Kevin Grace

Reduced Rare-Earth Flux-Switching Machines for Traction Applications

There has been growing interest in electrical machines that reduce or eliminate rare-earth material content. Traction applications are among the key applications where reducing cost and, hence, reduction of rare-earth materials are key requirements. This paper will assess the potential of different variants of flux-switching machines (FSMs) that either reduce or eliminate rare-earth materials in the context of traction applications. Two designs use different grades of dysprosium-free permanent magnets (PMs), and the third design is a wound-field variant that does not include PMs at all. A detailed analysis of all three designs in comparison to the required set of specifications will be presented. The key opportunities and challenges will be highlighted. The impact of the high pole-count/frequency of the FSMs will also be evaluated. Experimental results for one of the designs with dysprosium-free PMs will also be presented.

Robust non-permanent magnet motors for vehicle propulsion

There has been growing interest in electrical machines that reduce or eliminate rare-earth material content. Traction applications are among the key applications where reducing cost and hence reduction or elimination of rare-earth materials is a key requirement. This paper will assess the potential of three non-permanent magnet options in the context of vehicle propulsion applications: 1) a conventional Switched Reluctance Machine (SRM), 2) a DC-biased Reluctance Machine (DCRM) and, 3) a Wound Field Flux Switching Machine (WFFSM). The three machines were designed to achieve the hybrid vehicle traction requirements of 55kW peak and 30kW continuous over a speed range going from 2800rpm to 14000rpm. Their performance will be compared and the key opportunities and challenges will be highlighted. Preliminary experimental results for the DCRM will be presented.

Reduced rare-earth flux switching machines for traction applications

There has been growing interest in electrical machines that reduce or eliminate rare-earth material content. Traction applications are among the key applications where reducing cost and hence reduction of rare-earth materials is a key requirement. This paper will assess the potential of different variants of flux-switching machines that either reduce or eliminate rare-earth materials in the context of traction applications. Two designs use different grades of Dysprosium-free permanent magnets and the third design is a wound-field variant that does not include permanent magnets at all. Detailed analysis of all three designs in comparison to the required set of specifications will be presented. The key opportunities and challenges will be highlighted. The impact of the high pole-count/frequency of the flux-switching machines will also be evaluated. Preliminary experimental results for one of the designs with Dysprosium-free permanent magnets will also be presented.

Sinusoidal Reluctance Machine With DC Winding: An Attractive Non-Permanent-Magnet Option

Important global efforts are underway toward lowering the cost of electric machines for electric and hybrid vehicles by reducing or eliminating the use of rare earth materials which have been experiencing significant price increases and volatility. Non-permanent magnet electric machines are a potential solution and are increasingly investigated by researchers worldwide. This paper presents a DC biased reluctance machine which is structurally similar to a conventional switched reluctance machine. This type of machine has a DC field winding and an AC three phase armature winding. It uses a conventional three phase inverter for the armature and an additional auxiliary DC/DC converter for the field winding. This reluctance machine is designed to achieve hybrid vehicle traction requirements of 55kW peak at 2800 rpm and 30kW continuous over a speed range going from 2800 rpm to 14000 rpm.

Sinusoidal reluctance machine with DC winding: An attractive non-permanent magnet option

Important global efforts are underway toward lowering the cost of electric machines for electric and hybrid vehicles by reducing or eliminating the use of rare-earth materials which have been experiencing significant price increases and volatility. Non-permanent-magnet (non-PM) electric machines are a potential solution and are increasingly investigated by researchers worldwide. This paper presents a DC-biased reluctance machine, which is structurally similar to a conventional switched reluctance machine. This type of machine has a DC field winding and an AC three-phase armature winding. It uses a conventional three phase inverter for the armature and an additional auxiliary DC/DC converter for the field winding. This reluctance machine is designed to achieve hybrid vehicle traction requirements of 55 kW peak at 2800 r/min and 30 kW continuous over a speed range going from 2800 to 14 000 r/min.

Test results for a high temperature non-permanent magnet traction motor

Commercially available hybrid and electric vehicles are generally using rare earth PM motors because of their compactness and very good efficiency. But the supply security and price volatility of rare-earth materials are still major concerns for the hybrid and electric vehicle industry. Hence, global efforts are underway in several countries on using reduced or non-rare earth materials, developing non-permanent magnet solutions and taking cost out by trading off between material properties and cost. Non-permanent magnet machines are generally known to be less power dense than permanent magnet counterparts. But the absence of permanent magnets in these machines makes them well suited for high temperature applications provided appropriate stator winding insulation materials are used. This offers a degree of freedom in improving their power density because they can operate at higher electrical loading while maintaining acceptable efficiency. This paper presents a high temperature DC biased reluctance machine which is structurally similar to a conventional switched reluctance machine. This non-permanent magnet machine has a DC field winding and an AC three phase armature winding. The machine is equipped with a high temperature 280oC rated insulation system. Test results showing machine performance under continuous operation against the FreedomCar 2020 specifications as well as at high temperature up to 280oC are presented. A 43% improvement in power density was achieved by going to high temperature.

Performance testing and analysis of synchronous reluctance motor utilizing dual-phase magnetic material

While interior permanent magnet (IPM) machines have been considered state of the art for traction motors, synchronous reluctance (SynRel) motors with advanced materials can provide a competitive alternative. IPM machines typically utilize neodymium iron boron permanent magnets, which pose an issue in terms of price, sustainability, demagnetization at higher operating temperatures, and uncontrolled generation. On the other hand, SynRel machines do not contain any magnets and are free from these issues. However, the absence of magnets as well as the presence of bridges and centerposts limit the flux-weakening capability of a SynRel machine, and limit the achievable constant power speed ratio without having to significantly oversize the machine and/or the power converter. In this paper, a new material referred to as the dual-phase magnetic material, where nonmagnetic regions can be selectively introduced within each lamination, will be evaluated for SynRel designs. The dual-phase feature of this material enables nonmagnetic bridges and posts, eliminating one of the key limitations of the SynRel designs in terms of torque density and flux weakening. This paper will present the design, analysis, and test results of an advanced proof-of-concept SynRel design utilizing dual-phase material with traction applications as the ultimate target application.

Carbon-fiber-wrapped synchronous reluctance traction motor

Synchronous reluctance machines are very appealing for high speed traction applications due to their robustness, simple structure, absence of magnets, and simple control. The absence of magnets means that synchronous reluctance machines are not susceptible to price variability and sustainability of rare-earth materials. Also, there are no concerns about demagnetization or uncontrolled generation mode. However, the challenge of achieving a good constant power to speed ratio is dependent on the mechanical aspects of the design. Conventional synchronous reluctance designs perform poorly compared to permanent magnet machines due the presence of bridges and/or center posts that provide a path for performance-robbing leakage flux. Elimination or reduction of these features presents a challenge for rotor mechanical retention due to the reduction in radial stiffness that these members provide. A carbon-fiber sleeve on the rotor will provide the needed mechanical strength to enable a reduction of bridges and/or center posts. This paper will present the design details, analysis, manufacturing and test results of a proof-of-concept carbon-fiber-wrapped synchronous reluctance machine targeting traction applications.

Test Results for a High Temperature Non-Permanent-Magnet Traction Motor

Non-permanent-magnet machines are generally known to be less power dense than permanent magnet counterparts, but the absence of permanent magnets in these machines makes them well suited for high temperature applications. This offers a degree of freedom in improving their power density, because they can operate at higher electrical loading while maintaining acceptable efficiency. This paper presents a high temperature dc-biased reluctance machine that is structurally similar to a conventional switched reluctance machine. This non-permanent-magnet machine has a dc field winding and an ac three-phase armature winding. The machine is equipped with a high temperature 280 °C rated insulation system. Test results showing machine performance under continuous operation against the FreedomCar 2020 specifications as well as at high temperature up to 280 °C are presented. Compared with an initial design using conventional insulation designed for operation at 200 °C, the high temperature insulation system enabled the machine to operate at twice the temperature rise and achieve 43% increase in power.