A kitchen electric heating device and its control device

Abstract

The present application relates to a kitchen electric heating device and its control device, including: a first switch circuit and a main control circuit; the first switch circuit is connected in series in the filter capacitor branch of the LC filter circuit; the control of the main control circuit is connected to the control end of the first switch circuit. When the kitchen electric heating device is in the low-power working mode and in the intermittent working process, after the main control circuit detects that the AC grid input voltage reaches the valley point, it outputs a control signal to control the first switch circuit to turn off, so that the filter capacitor of the LC filter circuit does not store energy during the intermittent working process. The present application can avoid the generation of peak current due to the capacitor path at the moment when the IGBT is turned on, resulting in unnecessary power loss, while protecting the IGBT from being damaged and improving the safety and reliability of the induction cooker operation.

Description

Technical Field

[0001] The present application relates to a kitchen electric heating device and its control device, belonging to the technical field of automatic control. Background Art

[0002] At present, in kitchen heating devices, there are mainly two heating methods: natural gas heating and electric heating. Among them, the induction cooker is the mainstream. The induction cooker is also known as an electromagnetic stove. In the use of induction cookers, it is a very common phenomenon and the most basic requirement to adjust the heating power at any time. The control circuit can adjust the heating power of the induction cooker by changing the switching frequency of the IGBT in the energized circuit or by changing the peak current of the heating coil of the induction cooker. In the case of high-power heating, the induction cooker is in a continuous and uninterrupted working state. To achieve low-power output of the induction cooker, it can only be satisfied by an intermittent working state.

[0003] Since an LC filter circuit is provided at the grid voltage input end of the induction cooker for filtering, during the intermittent working process, the induction cooker will pause for several cycles without working. During this period, the filter capacitor in the LC filter circuit is fully charged and has nowhere to release, and the voltage reaches the peak value of the grid voltage input. When the induction cooker is powered on and works next time, the filter capacitor will form a fast discharge path through the IGBT.

[0004] The discharge path of the filter capacitor will generate a spike voltage and a piercing sound. Moreover, since the current in the discharge path does not output power externally, a large impact current will be generated inside the IGBT in the discharge path, resulting in extremely large instantaneous losses of the IGBT, causing it to heat up, and in severe cases, the IGBT will be burned out in a short time. Summary of the Invention

[0005] The present application provides a control device for a kitchen electric heating device, which can solve the problem in the prior art that in the intermittent working mode of the kitchen electric heating device, the filter capacitor in the control device has nowhere to release the stored energy, resulting in an instantaneous current mutation, thereby generating a piercing sound and burning out the IGBT due to a large impact current.

[0006] To solve the above technical problems, the present application provides the following technical solutions:

[0007] In the first aspect of the embodiments of the present application, a control device for a kitchen electric heating device is provided, including:

[0008] A first switch circuit and a main control circuit;

[0009] The first switch circuit is connected in series in the filter capacitor branch of the LC filter circuit, and the LC filter circuit is arranged at the AC grid voltage input end of the kitchen electric heating device;

[0010] The first control output terminal of the main control circuit is connected to the control terminal of the first switch circuit. When the kitchen electric heating device is in the intermittent working process, after the main control circuit detects that the AC grid input voltage reaches the valley point, it outputs a control signal to control the first switch circuit to turn off, so that the filter capacitor of the LC filter circuit does not store energy during the intermittent working process.

[0011] The AC voltage detection port of the main control circuit is connected to the AC grid voltage input terminal for detecting the AC grid input voltage.

[0012] The second aspect of the embodiments of the present application provides a kitchen electric heating device, including the control device described in the first aspect of the embodiments of the present application.

[0013] The beneficial effects of the present application are as follows: By connecting a first switch circuit in series in the filter capacitor branch of the LC filter circuit, the present application can control the disconnection of the discharge circuit of the filter capacitor in the intermittent working mode of the induction cooker, so that the filter capacitor does not store electricity in the intermittent working mode, preventing the generation of spike current due to the capacitor path at the moment when the IGBT is turned on at the end of the intermittent working mode, resulting in unnecessary power loss, while protecting the IGBT from being damaged and improving the safety and reliability of the induction cooker during operation.

[0014] When it is necessary to reduce the output power of the induction cooker in the present application, the interval time of the intermittent working mode can be adjusted to avoid the situation that the resonance waveform does not cross zero due to insufficient energy, and reduce the energy loss when the IGBT is turned on next time.

[0015] Since the interval time of the intermittent working mode is precisely adjustable, and its minimum time interval can reach one-half of the power grid cycle (that is, at 50 Hz power frequency, the minimum time interval can reach 0.01 seconds), the present application can control the induction cooker to achieve arbitrary power output through the first drive module without generating noise.

[0016] The above description is only an overview of the technical solutions of the present application. In order to be able to understand the technical means of the present application more clearly and implement them in accordance with the content of the description, the following describes the preferred embodiments of the present application in detail in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is the circuit schematic diagram of the control device of the kitchen electric heating device provided by an embodiment of the present application.

[0018] Figure 2 is the circuit schematic diagram of the control device of the embodiments of the present application;

[0019] Figure 3 is Figure 2 the waveform diagram of some models. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] The following will further describe in detail the specific implementation manners of the present application in conjunction with the accompanying drawings and embodiments. The following embodiments are used to illustrate the present application, but not to limit the scope of the present application.

[0021] Figure 1 FIG. 5 is a circuit schematic diagram of a control device for a kitchen electric heating device provided by an embodiment of the present application. The kitchen electric heating device can be an induction cooker. Hereinafter, taking the induction cooker as an example, the control device of the present invention will be described.

[0022] As Figure 1 and Figure 2 shown, the control device described in the embodiment of the present application includes: a main control circuit and an IGBT switching circuit. The IGBT switching circuit is connected in series in the power supply circuit of the induction cooker. The main control circuit is used to control the on and off of the IGBT switching circuit according to the magnitude of the current flowing through the heating coil L2 and the resonance condition between the heating coil L2 and the capacitor C3.

[0023] When the induction cooker works, the main control circuit controls the IGBT switching circuit to turn on, and the heating coil L2 of the induction cooker starts to store energy. The current flowing through the heating coil L2 continuously increases with time. When the main control circuit detects that the current flowing through the heating coil L2 reaches a preset current value, it controls the IGBT switching circuit to turn off.

[0024] The heating coil L2 of the induction cooker is a high-frequency resonant inductive element. A capacitor C3 is connected in parallel with L2 to form an LC resonant circuit. The heating coil L2 and the capacitor C3 continuously charge and discharge to generate an alternating magnetic field to heat the conductor. As the resonant energy decreases, when the main control circuit detects that the resonant voltage passes through zero, it outputs a control signal to control the IGBT switching circuit to turn on and charge and store energy in L2 again.

[0025] When the induction cooker is in the high-power working mode, the IGBT switching circuit is continuously turned on and the working cycle is uninterrupted; while in the low-power working mode, it will pause for several working cycles without working and adopt an intermittent working method, and the IGBT switching circuit is intermittently turned on.

[0026] Figure 2 FIG. 6 shows the circuit schematic diagram of the control device of the embodiment of the present application. As Figure 2 shown, the main control circuit includes a current detection module, a voltage detection module, a second driving module, and a PWM control module. Among them,

[0027] The current detection module is used to detect the current flowing through the heating coil of the induction cooker and output the detection result to the PWM control module.

[0028] The control output terminal of the PWM control module is connected to the control terminal of the IGBT switch circuit through the second drive module. When the induction cooker is working, the PWM control module sends a control signal to the second drive module to drive the IGBT switch circuit to turn on. When it is detected that the current flowing through the heating coil L2 reaches the preset value, the PWM control module outputs a control signal to the second drive module to drive the IGBT switch circuit to turn off.

[0029] The voltage detection module is used to detect the resonant voltage of the heating coil L2 and send the detection result to the PWM control module. When the PWM control module receives that the resonant voltage passes through zero and the resonant energy is too low, it outputs a PWM signal to the second drive module to drive the IGBT switch circuit to conduct again.

[0030] The IGBT switch tube Q1 is connected in series in the power supply circuit of the induction cooker.

[0031] In this embodiment, the selected IGBT switch tube is an N-channel IGBT. Of course, a P-channel one can also be selected. This embodiment does not limit the specific type of IGBT. In other embodiments, of course, other types of transistors can also be selected as long as the corresponding functions can be achieved.

[0032] Taking the N-channel IGBT in this embodiment as an example, the emitter of the IGBT switch tube is connected to one end of the current detection resistor R1, and the other end of the current detection resistor R1 is grounded. And the series connection point of the emitter of the IGBT switch tube and the resistor R1 is also connected to the input end of the current detection module. The current detection module determines the current flowing through the heating coil L2 by detecting the voltage value across the resistor R1.

[0033] The collector of the IGBT switch tube is connected to the heating coil L2 of the induction cooker, and the collector of the IGBT switch tube is also connected to the input end of the voltage detection module. The voltage detection module determines the resonant voltage of the resonant circuit composed of the heating coil L2 and the resonant capacitor C3 by detecting the voltage at the collector of the IGBT switch tube Q1.

[0034] The drive signal output terminal of the second drive module is connected to the gate of the IGBT switch tube Q1. The second drive module outputs a drive signal to the gate of the IGBT switch tube Q1 to control the on-off of the IGBT switch tube.

[0035] Further, the control device further includes a MOS switch circuit, and the MOS switch circuit is connected in series in the capacitor branch of the LC filter circuit.

[0036] Among them, the LC filter circuit is arranged at the grid voltage input end and is used to filter the input voltage. The LC filter circuit includes an inductor L1 and a capacitor C2 connected in parallel. One end of the inductor L1 is connected to the grid input voltage, the other end of the inductor L1 is connected in series with the heating wire coil L2, one end of the capacitor C2 is connected to the series connection point of the inductor L1 and the heating wire coil L2, and the other end of the capacitor C2 is connected to the MOS switch circuit.

[0037] The MOS switch circuit includes a MOS switch tube Q2. The input end of the MOS switch tube Q2 is connected to the capacitor C2, and the output end is grounded. Refer to Figure 2 , this MOS switch tube Q2 is an N-channel MOS tube, the source is grounded, and the drain is connected to the capacitor C2. Of course, a P-channel MOS tube or other suitable switch tube can also be used, which is not limited in the embodiments of the present application.

[0038] In this embodiment, the induction cooker enters the intermittent mode at the bottom of the AC grid voltage, turns off the IGBT, and at the same time, the main control circuit controls the MOS switch tube connected in series with the filter capacitor C3 to turn off; when the intermittent time set by the main control circuit ends, the IGBT is restarted at the bottom of the AC grid, and at the end of the intermittent mode, before the IGBT is turned on, the main control circuit controls the MOS switch tube connected in series with the filter capacitor C2 to turn on in advance.

[0039] In the intermittent working process of the induction cooker in the embodiments of the present application, by controlling the MOS switch tube Q2 to turn off, the path of the capacitor C2 is cut off, ensuring that the capacitor C2 does not store energy during the intermittent working process of the induction cooker. Thus, it can be ensured that at the moment when the IGBT switch tube Q1 is turned on at the end of the intermittent working mode, since there is no energy stored on the capacitor C2, the collector of Q1 will not have a spike current due to the path of the capacitor C2, protecting the IGBT from being damaged. At the same time, unnecessary power consumption can be avoided, the efficiency is improved, and it is safe and reliable.

[0040] Optionally, the main control circuit further includes a first driving module, a power adjustment module, and an AC detection module.

[0041] The voltage detection port of the AC detection module is connected to the grid voltage input end, and the signal output end of the AC detection module is connected to the power adjustment module. The AC detection module is used to detect the AC grid input voltage and output it to the power adjustment module.

[0042] The output end of the power adjustment module is connected to the PWM control module. The power adjustment module is used to output a power adjustment signal to the PWM control module according to the detected grid voltage.

[0043] The PWM signal output terminal of the PWM control module is connected to the first driving module, and the signal output terminal of the first driving module is connected to the gate of the MOS switch tube Q2. The PWM control module outputs a PWM signal according to the power adjustment signal to control the operation of the MOS switch tube Q2.

[0044] Further, the main control circuit further includes a single-chip microcomputer. The signal input terminal of the single-chip microcomputer is connected to the human-computer interaction module, and the signal output terminal of the single-chip microcomputer is connected to the power adjustment module.

[0045] The human-computer interaction module is used to input a power demand signal (i.e., a signal with different power magnitudes) to the single-chip microcomputer. The single-chip microcomputer analyzes and processes the power demand signal, outputs a power adjustment plan to the power adjustment module. The power adjustment module determines the switching frequency of Q1, the peak current of the heating wire coil, and the output signal of the first driving module according to the power adjustment plan, and sends them to the PWM control module. The PWM control module outputs a PWM signal to control the operation of Q1 and Q2.

[0046] In the intermittent working mode, the single-chip microcomputer can give a plan with an arbitrary intermittent time interval. Its minimum intermittent time can reach half of the AC power grid cycle (i.e., under 50Hz power frequency, the minimum intermittent time can reach 0.01 seconds). On this premise, any power output can be controlled to achieve the effect of uniform heating at any power output.

[0047] Further, the main control circuit further includes a protection module. The signal output terminal of the protection module is connected to the PWM control module. The protection module is used to detect the abnormal working state of the kitchen electric heating device and output a protection signal to the PWM control module to turn off the second switching circuit.

[0048] This application can ensure that when the induction cooker is in the non-intermittent working mode, the charging of the heating wire coil can be sufficient in each rectified power grid cycle, that is, to ensure sufficient resonant energy and each resonance can pass through zero. In the intermittent working mode, the single-chip microcomputer can give a plan with an arbitrary intermittent time interval. Its minimum intermittent time can reach half of the AC power grid cycle (i.e., under 50Hz power frequency, the minimum intermittent time can reach 0.01 seconds). On this premise, any power output can be controlled to achieve the effect of uniform heating at any power output.

[0049] The specific working process of the control device in the embodiment of this application is as follows:

[0050] Input a power demand signal to the single-chip microcomputer through the human-computer interaction module. The single-chip microcomputer gives a control plan to the PWM control module. The PWM control module determines the switching frequency of the IGBT switch tube Q1, the peak current of the heating wire coil, and the output signal of the first driving module.

[0051] When the induction cooker needs to output high power (for example, 900 - 2000W), the second drive module outputs a high - level signal to turn on the IGBT switch tube Q1. The output of the first drive module is always high, and the MOS switch tube Q2 is kept continuously conducting to ensure the normal operation of the capacitor C2. A current starts to flow through the heating coil L2 and increases with time. When the current detection module detects that the voltage at the collector of the IGBT switch tube Q1 reaches the set value, that is, when the current flowing through the heating coil L2 reaches the preset current value, the PWM control module outputs a control signal to the second drive module to turn off Q1. Since the current on the heating coil L2 does not change suddenly, L2 and C3 start to resonate. As the resonant energy decreases, the resonant voltage also continuously decreases. When Q1 conducts next time, it is necessary to ensure that the voltage detection module detects that the resonant voltage at the collector end of Q1 passes through zero.

[0052] When the system needs to output low power (for example, 300 - 600W), according to the AC voltage of the AC power grid detected by the AC detection module, it enters the intermittent working mode at the bottom of the AC power grid voltage. The PWM control module outputs a PWM signal to the first drive module to drive Q2 to turn off when the voltage VIN on the capacitor C2 reaches the valley point. (Among them, the voltage VIN on the capacitor C2 is synchronized with the grid voltage AC.) Thus, it is ensured that within several cycles when Q1 stops working, no electricity is stored on the capacitor C2. Until the set delay time of the intermittent working reaches and it is at the bottom of the grid voltage signal, the first drive module is turned on to turn on Q2 again; when the PWM control module receives the signal of Q2 conduction, it then controls Q1 to conduct. Figure 3 The following shows the signal waveform diagram in the intermittent working mode of the embodiment of the present application.

[0053] The first drive module can ensure that in the intermittent working mode, even if the induction cooker does not work for several cycles, no energy is stored on the capacitor C2. Thus, when Q1 is turned on again, no spike current will appear on the collector of Q1 due to the capacitor path, thereby improving the EMI characteristics of the control device.

[0054] The present application can realize continuously adjustable output power of the induction cooker. By connecting a MOS switch circuit in series with the filter capacitor C2 and setting a power adjustment module and a first drive module to control the operation of the MOS switch circuit, when Q1 conducts instantaneously, the current does not suddenly change from zero to a large value, reducing unnecessary losses and improving the safety performance of the induction cooker.

[0055] The technical features of the above - described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above - described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0056] The embodiments described above merely represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A control device for a kitchen electric heating device, characterized in that, The control device includes: a first switch circuit, a second switch circuit, and a main control circuit; The first switch circuit is connected in series to the filter capacitor branch of the LC filter circuit, and the LC filter circuit is arranged at the AC grid voltage input end of the kitchen electric heating device; The first control output end of the main control circuit is connected to the control end of the first switch circuit. When the kitchen electric heating device is in the low-power working mode and in the intermittent working process, after the main control circuit detects that the AC grid input voltage reaches the valley point, it outputs a control signal to control the first switch circuit to turn off, so that the filter capacitor of the LC filter circuit does not store energy during the intermittent working process; When the intermittent working mode ends and before the second switch circuit is turned on, the main control circuit controls the first switch circuit to turn on; The AC voltage detection port of the main control circuit is connected to the AC grid voltage input end for detecting the AC grid input voltage; The second switch circuit is connected in series to the power supply loop of the kitchen electric heating device; The second control output end of the main control circuit is connected to the control end of the second switch circuit. When the kitchen electric heating device is working normally, if the main control circuit detects that the current flowing through the electric heating device reaches the set value, it outputs a control signal to control the second switch circuit to turn off; The current signal detection port of the main control circuit is connected to the signal output end of the second switch circuit for detecting the current flowing through the electric heating device; The main control circuit includes a first driving module, an AC detection module, a power adjustment module, and a PWM control module. The signal input end of the AC detection module is connected to the grid voltage signal, the signal output end of the AC detection module is connected to the input end of the power adjustment module, the output end of the power adjustment module is connected to the PWM control module, the PWM signal output end of the PWM control module is connected to the first driving module, and the signal output end of the first driving module is connected to the control end of the first switch circuit.

2. The control device for a kitchen electric heating device according to claim 1, characterized in that, The main control circuit further includes a current detection module, a voltage detection module, and a second driving module. The input end of the current detection module is connected to the output end of the second switch circuit, the output end of the current detection module is connected to the input end of the PWM control module, the input end of the voltage detection module is connected to the input end of the second switch circuit, the output end of the voltage detection module is connected to the input end of the PWM control module, the PWM signal output end of the PWM control module is connected to the input end of the second driving module, and the driving signal output end of the second driving module is connected to the second switch circuit.

3. The control device for a kitchen electric heating device according to claim 2, characterized in that, The main control circuit further includes a single-chip microcomputer. The signal input end of the single-chip microcomputer is connected to the human-computer interaction module. The signal output end of the single-chip microcomputer is connected to the power adjustment module. The human-computer interaction module is used to input a power demand signal to the single-chip microcomputer. The single-chip microcomputer outputs a power adjustment plan to the power adjustment module according to the power demand signal. The power adjustment module is used to output a power adjustment signal that meets the power adjustment plan to the PWM control module.

4. The control device for a kitchen electric heating device according to claim 3, characterized in that, The main control circuit further includes a protection module, the signal output end of the protection module is connected to the PWM control module, and the protection module is used for detecting an abnormal working state of the kitchen electric heating device and outputting a protection signal to the PWM control module to turn off the second switching circuit.

5. The control device for a kitchen electric heating device according to claim 1, characterized in that, The first switching circuit is a MOS transistor switching circuit, including a MOS switching transistor, the MOS switching transistor is serially connected to the capacitor branch of the LC filter circuit, and the gate of the MOS switching transistor is connected to the drive signal output end of the first drive module.

6. The control device for a kitchen electric heating device according to claim 2, characterized in that, The second switching circuit is an IGBT switching circuit, including an IGBT switching transistor, and the IGBT switching transistor is serially connected in the power supply loop of the kitchen electric heating device; The gate of the IGBT switching transistor is connected to the drive signal output end of the second drive module; A current detection resistor R1 is connected to the emitter of the IGBT switching transistor, and the series connection point of the emitter of the IGBT switching transistor and the current detection resistor R1 is connected to the input end of the current detection module; The collector of the IGBT switching transistor is connected to the heating wire coil of the kitchen electric heating device, and the collector of the IGBT switching transistor is connected to the input end of the voltage detection module.

7. A kitchen electric heating device, characterized in that, It includes the control device according to any one of claims 1-6.

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