Showing papers on "Isolation transformer published in 2004"

Split core sensing transformer

Abstract: Separable toroidal segments reduce the size of a sensing transformer that can be installed on an electrical conductor while connected to a device

A novel active power quality compensator topology for electrified railway

Abstract: To improve the power quality of traction power system, a novel active power quality compensator (APQC) and a new compensating currents detection method are proposed. The APQC consists of a three-phase voltage source converter and a Scott transformer. The Scott transformer, taken as an isolation transformer, not only connects the three-phase converter to the traction power system, but also converts the traction power system to a nearly balanced three-phase power system. Therefore, a general three-phase converter could be used in APQC. Regarding the traction substation as a compensating object, the power quality of a traction substation can be improved integrally. Simulation and prototype experimental results show that the proposed APQC is able to compensate reactive power, harmonic, and negative-sequence currents in two feeders of a traction substation.

Multilevel converter based intelligent universal transformer

Abstract: A multilevel converter-based, intelligent, universal transformer includes back-to-back, interconnected, multi-level converters coupled to a switched inverter circuit via a high-frequency transformer. The input of the universal transformer can be coupled to a high-voltage distribution system and the output of the universal transformer can be coupled to low-voltage applications. The universal transformer is smaller in size than conventional copper-and-iron based transformers, yet provides enhanced power quality performance and increased functionality.

Zero-voltage-switching half-bridge DC-DC converter with modified PWM control method

Abstract: Asymmetric control scheme is an approach to achieve zero-voltage switching (ZVS) for half-bridge isolated dc-dc converters. However, it is not suited for wide range of input voltage due to the uneven voltage and current components stresses. This paper presents a novel "duty-cycle-shifted pulse-width modulated" (DCS PWM) control scheme for half-bridge isolated dc-dc converters to achieve ZVS operation for one of the two switches without causing the asymmetric penalties in the asymmetric control and without adding additional components. Based on the DCS PWM control scheme, an active-clamp branch comprising an auxiliary switch and a diode is added across the isolation transformer primary winding in the half-bridge converter to achieve ZVS for the other main switch by utilizing energy stored in the transformer leakage inductance. Moreover, the auxiliary switch also operates at ZVS and zero-current switching (ZCS) conditions. Furthermore, during the off-time period, the ringing resulted from the oscillation between the transformer leakage inductance and the junction capacitance of two switches is eliminated owing to the active-clamp branch and DCS PWM control scheme. Hence, switching losses and leakage-inductance-related losses are significantly reduced, which provides the converter with the potential to operate at higher efficiencies and higher switching frequencies. The principle of operation and key features of the proposed DCS PWM control scheme and two ZVS half-bridge topologies are illustrated and experimentally verified.

A novel three-phase three-port UPS employing a single high-frequency isolation transformer

Abstract: A three-phase PWM rectifier and a three-phase PWM inverter are coupled via two four-quadrant full-bridge converter cells and a high-frequency isolation transformer. By employing a third transformer winding and further full-bridge cell battery energy storage is incorporated into the power transfer between rectifier and inverter resulting in a three-port UPS concept. The phase shift control of the power flow between the ports is analyzed for square-wave operation of the full-bridge cells. Furthermore, the utilization of the degrees of freedom of the system control, i.e. the extension to duty cycle control for optimizing the system behavior is discussed and control laws ensuring minimum overall system losses are derived. Finally, a control-oriented converter model is proposed and the decoupled control of the power flow of the ports is treated briefly. All theoretical considerations are verified by simulations using PSIM.

Multilevel power amplifier architecture using multi-tap transformer

Abstract: A multi-level power amplifier architecture using a multi-tap transformer implemented on a single CMOS integrated circuit wireless communications device is described. By providing a multi-tap transformer for coupling a plurality of power amplifiers to a shared output impedance, such as an antenna, power transmission may be made at different levels while maintaining efficiency. With a multi-tap transformer having “N” taps featuring “N” different impedance levels, each tap may be connected to an amplifier cell which delivers power into the transformer at the tap for coupling to the output load. Any one of the “N” amplifier cells can be turned on at once along with any combination of the “N” amplifier cells.

Multifunction hybrid intelligent universal transformer

Abstract: A multifunction hybrid intelligent universal transformer includes a conventional transformer coupled with power electronics on the secondary side to enhance the functionality of power conversion. The universal transformer includes features for overcoming the deficiencies associated with conventional transformers, including voltage sag compensation, instantaneous voltage regulation, outage compensation, capacitor switching protection, harmonic compensation, single-phasing protection, DC output, and variable frequency output.

Implantable lead-based sensor powered by piezoelectric transformer

Abstract: In general, the invention is directed to an IMD having a piezoelectric transformer to power a lead-based sensor. The IMD powers the piezoelectric transformer with a low amplitude signal. The piezoelectric transformer serves to convert the voltage level of the low amplitude signal to a higher voltage level to drive the sensor. produced by a battery in the IMD to voltage levels appropriate for IMD operation. A piezoelectric transformer offers small size and low profile, as well as operational efficiency, and permits the IMD to transmit a low amplitude signal to a remote sensor deployed within an implantable lead. In addition, the piezoelectric transformer provides electrical isolation that reduces electromagnetic interference among different sensors.

Design considerations for a medium frequency transformer in a line side power conversion system

Abstract: Design considerations are presented for a medium frequency transformer in a line side power conversion system for electric railway traction. The system employs soft commutation in order to reduce switching losses and allow for high operating frequency of the transformer. Two different designs are evaluated; The first one is dry insulated and the second one is liquid-immersed. Calculations indicate that a 1 MVA transformer operating at 4 kHz could be realized with an active weight of below 150 kg for both dry and liquid-immersed transformer concepts. The transformers are modeled magnetically, electrically and thermally, and a geometric optimization procedure based on a cost function is applied to achieve an optimum design.

Systems and methods for fault protection in a balancing transformer

Abstract: An apparatus and methods for balancing current in multiple negative impedance gas discharge lamp loads. Embodiments advantageously include balancing transformer configurations that are relatively cost-effective, reliable, efficient, and good performing. Embodiments include configurations that are applicable to any number of gas discharge tubes, such as cold cathode fluorescent lamps. The balancing transformer configuration techniques permit a relatively small number of power inverters, such as one power inverter, to power multiple lamps in parallel. One embodiment of a balancing transformer includes a safety winding which can be used to protect the balancing transformer in the event of a lamp failure and can be used to provide an indication of a failed lamp.

Transformer for producing high electrical currents

Abstract: A transformer ( 1 ) serves to produce high electrical currents, in particular, for transforming high alternating and power pulse currents for producing magnetic fields in magnetic technology for magnetizing magnets and magnetic systems, as well as in conversion technology for forming electrically conductive materials by means of a magnetic field. The transformer has at least one primary coil ( 2 ) and at least one secondary part ( 3 ), which are connected with bus bars ( 4, 5 ). The secondary part ( 3 ) of the transformer ( 1 ) includes at least one electrically conductive plate ( 6 ), in which at least one cut-out penetrating the plate ( 6 ) is disposed. At least one slit ( 8 ) originating from the cut-out ( 7 ) is provided, which separates the plate ( 6 ) on one side of each cut-out ( 7 ) into two parts and produces the required bus bar ( 5 ).

A self-driven active clamp forward converter using the auxiliary winding of the power transformer

Abstract: This study proposes a new self-driven active clamp forward converter eliminating the extra drive circuit for the active clamp switch. The converter used the auxiliary winding of the power transformer to drive the active clamp switch and a simple RC circuit to get the dead time between the two switches. The operation principle was presented and experimental results were used to verify theoretical predictions. A 100-W (5 V/20 A) prototype converter that only exhibited 1.5-turn winding number in the auxiliary winding was sufficient to drive the active clamp switch on the input of 50 V. Finally, the measured efficiency of the converter was presented and the maximum efficiency of 91% was obtained.

Transformer isolator for digital power supply

Abstract: A system for providing voltage isolation includes the first and second chips, each containing functional circuitry. The chips are interconnected via at least one RF isolation link that provides voltage isolation between the first chip and the second chip.

DC to DC converter with high frequency zigzag transformer

Abstract: A DC to DC converter including a zigzag transformer. The transformer operates at high frequency with integrated magnetics and does not provide isolation. The multiphase converter has gate inputs with PWM signals appropriately phase-shifted depending on the number of phases to make balanced phase voltages across the transformer windings. The switching frequency of the converter is relatively low but fast transient response can be achieved by adding an integrated zigzag transformer.

Active current transformer circuits for low distortion sensing in switched mode power converters

Abstract: The current transformer (CT) is frequently used for sensing applications in switched mode power converters. Advantages are that galvanic isolation is inherently incorporated, bandwidth is high, losses are low and that a high-amplitude output signal may be derived. Because of this combination of advantages it may be preferred to other current sensing technologies such as the Hall-effect sensor or the sense resistance. However, it exhibits some limitations. A compromise exists between the amplitude of the output signal and the distortion present in it due to droop. Droop results as some of the input current under measurement diverts away from the "ideal" transformer within the CT's equivalent circuit and into its magnetizing branch. In addition, where the CT is used for sensing unidirectional current pulses, the duty cycle of the pulses has to be restricted if saturation of its core material is to be avoided. This paper describes techniques based on the incorporation of an active load and synchronous rectification for reducing the distortion due to droop and allowing operation at extended duty cycles. Experimental results are given for a dual transformer arrangement used to sense the choke current drawn by a boost converter circuit.

Boost rectifier with half-power rated semiconductor devices

Abstract: A rectifier has two half-controlled bridge rectifiers which are connected in parallel to provide DC power to DC bus lines. Each bridge rectifier receives AC power through inductances such as series inductors or an isolation transformer with a single primary and two secondaries. Each bridge rectifier has a full bridge of diodes, with active switching devices connected in parallel with half of the diodes in the bridge. The switching devices can be controlled to provide unity power factor at the AC input lines, allowing lower rated diodes and switching devices to be used.

AC/DC monitor system

Abstract: A combined AC/DC monitoring system simultaneously monitors an AC power supply and a DC power supply in a mobile unit. The monitoring system is electrically isolated from an AC input source through an AC isolation transformer. A microcontroller digitally provides various computed variables from various digitized input signals. The monitoring system simultaneously displays a plurality of the computed variables while the system monitors for various user-selected high/low conditions of the computed variables. The system monitors AC power surges and can alternately displays a high voltage level for a predetermined time and a low voltage level for a predetermined time. An algorithm determines whether the AC voltage is a true sine wave or otherwise. The system monitors DC current on the high side, or positive terminal, of a battery. User selectable DC shunts are provided to measure a range of DC currents.

Systems and methods for driving large capacity AC motors

Abstract: A drive system for driving large capacity motors includes a motor and a variable frequency drive which accepts input from a three-phase power source. The drive system includes a step-up transformer, preferably of a high-capacity three-phase type, positioned between and electrically connected to the motor and the variable frequency drive to thereby step-up voltage received from the variable frequency drive to be supplied to the motor. The transformer includes a transformer chamber formed in the transformer tank containing a cooling fluid for cooling transformer internal components. A plurality of inductors forming part of a harmonic filter are positioned within the transformer chamber such that they can be protected from the environment and simultaneously cooled with other transformer internal components by the dielectric fluid. The filter includes capacitors that are preferably mounted outside of the tank.

A highly efficient contactless electrical energy transmission system

Abstract: This paper proposes a new concept for contactless electrical energy transmission system for an elevator and an automated guided vehicle. The system has rechargeable batteries on the car and electrical energy is supplied at a specific place. When electric power is supplied to the car, it runs automatically and approaches the battery charger. Therefore, a comparatively large gap is needed between the primary transformer at the battery charger and the secondary transformer on the car in order to prevent damage which would be caused by a collision. In this case, a drop of the transformer coupling rate due to the large gap must be prevented. In conventional contactless electrical energy transmission technology, since electric power is received by a pickup coil from a power line, a large-sized transformer is required. When the distance over which the car runs is long, the copper loss of the line also increases. The developed system adopts a high-frequency inverter using a soft switching method to miniaturize the transformer. The system has a coupling rate of 0.88 for a transformer gap length of 10 mm and can operate at 91% efficiency. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(1): 66–74, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10290

Novel soft-commutation DC-DC power converter with high-frequency transformer secondary side phase-shifted PWM active rectifier

Abstract: This paper presents a novel circuit topology of the voltage source type zero voltage soft-switching (ZVS) full bridge DC-DC power converter with an isolated high-frequency transformer, which incorporates zero-current soft-switching (ZCS) phase-shifted (PS)-PWM active power switches in series with diodes of two bridge arms of a full-bridge rectifier on the high-frequency transformer secondary side. This high-frequency linked DC-DC power converter can achieve ZVS for noncontrolled active power switches on the primary side of the transformer and ZCS for PS-PWM active switches on the secondary side of the transformer under wide load variations as well as a wide PS-PWM regulation range. The switching power losses and conduction power losses of the active devices of the proposed DC-DC converter can be considerably reduced. The proposed DC-DC converter blocks circulating current flowing through the semiconductor switching devices on the transformer primary side as compared to the lossless snubbing capacitor and transformer leakage and magnetising inductor-assisted soft-switching full-bridge DC-DC converter with ZVS PS-PWM scheme on the transformer primary side. The steady-state operating principles of the proposed DC-DC converter are evaluated and discussed, based on the simulation and experimental results obtained from a 2 kW-40 kHz breadboard set-up using IGBTs.

Three-level LLC series resonance DC/DC transformer

Abstract: This invention LLC serial resonance DC/DC converter includes a bleeder capacitor, an inverter composed of four serial switches, a resonance circuit, a clamp, an isolation transformer, a commutating circuit and a filter, capable of realizing large input/output voltage regulation sphere with small frequency variable sphere by LLC resonance circuit with dual intrinsic resonance frequency, at the same time, the switch is effectively clamped by a pair of clamp diodes, so that each switch voltage stress is half of the input voltage and ZVS is realized in all sphere without any additional circuit, the commutation diode works at the ZCS state.

Calculating the coupling factor in a multilayer coaxial transformer with air core

Abstract: High-voltage transformers can be built with coaxial transmission lines. This paper describes a transformer design that uses the coaxial screen as primary winding and the inner conductor as secondary. An advantage of transmission line transformers is that the insulation problem is solved and the construction can be kept simple; the coupling between the primary and secondary coils is high even though the transformer uses an air core. The air core brings another advantage: the capacity to store large quantities of magnetic energy. The combination of a high coupling factor and large energy storage capacity makes this transformer ideal for charging high-voltage capacitors fast. The winding type for the transformer is alternating Archimedean spirals. Here, we present a magnetic field analysis of the transformer's primary, secondary, and mutual inductance using a finite-element solver. We compare the measured magnetic flux density versus the calculated value. The step-up winding ratio of the transformer influences the coupling factor marginally if the construction has an even number of spiral layers for each set of windings. However, the result from the finite-element solver predicts a drop in coupling factor if the step-up transformer construction has an odd number of spiral layers. The copper conductors used in the transformer resemble isotropic copper pipes.

Galvanically isolated voltage sensing circuit

Abstract: Method and apparatus for galvanically isolated voltage sensing circuit. A circuit includes a scaling device that provides a scaled signal of an input voltage to a modulator. An oscillator provides a carrier frequency to the modulator, the modulator modulating the scaled signal with the carrier frequency to produce a modulated scaled signal. An isolation transformer is coupled to an output of the modulator. The isolation transformer receives the modulated scaled signal. A demodulator is coupled to an output of the isolation transformer and demodulates the modulated scaled signal to produce an input voltage signal representative of the scaled signal.

High performance bidirectional Cuk converter for telecommunication systems

Abstract: Telecommunication systems mainly need highly reliable power supplies with high efficiency. Other important issues are related to the noise and electromagnetic interference (EMI), which are produced by the power supply. Low EMI means low shielding cost and low distortion of the main communication signal. To meet such essential requirements, a high performance bidirectional Cuk converter-based power supply is proposed in this paper. The converter provides high efficiency, low noise, and low EMI. In addition, the converter has high power density, low cost, and electric isolation. These advantages are achieved from integrating the magnetic components of the converter, the input inductors, the output inductor, and the isolation transformer, on one magnetic assembly. In this paper, the conventional 42 VDC power supply architecture for telecommunication systems is briefly described. A modified system that utilizes the integrated magnetics bidirectional Cuk converter is explained. Finally, the full design integrated Cuk converter, simulation results, and practical performance evaluation are presented.

Estimation of core loss of transformer under non-sinusoidal voltage supply

Abstract: This paper presents the 1-phase transformer core loss estimation under non-sinusoidal voltage supply. The Epstein test apparatus, with grain oriented magnetic steel side MS (0.3 mm), inverter and low pass filter is used in estimation of core loss. The calculated results are compared with the measured value and are useful for the appropriate single-phase transformer design under non-sinusoidal voltage supply.

Designing a radial mode laminated piezoelectric transformer for high power applications

Abstract: This research was aimed to develop a good understanding of the laminated piezoelectric transformer designs and their related properties, such as bonding materials, electrode materials and constructive parameters. We found that Stycast/spl reg/ 1264 is a promising bonding material to improve transformer characteristics in terms of mechanical quality factor, efficiency and output power. Size and shape of the piezoelectric element also affect the transformer's performance. It showed that the power capability of piezoelectric transformer can be increased when the disk-shape and bigger size of piezoelectric elements are used. From this study, the maximum output powers of approximately 7 and 36 W were obtained for 23.8 and 45.0 mm diameter piezoelectric transformers with the same total thickness, respectively. These laminated transformers exhibit approximately three times higher power density than a rectangular Rosen-type piezoelectric transformer with a similar volume.

Simplified topology for HID lamps

Abstract: An HID ballast includes a flyback power converter with a simplified topology that permits power factor correction while supplying constant output power to drive an inverter supplying low frequency modulated power to the HID lamp. A switch is coupled in series with a transformer in the power converter to control current through the transformer to provide constant output power. The off time of the switch contributes to controlling the power factor of the ballast circuit. The transformer is operated in critical conduction mode, with an indication of zero current in the transformer used to determine the control for the switch. An output of the flyback power converter provides a feedback signal to obtain constant power output based on switching intervals applied to the switch coupled to the transformer. This simplified topology reduces part counts while providing a robust control that can be flexibly applied to a number of HID lamps.

Performance evaluation of the isolated bidirectional Cuk converter with integrated magnetics

Abstract: In this paper, an isolated bidirectional DC/DC Cuk converter featuring high power density, zero input/output current ripples, and symmetrical design is presented. The magnetic components of the converter, which include the input inductor, the output inductor, and the isolation transformer, are assembled together in one magnetic structure. The magnetic assembly is modeled and designed using the gyrator-capacitor (G-C) approach. Simulation and experimental results are presented to verify the converter performance in both forward and backward modes of operation. The effect of the switching frequency on the percentage current ripples is discussed.

A bidirectional high-frequency link inverter using center-tapped transformer

Abstract: In this paper, a bidirectional high-frequency link inverter is proposed. The main feature of the inverter is that the electrical isolation is provided by a high-frequency center-tapped transformer. Furthermore, the sinusoidal pulse width modulation method is modified so that the transformer can be utilized near to its full potential. As a result, the power switches count is reduced, and the efficiency increased. A 1 kW prototype inverter is built and typical results are presented.