JPH0481087B2 - - Google Patents

Description

[Detailed Description of the Invention] <<Field of the Invention>> The present invention relates to a combustion control device for a water heater that controls and maintains the outlet temperature at a target temperature.
In particular, the present invention relates to devices that can monitor the status of each device.

<<Background of the Invention>> A water heater combustion control device currently under development (unpublished) by the present applicant is implemented by a microcomputer, and is determined from the target temperature, the water inlet temperature of the heat exchanger, and the amount of inflow water. The target control amount F ₁ (corresponding to the target combustion amount) and the predetermined control amount determined by PID calculation according to the deviation between the hot water temperature and the target temperature.
The combustion amount of the burner is controlled by the deviation F from _F2 ,
This is to ensure that the hot water temperature matches the target temperature.

Therefore, the hot water temperature control operation performed here can be expressed as F=F ₁ +F ₂ (1). Here, F ₁ is given by the following equation by feed forward control.

F ₁ =W・(SPn−WPn) ……(2) W: Inflow water amount SPn: Set temperature WPn: Inlet water temperature Furthermore, F ₂ is given by the following equation by feedback control (PID calculation equation).

F ₂ = Kp {△En＋θ／Ti _o 〓 ⁱ⁼⁰ △Ei＋Td／θ (△En−△E _o-1 )} ……(3) △Ei＝SPi−MPi Kp: Proportional gain Ti: Integral time Td: Differential time θ: Sampling time ΔEi: Deviation SPi: Set temperature MPi: Output temperature Note that the subscript n is the current sampling value, and the subscript _o-1 is the previous sampling value.

From the above equation (1), it is understood that this hot water temperature control operation modifies the target control amount using the PID calculation value. This is due to the following reason. 1st
The figure shows the hot water temperature control characteristics when the set temperature is changed from 40℃ to 80℃. In the figure, each device, such as a temperature sensor that detects the hot water temperature and a water flow sensor that detects the amount of inflow water, usually has a predetermined variation. Therefore, if the combustion amount is controlled only by the target control amount, the hot water temperature may greatly exceed the target temperature (curve A in the diagram) or may not reach the target temperature (curve B in the diagram). In other words, the control characteristics of the tapping temperature vary within the range of curves A and B. Therefore, the outlet hot water temperature is fed back, an integral calculation operation is performed based on the deviation between this and the target temperature, and corrections are made one by one using this calculation value. Then, the hot water temperature is
As shown by curve C, the target temperature is controlled and maintained regardless of variations in equipment. In other words, the correction operation can be sufficiently performed using only integral calculations. However, since the response characteristics are poor if only the integral calculation operation is used, PID control was adopted in which proportional calculation operation and differential calculation operation were added (curve D in the figure).

Incidentally, the integral calculation operation continues as long as there is a deviation, but since it is a correction operation for the target control amount, if the variation exceeds a predetermined range, there is a risk of over-integration. This becomes a cause of impairing the stability of the tapped water temperature at saturation.

However, even if a situation in which the hot water temperature becomes unstable actually occurs, the cause of the situation cannot be detected with the above-described configuration.

<<Object of the invention>> The object of the invention is to provide a combustion control device for a water heater that can monitor the status of various devices such as a temperature sensor and a water flow sensor, and improve the stability of water temperature. It is about providing.

<<Structure and Effects of the Invention>> In order to achieve the above object, the present invention provides a feed system that calculates a target control amount that determines the required combustion amount in a burner based on a target temperature, an inlet water temperature of a heat exchanger, and an inflow water amount. arithmetic means using word control;
A PID calculating means using feedback control that follows changes in the hot water outlet temperature and calculates a predetermined control amount according to the deviation between the hot water outlet temperature and the target temperature, and a combustion amount in the burner according to the deviation between the target control amount and the predetermined control amount. A combustion control device for a water heater, comprising: means for calculating the PID calculation means;
It is characterized in that the integral range is limited within the maximum error range of the target control amount calculated by the feed forward control.

According to this configuration, the range of integral calculation by the feedback control is limited to the maximum error range of the target control amount calculated by the feedback control. Therefore, in the integral calculation operation, over-integration will not occur, and the stability of hot water tapping will be improved. Also,
If the integral calculation operation is to be performed beyond the limit range, it can be seen that the variations in each device such as the temperature sensor and the water amount sensor are larger than a predetermined value.

In other words, it is possible to monitor the condition of each device, such as changes over time.

<<Description of Embodiment>> FIG. 2 is a basic configuration diagram of a water heater equipped with a combustion control device according to an embodiment of the present invention. In the figure, the main body 1 of the water heater is formed into a vertical cylindrical shape,
A burner 2 is disposed on the bottom side, and a heat exchanger 3 is disposed on the top thereof. Note that an exhaust fan (not shown) is attached to the upper exhaust port of the heat exchanger 3.

A water supply pipe 4 is provided on the water inlet side of the heat exchanger 3, and a water flow sensor 5, a water flow switch 6, and an inlet water temperature sensor 7 are attached to the water supply pipe 4, respectively. Further, on the outlet side of the heat exchanger 3, there is provided a hot water supply pipe 8 which is branched and connected to a plurality of channels (three in this embodiment), and a temperature sensor 9 is attached to the branch point of this hot water supply pipe 8. It is being

In the gas supply conduit 10 leading to the burner 2, a gas flow rate adjustment valve 11, a gas governor 12, and an electromagnetic switching valve 13 are respectively arranged from the burner 2 side.
An igniter 14 and a flame detector 15 are provided in association with the burner 2, respectively.

The water amount sensor 5 continuously detects the amount of water in the water supply pipe 4 and outputs this to the controller 16.

The water flow switch 6 outputs a water flow presence/no water flow signal to the controller 16 in response to generation/disappearance of water flow in the water supply pipe 4 due to the opening/closing operation of the switch. The controller 16 receives a water flow/no water flow signal from the water flow switch 6 and starts or stops a predetermined operation.

The inlet water temperature sensor 7 is composed of, for example, a thermistor, and detects the water temperature and outputs it to the controller 16.

The temperature sensor 9 is composed of, for example, a thermistor, and is connected to a processing circuit in the controller 16 together with a temperature setting device 17.

The gas flow rate adjustment valve 11 is driven by the controller 16, and the valve opening degree changes continuously from fully closed to fully open, thereby adjusting the amount of gas supplied to the burner 2.

The gas governor 12 has a function of keeping the pressure of combustion gas constant.

The electromagnetic switching valve 13 is driven by the controller 16 to fully close and fully open the valve.

The igniter 14 is driven by the controller 16,
Attempt to ignite the gas ejected from burner 2.

The flame detector 15 converts flame current into a binary signal in response to a fire occurring in the burner 2, and outputs this to the controller 16.

The controller 16 includes a sequence circuit that controls the sequence from start to stop of combustion, and a hot water temperature control circuit that maintains the outlet temperature at a target temperature, and each circuit operation is performed by a microcomputer.

FIG. 3 is a block diagram showing the configuration of the hot water temperature control circuit in the configuration of the controller 16 as an operation system diagram for controlling the hot water temperature. This hot water temperature control circuit 3
1 includes a target control amount calculation section 311, a temperature deviation detection section 312, a PID calculation section 313, a control amount deviation detection section 314, and a combustion control section 315.

Now, when one door is opened and a water flow signal is input from the water flow switch 6, the electromagnetic switching valve 13 is opened and the gas flow rate adjustment valve 11 is slightly opened by the operation of the sequence circuit. The igniter 14 is driven, and combustion in the burner 2 starts. After that, depending on the operation of the hot water temperature control circuit 31,
The hot water temperature is controlled so as to reach the target temperature.

The target control amount calculation unit 311 calculates a target that defines the required combustion amount in the burner 2 based on the inflow water amount e detected by the water amount sensor 5, the water temperature f detected by the inlet water temperature sensor 7, and the set temperature b by the temperature setting device 17. Calculate the control amount _F1 . This arithmetic expression is the second expression.

In the temperature deviation detection unit 312, the detected hot water temperature a by the temperature sensor 9 and the set temperature b by the temperature setting device 17 are detected.
The deviation c from that is calculated.

The PID calculation unit 313 calculates a predetermined control amount F ₂ based on the deviation c. The calculation formula for this PID calculation corresponds to the third formula above, and the difference is the integral term (second
term), the range of integration is limited.

That is, as described above, there is a predetermined variation in the detection values of each device such as the water amount sensor 5, the water inlet temperature sensor 7, and the temperature sensor 9, and this variation usually falls within a certain range. Therefore, the target control amount F ₁ calculated by the target control amount calculating section 311 will vary within a predetermined range, but this range can be known in advance. On the other hand, since the integral calculation operation is to modify the target control amount as described above, the operation range of the integral calculation operation only needs to be within the range in which the target control amount varies. Specifically, a limit is placed on the number of bits in the register for integral calculations. This not only greatly reduces the number of bits in the calculation register, but by monitoring the status of the calculation register, it is possible to check the operating status of the integral calculation and the status of each device, such as changes over time. be.

In the control amount deviation detection unit 314, the target control amount F ₁
and the predetermined control amount _F2 . In other words,
The calculation of the first equation is performed.

The combustion control unit 315 adjusts the valve opening of the gas flow rate regulating valve 11 and the combustion amount in the burner 2 based on this control amount deviation F.

The above operations are repeated to control and maintain the tapped water temperature at the set temperature.

[Brief explanation of drawings]

FIG. 1 is a characteristic diagram illustrating the hot water temperature control characteristics of a combustion control device for a water heater currently being developed (unpublished) by the present applicant, and FIG. FIG. 3 is a basic configuration diagram showing the control device. FIG. 3 is a block diagram showing the operational system for controlling the hot water temperature of the device of the above embodiment. 2...Burner, 3...Heat exchanger, 5...Water flow sensor, 6...Water flow switch, 7...Water inlet temperature sensor, 9...Temperature sensor, 11...Gas flow rate adjustment valve, 14...Igniter , 16...controller, 1
7...Temperature setting device, 31...Hot water temperature control circuit, 31
1...Target control amount calculation section, 312...Temperature deviation detection section, 313...PID calculation section, 314...Controlled amount deviation detection section, 315...Combustion control section.

Claims (1)

[Claims] 1 Calculation means using feed forward control that calculates the target control amount that determines the required combustion amount in the burner based on the target temperature, the water inlet temperature of the heat exchanger, and the amount of inflow water, and the calculation means that follows the change in the outlet temperature and calculates the outlet temperature and the target. A water heater comprising: PID calculation means using feedback control for calculating a predetermined control amount according to a temperature deviation; and means for calculating a combustion amount in a burner according to a deviation between the target control amount and the predetermined control amount. The combustion control device is characterized in that, in the integral calculation operation of the PID calculation means, an integral range is limited to a maximum error range of the target control amount calculated by the feed forward control. Combustion control device for water heaters.