Laboratory of Power Electronics

Laboratory Head: Ing. Radko Semerád

under construction

Industrial drive with induction motor (IM) fed from high-voltage (hv) inverter

Various types of multilevel VSIs suitable for high-voltage applications have been analysed. In view of the demand of 10kV output ac voltage and only single supply voltage (Udc) in the dc link, the topology of a four-level inverter with flying capacitors has been chosen. In this topology, the ac voltage is being generated on the output of each phase using pulse width modulation (PMW) from four voltage levels: 0V, 1/3Udc, 2/3Udc and Udc. To make the inverter function properly, it was necessary to manage the so-called voltage balancing on VSI flying capacitors, i.e. to keep stable 1/3Udc and 2/3Udc voltages on these capacitors during operation. A multilevel space vector modulator (SVM) has been designed. Numerical models for a balancing unit, multilevel SVM modulator and for the four-level inverter have been created in Matlab/Simulink. The designed algorithms have been successfully verified by simulations and then implemented into the controller. Firstly, a special controller board with hardware support for the multilevel modulator and with the balancing unit and secondly, a system of voltage and current measurements in high voltage converters with data stream transfers via optical fibres have been designed and in cooperation with ČKD-E realized. A stator flux vector control (SFVC) has been modified for the control of hv IM fed from the four-level VSI, numerically simulated and subsequently implemented into the controller. The functionality of the designed algorithms and the control hardware have been verified at first in the Institute of Thermomechanics on a 2,2 kW model drive with a low voltage four-level converter with flying capacitors and then on a prototype of a hv converter INVERT 10kV in the ČKD-E test room. The results of experiments have proved the full operability of the designed power drive.
Cooperation: ČKD elektrotechnika, a.s. (ČKD-E)
Research team: Ing. P. Kokeš, Ing. R. Semerád

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