Abstract : The demand for high-voltage, high-capacity variable frequency speed control devices in industrial applications is becoming increasingly urgent, leading to the development of direct high-voltage frequency converters. This is a high-tech field with high technical content and significant development challenges. This paper introduces the working principle and typical system configuration of a three-level IGCT direct high-voltage frequency converter. The paper summarizes the starting, stopping, and bypass operation logic and interlocking logic of the high-voltage frequency converter; a programmable logic controller (PLC) monitoring and protection system for the high-voltage frequency converter is designed, and the design concept and key technologies involved in the implementation process and their solutions are explained. The system design has certain universality and is intended to provide a reference for the design, development, and use of high-voltage frequency converters. Keywords : High-voltage frequency converter, IGCT, three-level PLC. Variable frequency speed control technology has been widely used in low-voltage (380V) motors, and general-purpose frequency converter technology is also mature. High-voltage frequency converters (frequency converters with input/output voltage between 6 and 10kV, referred to domestically as high-voltage frequency converters and internationally as medium-voltage frequency converters) are a high-tech field with high technical content and significant development challenges. Many research institutions and large electrical companies both domestically and internationally have invested significant human and material resources in research on high-voltage frequency converters, which are widely recognized as one of the most promising directions in the fields of power electronics and electric drives. Fluid mechanics tells us that the flow rate of fans and pumps is directly proportional to their speed; the pressure head is directly proportional to the square of the speed; and the shaft power is directly proportional to the cube of the speed. Practice has shown that the energy-saving rate of using high-voltage frequency converters ranges from 15% to 45%, with an investment payback period of 2 to 3 years. Well-known foreign electrical companies such as SIEMENS, ABB, ROBICON, and AB have mature high-voltage, high-capacity frequency converter products on the market, but their high price is a drawback. In my country, over 95% of high-voltage, high-capacity frequency converters are imported. The manufacturing technology level of high-power power electronic devices in China is relatively low, and high-power devices such as IGCT high-voltage H-IGBTs are entirely dependent on imports. Research on high-voltage frequency converters in China is still in its early stages. The research on high-voltage frequency converters consists of the main circuit structure and parameters, the core controller, the monitoring and protection system, and the peripheral logic programmable logic controller (PLC) control system. [b][align=center]For details, please click: Functional Design and Implementation of High-Voltage Frequency Converter PLC Monitoring and Protection System[/align][/b]