Grid Forming Batteries: One Big Step to a Sustainable Journey

As we continue to step towards a net-zero future it is essential that we transition to renewable energy in a responsible, reliable, and safe way. With the increase in penetration of variable renewable energy and energy storage and the decrease of conventional gas or coal powered generators, questions have been raised about the reliability of a low inertia electrical network. Inertia in an electrical network refers to the energy stored in the large rotating generators and is a key reason as to why the grid remains stable when a disturbance or fault occurs. With renewable energy becoming a large contributor to our sources of energy where there is comparatively less inertia, how do we keep the system strength of our network?

Battery Energy Storage Systems (BESS) have been pivotal to the transition from conventional energy sources to renewable sources and provide many other benefits due to its flexibility. They have proven to help manage the variability of supply of energy from sources such as solar PV and wind farms and output the supply to the grid to meet the demand for consumers. Services such as Frequency Control Ancillary Services (FCAS) and Fast Frequency Response (FFR) can provide support to the network along with additional revenue streams for suppliers. As you may already know, the output voltage of a battery is Direct-Current (DC) but the electricity in the grid is Alternating Current (AC) oscillating at 50Hhz. The use of power electronics is used to convert DC voltage to the grid’s 50Hz AC voltage we use here in Australia. One familiar and thoroughly studied technique used in power electronics is Phase Lock Loop (PLL) to convert the DC voltage to AC voltage by targeting the phase of the source voltage (the grid) and using the output as a feedback loop to synchronise with the grid’s frequency. This control method is commonly used in Grid-Following batteries and is already helping us power our homes in various parts of Australia. However, in the event of a fault such as a lightning strike to a transmission line or pole, having only Grid-Following batteries may not be enough in a low inertia system.

Grid-Forming batteries are currently being seen in the industry as a leap forward in technological advances as they provide more than just delivering power to the grid. These batteries are a display of how far control systems, power electronics, software and power engineering has advanced in these recent times of massive changes. Grid-Forming batteries use the fundamental relationships of how the grid and conventional generator operates in its control system as opposed to Grid-Following batteries which just track frequency. Due to the complex control method, they behave like synchronous generators providing inertia to the network which inherently improves the system strength of the grid. As they are also not dependent on the grid’s frequency, they can also provide other support services outside of inertia such as Black Start and Islanding. Hurdles will continue to come with the inevitable closure of conventional generators and sustainable sources of energy, however as we further understand the system strength of the grid dominated by renewable energy and further develop Grid-Forming batteries, we can hope to see a big step towards the transition of a cleaner future.

This article was written by our Graduate Engineer Edwin Siputro who has recently completed his thesis topic “Modelling Grid Forming Battery Energy Storage Systems in PSCAD”.