Vector control is by controlling the inverter output current size, frequency and phase, used to maintain the flux inside the motor as a set point, to produce the required torque. It is inspired from the DC motor speed control method, the use of modern computer technology to solve a large number of computational problems, making the vector control method has been successfully implemented as a high-performance induction motor control.
Asynchronous motor vector control is based on the dynamic mathematical model. The derivation of the mathematical model is a specialized problem. No mathematical deduction here, only a brief description of the concept of vector control.
(1) DC motor speed characteristics.
DC motor has two sets of windings, that is, excitation windings and armature windings, their magnetic fields differ from each other in space by π / 2 electrical angle, and the two sets of windings are independent of each other in the circuit. DC motor excitation winding current IF generated when the main flux ΦM armature winding load current IA, resulting in a magnetic field ΦA, the two magnetic fields in the space of mutual difference π / 2 electrical angle. DC motor electromagnetic torque can be used (2-4) said, that is
T = CTΦMIA
When the excitation current IF is constant, ΦM the size of the same. The DC torque generated by the DC motor is proportional to the armature current IA, so that the speed can be adjusted by adjusting ΦA. When IA is certain, the size of the control IF can be adjusted ΦM, also can speed. This means that the DC motor can be regulated only by adjusting one of the two magnetic fields. This speed control method makes the DC motor has good control performance.
(2) speed characteristics of induction motor.
Although there are two sets of asynchronous motor winding, that is, stator windings and rotor windings, but only the stator windings and external power phase, the stator current is drawn from the power supply current, the rotor current is induced by electromagnetic induction current. Therefore, the stator current of asynchronous motor should include two components, namely excitation component and load component. The excitation component is used to build the magnetic field; the load component is used to balance the rotor current magnetic field.
(3) DC motor and AC motor comparison.
① DC motor excitation circuit, armature circuit independent of each other, and the induction motor will both focus on the stator circuit.
② DC motor main magnetic field and armature magnetic field mutual difference π / 2.
③ DC motor is by adjusting one of the two magnetic fields to adjust the speed, while the asynchronous motor can not.
(4) Consideration of speed regulation of induction motor.
Since DC motor speed control has so many advantages that the performance of the motor after speed regulation is very good, then the induction motor stator current can be decomposed into excitation current and load current, and separately controlled, and they formed by the magnetic field In space can also be the difference between π / 2? If you can achieve the above ideas, asynchronous motor speed control and DC motor can be almost the same.