Three-Phase Isolated Boost DC-DC Converter for High Voltage Applications

The voltage fed DC-DC converter has been suffering from problems associated with large transformer leakage inductance due to high transformer turn ratio when it is applied to low-voltage, high-current step-up application such as fuel cells. This paper proposes a new three-phase voltage fed DC-DC converter, which is suitable for high-voltage, high-current applications. The transformer turn ratio is reduced to half owing to ?-Y connection. The zero-voltage and zero-current switches (ZVZCS) for all switches are achieved over wide load range without affecting effective duty cycle. A clamp circuit not only clamps the surge voltage but also reduces the circulation current flowing in the high-current side, resulting in significantly reduced conduction losses. The duty cycle loss can also be compensated by operation of the clamp switch.The detailed design and operating principles are described and simulated using Pspice. The proposed converter is very attractive for electrolyser application.Keywords: High power DC–DC converter, three-phase DC-DC converter, active clamp circuit, Isolation transformer

Analysis and Design of a Single Ended Resonant Reset Forward Converter

A resonant reset forward converter was developed as one of the topologies of the forward converter because it offered the simplest technique of transformer core resetting. The resonant reset topology does not require any external passive components or any tertiary winding to facilitate the core reset but it utilizes the magnetizing inductance of the transformer and the parasitic capacitances of the devices to bring down the core flux to its initial position and hence avoids core saturation of the transformer, which is the principle working device in the converter from the point of view of electrical isolation and reproduction of good quality dc voltage at the output (or the load). The saturation of the transformer would have otherwise led to heavy inrush current resulting in huge losses and degradation in efficiency of the converter. Thus in a low power dc-dc converter this resonant reset topology of the forward converter offers significant advantages. The small signal model of the converter which was proposed using the switch averaging method was validated using the software PSPICE and it gave perfect ripple free dc waveform at the output. The closed loop stage involved the development of a type IIIB controller to generate a sufficient phase margin and hence improve stability. The Optocoupler was also used in the feedback for the purpose of maintaining the electrical isolation and the pole which it generated (due to Miller’s capacitance) was compensated by manually placing a combination of a parallel resistor and capacitor at the output of the collector terminals of the transistor of the Optocoupler. Finally the hardware developments were done for the voltage mode controlled feedback loop using IC UC 3525A which gave satisfactory results for various load tests and desired input voltage fluctuations

Torsional Interaction Studies on a Power System Compensated by SSSC and Fixed Capacitor

In this paper, a static synchronous series compensator (SSSC), along with a fixed capacitor, is used to avoid torsional mode instability in a series compensated transmission system. A 48-step harmonic neutralized inverter is used for the realization of the SSSC. The system under consideration is the IEEE first benchmark model on SSR analysis. The system stability is studied both through eigenvalue analysis and EMTDC/PSCAD simulation studies. It is shown that the combination of the SSSC and the fixed capacitor improves the synchronizing power coefficient. The presence of the fixed capacitor ensures increased damping of small signal oscillations. At higher levels of fixed capacitor compensation, a damping controller is required to stabilize the torsional modes of SSR

Contactless measurement of electric current using magnetic sensors

We review recent advances in magnetic sensors for DC/AC current transducers, especially novel AMR sensors and integrated fluxgates, and we make critical comparison of their properties. Most contactless electric current transducers use magnetic cores to concentrate the flux generated by the measured current and to shield the sensor against external magnetic fields. In order to achieve this, the magnetic core should be massive. We present coreless current transducers which are lightweight, linear and free of hysteresis and remanence. We also show how to suppress their weak point: crosstalk from external currents and magnetic fields

Theoretical and experimental study of AC loss in HTS single pancake coils

The electromagnetic properties of a pancake coil in AC regime as a function of the number of turns is studied theoretically and experimentally. Specifically, the AC loss, the coil critical current and the voltage signal are discussed. The coils are made of Bi2Sr2Ca2Cu3O10/Ag (BiSCCO) tape, although the main qualitative results are also applicable to other kinds of superconducting tapes, such as coated conductors. The AC loss and the voltage signal are electrically measured using different pick up coils with the help of a transformer. One of them avoids dealing with the huge coil inductance. Besides, the critical current of the coils is experimentally determined by conventional DC measurements. Furthermore, the critical current, the AC loss and the voltage signal are simulated, showing a good agreement with the experiments. For all simulations, the field dependent critical current density inferred from DC measurements on a short tape sample is taken into account.Comment: 22 pages, 15 figures; contents extended (sections 3.2 and 4); one new figure (figure 5) and two figures replaced (figures 3 and 8); typos corrected; title change

A Flexible DSTATCOM Operating in Voltage or Current Control Mode

The topology and control are discussed of a distribution static compensator (DSTATCOM) that can be operated flexibly in the voltage or current control mode. In the voltage control mode, the DSTATCOM can force the voltage of a distribution bus to be balanced sinusoids. In the current control mode, it can cancel distortion caused by the load, such that current drawn by the compensated load is pure balanced sinusoid. Both these objectives are achieved, irrespective of unbalance and harmonic distortions in load currents or source voltages. The chosen DSTATCOM topology includes three single-phase voltage source inverters connected in parallel to a filter-capacitor, which allows the high-frequency component of the current to pass. A switching control scheme is proposed, and its suitability is proved for this problem. The proposed scheme is verified using computer simulation studie

Effective control of the error in a direct measurement of core-loss power

Accuracy of a direct measurement of core-loss power is severely limited in many applications by the extra phase shift between the measured voltage and current. An analysis of the error is for the first time performed, which not only unfolds the hidden physical nature behind it, but also reveals a simple and effective method to control the sensitivity and hence the error. This method can also be used to satisfy a prescribed tolerance. Extensive measurements on a TDK PC40 core yield results which support the analysis

Static shunt and series compensations of an SMIB system using flying capacitor multilevel inverter

The flying capacitor multilevel inverter (FCMLI) is a multiple voltage level inverter topology intended for high-power and high-voltage operations at low distortion. It uses capacitors, called flying capacitors, to clamp the voltage across the power semiconductor devices. A method for controlling the FCMLI is proposed which ensures that the flying capacitor voltages remain nearly constant using the preferential charging and discharging of these capacitors. A static synchronous compensator (STATCOM) and a static synchronous series compensator (SSSC) based on five-level flying capacitor inverters are proposed. Control schemes for both the FACTS controllers are developed and verified in terms of voltage control, power flow control, and power oscillation damping when installed in a single-machine infinite bus (SMIB) system. Simulation studies are performed using PSCAD/EMTDC to validate the efficacy of the control scheme and the FCMLI-based flexible alternating current transmission system (FACTS) controllers

Hysteresis Current Control Operation of Flying Capacitor Multilevel Inverter and Its Application in Shunt Compensation of Distribution Systems

Flying capacitor multilevel inverter (FCMLI) is a multiple voltage level inverter topology intended for high voltage and power operations with low distortion. It uses capacitors, called flying capacitors for clamping the voltage across the power semiconductor devices. In this paper, the implementation of a distribution static compensator (DSTATCOM) using an FCMLI is presented. A hysteresis current control technique for controlling the injected current by the FCMLI-based DSTATCOM is discussed. A new method for controlling the flying capacitor voltages is proposed which ensures that their voltages remain constant and at the same time maintain the desired current profile under the hysteresis current control operation. Simulation studies are performed using PSCAD/EMTDC to validate the efficacy of the control scheme and the FCMLI-based DSTATCOM

Integrated series transformer in cascade converters for photovoltaic energy systems

This paper proposes a novel configuration for photovoltaic applications based on a cascade converter topology. The series connection between modules is achieved through the magnetic core of the integrated series transformer, therefore an inherent isolation is provided without the requirement of a dc-dc conversion stage. Such isolation approach between each module allows operation at high voltage levels without harming the PV panel insulation. The main principles that support this proposal, as well as, simulation results are presented to validate the configuration.Peer ReviewedPostprint (author's final draft