Method for operating electric drive system, computer program product, data carrier, electric drive system, motor vehicle

Abstract

The invention relates to a method for operating an electric drive system (1), in particular for a motor vehicle, the electric drive system (1) having a power electronics unit (2), in particular a voltage converter, an electric machine (3) that can be controlled by the power electronics unit (2), and a battery (4) that is or can be electrically connected to the power electronics unit (2), and the battery (4) is electrically connected or can be electrically connected to the power electronics unit (2). The power electronics (2) has at least one electrical phase (5) for actuating the electric machine (3). According to the invention, at least one voltage value of an intermediate circuit voltage (U1) of the power electronics (2) is estimated from a predefined rotational speed and / or torque requirement for the electric machine (3) using a mathematical model of the drive system (1), at least one current value for the current of one of the phases (5) of the electric machine (3) and / or at least one current value for the current of the rotor is specified as a function of a rotational speed and / or torque requirement for the electric machine (3) and as a function of the estimated intermediate circuit voltage (U1), and the electric machine (3) is controlled as a function of the specified current values.

Description

Technical Field

[0001] The invention relates to a method for operating an electric drive system, in particular an electric drive system for a motor vehicle, wherein the electric drive system has a power electronics system, in particular a voltage converter, an electric motor which can be controlled by the power electronics system, and a battery which is electrically connected or can be electrically connected to the power electronics system, and wherein the power electronics system has at least one electrical phase for controlling the electric motor.

[0002] The invention further relates to a computer program product which, when executed on a computer device, implements the above-described method. The invention further relates to a data carrier having such a computer program product and an electric drive system having a computer device which is specially designed to execute the computer program product or the above-described method. Finally, the invention relates to a motor vehicle having such an electric drive system. Background Art

[0003] Methods, electric drive systems and motor vehicles of the type mentioned above are known in the prior art. Therefore, in electric machines for traction drives of electric vehicles, which are designed as separately excited synchronous machines, the rotor flux and the inductor voltage induced thereby are usually set by means of the excitation current. This excitation current regulation is usually carried out in a highly dynamic manner, in particular with a fast two-point regulator or a fast PI regulator. Since the inductance of the rotor of the electric machine is usually very large, changes in the stator current can only be achieved relatively slowly despite highly dynamic regulation.

[0004] The stator current in the d and q directions for the field-oriented regulation and the corresponding current target values ​​for the rotor current with the best efficiency are stored, for example, as a table. These values ​​are usually predetermined by the field-oriented regulation and the rotor current regulation, wherein these target values ​​are set as dynamically and accurately as possible by the corresponding regulation. For efficiency reasons, for example, in the traction drive for electric vehicles, when the torque requirement is low, the rotor current with the best efficiency and thus low will be set. If a large torque is now required quickly, as mentioned above, the rotor current necessary for this can only be provided after a certain duration. Therefore, a rise limiter is used, in particular, for the current target value for the stator current, so as to first establish the necessary rotor current and then establish the appropriate stator current, because the stator current cannot set enough torque without the rotor current.

[0005] In order to control the motor as efficiently as possible by the power electronics assigned to the motor, the necessary stator current must be set with the lowest possible intermediate circuit voltage. For example, the motor and the power electronics are designed so that they can still provide the required torque when the lowest intermediate circuit voltage occurs. The characteristic field of the current target value for field-oriented regulation is calculated accordingly for the exact lowest intermediate circuit voltage. As long as the motor and the power electronics are operated at a steady-state power grid or are powered by the power grid, the intermediate circuit voltage is relatively stable, so that it is sufficient to use only the characteristic field for a constant intermediate circuit voltage. However, if the motor and the power electronics are operated at a mobile energy storage device, i.e., a battery or accumulator, or are powered by it, as provided by the method according to the invention, the fluctuation of the intermediate circuit voltage may be expected to increase significantly depending on the state of the energy storage device.

[0006] For example, the regulation and characteristic field for the current target value are set to the lowest intermediate circuit voltage that occurs in order to ensure that there is sufficient regulation reserve and that the regulation behavior leads to a favorable current regulation. Therefore, when the electric torque is set, the battery is loaded and the intermediate circuit voltage drops significantly. For this purpose, it is usually assumed that the lowest intermediate circuit voltage that occurs, i.e. the maximum drop in the intermediate circuit voltage, is the "worst" state of the battery, in which the battery has, for example, the maximum discharge, the lowest temperature and the late or most severe aging state. In addition, the maximum electrical power consumption of all auxiliary consumers and drives is usually assumed. Summary of the invention

[0007] The method according to the invention with the features of claim 1 is characterized in that at least one voltage value of the intermediate circuit voltage of the power electronics is estimated based on a predetermined speed and / or torque requirement for the electric machine using a mathematical model of the drive system, so that at least one current value for the current of one of the phases of the electric machine and / or at least one current value of the current of the rotor is predetermined based on the speed and / or torque requirement for the electric machine and based on the estimated intermediate circuit voltage, and the electric machine is controlled based on the predetermined current value. Usually, when controlling the electric machine, as described above, an excitation current is predetermined in order to set a specific torque for the electric machine, in particular at a predetermined speed of the electric machine. The excitation current is selected from a characteristic field (voltage drop under load) based on the minimum available intermediate circuit voltage, wherein the "worst case" (state of the battery and the drive system) is usually assumed. By estimating the intermediate circuit voltage accordingly and taking into account the estimated intermediate circuit voltage for the predetermined current value, it is advantageously ensured that the electric machine is operated or controlled by the power electronics with a further improved electrical efficiency in comparison. Particularly preferably, the current values ​​for the excitation current and the stator current are predetermined respectively. The efficiency during control is increased by the method according to the invention, because the actual or estimated intermediate circuit voltage when the torque is reached is usually higher than the minimum intermediate circuit voltage that occurs, for example because the battery is fully charged or only partially discharged, is new or cold, and the intermediate circuit voltage drop under load is therefore much smaller than assumed. By the method according to the invention, the (higher) intermediate circuit voltage that is actually expected is estimated, and for control, in particular, a matching characteristic field with a higher intermediate circuit voltage is selected and the control is optimized thereby. The core of the method is the optimization of the corresponding control and regulation concept. In particular, at a known speed for a predetermined torque target value, the voltage value of the intermediate circuit voltage is estimated using a mathematical model of the drive system. The mathematical model particularly takes into account at least one parameter of the battery, the power value of the power consumption of the electric drive system and / or the efficiency of the motor and the power electronics device, in particular according to the speed and / or torque requirement. If the electric drive system is used in a motor vehicle, the speed is particularly dependent on the driving speed of the motor vehicle. The torque target value is determined in particular by the corresponding regulation stage, such as a control device and / or according to the corresponding expectations of the user of the electric drive system, in particular the acceleration expectations of the driver of the motor vehicle. The current values ​​for the torque target value, in particular the current values ​​for the stator current and the rotor current, are set at the current speed, as described above, by means of the intermediate circuit voltage of the power electronics set in this steady state. The current values ​​are not initially set according to an assumed too low intermediate circuit voltage, which is then corrected, for example, when the torque target value is reached, but the current values ​​are already correctly set in a steady state by the method according to the invention to match the expected, i.e. estimated, intermediate circuit voltage. The corresponding iteration steps for correcting the current values, as described above, are advantageously eliminated in the method according to the invention.In order to set the current value correctly immediately, a mathematical model of the drive system is required. The advantage of this method is that the torque target value and the intermediate circuit voltage to be expected at the speed are estimated at least approximately in advance by the model and the optimal characteristic field or regulator parameters are selected almost without delay. As described above, the dynamics and efficiency of the drive system are improved in this way. No additional hardware is required, but only the corresponding regulation and the corresponding mathematical model for the intermediate circuit voltage.

[0008] According to a preferred embodiment of the present invention, the mathematical model takes into account the resistance value of the internal resistance of the battery and / or the voltage value of the open circuit voltage of the battery. Taking into account the resistance value and / or the voltage value advantageously ensures that the load and / or the wear state of the battery are imaged in the mathematical model.

[0009] It is particularly preferred that the resistance value and / or the voltage value are determined as a function of the battery temperature and / or the life of the battery. This determination of the resistance value and / or the voltage value creates a particularly simple possibility for determining them. Particularly preferably, the resistance value and / or the voltage value are adjusted by a battery management system implemented on a control device assigned to the battery as a function of the temperature and aging of the battery. Since the temperature changes relatively slowly and the aging is very slow, the temperature and aging values ​​are alternatively transmitted to another control device, in particular a computer device, which executes the method according to the invention, for example via a vehicle bus that already exists, in order to adapt the resistance value and / or the voltage value there.

[0010] According to a preferred embodiment of the invention, the mathematical model takes into account the power values ​​of the power consumption of the electrical consumers connected to the battery. By taking into account the power consumption, it is advantageously ensured that the mathematical model is closer to the actual load situation of the electric drive system.

[0011] It is particularly preferred to provide that the mathematical model takes into account the power value of the electric drive power of the drive system. By taking into account the electric drive power, the advantage is that the mathematical model is closer to the actual load situation of the electric drive system.

[0012] According to a preferred embodiment of the invention, it is provided that the current value for a predetermined speed or torque requirement is retrieved from a characteristic field, in particular a lookup table, which is assigned to the estimated voltage value of the intermediate circuit voltage. The use of such a characteristic field provides a particularly simple and reliable possibility for retrieving the current value.

[0013] It is particularly preferred that a mathematical model is constructed as an observer, wherein a voltage value for the estimation of the intermediate circuit voltage is compared with a measured voltage value. The advantage achieved thereby is that the accuracy of the estimation of the intermediate circuit voltage is further increased. After the comparison of the voltage values, in particular the state is adjusted. When an extended Kalman filter is used, its parameters are particularly preferably also adjusted. Further preferably, the adjustment or correction of the state or parameter is stopped when the model is used to estimate the intermediate circuit voltage for the desired future applied torque.

[0014] The computer program product according to the invention for execution on a computer device having the features of claim 8 is characterized in that, when used as intended, it carries out the method according to the invention. This results in the advantages already mentioned.

[0015] A data carrier according to the invention having the features of claim 9 is characterized by a computer program product according to the invention stored thereon.

[0016] An electric drive system, in particular an electric drive system for a motor vehicle, having the features of claim 10 comprises a power electronics device, in particular a voltage converter, an electric motor that can be controlled by the power electronics device, and a battery that is electrically connected or can be electrically connected to the power electronics device, wherein the power electronics device has at least one electric phase for controlling the electric motor. The electric drive system is characterized by a computer device that is specially designed to implement the method according to the invention or to execute the computer program product according to the invention. This also brings about the advantages already mentioned above. Preferably, the computer device is a controller assigned to the electric drive system, in particular arranged in a motor vehicle. The motor is in particular a separately excited synchronous motor as described above. Alternatively, the motor is another separately excited motor controlled by the power electronics device, a permanent magnet excited or electrically excited synchronous motor or an asynchronous motor. The electric drive system is in particular provided for use in industrial machinery or household appliances, in particular white goods.

[0017] The motor vehicle having the features of claim 11 is characterized by an electric drive system according to the invention. This also results in the advantages mentioned above. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Further preferred features and feature combinations emerge from the preceding description and from the claims. The invention will be explained in more detail below with reference to the drawings.

[0019] Figure 1 shows a schematic diagram of the electric drive system,

[0020] Figure 2 shows a first equivalent circuit diagram for the mathematical model of the drive system,

[0021] Figure 3A second equivalent circuit diagram for the model is shown, and

[0022] Figure 4 A method for operating a drive system is shown. DETAILED DESCRIPTION

[0023] Figure 1 The schematic diagram of an electric drive system 1 is shown. The electric drive system 1 has power electronics 2 , in the present case a voltage converter, in particular an inverter, an electric machine 3 which can be controlled by the power electronics 2 , and a battery 4 which is electrically connected to the power electronics 2 .

[0024] The power electronics 2 is designed to control at least one electrical phase 5, in the present case all three electrical phases 5, of the electric machine 3. For this purpose, the power electronics 2 is assigned to a computer device 6, in particular a control device.

[0025] Figure 2 A first equivalent circuit diagram is shown for a mathematical model of an electric drive system 1. This model can be used to estimate the intermediate circuit voltage U1 of the power electronics 2. For this purpose, the equivalent circuit diagram has electrical switching elements which model the parameters of the battery 4 as well as auxiliary loads and the drive itself.

[0026] The equivalent circuit diagram is derived from the equivalent circuit diagram known in the technical literature. The parameters of the battery 4 are represented by two resistors R1, R2, which are connected in parallel with the capacitors C1, C2 respectively and thus form an RC element. There is also another resistor R0 arranged in series with the inductor L0.

[0027] These components together represent the relevant parameters of the battery 4. The battery 4 has an open circuit voltage U0 and an output voltage U2. For example, an auxiliary consumer characterized by an electrical power P3, a current I3 and a voltage U3 is connected to the battery 4.

[0028] Finally, the power electronics 2 are connected to the battery 4 , wherein further losses, in particular the connection between the battery 4 and the power electronics 2 , for example line losses in the onboard power system, are represented by a further resistor R4 and an inductor L4 .

[0029] The corresponding intermediate circuit voltage U1, intermediate circuit current I1 and intermediate circuit power P1 are then generated in the power electronics 2. Once the values ​​of the corresponding electrical components are known, they can be estimated using the model.

[0030] For the calculation of the intermediate circuit voltage U1 for regulation purposes, the steady-state intermediate circuit voltage is mainly relevant. For the calculation of the intermediate circuit voltage, a simplified equivalent circuit diagram is sufficient. Figure 3 The second equivalent circuit diagram for this model is shown in FIG.

[0031] Not shown Figure 2 Of the above parameters of the battery in the circuit, only a single resistor R5 is shown, which represents the overall internal resistance of the battery. In order to estimate the intermediate circuit voltage U1, the open circuit voltage U0 and the internal resistance R5 are therefore sufficient as parameters of the battery 4. The losses between the wiring and the power electronics 2 and in the circuit are also represented only by the resistor R4. The remaining electrical components are omitted.

[0032] Final Reference Figure 4 An advantageous method for operating the electric drive system 1 is also described. Figure 4 The method is illustrated with the aid of a flow chart. In particular, the method ensures that the electric machine 3 is operated and controlled in the most efficient manner possible.

[0033] In step S1, the method begins with the receipt of a predefined speed and / or torque request for the electric machine 3. In particular, the computer device 6 is specially designed to carry out the method described below or a computer program product for carrying out the method.

[0034] In step S2, a mathematical model, preferably based on Figure 3 The equivalent circuit diagram for the mathematical model shown in , estimates at least one voltage value of the intermediate circuit voltage U1 of the power electronics 2 as a function of the rotational speed and / or torque requirement.

[0035] For this purpose, as described above, the mathematical model in particular takes into account at least one resistance value of the internal resistance R5 of the battery 4 and a voltage value of the open circuit voltage U0 of the battery 4 , which are known in particular from the battery temperature and / or the life of the battery 4 .

[0036] Furthermore, the mathematical model in particular takes into account at least one power value of the electrical power consumption P3 of the electrical consumers connected to the battery 4 , a power value of the electrical drive power of the drive system 1 and / or losses in or between the wiring and the power electronics 2 , in particular as represented above by the resistance value of the corresponding resistor R4 .

[0037] In step S3, at least one current value for the current of one of the phases 5 of the electric machine 3 and / or at least one current value for the current of the rotor is predefined as a function of the speed and / or torque requirement for the electric machine 3 and the intermediate circuit voltage U1 estimated in step S2. In particular, the current value is retrieved from a characteristic field assigned to the estimated voltage value of the intermediate circuit voltage U1.

[0038] In step S4 , the electric motor 3 is finally actuated according to the predefined current value. The method ends here.

Claims

1. A method for operating an electric drive system (1), in particular an electric drive system for a motor vehicle, wherein: The electric drive system (1) comprises a power electronics device (2), in particular a voltage converter, an electric motor (3) which can be driven by the power electronics device (2), and a battery (4) which is electrically connected or can be electrically connected to the power electronics device (2), wherein the power electronics device (2) has at least one electric phase (5) for driving the electric motor (3), characterized in that: - using a mathematical model of the drive system (1), estimating at least one voltage value of an intermediate circuit voltage (U1) of the power electronics (2) as a function of a predetermined speed and / or torque requirement for the electric machine (3), - predetermining at least one current value for a current of one of the phases (5) of the electric machine (3) and / or at least one current value for a current of the rotor as a function of a speed and / or torque requirement for the electric machine (3) and as a function of an estimated intermediate circuit voltage (U1), and - the electric motor (3) is actuated according to a predefined current value.

2. The method according to claim 1, characterized in that: The mathematical model takes into account the resistance value of the internal resistance (R5) of the battery (4) and / or the voltage value of the open circuit voltage (U0) of the battery (4).

3. The method according to claim 2, characterized in that The resistance value and / or the voltage value are obtained according to the battery temperature and / or the life of the battery (4).

4. The method according to any one of the preceding claims, characterized in that The mathematical model takes into account the power values ​​of the electrical consumption power (P3) of the electrical consumers connected to the battery (4).

5. The method according to any one of the preceding claims, characterized in that The mathematical model takes into account the power values ​​of the electric drive power of the drive system (1).

6. The method according to any one of the preceding claims, characterized in that A current value for a predefined rotational speed or torque requirement is retrieved from a characteristic field, in particular a look-up table, which is assigned to an estimated voltage value of the intermediate circuit voltage (U1).

7. The method according to any one of the preceding claims, characterized in that The mathematical model is designed as an observer, in which an estimated voltage value for the intermediate circuit voltage (U1) is compared with a measured voltage value.

8. A computer program product for execution on a computer device (6), characterized in that The computer program product, when used as intended, carries out the method according to any one of the preceding claims.

9. Data carrier having a computer program product according to claim 8.

10. An electric drive system (1), in particular an electric drive system for a motor vehicle, comprising a power electronics system (2), in particular a voltage converter, an electric machine (3) which can be controlled by the power electronics system (2), and a battery (4) which is electrically connected or can be electrically connected to the power electronics system (2), wherein: The power electronics system (2) has at least one electrical phase (5) for controlling the electric machine (3) and is characterized by a computer device (6) which is specially designed to execute a computer program product according to claim 8.

11. A motor vehicle, characterized in that The electric drive system (1) according to claim 10.

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