Coal mine upgrading is an important part of coal production. However, due to the special environment and safety requirements of coal mine production, the application of frequency converters in coal mines started relatively late. With the in-depth development of China's market economy, the increase in production, consumption and efficiency of coal mines has been mentioned as an important position, and energy-saving renovation of equipment is imperative. Frequency conversion speed regulation has also been applied in coal mine fixed machinery, lifting transportation and coal mining machine and achieved good results. This paper discusses the application of frequency conversion speed regulation in coal mine lifting transportation system.
1. The development and principle of frequency conversion speed regulation
1.1 Overview of the development of variable frequency speed regulation
Mine lifting is the key to mine production. Therefore, no matter which kind of hoist, the requirements for electric drive are very high, because the performance of the electric drive system and the reliability are directly related to the efficiency of mine production and mine production. The normal progress.
At present, the electric drive system of mine hoist in China mainly includes: for large-scale mine hoist, mainly adopts DC drive system, there are DC motor-DC generator system and thyristor converter-DC motor system; both systems exist The inherent disadvantages of DC motors, such as low efficiency and large maintenance workload. For medium and small hoists, AC electric drive systems are often used, such as AC winding motor, motor rotor switching resistance speed control. Although the electric drive system is simple, it is stepped speed regulation. Poor performance, low efficiency, a large amount of electrical energy is consumed in the rotor resistance of the motor, and the reliability is also poor.
The application of variable frequency speed control technology to mine hoist is the development direction of mine hoist electric drive system. China has several large-scale mine hoists using AC-AC variable frequency speed control system, which has achieved good results, but its shortcomings are low power factor, large harmonics, harmonics and power factor compensation devices. With the development of frequency control technology, AC-DC-AC voltage frequency control technology has begun to be applied in mine hoists.
The high-power frequency conversion device can invert the power frequency three-phase AC with the set parameters, so that the output is an AC of a corresponding set frequency. The change of the output frequency of the inverter will cause the output speed of the motor to change, and the relationship between the two is approximately linear. In this way, it plays a role in speed regulation. In the circuit system, in order to ensure the normal operation safety, the equipment must be grounded reliably. Therefore, the grounding end of the inverter should also be grounded reliably. In the main circuit, the terminal for connecting the brake unit and the braking resistor is used to prevent the workpiece from driving the motor when the hoist is running in the vertical direction, and a large regenerative electromotive force is generated, that is, the pumping voltage is too high. The phenomenon of damage to the inverter appears. Adding an external braking resistor or an external braking unit can consume part of the energy and improve the working capacity of the inverter. According to the principle of frequency conversion and speed regulation, the frequency setting circuit is connected to the control input loop of the frequency converter, and the analog quantity output by the PLC, that is, the voltage or current signal is used to control the output frequency of the frequency converter. The inverter output frequency at this time is proportional to the set voltage or current input. In order to monitor the running status of the inverter and find the abnormality in time, the abnormal signal of the inverter is taken out to the input module of the PLC to serve as the accident alarm signal of the inverter.
1.3 advantages of frequency control
(1) Realize stepless smooth acceleration and deceleration to improve the safety level of the lifting system.
(2) Saving energy.
(3) Replace the relay with the built-in programming software of the inverter to achieve the speed control and reduce the equipment maintenance workload.
(4) The starting current is low, and the system and the power grid have no impact and power saving effect. When starting, there is no need to start the series metal resistance, which reduces the startup energy consumption.
(5) The system has complete protection functions and high operational safety performance.