Closed-loop Linearization Research Articles

Design of a fast steering mirror driven by piezoelectric ceramics

To solve the small-optical aperture and stroke problem of existing fast steering mirror (FSM), we focus on the design of FSM driven by piezoelectric ceramics in space laser communication and lidar systems. The structure design of the FSM and the theoretical analysis of the piezoelectric actuators are carried out. The special structure and installation process of the mirror assembly are designed to ensure the accuracy of the mirror surface. Theoretical calculation and simulation analysis are conducted to evaluate the mirror’s output angle. The dynamic model of the FSM is established to analyze the stiffness. The operating principle and characteristic analysis results of FSM are verified by experimental tests. The results show that the FSM can provide a mechanical excursion angle of ±2.35 mrad, the closed-loop linearity of X axis and Y axis are 0.71% and 0.67%, respectively, and the closed-loop bandwidth of the FSM is 28 Hz. The surface shape accuracy of the mirror after installation can reach 1 / 50λ.

Design of Genetic Programming Control Algorithm for Low-Temperature PEM Fuel Cell

An effective control system for the air supply in fuel cell systems (FCS) is required to prevent oxygen starvation and to maximize the net power. For this purpose, conventional feedback and adaptive controllers are designed using genetic programming (GP). To minimize the time required for the GP convergence, FCS models of different complexity are studied and a comparison between them is carried out. Guidelines on applying the GP approach based on data obtained from simulations are developed along with a specially designed cost function that promotes closed-loop linearization. The advantage of this design method lies in its applicability to complex nonlinear systems for which nonlinear control methods may not be applicable. Adaptation is added to the oxygen excess ratio (OER) regulation problem by training a neural network that provides the optimal OER reference based on the stack current and temperature. The performance of both the regulation and adaptive controllers is tested under noise in the compressor flow and the stack current measurements. The robustness of the GP controllers is observed through the frequency response analysis.

Optimal tuning of cascaded control architectures for nonlinear HVAC systems

Cascaded controllers have been shown in recent literature to significantly reduce hunting behavior and improve the performance of a variety of HVAC systems. The cascaded architecture uses multiple proportional-integral-derivative loops, standard in industry and building automation controls, to minimize the effects of load dependent nonlinearities. This article builds on previous work by defining and demonstrating the properties of two nonlinear gap metrics that quantify the closed-loop linearization of the cascaded control structure and enable proper tuning of the inner-loop proportional gain. This is followed by the development of a linear quadratic framework that enables simultaneous tuning of inner- and outer-loop control gains. The proposed gap metrics and tuning procedures are demonstrated with two case studies. A simple single input, two output example plant is used to demonstrate the benefits of the proposed tuning method compared to standard proportional-integral-derivative control and successive loop closure tuning techniques. The tuning approach is also applied to the control of a two-ton, residential heat pump system. The proposed metrics and tuning techniques showed significant improvement in control over standard proportional-integral-derivative control tuning methods in both simulation and experiment.

Design and Implementation of a 46-kS/s CMOS SC Dual-Mode Capacitive Sensor Interface With 50-dB SNR and 0.7% Nonlinearity

This paper presents the design and implementation of a 46-kS/s CMOS switch-capacitor dual-mode capacitive sensor interface circuit for inkjet-printed capacitive humidity sensors. The specifications of the interface circuit, which includes a capacitance-to-voltage (C2V) converter combined with an analog-to-digital converter (ADC), are optimized at system level, emphasizing the C2V operation followed by the data converter. A closed form of the maximum output range of a single-stage C2V is provided to prevent cascade amplification. The gain-boosting technique is utilized in the operational transconductance amplifier design to improve the closed-loop linearity. The correlated double sampling technique attenuates the dc offset and low-frequency flicker noise from C2V. A 10-b successive approximation register ADC digitizes the output of C2V. The total area of the digital-to-analog (DAC) array is limited not only by the matching behavior, but also by the noise performance of C2V. The rail-to-rail ability is required to render the compatibility with various possible sensor inputs. A single-ended cascaded binary-weighted capacitive DAC is used to implement the charge redistribution binary search algorithm. The circuit is implemented in a 0.18- mu m CMOS technology and occupies an area of 1.2 mm(2). The tested prototype shows 0.69% nonlinearity in mode 1 and 1.38% nonlinearity in mode 2. The SNR of mode 1 is 50.1 dB and that of mode 2 is 36.5 dB, which meets the specification of 7.32 b in mode 1 and 5.32 b in mode 2. The total power consumption of the capacitive sensor interface is 70 mu W.

Study on Linearity Correction Scheme for VCO Tuning Characteristics

The linearity correction scheme for VCO tuning characteristics is the key to determine the performance of FMCW radar system. The paper introduces the basic definition of VCO tuning linearity. The linearity correction scheme for VCO tuning characteristics mainly inclues three basic schemes, they are the reactance compensation, open loop and closed loop linearity correction scheme. Analyzing the basic principle of every correction scheme detailedly, and doing a key analysis of the closed loop digital correction scheme; Discussing their advantages and disadvantages, and introducing the latest research progress of VCO linearity correction schemes in detail.

An Efficient Method of Eliminating the Range Ambiguity for a Low-Cost FMCW Radar Using VCO Tuning Characteristics

This paper describes a simple method of eliminating the range ambiguity and the design approach for low-cost and small-size homodyne frequency-modulated continuous-wave (FMCW) radars. The range measurement accuracy could be efficiently improved by proper time gating of the beat signal without any closed-loop linearity compensation circuitry for typical varactor-tuned voltage-controlled oscillators (VCOs). The presented selectively gated fast Fourier transformation method is immune to the frequency shift of the VCOs. A W-band FMCW radar using a raw varactor-tuned VCO having the percent linearity of 7.16% was implemented, and achieved less than 2% ranging error of the target lying at 200 m. Owing to the simple structure and fast processing speed, this method is applicable to the various low-cost radar sensors for ranging and detection

Non-Linear Discrete Time Modelling and Control of a Pilot Neutralization Chemical Reactor

Many continuous industrial processes working inside a large operating range can be modelled by variable parameter and/or bilinear continuous state equations. In the case of processes with variable parameters, the state affine models allow to get a discrete approximated representation. An original direct identification method, involving a variable parameter filter, is processed inside the whole operating range in order to estimate the model coefficients. A dual approach leads to state affine control algorithms by gathering a family of linear controllers into a unique control law. In the case of bilinear continuous processes, their discrete model is of linear time-varying type. A way for digitally controlling them can be a closed loop linearization which leads to an implicit control law. An improvement can be obtained by adding integrators. Experimental results got, in each operating case (variable parameter or bilinear system), from a pilot neutralization reactor show the applicability of the methods.

Digital Control of Bilinear Continuous Processes. Application to a Chemical Pilot Plant.

Many continuous industrial processes working inside a large operating range can be modelled by bilinear continuous state equations. Their corresponding discrete model is of linear time–varying type. A way for digitally controlling those processes can be a closed loop linearization. The control Law being implicit, the solution needs, during each sampling period, the use of a numerical iterative algorithm. This non–linear state feedback control law also requires observing the state of the process ; it is shown how a discrete non-linear observer is derived from the discrete model. Simulation results are given concerning a monovariable process (chemical pilot plant) and a multi–variable system (D.C. motor). The robustness of the control law is pointed out and it is shown how to get a decoupling control. Finally, experimental results from an application to the digital control of a chemical pilot plant are presented and discussed.

Linearizing Control of a Class of Non-Linear Continuous Processes

Most of the continuous industrial processes working inside a large operating range can be modelled by non-linear state equations that are linear in control. A way for controlling those processes can be a closed loop linearization. It is shown that, when the solution exists, we get an explicit non-linear state feedback control law. The linearizability condition is demonstrated and it is shown that the control law may involve some singularities. Two practical applications on chemical and hydraulic pilot plants are presented.

A Digital Simulation System of Linear and Bilinear Processes with Observers for State Feedback Control Design

A conversational Fortran IV software has been built in order to facilitate the design of control systems for linear and bilinear processes. It allows simulation, analysis, observation, and control of those processes. It presents a "menu-driven" structure and a high interactivity with animated bloc-diagrams.Two applications are presented in the field of closed loop linearization of bilinear processes : neutralization pilot plant and D.C. motor. Still in progress, this software is open to introduction of new modules

Statistical Closed-Loop Linearization Technique for Evaluating the Response of Automatic Control Sysmtems Containing Nonlinear Elements with Memory

Statistical Closed-Loop Linearization Technique for Evaluating the Response of Automatic Control Sysmtems Containing Nonlinear Elements with Memory