Constant power control method and circuit of induction cooker

Abstract

The invention provides a constant power control method and circuit of an induction cooker. The control method comprises the following steps: acquiring an input voltage signal Vin; in the circuit starting stage, the power switch tube is controlled to be conducted for preset time, a resonance voltage signal of the resonance circuit is collected within the preset conduction time, and a rising rate parameter is calculated based on the rising section of the resonance voltage signal; in the circuit operation stage, peak voltage of a resonance voltage signal of the resonance circuit in the current period is sampled, and the difference value between the peak voltage and a preset voltage threshold value is calculated; when a difference value between the peak voltage and a preset voltage threshold value is smaller than a first preset value, the control circuit calculates an adjusting quantity used for adjusting the conduction time of the power switch tube based on the difference value between the peak voltage and the preset voltage threshold value, the input voltage signal and the rising rate parameter; and adjusting the conduction time of the power switch tube in the next period according to the adjusting quantity, so that the peak voltage is stabilized at the preset voltage threshold, and the output power of the resonance circuit is constant.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic heating control, and in particular to a constant power control method and circuit for an electromagnetic cooker. Background Art

[0002] Electromagnetic heating technology is widely used in household and industrial heating equipment. Its core principle is to generate an alternating magnetic field at the bottom of the heating vessel, achieving contactless heating through the eddy current effect. In practice, to achieve varying power output, control systems typically adjust the current in the coil by adjusting the on-time of the power transistor, thereby affecting the output power. However, under high voltage or high power output conditions, the resonance between the inductor and the load capacitor causes a significant increase in the voltage at the resonant node, increasing the voltage withstand requirements of the power device.

[0003] In existing constant power control circuits, the on-time of the power switch is usually adjusted based on the overvoltage protection (OVP) mechanism. The OVP voltage is usually set to match the voltage withstand capability of the power switch. That is, in actual applications, to ensure that the power switch is not broken down by high voltage, its OVP voltage value will be lower than the maximum voltage withstand level of the power switch, and will be set accordingly based on the specific voltage withstand parameters of the selected device. When it is detected that the resonant voltage exceeds the set overvoltage threshold, the control circuit will shorten the on-time of the power switch in the next cycle to prevent the device from being damaged by overvoltage. However, in high-voltage or high-power output scenarios, this type of protection strategy is prone to control response lag, resulting in obvious "large and small waves" in the output waveform. That is, the resonant voltage periodically exceeds the target range and triggers protection, which in turn causes unstable output power. In addition, frequent entry into the overvoltage protection state not only affects the service life of the power tube, but also limits the maximum output capacity of the constant power control circuit to a certain extent. Summary of the Invention

[0004] The object of the present invention is to provide a constant power control method and circuit for an induction cooker, so as to solve the problems of unstable power and limited life of power tubes in existing constant power control circuits when outputting high voltage or high power.

[0005] To achieve the above objectives, the present invention discloses the following technical solutions:

[0006] In one aspect, the present invention provides a constant power control method for an induction cooker, which is applied to a constant power control circuit of the induction cooker. The constant power control circuit includes a resonant circuit, a sampling circuit, a control circuit, and a power switch tube. The control method includes:

[0007] Obtaining an input voltage signal Vin;

[0008] During the startup phase of the constant power control circuit, the power switch tube is controlled to be turned on for a preset time, a resonant voltage signal of the resonant circuit is collected during the preset on-time, and a rising rate parameter is calculated based on a rising segment of the resonant voltage signal;

[0009] During the operation phase of the constant power control circuit, the peak voltage of the resonant voltage signal of the resonant circuit in the current cycle is sampled by the sampling circuit, and the difference between the peak voltage and a preset voltage threshold VS_MAX is calculated;

[0010] When the difference between the peak voltage and the preset voltage threshold VS_MAX is less than a first preset value, the control circuit calculates an adjustment amount for adjusting the conduction time of the power switch tube based on the difference between the peak voltage and the preset voltage threshold VS_MAX, the input voltage signal, and the rise rate parameter;

[0011] According to the adjustment amount, the on-time of the power switch tube in the next cycle is adjusted so that the peak voltage is stabilized at the preset voltage threshold VS_MAX, thereby maintaining the output power of the resonant circuit constant.

[0012] Optionally, the control circuit calculates the adjustment amount for adjusting the conduction time of the power switch tube based on the difference between the peak voltage and the preset voltage threshold VS_MAX, the input voltage signal, and the rise rate parameter using the following specific formula:

[0013] ΔT=-a*(Vin / Vref)*(k / kref)*(|ΔVS| / Vnom)*Ton;

[0014] Among them, ΔT is the adjustment amount of the conduction time of the power switch tube, k is the rise rate parameter, ΔVS is the difference between the peak voltage and the preset voltage threshold VS_MAX, Ton is the conduction time of the power switch tube in the current cycle, Vref is the input voltage reference value, kref is the rise rate reference value of the resonant voltage signal, Vnom is the voltage deviation reference value, and a is a constant.

[0015] Optionally, the calculation formula of the rising rate parameter is:

[0016] k=ΔU / ΔT=ΔUrise / Trise=PKHOLD / Trise;

[0017] Among them, ΔU is the voltage change, ΔT is the time change, ΔUrise is the voltage increment of the rising segment of the resonant voltage signal, Trise is the time of the rising segment of the resonant voltage signal, and PKHOLD is the peak value of the resonant voltage signal.

[0018] Optionally, the preset voltage threshold VS_MAX is smaller than the overvoltage protection voltage of the power switch tube, so that the control circuit completes the adjustment of the on-time before the resonant voltage reaches the overvoltage protection voltage, thereby avoiding triggering the overvoltage protection.

[0019] Optionally, the preset on-time is set to satisfy the requirement that under conditions of heating vessels of different materials, the peak value of the resonant voltage signal is less than the overvoltage protection voltage, so as to prevent the constant power control circuit from triggering overvoltage protection during the startup phase.

[0020] Optionally, the method further includes:

[0021] The on-time of the power switch tube is determined according to the target output power setting value, and the on-time is kept unchanged when the difference between the peak voltage and the preset voltage threshold VS_MAX is greater than a first preset value.

[0022] A second aspect of the present invention provides a constant power control circuit for an induction cooker, the circuit comprising a resonant circuit, a sampling circuit, a control circuit, a drive circuit and a power switch tube Q1;

[0023] The resonant circuit is connected to the first end of the power switch tube Q1 and is used to generate a resonant voltage signal after the power switch tube Q1 is turned on;

[0024] The sampling circuit is connected to the resonant circuit and is configured to collect the resonant voltage signal and output the rising section and peak voltage signal of the resonant voltage to the control circuit;

[0025] The control circuit is connected to the sampling circuit and is configured to control the power switch tube Q1 to be turned on for a preset time during a startup phase of the constant power control circuit, and calculate a rise rate parameter based on a rising segment of the resonant voltage signal; during an operation phase of the constant power control circuit, sample the peak voltage of the resonant voltage signal in a current cycle, and calculate an adjustment amount for adjusting the conduction time of the power switch tube Q1 based on a difference between the peak voltage and a preset voltage threshold VS_MAX, an input voltage signal, and the rise rate parameter;

[0026] The driving circuit is connected to the control circuit and the control end of the power switch tube Q1, and is configured to receive the adjustment amount and drive the power switch tube Q1 so that the peak voltage is stabilized at the preset voltage threshold VS_MAX, thereby maintaining the output power of the resonant circuit constant.

[0027] Optionally, the resonant circuit includes a first inductor L1 and a first capacitor C1; the first end of the first inductor L1 is connected to the first end of the power switch tube Q1, the second end of the first inductor L1 is connected to the first end of the first capacitor C1, and the second end of the first capacitor C1 is connected to the first end of the first inductor L1 and the sampling module.

[0028] Optionally, the constant power control circuit further includes a rectification and filtering module, and the rectification and filtering module includes:

[0029] A second capacitor C2, wherein both ends of the second capacitor C2 are connected to the AC input terminal ACIN;

[0030] a first diode D1, an anode of which is connected to the first end of the second capacitor C2, and a cathode of which is connected to the second end of the first inductor L1;

[0031] a second diode D2, a cathode of which is connected to the anode of the first diode D1, and the anode of the second diode D2 is grounded;

[0032] a third diode D3, an anode of which is connected to the second end of the second capacitor C2, and a cathode of which is connected to the second end of the first inductor L1;

[0033] a fourth diode D4, a cathode of which is connected to the anode of the third diode D3, and the anode of the fourth diode D4 is grounded;

[0034] A third capacitor C3 , wherein a first end of the third capacitor C3 is connected to the second end of the first inductor L1 , and a second end of the third capacitor C3 is grounded.

[0035] Optionally, the constant power control circuit further includes:

[0036] A first resistor R1 , wherein a first end of the first resistor R1 is connected to a second end of the power switch tube Q1 , and a second end of the first resistor R1 is grounded.

[0037] According to the present invention, during the startup phase of the constant power control circuit, the power switch is controlled to conduct for a preset time, the resonant voltage signal is collected, and its rising segment is extracted to calculate the rise rate parameter. During the operation phase, the difference between the peak voltage and the set threshold, the input voltage value, and the aforementioned rise rate parameter are combined to dynamically adjust the power switch conduction time for the next cycle, thereby maintaining the resonant voltage below the preset threshold, effectively avoiding triggering overvoltage protection and ensuring stable system operation. Compared to traditional methods that rely solely on fixed threshold triggering protection, this method possesses the dual capabilities of feedforward prediction and feedback regulation, can promptly suppress the risks of voltage overshoot, and significantly improve the reliability and service life of the power tube.

[0038] Furthermore, the present invention takes into account the adaptability of the preset on-time setting for heating utensils of different materials, ensuring adaptability to both high- and low-impedance cookware during startup, preventing the initial resonant voltage from exceeding the limit. Furthermore, by introducing adjustment factors related to the input voltage and the rate of rise, adaptive adjustment of the on-time is achieved, enabling the system to maintain a relatively constant heating power output even under high-voltage or heavy-load conditions. This alleviates issues such as large output power fluctuations, uneven heating of the cookware, and false protection triggering in traditional control systems, thereby improving overall heating performance and user experience.

[0039] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A schematic flow chart of a constant power control method for an induction cooker according to an embodiment of the present invention is shown;

[0041] Figure 2 A topology diagram of a constant power control circuit of an induction cooker according to an embodiment of the present invention is shown;

[0042] Figure 3 shows a waveform diagram of a peak and valley detection signal S_VS according to an embodiment of the present invention;

[0043] Figure 4 shows a waveform diagram of a constant power control circuit according to an embodiment of the present invention;

[0044] Figure 5 shows a waveform diagram using a conventional constant power control method;

[0045] Figure 6 FIG. 4 shows an envelope comparison diagram of a constant power control circuit according to an embodiment of the present invention. DETAILED DESCRIPTION

[0046] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. It will be understood that the specific embodiments described herein are only used to explain the present application, rather than to limit the present application. It should also be noted that, for ease of description, only some, rather than all, structures related to the present application are shown in the accompanying drawings. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0047] As used herein, the terms "comprise," "comprising," and "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0048] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0049] Figure 1 The schematic flow chart of the constant power control method of an induction cooker according to one embodiment of the present invention is shown. The constant power control method of an induction cooker is applied to the constant power control circuit of the induction cooker, which includes a resonant circuit, a sampling circuit, a control circuit and a power switch tube. Figure 1 As shown, the constant power control method of the induction cooker includes the following steps:

[0050] Step S100: obtaining an input voltage signal Vin.

[0051] In this step, the constant power control circuit receives external AC power, which, after rectification and filtering, forms a DC high-voltage signal HV, also known as the input voltage signal Vin. Because voltage fluctuations in the voltage signal Vin can significantly affect the amplitude of the subsequent resonant voltage, thereby affecting the conduction safety and control accuracy of the power switch, the present invention incorporates the voltage signal Vin into the power switch conduction time regulation logic as a key control factor. Unlike traditional solutions that only detect voltage during the startup phase, the present invention continuously acquires the voltage signal Vin during operation, dynamically responding to grid fluctuations and improving the stability of system operation and the accuracy of constant power control.

[0052] Step S200: During the startup phase of the constant power control circuit, the power switch is controlled to conduct for a preset time, a resonant voltage signal of the resonant circuit is collected during the preset conduction time, and a rising rate parameter is calculated based on a rising segment of the resonant voltage signal.

[0053] In step S200, during the initial startup phase of the constant power control circuit, since it is not yet possible to determine the material, electrical characteristics, or presence of a valid load on the placed cookware, directly driving the power switch Q1 with a long on-time could cause the resonant voltage to rise sharply, triggering the overvoltage protection (OVP) mechanism and thus affecting normal startup. Therefore, the present invention sets a fixed, corresponding preset on-time according to different output powers, controlling the power switch Q1 to conduct only for a short period of time, keeping the constant power control circuit in a controlled pre-charge state and effectively avoiding the risk of voltage overshoot during the initial startup phase. Within this preset on-time window, the control circuit captures the rising segment of the resonant voltage signal and calculates the rise rate parameter k based on the voltage and time variation during this segment. This parameter reflects the energy coupling characteristics between the constant power control circuit and the current cookware, indirectly characterizing the cookware's material type and thermal response capability, and providing a basis for subsequent control strategies. Furthermore, by capturing the changing trend of the resonant voltage rather than its static amplitude, the present invention enables rapid characteristic determination and initial modeling during the initial startup phase, shortening the identification cycle and improving response speed.

[0054] In some embodiments, the preset on-time is set to meet the requirement that under the conditions of heating utensils of different materials, the peak value of the resonant voltage signal is less than the overvoltage protection voltage, so as to prevent the constant power control circuit from triggering the overvoltage protection during the startup phase. The preset on-time is usually determined based on the system experimental calibration, and its value should be based on the premise that the overvoltage protection threshold of the power switch tube is not triggered under different pot materials and typical high-voltage working conditions, taking into account both safety and recognition accuracy. The preset on-time is usually determined through experimental calibration, and its setting not only takes into account the maximum operating voltage of the constant power control circuit and the voltage resistance of the power tube, but also covers the energy response characteristics of common pot materials (such as stainless steel, iron, aluminum, etc.) during initial heating. By unifying the on-time limit circuit initial excitation intensity, it can be ensured that under the premise of unclear load characteristics, the control circuit can still safely sample the rising process of the resonant voltage, avoiding on-time fluctuations caused by instantaneous sampling errors or external interference, thereby improving the stability of the control strategy.

[0055] Step S300 : During the operation phase of the constant power control circuit, the peak voltage of the resonant voltage signal of the resonant circuit in the current cycle is sampled, and the difference between the peak voltage and a preset voltage threshold VS_MAX is calculated.

[0056] After the cookware is identified and enters normal operation, the constant power control circuit continuously samples the peak voltage of the resonant voltage during each cycle. This peak voltage serves as a direct indicator of operational stability, taking into account variations in the resonant response due to input voltage fluctuations or load changes during actual operation. It is also compared with a preset voltage threshold, VS_MAX, which is a pre-set safety upper voltage limit that will not trigger OVP protection, based on the voltage withstand capability of the power switch Q1, the characteristics of the cookware, and the operating environment. The voltage deviation ΔVS, obtained by comparing the peak voltage with the preset voltage threshold VS_MAX, can help determine whether the current on-time of the power switch Q1 is excessively long and whether there is a risk of overshoot. This helps determine the on-time adjustment of the power switch Q1 during the next cycle.

[0057] In step S400 , when the difference between the peak voltage and the preset voltage threshold VS_MAX is less than a first preset value, the control circuit calculates an adjustment amount for adjusting the conduction time of the power switch tube based on the difference between the peak voltage and the preset voltage threshold VS_MAX, the input voltage signal, and the rise rate parameter.

[0058] In this step, the constant power control circuit is in a stable operation phase. The control circuit continuously monitors the peak voltage of the resonant circuit in each cycle and compares it with a preset voltage threshold VS_MAX. When the peak voltage approaches the preset voltage threshold VS_MAX, that is, the voltage difference between the two is lower than a first preset value, it indicates that the system operation is close to the safe upper limit range of the power switch tube Q1. If not adjusted in time, overvoltage is likely to occur in the next cycle, triggering OVP protection, causing system output power fluctuations and even affecting overall stability. To this end, the present invention dynamically calculates the on-time adjustment value ΔT by comprehensively considering the voltage deviation of the current cycle, the input voltage signal Vin, and the rise rate parameter k. This is used to actively correct the on-time Ton of the power switch tube in the next cycle, thereby maintaining constant power output without triggering OVP protection.

[0059] The regulation process of step S400 prevents the system from entering the overvoltage protection state by adjusting the conduction time of the power switch tube in advance. Unlike the traditional method that relies on feedback regulation after triggering protection, the present invention adopts a predictive regulation strategy based on operating trends to improve the speed and stability of the control response. The calculation of the regulation amount ΔT comprehensively considers the voltage difference of the current cycle, the input voltage Vin, and the rise rate parameter k extracted during the startup phase, accurately reflects the combined impact of power supply fluctuations and load changes, and realizes dynamic adjustment of the conduction time. This strategy enhances the system's adaptability to grid disturbances and changes in cookware, reduces the frequent triggering of overvoltage protection, ensures that the constant power control circuit operates stably in a safe area close to the power upper limit, and expands its operating range and maximum output power.

[0060] In step S500 , the on-time of the power switch tube in the next cycle is adjusted according to the adjustment amount, so that the peak voltage is stabilized at a preset voltage threshold VS_MAX, thereby maintaining the output power of the resonant circuit constant.

[0061] In step S500, the control circuit adjusts the on-time of the power switch Q1 for the next cycle based on the calculated adjustment value ΔT, thereby regulating the inductor current and energy storage process, affecting the peak value of the resonant voltage. By combining trend prediction with feedback correction, the system can automatically optimize the on-time during dynamic operation, ensuring that the resonant voltage always remains within the preset threshold VS_MAX and the peak voltage is stabilized at the preset voltage threshold VS_MAX. This allows the resonant circuit to dynamically stabilize the output power during long-term operation, avoiding power swings caused by periodic overshoots and preventing the triggering of overvoltage protection. The present invention not only ensures the safe operation of the power tube, but also maintains stable heating power, improves heating efficiency, and improves adaptability to different cookware.

[0062] According to the above embodiment, during the startup phase of the constant power control circuit, the power switch is controlled to conduct for a preset time, the resonant voltage signal is collected, and its rising segment is extracted to calculate the rise rate parameter. During the operation phase, the difference between the peak voltage and the set threshold, the input voltage value, and the aforementioned rise rate parameter are combined to dynamically adjust the on-time of the power switch in the next cycle, thereby maintaining the resonant voltage below the preset threshold, effectively avoiding triggering overvoltage protection and ensuring stable system operation. Compared to traditional methods that rely solely on fixed threshold triggering protection, this method has the dual capabilities of feedforward prediction and feedback regulation, can promptly suppress the risks caused by voltage overshoot, and significantly improve the operating reliability and service life of the power tube.

[0063] In one embodiment, the control circuit calculates the adjustment amount for adjusting the on-time of the power switch based on the difference between the peak voltage and the preset voltage threshold VS_MAX, the input voltage signal, and the rise rate parameter. The specific formula is:

[0064] ΔT=-a*(Vin / Vref)*(k / kref)*(|ΔVS| / Vnom)*Ton;

[0065] Among them, ΔT is the adjustment amount of the power switch tube conduction time, k is the rise rate parameter, ΔVS is the difference between the peak voltage and the preset voltage threshold VS_MAX, Ton is the conduction time of the power switch tube in the current cycle, Vref is the input voltage reference value, kref is the rise rate reference value of the resonant voltage signal, Vnom is the voltage deviation reference value, and a is a constant.

[0066] The adjustment amount calculation formula used in this embodiment integrates multiple key factors, including the input voltage Vin, the resonant voltage rise rate k, and the voltage deviation ΔVS between the peak voltage and the preset threshold VS_MAX. It can accurately reflect the combined impact of power supply fluctuations and load changes within the current cycle. At the same time, each variable is normalized using reference values ​​such as Vref, kref, and Vnom, effectively reducing the interference of different operating conditions, voltage levels, or changes in cookware parameters on the adjustment results, thereby enhancing the adaptability and versatility of the control strategy. The constant a in the formula serves as a control sensitivity factor and can be flexibly configured according to different hardware platforms and system dynamic characteristics. The adjustment amount ΔT in the formula is proportional to the current on-time Ton, making the on-time correction adaptive and avoiding excessive adjustment amplitude or insufficient response. In addition, the negative sign in the formula indicates that the adjustment is to shorten the on-time of the next cycle, that is, Ton_new = Ton + ΔT = Ton - |ΔT|, to reduce the peak voltage of the next resonant cycle. The regulation mechanism constructed through this formula achieves predictive adjustment of the on-time in each cycle, enabling the system to proactively adapt to grid fluctuations and load changes, and ensuring stable operation of the constant power control circuit at high power output.

[0067] In one embodiment, the specific formula for adjusting the on-time of the power switch can also be expressed as: ΔT∝-[(Vin*k*|ΔVS|) / (Vref*kref*Vnom)]*Ton. The symbol ∝ indicates a proportional relationship, indicating that the magnitude of ΔT increases proportionally with the input voltage Vin, the rate of rise k, and the voltage deviation |ΔVS|. This is used to dynamically adjust the on-time to ensure that the control is more consistent with the current operating state.

[0068] In one embodiment, the calculation formula of the rise rate parameter is:

[0069] k=ΔU / ΔT=ΔUrise / Trise=PKHOLD / Trise;

[0070] Among them, ΔU is the voltage change, ΔT is the time change, ΔUrise is the voltage increment of the rising segment of the resonant voltage signal, Trise is the time of the rising segment of the resonant voltage signal, and PKHOLD is the peak value of the resonant voltage signal.

[0071] This formula directly uses the process of the resonant voltage growing from zero to its peak value during the initial startup phase as the representative section of the load response characteristics. This not only simplifies the sampling and processing process, but also avoids reliance on multiple feature point judgments, improving the system's recognition stability under complex working conditions. In addition, because different cookware materials have significantly different voltage rise rates under the same excitation conditions, such as iron pots rising quickly and aluminum pots rising slowly, the parameter k can effectively distinguish the type of cookware material and assist in determining the speed of the current energy coupling. This parameter k can be directly introduced into the on-time adjustment formula as a basis for measuring the load response characteristics, establishing a connection between startup phase sampling and operation phase control, and enhancing the consistency and adaptability of the control strategy.

[0072] In one embodiment, the preset voltage threshold VS_MAX is less than the overvoltage protection voltage of the power switch tube, so that the control circuit completes the on-time adjustment before the resonant voltage reaches the overvoltage protection voltage, thereby avoiding triggering the overvoltage protection. According to the above embodiment, when the resonant voltage approaches the preset voltage threshold VS_MAX, the control circuit of the present invention adjusts the on-time of the power switch tube Q1 in the next cycle so that the highest point of the resonant voltage is maintained near the preset voltage threshold VS_MAX. Setting the preset voltage threshold VS_MAX less than the overvoltage protection voltage of the power switch tube can ensure that the resonant voltage does not reach the overvoltage protection voltage, avoid voltage overshoot that causes the protection mechanism to be triggered, thereby ensuring stable system operation and improving output power continuity and control reliability.

[0073] In one embodiment, the on-time of the power switch is determined according to the target output power setting value, and the on-time is kept unchanged when the difference between the peak voltage and the preset voltage threshold VS_MAX is greater than a first preset value.

[0074] In this embodiment, the control circuit of the present invention can predetermine the on-time of the power switch tube based on the set value of the target output power, and maintain this on-time as a reference during operation. When the difference between the peak voltage of the resonant voltage and the preset voltage threshold VS_MAX is detected to be greater than a first preset value, the current on-state is considered to be within a safe range, and therefore no on-time adjustment is required. The on-time adjustment mechanism is only activated when the peak voltage of the resonant voltage is detected to be close to the preset voltage threshold VS_MAX, that is, the difference between the two is less than the first preset value. By maintaining a constant on-time when voltage conditions permit, unnecessary adjustment behavior can be reduced and control stability can be improved.

[0075] According to the above embodiment, the preset on-time setting takes into account the adaptability of heating utensils of different materials, ensuring adaptability to high- and low-resistance cookware during the startup phase and preventing the initial resonant voltage from exceeding the limit. Furthermore, by introducing adjustment factors related to the input voltage and the rate of rise, adaptive adjustment of the on-time is achieved, allowing the system to maintain a relatively constant heating power output under high-voltage or heavy-load conditions. This alleviates issues such as large output power fluctuations, uneven heating of the cookware, and false protection triggering in traditional control systems, thereby improving overall heating performance and user experience.

[0076] Figure 2 FIG. 1 shows a topology diagram of a constant power control circuit of an induction cooker according to an embodiment of the present invention. Figure 2 As shown, the constant power control circuit includes a resonant circuit, a sampling circuit, a control circuit, a drive circuit, and a power switch Q1. The resonant circuit is connected to a first terminal of the power switch Q1 and is configured to generate a resonant voltage signal after the power switch Q1 is turned on. The sampling circuit is connected to the resonant circuit and configured to collect the resonant voltage signal and output the rising phase of the resonant voltage and a peak voltage signal PKHOLD to the control circuit. The control circuit is connected to the sampling circuit and configured to control the power switch Q1 to be turned on for a preset time during the startup phase of the constant power control circuit and calculate a rise rate parameter based on the rising phase of the resonant voltage signal. During the operation phase of the constant power control circuit, the peak voltage of the resonant voltage signal within the current cycle is sampled and, based on the difference between the peak voltage and a preset voltage threshold VS_MAX, the input voltage signal, and the rise rate parameter, an adjustment variable is calculated for adjusting the on-time of the power switch Q1. The drive circuit is connected to both the control circuit and the control terminal of the power switch Q1 and is configured to receive the adjustment variable and drive the power switch Q1 so that the peak voltage stabilizes at the preset voltage threshold VS_MAX, thereby maintaining a constant output power of the resonant circuit.

[0077] In one embodiment, the sampling circuit further samples the peak and valley detection signal S_VS of the resonant circuit. Figure 3 FIG. 4 shows a waveform diagram of a peak and valley detection signal S_VS according to an embodiment of the present invention. Figure 3 As shown, the peak and trough detection signal S_VS is used to mark the peak and trough positions in the resonant waveform, which helps the control circuit identify the starting point and end point of the first complete resonant cycle or determine whether the waveform is completely formed, ensuring that the extracted peak voltage and rise time are valid and representative, thereby improving the accuracy of the rise rate parameter calculation and the stability of the control strategy.

[0078] In one embodiment, the above-mentioned resonant circuit, sampling circuit, control circuit, and driving circuit can all be integrated into a typical application circuit constructed by the KOP9028A chip to achieve an integrated design of the overall control function.

[0079] In one embodiment, the resonant circuit includes a first inductor L1 and a first capacitor C1. The first end of the first inductor L1 is connected to the first end of the power switch Q1, the second end of the first inductor L1 is connected to the first end of the first capacitor C1, and the second end of the first capacitor C1 is connected to the first end of the first inductor L1 and the sampling module. In this embodiment, the first inductor L1 and the first capacitor C1 are connected in parallel to form a resonant circuit, ensuring that current can flow through the first inductor L1 when the power switch Q1 is turned on, thereby storing and releasing energy.

[0080] In one embodiment, the constant power control circuit further includes a rectifier and filter module. The rectifier and filter module includes a second capacitor C2, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, and a third capacitor C3. The two ends of the second capacitor C2 are connected to the AC input terminal ACIN. The anode of the first diode D1 is connected to the first end of the second capacitor C2, and the cathode of the first diode D1 is connected to the second end of the first inductor L1. The cathode of the second diode D2 is connected to the anode of the first diode D1, and the anode of the second diode D2 is grounded. The anode of the third diode D3 is connected to the second end of the second capacitor C2, and the cathode of the third diode D3 is connected to the second end of the first inductor L1. The cathode of the fourth diode D4 is connected to the anode of the third diode D3, and the anode of the fourth diode D4 is grounded. The first end of the third capacitor C3 is connected to the second end of the first inductor L1, and the second end of the third capacitor C3 is grounded.

[0081] In this embodiment, the constant power control circuit further includes a rectifier and filter module for converting the AC input voltage into a DC high-voltage power supply voltage HV. This module consists of a second capacitor C2, four diodes D1 to D4, and a third capacitor C3, which are connected in a bridge-type rectifier diode to achieve full-wave rectification of the AC power. The second capacitor C2 is directly connected to the AC input terminal ACIN. The rectified DC high-voltage power supply voltage HV is the first terminal voltage of the third capacitor C3. This high-voltage power supply provides the necessary energy support for the subsequent resonant circuit and control circuit.

[0082] During operation, when the power switch Q1 is on, the HV voltage charges the first inductor L1. When the power switch Q1 is off, the first inductor L1 and the third capacitor C3 resonate through charging and discharging, thereby forming a rapidly changing magnetic field. At this time, the voltage at the first terminal of the first inductor L1, i.e., the voltage at the VS terminal, is equal to the superposition of the HV voltage and the voltage drop across the first inductor L1. That is, the HV voltage plus the voltage caused by the current change in the first inductor L1 (U = L·di / dt), providing the basis for the resonant voltage signal, realizing the energy conversion process of constant power control.

[0083] In one embodiment, the constant power control circuit further includes a first resistor R1, a first end of which is connected to the second end of the power switch Q1, and a second end of which is grounded. The first resistor R1 is connected in series between the power switch Q1 and ground and is primarily used to sample the current of the power switch Q1. By detecting the voltage across the resistor, the control circuit can accurately obtain the current of the power switch Q1, thereby monitoring the operating status and load condition of the power switch Q1. Furthermore, the first resistor R1 can provide a feedback signal when the current is abnormal, helping the control circuit to promptly initiate protective measures to prevent device damage.

[0084] Figure 4 FIG. 1 shows a waveform diagram of a constant power control circuit according to an embodiment of the present invention. Figure 4 As shown, when the control circuit (CTRL) detects that the peak value of the resonant voltage is close to the preset voltage threshold VS_MAX, it will actively shorten the on-time of the power switch tube Q1 in the next cycle, and adjust the original on-time ton1 to a shorter ton2, thereby suppressing the peak voltage of the subsequent resonant waveform to ensure that it does not exceed the preset voltage threshold VS_MAX. This control method is different from the traditional response-type protection mechanism, and can complete the dynamic correction of the on-time before the overvoltage protection (OVP) occurs, effectively avoiding a sudden drop in output power or system jitter. By adjusting the on-time in advance, the present invention can achieve stable operation under conditions close to the power upper limit, improve the power utilization and control accuracy of the system, and better meet the constant power control requirements of the constant power control circuit under high power output state.

[0085] Figure 5 The waveform diagram of the traditional constant power control method is shown. Figure 6 FIG. 1 shows an envelope comparison diagram of a constant power control circuit according to an embodiment of the present invention. Figure 5 As shown, the traditional constant power control method is based on the overvoltage protection (OVP) mechanism to adjust, so that the output waveform VS of the resonant circuit has obvious fluctuations. Figure 6 , HV is the high voltage DC power supply voltage after rectification and filtering, VS is the output voltage of the resonant circuit, which is kept stable below HV while ensuring that it does not exceed the maximum withstand voltage limit of the power switch tube Q1. IGBT The present invention sets a preset voltage threshold VS_MAX to ensure that the resonant voltage VS does not exceed the withstand voltage limit of the power switch Q1. When the resonant voltage VS approaches the threshold, the on-time of the power switch Q1 is actively adjusted to prevent voltage overshoot. Figure 5 It can be seen that compared with the traditional control strategy, the envelope curve of the resonant voltage VS is more stable, avoiding the voltage overshoot peak, I IGBTThe change in the current curve also shows more stable conduction characteristics, thereby improving the safety and control accuracy of the system.

[0086] In the above-mentioned constant power control circuit of the induction cooker, the specific implementation of each module refers to the relevant content of the embodiment of the above-mentioned constant power control method of the induction cooker, and will not be described in detail here.

[0087] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0088] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A constant power control method for an induction cooker, characterized in that: In a constant power control circuit applied to an induction cooker, the constant power control circuit includes a resonant circuit, a sampling circuit, a control circuit, and a power switch tube. The control method includes: Obtaining an input voltage signal Vin; During the startup phase of the constant power control circuit, the power switch tube is controlled to be turned on for a preset time, a resonant voltage signal of the resonant circuit is collected during the preset on-time, and a rising rate parameter is calculated based on a rising segment of the resonant voltage signal; During the operation phase of the constant power control circuit, the peak voltage of the resonant voltage signal of the resonant circuit in the current cycle is sampled by a sampling circuit, and the difference between the peak voltage and a preset voltage threshold VS_MAX is calculated; When the difference between the peak voltage and the preset voltage threshold VS_MAX is less than a first preset value, the control circuit calculates an adjustment amount for adjusting the conduction time of the power switch tube based on the difference between the peak voltage and the preset voltage threshold VS_MAX, the input voltage signal, and the rise rate parameter; According to the adjustment amount, the on-time of the power switch tube in the next cycle is adjusted so that the peak voltage is stabilized at the preset voltage threshold VS_MAX, thereby maintaining the output power of the resonant circuit constant.

2. The constant power control method according to claim 1, wherein: The control circuit calculates the adjustment amount for adjusting the on-time of the power switch tube based on the difference between the peak voltage and the preset voltage threshold VS_MAX, the input voltage signal, and the rise rate parameter. The specific formula is: ΔT=-a*(Vin / Vref)*(k / kref)*(|ΔVS| / Vnom)*Ton; Among them, ΔT is the adjustment amount of the conduction time of the power switch tube, k is the rise rate parameter, ΔVS is the difference between the peak voltage and the preset voltage threshold VS_MAX, Ton is the conduction time of the power switch tube in the current cycle, Vref is the input voltage reference value, kref is the rise rate reference value of the resonant voltage signal, Vnom is the voltage deviation reference value, and a is a constant.

3. The constant power control method according to claim 2, wherein: The calculation formula of the rising rate parameter is: k=ΔU / ΔT=ΔUrise / Trise=PKHOLD / Trise; Among them, ΔU is the voltage change, ΔT is the time change, ΔUrise is the voltage increment of the rising segment of the resonant voltage signal, Trise is the time of the rising segment of the resonant voltage signal, and PKHOLD is the peak value of the resonant voltage signal.

4. The constant power control method according to claim 3, wherein: The preset voltage threshold VS_MAX is smaller than the overvoltage protection voltage of the power switch tube, so that the control circuit completes the adjustment of the on-time before the resonant voltage reaches the overvoltage protection voltage, thereby avoiding triggering the overvoltage protection.

5. The constant power control method according to claim 4, characterized in that: The preset on-time is set to satisfy the requirement that, under the conditions of heating vessels made of different materials, the peak value of the resonant voltage signal is less than the overvoltage protection voltage, so as to prevent the constant power control circuit from triggering overvoltage protection during the startup phase.

6. The constant power control method according to claim 5, characterized in that: The method further comprises: The on-time of the power switch tube is determined according to the target output power setting value, and the on-time is kept unchanged when the difference between the peak voltage and the preset voltage threshold VS_MAX is greater than a first preset value.

7. A constant power control circuit for an induction cooker, characterized in that: The circuit includes a resonant circuit, a sampling circuit, a control circuit, a drive circuit and a power switch tube Q1; The resonant circuit is connected to the first end of the power switch tube Q1 and is used to generate a resonant voltage signal after the power switch tube Q1 is turned on; The sampling circuit is connected to the resonant circuit and is configured to collect the resonant voltage signal and output the rising section and peak voltage signal of the resonant voltage to the control circuit; The control circuit is connected to the sampling circuit and is configured to control the power switch tube Q1 to be turned on for a preset time during a startup phase of the constant power control circuit, and calculate a rise rate parameter based on a rising segment of the resonant voltage signal; during an operation phase of the constant power control circuit, sample the peak voltage of the resonant voltage signal in a current cycle, and calculate an adjustment amount for adjusting the conduction time of the power switch tube Q1 based on a difference between the peak voltage and a preset voltage threshold VS_MAX, an input voltage signal, and the rise rate parameter; The driving circuit is connected to the control circuit and the control end of the power switch tube Q1, and is configured to receive the adjustment amount and drive the power switch tube Q1 so that the peak voltage is stabilized at the preset voltage threshold VS_MAX, thereby maintaining the output power of the resonant circuit constant.

8. The constant power control circuit according to claim 7, characterized in that: The resonant circuit includes a first inductor L1 and a first capacitor C1; the first end of the first inductor L1 is connected to the first end of the power switch tube Q1, the second end of the first inductor L1 is connected to the first end of the first capacitor C1, and the second end of the first capacitor C1 is connected to the first end of the first inductor L1 and the sampling module.

9. The constant power control circuit according to claim 8, characterized in that: The constant power control circuit further includes a rectifier and filter module, which includes: A second capacitor C2, wherein both ends of the second capacitor C2 are connected to the AC input terminal ACIN; a first diode D1, an anode of which is connected to the first end of the second capacitor C2, and a cathode of which is connected to the second end of the first inductor L1; a second diode D2, a cathode of which is connected to the anode of the first diode D1, and the anode of the second diode D2 is grounded; a third diode D3, an anode of which is connected to the second end of the second capacitor C2, and a cathode of which is connected to the second end of the first inductor L1; a fourth diode D4, a cathode of which is connected to the anode of the third diode D3, and the anode of the fourth diode D4 is grounded; A third capacitor C3 , wherein a first end of the third capacitor C3 is connected to the second end of the first inductor L1 , and a second end of the third capacitor C3 is grounded.

10. The constant power control circuit according to claim 9, characterized in that: The constant power control circuit further includes: A first resistor R1 , wherein a first end of the first resistor R1 is connected to a second end of the power switch tube Q1 , and a second end of the first resistor R1 is grounded.

Images