Device and method for heating a traction battery in an electric or hybrid vehicle

Abstract

The invention relates to a device for heating a traction battery (2) for an electric or hybrid vehicle, wherein the device has at least one device (7) for detecting or determining a temperature of the traction battery (2), a cooling circuit (9), and at least one electrical component with at least one GaN power transistor (11) or SiC power transistor, wherein the traction battery (2) and the electrical component are thermally coupled to the cooling circuit (9), wherein in an operating state, the at least one GaN or SiC power transistor is operated in the reverse direction, wherein a control device (10) of the at least one GaN or SiC power transistor is designed such that, depending on the temperature of the traction battery (2), no gate-source voltage is supplied to the GaN or SiC power transistor in the reverse direction for a predetermined time, wherein the predetermined time is greater than an initial delay time,and a procedure.,

Description

[0001] The invention relates to a device and a method for heating a traction battery in an electric or hybrid vehicle.

[0002] Due to the cell chemistry of the battery cells in a traction battery, their performance is limited at cold temperatures. Therefore, it is known to heat the traction battery at low outside temperatures until it reaches a desired temperature. Various approaches have been presented for this purpose. One approach, for example, is the use of PTC elements. Another approach is the utilization of waste heat from other components in the vehicle.

[0003] Such an approach is known, for example, from DE 10 2021 128 931 A1, which utilizes the power loss of an inverter. It proposes operating the power semiconductors with a reduced gate-source voltage in forward mode, i.e., operating the power semiconductors in linear mode to generate more heat loss due to the increased forward resistance. The power semiconductors are SiC transistors, for example. Depending on the desired heating power, the gate-source voltage can then be reduced. One problem with this is that, due to the cell structure of such power semiconductors, local overheating of the power semiconductor can occur.

[0004] From DE 10 2022 106 506 A1 a generic device for heating a traction battery in an electric or hybrid vehicle is known.

[0005] From DE 10 2022 103 289 A1, another heating device is known which utilizes the heat loss from power semiconductors.

[0006] The invention is based on the technical problem of improving a device for heating a traction battery by utilizing heat loss from electrical components and of providing an associated method.

[0007] The solution to the technical problem is provided by a device having the features of claim 1 and a method having the features of claim 5. Further advantageous embodiments of the invention emerge from the subclaims.

[0008] The device for heating a traction battery for an electric or hybrid vehicle comprises at least one device for detecting or determining a temperature of the traction battery, a cooling circuit, and at least one electrical component with at least one GaN power transistor, wherein the traction battery and the electrical component are thermally coupled to the cooling circuit. The electrical component is designed as a pulse-controlled inverter. The electrical component is designed such that, in an operating state, the at least one GaN power transistor is operated in the reverse direction. A control device of the at least one GaN power transistor is designed such that, depending on the temperature of the traction battery, it does not supply any gate-source voltage to the GaN power transistor in the reverse direction for a predetermined time, wherein the predetermined time is greater than an initial delay time.This can be used to generate a lot of waste heat very effectively. This takes advantage of the fact that GaN power transistors do not have a body diode, but exhibit similar behavior. SiC power transistors do have a body diode, but its behavior is significantly worse than that of Si power transistors. It is therefore common practice to apply a gate-source voltage in the reverse direction in order to reduce the on-resistance in the reverse direction. Circuit configurations are possible (e.g. a half-bridge in an inverter) where no gate-source voltage is applied for an initial delay time to avoid a short circuit. Such an initial delay time can be 100 ns, for example. However, circuit configurations are also possible where no short circuits are to be feared due to reverse operation. In this case, the initial delay time can also be zero.According to the invention, the time during which the GaN and SiC power transistor (if present) is operated in the reverse direction without gate-source voltage is now extended, whereby in the extreme case the gate-source voltage is zero during the entire phase in the reverse direction.

[0009] The pulse-controlled inverter is designed as a 3-level T-type pulse-controlled inverter, with the GaN power transistors arranged at a neutral point. The other power transistors (high-side switch and low-side switch) can then be SiC or Si IGBTs.

[0010] In one embodiment, the device comprises a voltage measuring device for measuring the drain-source voltage in order to more accurately determine the power dissipation by multiplying it by the current.

[0011] In a further embodiment, the device comprises a unit for determining a junction temperature of the at least one GaN or SiC power transistor, wherein the control device is configured to reduce the predetermined time depending on the determined junction temperature. Due to the heating, the on-state resistance increases, so that more heat loss is generated. If the power transistor is then repeatedly operated in reverse direction, which is the case during freewheeling in an inverter, it may be necessary to shorten the predetermined time again in a reverse direction phase in order to prevent the junction temperature from reaching a critical limit.

[0012] In a further embodiment, the device is designed such that a heating output is determined depending on the temperature of the traction battery, wherein the control device is designed to set the predetermined time depending on the required heating output. The cooling water temperature is preferably included in the calculation of the heating output. The heating output can be determined continuously, so that the control device can query whether heating output is still required before initiating the reverse direction. If heating output is no longer required, the power transistor is again controlled with its initial delay time.

[0013] The method for heating a traction battery for an electric or hybrid vehicle is carried out by means of at least one device for detecting or determining a temperature of the traction battery, a cooling circuit, and at least one electrical component with at least one GaN power transistor, wherein the traction battery and the electrical component are thermally coupled to the cooling circuit. The electrical component is designed as a pulse-controlled inverter. In one operating state, the at least one GaN power transistor is operated in the reverse direction, wherein a control device of the at least one GaN power transistor, depending on the temperature of the traction battery, does not supply any gate-source voltage to the GaN power transistor in the reverse direction for a predetermined time, wherein the predetermined time is greater than an initial delay time.

[0014] The pulse-controlled inverter is designed as a 3-level T-type pulse-controlled inverter, with the GaN power transistors arranged at a neutral point. The other power transistors (high-side switch and low-side switch) can then be SiC or Si IGBTs.

[0015] With regard to the further details of the procedure, reference is made in full to the preceding statements.

[0016] The invention is explained in more detail below using preferred embodiments. The figures show: Fig. 1 a schematic representation of a traction network of an electric or hybrid vehicle, Fig. 2 a schematic representation of a non-claimed inverter with GaN power transistors and Fig. 3 a schematic representation of a 3-level T-type pulse inverter with GaN power transistors at a neutral point.

[0017] In the Fig. 1 schematically shows a traction network 1 of an electric or hybrid vehicle. The traction network 1 has a traction battery 2, a pulse-controlled inverter 3, and an electric motor 4. The traction battery 2 is connected to the DC voltage side of the pulse-controlled inverter 3 via a relay 5, with at least one intermediate circuit capacitor 6 arranged in parallel. The traction network 1 also has a device 7 for detecting the temperature of the traction battery 2. The device 7 can, for example, be at least one temperature sensor. The device 7 can also have several temperature sensors assigned to different battery cells of the traction battery 2. It can be provided that the different temperature values are averaged, or that the lowest temperature is defined as the temperature of the traction battery 2.Furthermore, a device 8 is provided which, based on the temperature of the traction battery 2 and the temperature of a coolant in a cooling circuit 9, determines the heating power that must be supplied to the cooling circuit in order to heat the traction battery 2 to a desired target temperature. The traction battery 2 and the pulse-controlled inverter 3 are thermally coupled to the cooling circuit 9. The determined heating power is transferred to a control device 10 for the power transistors of the pulse-controlled inverter 3. The power transistors are designed as GaN or SiC power transistors.

[0018] In the Fig. Figure 2, for example, shows a pulse-controlled inverter 3 with GaN power transistors 11. In motor mode, the GaN power transistors 11 are operated in the forward direction, and in recuperation mode in the reverse direction. For technological reasons, GaN power transistors 11 do not have a body diode, which can be used for freewheeling in Si IGBTs. However, GaN power transistors exhibit a body diode-like behavior. However, the resistance is very high, so that even small currents generate large power losses. During normal operation (i.e., when heating is not required), a gate-source voltage is applied to reduce the resistance in the reverse direction. Furthermore, an initial delay time is provided before the gate-source voltage is applied.This initial delay time serves to prevent both GaN power transistors 11 of a half-bridge from being conductive at the same time, which would lead to a short circuit. This initial delay time is, for example, 100 ns. To heat the traction battery 2, this delay time is extended and the poor reverse conductivity is specifically exploited to generate heat loss. This effect is amplified by the fact that, for the same current, the drain-source voltage increases with increasing temperature, so that the losses become even greater. The generated heat loss can be easily determined if the current is known. The corresponding drain-source voltage can either be taken from the data sheets as a look-up table or measured using a voltage measuring device. The predetermined time is determined by the control device 10 (see . Fig. 1) to the gate drivers of the GaN power transistors 11 (not shown).

[0019] In general, the power loss of a half bridge is PSD−HB=(IL⋅VSD1⋅tSD1)⋅fSW+(IL⋅VSD2⋅tSD2)⋅fSW

[0020] I L the load current or drain current, V SD1 the drain-source voltage across the upper GaN power transistor 11 in the reverse direction and V SD2 the drain-source voltage across the lower GaN power transistor 11. t SD1 is the time during which no gate-source voltage is applied to the upper GaN power transistor 11 and t SD2 is the time during which no gate-source voltage is applied to the lower GaN power transistor 11. f SW is the clock frequency used to switch between the upper and lower GaN power transistors 11, which is selected depending on the frequency of the alternating voltage generated by the electric machine. t SD1 or t SD2 correspond to the predetermined time. If t SD1 and t SD2each chosen as half a period, then 1tSD1+tSD2=fSW i.e. the GaN power transistors 11 are permanently operated in reverse direction without gate-source voltage.

[0021] Such a pulse inverter 3 can, for example, operate at a load current of 500 A at V SD= 2 V, each generates 1 kW of power loss per half-bridge when the GaN power transistors 11 are continuously operated in reverse without gate-source voltage. The desired heating power can be set by adjusting the predetermined time. Heating can then continue until the traction battery 2 reaches the desired temperature. The GaN power transistors 11 can then be operated again with their initial delay time. The statements also apply analogously to SiC power transistors. The junction temperature of the power transistors must be monitored to ensure that it does not reach critical values.

[0022] In the Fig.Figure 3 shows an alternative embodiment of a pulse-controlled inverter 3, which is designed as a 3-level T-type pulse-controlled inverter. The high-side switches and the low-side switches are designed as Si-IGBTs 12 with a body diode 13, with two oppositely connected GaN power transistors 11 being arranged in the neutral path with the neutral point N. The oppositely connected GaN power transistors 11 can also be replaced by a bidirectional GaN power transistor 11 each. SiC power transistors can also be used instead of the Si-IGBTs, allowing even more power dissipation to be generated. List of reference symbols 1 traction network 2 traction batteries 3 pulse inverters 4 Electric machine 5 relays 6 DC link capacitor 7 Furnishings 8 Furnishings 9 Cooling circuit 10 Control device 11 GaN power transistor 12 Si IGBTs 13 Body diode

Claims

[1] A device for heating a traction battery (2) for an electric or hybrid vehicle, wherein the device comprises at least one device (7) for detecting or determining a temperature of the traction battery (2), a cooling circuit (9), and at least one electrical component with at least one GaN power transistor (11), wherein the electrical component is designed as a pulse-controlled inverter (3), wherein the traction battery (2) and the electrical component are thermally coupled to the cooling circuit (9), wherein in an operating state the at least one GaN power transistor (11) is operated in the reverse direction, wherein a control device (10) of the at least one GaN power transistor (11) is designed such that, depending on the temperature of the traction battery (2), no gate-source voltage is supplied to the GaN power transistor (11) in the reverse direction for a predetermined time,where the predetermined time is greater than an initial delay time, , characterized by that the pulse inverter (3) is designed as a 3-level T-type pulse inverter, wherein the GaN power transistors (11) are each arranged as two oppositely connected GaN power transistors (11) or as bidirectional GaN power transistors (11) at a neutral point, wherein high-side switches and low-side switches are designed as Si-IGBTs (12) and body diode (13) or as SiC power transistors. [2] Device according to claim 1, characterized by that a voltage measuring device is provided for measuring the drain-source voltage. [3] Device according to claim 1 or 2, characterized bythat the device has a unit for determining a junction temperature of the at least one GaN power transistor (11), wherein the control device (10) is designed to reduce the predetermined time depending on the determined junction temperature. [4] Device according to one of the preceding claims, characterized by that the device is designed such that a heating power is determined as a function of the temperature of the traction battery (2), wherein the control device (10) is designed such that it sets the predetermined time as a function of the required heating power. [5] A method for heating a traction battery (2) for an electric or hybrid vehicle, by means of at least one device (7) for detecting or determining a temperature of the traction battery (2), a cooling circuit (9), and at least one electrical component having at least one GaN power transistor (11), wherein the traction battery (2) and the electrical component are thermally coupled to the cooling circuit (9), wherein the electrical component is designed as a pulse-controlled inverter (3), wherein in an operating state, the at least one GaN power transistor (11) is operated in the reverse direction, wherein a control device (10) of the at least one GaN power transistor (11) supplies no gate-source voltage to the GaN power transistor (11) in the reverse direction for a predetermined time depending on the temperature of the traction battery (2), wherein the predetermined time is greater than an initial delay time, characterized bythat the pulse inverter (3) is designed as a 3-level T-type pulse inverter, wherein the GaN power transistors (11) are each arranged as two oppositely connected GaN power transistors (11) or bidirectional GaN power transistors as (11) at a neutral point, wherein high-side switches and low-side switches are designed as Si-IGBTs (12) and body diode (13) or as SiC power transistors. [6] Method according to claim 5, characterized by that a heating power is determined depending on the temperature of the traction battery (2), wherein the control device (10) sets the predetermined time depending on the required heating power.

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