Pulse Width Modulation Duty Cycle Research Articles

Multi-state and Interleaved Converters With Passive Impedances for Current Sharing

This paper presents multilevel switching cells that allow the generation of high-power nonisolated dc-dc, ac-dc, dc-ac, and ac- ac converters. The cells are classified in two groups: multi-state switching cells (MSSC) based on autotransformer and interleaved switching cells (ISC) based on inductors. Each switching cell has an impedance based on a small inductor Lsh connected between the legs, which is named current sharing circuit (CSC) and guarantees zero average voltage across the involved magnetic components, therefore compensating eventual differences between the PWM (pulse width modulation) duty cycles. The small inductor causes the duty cycle to be reduced, and consequently its inductance is typically very small. In order to verify the current sharing between the magnetic components, two dc-dc buck converters operating at 25 kHz and rated at 1 kW, where the input voltage is 200 V and the output voltage is 60 V , are implemented and evaluated in laboratory.

Wearable Virtual White Cane: Assistive Technology for Navigating the Visually Impaired1

Wearable Virtual White Cane: Assistive Technology for Navigating the Visually Impaired1

Reverse polarity optical-OFDM (RPO-OFDM): dimming compatible OFDM for gigabit VLC links

Visible light communications (VLC) technology permits the exploitation of light-emitting diode (LED) luminaries for simultaneous illumination and broadband wireless communication. Optical orthogonal frequency-division multiplexing (O-OFDM) is a promising modulation technique for VLC systems, in which the real-valued O-OFDM baseband signal is used to modulate the instantaneous power of the optical carrier to achieve gigabit data rates. However, a major design challenge that limits the commercialization of VLC is how to incorporate the industry-preferred pulse-width modulation (PWM) light dimming technique while maintaining a broadband and reliable communication link. In this work, a novel signal format, reverse polarity O-OFDM (RPO-OFDM), is proposed to combine the fast O-OFDM communication signal with the relatively slow PWM dimming signal, where both signals contribute to the effective LED brightness. The advantages of using RPO-OFDM include, (1) the data rate is not limited by the frequency of the PWM signal, (2) the LED dynamic range is fully utilized to minimize the nonlinear distortion of the O-OFDM communication signal, and (3) the bit-error performance is sustained over a large fraction of the luminaire dimming range. In addition, RPO-OFDM offers a practical approach to utilize off-the-shelf LED drivers. We show results of numerical simulations to study the trade-offs between the PWM duty cycle, average electrical O-OFDM signal power, radiated optical flux as well as human perceived light.

An Adjustable Voltage Signal Filament Conversion Alarm System

A new adjustable voltage signal filament conversion alarm system is proposed which based on the traditional conversion monitoring system of train signal filament. This system adopts the embedded DSP processor monitoring the state of filament and uses the DSP to control PWM (Pulse-Width Modulation) duty cycle for preheating the filament，then gradually lit it. It avoids the breakdown of the filament break. The power line carrier technology is used for alarming signal transmission. This system is more practical than the traditional, which shortens filament switch time and improves the alarm accuracy.

Study on Neural Network Control Strategy of Electric Vehicle in-Wheel Motor

The brushless direct current motor(DC) simulation model based on neural network control strategy is developed, according to the physical structure of the motor, after the analysis of in-wheel motor mathematical model. The simulation has pulse width modulation (PWM) generation module,which can adjust the PWM duty cycle to regulate the motor speed. Simulation results show that there is good agreement between the output ofsimulation model and the theoretical analysis.The application of neural networkcontrol in brushless DC motor offers the advantages of rapid response, without overshoot ,and higher steady-state accuracy.

Monitoring Solar Home Systems With Pulse Width Modulation Charge Control

With the high cost of grid extension and approximately 1.6 billion people still living without electrical services, the solar home system is an important technology in the alleviation of rural energy poverty across the developing world. The performance monitoring and analysis of these systems provide insights leading to improvements in system design and implementation in order to ensure high quality and robust energy supply in remote locations. Most small solar home systems now use charge controllers using pulse width modulation (PWM) to regulate the charge current to the battery. A rapid variation in current and voltage resulting from PWM creates monitoring challenges, which, if not carefully considered in the design of the monitoring system, can result in the erroneous measurement of photovoltaic (PV) power. In order to characterize and clarify the measurement process during PWM, a mathematical model was developed to reproduce and simulate measured data. The effects of matched scan and PWM frequency were studied with the model, and an algorithm was devised to select appropriate scan rates to ensure that a representative sample of measurements is acquired. Furthermore, estimation methods were developed to correct for measurement errors due to factors such as nonzero “short circuit” voltage and current/voltage peak mismatches. A more sophisticated algorithm is then discussed to more accurately measure PV power using highly programmable data loggers. The results produced by the various methods are compared and reveal a significant error in the measurement of PV power without corrective action. Estimation methods prove to be effective in certain cases but are susceptible to error during conditions of variable irradiance. The effect of the measurement error has been found to depend strongly on the duty cycle of PWM as well as the relationship between scan rate and PWM frequency. The energy measurement error over 1 day depends on insolation and system conditions as well as on system design. On a sunny day, under a daily load of about 20 A h, the net error in PV energy is found to be 1%, whereas a system with a high initial battery state of charge under similar conditions and no load produced an error of 47.6%. This study shows the importance of data logger selection and programming in monitoring accurately the energy provided by solar home systems. When appropriately considered, measurement errors can be avoided or reduced without investment in more expensive measurement equipment.

A Biomimetic Squid Funnel Actuated by Shape Memory Alloy Wires

Inspired by the squid’s funnel which can bend flexibly, a kind of biomimetic squid funnel actuated by shape memory alloy (SMA) wires was developed for controlling the jet direction in this article. With the application of Pulse Width Modulation (PWM) technique, experimental investigation was conducted. And the results show that, the bending angle of the biomimetic squid funnel can be controlled by changing PWM duty cycle and the final stable resistance of SMA wire decreases while the duty cycle is increased. The relationship between the banding angle of the biomimetic squid funnel and the resistance of SMA wire is approximately inverse linear. The feasibility of jet direction control with the biomimetic squid funnel was verified by a simulated jetting experiment.