Active Damping of Power Control for Grid-Forming Inverters in LC Resonant Grids

Abstract

This paper derives the small-signal model of gridforming (GFM) inverters considering the presence of shunt capacitor in the power grid. It is pointed out that the shunt capacitor introduces two additional resonant peaks in the loop gain of power control loops, in addition to the fundamentalfrequency resonant peak that is identified in the prior art. Based on the findings, the active damping control is modified to dampen all three resonant peaks to guarantee the stable operation of GFM inverters. Finally, simulation and experimental tests are carried out to corroborate the theoretical analysis.

Stability Analysis and Active Damping Design for Grid-Forming Converters in LC Resonant Grids

“…By using (6) to replace the corresponding term in (5), the small-signal representation of the relationship between x x x s dq and x x x c dq can be expressed as…”

“…14. In this case, the previous assumption in the literature of ignoring the influence of ac capacitors when designing power control loops of GFM converter is justified [6].…”

“…To validate the theoretical analysis, time-domain simulations were performed using MATLAB/Simulink and the PLECS blockset, with the detailed electronic model shown in Fig. 2 [6]. The main parameters used in the simulations are listed in Table 1.…”

“…According to [5], GFM converters maintain terminal voltage by regulating its reactive power and synchronize with the power grid by regulating the output active power. Therefore, it is essential to design active and reactive power control loops to ensure the stable operation of GFM converters [6]. When GFM converters are connected to an inductive grid impedance with an inductor filter, it is discovered in [7] and [8] that there is a resonant peak at the grid fundamental frequency in the loop gain of the active power control (APC), which can cause unstable operation of GFM converters [9].…”

“…In scenarios involving large shunt ac capacitors (e.g. contributed by shunt capacitor branch utilized for reactive power compensation or capacitive loads), ignoring the influence of shunt ac capacitors in designing the active damping control may result in an inability to stabilize the GFM converter, as partly presented in our previous work [6]. Therefore, the primary contributions of this paper are:…”