CN102707620A - Backpressure control system of large air-cooler unit - Google Patents

Abstract

The invention discloses a large-scale air-cooling unit back pressure control system, which belongs to the automatic control system of a thermal power plant, including: a PID module, a back pressure automatic setting module, a feed-forward signal, a control parameter variable gain module and a step-cut optimization module. The function module, integral module, selection module, addition and subtraction module, division module, multiplication module, and pulse module in the control system are built into real-time online optimization logic to form an independent automatic control system for dynamic tracking and stable control, which solves the problem of large-scale air cooling The back pressure control system of the unit has a large overshoot, which makes it difficult to realize the technical problem of full automation. It can be widely used in the steam turbine back pressure control of large air-cooled units.

Description

A Back Pressure Control System of Large Air Cooling Unit

technical field

The invention relates to an automatic control system, in particular to a back pressure closed-loop automatic control system of a large air cooling unit.

Background technique

The back pressure control system of the air-cooled unit mainly calculates the cooling air flow required by the exhaust steam of the condensing turbine through the measured value of the back pressure. , fan speed and steam isolation valve position are adjusted to finally control the back pressure of the turbine to operate within a safe and economical range.

The existing large-scale air-cooled unit back pressure control system basically has the following problems: (1) With the change of ambient temperature and unit load, the operator has to manually increase or decrease the automatic back pressure setting value to meet the needs of unit operation . (2) The speed reduction program of the countercurrent fan in winter will cause a regular disturbance to the back pressure control, which is especially obvious when the load is relatively low and there are few running air-cooling fans. (3) After the air-cooling step is switched, the number of running fans changes, and the back pressure control PID parameters will not match the actual working conditions, resulting in poor regulation performance of the control loop. (4) The setting interval of air-cooling step switching is too short. When the adjustment characteristics of the control loop become poor, it will cause the step sequence to switch back and forth, which will increase the interference on the control loop. The existence of these problems causes the control performance of the back pressure of the steam turbine to decline, and even fails to meet the requirements of the control index, which directly affects the safe and economical operation of the unit.

Contents of the invention

The object of the present invention is to provide a back pressure control system of a large air-cooling unit, which can overcome the above disadvantages and realize full automatic control of the air-cooling unit.

The technical solution of the present invention is: a large-scale air-cooling unit back pressure control system, characterized in that: the control system includes: PID control loop, back pressure automatic setting module, feedforward signal, control parameter variable gain module and step-cutting Optimization module; among them: the PID control loop takes the back pressure of the steam turbine as the target setting value, and the back pressure automatic setting module takes into account the insufficient cooling capacity of the air-cooled island tube bundle in summer and the antifreeze performance in winter, referring to the operation specifications of the steam turbine factory and according to the actual operation of the unit , designed the relationship function of ambient temperature, unit load and back pressure. The higher the unit load and ambient temperature, the higher the turbine back pressure setting. The back pressure control is changed from a traditional manual setting simple control system to an intelligent control system that automatically sets the best economical back pressure setting value. A feed-forward signal is used on the PID module to prevent the influence of reverse flow fan speed reduction and anti-freezing on the back pressure control. The feed-forward signal is a reverse step signal, and the step time is determined by the reverse flow fan speed reduction program. The step signal is sent to the back pressure control system as a feed-forward signal after being speed-limited by the speed-limiting block, so as to offset the impact of reverse flow speed reduction on the system. the

In order to obtain better adjustment quality, a control parameter variable gain module is used in the control system. When the step sequence increases or decreases, the number of fans in operation changes, and the open-loop gain of the system changes accordingly. Through this module, the back-to-back The closed-loop proportional coefficient of the pressure control system is adjusted accordingly to adapt to the change in the number of controlled objects and ensure the adjustment quality of the control system. the

The step-cutting optimization module is to prevent the system oscillation caused by the continuous switching of the step sequence, avoid unnecessary start-up and stop of the fan when the running fan still has adjustment margin, and add a condition to the traditional air-cooling step-cutting program: the frequency of the running fan reaches the upper limit Only when the fan frequency reaches the lower limit can the step be cut upward;

The invention has the advantages of forming an independent automatic control system for dynamic tracking and stable control, which solves the technical problem that the back pressure control system of large air-cooling units has large overshoot and is difficult to realize full automation, and can be widely used in steam turbines of large air-cooling units Back pressure control.

Description of drawings

Fig. 1 is a schematic diagram of a back pressure control system of a large air-cooling unit according to the present invention.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments.

The present invention adopts the following new ideas

(1) Increase the optimal economic back pressure automatic setting circuit

Considering the insufficient cooling capacity of the air-cooled island tube bundle in summer and the anti-freezing performance in winter, referring to the operating specifications of the steam turbine plant and according to the actual operation of the unit, the relationship function of ambient temperature, unit load and back pressure is designed. The back pressure control is changed from a simple control system with manual setting to an intelligent control system that automatically sets the best economical back pressure setting value.

(2) Increase the anti-interference circuit

In order to ensure the stability of the unit and the back pressure control, and to prevent the influence of the anti-freezing of the reverse flow fan on the back pressure control, a reverse step feed-forward signal is added to the back pressure control loop, and the step time is determined by the reverse flow fan speed reduction control program. decision, as shown in Figure 1. The step signal is sent to the back pressure control loop as a feed-forward signal after being speed-limited by the speed-limiting block, so as to offset the influence of the reverse flow speed reduction on the system.

(3) Self-adaptation of back pressure control parameters

When the step sequence increases or decreases, the number of running fans changes, and the open-loop gain of the system changes accordingly. If the step sequence changes, the number of fans running in parallel changes, and the open-loop gain changes. In order to obtain better adjustment quality, After the step sequence changes, the closed-loop proportional coefficient of the back pressure control loop is adjusted accordingly to adapt to the change in the number of controlled objects, as shown in Figure 1.

(4) Step-by-step logic optimization

In the traditional air-cooling step-cutting logic, the trigger condition for step sequence increase (step-up) is that the actual back pressure (BP _measurement ) exceeds the set back pressure (BP _S ) by 1.4 times; or when the BP _measurement is between 1.1 and 1.4 times of BP _S Time, the difference between BP _measurement and 1.1 times BP _S is integrated with time, when the integral value reaches the set value, and the back pressure is on the rising edge. The trigger condition for step reduction (step down) is that the BP _measurement is lower than 0.6 times the BP _S ; or when the BP _measurement is between 0.6 and 0.9 times the BP _S , the difference between the BP _S of 0.9 times and the BP _measurement is integrated over time , when the integral value reaches the set value and the back pressure is on the falling edge.

Now the logic is modified to increase the operating fan frequency to the upper limit when the BP _measurement is between 1.1 and 1.4 times the BP _S step-up condition; the BP _measurement is between 0.6 and 0.9 times the BP _S step-down condition to increase the operating fan frequency to the lower limit.

When the BP _measurement is between 0.9 and 1.1 times of BP _S or the step sequence changes, the integral value needs to be continuously cleared, that is, the current step sequence is maintained. The back pressure of the unit is mainly adjusted by changing the frequency of the running fan.

After each step change, there is a 1 minute dead zone during which the step remains the same.

The invention enhances the anti-interference ability of the back pressure control system and improves the control precision. The control system has a strong ability to adapt to disturbance conditions, and has a perfect adjustment effect on back pressure under normal conditions. It has a fast response speed and a high level of automation, which greatly reduces labor intensity.

Claims (1)

1. large-scale air cooling unit back pressure control system, it is characterized in that: said control system comprises: pid control circuit, back pressure automatic setting module, feed-forward signal, controlled variable variable-gain module and cut the step optimal module; Wherein: pid control circuit is the goal-setting value with the turbine back pressure; The back pressure automatic setting module is considered the not enough and preventing freeze in winter performance of the summer capacity of air cooling island tube bank; With reference to the steam turbine plant operations specification, according to the unit practical operation situation, environment temperature, unit load and back pressure relation function have been designed; Unit load and environment temperature are high more, and the turbine back pressure setting value is high more; Back pressure control is changed into the intelligence control system of automatic setting optimal economic back pressure set value by the simple control system of conventional manual setting; On the PID module, use a feed-forward signal in case the antifreeze influence to back pressure control of non-return flow fan reduction of speed, feed-forward signal is a reverse step signal, and snap time is determined by adverse current blower fan reduction of speed program; Step signal is delivered to the back pressure control system as feed-forward signal after speed limit piece speed limit, balance out the influence that the adverse current reduction of speed brings to system; In control system, use a controlled variable variable-gain module; When the step preface increases or reduces; The blower fan platform number of operation changes, and the open-loop gain of system is corresponding, and variation has taken place, and through this module back pressure control system closed loop proportional coefficient is adjusted accordingly; Change to adapt to the controlled device number, guarantee the regulation quality of control system.

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