RU2001313C1 - Method for controlling well pump submerged motor - Google Patents

Abstract

SUMMARY OF THE INVENTION: The thyristor frequency converter and the output voltage of the supply current are varied. The pressure at the pump outlet is measured and the predetermined law of its change is maintained in the start and stop modes. Frequency and output voltage changes are performed in steps. In the start-up mode of the electric motor, a step-by-step change in the start-up and voltage is carried out during an increase in the rotor speed from the initial value to half the nominal frequency by quasi-frequency control of the thyristor converter. The first time derivative of the pump output pressure is kept constant over time. The rotor speed increases to the nominal value. by phase control of the converter. At the same time, the second derivative of the pressure at the pump output is kept constant in time. In the stop mode, these operations are performed in reverse sequence. The duration of the electric motor operation in the start mode is set in accordance with the given dependence. 5 ill.

Description

IS

The invention relates to the control of a submersible electric motor of a downhole water-lifting pump and can be used when it is necessary to increase the reliability of the pumping unit, improve the quality of operation of artesian wells and power supply systems.

A known method for controlling a borehole water pump with a submersible motor is direct start, in which when the start signal is received from the process sensors, the rated voltage is applied to the stator windings of the motor, after which the motor reaches the rated speed in less than 1 s. When a stop signal is received from technological sensors, the voltage from the stator windings of the motor is removed and it is also turned off in less than 1 s.

The disadvantage of this technical solution is that as a result of the direct start-up of the submersible motor after two three years of operation, there is an increased removal of sand from the wells (sanding), which leads to premature destruction of the well. Sanding also causes the pump unit to fail.

Direct start-up, accompanied by 6-7 times the rated starting currents of the electric motor, requires the use of transformers of high power, which is uneconomical.

In addition, during direct start-up, mechanical damage to the frontal parts of the electric motor occurs.

With direct braking of the submersible motor, there is a danger of water hammer, which breaks the valves in the pipeline, and in the absence of a check valve, the water filling the pressure pipe leaves it through the pump into the well, causing the electric motor to rotate in the opposite direction. those. operate in turbine mode, which can cause damage to the pump blades if a start signal arrives at this moment

There is also known a method of controlling a submersible electric well pump, which comprises controlling the voltage that is applied to the stator windings when a start and reverse signal is received using dynamic braking when a stop signal is applied.

The disadvantage of this technical solution is that when regulating voltage, the stator currents can be two to three times

exceed the nominal values, which is especially manifested at low speeds of the electric motor. At low voltage values on the stator windings of the motor, very soft mechanical characteristics are obtained, which make it difficult to control the speed of the electric motor in an open control system. The rotational speed of the electric motor at low voltages is unstable and very dependent on the load. With submersible motors, the speed of rotation is very dependent on the type of well pump and on the penetration of the motor and pump into the well.

In addition, a device implementing this method is cumbersome and expensive since it requires the use of a separate reverse station using dynamic braking.

The closest technical solution that can be adopted as a prototype is a method of starting a low-inertia asynchronous electric motor, in which a voltage is applied to the stator windings equal to the starting voltage, and then this voltage is reduced exponentially with a constant time, not exceeding five periods of the mains voltage to the rated voltage at which the rotor of the motor still rotates, after which the supply voltage is increased exponentially with a time constant not exceeding the impact oennogo predetermined start time.

An apparatus for implementing this method comprises a thyristor converter, a control unit, a voltage driver, a synchronization unit (gate signals), and a pulse-phase drive unit.

The disadvantage of this technical solution is that when a voltage equal to the breaking voltage is applied to the stator windings without introducing the constant damage necessary for the electric motor to reach the required speed, the motor will not start to rotate (or will not start), while the decrease in voltage for five periods has no effect on starting the engine, it will be in a locked state.

In addition, at low rotational speeds of the electric motor, currents can exceed two to three times the nominal values, and at low voltages the stator windings have soft mechanical characteristics that make it difficult to control the rotational speed of the electric motor. The rotational speed of the electric motor at low The voltage is unstable and very dependent on the load of the electric motor, i.e., it depends on the type of borehole pump and on the penetration of the electric motor and pump into the well,

The disadvantage is that the electric motor cannot be braked smoothly, since direct braking causes a water hammer and breakage of shutoff valves in the pipeline, and in the absence of a check valve, a water column filling the well and leaving through the pump can break the pump vanes .

The aim of the invention is to increase the reliability of the electric motor and the borehole pump while reducing the degree of destruction of the wells.

This goal is achieved by the fact that in the proposed method for controlling the submersible motor of a borehole water pump, comprising changing with a thyristor frequency converter and the output voltage of the supply current, measuring the pressure at the pump output and maintaining a given law, changing it at start and stop modes, the aforementioned the frequency and output voltage are changed stepwise; in the start-up mode of the electric motor, the frequency and output voltage are stepwise changed the period of increasing the frequency of rotation of the rotor of the electric motor from the initial value to half the nominal frequency by quasi-frequency control of the thyristor Converter, while maintaining the constant value of the first derivative of the pressure at the pump output over time, increasing the frequency of rotation of the rotor of the electric motor to the nominal value is carried out by phase control of the thyristor with the transducer and at the same time maintain a constant value of the second derivative of the pressure at the pump output over time, then IU mentioned stop operation is performed in reverse sequence, wherein the duration of the motor from start to the rated rotational speed set value according to the relation

t-

Z i 1

k b

where T is the operating time of the submersible motor from the initial moment of start up to the nominal value of the rotational speed;

t $ - well operation time from the moment of its commissioning;

v is the velocity of the water flow cooling the submersible electric motor;

k is the coefficient of proportionality, depending on the power of the electric motor, 0 k - 1.0-10.95;

N is the number of stages of the frequency of rotation of the electric motor.

In FIG. 1 shows a block diagram of a device for implementing the proposed method; in FIG. 2 is a timing diagram of the state of a thyristor converter; in FIG. 3 is a schematic diagram of a connection of a strobe signal unit, a phase sequencing unit 0, and an input signal generating unit; in FIG. 4 is a schematic diagram of the connections of the control pulse unit and the thyristor converter; in FIG. 5 is a schematic diagram of connections of 5 microcomputer connections, a buffer register, and read-only memory.

The submersible motor control device of the borehole water pump that implements the proposed method 0 (Fig. 1) comprises a thyristor converter 1, the load of which is an asynchronous motor with a squirrel-cage rotor 2, a block of control pulses 3, a block of gate signals 5 , phase sequence determining unit 5. the forming unit is similar; signals 6, microcomputer 7, buffer register 0, read only memory 9.

03, the KR1816BE35 microcircuit was used as a microcomputer, two K561TMZ microcircuits were used as buffer register 8, and the KR573RF2 microcircuit was used as a permanent storage device.

5 The essence of the proposed method for controlling the submersible electric motor of the SKBEZHINNY water-lifting pump is as follows. After a start signal is received from the process sensors, a start-up period of 0 from the start-up moment to reaching the half-speed of the nominal speed is carried out quasi-frequency. control of the thyristor converter, moreover, the frequency and magnitude 5 of the output voltage of the thyristor converter supplied to the stator winding are changed stepwise, while the first derivative of the water pressure is kept constant and -, c, the output is time constant, then ocv is

control the thyristor converter and increase the frequency of rotation of the electric motor to a nominal value, while maintaining a constant value of the second derivative of the pressure at the pump output over time, providing a constant increase in pressure in the pressure pipe.

After the stop signal is received from the process sensors, a stepwise reduction of the rotational speed of the electric motor from maximum to minimum is carried out with the reverse sequence of operations described above during step start.

The implementation of the proposed method is achieved by the formation of a certain law of turning on the gates of the thyristor converter 1 (sequence and periodicity). This law (algorithm) must contain periodically repeating time intervals when a voltage of a given value is connected to the load (stator winding of the electric motor) and at certain intervals, during which the load is disconnected from the network (Fig. 2).

Two series of pulses (Fig. 2) m and n are generated, with the help of which the duration of the on and off state of the valves of the thyristor converter, and therefore the motor, is discretely set. During the pulse repetition period, the thyristor converter valves are open, and the pulse repetition period the thyristor converter valves are closed.

By setting different ratios of the values of type, different frequencies of the main component of the voltage at the output of the thyristor converter are obtained, and the bias of the control pulse supplied to the corresponding pair of gates of the thyristor converter relative to the point of natural switching 1 (Fig. 2) by an angle a. control the voltage supplied by the pump, remains constant within the time the motor is at one stage of the speed, i.e. P (tc) const, where P is the first derivative of the pressure of the water in the pressure pipe: tc is the duration of the electric motor at one stage.

This makes it possible to control the motor at low speeds regardless of its load and penetration into the well, while ensuring rigorous mechanical characteristics

In the event that the number n is 0. and the pulses m follow continuously, phase control is carried out with voltage regulation by changing the angle

and. (open the gates of the thyristor converter). In this case, the water pressure developed by the pump increases with constant acceleration during the entire time the phase mode

control, i.e. P (tf) const, where P is the second derivative of the pressure of the water in the pressure pipe; f is the operating time of the submersible motor in the phase control mode.

By varying the angle of control of the thyristor converter valves, a gradual increase in the main component of the voltage supplied to the stator winding is achieved, and. hence,

gradually increasing the speed of the electric motor with constant acceleration.

The developed algorithm is written as a program in read-only memory

device.

The time of step start and step stop is determined by the duration of the electric motor and in proportion to the operating time

artesian well from the beginning of its input, that is, depends on the degree of sanding, and also in proportion to the speed of the water flow cooling the submersible motor, i.e. its degree

cooling, and depends on the number of steps that make up the entire cycle of step start or step braking, i.e.

1

T Ј k te v,

i 1

where T is the operating time of the submersible motor from the initial moment of start up to the nominal value of the rotational speed; B - operating time artesian

wells from the beginning of its commissioning:

v is the velocity of the water flow cooling the submersible engine;

N is the number of starting and braking steps;

k is the coefficient of proportionality, depending on the power of the electric motor, to 1.0-10.95.

The operating time at each stage tc and the number of stages N are recorded in read-only memory

The program consists of silt cyclone (see Fig.

5).

The cycle is equal to one grid voltage sequence. In order to obtain the highest operating mode of the electric motor, six pulses must pass at intervals of 60 ° between them and with a certain sequence of switching on the valves of the thyristor converter in one mains voltage period.

The program is synchronized by the mains: The start of the cycle is determined by an external interrupt (the occurrence of a building signal), i.e. passing through zero voltage of the supply network (for example, phase A). When a direct sequence of alternating phases of the supply network is connected to the thyristor converter 1, the necessary sequence of switching on the corresponding pairs of thyristor converter valves (Figs. 1 and 2) 1s and 1i and 1e is obtained; 1h and 1e; 1z and 12; ) and 1g.

In this case, the symmetry of the electric motor operation is not violated, that is, six pulses pass during the mains voltage period and the sequence of switching on the pairs of thyristor converter valves corresponds to the direct sequence of phase rotation of the supply network.

After the appearance of an external interruption (gate signal), the microcomputer, in accordance with the algorithm, counts the angle a, i.e. it determines the magnitude of the voltage supplied to the stator winding of the electric motor, and then requests the number of pulses m to turn on the valves needed for this stage of the motor speed and generates signals to turn on the valves in the above sequence.

Claims (1)

The claims METHOD FOR CONTROLLING A SUBMERSIBLE ELECTRIC MOTOR OF A Borehole PUMP, INCLUDING a change with the thyristor frequency converter and the output voltage of the supply current, measuring the pressure at the pump output and maintaining a predetermined law of its change at the start and stop modes, and changing the frequency and output voltage characterized in that in the start-up mode of the electric motor, a stepwise change in the frequency and output voltage is carried out during an increase in the rotational speed of the electric rotor the motor from the initial value to half the rated frequency by quasifrequency control of the thyristor converter, while maintaining the constant value of the first derivative of the pressure at the pump output over Next, the microcomputer asks for the number of pulses p - to turn off the valves and turns off the thyristor converter for a given time interval. At the beginning of each cycle, the program checks to see if the run time at one stage (tc) has ended. If the operating time at one stage is over, i.e. tc is 0, the program proceeds to the processing of the next stage, and the program polls the number of stages N. If N is 0, then the step start or braking is completed and the engine either reaches the rated speed when the step start is performed, or it stops when the step braking is performed. In accordance with the foregoing, the proposed method for controlling the submersible motor provides step-by-step start and step-by-step braking, which increases the reliability of the pump unit and the electric motor. In this case, the well is not destroyed, therefore, its service life is significantly increased. As experience in the operation of the prototype showed, the proposed technical solution allows to increase the service life of artesian wells and the service life of well pumps with submersible electric motors by more than two times due to a decrease in the level of sanding of wells. (56) Maksimov V.P., et al. Regulated control of the drive of installations of external electric pumps. Review inf issue 5 M, VNI-IENG 1981.0. 13-15 42 0 fifty 5 belt, increasing the frequency of rotation of the rotor of the electric motor to the nominal value is carried out by phase control of the thyristor converter and at the same time the second derivative of the pressure at the output of the pump is constant over time, in stop mode, the above operations are performed in the reverse order, while the duration of the electric motor on start mode set in accordance with the dependence / V  2A .. V- where T is the operating time of the submersible j / ie-apo motor from the initial moment of gig t to the nominal value of the rotational speed i.e., the operating time of the well with the beginning of her input; v is the velocity of the water flow, cooling + .-., total submersible electrode A B U t Seri hippulse P Impulse Series Musical condition FIG. 2 O-gOT-O-g-b-g-6-i , © TTTJJ 5SP & 9 U D D 0 iwi and Sfillaljl  a g State of emergency Pj 4) .BTSh ° n    st ek-fc. V "h O “QtQ O b“ O O "Ci o ha sd ca 5  e v isasslS HDhCHN  : 53 HHV V X x Pj 4) .BTSH /// /// ggSfJO g S v oe og tag tg a og a " o-e X . 5l «k. ssskhyTy. ЈЈ 1 G t-1 1 : "" y 1 r 0 Q $ Ae4