A 3-point PWM converter with less low order harmonics

It is well understood that pulse width modulation offers several advantages over other methods when used for the control of power (especially for the control of induction motors). The advantages being that a nearly sinusoidal voltage may be generated and applied to the load. Depending on the switching frequency, higher frequency harmonics are generated which may be filtered out (if desired) with a low rating filter. Single pulse width modulation is obtained by a single pulse bridge inverter with voltage levels of 0, +V, 0, -V volts (also called a 2-point inverter). Multiple pulse width modulation is obtained by a combination of two, single pulse width modulation inverter wave forms suitably shifted with each other using a transformer which results in a waveform of 0, +V, +2V, +V, 0, -V, -2V, -V, 0 volts. Further, in the proposed investigation, a single bridge inverter with a string of switching devices is suggested to be used thereby avoiding the use of transformer for combining the wave forms. Experimental verification is made to verify the satisfactory working of the 3-point inverter in the generation of the pulse width modulation waveform without using a transformer. Due to the absence of the transformer, the circuit suggested for the purpose is light and efficient.