Research and development of electromagnetic instant water heater
Based on the in-depth study and trial production of electromagnetic heating instant water heaters, this paper proposes the idea of using electromagnetic induction energy transfer and eddy current heating to produce high-efficiency, water-electricity completely isolated safe instant electric water heaters.
Electric water heaters are divided into two types: water storage type and instant type. Among them, the water storage type electric water heater has a long heating process, and it needs to start heating 1-2 hours in advance when it needs water. The heat loss is large due to heating, and the thermal efficiency is low; in addition, the volume is large and the installation space is large, and these disadvantages are limited. Its use. The instant water heater has the advantages of being hot and ready to use, small size, convenient installation and use. In order to obtain high thermal efficiency, the instant water heater adopts a heating method in which the heating wire and the electric heating plate are directly installed in the water, but the result of this will cause a safety hazard of electric leakage. Although some manufacturers have adopted safety measures such as adding a shielded metal mesh at the water outlet, these have not fundamentally solved the problem. For manufacturers that emphasize safety, new heat-generating materials such as electric heating films, PTC heating elements, and non-metal heating materials are used to heat the water pipes made of quartz glass to achieve separation of water and electricity and ensure safety. However, due to the relatively high price of new materials, the price of water heaters is relatively high, and the main reason is that the heat is reduced by the heating of the quartz glass tubes, so that the electric heating power required is relatively large. In short, the above two types of electric water heaters have such problems in terms of safety, efficiency, convenience, and cost. In response to the above problems, I tried to develop a new type of electromagnetic instant water heater to overcome the shortcomings and shortcomings of the above water heater.
2 The principle of electromagnetic instant water heaters We all know that the metal magnetically conductive material is placed in a high-frequency electromagnetic field, the eddy current will be generated in the metal, and the temperature is raised. This method of using eddy current heating has been widely used in industrial and civil applications. The advantage is that this induction heating method has a high power density, the power per unit heating surface can reach 0.1-2 kW/cm2, and the heating speed is extremely fast, and the metal surface can be heated to 800-1000 in several seconds to several tens of seconds. According to this characteristic, the electromagnetic instant water heater transmits sufficient energy through electromagnetic conversion, and the metal magnetic conductive material immersed in the insulated and insulated water tank is rapidly heated and heated, thereby rapidly heating the water flowing through the water tank. This is how the electromagnetic water heater works.
3 The structure and characteristics of the electromagnetic instant water heater are shown as the structure of the water heater developed. It is mainly composed of a water tank, a heating coil L, a shielding plate, a circuit board, a sink bracket and an outer casing. The water tank and heating coil L constitute the main part of the water heater's transduction. The design of the water tank and the design of the main circuit reflect the characteristics of the water heater.
3.1 Structure and Features of the Sink The structure of the water heater sink is as shown. It is injection molded from a heat-resistant insulating material having a certain mechanical strength. A circular non-pound steel sheet is sandwiched between the water tank and has the same diameter as the heating coil L. The function of the heating coil L is to convert a high-frequency current coming from the wiring board into a high-frequency magnetic field, and generate a eddy current in the non-pound steel sheet in the water tank to heat the flowing water inside. In order to meet the power demand, the coil current is larger than the test voltage 220V current 20A). In order to reduce the loss on the heating coil L and reduce the effect of the high-frequency current skin effect, the coil adopts multiple strands of fine enameled wire, which are first woven together. And then wound into a disc shape. In addition, a heat-resistant barrier is added inside the water tank on both sides of the non-pound steel sheet. The first function is to separate the non-pound steel heating plate from the water tank to prevent direct contact between the two; the second is to guide the flow of water and increase the flow distance. Let the water flow be fully heated. The shielding plate is made of a material that is strongly magnetically conductive, and functions to shield the magnetic lines behind the heating coil from being shielded from the circuit portion. The sink bracket is mainly used to fix the water tank, and the material is non-magnetic material. The inner casing mainly separates the circuit including the coil) and the water guide to prevent leakage or leakage of the circuit when the water tank leaks. The outer casing provides protection for the entire water heater.
For the above-mentioned structure of the water heater multiple times, mainly including the power and drive parts, detection and power adjustment and protection comparison circuit, etc., in order to improve the reliability and stability of the circuit, integrated circuit components are used.
3.2.1 The power and drive circuit adopts a bridge inverter circuit composed of a novel power switching device IGBT insulated gate bipolar transistor.
First of all, the IGBT component itself has higher withstand voltage and output power of several kilowatts to several tens of kilowatts compared with power electronic devices previously used for household electric heaters, large input impedance, small voltage drive power, and high operating frequency! 20kH-) and high comprehensive performance. Secondly, the main circuit uses a bridge inverter circuit composed of four IGBT power components. Compared with the power circuit composed of a single tube, although the circuit power and the driving elements are increased and the form is complicated, the stability and reliability thereof are increased. Output frequency and inductance, capacitance parameters in the single-tube circuit shown. The current output to the inductor L has a direct influence on the circuit voltage. Taking a set of data in the experiment as an example, when the electromagnetic heater current is about 7A, the voltage across the power tube is subjected to a voltage peak of about 700 volts when the current is increased. By 10A, the tube withstand voltage is increased to more than 900 volts. This indicates that the voltage experienced by the power component is greatly affected by changes in the output current. It is required that the component has high withstand voltage and thus the price is high; in addition, the circuit detuning and high voltage cause the power component damage rate to be high, which is manifested as poor circuit stability and reliability. With the bridge inverter circuit, the highest voltage that the power component is subjected to is the rectified DC voltage, and the circuit can change the current of the electromagnetic coil L without affecting the highest voltage that the component is subjected to. Therefore, this circuit is more stable and reliable.
The driver circuit uses two integrated drivers, which are suitable for driving power devices such as M0S-FETJGBT with various schematics of the single-tube circuit. Its circuit chip size is small DIP14), high integration can drive the same bridge arm two-way), fast response, floating voltage is less than 600V), strong drive capability, built-in undervoltage lockout, and its low cost and easy to debug. It is equipped with an external protection blocking port. The high-frequency signal is sent to the driver. The driver outputs two driving signals with sufficient dead time to the IGBT control terminal to control VT1, VT3 or VT2, and VT4 is turned on/off to ensure power. Circuit safety switching. Thereby an alternating current is formed on the inductance L.
3.2.2 Detection and power adjustment circuit SG3524 domestic model CW3524) is a dual-in-line 16-pin ceramic or plastic package integrated block. The device has a complete P:M power control function, the operating frequency can be greater than 100kHz, it provides a positive and negative two-way square wave oscillation signal to the drive circuit. By adjusting the magnitude of the load feedback voltage signal of the input 3524, the output current of the main circuit can be conveniently adjusted, and the stepless adjustment of the power is simply realized.
3.2.3 Protection Circuit Protection circuit adopts voltage comparator LM339, which has the characteristics of low power consumption and high performance. The output of the comparison circuit is connected to the pulse blocking end of the 3524 driver, and the protection is mainly provided to prevent the air-burning protection. The water flow detection switch is installed on the water side after the water system is detected. When the water flows, the comparator outputs a low level, 524 works, and the water heater heats; when no water flow is detected or the water valve A is closed, the comparator output High level, blocking 3524 output, the water heater stops heating.
The overheat protection uses the thermistor detection. When the temperature exceeds the preset maximum temperature, the comparator outputs a high level, and the 3524 output is blocked 3524; when the temperature is lower than the preset maximum temperature, the comparator outputs a low level and does not work.
Use water flow detection and overheating to ensure the safety of the water heater.
Overcurrent protection. It is realized by detecting the voltage at both ends, which is less than the set value, and the 3524 works normally. It is larger than the set value and the output is blocked by 3524.
With normal overvoltage, undervoltage and leakage protection.
3.2.4 The power supply part of the water heater is 4.5k: its main circuit current is 20 amps, and it is rectified with a 35A/600V bridge stack. Because the main circuit does not require high ripple, the filter circuit only adds a 2% F/ 400V capacitor. The control power supply is powered by a single power supply. The required power quality is high. After rectification, it is regulated by a three-terminal voltage regulator circuit and 815) to provide a stable voltage to the P:M circuit, the drive circuit and the protection circuit. The entire power supply circuit is simpler.
4 Conclusions Because this kind of instant water heater uses electromagnetic induction principle heating, adopts special water tank structure design, plus stable and reliable circuit design and perfect protection measures, compared with other water heaters, it has water and electricity separation, good safety and fast heating. High efficiency and moderate cost. In addition, the simple and unique structure of the water heater sink makes the cost of this key component almost at the lowest price, which brings a new way to scale treatment. When the scale of the water tank is reached to a certain extent, the new water tank can be replaced in time, and the old water tank can be recycled. use. Thereby ensuring heat transfer efficiency and eliminating waste water from the waste water tank. In short, this new water heater has a greater improvement in cost performance than the previous water heater, which brings great convenience to users' use and maintenance, so it must have broad market prospects.