In CNC machine tools, the electric spindle usually adopts the frequency conversion speed control method. There are mainly three control methods: ordinary frequency conversion drive and control, vector control drive drive and control, and direct torque control.
Ordinary frequency conversion is scalar drive and control, and its drive control characteristic is constant torque drive, and the output power and speed are proportional. The dynamic performance of ordinary variable frequency control is not satisfactory enough, the control performance is not good at low speeds, the output power is not stable enough, and it does not have the C-axis function. However, it is cheap and simple in structure, and is generally used in grinding machines and ordinary high-speed milling machines, etc.
Vector control technology imitates the control of DC motors, orientates the rotor magnetic field, and realises the drive and control by means of vector transformation, which has good dynamic performance. The vector control drive has a large torque value at the time of first start-up, coupled with the simple structure of the motor spindle itself, the inertia is very small, so the start-up acceleration is large, and it can be achieved to reach the permissible limit speed instantaneously after start-up. This kind of drive and there are two kinds of open loop and closed loop, the latter can achieve position and speed feedback, not only has a better dynamic performance, but also can achieve the C-axis function; while the former dynamic performance is a little worse, and does not have the C-axis function, but the price is cheaper.
Direct torque control is another new type of high-performance AC speed control technology developed after vector control technology, with novel control idea, simple and clear system structure, more suitable for high-speed spindle drive, and better able to meet the requirements of high-speed spindle high speed, wide speed range, high-speed instantaneous quasi-stopping dynamic and static characteristics of the requirements of the field of AC drive, has become a hot technology.
