Zero-crossing Point Research Articles

Linear Equivalent Model for VHF Class Φ2 Inverter Based on Spectrum Quantification Method to Reduce GaN Reverse Conduction Loss

Reverse conduction loss of GaN high electron mobility transistors (HEMTs) in very high frequency (VHF) converters is non-neglectable due to the absence of body diode. To reduce the reverse conduction time, this paper proposes a linear equivalent model for class <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Phi _{2}$ </tex-math></inline-formula> inverter to derive optimal duty cycles for different working conditions. The proposed model is derived from frequency-domain perspective, which simplifies the derivation process and provides an intuitive physical insight for class <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Phi _{2}$ </tex-math></inline-formula> inverter. Firstly, the power switch is modeled as a current source according to time-domain expressions of inductor current, which simplifies the circuit to a linear network. Based on quantitative analysis of the current source spectrum characteristics, the linear network response to the current excitation is derived, which forms the linear equivalent model. Then, drain voltage of the main switch under different working conditions is obtained. With the zero-crossing point of the drain voltage, numerical solutions of the optimal duty cycles are calculated. Finally, the optimal duty cycles are implemented with a high-resolution duty cycle generation circuit in a 27.12MHz prototype, which achieves not only a peak efficiency of 93.6% at full load, but also higher efficiency over the whole load and input voltage range compared to conventional fixed duty cycle.

An Optimized Digital Synchronous Rectification Scheme Based on Time-Domain Model of Resonant CLLC Circuit

Uncontrolled rectification on the secondary side of the resonant CLLC circuit causes a large amount of conduction loss. Accurate synchronous rectification (SR) can reduce conduction loss by replacing rectifier diodes with mosfets’ channels exactly. The accuracy of the SR signals depends on the determination of the zero-crossing points of the secondary side resonant current. In this article, an accurate time-domain model is introduced for the resonant CLLC circuit to obtain these zero-crossing points. This modeling method is more accurate than first harmonic approximation and requires less computational effort than extended harmonics approximation. Compared with previous time-domain modeling methods, the proposed time-domain model gives detailed circuit state expressions and covers the entire circuit operating states. Relying on the accurate circuit model, the SR scheme proposed in this article can adaptively generate SR signals in different frequency ranges and has the ability to switch modes smoothly. And this method can be used for the later efficiency optimization of CLLC converters that do not originally have SR function, only through the control program update. Moreover, the robustness of the proposed SR method is analyzed, and the proposed concept is verified through a 3-kW resonant CLLC prototype.

A New Phase-Delay-Free Commutation Method for BLDC Motors Based on Terminal Voltage

It is well known that there is the commutation interference pulse in zero-crossing points (ZCPs) of back electromotive force (EMF) for brushless direct current (BLdc) motors. Generally, the interference pulse is handled by a low-pass filter (LPF) with a low cutoff frequency. However, the phase delay caused by LPF will deteriorate the performance of BLdc motors. In this letter, a novel phase-delay-free commutation method based on terminal voltage is proposed. The ZCPs and commutation freewheeling signals are obtained according to terminal voltages. Then, the main part of commutation interference pulse is removed through detected freewheeling signals. Finally, the remaining part is eliminated through a fixed delay digital filter (FDF). Comparing with the conventional commutation methods, the faster starting and the phase-delay-free commutation are achieved reliably by the proposed method. The effectiveness of the proposed method is verified through an 80 W BLdc motor.

Virtual Third Harmonic Back EMF-Based Sensorless Drive for High-Speed BLDC Motors Considering Machine Parameter Asymmetries

This article investigates the virtual third harmonic back electromotive force (EMF)-based sensorless drive method for high-speed brushless dc (BLDC) motors. Conventional zero-crossing point (ZCP) detection methods of virtual third harmonic back EMF require hardware low-pass filters and voltage comparators, causing serious phase lag. To avoid the undesired phase lag of hardware, the proposed method employs algorithmic oversampling technique to reconstruct the envelope of virtual third harmonic back EMF. Besides, the number of sampling points is dynamically adjusted according to the pulsewidth modulation duty ratio to guarantee the accuracy of ZCP detection. In addition, the influence of asymmetric motor parameters, i.e., phase resistance and inductance, on sensorless commutation is analyzed in depth. With asymmetric impedances, ZCPs of virtual third harmonic will deviate from their ideal positions. Consequently, the commutation events, which are searched based on ZCPs, will also be triggered at inaccurate positions and then the control performance will be deteriorated. In order to suppress the negative influence, a novel phase compensation method is proposed. All the theoretical analyses are validated by experiments at a 60 000 r/min BLDC drive platform.

Synchronous Spectrofluorimetry Coupled with Third-Order Derivative Signal Processing for the Simultaneous Quantitation of Telmisartan and Chlorthalidone Drug Combination in Human Plasma.

This study is the first to develop and optimize a method for the simultaneous determination of chlorthalidone (CLT) and telmisartan (TEL) in, human plasma samples as well as in their newly released pharmaceutical tablet form, (Telmikind-CT 40®). The method is based on measuring fluorescence intensity, employing synchronous fluorescence mode coupled to third-order derivative signal processing, 0.5% w/v cetyl trimethyl ammonium bromide was used as cationic surfactant to enhance the fluorescence signal intensity and improve method sensitivity. The third-order derivative synchronous spectra of CLT and TEL are well separated with two zero-crossing points which allowed for the determination of CLT and TEL at 362nm and 351nm, respectively. Different experimental parameters were carefully investigated and optimized, calibration curves were constructed over concentration ranges of 20-1200ng.mL-1 and 5-800ng.mL-1 for CLT and TEL respectively. The developed method is simple and rapid, analytical parameters were validated according to ICH guidelines and high sensitivity was achieved as represented by limits of detection (LOD) of 4.69 and 1.58ng.mL-1 for CLT and TEL respectively.

Research on Zero-crossing Point Prediction Technology of CFI Based on A New Adaptive LS Algorithm

Fast identification of fault current parameters and accurate prediction of current waveform zero-crossing are the key technologies of controlled fault interruption(CFI). Aiming at the problem that the least squares(LS) algorithm has truncation error, this paper propose a new adaptive least square(LS) algorithm using the change rate of the fault current, avoiding the approximation of the attenuated DC decaying component. Based on the fault current simulated by MATLAB, the results show that the new algorithm has higher accuracy when the noise is not less than 40dB and the data window is more than 10ms. For the actual simulated fault current data by PSCAD, the proposed algorithm also had high accuracy, which can meet the requirements of CFI.

Novel Bidirectional DC Solid-State Circuit Breaker With Operating Duty Capability

DC microgrids have received remarkable interest in both the academia and the industry for over a decade, yet the protection of dc microgrids remains as a major challenge. This challenge is rooted in the nonexistence of natural zero-crossing point in dc microgrids which rapidly increase the fault current. In this article, a novel bidirectional dc solid-state circuit breaker (dc SSCB) to reinforce the bidirectional flow of energy which significantly boosts the overall efficiency of the power supply of dc microgrids is presented. The proposed topology can perform the operating duty of reclosing and rebreaking, and the commutation capacitor is charged and recharged naturally without any complex control of the main or auxiliary thyristors, which is considered atypical of existing topologies. A clear and detailed analysis of the operation of the proposed topology is presented. Finally, the experimental results are presented to confirm the effectiveness of the proposed novel bidirectional dc SSCB.

A measurement method for three-dimensional inner and outer surface profiles and spatial shell uniformity of laser fusion capsule

We propose a novel laser differential confocal measurement method with high spatial resolution for the simultaneous measurement of 3D inner and outer surface profiles and spatial shell uniformity of capsules. The zero-crossing point of characteristic curve of a laser differential confocal sensor (LDCS) exactly corresponds to the focal point; therefore, the proposed method performs high-precision and fast fixed-focus measurements on the vertexes of the surfaces of the capsule along its radial direction using the sensor. Then through the precision rotation measurement of the circumference trace and multi-directional meridian contour measurement of the capsule around the horizontal axis, the simultaneous high-precision measurement of 3D inner and outer surface profiles and spatial shell uniformity of the capsule can be achieved. To the best of our knowledge, the proposed method is the first to achieve high-precision and non-destructive measurement of 3D inner and outer surface profiles and spatial shell uniformity of the capsule simultaneously, and it provides a novel technical approach for achieving high-precision and non-destructive measurement of geometric parameters of ICF capsules.

Inductive Power Transfer Systems With Digital Switch-Controlled Capacitor for Maximum Efficiency Point Tracking

Inductor–capacitor–capacitor-series (LCC-S) compensation topology has been widely used in inductive power transfer (IPT) systems due to its constant coil current regardless of the load and the coupling coefficient. Usually, the inductance of transmitter coil is sensitive to misalignments of the magnetic coupler when the asymmetrical coil structure with a smaller size receiver coil is adopted. The fluctuation of the inductance of transmitter coil will increase the power losses in the primary inverter. To compensate the fluctuation of the transmitter coil inductance, a digital switch-controlled capacitor (D-SCC) for maximum efficiency point tracking (MEPT) of LCC-S compensated IPT system is proposed. Consequently, the proposed LCC-S compensated IPT system can achieve high efficiency against the fluctuation of transmitter coil inductance. In traditional switch-controlled capacitor, high- frequency current sensor is required for the synchronization between the transmitter coil current and the driver signals of the switch-controlled capacitor. Nevertheless, the drive signals of D-SCC can be generated directly by the DSP controller in the primary side without detecting zero-cross points of the transmitter coil current, which can improve the system reliability and reduce the cost. Furthermore, the MEPT based on D-SCC is easy to be implemented because only the input dc current measurement is required. A 3.3-kW prototype is presented to verify the validity of the proposed D-SCC-based MEPT.

An Overall System Delay Compensation Method for IPMSM Sensorless Drives in Rail Transit Applications

In rail transit application, the multimode pulsewidth modulation (PWM) is used to take full advantage of the dc-bus voltage in wide speed range. To improve the sensorless control performance of interior permanent magnet synchronous motor (IPMSM) drives in this condition, an overall system delay compensation method is proposed for a hybrid position observer that combines a simple square-wave voltage injection with a nonsingular terminal sliding mode observer. Due to the delay effect, the currents and position estimation performance are deteriorated, such as more severe dq-axis currents coupling and fluctuation of estimated position error. In order to solve these problems, the analysis of delay characteristics in the IPMSM sensorless drives is first presented. For carrier-based modulation, the compensation time is obtained through a self-tuning PI regulator based on predictive q-axis voltage error. Then, the three-phase reference currents are utilized to judge the direction near zero-crossing point and the parameters robustness is also analyzed. For optimal PWM modulation, the voltage vector angle and modulation depth are predicted in a simple way, and the delay effect can be eliminated. Furthermore, the harmonics distribution in sensorless control is described by power spectral density. Finally, the effectiveness of proposed strategy is verified by experimental results with a 3.7-kW IPMSM sensorless drive platform.

A Wide Dynamic Range Laser Radar Receiver Based on Input Pulse-Shaping Techniques

This paper presents a Time-of-Flight laser radar receiver based on pulse-shaping at the input to the receiver channel, in which the first zero-crossing point of the converted pulse is marked as the timing moment. In this technique, an LC resonator is combined with a nonlinear feedback TIA to achieve high accuracy and high precision within a wide dynamic range. The key advantage is that the receiver does not require any post compensation or gain control techniques so that the total complexity of the TOF radar is reduced considerably. Measurements made in a $0.35~\mu m$ standard CMOS process show a bandwidth of $230MHz$ and an input-referred noise of $70nA$ RMS. The receiver chip consumes $155mW$ power from a $3.3V$ supply. The single-shot precision and accuracy of the receiver within a dynamic range of 1:50,000 are $ \sim 15mm(SNR=12)$ and $\sim \pm 15mm$ respectively. A wider dynamic range can be achieved with a larger accuracy tolerance. The functionality of the proposed receiver channel is also verified over an input pulse variation and temperature range of $0~^{\mathrm {o}}\text{C}$ to $50~^{\mathrm {o}}\text{C}$ .

A New Approach of Position Sensorless Control for Brushless DC Motor

Background: Position sensorless control technique for Permanent Magnets-Brush Less Direct Current (PM-BLDC) motor drive is considered in this paper. Materials and Methods: A new estimation based on sensorless technique is proposed for PMBLDC motor. Artificial Neural Network (ANN) is aided for the purpose. Results: The inputs to the ANN are the voltages of PM-BLDC motor and it estimates the sample signals to feed Zero Crossing Point (ZCP) detection circuit. The ZCP detection circuit provides ZCP signals for commutation logic which gives the commutation sequence to power switches. In order to provide the correct sample signal to ZCP detection circuit, the ANN is well trained by Genetic Algorithm (GA). The proposed sensor less control model is implemented in MATLAB/SIMULINK working platform. Conclusion: Field Programmable Gate Array (FPGA) is used to implement the proposed method. Experimental results verify the analysis and demonstrate the advantages of the proposed method.

A:Determination of Novel Promising Combination of Linagliptin and Pioglitazone HCl in Bulk and Laboratory Synthetic Mixture by Earth-Friendly Three Spectrophotometric Methods

The combination between peroxisome proliferator-activated receptor-gamma (PPAR-γ) agonists and dipeptidyl peptidase-IV (DPP-IV) inhibitors is proven to be a more effective management of type-II diabetes mellitus (T2DM), compared to either each as single therapy. One of the novelist promising combination is linagliptin (LIN) and pioglitazone HCl (PIO) within clinical trials phase-III. Three simple, precise, accurate, reliable, and earth-friendly spectrophotometric techniques were defined and validated for resolving this novel pharmaceutical combination within laboratory synthetic mixtures and bulk form without the need of previous separation. Method-I was first-derivative (D1) spectrophotometry based on estimating LIN at 247.80 nm absorbance (PIO's zero-crossing point) and PIO at 258.40 nm absorbance (LIN's zero-crossing point) exhibiting mean percentage recoveries of 100.55% and 99.40%, respectively. Method-II was area under curve (AUC) technique involving area measurements at two designated wavelength ranges; 292-305 nm and 265-279 nm for respective LIN and PIO determination and with respective mean percentage recoveries 99.65% and 99.67%. Method-III was isosbestic point spectrophotometry where collective concentrations of both analytes were estimated at isosbestic point. 273.05 nm. Concerning PIO, the concentrations were furnished through simple deduction of LIN concentration, previously determined by AUC technique, and a mean % recovery of 99.88 % was obtained. All three proposed techniques were linear over concentration range 6-30 μg/mL and 5-50 μg/mL for LIN and PIO, respectively. Moreover, such techniques were validated as through the laboratory-prepared mixtures as refer to the International Council for Harmonization (ICH) guidelines.

Investigation of micellar enhancement in simultaneous assay of rosuvastatin and amlodipine in their fixed-dose combined tablets

The native fluorescence of both rosuvastatin and amlodipine was investigated to carry out a new facile method for their simultaneous determination based on synchronous fluorimetric technique. It was found that addition of Tween-80 in a concentration above its critical micelle concentration causes significant increase in the sensitivity of the measurements for the two studied drugs. The developed method measured the first derivative synchronous amplitude (1D) for rosuvastatin at the zero-crossing point of amlodipine and vice versa over the linear ranges of (1.0–10.0 µg/mL) and (0.2–5.0 µg/mL) for rosuvastatin and amlodipine, respectively. All the validation criteria were assessed according to ICH guidelines. The method was further continued to the determination of the two drugs in pure forms, synthetic mixtures, single and combined Tablets with good percentage recoveries that ranged from about (98.0–102.0%). A comparison between the results of the suggested spectrofluorimetric method and previous reports for determination of each of the studied analytes has been carried out and statistical analysis revealed good agreement.

BLDC Motor Speed Measurement Using ZCP Detection for Fuzzy Speed Controlling

Sensorless Brushless DC (BLDC) motors have many advantages because of their greet characteristics which make them an interested field of research home and abroad. One of the biggest issues which face BLDC motors is the rotor position detection, as they are electrically commutated the rotor position must be detected with or without sensors. The position detection is used for commutation, speed measurement and speed control. The traditional method for BLDC motor rotor position detection which depends on Hall sensors has lots of problems that decrease the system reliability, so sensorless BLDC motor drives are extensively used. The sensorless position detection methods mostly use Zero Crossing Point (ZCP) detection techniques which depend on motor back EMF detection. In this paper, a suggested method of ZCP detection for speed measurement is presented for BLDC motor, to decrease driver cost and increase system reliability, also the ZCP detection method can be for commutation and speed measurement. Simulation results are shown to prove system effectiveness

A zero-crossing point prediction algorithm of short-circuit current for mine-used phase-controlled switching

A zero-crossing point prediction algorithm of short-circuit current for mine-used phase-controlled switching

The Design and Implementation of a Sensorless Power Tool Based on a Microcontroller

Power tools are basic working tools used for production and manufacturing in the machinery and mechanical industries. The motor drive plays an important role in power tool applications. The performance of the motor drive will then directly or indirectly affect the quality and precision of the processing metal components. Most of the traditional motor drive control of a brushless direct current (BLDC) motor employs the Hall-effect position sensors to detect the rotor position. However, the installing sensors are prone to degrading the performance due to variations in temperature and the harsh environment. This disadvantage can be overcome with sensorless solutions. Among these sensorless solutions, the zero-crossing point detection of the back electromotive force (BEMF) is popular. Nevertheless, for the 180-degree conduction mode, it is impossible to directly detect the BEMF because of the three terminals of the motor which are conducted at any time for an electrical cycle. Therefore, a novel sensorless circuit approach based on the terminal line to line voltage is proposed in this paper. Moreover, an improved circuit scheme with a Schmitt trigger for sensing the BEMF is also proposed and implemented to obtain the precisely resembling Hall-effect signals. Finally, a prototype of a sensorless BLDC motor drive with a 180-degree conduction mode speed control for power tools is designed and implemented in this paper. The experimental results show that the proposed circuit works properly and validates the feasibility and fidelity of the motor drive system.

An enhanced first derivative synchronous spectrofluorimetric method for determination of the newly co-formulated drugs, amlodipine and celecoxib in pharmaceutical preparation and human plasma.

A new combination of amlodipine and celecoxib has been recently introduced in order to relieve the symptoms of osteoarthritis and help treat hypertension that commonly associated with osteoarthritis. The current study is the first to develop and optimize a sensitive, simple and accurate first derivative synchronous spectrofluorimetric method for the simultaneous determination of amlodipine and celecoxib in bulk powder, pharmaceutical preparation and spiked human plasma. The method implies the use of synchronous methodology using Δλ=100nm and measuring the fluorescence amplitudes of the first derivative each at the zero-crossing point of the other. For amlodipine and celecoxib, the emission wavelengths were at 455nm and 368nm, after excitation at 367nm and 264nm, respectively. The method was found to be linear over a wide concentration ranges of (5-600ng/ml), (100-2000ng/ml) with lower limits of detection of (1.16ng/ml) and (17.16ng/ml) for amlodipine and celecoxib, respectively. Enhancement of the fluorescence intensity was achieved by complex formation between the studied drugs and the surfactant sodium dodecyl sulfate and optimizing other experimental conditions. The method was further extended for application for determination of the studied drugs in spiked human plasma with excellent % recoveries of (95.20±6.095) and (98.67±6.394) for amlodipine and celecoxib, respectively. Validation of the method was successfully implemented according to recommendations delivered by guidelines of the International Conference on Harmonization.

Highly Reliable and Efficient Voltage Optimizer Based on Direct PWM AC-AC Buck Converter

A voltage optimizer (VO) to regulate overrated electricity supply voltages to optimized values with high reliability and efficiency has been developed based on a direct PWM ac-ac buck converter. A comprehensive control strategy is proposed for the ac-ac converter to address existing commutation problems and also to offer a fault handling capability against short circuits. A number of switching states are defined depending on the input voltage, whereby continuous and reliable current paths are maintained at all times especially around voltage zero-crossing points, and safe transitions between them are achieved as well. Based on a detailed power loss analysis, a hybrid scheme with silicon carbide (SiC) MOSFETs and silicon IGBTs is proposed which significantly improves the efficiency while minimizes the cost, and simultaneously enables the use of a high switching frequency, with the potential to reduce the volume of a VO. Results from simulation and experiment confirm that the proposed strategies give reliable operation of the VO with an efficiency higher than 99%.

A NEW VALIDATED THIRD ORDER DERIVATIVE SPECTROSCOPIC METHOD FOR SIMULTANEOUS ESTIMATION OF METOPROLOL SUCCINATE AND RAMIPRIL IN TABLET DOSAGE FORM

Objective: The objective of the present work is to develop and validate a new UV derivative spectrophotometric method for simultaneous estimation of metoprolol succinate and ramipril in methanol: water (50:50v/v).&#x0D; Methods: “Zero crossing technique” was chosen for quantitative determination. The zero-crossing points (ZCP’s) were found to be 209 nm where metoprolol succinate was quantified and 211 nm where ramipril was quantified. This method was then subjected to accuracy, linearity, sensitivity and reproducibility according to ICH guidelines to ensure and confirm its validity.&#x0D; Results: The method was found to be obeying Beer’s law in the range of 10-50 µg/ml and 5-25 µg/ml for metoprolol succinate and ramipril, respectively. The % recoveries were observed between the range of 99.2-100.2 for metoprolol succinate and 99.57-99.86 for ramipril. The intra-day and inter-day results showed reproducibility.&#x0D; Conclusion: It can be concluded that the developed third-order UV derivative spectroscopic method for the simultaneous determination of metoprolol succinate and ramiprilcan be recommended for routine quantitative analysis.