DE102017007427A1 - Controlling an inverter connected to a three-phase permanent magnet electric machine - Google Patents

Abstract

The invention relates to a method for controlling an inverter (12) connected to a three-phase permanent-magnet electric machine (10), in which the electric machine (10) is acted upon in the manner of a vector control by electrical energy, for which purpose one of the electrical machine (12) 10) is provided with respect to the torque to be provided (14, 16), a first d-vector and an associated first q-vector are determined and depending on the first d-vector and the first q-vector phase currents ( 30, 32, 34) of the electric machine (10) are set, wherein for the torque to be provided (16) at least a second d-vector and an associated second q-vector are determined, and the phase currents (30, 32, 34) alternately in accordance with the first d-vector and the associated first q-vector or according to the at least one second d-vector and the associated second q-vector n.

Description

The invention relates to a method for controlling an inverter connected to a three-phase permanently excited electrical machine, in which the electric machine is subjected to electrical control in the manner of a vector control, for which purpose a torque to be provided by the electric machine is specified with respect to the torque to be provided first d-vector and an associated first q-vector are determined and dependent on the first d-vector and the first q-vector phase currents of the electric machine can be adjusted. The invention further relates to a control device for controlling an inverter connected to a three-phase permanently excited electric machine, wherein the control device is designed to apply electrical energy to the electric machine in the manner of a vector control, for which purpose the control device makes reference to a torque to be provided by the electric machine determines a first d-vector and an associated first q-vector and adjusts phase currents of the electrical machine depending on the first d-vector and the first q-vector.

Inverters connected to three-phase permanent magnet electrical machines as well as control methods for such inverters are well known in the art. A three-phase permanent-magnet electric machine of the generic type generally serves to realize a synchronous machine. The three-phase permanent magnet electric machine usually has a rotor which is fitted in the circumferential direction with permanent magnets, wherein the polarities of the permanent magnets with respect to the magnetic field provided by the permanent magnets in the circumferential direction with each permanent magnet alternates. The permanent magnets are usually arranged on an outer circumference of the rotor. In addition, they can also be sunk into an outer surface of the rotor, which in the prior art is also referred to as buried permanent magnets.

The rotor is rotatably mounted in a generally cylindrical opening of a stator of the electric machine. The stator has stator-side windings for providing a stator-side magnetic field. In a three-phase electric machine at least three windings are provided, which can be acted upon by alternating electrical currents. The corresponding alternating electrical currents, also called phase currents, are usually out of phase with each other, for example by 120 °. As a result, a rotating rotating field can be generated on the stator side, which is linked to the magnetic field of the rotor and, during motor operation, provides rotation of the rotor or torque.

So that the phase currents can be provided by the inverter in a predeterminable manner, the control device is provided, which may be comprised by the inverter. But it can also be provided as a separate module and connected to the inverter. In order to be able to provide the phase currents, the inverter comprises a DC voltage intermediate circuit, to which phased series circuits each consisting of two series-connected switching elements are connected. At the center terminals of the series circuits, the corresponding phase currents are provided. By means of the control device, the switching elements are controlled in a suitable manner, so that the phase currents can be set as desired.

A vector control serving to control the aforementioned arrangement discloses, for example, the US 2017/0085199 A1 US-A-4/613511 discloses a method and apparatus for generating current commands for a three-phase permanent magnet electric machine. US 2017/0085199 A1 teaches, for a torque to be provided, the d-vector and the associated q-vector on the basis of look-up tables. Since only discrete values for discrete torques to be provided can be found by means of such tables, US 2017/0085199 A1 teaches an interpolation method in order to also be able to determine intermediate values for torques to be provided. The interpolation method is based on the lookup tables.

Basically, the use of vector control, also called field-oriented control, has proven itself. Such methods and control devices are used in particular also in electric drive systems, as they are found, for example, in electric vehicles, hybrid vehicles or the like. In the case of motor vehicles, the three-phase permanent-magnet electric machine or synchronous machine, in particular with buried permanent magnets (English: Interior Permanent Magnet Synchronous Machine (IPMSM)), is used for the most part.

A torque to be provided by the electric machine or required target torque can be determined according to the following equation (1). It turns out that a value for the torque to be provided can be achieved by a large number of combinations of first d vectors with associated first q vectors. M = 3/2 · p · (Ψ _PM · i _q + (L _d - L _q ) · i _d · i _q ) (1)

In practical operation shows that especially at low speeds of the electric machine, preferably when providing a torque at a speed in a range of almost zero or at zero uneven stress on the switching elements of the inverter can be the result. Since the respective phase currents are directly dependent on the first d-vector and the associated first q-vector, this also results in the associated loads for the switching elements of the inverter. In particular, at the speed zero of the electric machine, it may thus happen that the power supply for a long period of time is to be taken over only by some of the switching elements of the inverter, whereas other switching elements of the inverter are hardly or not at all supplied with electric current. This can result in uneven loading of the inverter, in particular its switching elements. As a result, power limitations of the inverter, for example, due to a thermal load limit or the like can be achieved in an undesirable manner or the reliability of the inverter or its switching elements are limited.

The invention is based, to claim the switching elements of the inverter uniformly the task.

As a solution, the invention proposes a method and a control device according to the independent claims.

Advantageous developments will become apparent from the features of the dependent claims.

In terms of the method, it is proposed in particular for a generic method that at least a second d-vector and an associated second q-vector be determined for the torque to be provided, and the phase currents alternately according to the first d-vector and the associated first q-vector or according to FIG at least a second d-vector and the associated second q-vector are set.

With regard to a generic control device, it is proposed, in particular, that the control device is designed to determine at least one second d-vector and an associated second q-vector for the torque to be provided, and the phase currents alternately according to the first d-vector and the associated first q-vector. Vector or the at least one second d-vector and the associated second q-vector set.

In addition, the invention also relates to a motor vehicle with drive means comprising a three-phase permanent magnet electric machine and an inverter which is connected to the electric machine and is controlled by means of a control device according to the invention.

The invention is based on the idea that, for a torque to be provided by the electric machine, a plurality, in particular an almost infinite, multiplicity of possible combinations of d vectors and associated q vectors can be available in order to obtain the desired torque to be provided by means of the electric machine realize. Since the phase currents can be correspondingly assigned to each vector pair from the respective d-vector and the associated q-vector, the phase currents are dependent on the respective selected value pair of the d-vector and the associated q-vector. By alternately switching between the value pairs of d vectors with associated q vectors thus the phase currents can be influenced, so that the current applied to the switching elements of the inverter varies accordingly. In contrast, effects on the torque can be largely avoided. This makes it possible to avoid or reduce the otherwise uneven current load on the switching elements, but to distribute them to as many switching elements, preferably all switching elements of the inverter. This not only a more uniform thermal load of the inverter can be achieved in total, but it can also be reduced premature aging of individual switching elements due to a high current load. Overall, there is an improved reliability of the inverter as well as the drive system and equipped with the drive system motor vehicle.

The d-vector and the associated q-vector can each be assigned to a respective corresponding current, which is why this is also referred to as d-current and associated q-current.

The invention is therefore based on the idea of providing, in addition to the first value pair from the first d-vector and the associated first q-vector, at least one second value pair from the second d-vector and the associated second q-vector, between which it is possible to switch alternately , Of course, further value pairs can be provided in addition, so that a switch between a plurality of value pairs is possible. It is ensured with each of the predetermined value pairs, that the electric machine is able to actually realize the torque to be provided.

Although the invention is initially directed to a three-phase permanent magnet electric machine, it can of course be provided that the electrical machine has a multiple of three phases, such as a six-phase permanent magnet electric machine, a nine-phase permanent magnet electric machine or the like. Of course, with the increase in the number of phases also increases the cost of the inverter and the vector control. The person skilled in the art will adapt this accordingly.

The advantages and effects stated for the method according to the invention naturally also apply equally to the control device according to the invention and to the motor vehicle equipped with the control device according to the invention and vice versa. Accordingly, device characteristics and vice versa can be formulated for process characteristics.

Further advantages, features and details of the invention will become apparent from the following description of a preferred embodiment and from the drawings. The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and / or in the figures alone can be used not only in the respectively specified combination but also in other combinations or in isolation, without the scope of To leave invention.

Showing:

1 A schematic diagram representation for determining a d-current and an associated q-current for a maximally provided by a synchronous machine torque;

2 A schematic diagram of an inverter connected to a three-phase synchronous machine, in which an actual current load of switching elements of the inverter is shown;

3 A schematic diagram representation of a space vector diagram in which a stress according to 2 is shown;

4 A schematic representation of us 1 however, for a smaller than the maximum deployable torque;

5 A schematic diagram representation as 2 , but for a claim according to 4 ; and

6 A schematic diagram representation of a space vector diagram such as 3 , but for the supply of electricity according to 4 ,

In the figures, like reference numerals designate like features and functions.

1 shows a schematic diagram representation of a way to determine a value for a d-current and an associated q-stream as a pair of values for a d-vector with an associated q-vector. The diagram includes an abscissa associated with the d-current I _d . An ordinate is assigned to the q-current I _q . It can be seen from the diagram that a maximum current is possible for the d-current as well as for the q-current, which is represented by a circle 26 is represented as I _max . An ellipse 28 is assigned to a maximum voltage U _max . An intersection of the ellipse 28 with the circle 26 defines a range of values 36 within which values for the d-current I _d and the associated q-current I _q can be selected.

In 1 is also by means of a graph 14 a hyperbola for one of a synchronous machine 10 maximum deliverable torque shown. It can be seen that the graph 14 the circle 26 as well as the value range 36 at a given operating point 40 affected. At a torque to be provided by the synchronous machine 10 as the maximum torque, a combination of the values for the d-current I _d and the q-current I _q due to a maximum thermal load is fixed. For this operating point 40 can be a maximum stress of individual switching elements 38 an inverter 12 ( 2 ) result, because here, for example, at low speeds, a current with a low frequency or as an extreme case at standstill can set a DC. This is for a very long time at low speeds or at a speed of zero by always the same corresponding switching elements 38 to lead (compare 2 ).

2 shows a schematic diagram representation of the three-phase synchronous machine 10 connected inverter 12 in which the current load of the switching elements 30 of the inverter 12 represented by shaded gray rectangular fields.

3 shows a schematic diagram representation of a space vector diagram, according to the basis of the 1 and 2 explained ratios, the current load by means of an arrow [100] is shown.

To provide smaller torques than the maximum torque 14 the synchronous machine 10 For the determination of the d-current I _d and the q-current I _q , it is customary to use a method in which a maximum torque per ampere is to be achieved (maximum torque per ampere (MTPA)). In this case, with the aim of reducing the active power losses, the corresponding combination of the d-current I _d with the associated q-current I _{q is} determined, thus by the inverter 12 only smallest phase currents 30 . 32 . 34 are to be provided. This is shown by the arrow [100] in the diagram of FIG 3 , But here too there is the problem of unilateral stress of the switching elements 38 of the inverter 12 , Especially at low speeds or at standstill of the synchronous machine 10 ,

4 shows in a schematic diagram representation of a diagram such as 1 , in which now, however, the torque to be provided by means of a graph 16 is shown. The torque to be provided is smaller than that of the synchronous machine 10 maximum deployable torque, which in 1 with the graph 14 is shown. As a result, the graph runs 16 through the range of values 36 through and does not only affect this. This results in vectors 20 . 22 . 24 realize different combinations of d-currents I _d with associated q-currents I _q , but with a respective combination always the same torque to be provided by the synchronous machine 10 can be realized. The limit of variability is through the range of values 36 limited.

By now switching between selected value pairs from a respective d-current with a respective associated q-current, it is thus possible, despite different phase currents 30 . 32 . 34 the torque 16 to be provided. The variation using the vectors 20 . 22 . 24 causes the switching elements 38 of the inverter 12 be charged differently than it is based on 2 is shown. The distribution of the burden arising from the control procedure according to 4 results is based on 5 shown, which is a schematic diagram representation 2 shows. The claimed switching elements 38 are again marked with a gray box. It can be seen that compared to the representation according to 2 almost all of the switching elements 38 Now be charged with electrical current, so that also the relevant stress on the switching elements 38 better distributed.

In one of the 3 corresponding diagram representation the effects are again clarified. It can be seen that in one by the vectors 22 and 24 spanned angle range 42 an almost continuously selectable combination of d-currents with associated q-currents can be realized. This allows to distribute the power accordingly.

By the method of the invention and the appropriately equipped control device, among other things, a thermal stress on the switching elements 38 of the inverter 12 especially in the range of low speeds up to the standstill of the synchronous machine 10 be distributed more evenly, so that individual of the switching elements 38 do not need to be particularly strong. Typical situations in a proper driving operation of the motor vehicle, in which such stresses may occur, for example, an approach to the curb, a standstill on a slope, wherein a downgrade force by the synchronous machine 10 is compensated, a Ankriechen to a slope as well as a continuous change between reversing and driving forward.

For a good effect of the invention to be achieved, a respective adjustment of the phase currents should 30 . 32 . 34 for a predeterminable period of less than 10 ms, preferably less than 0.5 ms, more preferably less than 100 μs, take place.

It can also be provided that the method is performed only when falling below a predetermined speed, for example at a speed of less than 100 revolutions per minute, preferably less than 5 revolutions per minute.

However, the invention can also provide that an adjustment range for the d-vector and the associated q-vector is determined and the adjustment range is passed through continuously. In this case, of course, change the phase currents 30 . 32 . 34 accordingly continuously dependent on the setting range.

LIST OF REFERENCE NUMBERS

10

synchronous machine

12

inverter

14

maximum torque

16

torque to be provided

18

vector

20

vector

22

vector

24

vector

26

circle

28

ellipse

30

phase current

32

phase current

34

phase current

36

value range

38

switching element

40

operating point

42

angle range

I _d

d flow

I _q

q-current

I _max

maximum current

U _max

Maximum tension

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

• US 2017/0085199 A1 [0005]

Claims (7)

Method for controlling a three-phase permanently excited electric machine ( 10 ) connected inverter ( 12 ), in which the electric machine ( 10 ) is acted upon in the manner of a vector control with electrical energy, for which purpose one of the electrical machine ( 10 ) torque to be provided ( 14 . 16 ), with respect to the torque to be provided ( 14 . 16 ) a first d-vector and an associated first q-vector are determined and depending on the first d-vector and the first q-vector phase currents ( 30 . 32 . 34 ) of the electric machine ( 10 ), characterized in that for the torque to be provided ( 16 ) at least a second d-vector and an associated second q-vector are determined, and the phase currents ( 30 . 32 . 34 ) can be set alternately according to the first d-vector and the associated first q-vector or according to the at least one second d-vector and the associated second q-vector. Method according to Claim 1, characterized in that a respective adjustment of the phase currents ( 30 . 32 . 34 ) For a predetermined period of less than 10 ms, preferably less than 0.5 ms, more preferably less than 100 microseconds takes place. A method according to claim 1 or 2, characterized in that the method only at a rotational speed of the electric machine ( 10 ) of less than 100 revolutions per minute, preferably less than 5 revolutions per minute. Method according to one of the preceding claims, characterized in that for the torque to be provided ( 16 ) each have a range of values ( 36 ) is determined for the d-vector and the associated q-vector, the at least one second d-vector and the one associated second q-vector from the respective value range ( 36 ) to be selected. Method according to one of the preceding claims, characterized in that the method only for a torque to be provided ( 16 ), which is smaller than one through the electric machine ( 10 ) maximum deliverable torque ( 14 ). Method according to one of the preceding claims, characterized in that the at least one second d-vector and the associated second q-vector are determined such that a switching element ( 38 ) of the inverter ( 12 ) is only applied for a predeterminable period of time with an electric current. Control device for controlling a three-phase permanently excited electrical machine ( 10 ) connected inverter ( 12 ), wherein the control device is formed, the electrical machine ( 10 ) to apply electrical power to the device in the manner of a vector control, for which purpose the control device makes reference to one of the electrical machines ( 10 ) torque to be provided ( 14 . 16 ) determines a first d-vector and an associated first q-vector and dependent on the first d-vector and the first q-vector phase currents ( 30 . 32 . 34 ) of the electric machine ( 10 ), characterized in that the control device is further configured for the torque to be provided ( 16 ) to determine at least a second d-vector and an associated second q-vector, and the phase currents ( 30 . 32 . 34 ) alternately according to the first d-vector and the associated first q-vector or according to the at least one second d-vector and the associated second q-vector.

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