Method for controlling a multi-phase electric machine by way of space vector modulation, control device, and drive arrangement

Abstract

A method is provided for controlling a multi-phase electric machine, wherein a stator of the electric machine includes a first sub-system and a second sub-system having the same number of phases and separate star points. The method includes controlling an inverter device by way of space vector modulation in order to generate output voltages for each of the phases, and outputting the output voltages as pulse sequences, wherein each of the pulse sequences in the second sub-system is output inverted with respect to respective pulse sequence in the first sub-system.

Claims

1. A method for controlling a multi-phase electric machine, wherein a stator of the electric machine has a first subsystem and a second subsystem with a same number of phases and separate star points, the method comprising: in order to generate output voltages for the respective phases, controlling an inverter apparatus by way of space vector modulation, and outputting the output voltages as pulse sequences, wherein: the pulse sequences in the second subsystem are output in an inverted manner with respect to respective pulse sequences in the first subsystem, and a positive intermediate circuit voltage and a negative intermediate circuit voltage are output in the respective pulse sequences in the first subsystem.

2. The method according to claim 1, wherein: the respective pulse sequences describe a first zero voltage vector and a second zero voltage vector, the first zero voltage vector is output in the first subsystem if the second zero voltage vector is output in the second subsystem, and the second zero voltage vector is output in the first subsystem if the first zero voltage vector is output in the second subsystem.

3. The method according to claim 1, wherein: each phase of the first subsystem is assigned a corresponding phase of the second subsystem, and the pulse sequences of the phases of the first subsystem are inverted for the corresponding phases of the second subsystem.

4. The method according to claim 1, wherein: the pulse sequences in the respective subsystems are output such that the pulse sequences are symmetrical in a centered manner.

5. A control device for controlling an inverter apparatus for an electric machine, wherein stator of the electric machine has a first subsystem and a second subsystem with a same number of phases and separate star points, and the control device is configured to carry out a method comprising: in order to generate output voltages for the respective phases, controlling an inverter apparatus by way of space vector modulation, and outputting the output voltages as pulse sequences, wherein: the pulse sequences in the second subsystem are output in an inverted manner with respect to respective pulse sequences in the first subsystem, and a positive intermediate circuit voltage and a negative intermediate circuit voltage are output in the respective pulse sequences in the first subsystem.

6. A drive arrangement for a vehicle, the drive arrangement comprising: a control device according to claim 5, an inverter apparatus, and an electric machine.

7. The drive arrangement according to claim 6, wherein: the electric machine has a six-phase design.

8. The drive arrangement according to claim 6, wherein: the inverter apparatus has a first inverter for the first subsystem and a second inverter for the second subsystem.

9. A computer product for controlling a multi-phase electric machine, wherein a stator of the electric machine has a first subsystem and a second subsystem with a same number of phases and separate star points, the computer product comprising a non-transitory computer readable medium having stored thereon program instructions which, when executed on a processor, carries out the acts of: in order to generate output voltages for the respective phases, controlling an inverter apparatus by way of space vector modulation, and outputting the output voltages as pulse sequences, wherein: the pulse sequences in the second subsystem are output in an inverted manner with respect to respective pulse sequences in the first subsystem, and a positive intermediate circuit voltage and a negative intermediate circuit voltage are output in the respective pulse sequences in the first subsystem.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic illustration of a drive arrangement for a vehicle, wherein the drive arrangement has a six-phase electric machine.

(2) FIG. 2 shows a pulse sequence which is fed into a phase of a first subsystem of the electric machine, and a pulse sequence which is fed into a phase of a second subsystem of the electric machine.

(3) FIG. 3 shows measurements which describe the electromagnetic interference when controlling the electric machine according to the prior art and when controlling the electric machine in accordance with a method according to embodiments of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(4) In the figures, identical or functionally identical elements are provided with the same reference signs.

(5) FIG. 1 shows a schematic illustration of a drive arrangement 1 which can be used in a vehicle which is driven in an at least partially electric manner. The drive arrangement 1 comprises a multi-phase electric machine 2. In the present case, the electric machine 2 has a six-phase design. The electric machine 2 comprises a stator 3 having a first subsystem 4a and a second subsystem 4b. In this case, three phases Ph1a, Ph2a and Ph3a are assigned to the first subsystem 4a and three phases Ph1b, Ph2b and Ph3b are assigned to the second subsystem 4b. In this case, the phases Ph1a, Ph2a and Ph3a of the first subsystem 4a are connected to a first star point S1 and the phases Ph1b, Ph2b and Ph3b of the second subsystem 4b are connected to a second star point S2. In this case, the star points S1, S2 are separate from one another and are not electrically connected. The electric machine 2 also comprises a rotor 5 which has a shaft 6 and is rotatable with respect to the stator 3. This shaft 6 is rotatably mounted using a bearing or a rotor bearing.

(6) The drive arrangement 1 also comprises an intermediate circuit 7 having a first capacitor C1 and a second capacitor C2. A center tap 8 is provided between the first capacitor C1 and the second capacitor C2 and is connected to ground. A voltage drop of U.sub.dc/2 is produced across the respective capacitors C1, C2. The drive arrangement 1 also comprises an inverter apparatus 9 comprising a first inverter 10a and a second inverter 10b. In this case, the first inverter 10a is assigned to the first subsystem 4a and the second inverter 10b is assigned to the second subsystem 4b. The respective inverters 10a, 10b have a half-bridge having an upper switching element and a lower switching element for each of the phases Ph1a, Ph2a, Ph3a, Ph1b, Ph2b and Ph3b.

(7) The drive arrangement 1 also comprises a control device 11 which is used to control the inverter apparatus 9 or the inverters 10a, 10b. The control device 11 can be used to transmit control signals to the respective switching elements of the inverters 10a, 10b. These control signals can be used to open or close the switching elements. In this case, provision is made for the control device 11 to control the inverters 10a, 10b or the switching elements of the inverters 10a, 10b by way of space vector modulation. A pulse sequence is output at the respective inverters 10a, 10b as an output voltage.

(8) In this respect, the upper region of FIG. 2 shows, by way of example, a pulse sequence U.sub.Ph1a, which is used to control the first phase Ph1a of the first subsystem 4a, as a function of the time t. This pulse sequence U.sub.Ph1a changes, by way of example, between a positive intermediate circuit voltage +U.sub.dc/2 and a negative intermediate circuit voltage −U.sub.dc/2. In this example, the positive intermediate circuit voltage +U.sub.dc/2 is generated by outputting a first zero voltage vector and the negative intermediate circuit voltage −U.sub.dc/2 is generated by outputting a second zero voltage vector. In order to output the first zero voltage vector, all upper switching elements in the first inverter 10a are closed, for example, and, in order to output the second zero voltage vector, all lower switching elements in the first inverter 10a are closed, for example.

(9) There is no voltage difference between the phases Ph1a, Ph2a and Ph3a in the first subsystem 4a when generating the respective zero voltage vectors. This control or this pulse sequence U.sub.Ph1a results in a compensation current I.sub.C1 in the first subsystem 4a. As can be seen in the equivalent circuit diagram of the electric machine 2 from FIG. 1, the subsystems 4a, 4b of the stator 3 are capacitively coupled to ground. This is illustrated in the present case by the capacitors C3. Capacitive coupling which is described by the capacitors C4 also results between the stator 3 or the subsystems 4a, 4b and the rotor 5.

(10) The compensation current I.sub.C1 in the first subsystem 4a alone would result in a flow of current to ground via the rotor bearing as a result of the capacitive coupling between the first subsystem and the rotor 5. In the equivalent circuit diagram, the rotor bearing is described by the resistor R.sub.b. This current through the rotor bearing would damage the rotor bearing. In addition, electromagnetic interference would result from the compensation current.

(11) The lower region of FIG. 2 illustrates a pulse sequence U.sub.Ph1b or voltage which is used to control the first phase Ph1b in the second subsystem 4b. In this case, the first phase Ph1b in the second subsystem 4b corresponds to the first phase Ph1a in the first subsystem 4a. The pulse sequence also results in a compensation current I.sub.C2 in the second subsystem 4b. As is clear from FIG. 2, the pulse sequence U.sub.Ph1b is an inverted pulse sequence with respect to the pulse sequence U.sub.Ph1a. If the positive intermediate circuit voltage +U.sub.dc/2 is applied to the first phase Ph1a in the first subsystem 4a, the negative intermediate circuit voltage −U.sub.dc/2 is applied to the first phase Ph1b in the second subsystem 4b. If the negative intermediate circuit voltage −U.sub.dc/2 is applied to the first phase Ph1a in the first subsystem 4a, the positive intermediate circuit voltage +U.sub.dc/2 is applied to the first phase Ph1b in the second subsystem 4b. This results in the compensation currents I.sub.C1 and I.sub.C2 compensating for one another. This makes it possible to at least reduce the flow of current through the rotor bearing and to prevent damage to the rotor bearing.

(12) Furthermore, the electromagnetic compatibility (EMC) can be improved by way of the above-described control of the inverters 10a, 10b. In this respect, FIG. 3 shows a graph in which the frequency f is plotted on the abscissa and the level P in dB is plotted on the ordinate. In this case, a curve 12 describes the interference for controlling the electric machines 2 according to the prior art. During this control, the compensation currents I.sub.C1 and I.sub.C2 of the first subsystem 4a and of the second subsystem 4b do not compensate for one another. By comparison, a curve 13 shows the interference for control in which the pulse sequences U.sub.Ph1a and U.sub.Ph1b in the subsystems 4a, 4b are output in an inverted manner. The respective curves 12, 13 were determined during measurements in a drive train of a vehicle between a positive high-voltage connection and a negative high-voltage connection. When comparing the two curves 12 and 13, it can clearly be seen that the offset of the pulse sequences U.sub.Ph1a and U.sub.Ph1b with respect to one another can considerably reduce the interference. The electromagnetic compatibility can therefore be improved.

LIST OF REFERENCE SIGNS

(13) 1 Drive arrangement

(14) 2 Electric machine

(15) 3 Stator

(16) 4a First subsystem

(17) 4b Second subsystem

(18) 5 Rotor

(19) 6 Shaft

(20) 7 Intermediate circuit

(21) 8 Intermediate tap

(22) 9 Inverter apparatus

(23) 10a, 10b Inverter

(24) 11 Control device

(25) 12, 13 Curve

(26) C1, C2, C3, C4 Capacitor

(27) f Frequency

(28) I.sub.C1, I.sub.C2 Compensation current

(29) P Level

(30) Ph1a, Ph2a, Ph3a Phase

(31) Ph1b, Ph2b, Ph3b Phase

(32) R.sub.b Resistor

(33) S1, S2 Star point

(34) t Time

(35) U.sub.dc/2 Intermediate circuit voltage

(36) U.sub.Ph1a, U.sub.Ph1b Voltage