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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - INSIGHT (ImplementatioN in real SOFC Systems of monItoring and diaGnostic tools using signal analysis to increase tHeir lifeTime)

Teaser

Summary

The INSIGHT project aims at developing a Monitoring, Diagnostic and Lifetime Tool (MDLT) for Solid Oxide Fuel Cell (SOFC) stacks. The project will implement prediction methodologies and demonstrate their effectiveness by on-field tests on a real micro-Combined Heat and Power system for residential applications. To achieve a cost-efficient and robust solution, 2 advanced complementary techniques will be exploited, Total Harmonic Distortion (THD) and Electrochemical Impedance Spectroscopy (EIS), in addition to conventional Stack Dynamic Signals Analysis (SDSA).
SDSA have been conceived before, while THD and EIS have already demonstrated great effectiveness in PEM fuel cells diagnosis and are available. Thus, these methodologies will be smartly adapted to SOFC systems to improve their lifetime and therefore the reduction of Total Cost of Ownership (TCO) that will make SOFC more competitive to penetrate the market. INSIGHT outcomes will open the perspective to decrease the costs of service and SOFC stack replacement by 50%, which would correspond to a reduction of TCO by 10%/kWh by prolonging SOFC lifetime by 5%, increasing availability by 1%. These, within the limit of adding 3% to the total SOFC systemâ€™s cost.

Work performed

Obj 1: To implement an advanced Monitoring, Diagnostic and Lifetime Tool to prolong SOFC lifetime and increase availability.
The most critical faults to be studied have been defined: fuel starvation, carbon deposition and gas leakage. A test protocol and the testing matrix have been defined, considering tests of short stacks, complemented by segmented cells to obtain local measurements. EIS associated to DRT (Distribution of relaxation time) analysis, THD and PRBS (pseudo random binary signal) measurements as well as conventional signals have been considered.
Conventional signal can be considered for diagnostic use thanks to a statistical treatment. EIS is very valuable, supported by DRT analysis for a more accurate analysis. Nonlinear perturbations techniques (THD and PRBS) have been found to be quick analysis tools, with an answer consistent with conventional EIS measurements. However, some faults are easier to detect than others, and the averaging effect when monitoring the signal of a whole stack and not of its individual repeating units can complicate and even hinder the signal.
First metrics have been identified for diagnostic and for degradation modelling. A diagnostic algorithm based on EIS for Detection and Isolation of faults has been considered. A new methodology to derive metrics from frequency data, excited with periodic broadband signals has been invented and a patent application is in progress. WP2 data have been analysed with a in-house developed routine to obtain DRT analysis.
Obj 2: To develop the hardware for the implementation of advanced Monitoring, Diagnostic and Lifetime algorithms on real SOFC system with low cost (less than 3% of system cost).
The board design has been done and the first release has been developed and tested. It has been also connected to the lab SOFC system for testing the voltage and current channels as well as to provide the first data to be processed off-line. A two levels firmware has been conceived and developed.
To permit THD, EIS and PRBS measurements, works have been done to modify the DC/DC converter integrated in SOFC system. Communicationâ€™s board of modified DC/DC converter has been tested.
Obj 3: To identify control actions able to mitigate the impact of both degradation mechanisms and faults on performance and durability of SOFC.
Based on WP2 data a mitigation matrix has been designed to correlate the 3 faults with detection and mitigation variables.
Regarding modelling of the degradation, a physically-based model for EIS has been validated for LSCF electrode, and inter-diffusion induced microstructural degradation on the oxygen electrode side has been studied to predict diffusion (composition) profiles and serial resistance increase during cell fabrication and long-term operation. An EIS model has been validated to reproduce the expected variation trend upon operating conditions variation. Thermo-mechanical degradation has also been studied through creep measurement and fracture strength on real samples. Finally, a fast-lumped model capable of reproducing the real system behaviour has been developed.
Regarding algorithm for fault detection and isolation, a Preliminary Fault Signature Matrix (FSM) structure has been designed. A preliminary link between features extraction and detection process has been established.

Final results

CEA Expected results: Local current monitoring and model correlation, study the local conditions (current, fuel utilisation (FU)) to better understand their impact on cell degradation.
Be able to get this information on classical cells without the need of special geometries/manufacturing.
Results Y1: Measurement done on a classical SP cell using a current collector with 9 local voltage measurements; Good correlation between experiment and model; Large difference in terms of current density along the cell diameter: 2 times larger at the center than at the periphery in case of high FU (> 80%).
DTU Expected results: Implemented set of diagnostic tools for stacks/systems into a practical device.
Results Y1: With the aim to identify \'failure metrics\' for early failure detection of fuel starvation, 2 possible starvation incidents were simulated. Signatures of conventional signals of both experiments were qualitatively and quantitatively analyzed. Via statistical treatment of the voltage output signal a time-domain pattern was found to allow identification of \'faulty\' conditions.
UNISA Expected results: Monitoring, Diagnostic, Lifetime, Mitigation tools and HW & firmware engineering for on-board use.
Results Y1: Algorithm for fault diagnosis, degradation modelling and mitigation strategies. The high level (HL) software has been conceived to include extrnal code taking as input the acquired data for performing on board the diagnostic methods. To assure the correct data exchange and a proper hardware configuration, the HL software executes each diagnostic method as a call to the corresponding C function.
EPFL Expected results: Addition of new diagnostic tools on existing instrumented advanced stack test benches for validation and Improved lifetime prediction tool calibrated with spatially resolved measurement data, e.g. signal response from a SRU with a known local defect introduced on purpose.
Results Y1: EIS/DRT/resistances quantification. Measurement on 2-cell short stack with a segmented SP cell; Possibility to create spatial maps (current density); EIS combined with DRT to quantify elementary processâ€™ contributions.
IJS Expected results: PRBS-based diagnosis and prognosis
Results Y1: work on a novel health assessment procedure using non-sinusoidal perturbation in terms of step-like PRBS. The time evolution of the related model parameters is modelled as a stochastic process, used to predict the future trend.
BITRON Expected results: MDLT HW device.
Results Y1: Main architecture defined and first release ok.
SolidPower & HTC Expected results: Small size high efficiency micro-cogenerator SOFC based systems, for small commercial and residential markets.
results Y1: Modified DC/DC converter for the project done and validated.