A control method in a wireless power receiver that receives power wirelessly from a wireless power transmitter, the method comprising: receiving the power wirelessly from the wireless power transmitter; rectifying the wirelessly received power; modulating the rectified power by connecting or disconnecting a resistor or a capacitor of a modulator to the wireless power receiver; and monitoring a ripple in an output voltage of the rectified power; the method being characterized by further comprising detecting time-series voltage values of the rectified power in real time; calculating an absolute value of the ripple in said output voltage based on the difference between the time-series voltage values; comparing the absolute value of the ripple in said output voltage with a preset threshold; if the absolute value of the ripple in said output voltage of the rectified power is greater than or equal to the preset threshold, changing a value of one of the resistor and the capacitor while monitoring the absolute value of the ripple in said output voltage during the modulation of the rectified power in real time, wherein changing is performed until the absolute value of the ripple in said output voltage is suppressed below the preset threshold; and charging a battery based on a changed value of the rectified power which is changed according to the changed value of the one of the resistor and the capacitor. receiving the power wirelessly from the wireless power transmitter; rectifying the wirelessly received power; modulating the rectified power by connecting or disconnecting a resistor or a capacitor of a modulator to the wireless power receiver; and monitoring a ripple in an output voltage of the rectified power; the method being characterized by further comprising detecting time-series voltage values of the rectified power in real time; calculating an absolute value of the ripple in said output voltage based on the difference between the time-series voltage values; comparing the absolute value of the ripple in said output voltage with a preset threshold; if the absolute value of the ripple in said output voltage of the rectified power is greater than or equal to the preset threshold, changing a value of one of the resistor and the capacitor while monitoring the absolute value of the ripple in said output voltage during the modulation of the rectified power in real time, wherein changing is performed until the absolute value of the ripple in said output voltage is suppressed below the preset threshold; and charging a battery based on a changed value of the rectified power which is changed according to the changed value of the one of the resistor and the capacitor. calculating an absolute value of the ripple in said output voltage based on the difference between the time-series voltage values; comparing the absolute value of the ripple in said output voltage with a preset threshold; if the absolute value of the ripple in said output voltage of the rectified power is greater than or equal to the preset threshold, changing a value of one of the resistor and the capacitor while monitoring the absolute value of the ripple in said output voltage during the modulation of the rectified power in real time, wherein changing is performed until the absolute value of the ripple in said output voltage is suppressed below the preset threshold; and charging a battery based on a changed value of the rectified power which is changed according to the changed value of the one of the resistor and the capacitor.