Owing to a lot of nonlinear constraints to be dealt with

the efficiency of alternating current optimal power flow(ACOPF)algorithm is not high. Moreover

it will not converge when handling power systems with small reactance branches and heavy load buses. In contrast

direct current optimal power flow(DCOPF)can solve problems fast and handle pathological power systems but fails accuracy. In the circumstance

a modified direct current optimal power flow(MDCOPF)algorithm based on the net loss equivalent load model is proposed. First

the net loss equivalent load is used to replace the line loss and the accuracy of DCOPF is improved effectively. Then

the MDCOPF is solved by using the simplified primal-dual interior point method to improve the computational efficiency. Finally

the simulation results of IEEE 30-bus

300-bus

Polish 2736-bus

and 3120-bus test systems prove satisfactory in computational accuracy and efficiency. In addition

it has a strong computing capability for pathological power systems without the solution of the alternating current power flow.