Transformer Topology Research Articles

Toward Power Quality Management in Hybrid AC-DC Microgrid Using LTC-L Utility Interactive Inverter: Load Voltage-Grid Current Tradeoff

AC–DC hybrid microgrid (HMG) is introduced as the future distribution network to utilize both benefits of alternative and direct currents. Generally, HMG is consisted of ac and dc loads, renewable energy-based distributed generators (DGs), controllable DGs and energy storage systems, and a utility interactive inverter (UII), which provides a bi-directional connection between ac and dc subsystems. In this paper, a inductor, transformer, capacitor, and inductor (LTC-L) topology for the UII has been proposed for managing the power quality of ac subsystem of the HMG. The control strategy of the UII is flexibly changed based on the operating-mode of the HMG. Using the proposed control strategy of the UII in grid-connected mode, not only the voltage quality of the ac-subsystem will be improved, but also the quality of the grid current will be enhanced, considerably. In standalone mode, UII acts as an uninterruptable power supply to minimize the shedding of ac or dc loads. A voltage–current cascaded control structure is used for employing the proposed control strategies. Moreover, two control approaches are investigated on the proposed LTC-L topology of UII, sinusoidal voltage reference (supplying load with pure sinusoidal voltage) and nonsinusoidal voltage reference (supplying load with nonsinusoidal voltage for mitigating grid current harmonics). Effectiveness of the proposed topology and the control strategies are evaluated through a numerical study and discussing the results.

Experimental investigations of argon spark gap recovery times by developing a high voltage double pulse generator.

The voltage recovery in a spark gap for repetitive switching has been a long research interest. A two-pulse technique is used to determine the voltage recovery times of gas spark gap switch with argon gas. First pulse is applied to the spark gap to over-volt the gap and initiate the breakdown and second pulse is used to determine the recovery voltage of the gap. A pulse transformer based double pulse generator capable of generating 40 kV peak pulses with rise time of 300 ns and 1.5 μs FWHM and with a delay of 10 μs-1 s was developed. A matrix transformer topology is used to get fast rise times by reducing L(l)C(d) product in the circuit. Recovery Experiments have been conducted for 2 mm, 3 mm, and 4 mm gap length with 0-2 bars pressure for argon gas. Electrodes of a sparkgap chamber are of rogowsky profile type, made up of stainless steel material, and thickness of 15 mm are used in the recovery study. The variation in the distance and pressure effects the recovery rate of the spark gap. An intermediate plateu is observed in the spark gap recovery curves. Recovery time decreases with increase in pressure and shorter gaps in length are recovering faster than longer gaps.

Research on the MPPT Stability of the Single-Stage and Single-Phase Photovoltaic Grid-Connected System

At present the multi-stage transformation topology are more used in photovoltaic (PV) grid-connected system, although the control of this structure is relatively simple but the conversion efficiency is difficult to improve due to increase in transformation series. The single stage topology has a simple topology with high reliability and efficiency because of low power consumption, but control algorithm is more complex because of its power convert main circuit without DC-DC. This paper describes a method for maximum power point tracking (MPPT) in the single-stage and single-phase PV grid-connected system. In the paper, the nonlinear output characteristics of the PV including I-V & P-V are obtained in changed solar insulations or temperature based on MATLAB, and the MPPT algorithm which is based on the particle swarm optimization (PSO) method is also described. The simulation model of the single-stage and single-phase PV grid-connected system is built , and simulation results show the MPPT algorithm has excellent dynamic and static performances ,which verifies the PSO method is effective for MPPT in the single-stage and single-phase PV grid-connected system.

Decentralised adaptive output feedback synchronisation tracking control of spacecraft formation flying with time-varying delay

This study deals with the problem of decentralised cooperative position tracking with time-varying delays of interconnect communication in the leader-follower spacecraft formation flight. More specifically, a class of low-pass linear filters is developed to derive a control law without absolute and relative velocity measurement, which is significant for practical applications with low-cost configurations of spacecrafts. Using a well-chosen Lyapunov function, it proves that the proposed control law can make the spacecrafts in formation flying achieve global convergence to the desired position and velocity relevant to the leader, in the face of modelling uncertainties, external disturbances, as well as non-uniform time-varying delays in communication links. Moreover, to release the heavy communication pressures of the leader, a modified control law is designed by introducing a finite-time sliding-mode estimator for a tree-type transformation topology of the formation, in which delays only affect the state (position and velocity) information received from neighbours of each spacecraft. Finally, simulation results are presented to demonstrate the effectiveness of the proposed control schemes.

Analysis and Design of Millimeter-Wave Low-Power CMOS LNA With Transformer-Multicascode Topology

In this paper, the analysis and design of a CMOS multicascode configuration with a noise-reduction transformer topology are presented. Two low-power (LP), miniature, and wideband low-noise amplifiers (LNAs) were designed and fabricated for demonstration. One with a transformer triple-cascode configuration was designed at <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> -band, and the other with a transformer quadruple-cascode configuration was designed at <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> -band. Both of the two LNAs were fabricated using 90-nm LP CMOS technology. To minimize the noise figure (NF) and maximize both the small-signal gain and 3-dB bandwidth, the noise-reduction transformers are designed and placed between transistors of the triple- and quadruple-cascode devices. Based on this approach, the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> -band LNA has a gain of 20.3 dB and an NF of 4.6 dB at 40 GHz, with a power consumption of 15 mW. Both of the LNA utilize a 3-V supply voltage, but the drain source voltage of each device in the multicascode configuration is below 1 V. The <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> -band LNA presents a gain of 12.7 dB from 43 to 58 GHz and a minimum NF of 4.7 dB at 62.5 GHz with a power consumption of 18 mW. The chip size of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> - and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> -band LNAs are 0.42×0.45 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 0.45×0.48 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , including all the testing pads. Compared with the conventional cascode LNAs, the proposed transformer triple-cascode LNA has a better NF, wider 3-dB bandwidth, and lower power consumption, whereas the transformer quadruple-cascode LNA features even higher gain performance.

Design procedure for compact pulse transformers with rectangular pulse shape and fast rise times

Microseconds range pulse modulators based on solid state technology often utilize a pulse transformer, since it could offer an inherent current balancing for parallel connected switches and with the turns ratio the modulator design could be adapted to the available semiconductor switch technology. In many applications as e.g. radar systems, linear accelerators or klystron/magnetron modulators a rectangular pulse shape with a fast rise time and a as small as possible overshoot is required. In reality, however, parasitic elements of the pulse transformer as leakage inductance and capacitances limit the achievable rise time and result in overshoot. Thus, the design of the pulse transformer is crucial for the modulator performance. In this paper, a step by step design procedure of a pulse transformer for rectangular pulse shape with fast rise time is presented. Different transformer topologies are compared with respect of the parasitic elements, which are then calculated analytically depending on the mechanical dimensions of the transformer. Additionally, the influence of the core material, the limited switching speed of semiconductors and the nonlinear impedance characteristic of a klystron are analyzed.

Intelligent Transformer: Possibilities and Challenges

Intelligent Transformer: Possibilities and Challenges This paper covers the concept of an intelligent transformer that is a good candidate to replace a conventional low frequency transformer in the microgrids. As the power production and consumption can vary in a wide range, the new substations have to meet many requirements to guarantee reliable energy management in the autonomous networks. Different topologies of intelligent transformers can be used to meet these requirements. Therefore the advantages and disadvantages of the existing topologies were analyzed. The future trends and challenges are also discussed.

An electronic driver for improving the open and closed loop electro-mechanical response of Dielectric Elastomer actuators

Actuators based on Dielectric Elastomers are a promising technology in robotic and mechatronic applications. The overall actuator performances are influenced by the non-linear and highly coupled electrical and mechanical behavior of the employed materials. To date, the practical electro-mechanical response and controllability of actuators based on Dielectric Elastomers are limited by the inadequacy of the employed driving circuits, which are based on voltage-regulated converters. In this paper, first a novel activation strategy is proposed for Dielectric Elastomer actuators, which is based on a custom electronic driver derived from the flyback transformer topology. Second, two closed-loop controllers employing the proposed electronic driver are presented and compared for the accurate and fast regulation of the position of Dielectric Elastomer actuators. Experimental results are reported which show that the proposed electronic driver outperforms the traditional driving circuits in terms of energy efficiency, fast open-loop actuator activation and good closed-loop actuator controllability.

Low-power single-to-differential LNA at S-band based on optimised transformer topology and integrated ESD

A single-ended to differential low-power low-noise amplifier (LNA) designed and implemented in 0.18 mum CMOS technology is presented. The device takes advantage of a current reuse strategy by stacking two common-source differential transistor pair stages for minimum current dissipation, together with the design of optimised high Q differential transformers and inductors in order to minimise the impact of parasitics. The fully integrated, including ESD protection diodes, 2.1 GHz LNA consumes 1.1 mW at 1.2 V supply voltage and presents 29.8 dB gain, 4.5 dB noise figure, -21.1 dBm 1 dB compression point, -11.6 dBm input third-order intercept point and -12.3 dB input return loss performance.

A 1-V, 5.5-GHz, CMOS LNA With Multiple Magnetic Feedback

A CMOS low-noise amplifier that utilizes multiple monolithic transformer magnetic feedback to simultaneously neutralize the gate-drain overlap capacitance of the amplifying transistor and achieve high gain at high frequencies when driving an on-chip capacitance is presented. The multiple transformer topology permits negative and positive feedback to be applied constructively, allowing for a stable design with adequate gain and large reverse isolation without noise figure (NF) degradation. Simulation results indicate voltage conversion gain of 17 dB, NF of 1.6 dB, and best-case third-order input intercept point of 13 dBm. The design is being implemented in a 0.13-mum CMOS technology

Analysis of the Equal-Delay Topology for Transformers and Hybrid Networks

A complete scattering matrix representation for the ideal equal-delay topology for transformers and hybrid networks is presented. It is shown that while the operation of the hybrid as a 180deg power combiner, current balun, or voltage balun is essentially frequency independent, the operation as a 0deg power combiner or splitter is not. Instead, the isolation between the 0deg and 180deg ports is finite and frequency dependent. Moreover, the reflection coefficient at the sum port is nonzero and frequency dependent. These characteristics lead to the conclusion that while the equal-delay 180deg power splitter/combiner is fundamentally frequency independent, its 0deg counterpart is limited to operation well below the fundamental quarter-wave frequency of the constituent transmission lines. Full three-port scattering parameter representations, which are compatible with the calibration and analysis approach given in the CISPR 16-1 specification, are given for the three fundamental transformer and balun types derivable from the equal-delay hybrid: 1 the Guanella voltage balun, 2 the Guanella current balun, and 3 the 180deg power divider or terminated hybrid balun, as specified in the CISPR 16-1 specification

Power tracking for nonlinear pv sources with coupled inductor SEPTIC converter

The photovoltaic (PV) generator exhibits a nonlinear i-v characteristic and its maximum power (MP) point varies with solar insolation. In this paper, a V2-based MP point tracking (MPPT) scheme is developed using a buck-boost transformation topology. Although several buck-boost transformation topologies are available we have considered here a coupled inductor SEPIC converter for experimentation. To achieve almost ripple-free array current we have used ripple steering phenomena with the help of integrated inductor. This integrated inductor not only reduces the magnetic core requirements but also improves converter performance. Mathematical models are formulated and tracking algorithm is evolved. A combined PV system simulation model is developed in the SIMULINK. For a given solar insolation, the tracking algorithm changes the duty ratio of the converter such that the solar cell array (SCA) voltage equals the voltage corresponding to the MP point. This is done by the tracking algorithm, which mainly computes the power proportional to square of terminal voltage and changes the duty ratio of the converter so that this power is maximum. The proposed algorithm is implemented in real-time with the help of Analog Device ADMC-401 DSP evaluation module. The tracking program is developed to perform experimental investigations using analog-to-digital converter (ADC) interrupt. Using this processor we are able to track the MP within 200 ms. The proposed peak power tracking effectiveness is demonstrated through simulation and experimental results.

Design of an ultra compact electronically tunable microwave impedance transformer

A novel ultra compact microwave tuneable impedance transformer topology is proposed. It consists of a classical /spl pi/ CLC network where an equivalent tuneable inductance is realised with a high impedance transmission line in series with fixed inductance and a diode's varactors. The realised hybrid prototype at 900 MHz operating frequency is only 0.06/spl lambda/-long. Impedance loads from 16.5 to 280 /spl Omega/ can be matched with a return loss better than -20 dB, and the relative bandwidth equals /spl plusmn/36% for a fixed 50 /spl Omega/ load.

Control of high-frequency AC link electronic transformer

An isolated high-frequency link AC/AC converter is termed an electronic transformer. The electronic transformer has size and cost advantages over a conventional transformer because of high-frequency operation of the magnetic core. Of the various topologies of electronic transformer, the high-frequency AC link electronic transformer achieves high-frequency AC power transformation without a DC link. The circuit uses the standard H-bridge, one on either side of the high-frequency transformer. A novel PWM scheme is proposed, which symmetrically delays and advances the phase of the left and right legs of the front-side converter with respect to the output-side converter. The proposed scheme introduces freewheeling sub-periods, which results in zero voltage switching in the output-side converter. The electronic transformer as an AC automatic voltage regulator (AVR) offers distinct advantages over a conventional servo voltage stabiliser in terms of size and speed of response. The AVR application is discussed and experimental results of a 500 VA AVR are presented. A four-quadrant switch presents difficulties in turning off inductive load current because of the absence of a freewheeling path in the switch. A biasing circuit is proposed to convert the potentially lossy switching transition into lossless transition. Simulation and experimental results with the biasing circuit are presented.

Experimental study of integrated tunable transformer

A new tunable integrated transformer topology together with its tuning method is presented. The proposed tunable topology consists of a conventional tapped transformer and a coupled inductor. The phase shift between the input power into the primary winding and that into the coupled inductor was used to control the electrical characteristics such as maximum stable gain, input impedance and quality factor. The new tunable transformer achieved about 3dB higher maximum stable gain and 2.8 times higher quality factor compared to the conventional transformer.

Wideband equivalent circuit modelling and parameter estimation methodology for two-winding transformers

A wideband, lumped-parameter equivalent circuit model topology for two-winding power transformers is proposed. This model topology is designed to reflect the internal electromagnetic behaviour of such transformers. A parameter estimation methodology is presented for determining the parameters of the proposed model structure from measured frequency responses of the open- and short-circuit input impedances and the voltage transformation ratios. Measured and simulated frequency- and time-domain results are presented for a 16 kVA, 22 kV/240 V distribution transformer. These results show that the proposed model accurately predicts the transformer terminal responses in the frequency range between 10 Hz and 100 kHz.

Design Criteria for Transformers in High Voltage Output, High Frequency Power Converter Applications

SummaryWhen a dc high voltage needs to be obtained from low voltage inputs (main voltage), the necessary power converter needs a high value for its transformation ratio; consequently, a large number of turns is often necessary for secondary windings and some parasitics appear (large leakage inductance and large capacitance). Thus, it is usual to design a resonant converter to include both inductance and capacitance in the power topology. However, as the parasitics are used to obtain the resonance, their value (and their spreads) are critical. The present paper proposes several criteria in order to establish an adequate method for constructing the transformer, and a new topology for transformers and a model for parasitic capacitances are also presented taking into account high voltage and high frequency problems and limitations of materials.

Winding topology for transformers

As one factor to improve the high-frequency performance of pulse transformers, the reduction of the leakage inductances associated with leakage flux between primary and secondary windings is addressed. The author introduces the concept of making such windings out of coaxial (or higher-order multiaxial) cables, with the outer shields of primary and secondary windings bounded together, so as to effectively remove this leakage inductance. >