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.
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.
DC–DC power converters have generated much interest, as they can be used in a wide range of applications. In micro-inverter applications, flyback topologies are a relevant research topic due to their efficiency and simplicity. On the other hand, solar photovoltaic (PV) systems are one of the fastest growing and most promising renewable energy sources in the world. A power electronic converter (either DC/DC or DC/AC) is needed to interface the PV array with the load/grid. In this paper, a modified interleaved-type step-up DC–DC flyback converter is presented for a PV application. The topology is based on a multi-winding flyback converter with N parallel connected inputs and a single output. Each input is supplied by an independent PV module, and a maximum power point tracking algorithm is implemented in each module to maximize solar energy harvesting. A single flyback transformer is used, and it manages only 1/N of the converter rated power, reducing the size of the magnetic core compared to other similar topologies. The design of the magnetic core is also presented in this work. Moreover, the proposed converter includes active snubber networks to increase the efficiency, consisting of a capacitor connected in series with a power switch, to protect the main switches from damaging dv/dt when returning part of the commutation energy back to the source. In this work, the operating principle of the topology is fully described on a mathematical basis, and an efficiency analysis is also included. The converter is simulated and experimentally validated with a 1 kW prototype considering three PV panels. The experimental results are in agreement with the simulations, verifying the feasibility of the proposal.
This paper proposes a decoupled control of a dc-dc modular multilevel converter (MMC) based on a double-T topology intended for multi-terminal high voltage direct current (MT-HVdc) transmission systems or emerging distribution systems operating in medium voltage direct current (MVdc). The aim of the proposed control strategy is to obtain an input current with reduced harmonic content and to eliminate the output ac common-mode voltage, which is not allowed in MT-HVdc systems. The control strategy consists of injecting two circulating ac currents and two dc currents that allow the energy balance between the arms of the converter and the general energy balance of the topology. The dc and ac currents are decoupled and allow control over load variations and reference changes in the dc-links. The proposed topology is mathematically modeled and the control method is then derived. Simulation results are presented to validate the proposed system.
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