GB2377097A

GB2377097A - Electrical induction machine with multi-phase converter

Info

Publication number: GB2377097A
Application number: GB0206212A
Authority: GB
Inventors: Roman Gronbach; Reinhard Rieger
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2001-03-16
Filing date: 2002-03-15
Publication date: 2002-12-31
Anticipated expiration: 2022-03-15
Also published as: GB2377097B; GB0206212D0; FR2822307A1; DE10112818A1; FR2822307B1

Abstract

An electrical induction machine comprises phase branches U, V, W connected in star configuration 12 or delta configuration. The electrical induction machine comprises a multi-phase converter with half bridge switches 9 having offset control. The windings 13 of the machine are connected with the half bridges of the converter by way of feed lines 15. The electrical induction machine has pulse width modulation control, which correspond with the phase number n and are displaced by 360{/n, and has at least one star point 20, 21 in the case of a star connection of the windings and separate current circuits in the case of a delta connection of the windings so as to allow a reduction in the pulse width modulation switching frequency, in particular a reduction by half when n = 2. Separating means may be connected between the windings to maximise leakage inductances. Discrete decoupling inductances (7, Fig 2) may be included in the feed lines.

Description

ELECTRICAL INDUCTION MACHINE WITH MULTI-PHASE CONVERTER

The present invention relates to an electrical induction machine.

Electrical induction machines can be operated particularly advantageously at multi-phase converters. In the case of three-phase machines the individual feed lines are connected together in either star or delta configuration. The feed lines each lead to the converter.

The multi-phase converter includes a number, which corresponds with the phase number of the electrical induction machine, of half bridges which have offset switching and are decoupled from one another. Different sets of solutions for the offset keying of multi-phase converters exist.

A converter for transforming electrical energy is disclosed in DE 199 47 476.1, which comprises at least one half bridge and is provided for a vehicle on-board mains. The half bridge for its part is provided with at least one high-side switch and at least one low-side switch: The highside and low-side switches have a common terminal in connected with the means producing the electrical energy. Connected in parallel with the half bridge is an intermediate circuit capacitor, the capacitance of which is to be kept as small as possible.

For that purpose the drive control of the switches of the half bridge is carried out in offset manner so that the current to be supplied by the intermediate circuit capacitor remains as low as possible.

DE 196 46 043 A1 discloses a converter for the transformation of electrical energy, in which voltage supplied from a three-phase alternator is transformed in a vehicle on-board mains. In this known system the three-phase alternator is also operated as a starter Thus, the three-phase machine can function not only as a starter, but also as an alternator.

For optimal regulation of the output voltage in the case of alternator operation the three-

phase machine is connected with the on-board mains inclusive of the battery by way of an intermediate circuit capacitor via a keyed rectifier bridge The rectifier bridge comprises six pulse current inverter elements which are controlled in drive by on-board mains control apparatus. For the offset switching or keying of converters there are different solutions which have as a core the decoupling of windings with offset keying. The decoupling takes place either internally or externally of the electrical induction machine by way of discrete decoupling inductances in the feed lines or by way of current-compensated chokes.

According to the present invention there is provided an electrical induction machine the phase branches of which are connected according to star connection or delta connection and are operated at a multi-phase converter, the half bridges of which have offset keying and the windings are connected with the converter by way of feed lines, characterized in that the machine comprises several pulse-width-modulation systems corresponding with the number n of phases and displaced by 360 /n.

Preferably, the phase branches have separate individual windings per phase and separators are preferably provided between the individual windings in order to generate highest possible leakage inductances. Each individual winding is preferably connected by way of a feed line with an offset-keyed half bridge of the converter.

In the case of star connection of the separate windings at least one star point can be formed and in the case of delta connection of the separate individual windings separate current circuits can be formed. For preference, the half bridges of the converter are operated at reduced converter frequency in the case of formation of separate star points or separate current circuits. Preferably, the half bridges with which the individual phases of the phase branches of the individual windings are associated contain power semiconductors, with which a blocking diode is connected in parallel A machine embodying the present invention has the advantage that it can be constructed with separate individual windings for the individual phases and phase branches. The offset phases can be executed in separate winding heads which allow a highest possible leakage inductance. The phases are decoupled from one another by means of the leakage inductance achieved, so that the decoupling inductances, which are required in the mentioned examples of the prior art, in the case of half bridges with offset keying are

not needed.

The electrical induction machine contains n pulse-width-modulation systems rotated through 360 /n, wherein the star points of the separate individual windings of the winding packet are separate. Additional free- wheel states in the windings thereby arise. The pulse-width-modulation frequency is substantially reduced for like magnetic loading of the electrical induction machine. In the case of n = 2, i.e. for two phases per phase branch, the pulse-width-modulation frequency is halved. The halving of the pulse-width

modulation frequency has the consequence that the switching losses in the power semiconductors, for example transistors or MOSFET transistors, which behave proportionally to the pulse-width-modulation frequency, are reduced in proportion with the reduction in the pulse-width-modulation frequency.

In the case of constant electrical parameters with respect to the machine data and with like inductances, the switching frequency of the converter can be reduced by means of a machine embodying the invention, wherein the flux coupling in the machine is substantially maintained. The floating of the star point, which is characteristic for three-phase star-

connected machines, is also maintained.

Embodiments of the present invention will now be more particularly described by way of example with reference to the drawings, in which: Fig. 1 is a diagram of schematic and specific circuits of a half bridge with offset switching for n = 2 phases per phase branch; Fig. 2 is a circuit diagram of an electrical star-connected induction machine with discrete inductances in the feed lines to the converter, Fig. 3 is a circuit diagram of a first electrical induction machine embodying the invention and having separate individual windings with a common star point; Fig 4 is a circuit diagram of a second electrical induction machine embodying the invention and having separate windings with several star points; Figs. 5.1, 5.2 and 5.3 are diagrams showing pulse-width-modulated drive control, voltage path and current path for a machine having windings with a connected star point for a phase angle of 180 ;

Figs. 6.1, 6.2 and 6.3 are diagrams showing pulse-width-modulated drive control, voltage path and current path for a machine having windings with separate star points for a phase angle of 180 ; Figs. 7.1, 7.2 and 7.3 are diagrams showing pulse-width-modulated drive control, voltage path and current path for a machine having windings with a connected star point for a phase angle of 210 ; and Figs. 8.1, 8.2 and 8.3 are diagrams showing pulse-width-modulated drive control, voltage path and current path for a machine having windings with separate star points for a phase angle of 210 .

Referring now to the drawings, there is shown in Fig. 1 the circuit of a half bridge with offset switching or keying for n = two phases per phase branch. In the following, circuits are described by reference to the specific case for two phases per phase branch 3, i.e. U. V, W. This is, however, transferrable to any desired phase number and is not limited to two phases per phase branch.

In the case of the half bridge of Fig. 1, which is connected with a phase branch 3 comprising two phases 2, a discrete decoupling inductance 7 is included in each phase 2.

The half bridge 1 schematically indicated in the leffhand part of Fig 1 has a capacitor 8, which represents the intermediate circuit capacitance, connected in parallel with switches 9 on the high side of the half bridge and switches 9 on the low side of the half bridge. In the righthand part of Fig. 1 there is shown a half bridge 1 in which the switches 9 schematically reproduced in the ieffhand part are formed by power semiconductors. A respective transistor 4 is included on each of the high side and low side of the half bridge, the transistor base thereof being identified by the reference numeral 5. A blocking diode 6 is connected in parallel with each power semiconductor, which can be, for example, a transistor 4 or a field-effect transistor. The respective phases 2 of the phase branch 3 - be

it the U. V or W phase branch 3 - are connected in the transistor paths intermediate the power semiconductors 4 on the low side and the high side of the half bridge 1.

In the case of the configurations of half bridges 1 shown in Fig. 1, the half bridges being included in a multi-phase converter associated with an electrical induction machine, there is present in each case a discrete decoupling inductance 7 additionally included in each

phase of a phase branch of the machine. The inductances 7 represent the components which decouple the individual half bridges 1 from one another in the case of offset switching. An electrical, star-connected induction machine in which discrete decoupling inductances 7 are included in the feed lines to the converter is shown in Fig. 2.

According to this illustration for the specific case of n = two phases 2 per phase branch 3, i.e. U. V and W. each of these phase branches is connected with a half bridge 1 (of Fig. 1) of a converter. The individual phases 2 are denoted by Us or U2 for the phase branch U. The switches 9, which here are illustrated only schematically by the switch symbol but can be the same as in Fig. 1, included in the phases Us and U2 contain the transistors and diodes 4, 5 and 6 reproduced in the righthand part of Fig. 1. A separate decoupling inductance 7 is included in each feed line to the switches 9.

The phase branch V is similarly subdivided into two phases V1 and V2, and a separate decoupling inductance 7 is again included in each feed line to the switches 9. The same applies to the phase branch W. the phases of which are denoted by W. and W2.

The windings 10, which are, for example, connected in star connection 12 with a common star point 11, of the electrical induction machine are operated by means of the converter at a given switching frequency thereof, for example a pulse-width-modulation frequency of 30 kHz In the case of this mode of operation of an machine, switching losses proportional to the pulse-width-modulation frequency employed occur in the power semiconductors from which the switches 9 are formed. Moreover, the decoupling inductances 7 have to be provided for each of the phases U., Us, V', V2, W. and W2.

Fig. 3 shows an electrical induction machine which embodies the present invention and the windings 13 of which have the form of separate individual windings connected in star connection 12 with a common star point 14. The associated converter is again operated at a given pulsewidth-modulation frequency. The decoupling inductances provided in the individual feed lines 15 to the half bridges 1 of the converter in Fig. 1 and Fig. 2 are redundant. Fig. 4 shows an electrical induction machine with separate individual windings 13 in which the star connection 12 comprises several star points. Analogously to Fig. 3, the windings

13 are each connected by way of a feed line 15 with the corresponding switch 9 of the half bridge of the converter. The phase branches U. V, W each comprise two phases U., U2 or V,, V2 or W., W2. The half bridges have offset keying and comprise the power semiconductors shown in Fig. 1 in the righthand part, for example transistors or field-effect

transistors and blocking diodes connected in parallel therewith. In this embodiment the decoupling inductances 7 previously required in the feed lines 15 are again redundant.

In the case of the embodiment reproduced in Fig. 4 the windings of the electrical induction machine are separate individual windings 13 and the phases U., U2, V1, V2 and W., W2, which have offset keying by way of the half bridges 1, of the phase branches U. V and W have separate winding heads separated from one another by winding head separators 23.

There is thereby achieved a high leakage inductance which on the one hand assists the mutual decoupling of the phases U., U2 and V,, V2 and W., W2 and on the other hand obviates any need for the discrete decoupling inductances 7 previously provided in the feed lines. The separate machine windings 13 provided in the embodiment of Fig. 4 are connected at several star points, in this example of embodiment two star points 20 and 21.

For the specific case of n = two phases 2 per phase branch U. V, W. i.e. the phases U., U2 for the phase branch U. the phases V,, V2 for the phase branch V and the phases We, W2 for the phase branch W. the electrical induction machine contains n = 2 pulse-width-

modulation systems angularly spaced by 360 divided by n. By virtue of the formation of several star points, additional free-wheel states occur in the phases U1, U2, V,, V2 and W., W2 of each controlling half bridge 1 of the converter. Through this connection possibility of separate windings 13 of an electrical induction machine there results, in the case of n = two phases per phase branch U. V, W. a halving of the switching frequency, i.e. the pulse-

width-modulation frequency, by which the individual half bridges of the converter per phase branch are operated. By halving the pulse-widthmodulation frequency the switching losses at the power semiconductors respectively forming the switches 9 at the high side and low side of the half bridges 1 (of illustration in the righthand part of Fig. 1) can be correspondingly reduced. The connection possibility of separate windings 13 of an electrical induction machine allows, at low cost, a limitation of the switching losses in the associated converter.

If instead of the star connection, shown in Fig. 4, of the separate machine windings 13 there is used a delta connection, a machine winding of the electrical induction machine with two separate current circuits 22. 1 and 22.2 is obtained. In this connection possibility

the switching frequency of the power semiconductors 4, 5 and 6 in the half bridges 1 of the converter at which the electrical induction machine is operated is again halved. In addition, in the connecting of the separate machine windings 13, for example by realisation of separate winding heads, a limitation of the losses of the power semiconductors in the half bridges of the converter can be effected.

A pulse-width-modulated drive control, the associated voltage course and the current course for windings with connected star point at a phase angle of 180 are shown in Figs. 5.1, 5.2 and 5.3. In Fig. 5.1 there is shown a pulse-width-modulation drive control apparatus 31 which controls the individual phases U1, V,, W. as well as U2, V2, W2 of the phase branches U. V, W of the electrical induction machine. The phase control courses 32 which arise correspond with a phase angle displacement of 180 , recorded over the time axis 30.

In the illustration according to Fig 5.2, the voltage course 33 is similarly recorded over the time axis 30. Fig. 5.2 shows the course of the voltage, which runs with substantially rising and falling flanks, for a phase angle of 180 , wherein a maximum amplitude 35 of approximately 52 amperes arises in the current course according to the illustration in Fig. 5.3. In Figs. 5.1, 5.2 and 5.3 the windings of the electrical induction machine in star connection 12 are connected at a common star point (of Fig. 2).

A pulse-width-modulated drive control and in addition the voltage course and the current course for windings with separate star point, similarly for a phase angle displacement of 180 , are evident from the illustrations of Figs. 6.1, 6.2 and 6.3. Analogously to the illustration according to Fig. 5.1, the drive control courses 32, which are produced by the pulse-width-modulation drive control apparatus 31, for the individual phases U., V,, W. as well as U2, V2 and W2 for the phase branches U. V and W of the windings of an electrical induction machine are illustrated. These correspond with the illustration according to Fig 5 1 for a phase angle displacement of 180 .

The illustrations according to Figs. 6.1, 6.2 and 6.3 relate to a winding connection variant 40 with separate star points of the 180 phase angle displacement. It can be inferred from Fig 6.2 that in this connection variant of the windings of an electrical induction machine a voltage course 41, which is recorded over the time axis 30, of staircase-shaped configuration arises The current course 42, which results therefrom and approximates a

sine course and the maximum amplitude 43 of which amounts to merely 24 amperes, is evident from Fig. 6.3. A comparison of the maximum amplitude 35 according to Fig. 5.3 with the maximum amplitude 43 according to Fig. 6.3 shows that the current ripple is almost halved, so that the possibility exists of halving the given pulse-width-modulation drive control frequency in converters by provision of several star points 20 and 21 (of Fig. 4)- ln Figs. 7.1, 7.2 and 7 3 there is reproduced a pulsewidth-modulated drive control applicable to a winding connection variant 50 with separate star points for a phase angle displacement of 210 .

The individual phases U., V,, W. as well as U2, V2, W2 of the phase branches U. V, W of the windings of an electrical induction machine are keyed in offset manner by way of a drive control pulse 51 from the pulsewidth-modulation drive control apparatus 31. In correspondence with this keying there arises the course of the voltage 52 which is recorded in Fig. 5.2 over the time axis 30 and which extends at a substantially constant level. The current course 53 resulting in the case of the star connection 12 with a common star point for a 210 phase angle displacement is shown in Fig. 7.3. In this connection variant 50 of the windings of an electrical induction machine the current of approximately 33 amperes has a maximum amplitude 54. The current course 53 approximates a sinusoidal course with, by contrast to the course reproduced in Fig. 6.3, flattenedoff peaks.

Figs. 8.1, 8.2 and 8.3 show the pulse-width-modulated drive control of the individual phases, the voltage course and the current course for windings with a separate star point for a phase angle displacement of 210 when the windings are connected together by separate star points. Analogously to the illustration according to Fig. 6.2 a voltage course 61, which is recorded over the time axis 30, extending in staircase shape arises in the case of the star connection 12 of the windings with separate star points. The maximum arising amplitude, which according to this connection variant of the windings amounts to merely 7 amperes, is denoted by 63 in the current course 62, which approximates a sinusoidal course, in Fig. 8.3.

With the connection possibility of the windings, which are executed as separate windings with separate winding heads, of an electrical induction machine the pulse-width-

modulation switching frequency of the power semiconductors included in the half bridges 1 of the converter can be substantially reduced in the specific case of two phases 2 per phase branch U. V, W for the same parameters of the machine with respect to machine data as well as the inductances. In the specific case of two phases per phase branch the switching frequency can be halved. The inevitable switching losses in the case of offset keying in the converter are thereby corresponding halved. The flux coupling of the windings of an electrical induction machine produces a floating, i.e. a slight displacement of the star point. A characteristic course of this displacement of the star point results for three phase branches U. V, W of the windings of an electrical induction machine. Several three-phase systems displaced by 360 divided by n (phase number of the phase branches) can be formed in the electrical induction machine. Each of the three phase systems can be operated independently, whereby the flux coupling is maintained.

Claims

1. An electrical induction machine comprising a plurality of windings having phase branches connected in star or delta configuration and a multi-phase converter having a plurality of half bridges connected with the phase branches and operated with offset keying, the half bridges comprising pulse-width-modulation systems corresponding in number with the number of phases of each phase branch and mutually displaced by the quotient of 360 and that number.

2. A machine as claimed in claim 1, wherein the phase branches comprise an individual one of the windings for each phase.

3. A machine as claimed in claim 2, comprising separating means disposed between the windings to maximise leakage inductances.

4. A machine as claimed in claim 2 or claim 3, wherein each winding is connected by a respective feed line with a respective one of the half bridges.

5. A machine as claimed in any one of the preceding claims, wherein the phase branches are connected by a star connection with at least one star point.

6. A machine as claimed in any one of claims 1 to 4, wherein the phase branches are connected by a delta connection with separate current circuits.

7. A machine as claimed in claim 5 or claim 6, wherein the half bridges are operated at reduced converter frequency.

8. A machine as claimed in claim 2, wherein the individual phases of each phase branch comprise power semiconductors and a respective blocking diode connected in parallel with each semiconductor.