Use of LCL filter along with a voltage source inverter (VSI) requires damping of resonance. Active damping (AD) methods are preferable compared with passive damping methods from efficiency point of view. Recent researches show that achieving stable operation of a grid connected VSI with LCL filter at a low switching frequency to resonance frequency ratio can cause instability. In this study a resonant integrator (RI) based second order filter (RISF) has been proposed for AD of LCL filter resonance for stable operation at low switching frequency to resonance frequency ratio. The method extracts resonance frequency capacitor current from sensed capacitor voltage in a per phase manner and does not need any additional sensors. The modelling and analysis of the closed loop system with PR current controller and proposed AD has been carried out in discrete domain including all delay effects. Experimental results have been included in support of the theoretical analysis.
Abstract:Synchronous reference frame phase locked loop (SRF-PLL) is a well established technique used for maintaining synchronism of a grid connected VSI with an electric grid. Many methods of PLL are present in the literature to achieve improved performance under nonideal grid condition. These solutions are based on SRF-PLL structure along with some modification to achieve improved performance. It is observed that faster and better performance are achieved at the expense of more computations. Moving average filter (MAF) SRF-PLL structure is one such solution that consumes less resources and gives a reasonably fast response. In this work the performance of a MAF-SRF-PLL structure is evaluated in terms of unit vector distortion and settling time under various nonideal grid conditions. Its performance is compared with that of two differently designed SRF-PLLs. This evaluation gives a clear idea about possible utilizations of these PLL structures under different possible nonideal grid conditions.
Closed loop control of a grid connected VSI requires line current control and dc bus voltage control. The closed loop system comprising PR current controller and grid connected VSI with LCL filter is a higher order system. Closed loop control gain expressions are therefore difficult to obtain directly for such systems. In this work a simplified approach has been adopted to find current and voltage controller gain expressions for a 3 phase 4 wire grid connected VSI with LCL filter. The closed loop system considered here utilises PR current controller in natural reference frame and PI controller for dc bus voltage control. Asymptotic frequency response plot and gain bandwidth requirements of the system have been used for current control and voltage controller design. A simplified lower order model, derived for closed loop current control, is used for the dc bus voltage controller design. The adopted design method has been verified through experiments by comparison of the time domain response.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.