Power factor control and soft-start of a grid connected induction machine using floating bridge inverter

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This Project will investigate technology that was the subject of a preliminary US patent application, submitted 14th January 2013, financially supported by TEC Edmonton and entitled "Grid-connected induction machine with controllable power factor". Motor driven systems consume 44%-46% of global electrical energy generation, with induction machines being the prime means for consuming electrical power in many industrial applications, such as pumps, compressors and fan loads. These machines draw more current than is needed for the loads that they supply. This excessive current is known as reactive current, hence reactive power, and monitored by the performance known as power factor: unity being ideal and less than unity and lagging being less than ideal. Induction machines are known to be a significant contributor of lagging power factor for any given power system. The idea of a grid-connected induction machine operating at unity power factor is considered very desirable, and even leading power factor is desired as such a machine would compensate for the lagging power factor of other machines connected to the grid. This would alleviate many problems experienced in industrial plants and improve the efficient transmission and distribution of electrical power. In the approach developed by the applicants, a commercial three-phase induction machine with a cage rotor has been operated at a leading power factor. Unlike previous attempts that use a means of current injection, a simple power electronic converter uses a voltage injection technique to enable phase shifting of the machine current relative to the grid. This voltage injection is achieved using low cost power electronics with fewer components when compared with other technologies presently being used. The new technology also alleviates a second significant technical problem associated with induction machines, reduced voltage starting to reduce starting currents and hence reduce voltage disturbances of the utility grid voltage. This dual function makes the technology more commercially viable. Preliminary experimental results have proven that the technology works as predicted and this program will take the next step in proving the commercial viability of the new technology.