New applications of frequency converters such as solar energy have growing need to determine the efficiency of a converter with good precision. The component level losses are not easy to measure as the input and output of converter components are not sinusoidal. The calorimetric method gives an approach for measuring the losses directly rather than using the difference of the electrically measured quantities. This paper compares the feasibility of the described methods in an active rectifier input filter power loss measurement. The calorimetric method is superior in accuracy, but the measurement time is multiple compared to the electrical method. Electrical measurement instrument calibration by comparison with calorimetric method could have significant practical applications resulting in a combined system with high accuracy and short measurement duration.

Uncertainties in measurement due to varying environmental conditions make the benchmarking of frequency converter's intermediate circuit capacitors difficult. The effect of changes in supply network quality, especially the changes in harmonic distortion, to capacitor's temperature-rise is analyzed. The capacitor lifetime is as a function of its temperature and thus more precise measurements and knowledge of the dependencies will lead to a more cost-efficient and reliable design. According to the tests all studied supply network parameters and unidealities in temperature measurement affect clearly the results. All discussed properties must be known if a test is to be repeated under the same conditions. An unexpected finding in the tests was that high frequency supply voltage distortion decreases capacitor temperature and thus extends its lifetime.