Research On Least Square Method Power Flow Algorithm For Ungrounded Distribution Network And Voltage Regulator

Three-phase power flow ealculation in distribution network is the basis of distribution network analysis,the key and main content of distribution management system.With the development of power industry,three-phase parameter asymmetry and three-phase load imbalance in distribution network are becoming more and more prominent,so three-phase power flow calculation should be carried out.In China,the neutral ungrounded operation mode is widely used in medium-voltage distribution system,while the existing distribution network power flow is mostly aimed at the grounded system,the research on the power flow calculation of ungrounded distribution network is few and insufficient.Because of the zero sequence current constraint,the zero sequence current constraint equations must be introduced into the power flow equations,which make the equations redundant and difficult to solve.In order to make the nvunber of equations equal to the number of state variables to be solved,the three-phase power of a terminal can not be independently given,which is not in according with the actual situation of distribution load.Based on the current-injection Newton power flow algorithm and the idea of least square method,this paper takes the sun of weighted residual squares as the objective function,sets different weights for the terminal current-injection residual and zero-sequence current residual,expects to get a set of state solutions,the objective function reaches the minimum value,and thus achieves the optimum.Distribution network feeder is long,load varies greatly,which easily causes the voltage of some terminals not to meet the requirements of power supply.The voltage regulator can be adapted to the distribution network to automatically adjust the voltage level of the distribution network.The adnittance matrix mathematical model of three-phase voltage regulator is established by introducing the impedance of voltage regulator,which can be applied to Newton method and other algorithms.Double-layer cycle is used in the power flow program,outer cycle is used to calculate the tap stalls of regulator,and inner cycle is used to calculate power flow under a certain tap stalls.The impedance of voltage regulator is very small,and the voltage drop on it is also very small.Ignoring the impedance of the voltage regulator has little influence on the calculation results.The admittance matrix model of voltage regulator-line unit can be established,which can be well applied to Newton method and other algorithms.Through the example analysis,it is proved that the least square method power flow algorithm of ungrounded distribution network can converge reliably and achieves a good accuracy.Distribution network voltage regulator can automatically track load:fluctuation and adjust tap stalls,effectively improve the voltage level to meet the requirements of distribution network voltage supply.