Application of high power and high voltage inverter in main fan

The main fan of the west wind shaft of Zhangcun Coal Mine is the lifeblood of the mine ventilation system. It consists of two AGF-606-2.442-1.2-2 axial flow fans and JR1510-8 motors produced by the Fan Factory of Shenyang Engine Research Institute. The power is 475kW, the speed is 750r/min, the voltage is 6000V, and the starting mode is high-open series frequency sensitive resistor starting. The starting current is large and the impact on the motor is large. After the main fan is started, it runs at industrial frequency and cannot adjust the air volume according to the change of the air volume used in the mine. The waste of electric energy is relatively serious. Therefore, in September 2007, the 1# main fan of Xifeng Well was transformed with variable frequency control. A set of Diamond-HV-06/600 high-voltage inverters produced by Beijing Kangdexin Electric Technology Co., Ltd. was connected to the main circuit of the system to control the 1# main fan. The inverter debugging work was completed on September 30, 2007. The fan started smoothly when it started, and the inverter was officially put into operation with the underground load.
1 Principle of variable frequency speed regulation of asynchronous motors The
variable frequency speed regulation of asynchronous motors is achieved by changing the synchronous speed by changing the stator power supply frequency. In the speed regulation, a small slip rate can be maintained from high speed to low speed, so the slip power consumption is small and the efficiency is high. It is the most reasonable speed regulation method for asynchronous motors. It can be seen
from the formula n=6Of/p(1-s) (where: n is the motor speed; f is the frequency; P is the number of pole pairs of the motor; s is the slip rate) that if the power supply frequency f is changed evenly, the synchronous speed of the motor can be changed smoothly. Variable frequency speed regulation of asynchronous motors has the advantages of wide speed regulation range, high smoothness and hard mechanical characteristics. Currently, variable frequency speed regulation has become the most important speed regulation method for asynchronous motors and has been widely used in many fields.
Frequency conversion speed regulation has the following significant advantages:
1) The "big horse pulling a small cart" phenomenon caused by the equipment design margin is naturally very wasteful because the motor rotates at a fixed speed and cannot be adjusted. Frequency conversion regulation completely solves this problem;
2) The large amount of throttling losses caused by load dampers or valve adjustments no longer exist after frequency conversion;
3) Certain working loads need to be adjusted frequently, and the damper adjustment linearity is too poor to keep up with the speed of working condition changes, so the energy consumption is very high, while frequency
conversion regulation responds very quickly and is basically synchronized with the working condition changes;
4) The power factor of the asynchronous motor is increased from about 0.85 before frequency conversion to more than 0.95 after frequency conversion;
5) Zero speed starting can be achieved without starting impact current, thereby reducing the starting load and reducing impact torsional vibration;
6) The high-voltage inverter itself has very small losses, and the overall efficiency is above 97%.
2 Equipment selection and scheme design
2.1 Equipment selection
In the past, the motor variable frequency speed regulation adopted the high-low frequency conversion method to adjust the speed. The frequency converter was a low-voltage frequency converter, and the input step-down transformer was used to first reduce the grid voltage, and then a low-voltage frequency converter was used to achieve frequency conversion. For the motor, there are two ways. One way is to use a low-voltage motor; the other way is to still use the original high-voltage motor, and it is necessary to add a step-up transformer between the frequency converter and the motor, that is, the high-low-high frequency conversion method. This was a transitional technology when the high-voltage frequency conversion technology was not mature at that time. This approach uses a low-voltage frequency converter, and the capacity is relatively small, which has a large harmonic on the grid side. Now the technology of high-voltage frequency converters has matured. After research, it was decided to adopt a one-time solution and directly use a high-voltage frequency converter to perform frequency conversion control transformation on the main fan fan. After comparing the cost-effectiveness of many parties, a set of Diamond-HV-06/600 high-voltage frequency converters produced by Beijing Kangde Xindian Technology Co., Ltd. was selected. It was first applied to the 1# main fan fan of the west wind shaft of the mine, and then promoted after the application matured.
2.1.1 Technical parameters of Diamond-HV-06/600 high-voltage inverter
Inverter capacity: 600 kVA;
Applicable motor power: 475 kW;
Input frequency: 45-55 Hz;
Rated input voltage: 6 kV ± 10%;
Input power factor: 0.95 (>20% load);
Inverter efficiency: >0.96 under rated load;
Output frequency range: 0-60 Hz;
Output frequency resolution: 0.01 Hz;
Operating ambient temperature: -10-40°;
Cooling method: forced air cooling.
2.1.2 Performance characteristics of high-voltage inverter
1) The high-voltage variable-frequency speed regulation system adopts a direct "high-to-high" conversion form, which is a unit series multi-level topology structure. The main structure consists of multiple groups of power modules connected in parallel.
2) The frequency conversion device control adopts two control methods: LED keyboard control and human-machine interface control. The two methods are mutually standby. Both methods can increase and decrease loads, start and stop the machine from the local interface. The device retains fault records for at least one year.
3) The inverter can provide two communication functions: standard RS-485 and communication interface with touch screen processor expansion.
4) In the speed adjustment range of 20% to 100%, the power factor of the input end of the machine reaches 0.95 without any power factor compensation.
5) The inverter has no requirements for the length of the output cable, and the inverter protects the motor from the influence of common mode voltage and dV/dt stress.
6) The output current harmonics of the inverter are not greater than 2%, which meets the most stringent requirements of IEEE 519 1992 and China's power supply department for voltage distortion, and is higher than the requirements of the national standard GB14549-93 for harmonic distortion. The output waveform of the inverter will not cause resonance of the motor, and the torque pulsation is less than 0.1%.
7) The current harmonics fed back by the frequency converter to the power grid are no more than 4%, which meets the most stringent requirements of IEEE 519 1992 and China's power supply department for voltage distortion, and is higher than the requirements of the national standard GB14549-93 for harmonic distortion.
8) The frequency converter has a strong adaptability to the fluctuation of the power grid voltage. When the power grid voltage fluctuates by 10% to +10%, it must output at full load. It can withstand a 30% drop in the power grid voltage and continue to operate at a reduced rating, which can meet the requirements of large voltage fluctuations in coal mines.
9) The frequency converter is equipped with the following protections: overvoltage, overcurrent, undervoltage, phase loss protection, short circuit protection, stall protection, inverter overload, motor overload protection, semiconductor device overheating protection, instantaneous power failure protection, etc., which are linked to the 6kV switch on the input side. The performance of the protection meets the requirements of relevant national standards. It also provides alarms such as faults, power failures, and shutdowns.
10) The frequency converter has a fault self-diagnosis function, which provides Chinese indication of the type and location of the fault, and displays it locally, making it easy for operators and maintenance personnel to identify and solve the problems. The frequency converter monitors the ambient temperature. When the temperature exceeds the ambient temperature allowed by the frequency converter, the frequency converter will provide an alarm.
11) The system can operate continuously in an environment with electronic noise, radio frequency interference and vibration, and can meet the national standards for electromagnetic compatibility.
2.2 Main fan frequency conversion control modification plan
2.2.1 High-voltage frequency converter main circuit wiring

The connection between the frequency converter and the main fan is shown in Figure 1. DL is the 6kV switch for the main fan; K1, K2, and K3 are isolation switches for the frequency converter, K3 is the power frequency switch, and K1 and K2 are frequency converter switches; the 6kV power supply is input to the high-voltage frequency converter through the frequency converter switch K1, and the output of the frequency converter is sent to the motor through the outgoing switch K2; the 6kV power supply can also directly start the motor through the bypass switch K3. The functions of the incoming and outgoing switches (K1, K2) and the bypass switch (K3) are: once the frequency converter fails, the incoming and outgoing switches can be immediately disconnected to isolate the frequency converter, and the bypass switch can be manually closed to start the motor under the power frequency power supply.
2.2.2 Working mode
The working mode of the system has changed to the original main fan system using two fans in one use and one standby mode. Now one of the fans is changed to the variable frequency drive mode, and the other fan system maintains the original operation mode unchanged. The frequency converter uses a bypass cabinet for industrial frequency conversion switching, which ensures that in the event of a frequency converter failure, the direct switching operation enters the industrial frequency operation mode. The switching speed is fast and can fully meet the requirements of starting the fan within 10 minutes, ensuring that production operation is not affected. In addition, the reverse wind operation is simpler and more reliable than before, and can fully meet the requirements of achieving reverse wind within 10 minutes.
3 Realization of the speed regulation function
of the frequency converter 3.1 Speed ​​regulation principle of high-voltage frequency converter
The high-voltage frequency converter is an AC-DC-AC voltage source type frequency conversion speed regulation system. The current waveform output by the frequency converter is very close to the ideal sine waveform, and the harmonic components that are harmful to the power grid are low. The frequency and amplitude of the inverter output voltage can be adjusted by changing the frequency and amplitude of the modulation wave.
Each phase of the 6kV high-voltage frequency converter is superimposed by three units. The DC voltage of each unit is 1800V, and the maximum output AC voltage of each unit is 1275V. The structure circuit of the rectifier inverter power unit is shown in Figure 2.

After diode full-bridge rectification and capacitor filtering, the IGBT inverter output is controlled by SPWM mode, as shown in Figure 3.

The superimposed inverter output frequency and amplitude adjustable sine wave line voltage realize variable frequency speed control of the motor. The diode rectifier circuit has a high power factor in the entire operating range. Due to the existence of the DC link filter capacitor, the reactive current required by the load can be provided by the filter capacitor instantaneously through the freewheeling diode during the switching cycle of the inverter power device, so it is generally not reflected on the rectifier input side, resulting in a high input power factor.
3.2 How to adjust the speed of the high-voltage inverter in the high-efficiency area of ​​the fan
Under the existing conditions, the fan manufacturer provides the fan operating speed range as follows: ①n<213r/min; ②, n>732r/min; ③406r/min The adjustable speed range of the fan is small, and the frequency conversion control transformation is not very meaningful. After consultation with the fan manufacturer, if some small changes are made to the fan, the number of front support plates is increased by 2, and the speed range can be expanded to: ①n>580 r/min; ②, n<500 r/min.
To ensure the reliability of the fan operation, first keep the 1# fan blade at the original angle (0° angle) and run the inverter at the power frequency state. After running for a period of time and the inverter runs stably and reliably, increase the number of front support plates of the fan by 2, and then adjust the fan to a large angle (5° angle or 10° angle) for operation. The inverter can adjust the frequency and reduce the frequency operation. According to the amount of air used in the well, the fan can be controlled by frequency conversion and run, and the fan can be kept in the high-efficiency zone to improve the operating efficiency of the fan.
4 Application Status
The fan was debugged on September 30, 2007. During the debugging, the fan was operated at two states: 0° and 5°. At 0°, the fan still operated at the power frequency state, which did not play the role of regulating the air volume, but the motor achieved zero speed start-up, without starting impact current, thereby reducing the starting load, reducing impact torsional vibration, and reducing the impact on the power grid. The power factor of the system is improved, the input current of the power grid is reduced, the power loss on the line is reduced, and the vibration of the fan is also reduced.
When the fan blade angle is adjusted to 5°, the frequency converter is frequency-adjusted, and the frequency converter frequency is reduced to 41.5Hz to meet the underground air volume requirements. The comparison of the operating parameters before the fan frequency conversion control is shown in Table 1.

In order to ensure the reliability of the fan operation, the fan blade of the 1# fan in the West Wind Well is kept at the original angle (0° angle) and the frequency converter is operated at the power frequency state. After running for a period of time and the inverter runs stably and reliably, add 2 more front support plates to the fan, and then adjust the fan to a large angle (5° or 10°). The inverter can adjust the frequency and reduce the frequency operation. According to the amount of air used underground, the fan can be operated under variable frequency control, and the fan can be kept in the high-efficiency zone to improve the operating efficiency of the fan.
It can be seen that after the fan realizes variable frequency operation, the starting performance of the fan is improved, the fan vibration is reduced, the motor power factor is significantly improved, the fan efficiency is significantly improved, the motor operating current is reduced, and the power consumption is significantly reduced, achieving energy saving effect.
The use of variable frequency speed regulation realizes the following functions: ① Realize smooth start-up and stepless variable frequency speed regulation of the main fan to improve the efficiency of the fan; ② Adjust the air volume and save electricity according to the needs of the underground; ③ Realize the rapid switching of the fan between the power frequency and variable frequency working modes.
5 Economic Benefit Analysis
The power saving rate of high-voltage frequency converter is generally about 30%. The operation of the main fan No. 1 in Xifengjing is calculated as 180 days a year (1# and 2# fans are switched), and it runs for 24 hours a day. The annual power saving is: 475×30%×24×180=615600kW·h.
Calculated at 0.5 yuan per kilowatt-hour, the annual savings are: 0.5×615600=307800 yuan.
6 Conclusion
This is the first time that the main fan has been successfully applied with high-voltage frequency converter within Lu'an Group. In China's coal industry, high-voltage frequency conversion transformation of mine fans is rare. Practical application shows that the application of high-voltage frequency converter in the system transformation of the main fan of coal mines will surely achieve good operating results and economic benefits. The promotion of the use of frequency converters in the transformation of coal mining industry will have a very significant effect on energy saving.