Real-time Digital Control System Research Articles

Digital Control and Power Systems for the Pegasus-III Experiment

The PEGASUS-III experiment is a solenoid-free, low aspect ratio spherical tokamak that will serve as a dedicated U.S. platform for comparative nonsolenoidal tokamak plasma startup studies. Approximately 175 megavolt-ampere (MVA) of reconfigured and expanded programmable power systems, 7 MJ of new stored energy, and new digital control and protection systems for the facility are being commissioned to support PEGASUS-III upgrades. These include: increased toroidal field (0.15–0.6 T); new divertor and poloidal field coils; increased pulse length; local and coaxial helicity injectors for solenoid-free plasma initiation; radio frequency (RF) systems for heating and current drive; and a diagnostic neutral beam (DNB). A new real-time digital control system implements 16 proportional-integral differential (PID) feedback controllers with 25 kHz loop rates to control the electromagnets and helicity injectors. The poloidal field coils, helicity injector arc currents, and toroidal field are driven by 36 3.6 MVA (4 kA, 900 V) insulated-gate bipolar transistor (IGBT) buck converters. Helicity injector bias voltage and current will be provided by a set of four 10.8 MVA multi-level buck converters (MLBCs). Each is comprised of an 1800 V integrated gate-commutated thyristor (IGCT) stage and a ±900 V IGBT stage in series, providing controllable <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I_{\mathrm {inj}}\le 4$ </tex-math></inline-formula> kA at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm {inj}}\le 2.7$ </tex-math></inline-formula> kV. A field programmable gate array (FPGA)-based digital fault protection system multiplexes controller commands to individual power semiconductors in these supplies, monitors their operational status, and executes shutdown sequences within <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10~\mu \text{s}$ </tex-math></inline-formula> of fault detection. An 80 kV, 4 A zero-voltage-switching (ZVS) resonant converter with < 1% output ripple is under development for the DNB and is being evaluated as a topology to drive RF sources.

이륜 역진자 로봇의 제어 시스템 개발을 위한 설계 고려사항

This paper addresses some practical design considerations to build a two-wheeled inverted pendulum (TWIP) robot control system. The first issue is to identify the relationship between the primary parameters of the TWIP robot and the guaranteed stability of the time-delayed control loop. Secondly, the required data update rate and the required sensor/actuator performance are suggested for implementing a real-time digital control system. The final issue is concerned with improving the driving performance by investigating the reliability of the inertial sensor for attitude control and the backlash problem in the transmission mechanism.

Wind-Tunnel Tests for Active Flutter Control and Closed-Loop Flutter Identification

In this study, active flutter control and closed-loop flutter identification were experimentally studied for a low-aspect-ratio wing model in an Nanhang-2 subsonic wind tunnel. To actively suppress the flutter of the wing model in wind-tunnel tests, a real-time digital control system was developed so as to complete the data acquisition, digital signal processing, computation of the control strategy, and servo control of the actuator. Using the digital control system, wind-tunnel tests were conducted to examine the flutter control of the wing model. The experimental results showed that the linear feedback controller designed via the optimization of pole assignment can effectively suppress the flutter instability. Moreover, for the high-dimensional aeroservoelastic system, the online estimation of closed-loop flutter modes is a challenging problem because the flutter identification from closed-loop measurements may lead to biased estimates, and the identification efficiency must be improved. Therefore, as the second task of this study, the online closed-loop flutter identification of the wing model was explored. To efficiently identify the flutter modes, a fast recursive subspace identification method was used. The experimental results show that the natural frequencies and modal damping ratios of the closed-loop flutter modes could be accurately tracked over a wide range of flow speeds.

On the Fractional PID Control of a Laboratory Servo System

In this paper are investigated several types of fractional-order PID controllers in the velocity control of a servo system. The fractional controller is more flexible and gives the possibility of adjusting carefully the dynamical properties of a control system. The servo system is controlled by using a real-time digital control system based on MATLAB/Simulink. Results are compared with those obtained from classical PID controllers. Experimental responses are presented and analyzed, showing the effectiveness of the proposed fractional-order algorithms.

Structural vibration control using linear magnetostrictive actuators

Terfenol-D is one of several magnetostrictive materials with the property of converting energy into mechanical motion, and vice versa. We designed and fabricated a linear magnetostrictive actuator (MSA) using Terfenol-D as a control device. In order to grasp the dynamic characteristics of the actuator, a series of experimental and numerical tests were performed. Induced-strain actuation displacements of the actuator measured by the test and predicted by magnetic analysis agreed well, and blocked forces, according to the input currents, were estimated from the testing results. A modeling method representing the exerting force of the actuator was confirmed through some testing results. We also explored the effectiveness of the linear MSA as a structural control device. A series of numerical and experimental tests was carried out with a simple aluminum beam supported only at each end by such an actuator. After the equation of motion of the controlled system was obtained by the finite element method, a model reduction was performed to reduce the number of degrees of freedom. A linear quadratic feedback controller was implemented on a real-time digital control system to dampen the first four elastic modes of the beam. Through some tests, we confirmed the capability of the actuator for controlling beam-like structures.

Continuous Time Model Predictive Control for a Magnetic Bearing System

The nature of active magnetic bearings has many advantages over the conven- tional bearing, as its operation is energy e-cient and potentially leads to cleaner and noise-free environment. However, the successful operation of an active magnetic bearing system requires a complex real-time control system, because of its unstable characteristics, as well as its nature of being a multi-input and multi-output system. This paper presents design and implementation of a continuous time model predictive control algorithm (CMPC) to an active magnetic bearing sys- tem (AMB). In this application, the plant continuous time model is identifled from experimental data using prediction error method. The control performance of this algorithm is studied using an experimental AMB laboratory system. A host-target development environment of real-time digital control system with hardware in the loop (HIL) is implemented and demonstrated by controlling a nonlinear, open-loop unstable, and multivariable magnetic levitation device.

Magnetic diagnostic system of the DIII-D tokamak

External measurements of the magnetic field surrounding a hot, magnetically confined plasma yield important information about the state of the plasma, since the external field is generated in part by electric currents within the plasma itself. Therefore, magnetic diagnostics are an essential part of both the operation and the physics experiments in tokamaks and other magnetic confinement devices. The magnetic diagnostic system of the DIII-D tokamak includes approximately 250 inductive sensors of various types: axisymmetric poloidal flux loops, diamagnetic-flux loops, magnetic probes and saddle loops for the measurement of local magnetic field, and Rogowski loops for the measurement of coil currents and plasma current. The primary uses of the data include plasma shape and position control with a real-time digital control system, postdischarge equilibrium reconstruction, spectrum analysis in time and space of plasma instabilities, and direct feedback control of slowly growing instabilities. The sensors, instrumentation, calibration, applications, and operating experience are described.

Correctness verification and performance analysis of real-time systems using stochastic preemptive time Petri nets

Time Petri nets describe the state of a timed system through a marking and a set of clocks. If clocks take values in a dense domain, state space analysis must rely on equivalence classes. These support verification of logical sequencing and quantitative timing of events, but they are hard to be enriched with a stochastic characterization of nondeterminism necessary for performance and dependability evaluation. Casting clocks into a discrete domain overcomes the limitation, but raises a number of problems deriving from the intertwined effects of concurrency and timing. We present a discrete-time variant of time Petri nets, called stochastic preemptive time Petri nets, which provides a unified solution for the above problems through the adoption of a maximal step semantics in which the logical location evolves through the concurrent firing of transition sets. We propose an analysis technique, which integrates the enumeration of a succession relation among sets of timed states with the calculus of their probability distribution. This enables a joint approach to the evaluation of performance and dependability indexes as well as to the verification of sequencing and timeliness correctness. Expressive and analysis capabilities of the model are demonstrated with reference to a real-time digital control system.

Development of a real-time digital control system with a hardware-in-the-loop magnetic levitation device for reinforcement of controls education

This paper discusses the development of a real-time digital control system with hardware in the loop (HIL) for modeling and controls education. This environment requires software tools by MathWorks, Inc. and a C++ compiler. The hardware tools include an off-the-shelf data acquisition card and the desired hardware to be controlled. The use of a single environment for dynamic system analysis, control law development, simulation evaluation, and final implementation on an HIL system has many educational advantages as compared to multienvironment settings. This host-target real-time environment is implemented and demonstrated by controlling a nonlinear, open-loop unstable, and time varying custom-built magnetic levitation device. The values of any parameter (control law, reference trajectory) in the Simulink model can be changed dynamically on the host computer without recompiling the control code, and their effects are observed in real-time on the HIL system. This environment allows for extensive experimentation, development of linear and nonlinear controllers, and performance comparison with HIL as shown in the presented examples. The educational features of this environment are presented throughout the paper and were verified in a class setting.

Real-Time Implementation of H∞ Based Power System Stabilizer

An H∞ based power system stabilizer (HPSS) design methodology and computer simulation result was discussed In (Chen and Malik, 1995). The real-time digital control system for implementation of proposed HPSS is described in this paper. The purpose of the micromachine setup is to further develop and test the HPSS in the laboratory environment. The system consists of an Intel iSBC388/21 single-board computer, a data acquisition system and a PC based man-machine interface. The single-board computer serves as a ROM based embedded digital controller. The PC based man-machine interface provides convenient development interface for the physical system and the developer. The proposed HPSS algorithm is tested and the results are summarized in this paper.