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.

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.

Electrical Interview Questions and Answers,

Electrical interview question:why, when birds sit on transmission lines or current wires doesn't get shock?
Answer:Its true that if birds touch the single one line (phase or neutral) they don't get electrical shock... if birds touch 2 lines than the circuit is closed and they get electrical shock.. so if a human touch single one line(phase) then he doesn't get shock if he is in the air (not touching - standing on the ground if he is standing on the ground then touching the line (phase) he will get a shock because the ground on what we standing is like line (ground bed - like neutral)। and in the most of electric lines the neutral is grounded..so that means that human who touch the line closes the circuit between phase and neutral.

Electrical interview question:what is meant by armature reaction?

Answer:The effect of armature flu to main flux is called armature reaction. The armature flux may support main flux or opposes main flux.

Electrical interview question:what happen if we give 220 volts dc supply to d bulb r tube light?

Answer:Bulbs [devices] for AC are designed to operate such that it offers high impedance to AC supply. Normally they have low resistance. When DC supply is applied, due to low resistance, the current through lamp would be so high that it may damage the bulb element.

Electrical interview question:Which motor has high Starting Torque and Staring current DC motor, Induction motor or Synchronous motor?

Answer:DC Series motor has high starting torque. We can not start the Induction motor and Synchronous motors on load, but can not start the DC series motor without load.

Electrical interview question:what is ACSR cable and where we use it?

Answer:ACSR means Aluminium conductor steel reinforced, this conductor is used in transmission & distribution.

Electrical interview question:What is vaccum currcuit breaker.define with cause and where be use it Device?

Answer:A breaker is normally used to break a ciruit. while breaking the circuit, the contact terminals will be separated. At the time of seperation an air gap is formed in between the terminals. Due to existing current flow the air in the gap is ionised and results in the arc. various mediums are used to quench this arc in respective CB's. but in VCB the medium is vaccum gas. since the air in the CB is having vaccum pressure the arc formation is interrupted. VCB's can be used upto 11kv.

Distributed Control System (DCS) in Power Plant

Usage of Single Computer for control of all the process variables of plant would result in the loss of control action in the plant if failure occurs to the master single computer. Also, time required for accessing large data, processing the received data and controlling of the entire plant by single computer will takes more time and slows down the process system

Distributed Control System:

In distributed control system, different process systems in the plant will have their control system loop. Thus in distributed control system number of individual control loops will be present. Several Microprocessors were employed at the different locations of the power plant and dedicated to provide services for individual process system of the plant and monitor and control each process of the plant (This is unlike SCADA master-slave architecture, in DCS all microprocessors will be masters). Every processor at different locations of the plant acquire the data from its process system, process the received data and provides control functions and also stores the required data. These microprocessors are connected to each other and also connected to the station master computer through which operator can see the information and take control actions if necessary. Control system in power plant will have distribution in both topologically and functionally. Functional distribution such as operation of boiler side values, fans, turbine values, boiler oil firing, boiler coal firing for carrying out such different functions Microprocessors are distributed.

Topological distibutuion is achieved by employing closed loops for operation of different equipment such as boiler steam A equipment, boiler steam B equipment, boiler oil firing AB/CD/EF elevations will have dedicated control loop

This type of distribution results in increase in speed and reliability of the control system.

Electronic Number Lock

A lock is an integral part of every house. A man can have peace of mind only when he has a proper mechanism to lock his house when he is away. At present mechanical locks are being used. These locks have levers in them that are used to lock or unlock the unit. Keys that have a particular pattern of cuts and notches on them control these levers. Each lock opens only if the pattern of cuts and notches inside it match with the pattern on the key.The main disadvantage of this mechanism is that one cannot open the lock if one has lost or misplaced the key. The house owner will be stranded outside his house if he loses the keys to his front door. This conventional lock-and-key mechanism poses a lot of security problems too. Any number of duplicate keys can be easily made from the original key. These duplicate keys may be used for unauthorized access without the knowledge of the owner. Burglars may find the right key to open the lock by trying different keys one after the other from a bunch of keys. An expert thief doesn't even need a proper key to open a lock. He can merely do it with a hairpin. If everything else fails, the thief can physically break open the lock.

UPS Monitoring System

Whenever the power fails, usually the UPS starts making a beep sound. This is the usual method employed in almost all the UPS to make us aware that there is no power from supply mains.But this is not an efficient method, for instance if we are too much concentrated in a subject we may not listen to the beep. Again, the beeping sound mechanism can be fatal if we are doing a very important job and the buzzer, which makes the beeping sound, fails.
Yet another important application of this project is in the case of networked systems in which a very large number of systems are connected to a single high capacity UPS .In such cases the different systems may be kept at a large distance apart or even kept at different rooms. In these cases the beep sounding mechanism is not at all sufficient because all the users may not hear the sound. The two important points which illustrates the seriousness of the above mentioned situations are:
1)The valuable data that we are manipulating may be lost forever.

Door Access Control System

The need for advanced security in Banks, Hospitals, Business centers and other High security buildings has grown increasingly more challenging and demanding during the last few years posing many unanswered questions before the lawmakers and officials. Many new types of Security threats are more immediate than before, increasing the risk of a serious security breach and exposing the security systems to risk of dangerous liability problems .Based on the problems and challenges in the field of security, Amrita Research Labs started research work to provide a complete solution to overcome all the security threats by designing an access control system.Access Control Systems provide the ability to monitor and restrict movement of people during and after working hours .Unrestricted access into various areas within the facility enhances the risk of a potential breach, which could result in loss of property or data, injury to the personnel, arson or sabotage. Access Control Systems must be implemented in multiple levels starting from the main entrance to the facility .The System should ideally get enhanced to include critical areas within the premises .The level of security achieved would depend on the technology and on the design of the system.

Automatic Power Management SystemAutomatic Power Management System

The need and vitality of power management systems in large industries, where electrical connections will be on a contract basis, has become a matter of prime importance, mainly because of the electricity billing system, where they have to pay a particular amount for a predefined usage quantity. In the electricity billing system, the reading at a particular instant shows the amount of power usage in the entire firm at that instant. If in some instant, the total usage goes above the contract quantity, the industry will have to pay a huge amount for the additional usage. Hence they have to prevent such extra usage. But if the wattmeter reading is within the predefined value, the industry needs to pay only the specified amount. No additional charge is taken from them. Thus power has become one of the major crisis of the modern world. Automatic Power Management System limits this major crisis of power in the modern world to a certain extent by the efficient use of power & eliminating power wastage. In this system, the unnecessary power usages by the low priority devices is cut down and thereby reduce the electricity bills. The electricity bill will be limited to the predefined usage charge only. No huge additional amount is to be paid when using automatic power management system.This is a very simple and efficient means by which the electricity bills in the industries can be limited.

PWM Control Of DC Series Motor In Electric Vehicle

Nowadays it is common to see motion controls in large number of industrial and domestic applications, such as traction, rolling mills, paper machines, textile mills, fan, pumps, robots, etc. Systems employed for motion control are called as drives. These drives are used to produce translational, rotational or both. The drives employing electric motors are known as electric drives. For traction purpose an electric motor is used to drive the vehicle. They are of two types, ac and dc drives.Electric drives are widely used because they have flexible control characteristics. They are available in wide range of torque, speed and power. They do not pollute the environment. Drives can be provided with automatic fault detection system to control the drive operation in a desired sequence. The main objective of this project is to design a DC drive for driving an electric vehicle. For this we had to select a DC motor, battery, speed regulating circuit. Pre hand of this we had to design a mechanical model that resembles a car. The design is of primary importance. The rating of all the project components depends on this model. Hence this model can be developed into a commercial vehicle if the rating of motor, battery and controller is so designed to satisfy the requirements of the vehicle in need.

Personal Entertainment Network Systems (PENS)

Television has become a necessity more than a luxury. Watching TV has become a hobby and amusement. But it some times happens that two of our favourite programs may coincide with their timings. It is also not possible to record another channel in our VCP/R while watching one in our TV. This project PERSONAL ENTERTAINMENT NETWORK SYSTEMS (PENS) briefed here provides a solution to this problem and also provides some special features. Using this device we can record a channel while watching another one. We can also set the device to enable the recording of a particular channel on a particular time in advance. This feature makes us record our favorites program even when out of station. And the most exciting feature of this device is that we can also perform all these functions through a telephone.The PENS is connected between the TV and the VCP/R and also to the telephone line thus forming a network of personal systems. Thus comes the name PENS. The keypad provided in the product helps us to type the code for settings same as that using an ordinary telephone that will be in accordance with the conventional DOT standards.

Micro Controller based Security System using Sonar

The problem facing many institutions like museums and banks is that of security round the clock. Security guards are expensive and burglars have learned to evade conventional security devices like infrared beams, thermal sensors etc. The use of SONAR in a security system, as used in our project, is a novel idea, and as far as we could determine, extremely difficult, if not impossible, to evade. The infrared beams have the disadvantages of covering just a limited area in a room
and to cover a whole room requires many of these beams. This makes this technology very expensive. It is also by no means foolproof and can be evaded by experts as has been so ably demonstrated in so many Hollywood films. Temperature sensors can also be evaded as they can either be made extremely sensitive and risk false tripping of the alarm due to changes in ambient temperature or made less sensitive at the risk of allowing evasion. The use of SONAR offers us many advantages. It is nearly foolproof, albeit it be at the expense of being extremely sensitive to the point that the only way to avoid tripping of the alarm is to make sure that the room it is covering is free from any movements. In this project we have designed and developed a unique security system that utilises the capabilities of microcontroller and a special purpose SONAR
module. It is also extremely cost-effective when compared to similar systems currently in use.

Smart Fan: A Human Tracking Fan System

The two PIR sensors are separated in the middle. The purpose of this is to separate the sensors’ field of view.

When a sensor detects the right amount of infra-red light a comparator output goes high. We use the microcontroller to generate an interrupt on the comparator’s rising edge. The interrupt then signals a task that begins rotating the platform’s motor. The rotation is clockwise if the left sensor has detected a person or counter clockwise if the right sensor has detected a person. Once the fan is directed at the person’s location, there is just enough infra-red light in the second sensor’s field of view to trigger its comparator. This generates an interrupt that signals a task to either stop or redirect the motor, depending on the setting. At this point the customer is nice and cool without exerting any effort.

An example of the fan’s operation is illustrated in the block diagram below.