Australia is one of the leading countries in energy transition, and its largest power system is intended to securely operate with up to 75% of variable renewable generation by 2025. High-inertia synchronous condensers, battery energy storage systems, and grid-forming converters are some of the technologies supporting this transformation while facilitating the secure operation of the grid. Synchronous condensers have enabled 2500 MW of solar and wind generation in the state of South Australia, reaching minimum operational demands of ≈100 MW. Grid-scale battery energy storage systems have demonstrated not only market benefits by cutting costs to consumers but also essential grid services during contingencies. Fast frequency response, synthetic inertia, and high fault currents are some of the grid-supporting capabilities provided by new developments that strengthen the grid while facilitating the integration of new renewable energy hubs. This manuscript provides a comprehensive overview, based on the Australian experience, of how power systems are overcoming expected challenges while continuing to integrate secure, low cost, and clean energy.

Grid-forming (GFM) converters with the widely adopted power-synchronization controller (PSC) are exposed to the risk of losing synchronization, due to their limited power transfer capability under severe symmetrical faults. The output of the PSC, i.e., internal angular frequency, is forced to deviate from its reference, leading to an uncontrollable power angle during the fault. Hence, GFM converters become sensitive to fault depth and duration, suffering from long recovery time. This article proposes a current-limiting GFM control that is capable of limiting fault current and maintaining grid synchronization during severe faults. A current-synchronization controller (CSC) is developed to replace the PSC. The proposed CSC works compatibly with a current limiter and behaves as a PSC during normal conditions to provide synthetic inertia and a phase-locked loop during severe faults with enhanced synchronization stability. Based on the developed steady-state model, it shows that GFM converters under the proposed control directly transition to a faulted steady state when a fault occurs and maintain a constant power angle until the fault is cleared. This helps converters to regain the prefault steady state within a shorter recovery period. The proposed method is validated by a comprehensive comparison with existing current-limiting methods, as well as experimental results under different control parameters, power settings, and system strength.

Power electronic transformer (PET) composed of modular dual active bridge (DAB) blocks has a promising future in AC/DC hybrid distributed network because of its energy routing ability. The key element that restrains the development of PET is the vulnerability of power electronic devices during faults, especially DC faults. Considering that DC faults (mostly line faults) have very short transient process and no obvious fundamental frequency, fault location is difficult to be realized for DC lines in distributed network. To solve these problems, this paper analyzed the fault characteristics of DC line faults with respect to the basic structure of modular DAB block and proposed a two-terminal fault location method based on transient voltages measured in DC line boundaries. To evaluate the validity of proposed method, numerous simulations with different fault conditions were implemented in PSCAD/EMTDC. The simulation results indicate that the proposed fault location method located the faulted point quickly and correctly.

Impedance-based stability analysis is widely adopted for small-signal stability demonstration of power electronics dominated power systems. Stability assessment can be performed using either nodal admittance or bus admittance (i.e. equivalent admittance of a network viewed from a specific bus). This paper demonstrates that stability analysis using the bus admittance may not always produce correct results, even though it is easier to implement. Unstable multi-bus systems can be wrongly identified as stable by the single-bus analysis, in the cases where other buses play a dominant role in causing instabilities. A detailed comparison between nodal and bus admittance stability analysis is presented, leading to recommendations for their practical use. A phase-based method is proposed to facilitate the acquisition of eigenloci encirclement around the critical point, which can be used in the stability analysis based on either nodal or bus admittance. Following the conclusion of our work, we recommend multi-bus analysis in white-box model applications for instability mode analysis and stability-oriented design. Single-bus analysis is preferable in black-box model applications due to its simplicity. It is also suggested to select a bus for analysis from those connected to a high share of inverter-based resources, to ensure the correctness of results.