阅读说明：本技术 定频控制的crm降压-反激pfc变换器 (CRM decompression-flyback pfc converter of fixed-frequency control ) 是由 马春伟 姚凯 张震 邬程健 管婵波 李凌格 陈杰楠 于 2019-06-26 设计创作，主要内容包括：本发明提供了一种采用定频控制的CRM降压-反激PFC变换器,包括主功率电路、输入电压数字前馈电路、输出电压差分电路、反馈电路、状态判断电路、驱动信号生成电路、比较电路与乘法电路。本发明引入输入电压数字前馈电路、输入电压比较电路和选通电路,实现双定频的控制方式,使得变换器在Buck阶段与Flyback阶段开关管的开关频率分别保持为不同的恒定值。(The present invention provides a kind of CRM decompression-flyback pfc converters using fixed-frequency control, including main power circuit, input voltage digital feed forward circuit, output voltage difference channel, feed circuit, status determination circuit, drive signal generation circuit, comparison circuit and mlultiplying circuit.Present invention introduces input voltage digital feed forward circuit, input voltage comparison circuit and gating circuits, double control modes for determining frequency are realized, so that converter remains different steady state values from the switching frequency of Flyback stage switch pipe in the Buck stage respectively.)

1. a kind of CRM decompression-flyback pfc converter of fixed-frequency control, which is characterized in that including main power circuit (1) and control Circuit, the main power circuit (1) include input power v_in, electromagnetic interface filter, rectifier diode D₁-D₆, main circuit primary side electricity Feel L_p, main circuit pair power transformation sense L_s, zero passage detection inductance L_ZCD, switching tube Q_bWith switching tube Q_b/b, sustained diode_o, output electricity Hold C_o, load R_L；

Input voltage source v_inIt is connect with the input port of electromagnetic interface filter,

The output port and rectifier diode D of electromagnetic interface filter₁-D₄The rectifier bridge and D of composition₃-D₆The rectifier bridge input port of composition Connection,

Rectifier diode D₃、D₄Just extremely reference potential zero point,

Rectifier diode D₅、D₆Cathode and main circuit primary inductor L_pIt is connected,

Main circuit primary inductor L_pThe other end and switching tube Q_fOne end connection,

Rectifier diode D₁、D₂Cathode and main circuit secondary inductance L_sConnected and and sustained diode_oCathode connection,

Main circuit secondary inductance L_sWith output capacitance C_oAnode and load RL be connected,

Output capacitance C_oCathode and load RL together with sustained diode_oIt is connected to the Q of switching tube_bOne end,

Zero passage detection inductance L_ZCDWith main circuit inductance Lp and L_sAll couple,

Zero passage detection inductance L_ZCDOne end connect with reference potential zero point and the other end and current-limiting resistance R_ZCDConnection,

Current sampling resistor R_sOne end ground connection and the other end and switching tube Q_fWith switching tube Q_bConnection.

2. converter according to claim 1, which is characterized in that control circuit includes Master control chip (2), sample circuit (3), D/A converting circuit (5), output voltage difference channel (4), feed circuit (6), status determination circuit (7), driving signal Generative circuit (8), comparison circuit (9) and mlultiplying circuit (10)；

The positive input of output voltage difference channel (4) and the output voltage anode V of main circuit (1)_o+ be connected,

The negative input of output voltage difference channel (4) and the output voltage anode V of main circuit (1)_oIt is connected,

The input terminal of the output end of output voltage difference channel (4) and the first input end of sample circuit (3) and feed circuit (6) It is connected,

Voltage v after the second input terminal and the main circuit rectification of sample circuit (3)_gIt is connected,

First output end of sample circuit (3) is connect with the ADC2 mouth of Master control chip (2),

The second output terminal of sample circuit (3) is connect with the ADC1 mouth of Master control chip (2),

First output port of Master control chip (2) is connect with the input port of D/A converting circuit (5),

The output port of D/A converting circuit (5) and the input terminal v of multiplier_xConnection,

The output port of feed circuit (6) and the input terminal v of multiplier_yConnection,

The output end of multiplier is connect with the positive input of comparison circuit (9),

The negative input and main circuit v of comparison circuit (9)_RsConnection,

The output end of comparison circuit (9) is connect with the input terminal of drive signal generation circuit (8),

The input terminal of drive signal generation circuit (8) passes through current-limiting resistance R_ZCDWith main circuit zero passage detection winding L_ZCDConnection,

Drive signal generation circuit (8) output end is connect with the input terminal of status determination circuit (7),

The end of drive signal generation circuit (8) and the switching tube Q of main power circuit (1)_bConnection,

The end of drive signal generation circuit (8) and the switching tube Q of main power circuit (1)_fConnection.

3. converter according to claim 2, which is characterized in that

The sample circuit (3) is by the input voltage v of converter_gWith output voltage V_oIt is converted into that the acquisition of coremaking piece can be controlled Voltage v_{g_dsp}With V_{o_dsp}；

It include locking phase program, input voltage peak value sampling program, output voltage sampling routine and control in the Master control chip (4) Processing procedure sequence, v_{g_dsp}It is connected with the ADC1 interface of control chip, locking phase program and input voltage peak is given to by the numerical value after sampling It is worth sampling routine, V_{o_dsp}It is connected with the ADC2 interface of control chip, output voltage sampling routine is given to by the numerical value after sampling, The output of locking phase program, input voltage peak value sampling program and output voltage sampling routine is given to master control program, master control processing procedure Sequence calculates the numerical value of the profile of inductive current；

The input terminal of the D/A converting circuit (5) is connect with control chip by SPI protocol, the inductive current that will be received Profile numerical value conversion be voltage output.

4. transformer according to claim 2, which is characterized in that the status determination circuit (7) includes first comparator Comp1, resistance R₅、R₆, reference voltage source V_boundary, two with door, a NOT gate and a driving circuit；

The noninverting input of first comparator Comp1 is through divider resistance R₅、R₆With the diode rectifier circuit of main power circuit (1) Voltage v after rectification_gIt is connected,

The reverse input end and reference voltage source V of first comparator Comp1_boundaryConnection,

The output end of first comparator Comp1 is connected with first with the input terminal of an input terminal of door AND Gate1 and NOT gate,

The output end of NOT gate is connect with second with an input terminal of door AND Gate2,

Two connect with the input terminal of the output end of door and driving circuit, and the output end of driving circuit is separately connected main power circuit (1) two switching tube Q_bWith Q_f。

5. transformer according to claim 2, which is characterized in that L6561 or L6562 can be used in drive signal generation circuit Etc. models integrated IC circuit, amplifier used in output voltage difference sample circuit (4) and output voltage feed circuit (6) The models operational amplifiers such as TL074, TL072, LM358, LM324 are selected, multiplier (10) is using integrated IC circuit or deviding device Part forms, and selects the logic of the models such as SN74HC08N, CD4011BE or 74HC32N used in status determination circuit (7) with door Chip, driving circuit can select the driving chip of the models such as IR2110, TLP2590 or use totem driving circuit, control Coremaking piece can select the chips such as TMS320F28335 or TMS320F28377.

Technical field

The present invention relates to a kind of AC/DC convertor technology, CRM decompression-flyback PFC of especially a kind of fixed-frequency control becomes Parallel operation.

Background technique

The problems such as due to input current dead zone and switching tube floating ground, traditional BuckPFC converter is in many applications It is difficult to meet technical requirement on design.In order to solve these problems, it is thus proposed that decompression-flyback PFC converter, the converter Buck topology and Flyback topology are combined together, when input voltage is greater than output voltage, Buck topology work, when defeated Enter voltage less than output voltage, the work of Flyback topology.But traditional CRM decompression-flyback pfc converter is using fixed Turn-on time control, when two topologys of converter work, turn-on time is equal, so that half of power frequency period under the control mode Interior switching tube switching frequency variation range is larger and power factor is lower in low pressure range, it is difficult to meet performance requirement.

Traditional CRM decompression-flyback pfc converter each switch periods switching tube turn-on time is identical.Advantage is control System is simple, high pressure range power factor is high, diode is without reverse-recovery problems；The disadvantage is that switching tube switchs in half of power cycle Frequency transformation range is big, low voltage range power factor is very low, EMI design is complicated, efficiency is lower.

Summary of the invention

The purpose of the present invention is to provide a kind of CRM of fixed-frequency control decompression-flyback pfc converters.

Realize the technical solution of the object of the invention are as follows: a kind of CRM decompression-flyback pfc converter of fixed-frequency control, including master Power circuit and control circuit, the main power circuit include input power v_in, electromagnetic interface filter, rectifier diode D₁-D₆、 Main circuit primary inductor L_p, main circuit pair power transformation sense L_s, zero passage detection inductance L_ZCD, switching tube Q_bWith switching tube Q_b/b, two pole of afterflow Pipe D_o, output capacitance C_o, load R_L；Input voltage source v_inIt is connect with the input port of electromagnetic interface filter, the output end of electromagnetic interface filter Mouth and rectifier diode D₁-D₄The rectifier bridge and D of composition₃-D₆The rectifier bridge input port of composition connects, rectifier diode D₃、D₄ Just extremely reference potential zero point, rectifier diode D₅、D₆Cathode and main circuit primary inductor L_pIt is connected, main circuit primary inductor L_p The other end and switching tube Q_fOne end connection, rectifier diode D₁、D₂Cathode and main circuit secondary inductance L_sConnected and and afterflow Diode D_oCathode connection, main circuit secondary inductance L_sWith output capacitance C_oAnode and load RL be connected, output capacitance C_o's Cathode and load RL together with sustained diode_oIt is connected to the Q of switching tube_bOne end, zero passage detection inductance L_ZCDWith main circuit Inductance Lp and L_sIt all couples, zero passage detection inductance L_ZCDOne end connect with reference potential zero point and the other end and current-limiting resistance R_ZCD Connection, current sampling resistor R_sOne end ground connection and the other end and switching tube Q_fWith switching tube Q_bConnection.

Further, control circuit includes Master control chip, sample circuit, D/A converting circuit, output voltage differential electrical Road, feed circuit, status determination circuit, drive signal generation circuit, comparison circuit and mlultiplying circuit；Output voltage difference channel Positive input and main circuit output voltage anode V_o+ be connected, the negative input of output voltage difference channel and main electricity The output voltage anode V on road_oIt is connected, the output end of output voltage difference channel and the first input end of sample circuit and feedback The input terminal K of circuit is connected, the voltage v after the second input terminal and the main circuit rectification of sample circuit_gIt is connected, the of sample circuit The connection of the ADC2 of one output end and Master control chip mouth, the second output terminal of sample circuit and the ADC1 mouth company of Master control chip It connects, the first output port of Master control chip and the input port of D/A converting circuit connect, the output end of D/A converting circuit The input terminal v of mouth and multiplier_xConnection, the output port of feed circuit and the input terminal v of multiplier_yConnection, the output of multiplier End is connect with the positive input of comparison circuit, the negative input and main circuit v of comparison circuit_RsConnection, comparison circuit it is defeated The input terminal of the connection of the input terminal of outlet and drive signal generation circuit, drive signal generation circuit passes through current-limiting resistance R_ZCDWith Main circuit zero passage detection winding L_ZCDThe input terminal of connection, drive signal generation circuit output end and status determination circuit connects, and drives The end of dynamic signal generating circuit and the switching tube Q of main power circuit_bConnection, the end of drive signal generation circuit and main power circuit Switching tube Q_fConnection.

Further, the sample circuit is by the input voltage v of converter_gWith output voltage V_oIt is converted into be controlled The voltage v of chip acquisition_{g_dsp}With V_{o_dsp}；Include in the Master control chip locking phase program, input voltage peak value sampling program, Output voltage sampling routine and control program, v_{g_dsp}It is connected with the ADC1 interface of control chip, is given to by the numerical value after sampling Locking phase program and input voltage peak value sampling program, V_{o_dsp}It is connected with the ADC2 interface of control chip, passes through the numerical value after sampling Be given to output voltage sampling routine, locking phase program, input voltage peak value sampling program and output voltage sampling routine export to To master control program, master control program calculates the numerical value of the profile of inductive current；The input terminal of the D/A converting circuit with It controls chip to connect by SPI protocol, is voltage output by the numerical value conversion of the profile of the inductive current received.

Further, the status determination circuit includes first comparator Comp1, resistance R₅、R₆, reference voltage source V_boundary, two with door, a NOT gate and a driving circuit；The noninverting input of first comparator Comp1 is through divider resistance R₅、R₆With the voltage v after the diode rectifier circuit rectification of main power circuit (1)_gIt is connected, first comparator Comp1's is reversed Input terminal and reference voltage source V_boundaryConnection, one of the output end of first comparator Comp1 and first and door AND Gate1 Input terminal is connected with the input terminal of NOT gate, and the output end of NOT gate is connect with second with an input terminal of door AND Gate2, and two It is connect with the input terminal of the output end of door and driving circuit, the output end of driving circuit be separately connected main power circuit two open Close pipe Q_bWith Q_f。

Further, the integrated IC circuit of the models such as L6561 or L6562, output electricity can be used in drive signal generation circuit Pressure difference divides amplifier used in sample circuit and output voltage feed circuit to select TL074, TL072, LM358, LM324 etc. Model operational amplifier, multiplier using integrated IC circuit or discrete device composition, used in status determination circuit with Men Xuan With the logic chip of the models such as SN74HC08N, CD4011BE or 74HC32N, driving circuit can select IR2110, TLP2590 Etc. models driving chip or use totem driving circuit, control chip can select TMS320F28335 or The chips such as TMS320F28377.

Compared with prior art, the present invention having the advantage that (1) using half of power frequency week when constant switching frequency control The switching frequency of two Topology Switch pipes remains steady state value in phase；(2) constant switching frequency control is compared to traditional fixed conducting Time controls in low pressure range, and PF is significantly improved；(3) inductive current virtual value declines to a great extent under novel control mode, To make the efficiency of entire converter improve a lot；(4) using the output voltage ripple phase under constant switching frequency control Traditional turn-on time control of determining is compared to reduce very much.

The invention will be further described with reference to the accompanying drawings of the specification.

Detailed description of the invention

Fig. 1 is CRM decompression-flyback pfc converter main circuit schematic diagram.

Fig. 2 is CRM decompression-flyback pfc converter inductive current and switching tube current waveform figure in a switch periods.

Fig. 3 is the waveform diagram of input current under Traditional control.

Fig. 4 is Traditional control lower switch frequency variation diagram.

Fig. 5 is PF change curve schematic diagram under Traditional control.

Constant switching frequency controls lower PF change curve schematic diagram when Fig. 6 is the different turn ratioes.

Fig. 7 is two kinds of control lower switch frequency variation curve schematic diagrames.

Fig. 8 is two kinds and controls lower PF change curve schematic diagram.

Fig. 9 is two kinds and controls lower Harmonics of Input curve synoptic diagram.

Figure 10 is two kinds and controls lower inductance primary and secondary side current effective value curve synoptic diagram.

Figure 11 is two kinds of change curve schematic diagrames for controlling lower output voltage ripple.

Figure 12 is CRM decompression-flyback pfc converter main power circuit and the control circuit combination signal of fixed-frequency control Figure.

Primary symbols title in above-mentioned figure: v_in- supply voltage, i_in- input current, RB-rectifier bridge, v_g- rectification Output voltage afterwards, i_L- inductive current, L-inductance, Q_b—Q_b/b- switching tube, D_fw—D_sk- diode, C_o- output filtering Capacitor, R_L- load, V_o- output voltage, R_{s_b/b}—R_{s_b/b}- sampling resistor, V_refThe benchmark of-output voltage feedback control Voltage, v_EAThe error voltage signal of-output voltage feedback control exports, t-time, ω-input voltage angular frequency, V_m- defeated Enter voltage peak, v_{gs_b}- switching tube Q_bDriving voltage, v_{gs_b/b}- switching tube Q_b/bDriving voltage, T_s- converter switches Period, f_s- converter switches frequency, PF-power factor, I_{L_pk}- inductive current peak, I_{in_rms}- input current virtual value, t_on- converter turn-on time, t_off- converter turn-off time, i_in- input current, P_in- input power, Δ V_o- output Voltage ripple.

Specific embodiment

Fig. 1 is Buck-FlybackPFC inverter main circuit.

Make following hypothesis: (1) all devices are ideal original part；(2) output voltage ripple compared with its DC quantity very It is small；(3) switching frequency is much higher than input voltage frequency.

Fig. 2, which gives, switchs tube current and inductive current waveform in one switch periods of critical current mode consecutive hours, Middle Fig. 2 (a) is waveform diagram when Buck topology works, and Fig. 2 (b) is waveform diagram when Flyback topology works.Work as input voltage v_gLess than output voltage V_oWhen, the work of Flyback topology, Q_bShutdown, Q_fWhen conducting, D_oCut-off, inductance L_pThe voltage at both ends is v_g, Its electric current i_LpWith v by zero_g/L_pSlope linear rise, output filter capacitor C_oPowering load；Work as Q_fWhen shutdown, according to Ampere-turn conservation i_LsPass through D_oAfterflow, at this time L_sThe voltage at both ends is-V_o, i_LsWith V_o/L_sSlope decline, and i_LsIt can be new A period drop to zero when starting.As input voltage v_gGreater than output voltage V_oWhen, the work of Buck topology, Q_fShutdown, Q_bIt leads When logical, D_fwCut-off, inductance L_sThe voltage at both ends is v_g-V_o, electric current i_LsWith (v by zero_g-V_o)/L_sSlope it is linear on It rises, v_gGive output filter capacitor C_oAnd load supplying；Work as Q_bWhen shutdown, i_LsPass through D_oAfterflow, at this time L_sThe voltage at both ends is-V_o, i_LsWith V_oThe slope of/L declines, and i_LsZero can be dropped to when a new period starts.

Without loss of generality, the v of input ac voltage is defined_inExpression formula is

v_in=V_msinωt (1)

Wherein V_mIt is respectively the amplitude and angular frequency of input ac voltage with ω.

So voltage of the input voltage after rectifier bridge rectifies becomes

v_g=V_m|sinωt| (2)

In half of power frequency period, converter is divided into the work of Buck topology and Flyback topology two working stages of work. Input voltage v after rectification_gGreater than output voltage V_oWhen, the work of Buck topology.If assume the conducting of Buck Topology Switch pipe Between be t_{on_buck}, when switching tube is open-minded, input voltage v_gTo inductance, output capacitance and load supplying, then available Buck mode The peak value i of secondary inductor current in next switch periods_{Ls_pk_buck}Expression formula it is as follows:

Wherein V_oFor output voltage, L_sFor secondary inductance inductance value.

When switching tube turns off inductance afterflow, according to the available turn-off time t of voltage-second balance principle_{off_buck}Expression formula:

According to the expression formula of the available Buck stage switch frequency of formula (4):

According to formula (3) and formula (5), the electric current that one switch periods flows through inductance when available Buck topology works is averaged Value is

As input voltage v_gLess than output voltage V_oWhen, the work of Flyback topology.If assuming, Flyback Topology Switch pipe is led The logical time is t_{on_flyback}, when switching tube is open-minded, input voltage v_gIt powers to primary side inductance, in an available switch periods The peak value i of primary side inductive current_{Lp_pk_flyback}Expression formula it is as follows

L in formula_pFor primary side inductance inductance value.

As switching tube shutdown, secondary inductance L_sAfterflow, inductance is to capacitor and load supplying, according to ampere-turn conservation and weber The available secondary inductance peak value i of equilibrium principle_{Ls_pk}With turn-off time t_{off_flyback}Expression formula:

i_{Ls_pk}(ω t)=ni_{Lp_pk}(ωt) (8)

Wherein

According to the expression formula of the switching frequency in formula (9) available Flyback stage:

According to formula (7) and formula (10), it is average that one switch periods of available Flyback topology work flow through input current Value is

Due in the inoperable dead zone of Buck circuit, Flyback topology work, so the converter is all in entire power frequency Dead zone is all not present in phase.Input current i can be obtained by above-mentioned derivation_inAre as follows:

Wherein

According to formula (6) and formula (11), the expression formula of switching frequency in available half of power frequency period:

When the turn-on time in two working stages is identical and constant, i.e.,

t_on=t_{on_buck}=t_{on_flyback} (14)

It can be drawn under different input voltages according to formula (13), the waveform of input current in half of power frequency period, such as Shown in Fig. 3；It can be drawn under different input voltages according to formula (14), the change of switching tube switching frequency in half of power frequency period Change waveform, as shown in Figure 4.From figure 3, it can be seen that although Flyback converter compensates for Buck converter in low pressure range The dead zone part of input current, but the waveform of input current differs farther out with sine at this time, there are many harmonic content.It can from Fig. 4 To find out, turn-on time control method Buck topology and Flyback Topology Switch pipe switching frequency are determined in half of power frequency period Variation range is larger, is unfavorable for the design of EMI.

Assuming that the efficiency of converter is 100%, i.e. input power is equal to output power, can be obtained according to power-balance

The expression formula that Traditional control determines turn-on time can be obtained according to formula (16):

It is according to the expression formula that above formula acquires PF

The PF curve under Traditional control can be made according to formula (18), as shown in Figure 5.It can be seen from the figure that PF value with The increase of input voltage and increase.In low pressure range, PF value is lower, is for 90V in input voltage, and PF value is only 0.888。

It can be seen that under Traditional control by above-mentioned inference, the still Flyback Topology Switch of either Buck topology The switching frequency variation range of pipe is all bigger, is unfavorable for very much the design of EMI.And the thinking of constant switching frequency control strategy is Keep the switching frequency of the switching tube of Buck topology and Flyback topology constant and equal in half of power frequency period, even

Buck topology can be respectively obtained according to formula (18) to be connected in half of power frequency period with Flyback Topology Switch pipe The expression formula of time:

According to formula (7), formula (12), formula (21) and formula (22), the expression of input current in available half of power frequency period Formula:

2.2 optimal turn ratio selections

Assuming that the output power of converter is P_o, the efficiency of converter is 100%, it can be obtained according to power-balance principle:

According to the expression formula of formula (24) available K.

The expression formula of the PF under double fixed frequencies can be write out according to formula (22)

It can be drawn under the different turn ratioes according to formula (24), the CRM Buck-Flyback controlled using constant switching frequency The power factor curve of pfc converter, as shown in Figure 6.It can be seen from the figure that as turn ratio n=2, the PF curve of converter For highest, converter can obtain optimal power factor.

By above-mentioned analysis it is found that keep constant the switching frequency of converter in switch periods, only need to make to convert Turn-on time t of the device work under Buck mode and Flyback mode_{on_buck}With t_{on_flyback}Become by formula (19) and formula (20) Change, but formula (19) and formula (20) are about V_o、V_m, L and P_oFunction, argument of function is more, if being built using analog circuit Control circuit, then feedforward control circuit will be very complicated.The design uses digital feed forward circuit control, by input voltage peak Value V_m, output voltage V_oEtc. parameters by sample circuit input sample to control chip in, by control chip computing function, The peak envelope curve for calculating inductive current is exported by D/A converting circuit and gives driving generative circuit.Control circuit is as schemed Shown in 12.

The integrated IC circuit of the models such as L6561 or L6562, output voltage difference can be used in above-mentioned drive signal generation circuit Amplifier used in sample circuit (4) and output voltage feed circuit (6) selects TL074, TL072, LM358, LM324 etc. Model operational amplifier, multiplier (10) are believed using integrated IC circuit or discrete device composition, status determination circuit (7) and driving The logic chip for selecting the models such as SN74HC08N, CD4011BE or 74HC32N used in number generative circuit (8) with door, drives Dynamic circuit can select the driving chip of the models such as IR2110, TLP2590 or use totem driving circuit, control chip The chips such as TMS320F28335 or TMS320F28377 can be selected.

By formula (18) it can be seen that under different input voltage grades, half of power frequency period when being controlled using constant switching frequency The switching frequency of interior two Topology Switch pipes remains steady state value.The switching frequency variation of two switching tubes compared with Traditional control Range reduces very much, simplifies the design of EMI.Fig. 7 is different control modes in power frequency period under 110VAC and 220VAC Switching frequency changes waveform.

PF value change curve when Traditional control and Novel control can be made respectively by formula (24) and formula (17), such as Fig. 8 It is shown.It can be seen from the figure that constant switching frequency control determines turn-on time control in low pressure range compared to tradition, PF has It is apparent to improve；The PF that constant switching frequency controls in high pressure range has certain decline, but is compared to when determining conducting Between minimum PF " 0.88 ", the PF under constant switching frequency control may remain in 0.91 or more, so constant switching frequency PF is significantly improved relative to Traditional control PF.

In order to analyze the harmonic wave of input current, Fourier analysis can be carried out to formula (21).The fourier of input current point Solution form are as follows:

Wherein

T in formula_lineIt is power frequency period.

Formula (21) are substituted into formula (26), be computed can obtain constant switching frequency control contained by lower input current each time it is humorous Wave.Wherein, cosinusoidal component and even sine component are 0.

Constant switching frequency control can be obtained by formula (21) and formula (26) and traditional 3,5,7 times for determining turn-on time control are humorous Wave current amplitude I₃、I₅、I₇To fundamental current amplitude I₁Per unit valueAs shown in Fig. 9.

According to IEC61000-3-2, Class D standard requirements, the ratio between 3,5,7,9 subharmonic of input current and input power Formula (27) should be met

It can be seen in figure 9 that 3,5,7 subharmonic are below IEC61000-3-2, Class under any input voltage The limit value of D standard.

It can be obtained in a switch periods by formula (3), formula (4), formula (7) and formula (9) former under Buck mode and Flyback mode Side inductive current and secondary power transformation inducing current virtual value square are

Above-mentioned formula is asked in half of power frequency period root mean square can obtain primary side and secondary power transformation inducing current virtual value

By formula (16), formula (19) and formula (20) substitute into above formula, can in the hope of under traditional control method with constant switching frequency Control the virtual value change curve of lower inductive current, such as Figure 10.It can be seen that inductive current virtual value under novel control mode It declines to a great extent, so that the efficiency of entire converter be made to improve a lot.

According to the calculation formula of Instantaneous input power per unit value

Formula (12) are substituted into above formula, the Instantaneous input power per unit value p under Traditional control can be obtained^* _{in_cot}；By formula (21) generation Enter above formula can obtain constant switching frequency control under Instantaneous input power per unit value p^* _{in_dcf}。

WhenWhen, storage capacitor C_oCharging；WhenWhen, C_oElectric discharge.Assuming that being led surely since ω t=0 Under logical time control and change turn-on time controlWaveform time axial coordinate corresponding with 1 intersection point be respectively t₁With t₂, then storage capacitor C_o(a reference value is defeated in half of power frequency period to the ceiling capacity per unit value stored in half of power frequency period Energy out) be respectively

According to the calculation formula of capacitive energy storage,WithIt is represented by again

Wherein Δ V_{o_1}With Δ V_{o_2}It is the output voltage ripple value determined under turn-on time and constant switching frequency control respectively.

Fig. 8 can be made by formula (36) and formula (37), it can be seen from the figure that using the output under constant switching frequency control Voltage ripple is compared to traditional turn-on time control of determining and reduces very much, when input voltage is 264VAC, constant switch frequency It is only the 46.5% of Traditional control that rate, which controls output voltage ripple,.