JPS6123441B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides steam temperature control that controls the turbine inlet temperature of steam supplied from the boiler of a thermal power plant to a constant set value by automatically adjusting the heater spray valve opening. This relates to a control device.

An example of a conventional device and its problems will be explained with reference to FIGS. 1 and 2. FIG. 1 shows a block diagram of a conventional main steam temperature control system.

In Figure 1, B is a boiler, G is a generator, 1
is a high pressure turbine, 2 is an intermediate pressure turbine, 3 is a low pressure turbine, 4 is a pressure reducer, 5 is a primary superheater, 6 is a secondary superheater, 7 is a reheater, 8 is a spray valve, 9 is a spray injection pipe It is.

The saturated steam evaporated by the boiler B is superheated in the primary superheater 5 and the secondary superheater 6, and is supplied to the high-pressure turbine 1 as high-temperature, high-pressure steam. The main steam temperature, that is, the high-pressure turbine inlet steam temperature, is regulated by the following values. Normally, the allowable fluctuation range of main steam temperature is ±10℃ of the rated value, but
Since the time constant of steam temperature is generally very long, 3 to 15 minutes, the main steam temperature is controlled in advance by predicting fluctuations in the main steam temperature.

FIG. 1 shows an example of this advance control circuit.

10, 11, and 12 are detection signals of main steam temperature, main steam flow rate, and desuperheater outlet temperature, respectively. 1
3 is a subtracter for determining the deviation between the main steam temperature signal 10 and its set value 14, and 15 is a proportional integrator for proportionally integrating the output of this subtracter. A function generator 16 receives the main steam flow rate signal 11 as an input, converts it into a load advance control signal, and sends it to the adder 21. The output characteristics of the function generator 16 are shown in FIG. 17 is a function generator which also receives the main steam flow rate signal 11; 18 is a set value of the attemperator outlet temperature; 19 is a subtractor for calculating the deviation between this set value 18 and the attemperator outlet temperature signal 12; and 20 is this subtraction. This amplifier amplifies the output of the adder 19 and sends it to the adder 21. Adder 21 adds the outputs of proportional integrator 15, function generator 16, and amplifier 20 and outputs spray valve opening command signal 22.

As described above, in the conventional main steam control circuit, the load (=main steam flow rate) advance control and the desuperheater outlet temperature advance control are performed as advance control of the main steam temperature.

However, in the case of such a conventional control circuit, the actual rise in main steam temperature cannot be detected, resulting in a response lacking in adaptability.

The present invention has been developed with this in mind, and by adding a differential value (=amount of change) of the main steam temperature to perform advance control, it is possible to cope with rapid fluctuations in the main steam temperature. It is an object of the present invention to provide a main steam temperature control device that can provide efficient control.

In order to achieve the above object, in the present invention,
The steam temperature is differentiated at high speed using a differentiation circuit, the harmonic components are filtered using a first-order lag device, the harmonic components are amplified using a high gain using an amplifier, and the output of the amplifier is limited within a desired value using a limit circuit, while subtraction is performed. A spray valve control signal is obtained by determining the difference between the steam temperature and its set value using a device, adjusting it using a proportional integrator, and adding it to the output of the limit circuit using an adder.

FIG. 3 shows a block diagram of an embodiment of the present invention. In FIG. 3, 23 is the main steam temperature signal 10
A differentiating circuit that receives as input and differentiates it at high speed, 2
4 is a first-order lag device for smoothing the waveform of this differential signal, 25 is a high-gain amplifier for amplifying the output of this first-order lag device 24, and 26 is a limiter circuit.
Other symbols are the same as in the conventional circuit of FIG.

The operation of the embodiment circuit diagram shown in FIG. 3 will be explained.

Using the main steam flow rate signal 11, a function generator 16 generates a preceding signal for the spray valve opening. This signal is
This is the advance control signal for the spray valve opening determined by the main steam flow rate.

The main steam temperature signal 10 is differentiated at high speed by a differentiating circuit 23. Generally, the rate of change in steam temperature is about 0.05° C./sec at most, so the time constant of the differential circuit is suitably about 1 to 3 seconds. The differentiated signal is input to the first-order lag unit 24. The first-order lag device removes minute harmonic noise caused by the high-speed differentiation circuit in the previous stage. The amplifier 25 is
This signal is amplified several hundred times. This is to speed up the response of the system. The limiter circuit 26 limits the amplifier output within the normal spray control value range (approximately 80% of the spray control range) and outputs it as a temperature advance signal. This is to avoid being affected by disturbances caused by amplification with a high gain.

Further, the difference between the main steam temperature signal 10 and a set value is determined by a subtracter 13. Furthermore, the deviation is
The proportional integrator 15 provides a main steam temperature control signal.

And advance control signal 30 for spray valve opening degree.
, the temperature advance signal 28 , and the main steam temperature control signal are added by an adder 21 to form a spray valve opening control command signal 22 . The spray valve opening degree is adjusted and operated based on this command signal.

In this embodiment, since the main steam temperature change is captured and amplified over a wide range, a rapid response to the main steam temperature change can be obtained.

In conventional control systems, one using PID is considered. For example, after determining the difference between the main steam temperature signal and a set value, the main steam temperature signal is adjusted by PID and used as the main steam temperature control signal. However, the differentiator of this control system cannot obtain the temperature advance signal of this embodiment. In other words, the PID transfer function is expressed as follows: _Ga (S)=k(1+1/Ti.s+Td.s) (Ti and Td are time constants of I and D). Further, generally, the process characteristic of the main steam temperature can be approximated by G _b (S)=e ^-LS /T·S. (L, T are the dead time of the process, time constants) In this case, the most appropriate k,
The values of Ti and Td are determined as follows, since the transient response is to provide 25% damping (damping ratio 1/4).

k=1.2T/L, Ti=2L, Td=0.5L Main steam temperature dead time, time constant is rated at 1
minutes, about 10 minutes, so by substituting these, we get
k=12, Ti=2 minutes, Td=30 seconds. In this control system, the rise in main steam temperature is detected slowly. This is because the time constant is as long as 30 seconds, and the output when the main steam temperature changes is small. This cannot serve as a temperature advance signal.

However, according to the present invention, the spray valve opening response can be quickly responsive. That is, the differentiator in the present invention is independent of PI and rapidly captures changes in main steam temperature.
The main steam temperature signal can generally be approximated to a lamp input; for such an input, the output of a typical differentiator is E _put = αT (1 − e ^-t/T ), where α is The rate of change in steam temperature is approximately α = 0.05℃/
sec. ). By the way, the spray valve opening required to change the main steam temperature by 1°C is 1%, so if the time constant of the differentiator is T = 30 seconds as in the conventional example, the spray valve will open after 120 seconds. , which will open by 6%. This means that it takes 2 minutes to make a 6°C correction. This cannot be said to be a fast response, so while T is set to about 1 to 3 seconds, the signal is amplified with a high gain using an amplifier, and is used as a temperature control signal separate from the PI system. If T = 1 second and the amplifier gain is increased to 500 times, the response will be 510 times that of the conventional system, but simply increasing the gain will make the control system unstable and cannot be used as a control system.

Therefore, the differentiator of the present invention is superior to conventional devices.
Unlike a PID differentiator, it is equipped with a first-order lag device and a limit circuit, and also directly differentiates the main steam temperature signal. The purpose of having the first-order delay device is to remove high-frequency components caused by high-speed differentiation and to prevent malfunctions caused by disturbances. Furthermore, the reason why the limit circuit is provided is to prevent an excessive signal from being added to the spray valve opening signal due to noise. Furthermore, directly differentiating the main steam temperature signal changes the set value 14 at plant start-up, but the differentiator of the present invention directly detects this change and outputs a temperature advance signal to affect the control system. This is to ensure that there is no such thing.

According to the present invention, the load advance control signal 30 responds to the dead time of the main steam temperature, and the temperature advance control signal 28 responds to the delay due to the time constant of the steam temperature to adjust the spray valve opening. . Therefore, the spray valve opening degree control command signal can be generated even with respect to the dead time and time constant of the steam temperature, and steam temperature control with quick response can be performed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional example, FIG. 2 is a characteristic diagram of the function generator 16, and FIG. 3 is a block diagram of an embodiment of the present invention. 10...Main steam temperature signal, 11...Main steam flow rate signal, 13...Subtractor, 14...Set value, 15...Proportional integrator, 16...Function generator, 21...Adder, 22...
Spray valve opening command signal, 23... Differential circuit, 24
...First-order lag device, 25...Amplifier, 26...Limiter circuit.

Claims (1)

[Claims] 1. A steam temperature control device that adjusts the turbine inlet steam temperature of steam supplied from a boiler by a spray amount and controls it to a set value, including a differentiation circuit that differentiates the turbine inlet steam temperature, and a first-order lag that filters the differential signal. a first system comprising a filter, an amplifier for amplifying the filtered signal, and a limiter circuit for limiting the amplified signal; and determining the difference between the turbine inlet steam temperature and the set value. A second system having a subtracter, a proportional integrator that proportionally integrates the difference signal, and an adder that adds the signals of the two systems to obtain a spray valve control signal. Steam temperature control device.