A measurement system for determining inductor losses in inverters in the MHz range

Inhalt:
Inductors in resonant inverters are exposed to high currents and frequencies. As a consequence, the high losses occurring in these components are usually the most significant loss factor for the entire circuit and thus limit the efficiency and size of the power electronic system. Little attention is given to this fact in many publications on inverters in the MHz range due to the wide use of air-core coils. However, these lead to relatively large sizes and thus to problems of electromagnetic compatibility. To optimize an HF inverter with respect to size and losses, therefore, it is necessary to measure the losses of a specific coil design based on a suitable core material. However, standard measurement methods have the drawback of either being very complex or measuring the losses only with a small excitation. But to determine the losses that occur in practice requires a measurement system that can be used both at high core frequencies and excitations. Such a measurement is needed particularly if the core manufacturer provides insufficient or no material data in the relevant frequency and excitation range. This paper therefore describes a simple measurement method for determining the losses in an inductor on the basis of a damped oscillation that can be used up to frequencies in the MHz range and for excitations of several amperes. Experimental results are given and compared with analytical loss calculations based on manufacturer data.