Optimal Turn-on Research Articles

Advanced Mechanical Transfer of Micro-LEDs Enabled by Structurally Modified Wide Sapphire Nanomembranes through Thermal Reflow of Photoresist.

Micro light-emitting diodes (micro-LEDs) are pivotal in next-generation display technologies, driven by the need for high pixel density. This study introduces a novel methodology utilizing wide sapphire nanomembranes (W-SNM) as a dual-purpose template for high-quality epitaxial growth and the mechanical lift-off of individual micro-LEDs. Micro-LEDs grow individually on W-SNM, obviating the chip singulation process. By employing mechanical fracturing of the thin W-SNM, our method facilitates the transfer of micro-LEDs without the conventional laser lift-off (LLO) process. Previously introduced sapphire nanomembranes (SNM) have shown promise in enhancing epitaxial layer quality; however, they encountered challenges in managing micro-LED size variation and achieving efficient mechanical transfer. Here, we apply simple yet effective adjustments to the SNM structure, specifically, its elevation and widening. This strategic modification allows micro-LEDs to endure applied forces without incurring cracks or defects, ensuring that only the targeted W-SNM are selectively fractured. The mechanically transferred vertical 15 × 15 μm2 micro-LED device operates at an optimal turn-on voltage of 3.3 V. Finite element simulations validate the mechanical strain distribution between the W-SNM and GaN when pressure is applied, confirming the efficacy of our design approach. This pioneering methodology offers a streamlined, efficient pathway for the production and mechanical transfer of micro-LEDs, presenting new avenues for their integration into next-generation, high-performance displays.

Dynamic laser ablation loading of a linear Paul trap

We present a detailed method for accumulating Ca+ ions controllably in a linear Paul trap. The ions are generated by pulsed laser ablation and dynamically loaded into the ion trap by switching the trapping potential on and off. The loaded ions are precooled by buffer gas and then laser-cooled to form Coulomb crystals for verifying quantity. The number of ions is controlled by manipulating the trapping potential of the ion trap, partial pressure of buffer gas and turn-on time of the entrance end cap voltage. With single-pulse laser ablation, the number of trapped ions ranges from tens to ten thousand. The kinetic energy of loaded ions can be selected via the optimal turn-on time of the entrance end cap. Using multiple-pulse laser ablation, the number is further increased and reaches about 4×104 . The dynamic loading method has wide application for accumulating low-yielding ions via laser ablation in the ion trap.

A novel direct torque control method for switched reluctance motors based on optimal turn-on angle

A novel direct torque control method for switched reluctance motors based on optimal turn-on angle

Optimization of ZnO Nano Particles Preparation and Its Performance as Electron Transfer Layer in Quantum Light-Emitting Diode

In this paper, different diameters ZnO Nano Particles (ZnO NPs) are prepared through wet chemistry method. The size effects on Quantum light-emitting diodes (QLED) performance are investigated. In addition, the influences of reaction temperature, reaction time and reactant ratio on ZnO size and performance of QLED are also studied. Transmission electron microscope (TEM), Ultraviolet-Visible spectroscopy (UV-Vis) absorption spectra and photoluminescence (PL) spectra are employed to analyze the influence of preparation conditions on optical properties of the ZnO NPs packaged QLED. The results show that 2.5 nm ZnO NPs can be obtained at 25 °C for 6 hours when the Zn2+:OH- ratio is 1:1. In comparison to the 5 nm ZnO QLED, the EQE of the 2.5 nm ZnO QLED has increased from 1% to 7.8%, and the brightness has increased from 8000 to 13000 cd/m2. When ZnO NPs solution concentration is 30 mg/ml and spin speed is 4000 rpm, the optimal turn-on voltages and luminous intensity of QLED can also be attained.

Switching Time Delay Optimization for “SiC+Si” Hybrid Device in a Phase-Leg Configuration

Compared to SiC MOSFET, the switching loss of Si IGBT is much higher due to its slow switching speed and tail current. Si IGBT/SiC MOSFET hybrid switch device can reach to optimal performance with low static and dynamic loss, which can improve the current capacity of SiC devices and reduce the power loss of Si IGBT based converters. With the separated gate control signals, the switching moments of the two devices can be controlled independently to ensure Si IGBT under zero-voltage switching (ZVS) conditions. This measurement tends to reduce the switching loss of Si IGBT. However, the switching time delay between these two devices has significant impacts on its power loss. In this paper, the switching time delay optimization method is proposed to minimize the power loss of the hybrid switch. The static and dynamic characteristics of Si IGBT/SiC MOSFET hybrid-paralleled switch are studied, and a generalized power loss model for hybrid switch is developed. The influence of switching time delay on the characteristics of hybrid switch is analyzed and verified through double pulse tests in a phase-leg configuration. The experimental results show that the optimal turn-on delay time is that the two devices turn on at the same time and the turn-on loss can be reduced by about 73% compared with the solely Si IGBT and by about 52% compared with the solely SiC MOSFET. While the optimal turn-off sequence is that the Si IGBT turns off ahead of the SiC MOSFET. Under the proposed optimal turn-off delay time of the hybrid switch, the turn-off loss is reduced by about 61.4%. This optimization strategy is used in a Buck converter to verify the superiority of the SiC/Si hybrid switch and the optimal switching sequence. Simulation results show that the optimal switching sequence is consistent with theoretical analysis, and the efficiency is improved by 2.5% compared with Buck converter using solely Si IGBT.

Electromagnetic‐based maximum output power control in new two‐layer BLDC generator using optimal control of turn‐on and turn‐off angles in variable speed applications

In this study, by using the electromagnetic field analysis, the design of brushless DC generator with a novel construction and controller, appropriate for variable speed applications, is proposed. In the proposed machine, unlike the conventional structure, an assisted DC field coil is employed instead of permanent magnet excitation to provide a regulated voltage. Results of the electromagnetic field analysis show that including the DC field coil increases the controllability of the flux in different machine parts which provide a regulated terminal voltage in a wide speed range appropriate for variable speed applications. Moreover, the maximum power point tracking is achieved by controlling the DC field current along with producing optimal turn-on and turn-off angles for stator winding using the electromagnetic analysis based on optimal finite element analysis. Also, an appropriate controller is designed to control the DC field coil current. To verify the actual performance of the proposed configuration, a 1.5 Kw machine is manufactured and tested followed by the discussion on results. The obtained experimental results are in good agreement with the results of the electromagnetic analysis which confirm the maximum power trackability and robust output voltage regulation of the proposed conversion system under different shaft speeds and load conditions.

Maximum Output Torque Control in Improved Flux Path Homopolar Brushless DC Motor With Axillary Field by Using Optimal Control of Turn-ON and Turn-OFF Angles in Variable Speed Applications

This paper presents the principles of operation, electromagnetic behavior analysis, and a search technique based on the finite-element analysis in order to determine the optimum control parameters of an improved flux path Homopolar brushless dc motor (IFP-HBLDC). In the proposed IFP-HBLDC structure, a permanent magnet is replaced by a dc excited assisted field coil to control and regulate the flux. In this paper, for different values of speed, maximum torque is determined by calculating the optimal turn-on and turn-off angles and the optimal field current which provides more flexible control over wide ranges of speed. To such aim, the behavior of the commutation angles is analyzed first by a numerical technique using the 3-D electromagnetic field analysis, in which the analysis of the collected data has shown that the commutation angles providing the maximum electromagnetic torque. The technique was successfully used offline to determine the optimum firing angles for achieving the highest drive efficiency to maximize the electromagnetic torque in a prototype 1.5-kW three-phase IFP-HBLDC motor drive intended for variable speed application. The performance prediction and test results are found in good correlation.

Investigation of a Switched Reluctance Generator Using the Voltage Pulse Width Modulation Method

An analytical modeling method of the current for a Switched Reluctance Generator (SRG) using voltage Pulse Width Modulation (PWM) control is proposed. The current equation is achieved from the inductance model in combination with the voltage equation. The proposed inductance model is divided into four regions which depend on the pole arcs of the rotor and stator and the inductance at aligned and unaligned positions. A method to obtain a PWM duty cycle and the optimal turn-on and turn-off angles of the SRG undervoltage PWM control is presented. An SRG with 8 stator poles and 6 rotor poles was setup to validate the proposed method. The PWM duty cycle and optimal control variables based on the proposed method were used to control the SRG. The results indicated that the SRG could generate the optimum phase current over a wide speed range.

Simultaneous Optimization of Geometry and Firing Angles for In-Wheel Switched Reluctance Motor Drive

Interests in using rare-earth free motors such as switched reluctance motors (SRMs) for electric and hybrid electric vehicles continue to gain popularity, owing to their low cost and robustness. Optimal design of an SRM, to meet specific characteristics for an application, should involve simultaneous optimization of the motor geometry and control in order to achieve the highest performance with the lowest cost. This paper presents a constrained multiobjective optimization framework for design and control of an SRM based on a nondominated sorting genetic algorithm II. The proposed methodology optimizes SRM operation for high volume traction applications by considering multiple criteria including efficiency, average torque, and torque ripple. Several constraints are defined by the considered application, such as the motor stack length, outer diameter, minimum operating power, minimum desired efficiency, rated speed, rated current, and supply voltage. The outcome of this optimization includes an optimal geometry, outlining variables such as air gap length, rotor inner diameter, stator pole arc angle, rotor pole arc angle, rotor back iron, stator pole height, and stator inner diameter as well as optimal turn-on and turn-off firing angles. Then the machine is manufactured according to the obtained optimal specifications. Comprehensive finite-element analysis and experimental results are provided to validate the theoretical findings.

A simple turn-on and turn-off angles searching method for copper loss minimization of the switched reluctance motor

PurposeThe purpose of this paper is to present a simple and effective method to search the optimal turn-on and turn-off angles on-line for the control of the switched reluctance motor (SRM). The optimal turn-on and turn-off angles are defined as the ones that can meet torque production requirements with minimum copper loss.Design/methodology/approachThe optimal turn-on and turn-off angles are first defined based on the analysis of the SRM losses and torque production principles. Then the algorithm for optimal angles searching is developed, and the searching parameters are determined through analytical computation. The optimal angles are approached on-line with iterative process. Simulation and experiments are finally performed to verify the proposed method.FindingsThe presented method can meet torque production requirements while copper loss is minimized. The optimal turn-on and turn-off angles are generally approached within five phase cycles for most of the SRM operation modes. Furthermore, the SRM drive system using the presented method exhibits good dynamics during starting and sudden load operations.Practical implicationsThe presented method is simple, and implementation of it is easy. It is an eligible candidate for industrial applications where energy conversion efficiency is crucial.Originality/valueThe optimal turn-off angle definition that considers both torque production and copper loss minimization is proposed. The turn-on and turn-off angles are searched independently on-line with little SRM geometrical information. The searching steps are derived through analytical computation and qualitative analysis so that both the searching speed and algorithm convergence are balanced.

Improvement of power generation performance in a doubly salient permanent magnet generator with a capacitive energy recovery converter

In order to improve the power generation performance of a doubly salient permanent magnet generator (DSPMG), this study proposes a new converter called capacitive energy recovery converter (CERC), together with the corresponding control strategy. The CERC is composed of controllable devices, uncontrollable devices, and an energy storage circuit. The control strategy has been designed based on analysis of the electromagnetic characteristics of the DSPMG. With the proposed control strategy, the winding current of each phase can be controlled and increased separately, thus yielding large negative electromagnetic torque against the prime mover in a complete electric cycle. At the same time, the excitation sources are independent of the load part. As a result, power generation performance of the DSPMG with CERC is improved compared to that with a traditional three-phase full-bridge converter. A multi-objective optimisation problem is formulated to find the optimal turn-on and turn-off angles of two systems, which are used as control parameters in this comparison. Besides the lower voltage and torque ripples, the dynamic and fault-tolerant performance of the DSPMG with CERC is also superior. Both simulations and experiments have been conducted to verify the validity of the proposed converter and the control strategy.

퍼지 이론과 슬라이딩모드 제어를 이용한 스위치드 릴럭턴스 전동기의 토크리플 저감

This paper presents a torque ripple reduction algorithm for the switched reluctance motor drives using the fuzzy logic and the sliding mode control. A turn-on angle controller based on the fuzzy logic determines the optimal turn-on angle. In addition, a sliding mode torque control (SMTC) methods reduces torque ripples instantaneously in the commutation region. The proposed algorithm does not require complex system models considering nonlinear magnetizing or demagnetizing periods of the phase current. According to the rotor speed and torque, the proposed controller changes the turn-on angle and reference torque instantaneously until the torque ripples are minimized. The simulation and experimental results verify the validity of minimizing the torque ripple performance.

Optimal Excitation Angles of a Switched Reluctance Generator for Maximum Output Power

This paper investigates the optimal values of turn-on and turn-off angles, and ratio of flux linkage at turn-off angle and peak phase current positions of optimal control for accomplishing maximum output power in an 8/6 Switched Reluctance Generator (8/6 SRG). Phase current waveform is analyzed to determine optimal excitation angles (optimal turn-on and turn-off angles) of the SRG for maximum output power which is applied from a nonlinear magnetization curve in terms of control variables (dc bus voltage, shaft speed, and excitation angles). The optimal excitation angles in single pulse mode of operation are proposed via the analytical model. Simulated and experimental results have verified the accuracy of the analytical model.

A DC–DC Boost Converter With Variation-Tolerant MPPT Technique and Efficient ZCS Circuit for Thermoelectric Energy Harvesting Applications

This paper presents a dc-dc boost converter with the maximum power point tracking (MPPT) technique for thermoelectric energy harvesting applications. The technique realizes variation tolerance by adjusting the switching frequency of the converter. A finely controlled zero-current switching (ZCS) scheme together with the accurate MPPT technique enhances the overall efficiency of the converter because of an optimal turn-on time generated by a one-shot pulse generator that is proposed. Moreover, the ZCS technique can deal with low- and high-temperature differences applied to the thermoelectric generator. This allows a wider range of conversion ratios compared to those of conventional converters used for thermal energy harvesting. Experimentally, the converter implemented in a 0.35-μm BCDMOS process had a peak efficiency of 72% at the input voltage of 500 mV while supplying a 5.62-V output.

Analytical method to optimise turn-on angle and turn-off angle for switched reluctance motor drives

A new analytical method is proposed to produce optimal turn-on and turn-off angles, based on a non-linear inductance model of low-inductance region for switched reluctance motor (SRM). The optimal turn-on angle is derived from the non-linear model and electrical equation of SRM instead of the linear model while optimal turn-off angle is derived from the turn-on angle and flux-linkage. Considering the back electromotive force, the proposed method has more accuracy than the conventional analytical method and improves the efficiencies both at low speed and high speed. Simulation and experimental results demonstrate the validity and effectiveness of the proposed method, which is suited for low- and high-speed conditions both.

Study of Switching Characteristics of Static Induction Thyristor for Pulsed Power Applications

It is difficult to design a standard gate driver for optimal switching control of a static induction thyristor (SI-Thy) because of its unique internal structure and the direct commutation switching characteristic between the gate and cathode terminals during the transient turn-on and turn-off switching phases. Therefore, it is important to develop a simple and effective gate driver for achieving optimal fast turn-on and stable switching operations in an SI-Thy under hard-switching conditions. To achieve faster turn-on switching time with shorter gate delay time, impedance matching between the SI-Thy and the turn-on driving circuit component in the gate driver can be realized with additional circuit modification through this paper. To ensure higher stabilities in the turn-off switching phase, forced commutation techniques and additional auxiliary circuits in the gate driver have been devised to suppress the latchup and to eliminate potential ringing possibility. We have demonstrated that our designed and tested gate driver for realizing optimal switching characteristics of an SI-Thy is effective, particularly in the gate driving circuits for various pulsed-power switching applications.

Low-cost microprocessor-based alternating current voltage controller using genetic algorithms and neural network

A low-cost, high-performance microprocessor-based pulse width modulated (PWM) AC voltage controller with a novel harmonic reduction technique is proposed. Genetic algorithm is adopted to evaluate the optimal turn-on and turn-off angles in the PWM pattern such that the total current harmonic distortion is minimised. The evolved angles are only optimised at a desired output voltage. In the proposed design, an artificial neural network trained by sets of optimal angles is utilised, making the designed system applicable to all operating points. The simulation and experimental results verify that the proposed technique is a suitable technique, and its performance is comparable to the conventional techniques.

Optimization and Evaluation of Torque-Sharing Functions for Torque Ripple Minimization in Switched Reluctance Motor Drives

Two improved torque-sharing functions for implementing torque ripple minimization (TRM) control are presented in this paper. The proposed torque-sharing functions are dependent on the turn-on angle, overlap angle, and the expected torque. This study shows that for a given torque the turn-on angle and the overlap angle have significant effects upon speed range, maximum speed, copper loss, and efficiency. Hence, genetic algorithm is used to optimize the turn-on angle and the overlap angle at various expected torque demands operating under the proposed TRM control in order to maximize the speed range and minimize the copper loss. Furthermore, four torque-sharing functions are used to derive the optimized results. At the same time, a fast and accurate online approach to compute the optimal turn-on and overlap angles is proposed. Therefore, this paper provides a valuable method to improve the performances of switched reluctance motor drives operating under TRM control.

Optimal efficiency control of switched reluctance generators

This paper investigates the problem of optimal control for accomplishing maximum energy conversion in switched reluctance generators. A controller that determines the optimal turn-on and turn-off angles in the mode of single-pulse operation is proposed. The structure of the controller and its implementation are simple, since the knowledge of the magnetization curves is not required. The suggested generator drive operates in a wide speed range and provides constant dc-link voltage at a desired value, with maximum energy efficiency. Simulation and experimental results are presented to validate the effectiveness and the resulting improvements of the proposed control scheme.

Maximum Efficiency in Single-Pulse Controlled Switched Reluctance Motor Drives

The problem of choosing the firing angles for accomplishing maximum efficiency in single-pulse controlled switched reluctance motor drives is investigated. The suggested method is based on the optimal control of flux-linkage, through the firing angles, according to load torque requirements and depending on rotor speed. A controller that determines online the optimal turn-on and turn-off angles is proposed. The suggested controller does not affect the complexity of the drive and it is easily implemented, since knowledge of magnetization curves is not required. Moreover, it provides smooth transition between optimal single-pulse and pulse width modulation (PWM) current control modes and thus, optimal performance of the switched reluctance motor drive is attained over the entire speed range. Simulation and experimental results are presented to validate the resulting improvements of the proposed control scheme.