Study On Smooth Start-stop And Energy Self-recovery Control Technology Of Dynamic Voltage Restorer

With the rapid development of economy and the continuous advancement of modernization construction,electric energy has become one of the most widely used energy sources in production and life because of its clean,convenient,practical and efficient characteristics.However,in recent years,the scale of power system is increasing,power electronics technology is widel y used and developed rapidly,resulting in the increasingly serious power quality problems.And the gird voltage sag has become the most common power quality problem.In addition,the extensive application of sensitive load in high-end manufacturing industry makes the power users more and more demanding for power quality,especially for the grid voltage sag.Dynamic Voltage Restorer(DVR)is connected in series between the system and the sensitive load.It can solve many power quality problems such as the voltage sag,flicker,unbalances and so on.It has become an effective power equipment to ensure the normal operation of the sensitive equipment.However,phase angle jumping is often accompanied by the grid voltage sag,DVR not only compensates the grid voltage sag,but also suppresses the phase angle jumping,otherwise it will affect the normal operation of the phase sensitive load.Moreover,extra charging devices are usually used to recover the energy of the DC side of energy storage DVR,but it will result in increased cost and volume.In order to solve the above problems,the smooth start-stop and energy self-recovery control technology are proposed to solve phase angle jumping and DC side energy recovery of energy storage in the stable operation range.In this paper,the topology and working principle of dynamic voltage r estorer are introduced in detail and the limit output voltage range of DVR under the stable operation is analyzed.Considering the influence of the voltage sag depth,load fluctuation and load capacity of shunt converter on the output capability of DVR,the output voltage range of DVR is analyzed deeply.The mathematical models of converters are computed,the relationship between the modulation ratio of series converter and the gird voltage,load magnitude,DC voltage and converter circuit parameters is obtained,based on the load capacity of the shunt converter of keeping the DC voltage stable.Thus,the maximum output capability of DVR based on DC side stability is determined under the fixed circuit parameters.Considering that the grid voltage sag is often accompanied by phase angle jumping,and the traditional minimum energy compensation will also cause phase angle jumping in load voltage when the grid voltage sag and restore.Therefore,a minimum energy of smooth start-stop control strategy is proposed.DVR can smooth into and smooth out the minimum energy compensation using this control strategy.So that it can solve the problem of load voltage phase angle jumping as well as reduce the output of active power.In addition,taking into account the maximum output capability of DVR,the reference voltage is dynamically adjusted so that it is within the limit level during the compensation.Meanwhile,in order to realize energy self-recovery on DC side of energy storage DVR,the phase relationship between the load voltage and the grid voltage and the flow of active power in the system are analyzed,and the DVR energy self-recovery strategy based on phase angle control is proposed,which can guarantee the energy self-recovery of DVR when the gird voltage is normal.Therefore,the extra charging device is eliminated,as soon as with the smooth start-stop control technology in the initial and final stages of self-recovery,the amplitude of the load voltage is not affected during the whole energy self-recovery process,and the phase angle jumping is well suppressed.Finally,the simulation and experimental results verify the correctness of the theoretical analysis.