JPS59180230A - Temperature control system of water heater - Google Patents

Abstract

PURPOSE:To shorten the setting time at the time when load is changed and consequently improve the controllability by a method wherein the change of flow rate is fed forward to the input side of a limiter and at the same time the limit values of the limiter are changed in accordance with the changed flow rate. CONSTITUTION:A multiplier 7 inserted between a controller 1 and a limiter 2 multiplies the output signal e0 of the controller 1 with the flow rate signal Q to represent the rate of water flowing in a water heater 4 and the resultant signal eo.Q is inputted to the limiter 2. Further, the flow rate signal Q is supplied to the limiter 2 in order to change an upper limit value in accordance with its value and to change a lower limit value in accordance with its inverted value. The change of the upper limit value is performed by multiplying a preset value Kl1 with the flow rate signal Q and that of the lower limit value by multiplying a preset value Kl2 with the inverted flow rate signal -Q respectively. The limiting action against the input signal eo.Q at the limiter 2 is performed based upon the limit values Kl1.Q and -Kl2.Q, both of which are changeable in accordance with the flow rate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a temperature control method for instantaneous water heaters so that the hot water temperature always matches a desired set value. This figure shows the configuration of the control device, where 1 is a controller, 2 is a limiter, 3 is an operating end such as a fuel control valve, 4 is a water heater, and 5 is a detector that detects the temperature of hot water from the water heater 4. The controller 1 inputs the deviation (e, p-epV) between the outlet hot water temperature and position setting signal e s p and the outlet hot water temperature detection signal e which is the output of the detector 5, and sets this deviation to zero. It outputs an output such as i and e, and can take any operation form such as PI operation type or PID operation type.If it has an integral operation function, When a large deviation continues for a long time, such as when the temperature changes significantly, the integral component becomes excessive, and a reset windup phenomenon occurs in which the output signal does not follow even if the sign of the deviation is reversed. Reset windup prevention means are often provided to prevent this phenomenon.

Output signal e of controller 1. is input to limiter 2. This limiter 2 receives the signal e. If the value of is larger than the preset upper limit Kz1, set it to this upper limit Kt1, and if it is smaller than the preset lower limit Kz2, set it to this lower limit +).
2, respectively, and when it is between the upper limit Kt1 and the lower limit Kt2, the signal e. 5 will pass through as is. Then, the output signal 〇m of the limiter 2 is applied to the operating end 3. If this operating end 3 is a fuel control valve, the calorific value of the water heater 4 is controlled in accordance with the signal em, and the temperature of hot water is controlled. However, in this method, controllability is poor due to the delay element that the water heater has, and the temperature of the hot water does not stabilize in a short time when the load suddenly changes.

As an improved version of this method, the method shown in Figure 2 was developed. In the method shown in Fig. 2, the hot water temperature setting signal e s
A deviation e s p e 1 between p and the inlet water temperature signal ei indicating the temperature of the waste water supplied to the water heater 4 is detected, and this deviation is amplified by the amplifier 6 (having a gain KF) to produce a signal K p ( e sp e 1) is applied to the output ern of limiter 2. In this case, a feedforward element is added to the control system, so if the set value of the hot water tap temperature or the hot water tap flow rate, which occurs due to the specific usage of the water heater, is significantly changed, the control effect from the feedforward element will be is obtained, but the control effect from the controller side is that the value of the output signal em of limiter 2 is suppressed to the predetermined upper limit value of 71 or lower limit value Kt2, so the input signal MVQ value to the operating end is There are disadvantages in that the number of changes is limited and the settling time required for the actual tap water temperature to reach the set temperature is still long.

This invention was made in order to eliminate the drawbacks of the conventional control method as described above. The signal is varied in response to a flow signal indicating the flow of water into (or removed from) the water heater, and the upper limit and/or lower limit of the limiter is adjusted in response to this flow signal. It is an object of the present invention to provide a control method that can significantly shorten the settling time during load fluctuations and improve controllability by changing the value. The control system of the present invention can be similarly applied to the feedback-only control system shown in FIG. 1 and the control system including feedforward elements shown in FIG. 2.

An embodiment of the present invention will be described below with reference to the drawings. Figure 3 corresponds to the control system shown in Figure 1, where 1 is the controller, 2 is the limiter, 3 is the operating end, and 4 is the water heater, which are the same as shown in Figure 1. Since it is equivalent to , detailed explanation thereof will be omitted.

Further, reference numeral 7 indicates a multiplier inserted between the controller 1 and the limiter 2. This multiplier 7 receives the output signal e of the controller 1. Then, a calculation is performed to generate a flow rate signal Q indicating the flow rate of water flowing into the water heater 4 (or being taken out from the water heater 4), and the resultant signal A is sent to the limiter 2. Furthermore, the flow rate signal Q is supplied to the limiter 2 in order to change the upper limit value according to the value and to change the lower limit value according to the inverted value. Mitsutoi 1.1L0) Changes are made by multiplying the preset value Kt1 by the flow rate signal Q, and changes to the lower limit value are made by multiplying the preset value Kt2 by the inverted flow rate signal -Q. , input signal e at limiter 2.

The limit action for -Q is release.

Limit values Kt1・Q and -KZ changed according to
2. Performed by Q. 8B'1) This is an inverter for inverting the IL amount.

Furthermore, FIG. 4 shows a control system of the present invention corresponding to the feedforward control system shown in FIG.
In this case, the output signal K y (es p e r ) of the amplifier 6 that amplifies the deviation e sp e r between the outlet hot water temperature setting signal es p and the incoming water temperature signal ei
A multiplier 9 is provided which multiplies current current i g by Q, and the output signal of this multiplier 9 is Q ”Kr(esp ”r)
is used in place of the flow rate signal Q in the case of FIG. 3 to change the upper and lower limit values.

Further, the output signal of the multiplier 9 is added to the output no.

Here, according to the graph of FIG. 5, the upper limit value Kt
1 change behavior? explain. Now, the hot water temperature setting signal e
Assuming that s p and the inlet water temperature signal e are constant,
The level of the output signal Q-KF(eS, -el)=j of the multiplier 9 is proportional to the flow rate signal Q. Further, the output signal en of the limiter 2 is also proportional to the flow rate signal Q if the value of the output signal eo-Q of the multiplier 7 is between the upper limit value and the lower limit value. For example, when the value of the current flow rate signal Q is constant at Ql, if the hot water temperature setting signal e 5 p is suddenly changed to a high value, the detector 501111 force No. 16 e p v will not change at that point. Therefore, the output signal eo-Q of the multiplier 7 rises rapidly, and the output signal j of the input unit 9 also rises rapidly at the time of io1, so the tenth sleep limit value Kz1 also rises, If the output value of erTl is changed to Xjrl, it becomes equal to the upper limit value. Therefore, the output signal 1 of the limiter 2 and the output signal J of the subtracter 9 are
The operating terminal 30 input 1 is represented by the phase eII-t +1.
The No. 3 MV quickly rises to the upper limit value MV on this streamline, and as a result, rapid heating is performed due to a large manipulated variable.
When the It release signal Q decreases to Q2, the signal M V becomes 1
1p-+engine decreases to the maximum value MV2 at 6 steering Q2.

In other words, when the flow rate Q is suddenly changed from Ql to Q2, the signal QMV is limited by the effect of the feedforward number j and the limit value changed by this signal Q (the effect of Even if there is a sudden change from Q1 to Q2, e. does not respond to the IJ locus, so e. immediately after the sudden change is the same value as the above sudden change.However, eoQ does not respond to the sudden change in Q. In general, em undergoes a desired change due to the feedforward effect of e.Q, or the effect of being limited to a changed limit value. Note that the same operation should be performed for the lower limit value K12 as well.

In addition, although the above-mentioned description illustrated the case where both an upper limit and a lower limit are changed, you may make it change only one.

As described above, according to the present invention, the change in flow rate is fed forward to the input side of the limiter, and the limit value of the limiter is changed according to this flow rate, so that the set temperature, inlet water temperature, inlet flow rate, etc. Even if the load changes significantly, the follow-up speed until the predetermined hot water temperature is reached is fast, and the temperature is reached in a short time. For this reason, the deviation between the hot water temperature and its set temperature will not continue for a long time.
The influence of the reset windup phenomenon is also greatly alleviated.

[Brief explanation of the drawing]

1 and 2 are block diagrams showing the conventional temperature control method, and FIGS. 3 and 4 are block diagrams showing the temperature control method of the present invention, respectively.
0) is a graph to explain the operation of the system shown in the figure. DESCRIPTION OF SYMBOLS 1... Controller, 2... Limiter, 3... Operating end, 4... Water heater, 5... Detector, 6... Amplifier, 7, 9... Multiplier.

Claims (2)

[Claims] (1) Multiply the flow rate signal by the output signal of the controller, which is the input signal and the deviation between the hot water temperature signal and the hot water temperature setting signal, and the result of this calculation is applied between the upper limit value and the lower limit value. and controlling the operating end according to the output signal of the limiter, and changing at least one of the upper limit value and the lower limit value according to the flow rate signal. Water heater temperature control method. (2) Multiply the output signal of the controller, which uses the deviation between the hot water temperature signal and the hot water temperature setting signal as an input signal, by the flow rate signal, and apply this first calculation result between the upper limit value and the lower limit value. Further, a signal corresponding to the deviation between the inlet water temperature signal and the outlet temperature setting signal is multiplied by the flow rate signal, and the result of this second multiplication is combined with the result of the first operation. The operating end is controlled according to the phase, and the upper limit value and the lower limit value are changed according to the second calculation result to make the temperature of the water heater similar to t%. control method.