Reduction in Radiation Noise Level for Inductive Power Transfer Systems Using Spread Spectrum Techniques

Two proposed methods of reducing radiation noise caused by inductive power transfer (IPT) systems using spread spectrum techniques were experimentally demonstrated. In IPT systems for electric vehicles (EVs) or plug-in hybrid EVs (PHEVs), noise reduction techniques are necessary because the radiation noise from the IPT system for EVs or PHEVs must not exceed the limits defined by noise standards, such as the well-known regulation set by the International Special Committee on Radio Interference. In the proposed methods, the radiation noise from the transmission coils of the IPT system is spread in the frequency domain by randomly changing the output frequency of the inverter. The output frequency is selected according to the generation of pseudorandom numbers. In the first proposed method, spread spectrum with a uniform distribution (SSUD), the output frequency is selected from the frequency range of 80 to 90 kHz with an even distribution. In the second method, spread spectrum with a biased distribution (SSBD), the output current of the inverter is considered. The possibility of selecting an output frequency in the given range is biased in proportion to the combined impedance from the transmission coil and the resonance capacitors on the primary side. In experiments with a 3-kW prototype, when SSUD and SSBD were applied, the fundamental components of the radiation noise were suppressed by 4.45 and 8.27 dB · μA, respectively, in comparison with the noise obtained using the conventional system, which operates the inverter at a fixed frequency.