Investigation on adaptive pulse width modulation control for high speed on/off valve

Abstract

High speed on/off valves (HSV) have often been used to control flow or pressure in digital hydraulic systems due to higher switching frequency. However, the dynamic performance and energy efficiency are highly affected by the supply pressure and the carrier frequency. In this paper, a new adaptive PWM control method for HSV based on software is proposed. The proposed adaptive PWM consists of a reference PWM, an excitation PWM, a high frequency PWM, and a reverse PWM. First, the nonlinear model of the HSV was established, and the structural composition and working principle of the proposed adaptive PWM control strategy were presented. Secondly, individual feedback controllers for the excitation PWM, the high frequency PWM, and the reverse PWM were designed, respectively; and each of the individual feedback controllers was experimentally verified. Finally, the comparative experimental results demonstrated that, with the proposed adaptive PWM control, the rising delay time of the control pressure drastically reduces by 84.6 % (from 13 ms to 2 ms), the duty cycle's effective range remains large (12 %-85 %) even with high carrier frequency (100 Hz), and the temperature rise of the valve's coil shell is reduced by 61.5 %, compared to the three-voltage control. In addition, the dynamic performance and the energy efficiency of the HSV are not affected by the supply pressures and carrier frequencies, which proves that the proposed control strategy can improve the robustness and stability of the valve system.