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Permanent-magnet synchronous motors (PMSMs) with a sinusoidal back electromotive force are widely used in domestic appliances for the reduction of acoustic noises and energy consumption. PMSMs are generally controlled with a sinusoidal waveform current. Typically, PMSMs are controlled by vector-controlled sinusoidal drives, which require powerful computational resources. Hence, simpler sinusoidal wave drives such as V/f drives, which control the phase difference between the voltage and the current (power factor of PM motor), have been proposed for controlling PMSMs. This paper presents a new method that does not require current sensors but can be used to estimate the phase difference by sampling the voltage of the shunt resistor, which is used to detect the overcurrent supplied to the inverter. This method enables the detection of current and accurate estimation and appropriate control of the phase difference. Using this method, we could control the phase difference and achieve high efficiency, cost reduction, and high reliability.