Results from the magnetization of an 80？kVA power transformer, using a directly coupled nonfiltered three-phase voltage-source inverter (VSI), are presented. The major benefits of this topology are reduction in switching filter size as well as filter losses. Drawbacks include higher stress on the transformer windings and higher transformer magnetization losses. In this paper, the total magnetization losses are presented for different voltage levels. The transformer has been magnetized with the rated frequency of 50？Hz at various voltage levels. The saturation characteristics as well as the magnetizing resistance are derived as functions of the voltage. These are used as inputs for the simulations. The magnetization losses have been experimentally measured and simulated for three different DC levels. Results from the simulations show good agreement with the experimental results. As expected, the pulsed voltage waveforms generate larger magnetization losses than the corresponding 50？Hz case. The losses are strongly dependent on the DC level. 1. Introduction Many grid connected voltage source inverters (VSIs) have an associated LCL filter to eliminate the switching frequencies from the output [1–3]. If a step-up transformer is placed after the filter, its leakage inductance can reduce the size of the second inductor leg or completely replace it [4]. Alternatively, the transformer can be put directly after the inverter, with the LCL filter on the transformer secondary side. This will reduce the ampacity of the filter inductors, reducing both size and losses in the filter. The drawback of this is an increased voltage transient stress on the transformer windings that has to be taken into account in the transformer design. However, the total efficiency of the system may be improved, and this topology could be considered for grid connection of renewable energy sources. Stray capacitance between windings, which normally is neglected at steady state, may play a more central role. Semiconductor switching into magnetic components is not unusual in power electronics, for example, the flyback converter. However, these circuits are based on ferrite cores, optimized for the switching frequencies in the system. Little research is found in the area of continuous pulse modulation into laminated steel-core transformers and its associated losses. This paper presents a VSI with bipolar sinusoidal pulse-width modulation (SPWM) directly connected to a three-phase power transformer and the measured total magnetization losses. To get a reference case, the transformer is
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