23-06-2012, 04:14 PM
Photo Voltaic System Fed by AC load
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ABSTRACT
A model of combined Photovoltaic system with power factor correction technique is proposed in this project.The use of Photovoltaic system in our proposed system improves our focus towards the renewable energy. The block of a DC/DC converter served as voltage boosterA bidirectional inverter is applied is used to convert the DC to AC.The inverter can also be used as a charger to maintain the minimum required voltage level of the batteries when the PV power is insufficient. A continuity of power supply is maintained by two sources, ie PV cell and Battery.A parallel power factor circuit is arranged towards inverter to maintain the unity power factor.
The Negative Half-cycle
As the current flowing through the load is unidirectional, so the voltage developed across the load is also unidirectional the same as for the previous two diode full-wave rectifier, therefore the average DC voltage across the load is 0.637Vmax. However in reality, during each half cycle the current flows through two diodes instead of just one so the amplitude of the output voltage is two voltage drops ( 2 x 0.7 = 1.4V ) less than the input VMAX amplitude. The ripple frequency is now twice the supply frequency .
Solar energy system:
In general, the electric generating stations use all kind of fuel in order to produce the electric energy. this process pollutes the nature by smoking, for this reason scientific people study the using of the alternative energy (Renewable) in order to producing energy (such as solar, wind),this causes decreasing the pollution. The most common renewable energy using to produce electric energy is the solar energy because the sun may exist at each day.
Elements of the inverter:
The function of an inverter is to change a dc input voltage to asymmetrical Ac output voltage of desired magnitude and frequency. on the hand inverters are used in a wide range of applications, from small switching power supplies in computers, to large electric utility applications that transport bulk power. The inverter is so named because it performs the opposite function of a rectifier. a variable output voltage can be obtained by varying the input dc voltage and maintaining the gain of the inverter constant. On the other hand if the dc input voltage is fixed and it is not controllable, a variable output voltage can be obtained by varying the gain of the inverter, which is normally accomplished by pulse-width-modulation (PWM) control within the inverter .The inverter gain, may be defined as the ratio of the ac output voltage to dc input voltage. The output voltage waveforms of ideal inverters should be sinusoidal.
Dc Chopper
The Dc Chopper which is boost converter, also known as the step-up converter, this converter produces an output voltage greater than the source. The ideal boost converter has the five basic components, namely a power semiconductor switch, a diode, an inductor, a capacitor and a PWM controller. The basic circuit of the boost converter is shown in Fig. 1.9
main characteristics of the inverter:
Sinewave inverters
As explained earlier, most DC-AC inverters deliver a modified sine wave. output voltage, because they convert the incoming DC into AC by using MOSFET transistors as electronic switches. This gives very high conversion efficiency, but the alternating pulses. output waveform is also relatively rich in harmonics. Some appliances are less than happy with such a supply waveform, however. examples include light dimmers, variable speed drills, sewing machine speed controls and some laser printers. Because of this, inverter manufacturers do make a small number of models which are designed to deliver a pure sinewave output.