MOSFET BASED SINGLE PHASE INVERTER

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1. INTRODUCTION
1.1 GOAL
“To explain theme of the project”

• INVERTER
A device that converts DC power to AC power at desired output voltage and frequency is called an INVERTER. Some industrial applications of inverters are for adjustable speed ac drives, induction heating, stand by air craft power supplies, UPS (Uninterruptible power supplies) for computers, HVDC transmission lines etc. phase controlled converters , when operated in inverter mode, are called line commuted inverter. But line commuted inverters require at the output terminals an existing ac supply which is used for the commutation. This means that line-commuted inverters can’t function as isolated ac voltage sources or as variable frequency generators with dc power at the input. Therefore, voltage level, frequency and waveform on the ac side of line commuted inverters can not be changed. On the other hand, forced commutated inverters provide an independent ac output voltage of adjustable voltage and adjustable frequency and have therefore much wider applications.


BASIC INVERTER DESIGNS:
In one simple inverter circuit, DC power is connected to a transformer through the center tap of the primary winding. A switch is rapidly switched back and forth to allow current to flow back to the DC source following two alternate paths through one end of the primary winding and then the other. The alternation of the direction of current in the primary winding of the transformer produces alternating current (AC) in the secondary circuit.



MORE ADVANCED DESIGN:
In more advanced inverter designs various techniques are used to improve the quality of the sine wave at the transformer input, rather than relying on the transformer to smooth it. Capacitors and inductors (but not freewheel diode as it is AC) can be used to filter the waveform at the primary of the transformer. Also, it is possible to produce a more sinusoidal wave by having split-rail direct current inputs at two voltages, or positive and negative inputs with a central ground. By connecting the transformer input terminals in sequence between the positive rail and ground, the positive rail and the negative rail, the ground rail and the negative rail, then both to the ground rail, a stepped sinusoid is generated at the transformer input and the current drain on the direct current supply is less choppy. These methods result in an output that is called a "modified-sine wave". Modified-sine inverters may cause some loads, such as motors, to operate less efficiently.



• Winding resistance
Current flowing through the windings causes resistive heating of the conductors (I2 R loss). At higher frequencies, skin effect and proximity effect create additional winding resistance and losses.
• Eddy currents
Induced eddy currents circulate within the core, causing resistive heating. Silicon is added to the steel to help in controlling eddy currents. Adding silicon also has the advantage of stopping aging of the electrical steel that was a problem years ago.
• Hysteresis losses
Each time the magnetic field is reversed, a small amount of energy is lost to hysteresis within the magnetic core. The amount of hysteresis is a function of the particular core material.
• Magnetostriction
Magnetic flux in the core causes it to physically expand and contract slightly with the alternating magnetic field, an effect known as magnetostriction. This in turn causes losses due to frictional heating in susceptible ferromagnetic cores.
• Mechanical losses
In addition to magnetostriction, the alternating magnetic field causes fluctuating electromagnetic forces between the primary and secondary windings. These incite vibrations within nearby metalwork, creating a familiar humming or buzzing noise, and consuming a small amount of power.MF. In this way, the electrical energy fed into the primary winding.
• Stray losses
Not all the magnetic field produced by the primary is intercepted by the secondary. A portion of the leakage flux may induce eddy currents within nearby conductive objects, such as the transformer's support structure, and be converted to heat.