17-04-2012, 04:12 PM
BASIC CONCEPT OF PROPOSED SYSTEM
PROPOSED SYSTEM
The PWM fed speed control of Induction Motor using PC is discussed in detailed manner in this section. The block diagram consists of power supply circuit, Microcontroller, optocoupler, MAX232, Triac & LCD to display the output.
POWER SUPPLY
Power supply is a reference to a source of electrical power. A device or system that supplies electrical or other types of energy to an output load or group of loads is called a power supply unit or PSU. The term is most commonly applied to electrical energy supplies, less often to mechanical ones, and rarely to others.
STEP DOWN TRANSFORMER
A transformer is a static device by which electric power in one circuit is transformed into electric power of same frequency in another circuit. It can raise or lower the voltage in the circuit, but with a corresponding decrease or increase in current. It works on the principle of mutual induction in our project here we are using a step down transformer for providing a necessary supply to the electronic circuit (230-12V AC)
RECTIFIER UNIT
A DC level obtained from a sinusoidal input can be improved 100% using a process called full wave rectification. Here in our project for full wave rectification we use bridge rectifier. From the basic bridge configuration we see that two diodes (say D2 and D3) are conducting while the other two diodes (D1 and D4) are in off state during the period t=0 to T/2 accordingly for the negative cycle of the input the conducting diodes are D1 and D4. Thus the polarity across the load is the same.
FILTER
In order to obtain a DC voltage of 0 Hz, we have to use a low pass filter. So that a capacitive filter circuit is used where a capacitor is connected at the rectifier output and a DC is obtained across it. The filter wavelength is essentially a DC voltage with negligible ripples and it’s ultimately fed to the load.
REGULATORS
The output voltage from the capacitor is more filtered and finally regulated. The voltage regulator is a device, which maintains the output voltage constant irrespective of the change in supply variation, load variation and temperature changes. Here we use fix voltage regulator namely LM7805. The IC LM7805 is a+5V regulator which is used for the microcontroller.
DISADVANTAGES OF PWM
• Increase of switching losses due to high PWM frequency
• Reduction of available voltage
• EMI problems due to high-order harmonics