Valve Hysteresis Research Articles

Observation and Analysis of Ejector Hysteresis Phenomena in the Hydrogen Recirculation Subsystem of PEMFCs.

The optimization control and efficiency improvement of proton exchange membrane fuel cells (PEMFCs) are being paid more attention. Ejectors have been applied in PEMFC hydrogen recirculation subsystems due to the advantages of a simple structure and no power consumption. However, the hysteresis deviation of a proportional valve ejector is found in the loading and unloading processes such that the hysteresis phenomena can cause deviations in fuel cell control process and affect the power dynamic output stability of PEMFCs. This paper analyzes the causes and effects of proportional valve hysteresis phenomena through experiments and simulations. The results show that the resultant force of proportional valve armature is different in loading and unloading processes because of the hysteresis phenomena, and the maximum flow deviation is up to 0.42 g/s. The hysteresis phenomena of flow rate further cause a deviation of 68.7-89.3 kW in PEMFC power output. Finally, a control compensation model is proposed to effectively reduce the deviation. This study provides a reference for the control and optimization of PEMFC with ejector technology.

Dynamic Response Difference of Hydraulic Support under Mechanical-Hydraulic Co-Simulation: Induced by Different Roof Rotation Position and Hysteresis Effect of Relief Valve

As key supporting equipment in coal mining, hydraulic supports are vulnerable to impact pressure from roof movement and deformation. In this paper, a mechanical-hydraulic co-simulation platform for hydraulic supports is established. Moreover, the rationality of the simulation platform is verified. Based on this platform, the rigid-flexible coupling impact dynamics model of hydraulic support is built. Finally, by delaying the opening time of the relief valve, the energy dissipation problem of the relief valve hysteresis effect on the hydraulic support system under the rotary impact is discussed. The results indicate that the rotary load acting on the hydraulic support decreases gradually with the backward movement of the roof rotary position, which causes the peak pressure in the column to decrease (by 69 MPa). The hinge point load of different parts shows different load transfer laws. The hysteresis effect of the relief valve prolongs the energy release time of the system, increasing the pressure in the column by 23 MPa. The instantaneous opening speed of the relief valve spool reaches 15.7 m/s, and the hinge point between the top beam and the column is most sensitive to the hysteresis effect (impact coefficient increases by 0.63).

ENSURING CONTINUOUS HYSTERESIS OF SPROAD ACTION VALVE SAFETY VALVES

In the article principles of construction and design of spring valve units are considered, which allow to obtain a given dynamic quality to ensure constant hysteresis of spool safety valves of direct action. The analysis of efficiency of devices of correction of dynamic quality of spring valve units for ensuring their working capacity at variation of external operating factors by purposeful management of kinematic and force parameters of elastic-damping elements, and also the reasons influencing hysteresis It is noted that one of the reasons for the increase in hysteresis is damage to the rubber seals of the spool safety valves of direct action. Identifying the main causes of damage to rubber seals: constant friction of the edge of the radial holes of the spool on the seal ring; reverse the direction of the operating pressure; the pressure drop created by the axial hole of the spool when the valve is fully open. A spool spring valve with a mechanical spring having high throughput and low hysteresis is proposed. This characteristic was achieved through the use of high quality materials, which allowed to have a high throughput with minimal dimensions; optimization of geometrical characteristics of the flowing part of the valve; reducing the seal tension and, as a consequence, reducing the hysteresis. It is noted that the absence of contact of the radial holes of the spool with the rubber seal in the extreme off position protects the seal from plastic deformation during reverse flow. The prospect of further research in obtaining experimental dependences of the influence of spool speed, rubber stiffness, geometrical characteristics of the contact gap and pressure on the change of the valve hysteresis is revealed.

Vehicle braking force distribution with electronic pneumatic braking and hierarchical structure for commercial vehicle

Brake by wire that allows a number of braking functions exists on commercial vehicles under the name electronic pneumatic braking system, which can improve braking comfort and safety of commercial vehicle. The design of braking force distribution control method has drawn much more attention. Considering structure characteristics of electronic pneumatic braking system, a control method with a three-layer hierarchical structure is proposed. The first layer presents an estimation method towards vehicle mass and centre of gravity combining Kalman filter with recursive least square. The second layer is developed by designing a fixed relationship between the brake pedal displacement and vehicle braking deceleration. A deceleration control method that only uses brake pedal displacement as input is applied to make the vehicle follow the desired deceleration. The third layer includes a braking force distribution control method between the front and rear axles. The vehicle deceleration can be achieved with a smooth axle load transfer process based on linear matrix inequality. In addition, the controllers of wheel slip rate and valve hysteresis compensation are designed to improve control accuracy and efficiency. Utilizing a hardware-in-the-loop simulation test rig of electronic pneumatic braking system, the experiment results show that the control method can improve the braking performance of vehicle.

L1 Adaptive Control for Aircraft Air Management System Pressure-Regulating Bleed Valve

This paper presents an L1 adaptive controller for pressure control using an engine bleed valve in an aircraft air management system (AMS). The air management system is composed of two pressure-regulating bleed valves, a temperature control valve, a flow control valve, and a heat exchanger/precooler. Valve hysteresis due to backlash and dry friction is included in the system model. The nonlinearities involved in the system cause oscillations under linear controllers, which decrease component life. This paper is the unique in the consideration of these uncertainties for control design. This paper presents simulation results using the adaptive controller and compares them to those using a proportional–integral (PI) controller.

RELAY AUTOTUNING OF MULTIVARIABLE SYSTEMS: APPLICATION TO AN EXPERIMENTAL PILOT-SCALE DISTILLATION COLUMN

This paper describes the application of multivariable sequential relay autotuning techniques to a pilot scale distillation system under industrial DCS monitoring and control environment. Implementation aspects arising in any realistic industrial environment are fully discussed such as the architecture for on-line communication and information extraction as well as valve hysteresis and backlash compensation. The performance of alternative tuning strategies is compared for both set-point changes and disturbances rejection.

Comparison of two advanced steam temperature controllers for coal-fired boilers

A nonlinear process model based control (nonlinear PMBC) algorithm, which is based upon using a nonlinear approximate model, and a state variable control (SVC) algorithm have been tested on a medium fidelity simulation of a drum-type coal-fired boiler. A simple PI controller was also tested as a point of reference. The simulation was based upon the Cromby 2 model and was used to test each controller for 10 different upset scenarios that included soot blowing, load ramps and changes in burner tilts. The simulation had control valve hysteresis, control valve dynamics and temperature sensor dynamics added to it. The nonlinear PMBC controller had the best control performance yielding factors of < to 5 times reduction in steam temperature variability over the optimally tuned PI controller tor the 10 upset scenarios. The SVC controller outperformed the PI controller in 8 out of 10 of the upset scenarios, but typical variability reductions of only 20% were observed

An Adaptive Feedforward Control Algorithm for Computer Control of Wastewater Neutralization

The purpose of this paper is to show the development and testing of an adaptive feedforward control of a wastewater neutralization process. The adaptive controller is compared to a nonlinear proportional - integral-derivative (NPID) controller developed by Shinskey and Myron (1970). The process and controllers were simulated on a digital computer. The adaptive controller utilizes two pH probes, a feedforward probe and a feedback probe, with the latter used in the adaptive calculations of the feedforward gain. The feedback measurement provides the adaptive controller with a form of reset action.The process simulated for control combines a strong (hydrochloric) and weak (carbonic) acid neutralized by a strong base (sodium hydroxide). The adaptive controller was shown to give superior responses both for step changes in the strong acid and in the weak acid (buffer) concentration. One particular advantage of the adaptive controller is that it requires only two tuning parameters, while many controllers in use today require five or more tuning parameters.The sensitivity of the adaptive control to changes in certain parameters (probe noise and lag, valve hysteresis and lag, and dead time) was studied, as was the effect of a step change in flow rate to the system. Noise in the feedforward pH probe and the dead time between the reagent addition and the feedback probe had the largest effect on the adaptive controller performance.

Transient Response of a Time-Optimized Hydraulic Servomechanism Operating under Cavitation Conditions

The transient response of a time-optimized hydraulic servomechanism operating under cavitation conditions is analysed in this paper. Factors included in the analysis, in addition to actuator cavitation, are: valve dynamics, valve hysteresis, oil compressibility, actuator leakage and non-linear load friction. After the basic equations have been derived, the transient response is determined graphically using a modification of the technique introduced by McCloy in which the load-friction curve is superimposed on the valve pressure-flow curves. On this plot the load trajectory is determined, step-by-step. The transient response of the system is then determined. Experimental verification of the analysis is included.

The dynamic modeling, stability, and control of a continuous stirred tank chemical reactor

AbstractA realistic CSTR model was developed and verified experimentally. The reaction studied was the exothermic, base sodium hydroxide catalyzed decomposition of hydrogen peroxide. The model was used to evaluate the usefulness of the following stability analyses: steady state analysis, local linearization and Liapunov's direct method through Krasovskii's theorem. The effect of control valve hysteresis on the system was also investigated.