Method for operating an electric generator without rotor position sensor and auxiliary voltage source, control unit and vehicle

Abstract

The invention relates to a method for operating an electric generator with a rotor without a rotation angle sensor and auxiliary voltage source. The generator is designed to charge an energy storage unit 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 generator is operated in a first mode (3) with open terminals upon start-up. The generator is then switched to a second mode (4) with voltage control operation for controlling a voltage at the energy storage unit. In order to prevent overloading of the energy storage unit at the start of voltage control operation, phase voltages (φ(m)) of the generator measured with open terminals are recorded and, using these, rotational characteristics of the rotor are initialized and calculated until switching to the second mode (4).

Description

[0001] The present invention relates to a method for operating or controlling / regulating an electric generator with a rotor without a rotation angle sensor and auxiliary voltage source. The generator is designed, for example, to charge an energy storage unit, for example a short-term energy storage device, with electrical energy in order to use this 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] DE 100 42 524 A1 discloses a voltage supply device for a motor vehicle with an on-board voltage network that can be supplied with electrical energy by a first generator and a second auxiliary network that can be supplied with electrical energy by a second generator, wherein a control device for effecting an energy output is assigned to the second generator.

[0003] DE 198 46 319 C1 discloses a power supply circuit for a motor vehicle electrical system with two voltage supply branches. A method for operating an electric generator is described, in which the generator is configured to charge an energy storage device with electrical energy.

[0004] M. Bash, S. Pekarek, S. Sudhoff, J. Whitmore and M. Frantzen: A Comparison of Permanent Magnet and Wound Rotor Synchronous Machines for Portable Power Generation. In: Power and Energy Conference at Illinois (PECI), 2010, pp. 1-6.

[0005] This publication deals, among other things, with the advantages and disadvantages of permanent magnet generators (PMSM) and generators with field winding for excitation (WRSM), each with passive and active rectification.

[0006] CN 1 10 971 166 A discloses a control method for the starting process of a sensorless permanent magnet generator with open terminals.

[0007] CN 1 02 437 813 A discloses a method for determining rotor rotational characteristics for a generator with a rotor without a rotor position sensor and an auxiliary voltage source. An estimated speed and an estimated angle of rotation are determined from measured phase voltages of the generator.

[0008] CN 1 01 958 674 B teaches, among other things, a voltage control operation for controlling a voltage on an intermediate circuit with a sensor-based permanent magnet generator for use in a vehicle.

[0009] In situations where the waste heat generated by the exhaust gases of an internal combustion engine, for example, during a cold start, is not yet sufficient to ensure the effective operation of a catalyst, such as a three-way catalyst, in the 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.

[0010] For this purpose, the generator can be used with a rotor position sensor, for example a rotation angle sensor. The rotor position sensor continuously provides at least one rotational characteristic, such as a rotation angle of the generator's rotor, so that when controlled or regulated operation starts, a load torque of the generator and consequently a voltage across an energy storage unit, for example a capacitor, via which the electric heater of the catalytic converter is supplied with electrical energy, can be precisely adjusted. The disadvantage of this is that additional costs are required for the rotor position sensor and its integration into a control system. Furthermore, a failure of the rotor position sensor leads to a failure or at least to incorrect operation of the generator. Furthermore, additional installation space must be provided for the rotation angle sensor.

[0011] Alternatively, a generator without a rotor position sensor can be used. A battery, which can be provided in addition to a battery for supplying an on-board electrical system and can have a higher voltage, for example 48 V, than the battery for supplying an on-board electrical system, for example 12 V, can be provided as an auxiliary voltage source on the gate driver, allowing controlled operation of the generator as soon as it starts up. The auxiliary voltage source also requires additional costs and integration effort. Again, additional space is required to accommodate the auxiliary voltage source.

[0012] If the generator is to be designed without an auxiliary voltage and without a rotation angle sensor, the rotation angle must be initialized under speed with voltage requirements when switching from operation with open terminals to controlled operation. The voltage provided by the generator must remain within a specified range to prevent overvoltage from destroying the energy storage unit and the power electronics controlling the generator. The generator's power is adjusted to the power consumed by the heater. The generator charges the energy storage unit, and this supplies the output stage driver of the generator's power electronics with electrical energy as soon as a sufficiently high voltage is applied for clocked operation. The required phase voltage is set by clocking the generator, for example using pulse width modulation.

[0013] When the generator is started, it is initially operated in a first mode with open terminals and then in a second mode with regulated voltage. Between these two modes, an intermediate mode is introduced in which zero-current control is performed. This means that the generator is initialized, for example, by measuring the current flowing through the terminals and, using the resulting estimated voltage values ​​from the pulse-width modulation, setting a zero current with which the second voltage control mode is started. Since the generator rotor can already rotate, the zero-current condition prevents it from being overloaded if the energy storage unit has sufficiently large capacities.

[0014] If the capacity of the energy storage unit is dimensioned to smaller sizes and / or ages with a decrease in its capacity, an overload of the energy storage unit at a residual speed of the rotor cannot be ruled out.

[0015] The object of the present invention is to further develop a method for operating and controlling a generator for generating electrical energy for heating a heater for a catalytic converter. In particular, the object of the invention is to propose a method in which the energy storage unit can be minimized. Furthermore, the object of the invention is to propose a control unit for improved control of the method for a low-capacity energy storage unit and a vehicle with this control unit.

[0016] This object is solved by the subject matter of independent claims 1, 8 and 9. Dependent claims 2 to 7 represent advantageous embodiments of the subject matter of claim 1.

[0017] The present invention provides a method for operating an electric generator without a rotation angle sensor and auxiliary voltage source. The generator is designed to charge an energy storage unit 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 energy storage unit can be charged using direct current energy. The generator can provide alternating current or three-phase current energy. The energy storage unit can then be connected to the energy storage unit via a converter or rectifier, which has at least one switching element for rectifying the alternating current or three-phase current energy.

[0018] Consequently, the energy storage unit is used to buffer the electrical energy provided by the generator. The energy provided by the generator must therefore be supplied in equal measure to the energy required by the electric heater to heat the catalytic converter.

[0019] During startup, the generator operates with open terminals 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 energy storage unit. Consequently, the voltage or energy provided by the generator can be adjusted by appropriate pulsing.

[0020] The energy storage unit can be a capacitor. This allows the energy provided by the generator to be buffered in a simple and cost-effective manner.

[0021] 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.

[0022] 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 a long-term energy storage device is particularly suitable for a short-term energy storage device with a nominal voltage of 48 V.

[0023] 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.

[0024] Using the proposed method, a rotation angle-dependent phase voltage of the generator is detected with open terminals. This phase voltage is used to initialize, for example, estimate, the rotor's rotational characteristics. One aspect of the invention is to be able to initialize the sensorless control in "open terminal" mode by providing the measured phase voltages even at the lowest speeds.

[0025] The rotational characteristics of the rotor, such as its angle of rotation, speed and / or the like, can also be provided for higher speeds with open terminals after initialization.

[0026] Based on estimated torque parameters, such as the estimated speed, the system can switch from the first "open terminal" mode to the second, pulsed voltage control mode. At the same time, the system switches from the measured phase voltages to the estimated phase voltages as input for sensorless control.

[0027] In most cases, phase voltage measurement is not necessary for the operation of a permanent magnet synchronous machine when using the sensorless algorithm. Phase voltage measurement in combination with the commonly used phase voltage estimation is the best way to achieve a robust system. For example, this system uses a 48 V voltage, which allows phase voltage measurement without galvanic isolation using a voltage divider and at least one filter at a comparatively low cost.

[0028] The measured phase voltage of a driven generator with open terminals exhibits a sinusoidal rotating field. Depending on the charge level of the energy storage device, such as an electrical capacitor, the sinusoidal rotating field is cut off or distorted by the conducting freewheeling diodes. Ultimately, however, the voltage measurement measures the actual voltage and current applied to the generator, which are the required input variables for initializing the sensorless algorithm and are therefore important for providing the correct angle and speed signals for other functions.

[0029] If the motor starts at zero speed, the induced phase voltage will only distinguish itself from the noise at a minimum speed, for example, 20 rpm. If the current sensors also provide a signal that is distinct from the noise, it can be configured to allow initialization of the speed starting at this speed, and the resulting estimated speed and torque characteristics can be used.

[0030] Such an algorithm, without encoder sensors for detecting the torque values, can estimate the torque values ​​during operating times initialized well before the planned switchover from "open terminal" mode to "voltage control" mode. This can prevent unwanted voltage increases.

[0031] 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 rotor position sensor, or a sensorless control algorithm, is implemented in the control unit. Consequently, the same advantages can be achieved for the control unit as for the method according to the invention.

[0032] 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.

[0033] The present invention also provides a vehicle having the control unit according to the preceding aspect.

[0034] The invention is based on the Fig. 1 and Fig. 2 illustrated embodiment is explained in more detail. Fig. 1 a block diagram of a generator switching from the first mode with open terminals to the second mode with voltage regulation and Fig. 2 a diagram of a switch corresponding to the block diagram of the Fig. 1. with open terminals in the second mode with voltage regulation.

[0035] The Fig. Figure 1 shows the block diagram 1 of an algorithm 2 for controlling a generator to provide energy to charge an energy storage unit, which heats a heater for a catalyst of an exhaust gas control unit as long as the catalyst does not have a sufficient intrinsic temperature due to exhaust gas flow. Algorithm 2 divides the operation of the generator into two modes 3, 4, whereby at the beginning of generator operation, the first mode 3 is switched with the generator's terminals open. Based on the phase voltages φ(m) measured at the open terminals, the estimated rotation angle ω(g) and the estimated rotational speed n(g) are initialized using the measured phase currents i(m).Depending on these estimated variables, for example, if the estimated speed n(g) exceeds a predetermined value, the logic unit 5 decides whether to maintain the first mode 3 or switch to the second mode 4, in which the output stage is connected to the generator and the generator is controlled by voltage regulation. In the second mode 4, the estimated phase voltages φ(g) are used instead of the measured phase voltages φ(m). A switching parameter Mod is output at output A for setting the respective mode 3, 4.

[0036] The Fig. 2 shows with reference to Fig.Figure 1 shows diagram 10 of generator operation using algorithm 2. Between time t0 and time t1, operation occurs in the first mode 3 with open terminals. At time t1, the generator switches to the second mode 4, which features voltage regulation with active phase voltage synchronization, for example, using pulse-width modulation.

[0037] Partial diagram I shows the voltage U at the energy storage unit, for example, a capacitor supplying the heater with electrical energy. After switching from the first mode 3 with open terminals to the second mode 4 with voltage control with active clocking, the voltage U can increase rapidly and without overshoot from an initial voltage, for example, 35V, to a desired voltage of, for example, 48V using voltage control.

[0038] Part II shows the mode of the generator's output stage with the switching parameter Mod. Level 0 corresponds to the first mode 3 with open terminals, and the positive level 2 corresponds to the second mode 4 with voltage regulation of the output stage.

[0039] The third sub-diagram III shows the estimated speed n(g) of the rotor of the generator, which is estimated from measured phase voltages φ(m) up to time t1 and from the estimated phase voltages φ(g) after time t1.

[0040] The fourth sub-diagram IV shows the estimated angle of rotation w(g). This shows an absolutely continuous curve when switching from the first mode 3 with open terminals to the second mode 4 with voltage regulation.

[0041] The fifth sub-diagram V shows the phase voltages φ used for algorithm 2. In the first mode 3 with open terminals, the measured phase voltages φ(m) are used; in the second mode 4, the estimated phase voltages φ(g) are determined from the measured voltages U at the energy storage unit and the duty cycle.

[0042] The sixth sub-diagram VI shows the phase currents i(m). As the clock cycle begins after time t1, the voltage across the capacitor is increased to the desired 48V, causing a brief increase in current flow. List of reference symbols 1 block diagram 2 Algorithm 3 Mode 4 Mode 5 Logic unit 10 Diagram A Exit Mod switching parameters n(g) estimated speed i(m) measured phase current t time t0 time t1 time point U Voltage at the energy storage unit φ phase voltage φ(g) estimated phase voltage φ(m) measured phase voltage ω(g) estimated angle of rotation I Partial diagram II Partial diagram III Partial diagram IV sub-diagram V sub-diagram VI sub-diagram

Claims

[1] Method for operating an electric generator with a rotor without a rotor position sensor and auxiliary voltage source, wherein the generator is designed to charge an energy storage unit 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 in a first mode (3) at a start and is then switched to a second mode (4) with voltage control operation for controlling a voltage at the energy storage unit, characterized by that phase voltages (φ(m)) of the generator measured with open terminals are determined and using these rotational characteristics of the rotor are determined. [2] Method according to claim 1, characterized by that the rotational parameters are at least an estimated rotational speed (n(g)) and / or an estimated rotational angle (w(g)). [3] Method according to claim 1 or 2, wherein the rotational characteristics are determined as soon as the estimated phase voltages (φ(g)) differ significantly from a noise. [4] Method according to one of the preceding claims 1 to 3, characterized by that the energy storage unit is a capacitor [5] Method according to one of the preceding claims 1 to 4, characterized by that a nominal voltage of the energy storage unit is higher than the vehicle's electrical system voltage and in particular greater than 48V. [6] Method according to one of the preceding claims 1 to 5, characterized by that only the energy storage unit is used to heat the electric heater. [7] Method according to one of the preceding claims 1 to 6, characterized by that the generator is a dedicated generator. [8] Control unit designed and programmed to carry out the method according to one of claims 1 to 7. [9] A vehicle comprising the control unit according to claim 8.

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