CN110572023B - PFC circuit, current compensation method of input capacitor of PFC circuit and power conversion circuit - Google Patents
PFC circuit, current compensation method of input capacitor of PFC circuit and power conversion circuit Download PDFInfo
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- CN110572023B CN110572023B CN201910930921.0A CN201910930921A CN110572023B CN 110572023 B CN110572023 B CN 110572023B CN 201910930921 A CN201910930921 A CN 201910930921A CN 110572023 B CN110572023 B CN 110572023B
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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
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- 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
Abstract
The present invention relates to the field of PFC circuits, and in particular, to a current compensation method for an input capacitor of a PFC circuit, the PFC circuit, and a power conversion circuit. The invention disclosesThe current compensation method of the input capacitor of the PFC circuit comprises the step of adopting a compensation current icbsFor the current i flowing through the input capacitance cbb of the PFC circuitcbbCompensation is carried out, the compensation current icbsIs a sinusoidal current and has a frequency twice that of the input ac power. The invention can effectively reduce the influence of the current phase shift of the input capacitor of the power supply conversion circuit on the input current, improve the PF value and simultaneously not influence the current working state of the circuit.
Description
Technical Field
The invention belongs to the technical field of PFC circuits, and particularly relates to a PFC circuit, a current compensation method of an input capacitor of the PFC circuit and a power conversion circuit.
Background
Due to the problem of increasing shortage of energy, people are forced to pay more and more attention to the power utilization efficiency of electronic devices, and therefore, most of the existing power conversion circuits are provided with a Power Factor Correction (PFC) circuit to correct an input current to improve a Power Factor (PF) of the power converter, so as to improve the power utilization efficiency, as shown in fig. 1, a conventional flyback power conversion circuit with a PFC circuit (in which a power factor control circuit is omitted) is provided.
The conventional PFC circuit mainly aims at the current i flowing through the power switch mosmosSinusoidal control is performed, thereby increasing the PF value. A plurality of PFC circuits and power factor correction methods are available for realizing the current i flowing through the power switch mosmosA better sinusoidal control is performed, as disclosed in the patent publication: CN104702092A, high PF values and low THD have been achieved.
In practice, in order to overcome EMI (electromagnetic interference), an input capacitor cbb is generally added to the ac input terminal of the power converter, so that the input current i is inputin＝icbb+imos(ii) a Wherein icbbFor the current flowing through the input capacitance cbb, the expression is
From FIG. 2, the current i can be seencbbIs changed and is no longer sinusoidal, then even if the current i ismosRealize sinusoidal control due to current icbbResulting in an input current iinThe phase pattern changes and the conduction range becomes narrow as shown in fig. 2, therebyResulting in a reduction in PF value. Especially in the case of high input voltage or large capacitance cbb, the current icbbThe influence on the input current is larger, so the current i is influencedcbbCompensation is performed.
While the existing compensation current icbbThe method mainly comprises two methods: a. the capacitance value of the input capacitor cbb is reduced, but the low-voltage normal operation and EMI are influenced; b. slope compensation, as shown in FIG. 3, but with the addition of icbsThe positive offset value affects the control variable Vcomp of the power factor control circuit, and the current power changes, which is not easy to control.
Disclosure of Invention
The present invention is directed to a PFC circuit, a current compensation method for an input capacitor thereof, and a power conversion circuit, so as to solve the above-mentioned problems.
In order to achieve the purpose, the invention adopts the technical scheme that: a current compensation method for input capacitor of PFC circuit includes using compensation current icbsFor the current i flowing through the input capacitance cbb of the PFC circuitcbbCompensation is carried out, the compensation current icbsIs a sinusoidal current and has a frequency twice that of the input ac power.
Further, the compensation current icbsIs expressed as
Wherein, K1Is a first coefficient, facFor inputting the frequency of the AC power supply, tacIs 1/fac。
Further, the compensation current icbsIs expressed as
Wherein, K2Is the second coefficient, Vac0Is the effective value of the input voltage, CCTo compensate for the capacitance of the capacitor.
Furthermore, the capacitance value C of the compensation capacitorCInversely related to the capacitance value of the input capacitance cbb.
Further, a power factor control circuit is used for controlling a power switch in the PFC circuit to generate a compensation current icbsThereby to the current i flowing through the input capacitance cbb of the PFC circuitcbbCompensation is performed.
The invention also provides a PFC circuit, which adopts the current compensation method of the input capacitor of the PFC circuit to compensate the current i flowing through the input capacitor cbb of the PFC circuitcbbCompensation is performed.
The invention also provides a power supply conversion circuit which is provided with the PFC circuit.
The invention has the beneficial technical effects that:
the invention adopts sinusoidal current with the frequency twice of the frequency of the input alternating current power supply to the current i of the input capacitor cbbcbbThe compensation is carried out, the influence of the current phase shift of the input capacitor of the power supply conversion circuit on the input current can be effectively reduced, the PF value is improved, the influence on the low-voltage normal work and the EMI can be avoided, and the compensated current is alternating current and the original working state of the circuit can not be influenced.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
Fig. 1 is a circuit diagram of a flyback power converter circuit with a PFC circuit;
FIG. 2 shows the current i of the input capacitance cbbcbbFor input current iinSchematic of the effects of (x) (time on the abscissa and current on the ordinate);
FIG. 3 is a diagram of a conventional slope compensation (time on the abscissa and current on the ordinate);
FIG. 4 is a schematic diagram of various current waveforms (time on the abscissa and current on the ordinate) in accordance with an embodiment of the present invention;
FIG. 5 is a schematic diagram of the compensation effect of the embodiment of the present invention (time on the abscissa and current on the ordinate);
fig. 6 is a circuit diagram of a PFC circuit according to an embodiment of the present invention.
Detailed Description
To further illustrate the various embodiments, the invention provides the accompanying drawings. The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the embodiments. Those skilled in the art will appreciate still other possible embodiments and advantages of the present invention with reference to these figures. Elements in the figures are not drawn to scale and like reference numerals are generally used to indicate like elements.
The invention will now be further described with reference to the accompanying drawings and detailed description.
A current compensation method for input capacitor of PFC circuit includes using compensation current icbsFor the current i flowing through the input capacitance cbb of the PFC circuitcbbCompensation is carried out, the compensation current icbsIs a sinusoidal current and has a frequency twice that of the input ac power.
Specifically, in this embodiment, the compensation current icbsIs expressed as
Wherein, K1Is a first coefficient, facFor inputting the frequency of the AC power supply, tacIs 1/fac。K1Can be selected according to the actual circuit.
Compensating current icbsIs shown in FIG. 4, i in FIG. 4in(no CBB/CC) It is assumed that there is no input capacitor cbb in the power conversion circuit and no compensation current icbsAnd to the current i flowing through the power switch mosmosInput current after sinusoidal control, it can be seen that if the current i is applied to the power switch mosmosWhen PFC sine control is carried out, the input current i is at the timein(no CBB/CC) Is a sinusoidal current.
Compensating current icbsCurrent i to input capacitance cbbcbbAdding to obtain the error current ierror,
ierror＝icbs+icbb
Error current ierrorThe waveform of (2) is shown in FIG. 4, and it can be seen that after compensation, the error current ierrorThe influence on the input current becomes small.
The compensated effect is shown in FIG. 5, where iin(with CBB,no CC) The power supply conversion circuit has an input capacitor cbb and is used for converting the current i flowing through the power switch mosmosPerforming sinusoidal control, but without compensating current icbsAn input current to compensate; i.e. iin(with CBB,with CC) The power supply conversion circuit has an input capacitor cbb and is used for converting the current i flowing through the power switch mosmosPerforming sinusoidal control and using a compensating current icbsThe compensated input current, as can be seen from fig. 5, is compensated using the compensation current i described abovecbsAfter compensation, the current i is inputin(with CBB,with CC) The on-time of (2) becomes long, effectively reduces the influence of the current phase shift of the input capacitor cbb of the power conversion circuit on the input current, improves the PF value, simultaneously, does not need to reduce the capacitance value of the input capacitor cbb, thus not influencing the low-voltage normal work and EMI, and the compensated current is alternating current and does not influence the original working state of the circuit.
Preferably, in this embodiment, the compensation current icbsIs more specifically expressed as
Wherein, K2Is the second coefficient, Vac0For ac of power conversion circuitsEffective value of input voltage at input terminal, CCTo compensate the capacitance value of the capacitor. Increasing the effective value V of the input voltageac0This parameter is such that the current i is compensatedcbsWith the effective value V of the input voltageac0Is changed, the compensation effect is further improved.
In this embodiment, the capacitance C of the compensation capacitorCInversely related to the capacitance value of the input capacitance cbb, i.e. when the capacitance value of the input capacitance cbb is larger, the current icbbThe larger; the smaller the externally selected compensation capacitance Cc, the compensation current i is according to the above equationcbsThe larger the input capacitance cbb compensation can be effectively performed, but is not limited thereto.
In this embodiment, the power factor control circuit is used to control the power switch in the PFC circuit to generate the compensation current icbsThereby to the current i flowing through the input capacitance cbb of the PFC circuitcbbAnd compensation is performed, the circuit structure is simple, and the realization is easy.
The simulation is carried out by using a PFC circuit of the flyback power conversion circuit, and the simulation result is shown in the following table:
as can be seen from the above table, the current i to the input capacitance cbbcbbThe compensation is carried out, so that the PF value is effectively improved, and particularly the PF value is effectively improved when half load or light load is output.
The invention also provides a PFC circuit, which adopts the current compensation method of the input capacitor of the PFC circuit to compensate the current i flowing through the input capacitor cbb of the PFC circuitcbbCompensation is performed, and fig. 6 shows one of the circuit structures of the PFC circuit, where clk _ ac is a start signal of each sinusoidal ac half-wave, and Vset _ ramp is a ramp signal following an input ac signal; the peak value of the ramp signal of Vset _ ramp _ max. But not limited thereto, in other embodiments, the PFC circuit may also adopt other circuit structure forms.
The invention also provides a power conversion circuit which is provided with the PFC circuit, and the power conversion circuit can be a flyback power conversion circuit, a Boost power conversion circuit and the like.
The invention adopts sinusoidal current with twice input AC power frequency to the current i of the input capacitor cbbcbbThe compensation is carried out, so that the influence of the current phase shift of the input capacitor of the power supply conversion circuit on the input current can be effectively reduced, the PF value is improved, and the influence on the low-voltage normal work and the EMI can be avoided.
While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (5)
1. A current compensation method of an input capacitor of a PFC circuit is characterized in that: includes controlling a power switch in a PFC circuit using a power factor control circuit to generate a compensation current icbsThereby to the current i flowing through the input capacitance cbb of the PFC circuitcbbCompensation is carried out, the compensation current icbsIs a sinusoidal current with a frequency twice that of the input AC power supply, and the compensation current icbsIs expressed as
Wherein, K1Is a first coefficient, facFor inputting the frequency of the AC power supply, tacIs 1/fac。
2. The method of claim 1 for current compensation of an input capacitance of a PFC circuit, wherein: the compensation current icbsIs expressed as
Wherein, K2Is the second coefficient, Vac0Is the effective value of the input voltage, CCTo compensate for the capacitance of the capacitor.
3. The method of claim 2, wherein the step of compensating the input capacitance of the PFC circuit comprises: capacitance value C of the compensation capacitorCInversely related to the capacitance value of the input capacitance cbb.
4. A PFC circuit, characterized by: method for compensating the current i flowing through the input capacitance cbb of a PFC circuit using the input capacitance of a PFC circuit according to any of claims 1 to 3cbbCompensation is performed.
5. A power conversion circuit, comprising: a PFC circuit as claimed in claim 4.
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