Method and device for operating an electric machine, and electric machine

Abstract

The invention relates to a method for operating an electric machine (2) which has controllable power electronics (7) with at least one inverter (6), wherein the inverter (6) is controlled on the basis of a torque requirement for the electric machine (2) and a current temperature (Tist) of the electric machine (2) in order to achieve a target torque (Msoll). Provision is made for the target torque (Msoll) to be limited on the basis of the detected temperature (Tist) by means of a PID controller (12).

Description

[0001] Description

[0002] title

[0003] The present invention relates to a method for operating an electrical machine having controllable power electronics with at least one inverter, wherein the inverter is controlled as a function of a torque requirement for the electrical machine and of a current temperature of the electrical machine in order to fulfill a target torque.

[0004] Furthermore, the invention relates to a device for operating such an electrical machine, which has a control unit that controls the inverter depending on a torque requirement and a temperature of the electrical machine.

[0005] Furthermore, the invention relates to an electrical machine with the above-mentioned device.

[0006] State of the art

[0007] Methods and devices of the type mentioned above are already known from the prior art. In order to protect the electrically operating components of an electrical drive device, such as in particular an inverter or its semiconductor switches, which are operated to control the electrical phases of an electrical machine, the stator and / or the rotor from overheating, it is known to control the inverter in such a way that a permissible or predetermined maximum temperature is not exceeded. This is intended to prevent, for example, heat damage or excessive stress on the material due to continuous load. A so-called derating or regulation function is often used for this purpose, by which the power or power loss of the electrical machine is reduced over time to prevent further heating of the components.It is known to monitor the current temperature of the electric machine in order to limit the target torque depending on this temperature in such a way that, in particular, an excessive increase in temperature is prevented.

[0008] Disclosure of the invention

[0009] The method according to the invention with the features of claim 1 has the advantage that temperature overshoots under dynamic load requirements are advantageously prevented, thereby increasing the service life of the electric machine in particular. Furthermore, there is the advantage that undesired temperature or torque oscillations, which can arise for example from disturbances or other undesired system excitations, are prevented or at least reduced. At the same time, the driving feel is improved because a change in the torque limitation occurs less suddenly. According to the invention, the target torque is limited as a function of the detected temperature by means of a PID control or by means of a PID controller. The proportional component of the control takes into account the deviation between the target and actual temperature, in order to ensure in particular the stability of the control.The integrator or I component of the control advantageously takes into account the longer-term influence on the target torque of the electric machine or the longer-term temperature development. The differential component compensates for or reduces the tendency to overshoot. Together with the integral component and the proportional component, this also results in advantageous control of the target torque. This ensures that the torque is limited reliably in particular in order to prevent overheating or damage to the electric machine, and on the other hand a torque limitation that is noticeable to the user only occurs late. This means that the so-called derating or reduction in speed occurs later than with previously known methods and thus the high performance of the electric machine can be utilized for longer than before.Due to the advantageous design, the PD component of the control can be designed to avoid overshoots and oscillations, and the PI component can be designed to ensure that the maximum permissible temperature is not exceeded and that the maximum performance potential of the electrical machine can be achieved when torque requirements are continuously high.

[0010] Preferably, the target torque is specified as a function of the current speed of the electric machine. This enables, in particular, operating-point-dependent gain scheduling, which advantageously takes into account the electrical or electromagnetic behavior of the electric machines as a function of their speed.

[0011] Preferably, the target torque is also specified as a function of the operating voltage of the electric machine. The operating voltage of the electric machine is, in particular, continuously monitored. Taking the operating voltage into account, particularly in a pre-control of the electric machine, results in the advantage that the operating behavior of the electric machine can be better represented, which, for example, allows for greater control stability.

[0012] Furthermore, it is preferably provided that the target torque is specified as a function of the current torque of the electric machine. The current torque is calculated, for example, as a function of the current operating voltage and / or a current operating current or the operating currents of several electrical phases of the electric machine. Optionally, a torque sensor is provided that directly determines the current torque.

[0013] Preferably, the method is designed such that the integrator or I component of the control implements the above-mentioned anti-wind-up procedure and / or an effective limitation to the temperature range. This activates the operating range in which the I component acts, particularly to a temperature range close to the permissible temperature, so that the PID controller only influences the target torque. The integrator is preferably active when the currently detected temperature Ti St greater than the maximum permissible temperature T max , but not greater than 5°C to 15°C, in particular less than 10°C above the maximum permissible temperature T max is, ((T max + 10°C) > Ti St > T max ) or if the currently recorded temperature Ti St less than or equal to the maximum permissible temperature T max and the integrator component of the torque Mi is less than zero (TiSt <= T max and Mi < 0).

[0014] Preferably, the maximum permissible temperature is specified as a function of a maximum permanently permissible temperature of the electrical machine. This takes into account the temperature that, if present continuously, could lead to damage to the electrical machine. By setting the maximum permissible temperature to the maximum permanently permissible temperature, the service life of the electrical machine is advantageously extended. In particular, the maximum permanently permissible temperature is determined in advance through tests and / or calculations and stored, in particular, in a non-volatile memory of the electrical machine or a control unit of the electrical machine.

[0015] According to a preferred development of the invention, a PD control or a PI control is carried out depending on the current temperature. The differential component offers the option of replacing a control deviation with an operating point-dependent gain (gain scheduling). This makes it possible to achieve different effects depending on the temperature. For example, it is preferably provided that if the current temperature is below the permissible maximum temperature, PD control is carried out, and if the permissible maximum temperature is above the maximum permissible temperature, PI control is carried out. The operating point-dependent gain is preferably specified as a function of the speed of the electric machine in order to be able to differentiate between the system dynamics at low and high speeds.

[0016] Furthermore, it is preferably provided that a pre-control of the

[0017] The target torque is determined depending on the current speed and operating voltage. This ensures robust control of the electric machine.

[0018] The electrical device according to the invention with the features of claim 10 is characterized in that the control unit is specifically designed to carry out the method according to the invention when used as intended. This results in the advantages already mentioned above.

[0019] The electrical machine according to the invention with the features of claim 11 is characterized in that it comprises the device according to the invention. This results in the advantages already mentioned above.

[0020] 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.

[0021] Figure 1 shows an electric drive train of a motor vehicle with an electric machine in a simplified representation,

[0022] Figure 2 shows an advantageous method for operating the electrical machine in a schematic representation,

[0023] Figure 3 is a first diagram to explain the method and

[0024] Figure 4 shows a second diagram to explain the advantageous method.

[0025] Figure 1 shows a simplified representation of an electric drive system 1 for a motor vehicle (not shown in detail here). The drive system 1 has an electric machine 2, which has a rotor 3 and a stator 4 with, in this case, a three-phase drive winding 5. The phases U, V, W of the drive winding 5 are connected to a controllable inverter 6, which, in particular, has a semiconductor bridge for each of the phases U, V, W, preferably with two semiconductor switches connected in series. The inverter 6 is part of a power electronics unit 7 of the electric machine 2. The inverter 6 connects the electric machine to an energy source 8, in this case in the form of a battery or an accumulator. The energy source 8 provides direct current, which is converted into three-phase current by controlling the inverter 6 such that the electric machine 2 can generate a drive torque or target torque M required by a driver.so ii is fulfilled or at least substantially fulfilled. For this purpose, a control unit 9 is provided which is connected to the inverter 6 for its operation. The control unit 9 is designed in particular to control or actuate the semiconductor switches. The requested drive torque is converted into switching commands for the semiconductor switches by the software of the control unit 9, for example by means of pulse width modulation. The control unit 9 also regulates the target torque, by means of which in particular overloading, in particular overheating, of the electrical machine 2, in particular of the drive winding 5, is avoided.

[0026] Figure 2 shows a functional diagram through which a method for operating the electric machine 2 is explained in more detail below. The method offers advantageous thermal protection for the electric machine 2 and, in particular, its stator 4. The essential elements are:

[0027] A control 11 which determines the current temperature Ti St of the electrical machine 2, in particular of the stator 4, is recorded, in particular measured or calculated based on a model, and as an input variable with a parameterizable target value, in this case a maximum permanently permissible temperature T max the stator 4, optionally including safety tolerances or reserves, and using various control calculations, a maximum permissible torque M max determined or calculated for the electrical machine 2.

[0028] The core component of the control or process is a PID controller 12. This includes a proportional component that controls the deviation between the maximum permissible temperature T max and actual temperature Ti St taken into account to ensure stability of the temperature or temperature development. For this purpose, the PID control is designed in such a way that the maximum permissible temperature T max is either never exceeded or only briefly, and in any case not continuously. The integrator of the PID control ensures that the continuous performance of the electrical machine is maintained. Preferably, the integrator or integral component also includes an anti-wind-up control and logic that ensures that the integrator only operates near the permissible maximum temperature T maxis active and thus cannot become the sole dominant factor in the control structure. The derivative component has a factor f in particular to prevent overshoot of the temperature Ti, especially during short-term and high torque requirements. St to prevent. Preferably, the differential component also includes a PT1 element to suppress sensor noise.

[0029] In addition, there is a pre-control 13 which, depending on the current speed or rpm n and the current operating voltage Ui St the electrical machine 2 a maximum permissible torque Mn m This feedforward control 13 allows the PID controller to be more precisely designed for stable control during dynamic operation and achieves an overall improved system behavior.

[0030] Preferably, the PID control 12 is automated depending on the speed n of the electric machine 2 in order to automatically respond to different system reactions. Assume that a torque of 150 Nm (Newton meters) can be continuously achieved at a speed of 2000 rpm, while at a speed of 8000 rpm it is only 125 Nm. In such a case, it is advantageous, for example, if the temperature increase at 2000 rpm leads to a limitation of the torque by 10 Nm, while at a speed of 8000 rpm the maximum permissible torque is only reduced by 5 Nm. To achieve this, the feedforward control 13 is advantageously utilized in this case through scaling, which leads to improved control of the electric machine and an improved power reserve.Preferably, the pilot control 13 operates using a characteristic map that is adapted to the current speed or is designed to be speed-dependent. Figure 3 shows an example of a diagram showing the curve of torque M versus speed in the form of speed n. Two areas, A and B, are shown in which the PID control operates differently.

[0031] The proportional component of the PID controller 12 also offers the possibility of replacing a control deviation with a work-dependent gain setting. For example, depending on the current temperature value Ti St either a PD control or a PI control is used. For example, at a temperature lower than the permissible temperature Tmax, a PD control is used, and at a temperature Ti Stwhich is higher than the permissible temperature T max , a PI control. Additional excitations near the setpoint can be achieved by changing the gain of the derivatives depending on the temperature deviation from the setpoint or the permissible maximum value T max (control deviation) can be reduced.

[0032] The integrator component prevents wind-up of the system. For this purpose, as already mentioned above, the integrator operates in particular depending on the current temperature Ti St and the maximum permissible temperature T max only in selected situations. This is shown as an example in Figure 4. If the actual temperature exceeds Ti St the maximum permissible temperature T max , the integrator operates. If the temperature Ti St in a predetermined range below but close to the maximum permissible temperature T maxIf the integrator component results in further torque limitation, the integrator also operates. The effective ranges W in which the integrator operates are shown hatched in Figure 4. Otherwise, the integrator is preferably deactivated or ineffective.

[0033] The maximum permissible temperature T max is understood in particular as a permanently maximum permissible temperature, which is measured and / or calculated in advance. The permanently permissible maximum temperature is determined in such a way that the electrical machine 2, in particular the stator 4, is permanently protected from overheating and thus ensures a long service life.

Claims

Claims 1 . Method for operating an electrical machine (2) which has controllable power electronics (7) with at least one inverter (6), wherein the inverter (6) is controlled as a function of a torque requirement for the electrical machine (2) and of a current temperature (Ti St ) of the electrical machine (2) to fulfill a target torque (M S0 n), characterized in that the target torque (M S0 n) depending on the measured temperature (Ti S t) is limited by means of a PID control (12).

2. Method according to claim 1, characterized in that the target torque (M S0 n) is specified as a function of a current speed (n) of the electric machine (2).

3. Method according to one of the preceding claims, characterized in that the target torque (M S0 n) depending on an operating voltage (UiSt ) of the electrical machine (2).

4. Method according to one of the preceding claims, characterized in that the target torque (M S0 n) depending on a current torque (Mi St ) of the electrical machine (2).

5. Method according to one of the preceding claims, characterized in that the I-component of the control is an anti-wind-up method and / or an effective limitation to the range of a maximum permissible temperature (T max ) is carried out.

6. Method according to one of the preceding claims, characterized in that the maximum permissible temperature (T max ) is specified as a function of a maximum permanently permissible temperature of the electrical machine (2).

7. Method according to one of the preceding claims, characterized in that the maximum permanently permissible temperature is determined by tests and / or calculations.

8. Method according to one of the preceding claims, characterized in that depending on the current temperature (Ti St ) a PD control or a PI control is carried out.

9. Method according to one of the preceding claims, characterized in that a pilot control (13) of the target torque (M S0 n) depending on the current speed (n) and a current operating voltage (Ui St ) of the electrical machine (2).

10. Device for operating an electrical machine (2), which has controllable power electronics (7) with at least one inverter (6), and with a control unit (9) which controls the inverter (6) as a function of a torque requirement for the electrical machine (2) and a current temperature (Ti St ) of the electrical machine (2), characterized in that the control device (9) is specially designed to carry out a method according to one of claims 1 to 9 when used as intended.

11. Electric machine (2) for a motor vehicle, which has controllable power electronics (7) with at least one inverter (6), wherein the inverter (6) is controlled as a function of a torque requirement (M S0 n) for the electrical machine (2) and a current temperature (Ti St ) is controlled by the electrical machine (2), characterized by a device according to claim 10.

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