RU2690541C2 - Gas air-cooling apparatus control system - Google Patents

Abstract

FIELD: gas industry.

SUBSTANCE: invention relates to air cooling devices of gas and can be used for cooling of gas after compression at main gas pipelines compressor stations. Gas air-cooling apparatus control system comprises temperature setting unit, first controller, frequency converter, asynchronous motors, fans, heat exchanger and temperature sensor. Output of the first regulator is connected to the input of the frequency converter, the output of the frequency converter is connected to asynchronous electric motors kinematically connected to the fans influencing the air flow to the heat exchanger. System is equipped with second regulator, made in form of proportional-differential controller, second regulator input is connected to temperature sensor output, its output is connected to the second regulator first input, temperature setting unit output is connected to the first regulator first input. First regulator is in form of an integral regulator.

EFFECT: invention is aimed at improvement of dynamic characteristics and simplification of system tuning.

1 cl, 4 dwg

Description

The invention relates to apparatus for air cooling of gas and can be used, in particular, for cooling gas after compression of main gas pipelines at compressor stations.

The air cooler contains a heat exchanger through which the cooled gas is pumped through, and fans that create a flow of cooling air. A typical gas air cooler, for example, the 2AVG-75 apparatus widely used in gas cooling installations, contains two fans driven by short-circuited asynchronous motors. To control the rotational speed of the fans of each air-cooling unit, as a rule, one frequency converter is used, to the output of which both motors of the unit's fans are connected. The control system is performed in the form of a system with negative feedback on the gas temperature at the outlet of the apparatus. To ensure the stability of the system and the required dynamic characteristics, regulators are introduced into the system.

Known control system of air-cooled [RU 2330993]. The disadvantage of this device is not sufficiently high quality transients, in particular, the transition process changes the frequency of rotation of the fans with a step change of the temperature setting signal.

The closest in technical essence is the control system of the apparatus for air cooling of gas [Abakumov A.M., Alimov SV, Migacheva LA, Mosin VN Automatic control of the gas temperature at the outlet of the air-cooled apparatus / Bulletin of the Samara State Technical University. Series "Technical Sciences". No. 1 - 2011. Samara, 2011. P. 151-158], containing a temperature setting unit, an intensity adjuster (filter), a proportional-integral controller, a frequency converter, fan drive motors, a heat exchanger and a gas temperature sensor at the heat exchanger outlet. There are specific requirements for the control system of the air coolers. Along with the required quality parameters of temperature control, the system, in order to exclude dynamic overloads of the kinematic part of the fan drive, must ensure that the transition process changes the fan speed during a step change in the temperature reference signal without significant overshoot.

The disadvantage of the closest to the technical essence of the control system of the apparatus of air cooling of gas is that its performance quality regulation significantly change with a change in ambient temperature and dynamic characteristics of the electric drive.

In addition, in a known system, to reduce the overshoot of the transition process of changing the rotational speed of the fans with a stepwise change of the temperature reference signal, it is necessary to install an intensity setting device (aperiodic filter) at the system input.

In addition, the well-known system contains three adjustable parameters: the time constant of the intensity setting unit (filter), the time constant of the integrating transformation, and the time constant of the differentiating transformation of a proportional-integral regulator. The actual values of the system parameters by which the indicated time constants should be chosen are known only approximately. In this connection, the problem arises of experimentally adjusting the regulator and filter, taking into account the actual values of the system parameters. A large number of customizable parameters complicates system configuration.

The technical result of the use of the invention is to simplify the configuration of the system and improve the dynamic characteristics of the system in terms of variations in its parameters due to changes in external conditions.

The essence of the invention is that the control system of the gas air-cooling apparatus, comprising a temperature setting unit, a first regulator, a frequency converter, asynchronous motors, fans, a heat exchanger and a temperature sensor, the output of the first regulator is connected to the frequency converter input, an asynchronous electric motor, kinematically connected with fans acting on the heat exchanger with air flow, is additionally equipped with a second control with a proportional-differential controller, the input of the second controller connected to the output of the temperature sensor, its output connected to the second input of the first controller, the output of the temperature setting unit is connected to the first input of the first controller, while the first controller is designed as an integral controller, its time constant is selected by the ratio T _R1 = 2k _o k _E k _D T _E , where k _o , k _D are the transfer coefficients of the heat exchanger and the temperature sensor, k _E , T _E are the transfer coefficient and the time constant about the converter together with electric motors, respectively, and the time constant of the differential conversion of the proportional-differential controller is chosen equal to the calculated value of the time constant of the heat exchanger.

Significant differences are reflected in the new set of blocks and connections of the device. This set of blocks and connections allows to reduce variations in the quality of regulation with changes in ambient temperature and dynamic characteristics of the electric drive, as well as to simplify the setting of the system by reducing the number of adjustable parameters of regulators. In contrast to the known, the proposed control system for the air-cooling apparatus contains only two adjustable parameters: the time constant of the integrating transformation of the first controller and the time constant of the differential transformation of the second controller.

FIG. 1 shows a functional diagram of a control system for an air-cooled gas cooler; in fig. 2 is a block diagram of a control system for a gas air cooler; in fig. 3 - transients on the setting effect in the proposed control system of the device for air cooling of gas; in fig. 4 - graphs of the dependence of the regulation time in the known and proposed control system for an air-cooled gas cooler with variations in the time constant of the control object.

The control system of the gas air cooler (Fig. 1) contains a block 1 for setting the temperature, an integral regulator (I controller) 2, a frequency converter 3, asynchronous motors 4, fans 5, a heat exchanger 6, a temperature sensor 7, a proportional-differential controller (PD -regulator) 8.

The output of the temperature setting unit 1 is connected to the first input of the integral controller 2, the output of which is connected to the input of the frequency converter 3. The output of the frequency converter 3 is connected to asynchronous electric motors 4, kinematically connected with fans 5, affecting air flow to the heat exchanger 6 equipped with a temperature sensor 7. The output of the temperature sensor 7 through a proportional-differential controller 8 is connected to the second input of the integral controller 2.

The control system of the air cooler gas works as follows. At the input of the I-controller 2, the signal from the temperature setting unit 1 is compared with the signal from the temperature sensor 7 supplied to the second input of the I-controller 2 via the PD-controller 8. At the output of the I-controller 2, a signal is generated that determines the frequency and the output voltage of the frequency converter 3 and, accordingly, the voltage and frequency at the stator windings of the electric motors 4. The latter are driven by the rotation of the fans 5, which act on the heat exchanger 6 with cooling air flow. If the signal at the output of the temperature sensor 7 is equal to the signal of the temperature setting unit, then the control system is in the steady state. When the sensor signal 7 deviates from the signal of the temperature setting unit 1, the signal at the output of the I-controller 2 changes accordingly, the frequency and voltage at the output of the frequency converter 3 changes, the rotational speed of the electric motors 4 of the fans 5 changes. As a result, the intensity of the cooling air flow acting to the heat exchanger 6. This process continues until the signal at the output of the temperature sensor 7 becomes equal to the signal of the temperature setting unit 1. The result is a stabilization of the gas temperature at the outlet of the air cooler at a predetermined level.

The integral controller 2 gives the system astatic properties, i.e. allows you to suppress disturbances acting on the system. The proportional-differential regulator allows to compensate for the greatest inertia of the heat exchanger and to increase the speed of the system. Proper selection of the parameters of the regulators ensures the stability of the system and allows you to achieve the required accuracy of the stabilization of the gas temperature at the outlet of the air cooler.

To confirm this, we consider the block diagram of the proposed system with an air-cooled gas cooler (Fig. 2). It contains an integral I controller with a transfer function.

where T _R1 is the time constant of the integrating transform;

p is the Laplace operator.

The minus sign in the transfer function (1) shows that the positive increment of the input signal corresponds to the negative increment (decrease) of the output signal of the regulator.

вращения двигателей вентиляторовThe dynamic properties of the frequency converter, electric motors, fans, heat exchanger and temperature sensor are reflected in the same way as in the well-known system, the corresponding transfer functions. The transfer function of the frequency converter and the motor W _E establishes the relationship between the signal increment U _R1 at the input of the frequency converter and the frequency increment

fan motor rotation

where k _E and T _E is the transmission coefficient and time constant of the frequency converter together with electric motors.

отражает динамические свойства процесса теплообмена в теплообменнике под воздействием создаваемого вентиляторами потока воздуха, и устанавливает взаимосвязь приращения температуры θ газа на выходе теплообменника и приращения частоты вращения

вентиляторовTransmission function

reflects the dynamic properties of the heat exchange process in the heat exchanger under the influence of the air flow generated by the fans, and establishes the relationship between the temperature increment θ of the gas at the heat exchanger outlet and the rotational speed increment

fans

where k _o and T _o - transfer coefficient and time constant of the heat exchange process.

The minus sign in expression (3) reflects the fact that a positive increment in the rotational speed of the fans gives a negative increment in the gas temperature at the outlet of the air cooler.

The dynamic properties of the temperature sensor are described by the transfer coefficient k _D.

The dynamic properties of the PD controller (also called the boost link) are described by the transfer function

where T _R2 is the time constant of the differential transformation. In the proposed system, the time constant T _R2 is chosen equal to the time constant T _{o of the} object:

The time constant T _{R1 of the} integrating transform is selected by the condition

In a known system, in a straight circuit, a proportional set is established — an integral controller that compensates for the greatest constant T _{o of the} time of the heat exchange process in the heat exchanger. As a result, without using the intensity setter (filter at the system input), the transient process of changing the fan speed with a step change in the master signal proceeds with an unacceptable overshoot.

In the proposed system, a PD controller providing compensation for the greatest constant T _{o of the} time of the heat exchange process in the heat exchanger is installed in the feedback circuit. Due to this, the required character of the transient process of changing the rotational speed of the fans without using the intensity setter (filter) is achieved.

In accordance with the block diagram of the control system of the gas air-cooling apparatus, the dynamic characteristics of the proposed system were simulated. When modeling, as a calculated (reference) value, the time constant of the heat exchange process in the heat exchanger, as in the known system, is assumed: T _o = 300s. In accordance with expression (5), the time constant T _{R2 is} taken to be T _R2 = 300s.

The value of the time constant T _R1 in accordance with the expression (6) should be selected taking into account the time constant T _E. When using vector systems of frequency control of asynchronous motors, the time constant T _E can be considered as a “small” constant. In the case of connecting to a frequency converter of several motors, as is the case in the proposed system, parametric control systems for asynchronous motors are used. In this case, the value of the time constant T _E may be several seconds. When modeling, the value of T _E = 15c is assumed, the value of k _o k _E k _D = 1 The time constant of the I-controller, calculated by the formula (6), is T _R1 = 30s.

вращения двигателей вентиляторов при отрицательном единичном ступенчатом изменении сигнала на выходе блока задания температуры: кривая 9 для Т_Е=15с, при этом время t_p регулирования составляет 62с, а перерегулирование равно 4,3%; кривая 10 - для Т_Е=10с, в этом случае время регулирования - 66с, а перерегулирование равно нулю. Таким образом, вариации постоянной времени Т_Е несущественно влияют на показатели качества переходного процесса. Время регулирования для рассматриваемого переходного процесса в предлагаемой системе, как показывает анализ, примерно на 5%-10% меньше, чем в известной системе.FIG. 3 shows a graph of the transition frequency change

rotation of the fan motors with a negative unit step change of the signal at the output of the temperature setting block: curve 9 for T _Е = 15 s, while the regulation time t _p is 62 s and the overshoot is 4.3%; curve 10 is for T _Е = 10 s, in this case the regulation time is 66 s, and the overshoot is zero. Thus, variations in the time constant T _{E do} not significantly affect the quality indicators of the transition process. The regulation time for the considered transition process in the proposed system, as the analysis shows, is about 5% -10% less than in the known system.

When changing the external conditions of the system, especially the outdoor temperature, the time constant of the heat exchange process in the heat exchanger may vary. Based on the simulation, the influence of variations in the time constant T _{o of} the heat exchange process in the heat exchanger on the regulation time is investigated. According to the research in FIG. 4, plots of control time t _p versus time constant T _{o of} the heat exchange process in the heat exchanger are plotted: curve 11 for the proposed system; curve 12 is for a known system. Overshoot in the known and proposed system does not exceed 5%. As follows from the above graphs, the variation of the regulation time in the system under consideration is smaller than in the initial one.

The quality indicators of temperature control at the outlet of the gas air-cooling apparatus in the proposed control system of the gas air-cooling apparatus when the signal of the temperature setting unit changes and the effect of disturbance, as the analysis shows, are similar to the corresponding indicators in the known system.

Thus, the proposed control system for an air-cooled gas cooler makes it possible to ensure the required indicators of regulatory quality and simplify its adjustment by reducing the number of adjustable parameters.

Claims (1)

The control system of an air-cooled gas cooler containing a temperature setting unit, a first regulator, a frequency converter, asynchronous motors, fans, a heat exchanger and a temperature sensor, the output of the first regulator connected to the input of the frequency converter, the output of the frequency converter connected to asynchronous electric motors kinematically connected to fans affecting the heat exchanger with air flow, characterized in that it is additionally equipped with a second regulator; in the form of a proportional-differential controller, the second controller input is connected to the temperature sensor output, its output is connected to the second input of the first controller, the output of the temperature setting unit is connected to the first input of the first controller, while the first controller is designed as an integral controller, its constant time is selected by the relation T _R1 = 2k _o k _E k _D T _E , where k _o , k _D are the transfer coefficients of the heat exchanger of the temperature sensor, k _E , T _E are the transfer coefficient and the time constant of the frequency converter For together with electric motors, respectively, the time constant of the differentiating conversion proportional-differential controller is chosen equal to the calculated value of the time constant of the heat exchanger.

Images