CN114865921A - Charge balance control method and charge balance controller for DCM Flyback converter - Google Patents

Charge balance control method and charge balance controller for DCM Flyback converter Download PDF

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CN114865921A
CN114865921A CN202210431074.5A CN202210431074A CN114865921A CN 114865921 A CN114865921 A CN 114865921A CN 202210431074 A CN202210431074 A CN 202210431074A CN 114865921 A CN114865921 A CN 114865921A
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charge
ref
output
flyback converter
output voltage
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闵闰
张凯
童乔凌
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Huazhong University of Science and Technology
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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
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
    • 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
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • 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
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
    • H02M3/33523—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters with galvanic isolation between input and output of both the power stage and the feedback loop
    • 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
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

Abstract

The invention belongs to the technical field of power electronics, and particularly relates to a charge balance control method and a charge balance controller for a DCM Flyback converter, which comprise the following steps: the charge balance control is done in two switching cycles, wherein the following steps are performed in each switching cycle: based on the input and output of the converter in the current switching period obtained by sampling, calculating the output charge Q from the converter to the output capacitor when the duty ratio of the current switching period is high ch At the same time according to
Figure DDA0003610559350000011
Output voltage v of converter after pre-estimating two switching periods ext In the formula v out And
Figure DDA0003610559350000012
current switching period obtained for each sample is at Q ch Output voltage and its variation when equal to 0; based on Q ch 、v ext And a reference voltage v ref According to Q ref ＝C(v ref ‑v ext )‑Q ob Calculating a reference charge Q ref And the method is used for calculating the duty ratio of the digital pulse width modulation signal to control the switching of the converter in the next switching period. The invention predicts the output voltage after two switching periods, is used for calculating the reference charge of the next switching period without hysteresis, and improves the transient response to the circuit disturbance.

Description

Charge balance control method and charge balance controller for DCM Flyback converter
Technical Field
The invention belongs to the technical field of power electronics, and particularly relates to a charge balance control method and a charge balance controller for a DCM Flyback converter.
Background
The Flyback converter is widely used in the industrial field because of its simple scheme, small volume and electrical isolation characteristics. The converter may operate in Continuous Conduction Mode (CCM) or Discontinuous Conduction Mode (DCM). These two modes are superior and inferior. When the power level is relatively high, a Flyback converter operating in CCM mode can achieve higher efficiency and lower voltage stress than when operating in DCM mode. But in this mode the Flyback converter requires a high magnetic inductance and a large transformer size. In addition, since the Flyback converter transfer function at this time includes a right half-plane (RHP) zero point, the Flyback converter operating in the CCM mode has a limited bandwidth. The advantages of DCM compared to CCM are: only a small size transformer is required, reduction of diode reverse recovery effect, and elimination of the RHP zero point facilitate stable control, etc. A Flyback converter operating in DCM is widely used for PV-AC modules and PFC systems because it can be considered as an easily controlled current source.
In order to save cost, power, size and improve transient response of the converter, new approaches are constantly being explored on the basis of conventional converter control strategies. To achieve the best transient response, a voltage-based charge balance (VCB) controller is used for a Buck converter operating in CCM. The control method continuously adjusts the ON/OFF state of the main switch so that the inductor current can charge the output in the shortest time. However, this approach can degrade performance when it is implemented in digital circuitry, as it requires continuous sampling and computation. Furthermore, while this strategy may achieve the best dynamic response, it is only suitable for Buck converter applications. Based on this idea, average-current-based Charge-Balance control (ACCB) has been proposed and used for Flyback converters. The ACCB strategy is not continuous sampling and calculation, but based on Pulse Width Modulation (PWM), sampling and calculation is done once per switching period, which optimizes the transient response by calculating the appropriate duty cycle for the next switching period. The ACCB strategy is applicable to many different converters and can achieve the best dynamic response under PWM. However, the ACCB algorithm lags behind the reference charge by two switching cycles, which reduces the effect of the transient response of the circuit.
Disclosure of Invention
In view of the drawbacks and needs in the art, the present invention provides a charge balance control method and a charge balance controller for a DCM Flyback converter, which aims to improve transient response to circuit disturbances.
To achieve the above object, according to one aspect of the present invention, there is provided a charge balance control method for a DCM Flyback converter, the charge balance control being performed in two switching cycles, wherein the following steps are performed in each switching cycle:
calculating output charge Q from the Flyback converter to an output capacitor when the duty ratio of the current switching period is high based on the input and the output of the DCM Flyback converter with the current switching period obtained by sampling ch At the same time according to
Figure BDA0003610559330000021
Output voltage v of Flyback converter after pre-estimating two switching periods ext In the formula v out And
Figure BDA0003610559330000022
current switching period obtained for each sample is at Q ch When the output voltage is 0, the output voltage and the output voltage are changed, and T is the duration of a single switching period;
based on the output charge Q ch The output voltage v ext And a reference voltage v ref According to Q ref ＝C(v ref -v ext )-Q ob In the formula (2), Q ob ＝Q ch ，Q ch ＝Q ref z -1 ，z -1 Calculating a reference for a unit delay factor in a Z-transformElectric charge Q ref The reference charge Q ref And the method is used for calculating the duty ratio of the digital pulse width modulation signal to control the switching of the DCM Flyback converter in the next switching period.
Further, a constant compensation factor K is adopted to reduce the damping effect C Respectively correcting the output charges Q ch And a reference charge Q ref The correction method is as follows:
Figure BDA0003610559330000031
in the formula, K damp Representing the charge damping coefficient determined by calculation from the current actual circuit.
Further, K C ＝K damp 。
The present invention also provides a charge balance controller for a DCM Flyback converter, comprising: a charge observer, a voltage extrapolator, a VECB algorithm module, and a charge controller;
the charge observer, the voltage extrapolator and the VECB algorithm module are used for sampling the input and the output of the DCM Flyback converter in each switching period based on digital pulse width modulation, and when the charge quantity reaches the requirement of charge balance control, the following functions are executed in each switching period, and the charge balance control is completed in two switching periods:
the charge observer is used for calculating the output charge Q of the DCM Flyback converter to the output capacitor based on the input and the output of the DCM Flyback converter in the current switching period ch ；
The voltage extrapolator is used for inputting and outputting the DCM Flyback converter based on the current switching period
Figure BDA0003610559330000032
Output voltage v of Flyback converter after pre-estimating two switching periods ext In the formula v out And
Figure BDA0003610559330000033
current switching period obtained for each sample is at Q ch When the output voltage is 0, the output voltage and the output voltage are changed, and T is the duration of a single switching period;
the VECB algorithm module is to output the charge Q based on ch The output voltage v ext And a reference voltage v ref According to Q ref ＝C(v ref -v ext )-Q ob In the formula (2), Q ob ＝Q ch ，Q ch ＝Q ref z -1 ，z -1 Calculating a reference charge Q for a unit delay factor in the Z-transform ref The reference charge Q ref And the method is used for calculating the duty ratio of the digital pulse width modulation signal to control the switching of the DCM Flyback converter in the next switching period.
Further, the device also comprises a correction unit for adopting a constant-value compensation factor K for reducing the damping effect C Respectively correcting the output charges Q ch And a reference charge Q ref The correction method is as follows:
Figure BDA0003610559330000041
in the formula, K damp Representing the charge damping coefficient determined by calculation from the current actual circuit.
Further, K C ＝K damp 。
The present invention also provides a computer-readable storage medium including a stored computer program, wherein when the computer program is executed by a processor, the apparatus on which the storage medium is located is controlled to execute a charge balance control method for a DCM Flyback converter as described above.
Generally, by the above technical solution conceived by the present invention, the following beneficial effects can be obtained:
(1) in order to improve the transient response to the circuit disturbance, a voltage extrapolator is designed to predict the output voltage after two switching periods by adopting the zero output charge condition based on the differential value of the output voltage. This extrapolated output voltage is used to calculate the reference charge for the next switching cycle. In this way, the reference charge can be calculated without hysteresis, thereby improving the transient response to circuit disturbances.
(2) Aiming at the charge damping and the influence of the charge damping on the output voltage, the constant compensation factor is adopted in the circuit to reduce the steady-state error of the output voltage to the maximum extent.
Drawings
Fig. 1 is a flowchart illustrating steps executed in a single switching cycle of a charge balance control method for a DCM Flyback converter according to an embodiment of the present invention;
fig. 2 is a circuit diagram of a Flyback converter under the control of the ACCB algorithm according to an embodiment of the present invention;
fig. 3 is a schematic diagram illustrating changes in output voltage and charge of a Flyback converter under the control of an ACCB algorithm according to an embodiment of the present invention;
fig. 4 is a circuit diagram of a Flyback controller under the control of the VECB algorithm according to an embodiment of the present invention;
fig. 5 is a schematic diagram illustrating changes in output voltage and charge of a Flyback converter under the control of the VECB algorithm according to an embodiment of the present invention;
fig. 6 is a circuit diagram of a precision Flyback converter considering parasitic effects, transformer leakage inductance and RCD snubber circuit according to an embodiment of the present invention;
FIG. 7 is a view of a section v provided in an embodiment of the present invention in And v out A charge damping coefficient diagram of (a);
fig. 8 is a diagram of transient changes of output voltages corresponding to different control algorithms when R jumps from 30 Ω to 15 Ω according to an embodiment of the present invention, where (a) indicates that a PI control algorithm is used, (b) an ACCB control algorithm is used, and (c) a VECB control algorithm is used;
fig. 9 is a diagram of transient changes of output voltages corresponding to different control algorithms when R jumps from 150 Ω to 15 Ω according to an embodiment of the present invention, where (a) indicates that a PI control algorithm is used, (b) an ACCB control algorithm is used, and (c) a VECB control algorithm is used;
fig. 10 is a graph of output voltage transients when Vin jumps from 10V to 7.5V using different control algorithms according to an embodiment of the present invention, where (a) indicates using a PI control algorithm, (b) uses an ACCB control algorithm, and (c) uses a VECB control algorithm;
fig. 11 is a graph of output voltage transients when Vref jumps from 15V to 15.25V using different control algorithms according to an embodiment of the present invention, where (a) indicates that a PI control algorithm is used, (b) an ACCB control algorithm is used, and (c) a VECB control algorithm is used;
fig. 12 is a graph of output voltage transients corresponding to different control algorithms when Vref changes from 13V to 15V according to an embodiment of the present invention, where (a) indicates that a PI control algorithm is used, (b) an ACCB control algorithm is used, and (c) a VECB control algorithm is used.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Example one
A charge balance control method for a DCM Flyback converter, which completes the charge balance control in two switching cycles, wherein, as shown in fig. 1, the following steps are performed in each switching cycle:
calculating output charge Q from the Flyback converter to an output capacitor when the duty ratio of the current switching period is high based on the input and the output of the DCM Flyback converter with the current switching period obtained by sampling ch At the same time according to
Figure BDA0003610559330000061
Output voltage v of Flyback converter after pre-estimating two switching periods ext In the formula v out And
Figure BDA0003610559330000062
current switching period obtained for each sample is at Q ch When the output voltage is 0, the output voltage and the output voltage are changed, and T is the duration of a single switching period;
based on output charge Q ch Output voltage v ext And a reference voltage v ref According to Q ref ＝C(v ref -v ext )-Q ob In the formula (2), Q ob ＝Q ch ，Q ch ＝Q ref z -1 ，z -1 Calculating a reference charge Q for a unit delay factor in the Z-transform ref Reference charge Q ref And the method is used for calculating the duty ratio of the digital pulse width modulation signal to control the switching of the DCM Flyback converter in the next switching period.
The reason for the charge balance control method of the present embodiment and the rationality and advantages of the control method of the present embodiment will now be explained by the following explanations:
the Flyback converter circuit under the control of the conventional ACCB algorithm is shown in fig. 2, where d 1 Is the duty cycle of the Digital Pulse Width Modulation (DPWM) signal, C is the output capacitance, R is the load resistance, ADC is the digital-to-analog converter, V in Representing the supply voltage, Q ch Representing the output charge that the Flyback converter outputs to the output capacitor. The charge balance controller comprises a charge observer and a charge controller, the charge observer is used for estimating the output charge Q ch As a result of self observation (i.e. Q) ob ). ACCB algorithm module is based on Q ob Generating an appropriate Q ref Inputting the signal into a charge controller to regulate the duty ratio d as the charge controller 1 Such that the output voltage V is out Tracking V in two switching cycles ref The transient response of the circuit is improved.
I.e. when the output voltage V is out ＝V ref When the charge controller does not change the d of DPWM 1 Thus outputting V out The constant state is maintained; when the circuit is not in steady state, V out Deviation V erf The charge controller needs to change the d of DPWM 1 So that V is out Approach to V ref . ACCB algorithm ModuleBy detecting V out Whether or not to deviate from V ref To control the operation of the charge controller: if a deviation occurs, the Q is calculated from the charge observer ob To calculate the appropriate Q ref Sending the data to a charge controller to let the charge controller recalculate d 1 。
With regard to the ACCB algorithm, it is assumed that Q is in one switching cycle ch Tracking Q ref The output voltage can pass through Q ref Increase or decrease of. In addition, the ACCB algorithm operates by calculating the reference charge Q in the next switching cycle ref To improve the transient response. When v is shown in FIG. 3 out [k]Below v ref [k]When is, Q ch [k+1]＝Q ref [k]To adjust v out [k+2]To v ref [k]. Since the total charge flowing through the output capacitor is Q ch -Q dis In the discrete time domain, v is given within one switching period out The variations of (c) are as follows:
Figure BDA0003610559330000071
where Z is a basic unit in the Z transform.
The charge balance controller corresponding to the ACCB algorithm is designed to convert v into v within two switching periods out Is adjusted to v ref I.e. v ref ＝v out z 2 . To deduce v out z 2 The value of (1) multiplied by z +1 gives:
Figure BDA0003610559330000072
in formula 2, Q dis Equal to v during a switching cycle as a function of load and output voltage out And T/R. Since R is unknown, Q dis It cannot be calculated. To solve this problem, the formula (2) is multiplied by 1-z -2 Obtaining:
Figure BDA0003610559330000073
charge Q output to the load due to the presence of the output capacitor dis With little variation over several switching cycles, Q dis (z+1-z -1 -z -2 ) 0 is valid. Therefore, the following formula (4):
Figure BDA0003610559330000074
due to the presence of a charge observer and charge controller, Q ob ＝Q ch And Q ch ＝Q ref z -1 Is effective. Therefore, substituting v ref ＝v out z 2 Obtaining by formula (4):
Q ref ＝Q ob z＝Q ob (z -1 +z -2 -1)+C(v ref -2v out +v out z -2 ) (5)
based on (5), the ACCB algorithm calculates the appropriate Q ref To improve transient response.
In formula (5) Z is present -2 This represents Q ref There is a lag of two switching cycles. Therefore, equation (5) means that the correct Q is obtained although all the values of the parameters in the equation are known ref It must take two switching cycles. If the circuit is suddenly changed from a steady state to a non-steady state, it also means that the circuit takes two cycles to react to the sudden change, and a total of four switching cycles are required to finally complete the charge balance.
The ACCB algorithm is based on an assumption Q dis (z+1-z -1 -z -2 ) 0, this approximation equation is used to eliminate Q in the equation dis This is crucial, since Q dis ＝v out There are unknowns in T/R. Further, as shown in equation (5), the conventional ACCB algorithm calculates Q with a lag of two switching cycles ref It is clear that this hysteresis reduces the transient response.
Based on the above analysis, the present embodiment proposes a voltage extrapolation charge balance control strategy to eliminate the response lag, as shown in the figure4, the VECB algorithm module passes the detection V out Whether or not to deviate from V ref To control the operation of the charge controller. The VECB algorithm module calculates the reference charge Q by extrapolating the voltage ref The extrapolated voltage being at the output charge Q ch From the present output voltage v under 0 condition out Theoretical voltage after two switching cycles. Using the extrapolated voltage, a calculation can be made without hysteresis that can be used to track to the reference voltage v once ref Thereby improving the transient response to circuit disturbances.
The above-mentioned extrapolated voltage is calculated by a voltage extrapolator in fig. 3, which is based on the output voltage v sampled by the ADC in the figure out And
Figure BDA0003610559330000081
and (6) working. As shown in fig. 5, for a Flyback converter operating in DCM, the output current is zero when the duty cycle is low during each switching cycle, so the output capacitor C discharges and the output voltage is dv out Slope of/dt decreases, presence
Figure BDA0003610559330000082
Suppose 2T<<RC, this condition is valid in most application scenarios, and the decrease of the output voltage is almost linear. Thus based on measured v out And
Figure BDA0003610559330000083
extrapolation voltage v ext Given by:
Figure BDA0003610559330000091
i.e. if Q ch At zero output charge, the output voltage will drop to v in two switching cycles ext 。v ext Based on the current v out And dv out/ dt, are constantly refreshed, unless the circuit state changes, the value at each refresh is unchanged. For DCM state, when the switch is turned offAt this time, Q ch When the value is 0, dv can be obtained out/ dt。
In addition, in order to switch v in two switching cycles out Is adjusted to v ref The total output charge for the next two switching cycles should be C (v) ref -v ext ). Therefore, the discrete-time equation for the output charge should satisfy:
Q ch z+Q ch ＝C(v ref -v ext ) (7)
suppose Q is guaranteed by a charge observer and a charge controller ob ＝Q ch And Q ch ＝Q ref z -1 The VECB algorithm is given by:
Q ref ＝C(v ref -v ext )-Q ob (8)
compared with the formula (5), the algorithm is simpler, and Q is calculated ref There is no hysteresis in the process of (3).
From the above calculations, the closed loop Small Signal Models (SSM) of ACCB and VECB are respectively as follows:
Figure BDA0003610559330000092
Figure BDA0003610559330000093
Φ r_VECB (z)，Φ l_VECB (z) flyback converters, respectively, under the control of VECB
Figure BDA0003610559330000094
Relative to
Figure BDA0003610559330000095
Transfer function of and
Figure BDA0003610559330000096
relative to
Figure BDA0003610559330000097
The transfer function of (a) is selected,
Figure BDA0003610559330000098
a small signal representing the output voltage is present,
Figure BDA0003610559330000099
a small signal representing a reference voltage is provided,
Figure BDA00036105593300000910
a small signal representing a load R; phi r_ACCB (z) and Φ l_ACCB (z) represents the corresponding transfer function under ACCB control.
By comparing the formulas (9) and (10), it can be seen that { Φ } r_VECB (z)，Φ l_VECB (z) } relative to { Φ r_ACCB (z)，Φ l_ACCB (z), less affected by the coefficient a (a ═ T/RC). In addition thereto,. phi l_VECB Molecular ratio in (z) (. phi.) l_ACCB The molecules in (z) experience less time delay, indicating a faster transient response to circuit disturbances. Theoretical analysis therefore indicates the advantages of VECB control over traditional ACCB control. That is, whether ACCB or VECB, the controller is designed to regulate v in two switching cycles out To v ref With the difference that Q ref The former lags two cycles.
From the analysis of the above two algorithms, it can be known that the output charge Q is ch Calculated by a charge observer and adjusted by a charge controller. The charge observer and the charge controller ensure Q ob ＝Q ch And Q ch ＝Q ref z -1 . The conventional ACCB algorithm calculates Q with a lag of two switching cycles ref And thus the output voltage, this hysteresis reduces the transient response. And the voltage extrapolator in the VECB algorithm is based on the v obtained by sampling out And dv out/ dt, calculation of Q without hysteresis ref The transient response of the Flyback converter is improved.
Preferably, all of the above analyses are in an ideal state, and therefore Q ob ＝Q ch And Q ch ＝Q ref z -1 This premise holds true for both ACCB and VECB. This premise is ensured by the charge controller and the charge observer. However, there is a damping effect of the actual output charge. For an actual Flyback circuit, L is shown in FIG. 6 pt Is the leakage inductance of the main side, L st Is the leakage inductance of the secondary side; r pt Is the winding resistance of the main side, R st Is the winding resistance of the secondary side, R ds Is the on-resistance of the switching tube, R F Is the on-resistance of the diode, V F Is the on-resistance of the diode; r s 、C s 、D s Is the resistance, capacitance and diode of the RCD circuit, n: 1 is the turns ratio, in which case Q ob ＝Q ch And Q ch ＝Q ref z -1 No longer effective, charge damping coefficient K damp The output voltage steady state error is affected. Due to K damp The control effect of the charge controller and the charge observer is expressed as:
Figure BDA0003610559330000101
and because the discrete-time model of the circuit in the VECB control is as follows:
Figure BDA0003610559330000111
the steady-state error relative value caused by the damping effect is derived from the above equation and equation (11):
Figure BDA0003610559330000112
because of T/(RC)<0.01 and 0.8<K damp <1 is effective in most application scenes, and the relative error is less than 0.5 percent, and the magnitude of the relative error is equivalent to the ripple value of the output voltage, so that the relative error can be ignored.
Nevertheless, a constant compensation factor K can be used C To minimize the damping effect.The actual effect of the charge observer and charge controller after considering the compensation factor is shown as follows:
Figure BDA0003610559330000113
as shown in FIG. 4, Q ch Multiplying by K c ，Q ref Multiplying by 1/K c The compensation factor acting on Q simultaneously ch To O ob And Q ref To Q ch Among the conversions of (1).
The relative value of the steady state error after considering the compensation factor is therefore:
Figure BDA0003610559330000114
in order to minimize the steady state error, the damping coefficient K needs to be calculated from the actual circuit under different steady state conditions damp As shown in fig. 7.
Preferably, the corresponding K is determined according to formula (13) in the present embodiment C To eliminate steady-state errors due to damping effects, i.e. let K C ＝K damp The theoretical relative steady state error can be made equal to 0.
Therefore, the Q ensured by the charge observer and the charge controller has a damping effect on the actual output charge due to the parasitic effect and the like ob ＝Q ch And Q ch ＝Q ref z -1 No longer holds, a constant compensation factor K can be used C To minimize the damping effect.
The VECB control algorithm provided by the embodiment eliminates the lag of two periods in the charge balance calculation process of the traditional ACCB algorithm, and greatly improves the linear regulation rate and the load regulation rate of the Flyback converter for DCM and the transient response effect on the reference voltage jump. While using a constant compensation factor K C To minimize the damping effect.
Prepare the experimental circuit prototype and combine the VECB control proposed in this example with the conventional PI controlACCB control for comparison. At a given v in 10V and V out The experiment was performed and three indices were compared under 15V conditions.
(I) load regulation ratio
a. When the load resistance jumps from 30 Ω to 15 Ω, the output voltage transient response is as shown in fig. 8. Under PI control, the output voltage deviates 210mV and re-stabilizes within 170 us. Under ACCB control, the output voltage deviated 270mV and restabilized within 80 us. Under VECB control, the output voltage deviates 180mV and re-stabilizes within 40 us. Compared with the ACCB controller, the VECB controller proposed in this embodiment reduces the transient response time and voltage deviation by 50% at the time of load step.
b. The transient response of the output voltage when the load resistance jumps from 150 Ω to 15 Ω is shown in fig. 9. Under the PI controller, the output voltage deviates 370mV and re-stabilizes within 240 us. Under ACCB control, the output voltage deviated 420mV and restabilized at 100 us. Under VECB control, the output voltage deviates 300mV and re-stabilizes within 60 us. For ACCB and VECB controllers, the transient response is limited by charge saturation when the duty cycle reaches a maximum value v out /(v in +v out ). Thus, the output voltage transients are slower than in fig. 8. However, transient response under VECB control is still much faster than under PI and ACCB control.
From the above, compared with the ACCB controller, the VECB controller eliminates the lag of the charge balance algorithm, so that the transient response time and the voltage deviation are both reduced by 50%.
Linear regulation rate
According to closed-loop SSM, the output voltage is not affected by input voltage disturbances under the control of ACCB and VECB. The results of the experiment are shown in FIG. 10.
When v is in When the voltage jumps from 10V to 7.5V, the output voltage deviates 210mV under PI control and stabilizes again within 160 us. Under ACCB and VECB control, the output voltage deviates 130mV and re-stabilizes within 60us and 50us, respectively. Both the ACCB and VECB controllers showed a significant suppression of input voltage disturbances. The advantages of VECB comparison are more obvious.
(III) reference Voltage following
a. When v is ref The transient response of the output voltage at the transition from 15V to 15.25V is shown in fig. 11. For a converter with a PI controller, the output voltage realizes v within 130us ref The tracking of (2). Furthermore, a 40mV overshoot of 16% magnitude of the jump differential pressure is caused. Under ACCB control, the output voltage tracks v over 80us ref With a 20mV overshoot. Under the control of VECB, the following process of the output voltage has no overshoot.
b. When v is ref The transient response of the output voltage at the transition from 13V to 15V is shown in fig. 12. For a converter with a PI controller, the output voltage realizes v within 190us ref The tracking of (2). Furthermore, a 1.1V overshoot of 55% magnitude of the jump differential pressure is caused. The relative value of the overshoot is much higher than in fig. 11 (a) due to the duty cycle saturation and the circuit entering the temporary CCM mode during transients. Under the control of ACCB and VECB, the two output voltages both rise linearly and track v within 130us ref And no overshoot will occur. But the tracking time is much longer than in fig. 11 (b) and fig. 11 (c). This is because charge saturation occurs when the converter outputs its maximum voltage. Despite the charge saturation, the output voltage transients of ACCB and VECB are still relatively desirable.
From the above, the reference voltage following effect in the VECB control is superior to that of the ACCB control.
By combining the three indexes for comparison, experimental results show that the VECB controller provided by the embodiment is stable in small-signal and large-signal transients. In all measurements, the output voltage showed a very good transient response with no significant steady state error. The VECB controller greatly improves the transient response to circuit disturbances compared to the ACCB controller.
Example two
A charge balance controller for a DCM Flyback converter, as shown in fig. 4, comprising: a charge observer, a voltage extrapolator, a VECB algorithm module, and a charge controller; charge observer, voltage extrapolator and VECB algorithm module for digital pulse width modulation based DCM at each switching cycleThe input and output of the Flyback converter are sampled, and when the charge quantity reaches the required charge balance control, the following functions are executed in each switching period, and the charge balance control is completed in two switching periods: the charge observer is used for calculating the output charge Q of the DCM Flyback converter to the output capacitor based on the input and the output of the DCM Flyback converter in the current switching period ch (ii) a The voltage extrapolator is used for inputting and outputting the DCM Flyback converter based on the current switching period
Figure BDA0003610559330000141
Output voltage v of Flyback converter after pre-estimating two switching periods ext In the formula v out And
Figure BDA0003610559330000142
current switching period obtained for each sample is at Q ch When the output voltage is 0, the output voltage and the output voltage are changed, and T is the duration of a single switching period; a VECB algorithm module for outputting the output charge Q based ch The output voltage v ext And a reference voltage v ref According to Q ref ＝C(v ref -v ext )-Q ob In the formula (2), Q ob ＝Q ch ，Q ch ＝Q ref z -1 ，z -1 Calculating a reference charge Q for a unit delay factor in the Z-transform ref The reference charge Q ref And the method is used for calculating the duty ratio of the digital pulse width modulation signal to control the switching of the DCM Flyback converter in the next switching period.
Preferably, the device further comprises a correction unit for adopting a constant compensation factor K for reducing the damping effect C Respectively correcting the output charges Q ch And a reference charge Q ref The correction method is as follows:
Figure BDA0003610559330000143
in the formula, K damp Indicating calculated determination based on current actual circuitA charge damping coefficient.
Preferably, K C ＝K damp 。
The related technical solution is the same as the first embodiment, and is not described herein again.
EXAMPLE III
A computer-readable storage medium comprising a stored computer program, wherein when the computer program is executed by a processor, the storage medium controls an apparatus on which the storage medium is located to perform a charge balance control method for a DCM Flyback converter as described above.
The related technical solution is the same as the first embodiment, and is not described herein again.
It will be understood by those skilled in the art that the foregoing is only an exemplary embodiment of the present invention, and is not intended to limit the invention to the particular forms disclosed, since various modifications, substitutions and improvements within the spirit and scope of the invention are possible and within the scope of the appended claims.

Claims (7)

1. A charge balance control method for a DCM Flyback converter, characterized in that the charge balance control is done in two switching cycles, wherein the following steps are performed in each switching cycle:
calculating output charge Q from the Flyback converter to an output capacitor when the duty ratio of the current switching period is high based on the input and the output of the DCM Flyback converter with the current switching period obtained by sampling ch At the same time according to
Figure FDA0003610559320000011
Output voltage v of Flyback converter after pre-estimating two switching periods ext In the formula v out And
Figure FDA0003610559320000012
current switching period obtained for each sample is at Q ch When the output voltage is 0, the output voltage and the output voltage are changed, and T is the duration of a single switching period;
based on the output charge Q ch The output voltage v ext And a reference voltage v ref According to Q ref ＝C(V ref -V ext )-Q ob In the formula (2), Q ob ＝Q ch ，Q ch ＝Q ref z -1 ，z -1 Calculating a reference charge Q for a unit delay factor in the Z-transform ref The reference charge Q ref And the method is used for calculating the duty ratio of the digital pulse width modulation signal to control the switching of the DCM Flyback converter in the next switching period.
2. A charge balance control method according to claim 1, characterized in that a constant compensation factor K is used to reduce the damping effect C Respectively correcting the output charges Q ch And a reference charge Q ref The correction method is as follows:
Figure FDA0003610559320000013
in the formula, K damp Representing the charge damping coefficient calculated from the current actual circuit.
3. The charge balance control method of claim 2, wherein K is C ＝K damp 。
4. A charge balance controller for a DCM Flyback converter, comprising: a charge observer, a voltage extrapolator, a VECB algorithm module, and a charge controller;
the charge observer, the voltage extrapolator and the VECB algorithm module are used for sampling the input and the output of the DCM Flyback converter in each switching period based on digital pulse width modulation, and when the output charge quantity needs charge balance control, the following functions are executed in each switching period, and the charge balance control is completed in two switching periods:
the charge observer is used for DCM Fl based on the current switching periodThe input and the output of the Flyback converter calculate the output charge Q of the Flyback converter to the output capacitor in the current switching period ch ；
The voltage extrapolator is used for inputting and outputting the DCM Flyback converter based on the current switching period
Figure FDA0003610559320000021
Output voltage v of Flyback converter after pre-estimating two switching periods ext In the formula V out And
Figure FDA0003610559320000022
current switching period obtained for each sample is at Q ch When the output voltage is 0 and the output voltage changes, T is the duration of a single switching period;
the VECB algorithm module is to output the charge Q based on ch The output voltage v ext And a reference voltage v ref According to Q ref ＝C(V ref -V ext )-Q ob In the formula (2), Q ob ＝Q ch ，Q ch ＝Q ref z -1 ，z -1 Calculating a reference charge Q for a unit delay factor in the Z-transform ref The reference charge Q ref And the method is used for calculating the duty ratio of the digital pulse width modulation signal to control the switching of the DCM Flyback converter in the next switching period.
5. A charge balance controller according to claim 4, further comprising a correction unit for applying a constant compensation factor K for reducing the damping effect C Respectively correcting the output charges Q ch And a reference charge Q ref The correction method is as follows:
Figure FDA0003610559320000023
in the formula, K damp Representing charge resistance calculated from the current actual circuitThe damping coefficient.
6. A charge balance controller as claimed in claim 5, wherein K is C ＝K damp 。
7. A computer-readable storage medium, comprising a stored computer program, wherein when the computer program is executed by a processor, the computer program controls a device on which the storage medium is located to execute a charge balance control method for a DCM Flyback converter according to any one of claims 1 to 3.
CN202210431074.5A 2022-04-22 2022-04-22 Charge balance control method and charge balance controller for DCM Flyback converter Pending CN114865921A (en)

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Publication number Priority date Publication date Assignee Title
CN116683744A (en) * 2023-08-03 2023-09-01 深圳市首航新能源股份有限公司 Control method and equipment thereof

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116683744A (en) * 2023-08-03 2023-09-01 深圳市首航新能源股份有限公司 Control method and equipment thereof
CN116683744B (en) * 2023-08-03 2024-02-06 深圳市首航新能源股份有限公司 Control method and equipment thereof

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