Electrical drive system

Abstract

An electrical drive system having multiple drive units for motor vehicles, especially for pure electric vehicles, and a method for operating the drive system.

Claims

1. An electrical drive system for a motor vehicle, comprising: at least two electric machines as well as at least one inverter with silicon (Si) semiconductor components and at least one inverter with silicon carbide (SiC) semiconductor components, wherein the inverters are sine wave inverters. wherein the inverters generate a sinusoidal output voltage by pulse width modulation in chopper mode, wherein the switching frequency of the inverters lies in a range of 10 kHz to 25 kHz, wherein at least one electric machine of the at least two electric machines is supplied by the at least one Si inverter and is designed to drive a front axle of the motor vehicle, and at least one electric machine of the at least two electric machines is supplied by the at least one SiC inverter and is designed to drive a rear axle of the motor vehicle.

2. The electrical drive system as claimed in claim 1, wherein the inverter with silicon semiconductor components comprises at least one Si-IGBT and at least one Si-diode.

3. The electrical drive system as claimed in claim 1, wherein the inverter with silicon carbide semiconductor components comprises at least one SiC-MOSFET.

4. The electrical drive system as claimed in claim 1, wherein the inverter with silicon carbide semiconductor components comprises at least one Si-IGBT and at least one SiC diode.

5. A method for operating the electrical drive system in driving mode of the motor vehicle comprising: supplying electric machines supplied with alternating current solely via SiC inverters are used to drive the motor vehicle when a torque demand is less than a maximum torque that can be produced by the electric machines supplied via SiC inverters; and supplying electric machines supplied with alternating current by both SiC inverters as well as electric machines supplied with alternating current by Si inverters are used to drive the motor vehicle when the torque demand is greater than the maximum torque that can be produced by electric machines supplied with alternating current via SiC inverters, wherein the front axle of the motor vehicle is driven by at least one electric machine supplied by a Si inverter, and the rear axle of the motor vehicle is driven by at least one electric machine supplied by a SiC inverter, wherein the inverters are sine wave inverters, wherein the inverters generate a sinusoidal output voltage by pulse width modulation in chopper mode, wherein the switching frequency of the inverters lies in a range of 10 kHz to 25 kHz.

6. The electrical drive system as claimed in claim 2, wherein the inverter with silicon carbide semiconductor components comprises at least one SiC-MOSFET.

7. The electrical drive system as claimed in claim 2, wherein the inverter with silicon carbide semiconductor components comprises at least one Si-IGBT and at least one SiC diode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is represented schematically on the basis of embodiments in the drawings and shall be described further with reference to the drawings. There are shown:

(2) FIG. 1a a comparison of the power loss of different inverters;

(3) FIG. 1b a comparison of the power loss of different inverters;

(4) FIG. 2 a schematic representation of one embodiment of a drive system according to the invention with two different inverters.

DETAILED DESCRIPTION

(5) FIG. 1 shows a comparison of the power loss of different inverters at a constant load point for different clock frequencies: a) full-load operation, b) partial load operation). The inverters used were operated with a maximum power of 180 kW, a maximum voltage of 1200 V HL, an alternating current averaged over 10 s of 350 Arms. The inverters were designed for a maximum temperature at the junction of 175 C. (Si inverter) or 200 C. (SiC inverter).

(6) The loss data was determined from measurements. The boundary conditions for the calculation were cos Phi: 0.7; maximum modulation rate: 0.9; efficiency of e-machine+transmission: 0.9*0.94; DC voltage: 800V.

(7) As can be seen from FIG. 1a, the power loss of a SiC inverter in full-load operation (350 Arms, switching frequency 10 kHz) is 35% less than that of a Si inverter. The power loss is represented as the sum of the switching losses 11 and the conduction losses 12. The decrease is due to the much smaller switching losses 11. In partial load operation (FIG. 1b) with 175 Arms, there results in fact a reduction in the power loss of 55% at a switching frequency of 10 kHz. As can be seen, the differences in the losses are less in the high-load region than in the partial load region.

(8) FIG. 2 shows a schematic representation of a drive system 20 with two different inverters 24 and 25. One Si inverter 24 supplies a first e-machine 22, and one SiC inverter 25 supplies a second e-machine 22. The two inverters 24 and 25 are each connected by DC-HV cable 23 to a HV battery 21, which provides the direct current for the operation of the inverters 24 and 25. The first e-machine 22 connected to the Si inverter 24 may be arranged, for example, on the front axle of the motor vehicle and drive it, and the second e-machine 22 connected to the SiC inverter 25 can be arranged on the rear axle of the motor vehicle and drive it. Of course, more than two drive units may also be combined with each other in one vehicle.