Range Of Ac Voltage Research Articles

Room-temperature cost-effective in-situ grown MAPbBr3 crystals and their characterization towards optoelectronic devices

We report the in-situ, room-temperature synthesis of methylammonium lead bromide CH3NH3PbBr3 crystals using N-methyl formamide as a source of methylammonium (MA+) ions during the crystallization process to explore the structural, dielectric, and electronic properties of CH3NH3PbBr3 crystals for optoelectronic applications. Optical absorption and radio-luminescence measurements affirm the direct bandgap nature of the crystals. Impedance spectroscopy measurements with various applied AC voltages within the 20 Hz–10 MHz frequency range depict the influence of ionic motions on electrical transport across crystal planes. We have extracted electrical transport parameters in CH3NH3PbBr3 crystals from the Nyquist plots, which we found to be distinctly varied wherein two different AC voltage amplitude regimes, broadly for 10–50 mV and 100–500 mV AC voltage range.

Boosting Nine-Level Operation of Seven-Level Hybrid-Clamped (7L-HC) Converter

Seven-level hybrid clamped topology, which is a multilevel topology proposed in recent years, is a promising solution for motor drive systems due to its capability to operate in a wide frequency range. This letter enhances its favorable features by enabling the boosting nine-level operation, i.e., producing nine output voltage levels; wherein the peak phase voltage can be four-third of the dc voltage. This operation method does not require modifications to the topology or change in the voltage stress on capacitors and power switches. Instead, only minor modifications to the modulation are applied. This leads to the increase of the ac voltage range without any cost on hardware. This method shows great potential in speed expansion of the motor drive system. Experimental results validate the feasibility and performance of this method. This letter is accompanied by a video file demonstrating the speed expansion performance of the proposed method.

Identification of Railway Power Supply Voltage Sag Source Using Optical Fiber Voltage Sensor

With the construction of the smart grid and the continuous improvement of voltage levels, the traditional voltage sensor can no longer meet the development needs of the modern power system. There is an urgent need for a new high-quality voltage sensor to replace it. Aiming at the problems of complex structure, difficult adjustment, poor temperature stability, large optical power loss and inconvenient voltage introduction of the existing optical fiber voltage sensor, an optical fiber voltage sensor based on full polarization state detection without polarizer and analyzer is proposed. The sensor only contains three main components: Grin Lens, BGO crystal and total reflection mirror. It has few devices, simple structure and easy alignment. Moreover, the polarization state evolution and high voltage on the transmission line of Pockels effect of BGO crystal are analyzed. The voltage sag simulation model of the electrified railway is established. The sample data of different disturbance sources are obtained with the assistance of the designed optical fiber voltage sensor. S-transformation and Radial Basis Function (RBF) neural networks are introduced and combined with the prototype of electrified railway power quality detection and analysis device to identify voltage sag sources. The designed optical fiber voltage sensor is suspended. There is no electrode or grounding on the sensor, which saves expensive insulators and increases the sensor’s measuring range. The sensor has a good linear relationship in the power frequency AC voltage range of 0~10 kV at room temperature. It is proved that the design is effective. The working condition analysis of the actual railway power supply reveals that it can detect the voltage sag amplitude and disturbance time, and identify the type of voltage sag disturbance source.

Battery energy storage system with functions of wide AC voltage range and battery current filtering

ABSTRACT This paper develops a power conversion interface for a battery energy storage system (BESS). The power conversion interface is composed of a bidirectional DC-DC power converter and a three-port DC-AC power converter, and it has the functions of wide AC voltage range and battery current filtering. The three-port DC-AC power converter has a high-voltage DC port, a low-voltage DC port and an AC port. The high-voltage DC port and low-voltage DC port are, respectively, connected to the output of the DC-DC power converter and the battery set, and the AC port is connected to the grid. The three-port DC-AC power converter generates a five-level voltage or a three-level AC voltage at the AC port according to the amplitude of grid voltage. The bidirectional DC-DC power converter has two functions. One is to generate a higher DC voltage to the high-voltage DC port, and the other is to perform a DC active filter function for attenuating the low-frequency ripple of the charging/discharging current for the battery set. All or part of the charging/discharging power for the battery set is only processed by the three-port DC-AC power converter, which can improve the efficiency of the BESS. A hardware prototype with a digital signal processor controller is developed to verify the performance of the developed power conversion interface for the BESS.

Analysis and Design of a Double Fuzzy PI Controller of a Voltage Outer Loop in a Reversible Three-Phase PWM Converter

Aiming at the application of a reversible three-phase pulse width modulation (PWM) converter with a wide range of AC side voltage and DC side voltage, a double fuzzy proportional integral (PI) controller for voltage outer loop was proposed. The structures of the proposed controller were motivated by the problems that either the traditional PI controller or single fuzzy PI controller cannot achieve high performance in a wide range of AC and DC voltage conditions. The presented double fuzzy controller studied in this paper is a sub fuzzy controller in addition to the traditional fuzzy PI controller; in particular, the sub fuzzy controller can get the auxiliary correction of PI control parameters according to the AC side voltage and the DC side given voltage variation of PWM converter after the reasoning of the sub fuzzy controller, while the traditional fuzzy PI controller outputs the correction of PI control parameters according to the DC voltage error and its error change rate. In this paper, the traditional fuzzy PI controller can be called the main fuzzy controller, and the adaptive adjustment of PI control parameters of the voltage outer loop is the sum of the PI parameter correction output by the main fuzzy controller and the auxiliary PI parameter correction output by the sub fuzzy controller. Finally, the experimental results show that the reversible three-phase PWM converter can achieve excellent dynamic and static performance in a wide range of AC voltage and DC voltage applications by using the proposed double fuzzy PI controller.

High-power medium-voltage three-phase ac–dc buck–boost converter for wind energy conversion systems

This paper proposes three topologies of single-stage three-phase ac–dc buck–boost converters suitable for medium-voltage and high-power wind energy conversion systems (WECS). The proposed converters draw sinusoidal input currents with nearly unity power factor from wind generators over wide range of ac voltages and frequencies. The proposed converters reduce the voltage and current stresses on the self-commutated switching device compared to existing solutions; thus, promising for new generation of relatively cheap WECSs. The proposed converters operate in Discontinuous Condition Mode (DCM), with their ac terminals connected to three-phase generator with open ended windings, or to ac supply using three single-phase transformers with isolated windings at converter side. The validity of the proposed converters and its detailed theoretical analysis and discussions are confirmed using PSCAD/EMTDC simulations, and further corroborated by experimentations, considering different operating conditions.

Growth characteristics of electrical trees in epoxy resin at cryogenic temperatures

The electrical tree aging problem of epoxy resin has serious impacts on the insulation structure of superconducting magnet. It is necessary to investigate the growth characteristics of electrical trees in epoxy resin at cryogenic temperatures. The experimental system with a microscopic observation apparatus and a cryostat filled with the liquid nitrogen (LN2) was set up. Each group of samples was tested at a range of AC voltages from 8 kV rms to 20 kV rms and the partial discharge (PD) experiments were carried out at 298 K and 77 K. The results showed that the generation of electrical trees was resisted strongly at cryogenic temperatures. The growth of electrical trees was slower and the tree inception voltage increased obviously at cryogenic temperatures. Meanwhile, the degree of damage to materials caused by partial discharge at cryogenic temperatures was even more severe than that at room temperature.

Electrical tree characteristics of epoxy resin under AC voltage at 77 K

The insulation structure which is mainly composed of epoxy resin is a key part of the superconducting magnet system. Due to the special operating environments, superconducting coils must address the challenges of cryogenic liquids and various kinds of high voltages. In this paper, the electrical tree characteristics of epoxy resin at 77 K were investigated. An experimental setup with a partial discharge (PD) device and a cryostat filled with liquid nitrogen (LN2) was set up. Optical microscopy and confocal Raman spectrometer were applied to investigate the accumulation of degradation products within the tree channels. Each group of samples was tested at a range of AC voltages (50 Hz) from 8 kV rms (root mean square) to 20 kV rms and the PD experiments were carried out at both room temperature and 77 K. The results indicated that the color of electrical trees was darker and the tree structures were more complicated at 77 K compared with those at room temperature. The weak reaction between oxygen and the degradation products within the tree channels was responsible for the darker tree channels at 77 K. The density of electrical trees increased and the damage to materials caused by electrical trees was more serious at 77 K. Meanwhile, the tree inception probability decreased and the tree growth was inhibited obviously at 77 K. It’s also revealed that the degradation products within the tree channels were confirmed to be graphitic carbon based on the corresponding Raman spectra. The size of graphitic domains within the tree channels at 77 K was more than 2 times of that at room temperature, which contributed to the tree growth acceleration in the later growth stage at 77 K.

Adaptive DC voltage component modulation of sub‐modules in modular multilevel converters for efficiency optimisation during wide AC voltage range

Realisation of high-efficiency modular multilevel converters (MMCs) during wide AC grid voltage variation is a significant challenge for the voltage-source-converter based high-voltage direct-current system. In this study, the DC component of the sub-module output voltage is investigated to be a new control freedom by building the inherent relationship between the DC voltage component and active sub-module number. Then, the effect of AC voltage on DC voltage component is explored. The adaptive DC voltage component modulation is proposed to dynamically regulate the active sub-module numbers during wide AC voltage variation, resulting in the improved MMC conversion efficiency. Moreover, the detailed performance analysis shows that the adoption of the proposed modulation brings little effect on the sub-module capacitor voltage/current ripple, circulating current suppression as well as the AC and DC terminal voltages. Finally, the simulation and experiment results show that the adaptive DC voltage component modulation is effective to reduce the power losses during a wide AC voltage range.

AC impedance spectroscopy on Al/p-Si/ZnTPyP/Au heterojunction for hybrid solar cell applications

A p-Silicon/Zn-tetra pyridyl-porphyrin (ZnTPyP) heterojunction was fabricated by forming a ZnTPyP layer on a p-type Si single crystal substrate using a conventional thermal evaporation technique. Complex impedance measurements of the Al/p-Si/ZnTPyP/Au heterojunction were carried out at applied AC-voltage range from 0.2 V to 1 V, temperature range from 303 K to 353 K and over the frequency range from 100HZ to 2 MHz. Impedance spectra of the heterojunction under the standard illumination ranged from 0 to 40 mW/cm2 were reported and analysed.

Extended Controllability of HVDC Converters in the Vector Space

This paper investigates the controllability of modular multilevel converters for high voltage direct current applications. The paper provides an in-depth analysis of a computationally efficient method to calculate the required amount of triplen harmonic injection (THI) and to devise an overmodulation strategy based on a three-dimensional representation of the converter control voltages in the vector space. The proposed method allows simultaneous converter operation and power quality control in an extended ac voltage range without degrading the submodules (SM's) capacitor voltage ripple or spectra of generated waveforms with respect to well-known THI methods. The advantages of the presented technique with respect to traditional THI techniques are: first, the converter controllability is extended during ac-side voltage disturbances; second, the SM's capacitor voltage ripple is upper bounded; and third, the insulation stress due to the common-mode voltage at the transformer's secondary windings is minimized. The performance of the claimed features is supported by simulation results for both steady-state and transient operating conditions.

A Cascade Multilevel Z-Source Inverter for Photovoltaic System

This paper describes a multilevel Z-source inverter for solar photovoltaic applications. The conventional power conversion topology performs either buck or boost the input voltage for non linear load depending upon duty ratio and modulation index in a multiple stage conversion with the help of impedance source passive network (L and C), which is usually known as Z-Source, which couples the n level source with input to the power source and increase the power efficiency. The multilevel z network capabilities of inverter are operated in the shoot through state of duty cycle and it acts as a filter to reduces the level of harmonics, stabilize power factor and to increase the output AC voltage range of inverter. To overcome further harmonics, multilevel level operation z source inverter compensates the fundamental level of harmonic in renewable. Proposed work as a whole involves the simulation part to design multilevel inverter. The output of the simulation is obtained by Simulink model using MATLAB.

High-Precision Sensing of DC Bias in AC Grids

This paper proposes a novel method for detecting parasitic dc components in ac grids. The method uses a parallel-connected sensing reactor and a low-cost digital signal processor. From the reactor current, the algorithm derives a sum of even harmonics, considering at the same time their phase shift with respect to the fundamental. The method is insensitive to the measurement noise and offset, and it does not require additional passive filters. Precision better than 100 μV in 0.4-kV grids is maintained over a wide range of ac voltages. This paper details the detection method, provides the guidelines for the reactor design, and includes the key implementation details related to the signal acquisition-sampling and digital processing. High precision of the new sensor is thoroughly verified on an experimental setup connected to a 0.4-kV grid.

Automated Multi-Meter Method for the Scaling of Low AC Voltage from 200 mV to 2 mV

A set of seven single junction thermal converter Micropotentiometers (μPots) has been constructed at the National Institute for Standards (NIS), Egypt. This set has been built to cover the low ac voltage ranges from 2 mV to 200 mV at frequencies from 40 Hz up to 20 kHz. The construction of the μPots set has been presented and an adopted calibration method has been performed as well. This method has been performed by means of a step-down procedure using a Digital Multi-Meter (DMM). The scaling procedures have been carried out in sequential steps starting from the calibration of the 200 mV-μpot by using DMM that is accurately calibrated at its 200 mV ac voltage range down to 2 mV-μPot. Furthermore, a new automatic calibration system has been established to achieve the scaling procedures. This system has been specially designed using Laboratory Virtual Instrument Engineering Workbench (LabVIEW) software to overcome the deficiencies of manual methods. The automatic calibration has been investigated of all mPots at different frequencies. The ac-dc differences for the μPots and their uncertainty evaluation from 2 mV to 200 mV at different frequencies from 40 Hz to 20 kHz have been determined.

The Strain Response of Lead Zinc Niobate-Lead Titanate Piezocrystals: Phase Transitions and Non-Linear Effects

Single crystals of Pb(Zn 1/3 Nb 2/3 )O 3 -PbTiO 3 (PZN-PT) produce high levels of strains with large electromechanical coupling coefficients and they exhibit high dielectric permittivity. These properties make PZN-PT single crystals promising materials for transducer and actuator applications. The large strains in these materials are partly due to electric-field-induced rhombohedral–tetragonal phase transitions that are temperature dependent. We have studied the phase transitions in ⟨001⟩ oriented Pb(Zn 1/3 Nb 2/3 )O 3 -xPbTiO 3 single crystals for x = 4.5% and x = 8% by measuring the piezoelectric strains of the crystals as a function of applied electric field and temperature. We have used laser Doppler interferometry to make direct measurements of the strain responses of the two types of ⟨001⟩ and ⟨111⟩ oriented PZN-PT single crystals in the rhombohedral phase as a function of AC electric fields and DC bias fields. When the applied electric field exceeds a threshold value, the dielectric and piezoelectric constants become a function of the applied field, and hysteresis loops are observed. Our results show that a positive DC bias stabilizes the domain configuration in the crystals and increases the range of AC voltages over which the response is linear. The threshold field, at the onset of non-linearity, is found to have a linear relation with DC bias field in the field range investigated. Very large shear strains have been observed for crystals poled in the pseudocubic ⟨111⟩ direction with d 15 values in the neighbourhood of ∼5500 pC/N for PZN-4.5%PT and ∼7500 pC/N for PZN-8%PT.

Using the Multilevel Imbricated Cells Topologies in the Design of Low-Power Power-Factor-Corrector Converters

Power-factor-corrector (PFC) converters are now commonly used in low-power supply systems connected to AC networks. In addition to their basic PFC properties, they constitute the best technical solution to directly obtain the compatibility with a large range of AC voltages provided by different distribution networks around the world (typically, from 85 to 265 V rms). It is the main application of these converters. This function is achieved with an additional cost and volume, and this extra price to pay needs to be minimized. In this context, we first recall the main approaches of the design of conventional PFCs based on the boost converter topology. We emphasize the different critical points of the sizing that mainly concern the input choke and the silicon devices, in regard with the choice of the switching frequency. Few ways of improvement are then presented for these conventional PFCs. In a second part, always in the context of a large input voltage range, we consider the possibility to introduce the multi-level concept to reduce the input choke and filters. A solution using a multi-level flying capacitor two-cell converter is presented. It is shown that it can lead to a significant increase of the performances, with several options of sizing which can be suited to different requirements of the applications.

The influence of the alumina barrier-layer thickness on the subsequent AC growth of copper nanowires

In order to reveal the role of the alumina barrier-layer thickness, δb, on the copper nanowires electrochemical growth within the alumina pores, the experiments varying porous alumina template parameters and subsequent AC electrolysis conditions were performed. A linear dependence of δb on the final anodizing voltage, Ua,fin, was verified from 40 to 5V by the electrochemical impedance spectroscopy technique. The further decrease in Ua,fin was not followed by the concomitant decrease in δb presumably due to uneven formation of the native aluminum oxide in a reaction between the aluminum and ambient oxygen. The spectrometric analysis of deposited copper content has shown that the range of AC voltages used for copper nanowires growth within the alumina pores sharply increases with decrease in the Ua,fin and so, in the δb. The most favourable Ua,fin range for the uniform growth of copper nanowires is 15–7.0V. This is because: (i) the decrease in Ua,fin below 7V results in the alumina framework peeling off from the Al surface, during subsequent AC electrolysis; (ii) the AC filling of template with δb>20nm (Ua,fin>20V) leads to the breakdown of alumina.