Evaluation of Maintenance Strategies for Supercapacitor-Based Energy Storage Systems in E-STATCOM Applications - A Monte Carlo Simulation Study Using Weibull-Based Failure Modelling

This master’s thesis studies the effect of different maintenance strategies applied to the energy storage system (ESS) of an Enhanced Static Synchronous Compensator (E-STATCOM) comprising supercapacitors. 

As the share of inverter based renewable energy increases, the frequency stability of the power grid is reduced. This can be counteracted through the introduction of synthetic inertia provided by the E-STATCOM, where active power is absorbed or injected to maintain the nominal frequency. A rated capacity of 150 MW would result in an ESS containing thousands of supercapacitor cells. These cells degrade over time, with high temperature and voltage acting as accelerating factors. As supercapacitor-based ESSs are an emerging technology, there is also a lack of field data, making the question of maintenance a complex one.

The aim of the thesis is to determine which maintenance strategies are required for reliable and cost efficient operation, using Monte Carlo simulations. The thesis provides a structured framework for implementing Weibull failure modelling for an ESS, and for simulating and evaluating different maintenance strategies. The simulated maintenance methods are divided into two categories: Predetermined Maintenance and Condition-Based Maintenance (CBM). The simulation results clearly show that implementing CBM, in any form, improves the cost efficiency of E-STATCOM operation.

These results provide a foundation for future studies, where detailed cost analyses can be conducted to support the design and selection of maintenance strategies for a large scale supercapacitor based ESS in a E-STATCOM. This thereby contributes to more reliable and cost efficient operation of future power systems.