Study On The Control Of Inverter And Islanding Detection Based On Distributed Generation

As the complementarity of centralized generation, distributed generation systemcan promote the society to the development way of environmental protection, greenenergy, energy saving.The distributed generation technology will be the one of thedevelopment trend of intelligent power grid, how to effectively solve the grid inverter ofthe dead zone effect and switch frequency problem,and how to solve the probrem ofislanding detection when power balance between the output of inverter and theload,which is the key of distributed generation reliable operation and safety stable.Sothe research of the power grid inverter control and islanding detection is verysignificance thing.The main contents are as follows:①The article discusses and intrudeces the basic concepts and features of thedistributed generation, and the key technology research and significance of the gridpower system.②Various of micro-power mathematical models and its features were analied,asimplified photovoltaic cell,solid oxide fuel cell and super capacitor models werebuilded by using simulink software.According to the different characteristics of eachmicro-power,do sumulation analysis to each micro-power from diferent emphasespoint,the simulation results show that the micro-power models can simulate the actualpoeration very well.③When the distributed generation is connected with the big power system, thehigh eficiency and high frequency of the inverters and its related control technology isthe key research of distributed generation inverters,the main control problem is inverterdead zone dffect of control and inverter output sine wave can real-time tracking thenetwork voltage current frequency,phase and grid capacity of a given change,make thecurrent total of distortion become low,so as to reduce the influence of power gridharmonics. A method for hysteresis current control considering dead-time effect isproposed.Analyze the effect of voltage inverter and the features of bridge arm based onthe positive half-cycle and the negative half-cycle of filter inductor current ispresented, It can be drawn that dead-time just exists in the period of currentcommutation and in other time special IGBT trigger pulse was blocked by thedetermination of current direction.This means that the error pulse caused by dead-timeonly existed in the area of current zero crossing point and the influence of dead-time was reduced effectively.Based on the control of dead-time, combining with thecharacteristics of hysteresis current control,analysis the appropriate interval inverter ofswitching frequency quantitatively,then change the hysteresis-band real-time to achivethe fixed switching frequency of grid-connect inverter,so the method can reduce theswitching loss and improve power quality.④Introduce the definition of the islanding and some related standard of islandingdetection,then the article shows that som common test passive and active detectionmethods of islanding detection. It is difficult to detect islanding in grid-connectedgeneration research，especially when power balance between the output of inverter andthe load.A method of reactive power disturbance based on Q-f droop curves onislanding detection of grid-connected inverter system is proposed in this paper. Thisnew method forces the photovoltaic grid-conntcted generation to lose its stableoperation by drawing into a linear function relies on a Q-f droop curve between loadreative and frequency.Then detects the system frequency deviation by real time，anddraws into the function of reative disturbance to form a positive feedback effect，so thefrequency drifting is accelerated and the frequency of the output voltage of thephotovoltaic grid-connected inverter exceeds a preset threshold value，and then theislanding will be detected.Simulation shows that the proposed methed possessesnon-detection zone and fast detection speed and little influence on power quality.