In CNC machine tools,Electric spindleUsually, variable frequency speed regulation is used. There are currently three main control methods: universal variable frequency drive and control vector control drive and control, as well as direct torque control. So, what are the differences between these three control methods?

The common frequency conversion is scalar drive and control, with constant torque drive as its driving and control characteristics, and output power proportional to speed. The dynamic performance of ordinary variable frequency control is not ideal. Poor control performance at low speeds, unstable output power, and unavailable C-axis function. But the price is cheap. The structure is simple and generally used for grinding machines and ordinary high-speed milling machines.

Vector control technology simulates the control of DC motors and is oriented by the rotor magnetic field. The vector transformation method is used to achieve driving and control, and has good dynamic performance. The vector control driver has a large torque value at the beginning of startup. The electric spindle itself has a simple structure, low inertia, and high startup acceleration, and can achieve the allowable maximum speed after startup. This type of driver has two types: open-loop and closed-loop. The latter can provide feedback on position and speed. It not only has better dynamic performance, but also can achieve C-axis functionality. The former has poor dynamic performance and no C-axis function, but it is cheap in price.

Direct torque control is a new high-performance AC speed regulation technology developed using vector control technology. Its control concept is novel, the system structure is simple and clear, and it is more suitable for high-speed electric spindle drive, which can meet the requirements of high-speed electric spindle. The dynamic and static characteristics of high-speed wide speed range and high-speed instantaneous quasi stop have become popular technologies in the field of AC drive.

From the comparison, it can be seen that direct torque control is more suitable for driving electric spindles. The designed electric spindle direct torque control system has good dynamic and static characteristics, and the direct torque control method is applied to the electric spindle drive control system. It is feasible and more suitable for the fast response requirements of high-speed CNC machine tool drive control systems.