Patent Application
20120126728
Embodiments of the invention relate generally to electric machines and, more particularly, to an electric machine and power converter integrated within a single cooling loop, wherein the power converter comprises silicon carbide metal-oxide-semiconductor field effect transistors (MOSFETs).
The need for high power density and high efficiency electric machines (i.e., electric motors and generators) has long been prevalent for a variety of applications, particularly for hybrid and/or electric vehicle fraction applications. Due to energy supply and environmental reasons, there has been increased motivation to produce hybrid-electric and/or electric vehicles that are both highly efficient and reliable, yet reasonably priced for the average consumer. However, the drive motor technology available for hybrid-electric and electric vehicles has generally been cost-prohibitive, thereby reducing one (or both) of consumer affordability or manufacturer profitability.
Most commercially available hybrid-electric and electric vehicles rely on internal permanent magnet (IPM) electric machines for traction applications, as IPM machines have been found to have high power density and high efficiency over a wide speed range, and are also easily packaged in front-wheel-drive vehicles. However, IPM machines are not the only electric machines used for traction applications. Other types of electric machines, such as induction machines, have certain advantages that make them desirable for particular traction applications.
Regardless of the type of electric machine utilized, various power electronic devices are needed to provide power to the electric machine during operation. These power electronic devices have conventionally included silicon controlled rectifiers (SCRs), insulated gate bipolar transistors (IGBTs), and/or field effect transistors (FETs). In hybrid-electric and/or electric vehicle applications, a source of direct current is typically available from a battery or power supply system incorporating a battery or other energy converter. A power converter is employed to convert this power to alternating current (AC) waveforms for driving the one or more electric motors of the vehicle. The electric motors, in turn, serve to drive power transmission elements to propel the vehicle.
While power electronic devices are integral to the functionality of hybrid-electric and electric drive systems, there are inherent limitations to their size and placement in such applications. Due to varying environmental conditions in the regions surrounding the electric machine, such as heat generated by the electric machine during operation, the power converter of the system is typically mounted relatively far away from the electric machine to which it is coupled. This distant mounting point helps to prevent component failure in the power converter due to overheating. However, there are also several drawbacks to such distant mounting. One drawback is increased electromagnetic interference (EMI) due to the extended cable connections needed to couple the power converter with the electric machine. Another drawback is the need for a dedicated cooling loop to be provided for the power converter itself, a cooling loop that is entirely separate from any cooling loop utilized for the electric machine. This separate cooling loop significantly adds to the cost, weight, and complexity of the overall system, as well as increasing the overall size of the system.
It would therefore be desirable to have an apparatus and method of fabricating an electric motor and a power converter integrated within a single cooling loop.
In accordance with one aspect of the invention, an electric drive system is shown, the electric drive system comprising an electric machine comprising a rotor and a stator, a power converter electrically coupled to the electric machine and configured to convert a DC link voltage to an AC output voltage to drive the electric machine, and a single cooling loop, wherein the electric machine and the power converter are integrated within the single cooling loop.
In accordance with another aspect of the invention, a method of manufacturing an electric drive system is shown, the method comprising the steps of providing a silicon carbide (SiC) power converter having a plurality of SiC switching devices, the SiC power converter coupleable to a power source, providing an electric machine having a rotor and a stator, coupling the SiC power converter to the electric machine to drive the electric machine, and providing a cooling loop, wherein the SiC power converter and the electric machine are integrated within the cooling loop.
In accordance with another aspect of the invention, a vehicle drive system is shown, the vehicle drive system comprising a motor comprising a rotor and a stator, a DC link, a power converter electrically coupled between the DC link and the motor to drive the motor, wherein the power converter comprises a plurality of silicon carbide (SiC) switching devices, and a cooling loop, wherein the motor and the power converter are integrated within the cooling loop.
Various other features and advantages will be made apparent from the following detailed description and the drawings.
The drawings illustrate embodiments presently contemplated for carrying out the invention.
In the drawings:
Power converter 58 receives DC input voltage VDC 56 from DC link 46 and is converted or inverted to provide a suitable form of AC power for driving electric machine 66, described in detail below.
According to one embodiment, power converter 58 is a three-phase DC to AC inverter having a plurality of switching devices 68, 70, 72, 74, 76, 78. Each switching device 68-78 includes a silicon carbide (SiC) MOSFET 80, 82, 84, 86, 88, 90 and an associated anti-parallel diode 92, 94, 96, 98, 100, 102.
SiC is a crystalline substance that has material properties that make it an attractive alternative to silicon for high voltage and high power applications. For example, SiC has a large bandgap that provides a very low leakage current, which facilitates elevated temperature operation. In fact, semiconductor devices manufactured on a SiC substrate can withstand temperatures in excess of 200 degrees Celsius. SiC also has a high breakdown field that is about ten times that of silicon and a thermal conductivity that is about three times that of silicon, allowing higher power densities to be accommodated with SiC circuits. Further, SiC's high electron mobility enables high-speed switching. Thus, SiC has been considered as an advantageous material for use in the manufacture of next generation power semiconductor devices. Such devices include, for example, Schottky diodes, thyristors, and MOSFETs.
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Power converter 58 is configured to drive electric machine 66. In one embodiment, electric machine 66 is configured to be a permanent magnet electric machine having a permanent magnet rotor 110 and a stator 112. In alternative embodiments, however, electric machine 66 may be configured to be an induction machine or any other suitable electric machine capable of operation in fraction applications. Furthermore, electric machine 66 may also be coupled to a heat engine within an Auxiliary Power Unit (APU) for generating electrical power to aid in the operation of a Hybrid-Electric Vehicle (HEV) or a Plug-in Hybrid-Electric Vehicle (PHEV).
As previously mentioned, semiconductor devices manufactured on a SiC substrate are capable of withstanding temperatures in excess of 200 degrees Celsius. Thus, SiC MOSFETs 86-96 have a temperature rating of at least 200 degrees Celsius, a rating that is significantly higher than that of conventional power electronics. While conventional power converters coupled to electric machines are mounted a significant distance away from the electric machine and equipped with their own cooling loop due to high-temperature sensitivity of the power electronics, power converter 58, being equipped with SiC MOSFETs 80-90, does not require such remote placement.
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The overall weight, cost, and complexity of the drive system can be significantly reduced when utilizing single cooling loop 202 as shown in
Therefore, according to one embodiment of the invention, an electric drive system is shown, the electric drive system comprising an electric machine comprising a rotor and a stator, a power converter electrically coupled to the electric machine and configured to convert a DC link voltage to an AC output voltage to drive the electric machine, and a single cooling loop, wherein the electric machine and the power converter are integrated within the single cooling loop.
According to another embodiment of the invention, a method of manufacturing an electric drive system is shown, the method comprising the steps of providing a silicon carbide (SiC) power converter having a plurality of SiC switching devices, the SiC power converter coupleable to a power source, providing an electric machine having a rotor and a stator, coupling the SiC power converter to the electric machine to drive the electric machine, and providing a cooling loop, wherein the SiC power converter and the electric machine are integrated within the cooling loop.
According to yet another embodiment of the invention, a vehicle drive system is shown, the vehicle drive system comprising a motor comprising a rotor and a stator, a DC link, a power converter electrically coupled between the DC link and the motor to drive the motor, wherein the power converter comprises a plurality of silicon carbide (SiC) switching devices, and a cooling loop, wherein the motor and the power converter are integrated within the cooling loop.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
