Hardware for digitally controlled scanned probe microscopes

The design and implementation of a flexible and modular digital control and data acquisition system for scanned probe microscopes (SPMs) is presented. The measured performance of the system shows it to be capable of 14-bit data acquisition at a 100-kHz rate and a full 18-bit output resolution resulting in less than 0.02-Å rms position noise while maintaining a scan range in excess of 1 µm in both the X and Y dimensions. This level of performance achieves the goal of making the noise of the microscope control system an insignificant factor for most experiments. The adaptation of the system to various types of SPM experiments is discussed. Advances in audio electronics and digital signal processors have made the construction of such high performance systems possible at low cost

Characterization of a submillimeter high-angular-resolution camera with a monolithic silicon bolometer array for the Caltech Submillimeter Observatory

We constructed a 24-pixel bolometer camera operating in the 350- and 450-µm atmospheric windows for the Caltech Submillimeter Observatory (CSO). This instrument uses a monolithic silicon bolometer array that is cooled to approximately 300 mK by a single-shot 3 He refrigerator. First-stage amplification is provided by field-effect transistors at approximately 130 K. The sky is imaged onto the bolometer array by means of several mirrors outside the Dewar and a cold off-axis elliptical mirror inside the cryostat. The beam is defined by cold aperture and field stops, which eliminates the need for any condensing horns. We describe the instrument, present measurements of the physical properties of the bolometer array, describe the performance of the electronics and the data-acquisition system, and demonstrate the sensitivity of the instrument operating at the observatory. Approximate detector noise at 350 µm is 5 x 10^-15 W/√Hz, referenced to the entrance of the Dewar, and the CSO system noise-equivalent flux density is approximately 4 Jy/√Hz. These values are within a factor of 2.5 of the background limit

Rotors on Active Magnetic Bearings: Modeling and Control Techniques

In the last decades the deeper and more detailed understanding of rotating machinery dynamic behavior facilitated the study and the design of several devices aiming at friction reduction, vibration damping and control, rotational speed increase and mechanical design optimization. Among these devices a promising technology is represented by active magnetic actuators which found a great spread in rotordynamics and in high precision applications due to (a) the absence of all fatigue and tribology issues motivated by the absence of contact, (b) the small sensitivity to the operating conditions, (c) the wide possibility of tuning even during operation, (d) the predictability of the behavior. This technology can be classified as a typical mechatronic product due to its nature which involves mechanical, electrical and control aspects, merging them in a single system. The attractive potential of active magnetic suspensions motivated a considerable research effort for the past decade focused mostly on electrical actuation subsystem and control strategies. Examples of application areas are: (a) Turbomachinery, (b) Vibration isolation, (c) Machine tools and electric drives, (d) Energy storing flywheels, (e) Instruments in space and physics, (f) Non-contacting suspensions for micro-techniques, (g) Identification and test equipment in rotordynamics. This chapter illustrates the design, the modeling, the experimental tests and validation of all the subsystems of a rotors on a five-axes active magnetic suspension. The mechanical, electrical, electronic and control strategies aspects are explained with a mechatronic approach evaluating all the interactions between them. The main goals of the manuscript are: • Illustrate the design and the modeling phases of a five-axes active magnetic suspension; • Discuss the design steps and the practical implementation of a standard suspension control strategy; • Introduce an off-line technique of electrical centering of the actuators; • Illustrate the design steps and the practical implementation of an online rotor selfcentering control technique. The experimental test rig is a shaft (Weight: 5.3 kg. Length: 0.5 m) supported by two radial and one axial cylindrical active magnetic bearings and powered by an asynchronous high frequency electric motor. The chapter starts on an overview of the most common technologies used to support rotors with a deep analysis of their advantages and drawbacks with respect to active magnetic bearings. Furthermore a discussion on magnetic suspensions state of the art is carried out highlighting the research efforts directions and the goals reached in the last years. In the central sections, a detailed description of each subsystem is performed along with the modeling steps. In particular the rotor is modeled with a FE code while the actuators are considered in a linearized model. The last sections of the chapter are focused on the control strategies design and the experimental tests. An off-line technique of actuators electrical centering is explained and its advantages are described in the control design context. This strategy can be summarized as follows. Knowing that: a) each actuation axis is composed by two electromagnets; b) each electromagnet needs a current closed-loop control; c) the bandwidth of this control is depending on the mechanical airgap, then the technique allows to obtain the same value of the closed-loop bandwidth of the current control of both the electromagnets of the same actuation axis. This approach improves performance and gives more steadiness to the control behavior. The decentralized approach of the control strategy allowing the full suspensions on five axes is illustrated from the design steps to the practical implementation on the control unit. Furthermore a selfcentering technique is described and implemented on the experimental test rig: this technique uses a mobile notch filter synchronous with the rotational speed and allows the rotor to spin around its mass center. The actuators are not forced to counteract the unbalance excitation avoiding saturations. Finally, the experimental tests are carried out on the rotor to validate the suspension control, the off-line electrical centering and the selfcentering technique. The numerical and experimental results are superimposed and compared to prove the effectiveness of the modeling approach

First-fault detection in DC distribution with IT grounding based on Sliding Discrete Fourier-Transform

Since dc distribution minimizes the number of power conversion stages, it lowers the overall cost, power losses, and weight of a power system. Critical systems use IT grounding because it is tolerant to the first-fault. Hence, this is an attractive option for hybrid electric aircraft (HEA), which combines gas engines with electric motors driven by power electronic converters. This letter proposes an accurate implementation for the procedure of first-fault detection with IT grounding. The ac component injection along with the sliding discrete Fourier transform (SDFT) is used to estimate the fault impedance. The procedure is very accurate due to the heavy filtering of the implicit moving average filter. Further computation savings are obtained by using the double look-up tables, and the Goertzel algorithm for the SDFT. Results are validated by simulations and experiments

Artificial intelligence-based protection for smart grids

Lately, adequate protection strategies need to be developed when Microgrids (MGs) are connected to smart grids to prevent undesirable tripping. Conventional relay settings need to be adapted to changes in Distributed Generator (DG) penetrations or grid reconfigurations, which is a complicated task that can be solved efficiently using Artificial Intelligence (AI)-based protection. This paper compares and validates the difference between conventional protection (overcurrent and differential) strategies and a new strategy based on Artificial Neural Networks (ANNs), which have been shown as adequate protection, especially with reconfigurable smart grids. In addition, the limitations of the conventional protections are discussed. The AI protection is employed through the communication between all Protective Devices (PDs) in the grid, and a backup strategy that employs the communication among the PDs in the same line. This paper goes a step further to validate the protection strategies based on simulations using the MATLABTM platform and experimental results using a scaled grid. The AI-based protection method gave the best solution as it can be adapted for different grids with high accuracy and faster response than conventional protection, and without the need to change the protection settings. The scaled grid was designed for the smart grid to advocate the behavior of the protection strategies experimentally for both conventional and AI-based protections.This work is supported by Li Dak Sum Innovation Fellowship Funding (E06211200006) from the University of Nottingham Ningbo China.Peer ReviewedPostprint (published version

A Hardware-in-the-Loop Platform for DC Protection

With the proliferation of power electronics, dc-based power distribution systems can be realized; however, dc electrical protection remains a significant barrier to mass implementation dc power distribution. Controller Hardware-in-the-loop (CHiL) simulation enables moving up technology readiness levels (TRL) quickly. This work presents an end-to-end solution for dc protection CHiL for early design exploration and verification for dc protection, allowing for the rapid development of dc protection schemes for both Line-to-Line (LL) and Line-to-Ground (LG) faults. The approach combines using Latency Based Linear Multistep Compound (LB-LMC), a real-time simulation method for power electronic, and National Instruments (NI) FPGA hardware to enable dc protection design with CHiL. A case study is performed for a 1.5 MW Voltage Source Rectifier (VSR) under LL and LG faults in an ungrounded system. The deficiency in real-time simulation resolution of Commercial-off-the-Shelf (COTS) for dc fault transients is shown, and addressed by using LB-LMC RT solver inside NI FPGA hardware to achieve 50 ns resolution of dc fault transients

Controls and Interfaces

Reliable powering of accelerator magnets requires reliable power converters and controls, able to meet the powering specifications in the long term. In this paper, some of the issues that will challenge a power converter controls engineer are discussed.Comment: 16 pages, contribution to the 2014 CAS - CERN Accelerator School: Power Converters, Baden, Switzerland, 7-14 May 201

Design and development of power processing units for applications in electrically-propelled satellite systems

Electrospray technology provides a way to ionize specialized liquids by applying high voltages across a sharp porous tip and a metallic mesh. This technology is widely used in the field of mass spectroscopy for generating ions for testing purposes. The dawn of nano-satellites posed new challenges in the miniaturization of many conventional satellite sub-systems. One significant challenge faced in such a process was the miniaturization of the propulsion system. Electrosprays have started to find their application in the field of Aerospace Engineering and now are formally known as Electrospray Thrusters. These thrusters provide high specific impulse and are attractive substitutes to conventional gas propelled thrusters as they can be scaled down in size and can also provide extended mission times. Some of the new challenges faced in such applications are the generation of high voltages from a low voltage onboard battery, grounding, spacecraft charging, clearance, and reliability issues for long term usage. In this work, a complete design process is developed for the realization of such high voltages suitable for interfacing with an electrospray thruster. Simulation models for a new type of converter are assessed, and its feasibility is discussed. A hardware prototype is implemented, and the practical results are assessed. An analysis of the converter is presented, and the semiconductor and passive components are selected. Magnetic components are designed based on the analysis. Parallels are drawn between the theoretical and prototype model of the concept converter. Finally, the firmware of the converter is explained, and the communication protocol of the PPU is delineated. As the boards designed for the converter have to sustain high voltages and reliably operate in unfavorable environments, special PCB layout considerations must be used, which also forces a designer to look for various other materials for the PCB fabrication --Abstract, page iv

Coordination of Generator Protection and Control in the Over and Under Excited Regions

This thesis deals with the coordination of protection and control functions associated with the synchronous generators. The excitation control functions are a key component in maintaining the stability of machines and the network. The overall objective of coordination is simple; to allow excitation control functions, the automatic recovery from excursions beyond normal limits, and only take protective action as a last resort. This thesis focuses on four areas of generator control and protection : a) Loss of excitation protection, b) Dynamic underexcitation coordination, c) Dynamic Overexcitation coordination, and d) a generic protective relay development platform for hardware and software development. Loss of excitation (LOE) is a condition in the underexcited region that presents a risk of severe damage to a generator. The state of the art in the detection of a loss of excitation condition is based on the principle that, for a zero Thevenin voltage, the generator becomes a reactance as seen from the power system. The difficulty in detecting a loss of excitation is that several other disturbances may temporarily present a similar behavior, for instance a fault followed by a power swing. In this part of the work, a new algorithm for the detection of a loss of excitation condition is proposed by using the Support Vector Machine (SVM) classification method and a careful design of the necessary feature vectors. The proposed method is robust to changes in conditions including initial load, fault types, line impedance, as well as generator parameter inaccuracies. Coordination in the underexcited region presents difficulties due to the commonly used static characteristics instead of dynamic simulation. The underexcited limit presents an overload characteristic that is not normally known or used. Once the limit is exceeded, the limiting control action is a control loop that presents a dynamic behavior not typically represented in studies in the current industry practice. It is also important to properly model and include dynamic performance of protection functions. An important consideration not typically taken into account is the actual stability limit, which depends on the characteristics and the mode of excitation control used. This thesis includes all the above considerations necessary to achieve the required coordination using the more accurate dynamic simulations. Specific scenarios that present risk to the machine or the system are included to assess the coordination achieved. A real generator from the Alberta power system is used as a case study to demonstrate the proposed coordination methodology. Coordination in the overexcited region again presents practical difficulties due to static characteristics instead of dynamic simulation of conditions that exercise the overexcitation limits. The problems observed relate to coordination methodology and modeling methods for both protection and control limits. Once the limit boundary characteristic is exceeded, the limiting action is a control loop that presents dynamic behavior that needs to be represented. Similar considerations need to be made with the protection function protecting against rotor overload. Current modeling methods mostly use low bandwidth simulations, i.e., transient stability studies. A modeling methodology as well as specific model improvements to the IEEE ST1A excitation control model are proposed to achieve the required coordination. The ST1A type is one model that can represent a wide variety of system models from different manufacturers. The proposed modeling methodology applies to high bandwidth simulations such as electromagnetic simulations. Specific important scenarios, such as severe temporary reactive overload or severe power swing conditions, where the protection and control are required to coordinate but that present risk to the machine or the system are proposed as part of the coordination considerations. The detection of LOE conditions by the proposed SVM method and by traditional methods was implemented in hardware by using a digital signal processor (DSP) platform and tested using real time power system simulations. A new platform for real time protective relay development was designed and used for the purpose of implementation. In the proposed platform, a processor independent code is used so that development can be performed using native host computer development tools. By using the proposed platform-independent code, off line testing can be performed either interactively or in batch mode for evaluating multiple cases