Primary Side Research Articles

An active clamped L‐L type ZVS current‐fed front‐end DC–DC converter based solid state transformer in grid connected mode PV applications

AbstractThis paper utilised a solid‐state transformer (SST) with an active clamped L‐L type current fed front‐end converter for maximum power extraction (MPE) and voltage boost operation. The proposed system employed perturb and observe (P&O) based MPE and upheld the ZVS operation of all primary side switches and ZCS operation of all secondary side rectifier diodes for various insolation conditions. The proposed system developed a new fundamental extractor titled multi‐level cascaded dual double fundamental signal extractor (MCDDFSE) and is utilized in the control algorithm for synchronization with the utility grid. The main objective of the proposed system was to deliver a compact size, reduced weight and cheaper magnetic components‐based front‐end converter of SST on the photovoltaic (PV) array side and a fast, secure and trustworthy mitigation technique for the grid current harmonics on the utility grid side. The proposed system was trialled on the platform of OPAL‐RT (RT‐LABv2021.3.2.307) for various grid abnormalities and its behaviour was found well within the IEEE 519 standards.

Mode analysis and fault-tolerant method of open-circuit fault for a three-level dual active bridge DC-DC converter

The three-level dual-active-bridge (TL-DAB) DC-DC converter is a promising dc-dc converter for high-voltage and high-power systems. Open-circuit faults on power switches are crucial issues for the TL-DAB dc-dc converters, resulting in various performance degradations such as dc bias and divided capacitor voltage imbalance. The mode analysis after fault is necessary for fault detection and fault-tolerant control. Subsequently, fault-tolerant control is essential to reduce or overcome these issues. In the proposed fault-tolerant method, when the primary side inner switch or the secondary side switch breaks down, the gate-driving signal of the complementary switch is recommended to block and the effects can be removed. Finally, experiment results demonstrate that the issues caused by open-circuit faults can be reduced significantly with the proposed fault-tolerant method.

Accurate Modeling, Design, and Load Estimation of LCC-S Based WPT System With a Wide Range of Load

Modeling of the wireless power transfer (WPT) system is the premise to design and control it. First-harmonic-analysis (FHA) is a simple and effective method to model the WPT system, but its accuracy may decrease with the variation of load in a wide range. In this paper, harmonics are analyzed in the primary side of an LCC-S compensation network based WPT system, depicting a waveform of the output current of the inverter much closer to the real one compared with FHA based model. In the secondary side, the time-domain analysis is conducted both in CCM&DCM of the rectifier, deriving an equivalent input impedance featuring the non-linear characteristics of the system. Based on the proposed model, the parameters of the LCC network are designed, proving to tune the ZVS condition better than the FHA based method. Finally, the load of the system is estimated, achieving a high accuracy (with the estimating error less than 5%) in a wide range with a simple sampling method.

Efficiency Optimization and Power Allocation of Omnidirectional Wireless Power Transfer for Multiple Receivers

Omnidirectional wireless power transfer to multiple devices has become a research hotspot due to its high spatial freedom and flexible design. However, this power supply method often faces the problems of high leakage flux and different receiver power requirements. This article studied the effects of currents of transmitting coils on transmission efficiency mathematically. A method of maximum efficiency tracking and power allocation for omnidirectional wireless power transfer to multiple receivers was proposed, and a mutual inductance identification method based on primary feedback is presented. Through the parameters identified by the primary side feedback, the current amplitudes and phases of the Tx coils were adjusted to achieve maximum efficiency, and the flexible power requirements of multiple devices can be realized. Finally, the above methods are experimentally verified. The two receivers can be charged with 58.8% efficiency and the power ratio can be precisely controlled from 0 to 100 percent, which is difficult for conventional method.

Design and Implementation of High-Misalignment Tolerance WPT System for Underwater Vehicles Based on a Variable Inductor

Wireless charging for autonomous underwater vehicles (AUVs) has been widely explored recently by the merit of safety and convenience. However, due to the misalignment between charging coils in the horizontal and vertical directions, the system may not maintain constant current (CC) or constant voltage (CV) output. Therefore, this article proposes a mistuned IPT system structure and corresponding design methods to improve misalignment tolerance. The proposed IPT system adopts series-series compensation and includes a variable inductor (VI) on the secondary side. A general design method based on the established mathematical model is proposed. The worst scenarios (i.e., the maximum value of misalignment) are used for the optimization of the system parameters. The control strategy for VI without any communication link to the primary side is established. Finally, a 1 kW IPT system for tolerance of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> of 0.15-0.5 and output voltage of 74-150 V variation is set up. The experimental results show that the horizontal and vertical direction misalignment ranges reach ±47% and +140%, respectively, and the maximum system efficiency exceeds 96% for full power output. The proposed system improves the freedom and stability of charging in the harsh underwater environment.

Evaluating Transcranial Direct Current Stimulation as an Adjunct to Inpatient Physiotherapy in Paediatric Acquired Brain Injury: A Randomized Feasibility Trial

Purpose: Evaluate the feasibility of transcranial direct current stimulation (tDCS) as an adjunct to inpatient physiotherapy for children and youth with acquired brain injury (ABI). Method: This randomized feasibility trial allocated children (5–18 years of age with moderate to severe ABI) to receive either active or sham anodal tDCS immediately prior to 16 of their existing inpatient physiotherapy sessions. Participants, physiotherapists, assessors, and primary investigators were blinded to treatment allocation. Eligibility, recruitment, retention, tolerance, and preliminary treatment outcomes were evaluated against a priori feasibility targets. Results: Of 232 children admitted over 21 months, six were eligible (2.6%) and four were recruited (66.7%). One participant completed the entire study protocol, two were withdrawn for unrelated changes in medical stability, and one could not commence the study due to COVID-19 restrictions. Participants completed all tDCS sessions that were started with the primary transient side effect being sub-electrode itchiness. Conclusions: While the study was infeasible from eligibility and retention perspectives, study procedures (e.g., assessment, treatment, side effect tracking, physiotherapy documentation) were viable and should be applied to future paediatric tDCS studies.

Research on Tuning Control Technology for Wireless Power Transfer Systems for Concrete Embedded Sensors

Concrete embedded sensors play a very important role in structural health monitoring. However, the time of endurance of sensors remains a performance bottleneck and sensors need to be charged without damaging the structure as well. Wireless power transfer (WPT) technology is a promising approach to solving this problem. However, the electromagnetic characteristics of concrete medium can cause WPT systems to be untuned and can reduce the energy transmission efficiency of the system. In this paper, the induced medium loss and eddy current loss of a WPT system in concrete are calculated using analytical equations and finite element analysis method. The equivalent circuit model of a concrete–air transmedia WPT system is established according to the calculated losses and a composite tuning control technology is proposed based on the above analysis. In addition, the composite tuning control technology combines the advantages of frequency-modulation tuning and dynamic compensation tuning to ensure the overall resonance of the WPT system. The tuning control technology can ensure the whole resonance of the WPT system and make the natural resonant frequencies of primary and secondary sides consistent. The experimental results show that compared with the untuned control technology, the output power and efficiency of the tuned control system increased by 73% and 11.05%, respectively. The proposed tuning control technology provides direction for future charging of concrete-embedded sensors.

Three-dimensional numerical research on coupling heat transfer characteristics of PRHR HX under different water levels based on the experimental model

The passive residual heat removal system (PRHRs) is an important heat transfer system to ensure the removal of residual heat in non-LOCA conditions occurring in advanced Generation III nuclear reactors. The water level of the In-containment Refueling Water Storage Tank (IRWST) decreases due to long-term water evaporation under accident conditions and the later stages of PRHRs operation. Additionally, the water level also decreases during the water leakage accidents. The reduction of water level contributes to a decrease in the heat transfer area and the passive residual heat removal ability of the core. In order to investigate the coupling heat transfer characteristics of both primary and secondary side in the heat exchanger under different water levels, Three-dimensional numerical simulations of the PRHR HX's operation under different water levels was carried out based on the scaled-down IRWST&PRHR HX experimental model. The fluid flow and heat transfer processes inside and outside the C-type tubes were analyzed in detail. The results indicate that when heat transfer area is reduced by 50%, the overall heat transfer rate is reduced by about 41%, meanwhile the average heat transfer coefficient is about 37.4% higher than that under the full water level condition. It indicates that PRHR HX can maintain high passive residual heat removal capacity even under half water level, which provides an important reference for the design and safe operation of the PRHR HX.

Simulation and Optimization of the Operation Efficiency of Heat Exchange Units in Intelligent Heating Systems Based on Entransy Dissipation Thermal Resistance

So as to investigate heat exchange efficiency of heat exchange units under different operating conditions, this paper builds a simulation analysis model for heat exchange units in the framework of intelligent district heating systems based on the Modelica unified modeling language and the MWorks platform. Analyze the real-time operating efficiency of heat exchange units using entransy dissipation thermal resistance as an evaluation indicator of heat exchange efficiency. This paper analyzes the trend of heat exchange efficiency changes of heat exchange units when the primary side flow rate, secondary side flow rate, primary side inlet temperature, secondary side inlet temperature, and secondary side bypass pipeline valve opening change. The simulation results verify that when the primary side and the secondary side flow match, the entransy dissipation thermal resistance is the smallest, and its heat transfer efficiency is the highest. Under the simulation condition where the convective heat transfer coefficient is constant, the entransy dissipation thermal resistance is independent of the inlet temperature changes on the primary and secondary sides. The minimum entransy dissipation thermal resistance could be achieved, which represents the optimal real-time heat exchange efficiency state, when the valve opening of the mixed water heat exchange unit is 45% under the specific flow conditions.

A Detuned S-S Compensated IPT System With Two Discrete Frequencies for Maintaining Stable Power Transfer Versus Wide Coupling Variation

Stable power transmission is one of the key factors in the inductive power transfer (IPT) system. However, misalignment between the primary and secondary sides is almost inevitable in practice, affecting the system performance due to the coupling variation. With the widespread use of IPT technology, it is desired to transfer power from the primary side to the secondary side with a wide misalignment range as large as possible. To address this issue, the design method of the detuned circuit is widely applied in the IPT system. This paper analyzes the characteristics of the transfer power of the detuned series–series (S-S) topology with frequency variations and proposes a maintaining stable power transfer method versus wide coupling variation by adopting two discrete frequencies. Further, a design step is given to obtain the system parameters. Theoretical and experimental results are provided to demonstrate the misalignment performance of the proposed method. The results show that the coupling range is extended from [0.115-0.2] to [0.115-0.27] with the 5.6% fluctuation of the output power, and the corresponding efficiency varies from 91.46% to 95.52%.

Autonomous Pulse Frequency Modulation for Wireless Battery Charging With Zero-Voltage Switching

This paper proposes an autonomous pulse frequency modulation (APFM) scheme for wireless battery charging in which the self-excited oscillating (SEO) wireless power transfer (WPT) system can offer output power regulation with reliable zero-voltage switching (ZVS). The key is to utilize the self-excited oscillation feature to adjust the WPT operating frequency autonomously so as to deliver more power in the strong coupling region than the traditional forced-oscillating (FO) WPT system while the transmission efficiency can maintain at a high level. In the weak coupling region, the system becomes equivalent to the FO-WPT system. The pulse frequency modulation enables the system to adjust the output power by changing its duty ratio. Besides, reliable ZVS is achieved by extracting and processing the current signal at the primary side. Both theoretical analysis and experimental verification are provided to support the feasibility of the proposed APFM for SEO-WPT system.

The rationale and guiding principles to design a psychiatric curriculum for primary care nurses of India.

The National Mental Health Survey reports a huge treatment gap for all mental disorders. There is an acute shortage of mental health professionals in India. Hence, there is a dire need to support task-shift interventions by nurses in providing non-pharmacological interventions for persons suffering from mental health issues. The traditional psychiatric nursing curriculum emphasizes nurses' knowledge and skills rather than their competency in providing mental health care. We designed an innovative, digitally driven, modular-based primary care psychiatry program for nurses (PCPP-N) to incorporate mental health with physical health and emphasize redesigning nursing practice. In this paper, we discuss the rationale and guiding principles behind designing the curriculum of PCPP-N. The PCPP-N program is based on nine guiding principles to provide skill-based, pragmatic, and feasible modules of a higher collaborative care quotient (CCQ) and translational quotient (TQ) that are essential for upskilling primary care nurses. In this program, nurses are trained through telemedicine-based 'on-consultation training' augmented with collaborative video consultations. A tele-psychiatrist/tele-psychiatric nurse will demonstrate how to screen, identify, and plan treatment for patients with psychiatric disorders from patients coming for general medical care using the manual Clinical Schedules of Primary care psychiatry Nursing (CSP-N). The CSP-N manual includes a screener, simplified diagnosing guidelines relevant for nurses and primary care settings, nursing management, pharmacological management, and related side effects, counseling, and follow-up guidelines. This program helps the nurses in identifying the most commonly prevalent adult psychiatric disorders presenting to primary care. This PCPN curriculum contains pragmatic modules with higher CCQ and TQ. This curriculum is dynamic as the learning is interactive. Upskilling primary care nurses in integrating mental health with physical health may reduce the mental health burden. Further, the policymakers and administrators plan to integrate mental health along with physical health in national health programs.

Switch-Multiplexed Quasi-Two-Stage Isolated Bidirectional Buck-DAB Converter With Full Load ZVS Range

In this paper, a switch-multiplexed quasi-two-stage Buck-DAB (SMBDAB) and its modulation strategy are proposed. Under the quasi-two-stage Buck-DAB (QBDAB) architecture, one bridge of the primary side of the proposed converter is multiplexed as both the bridge of the Buck circuit and the DAB circuit to reduce the power switches. In addition, with the voltage-matching modulation, multiplexing still ensures that the voltages on both sides of the leakage inductor of the DAB circuit are always matched when the voltage gain of the converter changes. And thus the ZVS of all the switches can be achieved. Furthermore, the partial power transfer characteristics of the buck circuit still maintains, which could reduce the power rating of the inductor for the buck circuit. The working principle, power transfer characteristics, and full range ZVS design are analyzed. Finally, the effectiveness of the SMBDAB converter is verified through experimental results from a 1kW prototype.

Investigating Harmonic Distortion in Power Transformers Due to Geomagnetically Induced Current Flows

Geomagnetically induced currents (GICs) flow through grounding circuits into power systems, when triggered by geomagnetic disturbances. Power transformers (with grounding connections) are the primary path for GIC flows into power systems. The flow of GICs through a power transformer can create adverse impacts on its operation, including large increases in its reactive power demands and significant harmonic distortions in the primary side currents. This paper presents case studies and analyses of the adverse impacts of GIC flows on power transformers. Presented case studies are conducted on two power transformers with different core types, power ratings, and voltage ratings. Each of these power transformers is tested for various levels of GIC flows with its loading being kept unchanged. Results of conducted case studies conclude that the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2^{\text{nd}}$</tex-math></inline-formula> harmonic is the dominant in primary and side currents at all levels of GIC flows. Other harmonic components such as the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$3^{\text{rd}}$</tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$4^{\text{th}}$</tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ 5^{\text{th}},\ 6^{\text{th}},\ 7^{\text{th}}\ \text{and}\ 8^{\text{th}}$</tex-math></inline-formula> harmonic components, can be observed with lower magnitudes than the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2^{\text{nd}}$</tex-math></inline-formula> harmonic component.

Flexible On-load Voltage Regulating Transformer by Floating Capacitor Three-level AC/AC Converter

The flexible on-load transformer can be adapted to different application scenarios by adding different power electronic converter structures through the use of existing transformers. In this paper, a flexible on-load regulator transformer structure based on a floating capacitor multi-level AC/AC converter is proposed, which can compensate the input voltage on the primary side of the transformer in the same direction or the opposite direction, combine with the existing on-load tap-changer, and also achieve fast stepless voltage regulation. Finally, the effectiveness of the proposed new topology is verified by simulation and experiment.

Vulnerability and tuberculosis treatment outcomes in urban settings in England: A mixed-methods study.

Evidence on factors contributing to poor treatment outcome and healthcare priorities in vulnerable populations affected by tuberculosis (TB) in urban areas of England other than London is needed to inform setting-specific prevention and care policies. We addressed this knowledge gap in a cohort of TB patients and healthcare providers in Birmingham and Leicester, UK. A mixed-methods study was performed. Logistic regression was used to identify TB patients more likely to have poor treatment outcomes according to clinical and demographic characteristics and social risk factors (SRFs) in a 2013-18 cohort. 25 semi-structured interviews were undertaken in purposely selected individuals (9 patients and 16 healthcare professionals) to glean insights on their healthcare priorities and the factors that contribute to poor treatment outcome. The quantitative cohort comprised 2252 patients. Those who were ≥ 55 years of age, foreign-born from Central Europe, East Asia and Sub Saharan Africa and with MDR-TB were more likely to have poor treatment outcomes. According to patients and healthcare professionals, the factors that contribute to vulnerability to develop TB and poor treatment outcomes include poor working and living conditions, inadequate or absent welfare protection, poor primary healthcare responsiveness, treatment duration and side effects. These factors could be addressed by increased networking, partnership and integration between healthcare and social services and better integration between primary and secondary healthcare. In both cities, being ≥ 55 years of age, having MDR-TB and being of foreign-birth are predictors of unfavourable treatment outcome. Risk of poor treatment outcome and vulnerability seem to be multidimensional. A better understanding of specific vulnerabilities and how they affect patient care pathway is needed to design adequate support programmes.

A Novel Hybrid Control Strategy and Dynamic Performance Enhancement of a 3.3 kW GaN–HEMT-Based iL2C Resonant Full-Bridge DC–DC Power Converter Methodology for Electric Vehicle Charging Systems

The conventional resonant inductor–inductor–capacitor (L2C) DC–DC converters have the major drawbacks of poor regulation, improper current sharing, load current ripples, conduction losses, and limiting the power levels to operate at higher loads for electric vehicle (EV) charging systems. To address the issues of the L2C converter, this paper proposes an interleaved inductor–inductor–capacitor (iL2C) full-bridge (FB) DC–DC converter as an EV charger with wide input voltage conditions. It comprises two L2C converters operating in parallel on the primary side with 8-GaN switches and maintains the single rectifier circuit on the secondary side as common. Further, it introduces the hybrid control strategy called variable frequency + phase shift modulation (VFPSM) technique for iL2C with a constant voltage charging mode operation. The design requirements, modeling, dynamic responses, and operation of an iL2C converter with a controller are discussed. The analysis of the proposed concept designed and simulated with an input voltage of 400 Vin at a load voltage of 48 V0 presented at different load conditions, i.e., full load (3.3 kW), half load (1.65 kW), and light load (330 W). The dynamic performances of the converter during line and load regulations are presented at assorted input voltages. In addition, to analyze the controller and converter performance, the concept was validated experimentally for wide input voltage applications of 300–500 Vin with a desired output of 48 V0 at full load condition, i.e., 3.3 kW and the practical efficiency of the iL2C converter was 98.2% at full load.

Performance analysis of wireless power transfer using series-to-series topology

Wireless power transfer (WPT) is a technology used to transmit power using air as it medium of transfer. The function of the WPT is similar to a transformer. The power provided on the primary side will be transferred through air to the secondary side. The performance of the WPT is crucially depends on the air gap length, 𝛿 that separates primary and secondary side. In this paper discusses the performance of WPT using series-to-series topology. The performance of the WPT was estimated using finite element analysis (FEA). During the study, focus was given to effect of turn ratio, a, air gap length, 𝛿 and capacitor value at primary Cp, and secondary, Cs winding to voltage ratio of the WPT. The air gap length, 𝛿 was set to 1 and 2 mm while the capacitors were set depend on the ratio of primary to secondary winding capacitor, Cp/Cs. The WPT performance also being tested under no-load and loaded operation to observed it effect. As a result, the WPT with turn ratio, a at 0.37, air gap length, 𝛿 at 1 mm and ratio of primary to secondary winding capacitor, Cp/Cs at 0.5 produce the best voltage ratio compared to other settings.

An Novel Technique for Wireless Power Transfer Systems Based on the Parametric Set

High efficiency and high power level are important indicators of the Inductive Power Transfer (IPT) system. However, the problem of optimizing the efficiency of IPT has not been well solved, and improving control methods is one of the effective ways to solve this problem. In order to improve the existing secondary-side control scheme and achieve the goal of simultaneously achieving optimal transmission efficiency and stable output, this paper suggests a parameter-based control strategy for coordinating the primary and secondary sides in the IPT system. This paper suggests a parameter-based control strategy for coordinating the primary and secondary sides in the IPT system. The paper develops a model of the IPT system to find the best load, then analyzes the active rectifier, phase shift angle, and load relationship to create a parameter set for controlling quantities like α and β. From there, a new control strategy is proposed and its effectiveness is confirmed through simulations. The proposed strategy enhances transmission efficiency and output stability of the IPT system, making it highly applicable in areas like electric vehicle charging and wireless charging devices.

Open-Phase Fault Research on the Parallel-Connected 40-Pulse Rectifier With Multioutput Auto-Connected Phase-Shifting Transformer

In order to improve the normal operation power quality, the DC side harmonic reduction circuit (HRC) has been extended to the multi-pulse rectifiers (MPRs) based on five-phase bridge rectifier. The power quality under fault conditions is also an important aspect that affects the overall reliability of the rectifier system. This paper is focused on the open-phase fault research on the passive MPRs with auto-connected phase-shifting transformer. The parallel-connected 40-pulse rectifier based on the five-phase bridge rectifier is selected as the main research circuit. Under the primary or secondary side open-phase faults, the operation modes of the main circuit and the HRC are discussed. Based on the waveform information, the relations between the fault characteristics and the fault types are established, which is useful for fault detection. Under the primary side open-phase fault, the current proportions of the two parallel-connected bridge rectifiers are calculated. In comparisons with the 24-pulse rectifier, the quantitative relationship between the increase of phase number and the improvement of fault power quality is clarified. Based on the research methods and conclusions presented in this paper, the structure of the MPR can be designed that fulfills the specific power quality standard under fault cases or reserves a certain safety margin to reduce the damage to the rectifier system and the AC grid.