RU2314450C1 - Control device of valving electric drive - Google Patents

Abstract

FIELD: chemical and petrochemical industries.

SUBSTANCE: invention is designed for control devices of electric drives of valves, cocks, gates in transportation of oil and oil products. Proposed valve electric drive control device has optomechanical position sender and contactless voltage switch. Torque unit is made for calculating torque on shaft of induction motor as function of stator current of induction motor in electric drive, rotor speed, and current frequency, with possibility of calculating torque at output of electric drive transfer mechanism according to relationship M=K_t x M_im where M is torque at output of electric drive transfer mechanism, K_t = α x K_r, K_t is torque gain factor, α is correction factor taking into account state of electric drive and type of transmission, K_r is transfer ratio of transfer mechanism, M_im is torque on shaft of induction motor, with possibility of setting maximum torque at output of electric drive transfer mechanism. Rotor speed of induction motor for torque unit is found by readings of optomechanical position sender.

EFFECT: simplified design, reduced overall dimensions, increased reliability.

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Description

The invention relates to control devices for electric valves (valves, valves, taps). The invention can be used on pipelines in the transport of oil, petroleum products, in the chemical and petrochemical industries.

A control device for an electric drive is known (RF patent for the invention No. 2154219, F16K 31/05, published on 08/10/2000, Bulletin No. 22) comprising a torque limiting cam clutch, a converter, and a recording device connected to it. The converter is kinematically coupled to a torque limiting clutch. The torque limiting coupling is made in the form of a spring-loaded movable and fixed coupling halves. When the magnitude of the torque on the output shaft of the electric drive increases, the axial movement of the movable coupling half is transmitted to the converter, which, with the corresponding mechanically specified amount of torque for a given direction of rotation of the shaft, mechanically acts on the recording device. The recording device activates and turns off the electrical power to the electric motor. The disadvantage of this device is the inaccuracy of disabling the motor with the coupling in relation to a given torque and the unexpected operation of the coupling when the drive starts.

The shutdown error is from 40 to 100%. In addition, after the electric motor is disconnected from the mains, the parts of the electric drive experience an impact load, which leads to shock and wear and reduces the reliability and service life of the electric drive. The clutch unnecessarily loads the spindle of the shutoff valves due to the inertia of the rotating parts and creates shock loads on the parts of the actuator and on the valve.

A drive control device is known that is described in the Storage, Installation and Maintenance Manual “Valves for Pipe Fittings and Control Systems” (BIFFI, Italy, 1994). The device comprises an electromechanical torque limiting clutch and a potentiometric position sensor of the gearbox output link, while the clutch and the sensor are equipped with mechanisms for adjusting the operation of the motor switches, respectively, at a certain moment and at a certain position.

The disadvantages of this device due to the use of an electromechanical torque limiting clutch are the inaccuracy of disabling the electric motor, the presence of shock loads on the parts of the electric drive and valves when the electric motor is disconnected from the mains, which leads to their wear and tear, reduced reliability and service life. Setting the maximum torque requires removing the casing from this mechanism, making the device inconvenient to operate.

The disadvantage of the potentiometric position sensor of the output link of the gearbox is the variable measurement accuracy, depending on the path traveled by it. So, the measurement accuracy of the potentiometric sensor decreases with a small path along the hyperbolic function.

A device for controlling an electric drive is described in the brochure “Rotorque Class IQ Drives. A New Generation of Intelligent Maintenance-Free Three-Phase Electric Drives ”(Publication 110 R, 12/2000 Edition, Rotork, UK, USA). The device comprises a shutter position sensor of the output link of the electric drive gearbox, a torque sensor. The position sensor is a magnetic pulse counter based on the Hall effect. The position sensor converts the number of revolutions on the motor shaft into an electrical signal, which is compared with the specified end positions. The position sensor is powered by the mains. In the absence of power from the network, an electric battery supports data archiving and calibration of the final positions of the output link of the gearbox. The torque sensor is designed as a piezoelectric sensor. The axial load of the worm shaft of the electric motor with the help of a piezoelectric transducer is converted into an electrical signal that is directly proportional to the developed torque in the electric drive and compared with a given signal of the limiting torque.

The disadvantages of this device are as follows. When the resource of the electric battery is exhausted and when working with a manual backup in the position sensor, the calibration of the end positions is lost, and a new calibration is required. The axial load of the worm shaft of the electric motor can be distributed unevenly, which affects the accuracy of the torque sensor.

A device for controlling an electric drive is known, described in the brochure "Protection, control and monitoring of electric drives Accutronix MX" company Limitorque Corporation, 2000, and selected as the closest analogue. The device comprises an optomechanical position sensor of the output link of the transmission mechanism, a torque sensor. The optomechanical position sensor is an absolute position encoder (US Patent No. 5640007, G01D 5/347). The encoder's touch mechanism includes a light emitter and a light detector (phototransistors), which determine the range of code links provided between a pair of encoder wheels, whose rotation is consistent with the rotation of the shaft (rotor) of the electric motor. The optomechanical position sensor is non-volatile from power supply, that is, the absence of any power supply from the position sensor does not affect its determination of the position of the output link of the transmission mechanism. The torque sensor determines "stop operation", that is, it works on the principle of, for example, a strain gauge or a piezoelectric gauge. This device has the following disadvantages. The presence of a torque sensor during installation of the device on the electric drive leads to interference in the design of the transmission mechanism (gear) and to complicate, increase the size and reduce the reliability of the transmission mechanism and the electric drive as a whole. In addition, the selection of a torque sensor is required depending on the torque for which the electric drive is designed, and this complicates the assembly of the electric drive. When using similar torque sensors for some types of transmission mechanisms, for example, wave reducers with intermediate links, there is no linearity in determining the torque depending on the load on the electric drive, which reduces the accuracy of determining the torque and the reliability of the device.

The objective of the invention is to provide a drive control device that simplifies the design, reducing the size and increasing the reliability of the drive.

The technical result provided by the invention in comparison with the closest analogue is expressed in the creation of an electric drive control device that eliminates mechanical interference in the electric drive of the element of the device that determines the torque, as well as in improving the accuracy of determining the torque at the output of the transmission mechanism of the electric drive by this element, regardless of the load, for which the electric drive is designed, and for any type of gear mechanism.

Like the closest analogue, the device contains an optomechanical position sensor.

In contrast to the closest analogue, the device contains a non-contact voltage switch, configured to be included in the electric network supplying the induction motor of the electric drive, a torque unit configured to calculate the torque on the shaft of the induction motor as a function of the stator current of the asynchronous motor in the electric drive, rotational speed its rotor, current frequency and with the possibility of calculating the torque at the output of the electric drive gear ode according to the relationship

M = K _m × M _a.d. where

M - torque at the output of the transmission mechanism of the electric drive,

K _m = α × K _p

K _m - the gear ratio of the moment,

α - correction factor, taking into account the state of the drive and the type of transmission,

To _p - gear ratio of the gear mechanism of the electric drive,

M _a.d. - torque on the shaft of the induction motor,

and also with the possibility of setting the maximum torque at the output of the electric drive transmission mechanism and having a first input connected to a current sensor, a second input connected to an optomechanical position sensor, and an output connected to a contactless voltage switch, a position adjuster having a first position setting input, a second input connected to the optomechanical position sensor and an output connected to the contactless voltage switch, while the device is configured to determine frequencies the rotor of the induction motor for the unit torque as indicated by an optomechanical position sensor.

The block diagram of the device is shown in the drawing with the following notation: 1 - optomechanical position sensor, 2 - non-contact voltage switch, 3 - torque unit, 4 - current sensor, 5 - position adjuster.

The device contains a position sensor 1. The position sensor 1 is designed to determine the position of the output link of the transmission mechanism of the electric drive and is made optomechanical. Optomechanical refers to a sensor consisting of a number of optical disks interconnected by mechanical links with different gear ratios, depending on the encoding and decoding method (for example, Gray code, binary code, etc.).

The non-contact voltage switch 2 is configured to be included in the electric network supplying the asynchronous electric motor of the electric drive, and is a thyristor or any other voltage regulator. Contactless voltage switch 2 is used for smooth braking of an asynchronous electric motor with subsequent interruption of its electric power supply when a signal 2 comes out from the output of the torque unit 3 to the contactless voltage switch 2 about exceeding a given maximum torque at the output of the electric drive transmission mechanism. Smooth braking of an induction motor reduces the wear of the drive elements and increases the reliability of its operation.

Torque block 3 torque block is configured to calculate the torque on the shaft of the induction motor as a function of the stator current of the asynchronous electric motor in the drive, the rotational speed of its rotor, and the current frequency. The means for calculating the torque is a microprocessor. The microprocessor calculates the torque on the shaft of the induction motor M _a.d. in the function of parameters such as stator current I, current frequency w _s , rotor speed w _p , for example, in accordance with formulas (1-43) on page 20 and (1-19) of the book by A. Sandler, Sarbatova R.S. "Automatic frequency control of induction motors." M., "Energy", 1974, part 1, and in this case, instead of the parameter β, slip S is used, aw _1н = w _c :

M _a.d. = (m ₁ × I ₁ ² × r ₂ × S) / (w _c × C (S)),

C (S) = r ₂ ² / x ₀ ² + (1 + x ₂ ² / x ₀ ² ) × S ² ;

Where

m ₁ - the number of phases of the stator of an induction motor,

I ₁ is the stator current of an induction motor,

r ₂ , x ₂ , x ₀ - parameters of the equivalent circuit of an induction motor,

,S - slip in an induction motor, calculated by the formula

,

w _c - current frequency,

w _p is the rotational speed of the rotor of the induction motor.

Calculation of torque on the shaft of an induction motor M _a.d. can be performed using any other mathematical expressions that establish the relationship between the torque of an induction motor M _a.d. and such parameters as stator current I, current frequency w _c and rotor speed w _p , for example, according to formula (3-129) contained in the electronic textbook Electrical Machines of the Department of Electromechanics of the Moscow Power Engineering Institute on the INTERNET website http: // elmech.mpei.ac.ru/em/EM/EM_cont_0.htm, while w ₁ = w _c :

where m ₁ is the number of phases of the stator of an induction motor,

U ₁ - voltage of the supply network,

w ₁ = w _c - current frequency of the network,

, где w_c - частота тока, w_p - частота вращения ротора асинхронного электродвигателя,S - slip in an induction motor, calculated by the formula

where w _c is the current frequency, w _p is the rotational speed of the rotor of the induction motor,

c ₁ - module equal to 1.05 ÷ 1.02,

r ₁ r ₂ , x ₁ , x ₂ - parameters of the equivalent circuit of an induction motor.

When calculating the moment, as a function of current, expression (3-125) is used from the above source, connecting the supply voltage and the current in the phases of the induction motor

Where

I ₁ is the stator current of an induction motor,

Z ₁ , Z ₁₂ , Z ₂ are the complex resistances of the equivalent circuit of an induction motor.

Thus, for the claimed device does not matter the method of calculating the torque on the shaft of an induction motor M _a.d. as a function of the stator current of an induction motor in an electric drive, the rotational speed of its rotor, and the current frequency.

The torque unit 3 is also configured to calculate the torque M at the output of the transmission mechanism of the electric drive according to the dependence

M = K _m × M _a.d. where

M - torque at the output of the transmission mechanism of the electric drive,

K _m = α × K _p

K _m - the gear ratio of the moment,

α - correction factor, taking into account the state of the drive and the type of transmission,

To _p - the gear ratio of the gear mechanism,

M _a.d. - torque on the shaft of the induction motor.

The moment transmission coefficient K _{m is} determined taking into account the state of the electric drive and the type of transmission.

For example, for such a type of transmission as wave transmission with intermediate links, there are four main states of the electric drive, which can be taken into account when calculating the torque M at the output of the transmission mechanism:

1) seal work at start-up with shock application of torque,

2) work on the sealing of the working body of shut-off valves during start-up with a smooth application of torque,

3) work in motion,

4) the transition from driving mode to operating mode to seal the working body of valves.

It was established experimentally that for these basic states of the electric drive, the transmission coefficient at the moment of Km is respectively equal to: 0.8K _p ; 0.65K _p ; 0.9K _p ; 0.95K _p , where K _p - gear ratio of the gear mechanism, and 0.8; 0.65; 0.9; 0.95 is the correction factor α, taking into account the state of the electric drive and the type of transmission.

Then the torque M at the output of the transmission mechanism is calculated as a piecewise-step function according to the formula M = K _m × M _a.d. where M _a.d. - torque on the shaft of the induction motor.

For other types of gears, their own gear ratios for the moment K _m determined by taking into account the main states of this type of gear can be experimentally determined.

The torque unit 3 is configured to set the maximum torque at the output of the transmission mechanism of the electric drive. The limit torque can be set using an operator-programmed microprocessor installed in the torque unit 3. In this case, the torque unit 3 issues a command to the contactless voltage switch 2, which starts to limit the voltage so that the maximum torque at the output link of the transmission mechanism electric drive did not exceed the set. The dependence of the maximum torque at the output of the transmission mechanism on the supply voltage of the induction motor is tabulated in the memory of the microprocessor of the torque unit 3. If the torque at the output of the transmission mechanism of the electric drive is greater than the maximum torque specified in block 3, the drive goes into seal operation working body of stop valves up to stop and de-energize an induction motor by a signal from an optomechanical sensor 1.

The torque unit 3 has a first input connected to a current sensor 4, a second input connected to an optomechanical position sensor 1, and an output connected to a proximity switch 2.

, где w_c - частота тока, w_c - частота вращения ротора асинхронного электродвигателя.From the theory of electric drive it is known that the torque on the shaft of an induction motor is a function of f (I ² , S) of the square of the stator current I ² and slip S in an induction motor, and the slip is calculated by the formula

where w _c is the current frequency, w _c is the rotational speed of the rotor of the induction motor.

Data on the magnitude of the current 1 of the stator of the induction motor and the frequency w _{c of the} current is supplied to the torque unit 3 by connecting the first input of this unit 3 to the current sensor 4, which serves to determine the current in the stator winding of the asynchronous motor.

The device is configured to determine the rotational speed of the rotor of the asynchronous electric motor w _p for the torque unit 3 according to the indication of the optomechanical position sensor 1, to which the torque unit 3 is connected to the second input. The rotor speed w _{p of the} induction motor is determined by the reading of the optomechanical position sensor 1 according to the following relationships:

f (w _d ) T _and = N _w (1)

N _w = f (w _p ) (2),

where w _d - pulse frequency optomechanical position sensor 1,

f (w _d ) is a function of the pulse frequency of the optomechanical position sensor 1,

T _and - the time interval for which the pulse frequency of the optomechanical position sensor 1 is measured,

N _w - the number of pulses of the optomechanical position sensor 1 for the time interval T _and , which is a code and proportional to the rotor speed w _{p of the} induction motor,

w _p - rotational speed of the rotor of an induction motor,

f (w _p ) is a function of the rotational speed of the rotor of an induction motor.

For the time interval T _and determine the function f (w _d ). By the formula (1), a code is calculated (the number of pulses of the optomechanical position sensor 1) N _w proportional to the rotational speed of the rotor of the induction motor according to the formula (2). Thus, the code N _w obtained from the optomechanical position sensor 1 is proportional to the rotor speed w _p and is taken into account by the torque unit 3 when calculating the torque as a value corresponding to the rotor speed w _{p of the} induction motor.

In the device for realizing the possibility of determining the rotational speed of the asynchronous electric motor rotor w _p according to the indication of the optomechanical position sensor 1, there is a means for measuring the time interval T _and for which the pulse frequency of the optomechanical sensors 1 is measured, for example, a timer, and also the pulse counter of the optomechanical sensor 1.

At the output of block 3, connected to the contactless voltage switch 2, a signal is generated that the calculated current torque at the output of the transmission mechanism of the electric drive exceeds a predetermined maximum torque at the output of the transmission mechanism of the electric drive.

The position switch 5 has a first input for setting the position and a second input connected to the optomechanical position sensor 1, as well as an output connected to the contactless voltage switch 2. The position switch 5 is made in the form of a device that stores position signals specified through the first input and compares with them the signal arriving at the second input of the positioner 5 from the optomechanical position sensor 1 about the current position of the output link of the transmission mechanism of the electric drive. When the output link of the transmission mechanism reaches the set position at the output of the positioner 5, a signal is generated about this.

The output of the position adjuster 5 is connected to a non-contact voltage switch 2, which gradually slows down and turns off the electric motor when a signal from the output of the position adjuster 5 arrives at the output link of the transmission mechanism reaching the preset position.

The device operates as follows.

Alternately, the output link of the transmission mechanism of the electric drive is set to the necessary positions and signals in the form of position 5 are set in the form of codes corresponding to these positions. The transmission mechanism can be made, for example, in the form of a worm, wave gear, gearbox with intermediate links, backstage.

In the block of torque 3 set the maximum torque at the output of the transmission mechanism of the electric drive.

An asynchronous electric motor drives the transmission mechanism of the electric drive. The optomechanical position sensor 1 determines the position of the output link of the transmission mechanism along the entire path of its movement and provides information about the position in the form of signal codes.

When the output link of the transmission mechanism reaches the set position, the signal from the optomechanical position sensor 1 goes to the position adjuster 5. The position adjuster 5 compares it with the signal set in it and transmits a signal to its output when the set position is reached. The position switch 5 transmits a signal from its output to the contactless voltage switch 2. The contactless voltage switch 2 gradually slows down and turns off the electric motor in the electric drive.

The maximum torque at the output of the drive gear of the electric drive, set in the torque block 3 by a programmable way, is compared with the current torque calculated at the output of the drive gear of the drive calculated in the same block 3. A signal about exceeding the maximum torque at the output of the electric drive transmission mechanism is supplied to the output of the torque unit 3 connected to the contactless voltage switch 2. The contactless voltage switch 2 smoothly brakes and disconnects the asynchronous motor from the mains.

Claims (1)

A control device for an electric drive of shutoff valves, comprising an optomechanical position sensor, characterized in that it contains a non-contact voltage switch, configured to be included in the electric network supplying the asynchronous electric motor of the electric drive, a torque unit configured to calculate the torque on the shaft of the asynchronous electric motor as a function the stator current of an asynchronous electric motor in an electric drive, the rotational speed of its rotor, the current frequency and possibly the ability to calculate the torque at the output of the transmission mechanism of the electric drive according to the dependence M = K _m · M _a.d. , where M is the torque at the output of the transmission mechanism of the electric drive; K _m = α · K _p ; K _m - coefficient of transmission at the moment; α - correction factor, taking into account the state of the drive and the type of transmission; To _p - gear ratio of the gear mechanism; M _a.d. - torque on the shaft of the induction motor, and also with the possibility of setting the maximum torque at the output of the electric drive transmission mechanism and having a first input connected to a current sensor, a second input connected to an optomechanical position sensor, and an output connected to a contactless voltage switch, a position adjuster having a first position setting input, a second input connected to the optomechanical position sensor and an output connected to the contactless voltage switch, while the device is configured to determine frequencies the rotor of the induction motor for the unit torque as indicated by an optomechanical position sensor.