A method for controlling output power in a wireless power transfer WPT system including n coils, comprises: (a) providing a transmitting coil inductively coupled to a receiving coil; (b) providing an input current I 1 to the transmitting coil; (c) sensing an input voltage U 1 and the input current I 1 of the transmitter coil of the n coils; (d) identifying impedance related parameters in the WPT system, wherein the identifying comprises: (d.1) determining a set of measured input impedance based on the sensed input voltage U 1 and the sensed input current I 1,(d.2) measuring input impedances of the transmitting coil of the WPT system at different frequencies, wherein the set of measured input impedances includes an input impedance vector each input impedance in the vector ( Z k) measured at different frequencies f k, ( k = 1, 2, ··· m); (d.3) expressing the measured input impedances at the different frequencies as a following first matrix equation in terms of impedance related parameters: Z 1 Z 2 ⋯ Z m − 1 Z m = f d 12, d 23, ⋯, d n − 2 n − 1, d n − 1 n, C 1, C 2, ⋯, C n − 1, C n, R load wherein the impedance related parameters include a parameter d ll + 1 representing a distance between the l -th coil and the l +1 coil ( l = 1, 2, ··· n-1) and a parameter C i representing a capacitance of the capacitor connected to the i -th coil ( i =1, 2, ··· n); (d.4) estimating values of the impedance related parameters based only on the set of measured input impedances by applying an evolutionary algorithm to find optimum solutions to the first matrix equation; (e) based on the sensed input voltage U 1, the sensed input current I 1, and the impedance related parameters determined in step (d), estimating load impedance Z L of the WPT system, output current of the WPT system I n, power P out of the load, output voltage U o of the WPT system, and efficiency η of the WPT system, wherein the load is determined only based on the sensed input voltage U 1, the sensed input current I 1, and the identified impedance related parameters (f) generating feedback information based on the estimated parameters in step (e); and (g) controlling the operations of the transmitter coil based on the generated feedback information. (a) providing a transmitting coil inductively coupled to a receiving coil; (b) providing an input current I 1 to the transmitting coil; (c) sensing an input voltage U 1 and the input current I 1 of the transmitter coil of the n coils; (d) identifying impedance related parameters in the WPT system, wherein the identifying comprises: (d.1) determining a set of measured input impedance based on the sensed input voltage U 1 and the sensed input current I 1,(d.2) measuring input impedances of the transmitting coil of the WPT system at different frequencies, wherein the set of measured input impedances includes an input impedance vector each input impedance in the vector ( Z k) measured at different frequencies f k, ( k = 1, 2, ··· m); (d.3) expressing the measured input impedances at the different frequencies as a following first matrix equation in terms of impedance related parameters: Z 1 Z 2 ⋯ Z m − 1 Z m = f d 12, d 23, ⋯, d n − 2 n − 1, d n − 1 n, C 1, C 2, ⋯, C n − 1, C n, R load wherein the impedance related parameters include a parameter d ll + 1 representing a distance between the l -th coil and the l +1 coil ( l = 1, 2, ··· n-1) and a parameter C i representing a capacitance of the capacitor connected to the i -th coil ( i =1, 2, ··· n); (d.4) estimating values of the impedance related parameters based only on the set of measured input impedances by applying an evolutionary algorithm to find optimum solutions to the first matrix equation; (d.1) determining a set of measured input impedance based on the sensed input voltage U 1 and the sensed input current I 1,(d.2) measuring input impedances of the transmitting coil of the WPT system at different frequencies, wherein the set of measured input impedances includes an input impedance vector each input impedance in the vector ( Z k) measured at different frequencies f k, ( k = 1, 2, ··· m); (d.3) expressing the measured input impedances at the different frequencies as a following first matrix equation in terms of impedance related parameters: Z 1 Z 2 ⋯ Z m − 1 Z m = f d 12, d 23, ⋯, d n − 2 n − 1, d n − 1 n, C 1, C 2, ⋯, C n − 1, C n, R load wherein the impedance related parameters include a parameter d ll + 1 representing a distance between the l -th coil and the l +1 coil ( l = 1, 2, ··· n-1) and a parameter C i representing a capacitance of the capacitor connected to the i -th coil ( i =1, 2, ··· n); (d.4) estimating values of the impedance related parameters based only on the set of measured input impedances by applying an evolutionary algorithm to find optimum solutions to the first matrix equation; (e) based on the sensed input voltage U 1, the sensed input current I 1, and the impedance related parameters determined in step (d), estimating load impedance Z L of the WPT system, output current of the WPT system I n, power P out of the load, output voltage U o of the WPT system, and efficiency η of the WPT system, wherein the load is determined only based on the sensed input voltage U 1, the sensed input current I 1, and the identified impedance related parameters (f) generating feedback information based on the estimated parameters in step (e); and (g) controlling the operations of the transmitter coil based on the generated feedback information.