This paper compared coupled analysis results with the experimental results especially on the base speed. The base speed is important factor to design such a variable speed machine to detect the maximum output power. Although more accurate estimation is necessary on the base speed, it is difficult to estimate this behavior since this phenomenon is decided by a control dynamics by a current regulator and also by the output voltage which is affected by the dead time and on drop of the inverter. Some powerful software can analyze the coupled analysis which includes control logic, power electronics circuit and FEA. In this paper, the satisfied result can not be obtained by the usual coupled analysis is shown, and an analysis method which includes an iron loss effect to the output voltage is proposed and evaluated. By using this proposed method, not only the current waveform but also the voltage waveform which includes the voltage reference, are well matched to the experimental results.