Extending the performance limits of vector controlled AC drives

A range of industrial vector controlled inverter drives is now available for operation at power levels from 5 kW to 1 MW. The entire product range uses insulated gate bipolar transistors (IGBTs) as the power switch in a 3 phase voltage source bridge configuration. The drives provide full four quadrant operation through sinusoidal, line regenerative network bridges which are themselves identical IGBT based voltage source inverters. By adopting a fully controllable network bridge to manage the power flow to and from the DC link, the products achieve extremely low network harmonics and the feature of a fixed DC link voltage, the benefits of which are discussed further in this article. This paper considers two application examples to illustrate the performance levels that can be achieved with correctly specified vector controlled AC drives. The first example discusses the factors influencing high torque production below base speed and considers how motor and inverter characteristics can be tailored to optimise the overall system behaviour. The second example considers operation into the field weakening region. This is of particular interest for machine tool and coiler/un-coiler applications where wide constant horsepower characteristics are required