ADAPTIVE FEED-FORWARD COMPENSATOR FOR HARMONIC CANCELLATION IN ELECTRO-HYDRAULIC SERVO SYSTEM

Since the dead zone phenomenon occurs in electro-hydraulic servo system, the output of the system corresponding to a sinusoidal input contains higher harmonic besides the fundamental input, which causes harmonic distortion of the output signal. The method for harmonic cancellation based on adaptive filter is proposed. The task is accomplished by generating reference signals with frequency that should be eliminated from the output. The reference inputs are weighted by the adaptive filter in such a way that it closely matches the harmonic. The output of the adaptive filter is a harmonic replica and is injected to the fundamental signal such that the output harmonic is cancelled leaving the desired signal alone, and the total harmonic distortion （THD） is greatly reduced. The weights of filter are adjusted on-line according to the control error by using least-mean-square （LMS） algorithm. Simulation results performed with a hydraulic system demonstrate the efficiency and validity of the proposed adaptive feed-forward compensator （AFC） control scheme

Multichannel Adaptive Polarization Mode Dispersion Compensation with One Compensator in Dense Wavelength Division Multiplexing Transmission Systems

A simple two-section polarization mode dispersion(PMD) compensator is proposed for multichannel PMD compensation, which can compensate two or even more channels simultaneously. Because of the statistical characteristics and the frequency-dependence of PMD, for current single mode fiber with moderate PMD, the probability that all channels are severely degraded at the same time is extremely small, which makes it possible to compensate a dense wavelength division multiplexing(DWDM) transmission system with moderate PMD using this compensator. It is shown that the outage probability of a 40×43 Gb/s DWDM transmission system using this compensator is decreased significantly from 3.6×10-3 to 3.6×10-5.

Minimum eigenvalue based adaptive fault compensation for hypersonic vehicles

The attitude tracking control problem is addressed for hypersonic vehicles under actuator faults that may cause an uncertain time-varying control gain matrix.An adaptive compensation scheme is developed to ensure system stability and asymptotic tracking properties,including a kinematic control signal and a dynamic control signal.To deal with the uncertainties of the control gain matrix,a new positive definite one is constructed.The minimum eigenvalue of such a new control gain matrix is estimated.Simulation results of application to an X-33 vehicle model verify the effectiveness of the proposed minimum eigenvalue based adaptive fault compensation scheme.

An Adaptive Slope Compensation Circuit for Peak Current Mode of Boost Switching Power Supply

Based on the analysis of the basic principle of slope compensation, a high-precision adaptive slope compensation circuit for peak current mode boost DC/DC converter is designed. The circuit dynamically detects the input and output voltage of the boost circuit to realize automatic adjustment of the compensation amount with the change of duty ratio, which makes the ramp compensation slope optimized. The design uses a high-precision subtracter to improve the accuracy of slope compensation. While eliminating sub-slope oscillation and improving the stability of boost circuit, the negative impact of compensation on boost circuit is minimized, and the load capacity and transient response speed of boost circuit are guaranteed. The circuit is designed based on SMIC 0.18um CMOS technology, with simple structure, high reliability and easy engineering implementation. Spectre circuit simulator 17.1.0.124 64b simulation results show that the circuit has high compensation accuracy and wide input and output voltage range. When the working voltage is 3.3 V, the compensation slope can be adjusted adaptively under different duty cycles, and the minimum error between the compensation slope and the theoretical optimal compensation slope is only 0.42%.

OBSERVER/FILTER STRUCTURE BASED ADAPTIVE FRICTION COMPENSATION FOR HIGH PRECISION TURNTABLE

Two adaptive friction compensation schemes are developed for a high precision turntable system with nonlinear dynamic friction to handle two types of parametric uncertainties in the friction. Both schemes utilize a nonlinear observer/filter structure to compensate for uncertainties in corresponding friction parameters associated with the turntable system. Moreover, in the second scheme, adjustable gains are introduced into the dual nonlin- ear filters and they can be tuned to improve the position tracking performance. In both cases, a Lyapunov-like argument is provided for the global asymptotic stability of the closed-loop system. Simulation results demonstrate the effectiveness of the proposed schemes.

Adaptive Real-time Predictive Compensation Control for 6-DOF Serial Arc Welding Manipulator

Because of long driving chain and great system load inertia, the serial manipulator has a serious time delay problem which leads to significant real-time tracking control errors and damages the welding quality finally. In order to solve the time delay problem and enhance the welding quality, an adaptive real-time predictive compensation control（ARTPCC） is presented in this paper. The ARTPCC technique combines offline identification and online compensation. Based on the neural network system identification technique, the ARTPCC technique identifies the dynamic joint model of the 6-DOF serial arc welding manipulator offline. With the identified dynamic joint model, the ARTPCC technique predicts and compensates the tracking error online using the adaptive friction compensation technique. The ARTPCC technique is proposed in detail in this paper and applied in the real-time tracking control experiment of the 6-DOF serial arc welding manipulator. The tracking control experiment results of the end-effector reference point of the manipulator show that the presented control technique reduces the tracking error, enhances the system response and tracking accuracy efficiently. Meanwhile, the welding experiment results show that the welding seam turns more continuous, uniform and smooth after using the ARTPCC technique. With the ARTPCC technique, the welding quality of the 6-DOF serial arc welding manipulator is highly improved.

Study on the servo control system of MWEDM

An ultra-precision servo control system for MWEDM (micro wire electrical discharge machining) based on piezoelectric ceramic motor drivers was developed. The servo discharge detection adopts an average voltage detection method, utilizes statistical methods to analyze the measured data, then controls discharge gap and makes the process more stable. The servo feed system based on DSP microprocessors applies a PID controller with incomplete derivation to reduce overshoot to improve machining accuracy, and also adopts adaptive dead-zone inverse compensation to eliminate dead-zone caused by piezoelectric ceramic motions in low servo feed speed. The simulation results show that the methods proposed in this paper can make the system recover its linearity and converge the dead-zone parameters. It is proved that the method proposed is efficient in solving this problem. Cooperating with a micro energy pulse generator, this equipment’s machining accuracy is smaller than ±0.2 micron, and surface roughness Ra is less than 0.1 micron. Punch die and cavity die (micro gear die, module 100 micron, thickness 3.5 millimeter) have been machined independently in two die steel work-pieces. These pieces can mate very well to work, which shows that the servo control system satisfies the need of MWEDM for high precision micro fabrication.

Piecewise model-based adaptive compensation control for high-speed trains with unknown actuator failures

In order to deal with the uncertainties caused by different operation conditions and unknown actuator failures of high-speedtrains,an adaptive failures compensation control scheme is designed based on the piecewise model.A piecewise constant model is introduced to describe the variable system parameters caused by the variable operation environments,and a multiple-particle plecewise model of high-speed trains,with unknown actuator failures,is then established.An adaptive failure compensation controller is developed for the multiple-particle piecewise constant model,by using a direct model refering to the adaptive control method.Such an adaptive controller can not only compensate the uncertainties from unknown actuator failures,but also effectively deal with the uncertainties caused by different operating conditions.Finally,a CRH380A high-speed train model is taken as the controlled object for the simulation study.The simulation results show that the proposed controller ensures the desired system performance in the presence of unknown actuator failures and uncertain operation conditions.

Adaptive PMD compensation in 10-Gb/s RZ optical communication system

We report an experiment of adaptive compensation for first-order polarization mode dispersion (PMD) in 10-Gb/s return zero (RZ) optical communication system. The compensated differential group delay (DGD) is up to 30 ps. The quasi-real-time, less than one second, PMD compensation is realized. In the experiment, for the first time, the algorithm so-called particle swarm optimization (PSO) is used to control feedback compensation system.

Two-stage adaptive PMD compensation in 40-Gb/s OTDM optical communication system

An experiment of two-stage adaptive compensation for polarization mode dispersion (PMD) iu a 40-Gb/s optical time-division multiplexed communication system is reported. The PMD monitoring technique based on degree of polarization was adopted. The particle swarm optimization (PSO) algorithm was introduced in adaptive PMD compensation. The comparison was made to estimate the effectiveness between PSO algorithms with global neighborhood structure (GPSO) and with local neighborhood structure (LPSO). The LPSO algorithm is shown to be more effective to search global optimum for PMD compensation than GPSO algorithm. The two-stage PMD compensator is shown to be effective for both first- and second-order PMD, and he compensator is shown to be bit rate independent. The optimum searching time is within one huudred milliseconds.

Direct adaptive actuator failure compensation control:a tutorial

A resilient control system is expected to have the capacity to restore the desired system stability and tracking performance in the presence of uncertain system faults such as actuator failures.While redundant actuators are used for actuator failure accommodation,uncertain actuator failures,whose failure time,pattern,and values may be unknown,can bring new challenges to feedback control design as such uncertain failures can introduce large structural,parametric,and actuation uncertainties.Two technical issues are associated with using redundant actuators:how redundant actuators should be coordinated for effective failure compensation control,and how a feedback control law should be adaptively designed to compensate uncertain actuator failures.In this paper,we present a tutorial on direct adaptive failure compensation-based solutions to these issues for different types of control systems:state tracking using state feedback,output tracking using state feedback or output feedback,for linear,non-linear,and multi-input multi-output systems.We give an overview on such adaptive actuator failure compensation designs which have special capacities to effectively use actuation redundancy to handle uncertain actuator failures,using either direct or indirect adaptive control approaches for direct adaptive actuator failure compensation without explicit failure detection,for fast and effective failure accommodation.

Robust Adaptive Actuator Failure Compensation for a Class of Uncertain Nonlinear Systems

This paper presents a robust adaptive state feedback control scheme for a class of parametric-strict-feedback nonlinear systems in the presence of time varying actuator failures. The designed adaptive controller compensates a general class of actuator failures without any need for explicit fault detection. The parameters, times, and patterns of the considered failures are completely unknown. The proposed controller is constructed based on a backstepping design method. The global boundedness of all the closed-loop signals is guaranteed and the tracking error is proved to converge to a small neighborhood of the origin. The proposed approach is employed for a two-axis positioning stage system as well as an aircraft wing system. The simulation results show the correctness and effectiveness of the proposed robust adaptive actuator failure compensation approach.

Adaptive Output Feedback Control Using Fault Compensation and Fault Estimation for Linear System with Actuator Failure

The problem of linear systems subject to actuator faults（outage,loss of efectiveness and stuck）,parameter uncertainties and external disturbances is considered.An active fault compensation control law is designed which utilizes compensation in such a way that uncertainties,disturbances and the occurrence of actuator faults are account for.The main idea is designing a robust adaptive output feedback controller by automatically compensating the fault dynamics to render the close-loop stability.According to the information from the adaptive mechanism,the updating control law is derived such that all the parameters of the unknown input signal are bounded.Furthermore,a disturbance decoupled fault reconstruction scheme is presented to evaluate the severity of the fault and to indicate how fault accommodation should be implemented.The advantage of fault compensation is that the dynamics caused by faults can be accommodated online.The proposed design method is illustrated on a rocket fairing structural-acoustic model.

A current-mode DC-DC buck converter with adaptive zero compensation

To achieve fast transient response for a DC-DC buck converter,an adaptive zero compensation circuit is presented.The compensation resistance is dynamically adjusted according to the different output load conditions, and achieves an adequate system phase margin under the different conditions.An improved capacitor multiplier circuit is adopted to realize the minimized compensation capacitance size.In addition,analysis of the small-signal model shows the correctness of the mechanism of the proposed adaptive zero compensation technique.A currentmode DC-DC buck converter with the proposed structure has been implemented in a 0.35μm CMOS process,and the die size is only 800×1040μm;.The experimental results show that the transient undershoot/overshoot voltage and the recovery times do not exceed 40 mV and 30μs for a load current variation from 100 mA to 1 A.

A dynamic-biased dual-loop-feedback CMOS LDO regulator with fast transient response

This paper presents a low-dropout regulator （LDO） for portable applications with dual-loop feedback and a dynamic bias circuit. The dual-loop feedback structure is adopted to reduce the output voltage spike and the response time of the LDO. The dynamic bias circuit enhances the slew rate at the gate of the power transistor. In addition, an adaptive miller compensation technique is employed, from which a single pole system is realized and over a 59~ phase margin is achieved under the full range of the load current. The proposed LDO has been implemented in a 0.6μm CMOS process. From the experimental results, the regulator can operate with a minimum dropout voltage of 200 mV at a maximum 300 mA load and IQ of 113μA. The line regulation and load regulation are improved to 0. l mV/V and 3.4 μV/mA due to the sufficient loop gain provided by the dual feedback loops. Under a full range load current step, the voltage spikes and the recovery time of the proposed LDO is reduced to 97 mV and 0.142 μs respectively.

A Bionic Flexible-bodied Underwater Glider with Neutral Buoyancy

The buoyancy of traditional Underwater Glider(UG)with a rigid hull is aff ected by the changing marine parameters,making it difficult for the vehicle to dive deeper with good motion characteristics.In the present work,the development of a novel UG for neutral buoyancy,which is equipped with a Flexible-Liquid-Rigid(FLR)composite hull,is presented.The innovative hull that imitates the buoyancy regulation mechanism of marine organisms is easily adaptable to the changing marine environment.The rigid part of the composite hull withstands hydrostatic pressure for inner function modules of the vehicle.The liquid of the composite hull mainly serves as a buoyancy compensation to mitigate the eff ect of buoyancy variation caused by the changing marine parameters.The flexible covering provides a good hydrodynamic shape for the vehicle under the internal liquid pressure.The buoyancy variation due to the composite hull compression as well as changes of seawater density and temperature was comprehensively considered in the design process and integrated to the dynamic model.In addition,sea trials were performed to verify the motion characteristics of the proposed vehicle.The results reveal that the Flexible-bodied Underwater Glider(FUG)has a better gliding performance in practice.