Analytic calculation of touch and leakage currents of non-isolated EV chargers using a fast common mode calculation method and non-ideal passive component models

Non-isolated charging systems suffer from tremendous touch currents due to the significant extension of the common mode coupling path by the electric vehicle. Since safety limits are very tough, the selection of converter topology, modulation scheme and filters with respect to touch current behavior is a very ambitious process. With the aim to ease integral system design, research is done for common mode analysis methods, eliminating the demand for long duration time domain simulations. A time saving method to analyze the touch current behavior in common mode domain is applied on a single stage charging system setup by a 3-level converter, filter system and a major coupling path. Furthermore, this paper improves that time-saving failure current prediction method by including the influence of non-ideal passive component models on the calculation result. All calculation results are compared to laboratory measurements. Border conditions from corresponding standards are used to define the required frequency range. Besides the touch current, which typically occurs during the failure condition of a broken protective earth conductor, the leakage current flowing in the protective earth conductor during normal operation is analyzed. Finally, this paper points out the influence of an internal common mode bypass via the filter system on the touch and leakage current.