Induced Voltage Estimation for IPT Applications with Reduced Characterisation Requirements

The induced voltage in the primary coil of an IPT system is a quantity that can be used to model the interaction between the primary and any coupled receivers or magnetically permeable objects (e.g., a foreign object). This information is useful in a wide variety of applications ranging from foreign object detection to live system monitoring and synchronous rectification. Measurements of this quantity in an operating inverter can however prove challenging since the induced voltage cannot be directly probed as the voltage across the primary coil is the sum of the induced voltage and the voltage caused by its self-inductance. In this paper we propose an induced voltage estimation technique that is based on the measurement of the extracted DC input current of the inverter and the fundamental harmonic of one of the switching waveforms of the system. The advantage of this technique over other similar techniques in the literature is that it does not rely on a time-consuming pre-characterisation of the system. The technique uses a small set of pre-characterised loads at a fixed coupling with the primary coil to derive a mapping of the induced voltage real and imaginary parts as a function of the DC input current of the inverter and the fundamental harmonic of one of the switching waveforms, both of which are extracted as DC voltages, hence eliminating the requirement for high-performance instrumentation. In this paper we demonstrate that this technique can reach a RMSE (normalised to the induced voltage range for characterisation) of 4.1% for the real part and 3.3% for the imaginary part of the induced voltage using a pre-characterised inverter dataset as the baseline for comparison of these results. A practical example is shown, in which this technique is used to characterise an IPT transmitter so that induced voltage measurements can be performed if external environment or the state of tuning of the inverter change when the system is deployed for field testing.