Analys av verkningsgrad för en industriell DC-DC omvandlare
Examensarbete för kandidatexamen
This thesis is performed in collaboration with Kraftpowercon AB in Surte, Sweden. Focus has been on to identify the powerlosses in one of Kraftpowercons halfbridge DC-DC converters. First theoretical calculations are made, the calculations is verified with measurements of six different operation modes. In a later stage, methods like soft switching and synchronous rectifying are proposed to increase the efficiency for the converter. To achieve softswitching for the halfbridge, the LLC resonant converter topologies are implemented and examined. The report includes choice of components for the suggested modifications. Results of measurements show that approximately 40-45 % of total losses occur in the IGBT, most of this being switching losses. Furthermore 35-40 % being diode losses in the secondary stage. The LLC topology would ideally reduce switching losses 74 %, but only when the converter is used for specific operation modes. When this is not the case for the examined halfbridge converter, LLC topology provides no increase in efficiency. The synchronous rectifying solution is easily achieved, just replacing the diodes with MOSFETs. In an ideal case not taking into account the control system, synchronous rectifying could increase the efficiency to up to 91,6 %.
Elkraftteknik , Electric power engineering