The DC-AC inverters on the market today there are essentially twodifferent forms of AC output generated: modified sine wave, andpure sine wave1. A modified sine wave can be seen as more ofsquare wave than a sine wave; it passes the high DC voltage forspecified amounts of time so that the average power and rmsvoltage are the same as if it were a sine wave. These types ofinverters are much cheaper than pure sine wave inverters andtherefore are attractive alternatives.
Pure sine wave inverters, onthe other hand, produce a sine wave output identical to thepower coming out of an electrical outlet. These devices areable to run more sensitive devices that a modified sine wave maycause damage to such as: laser printers, laptop computers, powertools, digital clocks and medical equipment. This form of ACpower also reduces audible noise in devices such as fluorescentlights and runs inductive loads, like motors, faster and quieter dueto the low harmonic distortion.MethodologyThe construction of the pure sine wave inverter can be complexwhen thought of as a whole but when broken up into smallerprojects and divisions it becomes a much easier to manageproject.
The following sections detail each specific part of theproject as well as how each section is constructed and interactswith other blocks to result in the production of a 240 volt puresine wave power inverter.H-BRIDGE ; Driving four MOSFETs in an H-bridge configurationallows +270,270,or 0 volts across the load at any time. Toutilize PWM signals and this technology, the left and right sides ofthe bridge will be driven by different signals. The MOSFET driveron the left side of the bridge will receive a square wave at 50Hz,and the right side will receive the 50KHz PWM signal.
The 50Hzsquare wave will control the polarity of the output sine wave,while the PWM signal will control the amplitude. The MOSFETs tobe used in the design are the IRFB20N50KPbF Hexfet PowerMOSFET, rated for 500V at 20A with a Rds of .21ohm.43mm