WO2016019885A1

WO2016019885A1 - Method for controlling electric water heater

Info

Publication number: WO2016019885A1
Application number: PCT/CN2015/086240
Authority: WO
Inventors: 万华新; 李水清; 邵小荣; 王伟
Original assignee: 艾欧史密斯(中国)热水器有限公司
Priority date: 2014-08-06
Filing date: 2015-08-06
Publication date: 2016-02-11
Also published as: CN104121704A

Abstract

A method for controlling an electric water heater (1). The electric water heater (1) comprises at least two sets of PTC (301, 3) heating elements capable of conducting start control separately. After the electric water heat (1) is powered on, the at least two sets of PTC heating elements (301, 3) are controlled to be started in an alternate mode, and each time after the corresponding PTC heating element is started, the actual highest total power of the electric water heater (1) is less than the set highest total power. After the electric water heater (1) is powered on, the at least two sets of PTC heating elements (301, 3) do not start to work simultaneously; instead, the PTC heating elements (301, 3) are started in an alternate mode, so that excessive current and power are prevented, and circuit overload of the electric water heater (1) cannot occur.

Description

Electric water heater control method

Technical field

The invention relates to the technical field of electrical appliances, and in particular to a method for controlling an electric water heater.

Background technique

At present, electric water heaters mostly use PTC (Positive Temperature Coefficient) technology. PTC (Positive Temperature Coefficient) refers to a thermistor phenomenon or material with a sharp increase in resistance at a certain temperature and a positive temperature coefficient. . PTC thermistors can be used as temperature measurement and control in the industry. They are also used for temperature detection and adjustment of certain parts of automobiles. They are also widely used in civil equipment, such as controlling the water temperature of instant water heaters, the temperature of air conditioners and cold storages. Use its own heating for gas analysis and anemometers.

In the prior art, a liquid heating rod is provided. As shown in FIG. 1 , the liquid heating rod comprises a heating rod main body 1 and a temperature resistant plastic seat 2 connected by bolts. The heating rod main body 1 is made of a stainless steel outer casing 3 and a temperature resistant plastic sleeve. 4, the stainless steel outer casing 3 is disposed on the right side of the temperature resistant plastic sleeve 4, the inside of the stainless steel outer casing 3 is provided with two PTC thermistor heating elements 5, and the PTC thermistor heating element 5 is provided with a temperature resistant insulating film 6, A heat conductive aluminum profile 7 is disposed between the PTC thermistor heating element 5 and the stainless steel casing 3, and a spring 8 is disposed inside the PTC thermistor heating element 5, and the left end of the PTC thermistor heating element 5 is connected to the power line through the electrode sheet 9. 10. The power cord 10 passes through the temperature resistant plastic sleeve 4 and the power cord inlet and outlet 11 of the temperature resistant plastic seat 2 in sequence.

Similar to the structure shown in FIG. 1, the electric water heater of the prior art may include a plurality of PTC heating elements. However, when the electric water heater is energized, multiple PTC heating elements start to work at the same time, which may cause excessive current and power, causing the electric water heater circuit. Overload, device damage.

Summary of the invention

Embodiments of the present invention provide a method for controlling an electric water heater, which is used to avoid overloading of the electric water heater circuit and damage of the device caused by excessive current and power after the electric water heater is energized. The electric water heater includes at least two groups capable of separately performing start control. The PTC heating element controls the at least two sets of PTC heating elements to be staggered after the electric water heater is energized, and the actual maximum total power of the electric water heater is less than the set maximum total power after each startup.

In one embodiment, the time to control the at least two sets of PTC heating elements to be staggered is ≥ 20 seconds.

In one embodiment, the set maximum total power is 3.5 KW.

In one embodiment, the impact power of the activated PTC heating element tends to stabilize power and any unactivated The unactivated PTC heating element is controlled when the maximum impact power of the PTC heating element is less than or equal to the difference between the set maximum total power and the actual total power of the electric water heater.

In one embodiment, the method further includes:

After the electric water heater is energized, after controlling a group of the PTC heating elements to start, the group of PTC heating elements is controlled to start again after a predetermined time.

In one embodiment, the predetermined time is > 15 seconds.

In one embodiment, when the actual power of the PTC heating element is less than 50% of the stabilizing power of the PTC heating element, all PTC heating elements are controlled to open.

In an embodiment, the method further includes: controlling the electric water heater to issue an alarm signal.

In one embodiment, each set of the PTC heating elements is controlled to be activated by a relay.

In one embodiment, a PTC heating tube is disposed in the electric water heater, and the at least two sets of PTC heating elements are disposed in the PTC heating tube;

Or, the electric water heater is provided with at least two PTC heating tubes, and each PTC heating tube includes at least one set of PTC heating elements.

In the embodiment of the present invention, after the electric water heater is energized, at least two groups of PTC heating elements capable of separately controlling the electric water heater are controlled to be staggered, and the actual maximum total power of the electric water heater is less than the set maximum total power after each startup. Therefore, at least two sets of PTC heating elements do not start working at the same time after the electric water heater is energized, but the current and power are prevented from being excessively large by the staggered starting manner, the electric water heater circuit is not overloaded, and the device in the electric water heater is protected. Improve the safety of electric water heaters and extend the life of electric water heaters.

DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the description of the prior art will be briefly described below. Obviously, the drawings in the following description are only It is a certain embodiment of the present invention, and other drawings can be obtained from those skilled in the art without any creative work. In the drawing:

Figure 1 is a schematic view of a prior art liquid heating rod;

2 is a resistance-temperature graph of a PTC heating element in an embodiment of the present invention;

Figure 3 is a schematic view of a PTC heating element in accordance with an embodiment of the present invention;

4 is a schematic view of a PTC heating tube according to an embodiment of the present invention;

FIG. 5 is a diagram showing an example of a method of controlling an electric water heater according to an embodiment of the present invention.

detailed description

The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. The illustrative embodiments of the present invention and the description thereof are intended to explain the present invention, but are not intended to limit the invention.

The inventors have found that in the prior art, when a plurality of PTC heating elements are started at the same time after the electric water heater is energized, the current and power may be too large, causing the electric water heater circuit to be overloaded and the device to be damaged. 2 is a graph showing a resistance-temperature (R-T) curve of a PTC heating element in an embodiment of the present invention. In Figure 2, Rn is the rated temperature zero power resistance, Rmin is the minimum zero power resistance, TRmin is the temperature at the minimum resistance, Tc is the switching temperature or Curie temperature, Rc is the switching resistance, Rmax is the maximum resistance, and TRmax is the maximum resistance. The temperature at the time. As shown in Figure 2, during the initial stage of the PTC heating element, as the temperature increases, the resistance decreases first. When the resistance is minimum, the power is maximum, the current is maximum, and the corresponding power and current become the impact power and electric shock. When the temperature exceeds TRmin, the resistance increases, the power and current decrease, and finally stabilizes in the range of Tc plus or minus 5 °C to 10 °C. If multiple PTC heating elements are heated together, it is possible to achieve the maximum inrush current at the same time, causing overload of the user circuit. Therefore, in the embodiment of the present invention, it is considered to control the staggered activation of at least two groups of PTC heating elements in the electric water heater.

The electric water heater control method in the embodiment of the present invention controls at least two sets of PTC heating elements in the electric water heater to be staggered after the electric water heater is energized, and the actual maximum total power of the electric water heater is less than the set maximum total power after each startup; Each of the sets of PTC heating elements is capable of separate start control. In an embodiment, each set of PTC heating elements can be controlled by a relay. Each set of PTC heating elements can include a set of PTC chips, each set of PTC heating elements can be provided with a separate live neutral and controlled separately by a relay. Figure 3 is a schematic illustration of a PTC heating element in accordance with an embodiment of the present invention. As shown in FIG. 3, the electric water heater includes three sets of PTC heating elements 301, and each set of PTC heating elements 301 is individually controlled by a relay 302.

In the specific implementation, only one PTC heating tube may be disposed in the electric water heater, and at least two sets of PTC heating elements are disposed in the PTC heating tube; or, at least two PTC heating tubes may be disposed in the electric water heater, and each PTC heating tube includes at least one Group PTC heating elements. 4 is a schematic view of a PTC heating tube in accordance with an embodiment of the present invention. As shown in FIG. 4, the electric water heater 1 of the scheme 1 is provided with three PTC heating tubes 2, each PTC heating tube 2 includes a set of PTC heating elements 3; in the scheme 2, the electric water heater is provided with two PTC heating tubes, one of which is heated by PTC The tube comprises a set of PTC heating elements, the other PTC heating tube comprises two sets of PTC heating elements; the electric water heater of Scheme 3 is provided with a PTC heating tube, the PTC heating tube comprising three sets of PTC heating elements.

As mentioned above, after the electric water heater is energized, due to the characteristics of the PTC heating element itself, an inrush current will be generated. After a period of time, the inrush current is reduced to reach a stable current. If multiple sets of PTC heating elements are simultaneously activated, the maximum inrush current is reached at the same time. In the embodiment of the present invention, at least two sets of PTC heating elements are staggered and started, and will not be generated at the same time. The superposition of the maximum inrush current prevents the total current from being too large, thereby protecting the electrical components of the electric water heater. In an embodiment, after the electric water heater is powered on, at least two sets of PTC heating elements are controlled to be staggered, wherein specifically, the time during which the at least two sets of PTC heating elements can be controlled to be turned off can be set according to actual needs, for example, at least two groups of PTCs can be controlled. The time during which the heating element is staggered is ≥ 20 seconds. Moreover, after each startup of the PTC heating element, the actual maximum total power of the electric water heater is less than the set maximum total power. In the embodiment, the maximum total power can be set according to actual requirements, for example, it can be set to 3.5 KW.

In the specific implementation, in order to ensure that the actual maximum total power of the electric water heater is less than the set maximum total power, the impact power of the activated PTC heating element tends to stabilize the power, and the maximum impact power of any unactivated PTC heating element is less than or When the difference between the highest total power and the actual total power of the electric water heater is set, the PTC heating element that is not activated before starting is controlled.

In addition, the inventors have also found that the PTC heating element is repeatedly turned on, and a voltage effect occurs inside the PTC, which causes a large increase in the inrush current. For example, immediately after the PTC heating element is de-energized, the PTC heating element is activated again, causing the maximum inrush current to rise by about 40%. Therefore, in the embodiment, in order to prevent overloading of the whole machine component and the user circuit, the PTC heating element may be controlled to be discontinuously started, that is, after the PTC heating element is started, the PTC heating element is controlled to be started again after a predetermined time. The predetermined time can be set according to actual needs during implementation, for example, the predetermined time is ≥ 15 seconds.

FIG. 5 is a diagram showing an example of a method of controlling an electric water heater according to an embodiment of the present invention. In Figure 5, T ₁ is the temperature of the upper layer of water in the electric water heater, and T ₂ is the temperature of the lower layer of water in the electric water heater. Because the water temperature in the electric water heater has a gradient phenomenon, the temperature of the upper layer and the lower layer is detected, and T _s is the set temperature, T ₁ , T ₂ and T _s are all °C. As shown in Figure 5, after the electric water heater is energized, the heating control inlet is used for the first heating detection. It can be judged whether the condition T ₁ ≥T _s and T ₂ ≥T _s -4 are satisfied first. If it is satisfied, the heating will be stopped, otherwise the delay buffer time will be 25 seconds to control the discontinuous start of the PTC heating element to avoid the voltage effect caused by repeated opening of the PTC heating element. When the PTC heating element is activated, the three sets of PTC heating elements 1 to 3 in the electric water heater are staggered, for example, starting at intervals of 25 seconds.

In the embodiment, when the temperature of the PTC heating element is increased, the electric resistance is increased, the power is decreased, and when the power of the PTC heating element is largely lowered, the dry burning state can be determined, and the heating should be stopped. For example, when the actual power of the PTC heating element is less than 50% of the stable power of the PTC heating element, it is determined to be in a dry burning state, and by controlling all of the PTC heating elements to be disconnected, circuit damage due to dry burning can be avoided. Further, at this time, the electric water heater can be controlled to issue an alarm signal to perform a dry burning alarm.

In summary, in the embodiment of the present invention, after the electric water heater is energized, at least two groups of PTC heating elements capable of separately controlling the electric water heater are controlled to be staggered, and the actual maximum total power of the electric water heater is less than after each startup. Set the maximum total power, so that at least two sets of PTC heating elements do not start working at the same time after the electric water heater is energized, but avoid the current and power too much by staggering the starting mode, and will not cause the electric water heater circuit to overload and protect the electricity. The components in the water heater improve the safety of the electric water heater and extend the life of the electric water heater.

In the embodiment, the PTC heating element is also controlled to be discontinuously activated, thereby avoiding a voltage effect caused by repeated opening of the PTC heating element, causing a large increase in the inrush current.

The above described specific embodiments of the present invention are further described in detail, and are intended to be illustrative of the embodiments of the present invention. All modifications, equivalent substitutions, improvements, etc., made within the spirit and scope of the invention are intended to be included within the scope of the invention.

Claims

An electric water heater control method, the electric water heater comprising at least two sets of PTC heating elements capable of separately performing start control, wherein after the electric water heater is energized, the at least two sets of PTC heating elements are controlled to be staggered, and After each start, the actual maximum total power of the electric water heater is less than the set maximum total power.
The method of claim 1 wherein controlling the at least two sets of PTC heating elements to be staggered is initiated for > 20 seconds.
The method of claim 1 wherein said setting a maximum total power is 3.5 kW.
The method of claim 1 wherein the impact power of the activated PTC heating element tends to stabilize power and the maximum impact power of any unactivated PTC heating element is less than or equal to said set maximum total power and The unactivated PTC heating element is controlled to initiate a difference in the actual total power of the electric water heater.
The method of claim 1 further comprising:

After the electric water heater is energized, after controlling a group of the PTC heating elements to start, the group of PTC heating elements is controlled to start again after a predetermined time.
The method of claim 5 wherein said predetermined time is ≥ 15 seconds.
The method according to any one of claims 1 to 6, wherein all PTC heating elements are controlled to be disconnected when the actual power of the PTC heating element is less than 50% of the stable power of the PTC heating element.
The method of claim 7 further comprising: controlling said electric water heater to issue an alarm signal.
A method according to any one of claims 1 to 6, wherein each of said sets of said PTC heating elements is activated by a relay.
The method according to any one of claims 1 to 6, wherein a PTC heating tube is disposed in the electric water heater, and the at least two sets of PTC heating elements are disposed in the PTC heating tube;

Or, the electric water heater is provided with at least two PTC heating tubes, and each PTC heating tube includes at least one set of PTC heating elements.