1. Introduction <br> With the rapid development of the national economy, especially the entry of the WTO and the intensification of market competition, the energy issue has become particularly prominent. The strong investment in energy conservation and emission reduction has become a new bright spot for various industries to improve market competitiveness. In various industries, the application of electric motors is extremely extensive. It is the main driving force in working conditions enterprises. It is used in the dragging of large mechanical equipment such as fans, rolling mills and pumps in various industries such as metallurgy, petrochemical, electric power and mining. In particular, the power consumption of high-voltage motors is very large, accounting for 65-75% of the electrical energy consumption of all motors in the enterprise. For the energy saving of the motor, the energy saving of the high voltage motor is particularly prominent. At present, the motor system energy-saving project is positioned as one of the ten key energy-saving projects initiated by the National Development and Reform Commission. For the energy saving of the motor system, the use of thyristor frequency conversion technology is the most ideal energy-saving way in terms of speed regulation, starting and braking performance, especially in certain specific processes, medium, high voltage and high power. The energy saving effect of the high-voltage inverter of the motor is particularly obvious. In Figure 2: 3.5. Operational effect analysis Square root (3) × Ue × I × cosΦ = 1.732 × 6.450 × 65 × 0.816 = 592.5kW • h 3.6 Other effects produced by the application of high-voltage variable frequency speed control system Digital Signage outdoor digital signage outdoor Jumei Video(Shenzhen)Co.,Ltd , https://www.jmsxdisplay.com
2. Classification and energy-saving advantages of high-voltage inverter drive is <br> motion control system of the power converter. At present, China's high-voltage inverters show three major trends:
(1) Power unit series multi-level technology is still the mainstream of the market.
(2) Development towards high power.
(3) With the maturity of high-voltage frequency conversion technology, the demand for process control for frequency conversion speed regulation will be greatly expanded.
High-voltage inverters do not have a mature and consistent main circuit topology like low-voltage inverters , but are limited to the contradiction between voltage tolerance and high-voltage use conditions of power devices. Different inverter manufacturers at home and abroad use different power devices and different The main circuit structure is adapted to the requirements of various dragging devices, and thus there are also differences in various performance indexes and application ranges.
The classification of high-voltage inverters can generally be divided into two categories:
(1) AC-AC inverter (no DC link)
(2) AC-DC-AC inverter (with DC link).
Among them, the AC-DC-AC inverter can be called a current source type inverter according to the DC link using a large inductor to suppress the current pulsation, and the inverter with a large capacitance to suppress the voltage fluctuation is called a voltage source type inverter. Device. Figure 1 shows the block diagrams of three high-voltage inverters. 
Regardless of the type of high-voltage frequency converter, the advantages of energy saving are obvious under specific process requirements. In the past, the energy-saving speed regulation of high-power motors generally adopts the following methods: star/corner starter, auto-coupled step-down starter, matching capacitor replenisher, improved power factor terminal voltage, and matching electromagnetic governor (suitable For stepless speed regulation), reduce mechanical shock during start-up. The above several energy-saving speed regulation, energy-saving effect is not obvious, and the speed regulation range is narrow, the speed is unstable, the efficiency of the motor is low, the loss is large, and the fault often occurs, which cannot meet the needs of continuous production, low adjustment precision, slow response, and the like. The typical application of high-voltage inverters for energy saving is fan speed regulation and pump speed regulation. In order to ensure the reliability of production, all kinds of production machinery have a certain margin when designing with power drive. When the motor can't run under full load, in addition to meeting the power drive requirements, the excess torque increases the consumption of active power, resulting in wasted power. Fans, pumps and other equipment traditional speed control method is to adjust the air volume and water supply by adjusting the baffle and valve opening of the inlet or outlet. The input power is large, and a large amount of energy is consumed in the interception process of the baffle and the valve. in. When using variable frequency speed regulation, if the flow demand is reduced, the speed can be met by reducing the speed of the pump or fan.
It can be known from fluid mechanics that P (power) = Q (flow) × H (pressure), the flow rate Q is proportional to the primary of the rotational speed N, the pressure H is proportional to the square of the rotational speed N, and the power P is proportional to the cube of the rotational speed N If the efficiency of the water pump (or fan) is constant, when the required flow rate is required to decrease, the speed N can be proportionally decreased, and at this time, the shaft output power P has a square relationship. That is, the relationship between the power consumption of the pump motor and the rotational speed is approximately proportional. When the required flow rate Q is reduced, the inverter output frequency can be adjusted to cause the motor speed n to be proportionally reduced. At this time, the power P of the motor will be greatly reduced in a cubic relationship, which is 40% to 50% energy saving than the regulating baffle and the valve, thereby achieving the purpose of power saving, and at the same time improving system reliability and stability.
3. Case Analysis <br> Now, in 2006, the high-voltage inverter produced by Beijing Lied Huafu Electric Technology Co., Ltd. used in the dust removal fan of No. 6 blast furnace in Henan Jinan Iron and Steel Co., Ltd. is taken as an example, from the process, the structure of the inverter, and the principle of energy saving. And a detailed analysis of the energy saving effect.
In the production process of the blast furnace, the iron ore field generates a large number of chimneys and pollutes the environment. According to national regulations, dust removal is required. The dust-removing fan is a gap working system, that is, it is used when the blast furnace is tapped, and when it is not used, the usage rate is about 60%. Figure 2 shows the process cycle of the blast furnace ironmaking field.
A to B, E to F are blast furnace smelting time,
B to C, F to G are the acceleration time, which can be adjusted.
C to D, G to H are blast furnace tapping time,
D to E, H to I are deceleration times and can be adjusted.
Each time the blast furnace tapping time is about 50 minutes, it is set to 45 Hz for the high speed section, which can be adjusted; the blast furnace smelting time is about 30 minutes, which is the low speed section.
It is set to 5Hz and can be adjusted.
3.2 Scheme selection
According to the above process requirements, and because the motor equipped with the dust removal fan is a high voltage motor, frequent start and stop is not allowed. If the fan is operated at a power frequency for a long time, the air volume of the damper is adjusted to adjust the air volume to meet the production process requirements, and a large amount of electric energy is wasted on the valve. If the hydraulic coupler is used for speed regulation, it is known from previous experience that the hydraulic coupler has the following main disadvantages:
(1) The speed adjustment range is limited, 50~95%, the speed is unstable, the high speed section reduces the output capacity of the equipment, and the low speed section affects the performance of energy saving;
(2) The lower the speed, the lower the efficiency, and the lower the heat, the heat is strong;
(3) Low speed regulation, poor linearity, slow response, and less adapt to automatic control requirements;
(4) Although the motor can be started without load, it still has about 5 times of impact current, which affects the stability of the power grid;
(5) It must be inserted into the connecting shaft of the motor and machinery, which is not suitable for equipment modification; when the hydraulic coupler fails, there is no power frequency bypass system, the load machinery will not be able to operate, and it must be shut down for maintenance;
(6) Serious oil leakage, large environmental pollution; poor reliability, difficult maintenance, severe waste of manpower and impact on production.
After the above analysis, it is necessary to meet the process requirements, but also to achieve the purpose of speed regulation and energy saving. It is most ideal to use the high-voltage inverter to control the motor. The plan is set as one-to-one solution, as shown in Figure 3. The inverter adopts HARSVERT-A series high-voltage inverter produced by Beijing Lidehuafu Electric Technology Co., Ltd., which is specialized in manufacturing high-voltage frequency conversion.
The HARSVERT-A series high-voltage inverter is an AC-DC-AC voltage source type inverter, which adopts a direct "high-high" conversion form, which is a unit series multi-level topology structure. The main structure is formed by connecting multiple sets of power modules in series. The low voltage superimposed by each group produces the required high voltage output, which has less harmonic pollution to the power grid, less than 4% of input current harmonic distortion, and less than 2% harmonic distortion of the input voltage of the power grid, directly meeting the harmonic suppression standard of IEEE519-1992. High input power factor, no need to use input harmonic filter and power factor compensation device; good output waveform quality, output current harmonic distortion less than 2%, no motor additional heating and torque ripple, noise, output dv /dt, common mode voltage and other problems, you can use ordinary asynchronous motor without adding output filter. Each system has 21 power units in each system, and each 7 power units are connected in series to form one phase. The system structure is shown in the figure. 4 is shown. (1) is a high voltage switch; (2) is a dry phase shifting isolating transformer; (3) is a motor; (4) is a power unit; (5) is a main control box; (6) is a human machine interface; (7) It is a programmable controller; (8) is a current Hall; (9) is a voltage detection.
(1) Method of frequency conversion speed regulation <br> The output speed of AC asynchronous motor is determined by the following formula:
n=60f(1—S)/p......ï‚
Where: n-motor output speed; f-input power frequency; S-motor slip; p-motor pole pairs.
It can be known from the formula that the frequency conversion speed regulation is to adjust the output speed of the AC motor by changing the power frequency input to the AC motor.
The variable frequency speed control system directly receives the AC frequency of 50Hz from the power grid. After the AC-DC-AC frequency conversion method, the input power frequency AC power is converted into an AC power whose frequency and amplitude can be adjusted and directly output to the AC motor to realize the AC motor. Variable speed operation.
The working characteristics of the dust removal fan as a basic fan type load are shown in Fig. 5.
At two points A and B, the load power is PA=H1×Q1 and PB=H3×Q2. Although Q2<Q1, but H3>H1, the actual reduced power is limited.
If the baffle adjustment is not used, then the pipe network resistance characteristic keeps the curve 3 unchanged, the adjustment load speed is used to reduce the flow rate, the load is changed to the speed N2, the working characteristic is curve 2, the load works at point C, and the flow is still It is Q2, but the pressure is H2.
6# blast furnace tapping fan motor parameters: rated power 710kW, rated voltage 6000V, rated current 89 A, power factor 0.816, rated speed 740r/min.
At present, the actual input value when running with the inverter is: when the motor is at high speed (45Hz), the current is about 50-55A, and when the motor is low speed (5Hz), the current is 1.36A. According to the formula: Inverter input and output voltage U1 × Inverter input current I1 × Inverter itself power factor = Inverter output voltage U2 × Power frequency current I2 × Motor power factor, above the actual operating power frequency current: 59-65A when the motor is high speed The motor is 18A at low speed.
When the motor is at high speed, the input current is 55A, the input voltage is 6450V, the speed is 740r/min, and when the motor is low speed, the input current is 1.3A, the input voltage is 540V, and the speed is 76r/min.
Actually, the power frequency current is 65A when the inverter is not used. This may be related to the display error of the inverter. The energy-saving accounting is based only on the data displayed by the inverter. Ironmaking time and non-ironing time are considered at 60% to 40%. Consider 8,000 hours per year.
In the power frequency state of the motor, the annual power consumption is
Calculated by 0.5 yuan per kilowatt hour, 592.5 × 8000 × 0.5 = 2370124 yuan.
When the motor is frequency-converted: the speed is proportional to the frequency, and the relationship between power and speed is P/Pe=(n/ne)3.
Therefore, when the motor is at high speed: P=Pe×(n/ne)3/0.96=739.5kW•h,
The electricity fee is: 739.5 × (8000 × 60%) × 0.5 = 1774800 yuan,
When the motor is running at low speed: P=Pe×(n/ne)3/0.96=0.74 kW•h,
The electricity fee is: 0.74 × (8000 × 40%) × 0.5 = 1184 yuan.
The annual electricity bill is: 2370124-1774800-1184 = 594140 yuan, the savings ratio is: 594140/2370124 = 0.25, the power consumption savings is 25%, and the cost can be recovered in one and a half years.
(1) Reduced maintenance
After adopting the frequency conversion speed regulation, no matter which process condition, the system can be operated at a time close to the rated state by adjusting the rotation speed. Under normal circumstances, the application of the frequency conversion speed regulation system is mainly to reduce the rotation speed of the motor. Due to the slow start-up and the reduction of the rotational speed, the life of many components is extended accordingly; at the same time, the impact on the pipeline is greatly reduced, the maintenance period of the pipeline is effectively extended, the maintenance and repair expenses are reduced, and a large maintenance cost is saved.
(2) Reduced work intensity
Since the speed control system realizes computer interlock control between the running equipment and the standby equipment, the unit realizes automatic operation and corresponding protection and fault alarm, and the operation work is changed from manual to monitoring, completely realizing the unmanned operation of production, greatly reducing labor. Strength, increased production efficiency, and a reliable guarantee for optimal operation.
(3) Reduced the impact on the grid
After the frequency conversion adjustment, the system realizes soft start, the motor starting current is far less than the rated current, the starting time is extended accordingly, no big impact on the power grid, reducing the mechanical damage of the starting machinery torque to the motor, effectively extending the service life of the motor .
4 Conclusion
The high-voltage variable frequency speed control system is a frequency conversion speed control device that is directly connected in series between the high-voltage power supply and the high-voltage motor. With its safe and good running performance, it is rapidly replacing other speed-regulating products, and comprehensively enters energy-saving projects in various industries. The purpose of using high-voltage variable frequency speed control technology is to change the running speed of the equipment to adjust the working conditions of the field, greatly improve the automation degree of the system, not only meet the production requirements, but also save energy, and at the same time greatly reduce the maintenance. Enterprises bring considerable benefits. In the energy saving of the motor system, the high-voltage inverter plays an important role in its energy-saving efforts.
Application of high voltage frequency converter on mine hoist
Figure 1: Block diagram of three high voltage inverters
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Regardless of the type of inverter, judging its advantages and disadvantages, we must first look at the influence of the harmonics of its output AC voltage on the motor; secondly, the harmonic pollution and input power factor of the grid; again depends on its own energy loss (ie Efficiency) how.
3.1 Process
Figure 2: Process cycle of blast furnace ironmaking field
Figure 3: High-voltage inverter one-for-one solution
3.3 HARSVERT-A series high voltage inverter basic structure principle
Figure 4: HARSVERT-A series high voltage inverter system structure
3.4 Frequency control principle
(2) Energy-saving principle of frequency conversion speed regulation
Figure 5: Working characteristics of the dust removal fan
Curve 1 is the characteristic curve when the load is operated according to the rotational speed N1, curve 2 is the characteristic curve when the load is operated according to the rotational speed N2, and 34 is the resistance curve of the pipe network. Under the first load condition, the load operates at point A, the flow rate is Q1, and the pressure is H1. If the load is still running at the N1 speed, the baffle will adjust the flow to Q2, the pressure will rise to H3, and the load operating point will move to point B. Due to the interception of the baffle, the pipe network resistance curve changes from 3 to 4.
When using variable frequency speed regulation, the power factor is close to l at 50Hz full load, and the working current is much lower than the rated current of the motor. This is due to the improvement of the power factor caused by the filter capacitor in the inverter device, which can save 20% capacity for the grid. about.