A grid-tie PV inverter with the ability to improve power quality under unbalanced and distorted source voltage conditions

ABSTRACT

This paper proposes a grid-tie PV inverter that is able to improve power quality under conditions of both distorted and unbalanced source voltage. The presented strategy is based on the instantaneous power theory and uses a second-order generalized integrator-quadrature signal generator (SOGI-QSG). The presented control strategy is aimed at compensating reactive power, eliminating current harmonics, load balancing, and enabling the PV to inject maximum power to the grid. The advantages of the control system are the use of SOGI-QSG adaptive filter and frequency-locked loop (FLL), and removing the low-pass filter and phase-locked loop (PLL). DC–DC and DC–AC converters are utilized for connecting the PV to the grid. The DC–DC and DC–AC converters are responsible for maximum PV power tracking and achieving the control aims, respectively. Using 4-leg converter structure for grid-tie inverter enables achieving the control objectives in 3-phase 4-wire distribution network without any transformer. The presented control strategy is applied to a 3-phase 4-wire distribution network and is simulated in MATLAB/SIMULINK environment. The results of this simulation are then compared with the conventional instantaneous power method in areas including load balancing, reactive power compensation and the elimination of current harmonics, under unbalanced and distorted source voltage conditions.     

A precise dc motor speed control using deadbeat response technique

Abstract

An approach to the design of a simple and low‐cost digital system for precise DC motor speed control is introduced. A microcomputer is employed to measure the motor speed, implement the control algorithm, and generate the controlling signal. The motor speed is measured in terms of feedback pulse width. The control algorithm is a digital PI controller with specific parameters such that the system has deadbeat response to step input. The controlling signal is converted by a digital circuit to specify the conducting period for the SCRs of a three‐phase full‐wave controlled rectifier which provides the DC source for the DC motor. The interface between the microcomputer and the outside world needs only three lines. The experiment on a 2 HP separately excited DC motor shows that the speed is regulated within 0.05% and the settling time is about 1.5 seconds under 25% load disturbance for some specific speeds.     

Design,analysis and application of high set-up ZVT DC–DC converter with direct power transfer

In this paper, a new snubber cell for soft switched high set-up DC–DC converters is introduced. The main switch is turned on by zero-voltage transition and turned off by zero-voltage switching (ZVS). The main diode is turned on by ZVS and turned off by zero-current switching. Besides, all auxiliary semiconductor devices are soft switched. Any semiconductor device does not expose the additional current or voltage stress. The new snubber transfers some of the circulation energy to the output side when it ensures soft switching for main semiconductor devices. Thus, the current stress of auxiliary switch is significantly reduced. Besides, the total efficiency of converter is high due to the direct power transfer feature of new converter. A theoretical and mathematical analysis of the new converter is presented, and also verified with experimental set-up at 500 W and 100 kHz. Finally, the overall efficiency of new converter is 97.4% at nominal output power.     

An experimental study of on‐line computer control techniques applied to a double pipe heat exchanger

Abstract

Three different on‐line computer control methods, namely the identification and optimizing control technique, the direct design method and the digital form of P‐I‐D control, are applied to control the response of a double pipe heat exchanger. The relative merits of the methods are studied and discussed.

The experimental work is accomplished by the use of a HP‐1000 model 5L microcomputer. A digital voltmeter; the HP‐3456A, is used for reading and transferring data from the process to the computer. A data acquisition system, the HP‐3497A, contains a thermocouple relay and a D/A converter which can read input data from a thermocouple and also convert digital outputs to 4–20 mA signals required by control elements.

Results indicate that the identification and optimizing control technique gives superior performance in most cases, but requires longer computation time. Digital form of the P‐I‐D control requires the least computation time but yields poor performance and is limited in its potential for application to multivariable systems or to tracking problems.     

Design and implementation of PV-based three-phase four-wire series hybrid active power filter for power quality improvement

This paper proposes a Photovoltaic (PV)-based three-phase four-wire Series Hybrid Active Power Filter (SHAPF), it comprises of a Series Active Power Filter (SAPF) and an LC shunt passive filter. The proposed system eliminates both the current and voltage harmonics and compensates reactive power, neutral current and voltage interruption. A SAPF demands a source of energy for compensating the voltage sag/swell. This system found a new topology for SHAPF which utilizes the PV with DC–DC boost converter as a source of DC power for the series active filter. The compensation current reference evaluation is based on the twin formulation of the vectorial theory of electrical power theorem with Fuzzy Logic Controller (FLC). The PV array/battery managed DC–DC boost converter is employed to step up the voltage to meet the DC bus voltage requirement of the three-leg Voltage Source Inverter (VSI). The foremost benefit of the proposed system is that, it will provide uninterrupted compensation for the whole day. This system utilizes the renewable energy; accordingly saves the energy and provides the uninterruptable power supply to critical/sensitive load, through the PV array/battery bank during both day time and night time. An experimental model was established and results were obtained, which indicated the capability of the proposed control scheme.     

Feedforward simple control technique for on-chip all-digital three-phase AC/DC power-MOSFET converter with least components

A novel simple control technique for on-chip all-digital three-phase alternating current to direct current (AC/DC) power-metal oxide semiconductor field-effect transistors (MOSFET) converter with least components, which is employed to obtain small current and DC output voltage ripples as well as excellent performance, and using a feedforward simple control method for DC output voltage regulation is proposed. The proposed all-digital feedforward controller has the features of low cost, simple control, fast response, independence of load parameters and the switching frequency, it has no need for compensation, and high stability characteristics; moreover, the proposed controller consists of three operation amplifiers and few digital logic gates that are directly applied to the three-phase converter. The power-MOSFETs are also known as power switches, whose control signals are derived from the proposed all-digital feedforward controller. Instead of thyristors or diodes, the application of power-MOSFETs can reduce the loss of AC/DC converter that is proper to the power supply system. The input stage of an AC/DC converter functions as a rectifier and the output stage is a low pass inductor capacitor (LC) filter. The input AC sources may originate from miniature three-phase AC generator or low-power three-phase DC/AC inverter. The maximum output loading current is 0.8 A and the maximum DC output ripple is less than 200 mV. The prototype of the proposed AC/DC converter has been fabricated with Taiwan Semiconductor Manufacturing Company (TSMC) 0.35 mum 2P4M complementary MOS (CMOS) processes. The total chip area is 2.333 1.960 mm². The proposed AC/DC converter is suitable for the following three power systems with the low power, DC/DC converter, low-dropout linear regulator and switch capacitor. Finally, the theoretical analysis is verified to be correct by simulations and experiments.     

A self‐tuning run‐by‐run process controller for processes subject to random disturbances

Abstract

In this paper a self‐tuning run‐by‐run process controller is presented. The controller has the capability of choosing a control parameter dynamically in response to the underlying process disturbances. There are two modules in this controller: a self‐tuning loop trigger module and a run‐by‐run feedback control module. In the self‐tuning loop trigger module, two EWMA control charts are used sequentially to determine if there is a large or medium shift in the process output and to trigger a new self‐tuning loop accordingly. In the run‐by‐run feedback control module, the control parameter and control model are re‐tuned sequentially and a new process recipe is generated, on a run‐by‐run basis, to compensate for the process output's deviation from the target. Monte Carlo simulation results show that the self‐tuning run‐by‐run process controller is superior to the current run‐by‐run process controller with a fixed control parameter.     

A novel driver with adjustable frequency and phase for traveling‐wave type ultrasonic motor

Abstract

This paper describes the design of a traveling‐wave ultrasonic motor (TWUSM) drive circuit, intended to simultaneously employ both driving frequency and phase modulation control. The operating principles and a detailed analysis of the proposed driving circuit, consisting of voltage‐controlled oscillator (VCO), voltage‐controlled phase‐shifter circuit and non‐resonant power amplifier converter, are introduced. To drive the USM effectively, a two‐phase power amplifier converter using non‐resonant output was designed to provide a balanced two‐phase voltage source. Two‐phase output driving voltages could be maintained at the same peak voltage value as the driving frequency under varying phase‐modulation processes. Detailed experimental results are provided to demonstrate the effectiveness of the proposed driving circuit.     

Cost‐effective Atomic Layer Deposition Synthesis of Pt Nanotube Arrays: Application for High Performance Supercapacitor

Due to the unique advantages of Pt, it plays an important role in fuel cells and microelectronics. Considering the fact that Pt is an expensive metal, a major challenging point nowadays is how to realize efficient utilization of Pt. In this paper, a cost‐effective atomic layer deposition (ALD) process with a low N₂ filling step is introduced for realizing well‐defined Pt nanotube arrays in anodic alumina nano‐porous templates. Compared to the conventional ALD growth of Pt, much fewer ALD cycles and a shorter precursor pulsing time are required, which originates from the low N₂ filling step. To achieve similar Pt nanotubes, about half cycles and 10% Pt precursor pulsing time is needed using our ALD process. Meanwhile, the Pt nanotube array is explored as a current collector for supercapacitors based on core/shell Pt/MnO₂ nanotubes. This nanotube‐based electrode exhibits high gravimetric and areal specific capacitance (810 Fg^?1 and 75 mF cm^?2 at a scan rate of 5 mV s^?1) as well as an excellent rate capability (68% capacitance retention from 2 to 100 Ag^?1). Additionally, a negligible capacitance loss is observed after 8000 cycles of random charging‐discharging from 2 to 100 Ag^?1.     

一种实用的多端DC──AC系统潮流计算方法

介绍了一种新的ＭＴＤＣ—ＡＣ潮流计算方法，其特点是将各换流器分别经诺顿定理等效为一带换流内阻的电流源。首先给出各单元直流系统的网络方程和换流器方程，运用给定量经网络方程推出控制方程，再用牛顿法进行潮流选代计算。此方法灵活实用，并附有算例证明。     

AIGaAs/GaAs V‐Groove channeled substrate buried heterostructure laser diodes

Abstract

Channeled substrate buried (CSB) heterostructure laser diodes have been developed successfully. To fabricate CSB lasers a two‐step liquid‐phase epitaxial (LPE) growth in conjunction with the standard etching techniques was required. The first step of the LPE process was to grow a p‐type GaAs internal current confining layer on the n‐GaAs substrate, followed by the etching of parallel V‐grooves along the [011] direction. The second LPE process was to grow a four‐layer laser structure over the V‐grooves. Due to the smoothing effect, an active layer with a crescent‐shaped cross section was formed. Because of the undercutting effect during the etching process, the active layer became very wide, i. e.,～25μm. This resulted in a far‐field pattern along the junction plane with multifilaments. Each filament had a full angle at half maximun of 8～10°. The smallest threshold current was found to be 0.88 A, which corresponds to a threshold current density of 8 KA/cm². Its mode profile was in the range of 8,360 Å to 8,400 Å.     

Dynamics analysis of LFR model for a single‐stage high power factor correction diagonal half‐bridge flyback ac/dc converter

Abstract

By means of a graft scheme, a buck‐boost cell and a wide range diagonal half‐bridge flyback cell are combined to create a novel single‐stage high power factor correction (HPFC) diagonal half‐bridge flyback ac/dc converter in this paper. When both of the two cells operate in discontinuous conduction mode, the proposed converter exhibits high power factor and low bulk capacitor voltage stress independent of the load variations. Based on the Loss‐Free Resistor (LFR) model, a new technique, referred to as ac‐dc balancing method, is also proposed. It is useful to determine the dc values, voltage ripples, and phase angle shifts of the bulk capacitor and output voltage of the converter. Moreover, the component values are well designed according to the operation conditions and design specifications of the converter. Finally, a prototype of the proposed converter with output voltage 48 V and power 100 W is built to test the theoretical analysis. It is successfully validated by IsSpice simulations and experimental results.     

In0.52Al0.48As/InxGa1‐xAs(X=0.53, 0.6) Lattice‐matched and pseudomorphic HEMTS on INP substrates

Abstract

In_0.52Al_0.48As/In _x Ga_1‐x As(x=0.53 lattice‐matched, and x=0.6 pseudomorphic) high electron mobility transistor (HEMT) structures are grown by a Riber‐32P MBE system on (100) InP:Fe substrates. Devices with the gate‐length of 0.8μm show excellent channel pinch‐off characteristics from the I_ds‐V_ds curves. The saturation current density biased at V_gs =0.5V is 480 mA/mm for HEMTs(x=0.53) and 550 mA/ mm for pseudomorphic‐(PHEMTs, x=0.6). A peak extrinsic DC transconductance (g_m ) increases from 342 mS/mm to 395 mS/mm as the In composition increases from 53% to 60% for In_0.52Al_0–48As/ In _x Ga_1‐x As HEMTs. Microwave characteristics demonstrate that a current gain cutoff frequency (f_T ) also increases from 22 GHz to 25 GHz and a maximum oscillation frequency (f_max ) increases from 60 GHz to 83 GHz, at 300K. This demonstrates that with the increase of In content in In _x Ga_1‐x As channels, device performance is dramatically enhanced, which can be used for microwave circuit applications.     

Control of AC–DC grid side converter with single AC current sensor

Conventionally, two AC side current sensors are needed in vector control of grid side converter for AC–DC bidirectional power conversion. The present paper proposes a technique where the control can be achieved with the use of only one AC side current sensor. The control principle utilises the information of un-sensed second current sensor for its estimation, which is embedded and readily available in conventional control technique itself. In the proposed method, the grid side d–q axis reference currents of the current controllers are used for estimation of β-axis component of grid current, while the α-axis component of grid current is calculated by one AC side current sensor. Effect of voltage unbalance on the control is also studied in this paper. The proposed control is validated with detailed simulation and experimental observations for both steady-state and transient conditions. The proposed control gives satisfactory performance.     

Advanced control for PWM converter and variable-speed induction generator

The paper describes a simple control structure for a vector-controlled stand-alone induction generator (IG) used to operate under variable speeds. Deadbeat current control is developed for a voltage source PWM converter and the three-phase variable speed squirrel-cage IG to regulate DC-link and generator voltages with newly designed phase-locked-loop circuit. The required reactive power for the variable-speed IG is supplied by means of the PWM converter and a capacitor bank to build up the voltage of the IG without the need for a battery and to reduce the rating of the PWM converter with the need for only three sensors. This proposed scheme can be used efficiently for variable speed wind or hydro energy conversion systems. The measurements of the IG system at various speeds and loads are given and show that this proposed system is capable of good AC and DC voltages regulation     

Novel zero voltage switching dual-switch forward converter with ripple current cancellation

A zero voltage switching (ZVS) dual-switch forward converter with ripple current cancellation is presented. In the proposed converter, active clamp circuit is used to clamp the voltage stresses and to realise ZVS of all switching devices. Active clamp boost converter with power factor correction is used in the front stage of the proposed converter to draw a sinusoidal line current from the AC source and to maintain a constant voltage at the DC bus. The second stage of the proposed converter is a dual-switch forward converter with current doubler rectifier to obtain the isolated low output voltage. Active clamp circuit used in the DC/DC converter can recycle the energy stored in the leakage inductor and magnetising inductor so that the voltage stresses on the switches are limited and the ZVS feature is realised. The current doubler rectifier offers the ripple current cancellation at the output capacitor and reduces the current stress of the transformer secondary winding. The circuit configuration and principle of operation are analysed and discussed in detail. Experimental results with a laboratory prototype based on a 90-260 V_rms input and 12 V/30 A output were provided to verify the effectiveness of the proposed converter.     

Research on DC Protection Strategy in Multi-Terminal Hybrid HVDC System

Multi-terminal hybrid high-voltage direct current (HVDC) systems have been developed quickly in recent years in power transmission area. However, for voltage-source converter (VSC) stations in hybrid HVDC systems, no direct current (DC) filters are required. In addition, the DC reactor is also not installed at the line end because the DC fault can be limited by the converter itself. This means that the boundary element at the line end is absent, and the single-ended protections used in line commutated converter (LCC) based HVDC (LCC-HVDC) systems or VSC-HVDC systems cannot distinguish the fault line in multi-terminal hybrid HVDC systems. This paper proposes a novel single-ended DC protection strategy suitable for the multi-terminal hybrid HVDC system, which mainly applies the transient information and active injection concept to detect and distinguish the fault line. Compared with the single-ended protections used in LCC-HVDC and VSC-HVDC systems, the proposed protection strategy is not dependent on the line boundary element and is thus suitable for the multi-terminal hybrid HVDC system. The corresponding simulation cases based on power systems computer aided design (PSCAD)/electromagnetic transients including DC (EMTDC) are carried out to verify the superiority of the proposed protection.     

A key‐lock‐pair mechanism based on generalized Chinese remainder theorem

Abstract

A new key‐lock‐pair mechanism of access control in information system is proposed. Our method is inspired by Wu and Hwang's result. The most important and common advantages of our method are as follows: 1. The memory storage required for keys and locks is small.

2. The determination of an access right value is fast.

3. The construction of keys and locks is simple.

     

A transceiver system for dual‐simplex high‐bit‐rate digital subscriber lines

Abstract

High bit‐rate digital subscriber lines (HDSL) technology is a new technology that may provide bi‐directional transmission at a rate of 1.544 Mb/s in conventional copper wires. A transceiver system for dual‐simplex (DSX)‐HDSL is presented. Simulation results show that the DSX‐HDSL system combined with simple pair‐selection can provide 18Kft/24AWG service distance without line repeaters. In the presented DSX‐HDSL transceiver, 2B1Q code with (1‐D) precoding is used to reduce the inter‐symbol interference (ISI) and the dynamic range of signal. Hence, a 12‐bit or less A/D converter can satisfy the performance requirement. In addition, another switchable (1‐D) filter is used in the receiver to shorten the duration of channel response, therefore a (5, 32) hybrid‐decision‐feedback‐equalizer (DFE) can obtain an adequate performance.     

Multi‐Step Phase Transitions of Mn3O4 During Galvanostatic Lithiation: An In Situ Transmission Electron Microscopic Investigation

For study of electrochemical reaction mechanisms at nanoscale, in situ electrochemical transmission electron microscopy (EC‐TEM) exceeds many other methods due to its high temporal and spatial resolution. However, the limited amount of active materials used in previous in situ TEM studies prevents the model EC cells to operate in the constant‐current (galvanostatic) charge/discharge mode that is required for accurate control of electrochemical processes. Herein, a new in situ EC‐TEM technique is developed to investigate multi‐step phase transitions of Mn₃O₄ electrodes under the galvanostatic charge/discharge mode and constant‐voltage discharge mode. In galvanostatic mode, the lithiation of Mn₃O₄ undergoes multi‐step phase transitions following a reaction pathway of Mn₃O₄ + Li⁺ → LiMn₃O₄ + Li⁺ → MnO + Li₂O → Mn + Li₂O. It is also found that lithium ions prefer to enter Mn₃O₄ along the {101} direction to form LiMn₃O₄ with the help of transitional boundary phase of Li_xMn₃O₄. These results are in sharp contrast to that obtained under a constant‐voltage discharge mode, where only a single‐step lithiation process of Mn₃O₄ + Li⁺ → Mn + Li₂O is observed.