Abstract : This article briefly introduces the development, types, and working principle of high-voltage frequency converters. It provides a detailed description of how to select the right frequency converter based on load characteristics. Furthermore, it briefly discusses how to select frequency converters for energy saving in coal mines. Keywords : High-voltage frequency converter, type selection. The application of high-voltage frequency converters in domestic coal mine systems is still limited, especially for 6 kV fans, hoisting winches, and water pumps. These are all stationary equipment with large motor power, exceeding 300 kW, indicating significant potential for energy saving through technological upgrades. Even with other energy-saving methods, none have achieved the best results compared to using frequency converters, yet high-voltage motors in coal mines have not been widely adopted. The reasons for this situation are twofold: firstly, the withstand voltage of power electronic devices is not high (generally only 1.2 kV), and corresponding high-voltage frequency converter products have not yet been introduced domestically; secondly, their reliability is not very high. These continuously operating equipment in coal mines must have high safety guarantees. The application of high-voltage frequency converters in coal mines should be selected based on the converter's power, control method, and load type to meet the requirements of different loads, achieve reasonable matching and optimal control, and obtain better energy-saving effects. 1. Types of High-Voltage Frequency Converters There are two main types of high-voltage frequency converters: one is the high-low-high type; the other is the high-high type. The latter is further divided into multi-functional technology type and high-voltage-resistant component type. The high-low-high type high-voltage frequency converter, also known as an indirect high-voltage frequency converter, consists of input and output transformers and a low-voltage frequency converter. The input transformer is a step-down transformer, which reduces the high-voltage power supply to the voltage allowed by the frequency converter. After passing through the low-voltage frequency converter, it is then stepped up by the output transformer (step-up transformer) before being supplied to the high-voltage motor. This type of high-voltage frequency converter obviously undergoes two voltage conversions, which increases power loss and affects energy-saving effects. At the same time, it occupies a large area and generates a large amount of high-order harmonics, exhibiting significant drawbacks. However, its technical difficulty is relatively low, and the investment is relatively inexpensive, making it more suitable for variable frequency speed control of high-voltage motors with a power of less than 200 kW. [indent][b][align=center]For details, please click: Application and Rational Selection of High-Voltage Variable Frequency Drives in Coal Mines[/align][/b][/indent]