Heating device and applicable detection method thereof

Abstract

The present invention relates to a heating device, comprising: a resonant circuit, comprising: an inverter circuit, providing a resonant tank current and a resonant tank voltage; and a resonant tank, comprising a heating coil, a resonant tank capacitor, a resonant tank equivalent inductance and a resonant tank equivalent impedance; a detection unit, detecting the resonant tank current and the resonant tank voltage to obtain a reference current value, a first zero-crossing time point, a second zero-crossing time point, a time variation, a resonant period and a negative peak current value; and a control unit; wherein the detection unit calculates the inductance value of the resonant tank equivalent inductance based on the capacitance value of the resonant tank capacitor, the resonant period and a first calculation formula; and calculates the impedance value of the resonant tank equivalent impedance based on the resonant tank equivalent inductance, the time variation, the resonant period, the reference current value and the negative peak current value and a second calculation formula.

Description

Technical Field

[0001] This case involves a heating device, and more particularly, a heating device that utilizes the natural response characteristics of a resonant tank's discharge path during the negative half-cycle, and further calculates the resonant tank's equivalent inductance and equivalent impedance using the resonant tank's current and voltage information, and a suitable detection method. Background Art

[0002] With recent technological advancements, people have expanded beyond a single choice of heating devices for cooking. In addition to gas-powered heating devices, there are now a variety of options, including microwave ovens, infrared ovens, and electric stoves. Each of these heating devices has its own advantages and disadvantages, making them suitable for cooking a variety of ingredients and cooking environments, meeting the diverse needs of users.

[0003] Conventional heating devices, such as induction cookers, utilize heating coils to heat food containers, and then control the amount of heat applied to the food containers by adjusting the amount of power supplied to the heating coils. During heating, the location and material of the food container not only affect the amount of heat applied to the food container by the induction coil, but also affect the operating conditions and current value of the induction coil. Because different food containers made of different materials or the locations where they are placed will induce different equivalent parameters from the resonant tank equivalent inductance, existing heating devices utilize the resonant tank voltage, resonant tank current, and the phase between the resonant tank voltage and the resonant tank current to calculate the resonant tank equivalent impedance and the resonant tank equivalent inductance, and then utilize the operating results of the resonant tank equivalent impedance and the resonant tank equivalent inductance to adjust the electrical energy applied to the heating coil. However, this method requires additional voltage detection circuits and current detection circuits, resulting in drawbacks such as complex circuits and higher costs for existing heating devices.

[0004] Therefore, how to develop a heating device and a suitable detection method thereof that can improve the above-mentioned deficiencies of the prior art is an urgent problem that needs to be solved by those skilled in the art. Summary of the Invention

[0005] This invention relates to a heating device and a detection method suitable for the same. The heating device comprises a resonant tank, and the heating device utilizes the natural response characteristics of the resonant tank's discharge path during the negative half-cycle. The current and voltage information of the resonant tank are then used to calculate the resonant tank's equivalent inductance and equivalent impedance. This eliminates the need for excessive detection circuitry in the heating device, resulting in a simple circuit and low cost.

[0006] To achieve the above-mentioned objectives, a preferred embodiment of the present invention is a heating device comprising: a resonant circuit including an inverter circuit for providing a resonant tank current and a resonant tank voltage; and a resonant tank including a heating coil, a resonant tank capacitor, a resonant tank equivalent inductor, and a resonant tank equivalent impedance; a detection unit electrically coupled to the resonant circuit and detecting the resonant tank current and the resonant tank voltage to obtain a reference current value, a first zero-crossing time point, a second zero-crossing time point, a time variation, a resonant period, and a negative peak current value. The reference current value is the current value of the resonant tank current corresponding to a resonant tank voltage of zero. The time variation is the time interval from the time point when the resonant tank voltage is zero to the first zero-crossing time point. The resonant period is defined by the first zero-crossing time point and the second zero-crossing time point; and the control unit controls the inverter circuit to output the resonant tank current and the resonant tank voltage to control the heating power of the heating coil; wherein the detection unit calculates the inductance value of the resonant tank equivalent inductance based on the capacitance value of the resonant tank capacitor, the resonant period and the first calculation formula; the detection unit calculates the impedance value of the resonant tank equivalent impedance based on the resonant tank equivalent inductance, time variation, the resonant period, the reference current value and the negative peak current value and the second calculation formula; the control unit controls the heating power of the heating coil based on the inductance value of the resonant tank equivalent inductance and the impedance value of the equivalent impedance; wherein the first calculation formula is L eq is the inductance value of the equivalent inductance of the resonant tank, C r is the capacitance of the resonant tank capacitor, T is the resonant period; the second equation is R eq is the impedance value of the equivalent impedance of the resonant tank, I0 is the reference current value, Δt is the time change, I N is the negative peak current value.

[0007] To achieve the above-mentioned purpose, another preferred embodiment of the present invention is a detection method applied to a detection unit of a heating device, wherein the heating device further includes a resonant circuit, the resonant circuit includes an inverter circuit and a resonant tank, the inverter circuit provides a resonant tank current and a resonant tank voltage, the resonant tank includes a heating coil, a resonant tank capacitor, a resonant tank equivalent inductance, and a resonant tank equivalent impedance, the detection method comprising: (a) detecting the resonant tank current and the resonant tank voltage to obtain a reference current value, a first zero-crossing time point, a second zero-crossing time point, a time variation, a resonant period, and a negative peak current value, wherein the reference current value is the current value of the resonant tank current corresponding to when the resonant tank voltage is zero, the time variation is the time interval from the time point when the resonant tank voltage is zero to the first zero-crossing time point, and the resonant period is defined by the first zero-crossing time point and the second zero-crossing time point; (b) calculating the inductance value of the resonant tank equivalent inductance based on the resonant tank capacitor, the resonant period, and a first calculation formula, wherein the first calculation formula is L eq is the inductance value of the equivalent inductance of the resonant tank, Cr is the capacitance of the resonant tank capacitor, T is the resonant period; (c) the impedance value of the equivalent impedance is calculated based on the resonant tank equivalent inductance, time variation, resonant period, reference current value and negative peak current value and a second calculation formula, wherein the second calculation formula is R eq is the impedance value of the equivalent impedance of the resonant tank, I0 is the reference current value, Δt is the time change, I N is a negative peak current value; and (d) controlling the heating power of the heating coil according to the inductance value of the resonant tank equivalent inductance and the impedance value of the resonant tank equivalent impedance. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1A A schematic diagram of a heating device according to a preferred embodiment of the present invention;

[0009] Figure 1B for Figure 1A The circuit structure diagram of the heating device shown;

[0010] Figure 2 for Figure 1B Schematic diagram of the waveforms of the control voltage and the resonant tank current of the upper switching element of the heating device shown;

[0011] Figure 3 for Figure 1B A schematic diagram of the circuit structure of a zero-crossing detection circuit of a parameter acquisition unit of the detection unit shown;

[0012] Figure 4 For Figure 2 Under the architecture, it shows Figure 3 FIG. 1 is a schematic diagram showing a waveform of a pulse width signal output by a zero-crossing detection circuit;

[0013] Figure 5 for Figure 1B A schematic diagram of the circuit structure of a negative peak detection circuit of a parameter acquisition unit of the detection unit shown;

[0014] Figure 6 Schematic diagram of the steps of the detection method of the preferred embodiment of this case.

[0015] Description of Reference Numerals

[0016] 1: Heating device

[0017] 2: Power supply circuit

[0018] 3: Detection unit

[0019] 4: Control unit

[0020] 20: Inverter circuit

[0021] 21: Resonance tank

[0022] 22: Resonant Circuit

[0023] V in :Input voltage

[0024] Q h : Upper switch element

[0025] Q l :Lower switch element

[0026] T1: First end

[0027] T2: Second end

[0028] C r :Resonant tank capacitor

[0029] L eq :Equivalent inductance of resonant tank

[0030] R eq :Equivalent impedance of resonant tank

[0031] I r :Resonant tank current

[0032] I0: reference current value

[0033] Δt: time change

[0034] V r :Resonant tank voltage

[0035] I N :Negative peak current value

[0036] 30: parameter acquisition unit

[0037] 31: Microprocessor

[0038] 300: Zero crossing detection circuit

[0039] 301: Negative peak detection circuit

[0040] CT1: First current transformer

[0041] R1: first resistor

[0042] COM: Comparator

[0043] R2: Second resistor

[0044] C1: first capacitor

[0045] D z Zener diode

[0046] G: Ground terminal

[0047] CT2: Second current transformer

[0048] R3: The third resistor

[0049] R4: the fourth resistor

[0050] C amp :Negative Feedback Amplifier

[0051] D: diode

[0052] C2: Second capacitor

[0053] 310: First computing unit

[0054] 311: Second computing unit

[0055] t0, t1, t2, t3: time

[0056] T: Resonance period

[0057] 210: Heating coil DETAILED DESCRIPTION

[0058] Some typical embodiments that embody the features and advantages of this invention will be described in detail in the following description. It should be understood that this invention is capable of various variations in different implementations without departing from the scope of this invention, and that the description and drawings are intended to be illustrative in nature and not to limit this invention.

[0059] See also Figure 1A 、 Figure 1B and Figure 2 ,in Figure 1A This is a schematic diagram of the heating device of a preferred embodiment of the present invention. Figure 1B for Figure 1A The circuit structure diagram of the heating device shown in FIG. Figure 2 for Figure 1B The waveform diagram of the control voltage and resonant tank current of the upper switching element of the heating device is shown. In this case, the heating device 1 can be, but is not limited to, an induction cooker and includes a power supply circuit 2, a detection unit 3, and a control unit 4. The power supply circuit 2 includes a resonant circuit 22, which includes an inverter circuit 20 and a resonant tank 21. The inverter circuit 20 receives an input voltage V in , and includes at least one switching element, such as Figure 1B As shown, the inverter circuit 20 includes an upper switching element Q h And the lower switching element Q l , the upper switching element Q h And the lower switching element Q l The inverter circuit 20 is electrically connected in series to form a half-bridge inverter circuit, and the upper switch element Q h And the lower switching element Q lThe inverter circuit 20 switches the input voltage V in Converted to output resonant tank current I r and the resonant tank voltage V r In addition, the upper switching element Q h And the lower switching element Q l They respectively include a control end, a first current conducting end and a second current conducting end.

[0060] The resonant tank 21 includes a first end T1, a second end T2, a heating coil 210, a resonant tank capacitor C r , resonant tank equivalent inductance L eq And the equivalent impedance of the resonant tank R eq The first terminal T1 and the second terminal T2 are respectively electrically coupled to two current conducting terminals of one of the switching elements of the inverter circuit 20 , for example Figure 1B As shown, the first terminal T1 of the resonant tank 21 is electrically coupled to the lower switching element Q l的 The first current conducting end, the second end T2 of the resonant tank 21 is electrically coupled to the lower switch element Q l的 Second current conducting terminal. Resonant tank capacitor C r , resonant tank equivalent inductance L eq And the equivalent impedance of the resonant tank R eq are electrically connected in series between the first terminal T1 and the second terminal T2, and the resonant tank capacitor C r , resonant tank equivalent inductance L eq And the equivalent impedance of the resonant tank R eq The series electrical connection sequence between the first terminal T1 and the second terminal T2 is not limited to the following. Figure 1B The heating coil 210 can be changed according to the resonant tank current I provided by the inverter circuit 20. r and the resonant tank voltage V r The food container (not shown) placed on the heating device 1 is inductively heated. In addition, the resonant tank 21, the heating coil 210 and the food container constitute the equivalent inductance L of the resonant tank in the circuit. eq , and the resonant tank 21, the heating coil 210 and the food container also constitute the resonant tank equivalent impedance R in the circuit. eq In addition, the resonant tank capacitor C r The capacitance value is a known value.

[0061] From the above, we can see that the equivalent inductance L of the resonant tank is eq The inductance value of the resonant tank is related to the inductance value of the heating coil 210, the material of the food container and the position of the food container on the heating device 1. In other words, any change in the inductance value of the heating coil 210, the material of the food container and the position of the food container on the heating device 1 will cause the equivalent inductance L of the resonant tank to be changed. eqThe inductance value of the resonant tank changes. eq The impedance value of the resonant tank 21 has a corresponding relationship with the impedance value of the resonant tank 21, the material of the food container and the position of the food container on the heating device 1, that is, any change in the impedance value of the resonant circuit 22, the material of the food container and the position of the food container on the heating device 1 will make the equivalent impedance R of the resonant tank eq The impedance value changes.

[0062] The control unit 4 is electrically coupled to the inverter circuit 20 to control the inverter circuit 20 to output the resonant tank current I r and the resonant tank voltage V r , and control the heating power of the heating coil 210.

[0063] The detection unit 3 is electrically coupled to the resonant circuit 22, for example, electrically coupled to the first end T1 of the resonant tank 21 and the resonant tank capacitor C r and detect the resonant tank current I r and the resonant tank voltage V r , to obtain the reference current value I0, the time variation Δt, the first zero crossing time point, the second zero crossing time point, the resonance period T and the negative peak current value I N The reference current value I0 corresponds to the resonant tank voltage V r The resonant tank current I is zero r The current value, for example, the upper switching element Q of the inverter circuit 20 h In the negative half cycle, it switches from on to off, making the resonant tank voltage V r When the resonant tank current I r The instantaneous current value constitutes the reference current value I0 (such as Figure 2 The first zero-crossing time point is the resonant tank voltage V r After the resonant tank current I is zero r The time point at which the first time is zero (e.g. Figure 2 The second zero crossing time point is the resonance tank voltage V r After the resonant tank current I is zero r The second time point is zero (such as Figure 2 The time variation Δt is the resonance tank voltage V r The time interval from the time point of zero to the first zero crossing time point (eg Figure 2 The resonant period T is defined by the first zero crossing time point and the second zero crossing time point. N is the resonant tank current I r The maximum value at negative current (such as occurs at Figure 2 time t2 shown).

[0064] In addition, in this case, the detection unit 3 is based on the resonant tank capacitance C r The equivalent inductance L of the resonant tank is calculated by using the capacitance value, resonant period T and the first formula. eq The first calculation formula is as follows:

[0065]

[0066] Among them, L eq is the equivalent inductance L of the resonant tank eq The inductance value, C r is the resonant tank capacitance C r The capacitance value, T is the resonant period.

[0067] Furthermore, the detection unit 3 also detects the equivalent inductance L of the resonant tank. eq Inductance value, time variation Δt, resonance period T, reference current value I0, negative peak current value I N Calculate the equivalent impedance R of the resonant tank using the second equation eq The impedance value of , where the second equation is as follows:

[0068]

[0069] where R eq is the equivalent impedance of the resonant tank R eq The impedance value, I0 is the reference current value, Δt is the time change, I N is the negative peak current value.

[0070] See also Figure 3 、 Figure 4 and Figure 5 , and cooperate with Figure 1A 、 Figure 1B and Figure 2 ,in Figure 3 for Figure 1B The circuit structure diagram of the zero crossing detection circuit of the parameter acquisition unit of the detection unit shown in FIG. Figure 4 For Figure 2 Under the architecture, it shows Figure 3 The waveform diagram of the pulse width signal output by the zero-crossing detection circuit shown in FIG. Figure 5 for Figure 1B The circuit structure diagram of the negative peak detection circuit of the parameter acquisition unit of the detection unit is shown. The detection unit 3 further includes a parameter acquisition unit 30 and a microprocessor 31. The parameter acquisition unit 30 is electrically coupled to the resonant circuit 22, for example, electrically coupled to the first terminal T1 of the resonant tank 21 and the resonant tank capacitor C r and detect the resonant tank current I r and the resonant tank voltage V r , and the resonant tank voltage Vr Since the inverter circuit 20 is in the negative half cycle, it is zero. For example, since the upper switching element Q h When it is in the negative half cycle and switches from on to off and is zero, according to the resonant tank current I r and the resonant tank voltage V r Obtain the resonance period T and the resonance tank current I of the resonance tank 21 r The negative peak current value I N parameter information.

[0071] In this case, the parameter acquisition unit 30 can be implemented by circuit hardware or software. When the parameter acquisition unit 30 is implemented by circuit hardware, Figure 1B As shown, the parameter acquisition unit 30 includes a zero-crossing detection circuit 300 and a negative peak detection circuit 301. The zero-crossing detection circuit 300 is electrically coupled to the resonant tank 21, for example, electrically coupled to the first terminal T1 and the resonant tank capacitor C r and detect the resonant tank current I r and the resonant tank voltage V r , used to calculate the resonant tank current I r and the resonant tank voltage V r The obtained parameter information of the resonance period T, wherein the zero crossing detection circuit 300 includes a first current transformer CT1, a first resistor R1, a comparator COM, a second resistor R2, a first capacitor C1 and a Zener diode D z The input terminal of the first current transformer CT1 is electrically coupled to the resonant tank 21, for example, electrically coupled to the first terminal T1 and the resonant tank capacitor C r Between, to receive the resonant tank current I r The first and second ends of the first resistor R1 are electrically coupled to the output end of the first current transformer CT1, respectively, and the second end of the first resistor R1 is further electrically coupled to the ground end G. The positive input end of the comparator COM is electrically coupled to the first end of the first resistor R1 and the output end of the first current transformer CT1, and the negative input end of the comparator COM is electrically coupled to the second end of the first resistor R1 and the ground end G. The second resistor R2 is electrically coupled between the voltage source V1 and the output end of the comparator COM. The Zener diode D z The anode of the Zener diode D is electrically coupled to the ground terminal G. z The cathode of the first capacitor C1 is electrically coupled to the output terminal of the comparator COM and the ground terminal G, and is electrically coupled to the Zener diode D1. z Through the hardware structure of the zero-crossing detection circuit 300, the comparator COM can output a pulse width signal at the output terminal, wherein the resonant tank current I r Each time the pulse width signal passes through zero (i.e., through the zero crossing point), it corresponds to the resonant tank current I rThe zero crossing point switches between high and low levels. In addition, when the upper switching element Q h Switching from on to off and the resonant tank voltage V r After the pulse width signal output by the comparator COM reaches zero, the time length from the first level switching (corresponding to the first zero-crossing time point) to the second level switching (corresponding to the second zero-crossing time point) is actually equal to half of the resonant period T. The resonant period T can be obtained by multiplying half of the resonant period T by two. Therefore, the resonant period T is actually determined by the resonant tank current I r and the resonant tank voltage V r As defined, the zero-crossing detection circuit 300 is based on the resonant tank current I r and the resonant tank voltage V r Get information about the resonance period T.

[0072] The negative peak detection circuit 301 is electrically coupled to the resonant tank 21, for example, electrically coupled to the first terminal T1 and the resonant tank capacitor C r and detect the resonant tank current I r and the resonant tank voltage V r , used to calculate the resonant tank current I r Get the resonant tank current I r The negative peak current value I N The negative peak detection circuit 301 includes a second current transformer CT2, a third resistor R3, a fourth resistor R4, a negative feedback amplifier C amp , diode D and second capacitor C2. The input end of the second current transformer CT2 is electrically coupled to the resonant tank 21, for example, electrically coupled to the first end T1 and the resonant tank capacitor C r Between, to receive the resonant tank current I r The first and second ends of the third resistor R3 are electrically coupled to the output end of the second current transformer CT2, and the second end of the third resistor R3 is further electrically coupled to the ground end G. Negative feedback amplifier C amp The non-inverting input terminal of the negative feedback amplifier C is electrically coupled to the first terminal of the third resistor R3 and the output terminal of the second current transformer CT2. amp The inverting input of the negative feedback amplifier C amp The cathode of diode D is electrically coupled to the output terminal of negative feedback amplifier C. amp The output terminal of the negative peak detection circuit 301 is electrically coupled. The fourth resistor R4 is electrically coupled between the anode of the diode D and the ground terminal G. The second capacitor C2 is electrically coupled between the anode of the diode D and the ground terminal G, and is electrically coupled in parallel with the fourth resistor R4. Through the circuit structure of the negative peak detection circuit 301, the negative peak detection circuit 301 can detect the negative peak of the resonant tank current I r and the resonant tank voltage V r Get the resonant tank current Ir The negative peak current value I N information.

[0073] When the parameter acquisition unit 30 is implemented by software, an algorithm, a calculation formula and / or a parameter relationship table can be preset in the parameter acquisition unit 30 to obtain the parameter value of the resonant tank current I r and the resonant tank voltage V r And with the preset algorithm, calculation formula and / or parameter relationship, etc., to obtain the resonance period T and the resonance tank current I r The negative peak current value I N parameter information.

[0074] The microprocessor 31 may be formed by a digital signal processor (DSP) or a microcontroller unit (MCU), and is electrically coupled to the parameter acquisition unit 30, and includes a first calculation unit 310 and a second calculation unit 311. The first calculation unit 310 is preset with a first calculation formula and receives parameter information about the resonant period T from the parameter acquisition unit 30. The first calculation unit 310 calculates the resonant tank equivalent inductance L based on the capacitance value of the resonant tank capacitor Cr, the first calculation formula, and the received resonant period T. eq The inductance value of the resonant tank is output as eq The first calculation result of the inductance value

[0075] The second calculation unit 311 is preset with a second calculation formula and receives the equivalent inductance L of the resonant tank from the first calculation unit 310. eq The first calculation result of the inductance value, and based on the resonant tank current I r and the resonant tank voltage V r Obtain the reference current value I0, time variation Δt and resonant tank current I r The negative peak current value I N , and based on the equivalent inductance L of the resonant tank eq The inductance value, reference current value I0, time change Δt, resonant tank current I r The negative peak current value I N And the second formula calculates the equivalent impedance R of the resonant tank eq The impedance value of the output is the equivalent impedance R of the resonant tank eq The second calculation result of the impedance value.

[0076] In some embodiments, the control unit 4 of the heating device 1 can further obtain the equivalent inductance L of the resonant tank according to the first calculation result and the second calculation result output by the microprocessor 31. eq And the equivalent resistance of the resonant tank R eq , and then according to the equivalent inductance L of the resonant tankeq And the equivalent resistance of the resonant tank R eq Various controls are performed on the resonant circuit 22. For example, the control unit 4 can control the resonant tank equivalent inductance L according to the resonant tank equivalent inductance L. eq And the equivalent resistance of the resonant tank R eq The control unit 4 can determine whether the heating coil 210 is turned on or off and whether the food container is still on the heating device 1 according to the parameter value of the resonant tank equivalent inductance L. eq And the equivalent resistance of the resonant tank R eq The control unit 4 can also determine the load ratio of the heating power of the heating coil 210 according to the parameter value of the resonant tank equivalent inductance L eq And the equivalent resistance of the resonant tank R eq The output power of the heating device 1 is modified in real time according to the parameter value change, and the control unit 4 can adjust the output power of the heating device 1 according to the equivalent inductance L of the resonant tank. eq And the equivalent resistance of the resonant tank R eq The parameter value determines the material of the food container.

[0077] The following will roughly deduce the above-mentioned first equation (1) and second equation (2). Please cooperate with Figures 1A to 3 First, the main working principle of this case is based on the natural response characteristics of the resonant tank 21. When time t≧0, the resonant tank 21 enters the natural response, so the resonant tank current I r The general formula can be expressed as:

[0078] i r (t) = e -αt (B1 cosω d t+B2 sinω d t)---(3);

[0079] where i r (t) is the resonant tank current I r is a time function, α is the attenuation coefficient, ω d is the damping resonance frequency, B1 and B2 are arbitrary constants determined by the boundary conditions. Since the heating device 1 is an induction cooker, ω o 2 >>α 2 , so that the resonant tank 21 operates in the underdamped region (underdamped), and can simplify ω d = where ω o is the natural resonant frequency. By using the sum angle formula and rearranging equation (3), we can obtain:

[0080] i r (t) = I P e -αt sin(ω o t+θ)---(4);

[0081] Among them I P is the peak current of the resonance tank 21 during natural resonance, and θ is the angle.

[0082] In addition, in formula (4), some parameters have the following general formula:

[0083]

[0084] Therefore, equation (1) can be derived from equation (5), and the resonant frequency f o The relationship between the resonant period T is as follows:

[0085]

[0086] Since the upper switching element Q h When the working cycle is small, the discharge waveform of the resonant tank 21 in the negative half cycle is relatively complete. At this time, the zero-crossing detection circuit 300 can be used to obtain half of the resonant cycle T / 2, and then the first calculation unit 310 can be used to combine the half of the resonant cycle T / 2 with the formula (7) and substitute it into the formula (1) to obtain the equivalent inductance L of the resonant tank. eq inductance value.

[0087] In addition, since the resonant tank current I r is always zero, so in this case the resonant tank current I r The zero crossing point is used as the reference point and the calculation is performed in the form of relative angles. Figure 2 As shown, due to the upper switching element Q h When the resonant tank current I r The instantaneous current value constitutes the reference current value I0, so it is assumed that the upper switching element Q h Turn off the next switching element Q l The turn-on moment occurs at t=t0, and assuming that the upper switching element Q h After switching from on to off and becoming zero, the resonant tank current I r The first time of passing through the zero crossing point (the first zero crossing time point) occurs at an angle of π, and assuming that the resonant tank current I r The negative peak current value I N If it occurs at t = t2 (usually occurs at t = 3π / 2), then the following equations can be obtained by applying equation (4) to t = 0 and t = t2:

[0088] I0=I P sinθ---(8);

[0089]

[0090] Among them Figure 3It can be seen that the upper switching element Q h After switching from on to off, the resonant tank current I r The sampling time point of the reference current value I0 can be obtained by subtracting the time change Δt from the time point of the first zero crossing, and the resonant tank current I r The negative peak current value I N It occurs at t = 3π / 2, so the following formula can be obtained:

[0091]

[0092] Finally, by dividing equation (8) and equation (9) and combining them with equations (10) to (12), we can derive equation (2).

[0093] In some embodiments, the detection unit 3 may be, but is not limited to, composed of a controller.

[0094] In some embodiments, the inverter circuit 20 is not limited to Figure 1B The upper switching element Q h And the lower switching element Q l In other embodiments, the inverter circuit 20 may include a single switching element or four or more switching elements. When the inverter circuit 20 includes a single switching element, the first end T1 and the second end T2 of the resonant tank 21 are electrically coupled to the first current conducting end and the second current conducting end of the single switching element, respectively. When the inverter circuit 20 includes, for example, four switching elements and is a full-bridge inverter circuit, the first end T1 and the second end T2 of the resonant tank 21 are electrically coupled to the first current conducting end and the second current conducting end of the lower switching element in any bridge arm, respectively. Furthermore, in the embodiment where the inverter circuit 20 includes a single switching element or four or more switching elements, the operation of the heating device 1 of the present invention is similar to that described above and will not be further described here.

[0095] See also Figure 6 , which is a schematic diagram of the steps of the detection method of the preferred embodiment of this case. The detection method of this embodiment can be applied to Figure 1B The detection unit 3 of the heating device 1 shown includes the following steps.

[0096] Step S1: The detection unit 3 detects the resonant tank current I of the resonant tank 21. r and the resonant tank voltage V r Obtain the reference current value I0, the time variation Δt, the first zero crossing time point, the second zero crossing time point, the resonance period T and the negative peak current value I N .

[0097] Step S2: The detection unit 3 calculates the equivalent inductance L of the resonant tank according to the capacitance value of the resonant tank capacitor Cr, the resonant period T, and the first calculation formula. eqinductance value.

[0098] Step S3: The detection unit 3 detects the equivalent inductance L of the resonant tank. eq Inductance value, time variation Δt, resonance period T, reference current value I0, negative peak current value I N Calculate the equivalent impedance R of the resonant tank using the second equation eq impedance value.

[0099] Step S4, the control unit 4 calculates the equivalent inductance L of the resonant tank. eq The inductance value and the equivalent impedance of the resonant tank R eq The impedance value is used to control the heating power of the heating coil 210.

[0100] In some embodiments, step S4 may further include calculating the equivalent inductance L of the resonant tank. eq And the equivalent resistance of the resonant tank R eq Determine whether a food container is placed on the heating device 1. In step S4, it may further include determining the equivalent inductance L of the resonant tank. eq And the equivalent resistance of the resonant tank R eq Determine the heating power load ratio of the heating coil 210. Furthermore, in step S4, it may further include determining the equivalent inductance L of the resonant tank. eq And the equivalent resistance of the resonant tank R eq Determine the material of the food container on the heating device 1.

[0101] In summary, the present invention relates to a heating device and a detection method applicable thereto, wherein the heating device has a resonant tank, and based on the natural response characteristics of the discharge path of the resonant tank in the negative half-cycle, the heating device of the present invention utilizes the current information of the resonant tank and cooperates with the aforementioned first equation (1) and second equation (2) to respectively calculate the inductance value of the equivalent inductance of the resonant tank and the inductance value of the equivalent impedance of the resonant tank. Therefore, compared with the traditional heating device, the heating device of the present invention only needs to set up fewer detection circuits, thereby achieving the effect of simple circuit and low cost.

Claims

1. A heating device comprising: A resonant circuit comprising: an inverter circuit, providing a resonant tank current and a resonant tank voltage; and The resonant tank includes a heating coil, a resonant tank capacitor, a resonant tank equivalent inductance, and a resonant tank equivalent impedance; a detection unit electrically coupled to the resonant circuit and detecting the resonant tank current and the resonant tank voltage to obtain a reference current value, a first zero-crossing time point, a second zero-crossing time point, a time variation, a resonant period, and a negative peak current value, wherein the reference current value is a current value of the resonant tank current corresponding to when the resonant tank voltage is zero, the time variation is a time interval from the time point when the resonant tank voltage is zero to the first zero-crossing time point, and the resonant period is defined by the first zero-crossing time point and the second zero-crossing time point, the first zero-crossing time point being the time point when the resonant tank current is zero for the first time after the resonant tank voltage is zero, and the second zero-crossing time point being the time point when the resonant tank current is zero for the second time after the resonant tank voltage is zero; as well as a control unit, configured to control the inverter circuit to output the resonant tank current and the resonant tank voltage to control the heating power of the heating coil; The detection unit calculates the inductance of the resonant tank equivalent inductance based on the capacitance of the resonant tank capacitor, the resonant period, and a first calculation formula; the detection unit calculates the impedance of the resonant tank equivalent impedance based on the resonant tank equivalent inductance, the time variation, the resonant period, the reference current value, the negative peak current value, and a second calculation formula; and the control unit controls the heating power of the heating coil based on the inductance of the resonant tank equivalent inductance and the impedance of the resonant tank equivalent impedance. The first operational formula is L eq is the inductance value of the equivalent inductance of the resonant tank, C r is the capacitance value of the resonant tank capacitor, and T is the resonant period; The second operation formula is R eq is the impedance value of the equivalent impedance of the resonant tank, I0 is the reference current value, Δt is the time variation, I N is the negative peak current value.

2. The heating device according to claim 1 , wherein the detection unit comprises a parameter acquisition unit, which is electrically coupled to the resonant tank and detects the resonant tank current and the resonant tank voltage, and obtains the negative peak current value related to the resonant period and the resonant tank current according to the resonant tank current and the resonant tank voltage when the resonant tank voltage is zero.

3. The heating device according to claim 2, wherein the parameter acquisition unit comprises: a zero-crossing detection circuit electrically coupled to the resonant tank, detecting the resonant tank current and the resonant tank voltage, and obtaining the resonant period according to the resonant tank current and the resonant tank voltage; and The negative peak detection circuit is electrically coupled to the resonant tank, and detects the resonant tank current and the resonant tank voltage, and obtains the negative peak current value according to the resonant tank current and the resonant tank voltage.

4. The heating device according to claim 3, wherein the zero-crossing detection circuit comprises: a first current transformer, wherein an input terminal of the first current transformer is electrically coupled to the resonant tank to receive the resonant tank current; a first resistor, wherein a first end and a second end of the first resistor are respectively electrically coupled to the output end of the first current transformer, and the second end of the first resistor is further electrically coupled to the ground end; a comparator, wherein a positive input terminal of the comparator is electrically coupled to the first terminal of the first resistor and the output terminal of the first current transformer, and a negative input terminal of the comparator is electrically coupled to the second terminal of the first resistor and the ground terminal; a second resistor electrically coupled between the voltage source and the output terminal of the comparator; a Zener diode, an anode of the Zener diode being electrically coupled to the ground terminal, and a cathode of the Zener diode being electrically coupled to the output terminal of the comparator; as well as The first capacitor is electrically coupled between the output terminal of the comparator and the ground terminal, and is electrically coupled to the Zener diode in parallel.

5. The heating device according to claim 3, wherein the negative peak detection circuit comprises: a second current transformer, wherein an input terminal of the second current transformer is electrically coupled to the resonant tank to receive the resonant tank current; a third resistor, wherein a first end and a second end of the third resistor are respectively electrically coupled to the output end of the second current transformer, and the second end of the third resistor is further electrically coupled to the ground end; a negative feedback amplifier, wherein a non-inverting input terminal of the negative feedback amplifier is electrically coupled to the first end of the third resistor and the output terminal of the second current transformer, and an inverting input terminal of the negative feedback amplifier is electrically coupled to the output terminal of the negative feedback amplifier; a diode, a cathode of the diode being electrically coupled to an output terminal of the negative feedback amplifier; a fourth resistor electrically coupled between the anode of the diode and the ground terminal; A second capacitor is electrically coupled between the anode of the diode and the ground terminal, and is electrically coupled to the fourth resistor in parallel.

6. The heating device according to claim 4, wherein the detection unit further comprises a microprocessor, and the microprocessor comprises: a first calculation unit that presets the first calculation formula, calculates the inductance of the resonant tank equivalent inductor according to the capacitance of the resonant tank capacitor, the resonant period provided by the zero-crossing detection circuit, and the first calculation formula, and outputs a first calculation result to the control unit; and The second calculation unit presets the second calculation formula and receives the first calculation result provided by the first calculation unit, and obtains the reference current value, the time variation, and the negative peak current value of the resonant tank current based on the resonant tank current and the resonant tank voltage, and further calculates the impedance value of the resonant tank equivalent impedance based on the inductance value of the resonant tank equivalent inductance, the reference current value, the time variation, the negative peak current value of the resonant tank current, and the second calculation formula, and outputs the second calculation result to the control unit.

7. The heating device according to claim 6, wherein the microprocessor is composed of a digital signal processor or a microcontroller. The heating device according to claim 1 , wherein the heating device is an induction cooker.

9. The heating device according to claim 1, wherein the inverter circuit includes an upper switching element and a lower switching element electrically connected in series, the upper switching element and the lower switching element are switched on and off alternately, and the resonant tank includes a first end and a second end, the first end and the second end are respectively electrically coupled to two current conduction ends of the lower switching element.

10. A detection method, applied to a detection unit of a heating device, wherein the heating device further comprises a resonant circuit, the resonant circuit comprising an inverter circuit and a resonant tank, the inverter circuit providing a resonant tank current and a resonant tank voltage, the resonant tank comprising a heating coil, a resonant tank capacitor, a resonant tank equivalent inductance, and a resonant tank equivalent impedance, the detection method comprising: (a) detecting the resonant tank current and the resonant tank voltage to obtain a reference current value, a first zero-crossing time point, a second zero-crossing time point, a time variation, a resonant period, and a negative peak current value, wherein the reference current value corresponds to the current value of the resonant tank current when the resonant tank voltage is zero, the time variation is the time interval from the time point when the resonant tank voltage is zero to the first zero-crossing time point, and the resonant period is defined by the first zero-crossing time point and the second zero-crossing time point, the first zero-crossing time point being the time point when the resonant tank current is zero for the first time after the resonant tank voltage is zero, and the second zero-crossing time point being the time point when the resonant tank current is zero for the second time after the resonant tank voltage is zero; (b) calculating the inductance value of the resonant tank equivalent inductance based on the resonant tank capacitance, the resonant period, and a first calculation formula, wherein the first calculation formula is: L eq is the inductance value of the equivalent inductance of the resonant tank, C r is the capacitance value of the resonant tank capacitor, and T is the resonant period; (c) calculating the impedance value of the equivalent impedance based on the equivalent inductance of the resonant tank, the time variation, the resonant period, the reference current value, the negative peak current value, and a second calculation formula, wherein the second calculation formula is: R eq is the impedance value of the equivalent impedance of the resonant tank, I0 is the reference current value, Δt is the time variation, I N is the negative peak current value; as well as (d) controlling the heating power of the heating coil according to the inductance value of the equivalent inductance of the resonant tank and the impedance value of the equivalent impedance of the resonant tank.

11. The detection method according to claim 10, wherein the heating device is an induction cooker; and in the step (d), further comprising determining whether a food container is placed on the heating device based on the equivalent inductance and the equivalent resistance of the resonant tank.

12. The detection method according to claim 10, wherein the heating device is an induction cooker; and in the step (d), further comprising determining the heating power burden ratio of the heating coil based on the equivalent inductance of the resonant tank and the equivalent resistance of the resonant tank.

13. The detection method according to claim 10, wherein the heating device is an induction cooker; and in the step (d), further comprising determining the material of the food container on the heating device based on the equivalent inductance and the equivalent resistance of the resonant tank.

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