Persoonallisuuspsykologian perusteita kotimaisittain

Kirjallisuusarvostelu

Kultajyviä ammentamaan! : praktikumiohjaajiksi hakeutuvien motiivit yliopiston ja koulun yhteistyön edellytysten luotaajina

Helsingin yliopiston opettajankoulutuksessa on vuodesta 2002 lähtien kehitetty yhteistyötä erilaisten kentän oppilaitosten kanssa luomalla nk. kenttäkouluverkosto.

Tiedonkulun infrastruktuuri ja nopeus 1800-luvulla

Kirjallisuusarvostelu

Thermal modelling of semiconductor switches in three-level Neutral Point Clamped Medium Voltage DTC-inverter

The aim of this thesis is to investigate the thermal loading of medium voltage three-level NPC inverter’s semiconductor IGCT switches in different operation points. The objective is to reach both a fairly accurate off-line simulation program and also so simple a simulation model that its implementation into an embedded system could be reasonable in practice and a real time use should become feasible. Active loading limitation of the inverter can be realized with a thermal model which is practical in a real time use. Determining of the component heating has been divided into two parts; defining of component losses and establishing the structure of a thermal network. Basics of both parts are clarified. The simulation environment is Matlab-Simulink. Two different models are constructed – a more accurate one and a simplified one. Potential simplifications are clarified with the help of the first one. Simplifications are included in the latter model and the functionalities of both models are compared. When increasing the calculation time step a decreased number of considered components and time constants of the thermal network can be used in the simplified model. Heating of a switching component is dependent on its topological position and inverter’s operation point. The output frequency of the converter defines mainly which one of the switching components is – because of its losses and heating – the performance limiting component of the converter. Comparison of results given by different thermal models demonstrates that with larger time steps, describing of fast occurring switching losses becomes difficult. Generally articles and papers dealing with this subject are written for two-level inverters. Also inverters which apply direct torque control (DTC) are investigated rarely from the heating point of view. Hence, this thesis completes the former material.

Lennokkaasti lottien uskonnollisuudesta

Kirjallisuusarvostelu

Kristillisen naistyön 110 vuoden historia

Kirjallisuusarvostelu

Työelämän tutkimus- ja kehitystyö kohtaa arvioinnin - yhteiseksi hyödyksi : esipuhe

Arvioinnin teemanumero 2008.