CONTROLLER WITH AUTOMATIC FIELD-WEAKENING CONTROL

PURPOSE:To cause a field control to follow a speed change by detecting and amplifying the change of a motor terminal voltage, by comparing a weakening start voltage and a subtracted value with the existing voltage and with a base field current reference value to control a field current. CONSTITUTION:A voltage coinciding with a speed reference is applied from a speed regulating device 1 to a motor armature 2 and a field current reference signal is applied from a field current controller 4 to a field circuit 3. This time and the last time armature applied voltages 11 and 12 are detected by a detecting element 6 so that a change between them is detected 13, amplified 14, operated 15 together with the output of a weakening start voltage setter 5, compared with this time voltage and amplified 7. The output of an amplifier 7 and that of a base field current reference 8 are subtracted 9, limited 10 and inputted to a field current controller to control the current of a field 3. Thus, a field control quickly follows the abrupt speed change of a motor to prevent the overvoltage of an armature terminal.