A simple and efficient method for the estimation of iron loss under any nonsinusoidal voltage without multiple zero crossings (i.e. without minor hysteresis loops) is proposed, This method is based on the loss separation model, where iron loss is decomposed into hysteresis, classical and excess toss components. The voltage waveform is identified by the form factor coefficient, easily accessible. Knowledge of the voltage harmonic spectrum is not required in this method. The cases of rectangular pulse, PWM, and fundamental plus a controlled third harmonic voltages are treated and a satisfactory prediction of iron loss is obtained.