Drive control for a three-phase motor

Abstract

A drive control for a three-phase motor has an inverter with multiple switches for generating three-phase voltages on the windings of the three-phase motor, and a control device for controlling the switches of the inverter on the basis of pulse-width modulation. The control device is set up to control the switches in a switching period by using a switching pattern, wherein the switching pattern is composed of two active voltage space vectors and multiple null vectors, wherein the null vectors vary within the switching pattern.

Claims

1. A drive controller for a three-phase motor, comprising: an inverter having a plurality of switches for generating three-phase voltages at windings of the three-phase motor; and a processor for controlling the plurality of switches of the inverter based on pulse width modulation, wherein the processor controls the plurality of switches in a switching period using a switching pattern, wherein the switching pattern consists of two active voltage space vectors and a plurality of zero vectors, wherein the plurality of zero vectors vary within the switching pattern, and wherein the switching pattern is inverted during a switching period such that the active voltage space vectors are maintained while the plurality of zero vectors are inverted.

2. The drive controller according to claim 1, wherein a switching pattern defines a division of the zero vectors and/or a number of zero vectors.

3. The drive controller according to claim 1, wherein the processor calculates the zero vectors for each operating state of the three-phase motor and stores the zero vectors.

4. The drive controller according to claim 3, wherein an operating state has a specific rotation speed and a specific torque.

5. The drive controller according to claim 4, wherein the processor calculates the zero vectors offline.

6. The drive controller according to claim 5, wherein the processor stores the zero vectors in a lookup table.

7. The drive controller according to claim 3, wherein the processor calculates the zero vectors offline.

8. The drive controller according to claim 3, wherein the processor stores the zero vectors in a lookup table.

9. The drive controller according to claim 3, wherein the processor calculates the zero vectors based on an optimization algorithm, and the optimization algorithm is suitable for reducing losses of the three-phase motor over an entire operating range.

10. The drive controller according to claim 9, wherein the optimization algorithm is suitable for reducing the losses of the three-phase motor on a machine side or on an intermediate circuit side.

11. A three-phase motor comprising a drive controller according to claim 1.

12. The drive controller according to claim 11, wherein the three-phase motor is a motor vehicle three-phase motor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of a drive controller for a three-phase motor.

(2) FIG. 2 is a graph of the modulation curves depending on the phase angle.

(3) FIG. 3 is a graph of the modulation curves depending on the modulation index.

(4) Identical or functionally identical elements are identified using the same reference signs in the text which follows.

DETAILED DESCRIPTION OF THE DRAWINGS

(5) FIG. 1 shows a drive controller 1 for a three-phase motor 2. Here, the three-phase motor 2 is illustrated in an idealized manner by three coils L1 to L3 and the back-EMFs e.sub.a to e.sub.c which represent the three windings of the three-phase motor 2.

(6) In order to obtain a defined orientation of the flux density distribution in the three-phase motor 2, pulse width modulation of an input signal, which originates from an input voltage source 5, is employed in an inverter 3. In particular, voltage space vector modulation is performed.

(7) The inverter 3 has a half-bridge for each of the three phases 6 of the three-phase motor 2. The first half-bridge is formed by the switches S1, S2, the second half-bridge is formed by the switches S3, S4 and the third half-bridge is formed by the switches S5, S6. As a result, the output voltages of the three phases 6 can be applied both to the positive and also to the negative intermediate circuit potential. The intermediate circuit constitutes the transition from the input voltage source 5 to the inverter 3.

(8) Each half-bridge of the inverter 3 can assume two different switch positions. Since three half-bridges are required for a three-phase system, 2.sup.3 possible switch positions and therefore 8 switching states are produced as a result. Each active switch position corresponds to a different voltage configuration between the phases 6 and therefore also to a different voltage space vector. In this case, a voltage space vector defines the flux density distribution in the three-phase motor 2 by way of two variables, specifically the angle of the voltage space vector and its magnitude.

(9) A control device 4 is provided in order to drive the inverter 3 and its switches S1 to S6. In order to improve the driving of the three-phase motor 2 in comparison to known drive arrangements, the control device 4 is designed to control the switches S1 to S6 in a switching period using a specific, predefined switching pattern. In this case, the switching pattern consists of two active voltage space vectors and a plurality of zero (null) vectors, wherein the plurality of zero vectors vary within the switching pattern. In order to optimize the three-phase signal produced, in particular in order to reduce harmonics, since these cause distortions in the signals, the switching patterns used can be optimized using the zero vectors. Various, suitable optimization algorithms can be used for this purpose.

(10) FIGS. 2 and 3 show modulation curves for various modulation methods. In this case, FIG. 2 shows the change in the angle θ of the signals with respect to the harmonic distortion factor (HDF) and FIG. 3 shows the modulation index M.sub.i with reference to the harmonic distortion factor (HDF). The modulation index M.sub.i is understood to be a standardized inverter output voltage (inverter modulation) here.

(11) FIGS. 2 and 3 firstly show modulation curves for discontinuous modulation methods. These include the DPWMMIN (discontinuous minimum PWM), DPWMMAX (discontinuous maximum PWM), DPWM1 (discontinuous PWM) and DPWM3 (discontinuous 30° PWM) methods which each use one zero vector. Modulation curves for continuous modulation methods are also shown. These include the SVPWM (space vector PWM) and THIPWM1/4 (third harmonic PWM) modulation methods which use two zero vectors. The modulation method, as is employed by the control device described in FIG. 1, is referred to as OZP in FIGS. 2 and 3. Here, the number of zero vectors within a switching period changes depending on the modulation, the angle and the frequency.

(12) Curves C1 and K5 relate to SWPWM modulation. Curves C2 and K4 relate to THIPWM1/4 modulation. Curves C3/C4 and K2 relate to DPWMMIN/DPWMMAX modulation. Curve K3 relates to DPWM3 modulation. Curve K1 relates to DPWM1 modulation.

(13) As shown in FIGS. 2 and 3, a reduction in the distortion factor is achieved by the modulation (OZP) as is performed by the drive controller 1 of FIG. 1. This is indicated by curve C5 in FIG. 2 and curve K6 in FIG. 3. As shown in the figures, curve C5 and, respectively, K6 is optimized by corresponding optimization algorithms, which can be used in order to calculate the zero vectors, such that the distortion factor HDF is at the lowest in comparison to the existing modulation methods.

(14) The harmonics of the generated three-phase signal can be optimized by way of using a plurality of and/or different zero vectors in a voltage period. The distortion of the output signal can be reduced in this way.

REFERENCE SIGNS

(15) 1 Drive controller 2 Three-phase motor 3 Inverter 4 Control device 5 Input voltage source 6 Output phases C1-C4 Modulation curves depending on the phase angle e.sub.a-e.sub.c Back-EMFs K1-K6 Modulation curves depending on the modulation index L1-L3 Windings S1-S6 Switches