Inverter Drives

Abstract

As described in Chapter 5 (Induction machine) and Chapter 6 (Synchronous machine) the speed and torque are controllable in the rotating field machines. To achieve this, a power electronic actuator (inverter) must convert the three-phase voltage system of the mains with fixed frequency and voltage either to a three-phase voltage system (inverter with impressed voltage) with variable amplitude and frequency of the voltages, or to a three-phase current system (inverter with impressed current) with variable three-phase amplitude and frequency of the currents. As mentioned above, an inverter with impressed voltage can be transformed to an inverter with impressed current by a current control loop. The inverters have a much more complex circuitry than those of line commutated inverters used for DC-machines. For this reason a wide range of solutions was used in the past.