DE102011088786A1 - Method of operating power supply unit for electrical system of motor vehicle, involves controlling phase voltage of alternator on predeterminable reference value larger zero when power supply unit is operated in a standby state - Google Patents

Abstract

A current flowing through a rotor winding (29) of an alternator (10) power supply unit (100) is set by a rotor winding associated field controller (15). The alternating current (AC) voltage generated by the alternator is rectified by a rectifier (20) with rectifier elements (21). The power supply unit is operated in a standby state such that a phase voltage of the alternator is controlled on predeterminable reference value larger zero. Independent claims are included for the following: (1) computing unit for operating power supply unit; and (2) field controller for alternator.

Description

The present invention relates to a method for operating a power supply unit for an electrical system of a motor vehicle and to a field controller for an AC generator of such a power supply unit.

State of the art

As generators (alternators) claw-pole generators with electrical excitation are usually used in motor vehicles. The current through the rotor winding serves as a manipulated variable for controlling the rectified output voltage (hereinafter referred to as DC output voltage) and is specified by an associated field controller. The regulation prevents, for example, that due to the very different engine speeds the generator would deliver strongly fluctuating voltage values which could possibly damage the downstream electrical system.

Under certain driving conditions, a shutdown of the generator (so-called standby function) is desired, for example, to relieve the driveline. In such a case, the electrical system is usually powered by the vehicle battery until the generator is put back into operation. The shutdown of the generator takes place in the prior art by switching off the exciter current.

A disadvantage of this solution, however, is that when the on-board voltage drops (which, for example, is provided by the battery), the generator is switched on for a relatively long period of time since the excitation current has to be increased from zero. Therefore, it can lead to unwanted voltage drops in the electrical system.

It is therefore desirable to specify a possibility of operating a power supply unit in such a way that as quickly as possible from a first state, in which substantially no power is delivered to the on-board network of a motor vehicle ("standby"), into a second state, in the power is delivered in the electrical system of the motor vehicle, can be switched.

Disclosure of the invention

According to the invention, a method for operating a power supply unit for an electrical system of a motor vehicle and a field controller for an AC generator of such a power supply unit with the features of the independent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

With the solution according to the invention, the power supply unit can be operated so that can be switched very quickly from the first state to the second state. This is achieved by a phase voltage of the alternator (ie before the rectification) is controlled in the first state ("standby") to a predetermined setpoint greater than zero. For example, the rms value or the amplitude of the phase voltage can be regulated. A controllable phase voltage is applied between one phase connection of the generator and ground, another controllable phase voltage is applied between two phase connections of one phase of the generator.

For standby operation, the setpoint is specified in such a way that essentially no power is supplied to the vehicle electrical system. The on-board voltage is provided in this operating state solely by energy storage (mainly motor vehicle battery) in the electrical system. Nevertheless, a significant exciter current is still present, from which a customary exciter current can be reached very quickly, so that again a power output from the energy supply unit into the vehicle electrical system takes place. The power supply unit can therefore quickly provide power on the one hand in an emergency and on the other hand also buffer short-term voltage dips. The specification takes place, for example, by a control unit of an internal combustion engine, expediently taking into account the current on-board voltage. No current or power output into the electrical system takes place, for example, when the idle DC voltage of the power supply unit (that is, after the rectification, but in the imaginary open state without a connected electrical system) is greater than zero, but less than the on-board voltage.

The invention develops particular advantages in power supply units, the high voltages, for example. In the range of 28 V (truck) or 42 V (recuperation), or variable voltages between z. For example, provide 14V and 42V since high excitation currents are needed to operate at higher voltages and low / medium speeds (eg, 1500-6000 rpm) to obtain a delivery stream. In these applications, it is therefore traditionally the longest to switch the power supply unit back to the second state (power output).

In a preferred embodiment, the field controller to achieve the first state (eg. Via an interface / control eg. By the control unit) of the otherwise usual regulation of the DC output voltage of the power supply unit to a control of a Switched phase voltage of the generator. The phase voltage is decoupled from the on-board voltage by the rectifier.

In a preferred embodiment, the phase voltage is controlled so that it is smaller than the sum of the instantaneous on-board voltage and the voltage that drops at the rectifier elements of the relevant phase (for example, the forward voltage of two diodes in a bridge circuit). The so regulated phase voltage then leads to the fact that just no power is delivered to the electrical system.

Advantageously, the power supply unit is operated so that its phase voltage in the first state between 50% and 100% of the on-board voltage, preferably between 50% and 80% of the on-board voltage. It is advantageous if a desired value (for example 75% of the on-board voltage) is specified here, to which the phase voltage is regulated. To avoid fluctuations, this setpoint should ignore brief changes (shorter than, for example, 100 ms) in the on-board voltage (for example, a brief voltage dip when switching on a load). However, if the on-board voltage drops for a longer period of time (longer than eg 1 s), the setpoint should be adjusted accordingly.

The setpoint value can also be changed during operation, for example depending on the number, type (eg safety-critical or not) and / or currently active consumers of the power requirement. For example, the setpoint can be set at the lower end (eg, 50%) at high power consumption or, in the case of many consumers, since the fluctuations are expected to be small, and thus protection against voltage drops is less relevant. With low power consumption or with a few consumers switched on, the setpoint may, for example, be at the upper end (eg 80%), since larger fluctuations are to be expected here and therefore protection against voltage dips is relevant. The switching on or off of a consumer leads here namely to a relatively large change in performance.

Decreases the voltage on board so far that the phase voltage would have to fall below a predetermined or predetermined minimum value to avoid a power output, is switched back to the second state and the electrical system supplied in a known manner by the power supply unit. The minimum value may, for example, correspond to half the maximum permissible value of the phase voltage.

Conveniently, the power supply unit is operated so that its phase voltage is lowered stepwise or linearly after switching to the first state. So a sudden voltage drop can be avoided.

The switching between the two states and the specification of required parameters may conveniently be initiated by a control device (eg engine control unit or battery control unit). The field controller preferably has a suitable interface for this, for example a bus interface.

It is advantageous if in a recuperation mode is switched to the first state. In this case, the vehicle electrical system is additionally fed by energy production from the driving movement, so that the additional supply by the energy supply unit becomes less relevant. The invention therefore develops particular advantages when used in recuperation systems.

It is advantageous to switch to only the first state (standby) when the state of charge of the motor vehicle energy storage (eg battery) exceeds a predetermined or predefinable upper charge threshold and / or is always switched to the second state (power output), if the state of charge of the motor vehicle energy storage device falls below a predetermined or predefinable lower charge threshold value.

In the GB 2 255 243 A a configuration with different voltage levels is described in sub-board networks, wherein the generator is individually connectable to the sub-board networks. In such a switch from one sub-board network to another, overvoltage can occur both in the generator and in the sub-board networks. These can be advantageously avoided in the context of the invention, when the power supply unit is brought into the first state before switching and operated so that the phase voltage is smaller than the smallest Teilbordspannung. This leads to an increase in the lifetime of all the components involved.

An arithmetic unit according to the invention, for. As a control device of a motor vehicle is, in particular programmatically, adapted to perform a method according to the invention.

The implementation of the method in the form of software is also advantageous, since this causes particularly low costs, in particular if an executing control device is still used for further tasks and therefore exists anyway. Suitable data carriers for providing the computer program are in particular floppy disks, hard disks, flash memories, EEPROMs, CD-ROMs, DVDs Also a download of a program over computer networks (Internet, Intranet etc.) is possible.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described in detail below with reference to the drawing.

Brief description of the drawings

1 shows an embodiment of a generator with rectifier and field controller, as it can be based on the invention.

2 shows curves of the voltages involved in a preferred switching from the second state to the first state.

Embodiment (s) of the invention

In 1 is a power supply unit, as can be based on the present invention, shown in a circuit diagram and a total of 100 designated. The power supply unit has a generator component 10 and a rectifier component 20 on.

The generator component 10 is only schematically in the form of drudenfußförmig interconnected stator windings 11 and an exciter or rotor winding 12 shown. The rotor winding is controlled by a field controller 15 driven.

In the present example, a five-phase generator is shown. In principle, however, the present invention can also be used in less-or multi-phase generators, for example, three-phase generators.

The power converter component 20 is here designed as a bridge circuit and has diodes 21 on. These are, for example via busbars, with the respective stator windings 11 connected to the generator. Further, the diodes are connected to terminals B +, B-, between which a DC output voltage U _B (on-board voltage) for a vehicle electrical system including battery 30 and consumers 31 a motor vehicle is available.

DC side is the field controller 15 connected in parallel, by influencing the current through the exciter winding 12 regulates the output DC voltage. The field controller additionally has a connection 16 to a phase of the generator 10 to measure a phase voltage U _P. It is known to detect the frequency of the phase voltage U _P to derive the speed of the generator.

In the context of the invention, the power supply unit 100 be operated in two states, a first state ("standby"), in which substantially no power is delivered to the electrical system, and in a second state ("power output") in which power is delivered to the electrical system. To switch between these states, the field controller 15 in order to regulate a phase voltage U _P to a value below the instantaneous vehicle voltage U _B in the first state. The control is expediently such that the amplitude of the phase voltage lies below the sum of instantaneous on-board voltage U _B and the total forward voltage through the two diodes involved (eg approximately 1.4 V in the case of Si diodes), preferably approximately 80%. this sum. The on-board voltage U _B is in this case from the battery 30 and other energy storage in the electrical system generated.

An exemplary timing of switching from the second state to the first state will now be described with reference to FIG 2 explained.

In 2 is in a diagram 200 on the ordinate the respective voltage U against the time t on the abscissa for switching from the second state (power output) to the first state (standby) shown. A graph U _B corresponds to an on-board voltage and a graph U _P corresponds to an amplitude height of the phase voltage between a phase connection of the generator and ground. In the context of the invention can equivalently be a control of the phase voltage U _W between two phase terminals of a phase of the generator. This embodiment requires two connections to the stator windings.

For a period of time t <t ₀ , the power supply unit is operated in the second state, in which the electrical system from the power supply unit 100 is supplied. For this purpose, the on-board voltage U _B is regulated to a desired value, for example about 14 volts. The phase voltage U _P is an amount ΔU above the board voltage U _B , where ΔU corresponds to the voltage drop across the rectifier elements.

At time t ₀ is switched to the first state, ie instead of the on-board voltage U _B , the phase voltage U _P is now regulated. This is the field controller 15 so controlled that it regulates the phase voltage U _P instead of the on-board voltage U _B. The setpoint for the phase voltage is suitably chosen when switching so that the on-board voltage does not change. After the switching over, the phase _{voltage is} lowered stepwise or continuously to a target setpoint U _P0 (which is predetermined, in particular, by a control unit), which is reached at the time t ₁ . There is now no more power delivered by the power supply unit in the electrical system. A suitable value is for example at U _P0 <U _B0 + ΔU, for example at 95%, 90%, 85% or 80% of the value U _B0 + ΔU.

By lowering the phase voltage and the on-board voltage U _B decreases. At a time t ₂ , it reaches a value U _B0 , that of the battery 30 and other energy storage in the electrical system is determined. The on-board voltage can not fall below this value, whereas the phase voltage, which is separated by the rectifier from the electrical system, can be further reduced. In this operating condition, no power is supplied by the power supply unit in the electrical system, the electrical system is only from the energy storage such. B. the battery supplied.

A preferred switching from the second state to the first state takes place in the corresponding reverse manner, wherein a stepwise or continuous increase of the phase voltage takes place and then at the end of the increase is switched back to the regulation of the on-board voltage.

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

• GB 2255243A [0019]

Claims (14)

Method for operating a power supply unit ( 100 ) for a vehicle electrical system ( 30 . 31 ) of a motor vehicle, wherein the power supply unit ( 100 ) an alternator ( 10 ) with a stator winding ( 11 ) and a rotor winding ( 29 ), one of the rotor winding ( 29 ) assigned field controller ( 15 ) for specifying the by the rotor winding ( 29 ) flowing current and a rectifier ( 20 ) with rectifier elements ( 21 ) for rectifying the AC voltages generated by the AC generator (U _W ), wherein the power supply unit ( 100 ) is operated in a first state such that a phase voltage (U _P , U _W ) of the alternator ( 10 ) is regulated to a predefinable setpoint (U _P0 ) greater than zero. The method of claim 1, wherein the setpoint value (U _P0 ) is set so that substantially no current from the power supply unit ( 100 ) in the electrical system ( 30 . 31 ) is delivered. Method according to Claim 1 or 2, the desired value (U _P0 ) being specified such that the phase voltage (U _P , U _W ) is smaller than the sum of the instantaneous vehicle voltage (U _B ) and that at the rectifier elements ( 21 ) decreasing voltage (ΔU). Method according to one of the preceding claims, wherein the desired value (U _P0 ) is set so that the phase voltage (U _P , U _W ) is greater than or equal to 50% and less than 100% of the current on-board voltage (U _B ), preferably between 50% and 80%. Method according to one of the preceding claims, wherein the power supply unit ( 100 ) is operated in a recuperation mode in the first state. Method according to one of the preceding claims, wherein the power supply unit ( 100 ) is brought into the first state only when the state of charge of a motor vehicle energy storage ( 30 ) exceeds a predetermined or predefinable upper charge threshold. Method according to one of the preceding claims, wherein, in the case of a vehicle electrical system having a plurality of sub-electrical systems with different sub-board voltages, wherein the alternating-current generator can be connected individually to the sub-board networks, the power-supply unit (A) being switched from one sub-board network to another before the alternating-current generator is switched over. 100 ) is brought into the first state and operated so that the phase voltage is smaller than the smallest of the participating partial voltages. Method according to one of the preceding claims, wherein the power supply unit ( 100 ) is operated in a second state so that the on-board voltage (U _B ) is regulated to a predefinable desired value, wherein power from the power supply unit ( 100 ) in the electrical system ( 30 . 31 ) is delivered. Method according to claim 8, wherein the power supply unit ( 100 ) is brought into the second state when the state of charge of a motor vehicle energy storage ( 30 ) falls below a predetermined or predefinable lower charge threshold. Method according to claim 8 or 9, wherein the energy supply unit ( 100 ) is brought into the second state when the current vehicle voltage (U _B ) falls below a predetermined or predetermined minimum value. The method of claim 8, 9 or 10, wherein the phase voltage (U _{P ,} U _W ) when switching from the first to the second state and / or when switching from the second to the first state is changed continuously or in more than one stage. Arithmetic unit which is adapted to carry out a method according to one of the preceding claims, Field controller ( 15 ) for an alternator ( 10 ) a power supply unit ( 100 ) for supplying a vehicle electrical system of a motor vehicle, with a rotor winding connection for connecting a rotor winding ( 12 ) of the alternator ( 10 ), a phase winding terminal for connecting a phase winding ( 16 ) of the alternator ( 10 ), a DC voltage terminal for connecting the rectified output voltage of the AC generator ( 10 ) and a control unit connection via which the field controller can be set up to measure the amplitude of the voltage supplied by the alternator ( 10 ) phase voltage (U _P , U _W ) generated to a predetermined setpoint (U _P0 ) to regulate. Field controller ( 15 ) according to claim 13, which can be arranged via the control unit connection to the rectified output voltage of the alternator ( 10 ) to a predefinable setpoint.

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