In order to be real-time and accurate compensation in phase railway the fundamental reactive current and load side harmonic current, make the power factor of three-phase power supply side is 1, so as to achieve three phase equilibrium. Traditional use of orthogonal trigonometric function characteristics, use adder, multiplier, integrator, phase-locked loop can achieve the fundamental active current and reactive current detection, can avoid a lot of matrix and the inverse matrix calculations, make the whole operation circuit of low cost, the method is simple, easy to implement, but as a result of single-phase phase-locked loop characteristic of the phase delay for locking phase of voltage deviation, and low pass filter inherent delay, serious impact on its current initial values. Based on the above problem, considering the average filter characteristic of rapid detection performance, put forward a kind of load balance based on Scott transformer power supply model of the fundamental active current and fundamental reactive current improved detection methods, with average filter good response speed instead of low pass filter and single-phase PLL lock in the phase of the measured voltage. Simulation verify the accuracy and superiority of the method, the load side for single-phase fundamental wave active and reactive current and harmonic current effect is ideal.