Design of a low loss and cost-efficient choke for a general purpose frequency converter
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Kustannustehokkaan ja pienihäviöisen kuristimen suunnittelu yleiskäyttö taajuusmuuttajaan
Frequency converters are used to operate machines at speeds that are optimal for the process, thus allowing a high efficiency. Frequency converters help save energy but by doing so they also pollute the grid and cause disturbances. These disturbances can be seen in the grid current waveform as harmonic components. The most common way to mitigate harmonic current is to add inductance to the input of the converter by using a choke. In order to obtain a high efficiency for a choke, the design needs to be optimized. High efficiency needs to be obtained without increasing the size and cost of the choke. In DC and low frequency applications, most of the power losses occur in the windings of the inductor. Optimization process should be targeted to total wire DC-resistance. Small number of turns and large cross-sectional area are needed to achieve the goal. Different core shapes and winding methods can be used to achieve the best result. Several design constraint drive the design process. In high power applications high saturation current is usually needed. This means that laminated magnetic steel core is usually used due to the material’s high saturation flux density. Three different designs and prototypes are introduced in this thesis. All of the designs utilize different winding methods and core shapes. Matlab is used to optimize the designs and Maxwell is used for magnetic modelling. Inductance, resistance and thermal measurements are carried out on the new designs and reference chokes. Comparison is per-formed on properties and manufacturability of different solutions. Further development is suggested on the most promising designs.