Switching Frequency Research Articles

High-temperature ultraviolet photodetector and amplifying integrated circuits based on AlGaN/GaN heterostructure

Abstract In this work, an ultraviolet (UV) photodetection and amplifying integrated circuit (IC) based on an AlGaN/gallium nitride (GaN) heterostructure is demonstrated. The IC consists of a metal-heterostructure-metal photodetector (MHM-PD) and a high-electron-mobility transistor (HEMT)-based amplifier. The photoresponse of the MHM-PD increases at elevated temperatures due to the spatial separation of the photocarriers under the polarization electric field at the AlGaN/GaN heterointerface, as well as the photo-enhanced leakage current through the metal-heterostructure junction. At 250 °C, MHM-PD achieves a peak photoresponsivity of 14.5 A W−1 and a UV-to-visible rejection ratio of 104. As the thermal chuck temperature increases from 25 °C to 250 °C, the performance of the HEMT-based amplifier shows good thermal stability. Finally, the IC achieves a photoresponse of over 106 V W−1 and a switching frequency of 50 kHz at 250 °C with rise and decay time constants of 3.95 μs and 2.8 μs, respectively. These results show that the IC has a high-sensitivity and high-speed UV detection capability.

Performance evaluation of a bi-directional synchronous H6 inverter for AC/DC system interaction with SiC and Si-Based at different switching frequencies.

The bidirectional inverter connected to the grid is a crucial component of DC distribution systems, however its operation can have an impact on the systems' overall efficiency. The usual load profile of such systems in residential buildings is quite dynamic, with multiple periods of light load, especially when compared to high-demand sectors. This study examines and contrasts the impact of SiC and Si power MOSFETs on the best configuration of a 5 kW bidirectional H6 inverter specifically designed for residential use applications. Analytical modeling based on PSIM simulation results is employed to predict losses in a transformer-less synchronous H6 topology. Results of a 5 kW system indicate that silicon carbide (SiC) has an efficiency of up to 98.3%, surpassing the 93.6% efficiency attained with silicon (Si). Furthermore, this study explores potential of further improving efficiency by increasing the operating frequency to 50 kHz. The increase in frequency also leads to a reduction in the size of passive components. The experimental findings of a 1 kW system corroborate the efficacy of the proposed bidirectional synchronous H6 inverter topology, by demonstrating roughly the same trend in terms of the level of improvement over the baseline performance. It has been established that the use of SiC MOSFETs is superior to the use of Si MOSFETs, and that the appropriate operating frequency for bidirectional synchronous and comparable applications is 20 kHz rather than 50 kHz.

Fast-slow dynamics with non-zero sliding characteristics related to pitchfork bifurcation delay in the parametrically excited Duffing system with frequency switching

Fast-slow dynamics with non-zero sliding characteristics related to pitchfork bifurcation delay in the parametrically excited Duffing system with frequency switching

Optimal Variable Frequency Soft Switching for Interleaved Grid Tied Inverters in Electric Vehicle Charging Applications

Synchronized variable frequency soft-switching is analyzed and implemented in a 3-phase bidirectional grid-tied inverter. The common-mode connected topology and control allow for independent analysis of a single phase leg before six are combined into two interleaved, 3-phase inverters. Effective operation is enabled by discretizing the variable switching frequencies before synchronizing them with a control signal. The resulting inverter can operate at any power factor at power levels up to 50 kVA while maintaining zero-voltage switching (ZVS) throughout the grid cycle. Formal conditions for soft-switching and methods for achieving ZVS while maintaining global synchronization are presented. These conditions are then verified in a simulation. Finally, results for different power factors with and without interleaving are demonstrated in a prototype that achieves >98.1% efficiency when converting all real power.

Determining the Switching Frequency of a Transistor Converter for a Traction Collector Motor

The purpose of this work is to determine the switching frequency of a transistor converter for a traction collector motor of a locomotive based on the criterion of permissible current ripple. The stated goal is achieved by solving the following problem: a methodology for determining the consideration of changes in motor parameters when calculating the switching frequency of the transistor converter is proposed. The peculiarity of the proposed approach is that it takes into account the degree of saturation of individual parts of the magnetic system of the electric motor. The most significant result is an increase in the accuracy of calculating the switching frequency by taking into account the change in the inductance of the commutator motor windings when the degree of saturation of the magnetic system changes. The switching frequency for a DC traction motor with a pulse converter is calculated. Two main operating modes of the electric motor are considered: with full magnetic flux and with weakened magnetic flux. As a result of calculations, it was established that the dependence of switching frequency on currents is nonlinear. For the operating mode of the electric motor with full magnetic flux, the switching frequency is determined taking into account the processes in the field winding circuits and in the armature circuit windings. The most important results are the determination of the switching frequency of the pulse converter for powering and regulating the traction motor in all operating modes. The proposed methodology allows the selection of transistor devices for the converter according to the switching frequency.

Evaluating Contextual Models for Intensive Longitudinal Data in the Presence of Noise

Nowadays research into affect frequently employs intensive longitudinal data to assess fluctuations in daily emotional experiences. The resulting data are often analyzed with moderated autoregressive models to capture the influences of contextual events on the emotion dynamics. The presence of noise (e.g., measurement error) in the measures of the contextual events, however, is commonly ignored in these models. Disregarding noise in these covariates when it is present may result in biased parameter estimates and wrong conclusions drawn about the underlying emotion dynamics. In a simulation study we evaluate the estimation accuracy, assessed in terms of bias and variance, of different moderated autoregressive models in the presence of noise in the covariate. We show that estimation accuracy decreases when the amount of noise in the covariate increases. We also show that this bias is magnified by a larger effect of the covariate, a slower switching frequency of the covariate, a discrete rather than a continuous covariate, and constant rather than occasional noise in the covariate. We also show that the bias that results from a noisy covariate does not decrease when the number of observations increases. We end with a few recommendations for applying moderated autoregressive models based on our simulation.

Development of GaN-Based, 6.6 kW, 450 V, Bi-Directional On-Board Charger with Integrated 1 kW, 12 V Auxiliary DC-DC Converter with High Power Density

Automotive-grade GaN power switches have recently been made available in the market from a growing number of semiconductor suppliers. The exploitation of this technology enables the development of very efficient power converters operating at much higher switching frequencies with respect to components implemented with silicon power devices. Thus, a new generation of automotive power components with an increased power density is expected to replace silicon-based products in the development of higher-performance electric and hybrid vehicles. 650 V GaN-on-silicon power switches are particularly suitable for the development of 3–7 kW on-board battery chargers (OBCs) for electric cars and motorcycles with a 400 V nominal voltage battery pack. This paper describes the design and implementation of a 6.6 kW OBC for electric vehicles using automotive-grade, 650 V, 25 mΩ, discrete GaN switches. The OBC allows bi-directional power flow, since it is composed of a bridgeless, interleaved, totem-pole PFC AC/DC active front end, followed by a dual active bridge (DAB) DC-DC converter. The OBC can operate from a single-phase 90–264 Vrms AC grid to a 200–450 V high-voltage (HV) battery and also integrates an auxiliary 1 kW DC-DC converter to connect the HV battery to the 12 V battery of the vehicle. The auxiliary DC-DC converter is a center-tapped phase-shifted full-bridge (PSFB) converter with synchronous rectification. At the low-voltage side of the auxiliary converter, 100 V GaN power switches are used. The entire OBC is liquid-cooled. The first prototype of the OBC exhibited a 96% efficiency and 2.2 kW/L power density (including the cooling system) at a 60 °C ambient temperature.

Forced Dynamic Operation of Propylene Selective Oxidation to Acrolein on Bismuth-Molybdate Structured Catalysts

Forced dynamic operation (FDO) of selective oxidation of propylene to acrolein is evaluated on a structured alumina foam coated with a mixed metal oxide catalyst (bismuth molybdate-based). Reactor experiments examine feed composition modulation as a strategy to increase the yield of acrolein. At lower temperatures, separating the oxidant (O2) and reductant (C3H6) enhances propylene conversion and acrolein selectivity. Variation in the reaction-regeneration switching amplitude and frequency gives a 40% higher cycle-averaged acrolein yield compared to steady-state operation (SSO) for the same overall feed composition. The results suggest that FDO maintains a higher concentration of selective oxygen species during the propylene feed, while pre-oxidation of the catalyst maximizes the amount of selective oxygen species, leading to increased acrolein yield at the beginning of the reaction cycle. Experiments at lower temperature for both commercial promoted and in-house, unpromoted catalysts reveal both catalysts are most active and selective at their highest oxidation states.

Design and Verification of Adaptive CC/CV Mode Switching Wireless Power Transfer System for UAVs Based on High Switching Frequency Single-Switch LC Inverter

Design and Verification of Adaptive CC/CV Mode Switching Wireless Power Transfer System for UAVs Based on High Switching Frequency Single-Switch <i>LC</i> Inverter

Asynchronous Machines with PWM Inverters: A Novel Approach to DTC Enhancement

Abstract This paper presents some methods of direct torque control (DTC) improvement for asynchronous machine (AM) with PWM inverter. Asynchronous machine DTC is recognized to have a straightforward control structure and work similarly to field orientation control (FOC). Two new strategies are presented to retain this control structure while simultaneously improving the switching frequency and stator flux estimate performances of the DTC drive. Finally, some proposed schemes for improved DTC and simulation results are presented.

Power losses analysis for reduced switch 9-level cascaded H-bridge multilevel inverter

This study provides a thorough examination of power losses and total harmonic distortion (THD) in single-phase 9-level cascaded H-bridge multilevel inverters (CHB MLI) at low switching frequencies. The aim is to analyze the efficiency of a single-phase 9-level cascaded CHB MLI using three distinct switch configurations: 16-switch, 11-switch, and proposed 8-switch. The calculated switching angles are optimized using the feed-forward methodology. Two types of load conditions—R load and R-L load—are being examined. The results suggest that the proposed 8-switch design exhibits superior efficiency by limiting power losses compared to other topologies. Regarding THD, the conventional topology yields a somewhat lower value, however, the disparity is less than 1% when compared to both reduced switch topologies.

Power loss reduction of three-phase inverter in electric vehicle using variable switching frequency hybrid PWM

Power loss reduction of three-phase inverter in electric vehicle using variable switching frequency hybrid PWM

Variable-Vector-Based Model Predictive Control With Reduced Current Harmonic and Controllable Switching Frequency for PMSM Drives

Variable-Vector-Based Model Predictive Control With Reduced Current Harmonic and Controllable Switching Frequency for PMSM Drives

Improved vector selection model predictive control strategy for quasi‐Z‐source inverter virtual synchronous generator grid‐connected system

AbstractConventional inverter control methods reduce the grid inertia and are susceptible to parameter variations, resulting in a gradual weakening of grid stability. To address the above problems, an improved vector selection model predictive control strategy is proposed, with virtual synchronous generator technology to control the quasi‐Z‐source inverter. First, the influence of different operating states on the quasi‐Z‐source inverter state variables is analysed, and the established quasi‐Z‐source inverter‐virtual synchronous generator discrete‐time model predicts the input current, output capacitor voltage, and load current of the quasi‐Z‐source inverter network. Second, the inverter switching timing is analysed to establish the optimal switching vector set, and the optimal switching vector set is selected by defining the sub‐objective function, which reduces the average switching frequency of the system. Compared with the finite control set model predictive control, this strategy is to reduce the computation time of the system to obtain the optimal solution of the quasi‐Z‐source inverter, to improve the dynamic responsiveness of the system during the control process, and to improve the power quality. Finally, the effectiveness and correctness of the proposed algorithm are verified by experiments.

Hysteresis Current Controller With Fixed Switching Frequency and Phase for Interleaved Converters

Hysteresis Current Controller With Fixed Switching Frequency and Phase for Interleaved Converters

Accurate Evaluation of Commutations of 650 V GaN Power Switches Assisted by Electromagnetic Simulations in a 7 kW Dual Active Bridge Converter for Automotive Battery Charging Applications

The exploitation of high-voltage GaN power switches enables the development of power converters with superior characteristics with respect to components developed with heritage silicon-based technologies. One of the key advantages of GaN switches is their very fast commutation capability due to reduced parasitic capacitance and inductance with respect to silicon devices. The capability of an accurate evaluation of the switch commutations in the design phase is of crucial importance to maximize performance and avoid reliability or electromagnetic compatibility issues in the final converter. In this paper, an accurate evaluation of high-voltage GaN HEMT commutations is performed, exploiting detailed non-linear dynamic models of transistors and electromagnetic simulations of a PCB. A deep insight into the commutation waveforms in the intrinsic device (i.e., conductive drain current and intrinsic node voltages) is proposed to evaluate and explain the mechanisms of almost lossless turn-off and turn-on commutations in a 7 kW DAB converter. The influence on the performance of the PCB parasitics and the driver characteristics are accurately reproduced by simulations, suggesting important guidelines for the optimal design of power converters fully exploiting GaN HEMT’s potential. This detailed simulation/analysis approach for transistor commutation is typically adopted in Radio Frequency amplifier design but also becomes very valuable in power converter design when the very fast commutations of a GaN HEMT at a high switching frequency cannot be fully described and taken under control with conventional approaches used in power electronics design. The simulation results are confirmed by experimental data.

ABOUT THE USE OF DIGITAL HYDRAULIC VALVES IN INDUSTRY

The article discusses digital hydraulic valves, which are an innovative alternative to traditional proportional analog valves. Digital hydraulics utilize a combination of simple, reliable, and inexpensive ON/OFF type valves, offering high precision in flow and pressure control through programmable logic controllers. The main advantage of such systems is the reduction in energy consumption, as they eliminate the need for constant pump operation and have no internal leakage. The article highlights the economic benefits of digital valves, including lower initial investments due to their lower cost compared to proportional counterparts. Importantly, if one valve fails, the system remains operational, as the failure of individual components does not critically affect overall performance. Special attention is given to coding schemes and control methods, particularly binary coding and pulse number modulation. Binary coding allows for significantly improved regulation accuracy with a minimal number of valves and ensures system fault tolerance. The use of parallel-connected valves, which offer a wide range of states, allows precise control of flows and pressures without the need for switching after the desired positions are set. Additionally, digital hydraulic systems provide fast response times and precise control, making them effective for various industrial applications. Further research in this area could lead to the development of new technological solutions and broader implementation in the industry. The article also covers the technical aspects of such systems, particularly pulse-width modulation, the most common approach to controlling two-way valves. PWM achieves high regulation accuracy through frequency modulation, although low switching frequencies may cause pressure pulsations, which must be compensated through specialized system design or damping devices. In conclusion, digital hydraulic valves represent a promising solution for increasing the efficiency and reliability of hydraulic systems in modern industries, with the potential for significant reductions in energy consumption and operational costs.

Mixed-mode fast-slow oscillations in the frequency switching Duffing system with a 1:n frequency ratio

Mixed-mode fast-slow oscillations in the frequency switching Duffing system with a 1:n frequency ratio

Hybrid Control System for Cascaded H-bridge Multi-Level Inverter Based Shunt Active Filter for Photovoltaic Generation

This article presents a hybrid controller developed for a Shunt Active Filter (SAF) with Photovoltaic (PV) generation Structure. This structure, referred to as (PV-SAF/CHB-PN), uses a Multi-Level Inverter (MLI)-type-Cascaded H-Bridge (CHB) to realize several aspects: i- Increase the apparent switching frequency. ii- Generate approximately sinusoidal output voltage. iii- Minimize the output filter size. The hybrid controller, implemented via Petri Nets (PNs), optimizes the dispatch commitment among the H-Bridge modules and the arms of each modules. Thus, to compensate for perturbations, while generating the MPPT pf the PV panels, a PN current controller combined with a new analytical Hysteresis control approach, is employed. Meanwhile, a PN voltage controller balances the DC voltages across of the MLI-CHB inputs and achieves a practical stability using the Lyapunov method. The PV generators are integrated, via DC/DC converters, into the DC side of the SAF. Hence, Model Predictive Controller based Perturb and Observe (MPC-Based P&O-MPPT) algorithm optimizes the MPPT extraction without drift phenomena.Finally, a case study for textile factory using real measurements via power quality analyzers, demonstrates the effectiveness of 3 CHB modules structure in mitigating harmonic impacts of the main textile machine of (SL-50 kVA), validating the hybrid controller, and integrating green energy.

Thermal Characterization of Ferroelectric Al1-xBxN for Nonvolatile Memory.

Boron (B)-substituted wurtzite AlN (Al1-xBxN) is a recently discovered wurtzite ferroelectric material that offers several advantages over ferroelectric Hf1-xZrxO2 and PbZr1-xTixO3. Such benefits include a relatively low growth temperature as well as a thermally stable, and thickness-stable ferroelectric polarization; these factors are promising for the development of ferroelectric nonvolatile random-access memory (FeRAM) that are CMOS-compatible, scalable, and reliable for storing data in harsh environments. However, wurtzite ferroelectric materials may undergo exacerbated self-heating upon polarization switching relative to other ferroelectric materials; the larger energy loss is anticipated due to the higher coercive field and remanent polarization. This work provides insight into the polarization switching-induced self-heating of future FeRAM based on Al1-xBxN. It was experimentally observed that the thermal conductivity of Al1-xBxN thin films drops from 40.9 W m-1 K-1 to 4.35 W m-1 K-1 (which is 2 orders of magnitude lower than that of bulk AlN) when the B composition (x) increases from 0 to 0.18. The transient thermal response of an Al0.93B0.07N metal-ferroelectric-metal (MFM) capacitor was investigated using micro-Raman thermometry and validated via device thermal modeling. Further simulation studies reveal that the large heat generation rate and the low thermal conductivity is predicted to induce an instantaneous temperature rise that may exceed 150 °C in a FeRAM device based on a 5 nm thick Al1-xBxN film at GHz frequency switching. In addition, thermal crosstalk within a FeRAM cell array exacerbates the self-heating, resulting in a predicted steady-state temperature rise that is an order of magnitude higher than that of a single bit-cell.