Active control of pressure pulsation in a switched inertance hydraulic system

Abstract

The nature of digital hydraulic systems may cause pressure pulsation problems. For example, switched inertance hydraulic systems (SIHS), which are applied to adjust or control flow and pressure by a means that does not rely on dissipation of power, have noise problems due to the pulsed nature of the flow. An effective method to reduce the pulsation is important to improve system performance and increase efficiency. Although passive systems to reduce the noise have been shown to be effective in many situations, their attenuation frequency range is limited and they may be bulky. Furthermore, attenuation devices based on expansion chambers, accumulators or hoses are likely to be unsuitable for SIHS as they add compliance to the system and would impair the dynamic response. This thesis is concerned with issues relating to the development of an active noise canceller for attenuating the pressure pulsation which is caused primarily by pulsed flow from high-speed valves in SIHS.Active control methods are widely and successfully applied in the area of structureborne noise (SBN) and air-borne noise (ABN) cancellation. The idea is using the intentional superposition of waves to create a destructive interference pattern such that a reduction of the unwanted noise occurs. However, applications for fluid-borne noise (FBN) attenuation based on the 'Active noise control (ANC) principle' are rare due to the restriction of the hardware and experimental apparatus in previous researches.In this thesis, an adaptive controller has been developed for active control of pressure pulsation in hydraulic system. The principle of the adaptive LMS filter and details of the controller design are described and the implementation was carried out through simulation. The designed controller was applied on a vibration test rig initially prior to the hydraulic testing in order to investigate its advantages and limitations in practice.Extensive testing on a switched inertance hydraulic rig proved that the controller, which used a piezoelectric valve with fast response and good bandwidth, is effective and that it has several advantages over previous methods, being effective for low frequency cancellation, with a quick response, and is robust and versatile. II A novel method for the accurate measurement of unsteady flowrate in a pipe was proposed. This was applied and validated on a pipe, and was shown to give good results. This method solves the difficulty for measuring the unsteady flowrate currently by using easy-measured signals, such as pressures. It can be used widely for predicting the unsteady flowrate along the pipe. III ACKNOWLEDGEMENTS

Theoretical and Experimental Studies of a Switched Inertance Hydraulic System in a Four-Port High-Speed Switching Valve Configuration

“…The drive arrangement of the rotary valve is shown in Figure 4b. The distributed flow loss in the time-domain can be described as: (17) where is the wave propagation time = 2 ⁄ , c is the speed of sound [5,23].…”

“…The minimum flow loss occurs when the switching frequency and ratio satisfy Equation (17). Figure 10 shows the analytical and experimental flow loss versus switching ratio with the switching frequency of 100 Hz.…”

“…The noise (pressure pulsation) problem of an SIHS has been raised by researchers [2,3,17]. To reduce pressure pulsations, the active noise controller for an SIHS was designed, prototyped, and validated [17,18].…”

“…To reduce pressure pulsations, the active noise controller for an SIHS was designed, prototyped, and validated [17,18]. The by-pass and in-series configurations of the control systems are investigated in [18].…”

Theoretical and Experimental Studies of a Switched Inertance Hydraulic System in a Four-Port High-Speed Switching Valve Configuration  

“…The average flow rate qm from the HP port is (17) where is the wave propagation time = 2 ⁄ , c is the speed of sound [11].…”