Showing papers on "Isolation transformer published in 2007"

Transformerless Photovoltaic Inverters Connected to the Grid

Abstract: Renewable energy sources are getting more and more widespread, mainly due to the fact that they generate energy by keeping the environment clean. Most of these systems have an isolation transformer included, which if excluded from the system would increase the efficiency and decrease the size of PV installations, furthermore it would lead to a lower cost for the whole investment. But there are some safety issues regarding the missing galvanic isolation. This paper is aiming to analyze and compare the most common single-stage transformerless PV inverter topologies for single-phase and three-phase with respect to the leakage current generation. The best results, both for single-phase and three-phase systems, are obtained when the middle point of the input capacitors is connected to the neutral point, thereby minimizing the voltage fluctuations present at the terminals of the PV panel.

An Airborne Radar Power Supply With Contactless Transfer of Energy—Part I: Rotating Transformer

Abstract: Reliability and precision are key requirements for electronic systems in aerospace applications. Transferring electrical energy from a stationary to a moving device involves wearable parts such as slip rings and brushes. This paper examines the possibility of using a rotating transformer for contactless transfer of energy from the base to the revolving platform of an airborne radar system. The first part of the series focuses on the magnetic interface, investigating its electrical properties and their association with the core and windings geometry. The reader will gain an understanding of the merits and limitations of this technology and will be able to assess its suitability for other applications. The effects of the increased leakage and reduced magnetizing inductances of the transformer are investigated, and two winding layouts are proposed and characterized by measurements and finite-element analysis. Some equations are presented along with practical guidelines on designing a rotating transformer with a 0.25-2-mm air gap. The transformer voltage gain and efficiency plots are introduced as performance-assessment tools. The impact of the air-gap stray flux on the winding conduction losses is shown, and some electromagnetic-compatibility considerations are presented. Finally, a mechanical layout for a 1-kW rotating transformer is proposed.

Soft-Switching Zeta–Flyback Converter With a Buck–Boost Type of Active Clamp

Abstract: This paper presents the system analysis, design consideration, and implementation of a soft-switching zeta-flyback converter to achieve zero-voltage switching (ZVS). In the proposed converter, the zeta and flyback topologies are adopted in the output side to achieve the following features: to share the power components in the transformer primary side, to achieve the partial magnetizing flux reset, and to share the output power. The buck-boost type of active clamp is connected in parallel with the primary side of the isolation transformer to recycle the energy stored in the leakage inductor of isolated transformer and to limit the peak voltage stress of switching devices due to the transformer leakage inductor when the main switch is turned off. The active clamp circuit can make the switching devices to turn on at ZVS. Experimental results taken from a laboratory prototype rated at 240 W, input voltage of 150 V, output voltage of 12 V, and switching frequency of 150 kHz are presented to demonstrate the converter performance. Based on the experimental results, the circuit efficiency is about 90.5% at rated output power, and the output voltage variation is about 1%.

270 kVA Solid State Transformer Based on 10 kV SiC Power Devices

Abstract: With the advancement of semiconductor technology, solid state transformer (SST) with high voltage fast switching SiC power devices is becoming a valid option to replace the conventional transformers in power substation. In this paper, a 270 kVA solid state transformer based on 10 kV SiC power MOSFET has been proposed. The two stages of SST, five-level Vienna rectifier and five-level DC/DC converter are specifically designed and simulated in closed loop. The analysis of device losses is performed based on the device characteristics. A design of high frequency transformer is presented as well. The simulation results together with the loss analysis verify the functionality and feasibility of SST.

A Biosignal Instrumentation System Using Capacitive Coupling for Power and Signal Isolation

Abstract: Requirements for patient safety and a high interference rejection ratio in medical equipment create a demand for effective isolation devices. A system scale approach that uses capacitive coupling for power and signal isolation is presented. In addition, we describe the development of an instrumentation system prototype that applies microwaves for power exchange and bidirectional data transfer across the isolation barrier. The system consists of an isolated transducer unit, a central unit, and a single coaxial cable between the units. The isolation capacitance is as low as 1.6 pF, inclusive of the digital data transfer and power exchange up to 600 mW of isolated direct current (dc) power. The system is suitable for line-powered biopotential measurements and it is shown that reducing the isolation capacitance from 180 to 1.6 pF improves the power line rejection by 30 dB in a typical electrocardiogram (ECG) measurement setup.

Hybrid Transformer Model for Transient Simulation: Part I - Development and Parameters

Abstract: Summary form only given. A new topologically-correct hybrid transformer model is developed for low- and mid-frequency transient simulations. Power transformers have a conceptually simple design, but behaviors can be very complex. Selection of the most suitable representation for a given behavior depends on the type of transformer to be simulated, the frequency range, and other factors such as the internal design of the transformer and available parameters or design data. Here, a modular model suitable for frequencies up to 3-5 kHz is developed, utilizing a duality-based lumped-parameter saturable core, matrix descriptions of leakage and capacitive effects, and frequency-dependent coil resistance. Implementation and testing of this model was done for 15-kVA 208D-120Y 3-legged and 150 kVA 12, 470Y-208Y 5-legged transformers. The basis and development of the model is presented, along with a discussion of necessary parameters and the approaches for obtaining them.

Double ended converter with output synchronous rectifier and auxiliary input regulator

Abstract: A DC to AC power converter is disclosed. The power converter has four power-switching devices, two diodes, a step-up and isolation transformer, a capacitor-choke filter and a controller. Two power-switching devices located on the primary side of the transformer are switched to provide alternate cycles of an ac current to the primary side of the transformer, which magnetically couples the ac current to the secondary side of the transformer. Two power-switching devices on the secondary side of the transformer are switched to alternately allow the forward and return ac currents from the secondary side of the transformer in the output path to a load connected to the output of the DC to AC power converter.

Car power source apparatus

Abstract: The voltage detection circuit 3 is provided with an isolation transformer 4 having its primary side connected to battery 2 connection nodes 10, a switching device 5 connected to the primary side of the isolation transformer 4, an isolated input circuit 7 that switches the switching device 5 ON and OFF, and a secondary voltage detection section 8 that detects output voltage from the secondary side of the isolation transformer 4. In the voltage detection circuit 3, the series input circuit 6 of the isolation transformer 4 primary side and the switching device 5 are connected to battery 2 measurement nodes, the switching device 5 is switched ON and OFF with a given periodicity by the isolated input circuit 7, and the output voltage from the secondary side of the isolation transformer 4 is detected by the secondary voltage detection section 8 to determine the voltage across the measurement nodes.

Transformerless utility-grid-interactive inverter

Abstract: An electrical DC-to-AC power conversion apparatus is disclosed that is primarily intended for use with solar photovoltaic sources in electric utility grid-interactive applications. The invention improves the conversion efficiency and lowers the cost of DC-to-AC inverters. The enabling technology is a novel inverter circuit topology, where the bulk of the throughput power, from DC source to AC utility, is processed only once. The inverter does not require an isolation transformer and can be connected directly to a 480/277 Vac utility grid. The invention also allows the power converter to start into photovoltaic array having higher open circuit voltages. The invention also uses active ripple current cancellation to substantially reduce the cost, size and weight of the main filter inductors.

An Airborne Radar Power Supply With Contactless Transfer of Energy—Part II: Converter Design

Abstract: A magnetic link is established between the stationary and revolving frames of a radar system by means of a rotating transformer. Based on the magnetics analysis of Part I of the series, a design methodology is proposed for integrating a rotating transformer into a power electronic converter using the efficiency and voltage gain plots. It is shown that a phase-shifted full-bridge topology can effectively utilize the parasitic components of the transformer. The increased magnetizing current assists the resonant transition, and this, in turn, compensates for the increased conduction losses that a rotating transformer yields. The proposed design method secures the soft-switching operation of the converter over the entire load range and allows efficient operation and reduced electromagnetic emissions. The methodology is evaluated experimentally, and the resulting prototype demonstrates an average efficiency of 92.6% in the 0.2-1-kW output power range. The proposed topology extends the power capacity of the rotating transformer without compromising its size, cost, or performance. A comparison between the slip rings and rotating transformer solutions highlights the merits and weaknesses of each technology.

Device for feeding electrical energy from an energy source

Abstract: A device ( 1 ) for feeding electrical energy from an energy source with variable source voltage into an electric power supply network ( 15 ), said device ( 1 ) including a transformer ( 112 ) for galvanic isolation, a resonant inverter ( 11 ) with semi-conductor switches (a-d; A, B), one or several resonant capacitors ( 17; 18, 19; 20, 21 ) and one rectifier ( 113 ), is intended to provide high efficiency and have galvanic isolation. This is achieved in that the resonant inverter ( 11 ) is operated in the full resonant mode if the operating voltage is in an operation point (MPP) and in the hard-switching mode if the voltages exceed the operation point (MPP).

Modelling, simulation and measurement of fast transients in transformer windings with consideration of frequency-dependent losses

Abstract: For the specification of winding insulation of transformers, it is important to know the electrical stresses to which the winding can be exposed during fast transient oscillations. These oscillations occur during switching operations performed by circuit breakers, or when gas-insulated substations (GIS) are used. Therefore one of the priorities is to use a high-frequency transformer model capable to simulating fast transient oscillations in the windings. The model presented requires only information about the geometry of the winding and the core, as well the electrical and magnetic parameters for the used materials. In the transformer model, the frequency-dependent core and copper losses are included. Numerical computations are performed with and without the core losses being taken into account. Two types of measurement are taken to verify the validity of the model. First, the voltage transients are measured and computed by the application of a step impulse with a rise time of 50 ns. Then, the transformer is switched by a vacuum circuit breaker, and the multiple reignitions, which contain oscillations with a wide frequency range, are analysed. The results verify that the model is suitable to simulate the voltage distribution in transformer windings over a wide frequency range.

A Novel Transformer Structure for High power, High Frequency converter

Abstract: Power transformer structure is a key factor for the high power, high frequency converter performance which includes efficiency, thermal performance and power density. This paper proposes a novel transformer structure for the kilo-watt level, high frequency converter which is reinforce insulation needed for the secondary side to primary side. The transformer has spiral-wound primary layers using TIW (triple insulation wire) and PCB-winding secondary layers. All the windings are arranged by full interleaving structure to minimize the leakage inductance and eddy current loss. Further more, the secondary rectifiers and filter capacitors are mounted in PCB-winding secondary layers to further minimize the termination effect. A 1.2 KW (O/P: 12 V/100 A, I/P: 400 V) Mega Hz LLC converter prototype employed the proposed transformer structure is constructed, and over 96% efficiency achieved.

A Practical Copper Loss Measurement Method for the Planar Transformer in High-Frequency Switching Converters

Abstract: In this paper, a new and practical measurement method is proposed to characterize the planar transformer copper loss operating in a high-frequency switching mode power supply (SMPS). The scheme is easy to set up, and it provides an equivalent winding alternating current resistance, which is the result of all the field effects on the transformer windings to achieve more accurate copper loss characterization. A detailed error analysis for the proposed copper loss measurement method is conducted. The analysis results can provide useful guidelines on the SMPS transformer copper loss measurement scheme design. Measurement results on the copper loss of a planar transformer in a high-frequency dc/dc converter are presented. In order to verify the measurement results, a time-domain finite-element analysis transient solver is adopted to analyze the transformer copper loss. Good matching between the simulation and measurement results is achieved.

Non-contact rotary power transfer system

Abstract: A power delivery system includes a rotary transformer having a primary winding and a secondary winding and configured to transfer power between stationary coupling elements on a stationary side and rotational coupling elements on a rotational side. The rotational coupling elements share a central axis with the stationary coupling elements, and are adapted to rotate with respect to the stationary coupling elements. The power delivery system includes an isolation transformer that drives the primary winding of the rotary transformer, and a plurality of power inverter stages whose outputs are adapted to be summed and coupled to the rotary transformer. A plurality of output power converters receive transmitted power from the rotary transformer. A plurality of control elements, disposed on the rotating side, are configured to close a feedback loop on desired and actual performance of the output power converters, and to control the power inverter stages.

Power Transformer Characteristics and Their Effects on Protective Relays

Abstract: There are a variety of protective relays using different measuring techniques to provide reliable and secure transformer protection. This includes electro-mechanical, solid state and numerical relays. Within each group, various algorithms exist. Advancements made to transformer technology and design over the past 3 decades, have changed the characteristics of the transformer inrush current, and have often introduced incorrect operations in the existing harmonic restraint relays during energization

Transformer coils for providing voltage isolation

Abstract: A circuit package providing voltage isolation includes at least one output and first circuitry located in a substrate of the circuit package for performing an operation. A transformer located in the metal layers of the circuit package provides voltage isolation between the first circuitry and the at least one output.

Transformer winding defects identification based on a high frequency method

Abstract: The transformer diagnostic methods are systematically being improved and extended due to growing requirements for reliability of power systems in terms of uninterrupted power supply and avoidance of blackouts. Those methods are also driven by longer lifetime of transformers and demand for reduction of transmission and distribution costs. Hence, the detection of winding faults in transformers, both in exploitation or during transportation is an important aspect of power transformer failure prevention. The frequency response analysis method (FRA), more and more frequently used in electric power engineering, has been applied for investigations and signature analysis based on the admittance and transfer function. The paper presents a novel approach to the identification of typical transformer winding problems such as axial or radial movements or turn-to-turn faults. The proposed transfer function discrimination (TFD) criteria are based on the derived transfer function ratios, manifesting higher sensitivity.

DC power transmission system of voltage source converter using pulse-interleaving auxiliary circuit

Abstract: A DC power transmission system of a voltage source converter using a pulse-interleaving auxiliary circuit is disclosed. The converter system comprises an IGBT converter for converting an AC power to a DC power or the DC power to the AC power; an open Y-Y transformer and a Y-Δ transformer for stepping up or stepping down the AC power having a predetermined magnitude; a capacitor for dividing a DC voltage; and a DC Auxiliary circuit composed of a normal transformer and half-bridge for overlapping a pulse type input voltage to increase the number of pulses of an output waveform. In using a DC auxiliary circuit composed of normal transformer and 3-level half-bridge to increase the number of pulses of the output waveform by superposing the voltage in the form of the pulse, a normal transformer may be used instead of the tapped transformer to reduce the size thereof and to obtain an accurate transformer ratio, and a 3-level half-bridge may be used instead of the H-bridge to reduce the switching loss.

Circuit and associated method for reducing power consumption in an a power transformer

Abstract: A method and circuit is provided for reducing power consumption in a power transformer, typically incorporated into an electrical or electronic device such as a consumer device. In an embodiment, a detection/isolation circuit is coupled to an input of a power transformer/rectifier via a switching device. The switching device can be, for example, a solid state relay. The detection/isolation circuit is configured to sense the occurrence of no-load conditions in the power transformer and responsively disengage the power transformer from a coupled source of power (e.g., wall outlet) via the coupled switching device.

A Novel Active Power Filter for High-Voltage Power Distribution Systems Application

Abstract: In this paper, a novel principle of an active power filter based on the harmonic impedance control of a transformer is proposed for high-voltage power distribution systems application. A linear transformer with multiple secondary windings is adopted. The primary winding is shunted with harmonic-producing loads, while the secondary windings are connected with inverters. The primary harmonic current is detected and then tracked by the inverters with fixed compensation coefficient. When the harmonic current compensation condition is satisfied, the transformer can really exhibit nearly zero impedance to harmonic current and primary self-impedance to fundamental current. As a result, the harmonic currents in power systems can be led to flow into the transformer branch. The operation principle, the control scheme, and the harmonic current detection method are discussed in detail. Finally, simulated waveforms and experimental results are presented to verify the effectiveness of the active power filter

Multi-level frequency conversion driving apparatus with energy conservation unit

Abstract: The present invention belongs to the field of high voltage multilevel frequency conversion technology, characterized in that the main circuit composes of a H bridge series connection type frequency converter and a group of storage energy inverter devices. The H bridge series connection type frequency converter is powered by a multiple winding isolation transformer, the storage energy inverter device is connected with a passive power energy storage capacitor, the energy storage capacitor can be selected according to the corresponding system power level. The main switch device of the three-phase bridge arm of the frequency conversion driving device can choose the corresponding power semiconductor switch device according to the output voltage level and the different passing currents. The controller whose core is a high performance digital signal microprocessor forms the PWM control signal. The structure is added with a group of storage energy inverter devices in the base of the traditional H bridge series connection type frequency converter, so as to not only realize the purpose of using energy storage capacitor to store energy dynamically, but make the voltage harmonic content decrease, the present invention improves the efficiency and the performance of the frequency conversion driving device.

Pulse Shape Improvement in Core-Type High-Voltage Pulse Transformers With Auxiliary Windings

Abstract: High-voltage pulsed power technologies are rapidly emerging as a key to efficient and flexible use of electrical power for many industrial applications. One of the most important elements in high-voltage pulse-generating circuit technology is the transformer, generally used to further increase the pulse output voltage level. However, its nonideal behavior has significant influence on the output pulse shape. The most attractive winding configuration for high-voltage, the core-type transformer with primary and secondary on different core legs, is seldom used in pulsed applications, because of its weak magnetic coupling between windings, which would result in a slow-rising output voltage pulse. This paper shows that auxiliary windings, suitably positioned and connected, provide a dramatic improvement in the pulse rise time in core-type high-voltage pulse transformers. The paper derives a mathematical model and uses it to describe the observed behavior of the transformer with auxiliary windings. It discusses experimental results, obtained from a high-voltage test transformer associated with a high-voltage pulse generating circuit, and the simulation results obtained from the numerical evaluation of the developed differential equations implemented in Matlab and taking into account the measured transformer parameters

Method and system for a transformer in an integrated circuit package

Abstract: Aspects of a method and system for a transformer in an integrated circuit package are provided. In this regard, signals may be transmitted and/or received via an antenna communicatively coupled to a transformer embedded in multi-layer integrated circuit package. The windings ratio of the transformer may be configured based on an impedance of the antenna, an impedance of a transmitter coupled to the transformer, an impedance of an LNA coupled to the transformer, and/or a power level of the received and/or transmitted signals. The windings ratio may be configured via one or more switching elements which may be MEMS switches embedded in the multi-layer IC package. The transformer may comprise a plurality of loops fabricated on a corresponding plurality of metal layers in the multi-layer IC package, and the loops may be communicatively coupled with one or more vias. The multi-layer IC package may comprise ferromagnetic and/or ferromagnetic materials.

Apparatus to provide synchronous rectifying circuit for flyback power converters

Abstract: A synchronous rectifying circuit is provided for flyback power converter. A pulse generator is utilized to generate a pulse signal in response to a leading edge and a trailing edge of a switching signal. The switching signal is used for switching the transformer of the power converter. An isolation device such as pulse transformer or small capacitors is coupled to the pulse generator for transferring the pulse signal through an isolation barrier of a transformer. A synchronous rectifier includes a power switch and a control circuit. The power switch is connected in between the secondary side of the transformer and the output of the power converter for the rectifying operation. The control circuit having a latch is operated to receive the pulse signal for controlling the power switch.

Magnetizing inrush current suppression device and method for transformer

Abstract: To suppress, without additionally providing any interrupters having resistors or the like, an exciting inrush current occurring when a three-phase transformer is powered on by using three single-phase type interrupters at the same time or using a three-phase common operating mechanism type interrupter. In a transformer exciting inrush current suppressing method for suppressing an exciting inrush current occurring at the beginning of an excitation by coupling the phase terminals of a three-phase transformer (300) to a three-phase power supply (100) via three-phase interrupters (200), the phase voltages of a primary, secondary or tertiary side or the interline voltages during steady-state application of three-phase AC voltages to the transformer (300) are integrated to calculate steady-state magnetic fluxes (4,5,6) of the transformer phases; the polarities and magnitudes of residual magnetic fluxes (7,8,9) of the transformer phases after the interruption of the transformer by the interrupters (200) are calculated; and the three-phase interrupters are simultaneously closed when the phases, for which the polarities of the steady-state magnetic fluxes (4,5,6) of the transformer phases are identical with the polarities of the residual magnetic fluxes (7,8,9) of the transformer phases, are within a range (13) in which the three phases overlap with one another.

Apparatus and method for compressing exciting inrush current of transformer

Abstract: To suppress, without additionally providing any interrupters having resistors or the like, an exciting inrush current occurring when a three-phase transformer is powered on by using three single-phase type interrupters at the same time or using a three-phase common operating mechanism type interrupter. In a transformer exciting inrush current suppressing method for suppressing an exciting inrush current occurring at the beginning of an excitation by coupling the phase terminals of a three-phase transformer (300) to a three-phase power supply (100) via three-phase interrupters (200), the phase voltages of a primary, secondary or tertiary side or the interline voltages during steady-state application of three-phase AC voltages to the transformer (300) are integrated to calculate steady-state magnetic fluxes (4,5,6) of the transformer phases; the polarities and magnitudes of residual magnetic fluxes (7,8,9) of the transformer phases after the interruption of the transformer by the interrupters (200) are calculated; and the three-phase interrupters are simultaneously closed when the phases, for which the polarities of the steady-state magnetic fluxes (4,5,6) of the transformer phases are identical with the polarities of the residual magnetic fluxes (7,8,9) of the transformer phases, are within a range (13) in which the three phases overlap with one another.

A power transformer as a source of noise.

Abstract: This article presents selected results of analyses and simulations carried out as part of research performed at the Central Institute of Labor Protection – the National Research Institute (CIOP-PIB) in connection with the development of a system for active reduction of noise emitted by high power electricity transformers. This analysis covers the transformer as a source of noise as well as a mathematical description of the phenomenon of radiation of vibroacoustic energy through a transformer enclosure modeled as a vibrating rectangular plate. Also described is an acoustic model of the transformer in the form of an array of loudspeakers.

Method and system of current transformer output magnitude compensation in a circuit breaker system

Abstract: A method and system to detect currents in the saturation region of a current transformer for a circuit breaker is disclosed. An example method is sensing a fault condition with a current transformer in a circuit breaker. The characteristic curve of the current transformer in a saturation mode is determined based on peak current. A current is received on the transformer. A secondary current is output from the transformer. It is determined whether the secondary current is indicative of a fault current in the saturation mode of the transformer. The breaker is tripped if the secondary current is indicative of a fault current.

Low voltage stress power converter

Abstract: A circuit used to convert a DC input to an AC output comprises a pair of series circuits, one or two capacitors, and one transformer. Each of the series circuits is in parallel with the DC input and comprises a pair of series-connected switches and at least one transformer primary. Each capacitor couples the two series circuits, and is attached to each series circuit at a node between the respective transformer primary and switch. The center nodes between two series-connected switches are connected together. At least one secondary on the transformer provides the AC output. Optionally, multiple transformers may be utilized. Similar topologies may be used for rectification instead of inversion.