Introduction

Australia is leading the way in integrating renewable energy into its power system, with a goal of operating with up to 75% renewable energy by 2025. This transition involves significant challenges such as maintaining grid stability and system strength. These challenges are being addressed using advanced technologies like synchronous condensers, battery energy storage systems (BESS), and grid-forming converters.

Key Challenges

The integration of renewable energy sources introduces traditional stability issues, as the overall system inertia decreases when synchronous generators are replaced. This reduction can lead to instability in rotor angle, frequency, and voltage, as inverter-based resources (IBRs) do not inherently resist frequency changes. Additionally, the high penetration of IBRs brings new stability issues, including subsynchronous resonance (SSR) and converter-driven stability problems, which can cause harmful oscillations in current and voltage. Traditional power system protection and coordination rely on high fault currents provided by synchronous generators. IBRs typically provide lower fault currents, potentially compromising these protection systems. Furthermore, restoring power after an outage, known as black-start capability, is challenging for most IBRs, as they cannot perform this function independently.

Mitigation Measures

Several mitigation measures are in place to address these challenges. Operational constraints are used to ensure stability, limiting the output of IBRs or maintaining a minimum number of synchronous generators online. However, these measures are temporary and economically impactful. Reinforcing the grid with new transmission lines and installing devices like synchronous condensers can increase system strength and fault current capacity. Synchronous condensers provide mechanical inertia and voltage support. Special protection schemes that do not rely on high fault currents, such as differential and rate-of-change-of-frequency (RoCoF) protection, can be implemented. Improving inverter controls by transitioning from grid-following to grid-forming mode allows IBRs to actively support grid stability by providing services like voltage management and synthetic inertia.

Australian Experience

South Australia has successfully integrated a high percentage of renewable energy by installing synchronous condensers and battery storage systems. Synchronous condensers at Davenport and Robertstown provide fault current and inertia, supporting up to 2500 MW of IBRs. The Hornsdale Power Reserve, with a capacity of 150 MW and 194 MWh, has demonstrated significant benefits, including reducing regulation costs and providing fast frequency response during grid disturbances. The Dalrymple BESS, the first grid-forming battery in the National Electricity Market (NEM), enhances local grid reliability and provides essential services like frequency control and black-start capability.

Impact of Technologies

The combination of synchronous condensers and BESS has allowed Australia to operate with a high share of renewable energy while maintaining grid stability. These technologies have enabled significant renewable energy contributions, sometimes exceeding 100% of demand, with surplus energy exported to other regions. Ongoing projects and future plans include more BESS installations and grid upgrades to further support renewable integration and grid reliability.

Conclusion