Abstract
KEYWORDS - hydrogen, storage, electronics, safety, instrumentation
In hydrogen operated cars the fuel storage system is a vital part with remarkable requirements. Unlike conventional gasoline tanks, a hydrogen fuel storage system is more complex in operation and requires a very sensitive monitoring and control electronics. The operation within an automotive environment adds new challenges to the established industrial standards. This paper presents the topic from a systematic point of view.
Actually, hydrogen will be mainly stored either as highly compressed gas or as cryogenic liquid at very low temperatures.
Additionally to the auxiliary components it also includes an electronic control unit (ECU) for monitoring the fuel level, temperatures and pressures at various locations and for controlling valves and feed pumps, where applicable. Moreover, this ECU interacts with the central control unit of the engine or the central gateway over a CAN-Bus line.
The use of electrical power in the (possible) presence of a hydrogen-air mixture imposes a safety-thread unless appropriate precautions are made. All sensor interfaces have to be designed according to the guidelines for intrinsic safety. The general approach and also practical solutions will be presented.
Some parts of the electronic instrumentation may be critical for a safe operation of the storage systems. In case of a liquid hydrogen tank, the maximum fuel level must not be exceeded. These functions have to be handled with respect to the appropriate safety integrity level (SIL), as described in IEC 61508. The paper deals with these safety aspects and outlines requirements and solutions in conjunction with the automotive environment.
Several sensor elements only deliver small output amplitudes and may encounter ESD and EMI interferences. Moreover, the sensor interfaces act as safety barriers according to the regulations for intrinsically safe (Ex-i) circuit design. EMI / EMC filters and safety barriers are required but interfere with the sensor signals. By developing an advanced circuitry, these influences are minimized and the electronics fulfils its accuracy requirements over the full automotive temperature range and for a minimum life time of ten years.
Electrical functions, dependability and functional safety aspects pose challenges on the hardware and software design. In addition to them, a basically competitive design is a must for series production. While the paper focuses on the research aspects and the presentation of practical solutions, it also aims at presenting the design flow and the functional and regulatory boundary conditions.