The FGI high-voltage explosion-proof frequency converter has been successfully applied to high-power permanent magnet direct drive belt conveyors

1.Introduction

In response to the demands of intelligent coal mine construction, the intelligent drive control of high-pressure and high-power equipment such as underground main transportation belt conveyors, scraper conveyors, fans, and water pumps is particularly important. Taking the underground main transport belt conveyor as an example, as the core equipment for coal transportation, it has the characteristics of large capacity, heavy load, and long-term continuous operation. Although the existing hydraulic couplings can achieve smooth speed regulation within a certain range, they have problems such as large slip loss, low overall efficiency, dependence on the quality of hydraulic transmission oil for speed regulation performance, and large daily maintenance workload. The variable frequency speed regulation technology, with its advantages of wide speed regulation range, high precision, fast response, and the ability to achieve soft start, occupies an important position in the existing speed regulation systems - currently, some underground transportation machines in coal mines have adopted this technology, and its unique master-slave control function and large starting torque characteristics effectively ensure the stable and efficient operation of the transportation machine. Practice has shown that replacing the hydraulic couplings with high-pressure explosion-proof variable frequency devices for speed regulation control can provide a more complete system solution. The high-pressure explosion-proof variable frequency device has characteristics such as adjustable speed, small current high starting torque, load distribution function, and complete protection, and combined with the load characteristics of the belt conveyor, its application on underground belt conveyors in coal mines has become an inevitable trend.

2. Typical cases of high-voltage explosion-proof frequency converters

(1) Explanation of system principle

The Yingpanhao Coal Mine is located in Galaruut Town, Wusu Banner, Ordos City, Inner Mongolia Autonomous Region. Its designed production capacity is 12 million tons per year. The main transportation belt conveyor system on the northern wing of the mine uses FGI high-voltage explosion-proof frequency converter (model BPBJV2-1250/10). The input/output voltage of this equipment is 10kV, with a rated power of 1250kW. It is designed based on a cascaded topology structure, with 8 power units configured per phase. The drive system adopts a scheme where 4 motors at the head and 2 motors at the tail drive the belt conveyor collaboratively. The mine-used explosion-proof permanent magnet synchronous frequency converter motor for the belt conveyor is model TBVF-900YC, with a voltage of 10kV, a rated power of 900kW, and a rated speed of 60r/min. The entire drive system adopts a master-slave control architecture, and precise coordination among the six frequency converters is achieved through optical fiber communication to ensure the efficient and stable operation of the transportation system.

(2) The system structure of high-voltage explosion-proof frequency converter

The 10kV grid voltage achieves three functions through a phase-shifting transformer: Firstly, it reduces the input high voltage to a three-phase 690V independent power supply, providing isolated power supply for power units; Secondly, the input voltage of the unit is phase-shifted through the extended delta connection method to form a multi-pulse rectification structure, effectively reducing the harmonic distortion rate of the power grid. Finally, this structure provides an electrically isolated independent power supply for the cascading of power units. Unit cascading adopts carrier phase-shifting technology. By compensating for the phase difference of adjacent unit carriers, the output voltage approaches a sine wave.

The control system uses a high-speed DSP as the core processor and adopts a fully digital vector control algorithm. The main control unit and the power module communicate with each other through optical fiber for command transmission and status feedback, ensuring the real-time control accuracy and anti-interference ability of the system in explosive environments.

The high-voltage explosion-proof frequency converter uses the power unit series-parallel stacking technology. Each power unit receives the sine modulation wave from the main control unit, generates an SPWM output waveform after carrier phase shifting, and the output voltage waveforms of each unit are superimposed to form a sine wave, making the output waveform of the frequency converter basically similar to the sine wave of the power frequency voltage. Without the need for an output filter, it achieves no harmonic interference to the motor; due to the small dv/dt, there is no damage to the insulation of the motor and the cable, suitable for ordinary motors and cables, and at the same time realizes long-distance power supply for 5000m motors. The high-voltage explosion-proof frequency converter of Yingpanhao Coal Mine is placed in a 100-meter lateral alley 100 meters away from the belt conveyor. Due to the almost no harmonic interference on the power grid side and almost no harmonic interference to the motor, it is hailed as the "green harmonic-free frequency converter".

3. The application effect of high-voltage explosion-proof frequency converters in Yingpanhao Coal Mine

(1) Truly achieve soft start of belt conveyors. The frequency converter can output 2.2 times the rated torque when operating at low frequency. The starting time can be adjusted within 1 to 3600 seconds, meeting the heavy-load soft start requirements of the belt conveyor.

(2) Achieve precise power balance. Achieve torque balance when the four motors at the head and the two motors at the tail are driven simultaneously at a distance of 5,000 meters. The unbalance rate among each motor is less than 2%.

(3) Realize the online switching function. This 6-drive belt conveyor system operates in a mode where 5 devices are in operation and 1 is on standby. It supports the online input function of the entire inverter. When one of the 5 operating devices fails and exits, the standby inverter will immediately be put into use to ensure that the belt conveyor does not stop, operates reliably and more safely.

(4) Automatically adjust the running speed of the belt conveyor. In conjunction with the coal flow sensor, the running speed of the belt is automatically adjusted according to the load weight, achieving "fast running when there is more coal and slow running when there is less coal", significantly enhancing the transportation efficiency of the system.

(5) Energy conservation and consumption reduction have significant economic and social benefits. By using high-efficiency low-speed direct-connected permanent magnet synchronous motors and eliminating the reducer, the system efficiency and maintenance efficiency have been significantly enhanced. In practical applications, the soft start of the frequency converter reduces the system start-up impact, and the speed regulation based on the coal volume shortens the high-speed operation time of the belt conveyor system, greatly reducing the wear of mechanical systems such as the motor, rollers, idlers and belts, and extending the service life of the equipment. It reduces the on-site maintenance workload and costs of system equipment, lowers the labor intensity of workers, and significantly reduces the power consumption of motors operating at low speeds compared to high speeds. It is of great significance for saving electricity and reducing mechanical losses in the belt conveyor system.

The current mainstream power supply solution for frequency converters in the industry is to use a mobile transformer + frequency converter for power supply. This not only takes up a large area but also requires a large amount of wiring and connection work on-site. However, our company has integrated the transformer and the frequency converter into a single machine design, offering the option of 10kV and 6kV frequency converters. This significantly reduces the area required and the on-site construction work. The high-voltage explosion-proof frequency converter adopts a modular design concept. The function modules can be updated and maintained as needed, making it convenient for on-site maintenance of the product in the future.

(2) Multiple guarantees ensure worry-free operation

In addition to the online redundancy function of the equipment itself, each phase of a single frequency converter supports the redundancy of three power units. When a unit malfunctions, the system can automatically bypass the faulty unit to ensure that the production process is not affected.

(3) Load adaptive self-balance

Adapts to various loads for operation. Multi-level drive loads have automatic power balance, requiring no human intervention. It supports master-slave control for up to 10 units.

(4) Intelligent Mine Communication Interface

This intelligent mine communication interface meets the requirements for communication in intelligent mines and supports various network access methods such as optical fiber, network cable, and wireless. In the Mengpanhao Coal Mine, network ports are used for communication to transfer data to the surface data monitoring center. Remote monitoring and fault diagnosis: Relevant data monitoring, fault analysis, and component life prediction can be conducted through a PC or a mobile phone APP.