A Discrete-Time Control Method for Fast Transient Voltage-Sag Compensation in DVR

Abstract

This paper presents a discrete-time domain control scheme for balanced voltage sag compensation using a Dynamic Voltage Restorer (DVR), which is recognized to be an appropriate and economical power electronic device with which to ameliorate these disturbances. The proposed control method is implemented in the synchronous reference frame (SRF), with two nested regulators, one of which includes an integral action. This algorithm has some advantages with respect to other control algorithms, such as the fact that the proposed methodology permits all the closed-loop poles of the DVR system to be placed in the desired locations in order to define the dynamical behavior with a reduction in the number of the electrical magnitudes to be measured and without the need for state observers, as occurs in traditional control methods. What is more, the well-known inner current loop implemented in other control schemes, which is employed to attenuate the resonance of the plant, is unnecessary. Furthermore, the unbalanced voltage sag compensation can be achieved by adding a “plug-in” controller and following the same methodology presented for balanced voltage sags to design the controller. The good performance of the proposed control scheme is validated by means of simulation and experimental results carried out with a 5 kW DVR laboratory prototype. The discrete-time control method is also compared with two control schemes previously proposed in literature.

Keywords

• Discrete-time systems
• dynamic voltage restorer
• power quality
• power system control
• voltage sag