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Abstract: The energy-saving principle, basic working principle and system control process of the pump frequency conversion speed regulation system are introduced, and according to the actual application, Progress, but energy waste is staggering. According to the information reported, China's fans, pumps, air compressors total about 42 million units, installed capacity of about 110 million kilowatts. However, the actual operating efficiency of the system is only 30-40%, and the power consumption of the system accounts for more than 38% of the total generating capacity. This is due to many fans, the pump drag motor at a constant speed operation, and the production of wind, water flow requirements in a variable condition operation; there are many companies in the system design, the capacity to choose a larger system to match Unreasonable, often "big car", resulting in a lot of energy waste. Therefore, to do a good job in energy conservation of fans and pumps is of great significance to the development of the national economy. 1 pump frequency control operation of the energy-saving principle Figure 1 for the pump valve control, when the flow requirements from Q1 reduced to Q2, the valve must be closed. At this time the valve friction increases, the pipeline curve from R to R ', head lift from Ha to Hb, operating conditions point from a point b point. Figure 2 is the speed control, when the flow rate requirement decreases from Q1 to Q2, the characteristic of the pump depends on the speed as the resistance curve R is unchanged. If the speed is reduced from n to n ', the performance curve changes from (QH) to (QH)' and the operating point moves from point a to point c and the head drops from Ha to Hc. According to the centrifugal pump characteristic curve formula: N = RQH / 102η Where: N - pump working conditions shaft power (kw)  Q-- use conditions point flow (m3 / s) H; Head of the working point (m); R - output media unit volume weight (kg / m3) ; η - pump efficiency (%). The shaft power at point b and the shaft power at point c can be calculated as follows: Nb = RQ2Hb / 102η N N Nc = RQ2Hc / 102η  两 The difference between the two is: ΔN = Nc-Nb = R × Q2 × (Hb-Hc) / 102η That is, when the flow is controlled by the valve, ΔN power is wasted and wasted, and the loss increases as the valve keeps turning off. The use of speed control, the flow Q and speed n is proportional to the first power; head H and speed n is proportional to the square; shaft power P and speed n is proportional to the cube, that is, power and speed n into the power of the relationship between the third power decline. If not the method of closing the valve, but the motor speed down, then the same flow in the case of transport, the original consumption of the valve in the power can be avoided, and achieved good energy-saving effect, which is the principle of energy-saving pumps . The basic principle of 2 frequency conversion velocity modulation The basic principle of the frequency conversion velocity modulation is according to the rotational speed relations of the alternating current motor working principle: n = 60f (1-s) / p   In the type: f-- pumps the electrical machinery frequency power (Hz) ; P - pole pairs of the motor; from the type we can see that even change the motor stator winding power frequency f, you can smoothly change the synchronous motor speed. Motor speed is slow, the corresponding reduction of shaft power, motor input power also will be reduced. This is the energy-saving pump frequency control role. 3 pump frequency control system design At present, the pump control system in the use of frequency control technology, most of the open-loop state, which is artificially based on changes in technology or external conditions to change the frequency of the inverter, (4) Regulator (PID). The control process of the system is : Measured by the pressure transmitter to measure the outlet pressure and converted into its corresponding 4 ~ 20mA standard electrical signal sent to the regulator and the process control indicators required to be compared to arrive at the deviation. The deviation value is calculated by the regulator according to the pre-defined regulation rule to obtain the adjustment signal. The signal is directly sent to the inverter so that the inverter converts the AC input with 380V / 50Hz into the output with 0 ~ 380V / 0 ~ 400Hz continuously adjustable voltage and frequency AC, directly to the pump motor. 4 pump frequency control applications Note pump speed is generally slow down the problem. When the use of frequency control, the original design by the frequency of the state of the pump and motor operating parameters have undergone major changes, the other as pipeline characteristics curve, speed governor pump in parallel with the constant speed pump and other factors, will be Speed ​​range has a certain impact. Out of range speed control is difficult to achieve the purpose of energy conservation. Therefore, frequency conversion speed regulation can not be unlimited. Generally believed that the frequency control speed should not be lower than the rated speed of 50%, preferably at 75% to 100%, and should be combined with the actual calculation. 4.1 pump process characteristics on the speed range In theory, the pump speed efficient zone through the frequency of high-efficiency area around the end of the two similar conditions parabolic middle region. In fact, when the pump speed is too small, the efficiency of the pump will drop sharply, affected by this, high-speed pump speed atrophy, if the operating point has exceeded this area, it is not appropriate to use speed to save energy. 4.2 speed pump on the speed range In practice, the water supply system is often more than one pump parallel water supply. Due to the expensive investment, it is impossible to speed up all the pumps, so the general speed pump, fixed speed pump mixed water supply. In such a system, care should be taken to ensure that both the variable speed pump and the fixed speed pump operate at the high efficiency stage and achieve the optimum system. At this moment, the constant speed pump has a great influence on the speed regulating range of the speed regulating pump running in parallel with it. The main points of the following two situations: 4.2.1 with the same type of pump must be run side by side, although the scheduling flexibility, but can not take into account the high-speed pump and constant speed pump efficient work section, so speed operation in this case The range is very small. 4.2.2 When different types of pumps must run side by side, if the speed regulating pump can reach the rated speed, the right end of head of high efficiency section and the left end of high speed section of constant speed pump will be equal in lift. You can achieve the maximum range of speed operation. However, at this moment, the speed regulating pump and the constant speed pump must not be allowed to run in parallel after the exchange. 4.3 Effect of motor efficiency on speed range Generally, there is Nαn3 under similar working conditions. Therefore, the shaft power will drop rapidly as the speed decreases. However, if the output power of the motor is excessively offset from the rated power or the operating frequency is excessive Offset frequency, will make the motor efficiency drops too fast, eventually affecting the efficiency of the entire pump unit. And since the cold motor continuous low-speed operation, but also due to insufficient air volume affect the heat, threaten the safe operation of the motor.