JPH0692837B2 - Combustion control device for water heater - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a target temperature setting means for hot water temperature, a hot water temperature detecting means, a target temperature signal from the target temperature setting means, and a hot water temperature detecting means. The present invention relates to a combustion control device for a water heater including PID (proportional integral derivative) control means for calculating an opening of a fuel control valve based on a deviation from a detected temperature signal and outputting a valve drive current to the fuel control valve.

(Summary of the Invention) In the present invention, when the deviation between the target temperature signal and the detected temperature signal is fairly small, the target temperature is changed by switching the differential constant of the D (differential) operation control means in the PID control means to substantially zero. Even if the change in water amount is small with no change, the unstable fluctuation of the outlet water temperature is prevented, the energy is saved, and when the change in water amount is more than a predetermined value, the differential of the D operation control means. By switching the constant to a differential constant that is not substantially zero, high responsiveness of the tap water temperature is ensured.

(Prior art and its problems) The operation of the conventional combustion control device for a water heater having the configuration described in the field of (Invention) will be described based on the flowchart of FIG.

In step, the target temperature TS is input in the target temperature setting means, and in step, the detected temperature TN from the tap water temperature detecting means.
Is input and the PID calculation is executed in step to calculate the PID output M _n . In step, the valve drive current for the fuel control valve is calculated based on the PID output M _n , and in step, the fuel control valve is driven by the valve drive current, and the valve opening degree is detected temperature TN to the target temperature TS. Control to be.

The PID calculation is performed by the following equation.

In the equation (1), M _n is a manipulated variable or PID output for controlling the opening of the fuel control valve at the sampling timing t _n , and e _n is the target temperature TS _n and the detected temperature T at the timing t _n .
The deviation from N _n , that is, e _n = TS _n −TN _n (2).

Further, the K _P · e _n of the first term proportional term, the K _P is a proportionality constant.
Of the second term Is the integral term and K _I is the integration constant. The third term, K _D (e _n −
e _n-1 ) is a differential term, e _n-1 is a temperature deviation at the timing t _n-1 , and K _D is a differential constant.

The differential term M _D = K _D (e _n −e _n-1 ) is for enhancing the response to a sudden change. For example, when the amount of water changes, the outlet heated water temperature (detection temperature TN) is quickly stabilized.

From Equation (2), e _n-1 = TS _n-1 −TN _n-1 (3) Therefore, M _D = K _D (e _n −e _n-1 ) = K _D (TS _n −TS _{n -1} ) + K _D (TN _n-1 -TN _n ) (4).

No change of the target temperature TS, in the case of TS _n = TS _{n-1 is, M D = K D (TN} n-1 -TN n) becomes ...... (5).

When the target temperature TS is not changed, as shown in FIG. 8, _assuming that the hot water discharge temperature (detected temperature TN) is decreased as a result of the increase in the water amount (TN _n-1 > TN _n ), equation (5) This increases the differential term M _D. Thus, the valve opening degree of the fuel control valve is increased, the hot water temperature rises, the differential term M _D gradually decreases.

Hot water temperature rises to the original hot water temperature, becomes TN _n = TN _n-1, when the hot water temperature is stabilized, the differential term M _D is zero.

In order to make the response high, it is necessary to set the differential constant K _D large. When the change in the amount of water is large to a certain extent or more, the rising characteristic of the hot water outlet temperature becomes good due to this high responsiveness.

However, the conventional example having such a configuration has the following problems.

That is, when the amount of water changes with no change of the target temperature is smaller, differential term M _D will act in accordance with the variation amount of the hot water temperature corresponding to the amount of water changes. A slight change in the amount of water may be due to, for example, a subtle change in the amount of hot water used in the house or a subtle change in the amount of hot water used in a nearby home.
It is always occurring.

As shown in FIG. 9, in such a state where a minute change in the amount of water is constantly occurring, the outlet water temperature also slightly changes, so that the derivative term M _D also frequently acts, and as a result, the outlet water temperature constantly changes. A situation occurs in which it does not stabilize.

When hot water is used in such a state, the function itself by this hot water also becomes unstable. In particular, there is a problem that discomfort is great when using a shower. Further, since the fuel control valve is frequently driven to adjust the burner output, there is a problem in that energy is wasted.

To avoid this problem, it suffices to set the differential constant K _D to a small value, but then there is the fundamental problem that the response of the heated water temperature deteriorates.

(Object of the Invention) The present invention has been made in view of such circumstances, and prevents unstable fluctuations in the outlet water temperature even in the state where a minute change in the amount of water constantly occurs, and When the change in the amount of water is equal to or larger than a predetermined value, the high responsiveness of the hot water discharge temperature is ensured so that the user of hot water does not feel uncomfortable and energy is saved.

(Structure and Effect of the Invention) In order to achieve such an object, the present invention has the following structure.

That is, as shown in FIG. 1, the hot water heater combustion control apparatus according to the present invention includes a target temperature setting means 17, a hot water outlet temperature detecting means 18, and a target temperature signal from the target temperature setting means 17. And a PID control means 25 for calculating the opening degree of the fuel control valve 4 based on the deviation between the detected temperature signal from the hot water temperature detection means 18 and outputting a valve drive current to the fuel control valve 4. In the combustion control device, the differential constant of the D operation control means 24 in the PID control means 25 is set to a differential constant of substantially zero when the deviation is equal to or less than a predetermined value, and substantially when the deviation exceeds a predetermined value. Differential constant switching means 27 for switching to a non-zero differential constant
It is equipped with.

The operation of this configuration is as follows (see FIG. 6).

In a state where a minute change in the amount of water is constantly occurring, the outlet heated water temperature also slightly changes, so that a deviation occurs between the target temperature signal and the detected temperature signal.

However, since the deviation is less than or equal to the predetermined value, the differential constant switching means 27 switches the differential constant K _D to substantially zero. Therefore, the differential term M _D does not act, and as a result, unstable fluctuation of the outlet heated water temperature is prevented and the stable state is maintained. Also,
Energy saving is achieved by preventing unstable fluctuations in the tap water temperature.

From the above, when the deviation exceeds a predetermined value, it is not necessary to set the non-zero differential constant K _D that is switched by the differential constant switching means 27 to a small value, and it can be set to a large value.

Then, when there is a relatively large change in water amount and the deviation between the target temperature signal and the detected temperature signal exceeds a predetermined value, the differential term M _D having the differential constant K _D set to a large value acts and the fuel control valve The valve opening of No. 4 is controlled. Therefore, it is possible to suppress the fluctuation of the outlet heated water temperature caused by the change of the water amount within a short time. That is, the responsiveness is maintained at a high level, and the rising characteristics of the tapping temperature are improved.

As described above, according to the present invention, even in the state where a minute change in the amount of water is constantly occurring, an unstable change in the outlet water temperature is prevented, and when the change in the amount of water is a predetermined value or more, It is possible to secure high responsiveness of hot water temperature so as not to make users feel uncomfortable with hot water, and to prevent unstable fluctuations in hot water temperature, resulting in energy saving. To be done.

(Description of Embodiments) Hereinafter, the present invention will be described in detail based on embodiments illustrated in the drawings.

FIG. 2 is a block circuit diagram of a water heater to which the present invention is applied, and FIG. 3 is a block diagram of a combustion control device for a water heater according to an embodiment of the present invention.

In FIG. 2, reference numeral 1 is a burner, 2 is a fuel supply path connected to the burner 1, and the fuel supply path 2 is a solenoid valve (main valve) 3 for controlling fuel supply to the burner 1 and a fuel control valve (proportional valve). Valve 4 is interposed. In the vicinity of burner 1,
A spark plug 5 and a frame rod 6 are arranged. A combustion chamber 7 is provided above the burner 1, and the combustion chamber 7
A fan motor 8 is provided in an exhaust passage communicating with the.
The fan motor 8 controls exhaust gas and supplies combustion air to the burner 1.

Reference numeral 9 denotes a heat exchanger configured by winding a water supply pipe around the combustion chamber 7, and the exchanger 9 is connected to a plurality of tap holes 10 such as a curran and a shower.

11 is a stabilized power supply circuit, 12 is a drive circuit for the solenoid valve 3, 13 is a control circuit for the fan motor 8, 14 is a drive circuit for the spark plug 5, 15 is a flame detection circuit connected to the frame rod 6, 16
Is a combustion control device for a water heater according to an embodiment of the present invention.

The structure of the combustion control device 16 will be described with reference to FIG.

In FIG. 3, reference numeral 17 is target temperature setting means for hot water temperature, 18 is hot water temperature detecting means, and 19 is ROM (read only memory) storing proportional constant K _P , integral constant K _I and differential constant K _D. , 20 are PID calculation processing means for calculating the output M _n of the PID based on the deviation e _n between the target temperature signal b from the target temperature setting means 17 and the detected temperature signal a from the hot water temperature detection means 18, and 21 is It is a valve drive current calculation means for calculating the valve drive current value i _V of the fuel control valve 4 based on the PID output M _n .

The PID calculation processing means 20 includes P (proportional) operation control means 22, I
(Integral) operation control means 23 and D (differential) operation control means
24, each of which is based on the deviation e _n
The proportional constant K _P , the integral constant K _I , and the differential constant K _D are read from the ROM 19 and the proportional term, integral term, and derivative term shown in equation (1) are calculated. The PID calculation processing means 20 totals these and outputs the PID.
Calculate M _n .

The ROM 19, the PID calculation processing means 20, and the valve drive current calculation means 21 constitute PID control means 25 in the configuration of the invention.

26 based on the valve drive current i _V of the valve drive current calculating section 21, a fuel control valve drive means for driving the fuel control valve 4 to the valve opening corresponding to the valve drive current i _V.

27, input the deviation e _n , compare the value with a predetermined value Th,
And outputs the D operation prohibition signal D _P to D operation control unit 24 when more than a predetermined value Th, by prohibiting the operation of the D operation control unit 24, substantially the derivative constant, K _D, the D operation control unit 24 It is a differential constant switching means for switching to zero.

When the deviation e _n exceeds the predetermined value Th, the differential constant switching means 27 stops the output of the D operation prohibition signal D _P and causes the D operation control means 24 to operate, whereby the D operation control means 27. The differential constant K _D of is switched to a non-zero differential constant.

For example, as shown in FIG. 4, when the absolute value of the deviation e _n between the target temperature and the detected temperature is less than or equal to a predetermined value Th, K _D = 0 is set, and when the absolute value exceeds a predetermined value Th, the differential constant K is set. the _D example, is set to K _D = 10.

The operation of the combustion control device will be described below with reference to the flowchart of FIG.

In step, the target temperature TS is input to the target temperature setting means 17, in step the detected temperature TN from the tap water temperature detection means 18 is input, and in step, the deviation e _n between the target temperature TS and the detected temperature is calculated. In step, it is determined whether the absolute value of the deviation e _n is less than or equal to a predetermined value Th.

If the determination in this step is YES, that is, if a minute change in the amount of water is constantly occurring as shown in the first half of FIG. 6, the following flow is executed. That is, the process proceeds to step, the proportional constant K _P and the integral constant K _I are read from the ROM 19, the differential constant K _D is set to K _D = 0, and the PID calculation based on the above-mentioned equation (1) is performed. Execute to calculate PID output M _n . The arithmetic expression in this case is K _D =
Since it is 0, Becomes In step, the valve drive current i _V for the fuel control valve 4 is calculated based on the PID output M _n calculated in step, and in step, the fuel control valve 4 is driven by the valve drive current i _{V to} open the valve. Temperature is the target temperature
Control to become TS.

As described above, when the absolute value of the deviation e _n is below the predetermined value Th does not act differential term M _D, to prevent the unstable variation of the hot water temperature as a result, it is maintained in a stable state be able to. In addition, energy can be saved by preventing unstable fluctuations in the outlet heated water temperature.

Therefore, it is also possible to set a large value as the substantially non-zero differential constant K _D when the absolute value of the deviation e _n exceeds the predetermined value Th.

If the determination in the above step is NO, that is, as shown in the latter half of FIG. 6, there is a relatively large change in water amount, and the deviation e _n between the target temperature signal and the detected temperature signal exceeds the predetermined value Th. In that case, the following flow is executed. That is, the process proceeds to step, the proportional constant K _P , the integral constant K _I , and the differential constant K _D are read from the ROM 19, The PID output M _n is calculated by executing the normal PID calculation based on In step, PID output M _n calculated in step
The valve drive current i _V for the fuel control valve 4 is calculated based on the above, and in step, the fuel control valve 4 is driven by the valve drive current i _V , and the valve opening degree is detected as the target temperature TS.
Control to become.

As described above, when the deviation e _n exceeds a predetermined value Th, acts differential term M _D having a differential constant, K _D, which is set to a large value, the valve opening degree of the fuel control valve 4 is controlled It Therefore, it is possible to suppress the fluctuation of the outlet heated water temperature caused by the change of the water amount within a short time. That is, it is possible to maintain the high responsiveness and improve the rising characteristics of the tapping temperature.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a configuration of the present invention, FIGS. 2 to 6 relate to a combustion control device for a water heater according to an embodiment of the present invention, and FIG. 2 shows the present invention. FIG. 3 is a block circuit diagram of a water heater applied, FIG. 3 is a block diagram of a combustion control device for a water heater according to an embodiment of the present invention, FIG. 4 is an explanatory diagram of differential constant switching, FIG. 5 is a flowchart, and FIG. Is the time chart, 7th
9 to 10 relate to a conventional example, FIG. 7 is a flowchart, and FIGS. 8 and 9 are time charts. 4 ... Fuel control valve 17 ... Target temperature setting means 18 ... Hot water temperature detection means 24 ... D operation control means 25 ... PID control means 27 ... Differential constant switching means

Claims (1)

[Claims] 1. A target temperature setting means for the outlet heated water temperature,
The outlet temperature of the fuel control valve is calculated based on the deviation between the target temperature signal from the outlet temperature detecting means, the target temperature signal from the target temperature setting means, and the detected temperature signal from the outlet temperature detecting means. In a combustion control device for a water heater provided with a PID control means for outputting the differential constant of the D operation control means in the PID control means, when the deviation is a predetermined value or less, to a differential constant of substantially zero, A combustion control device for a water heater, comprising differential constant switching means for switching to a differential constant that is substantially not zero when the deviation exceeds a predetermined value.