WO2017178142A1

WO2017178142A1 - Method and control circuit for measuring a current in a multiphase electric machine

Info

Publication number: WO2017178142A1
Application number: PCT/EP2017/054261
Authority: WO
Inventors: Thomas Pötzl
Original assignee: Robert Bosch Automotive Steering Gmbh
Priority date: 2016-04-11
Filing date: 2017-02-24
Publication date: 2017-10-19
Also published as: CN108886333B; DE102016106564B4; DE102016106564A1; CN108886333A

Abstract

The invention relates to a method and a control circuit (10) for measuring a current in a multiphase electric machine (100) which has at least one first m-phase winding system (110) with m phases (u, v, w) and a second m-phase winding system (120) with m phases (u', v', w'). A high-side switch (HS) and a low-side switch (LS) are provided for each phase (u, v, w; u', v', w'), and each winding system forms a sub-machine (110; 120) of the electric machine (10). Thus, the machine has N=2m=6 phases. The current is measured using solely m=N/2 shunt resistors (R1, R2, R3), and the phases (u, u';...) of the winding connections (111, 121;...) of the sub-machines (110, 120) which are similar with respect to their phases, i.e. which are phase-offset to each other in a fixed manner (≥0), are conducted together via one of the shunt resistors (R1, R2, R3).

Description

Method and control circuit for current measurement in a polyphase electrical machine

The invention relates to a method for current measurement in a multi-phase electric machine according to the preamble of claim 1 and a control circuit designed for carrying out the method.

In principle, it is known to drive multiphase electric machines or rotary electric field drives with the aid of suitable modulation and commutation. Pulse-width modulation (PWM) has proven particularly suitable for brushless DC machines, with the respective type of commutation, such as the type of commutation, depending on the particular requirements. Sinusoidal commutation or block commutation is used. This type of control circuit can be applied to an electric machine having an arbitrary number of phases. In practice, however, electrical machines with three phases are most commonly found. However, there are also electrical machines with a higher number of phases, for example electric machines with six or nine phases. In a six-phase machine, this can be constructed from two winding systems with three phases each (u, v, w), whereby the machine can be electrically divided into two sub-machines, each with a three-phase structure. In the mentioned machines and operating modes, in particular in a block-commutated PWM, an accurate current measurement is of particular importance, since in these modes a current control is performed for which an accurate measurement of the actual currents is required.

The usual methods for current measurement in a multi-phase electric machine will be explained briefly with reference to the accompanying drawings, Figures 1 and 2, here:

As shown in Fig. 1, it is common in a three-phase machine or in a three-phase drive to use a control circuit per phase u, v and w each have a high-side switch HS and a low-side switch LS, which are realized for example by controlled MOSFET. The connection point between HS and LA leads to one of the three windings of the motor. The circuit is supplied on the supply side of a DC power source (eg battery), wherein in the DC intermediate circuit ZK (in series with the capacitor), a shunt resistor R is used, which allows a current measurement for the control of the machine. The fact that only one shunt is used, a cost-effective current measurement can be realized. However, a malfunction of the single current sensor may render the measurement unusable; also can not be recognized if distortions occur in the individual phases.

In principle, machines with more than three phases are known, including also three-phase drives, in which e.g. 2x3 phases are provided, thereby forming a first three-phase winding system with m = 3 phases (u, v, w) and a second three-phase winding system with m = 3 phases (u ', v', w '), so that each winding system a Partial machine represents the electric machine, so here, for example two sub-machines with three phases each. In particular, for machines having more than three phases (see Fig. 2), a shunt resistor per phase is used for current measurement, e.g. in each case on the lowside a shunt is used (see Fig. 2). As a result, a possibly occurring malfunction of a single current sensor is not so significant. However, the cost is much higher. If e.g. a six-phase machine is used, then usually six shunts are needed.

Accordingly, methods and controls are known, which are suitable for current measurement in a multi-phase electric machine, which at least a first m-phase winding system with m phases (u, v, w) and a second m-phase winding system with m phases (u ', v ', w'), wherein one high side switch (HS) and one low side switch (LS) are provided per phase (u, v, w; u ', v', w '), each winding system being a submachine (1 10, 120) of the electrical machine (10), The object of the present invention is to propose a method and a subsequently operating control circuit for current measurement in a multi-phase electric machine which does not have the abovementioned disadvantages, but advantageously overcomes them. In particular, a method and a control circuit are proposed, which is less susceptible to malfunction of the current sensors and yet can be realized inexpensively.

The object is achieved by a method having the features of patent claim 1 and by a control circuit having the features of the independent patent claim.

Accordingly, in an N-phase machine, the current measurement is made using N / 2 shunt resistors, wherein the similar phases of the winding terminals of the sub-machines, which are in a fixed phase offset (> 0) to each other, passed together over one of the shunt resistors become. Thus, the similar phases (which are in phase or which may also have a fixed phase offset> 0 with respect to one another) of the submachines are each jointly combined to form a shunt resistor. In the case of a six-phase rotary field drive, this means that, in each case, the two sub-machines guide the two, in particular in-phase phases (for example, u and u ') to a shunt resistor. Thus, only three shunts (N / 2 = 3) are needed, which saves costs without sacrificing the quality of the current measurement. The shunts may preferably be formed on a substrate, e.g. DBC or IMS; but they can also be formed on a printed circuit board (PCB) or a Moldmodul.

The control circuit operating according to the method can preferably be implemented in a control unit for an electric power steering system.

These and other advantages are also apparent from the dependent claims. For example, if the multiphase electric machine has two winding systems and thus two sub-machines each having three (m = 3) phases, then the first similar (in particular in-phase) phases are fed together via the first shunt resistor; the second identical (in particular in-phase) phases are led together via the second shunt resistor and the third identical (in particular in-phase) phases are led together via the third shunt resistor.

The shunt resistors are each arranged directly on the highside switches or directly on the low side switches; they can be formed on a substrate, in particular on a DBC substrate (Direct-Bonded Copper Substrate) or an IMS (Insulated Metal Substrate). They can also be formed on a printed circuit board (PCB) or a Moldmodul.

The current measurement is preferably carried out in such a way that it is carried out per sub-machine and in each case in a time interval or time in which all high-side switches or all low-side switches are through-controlled.

In the following, the invention and the advantages resulting therefrom are described in detail by means of exemplary embodiments and with reference to the accompanying drawings, which reproduce the following schematic representations:

Fig. 1 shows a conventional control circuit for a three-phase electric

Machine with central shunt in the intermediate circuit;

Fig. 2 shows a conventional control circuit for an n-phase electric machine with shunts in each phase;

Fig. 3 shows a control circuit according to the invention for a six-phase

electric machine, each with a shunt for two similar

Phases, here e.g. are in phase with each other; and

4 shows a time course for the control signals and for times at which current measurements are carried out. FIGS. 1 and 2, which show conventional circuits, have already been described above.

In contrast, Fig. 3 shows a control circuit 10, which is designed according to a first embodiment of the invention. By way of example, a machine having N = 6 phases is to be controlled, wherein 2x3 (m = 3) phases are formed, so that the machine can be regarded as being subdividable into 2 sub-machines. The 3 windings of a submachine are denoted by 1 10; the 3 windings of the other submachine are designated 120. Both sub-machines are controlled in parallel by the phase u with the phase u 'is in phase (or in a fixed phase offset to it), the phase v with v' and the phase w with w \

According to the invention, two phases, which are similar to one another, are now guided to a shunt resistor. Here, therefore, the first phases u and u 'are guided to the shunt resistor R1, the second phases v and v' are led to the shunt R2 and the third phases w and w 'are guided to the shunt R3. In Fig. 3, the shunt resistors R1-R3 are mounted on the low side LS; they can also be mounted on the highside HS. Overall, only half as many (N / 2) shunts are required as the machine has phases.

The term "similar phases" expresses that there are phases which each have a fixed phase offset X, which may also be zero (phase balance) This can be express by the following formulas:. U = U ^* sin (w ^* t) and u '= U ^* sin (w ^* t -X) v = V sin (w ^* t) and v' = V ^* sin (w ^* t -X) w = W ^* sin (w ^* t) and w '= W ^* sin (w ^* t -X) where X = {0 ... 360 °}

A preferred control of the high-side switch HS and the low-side switch LS or the phases is illustrated with reference to FIG. If all three Phases u, v and w of the first sub-machine are controlled through, here in the range of time T1, then a first current measurement can be made at the shunts R1 -R3. As a result, a current measurement for the first sub-machine 1 10 can be performed. At a later point in time T2, when all three phases u ', v' and w 'of the second sub-machine are controlled, a current measurement is again carried out on the shunts R1 -R3, the measurement now being valid for this sub-machine 120.

The control using the block commutated PWM explained here is adjustable so that no additional distortions occur and thus the quality of the current measurements is very high. Because of the multi-phase, the current in the DC link capacitor is less wavy.

Furthermore, in comparison to the conventional methods (see Fig. 1), an emergency operation even after failure of a shunt possible.

The combination of two phases of the two sub-machines described here on a shunt can be realized by the fact that the combination takes place in each case on a substrate, such. DBC or IMS.

In summary, a method and a control circuit 10 for current measurement in a polyphase electrical machine 100 are proposed which comprise at least a first m-phase winding system 110 with m phases u, v, w and a second m-phase winding system 120 with m phases u ', v ', w', wherein per phase u, v, w; u ', v', w 'a high-side switch HS and a low-side switch LS are provided, each winding system is a sub-machine 1 10; 120 of the electric machine 10 forms. Accordingly, the machine has N = 2m = 6 phases. The current measurement is performed using only m = N / 2 shunt resistors R1, R2, R3, the phases u, u '; ... the winding terminals 1 1 1, 121; ... the sub-machines 1 10, 120, which are similar in their phases, ie in a fixed phase offset> 0 to each other, are guided together over one of the shunt resistors R1, R2, R3. LIST OF REFERENCE NUMBERS

10 control circuit

100 electric machine

1 10, 120 first and second sub-machine (first and second winding system) u, v, w phases (voltages / currents) of the first sub-machine

u ', v', w 'phases (voltages / currents) of the second submachine

HS, LS high-side or low-side switch

15 DC link capacitor

R1, R2, R2 shunt resistors

T1, T2 times for current measurements

Claims

claims

1 . Method for current measurement in a polyphase electrical machine (100) comprising at least a first m-phase winding system (110) with m phases (u, v, w) and a second m-phase winding system (120) with m phases (u ') , v ', w'), wherein a high-side switch (HS) and a low-side switch (LS) are provided per phase (u, v, w; u ', v', w '), each winding system having a Part machine (1 10; 120) of the electrical machine (100) forms, characterized in that

the current measurement is carried out using m shunt resistors (R1, R2, R3), wherein the similar phases (u, u ',...) of the winding terminals (1 1 1, 121,...) of the sub-machines (1 10, 120)

together via one of the shunt resistors (R1, R2, R3) are guided.

2. The method according to claim 1, characterized in that the similar phases (u, u ', ...) are mutually in a fixed phase offset, which is greater than or equal to zero.

3. The method according to claim 1 or 2, characterized in that the

multi-phase electric machine (100) has two winding systems (1 10; 120) and thus two sub-machines, each having three (m = 3) phases (u, v, w; ...), whereby the machine (100) as a whole

has six (N = 2-m = 6) phases, the first like phases (u, u ') together over the first shunt resistor (R1), the second like phases (v, v') together over the second shunt Resistor (R2) and the third similar phases (w, w ') together over the third shunt resistor (R3) are performed.

4. The method according to any one of the preceding claims, characterized

in that the shunt resistors (R1, R2, R3) are each arranged directly on the high-side switches (HS) or directly on the low-side switches (LS).

5. The method according to any preceding claim, characterized in that each shunt resistor (R1, R2, R3) is formed on a substrate and in particular on a DBC substrate (direct-bonded copper

Substrates), an IMS (Insulated Metal Substrate) is formed.

6. The method according to any one of claims 1 -4, characterized in that each shunt resistor (R1, R2, R3) is formed on a printed circuit board (PCB) or a Moldmodul.

7. The method according to any one of the preceding claims, characterized

characterized in that the current measurement per submachine (1 10; 120) is made in a time interval or time (T1) in which all the highside switches (HS) or all lowside switches (LS) are turned on.

8. control circuit (10) for a multi-phase electric machine (100),

which comprises at least a first m-phase winding system (110) with m phases (u, v, w) and a second N-phase winding system (120) with m phases (u ', v', w '), wherein per phase (u, v, w; u ', v', w ') a high-side switch (HS) and a low-side switch (LS) are provided, each winding system comprising a sub-machine (1 10; 120) of the electric machine (100 ), characterized in that

the current measuring control circuit is provided using m shunt resistors (R1, R2, R3), the phases (u, u '; ...) of the winding terminals (1 1 1, 121; 1 10, 120), which are the same, are guided together via one of the shunt resistors (R1, R2, R3).

9. control circuit (10) for a multi-phase electric machine (100) according to claim 8, characterized in that the control circuit (10) is arranged to carry out the method according to one of claims 2-5.

10. control circuit (10) for a multi-phase electric machine (100) according to claim 8 or 9, characterized in that the control circuit (10) is integrated in a control unit of an electric power steering system, wherein the electric machine (100) is designed as an electric power motor ,