CN102497114A - Frequency conversion microwave oven power supply circuit and control method thereof - Google Patents

Abstract

The invention discloses a frequency conversion microwave oven power supply circuit and a control method thereof. The frequency conversion microwave oven power supply circuit comprises a signal processing control unit which comprises a microprocessor, a rectification filtering unit which carries out rectification filtering on alternating input voltage and then supplies power to a main power loop, a main power loop unit which is coupled with a secondary output loop unit through a transformer and supplies power to the secondary output loop unit, a voltage pick-up unit which obtains a voltage value of the alternating input voltage and sends the voltage value to the microprocessor, a current sampling unit which obtains a current value of the main power loop and sends the current value to the microprocessor, and a driving unit which receives a PWM signal from the microprocessor and drives a power switch tube of the main power loop unit. According to the frequency conversion microwave oven power supply circuit, element number is effectively reduced, the circuit is simple, operation is stable and reliable, cost is low, and power factor correction can be realized without using a special PFC chip.

Description

A kind of variable frequency microwave stove power circuit and control method

[technical field]

The present invention relates to variable frequency microwave stove power supply, relate in particular to a kind of variable frequency microwave stove power circuit and control method.

[background technology]

Mostly traditional variable frequency microwave stove power supply is single-stage resonance oscillation semi-bridge framework; On function, want its output voltage electric current will satisfy the requirement of magnetron operate as normal on the one hand; Also to accomplish the function of power factor calibration on the other hand, to satisfy of the requirement of its input voltage to harmonic wave.Above characteristics based on circuit; Conventional frequency converter microwave oven supply power control section adds that by the PFC chip microprocessor constitutes; Microprocessor be responsible for control panel on upper machine communication and power information handled the operation of back control PFC chip; While also returns to host computer with the work state information of converter power supply, and control circuit is complicated, and cost is high.

[summary of the invention]

The technical problem that the present invention will solve provides that a kind of circuit is simple, working stability is reliable, cost is lower, need not to use special PFC chip just can realize the variable frequency microwave stove power circuit of Active PFC.

Another technical problem that will solve of the present invention provides a kind of control method of above-mentioned variable frequency microwave stove power circuit.

In order to solve the problems of the technologies described above, the technical scheme that the present invention adopts is that a kind of variable frequency microwave stove power circuit comprises:

Signal processing control unit comprises microprocessor;

Rectification filtering unit is with supplying power to main loop of power circuit behind the AC-input voltage rectifying and wave-filtering;

Main loop of power circuit unit through transformer and the coupling of secondary output loop unit, supplies power to secondary output loop unit;

The voltage pick-up unit obtains the magnitude of voltage of AC-input voltage, and sends into microprocessor;

Current sampling unit obtains the current value of main loop of power circuit, and sends into microprocessor;

Driver element receives and fetches the pwm signal from microprocessor, drives the power switch pipe of main loop of power circuit unit.

Above-described variable frequency microwave stove power circuit; Described voltage pick-up unit comprises first divider resistance and second divider resistance of series connection; The positive pole of one termination rectification filtering unit output of first divider resistance and the second divider resistance electrical equipment series circuit, the negative pole of another termination rectification filtering unit output; The tie point of first divider resistance and second divider resistance connects microprocessor voltage signal input.

Above-described variable frequency microwave stove power circuit; Described current sampling unit comprises current sampling resistor and amplifier; Described current sampling resistor is connected on the rectification filtering unit negative pole of output end and connects main loop of power circuit unit through current sampling resistor, and the end that current sampling resistor is connected with main loop of power circuit unit connects microprocessor current signal input through described amplifier.

The technical scheme of the control method of more than one said variable frequency microwave stove power circuits may further comprise the steps:

A) obtain the reference work frequency f o of current frequency converter through tabling look-up;

B) the reference work frequency f o to current frequency converter revises, to basic operating frequency f1;

C) obtain the actual output frequency ft of pwm signal, drive the power switch pipe of main loop of power circuit unit with the actual output frequency ft of pwm signal.

Above-described control method; The step of obtaining the operating frequency of current frequency converter needs through tabling look-up comprises its instantaneous value ut and the corresponding form of operating frequency fo when in microprocessor, writing earlier a main loop of power circuit unit input specific voltage effective value Urms1; According to the instantaneous value of real limit AC-input voltage, obtain the reference work frequency f o of current frequency converter through tabling look-up again.

Above-described control method, b) the reference work frequency f o to current frequency converter revises, and is following to the step of basic operating frequency f1:

f1＝fo+Δf1

Wherein, Δ f1=Δ Vrms*K*u _t,

Δ Vrms be current input voltage effective value with the difference of the corresponding specific input voltage effective value Urms1 of reference work frequency f o, K is for revising proportionality coefficient, ut is the instantaneous value of the current input voltage in main loop of power circuit unit.

Above-described control method; The step of obtaining the actual output frequency ft of pwm signal comprises: through setting power and current input voltage effective value Urms theory of computation current instantaneous value io, with current sample obtain adopt transient current value i and theory of computation current instantaneous value io relatively obtains current error signal Δ i:

Δi＝i-io，

Basic operating frequency f1 is revised the actual output frequency ft that obtains pwm signal:

Ft=Δ f2+f1 or ft=fo+ Δ f1+ Δ f2

Wherein, Δ f2=Δ f2l+Kp (Δ i-Δ i ₁)+Ki* Δ i

In the following formula, Δ f2 is this frequency of amendment, and Δ f21 is last frequency of amendment, and Kp is that ratio is transferred

The joint coefficient, Δ i1 is last current error signal, Ki is the integration adjustment factor.

More than in 7 the described control method of arbitrary claim, described current input voltage effective value Urms obtains with the root mean square method:

$\mathrm{Urms}=\sqrt{\frac{{{\mathrm{<figure-callout\; id="1"\; label="u\; t"\; filenames="HDA0000113894280000011.png"\; state="\{\{state\}\}">u</figure-callout>}}_t}^2+{u_{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA0000113894280000011.png"\; state="\{\{state\}\}">t</figure-callout>}2}}^2+...{u_{\mathrm{tn}}}^2}{n}}$

Wherein, ut1 is for sample in t1 instantaneous voltage value constantly at a certain time interval, and ut2 is for sample in t2 instantaneous voltage value constantly at a certain time interval, and utn is for sample in tn instantaneous voltage value constantly at a certain time interval; N is the sampling number of a sine wave period of input ac voltage, equals sine wave period divided by sampling time interval.

Above-described control method comprises input power closed-loop adjustment step, and described closed-loop adjustment step adopts successive approximation method to realize.

Above-described control method, described input power obtains according to the instantaneous magnitude of voltage and the current value of sampling:

$\mathrm{Pin}=\frac{u_{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="HDA0000113894280000011.png"\; state="\{\{state\}\}">t</figure-callout>}1}*i_{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="HDA0000113894280000011.png"\; state="\{\{state\}\}">t</figure-callout>}1}+u_{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA0000113894280000011.png"\; state="\{\{state\}\}">t</figure-callout>}2}*i_{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA0000113894280000011.png"\; state="\{\{state\}\}">t</figure-callout>}2}+...u_{\mathrm{tn}}*i_{\mathrm{tn}}}{n}$

Wherein, ut1 and it1 are for sample in t1 instantaneous voltage value constantly at a certain time interval, and ut2 and it2 are for sample in t1 instantaneous voltage value constantly at a certain time interval; N is the sampling number of 1 sine wave period of input ac voltage, equals sine wave period divided by sampling time interval.

Variable frequency microwave stove power circuit of the present invention because of the effective component number that reduced, circuit is simple, working stability is reliable, cost is lower, need not to use special PFC chip just can realize Active PFC.

[description of drawings]

Below in conjunction with accompanying drawing and embodiment the present invention is done further detailed explanation.

Fig. 1 is the circuit theory diagrams of embodiment of the invention variable frequency microwave stove power circuit.

The graph of a relation of voltage and frequency when Fig. 2 is the fully loaded work of embodiment of the invention converter power supply.

Fig. 3 is the flow chart of embodiment of the invention control method power closed-loop adjustment.

[embodiment]

Controlled step one, the graph of a relation of voltage and frequency when obtaining the reference work frequency f o of current frequency converter: Fig. 2 through tabling look-up for the fully loaded work of a converter power supply.From figure, can know that for the converter power supply that works in specified output under the burning voltage, the phase place of its operating frequency and its input sine wave is closely-related, because phase place ω t and instantaneous voltage ut relation do

$u_t=\sqrt{2}\mathrm{Urms}*\sin \left(\mathrm{\&omega;t}\right)$

Wherein, Urms is a main loop of power circuit unit input voltage effective value; Therefore sinusoidal wave frequency has a corresponding relation with the instantaneous value ut of voltage, thisly concerns that we can express through the mode with tables of data in microprocessor, i.e. the mode that utilization is tabled look-up; Find the reference work frequency of current frequency converter through the size that detects input voltage instantaneous value ut; This frequency is called fo in this manual, different input instantaneous voltage corresponding different fo, the corresponding specific voltage effective value of the set of fo is called Urms1 in this manual therewith.

Controlled step two, the operating frequency fo that current frequency converter is needed revises, and obtains basic operating frequency f1: from Fig. 2, can also know with input voltage Urms and ut following relation is arranged for the groundwork frequency f under the different output voltages 1:

f1＝fo+Δf1

Δf1＝ΔVrms*K*u _t

In the following formula; Δ f1 is the frequency correction value under the current input voltage; F1 is the operating frequency under the current input voltage instantaneous value; Δ Vrms is the difference of current input voltage effective value and specific input voltage effective value Urms1, and K is a correction proportionality coefficient (constant according to test result adjust) relevant with rated voltage.Ut is the instantaneous value of the current input voltage in main loop of power circuit unit.

In microprocessor, the magnitude of voltage of single-chip microcomputer sampling is an instantaneous value, and the effective value that calculates its input voltage value adopts the root mean square method, and expression formula is following;

$\mathrm{Urms}=\sqrt{\frac{{{\mathrm{<figure-callout\; id="1"\; label="u\; t"\; filenames="HDA0000113894280000011.png"\; state="\{\{state\}\}">u</figure-callout>}}_t}^2+{u_{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA0000113894280000011.png"\; state="\{\{state\}\}">t</figure-callout>}2}}^2+...{u_{\mathrm{tn}}}^2}{n}}$

In the following formula; Ut1 is for sample in t1 instantaneous voltage value constantly at a certain time interval; Ut2 is for sample in t2 instantaneous voltage value constantly at a certain time interval, and n is the sampling number of a sine wave period of input ac voltage, and it equals sine wave period divided by sampling time interval.

Comprehensive above argumentation, step 1 be appreciated that into, ut and the corresponding form of operating frequency fo when writing a specific input voltage Urms in the elder generation in the microprocessor should use that tabular value is benchmark with maximum input voltage in the instance.Under different input voltages, earlier the mode through tabling look-up from microprocessor obtains a reference work frequency f o, and then adds a frequency correction value Δ f1 relevant with current input voltage value, can obtain a basic operating frequency f1.

Controlled step three: in order to realize the homophase of input current and voltage, need monitor the situation of change of input current constantly, to determine whether and the input voltage homophase.At first, need calculate theoretic transient current value, as shown in the formula:

$i_o=\frac{u_o}{R}$

$R=\frac{{\left(\mathrm{Urms}\right)}^2}{P}$

Io is the theoretical current instantaneous value under setting power P and the current input voltage Urms in the following formula, and uo is the input voltage instantaneous value, and R is the equivalent load resistance under the present load, the input power of P for setting.In the circuit of Fig. 1, adopted instantaneous current i, obtain a current error signal Δ i so:

Δi＝i-io

In order to eliminate this current error signal, be incorporated herein the PI regulating loop:

Δf2＝Δf2l+Kp(Δi-Δi1)+Ki*Δi

In the following formula, Δ f2 is for introducing the frequency of amendment after the current regulation loop, and Δ f21 be the last frequency of amendment of regulating, and Kp is proportional control factor (constant), the current error signal when Δ i1 be the last time adjusting, and Ki is integration adjustment factor (constant).Therefore obtain the PWM actual output frequency ft after current regulation loop:

ft＝Δf2+f1

ft＝fo+Δf1+Δf2

Accomplished the function of power factor calibration this moment, power output is also basically by nearly setting power simultaneously.

Controlled step four: because the error of current regulation loop always exists; Influenced by the microprocessor samples precision; Therefore the power output of this moment and the power of target power after Current Regulation are failed and are still had certain error, need to introduce the power closed-loop adjustment.In circuit, sampled instantaneous magnitude of voltage and current value, its input power is so:

$\mathrm{Pin}=\frac{{\mathrm{<figure-callout\; id="1"\; label="u\; t"\; filenames="HDA0000113894280000011.png"\; state="\{\{state\}\}">u</figure-callout>}}_t*i_{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="HDA0000113894280000011.png"\; state="\{\{state\}\}">t</figure-callout>}1}+{\mathrm{<figure-callout\; id="2"\; label="u\; t"\; filenames="HDA0000113894280000011.png"\; state="\{\{state\}\}">u</figure-callout>}}_t*i_{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA0000113894280000011.png"\; state="\{\{state\}\}">t</figure-callout>}2}+...u_{\mathrm{tn}}*i_{\mathrm{tn}}}{n}$

In the following formula; Ut1 and it1 are for sample in t1 instantaneous voltage value constantly at a certain time interval; Ut2 and it2 are for sample in t1 instantaneous voltage value constantly at a certain time interval; N is the sampling number of a sine wave period of input ac voltage, and it equals sine wave period divided by sampling time interval.Because the power adjustments loop is generally loop at a slow speed, adopt successive approximation method to get final product, control method is as shown in Figure 3.

Through three above-mentioned steps, final realization has promptly realized power factor, has accomplished again to magnetron the function of stablizing input power is provided, and compares traditional control method, has the following advantages:

One, effectively reduced component number, reduced whole cost.

Two; Adopt look-up table to obtain an original frequency and added the frequency correction under the different voltage initial conditions, the frequency f 1 of this moment is very near actual operating frequency, and the output area that makes the PI regulating loop need is dwindled greatly; Promptly can the output area of PI regulating loop be defined in the small range; That is to say that even the PI regulating loop is made mistakes, the deviation that actual operating frequency can be not excessive yet is in the frequency that needs in theory; Can not cause the situation of the bigger overcurrent of converter power supply appearance, improve the reliability of converter power supply.

Claims (10)

1. a variable frequency microwave stove power circuit is characterized in that, comprising:

Signal processing control unit comprises microprocessor;

Rectification filtering unit is with supplying power to main loop of power circuit behind the AC-input voltage rectifying and wave-filtering; Main loop of power circuit unit through transformer and the coupling of secondary output loop unit, supplies power to secondary output loop unit;

The voltage pick-up unit obtains the magnitude of voltage of AC-input voltage, and sends into microprocessor;

Current sampling unit obtains the current value of main loop of power circuit, and sends into microprocessor;

Driver element receives and fetches the pwm signal from microprocessor, drives the power switch pipe of main loop of power circuit unit.

2. variable frequency microwave stove power circuit according to claim 1; It is characterized in that; Described voltage pick-up unit comprises first divider resistance and second divider resistance of series connection; The positive pole of one termination rectification filtering unit output of first divider resistance and the second divider resistance electrical equipment series circuit, the negative pole of another termination rectification filtering unit output; The tie point of first divider resistance and second divider resistance connects microprocessor voltage signal input.

3. variable frequency microwave stove power circuit according to claim 1; It is characterized in that; Described current sampling unit comprises current sampling resistor and amplifier; Described current sampling resistor is connected on the rectification filtering unit negative pole of output end and connects main loop of power circuit unit through current sampling resistor, and the end that current sampling resistor is connected with main loop of power circuit unit connects microprocessor current signal input through described amplifier.

4. the control method of the said variable frequency microwave stove of claim 1 power circuit is characterized in that, may further comprise the steps:

A) obtain the reference work frequency f o of current frequency converter through tabling look-up;

B) the reference work frequency f o to current frequency converter revises, to basic operating frequency f1;

C) obtain the actual output frequency ft of pwm signal, drive the power switch pipe of main loop of power circuit unit with the actual output frequency ft of pwm signal.

5. control method according to claim 4; It is characterized in that; The step of obtaining the reference work frequency of current frequency converter through tabling look-up comprises that elder generation upward writes a main loop of power circuit unit input voltage effective value Urms and the corresponding form of operating frequency fo in the microprocessor; According to the magnitude of voltage of AC-input voltage, obtain the reference work frequency f o of current frequency converter through tabling look-up.

6. control method according to claim 5 is characterized in that, b) the reference work frequency f o to current frequency converter revises, and is following to the step of basic operating frequency f1:

f1＝fo+Δf1

Wherein, Af1=Δ Vrms*K*u _t,

Δ Vrms be current input voltage effective value with the difference of the corresponding specific input voltage effective value Urms1 of reference work frequency f o, K is for revising proportionality coefficient, ut is the instantaneous value of the current input voltage in main loop of power circuit unit.

7. control method according to claim 6; It is characterized in that; The step of obtaining the actual output frequency ft of pwm signal comprises: through setting power and current input voltage effective value Urms theory of computation current instantaneous value io, with current sample obtain adopt transient current value i and theory of computation current instantaneous value io relatively obtains current error signal Δ I:

Δi＝i-i ₀，

Basic operating frequency f1 is revised the actual output frequency ft that obtains pwm signal:

Ft=Δ f2+f1 or ft=fo+ Δ f1+ Δ f2

Wherein, Δ f2=Δ f2l+Kp (Δ i-Δ i ₁)+Ki* Δ i

In the following formula, Δ f2 is this frequency of amendment, and Δ f21 is last frequency of amendment, and Kp is a proportional control factor, and Δ i1 is last current error signal, and Ki is the integration adjustment factor.

8. according to the described control method of arbitrary claim in the claim 5 to 7, it is characterized in that described current input voltage effective value Urms obtains with the root mean square method:

$\mathrm{Urms}=\sqrt{\frac{{u_{t1}}^2+{u_{t2}}^2+...{u_{\mathrm{tn}}}^2}{n}}$

Wherein, ut1 is for sample in t1 instantaneous voltage value constantly at a certain time interval, and ut2 is for sample in t2 instantaneous voltage value constantly at a certain time interval, and utn is for sample in tn instantaneous voltage value constantly at a certain time interval; N is the sampling number of a sine wave period of input ac voltage, equals sine wave period divided by sampling time interval.

9. control method according to claim 4 is characterized in that, comprises input power closed-loop adjustment step, and described closed-loop adjustment step adopts successive approximation method to realize.

10. control method according to claim 9 is characterized in that, described input power obtains according to the instantaneous magnitude of voltage and the current value of sampling:

$\mathrm{Pin}=\frac{u_{t1}*i_{t1}+u_{t2}*i_{t2}+...u_{\mathrm{tn}}*i_{\mathrm{tn}}}{n}$

Wherein, ut1 and it1 are for sample in t1 instantaneous voltage value constantly at a certain time interval, and ut2 and it2 are for sample in t1 instantaneous voltage value constantly at a certain time interval; N is the sampling number of 1 sine wave period of input ac voltage, equals sine wave period divided by sampling time interval.

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