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Wednesday, 21 December 2011

ELIMINATION OF THE OUTPUT VOLTAGE IMBALANCE IN A HALF - BRIDGE BOOST RECTIFIER

The applications of ac–dc rectifiers are prerequisite nowadays in the power electronics industry. Due to tougher regulations on the input current harmonics, many topologies of the switch-mode boost-type power factor corrector (PFC) circuits have been presented in recent years. In this paper, a four-switch voltage-doubler boost rectifier is analyzed. A new control scheme is proposed to eliminate the output voltage imbalance when the load is unevenly distributed across the two output dc rails. Unipolar pulse width modulation switching patterns are adopted to slow down the discharging rate of the output capacitor with the lower voltage. No dc or out-of phase component is injected in the source current. Thus, the unity input power factor can be genuinely achieved. Two hysteresis comparators are employed in the presented controller. One is used for the source current to track its command. The other comparator is to confine the output voltage imbalance within a reasonable level. Modified averaged circuit models are adopted to derive the limits of the ratio of the dual loads for output voltage balance. Experimental results on prototype circuits confirm tightly with the theoretical analysis.

A HIGH-POWER-FACTOR SINGLE-STAGE SINGLE SWITCH ELECTRONIC BALLAST FOR COMPACT

A very high power factor electronic ballast that uses a single switch in the power circuit is proposed in this paper for compact fluorescent lamps (CFLs). The reason for the CFL’s increasing popularity is that it conserves energy, and subsequently, reduces energy cost when compared to traditional incandescent lamps. To minimize cost and to ensure that a compact electronic ballast circuit can be installed at the base of a CFL, commercial CFLs normally do not include a power factor correction (PFC) circuit in their electronic ballasts. This paper proposes new high-power-factor single-switch electronic ballast for CFL applications. The proposed power circuit is designed by integrating a SEPIC power factor corrector with a novel single-switch current-fed resonant inverter. The advantage of this single-switch electronic ballast is that it greatly simplifies the gate-drive circuit design due to the elimination of isolation devices that are otherwise required in the conventional half-bridge totem pole configuration. This topology features a reduction of at least two switches in the power stage compared to conventional two-stage approach for high-power-factor electronic ballasts. In addition, the proposed circuit is also able to achieve close-to-unity power factor by operating the integrated SEPIC power factor corrector in discontinuous conduction mode. The conduction loss of the switch in the proposed circuit is also significantly reduced compared to the conventional class-E single-switch resonant inverter. The proposed circuit has both lower peak current and voltage stress across the switch than that of the class-E resonant inverter. Operating principles and characteristics of the proposed circuit are provided in this paper.


A SINGLE STAGE HIGH POWER FACTOR AC/DC CONVERTER

Nowadays the ac/dc converters are widely used in many off-line power supplies. The increasing amount urges researchers to develop more efficient, smaller size, and low cost ac/dc converters. Traditionally, an ac/dc converter consists of a diode-bridge rectifier followed by a bulky capacitor and a high-frequency dc/dc converter. This kind of converter inevitably introduces highly distorted input current, resulting in a large amount of harmonics and a low power factor. paper proposes a single-stage high-power-factor ac/dc converter with symmetrical topology. The circuit topology is derived from the integration of two buck-boost power-factor-correction (PFC) converters and a full-bridge series-resonant dc/dc converter. Switch-utilization factor is improved by using two active switches to serve in the PFC circuits. A high power factor at the input line is assured by operating the buck-boost converters at discontinuous conduction mode. With symmetrical operation and elaborately designed circuit parameters, zero-voltage-switching on all the active power switches of the converter can be retained to achieve high circuit efficiency. The operation modes and design equations for the circuit parameters are proposed.

A NEW MPPT METHOD FOR LOW POWER SOLAR ENERGY HARVESTING

The solar cell V-I characteristic is nonlinear and varies with irradiation and temperature. In general, there is a unique point on the V-I or V-P curve, called the Maximum Power Point (MPP), at which the entire PV system (array, converter, etc…) operates with maximum efficiency and produces its maximum output power. The location of the MPP is not known, but can be located, either through calculation models or by search algorithms. Therefore Maximum Power Point Tracking (MPPT) techniques are needed to maintain the PV array’s operating point at its MPP.

Maximum Power Point Tracking, frequently referred to as MPPT, is an electronic system that operates the Photovoltaic (PV) modules in a manner that allows the modules to produce all the power they are capable of. MPPT is not a mechanical tracking system that “physically moves” the modules to make them point more directly at the sun. MPPT is a fully electronic system that varies the electrical operating point of the modules so that the modules are able to deliver maximum available power. Additional power harvested from the modules is then made available as increased battery charge current

A MODULE - INTEGRATED INVERTER FOR BUILDING INTEGRATED PHOTOVOLTAICS

The DC input from the PV module is fed to the buck inverter stage. A modulated high-frequency sine PWM issued for the buck MOSFET to generate the rectified sine output voltage/current across the buck output.

A modulated sine PWM generates modulated sine MOSFET current. The average of the sine modulated secondary diode current produces a rectified sine voltage/current across the output capacitor. An SCR full-bridge is used to unfold rectified output voltage/current to sinusoidal voltage/current. Therefore, the SCR is switched at line frequency.

The output of the inverter is synchronized with the grid by digital PLL. The MPPT controls the magnitude/ rms of the output current. The shape of the output current is controlled by current control loop. Sine modulated PWM operation of the buck MOSFETs transfers the packet of energy to the inverter output capacitor.

A MODULE - INTEGRATED INVERTER FOR BUILDING INTEGRATED PHOTOVOLTAICS

The DC input from the PV module is fed to the buck inverter stage. A modulated high-frequency sine PWM issued for the buck MOSFET to generate the rectified sine output voltage/current across the buck output.

A modulated sine PWM generates modulated sine MOSFET current. The average of the sine modulated secondary diode current produces a rectified sine voltage/current across the output capacitor. An SCR full-bridge is used to unfold rectified output voltage/current to sinusoidal voltage/current. Therefore, the SCR is switched at line frequency.

The output of the inverter is synchronized with the grid by digital PLL. The MPPT controls the magnitude/ rms of the output current. The shape of the output current is controlled by current control loop. Sine modulated PWM operation of the buck MOSFETs transfers the packet of energy to the inverter output capacitor.

Thursday, 8 December 2011

SMS Based Wireless Electronic Notice Board using GSM/CDMA/3G Mobile Phone

Notice Board is primary thing in any institution / organization or public utility places like bus stations, railway stations and parks. But sticking various notices day-to-day is a difficult process. A separate person is required to take care of this notices display. This project deals about an advanced hi-tech wireless notice board.
The project is built around the ATMEGA8L micro controller from Atmel. This micro controller provides all the functionality of the display and wireless control. It also takes care of creating different display effects for given text. Display is obtained on LED Matrix Display Array on a printed circuit board. A GSM/CDMA Mobile Can is used to enter the required text or notice. The scrolling speed of the text also can be changed according to user requirement.
After entering the text the SMS is sent to the no which is connected to the LED display. At any time the user can add or remove or alter the text according to his requirement. At the receiving end the GSM modem which is connected to the Max 232 receives the message and is connected to the microcontroller ATMEGA8L. The message which is already stored in the EEPROM is displayed on the LED Matrix Display Array.
This project uses regulated 5V, 500mA power supply. 7805 three terminal voltage regulator is used for voltage regulation. Bridge type full wave rectifier is used to rectify the ac output of secondary of 230/12V step down transformer.

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