Dipten Maiti

A Soft-Switched Flyback converter with recovery of stored energy in leakage inductance

This paper presents a 500W Soft Switched Flyback converter operating in discontinuous mode. The detailed circuit description, operation, characteristics, circuit equations and simulation results of the Active Clamp Flyback converter are presented here. The clamp capacitor absorbs leakage and a part of magnetizing energy stored in the primary winding of the Flyback transformer. Therefore the leakage voltage spike is reduced to a desired value. The dumped energy in the clamp capacitor is then transferred totally to the source by a LC resonating circuit. For main switch ZVS is achieved at turn OFF and ZCS is achieved at turn ON, as it is operated in discontinuous mode. ZCS is also achieved for the auxiliary switch both at turn ON and OFF. Thus switching loss is reduced and a part of the magnetically stored energy of the transformer, which is absorbed by the clamp capacitor, is sent back to the source, resulting in the efficiency of the converter being increase greatly. Thus, a Soft Switched high power rated Flyback Converter with good efficiency can be designed.

Efficiency and Cost Optimized Design of an Induction Motor Using Genetic Algorithm

In the context of electricity shortage and an attempt to save the environment, introduction of energy efficient motors in different fields of application has become a necessity. This paves the way for fusing the conventional machine design procedures with optimization techniques. Unfortunately, the mathematics of electrical machine design involves calculations with highly nonlinear equation sets, and hence the conventional analytical optimization techniques do not fit well. In this study, design of an efficiency-optimized squirrel cage induction motor is considered, where genetic algorithm is chosen as the tool for optimization. The various constraints considered are selected on the basis of material, mechanical, and performance considerations as approved by standards and practices. The influence of change of materials and change of upper limit of customers budget on different key motor design performance indicators are studied with and without cost constraints. Also, a systematic and statistics-based approach is proposed to achieve an optimized motor design, even at very low cost, provided relaxation of some constraints is allowed by the specific application. The optimized results are validated through tests on laboratory prototypes.

Studies on boost topologies for high boost ratio

Various problems come to the fore, in order to achieve high voltage boost using the basic form of non-isolated boost converter. A number of topological improvements have been suggested by researchers to achieve higher voltage boost ratio with their inherent pros and cons. This paper presents an overall study of four such converters including the boost converter, covering their basics of operation, comparison of various aspects, simulations and implementation details of the suitable one.

Optimization of a bi-directional hybrid current-fed-voltage-fed converter link

Bi-directional DC-DC converters facilitate controlled flow of energy in both directions. They are useful in battery charging/discharging, UPS, grid-connected renewable energy storage etc. Considerable amount of ongoing research deals with various improvements of these types of converters. This paper presents the optimized design methodology of an isolated bi-directional hybrid full-bridge converter.

A simple input current wave-shaping technique for three-phase diode and SCR converters

ABSTRACT Three-phase converters using diode or silicon-controlled rectifier (SCR) are widely employed to convert the commercial AC supply to DC. Such converters inject harmonics into the power supply system and thereby distort supply system voltage waveform. A simple input current wave-shape improvement technique using a shunt-connected harmonic current compensator is presented in this work, intended to reduce the total harmonic distortion (THD) of input current of three-phase diode and SCR phase-controlled rectifiers operating with inductive loads, by matching them to the specific converter as a combined package. The compensator proposed here comprises of a three-limb voltage source converter using insulated-gate bipolar transistor, working on instantaneous current and voltage measurements of the compensator only and not of the load. The technique uses a simple feedforward control for AC source current harmonic compensation of rectifiers without monitoring the AC line currents, i.e. use of online computation. The proposed system is simulated and tested on a laboratory prototype. The measured input current THD values without additional line filters are found to be below 8.3%, which is within acceptable limits, proving that the new technique is capable of compensating predetermined current harmonics of diode or SCRs.

Dual Delta Bank TCR for Harmonic Reduction in Three-Phase Static Var Controllers

The conventional “Delta” connected thyristor-controlled reactor (TCR) bank used for static var compensation and other applications is proposed to be split into two identical “Delta” banks each having kvar capacity half of the total TCR capacity. The study presented shows that such combination of two identical “Delta” connected reactor banks, one with phase switching by thyristors and the other with line switching thyristor arrangement can effectively reduce the harmonic generation of the TCR. Since both the three-phase banks are connected in delta, the zero sequence triplen harmonics generated due to phase control of thyristors remain trapped inside the delta, thus reducing the harmonic injection into the power system. Further, some other major characteristic harmonics are also minimized in the TCR line current. Thus, the proposed TCR yields a low current THD which meets the requisite harmonics standards and it can therefore be used as an economic solution for reactive power control over a reasonable range in high power grid without using any external harmonic filter or special phase shifting transformer. This paper describes in detail the modeling, analysis, and performance assessment of the proposed scheme. Simulation results are furnished to evaluate the output characteristics of the scheme under varying operating conditions. Finally, experimental results are presented, which proves the theoretical proposition.

Harmonic Cancellation in a Three-Phase Thyristor Controlled Reactor Using Dual Banks

A three-phase three-wire thyristor controlled reactor (TCR) topology is presented comprising of two reactor banks, involving simultaneous firing angle control of both banks having maximum kVAr in the ratio of 60:40. The first reactor bank is “Δ” connected and has phase switching whereas the second reactor bank is either “Δ” or equivalent “Y” connected with line switching. Such an arrangement prevents the triplen harmonics from entering into the supply system and some major characteristic harmonics can also be eliminated from the TCR line current due to the selection of the ratings of the two reactor banks. Thus, without using any additional filters or phase shifting transformer, this scheme enables reactive power control with a low current total harmonic distortion (THD) over a reasonable range of control, meeting requisite harmonics standards. Simplicity in construction and operational requirements of the proposed topology makes it a viable and cost effective solution. Its modeling, analysis, and performance assessment are presented. Simulation and experimental results support the theoretical proposition.

A single-phase isolated Z-source inverter

Z-Source inverters can overcome some of the limitations, inherent in traditional Voltage Source and Current Source Inverters and can provide boosted outputs. Most of the literature on Z-source inverters deals with 3-phase or 1-phase bridge inverters. This paper proposes a Single-Phase Z-Source Push-Pull Inverter topology. This scheme has several advantages compared to basic Z-source full-bridge inverter. Simulation result of the converter is presented as the proof of the concept.

Simple soft-switched (ZCS) boost converter suitable for power factor correction

A ZCS boost converter using two auxiliary switches, for active power factor correction (APFC), is proposed in this paper. All the switching devices used in this converter are turned-on and turned-off at ZCS with minimum current stress. The boost rectifier diode is also operated under soft-switched condition. The boost switch and one of the auxiliary switches have a common drive and are turned on simultaneously. This simplifies the control circuit required to drive the devices. The simulated switching waveforms verify the soft-switching behavior of all the switching devices.

Control of an alternating wave generator for voltage wave-shape and frequency

The requirements of generating various low frequency voltage waveshapes are usually catered by using linear amplifiers, which results in low overall efficiency. High frequency voltage source inverters with low pass filter at the output are not suitable for these applications, as it is difficult to produce waveshapes containing high frequency components, and variation in frequency. A Boost Inverter containing two boost converters, working to produce voltage waveshape of required specification but with 180° phase shift can produce such waveforms. This paper presents the operation, analysis, complete design and simulation result of such an inverter.