Showing papers on "Flyback transformer published in 2018"

High-Frequency Transformer Design for Modular Power Conversion From Medium-Voltage AC to 400 VDC

Abstract: This paper presents a high-frequency modular medium-voltage AC (4160 VAC or 13.8 kVAC) to low-voltage DC (400 VDC) system that is scalable in order to be used for different scale microgrids. A 15 kW, 500 kHz DC/DC converter is demonstrated as the most important stage of the system overall, which can be scalable to a 225 kW 4160 VAC to 400 VDC system. Motivation of a CLLC resonant converter and its design parameters determination is carefully illustrated. The high-frequency transformer is the key element for the DC/DC converter. Then, the paper focuses on high-frequency transformer design to realize high-voltage insulation, high efficiency, and high density at the same time. Based on a split winding UU core transformer structure, transformer insulation materials and dimension parameters are determined referring to the IEEE insulation standard. The transformer magnetic loss model is reviewed based on which loss design tradeoff is carefully analyzed. Different working frequency impact on transformer design over three different core materials is also presented. Finally, a 500 kHz transformer prototype has been developed and demonstrated with the IEEE standard required insulation tests. A whole CLLC resonant converter is also present with experiments results. The converter holds outstanding 98% efficiency and 2.9 kW/L power density.

Soft-Switching Solid-State Transformer (S4T)

Abstract: This paper presents a new topology for a fully bidirectional soft-switching solid-state transformer (S4T) The minimal topology, featuring 12 main devices and a high-frequency transformer, does not use an intermediate dc voltage link, and provides sinusoidal input and output voltages The S4T can be configured to interface with two- or multiterminal dc, single- or multiphase ac systems An auxiliary resonant circuit creates zero-voltage-switching conditions for main devices from no-load to full-load, and helps manage interactions with circuit parasitic elements The modularized structure allows series and/or parallel stacking of converter cells for high-voltage and high-power applications

A Wavelet-Based Transformer Differential Protection With Differential Current Transformer Saturation and Cross-Country Fault Detection

Abstract: The current transformer (CT) saturation phenomenon has been one of the main problems for the power transformer differential protection, leading to incorrect current measurements and relay misoperation. This paper proposes a fast and efficient transformer differential protection scheme with additional differential CT saturation and cross-country fault detection modules after the external fault detection, all of them based on the differential wavelet coefficient energy with border distortions in order to stabilize the relay during external faults and distinguish accurately CT saturation from cross-country internal faults. The proposed method was assessed by using representative simulations of internal faults, transformer energizations, and external faults with CT saturation followed by cross-country internal faults, and good results were achieved.

Highly Efficient Secondary-Resonant Active Clamp Flyback Converter

Abstract: Both high switching frequency and high efficiency are critical in reducing power adapter size. The active clamp flyback (ACF) topology allows zero voltage soft switching (ZVS) under all line and load conditions, eliminates leakage inductance and snubber losses, and enables high frequency and high power density power conversion. Traditional ACF ZVS operation relies on the resonance between leakage inductance and a small primary-side clamping capacitor, which leads to increased rms current and high conduction loss. This also causes oscillatory output rectifier current and impedes the implementation of synchronous rectification. This paper proposes a secondary-side resonance scheme to shape the primary current waveform in a way that significantly improves synchronous rectifier operation and reduces primary rms current. The concept is verified with a ${\mathbf{25}}\hbox{--}{\text{W/in}}^{3}$ high-density 45-W adapter prototype using a monolithic gallium nitride power IC. Over 93% full-load efficiency was demonstrated at the worst case 90-V ac input and maximum full-load efficiency was 94.5%.

Planar Transformers With Near-Zero Common-Mode Noise for Flyback and Forward Converters

Abstract: Flyback and forward converters are two commonly used topologies for isolated low-power applications. These converters are simple and cost effective and provide galvanic isolation, which make them desirable for low-power levels. In order to enhance the performance of these converters, planar transformers (PTs) can be used that feature lower height, considerably lower leakage inductance, excellent thermal characteristics, and repeatability. Selecting a proper winding arrangement for a PT is a significant challenge, in particular given the large capacitances involved in flat structures. While interleaved structures significantly reduce the ac resistance and leakage inductance of PTs, they also lead to very large interwinding capacitance, which produces significant levels of undesired common-mode (CM) noise that causes EMI problems. Reducing interwinding capacitance by using noninterleaved structures is not an ideal solution to the CM noise problem because of its side effects. Instead, this paper tackles the problem by proposing the concept of paired layers. According to this concept, there are layers in the primary and secondary sides that have the same $dv/dt$ , and therefore, their overlapping does not generate CM noise. These layers can be used to design highly interleaved structures that not only have very low ac resistance and leakage inductance, but also generate almost zero CM noise, although they may have a very large interwinding capacitance. In addition, a detailed parasitic capacitance model of PTs is proposed, which analytically validates the proposed concept and method. The experimental results show that the proposed PTs not only have very low ac resistance and leakage inductance, but also generate extremely low levels of CM noise. Considering that the proposed PT has interwinding capacitance equal to $\text{700 pF}$ , it is very interesting to see that it generates significantly less CM noise than does a traditional wire-wound transformer that has only $\text{10-pF}$ parasitic capacitance. Therefore, the proposed method gives designers the opportunity to minimize ac resistance and leakage inductance by using highly interleaved structures, without having to worry about CM noise caused by large interwinding capacitance.

Load Control Using Sensitivity Identification by Means of Smart Transformer

Abstract: The higher variability introduced by distributed generation leads to fast changes in the aggregate load composition, and thus in the power response during voltage variations. The smart transformer, a power electronics-based distribution transformer with advanced control functionalities, can exploit the load dependence on voltage for providing services to the distribution and transmission grids. In this paper, two possible applications are proposed: 1) the smart transformer overload control by means of voltage control action and 2) the soft load reduction method, that reduces load consumption avoiding the load disconnection. These services depend on the correct identification of load dependence on voltage, which the smart transformer evaluates in real time based on load measurements. The effect of the distributed generation on net load sensitivity has been derived and demonstrated with the control hardware in loop evaluation by means of a real time digital simulator.

An Electrolytic Capacitor-Less High Power Factor LED Driver Based on a “One-and-a-Half Stage” Forward-Flyback Topology

Abstract: A “one-and-a-half stage” forward-flyback converter for electrolytic capacitor-less light-emitting diode (LED) driver with high power factor (PF), high efficiency, low output ripple current, and long lifetime has been proposed and studied in this paper. The basic topology of the proposed topology is a single-switch forward-flyback converter for achieving high PF. In addition, a buck converter is inserted between the forward subconverter and the load for creating two paralleled power transfer paths. The most of input energy directly reaches the load through flyback subconverter, and only about 1/4 of total energy is transferred to the load through forward subconverter and buck converter. Therefore, the proposed topology is a “one-and-a-half stage” converter and can achieve higher efficiency than the traditional two-stage topologies. At the same time, power decoupling can be realized and the electrolytic capacitor can be eliminated. Optimal control scheme, detailed analysis, and design considerations for this improved converter are presented. Finally, an experimental prototype for 28 V/700 mA LED driver was built up to verify the theoretical analysis.

An Isolated High-Frequency Link Microinverter Operated with Secondary-Side Modulation for Efficiency Improvement

Abstract: This paper discusses the operation of a single-stage, isolated, high-frequency ac-link-based single-phase dc–ac converter, suitable for photovoltaic microinverter applications, controlled using phase modulation of the secondary-side cycloconverter devices. A detailed analysis is presented explaining the impact of prominent circuit nonidealities such as device capacitance and transformer leakage inductance on circuit behavior. The proposed extended-dead-time based modulation scheme helps in achieving zero-voltage-switching of the primary devices over the entire line cycle of the ac output and also offers the benefit of reduced transformer rms current due to absence of circulating current in the zero state. A flyback-based regenerative clamp circuit is used for mitigating voltage spikes on the secondary devices arising due to leakage inductance induced oscillations. A generic commutation strategy is also discussed, which makes operation with nonunity power factor loads also possible. Experimental results on a 260-W laboratory prototype under different load conditions are presented to illustrate the discussed principles and highlight the performance improvements.

Primary Side Control For Flyback Converter Operating in DCM and CCM

Abstract: Primary side regulation (PSR) technology has the characteristics of lower cost and standby power losses. However, there is no algorithm suitable for discontinuous conduction mode (DCM) and continuous conduction mode (CCM) operations of primary side control for flyback converter because of the difficulty in estimating the output voltage correctly. In this paper, a PSR control algorithm suitable for DCM/CCM flyback converter is proposed and implemented with digital micro controller. The voltage drop on the secondary winding and output diode at CCM operation is compensated by sensing the secondary side current at the instant when primary side switch is being turned-on. The secondary side current is zero at the voltage sensing instant and equal to the current at the instant when primary side switch is being turned-on as flyback operated at DCM. In addition, the proposed algorithm can be used to regulate either the output voltage or current very well. An experimental prototype with 150 W rated power is built to verify the feasibility of the proposed control. Experimental results show that the output voltage can be controlled with error less than 0.25%, and the output current error is less than 5%. The conversion efficiency is up to 92.8%.

Soft-Switched High Voltage Gain Boost-Integrated Flyback Converter Interfaced Single-Phase Grid-Tied Inverter for SPV Integration

Abstract: A two-stage grid-tied efficient solar photovoltaic (SPV) system with zero voltage switching (ZVS) and zero current switching (ZCS) at the dc–dc converter stage and adaptive synchronization at the inverter stage is proposed. In the first stage, an improved high step-up boost-integrated flyback converter with quasi resonant voltage multiplier cell is proposed. ZVS turn-on of all mosfet s and ZCS turn-off of all diodes of resonant voltage multiplier cell results in high efficient power conversion compared with the conventional boost-integrated flyback converters. Small-sized coupled inductor enhances magnetic utilization in this converter. Second stage consists of a single-phase H-bridge grid interfaced inverter with variable band hysteresis current control technique. Amplitude adaptive notch filter is used to extract fundamental unit voltage vector of grid voltage required for estimation of synchronized reference current for hysteresis controller. A 250 W laboratory prototype is developed and experimentally evaluated. Experimental results demonstrate efficient renewable energy conversion at dc–dc converter stage and quality power injection at dc–ac inverter stage of the proposed grid-tied SPV system under changing solar insulation levels.

New Bridgeless Buck PFC Converter with Improved Input Current and Power Factor

Abstract: The bridgeless buck power factor correction (PFC) converters feature the merits of low output voltage and high efficiency while their inherent dead angles in the input current will deteriorate the input current harmonics and power factor (PF) Aiming to reduce the dead angles, a new bridgeless buck PFC converter is proposed in this paper Through integrating the main buck circuit and the auxiliary flyback circuit with one magnetic core, the dead angles in the input current of the proposed bridgeless buck PFC converter is eliminated so that the PF and input current harmonics are improved The proposed bridgeless buck PFC converter is designed to operate in discontinuous conduction mode (DCM) with the merits of simple controller and nature current shaping ability A new logic control circuit is provided The detailed theoretical derivations and design consideration are presented The experimental comparison among the proposed bridgeless buck PFC converter, the conventional buck PFC converter, and the conventional bridgeless buck PFC converter is displayed to validate the effectiveness of the new converter

Investigating Switching Transformers for Common Mode EMI Reduction to Remove Common Mode EMI Filters and Y-Capacitors in Flyback Converters

Abstract: This paper investigated the common mode (CM) noise model for multiwinding switching transformers. Based on the proposed model, a Flyback transformer is investigated. A measurement technique is used to characterize and evaluate a switching transformer’s CM noise performance. Only a signal generator and an oscilloscope are needed in this measurement technique. Because there is no any in-circuit tests are needed, the technique can help quickly design and evaluate transformers in mass testing. CM noise reduction techniques, including the balance capacitor technique, core shielding technique, balance winding technique, and winding design technique, are investigated based on the developed two-capacitance model and measurement technique without introducing extra power loss. The near-field capacitive coupling due to transformer magnetic cores is analyzed, and a core shielding technique is applied to reduce the coupling. Experimental results validated the proposed model and the developed CM noise reduction techniques. The Flyback converter can finally meet electromagnetic interference (EMI) standards without using CM EMI filters and Y-capacitors.

An Efficient and Cost-Effective Hybrid MPPT Method for a Photovoltaic Flyback Microinverter

Abstract: This paper presents a grid-connected photovoltaic (PV) flyback inverter operating in discontinuous conduction mode (DCM) and controlled through an efficient, reliable, and cost-effective hybrid maximum power point tracking (MPPT) method. Although the proposed method can be applied to any grid-connected inverter topology, in this paper, it is applied on a modified flyback inverter circuit. Moreover, the proposed MPPT method is a two-stage scheme and hence, a hybrid solution, as it consists of a combination of fractional short-circuit current and hill climbing perturb and observe (P $\&$ O) method reformulated. The change in weather condition is accurately detected using the current limit technique such that the difference in short-circuit current and photovoltaic current is monitored continuously. It is demonstrated that the use of current limit enables the system to swiftly track the maximum power point (MPP) in abruptly changing environmental conditions. The proposed MPPT method needs only two sensors for current and voltage measurements and is, therefore, cost effective and reliable. The system is tested through simulations and real-time setup using dSPACE DS1104. The results prove the effectiveness of the proposed hybrid MPPT compared with the P $\&$ O method under uniform and dynamic weather conditions.

Design of a 10-kV·A Soft-Switching Solid-State Transformer (S4T)

Abstract: The soft-switching solid-state transformer (S4T) employs only 12 main active devices and an auxiliary resonant circuit to implement a bidirectional solid-state transformer, with an attractive feature of achieving a full range of zero-voltage-switching conditions for all the main devices. This paper covers detailed design of the power stage, auxiliary resonant circuit, and control of the S4T. The high-frequency transformer is an essential element for the S4T, and it has a unique feature of dc-biased flux. Design of such a high-frequency transformer is also discussed in detail in this paper. Soft startup, shutdown, and fast dynamic response under load transients are also attractive behaviors because of the low inertia of the S4T. Experimental results from a 208-V/10-kV·A S4T unit are presented.

Novel Control Scheme for an Interleaved Flyback Converter Based Solar PV Microinverter to Achieve High Efficiency

Abstract: The paper proposes an optimal control strategy for the interleaved flyback based microinverter to improve its efficiency over the entire operating range. This control scheme is based on the choice of an appropriate operating mode [1-converter discontinuous conduction mode (DCM), 1-converter boundary conduction mode (BCM), 2-converter DCM, and 2-converter BCM] at various instantaneous power magnitudes. The proposed control method reduces the fixed losses associated with the gate driver and the transformer at the low power level. It also reduces the switching losses that may result due to the extremely high-frequency operation of the BCM at the low power level. Additionally, it also reduces the conduction losses through low current peak due to BCM and equal current sharing between the two converters at the high power level. Switching losses, due to the low-frequency operation of the BCM at a high power level, are also reduced. Operating mode selection of the interleaved inverter at a particular power level is based on the information of optimal efficiency. Detailed calculations of peak current references have been carried out for the various operating modes of the interleaved flyback based microinverter. Simulation and experimental results have validated that the proposed control method results in better efficiency compared with the conventional (DCM, hybrid DCM/BCM, hybrid 1-converter/2-converter) control methods with the output current total harmonic distortion remaining within the specified limits.

High-Efficiency Single-Stage LLC Resonant Converter for Wide-Input-Voltage Range

Abstract: In this paper, a new single-stage half-bridge (HB) resonant $LLC$ converter additionally employing one resonant capacitor and two relays with one package is proposed, compared with a single-stage HB $LLC$ converter. Moreover, a center-tapped transformer is replaced with a coupled transformer. Since the proposed converter changes the turns ratio of the coupled transformer using a relay according to low- or high-input-voltage range, it can decrease the range of its needed voltage gain. It means that the proposed converter can be designed with large transformer magnetizing inductance compared with the conventional single-stage HB $LLC$ converter. As a result, the primary conduction and turn-off losses are reduced. Moreover, in low input voltage range, it has smaller total primary wire resistance of the transformer due to parallel connection of the coupled transformer, which decreases its conduction loss. In addition, additionally employed small-sized components can be inserted to the conventional system. To confirm the operation, features, and validity of the proposed converter, universal input with low line and high line and 16.5 V/60 W output laboratory prototype targeting laptop adapters with wide-input-voltage range is built and tested.

A Three-Phase Grid-Connected Microinverter for AC Photovoltaic Module Applications

Abstract: A photovoltaic (PV) microinverter converts the dc from a PV panel to ac directly, which has the advantages of improved energy harvesting, friendly “plug-and-play” operation, enhanced flexibility/expandability, excellent system redundancy, and no dc cabling/safety issue; therefore, it is an attractive solution for the grid-connected PV system. In ac PV module applications, the features such as power density, reliability, efficiency, and reactive power capability are essential for the microinverters. In order to overcome the drawbacks of the conventional microinverters, including the power density/reliability issues caused by the bulky input capacitors and the limited output reactive power capability, a three-phase microinverter without energy storage capacitors is proposed in this paper. The proposed microinverter consists of a flyback stage, a third-harmonic injection circuit, and a line-commutated current-source-type inverter. The flyback stage realizes maximum power point tracking, while the third-harmonic injection circuit is responsible for output power factor correction. In addition to having the potential of achieving compact structure, long lifetime, and high efficiency, the developed microinverter provides extended output reactive power control range and three-phase balanced output. Finally, the proposed topology and the method are verified by simulations and experimental results.

Step-Up Partial Power DC-DC Converters for Two-Stage PV Systems with Interleaved Current Performance

Abstract: This work presents a partial power converter allowing us to obtain, with a single DC-DC converter, the same feature as the classical interleaved operation of two converters. More precisely, the proposed topology performs similarly as the input-parallel output-series (IPOS) configuration reducing the current ripple at the input of the system and dividing the individual converters power rating, compared to a single converter. The proposed topology consists of a partial DC-DC converter processing only a fraction of the total power, thus allowing high efficiency. Experimental results are provided to validate the proposed converter topology with a Flyback-based 100 W test bench with a transformer turns ratio n 1 = n 2 . Experimental results show high performances reducing the input current ripple around 30 % , further increasing the conversion efficiency.

Investigation and Implementation of an Input-Series Auxiliary Power Supply Scheme for High-Input-Voltage Low-Power Applications

Abstract: Aiming at the high-input-voltage multiple-output low-power applications, an input-series two-transistor flyback auxiliary power supply scheme is proposed and investigated. In this converter, an integrated-transformer is adopted instead of the single-transformer in each series-module, all of the series-modules are operating synchronously, and the input voltage sharing (IVS) can be achieved automatically. The active IVS mechanism of this converter is analyzed, furthermore, through the influence analysis when the series-modules are operating asynchronously and the tolerance features of the key parameters are considered, the related design consideration of the input filter capacitor in each series-module is discussed. Finally, after the simulation verifications, a 60-W laboratory-made prototype of this auxiliary power supply composed of three series-modules is built, by which the feasibility of the presented scheme and the validity of the theoretical analysis are verified.

Design considerations of highly-efficient active clamp flyback converter using GaN power ICs

Abstract: High switching frequency and high efficiency are critical in reducing power adapter size. The active clamp flyback (ACF) allows soft switching under all line and load conditions, eliminating all leakage inductance and snubber losses. This paper discusses key design considerations for high density ACF converters by looking into ZVS condition, RMS current reduction, and EMI optimization. Current-dip effect and secondary resonant scheme are found to significantly improve efficiency. GaN power ICs, with low output charge & integrated drive with reduced parasitics, are ideal for high frequency ACF. A 65 W USB-PD adapter was built to 24 W/in3 cased power density and 93.4% worst case efficiency. The design met European CoC Tier 2 and US DoE Level VI efficiency requirement and the EN55022 Class B conducted EMI standard.

Modeling and Reduction of Radiated Common Mode Current in Flyback Converters

Abstract: For flyback converters with long cables attached, radiated common mode (CM) current is the dominant radiation source. Radiated CM current is caused by the CM voltage driving the CM noise propagation loop including the converter and the antenna. This paper proposes a radiated CM current model to quantify the relationship between the CM voltages, impedance and currents. It is discovered that the significant impact from the transformer on radiated CM current is primarily from the CM voltage transformation. To characterize the CM voltage transformation, a transformer CM model extraction method is proposed. Based on the model, for radiated CM current reduction, this paper reviews transformer structures and proposes an interwinding capacitive coupling minimized coaxial shielding technique. And this paper also studies on the EMI filter design for radiated CM current reduction. The proposed modeling and reduction techniques are verified through experiments performed on a flyback converter with cables attached.

A Generalized and Flexible Control Scheme for Photovoltaic Grid-Tie Microinverters

Abstract: In this paper, design and implementation of a flyback photovoltaic (PV) microinverter based on the direct digital synthesis (DDS) technique has been described for both the standalone and the grid-connected operation. The DDS technique adopted provides flexibility in the implementation of various control schemes of the PV microinverter on a simple low-cost digital signal processing type of microprocessor (dsPIC). As compared with the conventional look-up-table method used for generating sinusoidal output voltage waveforms by digital signal processing, a much higher resolution can be obtained in the voltage phase angle and magnitude owing to the adaptive nature of the look-up table implemented within the DDS architecture. The DDS technique is used in the implementation of all control schemes of a PV microinverter, such as maximum power point tracking (MPPT), phase-locked-loop (PLL), anti-islanding, and low-voltage ride-though (LVRT), with an integrated software run on a simple microcontroller. A dedicated computer simulation model is developed, where the PV panel model, the PLL in DQ reference frame, the MPPT algorithm, and the anti-islanding and LVRT features are all taken into account. The experimental results obtained on a 120-W PV flyback microinverter have verified the validity of the proposed technique for both the steady-state and the transient-state operation. The DDS technique is thus found to be quite convenient for application to module integrated converters.

Analytical Modeling and Implementation of a Coaxially Wound Transformer With Integrated Filter Inductance for Isolated Soft-Switching DC–DC Converters

Abstract: In this paper, we propose an approach for integrating a series filter inductance in a coaxially wound transformer (CWT) as a potential alternative to conventional solenoidally wound transformers (SWT) for high-power isolated soft-switching dc–dc converters. The critical elements that determine the size and the performance of soft-switching dc–dc converters are the isolation transformer and the filter elements. While conventional SWTs using a stray magnetic field as a filter inductance often suffer from a considerably increased loss, heat congestion, and electromagnetic interference, a CWT is rarely affected by high frequency and fringing effects. The desired properties are still valid while the required filter inductance is fully integrated with an isolation transformer using the proposed method. In addition, the evenly distributed magnetic fields in a concentric geometry enable accurate electrical and mechanical analysis and a specific application-oriented design. In this paper, the operating principles, design procedure, and loss modeling of a CWT with an integrated filter inductance are introduced. Its functionality and suitability for high-frequency applications were proven by theoretical analysis and experiments. A prototype transformer with an integrated inductance 4 mH was facilitated and evaluated in a 15 kV-SiC mosfet -based 6 k–400 Vdc stage for a solid-state transformer of up to 6.5 kW at a switching frequency of 20 kHz.

Impedance-based analysis of grid harmonic interactions between aggregated flyback micro-inverters and the grid

Abstract: Grid harmonic interactions due to aggregated flyback micro-inverters are investigated in this study. An impedance-based model based on the Norton model of flyback micro-inverters, which are with quasi-resonant peak-current control, is obtained by adopting the small-signal modelling approach. As a supplement to the existing output impedance modelling of string inverters with linear controllers, further study on micro-inverters under non-linear control is addressed in this study. Based on the derived impedance model, the admittance matrix of aggregated micro-inverters connected to the grid is formulated and the impedance-based analysis of the system stability is also presented. Consequently, by modelling the output admittance of the quasi-resonant peak-current controlled flyback micro-inverters, harmonic interactions with a distorted grid can be effectively forecasted. Results obtained from modelling, analysis and verifications have shown that the proposed method is a simple and valid way of dealing with the harmonic quasi-resonance problems.

Investigation of the Active Ripple Compensation Technique to Reduce Bulk Capacitance in Offline Flyback-Based LED Drivers

Abstract: This paper presents the study of an offline flyback-based light-emitting diode (LED) driver with reduced storage capacitance. An approach called active ripple compensation was used for minimizing the converter bulk capacitance. This technique is oriented to voltage-controlled pulse width modulation converters and is based on the modulation of the duty cycle, which allows for the reduction of the filtering capacitance by increasing the harmonic content of the input current up to the limits established by the standards. By means of the design procedure presented in this paper, the amount of capacitance reduction and input current distortion can be fully controlled and theoretically predicted. In addition, no extra sensors are required to implement the proposed technique, apart from the LED current sensor already available in most LED drivers. Experimental results from a 50-W laboratory prototype supplied from a 220-V 60-Hz grid were carried out. The results were compared with the conventional approach, attesting the superior performance of the proposed methodology.

Three-Phase Lines to Single-Phase Coil Planar Contactless Power Transformer

Abstract: This paper proposes a three-phase lines to single-phase coil planar contactless power transformer. The transformer has the primary consisting of three-phase line cables arrayed in parallel on a plane and the secondary of single-phase coil. The proposed transformer is studied for application to automatic guided vehicles (AGVs). Uniform power transfer that is independent of the position of the AGVs is an important issue for this transformer, because of the sparse arrangement of the primary lines. To ensure that the transformer achieves uniform power transfer, the structure and dimensions of the primary are studied using numerical analysis. Additionally, an equivalent model of the proposed transformer, which is applicable to the imbalanced conditions, is presented. The equivalent model proves analytically that balanced three-phase voltage and balanced three-phase current conditions, which can be created using appropriate circuit configurations, enable uniform power transfer. The results of experiments in which the prototype of the transformer is applied to the target AGV confirm that under balanced-current conditions, which can be generated using a three-phase LCL circuit, the proposed transformer can transfer sufficient uniform power to drive the AGV.

Loss Analysis for Efficiency Improvement of the Integrated Buck–Flyback LED Driver

Abstract: This paper presents a study of the losses in the integrated buck–flyback converter (IBFC) used as high-power-factor LED driver. The aim of the study is to investigate the possibilities of increasing the efficiency of the IBFC converter. The procedure of the improvement is done by obtaining the equations of the current through each component in terms of converter parameters. The current is found in an average value or rms value, depending on the type of the parasitic component, whether it is modeled by a parasitic forward voltage source or by a parasitic resistance, respectively. Using these equations and the parasitic model, the losses of each element of the converter are estimated. This paper proposes a technique to increase the efficiency of the IBFC by redesigning the converter parameters. Furthermore, this paper presents a case of study with a step-by-step efficiency enhancement process of an existing driver. The driver is operating under universal input conditions, and 38 V output, supplying an LED luminary of 26.5 W. The new design shows an improvement of the efficiency from 82% in the old design to 89% in the proposed one. Moreover, the new design shows an improvement in the power factor and the THD and a 50% reduction in the output current ripple. Furthermore, a reduction in the number of components has been achieved, as it is found by the analysis that by adjusting the converter parameters, one diode can be removed. Finally, the presented methodology is explained in detail so that it can easily be applied to other dc–dc converters.

Modeling, Analysis, and Implementation of High Voltage Low Power Flyback Converter Feeding Resistive Loads

Abstract: In High Voltage flyback converters, the dominant factor that influences a converter operation is the parasitic capacitance. A significant portion of input energy is utilized in charging the parasitic capacitances of the circuit, which is circulated back to the source at the end of every switching cycle. The circulating energy is a function of output voltage, load power, and parasitic capacitances and remains significant in High Voltage Low Power (HVLP) applications. This energy transfer phenomenon involving parasitic capacitances results in a reduced fraction of input energy reaching the load in every cycle, thereby resulting in an apparent deviation in the converter operating point compared to ideal flyback in case of resistive loads. An analytical energy-based model is derived, which includes the effect of parasitic capacitances, and is valid for steady state and dynamics of HVLP flyback converters feeding resistive loads. The influence of parasitic capacitances on the switch voltage of the converter is exploited to achieve Zero Voltage Switching (ZVS), thereby minimizing the turn- on loss. The proposed analytical model is verified through simulation and experimental results on 1.5 kV/ 5 W and 1.5 kV/ 200 mW resistive loads.

A Single-Stage LED Driver With High-Performance Primary-Side-Regulated Characteristic

Abstract: A traditional flyback LED driver is limited by its low performance, which usually does not meet the power factor (PF) and total harmonic distortion requirements according to Energy Star or IEC61000-3-2. The control loop from the secondary side to the primary side has low reliability and employs more components, which reduces the power density of the system and increases the cost. In this brief, based on single-stage single ended primary inductor converter (SEPIC) and flyback converter, a primary-side-regulated LED driver is proposed to improve the performance of the system. Working in DCM, the SEPIC circuit realizes the PF correction naturally. For the flyback converter, the proposed primary-side-regulated method improves the power density and guarantees accurate control of the output current. A 100-W prototype based on SEPIC-flyback was built to verify the analysis and the experimental results coincided with the analysis results satisfactorily.