A novel two-quadrant zero-voltage transition converter for DC motor drives

A novel zero-voltage-transition (ZVT) two-quadrant (2Q) power converter for DC motor drives is presented. It possesses the definite advantage that both main transistors and rectifiers can operate with zero-voltage switching in both motoring and regenerating modes, while both of these switches are only subjected to unity voltage and current stresses, namely the same as its PWM counterparts. This power converter is particularly useful for DC traction systems in which both motoring and regenerative braking are desired to have high efficiency. The corresponding theoretical analysis and its high-efficiency performance are supported by both simulation and experimental results.published_or_final_versio

A novel zero-current soft-switching converter for switched reluctance motor drives

A new zero-current-transition (ZCT) power converter for switched reluctance motor drive applications is presented. The proposed ZCT power converter possesses the definite advantages that both the main and auxiliary switches are operating with zero-current switching (ZCS), as well as minimum current and voltage stresses. It has a simple circuit topology, minimum component count and low cost. The ZCT technique can significantly reduce the switch-on or -off losses by forcing the current to zero prior to its turn-on or turn-off. The proposed power converter is especially advantageous for switched reluctance motor (SRM) drives demanding efficient regenerative braking, such as electric vehicle application.published_or_final_versio

Modeling of subharmonics and chaos in DC motor drives

In this paper, the nonlinear dynamics of both voltage-mode and current-mode controlled dc motor drive systems are presented. The investigation is based on the derivation of the discrete mappings that describe their system subharmonics and chaos in the continuous conduction mode of operation. It illustrates that different bifurcation diagrams can be obtained by using different modes of control while varying the same system parameters. A unified modeling approach for the period-1 and hence the period-p orbits as well as their stability analysis during both voltage-mode and current-mode of control is proposed and verified.published_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 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

Nonmigratory online deadline scheduling on multiprocessors

In this paper we consider multiprocessor scheduling with hard deadlines and investigate the cost of eliminating migration in the online setting. Let I be any set of jobs that can be completed by some migratory offline schedule on m processors. We show that I can also be completed by a nonmigratory online schedule using m speed-5.828 processors (i.e., processors 5.828 times faster). This result supplements the previous results that I can also be completed by a non-migratory offline schedule using 6m unit-speed processors [B. Kalyanasundaram and K. R. Pruhs, J. Algorithms, 38 (2001), pp. 2-24] or a migratory online schedule using m speed-2 processors [C. A. Phillips et al., Algorithmica. 32 (2002), pp. 163-200]. Our result is based on a simple conservative scheduling algorithm called PARK, which commits a processor to a job only when the processor has zero commitment before its deadline. A careful analysis of PARK further shows that the processor speed can be reduced arbitrarily close to 1 by exploiting more processors (say, using 16m speed-1.8 processors). PARK also finds application in overloaded systems; it gives the first online nonmigratory algorithm that can exploit moderately faster processors to match the performance of any migratory offline algorithm. © 2005 Society for Industrial and Applied Mathematics.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

Extra unit-speed machines are almost as powerful as speedy machines for flow time scheduling

We study online scheduling of jobs to minimize the flow time and stretch on parallel machines. We consider algorithms that are given extra resources so as to compensate for the lack of future information. Recent results show that a modest increase in machine speed can provide very competitive performance; in particular, using O(1) times faster machines, the algorithm SRPT (shortest remaining processing time) is 1-competitive for both flow time [C. A. Phillips et al., in Proceedings of STOC, ACM, New York, 1997, pp. 140-149] and stretch [W. T. Chan et al., in Proceedings of MFCS, Springer-Verlag, Berlin, 2005, pp. 236-247] and HDF (highest density first) is O(1)-competitive for weighted flow time [L. Becchetti et al., in Proceedings of RANDOM-APPROX, Springer-Verlag, Berlin, 2001, pp. 36-47]. Using extra unit-speed machines instead of faster machines to achieve competitive performance is more challenging, as a faster machine can speed up a job but extra unit-speed machines cannot. This paper gives a nontrivial relationship between the extra-speed and extra-machine analyses. It shows that competitive results via faster machines can be transformed to similar results via extra machines, hence giving the first algorithms that, using O(1) times unit-speed machines, are 1-competitive for flow time and stretch and O(1)-competitive for weighted flow time. © 2008 Society for Industrial and Applied Mathematics.published_or_final_versio

Dynamic bin packing of unit fractions items

LNCS v. 3580 entitled: Automata, Languages and Programming: 32nd International Colloquium, ICALP 2005, Lisbon, Portugal, July 11-15, 2005. ProceedingsThis paper studies the dynamic bin packing problem, in which items arrive and depart at arbitrary time. We want to pack a sequence of unit fractions items (i.e., items with sizes 1/ω for some integer w ≥ 1) into unit-size bins such that the maximum number of bins used over all time is minimized. Tight and almost-tight performance bounds are found for the family of any-fit algorithms, including first-fit, best-fit, and worst-fit. We show that the competitive ratio of best-fit and worst-fit is 3, which is tight, and the competitive ratio of first-fit lies between 2.45 and 2.4985. We also show that no on-line algorithm is better than 2.428-competitive. This result improves the lower bound of dynamic bin packing problem even for general items. © Springer-Verlag Berlin Heidelberg 2005.postprin