Wide Operating Region Research Articles

Operation Region of Doubly Fed Induction Generators Based on Rotor Slip under Maximum Power Point Tracking Control and Power Dispatch

Quantification to the operation region of wind turbine generators is critical for them to participate in active/reactive power dispatch and frequency/voltage control, functioning similarly to the synchronous generators. Although it is well known that operation region of doubly fed induction generators is decided by the current/capacity limits of the stator, rotor, and grid-side converter, it is found in this article that the operation region consists of a cluster of curves based on rotor slips and is thus related to wind speeds and control modes. The slip affects both reactive power capability and active power range. The solution to slip for maximum power point tracking control and power dispatch modes is proposed, including rotor speed limit and power flow constraints. Numerical results show that under the maximum power point tracking mode, higher wind speed yields lower rotor slip and a wider operation region. Under the power dispatch mode, pitch angle regulation yields the same operation region, while different power settings correspond to different VAR capabilities; rotor speed regulation yields different slips and operation regions. When keeping other conditions the same for power dispatch, the pitch angle regulation yields a larger operation region than rotor speed regulation.

Design of a Low-Torque-Ripple Fractional-Slot Interior Permanent-Magnet Motor

Despite a strong nonlinear behavior and a complex design, the interior permanent-magnet (IPM) machine is proposed as a good candidate among the PM machines owing to its interesting peculiarities, i.e., higher torque in flux-weakening operation, higher fault tolerance, and ability to adopt low-cost PMs. A second trend in designing PM machines concerns the adoption of fractional-slot (FS) nonoverlapped coil windings, which reduce the end winding length and consequently the Joule losses and the cost. Therefore, the adoption of an IPM machine with an FS winding aims to combine both advantages: high torque and efficiency in a wide operating region. However, the combination of an anisotropic rotor and an FS winding stator causes some problems. The interaction between the magnetomotive force harmonics due to the stator current and the rotor anisotropy causes a very high torque ripple. This paper illustrates a procedure in designing an IPM motor with the FS winding exhibiting a low torque ripple. The design strategy is based on two consecutive steps: at first, the winding is optimized by taking a multilayer structure, and then, the rotor geometry is optimized by adopting a nonsymmetric structure. As an example, a 12-slot 10-pole IPM machine is considered, achieving a torque ripple lower than 1.5% at full load.

Study on hydrogen-rich syngas production by dry autothermal reforming from biomass derived gas

In this study, the H2-rich syngas (H2 + CO) production from biomass derived gas (BDG) by dry autothermal reforming (DATR) is investigated. Methane and carbon dioxide is the major composition of biomass derived gas. DATR reaction combined benefits of partial oxidation (POX) and dry reforming (DR) reaction was carried out in this study. The reforming parameters on the conversion of methane and syngas selectivity were explored. The reforming parameters included the fuel feeding rate, CO2/CH4 and O2/CH4 molar ratios. The experimental results demonstrated that it not only supplied the energy required for self-sustained reaction, but also avoided the coke formation by dry autothermal reforming. It has a wide operation region to maintain the moderate production of the syngas. During the reforming process, the reformate gas temperature was between 650 and 900 °C, and energy loss percentage in reforming process was between 15 and 30%. Further, high CO2 concentration in the reactant had a considerable influence on the heat release of oxidation, and thereby decreased the reformate gas temperature. It caused the reduction of synthesis gas concentration and assisting/impeding combustion composition (A/I) ratio. However, it was favorable to CO selectivity because of the reverse water-gas shifting reaction. The H2/CO molar ratio between 1 and 2 was achieved by varying CO2/CH4 molar ratio. However, the syngas concentrations were affected by CO2/CH4 and O2/CH4 molar ratio.

Investigation on the performance of the single-phase LSPM motor for variable capacity type compressor

This paper investigates the performance of the line start permanent magnet (LSPM) motor which needs a high efficiency characteristic in a wide operation region. LSPM motor's performance indexes, such as efficiency, motor current, load angle and synchronous torque, have complex relationship with each other according to the main and auxiliary windings distribution, and the selection of running capacitor. The output characteristics can be defined by the winding structure which is calculated by d-q equivalent circuit and finite element method. The efficiency characteristic is verified by simulation as well as by experiment on the designed LSPM motor. From the results, we show that the redesigned model considering the winding structure and capacitor matching has a wide operating region.

A compact P-band coaxial relativistic backward wave oscillator with only three periods slow wave structure

A compact P-band coaxial relativistic backward wave oscillator (BWO) with only three periods slow wave structure (SWS) is investigated both theoretically and numerically. The characteristics of the coaxial SWS are analyzed when the SWS is changed from the structure with only outer conductor ripple to the structure with both inner and outer conductor ripples. It is found that the existence of the inner conductor ripple can reduce the period length of coaxial SWS to maintain the same operating frequency of the BWO and can largely increase the temporal growth rate and the spatial growth rate of the device. Then, the effects of SWS period numbers on the generation of the microwave in the P-band relativistic BWO are studied by PIC simulations. The results show that three periods SWS cannot only make the device more compact but also has a wide region of single-frequency operation and relatively large efficiency and output power in a wide range of the diode voltage. Typical simulation results show that, with a 585 kV and 7.85 kA electron beam guided by a 0.8 T solenoidal field, the microwave of 1.65 GW is generated at the frequency of 900 MHz, and the interaction efficiency is about 36%. Compared with the conventional P-band coaxial relativistic BWO with five periods SWS, the axial length of the SWS is reduced by about one half, which is only 38.4 cm, and the saturation time of the microwave signal is reduced by about 10 ns.

Design, Analysis, and Control of DC-Excited Memory Motors

In this paper, a new type of memory motors, namely the dc-excited memory motor, is proposed and implemented. The concept of dc-excited memory is due to the nature that the magnetization level of permanent magnets (PMs) in the motor can be regulated by a temporary dc current pulse and be automatically memorized. Based on an outer-rotor doubly salient motor structure, the proposed dc-excited memory motor can offer effective and efficient online air-gap flux control. Hence, it possesses the advantages of mechanical robustness, high efficiency, and wide constant power operation region. Both simulation and experimentation are carried out to verify the validity of the proposed motor.

Effects of different cetane number enhancement strategies on HCCI combustion and emissions

Cetane number is the accepted indicator for quantifying the autoignition characteristics of diesel fuels in compression ignition engines. Diesel fuel specifications typically require a minimum cetane number to achieve satisfactory combustion behaviour in conventional diesel engines. In contrast, a high cetane number fuel may not be beneficial for implementing high efficiency, clean combustion strategies such as homogeneous charge compression ignition (HCCI). The purpose of this study was to investigate cetane number effects on HCCI combustion and emissions. The experiments were conducted in a single-cylinder, variable compression ratio, cooperative fuel research engine operated in HCCI combustion mode. The fuels were finely atomized and partially vaporized in the intake manifold. The base fuel was a low cetane refining stream derived from oil sands sources. Three different methods were employed to increase the base fuel cetane number, namely hydroprocessing, cetane improver addition, and blending with a renewable fuel component. Results show that the three methods of cetane number enhancement produce significantly different HCCI combustion behaviour. The hydroprocessed fuels exhibited more stable and complete combustion than the base fuel, which resulted in a wider operating region, reduced carbon monoxide, unburned hydrocarbon, and nitrogen oxide (NO x) emissions, and lower indicated specific fuel consumption (ISFC). The main disadvantages of the hydroprocessed fuels were the higher exhaust gas recirculation rates required to retard the combustion phasing, which limits the maximum indicated mean effective pressure for a given intake pressure, and increased knock intensity due to a faster combustion process. In comparison, the other two methods of fuel cetane enhancement increased ISFC compared to the base fuel. The addition of nitrate cetane improver resulted in higher NO x emissions, while blending with a renewable fuel component increased hydrocarbon emissions. The experimental data provide evidence that the magnitude and phasing of low temperature heat release, as well as fuel volatility, play important roles in HCCI combustion.

Load-Following Control of Nuclear Reactors Based on Takagi-Sugeno Fuzzy Model

AbstractA Takagi-Sugeno (T-S) fuzzy control system is designed for load-following operation of nonlinear nuclear reactor whose operating points vary within a wide range. Linear models are first derived from the original nonlinear model on several operating points. Next the fuzzy controller is designed via using the parallel distributed compensation (PDC) scheme with the relative neutron density at the equilibrium point as the premise variable. Last the stability analysis is given by means of linear matrix inequality (LMI) approach, thus the control system is guaranteed to be stable within a large range. The simulation results demonstrate that the control system works well over a wide region of operation.

Model-Based Control of HCCI Engines Using Exhaust Recompression

Homogeneous charge compression ignition (HCCI) is one of the most promising piston-engine concepts for the future, providing significantly improved efficiency and emissions characteristics relative to current technologies. This paper presents a framework for controlling an HCCI engine with exhaust recompression and direct injection of fuel into the cylinder. A physical model is used to describe the HCCI process, with the model states being closely linked to the thermodynamic state of the cylinder constituents. Separability between the effects of the control inputs on the desired outputs provides an opportunity to develop a simple linear control scheme, where the fuel is used to control the work output and the valve timings are used to control the phasing of combustion. The controller is tested on both a single and multi-cylinder HCCI engine, demonstrating the value of a physical model-based control approach that allows an easy porting of the control structure from one engine to another. Experimental results show good tracking of both the work output and combustion phasing over a wide operating region on both engines. In addition, the controller is able to balance out differences between cylinders on the multi-cylinder engine testbed, and reduce the cycle-to-cycle variability of combustion.

Properties of leader-laggard chaos synchronization in mutually coupled external-cavity semiconductor lasers

The properties of the leader-laggard chaos synchronization (LLCS) in two mutually coupled external-cavity semiconductor lasers are studied systematically. We theoretically analyze the general conditions for the LLCS based on the symmetric operation mechanism and numerically investigate the influences of operation parameters, the mismatch robustness, the chaos pass filtering effects, the communication performance, and the security of the system. It is demonstrated that stable LLCS, which allows simultaneous bidirectional message exchange in virtue of mutual chaos pass filtering effect, can be achieved in a wide operation region; moreover, high-quality LLCS and satisfactory communication performance can be maintained under a relatively large device parameter mismatch. Compared with the isochronal chaos synchronization in the same system, LLCS provides a wider operation region, a better mismatch robustness, and a stronger chaos pass filtering effect. In addition, the investigations on the security of private key message transmission under some potential attacks indicate that the security can be enhanced by increasing the bit rate moderately, exchanging messages with different bit rates, or monitoring the LLCS.

Design and Control of an Axial-Flux Machine for a Wide Flux-Weakening Operation Region

This paper describes the strategy to design and control of an axial flux SPM machine for achieving a wide flux-weakening operating region. By using a slotted stator with fractional slot windings and additional cores enclosing end windings, the axial flux machine satisfies the specification of a wide constant power speed range. The design procedure is presented for increasing flux-weakening capability while obtaining low harmonic back-electromotive-force and low cogging torque. This technique is applied to design an 8 Nm axial flux prototype machine that exhibits about 3:1 flux-weakening range. To the aim of exploiting full capability of the machine, a flux-weakening controller is designed and implemented. This controller utilizes the voltage difference between the current regulator and the output voltage, limited by a voltage source inverter. With this method, the output torque in the flux- weakening region can be increased up to that of the six-step operation while maintaining the current control capability. The goodness of both design and control algorithm is proved by experimental tests on a prototype.

A Neuro-fuzzy Adaptive Power System Stabilizer Using Genetic Algorithms

This article presents the design technique of an adaptive power system stabilizer using adaptive neuro-fuzzy inference systems trained via data obtained from genetic algorithms. The parameters of a standard power system stabilizer are tuned using adaptive neuro-fuzzy inference systems to achieve a certain damping ratio and settling time at all load points within a wide region of operation. The overall transfer function of the system is derived in terms of the power system stabilizer parameters. A genetic algorithm is used to minimize a multi-objective optimization function that forces the damping ratio and settling time of the system to desired values. The optimization process is separately conducted at selected operating points to yield power system stabilizer parameters that change with load variations. Results of genetic algorithm optimization are used to form a training dataset of an adaptive neuro-fuzzy inference systems agent, which could give the power system stabilizer parameters at any load within the specified region of operation. Results of power system stabilizer testing show that the desired performance indices could be fulfilled from light load to over load under both lagging and leading power factor conditions. System performance shows a remarkable improvement of dynamic stability by obtaining a well-damped time response.

Takagi-Sugeno Fuzzy Coordinated Control System with Original Plant Fuzzy State Observer for a Power Unit

The Takagi-Sugeno (T-S) fuzzy multiple-variable integral control system with fuzzy state observer is designed for the coordinated control of multi-input-multi-output (MIMO) nonlinear boiler-turbine system whose operating points vary within a wide range. Linear models are first derived from the original nonlinear model on several operating points. Next the fuzzy multi-variable integral controller and the fuzzy state observer are designed via using the parallel distributed compensation (PDC) scheme, and the T-S fuzzy control system is constructed with the drum pressure as the premise variable. The problem that part of state variables can not be measured is successfully solved by introducing fuzzy state observer. Last the stability analysis is given by means of linear matrix inequality (LMI) approach, and the control system is guaranteed to be stable within a large range. The simulation results demonstrate that the control system works well over a wide region of operation.

Dynamic gain scheduled control of a Hawk scale model

AbstractWhen designing flight control laws using linearisations of an aircraft model about different flight conditions, some form of scheduling of the resultant gains will often be required to implement the controller over wide operating regions. In practice, the controller gains are often scheduled against relatively slowly-varying system states such as altitude or velocity. However, it may also be desirable to schedule gains against rapidly-varying states such as angle-of-attack, thereby generating a cyclic dependence through hidden coupling terms. Previous published work at Bristol has developed a numerical method of accounting for this dependence when scheduling state feedback gains against coupled states. The resulting ‘dynamic gain schedule’ is shown to significantly improve the transient response of the aircraft model during rapid manoeuvring and to reduce the chances of control surface actuator position limit saturation. In this paper, the novel design process, using eigenstructure assignment, is applied to a mathematical second-order longitudinal aircraft model which represents an approximate BAe Hawk wind-tunnel model. The dynamic gain scheduled controller is shown to work extremely well in practice when applied to the closed-loop experimental rig. Despite the highly nonlinear characteristics of the model aerodynamics and tailplane actuation system, as well as unmodelled high turbulence levels, dynamic gain scheduling demonstrates stable closed loop control even in regions where the nonlinearities are such that conventional gain scheduling fails to produce a stable response.

Development of carbon nanotubes vacuum field emission differential amplifier integrated circuit

The authors have recently presented a novel concept for the development of vacuum field emission (VFE) differential amplifier (diff-amp) based on a matched pair of carbon nanotube (CNT) triodes and reported the preliminary device characteristics. In this study, they report the development of a CNT VFE diff-amp using CNT emitter arrays with smaller gate aperture, obtaining better device performance after postsynthesis rapid thermal annealing treatment. A pair of well-matched 2μm circular triode arrays showed a gate turn-on voltage of ∼40V and displayed similar triode characteristics in the saturation region. Moreover, the proposed two-step analytical model shows that the common-mode rejection ratio (CMRR) in decibels has a linear relationship with the applied gate voltage for the improved dual-triode diff-amp. In addition, the diff-amp demonstrates high CMRR (34–58dB) over a wide operating region.

Sensorless Control of Induction Motor Drives Equipped With Inverter Output Filter

This paper deals with the speed sensorless vector control of an induction motor in a special case where the output voltage of the pulsewidth-modulated inverter is filtered by an inductance-capacitance (LC) filter. The system states are estimated by means of an adaptive full-order observer, and no additional voltage, current, or speed measurements are needed. The rotor speed adaptation is based on the estimation error of the inverter output current. Quasi-steady-state and linearization analyses are used to design an observer that enables a wide operation region, including very low and very high speeds. A torque-maximizing control method is applied in the field-weakening region. Simulation and experimental results show that the performance is comparable to that of a drive without the LC filter

Characteristics of a sulfur-passivated InGaP∕InGaAs∕GaAs heterostructure field-effect transistor

The effect of (NH4)2Sx treatment on the device characteristics of an InGaP∕InGaAs∕GaAs heterostructure field-effect transistor are studied and demonstrated. Experimentally, it is found that the sulfur-passivated device shows significant dc characteristics including higher forward voltage, lower leakage current, lower output conductance, and higher voltage gain. The superior microwave performances with flat and wide operating region of drain saturation current are simultaneously obtained. Furthermore, the improved thermal stabilities over wide temperature range of sulfur-passivated devices are attained. Based on these advantages, the studied device with (NH4)2Sx treatment shows the promise for high-temperature and high-performance microwave applications.

Improved In0.45Al0.55As/In0.45Ga0.55As/In0.65Ga0.35As Inverse Composite Channel Metamorphic High Electron Mobility Transistor

A δ-doped In0.45Al0.55As/InGaAs metamorphic high-electron-mobility transistor (MHEMT) using an In0.45Ga0.55As/In0.65Ga0.35As inverse composite channel has been fabricated successfully and demonstrated. The inverse composite channel significantly reduces Coulomb scattering and consequently improves electron mobility as well as carrier confinement. Experimentally, a high extrinsic transconductance of 321 mS/mm and a drain–source saturation current density of 342 mA/mm are obtained for a 0.65 ×200 µm2 gate at 300 K. Meanwhile, degradation of the studied device, in terms of parameters such as Gm,max, IDSS, and Vth, with increasing temperature is not evident. A positive temperature coefficient of Vth is observed. The measured fT and fmax for a 0.65-µm-gate device are 41.6 and 53 GHz, respectively. In addition, the studied device also shows good microwave performances in a flat and wide operation region. From VGS = -2.5 to 0.5 V, the values of fT and fmax are still over 33 GHz.

Coordination of converter and fuel cell controllers

Load following fuel cell systems depend on control of reactant flow and regulation of DC bus voltage during load (current) drawn from them. To this end, we model and analyse the dynamics of a fuel cell system equipped with a compressor and a DC–DC converter. We then employ model-based control techniques to tune two separate controllers for the compressor and the converter. We demonstrate that the lack of communication and co-ordination between the two controllers entails a severe tradeoff in achieving the stack and power output objectives. A co-ordinated controller is finally designed that manages the air and the electron flow control in an optimal way. We demonstrate our results during specific and critical load changes around a nominal operating point. Although our analysis does not cover wide operating region, it provides insight on the level of controller co-ordination necessary in non-hybridized fuel cell power supply. The shut-down and start-up procedures will be investigated in future work. Copyright © 2005 John Wiley & Sons, Ltd.

New type of SFQ-dc converter for use in oxide circuits

An SFQ-dc converter has been designed and fabricated for use in oxide RSFQ circuits. The SFQ-dc converter comprised a stack of SQUIDs, Josephson transmission line (JTL) for a set signal, and current-injection line for a reset signal. The SFQ-dc converter of this type was found to have wide operation region with respect to the junction critical current. The SFQ-dc converter was fabricated by the ramp-edge junction technology and could be successfully operated with the output voltage as much as 0.5 mV.