PWM (Pulse width modulated) solenoid valves possess the advantages of low cost, high flow rate gain, and simple structure. However, the use of a PWM solenoid valve causes both discontinuity and nonlinearity of the flow rate; this results in difficulties of modeling and of control. This paper presents our work on modelling a pneumatic PWM solenoid valve for engineering applications. Two models are presented: one is the instantaneous mass flow rate model which can be used in the simulation to study the dynamic behavior of pneumatic PWM control systems; another model is the equivalent mass flow rate model which is developed for facilitating the synthesis of pneumatic PWM servomechanisms. An equation for determining the maximum operating modulation ratio of the PWM solenoid valve is also presented. Simulated results using the established models are compared with the experimental results for both the static characteristics of a PWM solenoid valve and the dynamic behavior of a system composed of a PWM solenoid valve and a constant volume chamber.

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