Anders Hedegaard Hansen

Design of energy efficient SMISMO-ELS control strategies

Traditionally mechanical linked meter-in and meterout spool valves are used for velocity control of hydraulic differential cylinders. However with the demand for energy efficient systems the individual meter-in and meter-out valves draws massive attention. This paper propose an energy efficient actuator control and combines this with energy efficient system control. Finally energy neutral performance improvments are suggested for the subjacent actuator in an ELS system.

Reducing pressure oscillations in discrete fluid power systems

Discrete fluid power systems featuring transmission lines inherently include pressure oscillations. Experimental verification of a discrete fluid power power take off system for wave energy converters has shown the cylinder pressure to oscillate as force shifts are performed. This article investigates how cylinder pressure oscillations may be reduced by shaping the valve opening trajectory without the need for closed loop pressure feedback. Furthermore the energy costs of reducing pressure oscillations are investigated.

Simulation of Utilisation of Pressure Propagation for Increased Efficiency of Secondary Controlled Discrete Displacement Cylinders

A key component of upcoming secondary controlled fluid-power systems for e.g. wave energy is the implementation of discrete force control of cylinders by discrete variation of the cylinder displacement. However, as the discrete control is implemented by shifting between fixed system pressures in multiple cylinder chambers using on/off valves, the energy efficiency of the performed shifts is essential for the total system efficiency. However, pressure shifting on a volume, where the dynamics of pressure propagation in the pipelines is negligible have been proved to have an unavoidable minimum loss due to the compressibility of the fluid. This paper performs a simulation study, showing that an improved energy efficient shift may be implemented by utilising the pressure propagation in the line between valve and cylinder chamber.

Control of a 420 kN Discrete Displacement Cylinder Drive for the Wavestar Wave Energy Converter

To improve the power production of their 1 MW wave energy converter, Wavestar is developing a new transmission based on discrete hydraulics. The discrete hydraulic system allows all cylinders to supply a common accumulator storage while maintaining low-loss individual force control of the 20 absorbers. The system is implemented using multi-chambered cylinders, where the different chambers may be switched between three pressure lines using a manifold with fast on/off valves. Resultantly, a Discrete Displacement Cylinder (DDC) is obtained, where force control is implemented by shifting between different area/pressure combinations. Currently, a 420 kN DDC prototype has been implemented and tested at the newly commissioned full size wave energy testbench at Aalborg University. The initial design and control of the DDC had poorly damped switching transients. These issues treated in this paper. This leads to a new control, which gives a smooth operating DDC, while meeting the requirements to the efficiency of the drive.Copyright

Design of Bidirectional Check Valve for Discrete Fluid Power Force System for Wave Energy Converters

Discrete fluid power force systems consisting of a multi-chamber cylinder, a switching manifold and common pressure lines have been proposed as a technology for increasing the efficiency of the power take off system in ocean wave energy converters. However the force shifting of these discrete systems introduces large switching losses, especially when large pressure difference is present across the valves in the manifold. The current paper therefore focus on designing a bidirectional check valve for use in the switching manifold of the discrete force systems. The use of the bidirectional check valve enables passive force switching under minimal pressure difference, hence minimal energy loss. The bidirectional check valve is designed with a rated flow in the range of 1000L/min@5bar. The flow direction of the bidirectional check valve is set by the setting the pilot pressure. This paper presents a functionality test of a 125 L/min@5bar bidirectional check, leading to the design and modelling of a bidirectional check valve for ocean wave energy. It shows that a feasible bidirectional check valve may be configured by employing a multi-poppet topology for the main stage and utilising a 3/2 switching valve as pilot stage. The bidirectional check valve may operate both passive an active switching.Copyright

Energy Cost of Avoiding Pressure Oscillations in a Discrete Fluid Power Force System

In secondary valve controlled discrete fluid power force systems the valve opening trajectory greatly influences the pressure dynamics in the actuator chambers. For discrete fluid power systems featuring hoses of significant length pressure oscillations due to fast valve switching is well-known.This paper builds upon theoretical findings on how shaping of the valve opening may reduce the cylinder pressure oscillations. The current paper extents the work by implementing the valve opening characteristics reducing the pressure oscillations on a full scale power take-off test-bench for wave energy converters. Further the energy losses introduced during the shifting period is investigated and compared for two valve opening algorithms. The investigation of the energy loss is utilised to quantify the importance of a fast valve switching and the energy cost of reducing pressure oscillations.The paper will present measurements comparing pressure dynamics for two valve opening algorithms. In addition the paper will give a theoretical investigation of the energy loss during valve shifting and finally measurements of average power output from the power take-off system in various sea states are compared for the three pressure shifting times.Copyright

On/off multi-poppet valve for switching manifold in discrete fluid power force system PTO in wave energy converters

Fluid power systems are the leading technology for power take off systems in ocean wave energy converters. However, fluid power systems often suffer from poor efficiency, especially in part loads. This degrades the PTO system efficiency and therefore lowers the energy production. To overcome the issues with poor system efficiency, a discrete fluid power system is proposed as a main part of the PTO system. For the discrete system to be feasible large fluid power switching valves are needed. The current paper presents a two stage 1,000 L/min@5 bar multi-poppet on/off valve with a switching time less than 10 ms. The pilot stage is directly actuated and utilises internal valve pressure as supply and an external tank connection as drain. The current paper presents the multi-disciplinary design process leading to the final valve design. This includes the geometric design of the main stage, the choice of pilot valve, structural mechanical issues and modelling and simulation of various valve configurations. Hence...

Design of a multi-poppet on-off valve for wave energy converters

Fluid power systems are the leading technology for the power take off system in ocean wave energy converters. However, fluid power systems often suffer from poor efficiency, especially in part loads. This degrades the PTO system efficiency and therefore lower the energy production. To overcome the issues with poor system efficiency a discrete fluid power system is proposed as a main part of the PTO system. For the discrete system to be feasible large fluid power switching valves are needed. The current paper presents a two stage 1000 L/min@5bar multi-poppet on/off valve with a switching time less than 15 ms. The pilot stage is directly actuated and utilises internal valve pressure as supply and an external tank connection as drain. The current article presents the design process leading to the final valve design. This includes the geometric design of the main stage, the choice of pilot valve, structural mechanical issues and modelling and simulation of various valve configurations. Hence in the design process a wide variety of topics are combined to chose the best valve configuration.

Influence and Utilisation of Pressure Propagation in Pipelines for Secondary Controlled Discrete Displacement Cylinders

Efficient discrete force control of cylinders may be realised by having multi-chambered cylinders, where the pressure of the chambers are shifted between fixed pressure levels of a secondary controlled system. However, the pressure shifting on a volume where the dynamics of pressure propagation is negligible have been be proven to have an unavoidable minimum loss due to the compressibility of the fluid. This paper investigates the effect of the pressure propagation in the connection and concludes that except more complex shifting schemes are introduced, the minimum loss remains unchanged. The paper analysis however also demonstrates and suggests, that with a clever valve control and shifting scheme, increased efficiency of a shift is obtainable by utilising the pipeline inductance.

Human mobile inverted pendulum transporter — A mechatronic system case study

It is an inherent property of a mechatronic system that it involves several interacting sub-systems and the design process for such systems involves an in-depth understanding of a number of engineering disciplines. A truly mechatronic design requires use of advanced models during the design procedure combined with the formulation and the solution of an optimization problem involving a number of constraints related to performance, costs, geometry, availability of components etc. In this paper, we present a case-study of a more traditional design procedure for a highly multi-disciplinary device, which nevertheless illustrates the potentials of unifying classical engineering technologies (mechanics, electronics, control systems) with modern high-efficient inverter-fed permanent-magnet AC motors and the latest MEMS sensor technology. A full-scale fully operational prototype of a two-wheel mobile inverted pendulum has been built based on the presented design.