JPS6284257A - Combustion controller of hot water supplier - Google Patents

Abstract

PURPOSE:To improve an excessive overshoot at the time of excessive overshooting at the time of cold starting and also to improve an excessive undershoot at the time of resupplying hot water by forcibly rewinding an integral action circuit when the output from a differential action circuit exceeds the reference value. CONSTITUTION:When a fuel is ignited and the detected temperature begins to rapidly rises up, a large differential action output is produced in a differential amlifier 8. When a diferential value comparator 12 detects that this variation is larger than a reference level, an integral action rewind circuit 13 is actuated to use an integral action output from an integral amplifier 9 temporarily as a proportional action output. By this procedures, the fuel which is burning at maximum is controlled to a value determined by the proportional output from a proportional amplifier 7 and an integral amplifier 9 and as output from a differential amplifier 8, and thereafter the fuel burning is controlled by the integral output and the differential output in accordance with the variation of the hot water temperature.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a combustion control device for proportionally controlling the combustion of a water heater, and more specifically, to maintain the temperature of hot water at a set temperature. This invention relates to a combustion control device for a water heater equipped with an I)ID control circuit that compares the detected hot water temperature with the detected hot water temperature and proportionally controls the fuel supply amount based on the comparison result.

[Conventional technology]

In this type of combustion control device, from the viewpoint of energy saving, PID control means is employed which can automatically adjust the amount of fuel supply, that is, the amount of heat supplied, depending on the deviation between the set temperature and the detected temperature.

FIG. 4 is a block diagram showing its basic configuration.

In the figure, l is an instantaneous gas water heater to be controlled; 2
indicates a proportional valve that supplies gas to the water heater; the hot water temperature of the water heater is detected by a detection unit 3 such as a thermistor, the detected temperature is extracted as a voltage by a temperature detection circuit 4, and the value and setting are A deviation detection circuit 6 compares the value set in the circuit 5 and generates a control output based on the difference.

As for the control output, a proportional/differential amplifier 7 (8) generates a proportional operation output and a differential operation output, an integral amplifier 9 generates an integral operation output, and these outputs are combined by an summing amplifier 10 and sent to a proportional operation circuit 11. entered,
The output opens and closes the proportional valve 2 to control the fuel.

[Problem that the invention seeks to solve]

Water heaters equipped with PID combustion control devices as described above do not have any major problems during normal use, but excessive overshoot occurs during cold starts, and excessive undershoot occurs when hot water is re-discharged after being turned over for a short period of time. There is a problem that shoots occur.

That is, when using an instantaneous water heater due to the state of the water, the deviation between the detected temperature and the set temperature naturally shows a large value. When the faucet is opened to use the instantaneous water heater in such a state, the water flow switch is turned on, power is supplied to the automatic control circuit, and the combustion control device becomes operational.

When the combustion control device is in operation, the proportional amplifier 7 outputs an output determined by the water temperature - and the set temperature, and the differential amplifier 8 outputs an output proportional to the rate of change of the hot water temperature and in the opposite direction to the change direction of the hot water temperature. However, since there is no temperature change until fuel is supplied and ignition occurs, the output shows the set value reference voltage. Integrating amplifier 9 initially outputs the same voltage as the input voltage,
Depending on the charging speed of the integrating amplifier's negative feedback capacitor, the output will quickly reach its lowest limit.

On the other hand, when the water flow switch is turned on, the fan rotates, and after the combustion chamber purge time (usually about 2 seconds), ignition begins. During this time 1. Although the temperature deviation is large for a short period of time, and the time constant of the negative feedback circuit of the integrating amplifier is extremely short, the combustion control device generates a limit output that indicates the maximum gas amount even for a short period of time. .

Therefore, after the ignition operation, when ignition is confirmed by the ignition confirmation circuit, the maximum combustion state is reached immediately. Then, when the fuel starts to burn, the hot water temperature rises, and accordingly the output of the proportional amplifier 7 decreases, and the differential amplifier 8 generates an output in the direction of reducing the amount of fuel, but the integral amplifier 9 continues to output its limit output,
Only when the detected temperature gets very close to the set temperature does the output start to decrease.

That is, in the integral operation circuit 9, an operational amplifier that generates an amplification factor of 100 dB acts with a resistor input and a capacitor negative feedback circuit, and if the negative feedback capacitor is charged at the limit output, negative feedback will not occur and the set temperature will not reach the set temperature. Even if the temperature difference between the detected hot water temperature and the detected hot water temperature is extremely small, the limit output will continue to be output (the integral operation circuit will be in a fixed state), so even if the hot water temperature exceeds the set temperature and the fuel is reduced, The hot water temperature continues to rise due to the heat capacity of the heat exchanger, causing a large overshoot. This state is shown in FIG. In Figure 5, the dotted line shows the gas amount, and the solid line shows the hot water temperature.This figure shows the case where the temperature is set at 50°C, and the maximum hot water temperature is 75°C.
It has also reached

As in the above example, the integral operation circuit continues to output the limit output even when the hot water is re-dispensed and used repeatedly within a short period of time. That is, when hot water is re-discharged, the initial discharge temperature is much higher than the set temperature due to the after-boiling phenomenon, and the fuel supplied to the water heater becomes the minimum value, resulting in excessive undershoot.

In order to improve the above-mentioned problems, measures such as forced fuel cut-off methods and extension of post-high-lot time have been taken, but these methods do not improve the essential PID control, but rather improve the target therapy. Therefore, it does not have good characteristics, and recently attempts have been made to improve the characteristics by adding feedforward control to the feedback control, but it is not a fool's errand and is not sufficient. .

The present invention improves the problems of the prior art as described above, and improves the excessive overshoot at the time of cold start and the excessive undershoot at the time of re-releasing hot water, while using simple feedback type PID control. The purpose is to provide a combustion control device that can perform

[Means to improve problems]

In order to achieve the above object, the present invention provides a differential value comparator for rewinding the integral operation circuit of the PID control circuit by the output of the differential operation circuit, and when the output of the differential value comparator exceeds a reference value. The feature is that an integral operation rewind circuit that operates is added, and the integral operation circuit is forcibly rewinded when the output of the differential operation circuit exceeds a reference value. Even in a state where it continues to be released,
When the water is ignited, the temperature of the water changes, which causes the output of the differential operation circuit to change. This change is detected by a differential value comparator, and when the value exceeds a certain value, the integral operation rewind circuit is activated. Then, the integral operation circuit is returned to its initial operation state.

〔Example〕

Next, an example of the implementation of the present invention will be described based on FIGS. 1 to 3.

FIG. 1 is a block diagram of the combustion control device of the present invention, FIG. 2 is a circuit diagram showing a specific example thereof, and FIG. 3 is an operation explanatory diagram.

In these figures, l is the instantaneous gas water heater to be controlled, 2 is a proportional valve for gas, 3 is a detection unit such as a thermistor, 4 is a temperature detection circuit, 5 is a setting circuit, and 6 is a detected hot water heater. A deviation detection circuit between the temperature and the temperature set in the setting circuit 5, 7 is a proportional amplifier, 8 is a differential amplifier, 9 is an integral amplifier, 10 is an addition amplifier %11 is a proportional operation 1! 4 shows a circuit whose configuration is substantially the same as the conventional example shown in FIG.

In the present invention, the output of the differential amplifier 8 is detected by a differential value comparator 12, and an integral operation rewind circuit 13 is attached to the integral amplifier 9, which operates when the output exceeds a certain reference value. Specifically, as shown in Figure 2,
A switch such as a PET operated by the output of the differential value comparator 12 is connected in parallel with the negative feedback capacitor C of the integrating amplifier 9, and when the FET is turned on, the capacitor C is discharged to return the integrating amplifier 9 to its initial operating state. Do it like this. Also.

A resistor R is connected in series with this rewind stop switch, and when the switch FBT is on, the integrating amplifier 9
is made to work as a proportional operation circuit, and together with the original proportional amplifier 7, it is made to operate to narrow the proportional band.

By doing this, the output of the differential amplifier 8 is compared with the differential value comparator 12, and when it is out of the reference level, the FET
A voltage is applied to the gate of the FET to turn it on, discharging the capacitor C of the integrating amplifier 9, and making the integrating amplifier 9 a proportional operation circuit.

The reference value with which the differential output level is compared changes depending on how each PID operation is received, which is determined by the characteristics of the thermal converter, and is therefore set at a level at which better characteristics can be obtained through experiments.

Since the combustion control device of the present invention is configured as described above, it operates in the same manner as the conventional example shown in FIG. When the differential amplifier 8 starts to rise rapidly, a large differential operation output is generated, and when the differential value comparator 12 detects that the change in the operation output of the differential amplifier is larger than the reference level, the integral operation rewind circuit 13 is activated. As a result, the integral operation output from the integral amplifier 9 is temporarily made into a proportional operation output. As a result, the fuel that was being burned at maximum is controlled to the fuel determined by the proportional output from the proportional amplifier 7 and the integral amplifier 9 and the output from the differential amplifier 8 at the beginning of the temperature rise, and from then on due to changes in the hot water temperature. The fuel is controlled by the corresponding integral output and differential output.

Then, as the hot water temperature approaches the temperature corresponding to the controlled fuel and the rate of change in hot water temperature decreases, the differential output from the differential amplifier 8 becomes smaller, and the differential value comparator 12 becomes smaller than the reference level. When the differential operation output is detected, the integral operation rewind circuit 13 is stopped to return the integral amplifier to normal operation.

As described above, in the combustion control device of the present invention, as soon as the hot water temperature starts to change, the limit output from the integral operation circuit is released and proportional and differential operations are started to control the fuel. The temperature can be kept at the set temperature with a small overshoot. This is illustrated in Figure 3. In addition, in FIG. 3, the dotted line shows the gas amount, and the solid line shows the tapping temperature, when the set temperature is 50'C.

As described above, the present invention rewinds the integral operation circuit which has produced a marginal output due to the large output of the differential operation circuit caused by a relatively large temperature change, brings the PID control circuit into a normal operation state, and achieves extremely good characteristics. Combustion control can be performed.

The above-mentioned case where the integral operation circuit produces the limit output occurs not only at the time of cold start but also at the time of re-dispensing hot water when the instantaneous water heater is used repeatedly within a short period of time. In other words, when hot water is re-discharged, the after-boiling temperature is detected and the limit output is output to minimize the amount of fuel supplied, and as described above, the water temperature is significantly biased towards the lower temperature side than the set temperature, such as when using a shower. This creates an unpleasant situation where hot water temporarily turns into water. In addition, when the amount of water is small and the hot water is used at a low outlet temperature, when the minimum limit amount is reached, a cycling phenomenon occurs in the same manner as described above.

All of these phenomena can be improved by the present invention.

〔Effect of the invention〕

As described above, one aspect of the present invention is that the integral operation circuit operates at maximum fuel supply i.
jk'' or the limit output of the minimum fuel supply amount, the integral operation circuit is temporarily rewinded to bring the PID control circuit into a normal operating state, and combustion control with good characteristics can be performed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram, and FIG. 3 is an explanatory diagram showing gas amount and hot water temperature. FIG. 4 is a block diagram of a conventional device, and FIG. 5 is an explanatory diagram showing a conventional gas amount and hot water temperature. l... Instantaneous gas water heater, 2... Proportional valve for gas, 3
... Hot water temperature detection section, 4 ... Temperature detection circuit, 5 ... Setting circuit, 6 ... Deviation detection circuit, 7 ... Proportional amplifier,
8... Differential amplifier, 9... Integral amplifier, 10...
Calorie calculation amplifier, 11... Proportional operation circuit, Le... Differential value comparator, 13... Integral operation rewind circuit.

Claims (1)

[Claims] In a combustion control device for a water heater equipped with a PID control circuit that automatically controls a fuel supply amount based on a comparison result between a desired set temperature and a detected hot water temperature, an integral operation circuit of the PID control circuit is replaced with a differential operation circuit. 1. A combustion control device for a water heater, comprising: a differential value comparator for rewinding according to the output; and an integral operation rewind circuit that operates when the output of the differential value comparator exceeds a reference value.