CN111669042B - 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 PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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- H02M1/42—Circuits or arrangements for compensating for or adjusting power factor in converters or inverters
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- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
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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
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., are successively promulgated and revised by the International electrotechnical Commission and the aviation radio and technology Commission, and the current harmonic standards to be satisfied by AC-DC converters of different power classes are clearly specified. The active Power Factor Correction (PFC) technology can improve the Power Factor of the AC-DC converter, reduce the Total Harmonic Distortion (THD) of the input current, and has a light volume and a light weight, and a good harmonic suppression capability, and has been widely used to reduce the harmonic pollution of electronic devices 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 soft switch of the CRM boost PFC converter is realized by virtue of resonance of a boost inductor and a parasitic capacitor of a power switch device, however, the inductor current in a switching period deviates from an ideal triangular shape due to the resonance, 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 control of the traditional constant conduction time, the invention provides an improved constant conduction time control method, which realizes the advanced detection of the zero-crossing signal of the inductive current 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 freewheeling 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 a voltage source V level A generating circuit and a subtraction circuit; the subtraction circuit comprises an operational amplifier and a linear voltage reference V cc1 And R 7 、R 8 、R 9 And R 10 Four resistors, wherein the a terminal of the sampling resistor is connected with a linear voltage reference V cc1 One end and R 7 One end connected, linear voltage reference V cc1 The other end is grounded, R 7 The other end is connected with the positive input end of the operational amplifier and R 8 One end, R 8 The other end is grounded, R 9 One end is connected with V level The generating circuit is connected, and the other end is connected with the negative input end of the operational amplifier and R 10 One end, R 10 The other end is connected with the output end of the operational amplifier; for digital control mode, V level The generating circuit uses a fixed level generating circuit which is based on a linear voltage reference V cc3 And a resistor, wherein one end of the linear voltage reference is connected with R 16 One end is connected with the other endTo R 17 One end, R 16 The other end and R 17 The other end is connected with and outputs to R 9 (ii) a For the analog control mode, V level The generation circuit adopts a varying level generation circuit composed of an operational amplifier and its peripheral circuits, wherein the linear voltage reference V cc2 One end is grounded, and the other end is connected with R 11 One end, R 11 The other end is connected with the positive input end of the operational amplifier and R 12 One end and R 15 One end, R 12 The other end is grounded, R 15 The other end is connected with an output voltage sampling circuit, and the input voltage sampling circuit is connected with R 13 One end, R 13 The other end is connected with the negative input end of the operational amplifier and R 14 One end, R 14 The other end is connected with the output end of the operational amplifier and outputs to R 9 。
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 capacitor cin And an output voltage signal V across the load o The sampled values are respectively v cin /k 1 And V o /k 2 Wherein k is 1 As a division coefficient of the input voltage, k 2 The output voltage division coefficient.
2) Output voltage sampling value V o /k 2 And an output voltage reference V ref Comparing to obtain an error value Δ V o Calculating the constant on-time T by a PI regulator on This 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 calculated delay When R is 8 /R 7 ＝R 10 /R 9 When the temperature of the water is higher than the set temperature,
wherein, V level To a fixed level, V cc1 Is a linear voltage reference, L b For boost inductance, R s To sample the resistance, t ic Is signal propagation delay (sum of signal propagation delay of improved inductive current zero-crossing detection circuit, drive circuit and digital control unit), t d For part of the resonance time, when t d When =0, the control is the non-resonance constant conduction time control; r 7 、R 8 、R 9 、R 10 A resistor in the subtraction circuit;
5) According to the calculated delay time T delay And constant on-time T on And 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 capacitor cin And a voltage signal V output across the load o A value of v as a sampling value cin /k 1 And V o /k 2 Wherein k is 1 As a division coefficient of the input voltage, k 2 To output the voltage division coefficient, it is outputted to V level A varying level generating circuit when R 8 /R 7 ＝R 10 /R 9 When the method is used:
wherein, V level To change the level, V cc1 Is a linear voltage reference, L b For boost inductance, R s To sample the resistance, t ic For signal propagation delay, t d For part of the resonance time, when t d When =0, the control is the non-resonance constant conduction time control; r 7 、R 8 、R 9 、R 10 A 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 load o /k 2 Output to the voltage error regulator to generate a voltage error signal V error And 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 main technical characteristics that:
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 a circuit for improved inductor current zero crossing detection;
FIG. 7 is V level A fixed level generating circuit;
FIG. 8 is V level A 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. of in -an input voltage; i.e. i in -input current on the front side of the EMI filter; c in -an input filter capacitance; v. of cin -inputting the voltage across the filter capacitor; r s -a sampling resistance; l is b -a boost inductance; q b -a switching tube; c ds -a switching tube parasitic capacitance; v. of ds -the voltage across the drain and source of the switching tube; d b -a freewheeling diode; c dp -free-wheeling diode parasitic capacitance; c out -an output capacitance; v o -an output voltage; r L -a load resistance; r 1 -a voltage dividing sampling resistor; r is 2 -a voltage dividing sampling resistor; r 3 -a voltage dividing sampling resistor; r is 4 -a voltage dividing sampling resistor; k is a radical of formula 1 -an input voltage division factor; k is a radical of 2 -an output voltage division factor; v. of cin /k 1 -input voltage sample values; v o /k 2 -outputting the voltage sample value; v ref -a reference voltage; Δ V o -a voltage PI loop error value; t is on -a conduction time; t is a unit of delay -a delay time; ADC1, ADC 2-analog/digital converter; r 5 -voltage error regulator coefficient resistance; r 6 -voltage error regulator coefficient resistance; c 1 -voltage error regulator coefficient capacitance; v error -a voltage error signal; i.e. i L -the inductor current; v. of gs -a drive signal; v cc1 -a linear voltage reference; v cc2 -a linear voltage reference; v cc3 -a linear voltage reference; r is 7 -subtraction circuit coefficient resistance; r 8 -subtraction circuit coefficient resistance; r 9 -subtraction circuit coefficient resistance; r 10 -subtraction circuit coefficient resistance; r f1 -RC filter resistance; c f1 -an RC filter capacitance; r 11 -varying the level generating circuit coefficient resistance; r 12 -varying the level generating circuit coefficient resistance; r 13 -varying the level generating circuit coefficient resistance; r 14 -varying the level generating circuit coefficient resistance; r 15 -varying the level generating circuit coefficient resistance; r 16 -a fixed level generating circuit coefficient resistance; r is 17 -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 C in Sampling resistor R s Boost inductor L b And a switching tube Q b Freewheel diode D b An output capacitor C out And a load R L (ii) a The input end of the input voltage sampling circuit is connected with an input filter capacitor C in The 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 R s The 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 R L The output ends of the two ends 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 a voltage source V level A generating circuit and a subtraction circuit; the subtraction circuit comprises an operational amplifier and a linear voltage reference V cc1 And R 7 、R 8 、R 9 And R 10 Four resistors, wherein a sampling resistor R s Terminal a of and a linear voltage reference V cc1 One end and R 7 One end connected, linear voltage reference V cc1 The other end is grounded, R 7 The other end is connected with the positive input end of the operational amplifier and R 8 One end, R 8 The other end is grounded, R 9 One end is connected with V level The generating circuit is connected, and the other end is connected with the negative input end of the operational amplifier and R 10 One end, R 10 The other end is connected with the output end of the operational amplifier; v level The generating circuit uses a fixed level generating circuit which is based on a linear voltage reference V cc3 And a resistor, wherein one end of the linear voltage reference is connected with R 16 One end and the other end is connected with R 17 One end, R 16 The other end and R 17 The other end is connected with and outputs to R 9 。
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 C in And a sampling resistor R s Boost inductor L b And a switching tube Q b Freewheel diode D b An output capacitor C out And a load R L (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 C in The 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 R s The output end of the input voltage sampling circuit is connected with the output end of the RS trigger; the input end of the output voltage sampling circuit is connected with a load R L The 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 V level A generating circuit and a subtraction circuit; the subtraction circuit comprises an operational amplifier and a linear voltage reference V cc1 And R 7 、R 8 、R 9 And R 10 Four resistors, wherein the resistor R is sampled s Terminal a of and a linear voltage reference V cc1 One end and R 7 One end connected, linear voltage reference V cc1 The other end is grounded, R 7 The other end is connected with the positive input end of the operational amplifier and R 8 One end, R 8 The other end is grounded, R 9 One end is connected with V level The generating circuit is connected, and the other end is connected with the negative input end of the operational amplifier and R 10 One end, R 10 The other end is connected with the output end of the operational amplifier; v level The generation circuit adopts a varying level generation circuit composed of an operational amplifier and its peripheral circuits, wherein the linear voltage reference V cc2 One end is grounded, and the other end is connected with R 11 One end, R 11 The other end is connected with the positive input end of the operational amplifier and R 12 One end and R 15 One end, R 12 The other end is grounded, R 15 The other end is connected with an output voltage sampling circuit, and the input voltage sampling circuit is connected with R 13 One end, R 13 The other end is connected with the negative input end of the operational amplifier and R 14 One end, R 14 The other end is connected with the output end of the operational amplifier and outputs to R 9 。
Example three:
the improved constant-conduction-time control method of the CRM boost type 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) through 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 or even eliminated, no-resonance or partial-resonance control is realized, and the THD of the input current 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 unit in Voltage signal v at two ends cin And a load R L Output voltage signal V at both ends o The sampled values are respectively v cin /k 1 And V o /k 2 Wherein k is 1 As a division coefficient of the input voltage, k 2 The output voltage division coefficient.
2) Sampling value V of output voltage o /k 2 And an output voltage reference V ref Comparing to obtain an error value Δ V o Calculating the constant on-time T by a PI regulator on And 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 calculated delay When R is 8 /R 7 ＝R 10 /R 9 When the temperature of the water is higher than the set temperature,
wherein, V level To a fixed level, V cc1 Is a linear voltage reference, L b For boost inductance, R s To sample the resistance, t ic For signal propagation delay (sum of signal propagation delay of improved inductive current zero-crossing detection circuit, drive circuit and digital control unit), t d For part of the resonance time, when t d When =0, the control is the non-resonance constant conduction time control; r 7 、R 8 、R 9 、R 10 A resistor in the subtraction circuit;
5) According to the calculated delay time T delay And constant on-time T on And 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 detection circuit (shown in figures 6 and 8) of the inductance current is used for detecting the zero-crossing signal (shown in figure 2) of the inductance current in advance, the influence of signal propagation delay is compensated, the reverse resonance process is shortened and even eliminated, no resonance or partial resonance control is realized, and the THD of the input current is improved. The method is realized by adopting analog control and comprises the following steps:
1) Isolation sampling input filter capacitor C in Voltage v across cin And a load R L Two-terminal output voltage signal V o With a value v of the sample cin /k 1 And V o /k 2 Wherein k is 1 As a division coefficient of the input voltage, k 2 To output the voltage division coefficient, it is outputted to V level Variable level generating circuitWhen R is 8 /R 7 ＝R 10 /R 9 The method comprises the following steps:
wherein, V level To change the level, V cc1 Is a linear voltage reference, L b As a boost inductance, R s To sample the resistance, t ic For signal propagation delay, t d For part of the resonance time, when t d When =0, the control is the non-resonance constant conduction time control; r is 7 、R 8 、R 9 、R 10 A 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 R L Two-end output voltage signal sampling value V o /k 2 Output to the voltage error regulator to generate a voltage error signal V error And 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, a rectifier bridge, and an input filter capacitor C in Sampling resistor R s Boost inductor L b And a switch tube Q b Freewheel diode D b An output capacitor C out And a load R L . The circuit parameters used in the examples are: boost inductor L b Inductance of 176 μ H, parasitic capacitance C of power device ds +C dp =130pF. The test conditions were: input voltage v in 115V alternating current, input voltage line frequency of 360-800 Hz, and output voltage V o 270V, and the maximum output power is 160W. The examples were loaded at 50%, 75% and 100%, respectivelyThe input current THD is tested against the conventional constant on-time control.
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 interrupt program, the analog/digital conversion unit samples and inputs the sample into a filter capacitor C in Voltage signal v at two ends cin And a load R L Output voltage signal V at both ends o The sampled values are respectively v cin /k 1 And V o /k 2 Wherein k is 1 Take 63.5,k 2 Get 108, reference voltage V ref The 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 V o /k 2 And an output voltage reference V ref Comparing to obtain an error value Δ V o Calculating the constant on-time T by a PI regulator on 。
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 circuit level Using a fixed level generating circuit, take V level ＝0.025V。
Step four, the digital control unit calculates the required delay time T delay When R is 8 /R 7 ＝R 10 /R 9 The method comprises the following steps:
wherein, V cc1 Taking 2.9V,R 7 Take 10k omega, R 8 Take 10k Ω, R 9 Take 10k omega, R 10 Take 10k Ω, R s Take 300m Ω, t ic Take 130ns, t when using resonance-free control d Taking 0ns; when partial resonance control is employed, t d The length is selected as required, and 100ns is taken in the embodiment.
Step five: according to the calculated delay time T delay And constant on-time T on And 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 CRM boost type PFC converters 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 realizing the improved constant on-time control method of the CRM boost type PFC converter based on an analog control mode 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 C in Sampling resistor R s Boost inductor L b And a switching tube Q b Freewheel diode D b An output capacitor C out And a load R L . The circuit parameters used in the examples are: boost inductor L b Inductance of 176 μ H, parasitic capacitance C of power device ds +C dp =130pF. The test conditions were: input voltage v in 115V alternating current, input voltage line frequency of 360-800 Hz, and output voltage V o 270V, 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 C in Voltage v across cin A value of v as a sampling value cin /k 1 Wherein k is 1 Taking 63.5 as the input voltage division coefficient, sampling the load R L Output voltage signal V at two ends o With a value of V o /k 2 ，k 2 For outputting the voltage division coefficient, 108 is selected and outputted to V level A varying level generating circuit when R 8 /R 7 ＝R 10 /R 9 The method comprises the following steps:
wherein, V cc1 Taking 2.9V,R 7 Take 10k omega, R 8 Take 10k omega, R 9 Take 10k omega, R 10 Take 10k omega, R s Take 300m Ω, t ic Take 130ns, when using resonance-free control, t d Get 0ns, V cc2 Fetching 0V, R 11 Take 3.6k omega, R 12 Take 3.6k omega, R 13 Taking 9.1M omega, R 14 Take 2k Ω, R 15 Taking 8.2M omega; when partial resonance control is employed, t d Selected as required, 100ns in this example cc2 Fetching 0V, R 11 Take 920 omega, R 12 Take 920 omega, R 13 Taking 10M omega, R 14 Take 510 Ω, R 15 Take 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 V ref Taking 2.5V, load R L Two-end output voltage sampling signal V o /k 2 Connected to an error amplifying circuitGenerating an error voltage signal V error Can be adjusted by adjusting the resistance R 5 、R 6 And a capacitor C 1 Adjusting a proportionality coefficient and an integral coefficient of the voltage error adjuster; voltage error signal V error And a turn-off signal obtained by comparing the PWM signal with the sawtooth wave is sent to the R end of the RS trigger, and the RS trigger outputs a complete PWM signal to be sent to a driving circuit to generate 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 (5)
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 comprises a voltage error regulator and a driving signal generating circuit;
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;
for a digital control mode, 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; the input end of the improved inductive current zero-crossing detection circuit is connected with two ends of the sampling resistor, and the output end of the improved inductive current zero-crossing detection circuit is connected with the digital control unit; 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;
for the analog control mode, the drive signal generating circuit comprises an RS trigger, a sawtooth wave generating circuit and a comparator, and the output end of the drive signal generating circuit is connected with the drive circuit of the switch tube; the input end of the input voltage sampling circuit is connected with the two ends of the input filter capacitor, and the output end of the input voltage sampling circuit 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 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 the voltage error regulator and the 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 conversion circuit comprisesV level The circuit comprises a generating circuit and a subtraction circuit, wherein the subtraction circuit is composed of an operational amplifier and peripheral circuits thereof;
the subtraction circuit comprises an operational amplifier and a linear voltage referenceV cc1 AndR 7 、R 8 、R 9 andR 10 four resistors, wherein the terminal a of the sampling resistor is connected with a linear voltage referenceV cc1 One end andR 7 one terminal connected, linear voltage referenceV cc1 The other end is grounded,R 7 the other end is connected with the positive input end of the operational amplifier andR 8 at one end of the first and second connecting rods,R 8 the other end is grounded, and the other end is grounded,R 9 one end is connected withV level The generating circuit is connected, and the other end is connected with the negative input end of the operational amplifier andR 10 at one end of the first and second connecting rods,R 10 the other end is connected with the output end of the operational amplifier.
2. The improved constant on-time control circuit for the CRM boost PFC converter of claim 1, wherein: in the case of the digital control mode,V level the generating circuit employs a fixed level generating circuit that is referenced by a linear voltageV cc3 And a resistor, wherein one end of the linear voltage reference is connectedR 16 One end and the other end are connectedR 17 At one end of the first and second connecting rods,R 16 the other end is connected withR 17 The other end is connected with and outputs toR 9 。
3. According to the claimsAsk 1 the improved constant on-time control circuit of CRM boost type PFC converter is characterized in that: as for the manner of the analog control,V level the generation circuit adopts a varying level generation circuit composed of an operational amplifier and its peripheral circuits, wherein the linear voltage referenceV cc2 One end is grounded and the other end is connectedR 11 At one end of the first and second connecting rods,R 11 the other end is connected with the positive input end of the operational amplifier andR 12 one end andR 15 at one end of the first and second guide rails,R 12 the other end is grounded,R 15 the other end is connected with an output voltage sampling circuit, and an input voltage sampling circuit is connectedR 13 At one end of the first and second connecting rods,R 13 the other end is connected with the negative input end of the operational amplifier andR 14 at one end of the first and second guide rails,R 14 the other end is connected with the output end of the operational amplifier and output toR 9 。
4. A CRM boost PFC converter improved constant on-time control method is characterized in that: the method is implemented by a digital control mode by using the control circuit of claim 1 or 2, and comprises the following steps:
1) A/D converter of digital control unit samples voltage signal at two ends of input filter capacitorv cin And an output voltage signal across the loadV o The sampling values are respectivelyv cin /k 1 AndV o /k 2 whereink 1 In order to input the voltage division coefficient of the voltage,k 2 dividing the voltage coefficient for the output voltage;
2) Sampling value of output voltageV o /k 2 And an output voltage referenceV ref The error value is obtainedV o Calculating the constant on-time by a PI regulatorT on The output voltage is adjusted 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 time delay of the needed compensation is calculatedT delay When is coming into contact withR 8 /R 7 =R 10 /R 9 When the temperature of the water is higher than the set temperature,
wherein the content of the first and second substances,V level in order to be at a fixed level,V cc1 in order to be a linear voltage reference,L b in order to provide a boost inductance, the boost inductance,R s in order to sample the resistance, the resistance is sampled,t ic in order to delay the propagation of the signal,t d for part of the resonance time whent d When =0, the control is the non-resonance constant conduction time control;R 7 、R 8 、R 9 、R 10 a resistor in the subtraction circuit;
5) According to the calculated delay timeT delay And constant on-timeT on The ePWM module generates a corresponding PWM signal and outputs the PWM signal to the drive circuit to generate a drive signal.
5. 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 or 3 and adopting an analog control mode, and comprises the following steps:
1) Isolated sampling input filter capacitor voltage at two endsv cin And output voltage signal across the loadV o The sampled value isv cin /k 1 AndV o /k 2 in whichk 1 In order to input the voltage division coefficient of the voltage,k 2 to output the voltage division coefficient toV level A varying level generating circuit whenR 8 /R 7 =R 10 /R 9 The method comprises the following steps:
wherein the content of the first and second substances,V level in order to change the level of the electric power,V cc1 in order to be a linear voltage reference,L b in order to provide a boost inductance, the boost inductance,R s in order to sample the resistance, the resistance is sampled,t ic in order to delay the propagation of the signal,t d for part of the resonance time whent d When =0, the control is the non-resonance constant conduction time control;R 7 、R 8 、R 9 、R 10 a resistor in the subtraction circuit;
2) An improved inductive current zero-crossing detection circuit generates a zero-crossing detection signal to the S end of an RS trigger to generate a switching-on signal;
3) Sampling the output voltage signals at two ends of the loadV o /k 2 Output to the voltage error regulator to generate a voltage error signalV error And the RS trigger outputs a complete driving signal to the driving circuit to generate a driving signal.
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| An Online Monitoring Method of Circuit Parameters for Variable On-Time Control in CRM Boost PFC Converters;Xiaoyong Ren等;《IEEE TRANSACTIONS ON POWER ELECTRONICS》;第第34卷卷(第第2期 期);第1786-1797页 * |
| 同步整流Boost 变换器中过零检测电路的设计;黄莹等;《南京邮电大学学报（自然科学版）》;第第39卷卷(第第1期期);第68-73页 * |
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