Abstract : This paper proposes the replacement of DC speed regulation with AC inverter speed regulation, analyzes several typical inverter control methods, gives selection calculation formulas for inverters and their peripheral equipment, outlines the flexible application of PLC in inverter speed regulation, briefly describes some issues that need attention during inverter and PLC installation, and finally introduces the debugging of the inverter speed regulation system. Keywords: Inverter, PLC, Frame milling machine, Speed ​​regulation system 1 Introduction DC electric drive and AC electric drive were invented in the 19th century. Because DC drives are easy to implement for voltage and magnetic field regulation, and have mature control theories and systems, they can meet the ever-growing demands of industrial production for wide speed range, high precision, and rapid response. Therefore, for most of the 20th century, high-performance speed control systems used DC speed drives, while constant-speed electrical drives, accounting for approximately 80% of the total electrical drive capacity, used AC electrical drives. This division of labor was a globally recognized pattern for a period. The control principles of AC speed drives were established early on. While techniques such as voltage reduction speed control for asynchronous motors and rotor resistance speed control for wound-rotor asynchronous motors have been put into practical use, they have some shortcomings in terms of speed range, stability, reliability, and maintainability, limiting their application. After 1965, due to the continuous development and progress of power electronics technology, along with the proposal and improvement of new control theories, AC speed drives, especially high-performance variable frequency drives, have experienced rapid development. The cascade speed regulation of wound-rotor asynchronous motors, the commutatorless motor speed regulation using frequency converters, and the variable frequency speed regulation of squirrel-cage asynchronous motors have been successively put into practical use, completing the foundation for AC speed control drives with variable frequency speed regulation as the mainstream. The application of modern vector technology has enabled AC speed control drives to also possess the high performance of DC speed control drives. The commutator of a DC motor is its main weak point, limiting important technical indicators such as single-unit capacity, overload capacity, maximum voltage, and maximum speed, and also causing considerable trouble in the manufacturing and maintenance of DC motors. These shortcomings have significantly limited the application of DC motors. In contrast, squirrel-cage asynchronous motors in AC variable frequency speed control drives have a simple structure, are robust and durable, reliable in operation, convenient in maintenance, low moment of inertia, and good dynamic performance. Their single-unit capacity, voltage level, and maximum speed are all superior to those of DC motors. Currently, high-performance AC variable frequency speed control systems are fully comparable to DC speed control systems and can be used in situations where DC motors are unsuitable. The old dominance of DC speed control drives has been broken, and replacing DC speed control drives with AC speed control drives has become possible. [b][align=center]For details, please click: Application of Frequency Converters and PLCs in a 9-meter Gantry Milling Machine[/align][/b]