<P> A proposal suggested in Power Electronics magazine utilizes two voltages as an improvement over the common commercialized technology, which can only apply DC bus voltage in either direction or turn it off . The proposal adds intermediate voltages to the common design . Each cycle sees the following sequence of delivered voltages: v1, v2, v1, 0, − v1, − v2, − v1 . </P> <P> Three - phase inverters are used for variable - frequency drive applications and for high power applications such as HVDC power transmission . A basic three - phase inverter consists of three single - phase inverter switches each connected to one of the three load terminals . For the most basic control scheme, the operation of the three switches is coordinated so that one switch operates at each 60 degree point of the fundamental output waveform . This creates a line - to - line output waveform that has six steps . The six - step waveform has a zero - voltage step between the positive and negative sections of the square - wave such that the harmonics that are multiples of three are eliminated as described above . When carrier - based PWM techniques are applied to six - step waveforms, the basic overall shape, or envelope, of the waveform is retained so that the 3rd harmonic and its multiples are cancelled . </P> <P> To construct inverters with higher power ratings, two six - step three - phase inverters can be connected in parallel for a higher current rating or in series for a higher voltage rating . In either case, the output waveforms are phase shifted to obtain a 12 - step waveform . If additional inverters are combined, an 18 - step inverter is obtained with three inverters etc . Although inverters are usually combined for the purpose of achieving increased voltage or current ratings, the quality of the waveform is improved as well . </P> <P> Compared to other household electric devices, inverters are large in size and volume . In 2014 Google together with IEEE started an open competition to build a (much) smaller power inverter, with a $1,000,000 prize . </P>

What is the meaning of mains on in inverter