Research On The Nodal Voltage Stability Of Microgrid

Over the years, there has been a succession of wide outages worldwide whichexposed the fragility of the traditional power system and made people realize theimportance of establishing enough distributed generations (DG) around load centers.Besides, as the threats of exhaustion of global energy resources and environmentalpollutions is becoming more and more serious, one kind of new energy powergeneration mode is badly needed to optimize the structure of the power system, soresearches on distributed generations have great significance.The use of DGs was severely limited due to its high cost of single-machineintegration and difficult control, but Microgrid has provided an effective mechanismfor DGs to fully play their roles. However, Microgrid has a more complex problem ofvoltage stability than the traditional grid due to its structure and operationcharacteristics, so an in-depth research on the voltage stability of Microgrid is veryimportant.First, the traditional Zbus power flow method is improved, the PV nodecompensation technology is used to overcome its shortcoming of unable to managethe PV nodes. The10-node Microgrid model is established and the improved methodis used to calculate its power flow under grid mode and island mode, respectively.The results are compared to the results calculated by PSCAD to prove the feasibilityand correctness of the method.In allusion to the problem that the traditional voltage stability index based on thenetwork loss equivalence has great errors on dealing with the multi-node system, apower flow calculation method is proposed based on the existence of power flowwhich has no network loss equivalence during its deduction, this method has takenload distribution conditions and node voltages into account and is able to dealMicrogrid with ramifications, it is called first-kind voltage stability index and used tojudge the stability of each branch. The second-kind voltage stability index is deduced based on the V-I characteristics, it only needs two times of power flow calculation tojudge the voltage stability of each node in Microgrid. The relationship between twokinds of indexes in analyzed and the concrete steps of voltage stability calculation forMicrogrid is determined. The method is tested in the10-node Microgrid system andthe results are compared to the results obtained by the Thevenin equivalent method tovalidate it correctness.Finally, the proposed indexes are used to study the influences of integrations ofdifferent distributed generations on the voltage stability of Microgrid，especially theinfluences of different locations and capacities of PQ-type DG and PV-type DG onthe Microgrid, and reasonable configuration schemes are given.