Research On Dynamic Voltage Restorer

Dynamic Voltage Restorer(DVR), used to compensate voltage sags of power grid toprotect loads from impact of voltage sags，is one kind of electronics and electric devices,which has more benefits compared with traditional compensating devices for compensatingquality of power net.There are many cases that cause voltage sags of power grid，the most common casesare short-circuit fault, start-up of high-power induction motors and lightning strikeaccidents. Generally speaking, there are always phase changes in voltage sags. Whenvoltage sags which caused by short-circuit fault spread though the line, the phase changeangle is less than60°, although the distance between the fault point and PCC affects thephase changes. The measurement technique on voltage sags is one of the most importanttechniques for DVR, and it must detect voltage sags quickly and accurately. The mostcommon measurement techniques for voltage sags are detecting voltage sags by RMS,detecting voltage sags by acquiring fundamental harmonic voltage, detecting voltage sagsusing d-q transformation theory and using Fourier based algorithm minimizing quadraticerror. When using Fourier based algorithm minimizing quadratic error to detect voltagesags, if increasing the sampling frequency of the system, we can cut down some time fordetecting.The phase locking technique is also one of the most important techniques for DVR.The tracking speed of phase locking technique should be slow enough to protect load fromimpact of phase jumps. The most common phase locking techniques are technique based ondetecting zero crossing point of voltage, technique based on low-pass filters and techniquebased on d-q transformation theory. The setting time of phase locking technique based ond-q transformation theory should be1/6second approximately and there must be noovershoot for SPLL. To avoid impact of harmonic voltage on phase locking, we use a harmonic filter based on SOGI.DVR prototype used for protecting three-phase four-wire power net was manufactured.The work contains the design of inverter, the development of monitoring system and so on.Kinds of voltage sag causes were carried out for experimental research on compensation.