DE102011087145A1 - Method for protection of rectifier of multi-phase alternating current generator in motor vehicle, involves receiving receive phase signal to reduce or limit energizing current if necessary as function of determined forward voltage - Google Patents

Abstract

The method involves controlling rectified voltage generator by a controller (4) to control the excitation current (IERR) to a field winding (5) of the generator. The controller is adapted to receive a phase signal assigned with first phase (U), for determining a forward voltage (Ud,10,max,Ud,11,max) of semiconductor switch (10,11). The controller is also adapted to receive phase signal for reducing or limiting the energizing current if necessary as a function of determined forward voltage. An independent claim is included for controller having function for protecting rectifier of multi-phase alternating current generator for motor vehicle.

Description

The invention relates to the protection of a rectifier of a polyphase alternator in a motor vehicle.

Motor vehicles typically include an electric generator to supply electric consumers with electrical energy, which is supplied with mechanical energy via the drive of the vehicle. With the excess electrical power of the generator, the vehicle battery is charged.

As a generator, a polyphase alternator (three-phase generator) having three or more phases is generally used. In this case, the multiphase alternating current generator is typically realized as an electric synchronous machine which comprises a rotor rotating through the drive with an excitation winding for generating a field magnetic field and a stator with a multiphase stator winding. Since the electrical consumers are typically designed as DC consumers and the battery is charged for charging with DC, the multiphase AC generator is followed by a rectifier, which converts the multiphase AC signal into a DC voltage. In order to keep the rectified generator voltage constant even with variable load current and variable motor speed, a generator controller is used, which varies the excitation current of the field winding, so that a fluctuation of the generator voltage is compensated.

In 1 is an example of a conventional 14V generator with a rectifier 1 represented for a motor vehicle. Here, by way of example, a 3-phase generator is shown, but the generator can also have, for example, five or six phases. The 14 V generator converts a part of the mechanical power of the internal combustion engine into electrical power, thus ensuring the electrical power supply of the vehicle electrical system comprising the battery and the consumers 7 , The belt drive 2 transfers the mechanical power of the engine 3 , which is determined by the speed and the torque, from the crankshaft to the generator. The generated by the generator generator current I _{B +} is via the terminal B + to the electrical system 7 to charge the battery and to power consumers such as the ignition, the headlights or the blower. In 1 is the generator as a separately excited synchronous machine nine with built-in regulator 4 and rectifier 1 executed. The rotor of the synchronous machine nine carries a field winding 5 and is supplied for example via two slip rings with the excitation current I _ERR . The magnetic field of the exciter winding 5 For example, it is conducted via pole claws of magnetically permeable steel into the stator and induces an alternating voltage during rotation in the stator phases. The voltage amplitude depends on the generator speed n _GEN and the excitation current I _ERR . The generator speed n _{GEN of} the generator is proportional to the speed of the motor. For a given speed of the engine, the load torque on the crankshaft increases as the output current I _{B + increases} . The rectifier 1 converts the AC voltage of the stator phases into those for the electrical system 7 required DC voltage U _GEN . For the in 1 illustrated rectifier 1 a bridge circuit is used with a connected to the vehicle electrical system voltage high-side semiconductor switch and a connected to the ground low-side semiconductor switches per phase, so that each half of each phase of each phase are used for rectification. In a 3-phase alternating current generator, such a rectifier is also referred to as a six-pulse level calibrator. As a semiconductor switch can - as in 1 represented - for example, diodes or, alternatively, transistors, in particular MOSFETs (metal oxide semiconductor field effect transistor) can be used.

The generator controller 4 Adjusts the excitation current I _ERR to keep the voltage U _GEN between B + and B- constant even with changing load current I _{B +} and changing motor speed. The excitation current I _ERR is typically achieved by varying the duty cycle of the final stage 6 varies, the excitation current I _ERR of the exciter winding 5 supplies. With increasing duty cycle increases the excitation current I _ERR and depending on the load and the voltage and the current at the generator output.

Below the duty cycle of the power amplifier 6 is the duration of the switch-on time, in the power amplifier 6 is switched on and supplies power, understood in relation to a total viewing time. At a duty cycle of 100% is the final stage 6 Consistently switched on, with a duty cycle of 50% is the final stage 6 half of the time is switched on (the other half of the time, the current flows through the free-wheeling diode in parallel with the switching transistor of the power amplifier) and at a duty cycle of 0% is the final stage 6 constantly switched off. The duty cycle of the power amplifier 6 thus determines the size of the (average) exciter current I _ERR .

In the example in 1 has the generator controller 4 via a communication interface for a data bus in the vehicle. To the data bus are, for example, in addition to the generator controller 4 one or more other communication participants 8th connected, for example, the engine control unit. For example, the controller receives a set voltage specification via the communication interface from the engine control unit and reports its own status to the engine control unit. The communication interface is, for example, a communication interface for the LIN bus (LIN - Local Interconnect Network). For connection of the generator controller 4 to the bus is in 1 the connection LIN provided.

The controller is typically implemented today in the form of an ASIC (applicationspecific integrated circuit), ie as a monolithic semiconductor integrated circuit. The in 1 Illustrated via the LIN bus communicating generator controller ASIC (LIN Generator Controller ASIC) has five connections, with which he can, for example, detect the required generator sizes and communicate with the engine control unit. The outwardly visible functionality and interfaces of such a five-terminal LIN generator regulator ASIC have been specified in general terms; Such LIN generator regulator ASICs are available from various chip manufacturers. Two examples of such a five-terminal LIN generator regulator ASIC are the TLE8880 from Infineon and the CR665BC from Bosch.

• – B– (Batterie Minus): Masseanschluss, beispielsweise an den Motorblock über das leitfähige Gehäuse des Generators;
• – B+ (Batterie Plus): Anschluss zur Stromversorgung des Reglers und der Erregerwicklung sowie zur Spannungsmessung; die Verbindung zur Batterie erfolgt via den Kabelbaum im Fahrzeug;
• – LIN: Anschluss der LIN-Bus-Schnittstelle zur Kommunikation beispielsweise mit dem Motorsteuergerät; über den Anschluss LIN wird die Sollspannungsvorgabe empfangen und der Generatorzustand gemeldet;
• – EXC: Anschluss zum Einprägen des Erregerstromes in die Erregerwicklung;
• – PH: Anschluss zum Entgegennehmen des Phasensignals, welches das Potential einer Phase beschreibt; das Phasensignal dient zum Erfassen der Generatordrehzahl durch Bestimmen der Frequenz des Phasensignals (Phasenfrequenz) und zum Aufwecken des Reglers aus dem Standby-Modus, wenn eine definierte Wechselspannungsamplitude am Phasen-Anschluss PH erkannt wird.

The connections in 1 are defined as follows:

• - B- (battery negative): earth connection, for example to the engine block via the conductive housing of the generator;
• - B + (battery plus): connection for power supply of the regulator and the excitation winding as well as for voltage measurement; the connection to the battery via the cable harness in the vehicle;
• LIN: connection of the LIN bus interface for communication with, for example, the engine control unit; The nominal voltage specification is received via the LIN connection and the generator status is reported;
• - EXC: connection for impressing the excitation current into the exciter winding;
• - PH: terminal for receiving the phase signal, which describes the potential of a phase; the phase signal is for detecting the generator speed by determining the frequency of the phase signal (phase frequency) and for waking the controller from the standby mode when a defined AC amplitude is detected at the phase terminal PH.

In the LIN generator controller ASIC 4 The voltage at terminal B +, the voltage at terminal B-, the frequency of the terminal PH received phase signal and the excitation current I _ERR are detected and used for the regulation of the generator voltage U _GEN between B + and B-. In addition, the LIN generator controller ASIC has 4 via a built-in temperature sensor that connects to the controller ASIC 4 can protect against overheating. For high-temperature regulation, this reduces the internal setpoint voltage specification at high temperatures. A programmable memory area in the controller ASIC 4 allows generator or vehicle specific controller parameters to be stored.

The in 1 The five-port LIN controller ASIC has been reduced to the necessary interfaces. Each additional interface would lead to additional costs due to the complex connection technology in the generator. Apart from the exciter current I _ERR , no further currents are detected. The semiconductor switches (eg diodes or MOSFETs) of the rectifier 1 are from the generator regulator ASIC 4 not directly monitored and protected.

The semiconductor switches must therefore be designed in terms of their current carrying capacity and their operating temperature so that a relatively large safety margin is kept in order to avoid overloading of the semiconductor switches. The same applies to the connecting lines and the connections to the semiconductor switches. For a given generator power high costs and an increased space requirement for the rectifier arise due to the large-area design 1 , For a given design of the rectifier 1 the output power remains behind the theoretically possible output power due to the safety margin.

It is an object of the invention to overcome these disadvantages.

The object is solved by the features of the independent claims. Advantageous embodiments are described in the dependent claims.

A first aspect of the invention relates to a method for protecting a rectifier of a polyphase alternator in a motor vehicle. For example, the generator has three phases, five phases or six phases. The rectifier comprises a plurality of semiconductor switches, wherein each phase is associated with at least one semiconductor switch. Preferably, the rectifier comprises a bridge circuit with two semiconductor switches per phase: a high-side semiconductor switch and a low-side semiconductor switch. However, it would also be conceivable to provide a rectifier with exactly one diode per phase (this is also called a three-pulse rectifier in the case of a 3-phase three-phase current).

The rectified generator voltage is via a controller (preferably in the form of a Regulator ASIC), which influences the excitation current of a field winding of the generator. To adjust the excitation current, for example, the duty cycle of the output stage for generating the excitation current is changed.

The controller is configured to receive a phase signal of a first phase of the multiple phases of the polyphase AC generator. For example, the phase signal describes the potential of the first phase. As described above, such a phase signal is used in the prior art to determine the rotational speed of the generator via the frequency of the phase signal. According to the invention, the phase signal is used to monitor and protect the rectifier. For this purpose, the forward voltage of at least one semiconductor switch is determined using the phase signal, which is associated with the first phase. Preferably, the forward voltage of both the high-side semiconductor switch of the first phase and the forward voltage of the low-side semiconductor switch of the first phase is determined, provided that a high-side semiconductor switch and a low-side semiconductor switch are provided. For the purposes of the application, forward voltage is understood to mean the voltage across the semiconductor switch in the closed state, for example the forward voltage between the anode and cathode of a diode or the voltage of an N-MOSFET between source and drain.

According to the invention, the exciting current is reduced as required as a function of the determined forward voltage. Depending on the value of the forward voltage, the forward voltage can be reduced or not reduced. It can also be provided that the exciter current is limited as a function of the determined forward voltage, wherein it is not absolutely necessary that the limitation also results in a reduction of the exciter current (for example because the current through the semiconductor switch has fallen again due to a reduction in the generator load). , By limiting or reducing the exciter current, the forward voltage is typically also limited or reduced.

The invention is based on the idea that the phase signal allows conclusions about the potential at a connection point of a semiconductor switch and therefore can also be used to monitor the semiconductor switch. Preferably, the phase signal corresponds to the potential of the phase and the potential of the connection point of the semiconductor switch. For monitoring the semiconductor switch, the forward voltage of the semiconductor switch can be measured via the already existing phase signal. Since the other connection point of the semiconductor switch depending on the circuit of the semiconductor switch either to the positive vehicle electrical system voltage or ground hangs whose potentials are available anyway, the forward voltage across the semiconductor switch in dependence of the phase signal and the ground potential can be easily determined without an additional terminal pin would be necessary on the controller module. The forward voltage allows conclusions about the current or the temperature of the semiconductor switch. In a critical situation with regard to the current or the temperature of the semiconductor switch, the excitation current can thus be reduced on the basis of the monitoring of the forward voltage in order to protect the semiconductor switch and the rectifier. Since the load on the semiconductor switches is substantially equal, not all the semiconductor switches of the rectifier need to be monitored. It would also be conceivable to evaluate several phase signals of different phases.

The function allows the generator to be used to a greater extent so that more output power can be called up without overloading the semiconductor switches thermally or electrically. Alternatively, with regard to the current carrying capacity and the operating temperature, the requirements for the semiconductor switches and the rectifier can be reduced for a given output power, so that costs and installation space can be saved.

Preferably, the forward voltage is determined directly in the controller module; but it would also be conceivable to forward the phase signal via the controller and its communication interface to the engine control unit and to determine the forward voltage in the engine control unit.

The monitoring and protection function can for example be completely taken over by the generator controller, so that no further additional costs arise except for a possible modification of the generator controller. In particular, it can be provided that the interface between the controller module and the synchronous machine remains substantially unchanged and continue to equip the controller module with only five connections.

To protect the semiconductor switch, a threshold, i. H. a maximum forward voltage, be specified. The measured forward voltage is then compared to the threshold value. If the forward voltage is greater than the threshold (or alternatively greater than or equal to the threshold), the excitation current is reduced or limited.

The threshold value itself or a parameter for calculating the threshold value can be stored in the generator controller or transmitted via a LIN bus from the engine control unit to the generator controller.

The threshold value can be temperature-dependent.

If the forward voltage is the forward voltage of a semiconductor switch in the form of a diode, the threshold value preferably has a negative temperature gradient. If the forward voltage is the forward voltage of a semiconductor switch in the form of a MOSFET, the threshold value preferably has a positive temperature gradient.

For example, the threshold value at a specific reference temperature is indicated via a first parameter. The temperature gradient is described by means of a second parameter. From the two parameters, the threshold value can then be determined as a function of the temperature.

The temperature can be determined, for example, with the integrated temperature sensor of the generator controller. This temperature thus measured can be used directly to determine the temperature-dependent threshold; Alternatively, based on this temperature, an estimate of the temperature of the semiconductor switch may be made and this estimated temperature then used to determine the temperature gradient.

It is conceivable that the decision on the reduction or limitation of the excitation current is not based directly on a comparison of the measured forward voltage with a threshold, but based on the forward voltage is determined a further size, the further size then to decide on the reduction or Limiting the excitation current is used.

For example, the method may provide that the generator current or a current proportional thereto (for example, the current of one or more phases) is determined. For this purpose, for example, in the publication DE 10 2006 049 140 A1 described device for determining a generator current can be used. This particular current allows conclusions about the current through the semiconductor switch. Depending on the current thus determined (or the current through the semiconductor switch, which in turn determined from the generator current or the phase current) and in dependence of the forward voltage can be determined with knowledge of the dependencies of current, forward voltage and temperature to each other, the temperature of the semiconductor. Current, forward voltage and temperature can be stored for example in a map, with knowledge of the current and the forward voltage, the temperature of the semiconductor switch can be determined. Depending on the temperature thus determined, the excitation current can be reduced or limited. For this purpose, for example, the temperature can be compared with a threshold value for the temperature and the excitation current can be reduced or limited if the temperature is greater or alternatively greater than or equal to the threshold value.

Preferably, the forward voltage is determined in the controller and transmitted via the communication bus to the engine control unit. The engine control unit determines the generator current or the phase current and determines the temperature of the semiconductor switch as a function of the current. The engine control unit compares the temperature with the threshold value and, depending on the comparison via the communication bus, transmits a signal for reducing or limiting the exciter current to the controller.

The embodiment described above, in which a generator current (or a current of one or more phases) is calculated, is particularly suitable when using diodes as a semiconductor switch. Namely, diodes as semiconductor switches typically have the characteristic that the forward voltage drops with increasing temperature (with MOSFETs, on the other hand, typically the forward voltage increases with increasing temperature), while the forward voltage increases with increasing diode current.

Preferably, the excitation current is reduced or limited by the duty cycle of the output stage for generating the excitation current reduced or

is limited. It can be provided, for example, that the duty cycle is limited to a maximum duty cycle of less than 100% when the threshold value is exceeded (relative to the forward voltage or relative to a temperature), the maximum duty cycle decreasing as the threshold value is exceeded, for example in the form of a linearly falling straight line. For example, in the case of a MOSFET when a maximum forward voltage of 0.2 V is exceeded, the duty cycle can be linearly limited to values of less than 100% starting from 100% (for example, limited to 0% at a forward voltage of 0.3 V). Alternatively, it can be provided in the case of a diode that, when a maximum temperature of 200 ° C. is exceeded, the duty cycle is linearly limited to values of less than 100% starting from 100% (for example with a limitation to 0% at a temperature of 230 ° C.).

The rectifier preferably comprises a bridge circuit with a high-side semiconductor switch connected to the vehicle electrical system voltage and a grounded low-side semiconductor switch per phase.

In order to determine the forward voltage of the high-side semiconductor switch assigned to the first phase, the vehicle electrical system voltage can be subtracted from the time-varying phase signal. This difference signal is then preferably subjected to a maximum determination, for example, the maximum of the difference is determined within a certain time interval.

In order to determine the forward voltage of the low-side semiconductor switch assigned to the first phase, the phase signal can be subtracted from the ground potential. Since the ground potential is typically at 0 V, the sign of the phase signal can also be reversed. The resulting signal is then preferably subjected to a maximum determination, for example, the maximum of the difference is determined within a certain time interval. It is also conceivable to specify the forward voltage by means of a negative voltage value; In this case, even the inversion of the phase signal can be dispensed with and the phase signal subjected to a minimum determination instead of a maximum determination.

A second aspect of the invention is directed to a regulator having a function for protecting a rectifier, in particular a regulator ASIC. The controller is used to control the rectified generator voltage by adjusting the excitation current. The controller accepts a phase signal of a first phase. The controller is set up to determine, as a function of the phase signal, a forward voltage of at least one semiconductor switch which is assigned to the first phase. In addition, the controller is set up to reduce or limit the excitation current as a function of the determined forward voltage. Alternatively, it can also be provided that the controller is set up to transmit the forward voltage to an engine control unit and then, if necessary, to receive a corresponding signal for reducing or limiting the exciter current.

Preferably, the controller is a five-terminal LIN generator regulator ASIC.

The above statements on the method according to the invention according to the first aspect of the invention also apply correspondingly to the regulator according to the invention according to the second aspect of the invention; advantageous embodiments of the controller according to the invention correspond to the described advantageous embodiments of the method according to the invention.

The invention will be described below with reference to the accompanying drawings with reference to an embodiment. In these show:

1 a conventional 14V generator with conventional LIN generator regulator ASIC;

2 an embodiment of a LIN generator controller ASIC according to the invention with a function for protecting the rectifier;

3 three exemplary waveforms for the phase signal voltage U _PH ; and

4 two exemplary linear curves of the threshold value U _S for the forward voltage over the temperature T.

The in 1 illustrated 14V generator with conventional LIN generator controller ASIC 4 was already discussed in the introduction. 2 shows one opposite the in 1 illustrated conventional LIN generator regulator ASIC 4 extended LIN generator controller ASIC 4 ' , which has a function to protect the rectifier 1 having. The in 2 illustrated LIN generator controller ASIC 4 ' has all the features of in 1 represented LIN generator regulator ASIC, so that the description of in 1 shown LIN generator regulator in the same way for the in 2 applies to the LIN generator controller ASIC. In the example in 2 are in the rectifier 1 the semiconductor switches as MOSFETs (here N-MOSFETs) realized. The drain terminals D of the high-side MOSFETs are connected to the node B + of the positive vehicle electrical system voltage and the source terminals S of the low-side MOSFETs are connected to the ground node B-. The rectifier 1 but can in 2 like in 1 be realized by means of diodes. This is in 2 indicated by the diodes shown next to the MOSFETs, wherein in realization of the rectifier 1 as in 1 the cathodes K of the high-side diodes are connected to the node B + of the positive vehicle electrical system voltage and the anodes A of the low-side diodes are connected to the ground node B-. Instead of one in 1 shown generator with a 3-phase electric machine nine can also be a generator with, for example, a 5-phase, 6-phase or 7-phase electric machine nine be used. In addition, a mixed structure of the rectifier 1 both by means of diodes and MOSFETs conceivable in which, for example, the low-side semiconductor switch MOSFETs and the high-side semiconductor switch diodes correspond.

To protect the rectifier 1 is in the example in 2 the forward voltage of one high-side connected to B + Semiconductor switches 10 and a low-side semiconductor switch connected to B- 11 of the rectifier 1 measured over the already existing phase connection PH, with a phase of the synchronous machine nine connected is. At the in 2 For example, the phase terminal PH is connected to the phase U, for example; the phase terminal PH may instead be connected to any other phase. The phase closure supplies a phase signal U _PH , which corresponds to the potential of the phase U. It is conceivable that there is optionally a resistance between the phase U and the phase input PH. For measuring the forward voltage of the high-side semiconductor switch 10 will be in a block 12 the differential voltage U _{d, 10 determined} between the time-varying phase signal U _PH and the vehicle electrical system voltage U _{B +} according to U _{d, 10} = U _PH - U _{B +} . In this case, the vehicle electrical system voltage U _{B + is} typically not quite constant, but changes in time with a certain ripple. The phase signal U _PH corresponds to the voltage at the source terminal S or at the anode A of the high-semiconductor switch 10 , the vehicle electrical system voltage U _{B +} corresponds to the voltage at the drain terminal D or at the cathode K of the high-semiconductor switch 10 , so that the size U _{d, 10 of} the voltage across the semiconductor switch 10 in direction S to D and A to K, respectively.

For measuring the forward voltage of the low-side semiconductor switch 11 will be in a block 13 the voltage difference U _{d, 11} between the ground node collar determines the phase terminal PH (U _{d, 11} = U _B - - U _ph ). If the ground node B- in the controller 4 is a reference voltage and thus has a voltage of 0 V, the sign of the phase signal U _{PH can be} reversed (U _{d, 11} = 0 - U _ph = -U _ph ). In addition, even this sign reversal can be dispensed with if the forward voltage is given in the form of a negative voltage value. The phase signal U _PH corresponds to the voltage at the drain terminal D or at the cathode K of the low-side semiconductor switch 11 , the ground potential U _B- at the node B- corresponds to the voltage at the source terminal S and at the anode A of the low-semiconductor switch 11 , so that the size U _{d, 11 of} the voltage across the semiconductor switch 11 in direction S to D and A to K, respectively.

In 3 three exemplary curves for the phase signal voltage U _PH are shown. The period T of the phase signal voltage is inversely proportional to the generator speed n _GEN . In the case of the course 20 is the phase signal U _PH always smaller than the vehicle electrical system voltage U _{B +} and greater than the ground potential U _B- . In this case flows through the semiconductor switches 10 and 11 no electricity. The voltage across the semiconductor switch 10 Namely, from A to K in the case of a diode and from S to D in the case of a MOSFET which corresponds to the measured voltage U _{d, 10} is less than zero, and the voltage across the semiconductor switch 11 Namely, from A to K in the case of a diode and from S to D in the case of a MOSFET which corresponds to the measured voltage U _{d, 11} is less than zero. Due to the symmetry of the rectifier 1 and the synchronous machine nine The semiconductor switches of the other phases behave in the same way.

In the case of the course 21 is the phase signal U _PH temporarily larger than the board voltage U _{B +} and temporarily smaller than the ground potential U _B- . In this case flows through the semiconductor switches 10 and 11 a small current, because the voltage (= U _{d, 10} ) above the semiconductor switch 10 from A to K in the case of a diode or from S to D in the case of a MOSFET is temporarily greater than zero (then current flows through the switch 10 ) and the voltage (= U _{d, 11} ) across the semiconductor switch 11 from A to K in the case of a diode or from S to D in the case of a MOSFET is temporarily greater than zero (then current flows through the switch 11 ).

In the case of the course 22 the amplitude of the phase signal U _{PH is} even greater, so that the voltage across the semiconductor switch 10 and 11 increases and the current is greater than in the case of the course 21 is (here it is assumed that a constant temperature is present at the junction of the semiconductor switch).

When using a pull-down resistor against B- in the regulator 4 For example, a state that a low-side semiconductor switch is already easily conducting while the high-side semiconductor switch does not conduct the same phase for a long time may occur; then a small current flows through the low-side semiconductor switch, which, however, closes via the pull-down resistor and not via the vehicle electrical system, so that the generator still provides no power.

In the blocks 14 and 15 in 2 in each case the maximum U _{d, 10, max of} the measured voltage U _{d, 10} = U _PH - U _{B +} and the maximum U _{d, 11, max of} the measured voltage U _{d, 11} = 0 - U _ph = -U _{ph are} determined. The maximum is determined, for example, within a certain sliding time window. These maximum values U _{d, 10, max} and U _{d, 11, max} are also in 2 in the case of the course 21 located. When the forward voltage for the semiconductor switch 11 in the form of a negative voltage value, the minimum of the voltage + U _{ph is} determined instead of the maximum.

These maximum values U _{d, 10, max} and U _{d, 11, max} are used as measured values for the forward voltage of the semiconductor switches 10 respectively. 11 used. The forward voltage U _{d, 10, max of} the semiconductor switch 10 and the forward voltage U _{d, 11, max of} the semiconductor switch 11 be in the blocks 16 and 17 each compared with a threshold value U _S for the maximum permissible forward voltage. When the measured Forward voltage U _{d, 10, max is} greater than the threshold U _S , is the block 16 a logical 1, otherwise the block gives 16 a logical 0 off. The same applies to the block 17 , The output signals of the blocks 16 and 17 are subjected to a logical OR operation (see block 18 Alternatively, a logical AND operation can be used. If at the output the OR link 18 gives a logical 1, the forward voltage is at least one of the two semiconductor switches 10 and 11 greater than the threshold. If the threshold value U _{S has been} exceeded (ie a logical 1 is present at the output of the link), the controller reduces or limits 4 automatically the excitation current I _ERR and thus the output power of the generator by reducing or limiting the duty cycle of the power amplifier.

Alternatively, it would also be conceivable to determine the mean value or the maximum value of the measured forward voltages U _{d, 10, max} and U _{d, 11, max} and to compare this value with the threshold value U _S and to reduce or reduce the duty cycle as a function of this comparison limit.

In the 1 illustrated determination of the forward voltages U _{d, 10, max} and U _{d, 11, max} can be done in an analog or digital manner.

It can oppose 2 also only the forward voltage of a semiconductor switch of a phase can be determined and evaluated, for example, the high-side semiconductor switch 10 In this case, for example, the blocks 13 . 15 . 17 and 18 in 2 be deleted. If at the exit of the block 16 gives a logical 1, is the forward voltage of the semiconductor switch 11 greater than the threshold. If the threshold U _{S has been} exceeded, the controller reduces or limits 4 automatically the excitation current I _ERR and thus the output power of the generator by reducing or limiting the duty cycle of the power amplifier. The monitoring of the forward voltage only of the high-side semiconductor switch 10 For example, when using a pull-down resistor, which is in the regulator 4 between the PH port and the B port.

The threshold value U _S for the forward voltage can be determined, for example, as a function of the temperature. In 4 are two exemplary linear curves of the threshold value U _S for the forward voltage over the temperature T shown, for example, on the part of the controller ASIC 4 measured temperature. The history 30 is for example a rectifier 1 used, which uses MOSFETs for rectifying, and has a positive temperature gradient .DELTA.U _S / .DELTA.T. The history 31 is for example a rectifier 1 which uses diodes for rectifying, and has a negative temperature gradient ΔU _S / ΔT.

The threshold value U _{S, REF} at a reference temperature T _REF (for example at a temperature of 160 ° C, at which the controller aborts the current I _ERR ) and the temperature gradient ΔU _S / ΔT can be used as two parameters in the generator controller 4 be stored so that the regulator ASIC 4 depending on the current temperature T can determine the threshold value U _S. It can be provided that the parameters U _{S, REF} and ΔU _S / ΔT are transmitted via the LIN bus by the engine control unit to the controller ASIC and the controller ASIC determines the threshold value U _S.

At one too 2 alternative embodiments are those in the controller ASIC 4 measured flux voltages U _{d, 10, max} and U _{d, 11, max} or the average or maximum value of these forward voltages transmitted via the LIN bus to the engine control unit. In the engine control unit, the generator current I _{B +} or a current proportional to the generator current (for example, a phase current I _PH ) is determined, as for example in the document DE 10 2006 049 140 A1 is described. Depending on the current thus determined (or the current I _D through the semiconductor switch, which in turn is determined from the generator current I _{B +} or the phase current I _PH ) and depending on the received or received values for the forward voltage one or more, for example, based on a map Temperature values for the semiconductor switches 10 . 11 certainly. The one or more temperature values are compared to a threshold value for the temperature and the excitation current is reduced or limited if the temperature value is greater than or alternatively greater than the threshold value. The embodiment described above, in which a generator current (or a current of one or more phases) is calculated, is particularly suitable when using diodes as a semiconductor switch.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The 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

• DE 102006049140 [0030]
• DE 102006049140 A1 [0060]

Claims (15)

Method for protecting a rectifier ( 1 ) of a multiphase AC generator in a motor vehicle, wherein the rectifier ( 1 ) has a plurality of semiconductor switches, each phase is associated with at least one semiconductor switch and the rectified generator voltage via a controller ( 4 ), which regulates the excitation current (I _ERR ) of a field winding ( 5 ) of the generator and receives a phase signal (U _PH ) of a first phase (U) of the plurality of phases, comprising the steps of: - determining a forward voltage (U _{d, 10, max,} U _{d, 11, max} ) of at least one semiconductor switch ( 10 . 11 ) associated with the first phase (U) using the phase signal (U _PH ); and - reducing or limiting the excitation current (I _ERR ) as a function of the determined forward voltage (U _{d, 10, max} , U _{d, 11, max} ). Method according to claim 1, wherein the forward voltage (U _{d, 10, max,} U _{d, 11, max} ) is compared with a forward voltage threshold value (U _S ) and the excitation current (I _ERR ) is reduced or limited when the Flow voltage (U _{d, 10, max,} U _{d, 11, max} ) is greater than or equal to greater than equal to the threshold value (U _S ). The method of claim 2, wherein the threshold value (U _S ) is temperature-dependent. Method according to claim 1, comprising the additional steps of: - determining the current of the generator (I _{B +} ) or a current proportional to the generator current (I _D ; I _PH ); and determining the temperature of the at least one semiconductor switch ( 10 . 11 ), which is associated with the first phase (U), depending on the current and the forward voltage, the temperature is compared with a threshold for the temperature and the excitation current is reduced or limited, if the temperature is greater than or equal to greater than Threshold is. Method according to claim 4, wherein - the controller ( 4 ) determines the forward voltage (U _{d, 10, max} , U _{d, 11, max} ) and transmits it to an engine control unit, in particular via a LIN bus, and - the engine control unit determines the current and the temperature and the comparison of the temperature with the threshold value performs and depending on the comparison, a signal for reducing or limiting the excitation current to the controller ( 4 ) transmits, in particular via the LIN bus. Method according to one of claims 2-5, wherein - the excitation current (I _ERR ) is limited by the duty cycle of a stage ( 6 ) is limited to the generation of the excitation current (I _ERR ), and - the duty cycle is limited to a maximum duty cycle less than 100% when the threshold value (U _S ) is exceeded, with increasing the exceeding of the threshold, the maximum duty cycle decreases. Method according to one of claims 1-3, wherein - the controller ( 4 ) determines the forward voltage (U _{d, 10, max} , U _{d, 11, max} ) and - the controller ( 4 ) reduces or limits the exciting current (I _ERR ) as a function of the forward voltage. Method according to one of the preceding claims, wherein the semiconductor switch ( 10 . 11 ) associated with the first phase (U) corresponds to a diode. Method according to one of claims 1-7, wherein the semiconductor switch ( 10 . 11 ) associated with the first phase (U) corresponds to a MOSFET. Method according to one of the preceding claims, wherein the rectifier ( 1 ) comprises a bridge circuit with a high-side semiconductor switch connected to the vehicle power supply voltage and a low-side semiconductor switch connected to the ground per phase. The method of claim 10, wherein - the forward voltage (U _{d, 10, max} ) of the first phase associated high-side semiconductor switch ( 10 ) is determined by determining the difference between the time-varying phase signal (U _PH ) and the vehicle electrical system voltage (U _{B +} ); and / or the forward voltage (U _{d, 11, max} ) of the low-side semiconductor switch assigned to the first phase ( 11 ) is determined by determining the difference between the ground potential (U _B ) and the time-varying phase signal (U _PH ) or by reversing the sign of the phase signal (U _PH ). Method according to one of the preceding claims, wherein a maximum value or a minimum value of a measured variable is determined for determining the forward voltage (U _{d, 10, max,} U _{d, 11, max} ). Method according to one of the preceding claims, wherein the excitation current (I _ERR ) is reduced or limited by limiting the duty cycle or reduced. Controller ( 4 ) with a function to protect a rectifier ( 1 ) of a multiphase AC generator for a motor vehicle, wherein the rectifier ( 1 ) has a plurality of semiconductor switches and each phase is assigned at least one semiconductor switch, where the controller ( 4 ) is arranged to - regulate the rectified generator voltage (U _GEN ), - the excitation current (I _ERR ) of a field winding ( 5 ) of the generator, - to receive a phase signal (U _PH ) of a first phase (U) of the several phases, - a forward voltage (U _{d, 10, max,} U _{d, 11, max} ) of at least one semiconductor switch ( 10 . 11 ) using the phase signal (U _PH ), which is associated with the first phase (U), and wherein the controller ( 4 ) is further configured to - reduce or limit the excitation current (I _ERR ) as a function of the determined forward voltage (U _{d, 10, max,} U _{d, 11, max} ) or - the determined forward voltage (U _{d, 10, max,} U _{d, 11, max} ) to an engine control unit and to receive a signal for reducing or limiting the excitation current (I _ERR ) from the engine control unit. Controller ( 4 ) according to claim 14, wherein the controller is implemented as an ASIC and has exactly five terminals, namely - a ground terminal (B -), - a power supply terminal (B +), - a terminal (LIN) of a LIN-BUS interface, - a terminal (EXC) for impressing the exciter current (I _ERR ) into the excitation winding ( 5 ) and - a terminal (PH) for receiving the phase signal (U _PH )

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