Power System Stability With a High Penetration of Inverter-Based Resources

Abstract

Inverter-Based Resources (IBR) possess dynamics which are significantly different to those of synchronousgenerator-based sources and as IBR penetrations grow the dynamics of power systems are changing. The paper discusses the characteristics of the new dynamics and examines how they can be accommodated into the long-standing categorisations of power system stability in terms of angle, frequency and voltage stability. It is argued that inverters are causing the frequency range over which angle, frequency and voltage dynamics act to extend such that the previously partitioned categories are now coupled and further coupled to new electromagnetic modes. While grid-forming (GFM) inverters share many characteristics with generators, grid-following (GFL) inverters are different. This is explored in terms of similarities and differences in synchronisation, inertia and voltage control. The concept of duality is used to unify the synchronisation principles of GFM and GFL inverters, and thus is established the generalised angle dynamics. This enables analytical study of GFM-GFL interaction which is particularly important to guide the placement of GFM apparatuses and is even more important if GFM inverters are allowed to fallback to GFL mode during faults to avoid over-sizing to support short-term overload. Both GFL and GFM inverters contribute to voltage strength but with marked differences, which implies new features of voltage stability. Several directions for further research are identified including (i) extensions of nonlinear stability analysis to accommodate new inverter behaviours with cross-coupled time-frames. (ii) establishment of spatialtemporal indices of system strength and stability margin to guide the provision of new stability services and (iii) datadriven approaches to combat increased system complexity and confidentiality of inverter models.

Assessing Grid Strength of 100% Inverter-Based Power Systems

“…In this scenario, the VSC-HVDC provides the offshore grid frequency and voltage based on the GFM control [5], and wind turbines are embedded in the grid via phase locking loop (PLL) control (i.e. grid-following (GFL) control method) [7]. This case is a typical 100% inverterbased generation system.…”

“…It is worth noting that the oscillation risks from PLLbased inverters still exist in the 100% inverter-based scenario even though the GFM inverters are equipped in this hybrid system. Due to the distinct control laws between the GFM and PLL-based inverters in the same grid, the dynamic interaction of voltage-angle-frequency has also attracted an increasing Grid Strength Assessment for 100% Inverter-Based Power Systems via Generalized Short-Circuit Ratio Fuyilong Ma, Huanhai Xin, Di Wu interest to study [7], [16]. Different participation ratios of the GFM and PLL-based inverters in distribution system are tested in [17], which suggests the high penetration level of the GFM inverters can provide more stable frequency and voltage response in transients process.…”

Grid Strength Assessment for 100% Inverter-Based Power Systems via Generalized Short-Circuit Ratio

“…In (8), the admittance model ( ) o Y s can further be simplified. When considering a high voltage filter bandwidth (around 1-2kHz) [30], the transfer function of the voltage feedforward filter satisfies ff [1 ( )] 0 K s   , and the current feed-forward coefficient 1 i K  .…”

“…The synchronizing mechanism of GFL inverters is sensitive to the terminal voltage [5]- [6]. When the power grid with high penetration of inverter-based resources (IBRs) is under disturbances, there are small-disturbance stability issues [7]- [8], such as sub/super synchronous oscillations [9], resulting from the interaction between the fast-acting inverter control and the power network [10]- [11], especially in a weak AC grid due to its high impedances (i.e. the low grid strength) [12]- [14].…”

Continuous Estimation of Power System Inertia Using Convolutional Neural Networks

“…In recent years, the fraction of power generation capacity ascribed to renewable energy sources has been growing at a quickening pace [1]: this in turn has caused a substantial increase in the share of power sources connected to the grid by means of a power electronic interface known as an inverter, hence the name inverter-based resources (IBRs). Compared to synchronous generators, which constitute the major source of power in conventional power plants, IBRs have a fundamentally different dynamical behavior, which is expected to have significant implications for the overall dynamics and stability of the power grid [2,3].…”