Resonant link inverters for trapezoidal flux electrically commutated machines

摘要

To increase their usability wind and kinetic-tidal generators and Electric Vehicles (EVs) require efficient conversion between mechanical and electrical energy. The brushless dc machine (BLDCM) is entirely suitable for such a task, and to exemplify its use this thesis details a high efficiency kinetic-tidal energy generator test system. To maximise the energy yield it uses a low solidity turbine, an efficient transmission system, a BLDCM generator, and a maximum power point tracker. BLDCM cogging torque is also addressed. Measured results are presented, with the measured efficiency of the water-turbine being 30%in real-world conditions. Although the BLDCM is an efficient energy converter, it requires power electronic control; the soft-switched Actively Clamped Resonant DC Link Inverter (ACRLI) is an ideal choice for such. This thesis details a complete mathematical analysis of the ACRLI topology, and develops formulae for all important voltages, currents, and timing. A complete list of loss formulae for all major components, including a MOSFET clamp device, is presented. These formulae can be used to optimally design ACRLIs, and an optimal design for a 10 kW EV is described. Since the inductor in a high power ACRLI is problematic, this thesis addresses large ferritecored inductor design, analysing hysteresis and eddy current core loss and Litz wire conduction loss. An optimal but non-realisable design is shown, followed by a near-optimal, realisable and economical very low loss inductor design; an inductor was fabricated in accordance with this design and its measured loss in resonant link operation, being less than 20W for the 10kW high current inverter, is consistent with theory. The BLDCM’s applicability in the general EV field has been questioned due to its rectangular torque versus speed characteristic. To modify this characteristic a voltage booster could be used. The ACRLI can provide such boosting with the addition of a few components, the main one being a rectifier grade thyristor, thus creating the Actively Clamped Resonant DC Link-Boost Inverter (ACRL-BI) topology. This new topology is analysed along with an optimal thyristor dv=dt snubber, a suitable current control method with minimum switching frequency, and a novel driver interface for EV use. A 10 kWACRL-BI prototype was built and measured results of resonant and boost operation are shown.