CN102497114B - 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 frequency-conversion microwave oven power circuit and control method

[technical field]

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

[background technology]

Traditional frequency-conversion microwave oven power supply mostly is single-stage resonance oscillation semi-bridge framework, in function, want on the one hand its output voltage electric current will meet the requirement of the normal work of magnetron, also to complete on the other hand the function of power factor calibration, to meet the requirement of its input voltage to harmonic wave.Based on the above feature of circuit, conventional frequency converter microwave oven supply power control section adds that by PFC chip microprocessor forms, microprocessor be responsible for control panel on upper machine communication and power information is processed after control the operation of PFC chip, also the work state information of converter power supply is returned to host computer simultaneously, control circuit complexity, cost is high.

[summary of the invention]

The technical problem to be solved in the present invention is to provide that a kind of circuit is simple, working stability is reliable, cost is lower, without using special PFC chip just can realize the frequency-conversion microwave oven power circuit of Active PFC.

Another technical problem that will solve of the present invention is to provide a kind of control method of above-mentioned frequency-conversion microwave oven power circuit.

In order to solve the problems of the technologies described above, the technical solution used in the present invention is that a kind of frequency-conversion microwave oven power circuit, comprising:

Signal processing control unit, comprises microprocessor;

Rectification filtering unit, by backward AC-input voltage rectifying and wave-filtering main loop of power circuit power supply;

Main loop of power circuit unit, by transformer and secondary output loop element coupling, powers to secondary output loop unit;

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 the pwm signal of fetching from microprocessor, drives the power switch pipe of main loop of power circuit unit.

Above-described frequency-conversion microwave oven power circuit, described voltage pick-up unit comprises the first divider resistance and second divider resistance of series connection, the positive pole of one termination rectification filtering unit output of the 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 the first divider resistance and the second divider resistance connects microprocessor voltage signal input.

Above-described frequency-conversion microwave oven power circuit, described current sampling unit comprises current sampling resistor and amplifier, described current sampling resistor is connected on rectification filtering unit negative pole of output end and connects main loop of power circuit unit by current sampling resistor, and one 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 frequency-conversion microwave oven power circuit described in more than one, comprises the following steps:

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

B) the reference work frequency f o of current frequency converter is revised, 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 by tabling look-up comprises its instantaneous value ut form corresponding with operating frequency fo first write a main loop of power circuit unit input specific voltage effective value Urms1 in microprocessor time, according to the instantaneous value of real limit AC-input voltage, obtain the reference work frequency f o of current frequency converter by tabling look-up again.

Above-described control method, b) revises the reference work frequency f o of current frequency converter, as follows 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 and 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: calculate theoretical current instantaneous value io by setting power and current input voltage effective value Urms, the transient current value i that adopts that current sample is obtained relatively obtains current error signal Δ i with the theoretical current instantaneous value io of calculating:

Δi＝i-io，

Basic operating frequency f1 is revised to 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 above formula, Δ f2 is this frequency of amendment, and Δ f21 is last frequency of amendment, and Kp is that ratio is adjusted

Joint coefficient, Δ i1 is last current error signal, Ki is integral adjustment coefficient.

Control method in above to 7 described in arbitrary claim, described current input voltage effective value Urms obtains with mean square root method:

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

Wherein, ut1 is the instantaneous voltage value of sampling at a certain time interval in the t1 moment, and ut2 is the instantaneous voltage value of sampling at a certain time interval in the t2 moment, and utn is the instantaneous voltage value of sampling at a certain time interval in the tn moment; 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 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 the instantaneous voltage value of sampling at a certain time interval in the t1 moment, and ut2 and it2 are the instantaneous voltage value of sampling at a certain time interval in the t1 moment; N is the sampling number of 1 sine wave period of input ac voltage, equals sine wave period divided by sampling time interval.

Frequency-conversion microwave oven power circuit of the present invention because of the effective component number that reduced, circuit is simple, working stability is reliable, cost is lower, without use special PFC chip just can realize Active PFC.

[brief description of the drawings]

Below in conjunction with the drawings and specific embodiments, the present invention is further detailed explanation.

Fig. 1 is the circuit theory diagrams of embodiment of the present invention frequency-conversion microwave oven power circuit.

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

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

[embodiment]

Control step 1, the graph of a relation of voltage and frequency when obtaining the reference work frequency f o of current frequency converter: Fig. 2 by tabling look-up and being the fully loaded work of a converter power supply.As we know from the figure, for the converter power supply that works in specified output under a 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 close is

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

Wherein, Urms is main loop of power circuit unit input voltage effective value, therefore the instantaneous value ut of sinusoidal wave frequency and voltage has a corresponding relation, thisly be related to that we can express by the mode with tables of data in microprocessor, utilize the mode of tabling look-up, find the reference work frequency of current frequency converter by detecting the size of input voltage instantaneous value ut, this frequency is called fo in this manual, different input instantaneous voltage correspondences different fo, and the corresponding specific voltage effective value of the set of fo is called Urms1 in this manual therewith.

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

f1＝fo+Δf1

Δf1＝ΔVrms*K*u _t

In above formula, Δ f1 is the frequency correction value under current input voltage, f1 is the operating frequency under current input voltage instantaneous value, Δ Vrms is the difference of current input voltage effective value and specific input voltage effective value Urms1, K is a correction proportionality coefficient (constant according to test result adjust) relevant to 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 instantaneous value, and the effective value that calculates its input voltage value adopts mean square root method, and expression formula is as follows;

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

In above formula, ut1 is the instantaneous voltage value of sampling at a certain time interval in the t1 moment, ut2 is the instantaneous voltage value of sampling at a certain time interval in the t2 moment, the sampling number of the sine wave period that n is input ac voltage, and it equals sine wave period divided by sampling time interval.

Comprehensive above discussion, step 1 can be understood as, and first goes up the ut form corresponding with operating frequency fo while writing a specific input voltage Urms in microprocessor, and in this application example, tabular value is taking maximum input voltage as benchmark.Under different input voltages, elder generation by the mode of tabling look-up, obtains a reference work frequency f o, and then adds a frequency correction value Δ f1 relevant to current input voltage value from microprocessor, can obtain a basic operating frequency f1.

Control step 3: in order to realize the homophase of input current and voltage, need to monitor constantly the situation of change of input current, to determine whether and input voltage homophase.First, need to calculate theoretic transient current value, as shown in the formula:

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

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

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

Δi＝i-io

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

Δf2＝Δf2l+Kp(Δi-Δi1)+Ki*Δi

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

ft＝Δf2+f1

ft＝fo+Δf1+Δf2

Now completed the function of power factor calibration, power output is also substantially by nearly setting power simultaneously.

Control step 4: because the error of current regulation loop always exists, be subject to microprocessor samples Accuracy simultaneously, therefore power output now and the target power power after electric current regulates is defeated or have certain error, need to introduce 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 above formula, ut1 and it1 are the instantaneous voltage value of sampling at a certain time interval in the t1 moment, ut2 and it2 are the instantaneous voltage value of sampling at a certain time interval in the t1 moment, 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 power adjustments loop is generally loop at a slow speed, adopt successive approximation method, control method is as shown in Figure 3.

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

One, effectively reduce component number, reduce holistic cost.

Two, adopt look-up table to obtain an original frequency and added the frequency correction under different voltage initial conditions, frequency f 1 now has approached actual operating frequency very much, the output area that PI regulating loop is needed is dwindled greatly, the output area of PI regulating loop can be defined in a less scope, that is to say, even if PI regulating loop is made mistakes, actual operating frequency can be not excessive yet deviation in the frequency needing in theory, can not cause the situation of the overcurrent that converter power supply appearance is larger, improve the reliability of converter power supply.

Claims (6)

1. a control method for frequency-conversion microwave oven power circuit, is characterized in that, described frequency-conversion microwave oven power circuit comprises:

Signal processing control unit, comprises microprocessor;

Rectification filtering unit, by backward AC-input voltage rectifying and wave-filtering main loop of power circuit power supply;

Main loop of power circuit unit, by transformer and secondary output loop element coupling, powers to secondary output loop unit;

Voltage pick-up unit, obtains the magnitude of voltage of AC-input voltage after rectifying and wave-filtering, and sends into microprocessor; Current sampling unit, obtains the current value of main loop of power circuit, and sends into microprocessor;

Driver element, receives the pwm signal of fetching from microprocessor, drives the power switch pipe of main loop of power circuit unit;

Described control method comprises the following steps:

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

B) the reference work frequency f o of current frequency converter is revised, 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;

Wherein, the step of obtaining the reference work frequency of current frequency converter by tabling look-up comprises first going up and in microprocessor, writes a main loop of power circuit unit input voltage effective value Urms form corresponding with operating frequency, according to the instantaneous voltage value of AC-input voltage, obtain the reference work frequency f o of current frequency converter by tabling look-up;

Reference work frequency f o to current frequency converter revises, as follows 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 and the difference of the corresponding specific input voltage effective value Urms1 of reference work frequency f o, K is for revising proportionality coefficient, u _tbe the instantaneous value of the current input voltage in main loop of power circuit unit, Δ f1 is the frequency correction value under current input voltage;

The step of obtaining the actual output frequency ft of pwm signal comprises: calculate theoretical current instantaneous value io by setting power and current input voltage effective value Urms, transient current value i and theoretical current instantaneous value io that current sample is obtained relatively obtain current error signal Δ i:

Δi＝i-i _o，

Basic operating frequency f1 is revised to 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 above formula, Δ f2 is this frequency of amendment, and Δ f2l is last frequency of amendment, and Kp is proportional control factor, Δ i ₁for last current error signal, Ki is integral adjustment coefficient.

2. control method according to claim 1, it is characterized in that, described voltage pick-up unit comprises the first divider resistance and second divider resistance of series connection, the positive pole of one termination rectification filtering unit output of the first divider resistance and the second divider resistance series circuit, the negative pole of another termination rectification filtering unit output; The tie point of the first divider resistance and the second divider resistance connects microprocessor voltage signal input.

3. control method according to claim 1, it is characterized in that, described current sampling unit comprises current sampling resistor and amplifier, rectification filtering unit negative pole of output end connects main loop of power circuit unit by current sampling resistor, and one end that current sampling resistor is connected with main loop of power circuit unit connects microprocessor current signal input through described amplifier.

4. control method according to claim 1, is characterized in that, described current input voltage effective value Urms obtains with mean square root method:

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

Wherein, u _t1for sampling at a certain time interval at the instantaneous voltage value in t1 moment, u _t2for sampling at a certain time interval at the instantaneous voltage value in t2 moment, u _tnfor sampling at a certain time interval in the instantaneous voltage value in tn moment; N is the sampling number of a sine wave period of input ac voltage, equals sine wave period divided by sampling time interval.

5. control method according to claim 1, is characterized in that, comprises input power closed-loop adjustment step, and described closed-loop adjustment step adopts successive approximation method to realize.

6. control method according to claim 5, is characterized in that, described input power obtains according to instantaneous magnitude of voltage and the current value of sampling:

Wherein, u _tnand i _tnfor sampling at a certain time interval at instantaneous voltage value and the current value in tn moment, u _t1and i _t1for sampling at a certain time interval at instantaneous voltage value and the current value in t1 moment, u _t2and i _t2for sampling at a certain time interval at instantaneous voltage value and the current value in t2 moment; 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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