Method and device for operating a drive rail, and drive system

Abstract

The invention relates to a method for operating an electric machine (2) for a drivetrain, the electric machine (2) comprising a drive winding (6) having a plurality of phases (U, V, W), wherein the machine (2) is controlled, depending on a requested deceleration, to generate a braking power, wherein the braking power is specified depending on a current temperature (T) of the machine (2) and / or of power electronics (5) associated with the machine (2). According to the invention, when the current temperature (T) falls below a predetermined threshold value (TG), at least one electric phase current (IU, IV, IW) of the drive winding (6) is increased.

Description

[0001] Description

[0002] title

[0003] Method and device for operating a drive rail, drive system

[0004] The invention relates to a method for operating an electric machine for a drive train, for example of a motor vehicle, wherein the electric machine has a multi-phase drive winding, wherein the machine is controlled as a function of a requested deceleration to provide a braking power, wherein the braking power is predetermined as a function of a current temperature of the machine and / or power electronics associated with the machine.

[0005] Furthermore, the invention relates to a device for operating an electrical machine which has power electronics and a drive winding which can be operated by the power electronics and has at least one electrical phase.

[0006] Furthermore, the invention relates to a drive system for a motor vehicle, comprising an electric machine having power electronics and a drive winding operable by the power electronics and having at least one electrical phase.

[0007] State of the art

[0008] Methods and devices of the type mentioned above are known from the prior art. Electric motors are being used in motor vehicles in an increasing number of applications. In addition to their design as drive motors for the entire vehicle to accelerate or decelerate it, the use of electric motors in braking and steering systems is also known, for example, to implement so-called steer-by-wire or brake-by-wire solutions. Electric motors are also used, for example, in electromechanical brake boosters, which are designed to increase pressure in a hydraulic brake system depending on a requested deceleration in order to support or generate braking force.

[0009] To protect such an electric drive system from excessive overheating, it is known to put the drive system into degradation mode when a predetermined limit temperature is reached. This mode prevents further temperature increases but limits the performance of the electric machine. In such an emergency mode, the continued operation of the electric machine is ensured at or due to reduced performance.

[0010] Disclosure of the invention

[0011] The present method with the features of claim 1 has the advantage that the overall behavior of the electrical machine is optimized, so that the behavior of the electrical machine appears the same to the user, particularly regardless of the current operating temperature. Furthermore, costs are saved because the electrical machine and a control unit controlling the electrical machine can be operated optimally within the requirements without the need to implement additional protective measures. According to the invention, at least one electrical phase current of the drive winding is increased when the current temperature falls below a predetermined limit.This increases the electrical power loss and reduces the regenerative power, which results in a shorter braking distance or a higher braking power (negative mechanical power) at temperatures below the limit temperature or the limit value while maintaining the same regenerative power.

[0012] Preferably, the phase current is increased such that the braking power of the electric machine is the same above and below the limit value. This ensures that the braking performance of the electric machine does not change depending on the current temperature, so that the same braking performance can always be expected.

[0013] Furthermore, it is preferably provided that, to increase the phase current, a predetermined upper current limit is increased. Thus, by increasing the upper current limit, higher phase currents are permitted, which lead to the aforementioned advantages. Otherwise, the upper current limit is specified—as usual—depending on the design of the electrical machine and the current operating temperature in such a way that overloading, in particular overheating, is prevented.

[0014] Furthermore, it is preferably provided that as the temperature decreases below the limit value, the at least one phase current is increased. As the temperature continues to decrease, the phase current is thus further increased or the upper current limit is further increased. This advantageously compensates for the temperature decrease.

[0015] Particularly preferably, the current temperature of the electrical machine and / or the power electronics, in particular of the power path, is measured, estimated or calculated.

[0016] Preferably, the phase current is reduced as the temperature rises above the limit. This maintains the degradation concept for the machine and reliably prevents a thermally critical condition.

[0017] Particularly preferably, the phase current is increased in such a way that it correlates with a change in the electrical resistance of the machine, in particular the drive winding. This results in advantageous behavior of the electrical machine.

[0018] The device according to the invention with the features of claim 8 is characterized by a control unit that is specifically designed to carry out the method according to the invention when used as intended. This results in the advantages already mentioned above. The drive system according to the invention with the features of claim 9 is characterized by the device according to the invention. This results in the advantages already mentioned above.

[0019] Further advantages and preferred features and combinations of features emerge in particular from the above description and from the claims. The invention will be explained in more detail below with reference to the drawings.

[0020] Figure 1 shows an advantageous drive system in a schematic representation,

[0021] Figure 2 is a diagram explaining an advantageous method for operating an electric machine of the drive system.

[0022] Figure 1 shows a simplified representation of an advantageous drive system 1 for a drive train (not shown in detail here), for example, of a motor vehicle. The drive system 1 comprises an electric machine 2 that can be driven as a motor or generator. The electric machine 2 has a rotatably mounted rotor 3 and a stator 4 fixed to the housing. The rotor 3 is connected, for example, to a pump device of a hydraulic brake system, in particular in the form of an electromechanical brake booster.The drive system 1 further comprises power electronics 5, for example with a bridge circuit comprising a plurality of half-bridges, each of which has at least two controllable semiconductor switches, in order to energize a plurality of phases U, V, W of a drive winding 6 of the rotor 3 in such a way that the electric machine 2 generates a positive or negative or an accelerating or decelerating torque.

[0023] For this purpose, the drive system 1 has, in particular, a control unit 7, which is connected to the power electronics 5 and, depending on a requested deceleration, controls the power electronics 5 to brake or decelerate the electric machine 2. For this purpose, the power electronics 5 is controlled by the control unit 7 to generate a (target) braking power. The method described below creates a rapid braking of the machine 2 with the possibility of maximizing a phase current of the machine 2 in order to convert kinetic energy of the electric machine into thermal energy with the highest possible power. The thermal state of the drive system 1 is advantageously taken into account in this process.

[0024] For this purpose, at least one temperature of the drive system 1 is monitored. This includes, for example, the temperature of the drive winding 6, the power electronics 5, and individual components of the power electronics 5, such as the capacitors and / or switching elements used therein. Preferably, the temperature at the selected location is measured, estimated, or calculated, for example, using a thermal model.

[0025] Figure 2 shows a diagram that describes the advantageous method in more detail. The diagram shows the maximum phase current or an upper current limit value lp over the monitored temperature T. maxwith a dashed characteristic curve K1 according to a conventional method and with a solid characteristic curve K2 according to the method presented here. The characteristic curve K1 remains constant up to a limit temperature TG. When the temperature Tc is exceeded, the phase current lu, lv and / or Iw is further limited according to the characteristic curve K1 with increasing temperature, so that only decreasing phase currents are permitted with increasing temperature. This degradation concept ensures that when the permissible limit temperature TG is reached, the drive system 1 or at least one of its components is protected from overheating. By reducing the maximum phase current lp max This ensures that the power of the electrical machine 2 is reduced and thus further heating, in particular overheating, is prevented.

[0026] With the advantageous method shown by the characteristic curve K2, the procedure now differs in that below the limit temperature TG, the permissible phase current is increased as the temperature continues to decrease. The maximum phase current lp max is therefore varied depending on a measured, estimated or calculated temperature, in particular of the electrical machine 2 or the power path from the control unit 7 to the drive winding 6, so that the electrical power loss is increased and the previously required regenerative power is reduced and / or set to 0 watts.

[0027] This degradation scheme achieves a shorter braking distance or faster braking of rotor 3 while maintaining the same regenerative power, and lower pressure peaks in the hydraulic brake system are achieved, especially at low and room temperatures. The degradation curve for the maximum phase current lp maxis preferably derived from the required mechanical power. The power balance of the braking process of electric machine 2 can be described by: with PB= on-board power, IB = battery current, UB= operating voltage of the power electronics, Pmech= mechanical power, Pi oss = resistive power loss, MD = torque, co = rotor speed, I = phase current, R = electrical resistance of the power path. Typically, the maximum current is defined, but the resistance R, particularly of the drive winding 6, is temperature-dependent, so that R(T) applies. The resistive power loss P| OSS is therefore also temperature dependent (P| OSS (T)).

[0028] The requirement for machine 2 typically describes a maximum braking distance (analogous to pressure peaks in the braking system), which depends on the system properties, the maximum engine speed and the mechanical power P mech of machine 2. For high temperatures, mechanical power is provided in excess of the required power requirements because the ohmic power loss increases compared to a lower reference temperature. If the regenerative power is now set from a reference value to 0 watts, the mechanical power of electrical machine 2 decreases at, for example, room temperature. However, the thermal concept allows the maximum phase current of machine 2 to be increased in this state for the braking maneuver or braking process. Preferably, but not exclusively, the phase current correlates with the increase in electrical resistance R due to the changing temperature T.

[0029] The advantageous method thus reduces the regenerative power required to achieve the deceleration power to a minimum, which represents a significant cost advantage for the design of the drive system 1 and an on-board network into which the drive system 1 is integrated. This saves costs for the hardware in particular.

Claims

Claims 1 . Method for operating an electrical machine (2) for a drive train, wherein the electrical machine (2) has a drive winding (6) having a plurality of phases (U, V, W), wherein the machine (2) is controlled as a function of a requested deceleration to generate a braking power, wherein the braking power is predetermined as a function of a current temperature (T) of the machine (2) and / or of power electronics (5) assigned to the machine (2), characterized in that when the current temperature (T) falls below a predetermined limit value (TG), at least one electrical phase current (lu, lv, lw) of the drive winding (6) is increased.

2. Method according to claim 1, characterized in that the phase current (lu,lv,lw) is increased such that the braking power (PB) of the electrical machine (2) is the same above and below the limit value (TG).

3. Method according to one of the preceding claims, characterized in that to increase the phase current (lu,lv,lw) a predetermined upper current limit value (lp m ax) for the phase current (lu,lv,lw) is increased.

4. Method according to one of the preceding claims, characterized in that with decreasing temperature (T) below the limit value (TG) the at least one phase current (lu,lv,lw) is increased.

5. Method according to one of the preceding claims, characterized in that the current temperature (T) is measured, estimated or calculated.

6. Method according to one of the preceding claims, characterized in that with increasing temperature (T) above the limit value (TG) the phase current (lu,lv,lw) is reduced.

7. Method according to one of the preceding claims, characterized in that the phase current (lu, I v,lw) is increased in such a way that it correlates with a change in an electrical resistance (R) of the machine (2), in particular of the drive winding (6).

8. Device for operating an electrical machine (2) which has a power electronics (5) and a drive winding (6) operable by the power electronics (5) with at least one electrical phase (U, V, W), characterized by a control device which is specially designed to carry out a method according to one of the Claims 1 to 7.

9. Drive system (1) for a drive train, comprising an electric machine (2) which has power electronics (5) and a drive winding (6) operable by the power electronics (5) and having at least one electrical phase (U, V, W), characterized by a device according to claim 8.

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