CN106982485B

CN106982485B - Electromagnetic heating equipment and low-loss control device and method for IGBT (insulated Gate Bipolar transistor) tube

Info

Publication number: CN106982485B
Application number: CN201610029104.4A
Authority: CN
Inventors: 汪钊; 肖小龙; 李睿; 王彪
Original assignee: Foshan Shunde Midea Electrical Heating Appliances Manufacturing Co Ltd
Current assignee: Foshan Shunde Midea Electrical Heating Appliances Manufacturing Co Ltd
Priority date: 2016-01-15
Filing date: 2016-01-15
Publication date: 2020-11-20
Anticipated expiration: 2036-01-15
Also published as: CN106982485A

Abstract

The invention discloses a low-loss control method of an IGBT tube in electromagnetic heating equipment, which comprises the following steps: s1, detecting the zero crossing point of the alternating current input to the electromagnetic heating equipment; s2, judging whether the envelope voltage of the alternating current rises according to the zero crossing point, and increasing the duty ratio of a PWM signal for controlling the IGBT tube in each switching period of the IGBT tube until the envelope voltage reaches a peak voltage; and S3, when the envelope voltage reaches the peak voltage, the duty ratio of the PWM signal is reduced in each switching period of the IGBT tube. The method can reduce the turn-on loss of the IGBT tube, so that the electromagnetic heating equipment can continuously work under the condition of low power, and the hardware cost can be reduced. The invention also discloses a low-loss control device of the IGBT tube in the electromagnetic heating equipment and the electromagnetic heating equipment with the low-loss control device.

Description

Electromagnetic heating equipment and low-loss control device and method for IGBT (insulated Gate Bipolar transistor) tube

Technical Field

The invention relates to the technical field of electromagnetic heating, in particular to a low-loss control method of an IGBT (insulated gate bipolar transistor) tube in electromagnetic heating equipment, a low-loss control device of the IGBT tube in the electromagnetic heating equipment and the electromagnetic heating equipment with the low-loss control device.

Background

Under the condition of low-power heating of the current household electromagnetic heating equipment, if the turn-on voltage of an Insulated Gate Bipolar Transistor (IGBT) is high, the turn-on loss of the IGBT is large, the IGBT is easily subjected to overheat breakdown, and the continuous low-power heating range of the household electromagnetic heating equipment is narrow.

In the related art, the low-power schemes adopted by the household electromagnetic heating device mainly include two schemes of adjusting a resonant capacitor and a resonant inductor which participate in resonant operation, but the resonant circuits adopted by the two schemes are complex in structure and high in hardware cost.

Disclosure of Invention

The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. Therefore, an object of the present invention is to provide a low-loss control method for an IGBT tube in an electromagnetic heating device, which can reduce the turn-on loss of the IGBT tube, enable the electromagnetic heating device to continuously operate at low power, and reduce the hardware cost.

Another object of the present invention is to provide a low loss control device for IGBT tube in electromagnetic heating equipment. It is also an object of the invention to propose an electromagnetic heating device.

According to an embodiment of an aspect of the present invention, a low loss control method for an IGBT tube in an electromagnetic heating device is provided, including the following steps: s1, detecting the zero crossing point of the alternating current input to the electromagnetic heating equipment; s2, judging whether the envelope voltage of the alternating current rises according to the zero crossing point, and increasing the duty ratio of a PWM (Pulse Width Modulation) signal for controlling the IGBT in each switching period of the IGBT until the envelope voltage reaches a peak voltage; and S3, when the envelope voltage reaches the peak voltage, the duty ratio of the PWM signal is reduced in each switching period of the IGBT tube.

According to the low-loss control method of the IGBT tube in the electromagnetic heating equipment, envelope voltage change of alternating current is obtained by detecting the zero crossing point of the alternating current input to the electromagnetic heating equipment, when the envelope voltage of the alternating current rises, the duty ratio of a PWM signal is increased in each switching period of the IGBT tube until the envelope voltage reaches a peak voltage, then after the envelope voltage reaches the peak voltage, the duty ratio of the PWM signal is reduced in each switching period of the IGBT tube, so that the opening width of the IGBT tube is adjusted according to the periodic change of the envelope voltage, the IGBT tube is opened at a shorter opening degree when the envelope voltage is lower, the IGBT tube is opened at a longer width when the envelope voltage is higher, the opening loss of the IGBT tube can be reduced, the electromagnetic heating equipment can continuously work under the condition of low power, and the structure of a resonance circuit can be simplified, the hardware cost is greatly reduced.

According to an embodiment of the present invention, step S2 specifically includes: when the zero crossing point is detected, controlling a timer to start timing, and judging the timing time of the timer; if the timing time is greater than or equal to a first preset time and less than or equal to a second preset time, increasing the duty ratio of the PWM signal by a first preset step length in each switching period of the IGBT tube; and if the timing time is longer than the second preset time and shorter than a third preset time, increasing the duty ratio of the PWM signal by a second preset step length in each switching period of the IGBT tube, wherein the envelope voltage of the alternating current corresponding to the third preset time is equal to the peak voltage.

According to an embodiment of the present invention, step S3 specifically includes: if the timing time is greater than or equal to the third preset time and less than or equal to the fourth preset time, reducing the duty ratio of the PWM signal by a third preset step length in each switching period of the IGBT tube; and if the timing time is greater than the fourth preset time and less than a first time threshold, reducing the duty ratio of the PWM signal by a fourth preset step length in each switching period of the IGBT tube.

And when the timing time is greater than or equal to the first time threshold value, clearing the timer.

According to an embodiment of the present invention, the first preset step size, the second preset step size, the third preset step size and the fourth preset step size may all be equal.

According to the embodiment of the second aspect of the invention, a low loss control device for an IGBT tube in an electromagnetic heating apparatus is provided, which includes: a zero-crossing detection module for detecting a zero-crossing point of the alternating current input to the electromagnetic heating apparatus; the control module is connected with the zero-crossing detection module and used for increasing the duty ratio of a PWM signal for controlling the IGBT tube in each switching period of the IGBT tube when the envelope voltage of the alternating current is judged to be increased according to the zero-crossing point until the envelope voltage reaches a peak voltage, and reducing the duty ratio of the PWM signal in each switching period of the IGBT tube after the envelope voltage reaches the peak voltage.

According to the low-loss control device of the IGBT tube in the electromagnetic heating equipment, the envelope voltage change of the alternating current is obtained by detecting the zero crossing point of the alternating current input into the electromagnetic heating equipment through the zero-crossing detection module, when the envelope voltage of the alternating current rises, the duty ratio of the PWM signal is increased and controlled by the control module in each switching period of the IGBT tube until the envelope voltage reaches the peak voltage, then after the envelope voltage reaches the peak voltage, the duty ratio of the PWM signal is reduced by the control module in each switching period of the IGBT tube, so that the opening width of the IGBT tube is adjusted according to the periodic change of the envelope voltage, the IGBT tube is opened at a shorter opening when the envelope voltage is lower, and is opened at a longer width when the envelope voltage is higher, the opening loss of the IGBT tube can be reduced, and the electromagnetic heating equipment can continuously work under the condition of low power, and the structure of the resonant circuit can be simplified, and the hardware cost is greatly reduced.

According to an embodiment of the invention, the control module comprises a timer, wherein when the zero-crossing detection module detects the zero-crossing point, the timer starts to time, and the control module judges the timing time of the timer; if the timing time is greater than or equal to a first preset time and less than or equal to a second preset time, the control module increases the duty ratio of the PWM signal by a first preset step length in each switching period of the IGBT tube; if the timing time is longer than the second preset time and shorter than a third preset time, the control module increases the duty ratio of the PWM signal by a second preset step length in each switching period of the IGBT tube, wherein the envelope voltage of the alternating current corresponding to the third preset time is equal to the peak voltage.

According to an embodiment of the invention, if the timing time is greater than or equal to the third preset time and less than or equal to a fourth preset time, the control module decreases the duty ratio of the PWM signal by a third preset step length in each switching period of the IGBT tube; if the timing time is greater than the fourth preset time and less than the first time threshold, the control module reduces the duty ratio of the PWM signal by a fourth preset step length in each switching period of the IGBT tube.

And when the timing time is greater than or equal to the first time threshold, the control module clears the timer.

In addition, the embodiment of the invention also provides electromagnetic heating equipment which comprises the low-loss control device of the IGBT tube.

The electromagnetic heating equipment provided by the embodiment of the invention can adjust the opening width of the IGBT tube according to the periodic change of the envelope voltage, so that the IGBT tube is opened at a shorter opening degree when the envelope voltage is lower, and is opened at a longer width when the envelope voltage is higher, the opening loss of the IGBT tube can be reduced, the IGBT tube can continuously work under the condition of low power, the structure of a resonant circuit can be simplified, and the hardware cost is greatly reduced.

Drawings

Fig. 1 is a flowchart of a low loss control method for an IGBT tube in an electromagnetic heating apparatus according to an embodiment of the present invention;

fig. 2 is a schematic diagram of a rectified mains envelope according to an embodiment of the present invention;

FIG. 3A is a flow diagram of entering a zero-crossing interrupt, according to one embodiment of the present invention;

fig. 3B is a flow chart of an incoming IGBT transistor turn-on interrupt according to an embodiment of the present invention; and

fig. 4 is a block diagram illustrating a low loss control device of an IGBT tube in an electromagnetic heating apparatus according to an embodiment of the present invention.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.

The low-loss control method of the IGBT tube in the electromagnetic heating device, the low-loss control device of the IGBT tube in the electromagnetic heating device, and the electromagnetic heating device having the low-loss control device according to the embodiments of the present invention are described below with reference to the drawings.

Fig. 1 is a flowchart of a low loss control method for an IGBT tube in an electromagnetic heating apparatus according to an embodiment of the present invention. As shown in fig. 1, the low loss control method for the IGBT tube in the electromagnetic heating device includes the following steps:

and S1, detecting the zero crossing point of the alternating current input to the electromagnetic heating device.

The alternating current may be 220V alternating current mains.

In an embodiment of the present invention, a zero-crossing signal of the alternating current may be detected by a zero-crossing detection module to obtain a zero-crossing point, specifically, as shown in fig. 2 at time t1, the zero-crossing point is a zero-crossing point of the alternating current commercial power, and a curve in fig. 2 is an envelope of the commercial power after the commercial power is rectified, and corresponds to an envelope voltage of the alternating current.

And S2, judging whether the envelope voltage of the alternating current rises according to the zero crossing point, and increasing the duty ratio of the PWM signal for controlling the IGBT tube in each switching period of the IGBT tube until the envelope voltage reaches the peak voltage.

That is to say, in each half power cycle of the alternating current mains supply, from the zero crossing point, the envelope voltage of the alternating current gradually rises until the peak value is the voltage corresponding to the time t3 in fig. 2, and in the process of rising the envelope voltage, the duty ratio of the PWM signal is increased in each switching period, so as to increase the opening width of the IGBT tube, and thus the IGBT tube is opened with a longer width when the envelope voltage is higher.

And S3, when the envelope voltage reaches the peak voltage, reducing the duty ratio of the PWM signal in each switching period of the IGBT tube.

That is, from the peak value of the over-envelope voltage, the envelope voltage gradually decreases until the next zero-crossing point, for example, at the time t1 after t4 in fig. 2, during the decrease of the envelope voltage, the duty ratio of the PWM signal is reduced in each switching period, and the turn-on width of the IGBT tube is reduced, so that the IGBT tube is turned on with a shorter width when the envelope voltage is lower.

Therefore, in the embodiment of the present invention, a control module, such as an MCU (microcontroller), detects a zero crossing point of a mains envelope through a zero crossing detection module to detect a change of the mains envelope, the MCU controls a change of an IGBT tube opening width according to the change of the mains envelope, the MCU controls the IGBT tube to open with a PWM signal of a lower duty ratio when the envelope voltage of the mains periodically decreases to a lower level, and the MCU controls the IGBT tube to open with a PWM signal of a higher duty ratio when the envelope voltage of the mains is higher, so that an opening loss can be reduced, and the electromagnetic heating device can continuously operate at a lower power.

Specifically, according to an embodiment of the present invention, as shown in fig. 3A, the process of entering the zero-crossing interrupt includes the following steps:

s301, upon detection of a zero crossing, entering a zero crossing interrupt, e.g., generating a zero crossing interrupt every 10 ms.

And S302, starting a timer, wherein the timer starts to count time from 0, and the counted time is T.

S303, setting t1 < t2 < t3 < t4, where t1 is a first preset time, corresponding to the time t1 in fig. 2, for example, 0, t2 is a second preset time, corresponding to the time t2 in fig. 2, t3 is a third preset time, for example, 5ms, corresponding to the time t3 in fig. 2, and t4 is a fourth preset time, corresponding to the time t4 in fig. 2, and the first time threshold, for example, 10ms, corresponds to the time t1 after the time t4 in fig. 2.

And S304, returning.

As shown in fig. 3B, the flow of switching on and off the IGBT includes the following steps:

s401, switching on and interrupting the IGBT tube, generating the IGBT tube before the IGBT tube is switched on, switching on the IGBT tube once every time, and judging the timing time T of the timer.

S402, whether the timing time T is greater than or equal to T1 and less than or equal to T2 is judged. If yes, go to step S403; if not, step S404 is performed.

And S403, increasing the duty ratio of the PWM signal by a first preset step size m1, namely increasing the duty ratio of the PWM signal by m1, and then ending the process.

S404, judging whether the timing time T is more than T2 and less than T3. If yes, go to step S405; if not, step S406 is performed.

S405, increasing the duty ratio of the PWM signal by a second preset step size n1, namely increasing the duty ratio of the PWM signal by n1, and then ending the process. Wherein m1 and n1 may be equal or unequal. When m1 is equal to n1, the duty ratio of the control signal of the IGBT tube, namely the PWM signal, is gradually increased in the process of rising of the envelope voltage.

That is, according to an embodiment of the present invention, step S2 specifically includes: when the zero crossing point is detected, controlling a timer to start timing, and judging the timing time of the timer; if the timing time is greater than or equal to a first preset time and less than or equal to a second preset time, increasing the duty ratio of the PWM signal by a first preset step length in each switching period of the IGBT tube; and if the timing time is longer than the second preset time and shorter than a third preset time, increasing the duty ratio of the PWM signal by a second preset step length in each switching period of the IGBT tube, wherein the third preset time, namely the envelope voltage of the alternating current corresponding to the time t3, is equal to the peak voltage.

S406, whether the timing time T is greater than or equal to T3 and less than or equal to T4 is judged. If yes, go to step S407; if not, step S408 is performed.

S407, decreasing the duty ratio of the PWM signal by a third preset step m2, i.e. subtracting m2 from the duty ratio of the PWM signal, and ending the process.

S408, it is determined whether the counted time T is greater than T4 and less than the first time threshold, for example, 10 ms. If yes, go to step S409; if not, step S410 is performed.

And S409, reducing the duty ratio of the PWM signal by a fourth preset step size n2, namely subtracting n2 from the duty ratio of the PWM signal, and ending the process. Wherein m2 and n2 may be equal or unequal. When m2 is equal to n2, the duty ratio of the control signal of the IGBT tube, namely the PWM signal, is gradually reduced in the process of the envelope voltage reduction.

That is, according to an embodiment of the present invention, step S3 specifically includes: if the timing time is greater than or equal to the third preset time and less than or equal to the fourth preset time, reducing the duty ratio of the PWM signal by a third preset step length in each switching period of the IGBT tube; and if the timing time is greater than the fourth preset time and less than a first time threshold, reducing the duty ratio of the PWM signal by a fourth preset step length in each switching period of the IGBT tube, wherein the first time threshold corresponds to the next zero-crossing point moment.

S410, the timer is cleared, i.e., T is 0.

In one embodiment of the present invention, the first preset step size, the second preset step size, the third preset step size and the fourth preset step size may all be equal, that is, m 1-n 1-m 2-n 2. That is, each switching period controls the PWM signal to increase a certain duty ratio from the time point t1 to t3, and each switching period controls the PWM signal to decrease a certain duty ratio from the time point t3 to the next zero-crossing time.

The first preset step length, the second preset step length, the third preset step length and the fourth preset step length are all larger than or equal to 0.

Fig. 4 is a block diagram illustrating a low loss control device of an IGBT tube in an electromagnetic heating apparatus according to an embodiment of the present invention. As shown in fig. 4, the low loss control device 10 of the IGBT tube in the electromagnetic heating apparatus includes a zero-crossing detection module 100 and a control module 200, such as an MCU.

The zero-crossing detection module 100 is configured to detect a zero-crossing point of an alternating current input to the electromagnetic heating apparatus; the control module 200 is connected to the zero-crossing detection module 100, and the control module 200 is configured to increase a duty ratio of a PWM signal for controlling the IGBT in each switching period of the IGBT when it is determined that the envelope voltage of the alternating current rises according to a zero-crossing point until the envelope voltage reaches a peak voltage, and decrease the duty ratio of the PWM signal in each switching period of the IGBT by the control module 200 when the envelope voltage reaches the peak voltage.

That is to say, in each half power cycle of the alternating current mains supply, starting from a zero crossing point, the envelope voltage of the alternating current gradually rises until a peak value is a voltage corresponding to a time t3 in fig. 2, and in the process of rising the envelope voltage, the duty ratio of the PWM signal is increased in each switching cycle, so as to increase the opening width of the IGBT tube, so that the IGBT tube is opened with a longer width when the envelope voltage is higher; from the peak value of the over-envelope voltage, the envelope voltage gradually decreases until the next zero-crossing point, such as the time t1 after t4 in fig. 2, during the decreasing process of the envelope voltage, the duty ratio of the PWM signal is reduced in each switching period, and the turn-on width of the IGBT tube is reduced, so that the IGBT tube is turned on with a shorter width when the envelope voltage is lower.

Therefore, in the embodiment of the present invention, the control module 200, for example, an MCU (microcontroller), detects the zero crossing point of the mains power envelope through the zero crossing detection module 100 to detect the change of the mains power envelope, the MCU controls the change of the turn-on width of the IGBT tube according to the change of the mains power envelope, when the envelope voltage of the mains power periodically decreases to a low level, the MCU controls the IGBT tube to turn on with the PWM signal of a low duty ratio, and when the envelope voltage of the mains power is high, the MCU controls the IGBT tube to turn on with the PWM signal of a high duty ratio, so as to reduce the turn-on loss, and enable the electromagnetic heating device to continuously operate at a low power.

According to an embodiment of the present invention, the control module 200 includes a timer, wherein when the zero-crossing detection module 100 detects a zero-crossing point, the timer starts timing, and the control module 200 determines a timing time of the timer; if the timing time is greater than or equal to a first preset time and less than or equal to a second preset time, the control module 200 increases the duty ratio of the PWM signal by a first preset step length in each switching period of the IGBT; if the timing time is greater than the second preset time and less than a third preset time, the control module 200 increases the duty ratio of the PWM signal by a second preset step length in each switching period of the IGBT, where the envelope voltage of the alternating current corresponding to the third preset time is equal to the peak voltage.

If the timing time is greater than or equal to the third preset time and less than or equal to the fourth preset time, the control module 200 decreases the duty ratio of the PWM signal by a third preset step length in each switching period of the IGBT; if the timing time is greater than the fourth preset time and less than the first time threshold, the control module 200 decreases the duty ratio of the PWM signal by a fourth preset step length in each switching period of the IGBT.

And when the counted time is greater than or equal to the first time threshold, the control module 200 clears the timer, that is, T is 0.

Wherein the first preset step, the second preset step, the third preset step and the fourth preset step may all be equal, that is, m 1-n 1-m 2-n 2. That is, each switching period controls the PWM signal to increase a certain duty ratio from the time point t1 to t3, and each switching period controls the PWM signal to decrease a certain duty ratio from the time point t3 to the next zero-crossing time.

In addition, the embodiment of the invention also provides electromagnetic heating equipment which comprises the low-loss control device of the IGBT tube. The electromagnetic heating equipment can be household electromagnetic heating products such as an electromagnetic oven, an electromagnetic rice cooker or an electromagnetic pressure cooker.

In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the invention and to simplify the description, and are not intended to indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and are therefore not to be considered limiting of the invention.

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

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims

1. A low-loss control method for an IGBT tube in electromagnetic heating equipment is characterized by comprising the following steps:

s1, detecting the zero crossing point of the alternating current input to the electromagnetic heating equipment;

s2, judging whether the envelope voltage of the alternating current rises according to the zero crossing point, and increasing the duty ratio of a PWM signal for controlling the IGBT tube by preset step length in each switching period of the IGBT tube until the envelope voltage reaches the peak voltage; and

and S3, when the envelope voltage reaches the peak voltage, reducing the duty ratio of the PWM signal by a preset step length in each switching period of the IGBT tube.

2. The low-loss control method for the IGBT tube in the electromagnetic heating equipment according to claim 1, wherein the step S2 specifically comprises:

when the zero crossing point is detected, controlling a timer to start timing, and judging the timing time of the timer;

if the timing time is greater than or equal to a first preset time and less than or equal to a second preset time, increasing the duty ratio of the PWM signal by a first preset step length in each switching period of the IGBT tube;

and if the timing time is longer than the second preset time and shorter than a third preset time, increasing the duty ratio of the PWM signal by a second preset step length in each switching period of the IGBT tube, wherein the envelope voltage of the alternating current corresponding to the third preset time is equal to the peak voltage.

3. The low-loss control method for the IGBT tube in the electromagnetic heating equipment according to claim 2, wherein the step S3 specifically comprises:

if the timing time is greater than or equal to the third preset time and less than or equal to the fourth preset time, reducing the duty ratio of the PWM signal by a third preset step length in each switching period of the IGBT tube;

and if the timing time is greater than the fourth preset time and less than a first time threshold, reducing the duty ratio of the PWM signal by a fourth preset step length in each switching period of the IGBT tube.

4. The low loss control method for the IGBT tube in the electromagnetic heating equipment according to claim 3, characterized in that the timer is cleared when the timed time is greater than or equal to the first time threshold.

5. The low loss control method for the IGBT tube in the electromagnetic heating equipment according to claim 3, wherein the first preset step length, the second preset step length, the third preset step length and the fourth preset step length are all equal.

6. A low-loss control device for an IGBT tube in electromagnetic heating equipment is characterized by comprising:

a zero-crossing detection module for detecting a zero-crossing point of the alternating current input to the electromagnetic heating apparatus;

the control module is connected with the zero-crossing detection module and used for increasing the duty ratio of the PWM signal for controlling the IGBT tube by a preset step length in each switching period of the IGBT tube when the envelope voltage of the alternating current is judged to be increased according to the zero-crossing point until the envelope voltage reaches the peak voltage, and reducing the duty ratio of the PWM signal by the preset step length in each switching period of the IGBT tube after the envelope voltage reaches the peak voltage.

7. The low loss control device of IGBT tube in electromagnetic heating equipment of claim 6, characterized in that, the control module comprises a timer, wherein,

when the zero-crossing detection module detects the zero-crossing point, the timer starts timing, and the control module judges the timing time of the timer;

if the timing time is greater than or equal to a first preset time and less than or equal to a second preset time, the control module increases the duty ratio of the PWM signal by a first preset step length in each switching period of the IGBT tube;

if the timing time is longer than the second preset time and shorter than a third preset time, the control module increases the duty ratio of the PWM signal by a second preset step length in each switching period of the IGBT tube, wherein the envelope voltage of the alternating current corresponding to the third preset time is equal to the peak voltage.

8. Low loss control device for IGBT tubes in an electromagnetic heating apparatus according to claim 7,

if the timing time is greater than or equal to the third preset time and less than or equal to the fourth preset time, the control module reduces the duty ratio of the PWM signal by a third preset step length in each switching period of the IGBT tube;

if the timing time is greater than the fourth preset time and less than the first time threshold, the control module reduces the duty ratio of the PWM signal by a fourth preset step length in each switching period of the IGBT tube.

9. The low loss control device of an IGBT tube in an electromagnetic heating equipment according to claim 8, characterized in that when the timed time is greater than or equal to the first time threshold, the control module clears the timer.

10. The device for controlling low loss of IGBT in electromagnetic heating equipment according to claim 8, characterized in that said first preset step length, said second preset step length, said third preset step length and said fourth preset step length are all equal.

11. Electromagnetic heating equipment, characterized by comprising a low-loss control device of an IGBT tube according to any of claims 6-10.