• Thordur Ofeigsson
This project is focused on a low cost frequency converter equipped with diode rectifier and small DC link capacitor. The problems associated with this configuration are the high fluctuations introduced in the DC link voltage. Due to the small capacitor the diode rectifier harmonics are not rejected as the natural frequency of the DC link is above six times the grid side frequency. When this type of frequency converter is used to drive a squirrel cage induction motor the system is very sensitive to changes in speed. Quick changes in speed cause large overvoltages in the DC link voltage which in turn could trigger the overvoltage protection of the frequency converter. Therefore the dynamics of the system are very poor. The projects main goal is to analyse stability margins of the frequency converter and examine the influence of different parameters on the stability of the system. In order to analyse stability a mathematical model of the system has to be obtained. The model is then linearized to derive transfer functions that describe the influence of different inputs on the DC link voltage. The stability analysis can then be carried out using conventional control theory. The obtained stability margins are then evaluated with simulations in Matlab/Simulink. To fit with the topic of a low cost drive, a sensorless V/f control strategy is also designed and verified with simulations. The open loop V/f control and space vector modulation are then implemented on a DSP to examine the system behavior in practice. Experimental results were acquired and documented.
LanguageEnglish
Publication date2008
Publishing institutionInstitute of Energy technology
ID: 14427209