EDA realization of water level control of solar water heater

1 Introduction

[1] At present, the production and use of solar water heaters in China ranks first in the world [1][2]. With the improvement of people's living standards, the quality requirements for solar water heaters are getting higher and higher. Intelligent control solar water heaters are getting more and more popular. Water level control is one of the basic functions of intelligent control type solar water heaters, and it is an indispensable link to realize "automatic control". The so-called water level control is to achieve the function of automatically replenishing water when the water is in the water tank of the solar water heater and automatically stopping the water when the water is full. In the existing control scheme, the water level sensor controls the on and off of the semiconductor device according to different signals issued when water is lacking or full of water, thereby further controlling the opening and closing state of the relay and the solenoid valve to perform water supply or not. The automatic water stop function can be achieved after the water is full. However, the definition of “water shortage” often causes inconvenience to users. If the water shortage is defined as water tank water, when there is still a small amount of residual water at night, it will not be replenished in time, which will cause inconvenience to the next day. If the water shortage is defined as a specific water level, it will be below the water level. A mixed state [3] appears.

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This paper designs a new type of water level controller and adopts electronic design automation (EDA) technology [4][5]. It is integrated with Altera's MAX+PLUSII integrated development environment using the widely used VHDL hardware circuit description language. , simulation, and download to the programmable logic device EPF10K10TC144-3 to achieve control functions.

2 main functions of water level control

Intelligent water level control requires timely hydration without affecting normal use. The intelligent water level controller designed here can realize the functions of automatic water stop, conditional hydration and forced hydration, display and alarm after the water is full. As shown in Figure 1.

Water level control diagram

Figure 1 Schematic diagram of water level control

The “water level” is provided by the water level sensor in the water tank. It is divided into three gears: full water level, conditional water level and forced hydration level. The full water level is used to realize the automatic water stop function after the water is full; the conditional water level can be set at a certain water level, such as half tank water. When the water level of the water tank is lower than this setting (higher than the forced water level), the conditional water supply is realized: when the water is indicated It is forbidden to replenish water when it is valid (in water), otherwise it will be replenished; the mandatory water level can be set to water tank (or set at a lower water level), and the forced water replenishment function is realized at this time. For ease of use, the controller provides alarm and indication functions: the hydration indicator light is on when the water is replenished, and the user cannot use water at this time; when the water level of the water tank is lower than the conditional water level, the prompting music is issued. At this time, if the user wants to continue to use water intermittently, the hydration can be set through the keyboard. It is forbidden, so that even if it is not used, it will not be replenished, so that there is still hot water available in a short time. Therefore, when there is a music prompt, the user can cancel the “water replenishment prohibition” position in time to complete the water supply for the water tank; the water level of the water tank reaches the mandatory When the water level is replenished and the water is forbidden, an alarm signal is issued to cancel the water replenishment prohibition and timely replenish water to prevent the water tank from being dehydrated for a long time.

3 water level controller VHDL code

VHDL (Very-High-Speed ​​Integrated Circuit Hardware Description Language) is an IEEE industry standard hardware description language developed with the development of programmable logic devices (PLDs). This way of describing hardware circuits in language is easy to modify and save, and has strong behavior description ability, so it has been widely used in circuit design. The following is a VHDL code describing the water level control.



ENTITY bushui IS

PORT (ply,forbid : IN STD_LOGIC; - marked with water, prohibited with water

Level : IN INTEGER RANGE 0 TO 7; -- Water level

Valve,alm,music : OUT STD_LOGIC; --Hydrating solenoid valve, alarm, prompt music

Fil_l : BUFFER STD_LOGIC); -- hydration indicator

END bushui;





CASE forbid IS

WHEN '1' => valve <= '0'; fil_l <= '0'; -- no water replenishment

IF level <= 3 AND level > 1 THEN

Music <= '1';alm <= '0'; --Music hints that the water level is below the conditional hydration level

ELSIF level <= 1 THEN

Alm <= '1';music <= '0'; --The water level is lower than the mandatory hydration level alarm

ELSE music <= '0'; alm <= '0';


WHEN '0' => alm <= '0';

IF level = 7 THEN

Valve <= '0';fil_l <= '0';music <= '0'; stop hydrating when the water is full

ELSIF level<= 3 AND level > 1 THEN

Alm <= '0';music <= '1'; --Music hints that the water level is below the conditional hydration level

Valve <= not ply; fil_l <= not ply; -- replenish water without water

ELSIF level <= 1 THEN

Valve <= '1';fil_l <= '1';music <= '0'; --forced hydration

ELSE music <= '0'; valve <= fil_l;fil_l <= fil_l;


WHEN OTHERS => null;



END behav;

In the code, the water level is set to 0 to 7 levels. After integration, the water level is represented by a three-digit binary code, that is, the minimum distritable water level is one-eighth of the full tank. The conditional hydration level is set at “level= 3”, ie half tank water; the forced hydration level is set at “level= 1”, which is one eighth of the full tank.

4 simulation results

In order to verify the correctness of the design, the above code description is synthesized and simulated in Altera's MAX+PLUSII integrated development environment. The following is the simulation result of the design.

Simulation results

As can be seen from Figure 2, forbid (forbidden water) is mandatory, regardless of the water level, the position can stop replenishing water at any time; when the position is revoked, whether to continue to replenish water is related to the current water level: if it is lower than the hydration The water level will continue to replenish water (about 1.0us, 8.0us), otherwise it will not be replenished (about 3.4us). When forbid is invalid, the hydration is normally carried out according to the preset: when the water level of the water tank is lower than the forced water level, the water is forced to be replenished (about 1.0us), and the water level is between the forced water level and the conditional water level to conditionally replenish water (about 5.25us). ~5.75us), when the water is full, stop the hydration (about 9.7us). The hydration indicator fil_l is consistent with the hydration value. Music provides music tips in a timely manner. Alm gives an alarm (between 0.2us and 1.0us) when the water level is lower than the mandatory water level and is prohibited from hydrating. It can be seen that the circuit meets the design requirements.

5 Conclusion

The design adopts the advanced EDA technology used in electronic product design, which has the advantages of flexible design, quick modification, convenient debugging and short development cycle [4], and the designed electronic products have high reliability and high efficiency. The performance and price ratio is extremely competitive in the market. For example, the change of the set water level, the increase of the water level, and the adjustment of the alarm mode in the design can be easily modified directly from the VHDL source program without the support of the hardware circuit. The intelligent water level controller realized by this design can be used to realize the water level control alone or organically combined with other solar water heater control links (such as water temperature control) to form a true “automatic control” solar energy. The water heater provides hot water to the user all the time, overcomes the inconvenience caused by the use of hydration, and makes the use of solar water heaters a pleasure, thereby improving people's quality of life.

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