Function Of Pulse Width Modulation Research Articles

Analysis of optimal expansion dynamics in a reciprocating drive for a micro-CAES production system

This paper presents the unique design and processing conditions of a micro-CAES device that generates, stores and delivers electrical energy with highly efficient total energy conversion. The micro-CAES installation is divided into six parts, where air, the energy carrier, is compressed, stored, heated and expanded in appropriate sections. We focus mainly on the post-preparation section, where the air mass flow is pulse heated and controlled by Pulse Width Modulation (PWM), and the expansion section, where multiple piston drives are used to achieve maximum energy conversion efficiency or the required amount of electricity to be fed into the grid. We discover that the controllability of expansion process performance is improved by exploiting the inertia of the following elements in multiple reciprocating engines: piston, piston rod, connecting rod, crank, and crankshaft, connected with air injection dynamics and pulse heating by Thermal Energy Storage (TES). Furthermore, we investigate the efficiency using our own zero-dimensional mathematical model illustrating the complex dynamics of air processing. The mathematical model was compared with experimental data for the single-drive air expander, showing qualitatively and quantitatively satisfying model reliability. Moreover, we performed a sensitivity analysis to determine the best number of reciprocating drives involved in the expansion section and the best operating conditions. The use of the PWM function of mass flow of air supplied the expander with an index of 0.5 together with pulsating air heating in the expander installation, including three- reciprocating drives, allows a maximum total energy conversion efficiency of 81%. The presented piston drive expander seems to be a promising solution for micro-CAES in residential and industrial applications, especially where additional low-temperature waste heat is available, and an intermittent control strategy is implemented.

Charging and Discharging Characteristics of a Battery-Capacitive Energy Storage Device for Stand-Alone Photovoltaic System

The purpose of the research is to study the charging-discharging characteristics of a hybrid energy storage device which consists of two parallel connected battery and capacitive parts to assess the work efficiency of its circuit design as a part of standalone photovoltaic system. The charge current kinetics of a hybrid storage device from a solar panel was carried out under natural conditions at a specific power of incident solar radiation of 800–850 W/m2. The discharge current kinetics of battery and capacitive storages were obtained with a resistive load and disconnected solar battery. The dynamics of charging and discharging processes of the battery and capacitive parts of the energy storage device were monitored by the voltage rise/fall rate. The battery part of the drive is charging and starting the device based on a lead-acid gel battery with a charging capacity of 11 A·h, 12.8 V maximum voltage, and 15 A maximum discharge current. The capacitive part consisted of a new generation INSPECTOR Booster supercapacitor starting the device with an electrostatic capacity of 80 F, 15.5 V voltage, and 800 A starting current. As the energy source a solar battery was used, with a 12 V nominal voltage and 100 W peak power. A 6 Om rheostat with 15 A consumption current was used as a load during the storage device discharge. A Morningstar ProStar-15 charging/discharging controller with a pulse-width modulation function was used to monitor and control the photovoltaic system. Quantitative charging and discharging characteristics of a battery-capacity energy storage device were obtained for the use in the development of standalone photovoltaic system.

Performance Degradation of Automotive Power MOSFETs Under Repetitive Avalanche Breakdown Test

Avalanche ruggedness is one of the key factors for safe and reliable power converters deployed in various automotive subsystems. In this article, the avalanche capability of power MOSFETs is tested under different repetitive avalanche conditions to differentiate the die degradation and package degradation. While examining the degradation mechanisms, the corresponding electrical parameter shifts are analyzed to better understand the structural changes and root causes and identify potential precursors for condition monitoring. For this purpose, a high-resolution and cost-effective nanosecond current pulse generator (CPG) is designed. Due to the high-resolution pulsewidth modulation function of a digital signal processor (DSP), short current pulses can be generated in the order of 100 ps where the magnitude and duration of the current pulsewidth can be adjusted precisely. During the experiments, power MOSFETs are stressed under two different pulsewidths. It is observed that the ON-state resistance gradually increases in both cases, yet the roots of the degradations are different. The die degradation and package degradation are responsible for the changes in short pulse and long pulse, respectively. In the short pulse case, some devices show saturation in drain leakage current and ON-state resistance, while some others show a significant threshold voltage drop, which leads to a noticeable shift of transfer and output characteristics. The electrical parameter shifts indicate a possible gate degradation after the device aging. At the end of the tests, failure analyses are conducted on both devices under test (DUTs) under different stress conditions, revealing different failure mechanisms.

Highly Reliable Inference System of Neural Networks Using Gated Schottky Diodes

An inference system using gated Schottky diode (GSD) is proposed for highly reliable hardware-based neural networks (HNNs). We explain the characteristics of the GSD and present circuits that take into account the characteristics of the device. The reverse current of the GSD, which is the synaptic current, is saturated with respect to input voltage, which results in immunity of input and output noise and overcoming the IR drop problem in metal wire. In order to take advantages of this saturated $I-V$ characteristics, pulse-width modulation (PWM) of input data instead of amplitude modulation is proposed. In addition, by applying identical pulses to the bottom gate, the synaptic current of the GSD increases linearly, which makes it easy to transfer the calculated weights to the conductance of GSDs. By considering these characteristics, electronic circuits for PWM, current sum, and activation function are designed. Through SPICE simulation, we evaluate the inference accuracy of a 2-layer neural network. The classification accuracy rate of 100 images of MNIST test sets is 94% accuracy obtained with software.

Enhanced phase-sensitive OTDR system with pulse width modulation Brillouin amplification.

A pulse width modulation (PWM) Brillouin amplification has been proposed and demonstrated to improve the signal-to-noise ratio (SNR) and sensitivity of phase-sensitive optical time domain reflectometry (Ф-OTDR) especially for the far end of a sensing fiber. In the logarithmic unit, arbitrary gain distribution can be realized with the customizable PWM function. The gain distribution is adjustable by tuning the PWM parameters. To prove the concept, three typical gain distributions including up-ramp sawtooth, sine and triangle have been achieved with the corresponding driving functions. In experiments, a linear PWM pump light has been used to amplify the backscattering Rayleigh light. The signal at the leading end has been enhanced by about 11.5 dB. Meanwhile, 9 dB transmission attenuation (along 25 km SMF) has also been compensated excellently. To verify the effectiveness of attenuation compensation, two vibrations with a frequency of 100 Hz and 300 Hz have been recovered accurately at the trailing end. Besides, preamplifier and acoustic-optic modulator (AOM) was used to suppress the ASE noise and further improve the effective ER, respectively. With that, lower relative intensity noise (RIN) has been obtained in the proposed system compared to the conventional Brillouin amplification in Ф-OTDR. So the proposed PWM Brillouin amplification not only improves the SNR but also equalizes the sensitivity along whole sensing fiber. It avoids the complex calibration and suppresses the false alarm rate in field application. Foreseeably, this scheme is universal and can be adopted by other distributed fiber optic technique to enhance the system performance.

Stability Analysis With Considering the Transition Interval for PWM DC-DC Converters Based on Describing Function Method

The nonlinearity of the switching process in DC–DC converters can result in the inaccuracy and invalidation of traditional stability criterion based on linear modeling, which is very harmful in practice, especially for the DC-DC converters with high stability requirements. In this paper, the describing function method is adopted for the modeling of switching process, namely, pulse width modulation (PWM), in DC–DC converters, and the describing function of the PWM is derived in detail. Considering the nonlinear items in the obtained describing function of PWM, the selection of the parameters in these nonlinear items are first provided and proved in this paper. With the obtained describing function, the stability of the PWM DC–DC converter can be analyzed exactly. Taken a PWM boost converter as an example, the nonlinear model based on describing function and the linear model are established, respectively; furthermore, the stability analysis based on these two kinds of models are carried out. Comparing with the traditional linear stability criterion, the simulation and experimental results validate the effectiveness and accuracy of the stability analysis based on describing function method. Furthermore, the transition interval of the PWM DC–DC converter from a stable region to an unstable region can be determined exactly by the proposed stability analysis method, which is helpful to determine the stability margin in real engineering applications. Therefore, this paper provides a practical stability analysis method for PWM DC–DC converters.

Study of Emergency Power Based on Solar Battery Charging

To study an emergency power based on solar battery charging. Based on the electric-generation principle of solar panel, solar energy is changed into electrical energy. Through voltage conversion circuit and filter circuit, electrical energy is stored in the energy storage battery. The emergency power realizes the conversion from solar energy to electrical energy. The battery control unit has the function of PWM (Pulse-Width Modulation) charging, overcharging protection, over-discharging protection and over-current protection. It also realizes the fast and safe charging of energy storage battery. The emergency power could provide both 12V AC power for emergency equipment such as miniature PSA oxygen concentrator and 5V USB for electronic equipment (mobile phone, GPS device, rechargeable light, etc.).

Nonlinear observer-based adaptive tracking control for induction motors with unknown load

In this paper, we propose a nonlinear observer-based adaptive controller for induction motors with unknown load. With the use of the skew-symmetric property of induction motors, a two-stage design technique is applied to construct an observer-based controller for velocity tracking control. To demonstrate the effectiveness of the proposed scheme, a voltage-control type of drive system is set up to perform the task of velocity tracking. The main computing facility consists of two personal computers, PC 486 and PC 286, of which one is to perform the calculation of the control law and the other is to provide the function of pulse width modulation (PWM) and to generate the gating pulses. Satisfactory experimental results are shown in the paper.