K. Ramar

A Single-Switch AC/DC Flyback Converter Using a CCM/DCM Quasi-Active Power Factor Correction Front-End

This paper discusses the major issues that exist in the single-stage ac/dc converters with power factor correction (PFC) and presents a novel converter based on a quasi-active PFC scheme. Two additional windings wound in the transformer of a conventional dc/dc flyback converter are used to drive and achieve continuous current mode operation of an input inductor. In addition, direct energy transfer paths are provided through the additional windings to improve the conversion efficiency and to reduce the dc bus capacitor voltage below 450 V for universal line applications. The proposed converter can be easily designed to comply with IEC 61000-3-2 Class D requirement and to achieve fast output voltage regulation. By properly tuning the converter parameters, a good tradeoff between efficiency, dc bus capacitor voltage stress, and harmonic content can be achieved. Operating principles, analysis, and experimental results of the proposed method are presented.

A review on high frequency resonant inverter technologies for wireless power transfer using magnetic resonance coupling

Research on developing the applications of Wireless Power Transfer system (WPTS) has been increased considerably for the last few years. Plug-in Hybrid Electrical Vehicle & Electric vehicle charging is one of them. Due to operational and environmental benefit charging of these vehicles via Wireless Power Transfer (WPT) has been considered in academic and industrial research to obtain an environmental friendly future transportation system. Among various types of WPT system, Magnetic Resonant Coupling WPT (MRCWPT) has been appeared as an attractive technology for mid-range (200-300 mm), medium power (>2 kW) electric vehicle charging application. High frequency resonant Inverters play an important role in efficient MRCWPT vehicle charging system. Among different resonant inverter topology, class E and its variant have shown the potentiality in this type of WPT system due to its circuit simplicity, efficient high frequency operation by zero voltage switching (ZVS) etc. Along with this inverter some other potential inverter topologies have been discussed based on the last 5-6 years literature. Simulation results of class φ2 inverter which has currently been modifying by the authors have been presented to confirm the potentiality of this type of inverter and design challenges have been addressed. A practical robust WPT vehicle charging system (based on literature) has been presented for a charging gap of 200-300 mm. Authors are currently working on designing resonant inverter topology for this type of WPT vehicle charging system.

Single-ended traveling wave based fault location on two terminal transmission lines

A single-ended traveling wave (TW) based fault location algorithm has been presented in this paper. The distance of the fault is determined using the time difference between the first two consecutive alpha modes of the current TWs observed at one end of the line. To apply the TW principle to locate ground faults the faulted half of the line must be identified and for this purpose the impedance based technique is applied. The fundamental components of the voltage and current signals for impedance calculation are extracted using Fourier series. The proposed algorithm which combines the impedance based method with the TW based fault location has been tested with different types of faults, different fault resistance values and different fault inception angles using ATP/EMTP simulations.

Performance of Earthing Systems for Different Earth Electrode Configurations

Changes of behavior of earthing systems under high impulse conditions from its steady-state conditions have been found to occur in many studies. There are many factors that are thought to cause these changes. However, little studies so far have been conducted on the effects of earth electrode dimensions and configurations, particularly at field sites. This paper is to present and discuss the results of field site study on the performance of earthing systems of different configurations and dimensions.

Design consideration of dual axial flux motor for electric vehicle applications

Vehicle dynamic depends on the power rating as it tallies the required initial acceleration and overall performance. If the vehicle motor operational characteristics provides high torque at constant power, the power rating of the machine can be reduced. Besides, extended constant power range can also recover more kinetic energy during regenerative braking. Therefore, a motor with extended constant power and torque is advantageous for EV and HEV traction application. However, in order to obtain high torque at constant power range, the motors must be specially designed. Thus an Axial Flux Permanent Magnet (AFPM) with dual magnetic circuit is introduced as application specific motor for battery operated electric vehicle. Finite element analysis is carried out for the proposed structure. For the designed value of 1 kW machine it is able to produce 2.5 Nm torque at 150 rpm with a regeneration capability of close to 300V.

Ride-through capability of three-phase induction motor through a new winding strategy

About 40% of all reported induction machine faults are stator winding related. In critical applications where continuous operation of the machine is required, the faults pose a major challenge leading to stalling of the industrial operations. In this paper, a new winding configuration for the stator windings is proposed to have a better ride-through capability of the induction motor. This improvises the fault tolerance capability in such a way that two sets of stator windings, inner and outer windings, are used instead of single conventional winding. When both the windings are energized, the same torque-speed characteristic as in the conventional winding is achieved. The inner winding has marginally higher average torque than the outer winding because the inner winding is placed proximal to the air gap between stator and rotor. The fault tolerance capacity of the proposed configuration is investigated by inducing a fault situation on the inner winding. The outer winding considerably recovers the average torque of a faulty inner winding with a loss of 2% in operations.

A Simple Numerical Busbar Protection Technique Using Instantaneous Current Values

A simple busbar protection technique using the instantaneous values of current signals is proposed in this paper. The instantaneous current samples are collected for quarter cycle of the current wave starting from the instant of fault and the trip decision is made based on restrained differential protection principle.

An efficient quasi-active power factor correction scheme

This paper presents a novel input current shaper based on a quasi-active power factor correction (PFC) scheme. The power factor is improved by adding two auxiliary windings coupled to the transformer of a cascade dc/dc flyback converter. The auxiliary windings are placed between the input rectifier and the low-frequency filter capacitor to serve as a magnetic switch to drive an input inductor. Since the dc/dc converter is operated at high switching frequency, the auxiliary windings produce a high frequency pulsating source such that the input current conduction angle is significantly lengthened and the input current harmonics is reduced. It eliminates the use of active switch and control circuit for PFC. The input inductor can be designed to operate in discontinuous current mode (DCM) with lower harmonic content or continuous conduction mode (CCM) with higher efficiency. However, a trade-off between efficiency and harmonic content must be made. Operating principles, analysis, simulation and practical results of the proposed method are presented.