Identification of low‐frequency oscillation mode and improved damping design for virtual synchronous machines in microgrid

Grid-forming control strategies for black start by offshore wind power plants

“…The reactive power controller is based on standard inductive line Q − V droop, which adjusts the voltage amplitude reference for controlling the reactive power exchange with the grid. A virtual resistance is added to reduce sensitivity to small grid disturbances by providing additional damping and to reduce the synchronous oscillations of droop-controlled converters (Sun et al, 2019). The swing equation controller, essentially a low-pass filter, can be replaced with proportional-integral-derivative/leadlag controllers, for enhanced electromechanical dynamics, adjustable characteristics like independent tuning of inertia, damping and steady-state droop, or highly non-linear behaviour during grid faults and connection-disconnection processes (Sun et al, 2019).…”

“…Moreover, lower switching frequencies seem to shift the root locus closer to imaginary axis, restricting the range of stable operating points. Sun et al (2019) show the complexity associated with tuning VSG for damping the different oscillations, implicitly caused due to coupling terms in the state-space matrix. While virtual resistance helps damp the intrinsic synchronous mode of a single droop-controlled VSC, it introduces coupling between active and reactive powers, especially for multiple paralleled VSCs.…”

“…The inertia term J can then be tuned to provide further attenuation, but this introduces sub-synchronous oscillations which deteriorate with increased inertia. Finally according to Sun et al (2019), since smaller droop gains reduce the inter-oscillations, values for D and k q from D'Arco et al (2015b) have been taken as initial estimates and then fine-tuned for stable operation. It is important to note that improving one oscillation mode can trigger another and that the tuning strategy used for a single VSG might not be applicable to multiple VSGs (Sun et al, 2019).…”

“…Many countries have set out several energy strategies for a more secure, sustainable, and low-carbon economy like the European Union's (EU) 2018 (RED II) directive on the promotion of the use of energy from renewable sources that sets an overall goal across the EU for a 32 % share of renewables in the total energy consumption by 2030. Among the different renewable energy sources, wind energy has seen a rapid growth in the installed capacity worldwide, from about 6.1 GW in 1996 to about 591.5 GW in 2018 (Tavner, 2012), showing huge promise as one of the major electricity sources in the future.…”

Power Angle Small-Signal Stability Analysis of Grid-Forming Wind Turbine Inverter Based on VSM Control

“…However, a detailed state space modeling of the whole converter control scheme and electric circuits is used in these papers, some with more than ten state variables, which is opposite to the goal of simplification in this paper. Indeed, there are some simpler representations [25] [26], but they do not focus on the small-signal stability analysis and parameter design of the VSM-controlled inverter itself. Last but not the least, all the previous studies are based on VSM control schemes specific to those studies, like synchronverter [10], [12], [16]- [19], schemes developed by SINTEF [20]- [24], Osaka University [11], Kawasaki Technology Co. [24] and others [25].…”