Transient challenges of a BESS grid-forming integration project

Hydro-Québec conducted a pilot project using a battery energy storage system (BESS) operating as the source of an islanded network. The BESS operates in grid-connected mode when it is charging from the grid. The BESS will be operated in islanded mode when the main power source is unavailable. The technical specifications required the BESS to replicate the behaviour of a synchronous generator in grid-forming operation. The approach was to perform electromagnetic transient (EMT) simulations, and to compare it to on-site testing with transient recorder and BESS fault tests. The transient studies and test records allowed the identification of some performance issues related to this technology that may be difficult to observe with another approach. The transient phenomena are as important as the steady state performances and should be the main design factor for these types of projects. The paper shows some challenges and issues related to transients that improved the BESS. It also shows some corrections and recommendations that shall be applied for future projects. Some of those challenges are:•Control algorithms during a fault.•Overvoltages observed when transitioning from a grid-connected to an islanded state.•Power oscillations due to control instabilities.•Differences between fault tests results and simulations.