JPS5749378A - Controller for 3-phase induction motor - Google Patents

Abstract

PURPOSE:To obtain an ideal operational characteristic of a 3-phase induction motor by using a mode selection circuit adapted to select gate phase shifters for either normal/reverse rotation or D.C. braking according to logic outputs of two discrimination circuit parts and zero current detection circuit parts. CONSTITUTION:When a speed reference signal E1 is lowered in the level within a normal rotation command, the output E3 of a speed control amplifier 9 turns to the normal direction and the logic output L2 changes from L to H. The output E3 moves to E5 with a current limiting circuit 10 and a current controlling amplifier 11 so as to maintain the zero level until preparations are established for either braking or reverse rotation mode. While the logic output L2 and L3 are at H, with the output of a zero current detection circuit 13, hence the logic output L1 turning to H from L, a mode switching logic circuit 16 turns OFF a gate phase shifter 17 for normal rotation (circuit 4) and the logic output L6 goes to H to turn ON a gate phase shifter 19 for D.C. braking (circuit 6). When the command is changed to the reverse rotation, the logic output L3 of a rotation direction detection circuit 15 receives a D.C. braking in the period of H and turns to L so that the logic circuit 16 switches the logic output L5 to H thereby turning ON a gate phase shifter 18 for reverse rotation (circuit 5).