CN111669042A - CRM boost PFC converter improved constant-on-time control method and control circuit - Google Patents

CRM boost PFC converter improved constant-on-time control method and control circuit Download PDF

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CN111669042A
CN111669042A CN202010564249.0A CN202010564249A CN111669042A CN 111669042 A CN111669042 A CN 111669042A CN 202010564249 A CN202010564249 A CN 202010564249A CN 111669042 A CN111669042 A CN 111669042A
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voltage
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CN111669042B (en
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任小永
周玉婷
吴羽
陈乾宏
张之梁
施佳楠
徐正杰
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Nanjing University of Aeronautics and Astronautics
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Nanjing University of Aeronautics and Astronautics
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    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/42—Circuits or arrangements for compensating for or adjusting power factor in converters or inverters
    • H02M1/4208—Arrangements for improving power factor of AC input
    • H02M1/4225—Arrangements for improving power factor of AC input using a non-isolated boost converter
    • 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

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Abstract

The invention discloses an improved constant-conduction-time control method and a control circuit of a CRM boost PFC converter, and belongs to the field of electric energy conversion. The control circuit comprises a CRM boost PFC converter main power circuit and a control circuit, wherein the control circuit comprises an input voltage sampling circuit, an improved inductive current zero-crossing detection circuit, an output voltage sampling circuit, a digital control unit or an analog control unit; the analog control unit includes a voltage error regulator and a drive signal generation circuit. The invention realizes the advanced detection of the zero-crossing signal of the inductive current, compensates the influence of signal propagation delay, shortens or even eliminates the reverse resonance process, realizes the control of the constant conduction time without resonance or partial resonance and improves the THD of the input current by the improved inductive current zero-crossing detection circuit.

Description

CRM boost PFC converter improved constant-on-time control method and control circuit
Technical Field
The invention relates to an improved constant conduction time control and control circuit of a CRM boost PFC converter, and belongs to the technical field of power conversion.
Background
With the rapid development of power electronic devices, a large amount of harmonic current is injected into a power grid, and the power grid has serious harmonic pollution. For this reason, current harmonic standards such as EN61000-3-2, IEC555-2, DO-160G, etc., have been successively promulgated and revised by the International electrotechnical Commission and the aviation radio technical Commission, and the current harmonic standards to be satisfied by AC-DC converters of different power classes have been specifically specified. The active Power Factor Correction (PFC) technology can improve the Power Factor of the AC-DC converter (Power Factor), reduce the Total Harmonic Distortion (THD) of the input current, have light volume and weight, and good harmonic suppression capability, and have been widely used to reduce the harmonic pollution of the electronic device to the Power grid. The CRM boost PFC converter has become the most common topology for the single-phase PFC converter due to its advantages of small input current ripple, simple control, etc.
The realization of the soft switch of the CRM boost PFC converter benefits from the resonance of a boost inductor and a parasitic capacitor of a power switch device, however, the existence of the resonance causes the inductor current in a switching period to deviate from an ideal triangular shape, distortion occurs under the control of the traditional constant on-time, and the harmonic standard is difficult to meet. To improve the input current THD, variable on-time control is widely used. However, the variable on-time control based on the analog method is complicated and it is difficult to realize the optimal input current THD; the variable conduction time control based on the digital mode relates to complex operations such as evolution, division, multiplication and the like, has high requirements on a digital controller, and correspondingly increases the cost. In order to improve the input current THD without increasing the complexity of the control, improvements to the conventional constant on-time control are required.
Disclosure of Invention
Aiming at the problems of serious input current distortion, complex variable conduction time control, high cost and the like under the traditional constant conduction time control, the invention provides an improved constant conduction time control method, which realizes the advanced detection of an inductive current zero-crossing signal by improving an inductive current zero-crossing detection circuit, compensates the influence of signal propagation delay, shortens or even eliminates the reverse resonance process, realizes the non-resonance or partial resonance control and improves the input current THD.
The above purpose is realized by the following technical scheme:
a CRM boost PFC converter improved constant on-time control circuit comprises a CRM boost PFC converter main power circuit and a control unit, wherein the control unit comprises an input voltage sampling circuit, an improved inductive current zero-crossing detection circuit, an output voltage sampling circuit, a digital control unit or an analog control unit; the digital control unit comprises an analog-digital conversion unit, an interrupt system, an operation processing unit and an ePWM module; the analog control unit includes a voltage error regulator and a drive signal generation circuit.
The main power circuit comprises an EMI filter, a rectifier bridge, an input filter capacitor, a sampling resistor, a boost inductor, a switching tube, a fly-wheel diode, an output capacitor and a load; the driving signal generating circuit comprises an RS trigger, a comparator and a sawtooth wave generating circuit, and the output end of the driving signal generating circuit is connected with the driving circuit of the switching tube; the input end of the input voltage sampling circuit is connected with two ends of the input filter capacitor, and the output end of the input voltage sampling circuit is connected with an analog/digital conversion interface of the digital control unit or is connected with the input end of the improved inductive current zero-crossing detection circuit through an isolation link; the input end of the improved inductive current zero-crossing detection circuit is connected with two ends of the sampling resistor, the input voltage sampling circuit and the output voltage sampling circuit, and the output end of the improved inductive current zero-crossing detection circuit is connected with the S end of the digital control unit or the RS trigger; the input end of the output voltage sampling circuit is connected with two ends of a load, and the output end of the output voltage sampling circuit is connected with an analog-digital conversion interface of the digital control unit or a voltage error regulator and an improved inductive current zero-crossing detection circuit.
The improved inductive current zero-crossing detection circuit comprises a level conversion circuit, a comparator, an RC filter and a digital isolator; the level shift circuit comprises VlevelA generating circuit and a subtraction circuit; the subtraction circuit comprises an operational amplifier and a linear voltage reference Vcc1And R7、R8、R9And R10Four resistors, in which electricity is sampledTerminal a of resistor and linear voltage reference Vcc1One end and R7One end connected, linear voltage reference Vcc1The other end is grounded, R7The other end is connected with the positive input end of the operational amplifier and R8One end, R8The other end is grounded, R9One end and VlevelThe generating circuit is connected, and the other end is connected with the negative input end of the operational amplifier and R10One end, R10The other end is connected with the output end of the operational amplifier; for digital control mode, VlevelThe generating circuit uses a fixed level generating circuit which is based on a linear voltage reference Vcc3And a resistor, wherein one end of the linear voltage reference is connected with R16One end and the other end is connected with R17One end, R16The other end and R17The other end is connected with and outputs to R9(ii) a For the analog control mode, VlevelThe generation circuit adopts a varying level generation circuit composed of an operational amplifier and its peripheral circuits, wherein the linear voltage reference Vcc2One end is grounded, and the other end is connected with R11One end, R11The other end is connected with the positive input end of the operational amplifier and R12One end and R15One end, R12The other end is grounded, R15The other end is connected with an output voltage sampling circuit, and the input voltage sampling circuit is connected with R13One end, R13The other end is connected with the negative input end of the operational amplifier and R14One end, R14The other end is connected with the output end of the operational amplifier and outputs to R9。
A CRM boost PFC converter improves constant on-time control, the method adopts the improved inductance current zero-crossing detection circuit to realize the advanced detection of the inductance current zero-crossing signal, compensates the influence of signal propagation delay, realizes no resonance or partial resonance, improves the input current distortion caused by the reverse resonance of boost inductance and parasitic capacitance of a power switch device, reduces the input current THD without increasing the complexity of control, if the CRM boost PFC converter is realized by adopting a digital control mode, the method comprises the following steps:
1) A/D converter of digital control unit samples voltage signal v at two ends of input filter capacitorcinAndoutput voltage signal V across a loadoThe sampled values are respectively vcin/k1And Vo/k2Wherein k is1As a division coefficient of the input voltage, k2The output voltage division coefficient.
2) Output voltage sampling value Vo/k2And an output voltage reference VrefComparing to obtain an error value Δ VoCalculating the constant on-time T by a PI regulatoronThis section is used to regulate the output voltage to achieve a constant voltage output at different input voltages and output powers.
3) An improved inductive current zero-crossing detection circuit generates an inductive current zero-crossing signal in advance at the conduction stage of a freewheeling diode and synchronously triggers an ePWM module of a digital control unit.
4) To realize no resonance or partial resonance, the delay time T of the needed compensation is calculateddelayWhen R is8/R7＝R10/R9When the temperature of the water is higher than the set temperature,
Figure BDA0002547213870000031
wherein, VlevelTo a fixed level, Vcc1Is a linear voltage reference, LbFor boost inductance, RsTo sample the resistance, ticIs signal propagation delay (sum of signal propagation delay of improved inductive current zero-crossing detection circuit, drive circuit and digital control unit), tdFor part of the resonance time, when tdWhen the value is equal to 0, the control is the constant conduction time control without resonance; r7、R8、R9、R10A resistor in the subtraction circuit;
5) according to the calculated delay time TdelayAnd constant on-time TonAnd the ePWM module generates a corresponding PWM signal and outputs the PWM signal to the drive circuit to generate a drive signal.
A CRM boost type PFC converter improved constant-on-time control is realized by adopting analog control, and the method comprises the following steps of:
1) voltage v at two ends of isolation sampling input filter capacitorcinAnd a voltage signal V output across the loadoA value of v as a sampling valuecin/k1And Vo/k2Wherein k is1As a division coefficient of the input voltage, k2To output the voltage division coefficient, it is outputted to VlevelA varying level generating circuit when R8/R7＝R10/R9The method comprises the following steps:
Figure BDA0002547213870000041
wherein, VlevelTo change the level, Vcc1Is a linear voltage reference, LbFor boost inductance, RsTo sample the resistance, ticFor signal propagation delay, tdFor part of the resonance time, when tdWhen the value is equal to 0, the control is the constant conduction time control without resonance; r7、R8、R9、R10A resistor in the subtraction circuit;
2) the improved inductive current zero-crossing detection circuit generates a zero-crossing detection signal to the S end of the RS trigger to generate a switching-on signal.
3) Sampling value V of output voltage signals at two ends of loado/k2Output to the voltage error regulator to generate a voltage error signal VerrorAnd the RS trigger outputs a complete driving signal to the driving circuit to generate a driving signal.
Compared with the prior art, the invention has the following main technical characteristics:
1. the improved constant on-time control method of the CRM boost PFC converter provided by the invention can effectively improve the input current distortion caused by resonance between the boost inductor and the parasitic capacitor of the power switch device.
2. The improved constant-conduction-time control method provided by the invention realizes the advanced detection of the zero-crossing signal of the inductive current by improving the inductive current zero-crossing detection circuit, compensates the influence of signal propagation delay, shortens or even eliminates the reverse resonance process, can realize the control of no resonance or partial resonance, and effectively improves the THD of the input current.
3. The CRM boost PFC converter provided by the invention has the advantages that only one or two operational amplifiers are needed, the cost is lower, and the control is simple to realize.
4. The control circuit disclosed by the invention is simple in design, and the control of the improved constant on time of the CRM boost type PFC converter is easy to realize.
5. According to the improved constant-conduction-time control method of the CRM boost PFC converter, one or two operational amplifiers are added to realize the advanced detection of the zero-crossing signal of the inductive current, so that the complexity of control is not increased while the input current THD is effectively reduced.
Drawings
Fig. 1 is a main circuit of a CRM boost PFC converter;
FIG. 2 is a schematic diagram of advanced detection of an improved inductor current zero crossing detection circuit;
fig. 3 is a digital control circuit diagram (also referred to as an abstract figure) for realizing improved constant on-time control of the CRM boost PFC converter;
FIG. 4 is a flow chart of digital control;
fig. 5 is a circuit diagram for realizing an improved constant on-time control circuit of a CRM boost PFC converter by adopting an analog control mode;
FIG. 6 is an improved inductor current zero crossing detection circuit;
FIG. 7 is VlevelA fixed level generating circuit;
FIG. 8 is VlevelA varying level generating circuit;
fig. 9 is a comparison graph of input current THD for a CRM boost PFC converter employing conventional constant on-time control and improved constant on-time control;
fig. 10 is a comparison graph of efficiency of a CRM boost PFC converter employing conventional constant on-time control and improved constant on-time control;
the main symbol names in the above figures: v. ofin-an input voltage; i.e. iin-input current on the front side of the EMI filter; cin-an input filter capacitance; v. ofcin-input filter capacitor both ends electricityPressing; rs-a sampling resistance; l isb-a boost inductance; qb-a switching tube; cds-switching tube parasitic capacitance; v. ofds-the voltage across the drain and source of the switching tube; db-a freewheeling diode; cdp-free-wheeling diode parasitic capacitance; cout-an output capacitance; vo-an output voltage; rL-a load resistance; r1-a voltage dividing sampling resistor; r2-a voltage dividing sampling resistor; r3-a voltage dividing sampling resistor; r4-a voltage dividing sampling resistor; k is a radical of1-an input voltage division factor; k is a radical of2-an output voltage division factor; v. ofcin/k1-input voltage sample values; vo/k2-outputting the voltage sample value; vref-a reference voltage; Δ Vo-a voltage PI loop error value; t ison-a conduction time; t isdelay-a delay time; ADC1, ADC 2-analog-to-digital converter; r5-voltage error regulator coefficient resistance; r6-voltage error regulator coefficient resistance; c1-voltage error regulator coefficient capacitance; verror-a voltage error signal; i.e. iL-the inductor current; v. ofgs-a drive signal; vcc1-a linear voltage reference; vcc2-a linear voltage reference; vcc3-a linear voltage reference; r7-subtraction circuit coefficient resistance; r8-subtraction circuit coefficient resistance; r9-subtraction circuit coefficient resistance; r10-subtraction circuit coefficient resistance; rf1-RC filter resistance; cf1-an RC filter capacitance; r11-varying the level generating circuit coefficient resistance; r12-varying the level generating circuit coefficient resistance; r13-varying the level generating circuit coefficient resistance; r14-varying the level generating circuit coefficient resistance; r15-varying the level generating circuit coefficient resistance; r16-a fixed level generating circuit coefficient resistance; r17-fixed level generating circuit coefficient resistance.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings and examples.
The first embodiment is as follows:
the improved constant on-time control circuit of the CRM boost type PFC converter comprises a main power circuit (shown in figure 1) of the CRM boost type PFC converter and a control unit, wherein the main power circuit and the control unit are realized in a digital control mode, and the control unit comprises an input voltage sampling circuit, an improved inductive current zero-crossing detection circuit, an output voltage sampling circuit and a digital control unit.
As shown in FIG. 3, the main power circuit includes an EMI filter, a rectifier bridge, and an input filter capacitor CinSampling resistor RsBoost inductor LbAnd a switching tube QbFreewheel diode DbAn output capacitor CoutAnd a load RL(ii) a The input end of the input voltage sampling circuit is connected with an input filter capacitor CinThe output ends of the two ends are connected with an analog/digital conversion interface ADC1 of the digital control unit; the input end of the improved inductive current zero-crossing detection circuit is connected with a sampling resistor RsThe output ends of the two ends are connected with the digital control unit; the input end of the output voltage sampling circuit is connected with a load RLThe two ends and the output end are connected with an analog/digital conversion interface ADC2 of the digital control unit.
The improved inductive current zero-crossing detection circuit comprises a level conversion circuit, a comparator, an RC filter and a digital isolator; the level shift circuit comprises VlevelA generating circuit and a subtraction circuit; the subtraction circuit comprises an operational amplifier and a linear voltage reference Vcc1And R7、R8、R9And R10Four resistors, wherein the resistor R is sampledsTerminal a of and a linear voltage reference Vcc1One end and R7One end connected, linear voltage reference Vcc1The other end is grounded, R7The other end is connected with the positive input end of the operational amplifier and R8One end, R8The other end is grounded, R9One end and VlevelThe generating circuit is connected, and the other end is connected with the negative input end of the operational amplifier and R10One end, R10The other end is connected with the output end of the operational amplifier; vlevelThe generating circuit adopts a fixed level generating circuit and is fixedThe level generating circuit is based on a linear voltage reference Vcc3And a resistor, wherein one end of the linear voltage reference is connected with R16One end and the other end is connected with R17One end, R16The other end and R17The other end is connected with and outputs to R9。
Example two:
the invention relates to an improved constant on-time control circuit of a CRM boost PFC converter, which comprises a main power circuit of the CRM boost PFC converter and a control unit, wherein the main power circuit of the CRM boost PFC converter and the control unit are realized by adopting an analog control mode; the analog control unit includes a voltage error regulator and a drive signal generation circuit.
As shown in FIG. 5, the main power circuit includes an EMI filter, a rectifier bridge, and an input filter capacitor CinSampling resistor RsBoost inductor LbAnd a switching tube QbFreewheel diode DbAn output capacitor CoutAnd a load RL(ii) a The driving signal generating circuit comprises an RS trigger, a comparator and a sawtooth wave generating circuit, and the output end of the driving signal generating circuit is connected with the driving circuit of the switching tube; the input end of the input voltage sampling circuit is connected with an input filter capacitor CinThe output end of the two ends is connected with the input end of the improved inductive current zero-crossing detection circuit through an isolation link; the input end of the improved inductive current zero-crossing detection circuit is connected with a sampling resistor RsThe output end of the input voltage sampling circuit is connected with the S end of the RS trigger; the input end of the output voltage sampling circuit is connected with a load RLThe output ends of the two ends are connected with a voltage error regulator and an improved inductive current zero-crossing detection circuit.
The improved inductive current zero-crossing detection circuit comprises a level conversion circuit, a comparator, an RC filter and a digital isolator; the level shift circuit comprises VlevelA generating circuit and a subtraction circuit; the subtraction circuit comprises an operational amplifier and a linear voltage reference Vcc1And R7、R8、R9And R10Four resistors, wherein the resistor R is sampledsTerminal a of and a linear voltage reference Vcc1One end and R7One end connected, linear voltage reference Vcc1The other end is grounded, R7The other end is connected with the positive input end of the operational amplifier and R8One end, R8The other end is grounded, R9One end and VlevelThe generating circuit is connected, and the other end is connected with the negative input end of the operational amplifier and R10One end, R10The other end is connected with the output end of the operational amplifier; vlevelThe generation circuit adopts a varying level generation circuit composed of an operational amplifier and its peripheral circuits, wherein the linear voltage reference Vcc2One end is grounded, and the other end is connected with R11One end, R11The other end is connected with the positive input end of the operational amplifier and R12One end and R15One end, R12The other end is grounded, R15The other end is connected with an output voltage sampling circuit, and the input voltage sampling circuit is connected with R13One end, R13The other end is connected with the negative input end of the operational amplifier and R14One end, R14The other end is connected with the output end of the operational amplifier and outputs to R9。
Example three:
the improved constant-conduction-time control method of the CRM boost PFC converter is realized by adopting the circuit of the first embodiment, the zero-crossing signal of the inductive current is detected in advance (shown in figure 2) by the improved inductive current zero-crossing detection circuit (shown in figures 6 and 7), the influence of signal propagation delay is compensated, the reverse resonance process is shortened and even eliminated, the non-resonance or partial-resonance control is realized, and the input current THD is improved. The improved constant on-time control only needs one to two operational amplifiers, and has low cost and simple control.
The CRM boost PFC converter improves constant on-time control, is realized by adopting a digital control mode, and can be realized by the following steps:
1) A/D converter sampling input filter capacitor C of digital control unitinVoltage signal v at two endscinAnd a load RLOutput voltage signal V at both endsoThe sampled values are respectively vcin/k1And Vo/k2Wherein k is1As a division coefficient of the input voltage, k2The output voltage division coefficient.
2) Output voltage sampling value Vo/k2And an output voltage reference VrefComparing to obtain an error value Δ VoCalculating the constant on-time T by a PI regulatoronAnd is used for regulating the output voltage to realize constant voltage output under different input voltages and output powers.
3) An improved inductive current zero-crossing detection circuit generates an inductive current zero-crossing signal in advance at the conduction stage of a freewheeling diode and synchronously triggers an ePWM module of a digital control unit.
4) To realize no resonance or partial resonance, the delay time T of the needed compensation is calculateddelayWhen R is8/R7＝R10/R9When the temperature of the water is higher than the set temperature,
Figure BDA0002547213870000081
wherein, VlevelTo a fixed level, Vcc1Is a linear voltage reference, LbFor boost inductance, RsTo sample the resistance, ticIs signal propagation delay (sum of signal propagation delay of improved inductive current zero-crossing detection circuit, drive circuit and digital control unit), tdFor part of the resonance time, when tdWhen the value is equal to 0, the control is the constant conduction time control without resonance; r7、R8、R9、R10A resistor in the subtraction circuit;
5) according to the calculated delay time TdelayAnd constant on-time TonAnd the ePWM module generates a corresponding PWM signal and outputs the PWM signal to the drive circuit to generate a drive signal.
Example four:
the improved constant-conduction-time control method of the CRM boost type PFC converter is realized by adopting the circuit of the second embodiment, the zero-crossing signal of the inductive current is detected in advance (shown in figure 2) by the improved inductive current zero-crossing detection circuit (shown in figures 6 and 8), the influence of signal propagation delay is compensated, the reverse resonance process is shortened and even eliminated, the non-resonance or partial-resonance control is realized, and the input current THD is improved. The method is realized by adopting analog control and comprises the following steps:
1) isolation sampling input filter capacitor CinVoltage v acrosscinAnd a load RLOutput voltage signal V at two endsoA value of v as a sampling valuecin/k1And Vo/k2Wherein k is1As a division coefficient of the input voltage, k2To output the voltage division coefficient, it is outputted to VlevelA varying level generating circuit when R8/R7＝R10/R9The method comprises the following steps:
Figure BDA0002547213870000082
wherein, VlevelTo change the level, Vcc1Is a linear voltage reference, LbFor boost inductance, RsTo sample the resistance, ticFor signal propagation delay, tdFor part of the resonance time, when tdWhen the value is equal to 0, the control is the constant conduction time control without resonance; r7、R8、R9、R10A resistor in the subtraction circuit;
2) the improved inductive current zero-crossing detection circuit generates a zero-crossing detection signal to the S end of the RS trigger to generate a switching-on signal.
3) To load RLTwo-end output voltage signal sampling value Vo/k2Output to the voltage error regulator to generate a voltage error signal VerrorAnd the RS trigger outputs a complete driving signal to the driving circuit to generate a driving signal.
Example five:
the improved constant on-time control method of the CRM boost PFC converter is realized based on a digital control mode and is realized by adopting the circuit of the first embodiment.
FIG. 1 shows a main power circuit of a CRM boost PFC converter, including an EMI filter and a rectifierBridge, input filter capacitor CinSampling resistor RsBoost inductor LbAnd a switching tube QbFreewheel diode DbAn output capacitor CoutAnd a load RL. The circuit parameters used in the examples were: boost inductor LbInductance of 176 μ H, parasitic capacitance C of power deviceds+Cdp130 pF. The test conditions were: input voltage vinIs 115V alternating current, the frequency of an input voltage line is 360-800 Hz, and the output voltage V iso270V, and the maximum output power is 160W. The present example tests the input current THD against conventional constant on-time control at 50%, 75% and 100% load, respectively.
Fig. 3 is a circuit diagram of a digital control circuit for realizing improved constant on-time of a CRM boost PFC converter, in which an input voltage sampling circuit, an improved inductor current zero-crossing detection circuit, an output voltage sampling circuit, and a driving circuit are added in addition to a main power circuit, in this embodiment, the digital control unit employs a TI TMS320F28335 chip, a first analog/digital converter, a second analog/digital converter, an interrupt system, an operation processing unit, and the like are integrated in the chip, a sampling frequency of the analog/digital conversion unit is 100kHz, and a specific implementation control process thereof is as follows:
step one, when the digital control unit responds to the ADC interruption program, the analog/digital conversion unit samples and inputs the filter capacitor CinVoltage signal v at two endscinAnd a load RLOutput voltage signal V at both endsoThe sampled values are respectively vcin/k1And Vo/k2Wherein k is1Take 63.5, k2Get 108, reference voltage VrefThe output voltage control target is divided by the output voltage sampling coefficient, and the voltage is 2.5V.
Step two, outputting a voltage sampling value Vo/k2And an output voltage reference VrefComparing to obtain an error value Δ VoCalculating the constant on-time T by a PI regulatoron。
Step three, improving an inductive current zero-crossing detection circuit to generate an inductive current zero-crossing signal, and synchronously triggering an ePWM module, wherein V in a level conversion circuitlevelUsing a fixed level generating circuit, take Vlevel＝0.025V。
Step four, the digital control unit calculates the required delay time TdelayWhen R is8/R7＝R10/R9The method comprises the following steps:
Figure BDA0002547213870000091
wherein, Vcc1Taking 2.9V, R7Take 10k omega, R8Take 10k omega, R9Take 10k omega, R10Take 10k omega, RsTake 300m Ω, ticTake 130ns, when using resonance-free control, tdTaking 0 ns; when partial resonance control is employed, tdThe length is selected as required, and 100ns is taken in the embodiment.
Step five: according to the calculated delay time TdelayAnd constant on-time TonAnd the ePWM module generates a corresponding PWM signal and outputs the PWM signal to the drive circuit to generate a drive signal.
Fig. 9 and 10 are graphs comparing input current THD and converter efficiency for a CRM boost PFC converter employing conventional constant on-time control and modified constant on-time control, respectively. As can be seen from the comparison graph, the resonance-free constant on-time control provided by the invention can effectively improve the input current THD, but the realization of resonance-free destroys the original soft switching characteristic of the CRM boost PFC converter, and the converter efficiency is reduced to some extent, especially under the half-load condition; in order to improve the performance contradiction between the input current THD and the efficiency of the converter, the partial resonance constant conduction time control provided by the invention can improve the input current THD and simultaneously sacrifice the efficiency of the converter less.
Example six:
and (3) realizing the improved constant on-time control method of the CRM boost PFC converter based on an analog control mode, and realizing the improved constant on-time control method by adopting the circuit of the second embodiment.
FIG. 1 shows a main power circuit of a CRM boost PFC converter, including an EMI filter, a rectifier bridge, and an input filter capacitor CinSampling resistor RsBoost inductor LbAnd a switching tube QbFreewheel diode DbAn output capacitor CoutAnd a load RL. The circuit parameters used in the examples were: boost inductor LbInductance of 176 μ H, parasitic capacitance C of power deviceds+Cdp130 pF. The test conditions were: input voltage vinIs 115V alternating current, the frequency of an input voltage line is 360-800 Hz, and the output voltage V iso270V, and the maximum output power is 160W.
Fig. 5 is a circuit diagram of an analog control circuit for realizing improved constant on-time of a CRM boost PFC converter, in which an input voltage sampling circuit, an isolation link, an improved inductive current zero-crossing detection circuit, an output voltage sampling circuit, a driving circuit, a sawtooth wave generation circuit, a comparator, and a voltage error regulator are added in addition to a main power circuit, wherein the isolation link can adopt a voltage hall sensor or an isolation chip, and the specific control process is as follows:
step one, isolating and sampling an input filter capacitor CinVoltage v acrosscinA value of v as a sampling valuecin/k1Wherein k is1Taking 63.5 as the input voltage division coefficient, sampling the load RLOutput voltage signal V at two endsoThe sampled value is Vo/k2，k2For outputting the voltage division coefficient, 108 is selected and outputted to VlevelA varying level generating circuit when R8/R7＝R10/R9The method comprises the following steps:
Figure BDA0002547213870000101
wherein, Vcc1Taking 2.9V, R7Take 10k omega, R8Take 10k omega, R9Take 10k omega, R10Take 10k omega, RsTake 300m Ω, ticTake 130ns, when using resonance-free control, tdTake 0ns, Vcc2Taking 0V, R11Take 3.6k omega, R12Take 3.6k omega, R13Taking 9.1M omega, R14Take 2k Ω, R15Taking 8.2M omega; when partial resonance control is employed, tdAccording to the need to selectTake 100ns, V in this examplecc2Taking 0V, R11Take 920 omega, R12Take 920 omega, R13Taking 10M omega, R14Take 510 Ω, R15Take 9.1 M.OMEGA..
And step two, improving the inductive current zero-crossing detection circuit to generate a zero-crossing detection signal to the S end of the RS trigger to generate a switching-on signal.
Step three, reference voltage VrefTaking 2.5V, load RLTwo-end output voltage sampling signal Vo/k2Connected to the error amplifying circuit to generate an error voltage signal VerrorCan be adjusted by adjusting the resistance R5、R6And a capacitor C1Adjusting a proportionality coefficient and an integral coefficient of the voltage error adjuster; voltage error signal VerrorAnd comparing the output signal with the sawtooth wave to obtain a turn-off signal, sending the turn-off signal to the R end of the RS trigger, outputting a complete PWM signal by the RS trigger, sending the complete PWM signal to a driving circuit, and generating a driving signal.
The technical solutions of the present invention are not limited to the above embodiments, and all technical solutions obtained by using equivalent substitution modes fall within the scope of the present invention.

Claims (8)

1. A CRM boost PFC converter improved constant on-time control circuit is characterized in that: the CRM boost PFC converter comprises a CRM boost PFC converter main power circuit and a control unit, wherein the control unit comprises an input voltage sampling circuit, an improved inductive current zero-crossing detection circuit, an output voltage sampling circuit, a digital control unit or an analog control unit; the analog control unit includes a voltage error regulator and a drive signal generation circuit.
2. The improved constant on-time control circuit for the CRM boost PFC converter of claim 1, wherein: the main power circuit comprises an EMI filter, a rectifier bridge, an input filter capacitor, a sampling resistor, a boosting inductor, a switching tube, a freewheeling diode, an output capacitor and a load; the driving signal generating circuit comprises an RS trigger, a sawtooth wave generating circuit and a comparator, and the output end of the driving signal generating circuit is connected with the driving circuit of the switching tube; the input end of the input voltage sampling circuit is connected with two ends of the input filter capacitor, and the output end of the input voltage sampling circuit is connected with an analog/digital conversion interface of the digital control unit or is connected with the input end of the improved inductive current zero-crossing detection circuit through an isolation link; the input end of the improved inductive current zero-crossing detection circuit is connected with two ends of the sampling resistor, the input voltage sampling circuit and the output voltage sampling circuit, and the output end of the improved inductive current zero-crossing detection circuit is connected with the S end of the digital control unit or the RS trigger; the input end of the output voltage sampling circuit is connected with two ends of a load, and the output end of the output voltage sampling circuit is connected with an analog-digital conversion interface of the digital control unit or a voltage error regulator and an improved inductive current zero-crossing detection circuit.
3. The improved constant on-time control circuit for the CRM boost PFC converter of claim 2, wherein: the improved inductive current zero-crossing detection circuit comprises a level conversion circuit, a comparator, an RC filter and a digital isolator; the level shift circuit comprises VlevelThe circuit comprises a generating circuit and a subtraction circuit, wherein the subtraction circuit is composed of an operational amplifier and peripheral circuits thereof.
4. The improved constant on-time control circuit for the CRM boost PFC converter of claim 3, wherein: the subtraction circuit comprises an operational amplifier and a linear voltage reference Vcc1And R7、R8、R9And R10Four resistors, wherein the a terminal of the sampling resistor is connected with a linear voltage reference Vcc1One end and R7One end connected, linear voltage reference Vcc1The other end is grounded, R7The other end is connected with the positive input end of the operational amplifier and R8One end, R8The other end is grounded, R9One end and VlevelThe generating circuit is connected, and the other end is connected with the negative input end of the operational amplifier and R10One end, R10The other end is connected with the output end of the operational amplifier.
5. The improved constant on-time control circuit for the CRM boost PFC converter of claim 4, wherein: in the case of the digital control mode,Vlevelthe generating circuit uses a fixed level generating circuit which is based on a linear voltage reference Vcc3And a resistor, wherein one end of the linear voltage reference is connected with R16One end and the other end is connected with R17One end, R16The other end and R17The other end is connected with and outputs to R9。
6. The improved constant on-time control circuit for the CRM boost PFC converter of claim 4, wherein: for the analog control mode, VlevelThe generation circuit adopts a varying level generation circuit composed of an operational amplifier and its peripheral circuits, wherein the linear voltage reference Vcc2One end is grounded, and the other end is connected with R11One end, R11The other end is connected with the positive input end of the operational amplifier and R12One end and R15One end, R12The other end is grounded, R15The other end is connected with an output voltage sampling circuit, and the input voltage sampling circuit is connected with R13One end, R13The other end is connected with the negative input end of the operational amplifier and R14One end, R14The other end is connected with the output end of the operational amplifier and outputs to R9。
7. A CRM boost PFC converter improved constant on-time control method is characterized in that: the method is realized by a digital control mode by adopting the control circuit of claim 1, 2, 3, 4 or 5, and comprises the following steps:
1) A/D converter of digital control unit samples voltage signal v at two ends of input filter capacitorcinAnd an output voltage signal V across the loadoThe sampled values are respectively vcin/k1And Vo/k2Wherein k is1As a division coefficient of the input voltage, k2Dividing the voltage coefficient for the output voltage;
2) output voltage sampling value Vo/k2And an output voltage reference VrefComparing to obtain an error value Δ VoCalculating the constant on-time T by a PI regulatoronFor adjustingThe output voltage is saved so as to realize constant voltage output under different input voltages and output powers;
3) an improved inductive current zero-crossing detection circuit generates an inductive current zero-crossing signal in advance at the conduction stage of a freewheeling diode and synchronously triggers an ePWM module of a digital control unit;
4) to realize no resonance or partial resonance, the delay time T of the needed compensation is calculateddelayWhen R is8/R7＝R10/R9When the temperature of the water is higher than the set temperature,
Figure FDA0002547213860000021
wherein, VlevelTo a fixed level, Vcc1Is a linear voltage reference, LbFor boost inductance, RsTo sample the resistance, ticFor signal propagation delay, tdFor part of the resonance time, when tdWhen the value is equal to 0, the control is the constant conduction time control without resonance; r7、R8、R9、R10A resistor in the subtraction circuit;
5) according to the calculated delay time TdelayAnd constant on-time TonAnd the ePWM module generates a corresponding PWM signal and outputs the PWM signal to the drive circuit to generate a drive signal.
8. A CRM boost PFC converter improved constant on-time control method is characterized in that: the method is realized by adopting the control circuit of claim 1, 2, 3, 4 or 6 and adopting an analog control mode, and comprises the following steps:
1) voltage v at two ends of isolation sampling input filter capacitorcinAnd a voltage signal V output across the loadoA value of v as a sampling valuecin/k1And Vo/k2Wherein k is1As a division coefficient of the input voltage, k2To output the voltage division coefficient, it is outputted to VlevelA varying level generating circuit when R8/R7＝R10/R9The method comprises the following steps:
Figure FDA0002547213860000031
wherein, VlevelTo change the level, Vcc1Is a linear voltage reference, LbFor boost inductance, RsTo sample the resistance, ticFor signal propagation delay, tdFor part of the resonance time, when tdWhen the value is equal to 0, the control is the constant conduction time control without resonance; r7、R8、R9、R10A resistor in the subtraction circuit;
2) an improved inductive current zero-crossing detection circuit generates a zero-crossing detection signal to an S end of an RS trigger to generate a switching-on signal;
3) sampling value V of output voltage signals at two ends of loado/k2Output to the voltage error regulator to generate a voltage error signal VerrorAnd the RS trigger outputs a complete driving signal to the driving circuit to generate a driving signal.
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