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The research on DC-DC power converters has been a matter of interest for years since this type of converter can be used in a wide range of applications. The main research is focused on increasing the converter voltage gain while obtaining a good efficiency and reliability. Among the different DC-DC converters, the flyback topology is well-known and widely used. In this paper, a novel high efficiency modified step-up DC-DC flyback converter is presented. The converter is based on a N-stages flyback converter with parallel connected inputs and series-connected outputs. The use of a single main diode and output capacitor reduces the number of passive elements and allows for a more economical implementation compared with interleaved flyback topologies. High efficiency is obtained by including an active snubber circuit, which returns the energy stored in the leakage inductance of the flyback transformers back to the input power supply. A 4.7 kW laboratory prototype is implemented considering four flyback stages with an input voltage of 96 V and an output voltage of 590 V, obtaining an efficiency of 95%. The converter operates in discontinuous current mode then facilitating the output voltage controller design. Experimental results are presented and discussed.

The development of distributed generation, mainly based on renewable energies, requires the design of control strategies to allow the regulation of electrical variables, such as power, voltage (V), and frequency (f), and the coordination of multiple generation units in microgrids or islanded systems. This paper presents a strategy to control the active and reactive power flow in the Point of Common Connection (PCC) of a renewable generation system operating in islanded mode. Voltage Source Converters (VSCs) are connected between individual generation units and the PCC to control the voltage and frequency. The voltage and frequency reference values are obtained from the P–V and Q–f droop characteristics curves, where P and Q are the active and reactive power supplied to the load, respectively. Proportional–Integral (PI) controllers process the voltage and frequency errors and set the reference currents (in the dq frame) to be imposed by each VSC. Simulation results considering high-power solar and wind generation systems are presented to validate the proposed control strategy.

A multilevel modular DC-DC power conversion topology based on cascaded H-Bridge converters in a double П configuration is presented. The topology is intended to interconnect large power DC networks. A two level control hierarchy is used to regulate the DC voltage of each H-bridge module. At the top level, DC and circulating AC currents are used to control the total energy converter in all branches (both parallels and series) of each П arrange. At bottom level, the voltage balance of a converter branch, which comprises N H-bridge modules, is carried out by balancing (N-1) capacitor voltage deviations, with respect to the average capacitor voltage. The entire topology and control strategies are simulated in a PSIM environment. Simulation results with three H-bridge converters per branch are shown and preliminary experimental results with a low power prototype are also included.

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This paper presents the design, implementation and testing of a transducer to measure and monitor in real time leakage currents on high-voltage insulators. The new proposed transducer has the particularity of not affecting the insulation capacity of the insulator strings and can be installed without the need to de-energize the power system. The transducer is made up of a toroidal current transformer with a high permeability magnetic core, and an amplifier circuit, the output voltage of which is acquired, processed and transmitted by a dedicated device installed in the lower part of the HV tower. The leakage current is reconstructed from the transducer output voltage by applying the FFT technique and its own inverse transfer function. The transducer makes it possible to obtain the leakage current with its characteristic harmonics and the technique presented here reduces the electromagnetic noise present in the power systems. The proposed transducer was tested on an insulator inside an artificial fog chamber, built according to the IEC 60507 standard. Finally, the transducer was tested on an insulator string in a 220 kV substation. The results obtained show that the designed transducer correctly measures the leakage current on HV insulator strings and can be used for the on-line monitoring of pollution levels of insulator strings.

This paper presents a medium-voltage drive based on an open-end winding induction machine supplied by a multilevel power converter topology. The power converter consists of cascaded two-level three-phase voltage source inverters (VSI) connected to each side of the machine windings and each VSI is fed by an isolated DC supply. The topology has been previously reported in the literature as a sinusoidal pulse-width modulation operating in an open loop. In this work, a closed-loop model predictive control (MPC) strategy is proposed. MPC offers a much simpler method to control the power switches of the inverter compared to complex modulation strategies that are typically used in multilevel converters. Moreover, the advantage of reducing the common-mode voltage offered by the open-end winding configuration is fully exploited in this work. Simulation results are presented to validate the performance of the proposed topology and control method.