Theoretical basis for combining thermo-hydraulic and thermo-electric power conversion into one unit - thermo-hydraulic linear generator

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Hitherto, hydraulics is the preferred type of power conversion and transmission in mobile machinery. For years, at the applicants, they have successfully been dealing with the development of a simple and inexpensive drive unit of the thermo-hydraulic free piston engine (FKM) for mobile hydraulic hybrid technology, which is capable of providing the required hydraulic propulsion power to the machine as efficiently and with as low-emissions as possible. Current developments in electric engineering enable the development of new applications. The reasons for replacing conventional drives are the increased energy efficiency and / or the improved controllability. Therefore, out of functional and energetic reasons, the simultaneous supply of hydraulic and electric power in a primary unit for future mobile machines is desirable. The aim of the research project is to provide the theoretical basis for combining thermo-hydraulic and thermo-electric power conversion into one unit (thermo-hydraulic linear generator - THLG) in order to obtain a reliable estimate of the technical realisation and the technical complexity. The simultaneous and in its ratio freely selectable supply of hydraulic and electric power on the basis of the free piston principle is possible in principal. However this requires fundamental research concerning the interaction between both energy transformations, of a stable process control as well as the analysis and assessment of the physical process parameters concerning the future design of a prototype. Starting from a suitable system configuration of the FKM under specific requirements, a linear generator which is optimized in power density and adapted to the existing prototypes is developed. The combination of both power conversions requires a coordinated control strategy, which can be derived from the dependencies of the subsystems with each other and the dynamic behavior of the whole system. These must allow a power output which meets the requirements and is simultaneous and variable on the hydraulic and the electric side as well as ensure a stable operation. For this purpose different regulatory approaches for the inner-stationary operation of the subsystem linear generator, which is conditional to principles, and the highly dynamic behavior of the complete system THLG are to be investigated. In order to keep hardware costs low, sensorless position detection is preferred, since the control of the linear machine requires an exact knowledge of the position of the mover. The possible adaptation of hybrid sensorless methods over the whole speed range is analysed for the specific application THLG. The result is detailed information on a THLG, whether and under which technical efforts it is practicable. They include both, issues of energetics and control.