Abstract: This paper describes the principle and structure of a novel high-voltage variable frequency drive (VFD) application technology, focusing on the role of VFD coordinated control technology in ensuring safety, stability, and economy in high-voltage VFD application systems. It provides a new application method, system transformation means, and model for high-voltage VFDs. I. Introduction High-voltage variable frequency drive coordinated control technology, abbreviated as HCU technology, refers to a comprehensive coordinated control technology in high-voltage VFD application systems that achieves coordination between power frequency and variable frequency operation modes, between speed control and opening or valve control, and between equipment within the same system. The successful application of this technology fundamentally solves the impact of high-voltage VFDs 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 VFDs without significant changes or modifications to the hardware ports and control logic of DCS and other control systems on-site, achieving VFD energy saving in high-voltage equipment and perfectly integrating it with production processes. It truly realizes high reliability, safety, and stable operation of the VFD application system, while saving significant project investment and construction costs, achieving optimal system control performance and energy-saving benefits. II. HCU Technology Explanation HCU technology, from the perspective of high-voltage frequency converter application systems, focuses on researching and addressing the special operating processes and control structures of various industries. It comprehensively solves the system safety, stability, and production continuity issues in high-voltage frequency converter energy-saving systems during project implementation and operation when high-voltage frequency converter failures occur. It fundamentally solves the problems of system safety and self-handling stability capabilities jeopardized by high-voltage frequency converter failures. HCU technology is prominently reflected in the following aspects of high-voltage frequency converter applications: 1. Safety and Stability Because HCU technology focuses on the system safety handling mechanism when high-voltage frequency converters fail during application, the integrated structure 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; how to coordinate the action of dampers or valves to ensure that the unit's operating control indicators do not exceed standards, do not trigger protection, and do not stop the boiler or the machine, thus jeopardizing system safety. The integrated design of the HCU and frequency converter application system provides more robust protection against control logic processing speed issues, interlocking, and malfunctions. The system design is more professional, targeted, and reliable. This technology utilizes an independent CPU and control port, operating independently from the frequency converter's control unit. When the frequency converter fails, the independent CPU continues to operate, handling the power frequency operation mode during frequency converter accidents and automatically coordinating the adjustment of damper or valve openings, 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 control of the equipment to remote control at the moment of final failure, enabling monitoring and adjustment of equipment such as high-voltage switches, dampers, or valves operating at power frequency. It also achieves seamless switching, ensuring high safety and reliability in production operation. Designed and developed based on the DCS backend framework, this technology 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 application systems. The system safety structure is shown in Figure 1. [align=center] Figure 1: System Safety Structure Diagram[/align] Meanwhile, 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. In addition, the coordinated control technology also has fault location judgment and self-processing mechanisms. For example, when the speed regulation fails during frequency converter operation, the system automatically switches to 50Hz power frequency operation, handing over process control to the actuator. When the baffle adjustment becomes stuck or abnormal, the system can promptly transmit alarm information to the control room to report to the operators for timely handling. Simultaneously, it provides complete information such as fault time, location, cause, and associated status, facilitating maintenance and handling; at this time, problem troubleshooting can be performed at the equipment level, without needing to escalate to the DCS system level, greatly reducing the risk of fault handling. The HCU control technology, designed to integrate the technical characteristics of high-voltage frequency converters and the structure of application systems, enables resource sharing and efficient processing and application within the 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 boasts high system stability. The HCU is organically integrated with the frequency converter while maintaining complete physical isolation, ensuring independent operation and control of the system. Hardware-wise, a dual-CPU redundant structure and hot-swappable I/O modules are available, with 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. In other words, for on-site DCS and other control systems, there is no issue of switching between power frequency and variable frequency operation modes, or between controlling speed and controlling opening degree. Instead, it becomes a matter of controlling the start and stop of equipment and ensuring the stability of the process control variable that adjusts its load rate according to the production load. In actual on-site engineering applications, the high-voltage variable frequency system only needs to be used as a single device. No further modifications to the internal logic of the DCS or other control systems or the addition of I/O control ports are required. The original control logic and adjustment methods remain unchanged, greatly simplifying the on-site modification work, reducing project investment costs and labor costs. The interface structure between the system and the on-site control system before and after the variable frequency modification is shown in Figure 2. Taking DCS as an example: Before the modification, the DCS connected high-voltage switches, actuators, and other execution devices to the control and adjustment ports of the high-voltage main and auxiliary equipment. After the modification, 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 judgment and command issuance regarding which devices to start under what circumstances and what adjustment methods to perform are no longer implemented by the DCS. [align=center]Figure 2: Interface structure diagram of the system before and after frequency conversion modification and the field control system[/align] The DCS only needs to readjust the parameters of the existing regulation system to realize system operation. If a conventional high-voltage frequency conversion system modification structure is adopted, the system port and connection structure is shown in Figure 3. It is necessary to increase the capacity of I/O ports or occupy the original spare I/O points on the basis of retaining the existing control equipment ports on the DCS side, and carry out a lot of electrical modification construction. In addition, the frequency conversion modification project of the main and auxiliary equipment of the production system is not one or two pieces of equipment, but requires a lot of peripheral support and professional and customized system design. [align=center]Figure 3: Port and connection structure diagram of the system[/align] Based on the above reasons and current situation, the use of HCU technology in high-voltage frequency conversion applications can effectively solve various problems, making the high-voltage frequency conversion application system simpler and easier to implement. For operators, the operation and control method remains unchanged, the complexity of control does not increase with the addition of equipment, and the system is simple and easy to use. 3. High efficiency and energy saving The frequency conversion system integration realized by HCU technology also effectively realizes the resource optimization of the system. This can improve system equipment utilization and optimize 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 not only achieve systematic energy saving of high-voltage frequency converter products but also comprehensively consider saving project investment costs, reducing investment and construction expenses, 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 their further realization of high-efficiency 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.