Three-phase static series voltage regulator control algorithms for dynamic sag compensation

Momentary interruptions and voltage sags are responsible for many of the power quality problems found in typical industrial plants. A common solution to this problem is the installation of uninterruptible power supplies (UPS). However, these are costly and require maintenance. A cost-effective alternative is the use of static series regulators rated a fraction of the load power. The regulators provide voltage support by injecting a voltage in series with the load. The structure presented in this paper consists in transformer coupled voltage source inverters fed from a diode bridge rectifier converter connected to the AC supply. The paper discusses implementation and control issues. Steady state compensation capability curves are presented. Are proposed control algorithms that ensure a fast dynamic voltage restoration and are insensitive to the type of faults, disturbances and harmonics present on the power network. Performance is illustrated for typical single and three-phase faults. The dynamic performance is verified on DSP based prototype power compensators