Research On Three Phase Power Flow Of Distribution Network Considering Neutral Voltage Parameters

Because of the three-phase symmetry of the transmission network,the single-phase model can be used,and the requirements can be met only by calculating the single-phase power flow.In the distribution network,due to the asymmetry of three-phase load and network structure,it is necessary to calculate the three-phase power flow.When calculating three-phase power flow in ungrounded distribution network,the constraint condition that the sum of three-phase currents is 0 needs to be considered.Some literatures use the current injection Newton method to deal with this problem,and add the constraint condition that the sum of three-phase currents is 0.In order to make the number of constraint equations equal to the number of state variables,it is necessary to take the three-phase power at the node as the state variable to be solved.This treatment method is inconsistent with the power given value of distribution load.To solve the above problems,a three-phase power flow calculation method considering the neutral point voltage parameters is proposed.In this method,the constraint condition that the sum of three-phase currents is 0 is added to the power flow calculation of neutral ungrounded wye distribution network,and the neutral point voltage is taken as the state variable to participate in the calculation.In this way,in the process of solving with current injection Newton method,two equations of real part and imaginary part of neutral point current deviation are added on the original basis.At the same time,the real part and imaginary part of neutral point voltage are added on the original basis,so as to ensure that the number of equations is equal to the number of States to be solved,and the equations can find a unique solution.Firstly,the admittance matrix considering the neutral point as the variable is established,and the current phasor deviation equation of PQ node and PV node corresponding to phase to ground load and phase to phase load and the voltage amplitude deviation equation of PV node are listed.From this,the constant term matrix elements in the basic Jacobian matrix are derived,and then the corresponding correction term matrix elements are derived according to the phase to ground load and phase to phase load.Finally,the Jacobian matrix elements related to the PV node are supplemented to form a complete Jacobian matrix.By solving the correction equation,the correction quantity and the state variable are obtained.The accuracy of the three-phase power flow calculation method of distribution network considering neutral voltage parameters proposed in this thesis is verified by IEEE-4 node standard test system.The neutral ungrounded terminal of IEEE-4 node standard test system is connected to asymmetric load,and compared with the comparison method to verify the rationality of this method.The rationality of this method for large-scale system is further verified by 292 bus system.Compared with the existing literature,it solves the problem of giving the active power of PQ node and PV node in the existing methods,and can directly calculate the neutral point voltage,making the operation more concise.