A magnetic induction water heater circuit

Abstract

The present invention provides a magnetic induction water heater circuit, which relates to the technical field of water heaters. The magnetic induction water heater circuit includes: a control chip, a first rectifier circuit, a filter capacitor, a full-bridge inverter circuit composed of four switching tubes, a series resonance circuit, and a drive circuit; the two input terminals of the first rectifier circuit are connected to the AC input terminal, and the two output terminals are connected to the input terminal of the full-bridge inverter circuit; the output terminal of the full-bridge inverter circuit is connected to the series resonance circuit; the filter capacitor is arranged between the two output terminals of the first rectifier circuit; the series resonance circuit is used for heating; the control chip is connected to each switching tube of the full-bridge inverter circuit through the drive circuit and outputs a PWM signal to the full-bridge inverter circuit to make the series resonance circuit work at the resonance frequency. The magnetic induction water heater circuit directly outputs a PWM signal to the full-bridge inverter circuit by the control chip to make the series resonance circuit work at the resonance frequency, without setting a phase control circuit, simplifies the circuit structure, and has a low circuit delay.

Description

Technical Field

[0001] The present invention relates to the technical field of water heaters, and particularly to a magnetic induction water heater circuit. Background Art

[0002] An electromagnetic water heater is a heater that uses the principle of electromagnetic induction to convert electrical energy into magnetic heat energy. In the controller, a rectifier circuit converts the AC voltage into a DC voltage, and then a control circuit converts the DC voltage into a high-frequency voltage. A rapidly changing current passing through a coil generates a rapidly changing magnetic field. When the magnetic force lines inside the magnetic field pass through a metal container, countless small eddy currents are generated to heat the water inside.

[0003] Chinese Patent CN200780003949.5 discloses an induction heating device. The induction heating device includes: a resonant circuit; a power factor improvement circuit that boosts the rectified output and supplies it to an inverter while improving the power factor of commercial alternating current; and a load material detection unit that detects the material of the load. The inverter has switching elements that form a full-bridge circuit. In the technical solution of this patent document, a control circuit needs to be provided to control the full-bridge circuit, and the structure is relatively complex.

[0004] In the prior art, a magnetic induction water heater can control the operation of a resonant circuit through a full-bridge inverter circuit, and a control circuit needs to be provided to control the full-bridge inverter circuit, and the structure is relatively complex. Summary of the Invention

[0005] The technical problem to be solved by the present invention is, in view of the above deficiencies of the prior art, to provide a magnetic induction water heater circuit with a simple structure and a short control delay.

[0006] The magnetic induction water heater circuit includes: a control chip, a first rectifier circuit, a filter capacitor, a full-bridge inverter circuit composed of four switching tubes, a series resonant circuit, and a drive circuit;

[0007] Two input terminals of the first rectifier circuit are connected to an AC input terminal, and two output terminals are connected to an input terminal of the full-bridge inverter circuit; an output terminal of the full-bridge inverter circuit is connected to the series resonant circuit; the filter capacitor is arranged between the two output terminals of the first rectifier circuit; the series resonant circuit is used for heating;

[0008] The control chip is connected to each switching tube of the full-bridge inverter circuit through the drive circuit and outputs a PWM signal to the full-bridge inverter circuit to make the series resonant circuit operate at the resonant frequency.

[0009] Furthermore, the magnetic induction water heater circuit further includes: a first current transformer and a zero-crossing detection circuit; the first current transformer is coupled to the series resonance circuit and connected to the control chip through the zero-crossing detection circuit; the zero-crossing detection circuit is used to convert the current signal detected by the first current transformer into a square wave signal synchronized therewith.

[0010] Furthermore, the zero-crossing detection circuit specifically includes: a first resistor, a second resistor, a third resistor, a fourth resistor, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, a first operational amplifier, a second operational amplifier, and a first diode;

[0011] The first resistor is connected between the two output terminals of the first current transformer; the first end of the first resistor is grounded, and the second end is connected to the non-inverting input terminal of the first operational amplifier through the second resistor; the first capacitor is connected in parallel across the first resistor; the non-inverting input terminal of the first operational amplifier is grounded through the second capacitor; the inverting input terminal of the first operational amplifier is connected to the output terminal;

[0012] The output terminal of the first operational amplifier is connected to the non-inverting input terminal of the second operational amplifier through the third resistor; the inverting input terminal of the second operational amplifier is grounded; the third capacitor is connected between the two input terminals of the second operational amplifier; the negative electrode of the first diode is connected to the non-inverting input terminal of the second operational amplifier, and the positive electrode is grounded;

[0013] The first end of the fourth resistor is connected to a voltage source, and the second end is respectively connected to one end of the fourth capacitor and the output terminal of the second operational amplifier; the second end of the fourth capacitor is grounded; the output terminal of the second operational amplifier is connected to the control chip.

[0014] Furthermore, the magnetic induction water heater circuit further includes: a second current transformer and a current detection circuit; the second current transformer is coupled to the AC input terminal and connected to the control chip through the current detection circuit;

[0015] The current detection circuit includes: a fifth capacitor, a sixth capacitor, a seventh capacitor, a second rectifier circuit, a fifth resistor, a sixth resistor, a seventh resistor, and a third operational amplifier;

[0016] The two input terminals of the second rectifying circuit are connected to the two output terminals of the second current transformer; the fifth capacitor is connected between the two input terminals of the second rectifying circuit; the positive output terminal of the second rectifying circuit is connected to the non-inverting input terminal of the third operational amplifier through the fifth resistor, and the negative output terminal is grounded; a sixth resistor is connected between the two output terminals of the second rectifying circuit; the non-inverting input terminal of the third operational amplifier is grounded through the sixth capacitor; the inverting input terminal and the output terminal of the third operational amplifier are connected together; the output terminal of the third operational amplifier is connected to the first end of the seventh resistor, and the second end of the seventh resistor is grounded through the seventh capacitor and is connected to the control chip.

[0017] Further, the magnetic induction water heater circuit further includes: a voltage detection circuit; the voltage detection circuit includes: a fourth operational amplifier, an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor, a twelfth resistor, an eighth capacitor, a ninth capacitor, and an active full-wave rectifying circuit;

[0018] The inverting input terminal of the fourth operational amplifier is connected to the live wire of the AC input terminal through the eighth resistor, and the non-inverting input terminal is connected to the neutral wire of the AC input terminal through the ninth resistor; the non-inverting input terminal of the fourth operational amplifier is grounded through the tenth resistor and the eighth capacitor respectively; the eleventh resistor is connected between the inverting input terminal and the output terminal of the fourth operational amplifier; the output terminal of the fourth operational amplifier is connected to the input terminal of the active full-wave rectifying circuit; the output terminal of the active full-wave rectifying circuit is connected to the first end of the twelfth resistor; the second end of the twelfth resistor is grounded through the ninth capacitor and is connected to the control chip.

[0019] Further, the active full-wave rectifying circuit includes: a fifth operational amplifier, a sixth operational amplifier, a thirteenth resistor, a fourteenth resistor, a fifteenth resistor, a sixteenth resistor, a seventeenth resistor, an eighteenth resistor, a nineteenth resistor, a second diode, and a third diode;

[0020] The first end of the thirteenth resistor and the first end of the fourteenth resistor are connected to the output terminal of the fourth operational amplifier; the second end of the thirteenth resistor is connected to the inverting input terminal of the fifth operational amplifier; the second end of the fourteenth resistor is connected to the inverting input terminal of the sixth operational amplifier; the non-inverting input terminal of the fifth operational amplifier is grounded through the fifteenth resistor; the anode of the second diode is connected to the output terminal of the fifth operational amplifier, and the cathode is connected to the inverting input terminal of the fifth operational amplifier; the anode of the third diode is connected to the inverting input terminal of the fifth operational amplifier through the sixteenth resistor, and the cathode is connected to the output terminal of the fifth operational amplifier; the anode of the third diode is also connected to the inverting input terminal of the sixth operational amplifier through the seventeenth resistor; the non-inverting input terminal of the sixth operational amplifier is grounded through the eighteenth resistor; the inverting input terminal and the output terminal of the sixth operational amplifier are connected together through the nineteenth resistor; the output terminal of the sixth operational amplifier is used to connect to the first end of the twelfth resistor.

[0021] Further, the EPWM module of the TMS320F280x series chip is connected to the drive circuit, the ECAP module is connected to the zero-crossing detection circuit, and the AD module is connected to the current detection circuit and the voltage detection circuit.

[0022] Further, the magnetic induction water heater circuit further includes an NTC temperature probe; the NTC temperature probe is connected to the AD module of the TMS320F280x series chip.

[0023] Further, the drive circuit is a drive optocoupler.

[0024] Further, the switching tubes of the full-bridge inverter circuit are MOS tubes or IGBT switching tubes.

[0025] The magnetic induction water heater circuit directly outputs a PWM signal to the full-bridge inverter circuit by using a control chip, so that the series resonance circuit works at the resonance frequency, without the need to set a phase control circuit, simplifies the circuit structure, and has a low circuit delay. Description of the Drawings

[0026] Figure 1 is the circuit diagram of the magnetic induction water heater circuit in the embodiment of the present invention.

[0027] Figure 2 is the circuit diagram of the zero-crossing detection circuit in the embodiment of the present invention.

[0028] Figure 3 is the circuit diagram of the current detection circuit in the embodiment of the present invention.

[0029] Figure 4 is the circuit diagram of the voltage detection circuit in the embodiment of the present invention.

[0030] Figure 5It is a schematic diagram of phase-locked control of the series resonance circuit in an embodiment of the present invention.

[0031] Figure 6 It is a schematic diagram of temperature control of the magnetic induction water heater circuit in an embodiment of the present invention. Detailed implementation manners

[0032] The following are specific embodiments of the present invention and in combination with the accompanying drawings, the technical solutions of the present invention are further described, but the present invention is not limited to these embodiments.

[0033] Reference Figure 1 , the magnetic induction water heater circuit includes: a control chip IC1, a first rectifier circuit 1, a filter capacitor C10, a full-bridge inverter circuit 2 composed of four switching tubes, a series resonance circuit 3, and a drive circuit 4; wherein, the two input ends of the first rectifier circuit 1 are connected to the AC input end, and the two output ends are connected to the input end of the full-bridge inverter circuit 2; the output end of the full-bridge inverter circuit 2 is connected to the series resonance circuit 3; the filter capacitor is arranged between the two output ends of the first rectifier circuit 1; the series resonance circuit 3 is used for heating; the control chip IC1 is connected to each switching tube of the full-bridge inverter circuit 2 through the drive circuit 4, and outputs a PWM signal to the full-bridge inverter circuit 2 to make the series resonance circuit 3 work at the resonance frequency.

[0034] In an embodiment of the present application, the AC input end is 220V alternating current, which specifically includes a live wire end and a neutral wire end. The alternating current is rectified in the first rectifier circuit 1 and then input into the full-bridge inverter circuit 2 after rectification. The full-bridge inverter circuit 2 is used to drive the series resonance circuit 3 to make the series resonance circuit 3 work at the resonance frequency. The control chip IC1 contains a PWM controller and can output a PWM signal to drive the full-bridge inverter circuit 2. In this way, there is no need to set a phase control circuit, which simplifies the circuit structure and has a lower delay in the control process.

[0035] Specifically, in the full-bridge phase-shifted induction heating control, it is ensured that the output voltage frequency of the full-bridge inverter circuit 2 follows the natural frequency of the series resonance circuit 3 in real time and keeps the phase approximately synchronized.

[0036] In addition, actually, the voltage output by the full-bridge inverter circuit 2 leads the current of the series resonance circuit 3 by a certain phase to ensure that the system works in an inductive state and will not cause the switching tubes KT1~KT4 of the full-bridge inverter circuit 2 to be damaged due to capacitive hard switching.

[0037] In some embodiments, the switching tubes of the full-bridge inverter circuit 2 are MOS tubes or IGBT switching tubes.

[0038] In the embodiment of the present application, the driving circuit 4 is used to amplify the small signal output by the control chip IC1 for driving the switching tubes KT1 - KT4 of the full-bridge inverter circuit 2. In some embodiments, the driving circuit 4 is a driving optocoupler or a driving chip.

[0039] Further, the control chip IC1 is a TMS320F280x series chip of Texas Instruments.

[0040] In some embodiments, the magnetic induction water heater circuit further includes: a first current transformer CT1 and a zero-crossing detection circuit 5; the first current transformer CT1 is coupled to the series resonance circuit 3 and connected to the control chip IC1 through the zero-crossing detection circuit 5; the zero-crossing detection circuit 5 is used to convert the current signal detected by the first current transformer CT1 into a square wave signal synchronized therewith.

[0041] The first current transformer CT1 is used to detect the current signal of the series resonance circuit 3, convert it into a square wave signal through the zero-crossing detection circuit 5, and transmit it to the control chip IC1. The control chip IC1 can obtain the phase difference between the square wave signal and the output voltage of the full-bridge inverter circuit 2, and accordingly adjust the period of the output PWM signal to ensure that the output voltage frequency of the full-bridge inverter circuit 2 is approximately the same as the resonance frequency of the series resonance circuit 3.

[0042] Reference Figure 2 , the zero-crossing detection circuit 5 specifically includes: a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, a first operational amplifier U1, a second operational amplifier U2, and a first diode D1;

[0043] Among them, the first resistor R1 is connected between the two output terminals of the first current transformer CT1; the first end of the first resistor R1 is grounded, and the second end is connected to the non-inverting input terminal of the first operational amplifier U1 through the second resistor R2; the first capacitor C1 is connected in parallel across the first resistor R1; the non-inverting input terminal of the first operational amplifier U1 is grounded through the second capacitor C2; the inverting input terminal of the first operational amplifier U1 is connected to the output terminal; the output terminal of the first operational amplifier U1 is connected to the non-inverting input terminal of the second operational amplifier U2 through the third resistor R3; the inverting input terminal of the second operational amplifier U2 is grounded; the third capacitor C3 is connected between the two input terminals of the second operational amplifier U2; the negative electrode of the first diode D1 is connected to the non-inverting input terminal of the second operational amplifier U2, and the positive electrode is grounded; the first end of the fourth resistor R4 is connected to a voltage source, and the second end is respectively connected to one end of the fourth capacitor C4 and the output terminal of the second operational amplifier U2; the second end of the fourth capacitor C4 is grounded; the output terminal of the second operational amplifier U2 is connected to the control chip IC1.

[0044] The input of the zero-crossing detection circuit 5 is the first current transformer CT1. The current signal is converted into a voltage signal through the first resistor R1, followed by voltage buffering through the first operational amplifier U1, and then the zero-crossing of the current is detected by the second operational amplifier U2. Finally, a square wave signal synchronized with the input current signal is output.

[0045] In some embodiments, the second operational amplifier U2 is a comparator.

[0046] Reference Figure 3 , the magnetic induction water heater circuit further includes: a second current transformer CT2, a current detection circuit 6; the second current transformer CT2 is coupled to the AC input terminal and connected to the control chip IC1 through the current detection circuit 6;

[0047] Among them, the current detection circuit 6 includes: a fifth capacitor C5, a sixth capacitor C6, a seventh capacitor C7, a second rectifier circuit 61, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, a third operational amplifier U3; the two input terminals of the second rectifier circuit 61 are connected to the two output terminals of the second current transformer CT2; the fifth capacitor C5 is connected between the two input terminals of the second rectifier circuit 61; the positive output terminal of the second rectifier circuit 61 is connected to the non-inverting input terminal of the third operational amplifier U3 through the fifth resistor R5, and the negative output terminal is grounded; a sixth resistor R6 is connected between the two output terminals of the second rectifier circuit 61; the non-inverting input terminal of the third operational amplifier U3 is grounded through the sixth capacitor C6; the inverting input terminal and the output terminal of the third operational amplifier U3 are connected together; the output terminal of the third operational amplifier U3 is connected to the first end of the seventh resistor R7, and the second end of the seventh resistor R7 is grounded through the seventh capacitor C7 and connected to the control chip IC1.

[0048] The second current transformer CT2 is used to detect the current signal at the AC input terminal and input it into the current detection circuit 6. After being rectified by the second rectifier circuit 61, it is converted into a corresponding voltage signal through the sixth resistor R6, and finally output to the control chip IC1 through the third operational amplifier U3 for buffering. The control chip IC1 can obtain the input current at the AC input terminal based on this voltage signal to control the heating power of the water heater.

[0049] Reference Figure 4 , the magnetic induction water heater circuit further includes: a voltage detection circuit 7; the voltage detection circuit 7 includes: a fourth operational amplifier U4, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a twelfth resistor R12, an eighth capacitor C8, a ninth capacitor C9, and an active full-wave rectifier circuit 71;

[0050] Among them, the inverting input terminal of the fourth operational amplifier U4 is connected to the live wire ACL of the AC input terminal through the eighth resistor R8, and the non-inverting input terminal is connected to the neutral wire ACN of the AC input terminal through the ninth resistor R9; the non-inverting input terminal of the fourth operational amplifier U4 is grounded through the tenth resistor R10 and the eighth capacitor C8 respectively; the eleventh resistor R11 is connected between the inverting input terminal and the output terminal of the fourth operational amplifier U4; the output terminal of the fourth operational amplifier U4 is connected to the input terminal of the active full-wave rectifier circuit 71; the output terminal of the active full-wave rectifier circuit 71 is connected to the first end of the twelfth resistor R12; the second end of the twelfth resistor R12 is grounded through the ninth capacitor C9 and is connected to the control chip IC1.

[0051] The voltage detection circuit 7 is the live wire ACL and the neutral wire ACN of the AC input terminal; first, it passes through a differential circuit composed of the fourth operational amplifier U4, is converted into a voltage signal with respect to the ground, and then passes through the active full-wave rectifier circuit 71 to output a DC pulsating signal to the control chip IC1. The control chip IC1 can obtain the input voltage of the AC input terminal according to the DC pulsating signal to control the heating power of the water heater.

[0052] In some embodiments, the active full-wave rectifier circuit 71 includes: a fifth operational amplifier U5, a sixth operational amplifier U6, a thirteenth resistor R13, a fourteenth resistor R14, a fifteenth resistor R15, a sixteenth resistor R16, a seventeenth resistor R17, an eighteenth resistor R18, a nineteenth resistor R19, a second diode D2, and a third diode D3.

[0053] Among them, the first end of the thirteenth resistor R13 and the first end of the fourteenth resistor R14 are connected to the output terminal of the fourth operational amplifier U4; the second end of the thirteenth resistor R13 is connected to the inverting input terminal of the fifth operational amplifier U5; the second end of the fourteenth resistor R14 is connected to the inverting input terminal of the sixth operational amplifier U6; the non-inverting input terminal of the fifth operational amplifier U5 is grounded through the fifteenth resistor R15; the positive electrode of the second diode D2 is connected to the output terminal of the fifth operational amplifier U5, and the negative electrode is connected to the inverting input terminal of the fifth operational amplifier U5; the positive electrode of the third diode D3 is connected to the inverting input terminal of the fifth operational amplifier U5 through the sixteenth resistor R16, and the negative electrode is connected to the output terminal of the fifth operational amplifier U5; the positive electrode of the third diode D3 is also connected to the inverting input terminal of the sixth operational amplifier U6 through the seventeenth resistor R17; the non-inverting input terminal of the sixth operational amplifier U6 is grounded through the eighteenth resistor R18; the inverting input terminal and the output terminal of the sixth operational amplifier U6 are connected together through the nineteenth resistor R19; the output terminal of the sixth operational amplifier U6 is used to be connected to the first end of the twelfth resistor R12.

[0054] In some embodiments, the control chip IC1 is a TMS320F280x series chip.

[0055] The EPWM module of the TMS320F280x series chip is connected to the drive circuit 4, the ECAP module is connected to the zero-crossing detection circuit 5, and the AD module is connected to the current detection circuit 6 and the voltage detection circuit 7.

[0056] In some embodiments, the magnetic induction water heater circuit further includes an NTC temperature probe 8; the NTC temperature probe 8 is connected to the AD module of the TMS320F280x series chip.

[0057] See Figure 5 , the current synchronization signal output by the zero-crossing detection circuit 5 is captured by the ECAP module of the TMS320F280x series chip. During the capture interrupt, the period value of the current synchronization signal is obtained by using the ECAP module. At the same time, the count value of the EPWM module is captured. According to the captured count value of the EPWM module, the phase difference between the current synchronization signal and the output voltage of the full-bridge inverter circuit 2 can be judged; Figure 5 The set phase difference in [] is used to compensate for the signal delay generated by the drive circuit 4 and the full-bridge inverter circuit 2; after comparing the set phase difference with the actual phase difference, the adjustment amount is output via PID control, and then added to the period value of the current synchronization signal captured and output by the ECAP module, which is used to update the value of the TBPRD register of the EPWM module, thereby changing the period of the PWM. In this way, while ensuring that the output voltage of the full-bridge inverter circuit 2 and the current frequency of the series resonance circuit 3 are consistent, their phase difference is also approximately zero, which can be equivalent to a pure resistive load, achieving an input power factor of more than 99%, facilitating the simple calculation of the input power.

[0058] Figure 6 is a schematic diagram of the temperature control of the magnetic induction water heater circuit in the embodiment of the present invention. It compares according to the user's temperature setting and the actual temperature detected by the NTC temperature probe 8 installed at the water outlet. The temperature error is input to the PID regulator, and the required set power is output after PID adjustment; then the corresponding detection signals are obtained by the current detection circuit 6 and the voltage detection circuit 7, and the actual input current and voltage values are calculated through conversion by the AD module. After synchronous phase-locking as in Figure 5 , the input power factor reaches more than 99%. Therefore, the actual input power is equal to the product of the input voltage and the current; then the set power is compared with the actual power, and the power error is input to the PID regulator. Finally, the PID regulator outputs the adjustment amount to the TBPHS register of the EPWM module to adjust the phase difference between the two groups of PWM signals of EPWM1 and EPWM2, thereby completing the phase-shifted power control of the full-bridge inverter circuit 2.

[0059] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0060] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Those skilled in the art to which the present invention pertains may make various modifications or supplements to the described specific embodiments or use similar means for substitution, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A magnetic induction water heater circuit, characterized in that, The magnetic induction water heater circuit includes: a control chip, a first rectifier circuit, a filter capacitor, a full-bridge inverter circuit composed of four switching tubes, a series resonance circuit, and a drive circuit; The two input terminals of the first rectifier circuit are connected to the AC input terminal, and the two output terminals are connected to the input terminal of the full-bridge inverter circuit; the output terminal of the full-bridge inverter circuit is connected to the series resonance circuit; the filter capacitor is arranged between the two output terminals of the first rectifier circuit; the series resonance circuit is used for heating; The control chip is connected to each switching tube of the full-bridge inverter circuit through the drive circuit and outputs a PWM signal to the full-bridge inverter circuit to make the series resonance circuit work at the resonance frequency; The magnetic induction water heater circuit further includes: a first current transformer and a zero-crossing detection circuit; the first current transformer is coupled with the series resonance circuit and is connected to the control chip through the zero-crossing detection circuit; the zero-crossing detection circuit is used to convert the current signal detected by the first current transformer into a square wave signal synchronized with it; The first current transformer is used to detect the current signal of the series resonance circuit, convert it into a square wave signal through the zero-crossing detection circuit, and transmit it to the control chip; the control chip obtains the phase difference between the square wave signal and the output voltage of the full-bridge inverter circuit, and adjusts the period of the output PWM signal accordingly; The control chip includes an EPWM module and an ECAP module; The specific adjustment of the period of the output PWM signal is as follows: The ECAP module captures the current synchronization signal output by the zero-crossing detection circuit. In the capture interrupt, the ECAP module obtains the period value of the current synchronization signal, and at the same time captures the count value of the EPWM module. The phase difference between the current synchronization signal and the output voltage of the full-bridge inverter circuit is judged according to the captured count value of the EPWM module; the signal delay generated by the drive circuit and the full-bridge inverter circuit is compensated by setting the phase difference; after comparing the set phase difference with the actual phase difference, the adjustment amount is output through PID control, and then added to the period value of the current synchronization signal captured and output by the ECAP module to update the value of the TBPRD register of the EPWM module, thereby changing the period of the PWM.

2. The magnetic induction water heater circuit according to claim 1, wherein The zero-crossing detection circuit specifically includes: a first resistor, a second resistor, a third resistor, a fourth resistor, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, a first operational amplifier, a second operational amplifier, and a first diode; The first resistor is connected between the two output terminals of the first current transformer; the first end of the first resistor is grounded, and the second end is connected to the non-inverting input terminal of the first operational amplifier through the second resistor; the first capacitor is connected in parallel at both ends of the first resistor; the non-inverting input terminal of the first operational amplifier is grounded through the second capacitor; the inverting input terminal of the first operational amplifier is connected to the output terminal; The output terminal of the first operational amplifier is connected to the non-inverting input terminal of the second operational amplifier through the third resistor; the inverting input terminal of the second operational amplifier is grounded; the third capacitor is connected between the two input terminals of the second operational amplifier; the negative electrode of the first diode is connected to the non-inverting input terminal of the second operational amplifier, and the positive electrode is grounded; The first end of the fourth resistor is connected to a voltage source, and the second end is respectively connected to one end of the fourth capacitor and the output end of the second operational amplifier; the second end of the fourth capacitor is grounded; the output end of the second operational amplifier is connected to the control chip.

3. The magnetic induction water heater circuit according to claim 1 or 2, characterized in that, The magnetic induction water heater circuit further includes: a second current transformer and a current detection circuit; the second current transformer is coupled to the AC input terminal and is connected to the control chip through the current detection circuit; The current detection circuit includes: a fifth capacitor, a sixth capacitor, a seventh capacitor, a second rectifier circuit, a fifth resistor, a sixth resistor, a seventh resistor, and a third operational amplifier; Two input terminals of the second rectifier circuit are connected to two output terminals of the second current transformer; the fifth capacitor is connected between the two input terminals of the second rectifier circuit; the positive output terminal of the second rectifier circuit is connected to the non-inverting input terminal of the third operational amplifier through the fifth resistor, and the negative output terminal is grounded; a sixth resistor is connected between the two output terminals of the second rectifier circuit; the non-inverting input terminal of the third operational amplifier is grounded through the sixth capacitor; the inverting input terminal and the output terminal of the third operational amplifier are connected together; the output terminal of the third operational amplifier is connected to the first end of the seventh resistor, and the second end of the seventh resistor is grounded through the seventh capacitor and is connected to the control chip.

4. The magnetic induction water heater circuit according to claim 3, wherein The magnetic induction water heater circuit further includes: a voltage detection circuit; the voltage detection circuit includes: a fourth operational amplifier, an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor, a twelfth resistor, an eighth capacitor, a ninth capacitor, and an active full-wave rectifier circuit; The inverting input terminal of the fourth operational amplifier is connected to the live wire of the AC input terminal through the eighth resistor, and the non-inverting input terminal is connected to the neutral wire of the AC input terminal through the ninth resistor; the non-inverting input terminal of the fourth operational amplifier is respectively grounded through the tenth resistor and the eighth capacitor; the eleventh resistor is connected between the inverting input terminal and the output terminal of the fourth operational amplifier; the output terminal of the fourth operational amplifier is connected to the input terminal of the active full-wave rectifier circuit; the output terminal of the active full-wave rectifier circuit is connected to the first end of the twelfth resistor; the second end of the twelfth resistor is grounded through the ninth capacitor and is connected to the control chip.

5. The magnetic induction water heater circuit according to claim 4, characterized in that, The active full-wave rectifier circuit includes: a fifth operational amplifier, a sixth operational amplifier, a thirteenth resistor, a fourteenth resistor, a fifteenth resistor, a sixteenth resistor, a seventeenth resistor, an eighteenth resistor, a nineteenth resistor, a second diode, and a third diode; The first end of the thirteenth resistor and the first end of the fourteenth resistor are connected to the output terminal of the fourth operational amplifier; the second end of the thirteenth resistor is connected to the inverting input terminal of the fifth operational amplifier; the second end of the fourteenth resistor is connected to the inverting input terminal of the sixth operational amplifier; the non-inverting input terminal of the fifth operational amplifier is grounded through the fifteenth resistor; the positive electrode of the second diode is connected to the output terminal of the fifth operational amplifier, and the negative electrode is connected to the inverting input terminal of the fifth operational amplifier; the positive electrode of the third diode is connected to the inverting input terminal of the fifth operational amplifier through the sixteenth resistor, and the negative electrode is connected to the output terminal of the fifth operational amplifier; the positive electrode of the third diode is also connected to the inverting input terminal of the sixth operational amplifier through the seventeenth resistor; the non-inverting input terminal of the sixth operational amplifier is grounded through the eighteenth resistor; the inverting input terminal and the output terminal of the sixth operational amplifier are connected together through the nineteenth resistor; the output terminal of the sixth operational amplifier is used to be connected to the first end of the twelfth resistor.

6. The magnetic induction water heater circuit according to claim 4, wherein The EPWM module of the TMS320F280x series chip is connected to the drive circuit, the ECAP module is connected to the zero-crossing detection circuit, and the AD module is connected to the current detection circuit and the voltage detection circuit.

7. The magnetic induction water heater circuit according to claim 6, wherein The magnetic induction water heater circuit further includes an NTC temperature probe; the NTC temperature probe is connected to the AD module of the TMS320F280x series chip.

8. The magnetic induction water heater circuit according to claim 1, characterized in that, The drive circuit is a drive optocoupler.

9. The magnetic induction water heater circuit according to claim 1, wherein The switching tubes of the full-bridge inverter circuit are MOS tubes or IGBT switching tubes.

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