Abstract
Voltage control of standalone converters with LC filter is usually based on proportional-resonant or proportional-integral controllers, which often require further active damping methods to achieve stability. These solutions place design constraints in the selection of the closed-loop pole locations which limit the achievable bandwidth and increase the design complexity. In contrast, in state-space based controllers, the closed-loop poles can be placed freely through state feedback, which makes them particularly suitable for high order plants and/or low sampling frequencies. Among the modern control methods, direct pole placement is a simple technique that enables the establishment of a straightforward relationship between outcome and design, as opposed to more advanced approaches. This paper presents a discrete state-space voltage controller for standalone converters with LC output filter. The proposed method combines the direct pole placement technique with a virtual disturbance observer in order to compensate the effects produced by the load and model mismatches. The design process takes into account both the filter parameters and the sampling frequency, rendering the performance of the obtained controller independent of both. The result is a streamlined design procedure that leads to consistent outcomes for a wide range of plant parameter variations, requiring only one input: the desired closed-loop bandwidth.
Highlights
Voltage source inverters (VSI) have commonly been used for uninterruptible power supplies (UPS), distributed generation systems (DG), dynamic voltage restorers (DVR), ground power units (GPU) for airplanes and other high-performance AC voltage sources
In order to meet the requirements in terms of voltage waveform quality, an LC filter is commonly used at the output of the inverter which brings up the issue of damping the LC resonance otherwise system stability and/or waveform quality might be compromised
Dual-loop control strategies [4] have been widely employed in DG and UPS applications due to their good performance and inherent robustness
Summary
Voltage source inverters (VSI) have commonly been used for uninterruptible power supplies (UPS), distributed generation systems (DG), dynamic voltage restorers (DVR), ground power units (GPU) for airplanes and other high-performance AC voltage sources. Dual-loop control strategies [4] have been widely employed in DG and UPS applications due to their good performance and inherent robustness They involve the usage of an outer voltage loop to ensure steady-state tracking performance and an inner current loop to provide fast dynamic compensation for system disturbances and improving stability. The controller presented in [23] is developed in the discrete-time domain but it relies on the minimization of the output impedance at the fundamental frequency to increase the overall robustness This strategy requires the usage of bandpass filters to avoid differentiation, a tradeoff between noise amplification and the derivative range has to be established. As opposed to classical transfer function based designs, the closed-loop poles are placed in suitable locations regardless of the LC filter resonance and sampling frequencies and without requiring further damping nor decoupling terms.
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