power transistors High-side diode Low-side diode IGBT power switch Coolant circuit Vehicle battery

Claims

Patent claims 1. A method for heating a motor vehicle comprising a three-phase electric motor as traction motor, wherein a pulse-controlled inverter is provided for supplying power to the electric motor, wherein a coolant circuit is provided for cooling the electric motor and the pulse-controlled inverter using coolant, said coolant circuit using the coolant to supply heat to a heat exchanger for heating the passenger compartment and / or to the vehicle battery, wherein when the electric motor is stationary, a positive d current and / or negative d current is controlled in the d-axis, with the result that heat loss is generated, said heat loss being introduced into the coolant. 2.The method as claimed in claim 1, wherein the electric motor is supplied with the d current in the d-axis and generates heat loss, which is used as waste heat, both in the electric motor and in the pulse-controlled inverter, wherein the q current in the g-axis is equal to zero. 3.The method as claimed in claim 1 or 2, wherein as a result of the d current being set, no torque that could propel the motor vehicle is applied to the wheels of the motor vehicle.

4. The method as claimed in any one of the preceding claims, wherein the heat loss from the electric motor is generated as power losses from the winding of the electric motor and / or as eddy current losses in laminations and / or the heat loss in the pulse-controlled inverter is generated as on-state losses from the power switches and freewheeling diodes and / or as switching losses when the power switches are switched and / or line losses and / or losses in the DC-link capacitor during operation of the power switches. 5.The method as claimed in claim 1, 2 or 3, wherein the pulse-controlled inverter has an electronic circuit comprising power switches and freewheeling diodes, wherein the current through the power switches and the freewheeling diodes 1S modulated. 6.The method as claimed in claim 5, wherein the pulse-controlled inverter has high-side power transistors, |low-side power transistors, high-side diodes and low-side diodes, wherein the current through the high-side power transistors and the low-side diodes is controlled in a modulated manner and / or wherein the current through the low-side power transistors and the high-side diodes is controlled in a modulated manner.

7. The method as claimed in claim 5 or 6, wherein the current through the power transistors and diodes is pulse-modulated, in particular with a square-wave signal having a constant amplitude or a modulated amplitude.

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