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The connection of photovoltaic sources to a medium voltage dc collection network requires a dc-dc converter having specific grid-connected converter capabilities. This article presents the application of a phase-shifted full bridge (PSFB) converter for medium voltage dc collection networks suited to photovoltaic power plants. The unidirectional structure of the converter is beneficial in terms of cost and simplicity of hardware implementation of the MV circuit components. The design of the PSFB converter is presented considering ratings of 250 kW power, 1.2 kV input, and 20 kV output. A converter model and a novel PSFB input voltage control regulating the dc-link voltage are developed and verified. A tuning method is given taking into account the effect of different transformer leakage inductance values. The behaviour of the PSFB under the PV power production profile and MV network faults is studied in simulation and verified against a reduced-scale prototype with ratings of 30 kW and 350 V / 600 V operating at 20 kHz. The experimental verification of the control is performed considering a real PV power profile. The experimental results under faults show the same response as in simulations. The PSFB fault response is observed to be superior compared to other dc–dc topologies with capacitive output filter only, making it suitable for grid-connected operation.

Partial discharge (PD) measurement of an insulation system is widely used as a diagnostic tool for the quality control of high voltage apparatuses. In ac, the conventional method of PD detection is well established. However, under square voltages such as those generated across power electronic converters, the conventional method cannot discriminate between PDs and switching transients. In this context, this paper demonstrates PD detection under fast-rising square voltages by deploying a photomultiplier tube. For this, an experimental set-up generating unipolar square voltage (USV) waveforms is developed, generating a dV/dt in the range of 10-100 kV/ $\mu \text{s}$ . The device under test (DUT) comprises of needle-barrier plane configuration immersed in dielectric liquids. Barriers differing in permittivity and thicknesses are chosen to test with two types of dielectric liquids, to assess varying conditions. The results thus obtained show a lower partial discharge inception voltage (PDIV) in USV than in bipolar ac for the same DUT specimen. The phase-resolved (PR) PD patterns exhibit a higher PD occurrence during rising and falling front of the USV waveform. Experimental results demonstrate the relevance of the PMT as a PD detector for square voltage waveforms exhibiting high dV/dt in dielectric liquids.

A thermosyphon loop, designed for the thermal management of a large Medium voltage power converter 5 MW overall, corresponding to a 2.4 kW thermal load per cooling unit) is presented. The device is mainly made of an evaporator, a condenser and a reservoir connected with plastic liquid and vapor lines. Novec 649 (3M) has been chosen as the working fluid due to environmental and electrical concerns. A model of the loop is described, and its predictions are compared with experiments. A first comparison yields a maximum mean deviation of 20 % between experimental results and numerical simulation at the maximum coolant temperature. The main sources of errors are identified, and improvements are proposed for better model accuracy.