<P> A phase converter is a device that converts electric power provided as single phase to multiple phase or vice versa . The majority of phase converters are used to produce three - phase electric power from a single - phase source, thus allowing the operation of three - phase equipment at a site that only has single - phase electrical service . Phase converters are used where three - phase service is not available from the utility, or is too costly to install due to a remote location . A utility will generally charge a higher fee for a three - phase service because of the extra equipment for transformers and metering and the extra transmission wire . </P> <P> Three - phase induction motors may operate adequately on an unbalanced supply if not heavily loaded . This allows various imperfect techniques to be used . A single - phase motor can drive a three - phase generator, which will produce a high - quality three - phase source but with high cost for apparatus . Several methods exist to run three - phase motors from a single - phase supply, these can in general be classified as: </P> <Ul> <Li> Electronic means of creating three phases where the incoming power is rectified, and the three - phase power is synthesized with electronics . Power electronic devices directly produce a three - phase waveform from single - phase power, using a rectifier and inverter combination . This also offers the advantage of variable frequency . </Li> <Li> A digital phase converter uses a rectifier and inverter to create a single voltage with power electronics, which is added to the two legs of the single - phase source to create three - phase power . Unlike a phase - converting VFD, it cannot vary the frequency and motor speed, since it generates only one leg, which must match the voltage and frequency of the single - phase supply . It does have the advantage of a sine - wave output voltage and excellent voltage balance between the phases . </Li> <Li> Rotary phase converters constructed from a three - phase electric motor or generator "idler". These normally require some kind of starting aid and capacitors to improve phase balance and power factor . This is a two - motor solution . One motor is not connected to a load and produces the three - phase power, the second motor driving the load runs on the power produced . </Li> <Li> Static conversion techniques in which the motor is run at less than full efficiency mainly on two of the legs of the three - phase motor . Current is sometimes injected into the third leg with a capacitor or transformer arrangements that provide imperfect phase shift . In these systems the motor must be derated . </Li> <Li> Methods in which the connection of the windings of the motor, normally a wye or delta configurations, are replaced with novel connections . These techniques are covered in patents of Dr. Otto J.M. Smith, such as US Patent 5,545,965 . </Li> </Ul>

Single phase ac to 3 phase ac conversion