Weak current College】 【frequency conversion water supply system is the best choice --- Power By】 【China power house network.

<br> <br> Because of the various provinces of urbanization and the rapid development in recent years, a serious shortage of water power shortage. In many cities there are these limits of water. Countries out of the huge mass of water supply and drainage .engineering construction. According to statistics and forecasts, National City daily water 20 million m3 per day discharges of about 1 million m3, every year new expansion of water treatment plant near 600 000 m3 / d, sewage treatment capacity will reach 700 million m3 / d .. <br> <br> In the construction of water supply and drainage engineering and management, equipment management costs are very high, which works in approximately 50 per cent of energy consumption. Most new FCS, DCS, PLC control system cannot carry out network .monitoring, causing many resources consumption. There are many power stations, substation and congenital defect location unreasonable, power distribution cables too much too long, transformers and other equipment choice unreasonable, especially the pump selection, process flow overall arrangement, the power consumption of water .supply and sewerage system. Operation and management of water supply and sewerage plant should be considered in the light of technological and auxiliary electrical equipment distribution system of integrated design systems, dosing systems, pump systems of three direction key research, to develop each ton water integrated .manufacturing units of power consumption and drug consumption standard, that is, from investment per tonne of water to run the best price. Here, the best energy-saving pump technology selected for analysis and research. <br> <br> Case analysis <br .> <br> From the 1970s, dozens large scale water treatment plant design, station broke the General design of conservative selected pump method, using the Cascade or frequency conversion technology, so that the water supply system of factory water flow and head, to adapt .the configuration of the pipeline system changes that improve the efficiency of the pump running, try to make the economic rational distribution of water supply, maintaining network end pressure stability. <br> <br> Beijing water factory began to design-time, breaking the .conventional design practice, the process to the substation equipment selection, not the highest maximum flow and its corresponding pressure to work points to choose different capacity pump and pump combination; rather meet maximum design on the basis of the water, try to make the conversion efficiency .characteristic curve near system characteristic curve, that is, as far as possible the various speed pump combination of efficient area can set into a chance to work with the highest segment or point. The number of speed pump, running condition throughout the year in the pump .appears the most times the number of the number of the need, and the alternate pump selection speed pump. <br> <br> First look at pumping station. Various pumping station number combination of efficient centre line, are in the system properties on the .left side of the curve. When the design work bench, it should be efficient center line package into the maximum discharge point of a curve segment, move to the bottom right side of the curve, flow increase and head down to 4 pumps operating system characteristics .curve coincide or toward a comprehensive operation efficiency, water pump will be higher. From system analysis, pump while running 4 for the economy, taking into account the stages of construction, the first phase of selection of the two largest pump speed is more economic and .reasonable. <br> <br> See the distribution plant station configuration. From computerization, the first phase of 2 pump operation rate highest appears, followed by three, while various number combination of efficient area can pack into the daily high traffic on the basis .of a move to the lower right side, see the figure above. Increase the rated flow lower rated lift, enabling efficient pumps integrated with the centre line between the two or three pumps running system characteristic curve, while the second after running needs 4, and .then consider diurnal time variability, running pump are relatively reasonable speed pump. When a faulty pump speed control, three-tone must operate its comprehensive efficiency decreases, while the lift or higher work. Therefore, the alternate pump selection speed pump more economic and reasonable .. <br> <br> Water supply system optional several frequency conversion technology <br> <br> From the 1980s, China water industry really entered the era of the inverter. As the Beijing water factory, Shenzhen meilin water plant, Shenzhen Western water .system, pump station, large South-North transport pump station, Shanghai water company and water company, Shanghai drainage management company, Guangzhou, Dongguan, Xiamen, Fuzhou, Tianjin, Chongqing, Shijiazhuang, Kunming, Chengdu, Chaozhou, Daqing oil field, and .so water company of hundreds of large and medium-sized water treatment plant and pumping station will use variable frequency speed regulation device. Water pump motor capacity from 315KW to 2500KW, adopts frequency conversion and the number of the more than nearly 1000. 200KW following capacity .selection frequency conversion and more. <br> <br> Due to the current-inverter is bridge converter, harmonic richness, power grid hazards, harmonic measures more complex in terms of price and reliability advantages, lost in the Shui industrial areas have very little .use. 220KW and above pump units selectable frequency converter has the following six: <br> <br>? "-Low-frequency converter" <br> Advantage of the prices low frequency converter, the disadvantages are increased floor space and cost, increased .levels of transformer losses, reliability significantly reduces, at low speed, the transformer efficiency, low power factor. <br> <br>?-Voltage inverter <br> Domestic low-voltage inverter has done 1000KW, has achieved 2000KW abroad. Recommendations to .select 1.7KV, 2.3KV, 3.3KV multiphase special motors. <br> <br>?-Low voltage inverter <br> Its advantages are medium voltage power transmission loss is small, low-voltage inverter efficiency high, input transformer side adopts angle .(△) about the law, can absorb high-frequency harmonics in the system. <br> <br>?-MV inverter <br> A) MV IGBTPWM inverter. Rated power factor ≥ 0.96, system devices from 60 branches reduced to 24 .teams, circuit simplifies, reliability improves. B) MV IGCTPWM inverter. Rated efficiency> 98% rated power factor> 0.95. <br> <br>? In the multiple-multi-stage tandem voltage inverter <br> United States ROBICON company, .Japan Yaskawa, Fuji, Toshiba Corporation and other companies that have launchedMulti-multi-line voltage frequency converter. Using multilevel structure and low-voltage low-power frequency cell-line output IGBTPWM medium frequency power, power integrations. Rated efficiency ≥ 96% rated .power factor ≥ 0.95. But it must be pointed out that, in the same capacity with pressure equipment not only more expensive price and reliability also declined. <br> <br> About pump motor with vector control or direct torque control of variable speed control .of the programme of <br> <br> Vector control (VC) and direct torque control (DTC) is a high-performance AC variable frequency speed regulation system, are the torque control, are based on asynchronous motor design of dynamic mathematical models. .Vector control system is characterized by coordinate transformation, directed by flux, motor model requires motor parameters, directed by parameter changes affect accuracy. <br> <br> Direct torque control (DTC), speed loop, use torque feedback directly control motor stator flux .torque. DTC by rotor side parameter has little effect and VC affected by changes in parameters affecting large rotors, DTC robust strong than VC. <br> <br> DTC system by motor voltage and current calculated stator flux and torque, the use of pop .-pop control for frequency converter PWM control, its focus is on the voltage, and vector control focus is current, current regulation time lag exists, and the DTC does not have current control loop, no current reflect, motor can get large dv / dt ., larger accelerate current, resulting in a faster response to the current response and torque, DTC torque response faster than VC 4 ~ 5 times. <br> <br> DTC as a bang-bang control, the switching frequency instability, its current ratio .slightly bigger VC, inverter efficiency slightly lower than VC, so DTC control inverter stability index less than VC. Sensorless control is DTC and VC control system of a common research project and is not a DTC's invention patent, they all use the same mathematical model of .AC motor. DTC-speed control performance is not good, use flux control to compensate for the low-speed performance, DTC control system with low-speed, high speed when the ISR to DTC when transition. At the pump, chemical handling, dosing .system use DTC system, or VC systems, it is necessary to pay attention to selection or unhelpful. DTC and the VC system as a high-performance control system, is essentially the same, can achieve a high static and dynamic performance. DTC and the .VC systems, due to the differences in control methods, have their own characteristics, advantages and disadvantages of each, with focus on application areas. Vector control more adapted to a wide range of speed control system and servo system, direct torque control more suitable for .quick torque response, robust good large delay motion control system, both systems are inadequate, there are two kinds of system research and development work that move in the direction to overcome their weaknesses. <br> <br> <br> <br>.