I. Introduction High-voltage variable frequency coordinated control technology, or HCU technology for short, refers to a comprehensive coordinated control technology in high-voltage variable frequency application systems that achieves coordination between power frequency and variable frequency operation modes, speed control and opening or valve control, and among equipment within the same system. The successful application of this technology has fundamentally solved the impact of high-voltage frequency converters on system safety and stability during production system applications, further optimizing system processes and improving energy-saving effects. Simultaneously, the application of this technology allows for easy engineering applications of high-voltage frequency converters without requiring significant changes or modifications to the hardware ports and control logic of DCS and other control systems on-site, achieving variable frequency energy saving of high-voltage equipment and perfect integration with production processes. It truly realizes high reliability, safety, and stable operation of the variable frequency application system, while saving substantial project investment and construction costs, achieving optimal system control performance and energy-saving benefits. II. Explanation of HCU Technology HCU technology, from the perspective of high-voltage variable frequency application systems, focuses on researching and addressing the special operating processes and control structures of various industries. From the overall system design perspective, it solves the system safety, stability, and production system continuity issues in the event of high-voltage frequency converter failures during project implementation and operation. This fundamentally solves the problem of system safety and self-processing stability when faults occur in high-voltage frequency converter applications. HCU technology is particularly prominent in high-voltage frequency converter applications in the following aspects: 1. Safety and Stability: Because HCU technology focuses on the system safety handling mechanism when high-voltage frequency converters fail in applications, the integrated design of the frequency converter bypass device effectively solves problems such as how to achieve a smooth switch from frequency converter to power frequency in the case of frequency converter failures in the induced draft, primary air, and condensate systems of the power industry, and how to ensure that the control indicators of the unit operation process do not exceed the standard, do not fail to protect, and do not stop the boiler or the machine, thus jeopardizing system safety. The integrated design of HCU and the frequency converter application system provides more rigorous protection performance in terms of control logic processing speed, interlocking, countermeasures against malfunctions, and protection against misoperation. The system design is more professional, more targeted, and more safe and reliable. This technology uses an independent CPU and control port, operating independently from the control part of the frequency converter itself. When the frequency converter fails, the independent CPU can continue to operate, handling the automatic coordination of power frequency operation and damper or valve opening adjustments in the event of a frequency converter failure, meeting the process control requirements of industrial control systems such as DCS. Even in the event of a severe failure such as CPU or complete power loss during operation, this coordinated control technology can still transfer equipment control to remote control at the moment of final failure, enabling monitoring and adjustment of equipment used in power frequency conditions such as high-voltage switches, dampers, or valves. It also achieves seamless switching, ensuring high safety and reliability in production operation. This technology is designed and developed based on the DCS backend framework and can be equipped with dual CPU hot redundancy backup and hot-swappable I/O cards, enabling complete fault handling and maintenance during system operation, maximizing the fulfillment of on-site requirements for high-voltage frequency converter applications. The system safety structure is shown in Figure 1. Furthermore, the HCU technology integrates the issues of equipment operation mode conversion, control object change, safety protection, characteristic balancing, and inter-equipment coordination into targeted high-speed calculations. Its processing power, response speed, and the tightness of equipment and fault logic coordination within the frequency converter system are all higher than the system's processing capacity for frequency converter equipment. Furthermore, the coordinated control technology also possesses fault location judgment and self-processing mechanisms. For example, when speed regulation fails during variable frequency operation, the system automatically switches to 50Hz power frequency operation, handing over process control to the actuator. When jamming or abnormalities occur in the baffle adjustment, the system can promptly transmit alarm information to the control room for timely handling by operators. Simultaneously, it provides complete information on fault time, location, cause, and associated status, facilitating maintenance and handling; in this case, troubleshooting can be performed at the equipment level, without escalating to the DCS system level, greatly reducing the risk of fault handling. Designed in an integrated manner based on the technical characteristics of high-voltage frequency converters and the structure of application systems, HCU control technology enables resource sharing and efficient processing and application within the application system, resulting in higher performance in information processing, security defense, and control implementation. As the core control technology for high-voltage frequency converter systems, the HCU employs a CPU processor independent of the frequency converter control system, and is a system-level product and equipment-level application developed based on a mature system architecture, hardware foundation, and software platform. Therefore, it possesses high system stability performance. The HCU is organically integrated with the frequency converter, yet achieves complete physical isolation, ensuring the system can operate and be controlled independently. Hardware-wise, a dual-CPU redundant structure can be selected, with hot-swappable I/O modules and a mean time between failures (MTBF) of 200,000 hours, far exceeding the 20,000-hour MTBF safety standard of the high-voltage frequency converter itself. 2. Simple and Easy to Use: The high-voltage frequency converter control system designed with HCU technology integrates the high-voltage frequency converter, bypass switching device, high-voltage switch, and other related equipment into a single drive device. This means that for the field DCS and other control systems, there is no switching between power frequency and frequency conversion operation modes, or between controlling speed and control opening degree. Instead, it becomes a matter of controlling the start and stop of equipment and stabilizing the process control variables to adjust the load rate according to the production load. In actual field engineering applications, the high-voltage frequency converter system only needs to be used as a single device. No further modification to the internal logic of the DCS and other control systems or the addition of I/O control ports is required. The original control logic and adjustment methods remain unchanged, greatly simplifying the on-site modification work, reducing project investment costs and labor costs. Figure 2 shows the interface structure between the system and the field control system before and after the frequency conversion upgrade. Taking DCS as an example: Before the upgrade, the DCS connected high-voltage switches, actuators, and other execution devices to the control and regulation ports of the high-voltage main and auxiliary equipment. After the upgrade, these signals from the DCS are introduced into the HCU for signal processing, command allocation, and control object coordination through coordinated control technology to drive the execution equipment. The logic judgments and command issuance regarding which equipment to start under what circumstances and what type of regulation to perform are no longer handled by the DCS. The DCS only needs to readjust the parameters of the existing regulation system to achieve system operation. If a conventional high-voltage frequency conversion system upgrade structure is adopted, the system's ports and connection structure are shown in Figure 3. This requires expanding the capacity of I/O ports or occupying existing spare I/O points on the DCS side, resulting in extensive electrical modifications. Furthermore, the frequency conversion upgrade project for the main and auxiliary equipment of the production system is not limited to one or two devices but requires extensive peripheral support and specialized, customized system design. Based on the above reasons and current situation, using HCU technology in high-voltage frequency conversion applications can effectively solve various problems, making high-voltage frequency conversion application systems simpler and easier to implement. For operators, the operation and control methods remain unchanged; the addition of equipment does not increase the complexity of control, and the system is simple and easy to use. 3. High Efficiency and Energy Saving: The frequency converter system, implemented using HCU technology, effectively optimizes system resources. It improves equipment utilization and optimizes process energy-saving operation, achieving energy saving not only for equipment but also for the entire application system, reducing plant power consumption and improving equipment utilization. High-voltage frequency converter control systems equipped with HCU technology achieve systematic energy saving of high-voltage frequency converter products while comprehensively considering cost savings on project investment, reducing investment and construction costs, thereby significantly reducing equipment recovery investment. III. Conclusion Currently, with the increasing development of high-voltage frequency converter technology, there is more professional and in-depth research on the safety and stability of high-voltage frequency converters in application fields and further achieving high efficiency and energy saving. The research and promotion of high-voltage frequency converter coordination technology will inevitably play a positive and effective role in promoting energy conservation and consumption reduction in production.