Secondary Side Research Articles

An All Silicon Carbide 3 kV/540 V Series-Resonant Converter for Electric Aircraft Systems

In this work, an all silicon carbide (SiC) series-resonant converter (SRC) design is proposed and demonstrate to achieve a single stage dc-to-dc conversion from 3 kV to 540 V (±270 V) for future electric aircraft applications. The proposed SRC consists of a neutral-point-clamped converter using 3.3-kV SiC MOSFETs on the primary side, an H-bridge converter using 900-V SiC MOSFET on the secondary side and a high-frequency (HF) transformer. The detailed design methods for the SRC power stage and the HF transformer are presented. Especially, a tradeoff between the complexity for the cooling system and the need for high power density and voltage insulation is addressed in the transformer design, leading to a novel multilayer winding structure design to enhance the insulation capability and also the mechanical robustness. The proposed bobbin design is realized using additive manufacturing. The detailed analysis and modeling of the parasitic capacitance between sections introduced by fringe electrical field are presented. To validate the effectiveness of the proposed SRC design, a 25-kW converter prototype using 3.3-kV SiC discrete devices has been developed with a peak efficiency of 99.08% achieved in experimental studies.

Research on the Thermal Stratification Phenomenon at the Secondary Side of a Steam Generator in an Isolated Loop

In normal operation, there is no significant thermal stratification phenomenon in the tube bundle area of the steam generator of the nuclear power plant. However, this phenomenon is detected in marine nuclear power plant isolation loops in the presence of feedwater leakage. Therefore, an experiment was designed to verify the presence of thermal stratification, and the influence factors were analyzed by the RELAP5/MOD3.2 program. The results show that thermal stratification is mainly influenced by the initial water level at isolation, the initial pressure at isolation, the total leakage mass, and the internal circulation of the steam generator. Leakage flow has little effect on it. This phenomenon causes the coolant temperature at the primary side of the steam generator in the isolated loop to be lower than the temperature measured in the reactor inlet pipe or outlet pipe. This study aids the operator in determining the real coolant temperature at the primary side of the steam generator in the isolated loop and prevents reactivity insertion accidents when the isolated loop is put into operation.

Proposing a New Approach to Generate the Differential Trajectory of the Differential Relays Using COMTRADE Files

The differential relay is subject to transient events such as inrush current, which may affect its correct operation. Therefore, evaluating the reliable and accurate operation of differential relays is important, which is only possible by mapping the relay’s differential trajectory on its setting curve. However, except for the SIGRA software, creating a differential trajectory only for Siemens relays, there is a gap in developing a method to extract this trajectory for other commercial differential relays. Hence, in this paper, a new method for generating the differential trajectory of the differential relay from their six input currents and mapping it on the relay setting curve is presented. The proposed method uses the differential relay COMTRADE files to access the relay input currents during an incident. The currents recorded in the COMTRADE files belong to the secondary sides of the current transformers (CTs). Accordingly, the impacts of the current transformers’ connections and the protected transformer’s connection type should be considered in the proposed study. The ability of the proposed method to generate the differential trajectory for different incidents that occurred on the power transformers is evaluated using simulation studies and also according to the experimental tests. The results illustrate the efficiency of the proposed method in generating the differential trajectory from the COMTRADE files. In addition, comparing the results of the proposed method with the results created in SIGRA software shows the higher accuracy of the proposed method in producing the differential trajectory of the differential relay.

Maximum efficiency tracking design of wireless power transmission system based on machine learning

For the typical magnetically coupled wireless power transmission system, power consumption is often caused by the impedance effect of the primary and secondary sides, the loss and heat generation of the actual semiconductor devices and the change of the coupling coefficient caused by distance. The uncertainty of frequency tracking efficiency caused by high enough coil transmission with low load receiving efficiency and load impedance changes makes it difficult to stabilize the output of the optimal efficiency point of the system. In order to solve this problem, a wireless power transmission system is proposed based on the traditional wireless power transmission system a wireless power transmission system is proposed to predict and stabilize the variable impedance, so as to stably track the efficiency of the system in the resonant frequency range. It is not affected by load jitter, actual circuit parameters and environmental disturbance. The test results show that the transmission efficiency of tracking frequency and predicting impedance can be realized at a certain distance, and the difference between the prediction error and the actual efficiency is about 1%–3%.

Perancangan Alat Monitoring Arus Bocor pada Kabel 20 kV Menggunakan Filter Kalman Berbasis Internet of Things

<p><em>One of the problems that often occurs in the use of ground cables is insulation failure. This condition can cause leakage current in the 20 kV cable on the secondary side of the transformer. The greater the value of the leakage current, the more heat will cause the insulation to worsen. If this condition is not handled immediately, it can lead to the opportunity for a short-circuit current between the phase and ground. Therefore, an Internet of Thing-based monitoring tool is needed that can determine the amount of leakage current contained in the 20 kV cable on the secondary side of the transformer by applying the Kalman filter method and sending it to the substation operator using Wifi. Based on the test, it was found that the implementation of this monitoring tool obtained more constant measurement results than the actual measurement value using a measuring instrument with an average error per phase, 1.5594% phase R, 1.5535% phase S, 1.5548% phase T.</em></p>

LLC resonant converter based on PFM and secondary‐side short‐circuit control for on‐board charger

AbstractCommonly used lithium‐ion battery on‐board charger (OBC) for electric vehicles (EVs) needs a wide output voltage range, but the traditional LLC converter is hard to meet the need under the condition of high efficiency and high power density. In this paper, a resonant converter with hybrid modulation is proposed. The converter has a relatively simple topology and control method. Compared with the traditional LLC topology, only two diodes are replaced by MOSFETs on the secondary side of the transformer, and no auxiliary components are added. The primary‐side switches adopt PFM) and the secondary‐side switches adopt short‐circuit control in the proposed converter, which can realize a wide output voltage range, in a narrow switching frequency range with excellent soft‐switching performance. The proposed converter can effectively reduce the resonant current and the volume of transformer core and achieve energy delivery with high power density and high efficiency. The operation principles, voltage gain, and soft‐switching conditions of the converter are analyzed in this paper. Finally, a 3.3‐kW SiC‐based prototype with 400‐V input and 250‐ to 430‐V output is built to verify the feasibility and validity of the proposed converter.

The "Tethered Solvent" Effect - H-Bonding-Controlled Thermo-Halochromism of a Push-Pull Azo Chromophore via Its Secondary Amidoalkyl Acrylamide Side Chain.

The fascinating field of thermo-halochromism of azo chromophores still astounds with unexplored facets nourished by the intricate relationship between molecular structure variations and their spectroscopic signatures. In this respect, we investigated the thermally dependent absorption behaviour of acrylamide derivatives of o-methyl red, characterised by two secondary amide linkages with hydrogen bonding-active protons in the pendant alkyl substituent. The systems were studied by a combination of UV-vis, derivative, and difference, as well as 2D-NMR (Nuclear Overhauser Effect Spectroscopy, NOESY) spectroscopy. These experiments show that the thermo-halochromism is specifically influenced by hydrogen bonding interaction of the secondary amidoalkyl acrylamide side chain with the azobenzene core in dependence of the spacer length. Apparently, the substituent acts like a solvent, which is directly tethered to the chromophore and where the tether length determines the interaction by conformational freedom. We refer to this novel phenomenon as "H-bonding-controlled thermo-halochromism".

Artificial Water Channels—Progress Innovations and Prospects

Artificial Water Channels—Progress Innovations and Prospects

A three-region movable-boundary helical coil once-through steam generator model for dynamic simulation and controller design

A simple but accurate mathematical model is crucial for dynamic simulations and controller design of helical coil once-through steam generator (OTSG). This paper presents a three-region movable boundary dynamic model of the helical coil OTSG. Based on the secondary side fluid conditions, the OTSG is divided into subcooled region (two control volumes), two-phase region (two control volumes) and superheated region (three control volumes) with movable boiling boundaries between each region. The nonlinear dynamic model is derived based on mass, energy and momentum conservation equations. And the linear model is obtained by using the transfer function and state space transformation, which is a 37-order model of five input and three output. Validations are made under full-power steady-state condition and four transient conditions. Results show good agreements among the nonlinear model, linear model and the RELAP5 model, with acceptable errors. This model can be applied to dynamic simulations and controller design of helical coil OTSG with constant primary-side flow rate.

The Interconnected Relationship between Auxin Concentration Gradient Changes in Chinese Fir Radial Stems and Dynamic Cambial Activity

Auxin has been shown to exhibit a striking concentration gradient distribution in radial sections of angiosperm and gymnosperm species, in which peak auxin levels are concentrated in dividing cambial cells, while the absolute auxin concentration sharply declines toward developing secondary phloem and xylem regions. The coincidence of auxin concentration gradient across shoot tissues and xylem cell developmental gradient has prompted that auxin could act as “a plant morphogen” to provide a positional signal for cambial cell development. However, the specific location of vascular cambium and the lack of mutants altering auxin distribution in shoots of woody species made further verification experiments difficult to explore. To address this issue, different concentrations of exogenous IAA were applied to decapitated Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) trunks in this study to induce the change in the auxin concentration gradient in radial stems, and its effects on cambial activities were examined on the physiological, cellular and molecular levels. Our findings manifested that exogenous IAA treatments resulted in vast changes in endogenous hormone concentrations (including IAA, ZR, GA3 and ABA), cambial cell developmental behaviors and transcriptional activities of genes related to polar auxin transport (PAT), auxin signaling, the biosynthesis and signal transduction of other plant hormones and the genetic control of cambial activity. Based on above findings, we postulated a model of auxin concentration gradient involved in the control of cambial activity and secondary growth in tree trunks. In this model, the contrasting expression of AUX1/LAX and PIN family carriers in distinct Chinese fir wood-forming tissues dynamically modulates PAT into the cambial zone adjacent to the secondary phloem side and secondary xylem tissues, resulting in a sharp and wide auxin spatial gradient distribution across shoots in different stages of secondary growth, respectively. This change in auxin concentration gradient distribution in radial sections in turn acts on cambial developmental behaviors by modulating the expression of auxin signaling genes and key transcription factors and the production of other plant hormones in distinct woody tissues. Findings in this study provide important insights for understanding the biological significance of auxin concentration gradient existing in the radial stems of woody species.

An energy-based control scheme for optimal power quality management in 12-pulse rectifier integrated distribution systems

This paper proposes an energy-based control scheme for optimal power quality management in 12-pulse rectifier integrated distribution systems. In this 12-pulse rectifier integrated distribution system, instead of using a step-down transformer for voltage matching, a back-to-back converter is connected to the taps of star and delta windings on 12-pulse rectifier transformer’s secondary side via the coupling LC. Using the magnetic potential balance of harmonics and reactive components between the back-to-back converter and the load side of the 12-pulse rectifier, the power quality of distribution systems can be managed. This topology can improve the voltage and current adaptability of the converter, thereby saving the cost of voltage matching transformer and exploiting the filter converter capacity potential. To ensure global power quality performance, an energy-based control scheme is proposed to improve the power quality management performance by accelerating the energy dissipation of the system. Case studies are performed to verify the effectiveness and superiority of the proposed methodology on low dc-link voltage and power quality.

Transmission range extension strategy of parity–time‐symmetry‐based wireless power transfer system by a boost converter

AbstractThe wireless power transfer (WPT) system based on the parity–time (PT) symmetry can realize stable power transmission with constant efficiency and output power in the PT‐symmetric region. In some applications with long transmission distance requirements, such as medical treatment, it is meaningful to expand the PT‐symmetric region by reducing the critical coupling coefficient. Therefore, a novel WPT system based on PT symmetry with a boost converter in secondary side is proposed in this article to expand the transmission range. The circuit theory is used to analyze the presented system. Then two models with different drive signals of the boost converter are established and simulated respectively to show the effect of the proposed system compared with the original PT‐symmetry‐based WPT system. Finally, the experimental results verify that the proposed system can play a role in extending the stable transmission distance or in suppressing the output power growth of the PT‐symmetric‐based WPT system.

Main Circuit Topology and Electromagnetic Interference of Electric Vehicle Bidirectional Charger

In order to improve the electromagnetic compatibility performance of electric vehicle bidirectional chargers, the authors propose a main circuit topology and electromagnetic interference of the electric vehicle bidirectional charger. The design adopts the parallel connection of silicon carbide (SiC) MOSFETs and completes the bidirectional charging system based on the cascade connection of dual active bridge (DAB) and three-phase four-wire inverter. This paper mainly analyzes the influence of parasitic inductance on the drive and power loop of the T0-247 packaged switch in actual use, and according to the operating characteristics of the system, different gate resistors are used to reduce switching losses and improve system efficiency. And, we explore on how to reduce the overshoot voltage through the RC absorption circuit, thereby reducing the conducted interference. The result shows the following: the primary side absorption circuit resistance is 470 Ω and the capacitor is 47 nf, the secondary side absorption circuit resistance is 40 Ω and the capacitance is 4.7 nf, and the circuit power is 5000 W. Under the same conditions, without adding the RC absorption circuit, the conducted interference on the AC side does not meet the standard, and the amount of disturbance is large. After adding a suitable RC absorption circuit, the conducted interference on the AC side reaches the required value. Conclusion. This research provides a systematic design scheme and optimization method for designing power electronic devices using SiC.

A Topology-Reconfigurable LLC Resonant Converter for Wide Output Range Applications

A novel topology-reconfigurable LLC resonant converter for wide output range applications is proposed in this article. In the proposed wide output converter, a reconfigurable topology based on matrix transformer is presented, the primary sides of the matrix transformer are connected in parallel, the connection of the secondary sides can be changed by controlling the selector switch on the secondary side, which are categorized into HV and LV operation mode and suitable for different output levels. The HV operation mode whose secondary rectifiers are connected in series is employed for the high output level, while the LV operation mode whose secondary rectifiers are connected in parallel is employed for the low output level. Consequently, the output range is widened by configuring the connection structure. What's more, the switching frequency range can be reduced. Furthermore, the magnetizing current will be reduced by the parallel connection of the primary sides, and soft-switching operation is realized on all of the switches over the full operation range. Therefore, the proposed converter features a wide output voltage range along with high efficiency. Finally, an experimental prototype with 400 VDC input and 150 VDC/14 A-500 VDC/4.2 A output is fabricated and tested to verify the feasibility and effectiveness of the converter.

Low frequency Vibration Energy Harvester using Compliant Mechanism driven Rosen-type Piezoelectric Transformer

This paper represents an energy harvesting technique using a compliant mechanism driven Rosen type piezoelectric transformer from low frequency (3-10 Hz) reciprocal gripping motion. The finite element model of the compliant structure is synthesized using topology optimization implementing the density model and is coupled with a piezoceramic transformer to operate it by human hands. The mechanism can also be operated with the help of external mechanisms. As a case study, the proposed compliant mechanism is modelled considering acrylic plastic material. The mechanism can produce a maximum power of 62.7 μW for a 10 Hz gripping frequency while operating at its optimal conditions. The paper also discusses the resonance condition of the structure to check its marginal state. The harvested energy can be extracted across a load resistances attached at both primary and secondary side of the piezoelectric transformer.

Analysis of IPT Intermediate Coupler System for Vehicle Charging Over Large Air Gaps

Intermediate resonant pads have been recently used to increase the ground clearance for inductive power transfer (IPT) systems transferring power over large air gaps. This article investigates the best placement of a tuned intermediate pad to maximize the air gap by assessing the leakage magnetic fields and the apparent power effort. A mathematical analysis is used to design and control a two-coil system with an intermediate pad. The results show that SAE J2954 standard pads can transfer rated power over an extended air gap of 406 mm using an intermediate pad while adhering to the apparent power ratings of all pads and typical leakage constraints. As a comparison, an equivalent IPT system using only a primary and a secondary pad without the intermediate pad is shown to be unable to meet the apparent power and leakage requirements at these large air gaps. Additionally, this article shows and validates control and regulation of the intermediate pad and load current by switching the secondary side.

Comprehensive Analysis of Voltage Step-Up Techniques for Isolated SEPIC

High step-up converters are often used in photovoltaic applications due to low voltage of photovoltaic modules. In this paper, a study of several voltage step-up cells added on primary and secondary sides of an isolated dc-dc SEPIC (single ended primary inductor converter) is made, in order to increase its static gain and synthesize a family of converters. To perform this study and select the most appropriate resulting converter, theoretical and comparative analyzes are accomplished. They include a brief description of each converter, tables and curves with relevant information, such as voltage gain, voltage stresses and component count, and the identification of the use of coupled inductor or transformer based on the analysis of dc magnetizing current. Moreover, theoretical analysis and experimental results on a 50 kHz and 200 W prototype of selected isolated SEPIC with voltage doubler cell are presented to validate the proposed topology and concept.

Research on the Voltage Spike Suppression Strategy for Three-Phase High Frequency Link Matrix-Type Inverter

The problem of high-voltage spikes on the secondary side of a high-frequency transformer (HFT) in the commutation process of a three-phase high-frequency link matrix-type inverter (HFLMI) is studied. Considering the parasitic capacitance of MOSFETs, the mechanism of voltage spikes during HFLMI commutation is revealed. According to the characteristics of the topology, the later stage matrix converter (MC) is decoupled into two groups of conventional three-phase voltage type inverters by the de-re-coupling idea, and the space vector pulsewidth modulation (SVPWM) is carried out, respectively. The zero vector is inserted between two nonzero voltage vectors to accomplish smooth commutation for addressing the problem of voltage overshoot on the secondary side of HFT due to the switching of HFT leakage inductance and filter inductance to the same path. Due to the existence of parasitic capacitance, the voltage spikes caused by its resonance with the system’s stray inductance cannot be solved by optimizing modulation strategies. In order to further suppress voltage spikes, a flyback clamp circuit is proposed to absorb the leakage inductance energy. Ultimately, a prototype with a rated power of 200 W is developed for experimental verification. The results show that the peak efficiency of three-phase HFLMI with the flyback clamp circuit is 92.6% in the full power range, the voltage spikes on the secondary side of HFT are clamped to about 1.2 times the rated voltage, and all switches realize soft-switching.

A Bidirectional Integrated Equalizer Based on the Sepic–Zeta Converter for Hybrid Energy Storage System

In the hybrid energy storage system (HESS), the voltages between the battery cell and the supercapacitor cell are different, increasing the circuit and control complexity of the balance system. Therefore, a bidirectional integrated equalizer based on the Sepic–Zeta converter is proposed for the HESS, which realizes both battery string and supercapacitor string balance during the energy exchange. The inductors in the Sepic–Zeta converter are used as the primary side of the balanced multiwinding transformer. The Sepic–Zeta converter generates the current ripples to drive the multiwinding transformer. The secondary side generates currents to balance the HESS, and hence, the equalizer itself is essentially switchless. Therefore, the proposed circuit can reduce the complexity of the HESS. Experimental and comparative results show that the proposed equalizer achieves the balance of the HESS.

A Novel Integrated Matrix Magnetics for Isolated Single-Stage DC–DC Converter

With the development of data center, promotion for efficiency and power density of the voltage regulator module (VRM) is paid considerable attention. Isolated VRM is suitable for the high-conversion-ratio dc–dc application. However, isolated VRM has many magnetic components, which take up a large proportion of the total volume. In this article, a novel integrated matrix magnetics structure is proposed, which integrates two elemental transformers and four output inductors into a single core. By integrating several discrete magnetic components, the volume of passive components, and high-current interconnections are reduced, leading to high power density and high efficiency. The integrated matrix magnetics is employed in an isolated single-stage converter, which can provide high output current. In addition, primary switches can achieve zero-voltage-switching (ZVS), and synchronous rectifiers of secondary side can achieve ZVS and zero-current-switching, so efficiency can be further improved. Besides, equivalent output inductance, voltage conversion ratio and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</sub> calculation are derived to design the integrated matrix magnetics. Finally, a 48 V/1.8 V 144 W prototype of the isolated single-stage converter with integrated matrix magnetics is made and tested to verify the analysis.