EP3914469A1

EP3914469A1 - Method and device for actuating an electric machine, and electric drive system

Info

Publication number: EP3914469A1
Application number: EP20700983.8A
Authority: EP
Inventors: Thomas ZELTWANGER
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2019-01-25
Filing date: 2020-01-13
Publication date: 2021-12-01
Also published as: WO2020151968A1; DE102019200919A1; US20220103112A1; CN113302080A

Abstract

The invention relates to the actuation of an electric machine with a change between time-synchronous PWM clocking and angle-synchronous block clocking. It is proposed to provide an angle-synchronous clocking with adjustable voltage indicator length for the transition. In this way, jumps in the operating behavior of the electric machine can be minimized or optionally prevented completely during a change between time-synchronous clocking and angle-synchronous clocking.

Description

description

title

Method and device for controlling an electrical machine and electrical drive system

The present invention relates to a method for controlling an electrical machine. Furthermore, the present invention relates to a device for controlling an electrical machine and an electrical one

Drive system with such a device.

State of the art

Electric drive systems are becoming increasingly important.

For example, modern electrical drive systems are required for drive systems of fully or partially electrically powered vehicles. In the case of an electric drive, which is used, for example, in an electric vehicle, an electrical machine is fed by a multi-phase AC voltage. This alternating voltage can be provided by an electrical converter, for example. This electrical converter can, for example, from a DC voltage source such as one

Traction battery of an electric vehicle can be powered. For the generation of the AC voltage, the DC voltage is thus modulated in order to produce a desired rotational frequency and / or a desired torque on the electrical machine. This alternating voltage is generated, for example, by switching circuit breakers on and off in the converter.

Various modulation methods can be used here.

In particular, a distinction is made between time-synchronous and angle-synchronous methods. In the case of a time-synchronous method, pulse width modulation (PWM) can be used, for example

Voltage signal can be modulated. Each power switch of the converter is switched on and off at most once per PWM period. With an angle-synchronous procedure, the circuit breakers are dependent on electrical angle of the machine on or off several times per period on and off.

EP 1 441 436 A1 discloses a control system with a

Hardware unit for controlling an electrical machine. In particular, the regulation of the electrical machine can optionally take place in PWM or block mode.

Disclosure of the invention

The present invention discloses a method for driving an electric machine, a device for driving an electric machine and an electric drive system with the features of the independent claims. Further advantageous embodiments are the subject of the dependent claims.

Accordingly, it is provided:

A method for driving an electric machine with the steps of driving the electric machine in a first operating mode using a time-synchronous clocking with a predetermined maximum first voltage pointer length, a step for driving the electric machine in a second operating mode using a

angular synchronous clocking with an adjustable second

Voltage pointer length and a step for driving the electrical machine in a third operating mode using a

angular synchronous block timing with a predetermined third

Voltage pointer length.

It is also provided:

A device for controlling an electrical machine with a converter and a control device. The converter is designed to be coupled to an electrical machine. The converter is also designed to provide an electrical voltage under control of the electrical machine. In particular, the converter is designed to control the electrical voltage using control signals from the

Provide control device. The control device is connected to the converter electrically coupled. Furthermore, the control device is designed to

Provide control signals for controlling the converter.

In particular, the control device is designed to control the electrical machine in a first operating mode using a time-synchronous clocking with a predetermined maximum first voltage pointer length. Furthermore, the control device is designed to control the electrical machine in a second operating mode using an angle-synchronous clocking with an adjustable second voltage pointer length. Finally, the control device is designed to operate the electrical machine in a third operating mode using an angle-synchronous

Block timing with a predetermined third voltage pointer length

head for. The predetermined third voltage pointer length can in particular be constant and fixed.

Finally, it is provided:

An electrical drive system with a device according to the invention for controlling the electrical machine and an electrical machine which is electrically coupled to the converter of the device for controlling the electrical machine.

Advantages of the invention

The present invention is based on the knowledge that various control methods are possible for controlling electrical machines.

In particular, the alternating voltages for driving an electrical machine can be generated using a time-synchronous clocking or alternatively using an angle-synchronous clocking. Depending on the operating state, different control methods can be advantageous. The present invention is also based on the finding that a transition between a PWM-synchronous clocking and an angle-synchronous block clocking is a challenge.

It is therefore an idea of the present invention to take this knowledge into account and to provide a control for an electrical machine which enables an improved transition between a PWM-synchronous and an angle-synchronous clocking. For optimal operation, it is provided to use three different operating modes for generating the electrical voltages to control the electrical machine. In a first operating mode, the electrical voltages for controlling the electrical machine can be generated using a time-synchronized clocking, in particular a PWM clocking. Such a timing enables especially for smaller ones

Voltage pointers up to a certain maximum voltage pointer length provide very good regulation of the output voltages or output currents in a converter for controlling the electrical machine. In addition, such a time-synchronous clocking is particularly advantageous for electrical machines that only rotate slowly or even stand still. For very high ones

Output voltages, in particular at higher motor speeds, on the other hand, is an angularly synchronous clocking, in particular an angularly synchronous block clocking for generating the electrical voltages in the converter

Control of the electrical machine advantageous.

Due to theoretical and practical limits, pulse width modulated methods only achieve a modulation index <1. The higher the adjustable modulation index, the higher the voltage yield of the chip

voltage modulation on the electric motor with the same battery voltage.

The modulation index provided is a standardized quantity which results directly from the voltage pointer length. It defines itself as the quotient

Voltage pointer length and the voltage amplitude in block operation. In block mode, the voltage amplitude corresponds to that available

Input voltage, the battery voltage. For example, a modulation index of at most about 0.907 can currently be achieved with conventional PWM methods without overmodulation. In block mode with angle synchronous

In contrast, block clocking has a modulation index of 1. In the case of a direct transition from a PWM-synchronous clocking to an angle-synchronous block clocking, this difference in the modulation index must be overcome suddenly. However, such a transition has an acoustically, electrically and mechanically negative effect on the overall system.

To avoid this abrupt transition, it is therefore provided according to the invention to provide a further operating mode for the transition between time-synchronous PWM clocking and angle-synchronous block clocking, in which the clocking is synchronous with an adjustable one Voltage pointer length takes place. There are basically any

angle-synchronous control methods possible, which vary the

Allow voltage pointer length. In particular, a triple central pulse clocking, which is explained in more detail below, can be used, for example.

By using an angle-synchronous clocking with an adjustable voltage pointer length, in particular the modulation index can be continuously adapted from the limited modulation index of a time-synchronous PWM clocking to the modulation index of 1 of the angle-synchronous block clocking. In this way, jumps can be avoided.

According to one embodiment, there is a transition between driving the electrical machine in the first operating mode and driving the electrical machine in the third operating mode by driving the electrical machine in the second operating mode. As already stated above, an angularly synchronous clocking with a variably adjustable voltage pointer length can achieve a steady transition between the maximum voltage pointer length during the time-synchronous clocking in the first operating mode and the voltage pointer length with the angularly synchronous block clocking. In this way, the operating behavior of the electrical drive system can be improved in the transition between time-synchronous clocking and block clocking.

According to one embodiment, the adjustable second becomes during the transition from the first operating mode to the third operating mode

Voltage pointer length steadily from the predetermined maximum first

Voltage pointer length for the time-synchronous clocking up to the

predetermined third voltage pointer length of the angle synchronous

Block timing regulated. By continuously adjusting the adjustable second voltage pointer length, a continuous transition between the time-synchronous clocking and the angle-synchronous block clocking can be achieved. In particular, jumps can be avoided. This has a positive effect both on the mechanical behavior and on the acoustic properties.

According to one embodiment, the second operating mode comprises one

Middle pulse triple clock. With a middle pulse triple clocking, starting from a block clocking, two further switching operations can be provided. The Both additional switching operations can take place symmetrically to the center of the block, for example. In this way, a single block becomes one

Block timing divided into two symmetrical sub-blocks, the total length of the two sub-blocks being shorter than the block length of a block during block timing. In this way, angularly synchronous clocking with a reduced voltage pointer length can be achieved.

According to one embodiment, the pulse width of the middle pulse of the middle pulse triple clocking using the adjustable second

Voltage pointer length set. The second voltage pointer length can be adapted by varying the pulse width of the middle pulse. In particular, the voltage pointer length can be reduced in comparison to the maximum achievable voltage pointer length with block timing.

According to one embodiment, there is a transition from the second

Operating mode to the third operating mode when the pulse width of the

Mean pulse of the middle pulse triple clock falls below a predetermined minimum pulse width. The minimum pulse width defines which time must not be exceeded, during which a switching element of the converter is switched on and off or vice versa. The minimum pulse width can be specified in a converter, for example, on the basis of the component properties, in particular the properties of the switching elements. In addition, dead times or others may also occur

characteristic parameters for specifying the minimum pulse width are taken into account.

According to one embodiment, the adjustable second becomes during a transition from the third operating mode to the first operating mode

Voltage pointer length in the second operating mode is continuously regulated from a predetermined third voltage pointer to the predetermined maximum first voltage pointer. In this way, a steady, continuous transition from the angle-synchronous block clocking to the time-synchronous PWM clocking can be achieved.

In one embodiment, the second synchronous clocking comprises one

Pulse width modulation. The above refinements and developments can be combined with one another as desired. Further refinements, developments and implementations of the invention also include combinations of previously or below not explicitly mentioned with respect to the

Features of the invention described embodiments. In particular, the person skilled in the art will also consider individual aspects as improvements or

Add additions to the respective basic forms of the present invention.

Brief description of the drawings

The present invention is explained in more detail below with reference to the exemplary embodiments given in schematic figures of the drawings. Show:

Figure 1 is a schematic representation of a block diagram of a

electric drive system according to an embodiment;

Figure 2 is a schematic representation of a time-synchronized clocking;

Figure 3 is a schematic representation of an angular synchronous block timing;

FIG. 4: a schematic representation of an angle-synchronous clocking for an adjustable voltage pointer length; and

Figure 5 is a schematic representation of a flow chart as it one

Method for controlling an electrical machine according to one embodiment.

Description of the embodiments

FIG. 1 shows a schematic illustration of a block diagram of an electrical drive system 1 with a device 10 for controlling an electrical machine 30. The electrical drive system 1 comprises

for example an electrical machine 30 that can be fed by a power converter 11. For this purpose, the converter 11 can be fed, for example, from a DC voltage source such as a battery 30 or the like. The example of a three-phase electrical machine 30 shown here serves only for a better understanding and does not represent a restriction of the present invention. In addition, of course, any electrical machines 30 with a number of electrical phases differing from three are also possible. For example, it can also be a six-phase electrical machine 30 or an electrical machine 30 with any other number of phases. To control the electrical machine 30, the converter 11 can convert the DC voltage provided by the battery 20 into a suitable AC voltage

convert. In the case of a three-phase electrical machine 30, the converter 11 can convert the DC voltage into a three-phase, for example

Convert AC voltage. In particular, the amplitude of the AC voltage and / or the value of the output current from the converter 11 to the electrical machine 30 can be set on the basis of a predetermined setpoint S. For example, the converter 11 can be a converter with a plurality of half bridges. In particular, the converter 11 can comprise at least one half bridge with two switching elements for each phase of the electrical machine 30. For example, the converter 11 for a three-phase electrical machine 30 can have a B6 topology. The switching elements of the converter 11 can be under

Use of the setpoint specification S can be controlled by the control device 12 by means of suitable control signals. Here, the

Control device 12, for example, provide a control signal for each switching element of converter 11 in order to open or close the corresponding switching element. The following description describes in particular the control signal for a switching element of the switching elements of a converter 11. The control signals of the other switching elements are formed in the same way. The control of an upper switching element of a half bridge is complementary to the control of the corresponding lower switching element. In addition, dead times or the like may also have to be taken into account.

FIG. 2 shows a schematic representation of a control signal of a time-synchronous clocking for the control of a switching element in a converter 11 for controlling the electrical machine 30. For better understanding, only a few pulses are shown for a period of the output signal. As can be seen in Figure 2, the control of the

Switching element in the converter 11 based on a fixed time grid with the period T. Within each time grid, the corresponding Switching element switched on and off at most once. By varying the ratio between the on-time and the off-time, the

Voltage level of the output signal can be set accordingly.

For example, the period T of a clock can be 100 ps, so that the clock frequency of the signal is 10 kHz. Beyond that

any other period T or clock frequencies are of course also possible. As can also be seen in FIG. 2, a corresponding voltage level of the output signal A results as a function of the duty cycle of a pulse.

Figure 3 shows a schematic representation of a control signal for the

Control of a switching element in the converter 11 for a

angular synchronous block timing. As can be seen here, that is

corresponding switching element for half a period T of

Output signal turned on, and turned off for another half period. The period T varies depending on the frequency of the output signal A. In addition, however, the amplitude of the

Output signal A can not be influenced with an angular synchronous block clocking.

Figure 3 shows a schematic representation of a control signal for a

Semiconductor switching element of a converter 11 for an angular synchronous clocking with adjustable voltage pointer length, in particular for one

Middle pulse triple clock. Here too, the period T depends on the frequency of the output signal A. The middle pulse triple clock differs from the block clocking described in FIG. 3 in that two further switching operations are provided for each half-wave of the output signal A. A switch-on and switch-off process is provided symmetrically to the middle of half a period. This additional input or

Switch-off processes each result in a middle pulse M with a pulse width t_M in the middle of a block in the area of the drive system voltage pointer length TT / 4 and 3TT / 4. This center pulse M has the result that the amplitude of the output signal A with a center pulse triple clocking is lower than the amplitude of an output signal A ’, as is the case with an angle-synchronous

Block clocking would be the case. This is for better illustration

Output signal A according to the middle pulse triple clocking shown as a solid line, and the output signal A 'of an angular synchronous block clocking as a dashed line. By varying the pulse width t_M of the middle pulse M the

Voltage pointer length can be varied.

In real operation, it is not possible to set the time between one

Switch-on process and a subsequent switch-off process or a switch-off process and a subsequent switch-on process as short as desired. Rather, specified framework conditions must be observed. Therefore, the pulse width t_M of the middle pulse M cannot be chosen to be as short as desired. If, for example, the voltage pointer is to be increased as part of the regulation of an electrical machine 30, the pulse width t_M of the center pulse M is increasingly shortened in the case of a time-synchronous clocking. If the pulse width t_M of the middle pulse M reaches the minimum adjustable pulse width, there is an immediate transition to

angular synchronous block timing without center pulse M, as previously in

In connection with Figure 3 has been described. Conversely, if the voltage pointer length is to be reduced in the context of a regulation, it is only possible to transition from the angularly synchronous block clocking to the middle pulse triple clocking when the middle pulse M has a pulse width t_M which has at least the required middle pulse width.

For the operation of the electric drive system with the electric machine 30, it is possible to switch between the control methods described above, depending on the operating state. Particularly when the electrical machine 30 is at a standstill or at low speeds, the control is preferably carried out on the basis of a time-synchronous clocking in accordance with the pulse-width-modulated clocking described in connection with FIG. The time-synchronous clocking based on the PWM method generally only allows modulation up to a degree of modulation of approximately 0.907. If necessary, the degree of modulation can be increased somewhat by using overmodulation. However, such overmodulation also has disadvantages, so that it may not be desirable.

In contrast, the angularly synchronous block clocking as described in connection with FIG. 3 has a degree of modulation of 1.

Accordingly, this angularly synchronous block clocking is also connected to a fixed voltage pointer. With a direct transition from the

time-synchronous pulse width modulated clocking for angle-synchronous Block clocking, therefore, the difference in the degree of modulation from the maximum of PWM clocking to block clocking must be overcome by leaps and bounds.

In order to avoid such a jump, an angularly synchronous clocking with variable voltage pointer length can take place during the transition, as has been described by way of example in connection with FIG. 3.

Here, for example, a time-synchronous PWM clocking can take place for the control of the electrical machine 3. Such

Time-synchronous PWM clocking can take place, for example, up to a predetermined maximum voltage pointer length. If, starting from the PWM clocking, a transition is made to an angularly synchronous clocking, an angularly synchronous clocking with variable voltage pointer length, for example a middle pulse triple clocking, as described in connection with FIG. 4, is carried out first. Basically, however, there are others

Control method for an angular synchronous clocking with variable

Voltage pointer length possible. By varying the pulse width t_M des

Mean pulse M the voltage pointer length can be varied.

If necessary, it must be taken into account here that the rotational speed of the electrical machine has a sufficiently high electrical frequency, as is required for angularly synchronous clocking. In the further course, the voltage pointer length can be continuously adjusted and in particular increased during the angular synchronous clocking. If the voltage pointer length reaches an upper limit value during the angular synchronous clocking, it is relatively easy to transition to the angularly synchronous block clocking without a middle pulse. This can take place in particular if the pulse width t_M of the middle pulse M falls below a predetermined minimum pulse width.

Analogously, starting from the angularly synchronous block clocking into the angularly synchronous clocking, for example that described in FIG. 4

The middle pulse triple clock is changed, whereby the middle pulse must also have at least the required minimum pulse width.

The length of the voltage pointer can then be varied continuously and in particular reduced until a transition to a time-synchronous PWM clocking becomes possible. Of course, during operation in the

angular synchronous clocking with variable voltage pointer length too

necessary controller changes are continuously addressed. For example, the voltage pointer length can be adapted to the requirements. It is possible, for example, to switch back to PWM clocking after changing from PWM clocking to angularly synchronous clocking with a variable voltage pointer length without first changing to angularly synchronous clocking

To have changed block timing. Correspondingly, the

angular-synchronous block clocking can be changed to the angular-synchronous clocking with variable voltage pointer length and then back to the angular-synchronous block clocking, without a

time-synchronous PWM clocking has taken place.

FIG. 5 shows a schematic illustration of a flowchart as it is based on a method for controlling an electrical machine according to one embodiment. In step S1, the electrical machine 30 is activated in a first operating mode. In the first

Operating mode, the electrical machine is controlled under

Use of a time-synchronous clocking with a predetermined maximum first voltage pointer length. In step S3, the electrical machine is activated in a third operating mode. In the third

Operating mode, the electrical machine is controlled under

Using an angle-synchronous block timing with a predetermined third voltage pointer length. The transition between the first

Operating mode and the third operating mode can be done by driving S2 of the electrical machine 30 in a second operating mode. In the second operating mode, the control of the electrical machine 30 takes place using an angle-synchronous clocking with an adjustable second voltage pointer length.

The first voltage pointer length is determined in particular by the maximum degree of modulation of the time-synchronous clocking. The third

The voltage pointer length for the angularly synchronous block clocking results, for example, from the input voltage of the converter 11. The second voltage pointer length can also fluctuate, for example, between the maximum first voltage pointer length and the third voltage pointer length in the angularly synchronous block clocking operation. Due to the

required minimum pulse width can be the maximum achievable

Voltage pointer length for angular synchronous clocking with variable

The voltage pointer length may be slightly smaller than the third voltage pointer length in the angular synchronous block timing. In summary, the present invention relates to a control of an electrical machine with a change between time-synchronous PWM clocking and angle-synchronous block clocking. For this purpose, it is proposed to provide an angularly synchronous clocking with an adjustable voltage pointer length for the transition. In this way, jumps in the operating behavior of the electrical machine when changing between time-synchronous clocking and angle-synchronous clocking can be minimized or, if necessary, completely prevented.

Claims

Expectations

1. Method for controlling an electrical machine (30), with the steps:

Control (Sl) of the electrical machine (30) in a first

Operating mode using a time-synchronous clocking with a predetermined maximum first voltage pointer length;

Activation (S2) of the electrical machine (30) in a second

Operating mode using an angle-synchronous clocking with an adjustable second voltage pointer length; and

Control (S3) of the electrical machine (30) in a third

Operating mode using an angular synchronous block timing with a predetermined third voltage pointer length.

2. The method of claim 1, wherein a transition between the

Control (Sl) of the electrical machine (30) in the first

Operating mode and the control (S3) of the electrical machine (30) in the third operating mode by means of the control (S2) of the electrical machine (30) in the second operating mode.

3. The method of claim 2, wherein during the transition from the first operating mode to the third operating mode, the adjustable second voltage pointer length continuously from the predetermined maximum first voltage pointer length to the predetermined third

Voltage pointer length is regulated.

4. The method according to any one of claims 1 to 3, wherein the second

Operating mode includes a middle pulse triple clock.

5. The method of claim 4, wherein a pulse width (t_M) one

Center pulse using the adjustable second

Voltage pointer length is set.

6. The method according to claim 4 or 5, wherein a transition from the second operating mode to the third operating mode takes place when the pulse width (t_M) of the central pulse is a predetermined minimum pulse width

falls below.

7. The method according to any one of claims 1 to 6, wherein during a

Transition from the third operating mode to the first operating mode in the second operating mode, the adjustable second

Voltage pointer length steadily from predetermined third

Voltage pointer length is regulated up to the predetermined maximum first voltage pointer length.

8. The method according to any one of claims 1 to 7, wherein the time-synchronous clocking comprises pulse width modulation.

9. Device (10) for controlling an electrical machine (30), comprising: a converter (11) which is designed to be coupled to an electrical machine (30) and an electrical voltage for controlling the electrical machine (30) to provide; and a control device (12) which is electrically coupled to the converter (11) and which is designed to provide control signals for controlling the converter (11), the control device (11) being designed to

- to control the electrical machine (30) in a first operating mode using a time-synchronous clocking with a predetermined maximum first voltage pointer length, to control the electrical machine (30) in a second operating mode using an angle-synchronous clocking with an adjustable second voltage pointer length, and the electrical machine (30) in a third operating mode using an angle-synchronous block timing with a predetermined third voltage pointer length.

10. Electrical drive system (1), comprising: a device (10) for controlling an electrical machine (30) according to claim 9, and an electrical machine (30) with the converter (11) of the device (10) for controlling the electrical machine (30) is electrically coupled.