High Power Conversion Research Articles

Improved Analytical Triple-2D Leakage Inductance Model of Cone Winding Matrix Transformers

The transformer leakage inductance is one of the limiting factors for pulse shape quality in high voltage pulsed power (HVPP) converters that are essential in applications such as cancer treatment, particle accelerators, and free electron lasers. Cone winding matrix (CWM) transformers are commonly used in HVPP converters as they offer low leakage inductance and high insulation distance. This paper proposes an improved Triple-2D (iT2D) leakage inductance model for CWM transformers. The iT2D model identifies three basic cross sections of CWM transformers and calculates their associated leakage inductance contributions. The paper proposes an accurate and compact analytical formula of the leakage inductance contribution resulting from the magnetic energy stored in between the magnetic cores. For cross sections with cone windings, an expression is presented that computes the leakage inductance per unit length of non-parallel windings. The iT2D model is verified with measurements and finite element simulations of three transformer prototypes. The analytical solutions used in the iT2D model ensure applicability to arbitrary geometric aspect ratios and designs. Furthermore, the iT2D model is rapidly executable enabling its time-efficient integration in converter optimisations.

Buck Converter Current Measurement Using Differential Amplifier

The accuracy of the measured current is a preeminent parameter for Current Control based Power Converter applications to ensure genuine operation of the designed converter. The current measurement accuracy can be affected by several parameters which includes the type of technology used, components used for the selected technology, aging, usage, operating and environmental conditions. The effect of gain resistors and their manufacturing tolerances on differential amplifier-based buck converter current measurement is investigated in this work. The analysis mainly focused on the output voltage variation and its accuracy with respect to the change in gain resistance tolerances. The gain resistors with 5%, 1%, 0.5% and 0.1% manufacturing tolerances taken for the worst-case analysis and the calculated performance results are compared and verified with the simulation results. The Operational amplifiers (Op-Amp) for high frequency power converter applications must operate in a high frequency noise environment and the intended current measuring system must manage common mode noise disturbances paired with the signal to be measured. Based on the Common Mode Rejection Ratio (CMRR) the common mode voltages and noise signals will effectively get filtered out. Lesser CMRR results in lower common mode signal rejection, resulting in poor precision and noise rejection. In differential amplifiers, the CMRR predominantly depends on gain resistors. So, the variations in Common Mode Rejection Ratio due to gain resistor tolerances also analyzed and compared with the output voltage variations. Besides the effects of resistor tolerances, this paper also examines the effect of Op-Amp offset voltage on output accuracy specifically for low magnitude input currents. The obtained results from this analysis clearly shows that the gain resistors with 0.1% tolerance gives maximum accuracy with improved CMRR and accuracy at low magnitude input currents will get well improved by using Op-Amps with Low Offset voltage specifications.

Adaptive online auto-tuning using Particle Swarm optimized PI controller with time-variant approach for high accuracy and speed in Dual Active Bridge converter

<abstract> <p>Electric vehicles (EVs) are an emerging technology that contribute to reducing air pollution. This paper presents the development of a 200 kW DC charger for the vehicle-to-grid (V2G) application. The bidirectional dual active bridge (DAB) converter was the preferred fit for a high-power DC-DC conversion due its attractive features such as high power density and bidirectional power flow. A particle swarm optimization (PSO) algorithm was used to online auto-tune the optimal proportional gain (<italic>K<sub>P</sub></italic>) and integral gain (<italic>K<sub>I</sub></italic>) value with minimized error voltage. Then, knowing that the controller with fixed gains have limitation in its response during dynamic change, the PSO was improved to allow re-tuning and update the new <italic>K<sub>P</sub></italic> and <italic>K<sub>I</sub></italic> upon step changes or disturbances through a time-variant approach. The proposed controller, online auto-tuned PI using PSO with re-tuning (OPSO-PI-RT) and one-time (OPSO-PI-OT) execution were compared under desired output voltage step changes and load step changes in terms of steady-state error and dynamic performance. The OPSO-PI-RT method was a superior controller with 98.16% accuracy and faster controller with 85.28 s<sup>-1</sup> average speed compared to OPSO-PI-OT using controller hardware-in-the-loop (CHIL) approach.</p> </abstract>

Buck-Boost Type High Step-Down Low Power Modular Converter for Medium Voltage DC Systems

The medium-voltage dc (MVDC) system are intensely investigated by both industry and academy. However, how to realize a lower power circuit directly fed by MVDC is an important but easily neglected problem, which seriously affects the reliability of the dc system. The current high step-down circuits are mostly suitable for high-power applications, while the circuits for low-power applications are designed case by case. To address the obstacle, a generalized buck-boost type high step-down converter (BHSC) structure is proposed in this article. The submodules of BHSC are derived from basic dc–dc converter. As a result, the features of high modularity, simple structure, and low cost can be obtained, and each submodule operates independently without communication and synchronization to achieve voltage balance. Furthermore, a submodule strategy with Bang-Bang control, instead of hardware modification, is proposed to overcome the limitation of BHSC generality in medium-voltage (MV) and high-voltage (HV) applications, due to the operating current difference in different submodules of the cascaded structure. Therefore, BHSC can be easily extended to MV or HV by increasing the number of submodules. Finally, an experimental evaluation of a 1 kV/80 W prototype converter is presented, which can be applied as auxiliary power supply for high-power converter.

A Split-Source Self-Heater for Automotive Batteries Based on Traction Drive Reconfiguration

At cold climates, internally preheating batteries are essential and promising to alleviate the performance degradation of electric vehicles because of its rapid heating speed and uniform temperature distribution. To implement onboard internal battery heating, the integrated self-heater is developed to utilize traction motor drive reconfiguration, thereby eliminating extra expensive high-power converters and bulky passive components. However, previous integrated self-heaters introduce excessive voltage stress on dc-link capacitors, arousing a serious concern on the system reliability and safety. In this article, a split-source self-heater (SSSH) is proposed to reconfigure the battery pack as two series-connected sources, where the heating energy can be alternately exchanged via traction motor windings with reduced capacitor voltage stress. The theoretical model and operation principle of the proposed SSSH are deduced for practical controller design and suppression of annoying noises and vibrations. Based on the model, a supertwisting controller is developed to adjust the heating current and cell voltage regardless of nonlinear uncertainties during self-heating. The downscaled experiments verify that the proposed SSSH can preheat automotive batteries with 4.27 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> C/min heating speed and 0.24% state of charge/ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> C energy consumption rate. The induced torque ripple is reduced by 90%, and the capacitor voltage never exceeds the nominal value during self-heating.

ISM-Band Frequency Transformer Modeling for Isolated High-Power Conversions

In the last few years, the switching frequency of power electronic converters is extended to the several MHz range. ISM frequency bands are specified in this range for power electronic applications. Most converter circuits, such as resonance and soft-switching circuits require an accurate modeling of the circuit components, such as the high frequency inductors and transformers. This paper focuses on the evaluation of a practically simple but accurate high frequency transformer model. In first, a three-capacitor lumped model is chosen due to its simplicity as well as to the physics-oriented concept. Furthermore, the extraction of the parameters is straightforward. It is found that splitting the leakage inductances in two halves based on the winding capacitance would make the model more accurate for modeling high frequency characteristics. The paper analyzes the model and provides a closed form transfer function for the input impedance and the voltage gain. To verify the model, different kinds of transformer hardware are fabricated, and their input impedances are measured from 1 MHz to 30 MHz, which includes three ISM bands. The measurements are then compared with the impedance function developed from the model. The model shows well-matching with the measurement as compared to the conventional models. Finally, the model is validated experimentally by designing an isolated 13.56 MHz Class-E power conversion circuit, which includes a transformer with soft-switching. The soft-switching is designed based on the conventional, three-capacitor and the proposed model, respectively. The proposed model provides more accurate design for the inverter assuring soft-switching and optimum performance of the circuit.

Development of converter configuration and corresponding control strategy for wind turbines using permanent magnet synchronous generator: A Case study

This study aims to investigate a feasible converter architecture and corresponding control method for Wind Turbine (WT) systems using permanent magnet synchronous generators (PMSG). The converter configuration is designed based on the AC/DC/AC converter, including the Diode Bridge Rectifier (DBR) and Pulse Width Modulated Current Source Inverter (PWM-CSI), Buck-Boost Converter (BBC), and Bypass Chopper (BC). The control strategy for the proposed converter is developed to enhance the operating performance of WT-PMSG, which must satisfy four requisitions. Firstly, it proposes the control approach for the pitch angle to control the output power of the WT when the wind speed is over the rated value. The selected control variables are the generator speed and active power. Secondly, the Maximum Power Point Tracking (MPPT) is archived to the satisfaction of the full-range operation through the control strategy for the BBC. The control strategy is applied by the Proportional Integral (PI) controller. The control variables are the generator speed and the diode rectifier's output DC current. Thirdly, the control strategy for PWM-CSI controls the voltage at the connection point and the frequency of the inverter. Fourthly, the DC-link voltage is controlled to the constant value at various operating conditions. Simulation of a 3MW and 0.69 kV WT-PMSG was carried on in PSCAD software to verify under considering the variable wind speed and the three-phase fault. The obtained results prove the feasibility of the proposed WT-PMSG system that serves as an alternative for a high-power wind energy conversion system.

A computational study of thiophene containing small-molecule electron acceptors for non-fullerene organic photovoltaic cells

During the past few years, researchers have devoted extensive efforts to improve organic solar cell (OSC) performance to reach interesting power conversion efficiencies (PCE) exceeding 10 %. Among heterojunctions OSCs (BHJ) types, Fullerene based small molecule acceptors (SMAs) have proved to be a favorable option in virtue of their high-power conversion efficiency (PCE), good electronic conductivity and superior charge segregation. Yet, they represent some serious limitations, such as low light absorption over 600 nm, solubility in organic solvents, and inefficient processing. Accordingly, the so-called non-fullerene acceptors (NFA) organic group was developed and showed excellent characteristics over fullerene acceptors with their easily tunable band gap, strong absorption in the visible region, low voltage loss, good morphological stability and simple fabrication techniques. In the present paper, a series of non-fullerene electron acceptors (C1–C4) were designed by modifying the reference material R. we have obtained new conjugated organic structures by adding more functional capped units. The quantum chemical study (DFT/TD-DFT) approach was used to perform theoretical calculations in order to characterize the effect of end group redistribution via the frontier molecular orbital (FMO), optical absorption, reorganization energy in accordance with R. Using PTB7-Th as an electron donor, open circuit voltage (Voc), photovoltaic properties and intermolecular charge transfer have been also calculated for all the conceived compounds. The findings revealed that all engineered materials (C1–C4) possess narrow band gap and great optical characteristics. In addition the proposed structures have displayed comparatively lower electron and hole reorganization energies, we have found that C1 represents the lowest electron and hole reorganization energies, respectively 0.048 eV and 0.028 eV, consequently the highest electron and hole mobility [1]. These interesting outcomes could prove proposed electron acceptors to be excellent candidates in the improvement of optoelectronic properties of organic solar cell technology.

Design of multi-channel AlGaN/GaN Schottky diode for improving rectification efficiency in microwave power transmission

Schottky barrier diode (SBD) is the core of the rectification circuit in the microwave power transmission (MPT) system and suitable for high-power RF-DC conversion. However, the rectification efficiency of current commercial SBD cannot meet the requirements of the MPT system. Therefore, this paper proposes a microwave rectification circuit based on the multi-channel AlGaN/GaN SBD. The effect of diode parameters on the rectification efficiency has been investigated, such as the number of channels, the length of anode field plate (LAFP) and the thickness of insulation layer. Simulation results show that multiple AlGaN/GaN heterojunctions can significantly reduce the on-resistance of SBD and improve the rectification efficiency. The power capacity of SBD can be increased withthe optimised LAFP and the thickness of insulation layer, which enables efficient microwave rectification in high power applications. High RF-DC rectification efficiency of 85.1% is obtained at the input power of 33 dBm. The rectification efficiency exceeds 60% over a wide input power range (14–38 dBm). The results demonstrate the great potential of multi-channel AlGaN/GaN SBD for high-power MPT application.

Reliable Design and Control Implementation of Parallel DC/DC Converter for High Power Charging System

With the current popularity of Electric Vehicles (EV), especially in some critical EV applications such as hospital EV fleets, the demand for continuous and reliable power supply is increasing. However, most of the charging stations are powered in a centralized way, which causes transistors and other components to be subjected to high voltage and current stresses that reduce reliability, and a single point of failure can cause the entire system to fail. Therefore, a significant effort is made in this paper to improve the reliability of the charging system. In terms of charging system structure design, a distributed charging structure with fault tolerance is designed and a mathematical model to evaluate the reliability of the structure is proposed. In terms of control, a current sharing control algorithm is designed that can achieve fault tolerance. To further improve the reliability of the system, a thermal sharing control method based on current sharing technology is also designed. This method can improve the reliability of the charging system by distributing the load more rationally according to the differences in component performance and operating environment; FPGA-based control techniques are provided, and innovative ideas of pipeline control and details of mathematical reasoning for key IP cores are presented. Experiments show that N + 1 redundancy fault tolerance can be achieved in both current sharing and thermal sharing modes. In the current sharing experiment, when module 3 failed, the total current only fluctuated 800 mA within 500 ms, which is satisfactory. In the thermal sharing experiment, after module 3 failed, modules 1, 2, and 4 adjusted the current reasonably under the correction of the thermal sharing loop, and the total current remained stable throughout the process. The experimental results prove that the charging system structure design and control method proposed in this paper are feasible and excellent.

Wide Band Gap Devices and Their Application in Power Electronics

Power electronic systems have a great impact on modern society. Their applications target a more sustainable future by minimizing the negative impacts of industrialization on the environment, such as global warming effects and greenhouse gas emission. Power devices based on wide band gap (WBG) material have the potential to deliver a paradigm shift in regard to energy efficiency and working with respect to the devices based on mature silicon (Si). Gallium nitride (GaN) and silicon carbide (SiC) have been treated as one of the most promising WBG materials that allow the performance limits of matured Si switching devices to be significantly exceeded. WBG-based power devices enable fast switching with lower power losses at higher switching frequency and hence, allow the development of high power density and high efficiency power converters. This paper reviews popular SiC and GaN power devices, discusses the associated merits and challenges, and finally their applications in power electronics.

Investigative uses of overmodulation techniques in modular multilevel cascaded converter

Sinusoidal pulse width modulation (SPWM) is a method to generate the switching gate pulse of the converter. Overmodulation is a method where the modulation index exceeds the unity value and the system goes into the nonlinear region. To maintain the system in a linear region when operating in the overmodulation region, some techniques are developed. These techniques helped to operate the system in the linear range. Medium and high-power energy conversion systems mostly use a modular multilevel cascaded converter (MMCC), which has been an issue improving significantly in recent years. In this article, MMCC-based overmodulation techniques are compared with conventional PWM and analyzed on DC bus utilization (DBU), and total harmonic distortion (THD). MATLAB/Simulink digital platform used demonstrate overmodulation technique.

Design and Demonstration of a 100 kW High-Frequency Matrix Core Transformer for More Electric Aircraft Power Distribution

The rapid development of more electric aircraft (MEA) raises the demand for high-power converters with significant weight and volume reduction for onboard power distribution. The isolated dc/dc converter using the medium-frequency transformer (MFT) is a feasible solution. To design an MFT with improved electromagnetic and thermal performance, a matrix core transformer (MCT) architecture is proposed with accurate models in this article. With superior heat dissipation ability, the high current windings can be effectively cooled with both natural and forced air convection. In addition, an optimization methodology for MCT design is presented. As a result, the prototype of a 100-kW, 50-kHz MCT with an additive manufactured bobbin is built. The results of both finite element analysis (FEA) simulation and experimental study in a full power dual active bridge (DAB) with the MCT prototype are presented to verify the theoretical design. The power density and efficiency of the MCT reach 17.7 kW/L and 99.63%, respectively.

The Investigation of the Influence of a Cu2O Buffer Layer on Hole Transport Layers in MAPbI3-Based Perovskite Solar Cells.

The passivation engineering of the hole transport layer in perovskite solar cells (PSCs) has significantly decreased carrier accumulation and open circuit voltage (Voc) loss, as well as energy band mismatching, thus achieving the goal of high-power conversion efficiency. However, most devices incorporating organic/inorganic buffer layers suffer from poor stability and low efficiency. In this article, we have proposed an inorganic buffer layer of Cu2O, which has achieved high efficiency on lower work function metals and various frequently used hole transport layers (HTLs). Once the Cu2O buffer layer was applied to modify the Cu/PTAA interface, the device exhibited a high Voc of 1.20 V, a high FF of 75.92%, and an enhanced PCE of 22.49% versus a Voc of 1.12 V, FF of 69.16%, and PCE of 18.99% from the (PTAA/Cu) n-i-p structure. Our simulation showed that the application of a Cu2O buffer layer improved the interfacial contact and energy alignment, promoting the carrier transportation and reducing the charge accumulation. Furthermore, we optimized the combinations of the thicknesses of the Cu2O, the absorber layer, and PTAA to obtain the best performance for Cu-based perovskite solar cells. Eventually, we explored the effect of the defect density between the HTL/absorber interface and the absorber/ETL interface on the device and recommended the appropriate reference defect density for experimental research. This work provides guidance for improving the experimental efficiency and reducing the cost of perovskite solar cells.

A Low-Power, Fully Integrated SC DC–DC Step-Up Converter with Phase-Reduced Soft-Charging Technique for Fully Implantable Neural Interfaces

We present a high-power conversion efficiency (PCE) on-chip switched-capacitor (SC) DC–DC step-up converter for a fully implantable neural interface operating with less than a few tens µW from energy harvesting. To improve the PCE in such light loads and wide variations of voltage-conversion ratio (VCR), which is a typical scenario for ultra-low-power fully implantable systems depending on energy harvesting, a phase-reduced soft-charging technique has been implemented in a step-up converter, thereby achieving very low VCR-sensitive PCE variation compared with other state-of-the-art works. The proposed DC–DC converter has been fabricated in a standard 180 nm CMOS 1P6M process. It exhibits high PCE (~80%) for wide input and output ranges from 0.5 V to 1.2 V and from 1.2 V to 1.8 V, respectively, with switching frequencies of 0.3–2 MHz, achieving a peak efficiency of 82.6% at 54 µW loads.

Self-healing 2D/3D perovskite for efficient and stable p-i-n perovskite solar cells

Beyond the p-i-n perovskite solar cell's high-power conversion efficiency (PCE), its moisture instability is the most challenging factor in its commercialization. Recently, the innovative use of three and two-dimensional multi-structures, by creating a barrier against the penetration of moisture and oxygen, has played a very influential role in improving the PSC's long-term stability. Here, a new strategy, the anti-solvent quenching method, is used to construct multi-structure perovskite by involving cetyltrimethylammonium bromide (CTAB) as an active agent. The solar cell efficiency is significantly improved during the perovskite formation on the substrate by creating a multidimensional (2D/3D) heterojunction perovskite. The synergistic role of using 2D/3D heterojunction perovskite structures led to the 29.2% improvement (14.58–18.84) in the PCE. The attractive ability of the 2D/3D active layer in self-healing has increased the perovskite's long-term stability under harsh environmental conditions.

Influence mechanism of solder aging and thermal network model optimization of multi-chip IGBT modules

With the continuous increase in the scale of new energy grid-connected, high-power converter IGBT modules are widely used in wind, solar, and other new energy power generation systems. The safe and reliable operation of IGBT modules with parallel chips is becoming more and more important. In the multi-chip module, uneven solder aging will increase the thermal resistance of some chips, which will lead to an inaccurate estimation of the junction temperature of the multi-chip IGBT power module. To this end, this paper proposes to use the reconstructed thermal impedance matrix to modify the multi-chip thermal network model and estimate the junction temperature. By analyzing the nonlinear accelerated deterioration law between the aging degree of the solder layer and the self-thermal impedance and coupled thermal impedance of the IGBT module, the influence mechanism of different solder layer aging degrees inside the module on the thermal conduction radius and thermal diffusion angle is clarified. The thermal impedance matrix is reconstructed with the modified thermal diffusion angle, thus realizing the optimization of the thermal network model of the multi-chip IGBT module. The experimental results show that the junction temperature calculation results of the improved multi-chip IGBT module thermal network model are more in line with the finite element simulation than the traditional unimproved method, thus verifying the validity and accuracy of the model, and laying a solid foundation for the large-scale integrated multi-chip thermal analysis. Theoretical basis.

Carbon-based monochalcogenides for efficient solar and heat energy harvesting

A new generation of two-dimensional (2D) material has captivated significant attention in the energy conversion field owing to their promising optoelectronics and thermoelectric applications. The present work involves the systematic investigation of fundamental properties of single-layered 2D carbon-based monochalcogenides (CS, CSe, CTe) with planar, buckled and puckered geometry within the framework of density functional theory (DFT). The structural and lattice dynamics analysis disclose that puckered and buckled configurations are energetically and dynamically stable whereas planar structures depict instability. The anisotropic group velocity of longitudinal acoustic (LA) and transverse acoustic (TA) phonon modes in puckered systems may render the characteristics thermal transport properties. Additionally, for the first time, we scrutinized the thermoelectric and optical properties of these materials. At room temperature, the electron carrier mobilities are 174.698 and 160.830m2V-1s-1 of puckered and buckled CS systems, respectively are highest among all structures. The computed Seebeck coefficient, electrical conductivity and power factor manifests the high thermoelectric transport properties of puckered CS material. Further, the calculated solar parameters demonstrate an exceptionally high-power conversion efficiency of 19.61 % for puckered CTe. Present work indicates that puckered phase of CS and CTe show their potential for the heat and solar energy harvesting devices, respectively.

48-Pulse Voltage-Source Converter Based on Three-Level Neutral Point Clamp Converters for Solar Photovoltaic Plant

The demand for high-power converters for use in large-scale solar photovoltaic (PV) plants increases as the plant size continues to grow. The multipulse voltage-source converter (VSC) configurations are the viable option for high-power solar PV converter applications because they improve conversion efficiency due to low switching losses and allow direct integration with a medium-voltage (MV) grid. In this article, a 48-pulse VSC based on the fundamental frequency switching (FFS) three-level neutral point clamp (NPC) converter with a start–delta transformer configuration is used for large-scale solar PV plant application. It is also used as a PV-static synchronous compensator (STATCOM) to provide the required reactive power support to the grid to regulate the voltage. The solar PV plant configuration for a 100-MW capacity is modeled in MATLAB and implemented in the real-time OPAL-RT platform to verify its design and controls. The harmonics, static, and dynamic performances are demonstrated in detail.

Planar Common-Mode EMI Filter Design and Optimization for High-Altitude 100-kW SiC Inverter/Rectifier System

Silicon-carbide (SiC) devices are receiving popularity for high-power converter systems in aircraft due to many advantages over silicon counterparts. However, the electromagnetic interference (EMI) problems are more serious with the SiC devices operating at higher switching speeds and higher switching frequencies. The common-mode (CM) EMI filter design of the high-power SiC converter is especially challenging for high-altitude applications due to the harsher requirements of insulation and heat dissipation. The optimization of the parameters and physical design of a CM EMI filter in a 100-kW SiC inverter/rectifier system operating at 50 000 ft is conducted in this article to obtain the highest power density. The effect of the switching frequency on the EMI filter volume and the total power density of the converter system is analyzed. The lower breakdown voltage of air and the higher thermal resistance of natural convection make the conventional design of the CM choke infeasible at high altitudes. A printed circuit board (PCB)-based planar CM choke is designed with the consideration of partial discharge (PD) and heat dissipation at the altitude of 50 000 ft. The structure of the CM choke is optimized with embedded electric-field shielding plates, which controls the electric-field intensity in the air below 300 V/mm. The PCB windings improve the efficiency of heat dissipation at high altitudes and reduce the profile of the CM choke. A Pareto optimization is conducted to minimize the size of the choke and the volume of the final design is only 155 cm3. The experimental results show that the CM noise is reduced effectively with the CM EMI filter. PD is not observed even at the altitude of 50 000 ft and the thermal performance is excellent with a current of 190 A. With the optimization and the dedicated design of the CM EMI filter, the power density of the converter system is up to 33.3 kW/L.