Quasi-sine wave and inverter

A power inverter device which produces a multiple step sinusoidal AC waveform is referred to as a sine wave inverter. To more clearly distinguish the inverters with outputs of much less distortion than the modified sine wave (three step) inverter designs, the manufacturers often use the phrase pure sine wave inverter.

The square wave, modified sine wave, and quasi-sine wave all have a number of harmonics, which, as you know, are sine waves with frequencies that are odd multiples of the fundamental frequency and different amplitudes. Harmonics are especially troublesome in some applications, so high-quality sine wave inverters are the most widely used type.

The waveform in commercially available modified-sine-wave invertersresembles a square wave but with a pause during the polarity reversal. Switching states are developed for positive, negative and zero voltages. Generally, the peak voltage to RMS voltage ratio does not maintain the same relationship as for a sine wave.

Almost all consumer grade inverters that are sold as a "pure sine wave inverter"do not produce a smooth sine wave output at all, just a less choppy output than the square wave (two step) and modified sine wave (three step) inverters. However, this is not critical for most electronics as they deal with the output quite well.

An inverter can produce asquare wave, modified sine wave, pulsed sine wave, pulse width modulated wave (PWM) or sine wave depending on circuit design. The two dominant commercialized waveform types of inverters as of 2007 are modified sine wave and sine wave.

The result is a reduced harmonic content that has less distortion than the modified sine wave. This waveform is sometimes referred to as a quasi-sine wave, although this term is also sometimes used to describe the two-level modified sine wave. Figure 6 Three-Level Modified Sine Wave Creating a Quasi–Sine Wave