Technical Brief

Improving Performance of a Switched Inertance Buck Converter Via Positioning of Reservoir Flow Valve

[+] Author and Article Information
Travis Wiens

Department of Mechanical Engineering,
University of Saskatchewan,
57 Campus Drive,
Saskatoon, SK S7N 5A9, Canada
e-mail: t.wiens@usask.ca

Contributed by the Dynamic Systems Division of ASME for publication in the JOURNAL OF DYNAMIC SYSTEMS, MEASUREMENT, AND CONTROL. Manuscript received October 6, 2015; final manuscript received June 23, 2016; published online August 10, 2016. Assoc. Editor: M. Porfiri.

J. Dyn. Sys., Meas., Control 138(12), 124502 (Aug 10, 2016) (6 pages) Paper No: DS-15-1491; doi: 10.1115/1.4034045 History: Received October 06, 2015; Revised June 23, 2016

A typical switched inertance buck converter includes digital valves controlling the flow of fluid to the load from the pressure supply and also from the reservoir. These valves are typically located at the same position, often packaged in the form of a single three-way valve, but also sometimes in the form of a two-way high-pressure supply valve and check valve from tank. This results in the situation where attempts to increase flow boosting performance by exploiting reflected pressure waves to draw additional fluid from tank will also tend to draw additional fluid through the valve from the high-pressure supply, causing increased energy loss at the valve. This paper presents a strategy that avoids this tradeoff by locating the tank flow valve along the length of the inertance tube such that the timing of pressure waves arriving at the tank valve can be optimized separately from those arriving at the high-pressure supply valve. A simulation study is presented, in which valve placement and inertance tube resonance are optimized for flow gain or energy efficiency, with results in both cases better than a conventional system with colocated valves. Two strategies for avoiding cavitation are also presented.

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Fig. 1

Schematic of a switched inertance buck converter

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Fig. 2

Location of the check valve along the inertance tube

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Fig. 11

Check valve flows while varying the elevated reservoir pressure, while using two check valves as shown in Fig. 8. The line labeled “T–A,” is the flow from the atmospheric reservoir to the check valve located close to the switching valve, while “T–B” is the tuned check valve connected to the elevated reservoir pressure and located along the inertance tube (at the optimal V location’).

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Fig. 12

Energy and volumetric efficiency while using two check valves. Eliminating the T–A flow in Fig. 9 corresponds to better performance, but at the cost of requiring higher reservoir pressure.

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Fig. 10

Schematic showing location of additional check valve used to prevent cavitation at the switching valve exit

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Fig. 9

Energy and volumetric efficiencies as one varies the diameter of the tube between switching valve and check valve, under the same conditions as Fig. 6

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Fig. 8

Minimum reservoir pressure required to prevent cavitation as one varies the diameter of the tube between switching valve and check valve, with parameters at the optimal V position in Figs. 3 and 4

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Fig. 7

Flow traces for one cycle at the V operating point after the system has achieved equilibrium

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Fig. 6

Pressure traces for one cycle at the V operating point after the system has achieved equilibrium

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Fig. 5

Tradeoff of energy and volumetric efficiency along the E–V line in Figs. 3 and 4

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Fig. 4

Effect of resonance and check valve position on volumetric efficiency. The curve E–V denotes Pareto-optimal operating points trading off energy efficiency and volumetric efficiency (E and V are in the same position as in Fig. 3).

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Fig. 3

Effect of resonance and check valve position on energy efficiency. The best efficiency occurs at the point labeled E, with Pareto-optimal points following the curve to V, where the flow loss is minimized. Note that any point along this curve hasbetter energy efficiency and volumetric efficiency than a conventional converter with Lcv/L=0.




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