A new control scheme for a single ? phase diode clamped rectifier is proposed to achieve a unity power factor, balanced neutral point voltage and constant DC-bus voltage. Four power switches are used in the rectifier to generate a three-level PWM wave form on the rectifier terminal voltage.
The line current command is derived from a DC-link voltage regulator and an output power estimator. The hysteresis current Controller is used to track the line current command. To balance the neutral-point voltage, a capacitor voltage compensator is employed. The main advantages of using a three-level instead of a two-level PWM scheme are that the blocking voltage of each power switch is clamped to half the DC-bus voltage (if the off ?state resistance of power switches is equal),and the voltage harmonic on the AC side of rectifier is reduced.
A novel single phase neutral point diode clamped rectifier has been proposed to achieve high power factor, low current distortion, low peak factor, and stable capacitor voltages. The proposed rectifier can be controlled to operate in two- or-three ? level PWM.
Based on the model analysis, the switching signals of the power switches can be derived from the measured line current error and the mains voltage. Experimental results show a good line current waveform with almost unity power factor and low current harmonics to meet the requirements of IEC 1000-3-2 class A. The transient response due to load change is about one cycle and voltage drop is about 5V. According to measured results the proposed rectifier has the properties of high power factor, low current distortion and fast dynamic response, based on the proposed control algorithm.
what is the advantages,dis advantages,limitations and its applications.
more brief ideas and related concepts.
AUTOMATIC SOLAR TRACKER
Concept : We all are familiar with the Newton's corpuscular theory of light, that light is made up of small particles called “corpuscles” which travel in straight line with a finite velocity and energy.
SOLAR ENERGY :
It is the major Eco-friendly & Pollution less method of producing the electricity today.
Acc. to- U.S. solar research center: “ If we convert the Total Solar energy reaches to earth in one time into ELECTRICITY, then it will be more enough than whole power used by all the nations per year. “
Solar Panel :
It is a large component made up of the no of photovoltaic cells connected internally with each other. Used to grab the sunlight and to convert it into the ELECTRICITY.
What is a solar tracker ?
A Solar tracker is a device used for orienting a solar photovoltaic panel or lens towards the sun by using the solar or light sensors connected with the machine ( ex: stepper motor, servo motor, gas filled piston ).
Hence, The sun tracking systems can collect more energy than what a fixed panel system collects.
NEED OF SOLAR TRACKER
Commercial purpose :
• Increase Solar Panel Output
• max.efficency of the panel
• Maximize Power per unit Area
• Able to grab the energy through out the day .
Types of Solar Trackers
The sun's position in the sky varies both with the seasons (elevation) and time of day as the sun moves across the sky.
• Hence there are also two types of SOLAR TRACKER :
Single Axis Solar Tracker.
Dual Axis Solar Tracker.
• 1. Single Axis Solar Tracker
Single axis solar trackers can either have a horizontal or a vertical axle. The
horizontal type is used in tropical regions where the sun gets very high at noon, but
the days are short. The vertical type is used in high latitudes (such as in UK) where
the sun does not get very high, but summer days can be very long.
2. Dual Axis Trackers
Double axis solar trackers have both a horizontal and a vertical axle and so can track the Sun's apparent motion exactly anywhere in the world
This type of system is used to control astronomical telescopes, and so there is plenty of software available to automatically predict and track the motion of the sun across the sky.
Dual axis trackers track the sun both East to West and North to South for added power output (approx 40% gain) and convenience.
• Dual axis Solar tracker fig :
• Overview of Present Tracker Drive Types
Solar tracker Drives, can be divided into three main types depending on the type of drive and sensing or positioning system that they incorporate.
• 1. Passive trackers : use the sun’s radiation to heat gases that move the tracker across the sky.
• 2. Active trackers : use electric or hydraulic drives and some type of gearing or actuator to move the tracker.
• 3. Open loop trackers : use no sensing but instead determine the position of the sun through pre recorded data for a particular site.
1. Passive ( Gas ) Trackers
Passive trackers use a compressed gas fluid in two canisters each place in west & east of the tracker. The mechanism is in such a way that if one side cylinder is heated other side piston rises causing the panel to tilt over the sunny side.
This affects the balance of the tracker and caused it to tilt. This system is very reliable and needs little maintenance.
They are cheaper & effectively increase the efficiency of the solar panel.
gas tracker will very rarely point the solar panels directly to the sun, due to the temperature varies from day to day and Overcast days are also a problem can damage the panel.
when the sun appears and disappears behind clouds, causing the gas in the liquid in cylinders to expand and contract resulting in erratic movement of the device, often causes DAMAGE.
2. Active Trackers
Active trackers : measure the light intensity from the sun by using “ light sensors “ to determine where the solar modules should be pointing.
Light sensors are positioned on the tracker at various locations in specially shaped holders.
If the sun is not facing the tracker directly there will be a difference in light intensity on one light sensor compared to another and this causes to determine in which direction the tracker has to tilt with the help of the stepper or dc motor in order to be facing the sun. DRAWBACKS: On overcast days it will be not so working properly due to clouds.
3. Open Loop Solar Trackers
• DEFINATION : Open loop trackers determine the position of the sun using computer controlled algorithms or simple timing systems.
1. Timed Trackers-
A timer is used to move the tracker across the sky. Incremental movement throughout the day keeps the solar panel pointing the sun.
Advantages: can be utilize as one or two axes panels.
Disadvantage: Does not take into account the seasonal variation in sun position.
2. Altitude / Azimuth Trackers-
It uses the astronomical data or sun position algorithms to determine the position of sun for any given time and location by using micro controller.
Once the position has been calculated, the modules are moved using servo motors and there
position measured by encoders built into the tracker frame.
Energy is the primary and most universal measure of all kinds of work by human beings and nature. Primarily, it is the gift of the nature to the mankind in various forms. The consumption of the energy is directly proportional to the progress of the mankind. With ever growing population, improvement in the living standard of the humanity, industrialization of the developing countries, the global demand for energy increases day by day.
The primary source of energy is fossil fuel, however the finiteness of fossil fuel resources and large scale environmental degradation caused by their widespread use, particularly global warming, urban air pollution and acid rain, strongly suggests that harnessing of non-conventional, renewal and environmental friendly
As the sources of conventional energy deplete day by day, resorting to alternative sources of energy like solar and wind energy has become need of the hour.
Solar powered lighting systems are already available in rural as well as urban areas. These include solar lanterns, solar home lightning system, solar street lights, solar garden lights and solar power packs. All of them consist of four components; solar photovoltaic module, rechargeable battery, solar charge controller and load.
In the solar powered lightning systems, the solar charge controller plays an important role as the system’s overall success depends mainly on it. It is considered as an indispensible link between the solar panel, battery and load.
BLOCK DIAGRAM DESCRIPTION
It is the major part of the system. The microcontroller controls all the operations. The solar panel is aligned according to the intensity of sunlight under the control of the microcontroller.
The system consists of two sensors, each composed of LDR. One unit is made up of four LDRs. These are placed at the four corners of the solar panel. The intensity of sunlight is sensed by the LDR and the output is sent to the controller. The control unit analyzes it and decides the direction in which the panel has to be rotated, so that it gets maximum intensity of light.
The other unit of sensor is also composed of LDRs which is meant for the control of a lighting load.
Servo motor is used to rotate the panel in desired direction. It is controlled by the controller.
Solar panel is used for the conversion of solar energy directly into electricity. It is composed of photo voltaic cells, which convert solar energy into electrical energy.
It is meant to control the charging of battery. It sends the status of battery to the microcontroller unit.
It is for the storage of energy received from the panel. A rechargeable battery is normally employed for this purpose.
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