Method for operating an electric generator without a rotation angle sensor and auxiliary voltage source, control unit and vehicle

Abstract

Method for operating an electric generator without a rotation angle sensor and auxiliary voltage source, wherein the generator is configured to charge a short-term energy storage device with electrical energy in order to use the electrical energy to heat an electric heater for heating a catalyst of an exhaust aftertreatment system of a vehicle, wherein the generator is operated with open terminals in a first step (S100) at startup, in which the actual voltage (2) at the short-term energy storage device remains essentially constant and is significantly below the nominal voltage (1) of the short-term energy storage device, and in a second step (S150) is controlled or regulated for a predetermined time (t), preferably from 25 ms to 75 ms, particularly preferably from 50 ms, to initialize the rotation angle to a target current of 0 A.and then, in a third step (S200), switched to voltage control mode to control a voltage at the short-term energy storage device.

Description

[0001] The present invention relates to a method for operating or controlling / regulating an electric generator without a rotation angle sensor and auxiliary voltage source. The generator is designed to charge a short-term energy storage device with electrical energy in order to use the electrical energy to heat an electric heater for heating a catalyst of an exhaust gas aftertreatment system of a vehicle. The present invention also relates to a control unit designed and programmed to carry out the method according to the invention, as well as to a vehicle having the control unit.

[0002] In situations where the waste heat provided by exhaust gases is insufficient to ensure the effective operation of a catalyst, such as a three-way catalyst, in a vehicle's exhaust aftertreatment system to meet current emissions requirements, the catalyst is heated using an electric heater located on or near the catalyst. This requires a large amount of electrical energy, which is provided by a generator.

[0003] A generator with a rotation angle sensor or rotor position sensor can be used for this purpose. The rotation angle sensor continuously provides a rotation angle or rotor position of a generator rotor, so that when controlled or regulated operation is started, the load torque of the generator and consequently the voltage at an energy storage unit, which supplies electrical energy to the catalytic converter's electric heater, can be precisely adjusted. The disadvantage of this is that additional costs are required for the rotation angle sensor and its integration into a control system. Furthermore, a failure of the rotation angle sensor inevitably leads to a failure or at least to faulty operation of the generator. Furthermore, additional installation space must be provided for the rotation angle sensor.

[0004] Alternatively, a generator without a rotation angle sensor can be used. A battery, which can be provided in addition to a battery for supplying an on-board power supply and can have a higher voltage, e.g., 48 V, than the battery for supplying an on-board power supply, e.g., 12 V, can be provided as an auxiliary voltage source on the gate driver, allowing controlled operation of the generator even during start-up. The auxiliary voltage source also requires additional costs and integration effort. Again, additional space is required to accommodate the auxiliary voltage source.

[0005] If the generator is to be designed without auxiliary voltage and without a rotation angle sensor, the rotation angle must be initialized under speed with voltage requirements when switching from open-terminal operation to controlled operation. The voltage provided by the generator must remain within a specified range to avoid damage to the energy storage device.

[0006] It is therefore an object of the present invention to eliminate the aforementioned disadvantages. In particular, a rotation angle sensor and an auxiliary voltage source are to be avoided. Furthermore, an estimated rotation angle is to be appropriately initialized upon starting controlled operation of the generator, while an output voltage provided by the generator remains within a predetermined range.

[0007] This object is achieved by the method, the control unit, and the vehicle having the features according to the independent claims. Advantageous embodiments are the subject of the dependent claims.

[0008] The present invention provides a method for operating an electric generator without a rotation angle sensor and auxiliary voltage source.

[0009] The generator is designed to charge a short-term energy storage device with electrical energy in order to use the electrical energy to heat an electric heater for heating a catalyst of an exhaust aftertreatment system of a vehicle. The short-term energy storage device can be charged using direct current energy. The generator can provide alternating current or three-phase current energy. The short-term energy storage device can then be connected to the short-term energy storage device via a converter or rectifier, which has at least one switching element for rectifying the alternating current or three-phase current energy.

[0010] Consequently, a short-term energy storage device is used to buffer the electrical energy provided by the generator. The energy provided by the generator must therefore be adjusted to match the energy required by the electric heater to heat the catalytic converter.

[0011] The generator is operated with open terminals during startup to increase the energy storage voltage via the inverter's freewheeling diodes as the speed increases until a minimum threshold for operation in pulsed mode is reached. The generator then switches to voltage control mode or pulsed mode to control or regulate the voltage at the short-term energy storage device. Consequently, the voltage or energy provided by the generator can be adjusted by appropriate pulsing.

[0012] After operation with open terminals and before voltage control mode, the generator is controlled or regulated to a target current of 0 A for a predetermined time. Accordingly, the generator is controlled during the predetermined time such that a target current of 0 A is to be supplied. After the predetermined time has elapsed, the switchover or change to voltage control mode then takes place. During control or regulation to a target current of 0 A, the estimated rotation angle can be appropriately initialized so that in the subsequent voltage control mode it is ensured that the voltage supplied by the generator remains within the predetermined range. The predetermined time can preferably be set between 25 ms and 75 ms. Particularly preferably, the predetermined time can be set to 50 ms.

[0013] At the beginning of the control or regulation to a target current of 0 A, the rotation angle is initially set to a specified value, e.g., Pi, or a random value. The algorithm for controlling the generator without a rotation angle sensor then reduces an error that occurs due to the deviation of the specified rotation angle from the actual rotation angle by comparing calculated voltages and measured voltages. Consequently, the correct rotation angle and thus a speed of the generator can be determined or initialized. Such a method for tracking the rotation angle is known, for example, from EP 2 019 482 B1.

[0014] As a result, a rotation angle sensor and an auxiliary voltage source can be eliminated. This reduces costs and increases system robustness. Furthermore, a more compact generator design can be achieved.

[0015] Preferably, the specified time can be determined in advance based on tests. Accordingly, the time or duration required to appropriately initialize the rotation angle is determined in advance. This can be done, for example, on a test bench. A safety time can be added to the time determined by tests to obtain the specified time.

[0016] Advantageously, the predetermined time can be set according to the operating conditions of the generator, in particular the temperature of the generator and / or the voltage present at the short-term energy storage device, i.e., the intermediate circuit voltage, at the start of open-terminal operation. Consequently, the duration can be set as short as necessary, thus achieving an effective switchover to voltage control mode.

[0017] The short-term energy storage device can be a capacitor. This allows the energy provided by the generator to be buffered in a simple and cost-effective manner.

[0018] Advantageously, the nominal voltage of the short-term energy storage device, in particular of the capacitor, can be higher than the vehicle's electrical system voltage, which can be 12 V or 24 V. Particularly preferably, the nominal voltage of the short-term energy storage device can be 48 V. Consequently, the currents during charging of the short-term energy storage device can be kept low despite the high energy required.

[0019] Preferably, the short-term energy storage device can be used exclusively to heat the electric heater. Consequently, a long-term energy storage device, such as a battery, is omitted, thus saving further costs. Eliminating the long-term energy storage device is particularly suitable for a short-term energy storage device with a nominal voltage of 48 V.

[0020] The generator can be a dedicated generator. Consequently, the generator is intended solely for charging the short-term energy storage device. Consequently, no other tasks need to be considered when operating or controlling the generator.

[0021] Alternatively, the generator can be implemented as a motor-generator of the vehicle. The motor-generator can be used, for example, for a vehicle's start-stop system. Consequently, synergistic use of the motor-generator is possible.

[0022] The present invention further provides a control unit configured and programmed to carry out the method according to one of the preceding aspects. The control unit is thus configured to receive measured values ​​required to control the operation of the electric generator and to output determined control commands to corresponding components of the generator. Furthermore, an algorithm for controlling the generator without a rotation angle sensor, or a sensorless control algorithm, is implemented in the control unit. Consequently, the same advantages as for the method according to the invention can be achieved in the control unit.

[0023] The present invention also provides a vehicle having the control unit according to the preceding aspect.

[0024] The present invention is described in detail below with reference to the figures. They show: Fig. 1 a conventional flow chart for starting a generator with a rotation angle sensor; Fig. 2 shows a flow chart according to the invention for starting a generator without a rotation angle sensor; and Fig. 3 a time diagram when carrying out the steps of the flow chart according to the invention for starting the generator without a rotation angle sensor.

[0025] An embodiment of the present invention will be described below with reference to the figures.

[0026] Fig. 1 shows steps of a conventional flowchart for starting a generator that has a rotation angle sensor and is designed to charge a short-term energy storage device with electrical energy in order to use the electrical energy to heat an electric heater for heating a catalyst of an exhaust gas aftertreatment system of a vehicle. Since the rotation angle of the generator's rotor is continuously detected by the rotation angle sensor, a direct switch can be made from step S100, in which the generator is operated with open terminals, to step S200, in which a voltage control operation is carried out. In the voltage control operation in step S200, the rotation angle of the rotor detected by the rotation angle sensor is then used for open-loop or closed-loop control, in particular for field-oriented open-loop or closed-loop control, of the generator.

[0027] According to the invention, however, a rotation angle sensor and an auxiliary voltage source are to be dispensed with, so that the process consists of Fig. 1 is not applicable to a generator that does not have a rotation angle sensor or an auxiliary voltage source if, as in the present case, the estimated voltage is only available during pulsed operation. A rotation angle of a generator rotor is required for the field-oriented control applied during voltage regulation operation to ensure that the voltage applied by the generator to the short-term energy storage device remains within a specified range.

[0028] In Fig. Figure 2 shows a flowchart according to the invention for starting a generator that does not have a rotation angle sensor or an auxiliary voltage source. As mentioned, it is not possible to switch directly from step S100, in which operation with open terminals occurs, to step S200, in which voltage regulation is performed, because the rotation angle of the rotor is unknown at the time of switching. Consequently, there is a risk that the voltage at the short-term energy storage device will stray outside a predetermined range, which could lead to the destruction of the short-term energy storage device.

[0029] Therefore, after the open terminal operation in step S100, as shown in Fig. 2, for a given time t (see Fig. 3) switching to step S150, in which the generator is controlled or regulated to a target current of 0 A. At the beginning of step S150, the rotation angle of the rotor is initially set to a predetermined value, e.g., Pi, or a random value. The algorithm for controlling the generator without a rotation angle sensor and auxiliary voltage source then reduces an error between calculated voltages and measured voltages during step S150, in which the target current is set to 0 A, by adjusting or tracking the estimated rotation angle. Such a method for tracking the rotation angle is known, for example, from EP 2 019 482 B1. Consequently, the correct rotation angle and thus also a speed of the generator can be determined.

[0030] In Fig. Figure 3 is a timing diagram illustrating the measured value curves recorded during the generator start-up process according to the invention. In the first diagram from the top, the nominal voltage of the short-term energy storage device, i.e., the capacitor, is designated by reference numeral 1. The nominal voltage is set to 48 V in this case, i.e., higher than a typical vehicle electrical system voltage of 12 V or 24 V. This allows only a small current to be provided, even at high power levels. Reference numeral 2 denotes the actual voltage curve at the short-term energy storage device.

[0031] In the second diagram from the top, the curve of the estimated rotation angle is marked with the reference symbol 3. The actual curve of the rotation angle is marked with the reference symbol 4. In the two lower diagrams, the curve of the current I d with the reference number 5 and the course of the current Iq provided with the reference number 6.

[0032] In step S100, the generator is operated with open terminals, so that the actual voltage 2 at this state of charge and at a nearly constant speed at the short-term energy storage device remains essentially constant and is significantly below the nominal voltage 1 of the short-term energy storage device. During this period, as can be seen in the second diagram from the top, the estimated rotation angle 3 of the rotor is constant, i.e., unknown. In addition, the two currents I d 5 and I q 6 equals 0 A.

[0033] If the system were to immediately switch to voltage control mode, there would be a risk that the rotation angle would be significantly incorrect, resulting in a high current being delivered by the generator, which would cause voltage 2 at the short-term energy storage device to rise rapidly. Consequently, voltage 2 at the short-term energy storage device could rise beyond a permissible value, which could destroy the short-term energy storage device, i.e., the capacitor.

[0034] Accordingly, the system switches to step S150, where the generator is controlled or regulated to a target current of 0 A. This prevents the voltage at the capacitor from rising uncontrollably. As shown in the second diagram from the top in Fig.As can be seen in Figure 3, the rotation angle in the present embodiment is set to a predetermined value, in this case, Pi. However, it is also conceivable that the rotation angle assumed in S100 is retained. Since the rotation angle is incorrect at the beginning of S150, the algorithm for controlling the generator provides the two currents I d 5 and I d 6 (see the two lower diagrams), so that voltage 2 at the short-term energy storage device (see the first diagram) also increases slightly. Nevertheless, due to the control to a target current of 0 A, the generator actually only delivers a small current, so the voltage increase at the short-term energy storage device is limited.

[0035] During step S150, the generator control algorithm reduces the error between the estimated rotation angle and the actual rotation angle by comparing the voltages calculated using voltage equations with measured voltages. The time required to initialize the rotation angle can be determined in advance through experiments in which the rotation angle is actually detected using a rotation angle sensor. That is, the experiments determine the time at which an error between a measured rotation angle and an estimated rotation angle is essentially zero. This determined time can then be used as the predetermined time t for which step S150 is applied.a safety time can be added to the specified time so that even under different conditions it is ensured that an appropriate initialization of the rotation angle takes place during the specified time t.

[0036] The specified time t depends on the operating conditions of the generator, such as the temperature of the generator and / or the voltage at the short-term energy storage device when starting operation with open terminals. Consequently, the operating conditions can be taken into account when determining the specified time and a setting during generator operation.

[0037] The second diagram clearly shows that the actual rotation angle 4 of the rotor changes in a sawtooth pattern, as the rotor is already rotating at a certain speed. It can also be seen that no estimation of the rotation angle can be made during step S100. The rotation angle therefore remains the same. During step S150, the terminals are closed so that the algorithm for controlling the generator can initialize the rotation angle. After the specified time t has elapsed, i.e., after step S150, the estimated rotation angle 3 matches the sawtooth-like variation of the actual rotation angle 4.

[0038] After the predetermined time t has elapsed, it is then possible to switch to step S200, in which the voltage control operation, e.g. the field-oriented control or regulation of the generator, is carried out, since the rotation angle is initialized and thus a risk of an excessive increase in the voltage at the short-term energy storage device is prevented.

[0039] The method according to the invention can be carried out by a control unit. The control unit can be a dedicated control unit. Alternatively, the method can also be implemented in a control unit that performs other control tasks, such as a control unit for engine management. The control unit is accordingly designed and programmed to carry out the method according to the invention. The control unit is accordingly designed to receive measured values ​​required to control the operation of the electric generator and to output determined control commands to corresponding components of the generator. Furthermore, an algorithm for controlling or regulating the generator without a rotation angle sensor is implemented in the control unit. The control unit can be installed in a vehicle, such as a motor vehicle or a truck. List of reference symbols 1 Nominal voltage of the short-term energy storage device 2 actual voltage at the short-term energy storage 3 estimated rotation angle 4 actual rotation angle 5 I d 6 I q S100 Operation with open terminals S150 Control of the generator to a target current of 0A S200 Voltage control operation QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] EP 2 019 482 B1 [0013, 0029]

Claims

[1] Method for operating an electric generator without a rotation angle sensor and auxiliary voltage source, wherein the generator is designed to charge a short-term energy storage device with electrical energy in order to use the electrical energy to heat an electric heater for heating a catalyst of an exhaust gas aftertreatment system of a vehicle, wherein the generator is operated with open terminals during start-up (S100) and is then switched to a voltage control mode (S200) for controlling a voltage at the short-term energy storage device, characterized by , that after the operation with open terminals (S100) and before the voltage control operation (S200), the generator is controlled to a target current of 0 A for a predetermined time (t), preferably from 25 ms to 75 ms, particularly preferably from 50 ms (S150). [2] Method according to claim 1, wherein the predetermined time (t) is determined beforehand by means of experiments. [3] Method according to one of claims 1 or 2, wherein the predetermined time (t) is determined according to operating conditions of the generator, in particular a temperature of the generator and / or a voltage at the short-term energy storage device at the start of operation with open terminals. [4] Method according to one of the preceding claims 1 to 3, wherein the short-term energy storage device is a capacitor [5] Method according to one of the preceding claims 1 to 4, wherein the nominal voltage of the short-term energy storage device is higher than an on-board network voltage of the vehicle and in particular 48 V. [6] Method according to one of the preceding claims 1 to 5, wherein only the short-term energy storage is used to heat the electric heater. [7] Method according to one of the preceding claims 1 to 6, wherein the generator is a dedicated generator [8] Method according to one of the preceding claims 1 to 6, wherein the generator is implemented by a motor-generator of the vehicle [9] Control unit designed and programmed to carry out the method according to one of claims 1 to 8. [10] A vehicle comprising the control unit according to claim 9.

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