Abstract
Effective sinusoidal voltage regulation is of permanent importance for grid-forming converters. Usually, the following two types of schemes are employed to achieve a high level of performance: 1) single-loop voltage and 2) dual-loop voltage-current control. The performance of both schemes has comprehensively been evaluated in this work, based on the developed discrete-time model of the LC-filtered grid-forming converter. The challenges of insufficient stability margin, constraint bandwidth, and high sensitivity to parameter variation faced by the single-loop control scheme have been addressed, if the high-performance resonant controllers are employed for voltage regulation. Alternatively, the dual-loop control does not experience such issues with the inclusion of inner-current loop which provides active damping for the overall system. The essence of the inner-current loop is identified based on the discrete root locus analysis. Also, to obtain the highest damping and most enhanced stability, the criterion for current loop design has been addressed and a method for optimal tuning of the inner-current loop is developed, where the original plant with the one-sampling delay and the current gain are considered as the equivalent plant for the voltage controller. Experimental results have verified the effectiveness of the developed method for regulation of grid-forming converters.
Highlights
Effective sinusoidal voltage regulation is an aspect of paramount importance for grid-forming converters (GFCs) to achieve a high level of performance in a lot of different applications, such as virtual synchronous machine (VSG)/droop control for grid-tied converters [1], [2], dynamic voltage restorers [3], [4], ground power units for airplanes [5], [6], uninterruptable power supplies [7]–[10], and auxiliary inverters for rail trains [11], [12], just to name a few
LC filters can cause stability problems related to resonance, which theoretically, can be passively damped by adding resisters in series or parallel with the capacitors, just like the case of LCL filters which have been the subject of significant researchers [26]–[30] in recent years
EXPERIMENTAL RESULTS The experimental setup is shown in Fig.14(a), where it can be noted that it consists of an input- and output-transformer, a diode rectifier, and an inverter
Summary
Effective sinusoidal voltage regulation is an aspect of paramount importance for grid-forming converters (GFCs) to achieve a high level of performance in a lot of different applications, such as virtual synchronous machine (VSG)/droop control for grid-tied converters [1], [2], dynamic voltage restorers [3], [4], ground power units for airplanes [5], [6], uninterruptable power supplies [7]–[10], and auxiliary inverters for rail trains [11], [12], just to name a few. In [5], [12], [15], [31], and [32], the frequency response analysis is adopted This method is not suitable in this case, as it is hard or even impossible to determine the optimum gain for the current loop to get the most enhanced stability of GFCs. Because of that, a method based on damping optimization through the discrete root locus analysis is developed which addresses the original plant, the one-sample delay, and the current gain as the equivalent plant for the voltage controller, beginning with some analytical plots to better identify the constraints faced by existing methods
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