07-10-2010, 12:47 PM
Optimization of PI Controller Gains in Nonlinear Controller of STATCOM Using PSO and GA.pdf (Size: 238.89 KB / Downloads: 132)
This article is presented by:
N. Farokhnia
R. Khoraminia
G.B. Gharehpetian
Department of Electrical Engineering
Amirkabir University of Technology (Tehran Polytechnic)
Tehran, Iran
Optimization of PI Controller Gains in Nonlinear
Controller of STATCOM Using PSO and GA
Controller of STATCOM Using PSO and GA
Abstract
According to nonlinear operation of STATCOM, nonlinear controller has a better performance in comparison with linear controller. Regulating the DC capacitor voltage in STATCOM is a common task and can improve the system dynamic. The nonlinear control is based on exact linearization via feedback. A PI controller exists in this control system to regulate the capacitor voltage. In conventional scheme, the trial and error method has been used to determine PI controller coefficients. In this paper, the effect of PI gains on responses of Vdc, Id and Modulation Index (M) is presented. The exact calculation of optimized PI coefficients can be carried out to reduce disturbances and steady state error in DC link voltage. Therefore, in this paper, Particle Swarm Optimization (PSO) approach is used. It is shown that capacitor voltage tracks the reference value and vibrations are less than conventional status. Also, Genetic Algorithm (GA) has been used and compared with the results.
INTRODUCTION
STATic COMpensator (STATCOM) is a shunt Flexible AC Transmission System (FACTS) devices that can regulate line voltage at the Point of Common Coupling (PCC), balance loads or compensate load reactive power by producing the desired amplitude and phase of inverter output voltage. AC system is connected to a DC capacitor (energy storage device) through the inverter . There are many possible configurations of Voltage Source Inverters (VSI) and consequently many different configurations of STATCOMs . Many different control strategies such as Proportional-Integral (PI) controller, sliding mode controller and nonlinear controller have been suggested to control STATCOM. Because of nonlinear operation of STATCOM, nonlinear controller is preferred over linear controller . Moreover, in linear controller, four chosen sets of PI parameters may not be suitable for all ranges of operating points and finding these values are very time consuming and complex . In nonlinear controller, the Generalized Averaged Method has been used to determine the nonlinear time invariant continuous model of the system . This model has been used to present a nonlinear control law based on exact linearization via feedback for STATCOM . This method is particularly interesting because it transforms a nonlinear system into a linear one in terms of its input-output relationship. Only q axis current has been regulated, but it should be noted that unlike other shunt compensators, large energy storage device that have almost constant DC voltage, makes STATCOM more robust and it also enhances the response speed. Therefore, there are two control objectives implemented in STATCOM. First one is qaxes current and the second objective is capacitor voltage in DC link . The q-axes current tracks its corresponding reference value perfectly, but the capacitor voltage (Vdc) is not fixed on reference ideally because of presence of a PI controller between the reference of the d-axes current (