Comprehensive control for unified power quality conditioners

Abstract

This paper presents a comprehensive control strategy for unified power quality conditioners (UPQCs) to compensate for both voltage and current quality problems. The controllers for the series and shunt components of the UPQC are, equally, divided into three blocks: À main controller, which deals with the fundamental-frequency issues such as active and reactive power flow;`harmonic controller, which ensures zero-error tracking while compensating voltage and current harmonics;´the set-point generation block, which handles the different control objectives of the UPQC. The controller design procedure has been simplified to the selection of three parameters for each converter. Furthermore, the proposed strategy can be implemented measuring only four variables, which represents a reasonable number of sensors. In addition, a pulse width modulation (PWM)-based modulation with fixed switching frequency is used for both converters. The proposed control strategy has been validated experimentally under different conditions, including grid-frequency variations.

All-Pass-Filter-Based Active Damping for VSCs With LCL Filters Connected to Weak Grids

“…Alternatively, Huerta et al [16] select the controller gains by using a Linear Quadratic Regulator (LQR), obtaining robust performance in noisy environments. The design of the LQR controller has also been addressed by Ochoa et al [11], obtaining similar conclusions. As an alternative, Busada et al [17] propose a high-order controller that makes it possible to choose the closed-loop poles location with a single loop.…”

“…Bao et al [10] solved this limitation by using an observer and the resulting closed-loop system was robust. In addition, Ochoa et al [11] propose a Kalman filter to estimate the LCL filter state variables in noisy environments, obtaining accurate estimations. Among multivariable controller alternatives, the "virtual resistor" is commonly applied to emulate the effect of a resistance by using an inner control loop [12].…”

Comprehensive Design and Analysis of a State-Feedback Controller for a Dynamic Voltage Restorer

“…With this pole-placement alternative, the closed-loop pole position is chosen in order to minimize a specific cost function, and it is commonly known as LQR [48]. This alternative produces robust controllers and it is an adequate choice for power electronics converters [37,49].…”

“…where superscript T means transposed, while Q and R are weighting matrices that are used to tune the controller. Detailed information regarding the design procedure can be found in [36,37], and it is not included here for simplicity. For the scope of this paper, the transient speed of both alternatives (LQR and manual placement) was made similar.…”

“…Huerta et al [36] designed the controller gains of a VSC with an LCL filter by solving the LQR problem, with accurate results. A similar approach was applied by Ochoa et al [37] for a Universal Power Quality Conditioner (UPQC). A basic SF controller for DVRs was applied in our previous work [38].…”