A power control method for electric ceramic stove

Abstract

The present invention belongs to the technical field of electric ceramic stoves, and particularly relates to a power control method applied to electric ceramic stoves. The method comprises: step S1: detecting the power supply voltage with the shortest fixed period by MCU to obtain a sampling value N; step S2: obtaining the zero crossing point of the sampling signal and the half-period T of the sampling signal according to the time point T1 when the detected DC voltage is first higher than 0V and the time point T2 when the detected DC voltage is first lower than 0V in the AD AC detection period; step S3: obtaining the sum of all sampling values ​​N within the half-period T time as M, taking the average value of M of all half-periods T within 1 second as the quantized value of the power supply voltage amplitude; step S4: measuring the quantized value of the power supply voltage amplitude when the power supply is 220V and 50Hz; the present invention realizes high-precision control of the output power and stable continuous output.

Description

Technical Field

[0001] The invention belongs to the technical field of electric ceramic stoves, and in particular relates to a power control method applied to electric ceramic stoves. Background Art

[0002] The common heating control method at present is to convert the AC voltage into a square wave signal with the same phase through a zero-crossing detection circuit. After sampling the square wave signal to obtain the AC voltage zero-crossing point, there are two ways to control the output power. The first is to control by AC cycle: using the AC cycle as the control time unit, for example, outputting 20% ​​of the power means that in 10 consecutive AC half cycles, only 2 half cycles are used to turn on the heating. Figure 1 The second type is zero-crossing delay control: the average output power in a single AC half cycle is controlled according to the output start delay time after the zero-crossing point, as shown in Figure 2 shown.

[0003] However, the above two control methods have the following technical defects:

[0004] Controlled by AC cycle: Control accuracy is difficult to improve. The higher the required accuracy, the longer the overall control cycle will be. The output state will be in the fully open or fully closed state for a long time, and the output power will be unstable.

[0005] According to the zero-crossing delay control method: the change of the power supply voltage cannot be monitored. When the power supply voltage fluctuates, the output power will also fluctuate. If the output power needs to be compensated according to the power supply voltage amplitude, an additional voltage divider sampling circuit needs to be added on the basis of the original zero-crossing detection circuit, which increases the production cost. Summary of the invention

[0006] The purpose of the present invention is to overcome the above-mentioned shortcomings of the prior art. The present invention provides a power control method applied to an electric ceramic stove. The present invention obtains voltage phase and amplitude information of a half AC cycle through a voltage sampling circuit, thereby achieving high-precision control of output power and stable continuous output.

[0007] In order to solve the above technical problems, the present invention provides a power control method applied to an electric ceramic stove, comprising the following steps:

[0008] Step S1: MCU detects the DC voltage division of the AC power supply voltage at the shortest fixed period to obtain a sampling value N;

[0009] Step S2, according to the time point T1 when the detected DC voltage is first higher than 0V and the time point T2 when the detected DC voltage is first lower than 0V in the AD AC detection cycle, the zero crossing point of the AC power supply signal and the half cycle of the sampling signal are obtained. ;

[0010] Step S3: The sum of all sampling values ​​N within the half cycle T is obtained as , take the average value of M of all half cycles T within 1 second , as a quantized value of the supply voltage amplitude;

[0011] Step S4: Measure the quantized value of the power supply voltage amplitude when the power supply is 220V and 50Hz ;

[0012] Step S5: Set the target power to be P and the maximum power to be , according to the current The power is compensated, and the output power after compensation is ;

[0013] Step S6: Cut-off time ratio And output power ratio The relationship between them is as follows:

[0014] ;

[0015] in is a fixed value, The value range is ; The value range is ;

[0016] Step S7: According to ,get , and then get the zero-crossing delay opening time required to control the thyristor ;

[0017] Step S8: Finally, after the zero crossing is detected, the delay time Turn on the bidirectional thyristor and output the target power P.

[0018] Preferably, in step S1, the AC power supply voltage is converted into DC by a voltage-dividing sampling circuit in the MCU, and the DC voltage signal is converted into a digital voltage value by an analog-to-digital conversion module ADC inside the MCU.

[0019] Preferably, the voltage divider sampling circuit includes: a diode D1, resistors R1~R2 and a capacitor C1; one end of the diode D1 is connected to the neutral line ACN, and the other end is connected to one end of the resistor R2, the other end of the resistor R2 is connected to one end of the resistor R1, one end of the capacitor C1 and the MCU_AD end, and the other ends of the resistor R1 and the capacitor C1 are connected to the live wire ACL and the MCU_GND end.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] On the one hand, the sampling circuit of the present invention uses very few devices and only occupies one MCU port, which can reduce production costs; on the other hand, all information on controlling power can be obtained through only one sampling circuit, and the output power is compensated according to the amplitude and phase of the supply voltage to make the output power output stable and accurate, and the possibility of safety accidents caused by voltage abnormalities can be reduced. Moreover, the power control method of the present invention has a wide range of application scenarios in the field of AC heating, and all heating devices that are directly driven by AC and controlled by bidirectional thyristor circuits can use this method. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of control according to AC cycle in the prior art.

[0023] Figure 2 It is a schematic diagram of zero-crossing delay control in the prior art.

[0024] Figure 3 The present invention is a flow chart of a power control method applied to an electric ceramic stove.

[0025] Figure 4 It is a hardware principle diagram of the voltage divider sampling circuit of the present invention.

[0026] Figure 5 This is a schematic diagram of the MCU sampling timing of the present invention.

[0027] Figure 6 It is a curve diagram showing the relationship between the cut-off time ratio and the output power ratio of the present invention. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description. It should be noted that the accompanying drawings are in very simplified form and in non-precise proportions, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0029] like Figure 3 As shown, the embodiment of the present invention provides a power control method applied to an electric ceramic stove. Since high-precision output control is required, the output power control is performed by zero-crossing delay control. Specifically, the method includes the following steps:

[0030] 1) The MCU detects the power supply voltage at a fixed period as short as possible to obtain a sampling value N.

[0031] 2) If Figure 5 As shown, according to the time point T1 when the detected DC voltage is first higher than 0V and the time point T2 when the detected DC voltage is first lower than 0V in the AD AC detection cycle, the zero crossing point of the sampling signal and the half cycle of the sampling signal are obtained. .

[0032] 3) Get the sum of all N in T time , take the average value of M of all half cycles within 1 second , as a quantized value of the supply voltage amplitude.

[0033] 4) Measure the quantized value of the power supply voltage amplitude when the power supply is 220V and 50Hz .

[0034] 5) Let the target power be P and the maximum power be , according to the current Compensate the power, and the proportion of power after compensation .

[0035] 6) Deadline ratio And output power ratio The relationship between them is as follows:

[0036] ;

[0037] in is a fixed value, The value range is ; The value range is .

[0038] 7) According to the relationship in 6) above, ,get , and then the zero-crossing delay opening time required to control the thyristor is obtained as ;

[0039] 8) Finally, after the zero-crossing point is detected, the bidirectional thyristor is turned on after a delay time t to output the target power P.

[0040] In the step S1, the AC power supply voltage is converted into DC through the voltage-dividing sampling circuit in the MCU, and the DC voltage signal is converted into a digital voltage value through the analog-to-digital conversion module ADC inside the MCU.

[0041] like Figure 4As shown, the voltage-dividing sampling circuit includes: a diode D1, resistors R1~R2 and a capacitor C1; one end of the diode D1 is connected to the neutral line ACN, and the other end is connected to one end of the resistor R2, the other end of the resistor R2 is connected to one end of the resistor R1, one end of the capacitor C1 and the MCU_AD terminal, and the other ends of the resistor R1 and the capacitor C1 are connected to the live line ACL and the MCU_GND terminal. The circuit filters out the negative voltage part in the AC power supply signal through the diode characteristics of D1, and then converts the large voltage into a small voltage that can be accepted by the MCU port through the voltage-dividing circuit composed of R1 and R2, and finally filters out the slight fluctuations of the circuit through C1 to obtain a relatively stable DC voltage-dividing signal.

[0042] like Figure 5 As shown in the figure, the time for AD AC detection is concentrated in the positive cycle of the AC power supply signal, and the MCU

[0043] After confirming the zero-crossing points T1 and T2, part of the negative cycle of the AC power supply signal is used to sample other signals and calibrate the ADC module. Figure 6 Figure 3 is the relationship between the cut-off time ratio and the output power ratio. It can be seen that the output power ratio decreases as the cut-off time ratio increases. In the range of the cut-off time being less than 20% and greater than 80%, the control accuracy of the output power is higher.

[0044] The above description is only a description of the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention. Any changes or modifications made by a person skilled in the art in the field of the present invention based on the above disclosure shall fall within the scope of protection of the claims.

Claims

1. A power control method for an electric ceramic stove, characterized in that: The steps include: Step S1: MCU detects the power supply voltage at the shortest fixed period to obtain a sampling value N; Step S2: According to the time point T1 when the DC voltage is first higher than 0V and the time point T2 when the DC voltage is first lower than 0V in the AD AC detection cycle, the zero crossing point of the sampling signal and the half cycle of the sampling signal are obtained. ; Step S3: Get the sum of all sampling values ​​N within the half cycle T time as , take the average value of M of all half cycles T within 1 second , as a quantized value of the supply voltage amplitude; Step S4: Measure the quantized value of the power supply voltage amplitude when the power supply is 220V and 50Hz ; Step S5: Set the target power to be P and the maximum power to be , according to the current The power is compensated, and the output power after compensation is ; Step S6: Cut-off time ratio And output power ratio The relationship between them is as follows: ； in is a fixed value, The value range is ; The value range is ; Step S7: According to ,get , and then get the zero-crossing delay opening time required to control the thyristor ; Step S8: Finally, after the zero crossing is detected, the delay time Turn on the bidirectional thyristor and output the target power P.

2. A power control method for an electric ceramic stove as claimed in claim 1, characterized in that: In the step S1, the AC power supply voltage is converted into DC through the voltage-dividing sampling circuit in the MCU, and the DC voltage signal is converted into a digital voltage value through the analog-to-digital conversion module ADC inside the MCU.

3. A power control method for an electric ceramic stove as claimed in claim 2, characterized in that: The voltage-dividing sampling circuit includes: a diode D1, resistors R1~R2 and a capacitor C1; one end of the diode D1 is connected to the neutral line ACN, and the other end is connected to one end of the resistor R2, the other end of the resistor R2 is connected to one end of the resistor R1, one end of the capacitor C1 and the MCU_AD end, and the other ends of the resistor R1 and the capacitor C1 are connected to the live wire ACL and the MCU_GND end.

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