Development of Control Strategies for the SvDP-Concept
Authors
Nielsen, Michael Otto ; Jensen, Søren Juul
Term
4. term
Education
Publication year
2014
Submitted on
2014-06-03
Pages
141
Abstract
I mange hydrauliske systemer reguleres olieflowet med ventiler, hvilket kan give energitab. Denne afhandling undersøger Speed-variable Differential Pump (SvDP), hvor en ventil erstattes af to pumper monteret på samme servodrev for at øge energieffektiviteten. Vi opbyggede en ikke-lineær simuleringsmodel af pumpe-cylinder-systemet og validerede den med målinger fra et testanlæg hos Bosch Rexroth A/S. En analyse af systemet i stationær tilstand (steady state) viste, at trykniveauerne stiger, når pumperne roterer i negativ retning, og altid falder ved positiv rotation. I den nuværende konfiguration kan trykket derfor kun styres aktivt under negativ rotation. For at vurdere reguleringsydelsen designede vi bevægelsesbaner: to glatte, kvintiske (5.-gradspolynomielle) baner med realistiske krav til hastighed og acceleration, samt to rampebaserede baner med hastighedsspring. Modellen blev lineariseret omkring kritiske driftspunkter, hvilket gav to lineære modeller afhængigt af rotationsretningen. Vi designede en decentraliseret reguleringsstrategi, så SISO-regulering (single-input single-output) kunne anvendes. På grund af begrænset hastighedsmåling i testanlægget udviklede vi to sæt regulatorer: et konservativt sæt, der kunne implementeres, og et højtydende sæt til at vise potentialet. De højtydende regulatorer udnyttede trykfeedback for at øge dæmpningen (reduktion af svingninger), men de kunne ikke implementeres, fordi en støjende positionsmåling fik PI-hastighedsregulatoren (proportional–integral) til at give hak/sitren (chattering) i styresignalet. Det konservative sæt blev implementeret og testet og gav et proof of concept. Den eksperimentelle RMS-hastighedsfejl afveg 23–55 % fra simuleringerne. Antages en tilsvarende afvigelse for de højtydende regulatorer, kan man med bedre hastighedsfeedback forvente en RMS-hastighedsfejl på cirka 2–3 mm/s. Samlet set peger resultaterne på, at SvDP kan være et lovende alternativ til den traditionelle ventil–cylinder-konfiguration.
In many hydraulic systems, valves throttle oil flow to control motion, which can waste energy. This thesis studies the Speed-variable Differential Pump (SvDP), where a valve is replaced by two pumps on a shared servo drive to improve energy efficiency. We built a nonlinear simulation model of the pump–cylinder system and validated it with measurements from a Bosch Rexroth A/S test rig. A steady-state analysis showed that system pressures rise when the pumps rotate in the negative direction and always fall when rotation is positive. In the current configuration, this means pressure can only be actively controlled during negative rotation. To evaluate control performance, we designed motion trajectories: two smooth, quintic (fifth-degree polynomial) profiles with realistic velocity and acceleration limits, and two ramp-based profiles that impose a step in velocity. The model was linearized around critical operating points, yielding two linear models depending on rotation direction. We then designed a decentralized control strategy so that SISO (single-input single-output) control could be applied. Because the test rig provided poor velocity estimates, we developed two controller sets: a conservative set that could be implemented, and a high-performance set to indicate the concept’s potential. The high-performance controllers used pressure feedback to increase damping (reduce oscillations), but could not be implemented because a noisy position signal made the PI (proportional–integral) velocity loop chatter. The conservative controllers were implemented and tested, providing proof of concept. Experimentally measured RMS velocity errors differed from simulations by 23–55%. If a similar gap applies to the high-performance case, then with decent velocity feedback the expected RMS velocity error is about 2–3 mm/s. Overall, the results indicate that SvDP is a promising alternative to the traditional valve–cylinder configuration.
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