A novel two-quadrant zero-current transition converter for dc motor drives

A novel two-quadrant (2Q) zero-current-transition (ZCT) converter with the capabilities of 2Q power flow, and ZCT switching profile for DC motor drives is presented. It possesses the advantages that both the main and auxiliary switches can operate with zero-current switching (ZCS), reduced switching losses and stresses, minimum voltage and current stresses as well as minimum circulating energy during both the motoring and regenerating modes. This converter is particularly useful for DC traction systems in which both motoring and regenerative braking are desired to have high efficiencypublished_or_final_versio

Constant-frequency multi-resonant converter-fed DC motor drives

Low-inductance dc motors with high power density and low rotor inertia are becoming more attractive, particularly for servo applications. In order to maintain their current ripples within acceptable levels, power converters need to operate at high switching frequencies. However, the increase in switching frequencies realizable by hard-switching techniques accompanies the increase in switching losses and switching stresses. In this paper, recent soft-switching dc-dc converters are discussed for application to dc motor drives. The most feasible one, namely the zero-voltage-switching (ZVS) constant-frequency multi-resonant converter (CF-MRC), has been identified to be appropriate for dc motor drives. This soft-switching converter not only possesses the advantages of achieving high switching frequencies with practically zero switching losses and eliminating variable-frequency operation, but also provides full ranges of voltage conversion and load variation. A ZVS-CF-MRC-fed dc motor drive has been prototyped and tested. Experimental results verify the successful application of the ZVS-CF-MRC to dc motors drives, which takes definite advantages of high efficiency, small current ripples and minimum switching stresses.published_or_final_versio

A new zero-voltage-transition converter for switched reluctance motor drives

Firstly, a new zero-voltage-transition (ZVT) power converter for switched reluctance motor drives is presented. The proposed ZVT converter possesses the definite advantages that both main transistors and diodes can operate with zero-voltage switching (ZVS), unity device voltage and current stresses. Secondly, its zero-current counterpart is also presented, which offers both the main and auxiliary switches operating with zero-current switching (ZCS) and minimum current/voltage stress. They both have simple circuit topology, minimum component count and low cost. This family of power converters is especially advantageous for switched reluctance motor drives demanding efficient regenerative braking, such as in electric vehicle applications.published_or_final_versio

A six-phase transverse-flux-reversal linear machine for low-speed reciprocating power generation

In this paper, a 6-phase permanent-magnet flux-reversal linear machine for low-speed reciprocating power generation is presented. By increasing the phase number, the phase current is reduced for the same rated power which results in a lower ohmic loss. In addition, the thrust force ripple can be reduced accordingly. By borrowing the transverse-flux concept, the electric loading and the magnetic loading is decoupled and the thrust density can be improved accordingly. The stator of the proposed machine adopts the modular design, and each phase is magnetically decoupled with each other which gives more flexibility and controllability of the generator. Based on the same topology, the proposed machine can be extended to a machine with an arbitrary number of phase to suit different applications.published_or_final_versio

Bidirectional soft-switching converter-fed DC motor drives

Two new soft-switching DC-DC power converters, with the capabilities of bidirectional power flow and soft-switching (either zero-voltage transition or zero-current transition) are developed for DC motor drives. The proposed bidirectional zero-voltage-transition power converter possesses the definite advantages that both main transistors and rectifiers can switch with zero-voltage switching (ZVS) and unity device stresses during both motoring and regenerating modes of operation, while both the main and auxiliary switches of the bidirectional zero-current-transition power converter can operate with zero-current switching (ZCS) and minimum voltage/current stress. These converters are particularly useful for DC traction systems in which both motoring and regenerative braking are desired to have high efficiency.published_or_final_versio

A low-speed linear harmonic generator for grid-tied and stand-alone operation using hybrid excitation topology

Paper no. BP-09Since intermediate mechanical conversion mechanisms for speed, torque and motion conversion can be entirely eliminated, the direct-drive wave power generation attracts more and more attention [1]. Among various proposed generators, the permanent-magnet (PM) vernier generator is considered as a viable solution for the wave energy harvesting. This generator can efficiently harness this low-speed and high-power energy source via a so-called vernier effect by utilizing the effective harmonic magnetic field [2]. However, since only PMs are engaged for field excitation and the harmonic magnetic field is adopted, it is incapable to provide a flexible voltage control and power factor improvement. Moreover, the voltage regulation is incredible high. The purpose of this paper is to design a linear harmonic generator for producing electricity in a wave farm. Except for the PM excitation, the proposed generator is equipped with a set of DC field winding for the hybrid excitation. With this merit, the proposed generator exhibits a satisfactory performance for voltage regulation and power factor improvement which is desirable for both grid-tied and stand-alone operation [3]. © 2015 IEEE.published_or_final_versio

A quasi-experimental study on a new service option of short-term residential care for older stroke patients

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Maximum power point tracking control of a linear magnetic-geared generator for direct-drive wave energy conversion

This paper deals with control of a linear magneticgeared permanent-magnet generator for wave power generation using maximum power point tracking (MPPT) algorithm. Firstly, the linear magnetic-geared permanent-magnet generator structure is presented. The machine modeling is established based on the finite element analysis (FEA). Secondly, by analyzing the dynamic model of the wave power, the MPPT algorithm for directdrive wave power generation is discussed. Then, the performance for maximizing wave power absorption is verified and evaluated by the circuit simulator. The results verify that the MPPT algorithm is valid for the direct-drive wave power generation.postprin

Design and analysis of a new HTS axial-field flux-switching machine

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Art-making in a family medicine clerkship: how does it affect medical student empathy?

Background: To provide patient-centred holistic care, doctors must possess good interpersonal and empathic skills. Medical schools traditionally adopt a skills-based approach to such training but creative engagement with the arts has also been effective. A novel arts-based approach may help medical students develop empathic understanding of patients and thus contribute to medical students’ transformative process into compassionate doctors. This study aimed to evaluate the impact of an arts-making workshop on medical student empathy. Methods: This was a mixed-method quantitative-qualitative study. In the 2011-12 academic year, all 161 third year medical students at the University of Hong Kong were randomly allocated into either an arts-making workshop or a problem-solving workshop during the Family Medicine clerkship according to a centrally-set timetable. Students in the arts-making workshop wrote a poem, created artwork and completed a reflective essay while students in the conventional workshop problem-solved clinical cases and wrote a case commentary. All students who agreed to participate in the study completed a measure of empathy for medical students, the Jefferson Scale of Empathy (JSE) (student version), at the start and end of the clerkship. Quantitative data analysis: Paired t-test and repeated measures ANOVA was used to compare the change within and between groups respectively. Qualitative data analysis: Two researchers independently chose representational narratives based on criteria adapted from art therapy. The final 20 works were agreed upon by consensus and thematically analysed using a grounded theory approach. Results: The level of empathy declined in both groups over time, but with no statistically significant differences between groups. For JSE items relating to emotional influence on medical decision making, participants in the arts-making workshop changed more than those in the problem-solving workshop. From the qualitative data, students perceived benefits in arts-making, and gained understanding in relation to self, patients, pain and suffering, and the role of the doctor. Conclusions: Though quantitative findings showed little difference in empathy between groups, arts-making workshop participants gained empathic understanding in four different thematic areas. This workshop also seemed to promote greater self-awareness which may help medical students recognize the potential for emotions to sway judgment. Future art workshops should focus on emotional awareness and regulation.  published_or_final_versio