In this paper, the effect of steep-fronted voltage waveshapes infringing on a pulse-width-modulated (PWM) inverter fed induction motor is studied. The system, composed of a feeder cable and a stator winding, is modeled and simulated by using multiconductor transmission line theory in order to predict the voltage distribution among the coils of the stator winding. A recently developed time-domain equivalent circuit is used; it allows one to correctly describe the dielectric losses and the skin-effect in the conductors. The relationship among the voltage distribution inside the electrical insulation and parameters like the rise time of the applied voltage, the cable length, and the distributed losses is deeply discussed. Good agreement has been found among experimental and numerical results

Nearby lightning strikes are prone to induce overvoltage transients in photovoltaic (PV) modules and in their power conditioning circuitry, which can permanently damage the PV system. Therefore, it becomes important to establish a method for accurate assessment of such transients. To this aim, the authors propose a three-dimensional (3D) semi-analytical numerical method to study the electromagnetic transients caused in PV modules by nearby lightning strikes. The approach bases on a semi-analytical expression of the magnetic vector potential generated by a geometrically complex lightning channel. The proposed method is able to calculate the transient overvoltage in a PV module, both in common and differential-mode, taking also into account capacitive and inductive couplings between the internal circuit and the PV metallic frame. Both modes are required to design the surge protective devices (SPDs) in PV power systems. Comparing to the models in literature, the proposed approach explicitly considers the complex geometry of the lightning channel. Statistical analysis allows assessing the impact of channel geometry by randomly generating a number of likely lightning paths. Results show that the lightning-induced overvoltage in a PV module is highly dependent on factors such as distance to the lightning channel and lightning channel geometry.

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Photovoltaic (PV) systems are subject to nearby lightning strikes that can contribute to extremely high induced overvoltage transients. Recently, the authors introduced a 3D semi-analytical method to study the electromagnetic transients caused by these strikes in a PV module. In the present paper we develop an improved model of the PV module that: (a) takes into account high-frequency effects by modelling capacitive and inductive couplings; (b) considers the electrical insulation characteristics of the module; (c) includes the connection to a DC/DC converter. The whole process involves three major steps, i.e., the magnetic-field computation, the evaluation of both common-mode- and differential-mode-induced voltages across the PV module, and the use of the calculated voltages as input to a lumped equivalent circuit of the PV module connected to the DC/DC converter. In such a framework, the influence of the PV operating condition on the resulting electrical stresses is assessed; moreover, the relevance or insignificance of some parameters, such as the module insulation or the frame material, is demonstrated. Finally, results show that the induced overvoltage are highly dependent both on the grounding of the conducting parts and on the external conditions such as lightning current waveforms and lightning channel (LC) geometry.

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