Universal Grid-Forming Method for Future Power Systems

Abstract

Power system inertia typically refers to the energy stored in large rotating synchronous generators. Dynamics and stability of the traditional power system is closely linked to the natural inertia of these synchronous generators. In recent years, increasing amount of synchronous generators have been replaced by high amount of different type of inverter-based generating units connected at different voltage levels of the power system. Therefore, the dynamics and stability of future low-inertia power systems will be increasingly dominated by the control and synchronization of these inverter-based resources. One essential issue is that the typical grid-following control with phase-locked-loop (PLL) -based synchronization of inverter-based generation is not enough to guarantee frequency stability in future low-inertia power systems. Therefore, different grid-forming inverter control and synchronization methods have been proposed and developed. Currently there does not exist any universal grid-forming control and synchronization method. Therefore, this paper tries to propose a new universal frequency-locked-loop (U-FLL) -based synchronization method which is grid-forming for inverter-based generating units and grid-supporting for inverter-based loads. Advantageous operation of the new U-FLL synchronization and control strategy is confirmed by multiple simulations with different shares of inverter-based resources and synchronous generators in MV and HV hybrid power systems as well as with 100 % inverter-based LV, MV and HV networks.

Improvement of Power System Frequency Stability With Universal Grid-Forming Battery Energy Storages

“…One key difference between GFL and GFM behavior is in their response to a network disturbance as well as in their small-signal operation when connected to a weak or stiff grid [5]. More information about advantages and disadvantages of GFL and GFM control methods can be found from [10]. In [35] also summary about advantages and disadvantages of different GFM control methods (i.e.…”

“…3 and 6, Table 1) in CASE_HV_IBR are shown. It was concluded in [10] that the U-FLL-based synchronization can enable stable frequency, also after load increase, in 100 % IBR-based small HV network with 68 BESSs connected in MV network many kilometers away from each other (Fig. 6).…”

“…In this paper, the grid-forming and supporting universal frequency-locked-loop (U-FLL) -based control and grid synchronization for IBRs [10] is utilized when the effect of different control methods of IBRs are studied with PSCAD simulations using simple transmission network model. Regarding to the U-FLL, the target is that it would be applicable to different type of future variable inertia power systems with different share of rotating SGs and IBRs.…”

“…Therefore, a new universal gridforming/-supporting U-FLL-based synchronization (Fig. 1) for IBRs was proposed in [10]. More information about the general targets and related issues as well as details of U-FLL can be found from [10].…”

“…1) for IBRs was proposed in [10]. More information about the general targets and related issues as well as details of U-FLL can be found from [10].…”