Voltage/Frequency Speed Control of CNC Machining Center’s Spindles Retrofitted by Delta ASD-S 4.5kW High Performance VFD

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CNC machine tools include an essential element known as the spindle, which must operate at high speeds and sustain a consistent velocity even when torque fluctuates during use. Generally, this spindle is powered by an alternating current (AC) electric motor that serves as the torque source, facilitating the required rotational speed for various cutting tasks. This article aims to explore a method for controlling speed through variable frequency voltage control (VVVF or V/f), specifically for CNC machine spindles. Initially, a model of rotational speed is created based on Newton's second law, taking into account the interactions among the AC motor, gear system, and rotating spindle. Next, a mathematical representation of the induction motor is developed in the d-q axis framework to assist in crafting the speed controller. Subsequently, a closed-loop speed control mechanism is initiated; this process begins with defining a reference speed and then processing these values through an electrical circuit to produce the necessary voltage and frequency before supplying them to the AC motor model. System modeling and performance assessment concerning speed control and dynamic response under torque load were conducted using MATLAB/Simulink. The V/f control system was established with a high-efficiency Delta ASD-S 4.5kW Variable Frequency Drive (VFD) sourced from Delta Electronic Inc. in Taiwan, aimed at performing speed control regulation on the spindles mounted on the CNC Machining Center model ARCO A-56 APC. To manipulate the reference and system response, a PI controller was utilized in control loop.