Abstract : This paper introduces the application of high-voltage frequency converters in mine hoists. A brief introduction to the original mine hoist system is given, and the high-voltage hoisting frequency conversion speed control system is discussed. The operational results show that the modification was successful. Keywords : High-voltage frequency conversion hoisting speed control system, mine hoist, energy feedback 1. Introduction Mine hoists are crucial large-scale equipment in mine production, playing a vital role in mine production and safety. Therefore, their electrical drive and control devices have always been an important research area in the transmission industry worldwide. Traditionally, most mine hoists use an AC speed control system with a wound-rotor asynchronous motor and series resistance in the rotor circuit. Currently, most large and medium-sized mine hoists in operation use a thyristor DC reversible speed control system with magnetic field commutation. Modern AC speed control systems using fully digital frequency conversion speed control technology represent the advanced level of mine hoist technology. 2. Introduction to the Original Mine Hoist Speed ​​Control System Hebei Handan Fengfeng Mining Group Co., Ltd. is a large state-owned enterprise and one of the top 100 coal enterprises in China. The group company's Xin San Mine originally had a mine hoist. This hoist's winch used a wound-rotor asynchronous motor with speed regulation via rotor resistance. This system, being a stepped speed regulation system, suffers from drawbacks such as low torque at low speeds, high slip power, large starting and shifting current surges, significant vibration at medium and high speeds, unreliable and unsafe braking, poor handling of regenerative energy, and a tendency for overwinding at low speeds. It also has a high failure rate and low operating efficiency. Mining operations are continuous 24 hours a day, and even short-term downtime for maintenance can cause significant production losses. The group company leadership decided to upgrade the hoist's electrical control system. Jiaozuo Huafeng Company, China's largest production base for mine hoist electrical control systems, possesses strong technical capabilities. Therefore, a variable frequency hoist electrical control system manufactured by Huafeng Company was selected. Based on the requirements of Huafeng Company and Xin San Mine, we developed a dedicated high-voltage hoist frequency converter, filling a gap in the domestic high-voltage hoist industry. Because hoisting loads have many special requirements for frequency converters, ordinary frequency converters cannot be directly used on hoists. The main requirements for frequency converters for hoists are as follows: (1) High reliability is required (2) Four-quadrant operation is required to solve energy feedback (3) Complete digital control function is required (4) High technical indicators are required (e.g., starting torque more than twice, continuous operation below 150% of rated current, and protection for 200% of rated current for one minute) (5) Adaptability to harsh operating environment is required (6) Standard digital communication interface is required (7) The running speed curve is S-shaped, and acceleration and deceleration are smooth. The relevant parameters of the original mine hoist winch motor are: Model JR158-8 Power 380KW Current 47A Voltage 6000V Speed ​​735r/min 3. Xinfeng Optoelectronics Co., Ltd. JD-BP37 High Voltage Hoisting Frequency Controller According to the agreement with the user, our Shandong Xinfeng Optoelectronics Technology Development Co., Ltd. has equipped the hoist winch with our company's JD-BP37-400T (400KW) high voltage hoisting frequency controller. The following is an introduction to the JD-BP37 high-voltage hoisting frequency converter. 3.1 Introduction to the JD-BP37 High-Voltage Hoisting Frequency Converter The JD-BP37 high-voltage hoisting frequency converter uses the latest IGBT as the main control device, is fully digital, and features a color LCD touchscreen control. Designed with high reliability, ease of operation, and high performance as its goals, this high-quality frequency converter employs advanced vector control frequency conversion technology to achieve four-quadrant operation of the hoist. It is used for squirrel-cage motors or wound-rotor series resistance motors and can be used for both new mine installations and old mine renovations. The wind and solar high-voltage hoisting frequency converter uses several low-voltage inverter power units connected in series to achieve direct high-voltage output. The 6kV high-voltage hoisting frequency converter used has a transformer with 18 sets of secondary windings, divided into 6 power units/phases, for a total of 18 units across three phases. It uses 36-pulse rectification, and the harmonic components at the input end meet national standards. The system structure of the high-voltage hoisting frequency converter is shown in Figure 1. [align=center]Figure 1. High-voltage boost inverter system structure diagram[/align] The JD-BP37 high-voltage boost inverter speed control system consists of a phase-shifting transformer, power units, and a controller. 3.2 Power Unit Circuit Each power unit is structurally identical and interchangeable. Its main circuit structure is shown in Figure 2, which is a basic AC-DC-AC bidirectional inverter circuit. Three-phase full-bridge rectification is performed through a rectifier bridge. The rectified energy charges the filter capacitor, determining the bus voltage. Single-phase inversion is achieved through sinusoidal PWM control of the IGBT inverter bridge in inverter block B. When the motor enters the generating state, the diodes in inverter block B perform freewheeling and full-wave rectification, allowing energy to be transferred to the filter capacitor. As a result, the bus voltage rises. After reaching a certain level, inverter block A is started for SPWM inversion. Through the input inductor, the energy returns to the secondary of the phase-shifting transformer, and the transformer feeds the energy back to the grid. [align=center]Figure 2 Power Unit Circuit Structure[/align] 3.3 Input Side Structure The input side is powered by a phase-shifting transformer to each unit. Each power unit bears the motor current, 1/6 of the phase voltage, and 1/18 of the output power. Each of the 18 units has its own independent three-phase input winding on the transformer. The power units and the secondary windings of the transformer are mutually insulated. The secondary windings adopt an extended delta connection to achieve multiplexing and reduce the harmonic components of the input current. 3.4 Output Side Structure The output side is powered by a star connection formed by connecting the U and V output terminals of each unit in series. By recombining the PWM waveform of each unit, a stepped PWM waveform as shown in Figure 3 can be obtained. This waveform has good sinusoidal properties and a small dv/dt, which can reduce the insulation damage to the cable and motor. The motor does not need to be derated and can be directly used for the renovation of old equipment. At the same time, the harmonic loss of the motor is greatly reduced, eliminating the mechanical vibration caused by it and reducing the mechanical stress on the bearings and blades. [align=center]Figure 3 Stepped PWM waveform of phase voltage output from the frequency converter[/align] 3.5 Controller The core of the controller is implemented by the collaborative operation of a high-speed DSP and an industrial PC. The carefully designed algorithm can ensure that the motor achieves optimal operating performance. The industrial PC provides a user-friendly full-Chinese WINDOWS monitoring and operation interface, and can also realize remote monitoring and networked control. The controller is used for the logic processing of switch signals in the cabinet, as well as the coordination with various operation signals and status signals in the field, enhancing the flexibility of the system. 4. Main technical performance of JD-BP37 high-voltage boost frequency converter 4.1 High-voltage source type frequency converter, direct 6KV input, direct 6KV output, no need for any output transformer or filter, suitable for ordinary high-voltage motors, no damage to motor and cable insulation. 4.2 High input power factor, low current harmonics, no need for power factor compensation or harmonic suppression devices. 4.3 Modular design of unit circuits, simple maintenance, and good interchangeability. 4.4 Output stepped sine PWM waveform. 4.5 Can provide more than 2 times the starting torque. 4.6 Offers multiple braking methods including DC braking and regenerative braking. 4.7 Meets the four-quadrant operating requirements of motors. 4.8 ​​Fiber optic connection between the high-voltage main circuit and the controller ensures strong and weak current isolation, guaranteeing safety and reliability. 4.9 Comprehensive fault detection, precise fault protection, and accurate location display and alarm. 4.10 Built-in PLC allows for easy modification of control logic relationships, flexibly selecting on-site/remote control to adapt to changing on-site needs. 4.11 Employs carrier phase-shift control technology, significantly suppressing harmonic components of the output voltage and ensuring a perfect sine wave output waveform. 4.12 The control power supply is independent of the high-voltage power supply; the inverter output can be detected even without high voltage, facilitating on-site debugging, operator training, and maintenance. 4.13 Utilizes quasi-optimized SPWM modulation technology for high voltage utilization. 4.14 The power unit undergoes 24-hour high-temperature aging and 150% load testing, ensuring high reliability. 4.15 Chinese Windows operating interface with a color LCD touchscreen. The user-friendly and comprehensive monitoring system interface includes a host computer (commercial PC), slave computers (industrial PCs), and a microcontroller. The microcontroller provides users with a 4-digit LED display and a 12-key keypad, enabling full operation of the inverter, including parameter settings and various operating commands. The industrial PC uses a touchscreen and a universal keyboard, offering more complete functionality, including parameter setting, function setting, operation, data printing, fault diagnosis, etc. The host computer (commercial PC) is located in the central control room and can remotely measure and control multiple inverters. If there is only one inverter, the host computer can be omitted or customized by the customer. 4.16 It can receive and output multiple industrial standard signals. 4.17 It can print out operating reports. 5. Basic Control Requirements 5.1 DC Braking This hoist uses a frequency converter. DC braking plays a crucial role in the safe operation of the hoisting system. When the loaded vehicle stops midway, the PLC detects the stop signal and sends a signal to the controller, causing the hoist to smoothly decelerate from high speed to low speed. Then, the controller sends a DC braking signal to stop the hoist. After the PLC detects the mechanical braking signal, it sends a signal to the controller to remove the DC braking signal, allowing the hoist to operate using a mechanical brake or similar device. During startup, a DC braking signal is first applied to the hoist. After the PLC detects the mechanical brake signal, it sends a signal to the controller to remove the DC braking signal. Then, the controller applies a starting voltage to start the hoist. 5.2 Speed ​​Control To reduce mechanical shock during operation, continuous acceleration is ensured during hoist startup and shutdown. Since different frequencies correspond to different acceleration and deceleration rates, this device's control system uses a table to represent the acceleration and deceleration rates at different frequencies. During operation, the table is used to determine the corresponding acceleration and deceleration rate at each frequency, ensuring smooth hoist operation and reducing mechanical shock. 5.3 Automatic Speed ​​Limiting Protection Upon reaching the destination, a speed limit switch sends a deceleration signal. The PLC detects this signal and sends it to the controller, which then initiates an automatic deceleration program, gradually reducing the operating frequency to a lower speed as set. The hoist is equipped with a tachogenerator. When the tachogenerator sends an overspeed signal, the PLC detects this signal and sends it to the controller, initiating automatic deceleration. 5.4 Regenerative Energy Processing Regenerative energy is processed by the power unit, as shown in Figure 4: [align=center] Figure 4 Unit Control Block Diagram[/align] When the motor is in generator mode, the power unit bus voltage Vbus increases. When the bus voltage exceeds 1.1 times the grid voltage, the CPU outputs six SPWM waveforms based on the comparator and phase detection results, causing the IGBTs in inverter block A to operate. Through the input inductor, the motor's regenerative energy is finally fed back to the grid through the phase-shifting transformer. 6. Modification of the Original Speed ​​Control System by the Variable Frequency Speed ​​Control System To ensure safety and reliability, the variable frequency speed control system coexists with the original speed control system, serving as backups for each other and allowing for easy switching. Meanwhile, to ensure operators don't need to change their operating habits, both the mains and the frequency converter systems are operated using the original operating mechanisms, as shown in Figure 5: [align=center] Figure 5 Switching Control between Mains and Frequency Converter Systems[/align] 7. On-site Application and Operational Results The equipment modification project was successfully commissioned in April 2005. Using the frequency converter offers the following advantages: 7.1. The frequency converter system eliminates the need for the original electrical control speed regulator's AC contactor and speed control resistor, improving system reliability, improving the operator's working environment, and reducing noise and room temperature. 7.2. Continuous and convenient speed regulation with smooth adjustment. 7.3. Low-frequency and low-voltage soft start and soft stop are achieved, resulting in smoother operation, less mechanical shock, and prevention of track derailment. 7.4. The inrush current during startup and acceleration is small; the maximum current during acceleration does not exceed 1.3 times the rated current. Under heavy load, the hoist smoothly and steplessly ascends from low speed to maximum speed without large currents, reducing the impact on the power grid. 7.5. The addition of DC braking function makes parking of loaded vehicles smoother and effectively avoids the "slippage" phenomenon. 7.6. The adoption of regenerative braking technology successfully solves the problem of handling regenerative power generation energy during rapid deceleration or emergency stops of potential energy loads, ensuring the safe operation of the frequency converter. 7.7. Significant energy saving effect. Actual measurements show significant energy savings at low speeds, generally exceeding 37%. 7.8. With frequency conversion control, the original wound-rotor motor can be replaced with a conventional motor. This not only reduces costs—conventional motors save one-third of the investment compared to wound-rotor motors—but also avoids the burnout and maintenance of rotor carbon brushes. 8. Conclusion The frequency conversion speed control system for mine hoists has many advantages, including excellent control performance, simple operation, high operating efficiency, and low maintenance workload. With the increasing maturity of frequency conversion speed control technology and the inevitable trend of energy conservation requirements, it is becoming the development direction for mine hoist transmissions.