Closed-loop Digital Control System Research Articles

A Digital Closed-Loop Control System for MEMS Resonant Pressure Sensors Based on a Quadrature Phase-Locked Loop

A Digital Closed-Loop Control System for MEMS Resonant Pressure Sensors Based on a Quadrature Phase-Locked Loop

Dynamic simulation model of Fiber Optical Current Transformer considering error factors

The paper studies and establishes the dynamic model of fiber optical current transformer by MATLAB. The equivalent model of FOCT’s digital closed loop control system is created by reasonably simplifying deviation and feedback of FOCT. By analyzing the four components of FOCT’s main sources of error, 10 factors that cause FOCT measurement errors are obtained. Then the variable 10 error parameters are introduced into the model to establish a dynamic model of fiber optical current transformer considering the error factor. The model can evaluate the performance of the fiber optical current transformer by using the variable FOCT’s error parameters, Also, model dynamically combines the FOCT’s related parameters and environmental factors with the transformer’s transfer characteristics and reflects the influence of FOCT error factors on FOCT performance.

The Analysis and Design of Closed-Loop Control System for MEMS Vibratory Gyroscopes

A digital closed-loop control system with all digital phase locked loop (ADPLL) is designed and optimized, in order to improve the bias stability and transient response of the gyroscope. The nonlinear mathematical models for the closed-loop amplitude and phase control system are established. The linearization method is applied to analyze the nonlinear models. The control parameters of the drive loop are optimized. The experimental results show that the phase deviation between the demodulation reference signal of the drive loop and the sense signal is less than 0.25° in the temperature range from-40°C to 60°C, within 0.15° of the variation. At room temperature, the overshoot amount of the gyroscope control system is 4.5% with setting time of 0.12s. The bias stability is 1.45°h. Compared to the analog control scheme, the digital control system has advantages of short setting time, small overshoot, short phase locked time, large locked range, high phase precision, etc.

Circuit Design of Digital Closed Loop Control System for FOG

Fiber optic gyroscope (FOG) is a new angular rate sensor based on the Sagnac effect. It has been widely applied in the navigation control system of aircrafts, spacecrafts and ships. But its stability, reliability and miniaturization are always the research focuses and difficulties. This paper presented a circuit design method for the digital closed loop control system of FOG based on FPGA. Based on a large number of experiments, this paper summarized the parameter demands for each module of closed loop control circuit and designed a corresponding circuit using FPGA. The proposed dual closed loop technique improved the zero offset stability of FOG. The using of FPGA brought the digital signal processing by software, the system reliability and agility enhancement as well as the system miniaturization. Particularly, we discussed the problems of component selection and the anti-jamming measures for PCB design to improve the performances of the system. We also developed some samples of FOG using this design method. The experiments and tests show that the proposed method is efficient and valuable. The stabilities of zero-offsets of all samples are less than 0.075deg/h.

Circuit Design of Digital Closed Loop Control System for FOG

Circuit Design of Digital Closed Loop Control System for FOG

RTDS-Based Real-Time Simulation Model of Fiber Optical Current Transformer

This paper set up the real-time simulation model of FOCT by means of RTDS. The equivalent model of FOCTs digital closed-loop control system was created by simplifying that systems deviation and feedback .The temperature was also introduced in that model above according to the temperature change law of the optical fiber Verdet constant and λ/4 wave plate phase delay and the mathematical model about λ/4 wave plate parameters of the light intensity received by the detector. The results show that the real-time simulation model of FOCT is reasonable, and can simulate FOCTs steady state temperature characteristic. Its transient characteristic is not bad and it can be used for testing smart substations correlative equipment.

Experimental Study and Implementation of a Novel Digital Closed-Loop Control System for Coriolis Mass Flowmeter

Closed-loop control system undertakes the foundational task of maintaining the permanent vibration of the measuring tube for Coriolis Mass Flowmeter (CMF). In order to overcome the disadvantages of bad anti-jamming, slow response speed and high zero drift existing in conventional analog closed-loop system, a novel digital closed-loop control system is proposed in which the Multiplying Digital to Analog Converter is introduced to track the vibration signal of CMF in real time, together with the non-linear amplitude control method to vary the amplitude gain of the excitation signal, so that the measuring tube can be adjusted to vibrate with stable amplitude promptly. The real flow calibration experimental result shows that the maximum steady state relative error and repeatability are 0.147% and 0.039%, respectively. In addition, the start-up time of measuring tube can reach to 2.75 s.

Digital Controller Design for Sense Mode of Micro-Machined Gyroscope

This paper presents one kind of digital closed loop control system of MEMS (Micro Electro-Mechanical Systems) vibratory gyroscope, particularly concentrating on the sense mode of MEMS gyroscope. The controller consists of a sine wave source realized by CORDIC algorithm, multiplication demodulators, some low-pass filters and force feedback rebalance module. Compared with the open loop sense system of gyroscope, the closed loop sense system has larger measurement range and wider bandwidth. Besides, the sine wave source realized with CORDIC algorithm can save hardware resources. The digital system is demonstrated on a PCB with a FPGA on it. The test results show that the measurement range of the closed loop system can be increased to 3 times by the open loop, and the bandwidth can be extended to 262Hz from 27Hz of the open loop system.

Control of a PWM Convertor for Linear Generator as a Variable Impedance

We are developing a linear generator system as an onboard power source for Maglev vehicles. This linear generator system mainly consists of power collecting coils and has a Pulse Width Modulated convertor that functions as an impedance to compensate for reactive power in the generator circuit. The PWM convertor detects only instantaneous currents and realizes unity power factor control with excellent performance. Nevertheless, the measured impedance of the circuit differs from that estimated from the parameters of PWM convertor. The system becomes unstable when we set certain impedance values for the PWM convertor.We analyzed the control system as a closed loop digital control system and we derived impedance realized in the circuit We also obtained stable areas of impedance and currents from the conditions of stability of digital control system. The analyzed results of stability were in agreement with simulation results.

Stability investigation of closed-loop system based on the sampling period

Abstract The value of sampling period directly effects to the establishment of the signal with no deformity and the stability of the closed-loop digital control system. From a mathematical point of view this is clarified considering that such value is part of the values of the coefficients of the characteristic equation of the closed-loop system, and as a result it effects the distribution of poles in the complex plane. According to the theoretical and experimental observations, the paper presents and discuss over the problem of enlarging and decreasing of sampling period, especially it observes its influence to stability of closed-loop system.

Technique for enhancing the performance of discretized controllers

This paper introduces a method to partially compensate for the zero order hold effects of a closed-loop digital control system. By multiplying a given discretized controller in the Z-domain by a pole-zero pair, a significant closed-loop performance improvement has been achieved in many design examples.

Nanotribometer: a new instrument for nano-scale to micron-scale friction and wear measurements

A nanotribometer has been developed for exploring friction and wear in nanometer to micrometer diameter sliding contacts. The nanotribometer is based on a scanning force microscope design developed at NIST. Interferometers and capacitance gages are used in a closed-loop digital control system to accurately determine and control the position and motion of the sample. The force head can measure continuous changes in both normal and lateral forces over three orders of magnitude within the range of nN to mN. This large dynamic range is achieved through the use of a PIN diode position-sensitive-detector. High-cycle wear tests on polycarbonate, friction measurements on mica, and continuous indentations on polyethylene illustrate the range of applications.

Noninvasive glucose sensing utilizing a digital closed-loop polarimetric approach

A polarimetric glucose sensor utilizing a digital closed-loop controller was designed and implemented during this study. Its potential as a noninvasive glucose sensor was evaluated in vitro for both glucose-doped water and bovine aqueous humor mediums. A physiological hyperglycemic concentration range was used in both calibration and validation of each set of experiments. Ideally, the end application of this system could estimate blood glucose concentrations indirectly by measuring the amount of rotation of a light beam's polarization state after it propagates through the aqueous humor contained within the anterior chamber of the eye. The polarimeter designed in this study differs from similar investigated systems in that it utilizes a digital closed-loop control system. This type of controller was implemented in order to further improve system repeatability and stability without sacrificing accuracy. Unique to this investigation, independent validation sets other than those used to create each respective calibration model were obtained. The results of the glucose-doped water experiments yielded mean standard errors of prediction for calibration and validation of 6.91 and 8.84 mg/dl, respectively. The mean standard errors of prediction during calibration and validation of the glucose-doped aqueous humor experiments were higher at 27.20 and 27.47 mg/dl, respectively, due to medium degradation over time while exposed to air.

Robust Stability Bound on Linear Time-Varying Uncertainties for Linear Digital Control Systems under Finite Wordlength Effects

An approach is introduced to analyze the robust stability of linear digital control systems under both finite wordlength effects and linear time-varying parameter perturbations. Digital controllers are realized with floating-point arithmetic. The robust stability criterion (sufficient condition) presented in this paper can be used to obtain the stability bound on a linear time-varying uncertainty matrix due to the combination of parameter perturbations, feedback gain quantization error and computational roundoff errors. This bound provides a quantitative measure for control engineers to design an actual closed-loop digital control system with robustness. An example is given to illustrate the application of the proposed robust stability criterion.

Closed-loop model for general multirate digital control systems

The paper develops a model for a closed-loop digital control system that incorporates multirate sampling with dynamic compensation. The model completely represents system behaviour at a base sampling rate and at the integral multiple sampling rates in the system. A key feature of the model is that sampling rates can be modified conveniently, without significantly changing the structure of the model. Based on the multirate closed-loop system model, frequency-domain transfer characteristics of the system are developed. These functions are presented in such a way that the performance of different sampling regimes can be compared directly. The eigenvalues of the closed-loop system are also defined so that effects of sampling rate variation may be investigated. An example is included to illustrate use of the model

Reduced-Delay Compensation in Digital Control Systems

A reduced-delay compensation technique is presented to reduce the phase lag caused by the zero-order-hold and transportation lag in digital control systems. Reducing the phase lag would allow a higher control bandwidth to be used in closed loop digital control systems that one could normally achieve. The developed digital compensation can be easily integrated with the original digital controller by means of simple software modifications

Issues in the Closed-Loop Digital Control of Reactor Power: The MIT Experience

The 5 MWt MIT Research Reactor's license was recently amended to permit the general use of a closedloop digital control system for the adjustment of reactor power. This regulatory approval is significant because the avoidance of challenges to the reactor's safety system now depends on the design of the controller rather than, as was previously the case, on the characteristics of the actuator. Considerations involved in the granting of this license amendment are discussed including information on the technical basis for the controller, the prevention of challenges to the safety system, and the relation between the control and safety systems. The results of the initial use of the controller are presented together with a discussion of the possible applications of this controller.

Design of tunable digital set-point tracking and disturbance-rejection controllers for Lur'e plants with multiple non-linearities

Abstract The class of Lur'e plants with multiple non-linearities which are amenable to tunable error-actuated digital control ia characterized in terms of the properties of the transfer function matrices of the linear components of such plants. It is shown that this characterization greatly facilitates the design of closed-loop digital control systems incorporating such Lur'e plants which exhibit state-bounded absolutely stable tracking. These general results are illustrated by designing a tunable error-actuated digital set-point tracking and disturbance-rejection controller for a Lur'e plant in corporating a boiler furnace with four non-linear actuators.

Fast-sampling tracking systems incorporating Lur'e plants with multiple non-linearities

The class of Lur'e plants with multiple non-linearities which are amenable to fast-sampling error-actuated digital control is characterized in terms of the properties of the transfer function matrices of the linear components of such plants. It is shown that. this characterization greatly facilitates the synthesis of closed-loop digital control systems incorporating such Lur'e plants which exhibit state-bounded absolutely stable tracking. These general results are illustrated by synthesizing a fast-sampling tracking system incorporating a Lur'e plant with two non-linearities.

Discrete-time tracking systems incorporating Lur'e plants with multiple non-linearities

Abstract The concept of absolute tracking (Grujic and Porter 1980) is extended so as to embrace digital Lur'e control systems subjected to multiple unmeasurable disturbances and multiple unmeasurable command inputs. It is shown that the discrete-time tracking characteristics of closed-loop digital control systems incorporating Lur'e plants with multiple non-linearities can be established on the basis of the discrete-time absolute stability characteristics of associated free systems. These general results are illustrated by synthesizing a discrete-time tracking system incorporating a Lur'e plant with two non-linearities.