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Optimal Frequency Conversion Control Of Centrifugal Pump

- May 06, 2018 -

The centrifugal pump USES speed control to adjust the flow, instead of regulating the flow with the valve baffle and other throttling methods, it can obtain the obvious power saving effect. Frequency conversion is one of the most efficient methods in speed control. Because of the rapid development of semiconductor frequency conversion technology and many outstanding advantages, it has been widely used in industry.

At present, the conventional design idea of centrifugal pump frequency conversion is aimed at eliminating the valve throttling loss, which can achieve good energy saving effect in general. But in the centrifugal pump operation, besides the valve throttling loss, there are motor loss, centrifugal pump loss, pipe network loss and other losses. In practice, these losses affect each other. Therefore, it is necessary to consider these factors in a comprehensive way under the conditions of satisfying the required flow rate, so as to obtain the operating point of the minimum energy consumption of the unit, and then determine the output frequency of the frequency converter. As for the interaction between different pump stations and different centrifugal pumps and pipe networks in the complex fluid network, the working frequency of the total frequency converter should be designed to reduce the total energy consumption of the system. This paper only discusses single pump optimal frequency conversion control.

Optimal frequency conversion control problems of single stage centrifugal pump, the optimal frequency modulation control problem can be prescribed for the guarantee provided a given flow centrifugal pump, determine the speed of a centrifugal pump, the flow units consumed the least amount of electricity.

Effective power of the work.

Therefore, the electric power consumed by the unit flux is the rotation speed and displacement of the centrifugal pump, which needs to be measured in practice. The curve of curve 3 and curve 1 respectively represents the curve of l and l changes respectively.

System main program flow chart of the conclusion above a simple introduction of the Angle sensor of time-space conversion device, its sensing method, completely out of the traditional way of electromechanical device of the sensor, realized the amount into the space time quantity...

In order to give the analytical form of various properties, the following approximate formula can be obtained according to the test data and theoretical analysis.

Centrifugal chestnut pressure 2.1 a traffic P pipe network resistance pipe network resistance characteristic varies because of the network structure, and the differences between various variables with n variables, rotational speed n relationship of P, and V is corresponding to speed for n, inch variables.

The calculated value is low, and the reduction range is larger than the nominal speed.

5 drive motor of the efficiency curve of motor efficiency curve as shown in, can be simplified into two section, when the shaft power in general, the greater the motor power, the higher the highest efficiency (Ce), conic section flat (that is, the smaller the De value), such as YK can consider efficiency of approximate constant on the interstate.

So the centrifugal chestnut optimal frequency modulation control problem is: in equality constraint equation under the condition of () ~ (0), guarantee to achieve a given flow Qs, find out the optimal frequency n u make to minimize the objective function (2).

The calculation of the optimal frequency control problem is based on the principle of the previous paragraph. When the displacement is defined as Qs, it is required to determine the rotation speed n, and the minimum is achieved under the condition n+KQ>Qs. General suction pressure Pin is very small, negligible, by using the differential method can obtain the optimal solution to meet the three times of algebraic equation is solid solution of equation (10) : > n.s is the real optimal solution and numerical solution is needed to find out the optimal solution.

To define the conditions for solving n'>n. When running at the nominal speed, the flow Q>Q is reduced in the efficiency curve.

If centrifugal chestnut in speed n. When the pressure flow characteristic and efficiency respectively by the curve 1 'and 3', said the work pressure is P, then chestnut P 'is low, if appropriate increase speed to n ", the centrifugal pressure flow characteristic and efficiency of chestnut respectively by the curve 1 "and 3", said the LiJi when rotational speed n, fixed rotational speed n, efficiency higher than that of (3) type gauge if LiXiao benefits greater than the loss of AP, the speed of n, working automation technology and application, 2001 doubly-fed speed regulation system of all kinds of protection circuit Ren Yingyu guang-jie fu (daqing petroleum institute, Heilongjiang anda 151400) is introduced for doubly-fed motor speed control system of phase failure protection and under (a) voltage protection, over current protection circuit, working principle and actual application results and its circuit and working process of the details and instructions.

The structure of asynchronous motor is simple and low cost, its mechanical properties can meet the requirements of most production machines, and its importance is increasing day by day. With the protection device from electromechanical to microcomputer, the automatic performance of the protection device is higher and higher.

This system USES the microcomputer control of all-digital doubly-fed motor speed control system, the so-called doubly-fed, refers to the three-phase asynchronous motor stator and rotor windings, respectively from two separate three-phase symmetric power supply, including the power of the stator winding of fixed frequency power supply, power frequency and rotor by hand in a hand in the inverter power supply, the voltage amplitude, frequency and phase are adjusted according to the requirements of operation. The advantages of the digital control system lies in its self-diagnosis function, i.e. during the running of the drive, since the diagnostic function can check the function of the module and online status, you can monitor all the parameters, through the appropriate configuration of hardware and software to realize control of ac motor. This paper introduces the protection and overcurrent protection of fault phase protection and undervoltage (overpressure) on the rotor side of the motor.

In the operation of three-phase asynchronous motor, the phenomenon of single phase operation is destroyed due to the fault phase. More than 80 percent of the motor's burning is attributable to single-phase operation. Therefore, it is very important to take effective measures to protect the motor.

The secondary three-phase voltage of the rotor side synchronous transformer is used as the input signal of the fault protection circuit, as shown. When the three phases are normal, the central point potential is zero, and the normal closed relay Ji remains closed, and the output end is not broken. When there is at least one phase disconnection in the three-phase phase, the central point potential of the input terminal is no longer zero. After the diode bridge rectifier and capacitor filter, the output of the input terminal is broken. Believe, on the one hand, is breaking to the microcomputer system for fault analysis and processing, on the other hand, the triode T1 collector load normally closed relay J1 disconnect the motor rotor side attract of ac contactor coil circuit, ac contactor to disconnect the rotor circuit.

Under voltage (overvoltage) protection circuit, the voltage of the rotor side synchronous transformer, such as A phase voltage, is A better energy saving benefit.

In addition, from the efficiency curve of the motor, when the motor shaft power is lower than M, the efficiency of variable frequency control is not high because of the low efficiency of the motor.

When the speed n is greater than and the working flow Q is less than the nominal optimal flow, the conventional algorithm is the optimal frequency conversion control. 2. In normal working flow >, the optimal solution of frequency conversion adjustment needs to be analyzed by optimizing objective function (); 3. If the shaft power is less than N1, the conversion control gains little benefit.

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