Omid Beik

Multiphase machines for electric vehicle traction

To have greater impact on application it is desirable to integrate machines and their associated power electronic converters into complicated systems that share component count to minimise cost. However, while compactness of systems is achieved, reliability of the power conversion components can be compromised by the arduous nature of system operating environments. This paper investigates the impact of using higher phase numbers for electromagnetic machines and their associated power electronic converters specifically targeting improved specific and volumetric power density and increased lifetime. Key findings are improved prediction of iron-loss and electromagnetic power density, performance, packaging and hence cost.

Variable speed brushless hybrid permanent magnet generator for hybrid electric vehicles

Hybrid permanent magnet (HPM) generators have been proposed as engine mounted machines operating at fixed rotor speed and generating via simple passive rectifiers into a variable vehicle system DC-link voltage. As such, the machine excitation is controlled to maintain delivered power output. This paper studies the variable speed operation of a (HPM) generator in a series hybrid electric vehicle (SHEV) within some specific driving cycles. The study investigates different scenarios in terms of the possible operational regions for the HPM generator at different speeds. A HPM generator designed to deliver controlled power into a varying system DC-link voltage at fixed rotor speed is used as a reference design. Two further designs are then developed to study the impact of varying generator speed on machine design and excitation requirements. The loss analysis for the three designs is conducted including the losses in the passive rectification stages used in the system. Simulation studies are carried out for different HPM generator power levels at different speeds. The simulated performance characteristics of the HPM are validated via test data from a prototype machine and loading system.

Hybrid generator for wind generation systems

This paper proposes a new high voltage hybrid generator (HG) employed in a proposed off-shore wind generation system with HVDC interconnection and transmission. The proposed system is compared with an existing commercial wind generation system and shown to be more efficient, to have lower mass, hence potentially lower cost. The system in this paper offers a much simplified power conversion for wind turbines, in particular the gearbox (GB), low voltage generator, back-to-back voltage source converters (VSC) and turbine transformer typical of existing commercial systems are replaced with a high voltage direct drive HG and a passive rectifier. The proposed HG uses two rotor field excitations, permanent magnet (PM) and wound field (WF). Voltage and power control of the HG is facilitated via the machine WF energized by a brushless exciter. Further, the HG employs a multiphase stator winding that yields improved power density while essentially eliminating the smoothing devices that would otherwise be required. A prototype HG is built and tested to validate the effectiveness of the design.

An Offshore Wind Generation Scheme With a High-Voltage Hybrid Generator, HVDC Interconnections, and Transmission

A new offshore high-voltage dc (HVDC) wind generation scheme is proposed in this paper. The scheme implements a high-voltage hybrid generator (HG) as well as HVDC interconnection and transmission systems. The turbine power train of the proposed system is compared with a typical system installed in a commercial wind farm. The analyses demonstrate improvements in system losses and, hence, efficiency, power-train hardware, including cable system mass and, importantly, a reduction in major component count and installed power electronics in the nacelle and turbine tower, features that lead to reduced capital cost and maintenance. The resulting power conversion system is more simplified and more amenable to higher voltage implementation since it is not constrained by existing state-of-art power-electronic voltage source converter structures. Voltage control is facilitated via dc/dc converters located away from the turbine tower. To demonstrate the HG operational concept, measured results from a low-power laboratory prototype HG system are compared with analytical results and show good agreement.

High-Voltage Hybrid Generator and Conversion System for Wind Turbine Applications

This paper presents the design of a high-voltage hybrid generator (HG) and conversion system for wind turbine applications. The HG combines wound field (WF) and permanent magnet (PM) rotor excitations. At any given speed, the PM induces a fixed stator voltage, while the WF induces a variable controlled stator voltage. The HG alternating output is rectified via a passive rectification stage; hence, the machine net dc output voltage is controlled over a prescribed, but a limited range. The split ratio between PM and WF rotor sections is considered as varying from a fully WF rotor, or traditional synchronous generator, to some ratio of PM to WF excitation. The turbine operational characteristics and maximum wind velocity variations between turbines in a wind farm are used to define the WF to PM split ratio. Both a three-phase and a nine-phase stator winding design are investigated. The nine-phase winding results in 4.2% higher output RMS voltage that yields a more power dense solution. It further yields lower rectified dc-link voltage ripple. The HG mass, loss audits, and efficiency discussions are presented. In order to investigate the feasibility of the HG concept, a small scale laboratory prototype is designed, and operational test results presented that show good agreement with the simulation model results.