Design and Implementation of carrier based Sinusoidal PWM Inverter

SPWM or sinusoidal pulse width modulation is widely used in power electronics to digitize the power so that a sequence of volt- age pulses can be generated by the on and off of the power switches. The pulse width modulation inverter has been the main choice in power electronic for decades, because of its circuit simplicity and rugged control scheme SPWM switching technique is commonly used in industrial applications SPWM techniques are characterized by constant amplitude pulses with different duty cycle for each period. The width of this pulses are modulated to obtain inverter output voltage control and to reduce its harmonic content. Sinusoidal pulse width modulation or SPWM is the mostly used method in motor control and inverter application. In this development a unipolar and bipolar SPWM voltage modu- lation type is selected because this method offers the advantage of effectively doubling the switching frequency of the inverter voltage, thus making the output filter smaller, cheaper and easier to implement. Conventionally, to generate this signal, triangle wave as a carrier signal is compared with the sinusoidal wave, whose frequency is the desired frequency. In this paper single-phase inverters and their operating princi- ples are analyzed in detail. The concept of Pulse Width Modulation (PWM) for inverters is described with analyses extended to different kinds of PWM strategies. Finally the simulation results for a single-phase inverter (unipolar) using the PWM strategies described are presented (1),(2),(3). Index Term—Modulation, Sinusoidal pulse width modulation, Unipolar, Bipolar I. INTRODUCTION The dc-ac converter, also known as the inverter, converts dc power to ac power at desired output voltage and frequency. The dc power input to the inverter is obtained from an existing power supply network or from a rotating alternator through a rectifier or a battery, fuel cell, photovoltaic array or magneto hydrodynamic generator. The filter capacitor across the input terminals of the inverter provides a constant dc link voltage. The inverter therefore is an adjustable-frequency voltage source. The configuration of ac to dc converter and dc to ac inverter is called a dc-link converter. (2) Inverters can be broadly classified into two types, voltage source and current source inverters. A voltage-fed inverter (VFI) or more generally a voltage-source inverter (VSI) is one in which the dc source has small or negligible impedance. The voltage at the input terminals is constant. A current-source inverter (CSI) is fed with adjustable current from the dc source of high impedance that is from a constant dc source (2). A voltage source inverter employing thyristor as switches, some type of forced commutation is required, while the VSIs made up of using GTOs, power transistors, power MOSFETs or IGBTs, self commutation with base or gate drive signals for their controlled turn-on and turn-off. A standard single-phase voltage or current source inverter can be in the half-bridge or full- bridge configuration. The single-phase units can be joined to have three-phase multiphase topologies. Some industrial applica- tions of inverters are for adjustable-speed ac drives, induction heating, standby aircraft power supplies, UPS (uninterruptible power supplies) for computers, HVDC transmission lines, etc (1),(8).