EP2347503A1

EP2347503A1 - Motor system and method for operating a motor system

Info

Publication number: EP2347503A1
Application number: EP09781979A
Authority: EP
Inventors: Thomas Poetzl; Manfred Spraul
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2008-10-14
Filing date: 2009-08-19
Publication date: 2011-07-27
Also published as: US20110254478A1; CN102187564A; JP2012505632A; DE102008042805A1; WO2010043436A1

Abstract

The invention relates to a method for operating a control unit for an electric motor, wherein the control unit comprises a control circuit for controlling the electric motor and an intermediate circuit connected upstream of the control circuit, particularly having an intermediate circuit capacitance, comprising the following steps: - providing a controlled variable (SG) for controlling the electric motor (2); - setting a variable input voltage (UDC) and providing the set input voltage (UDC) via the intermediate circuit to the control unit (3); - operating the control circuit (3) as a function of an available intermediate circuit voltage (UC) which depends on the set input voltage (UDC), and as a function of the controlled variable (SG), in order to control the electric motor (2) according to the controlled variable (SG).

Description

- -

description

title

Engine system and method for operating an engine system

Technical area

The invention generally relates to a motor system with an electric motor, which is controlled by a power electronic drive circuit and is powered by a DC voltage source.

State of the art

In vehicles increasingly electric motors are used, which are variably controllable. For this purpose, such an electric motor is generally by a

Drive device controlled by a power electronic drive circuit, such. B. a B6 bridge, an H-bridge and the like, the

Have semiconductor switch. The drive circuit is generally controlled by a control unit which switches the semiconductor switches to be conductive or non-conductive.

Furthermore, the drive device on the input side of the drive circuit on a passive circuit, which usually has at least one capacitance, which is generally called DC link capacitance. Depending on the control of the drive circuit by a control unit and due to parasitic resistances, the voltage varies over the DC link capacitance - -

and there is a voltage and current ripple, which makes a corresponding dimensioning of the DC link capacity necessary. Due to the considerable load on the DC link capacitance due to the occurring voltage ribs and the dimensioning required thereby, a considerable part of the overall construction volume of the drive device for the electric motor is determined by the size of the DC link capacitance. In the future, the volume of construction of the discrete components in the intermediate circuit will continue to dominate the construction volume of the control unit and the control circuit, since the control unit and the control circuit will be increasingly miniaturized and more components will have to be arranged in the intermediate circuit due to increasing EMC requirements.

It is also known to drive electric motors in motor systems via a DC-DC converter, which generates from the supply voltage of a vehicle electrical system another and / or stabilized DC link voltage to drive the electric motor with a desired voltage.

It is an object of the present invention to provide a drive device for an electric motor in which the DC link capacitance can be provided with the lowest possible capacitance value, so that the size of the DC link capacitance can be reduced.

Disclosure of the invention

This object is achieved by a method for driving an engine system according to claim 1 and by a device, a drive system and a motor system according to the independent claims.

Further embodiments of the invention are specified in the dependent claims. - -

According to a first aspect, a method for operating a drive unit for an electric motor is provided, wherein the drive unit has a drive circuit for driving the electric motor and an intermediate circuit connected upstream of the drive circuit, in particular with a DC link capacity. The method comprises the following steps:

- Providing a manipulated variable for driving the electric motor;

- Setting a variable input voltage and providing the set input voltage via the DC link circuit to the drive unit; - Operating the drive circuit depending on an available DC link voltage, which depends on the set input voltage, and depending on the manipulated variable to control the electric motor according to the manipulated variable.

One idea of the above method is to minimize the overall volume of the DC link circuit, in particular a DC link capacitor arranged therein, by providing a lower load on the DC link capacitance. This is achieved by reducing the AC load on the DC link capacitance. The RMS current through the DC link circuit, which governs the AC load on a DC link capacitance, depends on the input current and the current received by the drive circuit, ie, on the input voltage and / or drive of the drive circuit. The current in the drive circuit can be influenced by adjusting the applied DC link voltage, which depends on the input voltage. As a result, the effective current through the intermediate circuit capacitance can also be set as a function of the voltage on the input side of the drive circuit, which also corresponds to the voltage across the intermediate circuit capacitance. For this reason, the above method can provide both to adjust the input voltage and to control the control unit such that the voltage across the DC link capacity depends on - -

the RMS current is set by the intermediate circuit capacitance in order to minimize the AC load of the DC link capacity as possible.

Furthermore, the variable input voltage can be dependent on the manipulated variable and / or dependent on a motor state variable, in particular a rotational speed, a torque, a motor current, one or more phase voltages, and / or depending on a state variable of the drive circuit, in particular its power loss, and / or dependent be set by a state variable of the DC link circuit, in particular an intermediate circuit voltage or a current through the DC link capacitance. In particular, the manipulated variable may correspond to an electrical power, a mechanical power, the desired rotational speed, the desired torque, the motor current, a motor voltage, an angular position or the phase voltage.

According to an embodiment, the adjustment of the input voltage and the operation of the drive circuit may be performed according to a function in which the RMS current is minimized by a capacitance of the DC link circuit.

It may be provided that the setting of the input voltage and the operation of the drive circuit is performed according to a function in which the losses in the DC / DC converter are minimized without predetermined RMS currents are exceeded by a capacity of the DC link circuit.

Furthermore, the function for adjusting the input voltage during operation or during an explicit teach-in phase can be learned by varying the input voltage and the driving of the electric motor by the drive circuit. - -

In particular, the one or more operating points of the at least one predetermined manipulated variable can be stored in a characteristic field.

Furthermore, the adjustment of the input voltage and the operation of the drive circuit can be performed by means of a gradient descent method.

According to a further aspect, an apparatus for operating an electric motor is provided, comprising: a drive circuit for driving the electric motor,

- A DC link circuit, which is arranged on the input side to the drive circuit and in particular has a DC link capacitance;

a control unit that is designed

- to receive a manipulated variable; to output a set value that causes a variable

Input voltage is output via the DC link circuit to the drive circuit;

- To operate the drive circuit, so that the electric motor is driven depending on an available DC link voltage, which depends on the set input voltage, and depending on the manipulated variable.

According to another aspect, there is provided a drive system for operating an electric motor, comprising:

the above device; a voltage converter for receiving the set-up variable to provide the variable input voltage depending on the set-up variable.

In another aspect, an engine system having an electric motor and the above drive system is provided.

Brief description of the drawings - -

Some embodiments are explained below with reference to the accompanying drawings. Show it:

Figure 1 is a schematic representation of an engine system with a drive device having a DC link capacitance; and

FIG. 2 shows a diagram for illustrating the dependence of an effective current normalized on the RMS current in the electric motor by the DC link capacitance of one degree of modulation.

Description of embodiments

Figure 1 shows a schematic representation of an engine system 1 with an electric motor 2, the z. B. may be formed in the form of a synchronous motor. The electric motor can be designed to be multi-phase. In the present case, the electric motor 2 has three phases.

The electric motor 2 is driven by a power electronic drive circuit 3. In the embodiment of Fig. 1, the drive circuit 3 is formed as a B6 bridge circuit having a number of inverter branches, which corresponds to the number of phases of the electric motor 2. Each inverter branch has semiconductor switches 4, namely a pull-high switch and a pull-low switch. In each case one of the pull-high switches and one of the pull-low switches 4 are arranged in series between a high DC link potential V _H and a low DC link potential V _L. Between the pull-high switch and pull-low switch 4 of each of the inverter branches a corresponding phase is tapped for providing to the electric motor 2. The pull-high switch therefore pulls the tappable phase of the inverter branch to the high DC link potential V _H, and the pull-low switch therefore pulls the tappable phase to the low DC link potential V _L. Each of the pull-high and pull-low switch 4 can be used as a power transistor, such as. B. as a field effect transistor, as a thyristor or - -

the like, and is provided by a control unit 5 by means of suitable control signals transmitted via control lines 6, e.g. a corresponding gate terminal, are supplied, driven.

Instead of the drive circuit 3 shown with the B6 bridge circuit and other switching power electronic drive circuits can be used, such. As an H-bridge and the like.

On the input side, the drive circuit 3 is connected to a DC link circuit which contains DC link capacitance 7. The intermediate circuit may comprise further passive components, in particular a choke coil. The

DC link capacitance 7 is connected to one connection with the high intermediate circuit potential V _H and to another connection to the low DC link potential V _L. The DC link capacitance 7 serves the purpose of switching the semiconductor switches 4 in the drive circuit 3

To reduce jump loads on the input side of the drive circuit 3, to less load a source of power supply.

The high and the low DC link potential V _H , V _L are provided by a voltage converter 8, in particular a DC-DC converter, which is connected on the input side to a vehicle electrical system of a motor vehicle or generally to an energy source. In the case of a motor vehicle, the DC-DC converter 8 is the input side with a battery (not shown) of the

Motor vehicle connected, which provides a battery _voltage U _ßat . The DC-DC converter 8 is variably controllable, ie according to a

DC-DC converter V, which is the DC-DC converter 8, e.g. as an electrical signal or as a digital or analogue quantity, via a

Setting line 9 is provided, the output voltage U _{DC of} the

DC voltage converter 8 can be variably adjusted. - -

Furthermore, a control unit 5 is provided, which is connected both to the DC-DC converter 8 and to the drive circuit 3. The control unit 5 is provided externally a manipulated variable SG as a default, which specifies an engine size with which the electric motor 2 is to be controlled. The manipulated variable may correspond, for example, to electrical power, mechanical power, desired speed, desired torque, motor current, motor voltage, angular position or phase voltage. From the manipulated variable SG results in which way the electric motor 2 is to be controlled, so that the electric motor 2 has a predetermined manipulated variable SG corresponding behavior. The control unit 5 can then control the DC-DC converter 8 and the drive circuit 3 in such a way that the motor variable corresponding to the manipulated variable SG is made available.

To reduce the size of the DC link capacitance 7, it makes sense to reduce their electrical load. The alternating current load of the DC link capacitance 7 is generally calculated using the following formula:

^■ - - _r - f ZDc ^' it) ^~ i PCi: i - ■' .- '^"a" £

where lc_ _Θ ff corresponds to the RMS current through the DC link capacitance, iDCDc (t) corresponds to the current provided by the DC-DC converter 8, and ipcu (t) corresponds to the (input-side) current received by the drive circuit 3. It can be seen that by approximating the converter current iDCDc (t) and the current through the control circuit ipcu (t), the amount of the effective current lc_ _Θ ff can be reduced by the DC link capacitance 7. The mean value and effective value of the current through the drive circuit 3 can be influenced by the level of a DC link voltage Uc applied across the DC link capacitance 7. - -

This can also be seen from the diagram of Figure 2. In the diagram of FIG. 2, an effective current I _{C e} ff normalized to the RMS current in the electric motor 2 is represented by the DC link capacitance _{C e} ff via a modulation factor M. The degree of modulation M behaves inversely proportional to the intermediate circuit voltage Uc and is thus influenced via the DC-DC converter 8. The parameter of the characteristic curves shown in FIG. 2 is the power factor cos (φ), which can generally be determined by the quotient of the active power through the apparent power of the electric motor. φ corresponds to the phase angle between current and voltage.

In order to minimize the effective current I _{C e} ff as much as possible through the DC link capacitance 7, the control unit 5 controls the DC-DC converter 8 in a suitable manner. By a residual voltage U _DC and the predetermined manipulated variable SG results in a corresponding control of the drive circuit 3. In this case, the control unit 5 should drive the DC-DC converter 8 only in such a way that output voltages are set within a voltage range. The voltage range is limited to voltages at which the requirement imposed on the electric motor 2 by the manipulated variable SG can be maintained, the drive circuit 3 does not fall into an undervoltage mode or the voltage strengths of the capacitor providing the intermediate circuit capacitance and the semiconductor switch in the drive circuit 3 are not exceeded become.

The drive circuit 3 may be e.g. by varying a duty cycle of a pulse width modulated drive or by varying a duty cycle of a space vector modulation the electric motor 2 different services to

Make available. Also, the modulation period of the

Specify space vector modulation by the control unit 5. The control unit 5 thus has degrees of freedom in the choice of the controls of the DC-DC converter 8 and the drive circuit 3 to the by the

Command value SG specified to set the motor size. - -

For example, it may be provided that the output voltage u _D c of the DC-DC converter 8 is set as low as possible by means of the DC link capacitance 7 in order to minimize the effective current lc_ _Θ ff. That is, the output voltage of the DC-DC converter 8 should be selected so that the required for the electric motor 2 power can still be achieved and the drive circuit 3 can be operated, ie the drive circuit 3 does not come into an undervoltage mode.

For this purpose, the control unit 5 has, for example, a map block 10 to which the externally provided manipulated variable SG is provided as an input variable and which, depending on the manipulated variable SG, supplies the DC-DC converter variable V to the DC-DC converter 8 and a control circuit manipulated variable S to a pulse generating unit 11 provides. The map block 10 may have a characteristic map in which, for example, an effective current I _{C e} ff is taken into account as a function of the voltage Uc applied across the DC link capacitance 7. Other input variables of the map block 10 may be measured variables, such as the engine speed and / or the angular position of a rotor of the electric motor 2, the phase _currents , the phase voltages and an output current I _{DCDC of} the DC-DC converter 8, which can also be measured. It is also possible to determine the DC-DC converter variable V independently of the manipulated variable SG provided, that is, only on the basis of measured variables. Alternatively, instead of or in addition to the manipulated variable SG provided, the current actual value of this variable could also be used as the input variable for the characteristic diagram. As an alternative to a characteristic diagram, V could also be determined from the specified input variables by means of algorithms or formulas stored in a processor.

The map can be specified statically. It is also possible to generate or modify the map in operation or in a teach-in mode by using different operating points for different operating points - -

Manipulated variables SG of the optimal operating points of the DC-DC converter 8 and the drive circuit 3 are determined and corresponding records are stored in the map for later retrieval.

The optimization goal - regardless of whether working with a static map or with an optimization in operation - may be not only the simple minimization of the effective current LC_ _Θ ff i ⁿ the intermediate circuit capacitor. 7 For example, it is also advantageous to keep the capacitor current and thus the heating of the DC link capacity below specified limits. The limit values could, for example, also be dependent on the temperature and / or the length of the current load of the DC link capacitance. If the limit values are exceeded, the motor current could immediately be reduced via the pulse generation unit 11 at the expense of the motor power, ie, disregarding the predetermined manipulated variable SG. Once a "better" DC-DC converter control value V has been found / adjusted, then the pulse generating unit 11 can again control the switches 4 in such a way that the higher motor current is provided and thus the manipulated variable SG is taken into account.

In addition to the optimization goal of reducing the DC link current, there could be further optimization goals, for example the reduction of the losses in the voltage converter 8.

The pulse generation unit 11 generates the drive pulses for the pull-high switch and pull-low switch 4 of the drive circuit 3 as a function of the drive control manipulated value S, for example, specifies a duty cycle of a space vector modulation to control them according to the drive control value S.

The adaptation of the output voltage of the DC-DC converter 8 and the control of the drive circuit 3 can be made adaptive by the RMS current through the DC link capacitance 7, for example by means of a - -

Current measuring transducer or a current measuring resistor detected and z. By using an optimization method such as the gradient descent method, by varying the converter voltage outputted from the DC-DC converter 8 and the duty ratio, or generally by varying the drive circuit control value S and the DC-DC converter V, the RMS current through the DC link capacitor 7 is minimized. By this way, the map for the engine system can be taught and z. B. in a suitable memory unit (not shown) in the map block 10 are stored. An adaptation on-the-fly with slow changes in the manipulated variable is possible with this method.

It can furthermore be provided that the output voltage of the DC-DC converter 8 is set to a specific voltage with the aid of the DC-DC converter control value V. The effective current I _{C e} ff through the DC link capacitance 7 is measured directly or estimated from the engine state variables. If the rms current I _e ff becomes too large, the output voltage of the DC-DC converter 8 is modified until the rms current _{C e} ff again falls below a certain current threshold value.

The control unit 5, the drive circuit 3 and the DC link capacitance 7 are usually provided in a control unit for an electric motor 2 as a unit. When implementing the above motor system, therefore, a setting line 9 for transmitting the DC-DC converter variable V to a separate and remote from the control unit DC-DC converter 8 is provided by the control unit 5 to drive the DC-DC converter 8 to minimize the AC load of the DC link capacitance 7 variably.

Claims

- -Claims:

1. A method for operating a drive unit for an electric motor (2), wherein the drive unit comprises a drive circuit (3) for driving the electric motor (2) and one of the drive circuit (3) upstream intermediate circuit, in particular with a DC link capacitance (7), with following steps:

- Providing a manipulated variable (SG) for driving the electric motor (2);

- Setting a variable input voltage (U _DC ) and providing the set input voltage (U _DC ) via the _DC link circuit to the drive unit (3);

- Operating the drive circuit (3) depending on an available intermediate circuit voltage (uc), which depends on the set input voltage (u _D c), and depending on the manipulated variable (SG) to the electric motor (2) corresponding to the manipulated variable (SG ) head for.

2. The method of claim 1, wherein the variable input voltage (U _DC ) depending on the manipulated variable (SG) and / or depending on a motor state variable, in particular a speed, a torque, a motor current, one or more phase voltage (s), and / or depending on a state variable of the drive circuit (3), in particular its power loss, and / or depending on a state variable of the DC link circuit (uc), in particular an intermediate circuit voltage or a current (lc_eff) is set by the DC link capacitance (7).

3. The method of claim 1 or 2, wherein the manipulated variable of an electrical power, a mechanical power, the desired speed, the desired torque, the motor current, a motor voltage, an angular position or the phase voltage corresponds. - -

4. The method according to any one of claims 1 to 3, wherein the setting of the input voltage (U _DC ) and the operation of the drive circuit (3) is performed according to a function in which the effective current (lc_ _Θ ff) is minimized by a capacitance of the DC link circuit ,

5. The method according to any one of claims 1 to 4, wherein the setting of the input voltage (U _DC ) and the operation of the drive circuit (3) is performed according to a function in which the losses are minimized in a voltage converter (8) without the predetermined RMS currents (lc_eff) are exceeded by a capacitance of the DC link circuit.

6. The method of claim 4 or 5, wherein the function for adjusting the input voltage (U _DC ) during operation or during an explicit learning phase by varying the input voltage (U _DC ) and the control of the electric motor (2) by the drive circuit (3) is learned.

7. The method of claim 4, 5, or 6, wherein the one or more operating points of the at least one predetermined manipulated variable (SG) are stored in a map.

8. The method of claim 4, wherein adjusting the input voltage and operating the drive circuit is performed by a gradient descent method.

9. A device for operating an electric motor (2), comprising:

a drive circuit for driving the electric motor (2),

- A DC link circuit, which is arranged on the input side to the drive circuit and in particular a DC link capacitor (7);

a control unit (5) which is designed to receive a manipulated variable (SG);

to output a setting variable (V) which causes a variable - -

Input voltage (U _DC ) is output via the _DC link circuit to the drive circuit (3);

- To operate the drive circuit, so that the electric motor (2) depending on an available intermediate circuit voltage (U _c ), which depends on the set input voltage (U _DC ), and depending on the manipulated variable (SG) is driven.

A drive system for operating an electric motor (2), comprising:

- An apparatus according to claim 9; - A voltage converter for receiving the set size (V) to provide depending on the set size (V), the variable input voltage (U _DC ).

11. Motor system with an electric motor (2) and with a drive system according to claim 10.