CN106993348B - Microwave oven magnetron power supply control method with pull-up active clamping branch - Google Patents

Microwave oven magnetron power supply control method with pull-up active clamping branch Download PDF

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CN106993348B
CN106993348B CN201710400455.6A CN201710400455A CN106993348B CN 106993348 B CN106993348 B CN 106993348B CN 201710400455 A CN201710400455 A CN 201710400455A CN 106993348 B CN106993348 B CN 106993348B
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voltage
power
frequency
power supply
circuit
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CN106993348A (en
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王春芳
李震
魏芝浩
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Qingdao University
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Qingdao University
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/66—Circuits
    • H05B6/664—Aspects related to the power supply of the microwave heating apparatus
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
    • H02M3/33523—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters with galvanic isolation between input and output of both the power stage and the feedback loop
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/4815—Resonant converters
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B2206/00—Aspects relating to heating by electric, magnetic, or electromagnetic fields covered by group H05B6/00
    • H05B2206/04—Heating using microwaves
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

The invention belongs to the technical field of electricity, and relates to a microwave oven magnetron power supply control method with a pull-up active clamping branch, which comprises the steps of initializing a single chip microcomputer program and receiving a corresponding microwave firepower combination and corresponding action time thereof; then judging whether a working key is pressed, adjusting the output power through constant power control during working, and firstly setting the corresponding power according to the output microwave fire power; then sending the detected voltage and current signals to a single chip microcomputer, and calculating by the single chip microcomputer to obtain input power; finally, the switching frequency of the power supply device is adjusted by comparing the input power with the set power, and the main switching tube and the auxiliary switching tube realize soft switching control through the control and adjustment of the single chip microcomputer, and the single chip microcomputer judges whether the corresponding firepower action time is finished or not at any moment in the working process; the circuit structure that it adopted is simple, and is with low costs, and the reliability is high, and is efficient, can change output voltage and power on a large scale and the accurate of miniverranging, and application prospect is extensive.

Description

Microwave oven magnetron power supply control method with pull-up active clamping branch
The technical field is as follows:
the invention belongs to the technical field of electricity, and relates to a microwave oven magnetron power supply control method with an active clamping circuit, in particular to a microwave oven magnetron power supply control method with a pull-up active clamping branch.
Background art:
at present, a magnetron power supply circuit of a household variable frequency microwave oven generally adopts an LLC resonance half-bridge inverter circuit topology or an LC resonance single-tube bipolar inverter circuit topology, and the LLC resonance half-bridge inverter circuit topology or the LC resonance single-tube bipolar inverter circuit topology has the problems of relatively complex circuit structure, relatively high power supply cost, easy direct connection and burning of upper and lower switch tubes of a bridge arm and the like; although the latter has the advantages of simple circuit structure, low cost, high efficiency, capability of realizing zero-voltage switching-on and zero-voltage switching-off control and the like, the latter also has some defects when the input voltage of the microwave oven is 220VacWhen the power supply is supplied with a 50Hz alternating current, the withstand voltage of a switching tube of the microwave oven is over 1200V in the operation process, so that the switching tube can only select an insulated gate field effect transistor (IGBT) with higher withstand voltage, the switching frequency of a single IGBT tube is required to be subjected to variable frequency modulation from 20kHz to 40kHz for linearly adjusting the output power of the magnetron, and after the switching frequency of the IGBT is more than 25kHz, the loss of the IGBT tube is increased along with the increase of the switching frequency, thereby restricting the further increase of the switching frequency, not further reducing the volume and the cost of the power supply device, and being not beneficial to the novel micro-switchThe popularization and application of the magnetron power supply of the wave oven. Therefore, the novel microwave oven magnetron power supply control method with the pull-up active clamping branch has application and development values.
The invention content is as follows:
the invention aims to overcome the defects of the prior art, a pull-up active clamping branch is added in an LC resonance single-tube bipolar inverter circuit topology for a magnetron power supply of a variable frequency microwave oven, the branch comprises an auxiliary switching tube, the switching frequencies of the main switching tube and the auxiliary switching tube are the same, soft switching control can be realized, no direct connection problem exists between the two tubes, and the reliability is improved; and under the condition of keeping the advantages of the original circuit, the withstand voltage of the switching tube is reduced to 2/3, a metal oxide transistor (MOSFET) can be used as the switching tube, the switching frequency can reach over 100kHz, and meanwhile, the technical scheme is provided for reducing the volume and the weight of the power supply and reducing the cost of the power supply due to the short conduction time and the low power consumption of the auxiliary switching tube.
In order to achieve the purpose, the invention is realized by adopting a magnetron power supply device of a microwave oven with a pull-up active clamping branch, and the specific control process comprises the following steps:
(1) the circuit is powered on, a single chip microcomputer program is initialized, and a corresponding microwave fire power combination and corresponding action time thereof transmitted by a microwave oven function menu or a manual setting signal are received; then judging whether a working key is pressed, if not, entering a standby state and detecting whether the working key is pressed, and if so, entering PWM (pulse width modulation) initialization; after PWM initialization, the single chip microcomputer sets the switching frequency and the PWM signal corresponding to each microwave fire according to the microwave fire combination and the corresponding action time of the microwave fire combination, and firstly outputs the switching frequency and the PWM signal corresponding to the first microwave fire in the microwave fire combination, and at the moment, the power supply device starts to work;
(2) when the power supply device works, the output power is adjusted through constant power control, and the corresponding power is set according to the output microwave firepower; then, the detected voltage and current signals are sent to a single chip microcomputer through an input voltage and current detection circuit, and the single chip microcomputer obtains input power by calculating the product of the input voltage and the input current; finally, the switching frequency of the power supply device is adjusted by comparing the input power with the set power, if the input power is greater than the set power, the single chip microcomputer reduces the output power by increasing the switching frequency, and if the input power is less than the set power, the single chip microcomputer increases the output power by reducing the switching frequency, so that the constant power control of the power supply device is realized; meanwhile, in the working process of the power supply device, the main switching tube and the auxiliary switching tube are controlled and adjusted by the single chip microcomputer to realize soft switching control, when the first voltage detection circuit detects that the voltage at the two ends of the clamping capacitor is increased, the single chip microcomputer changes the control signal of the auxiliary switching tube into high level, and the auxiliary switching tube realizes zero voltage switching-on; before the rising edge of the driving signal of the current main switching tube comes, the second voltage detection circuit detects the voltage values at the two ends of the drain source of the main switching tube, if the voltage at the two ends of the drain source of the main switching tube is not 0, namely zero voltage switching-on is not realized, the duty ratio of the main switching tube is reduced by the single chip microcomputer, and if the voltage at the two ends of the drain source of the main switching tube is 0, namely zero voltage switching-on is realized, the duty ratio of the main switching tube is not changed;
(3) the single chip microcomputer constantly judges whether the corresponding firepower action time is finished in the working process of the power supply device, and if not, the current switching frequency and the PWM signal are continuously maintained; if the microwave heating power is finished, judging whether the microwave heating power is the last microwave heating power, if not, outputting the switching frequency and the PWM signal corresponding to the next microwave heating power, and repeating the steps; if so, outputting a PWM blocking signal, blocking PWM output, and stopping the power supply device; when the program is running, it can detect that the end key is pressed or not, if it is not, the normal operation of the program is not changed, if it is, the PWM blocking signal can be directly entered, and the power supply device can be stopped to implement control of magnetron power supply of microwave oven.
The main structure of the magnetron power supply device of the microwave oven with the pull-up active clamping branch circuit comprises a rectifier bridge and an L1C1The circuit comprises a filter circuit, a sampling circuit, a pull-up active clamping branch circuit, a resonant capacitor, a main switching tube, a first diode, a high-frequency transformer, a high-frequency voltage doubling rectifying circuit, a discharge resistor, a magnetron, a control circuit and a first diodeThe diode is an anti-parallel diode of a main switching tube, and single-phase power frequency alternating current sequentially passes through a rectifier bridge and an L1C1The filter circuit is converted into direct current, the direct current is inverted into high-frequency alternating current by the main switch tube, the first diode and the pull-up active clamping branch circuit, the high-frequency alternating current is applied to two ends of a primary winding of the high-frequency transformer, after the voltage of the high-frequency transformer is boosted, two ends of a secondary winding of the high-frequency transformer generate high-frequency high-voltage alternating current, and the high-frequency high-voltage alternating current supplies power to the magnetron after passing through the high-frequency voltage doubling rectifying circuit; the alternating current generated by the filament winding on the secondary side of the high-frequency transformer directly supplies power for the magnetron filament; rectifying bridge rectifies single-phase power frequency alternating current L1C1The filter circuit is formed by electrically connecting a filter inductor and a filter capacitor and is used for power frequency filtering; the sampling circuit is formed by electrically connecting a first sampling resistor, a second sampling resistor and a current transformer, and the sampling circuit and an input voltage and current detection circuit of the control circuit are used for detecting input voltage and current; the pull-up active clamping branch circuit is formed by electrically connecting a clamping capacitor, an auxiliary switching tube and a second diode according to an electrical principle, the second diode is an anti-parallel diode of the auxiliary switching tube, a source electrode of the auxiliary switching tube is connected with a drain electrode of the main switching tube, one end of the clamping capacitor is connected with the drain electrode of the auxiliary switching tube, and the other end of the clamping capacitor is connected with an anode of the filter capacitor; when the power supply device is connected to 220VacWhen the voltage rises to the sum of the voltage of the filter capacitor and the voltage of the clamping capacitor, the voltage at the two ends of the drain source of the main switching tube is clamped at the two ends of the filter capacitor and the clamping capacitor, so that the withstand voltage of the main switching tube is reduced; the resonance capacitor is connected in parallel with the primary winding of the high-frequency transformer, and under the switching-on and switching-off changes of the main switching tube, the resonance capacitor resonates with the inductance of the primary winding to realize high-frequency inversion; the high-frequency transformer is formed by electrically connecting a primary winding, a secondary winding, a filament winding and a magnetic core with an air gap, the primary and secondary coupling coefficients of the high-frequency transformer are 0.5-0.95, the secondary winding is connected with a high-frequency voltage doubling rectifying circuit, the filament winding is connected with a filament of the magnetron to provide alternating current power supply for the magnetron, and the high-frequency transformer boosts the primary high-frequency alternating current and realizes electrical supply at the same time of boosting the primary high-frequency alternating currentIsolating; the high-frequency voltage-multiplying rectification circuit is formed by electrically connecting a first high-voltage rectification diode, a second high-voltage rectification diode, a first filter capacitor and a second filter capacitor, and supplies power to a magnetron after voltage-multiplying rectification and filtering are carried out on the voltage output by a secondary winding of the high-frequency transformer by the high-frequency voltage-multiplying rectification circuit; the discharge resistor provides a discharge loop for the first filter capacitor and the second filter capacitor; the magnetron is used for generating microwaves; the control circuit is formed by electrically connecting an input voltage and current detection circuit, a first voltage detection circuit, a second voltage detection circuit, a microwave oven function menu or manual setting signal, a single chip microcomputer, a driving circuit and an auxiliary power supply, wherein the input voltage and current detection circuit is used for detecting input voltage and current, and the single chip microcomputer is used for adjusting frequency according to detection data so as to change output voltage and realize constant power control; the first voltage detection circuit detects voltages at two ends of the clamping capacitor, when the voltages at the two ends of the clamping capacitor are detected to be increased, the single chip microcomputer changes a control signal of the auxiliary switching tube into a high level, the auxiliary switching tube is turned on at zero voltage, when the voltages at the two ends of the clamping capacitor are increased, the primary winding charges the clamping capacitor through the second diode, the second diode is turned on, and the voltages at the two ends of the drain source of the auxiliary switching tube are zero; the second voltage detection circuit detects the voltage at two ends of the drain and the source of the main switching tube; the microwave oven function menu or the manual setting signal provides the microwave fire power combination and the corresponding action time for the singlechip; the driving circuit drives the main switch tube and the auxiliary switch tube to be switched on and off under the control of the single chip microcomputer; the auxiliary power supply supplies power to the singlechip and the drive circuit.
Compared with the prior art, the high-frequency transformer of the power supply device can realize bidirectional excitation, so that the power supply device can output larger power; the main switch tube and the auxiliary switch tube have the same switching frequency, the direct connection problem does not exist, the soft switching can be realized, the auxiliary switch tube is only conducted for a short time in each switching period, and the conduction loss is greatly reduced; the high-frequency voltage-doubling rectifying circuit cascaded to the secondary side of the transformer enables asymmetric voltage output by the secondary side winding of the transformer to be effectively utilized, and the overall efficiency of the power supply device is further improved; the resonance capacitor connected in parallel on the primary side of the transformer resonates with the inductance of the primary side winding of the transformer, so that a higher voltage gain is provided between the output and the input of the power supply device, and under the condition that the turn ratio of the transformer is certain, the output voltage amplitude can be instantly improved through pulse frequency modulation, so that the magnetron of the variable frequency microwave oven can be quickly started; the clamping action of the pull-up active clamping branch circuit enables the withstand voltage of the main switching tube to be reduced by 1/3, the main switching tube and the auxiliary switching tube can adopt MOSFETs as switches, the switching frequency of the main switching tube and the auxiliary switching tube can reach more than 100kHz, the size and the weight of the power supply device are further reduced, and the cost of the power supply device is reduced; the circuit has the advantages of simple structure, low cost, high reliability and high efficiency, can accurately change the output voltage and power in a large range and a small range by a control method combining pulse width modulation and pulse frequency modulation, and has wide application prospect.
Description of the drawings:
FIG. 1 is a schematic diagram of the main circuit structure of the magnetron power supply device of a microwave oven with a pull-up active clamping branch according to the present invention.
Fig. 2 is a process flow diagram for implementing the control of the magnetron power supply device of the microwave oven with the pull-up active clamping branch according to the invention.
FIG. 3 is a waveform diagram illustrating the operation of a magnetron power supply apparatus for a microwave oven with a pull-up active clamp branch according to the present invention, wherein Ugs1As a main switch tube Q1Driving voltage of Ugs2For auxiliary switching tube Q2Driving voltage of Uds1As a main switch tube Q1Voltage across drain and source, Uds2For auxiliary switching tube Q2Voltage across drain and source, UC3Is a resonant capacitor C3Voltage across, IL2Is a primary winding L2Current of UC2Is a clamping capacitor C2The voltage across the terminals.
The specific implementation mode is as follows:
the technical solution of the present invention will be described in further detail with reference to the accompanying drawings and specific embodiments
Example (b):
the main structure of the magnetron power supply device of the microwave oven with the pull-up active clamping branch circuit comprises a rectifier bridge 1 and an L1C1Filter circuitWay 2, sampling circuit 3, pull-up active clamping branch 4 and resonant capacitor C3Main switch tube Q1A first diode VD1A high-frequency transformer 5, a high-frequency voltage-doubling rectifying circuit 6, and a discharge resistor R3A magnetron 7 and a control circuit 8, a first diode VD1As a main switch tube Q1The single-phase power frequency alternating current passes through the rectifier bridge 1 and the rectifier bridge L in sequence1C1The filter circuit 2 is then converted into direct current, and the main switch tube Q1A first diode VD1And a pull-up active clamping branch circuit 4 inverts the direct current into high-frequency alternating current, and the high-frequency alternating current is applied to a primary winding L of a high-frequency transformer 52Two ends of the secondary winding L of the high-frequency transformer 5 are boosted by the transformer3Two ends generate high-frequency high-voltage alternating current which supplies power to the magnetron 7 after passing through the high-frequency voltage doubling rectifying circuit 6; filament winding L of secondary side of high-frequency transformer 54The generated alternating current directly supplies power for the magnetron filament; the rectifier bridge 1 rectifies the single-phase power frequency alternating current, L1C1The filter circuit 2 is composed of a filter inductor L1And a filter capacitor C1The electric connection component is used for power frequency filtering; the sampling circuit 3 is composed of a first sampling resistor R1A second sampling resistor R2And current transformer CT1The sampling circuit 3 and the input voltage and current detection circuit 81 of the control circuit 8 are used together for detecting the input voltage and current; the pull-up active clamping branch 4 is composed of a clamping capacitor C2Auxiliary switch tube Q2And a second diode VD2Electrically connected according to the electrical principle, a second diode VD2For auxiliary switching tube Q2The anti-parallel diode and the auxiliary switch tube Q2Source and main switch tube Q1Drain connected, clamping capacitor C2One end of the auxiliary switch tube Q2The drain electrode is connected with the filter capacitor C1The positive electrodes of the two electrodes are connected; when the power supply device is connected to 220VacAC power supply and control circuit power-on, main switch tube Q1After being turned off, the main switch tube Q1The voltage at the two ends of the drain and the source is gradually increased, and when the voltage is increased to the filter capacitor C1And a clamp capacitor C2Main switch tube for voltage summationQ1The voltage at the two ends of the drain and the source is clamped on a filter capacitor C1And a clamp capacitor C2Two ends, lower the main switch tube Q1Pressure resistance; resonant capacitor C3Primary winding L of high-frequency transformer 52In parallel on the main switch tube Q1Under the on/off change of the capacitor C3And a primary winding L2The inductance of the inverter generates resonance to realize high-frequency inversion; the high-frequency transformer 5 is composed of a primary winding L2Secondary winding L3Filament winding L4Is electrically connected with a magnetic core T with an air gap, the primary side coupling coefficient and the secondary side coupling coefficient of the high-frequency transformer 5 are 0.5-0.95, and a secondary side winding L3A high-frequency voltage doubling rectifying circuit 6 and a filament winding L are connected4The high-frequency transformer 5 boosts the primary high-frequency alternating current and simultaneously realizes electrical isolation; the high-frequency voltage-multiplying rectifying circuit 6 is composed of a first high-voltage rectifying diode VD3A second high-voltage rectifier diode VD4A first filter capacitor C4And a second filter capacitor C5Electrically connected, a high-frequency voltage-doubling rectifying circuit 6 is used for winding the secondary winding L of the high-frequency transformer 53The output voltage is subjected to voltage doubling rectification and filtering and then supplies power to the magnetron 7; discharge resistor R3Is a first filter capacitor C4And a second filter capacitor C5Providing a discharge loop; the magnetron 7 is used for generating microwave; the control circuit 8 is formed by electrically connecting an input voltage and current detection circuit 81, a first voltage detection circuit 82, a second voltage detection circuit 83, a microwave oven function menu or manual setting signal 84, a single chip microcomputer 85, a drive circuit 86 and an auxiliary power supply 87, wherein the input voltage and current detection circuit 81 is used for detecting input voltage and current, and the single chip microcomputer 85 carries out frequency adjustment according to detection data so as to change output voltage and realize constant power control; the first voltage detection circuit 82 detects the clamp capacitor C2Voltage across the clamp capacitor C when detected2When the voltage at the two ends is increased, the singlechip 85 will assist the switch tube Q2The control signal of (2) becomes high level, and the auxiliary switch tube Q2Realize zero voltage turn-on when clamping capacitor C2When the voltage at both ends increases, the primary winding L2Through a second diode VD2Is a clamping capacitor C2Charging, second diode VD2Conducting auxiliary switch tube Q2The voltage across the drain and source is zero; the second voltage detection circuit 83 detects the main switch tube Q1Voltage across the drain and source; a microwave oven function menu or manual setting signal 84 provides a microwave fire combination and corresponding action time for the singlechip 85; the driving circuit 86 drives the main switching tube Q under the control of the singlechip 851And an auxiliary switching tube Q2Make-and-break; the auxiliary power supply 87 supplies power to the single chip 85 and the drive circuit 86.
The process for realizing the control of the magnetron power supply device of the microwave oven with the pull-up active clamping branch comprises the following steps:
(1) the circuit is powered on, a single chip microcomputer program is initialized, and a corresponding microwave fire power combination and corresponding action time thereof transmitted by a microwave oven function menu or a manual setting signal 84 are received; then judging whether a working key is pressed, if not, entering a standby state and detecting whether the working key is pressed, and if so, entering PWM (pulse width modulation) initialization; after the PWM initialization, the single chip microcomputer 85 sets the switching frequency and the PWM signal corresponding to each microwave fire according to the microwave fire combination and the corresponding action time thereof, and first outputs the switching frequency and the PWM signal corresponding to the first microwave fire in the microwave fire combination, at this time, the power supply apparatus starts to operate;
(2) when the power supply device works, the output power is adjusted through constant power control, and the corresponding power is set according to the output microwave firepower; then, the detected voltage and current signals are sent to the single chip microcomputer 85 through the input voltage and current detection circuit 81, and the single chip microcomputer 85 calculates the product of the input voltage and the input current to obtain the input power; finally, the switching frequency of the power supply device is adjusted by comparing the input power with the set power, if the input power is greater than the set power, the single chip microcomputer 85 reduces the output power by increasing the switching frequency, and if the input power is less than the set power, the single chip microcomputer 85 increases the output power by reducing the switching frequency, so that the constant power control of the power supply device is realized; meanwhile, in the working process of the power supply device, the main switching tube Q is controlled and adjusted by the singlechip 851And an auxiliary switching tube Q2Soft switching control is realized, and the first voltage detection circuit 82 detects the clamping capacitor C2When the voltage at the two ends is increased, the singlechip 85 will assist the switch tube Q2The control signal of (2) becomes high level, and the auxiliary switch tube Q2Realizing zero voltage switching-on; at the present main switch tube Q1Before the rising edge of the driving signal comes, the second voltage detection circuit 83 detects the main switch tube Q1Voltage value at both ends of drain-source, if the main switch tube Q1If the voltage across the drain and source is not 0, i.e. zero voltage turn-on is not realized, the single chip 85 reduces the main switch tube Q1If the main switching tube Q1When the voltage at two ends of the drain source is 0, namely zero voltage opening is realized, the main switch tube Q1The duty cycle of (d) is not changed;
(3) the single chip microcomputer 85 constantly judges whether the corresponding firepower action time is finished in the working process of the power supply device, and if not, the current switching frequency and the PWM signal are continuously maintained; if the microwave heating power is finished, judging whether the microwave heating power is the last microwave heating power, if not, outputting the switching frequency and the PWM signal corresponding to the next microwave heating power, and repeating the steps; if so, outputting a PWM blocking signal, blocking PWM output, and stopping the power supply device; when the program is running, it can detect that the end key is pressed or not, if it is not, the normal operation of the program is not changed, if it is, the PWM blocking signal can be directly entered, and the power supply device can be stopped to implement control of magnetron power supply device of microwave oven.
The working waveform diagram of the magnetron power supply device of the microwave oven with the pull-up active clamping branch circuit comprises the following stages:
t0-t1time period: at t0Time, main switch tube Q1Drive voltage U ofgs1Becomes high level when the primary winding L2The current of (1) is negative, the main switch tube Q1Non-conductive, primary winding L2Through a first diode VD1And a filter capacitor C1Follow current, main switch tube Q1Withstand voltage of 0 to t1Time of day, primary winding L2Becomes 0, the main switch tube Q1Is conducted to realize the mainSwitch tube Q1Zero voltage turn-on;
t1-t2time period: input voltage is primary winding L2Charging, primary winding L2Gradually increases to t2Time, main switch tube Q1Drive voltage U ofgs1Become low level, the main switch tube Q1Turning off;
t2-t3time period: resonant capacitor C3Is a primary winding L2Charging, primary winding L2Continues to increase until t3Time of day, resonant capacitance C3Is reduced to 0, the primary winding L2To a maximum;
t3-t4time period: primary winding L2Reverse is resonance capacitor C3Charging and resonance capacitor C3Is increased in the reverse direction of the voltage of the resonant capacitor C3Is less than the clamping capacitor C2Voltage of the second diode VD2Reverse cut-off to t4Time of day, resonant capacitance C3Is higher than the clamping capacitor C2Voltage of the second diode VD2Conducting;
t4-t5time period: primary winding L2While being a clamping capacitor C2And a resonance capacitor C3Charging, clamping capacitor C2Gradually increases until t5Time-of-day auxiliary switch tube Q2Drive voltage U ofgs2Goes high but the primary winding L2The current of (1) is still positive, the auxiliary switch tube Q2Is not conducted;
t5-t6time period: primary winding L2Continue to be a clamp capacitor C2And a resonance capacitor C3Charging, second diode VD2Conducting auxiliary switch tube Q2The voltage across is 0 to t6Time of day, primary winding L2Current of (1) is reduced to 0, and the clamping capacitor C2Is increased to a maximum while the resonant capacitor C is turned on3Is increased in the reverse direction to the maximum, resonant capacitance C3Starting with the primary winding L2Reverse charging, at this time resonant capacitor C3Voltage less than clamp capacitor C2Voltage of, auxiliary switching tube Q2Is conducted to realize the auxiliary switch tube Q2Zero voltage turn-on;
t6-t7time period: clamping capacitor C2Is a primary winding L2Reverse charging to t7Time-of-day auxiliary switch tube Q2Drive voltage U ofgs2Becomes low level and assists the switch tube Q2Turn-off, clamping capacitor C2Stopping as a primary winding L2Charging;
t7-t8time period: resonant capacitor C3Voltage reduction of primary winding L2Is reduced to t8Time of day, resonant capacitance C3Becomes 0;
t8-t9time period: primary winding L2Is a resonant capacitor C3Reverse charging, resonant capacitor C3Gradually increases until t9Time of day, resonant capacitance C3Is added to the filter capacitor C1Are equal;
t9-t10time period: primary winding L2Through a first diode VD1And a filter capacitor C1Follow current to t10Time, main switch tube Q1Drive voltage U ofgs1Becomes high level when the primary winding L2The current of (1) is negative, the main switch tube Q1And is not conductive.

Claims (2)

1. A microwave oven magnetron power supply control method with a pull-up active clamping branch is characterized in that: the method is realized by adopting a magnetron power supply device of the microwave oven with a pull-up active clamping branch, and the specific control process comprises the following steps:
(1) the circuit is powered on, a single chip microcomputer program is initialized, and a corresponding microwave fire power combination and corresponding action time thereof transmitted by a microwave oven function menu or a manual setting signal are received; then judging whether a working key is pressed, if not, entering a standby state and detecting whether the working key is pressed, and if so, entering PWM (pulse width modulation) initialization; after PWM initialization, the single chip microcomputer sets the switching frequency and the PWM signal corresponding to each microwave fire according to the microwave fire combination and the corresponding action time of the microwave fire combination, and firstly outputs the switching frequency and the PWM signal corresponding to the first microwave fire in the microwave fire combination, and at the moment, the power supply device starts to work;
(2) when the power supply device works, the output power is adjusted through constant power control, and the corresponding power is set according to the output microwave firepower; then, the detected voltage and current signals are sent to a single chip microcomputer through an input voltage and current detection circuit, and the single chip microcomputer obtains input power by calculating the product of the input voltage and the input current; finally, the switching frequency of the power supply device is adjusted by comparing the input power with the set power, if the input power is greater than the set power, the single chip microcomputer reduces the output power by increasing the switching frequency, and if the input power is less than the set power, the single chip microcomputer increases the output power by reducing the switching frequency, so that the constant power control of the power supply device is realized; meanwhile, in the working process of the power supply device, the main switching tube and the auxiliary switching tube are controlled and adjusted by the single chip microcomputer to realize soft switching control, when the first voltage detection circuit detects that the voltage at the two ends of the clamping capacitor is increased, the single chip microcomputer changes the control signal of the auxiliary switching tube into high level, and the auxiliary switching tube realizes zero voltage switching-on; before the rising edge of the driving signal of the current main switching tube comes, the second voltage detection circuit detects the voltage values at the two ends of the drain source of the main switching tube, if the voltage at the two ends of the drain source of the main switching tube is not 0, namely zero voltage switching-on is not realized, the duty ratio of the main switching tube is reduced by the single chip microcomputer, and if the voltage at the two ends of the drain source of the main switching tube is 0, namely zero voltage switching-on is realized, the duty ratio of the main switching tube is not changed;
(3) the single chip microcomputer constantly judges whether the corresponding firepower action time is finished in the working process of the power supply device, and if not, the current switching frequency and the PWM signal are continuously maintained; if the microwave heating power is finished, judging whether the microwave heating power is the last microwave heating power, if not, outputting the switching frequency and the PWM signal corresponding to the next microwave heating power, and repeating the steps; if so, outputting a PWM blocking signal, blocking PWM output, and stopping the power supply device; when the program is running, it can detect that the end key is pressed or not, if it is not, the normal running of the program is not changed, if it is, the PWM blocking signal can be directly outputted, and the power supply device can be stopped to implement control of magnetron power supply of microwave oven.
2. A magnetron power supply control method for a microwave oven with a pull-up active clamp branch as claimed in claim 1, characterized in that: the main structure of the magnetron power supply device of the microwave oven with the pull-up active clamping branch comprises a rectifier bridge and an L1C1The single-phase power frequency alternating current power supply device comprises a filter circuit, a sampling circuit, a pull-up active clamping branch circuit, a resonant capacitor, a main switch tube, a first diode, a high-frequency transformer, a high-frequency voltage doubling rectifying circuit, a discharge resistor, a magnetron and a control circuit, wherein the first diode is an anti-parallel diode of the main switch tube, and single-phase power frequency alternating current sequentially passes through a rectifying bridge and an L voltage doubling rectifying circuit1C1The filter circuit is converted into direct current, the direct current is inverted into high-frequency alternating current by the main switch tube, the first diode and the pull-up active clamping branch circuit, the high-frequency alternating current is applied to two ends of a primary winding of the high-frequency transformer, after the voltage of the high-frequency transformer is boosted, two ends of a secondary winding of the high-frequency transformer generate high-frequency high-voltage alternating current, and the high-frequency high-voltage alternating current supplies power to the magnetron after passing through the high-frequency voltage doubling rectifying circuit; the alternating current generated by the filament winding on the secondary side of the high-frequency transformer directly supplies power for the magnetron filament; rectifying bridge rectifies single-phase power frequency alternating current L1C1The filter circuit is formed by electrically connecting a filter inductor and a filter capacitor and is used for power frequency filtering; the sampling circuit is formed by electrically connecting a first sampling resistor, a second sampling resistor and a current transformer, and the sampling circuit and an input voltage and current detection circuit of the control circuit are used for detecting input voltage and current; the pull-up active clamping branch circuit is formed by electrically connecting a clamping capacitor, an auxiliary switching tube and a second diode according to an electrical principle, the second diode is an anti-parallel diode of the auxiliary switching tube, a source electrode of the auxiliary switching tube is connected with a drain electrode of the main switching tube, one end of the clamping capacitor is connected with the drain electrode of the auxiliary switching tube, and the other end of the clamping capacitor is connected with an anode of the filter capacitor; when the power supply device is connected to 220VacThe alternating current is supplied to the control circuit, and the main switch is turned on after the main switch tube is turned offThe voltage at the two ends of the drain source of the main switch tube is gradually increased, and when the voltage is increased to the sum of the voltage of the filter capacitor and the voltage of the clamping capacitor, the voltage at the two ends of the drain source of the main switch tube is clamped at the two ends of the filter capacitor and the clamping capacitor, so that the withstand voltage of the main switch tube is reduced; the resonance capacitor is connected in parallel with the primary winding of the high-frequency transformer, and under the switching-on and switching-off changes of the main switching tube, the resonance capacitor resonates with the inductance of the primary winding to realize high-frequency inversion; the high-frequency transformer is formed by electrically connecting a primary winding, a secondary winding, a filament winding and a magnetic core with an air gap, the primary and secondary coupling coefficients of the high-frequency transformer are 0.5-0.95, the secondary winding is connected with a high-frequency voltage doubling rectifying circuit, the filament winding is connected with a filament of the magnetron to provide alternating current power supply for the magnetron, and the high-frequency transformer boosts the primary high-frequency alternating current and simultaneously realizes electrical isolation; the high-frequency voltage-multiplying rectification circuit is formed by electrically connecting a first high-voltage rectification diode, a second high-voltage rectification diode, a first filter capacitor and a second filter capacitor, and supplies power to a magnetron after voltage-multiplying rectification and filtering are carried out on the voltage output by a secondary winding of the high-frequency transformer by the high-frequency voltage-multiplying rectification circuit; the discharge resistor provides a discharge loop for the first filter capacitor and the second filter capacitor; the magnetron is used for generating microwaves; the control circuit is formed by electrically connecting an input voltage and current detection circuit, a first voltage detection circuit, a second voltage detection circuit, a microwave oven function menu or manual setting signal, a single chip microcomputer, a driving circuit and an auxiliary power supply, wherein the input voltage and current detection circuit is used for detecting input voltage and current, and the single chip microcomputer is used for adjusting frequency according to detection data so as to change output voltage and realize constant power control; the first voltage detection circuit detects voltages at two ends of the clamping capacitor, when the voltages at the two ends of the clamping capacitor are detected to be increased, the single chip microcomputer changes a control signal of the auxiliary switching tube into a high level, the auxiliary switching tube is turned on at zero voltage, when the voltages at the two ends of the clamping capacitor are increased, the primary winding charges the clamping capacitor through the second diode, the second diode is turned on, and the voltages at the two ends of the drain source of the auxiliary switching tube are zero; the second voltage detection circuit detects the voltage at two ends of the drain and the source of the main switching tube; the microwave oven function menu or the manual setting signal provides the microwave fire power combination and the corresponding action time for the singlechip; the drive circuit is controlled by the single chipThe on-off of the main switch tube and the auxiliary switch tube is driven; the auxiliary power supply supplies power to the singlechip and the drive circuit.
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CN104936327A (en) * 2015-07-08 2015-09-23 王春芳 Magnetron power supply power transmission and control method used for microwave oven

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