DE102016106564B4 - METHOD AND CONTROL CIRCUIT FOR CURRENT MEASUREMENT IN A MULTIPHASE ELECTRICAL MACHINE - Google Patents

Abstract

Method for current measurement in a multi-phase electrical machine (100), which has 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'), a high-side switch (HS) and a low-side switch (LS) being provided for each phase (u, v, w; u', v', w'), with each winding system being a sub-machine (110; 120) of the electrical machine (100), characterized in that the current measurement is carried out using m shunt resistors (R1, R2, R3), the phases (u, u'; ...) of the same type being of the winding connections (111, 121; ...) of the sub-machines (110, 120) are routed together via one of the shunt resistors (R1, R2, R3).

Description

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

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

• Wie die 1 zeigt, ist es bei einer dreiphasiger Maschine bzw. bei einem Drehstromantrieb üblich, eine Steuerschaltung einzusetzen die pro Phasen u, v und w jeweils einen Highside-Schalter HS und einen Lowside-Schalter LS aufweist, welche z.B. durch angesteuerte MOSFET realisiert werden. Der jeweils zwischen HS und LA liegende Verbindungspunkt führt zu einer der drei Wicklungen des Motors. Die Schaltung wird auf der Einspeiseseite von einer Gleichstromquelle (z.B. Batterie) versorgt, wobei in den Gleichstromzwischenkreis ZK (in Reihenschaltung mit dem Kondensator) ein Shunt-Widerstand R eingesetzt wird, der eine Strommessung für die Ansteuerung der Maschine ermöglicht. Dadurch, dass nur ein Shunt verwendet wird, kann eine kostengünstige Strommessung realisiert werden. Allerdings kann eine Fehlfunktion des einzigen Stromsensors die Messung unbrauchbar machen; auch kann nicht erkannt werden, wenn Verzerrungen in den einzelnen Phasen auftreten.

The usual methods of measuring the current in a multi-phase electrical machine should be explained using the attached drawings, 1 and 2 , briefly explained here:

• As the 1 shows, it is usual in a three-phase machine or in a three-phase drive to use a control circuit which has a high-side switch HS and a low-side switch LS for each phase u, v and w, which are implemented, for example, by controlled MOSFETs. The connection point between HS and LA leads to one of the three windings of the motor. The circuit is supplied on the feed side by a direct current source (e.g. battery), with a shunt resistor R being used in the direct current intermediate circuit ZK (connected in series with the capacitor), which enables current measurement for controlling the machine. Because only one shunt is used, a cost-effective current measurement can be implemented. However, a malfunction of the single current sensor can render the measurement unusable; nor can it be recognized if distortions occur in the individual phases.

In principle, machines with more than three phases are also known, including three-phase drives in which, for example, 2x3 phases are provided, resulting in 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′) forms, so that each winding system represents a sub-machine of the electrical machine, ie here there are, for example, two sub-machines each with three phases. Especially for machines that have more than three phases (see 2 ) one shunt resistor per phase is used to measure the current, for example by using a shunt on the low side (see 2 ). As a result, a malfunction that may occur in an individual current sensor is not so significant. However, the cost is significantly higher. For example, if a six-phase machine is used, then six shunts are typically required.

Accordingly, methods and controls are known which are suitable for current measurement in a multi-phase electrical machine which has 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 per phase (u, v, w; u', v', w') a high-side switch (HS) and a low-side switch (LS) are provided, each winding system being a sub-machine (110; 120) of the electrical machine (10). Such a method and such a control, in which the current measurement is made using shunt resistors, for example, from U.S. 8,421,388 B2 known.

It is the object of the present invention to propose a method and a control circuit that works according to it for current measurement in a multi-phase electrical machine, which does not have the above-mentioned disadvantages but rather overcomes them in an advantageous manner. In particular, a method and a control circuit are to be proposed which are less susceptible to malfunctions of the current sensors and can nevertheless be implemented at low cost.

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, with the like phases of the winding terminals of the sub-machines, which are in a fixed phase offset (≥0) to each other, are routed together via one of the shunt resistors. The phases of the same type (which are in phase or can also have a fixed phase offset >0 to one another) of the sub-machines are each combined together on a shunt resistor. In the case of a six-phase rotary field drive, this means that the two particular in-phase phases (eg u and u′) of the 2 sub-machines are routed to a shunt resistor. Only three shunts (N/2 = 3) are therefore required, which saves costs without sacrificing the quality of the current measurement. The shunts may preferably be formed on a substrate such as DBC or IMS; however, they can also be formed on a printed circuit board (PCB) or a mold module.

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

These and other advantages also emerge from the dependent claims.

If the multi-phase electrical machine has, for example, two winding systems and thus two sub-machines, each of which has three (m=3) phases, then the first phases of the same type (in particular of the same phase) are conducted together via the first shunt resistor; the second similar (particularly in-phase) phases are routed together through the second shunt resistor and the third similar (particularly in-phase) phases are routed together through the third shunt resistor.

The shunt resistors are each arranged directly on the high-side 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 molded module.

The current measurement is preferably carried out in such a way that it is carried out for each sub-machine and in each case at a time interval or point in time in which all the high-side switches or all the low-side switches are turned on.

• 1 zeigt eine herkömmliche Steuerschaltung für eine dreiphasige elektrische Maschine mit zentralem Shunt im Zwischenkreis;
• 2 zeigt eine herkömmliche Steuerschaltung für eine n-phasige elektrische Maschine mit Shunts in jeder Phase;
• 3 zeigt eine erfindungsgemäße Steuerschaltung für eine sechsphasige elektrische Maschine mit jeweils einem Shunt für zwei gleichartige Phasen, die hier z.B. zueinander phasengleich sind; und
• 4 zeigt ein Zeitverlauf für die Steuerungssignale und für Zeitpunkte, in denen Strommessungen durchgeführt werden.

The invention and the resulting advantages are described in detail below using exemplary embodiments and with reference to the accompanying drawings, which show the following schematic representations:

• 1 shows a conventional control circuit for a three-phase electrical machine with a central shunt in the intermediate circuit;
• 2 Figure 12 shows a conventional control circuit for an n-phase electric machine with shunts in each phase;
• 3 shows a control circuit according to the invention for a six-phase electrical machine, each with a shunt for two similar phases, which are here, for example, in phase with one another; and
• 4 shows a time course for the control signals and for points in time at which current measurements are carried out.

the 1 and 2 , which show conventional circuits have already been described above.

In contrast, the 3 a control circuit 10 implemented according to a first embodiment of the invention. For example, a machine having N=6 phases is to be controlled, with 2×3 (m=3) phases being formed, so that the machine can be viewed as being divisible into 2 sub-machines. The 3 windings of one sub-machine are denoted by 110; the 3 windings of the other sub-machine are denoted by 120. Both sub-machines are controlled in parallel, in that phase u is in phase with phase u' (or in a fixed phase offset thereto), phase v with v' and phase w with w'.

According to the invention, two phases that are identical to one another are now fed to a shunt resistor. So here the first phases u and u' are led 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 led to the shunt R3. In the 3 are the shunt resistors R1-R3 attached to the lowside LS; they can also be attached to the Highside HS. Overall, only half as many (N/2) shunts are required as there are phases in the machine.

$$\text{v}=\text{V*sin}\left(\text{w*t}\right)\text{und v'}=\text{V*sin}\left(\text{w*t}-\text{X}\right)$$

$$\text{w}=\text{W*sin}\left(\text{w*t}\right)\text{und w'}=\text{W*sin}\left(\text{w*t}-\text{X}\right)$$

wobei X = {0 ... 360° }The term "phases of the same type" expresses the fact that these are phases that have a fixed phase offset X to one another, which can also be zero (phase equality). This can be expressed by the following formulas: $$\text{and}=\text{U*sin}\left(\text{w*t}\right)\text{and u'}=\text{U*sin}\left(\text{w*t}-\text{X}\right)$$

$$\text{v}=\text{V*sin}\left(\text{w*t}\right)\text{and V'}=\text{V*sin}\left(\text{w*t}-\text{X}\right)$$

$$\text{w}=\text{W*sin}\left(\text{w*t}\right)\text{and w'}=\text{W*sin}\left(\text{w*t}-\text{X}\right)$$

where X = {0 ... 360° }

Based on 4 a preferred control of the high-side switch HS and the low-side switch LS or the phases is illustrated. If all three phases u, v and w of the first sub-machine are switched through, here in the area of time T1, then a first current measurement can be carried out at the shunts R1-R3. As a result, a current measurement for the first sub-machine 110 can be carried out. At a later point in time T2, when all three phases u′, v′ and w′ of the second sub-machine are switched on, a current measurement is again carried out at the shunts R1-R3, the measurement now applying to this sub-machine 120 .

The control using the block-commutated PWM explained here can be adjusted in such a way that no additional distortions occur and the quality of the current measurements is therefore very high. This is because the current in the intermediate circuit capacitor becomes less ripple due to the multi-phase nature.
Furthermore, compared to the conventional methods (s. 1 ) emergency operation is also possible even after a shunt failure.
The combination of two phases of the two sub-machines on a shunt as described here can be implemented by combining them on a substrate, such as DBC or IMS.

In summary, a method and a control circuit 10 for current measurement in a multi-phase electrical machine 100 are proposed, which has 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', where per phase u, v, w; u′, v′, w′, a high-side switch HS and a low-side switch LS are provided, each winding system having a sub-machine 110; 120 of the electrical machine 10 forms. Accordingly, the machine has N=2m=6 phases. The current measurement is made using only m=N/2 shunt resistors R1, R2, R3, the phases u, u'; ... of the winding terminals 111, 121; ... of the sub-machines 110, 120, which have the same phases, i.e. have a fixed phase offset ≥0 to one another, are routed together via one of the shunt resistors R1, R2, R3.

Reference List

10

control circuit

100

electric machine

110, 120

first or second sub-machine (first or second winding system)

and many more

Phases (voltages/currents) of the first sub-machine

and many more'

Phases (voltages/currents) of the second sub-machine

HS, LS

Highside or lowside switch

15

intermediate circuit capacitor

R1, R2, R2

shunt resistors

T1, T2

Times for current measurements

Claims (10)

Method for current measurement in a multi-phase electrical machine (100), which has 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'), a high-side switch (HS) and a low-side switch (LS) being provided for each phase (u, v, w; u', v', w'), with each winding system being a sub-machine (110; 120) of the electrical machine (100), characterized in that the current measurement is carried out using m shunt resistors (R1, R2, R3), the phases (u, u'; ...) of the same type being of the winding connections (111, 121; ...) of the sub-machines (110, 120) are routed together via one of the shunt resistors (R1, R2, R3). procedure after claim 1 , characterized in that the phases of the same type (u, u', ...) are in a fixed phase offset with respect to one another, which is greater than or equal to zero. procedure after claim 1 or 2 , characterized in that the multi-phase electrical machine (100) has two winding systems (110; 120) and thus two sub-machines, which each have three (m = 3) phases (u, v, w; ...), whereby the machine (100) has a total of six (N=2*m=6) phases, the first similar phases (u, u') together via the first shunt resistor (R1), the second similar phases (v, v') together via the second shunt resistor (R2) and the third similar phases (w, w') together via the third shunt resistor (R3). Method according to one of the preceding claims, characterized in that the shunt resistors (R1, R2, R3) each directly the high-side switches (HS) or directly on the low-side switches (LS). Method according to one of the preceding claims, characterized in that each shunt resistor (R1, R2, R3) is formed on a substrate and in particular on a DBC substrate (Direct Bonded Copper Substrate), an IMS (Insulated Metal Substrate) is trained. Procedure according to one of Claims 1 - 4 , characterized in that each shunt resistor (R1, R2, R3) is formed on a printed circuit board (PCB) or a mold module. Method according to one of the preceding claims, characterized in that the current measurement per sub-machine (110; 120) is carried out in a time interval or point in time (T1) in which all high-side switches (HS) or all low-side switches (LS) are turned on . Control circuit (10) for a multi-phase electrical machine (100), which has 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 having a Sub-machine (110; 120) of the electrical machine (100), characterized in that the control circuit for measuring the current is designed using m shunt resistors (R1, R2, R3), the phases (u, u'; .. .) the winding connections (111, 121; ...) of the sub-machines (110, 120), which are of the same type, are routed together via one of the shunt resistors (R1, R2, R3). Control circuit (10) for a multi-phase electrical machine (100). claim 8 , characterized in that the control circuit (10) is designed, the method according to any one of claims 2 - 7 to execute. Control circuit (10) for a multi-phase electrical machine (100). claim 8 or 9 , characterized in that the control circuit (10) is integrated in a control unit of an electric power steering, wherein the electric machine (100) is designed as an electric power motor.

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