Design of a High Speed Switched Reluctance Machine for Automotive Turbo-Generator Applications

The efficient generation of relatively large quantities of electrical energy in vehicles is becoming an increasingly important issue, as a result of the increasing demands of ancillary electrical equipment and the emergence of hybrid power-train vehicles. An attractive solution to meeting these demands is to extract the electrical energy by means of a generator driven by a high speed exhaust mounted turbine, a technology which is beginning to emerge commercially. This paper is concerned with the design of a system, which extends this concept to enable both electrical generation and highly flexible air management. The heart of the system is a high-speed switched reluctance (SR) electrical machine, the rotor of which is located on a common shaft with the turbine and compressor wheels of a standard commercially available turbocharger.

The design synthesis of an SR machine capable of meeting the required performance specification is particularly onerous given the harsh environment in which it operates, specifically in terms of the restricted space envelope, the high ambient temperature and the very high rotational speeds. This paper describes, in detail, the design synthesis of an SR machine for a prototype 5kW system, a procedure which encompasses analysis of centrifugal stress in the rotor, aerodynamic losses, electromagnetic design synthesis and dynamic simulation. The description of the design synthesis is supported by experimental characterisation of a prototype SR machine.