In order to solve the problem that traditional ip-iq method can not accurately extract fundamental positive active and reactive current in three-phase asymmetric grid, three-phase voltage is added to the abc/α-β coordinate conversion synchronously, and numerical method is proposed to seek coordinates of instantaneous fundamental positive active (reactive) current vector in α-β coordinate system, and design TMS320F2812 as the core sampling system. It is proved that the way to get fundamental positive compensation command is accurate comparing with traditional ip-iq detection under the conditions of three-phase asymmetric grid in MATLAB / SIMULINK simulation environment.