A nonlinear control method of dynamic voltage restorers

Power quality and availability are becoming important issues for critical and sensitive loads. UPS is a complete solution for power quality problems, but high capital and running cost makes it an expensive solution. A series dynamic voltage restorer (DVR) provides load voltage support with a power rating equal to only a fraction of the load. At present, most of DVRs use feed-forward control because of the compensation response time requirement, this kind of control may introduce steady state error and on-site calibration problems. Although closed-loop PI regulation could not meet the dynamic response requirement, this paper demonstrates that a closed-loop nonlinear state variable control algorithm is a viable industrial solution. Practical issues, such as fault type analysis and controller design method, are included in the paper. The dynamic performance is analyzed and verified through simulation and experimental tests on a 2 kVA prototype.