| Abstract |
For inverters in the MW-range the switching frequency of each valve is limited to 100 - 300Hz. A very good control method if working with low switching-frequencies is Direct Self Control (DSC), developed 1984 by M. Depenbrock for voltage source inverter-fed induction motors. This control algorithm directly determines the switching states of the inverter and gives an optimal characteristic for stator flux and torque control. Compared to a conventional two-level inverter, smoother waveshapes of current, flux and torque are obtained by using a three-level GTO inverter. Direct Self Control modified for application with a three-level inverter also has to allow field-weakening which is necessary when stator-frequency is above rated stator frequency of the motor. This control scheme and practical results of its application, measured at a 20KW inverter-motor test-system, are discussed in this paper. |
