A Series-<italic>LC</italic>-Filtered Active Damper With Grid Disturbance Rejection for AC Power-Electronics-Based Power Systems

Abstract

This letter proposes an active damper with a series LC-filter for suppressing resonances in an ac power-electronicsbased power system. The added series filter capacitor helps to withstand most of the system voltage, hence allowing a lower rated converter to be used for implementing the active damper. Unlike an active power filter for mitigating low-frequency harmonics, the proposed damper dampens resonances at higher frequencies, whose values are dependent on interactions among multiple gridconnected converters and reactive elements of the system. Its control requirements are therefore different, particularly in the low-frequency range, where the series LC-filter is predominantly capacitive, rather than the usual inductive characteristics that exist between voltage-source converters and the grid (or load). This low-frequency challenge can fortunately be resolved by the proposed fourth-order resonant controller, in addition to the second-order resonant controller used for resonance damping. Experimental results obtained have confirmed the effectiveness of these controllers, and hence the feasibility of the active damper.

Two-Stage Battery Energy Storage System (BESS) in AC Microgrids with Balanced State-of-Charge and Guaranteed Small-Signal Stability

“…In Reference [27], a comprehensive z-domain model is derived in terms of a renewable energy system with parallel inverters, and a dead-band control with virtual impedance is applied to dampen the instabilities. In References [28,29], an inductive (L) or inductive-capacitive (LC) filtered damper is involved to actively regulate the impedance at the point of common coupling. A reliable operation with guaranteed small-signal stability should be realized to achieve the desired control objectives in a BESS, especially considering the LCL filters.…”

Impedance-Based High-Frequency Resonance Analysis of DFIG System in Weak Grids

“…The high frequency resonance between the grid connected converter and the RL weak network has been analyzed in [16]- [24]. The converter with series LC filter, rather than the traditional LCL filter, is studied in [17] to analyze the resonance. Moreover, the coupling between two converters connected to the same Point of Common Coupling (PCC) or different point of coupling via non-ideal grid is discussed in [25], and the bifurcation boundaries are also derived.…”

Passivity Enhancement of Grid-Tied Converters by Series LC-Filtered Active Damper

“…A simple alternative is to add an external active damper, which in effect, is another converter. This damping converter can be of a lower power rating like the series LC-filtered active damper presented in [12]- [14]. The schematic of the active damper is shown in Fig.…”

“…The ratio between these two admittances, or the so called minor loop gain, is known to influence the stability and harmonic resonances between them [18], [19]. Applying the same concept to a grid-tied converter, its output admittance Y oc can be viewed as Y S , while the grid admittance can be treated as Y L [12], [20]- [25], [29]. In the case where the grid converter cannot be modified, Y S remains unchanged, while Y L depends on various conditions of the grid and hence un-tunable.…”