Abstract
Microgrids are supposed to provide stable power for seamless utility-grid interaction under all conditions as stated by IEEE-1547 standard. But, the use of power electronic inverter makes the microgrid sensitive to transients than synchronous generator-based plants. This degrades the voltage/frequency responses during transients, which can lead to transient stability problem if not controlled properly. Hence, the design of effective closed-loop voltage and current (V/I) controllers is highly desired to control the inverter output against the disturbances. The V/I controllers are based on PI (proportional-cum-integral) formulas. Thus, the effectiveness of V/I controllers relies on how accurate that their gain parameters are tuned. Many PI-tuning methods have been developed in the literature, but, it is yet difficult to identify a suitable method for an application. Also, only a few researchers have focused on the microgrids due to the complexity involved in its controller design by the presence of V/I cascaded dual-loop. Hence, to address this problem, this paper proposes a novel way of designing V/I controller parameters by using pole-zero cancellation method. This method is implemented by deriving the microgrid’s small-signal model. This improves the transient response through reduced system order and/or alleviated sluggish/marginal-stable/unstable poles by adding zeros at same places where those poles are laid, to in effect cancel them. The efficacy of the proposed method over existing methods is assessed by plotting frequency and voltage responses under different test conditions. From the simulation results, it is witnessed that the proposed method relatively improved the transient characteristics of microgrids.Article HighlightsAnalyzes the applicability of conventional PI tuning methods for microgrid controllers’ design.Proposes a novel small signal model based pole-zero cancellation method for the design of microgrid controllers.Enhances the gain margin, which improves the stabilization capacity of the system when subjected to disturbances.Improves the transient behavior of frequency and voltage responses, which ensure the safety of sensitive loads.
Highlights
The modern power system is facing profound changes by the integration of more and more renewable energy sourced microgrid (RESM) plants to the utility-grid to get rid of issues with conventional fossil fuel-based energy
The fruitful operation of RESMs is majorly affected by the intermittent renewable energy availability and dependency on harmonic prone power electronic voltage source inverter (PEVSI)
To address the abovementioned issues, the state-of-the-art solutions suggest, optimal use of storage devices to handle the irregularity in renewable energy availability [4,5,6], refined multilevel or modular PEVSI configurations with reduced complications to handle harmonic distortion issues [7,8,9], and the development of different voltage and current (V/I) control methods [10,11,12] and droop control methods [13,14,15] to handle power quality and power sharing issues, respectively
Summary
Vprewfm Reference input (V) given to PWM generator Vsabc Inverter output voltage (V) Viabc Series branch voltage (V) of the filter Iiabc Current (A) drawn from the Inverter Vgabc Utility-grid voltage (V) Icabc Current (A) flowing in shunt branch of Filter dq Parameters. Lf Single phase representation of Rfabc, Laf bc Cf, Gf Single phase representation of Cfabc, Gfabc Rg, Lg Single phase equivalent of Rgabc, Lagbc Vs, Vi, Vo Single phase equivalent of Vsabc , Viabc , Voabc Ii, Ic, Io Single phase equivalent of Iiabc,Icabc,Ioabc. Ω Angular frequency (rad/sec) KPV, KIV PIC components of voltage controller KPA, KIA PIC components of current controller
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