CN109004840B - Control method for improving output precision of switching power supply - Google Patents

Control method for improving output precision of switching power supply Download PDF

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CN109004840B
CN109004840B CN201810785261.7A CN201810785261A CN109004840B CN 109004840 B CN109004840 B CN 109004840B CN 201810785261 A CN201810785261 A CN 201810785261A CN 109004840 B CN109004840 B CN 109004840B
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mode
voltage
output
module
sampling
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CN109004840A (en
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徐申
于利民
陶蓉蓉
陈威宇
孙伟锋
陆生礼
时龙兴
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Southeast University
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Southeast University
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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
    • 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
    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/14—Arrangements for reducing ripples from dc input or output
    • H02M1/15—Arrangements for reducing ripples from dc input or output using active elements

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

A control method for improving the output accuracy of a switching power supply is based on a control system consisting of a sampling module, an accuracy control module, an error calculation module, a PID module and a PWM module, wherein the control system is connected with the controlled switching power supply to form a closed loop, the mode switching is controlled by detecting the output voltage, when the output voltage exceeds the upper limit voltage, the circuit enters a DCM mode through the mode switching, the input energy is reduced, the output voltage is stabilized in a regulation range, when the output voltage is lower than the lower limit voltage, the circuit enters the CCM mode through the mode switching, the input energy is increased, and the output voltage is quickly recovered to the regulation range. In the normal regulation process, the change of the output voltage is limited between the upper limit voltage and the lower limit voltage, the voltage output ripple is reduced, and the precision is improved.

Description

Control method for improving output precision of switching power supply
Technical Field
The invention relates to a switching power supply, in particular to a control method for improving the output precision of the switching power supply, which can reduce the output ripple of the switching power supply and improve the output precision of the switching power supply.
Background
Switching power supplies are commonly used as power supplies for various types of electrical equipment to convert an unregulated ac or dc input voltage to a regulated ac or dc output voltage. Because the switching power supply needs to adapt to different working conditions, the requirement on the output precision performance of the power supply is higher and higher. As the process size is gradually reduced, the withstand voltage of devices in the chip is also reduced, if the power supply voltage is overlarge, the applied voltage or the consumed power of the chip device is easily overhigh and damaged, and if the power supply voltage is overlow, the performance of some devices is reduced, even the devices cannot work. When the output voltage accuracy is not high and the ripple is large, the performance of the chip is affected. Such as digital voltmeters, require an extremely accurate stable power supply inside to ensure the conversion precision of voltage/number; and for example, a power supply in the oscilloscope needs to be stable so as to ensure the accuracy of the deflection sensitivity, the scanning time and the like of the light spot.
In current power management, high power efficiency has become a necessary performance. In order to achieve high efficiency, many high-voltage power supplies (such as flyback converters with mains voltage as input) adopt a soft switching technology, and the switching is performed when the voltage at the drain terminal of a primary power tube drops to zero, that is, a valley bottom switching technology. Although the technology achieves high efficiency, the actual conduction time of the circuit is deviated from the conduction time calculated by a system theory, so that the output voltage ripple caused by the circuit is larger than that of a non-valley-bottom conduction circuit. Meanwhile, in an soc (system On chip) system, different modules have different current capabilities, and even if the same module has different working modes at different moments, the required current is also different. The current supplied by the power chip to the modules is not fixed, when the current supplied by the power chip just enables the power to work in a critical region of a Continuous Conduction Mode (CCM) and a Discontinuous Conduction Mode (DCM), and the power is a circuit with an output discontinuous structure, the circuit works in the CCM, the obtained output energy and the increment of the inductive current have hysteresis, and the energy is completely transmitted to the output end in the DCM due to the current period, so that no hysteresis exists between the obtained output energy and the increment of the inductive current. If the power supply enters the DCM after working with a plurality of CCMs, and enters the CCM after passing through a plurality of DCMs, the output voltage ripple is very large, and the output precision is very low.
In addition, for a power chip with low adjustment accuracy, when the chip works at the boundary of the DCM and the CCM, a load region, a large output voltage ripple and low accuracy also occur.
Therefore, due to the fact that the requirement for output precision is higher and higher, and the problem of low output precision caused by a soft switching control method is solved, and a control method for improving the precision of output voltage is provided. The voltage control circuit has good effects of reducing voltage overshoot and undervoltage and reducing output ripples, and is necessary for improving the output precision performance of the circuit.
The applicant's prior application of a control method for improving the dynamic response of a switching power supply provides a dynamic fast recovery algorithm for the problem that when the output load of a system is switched (for example, heavy load is switched to light load or light load is switched to heavy load), the output voltage generates large overshoot or undershoot, the output voltage can be recovered to the normal regulation range in as short a time as possible, thereby reducing the overshoot or undershoot of the output voltage, namely, the system belongs to dynamic regulation, the valley bottom conduction mode is adopted by the system, so that the difference of the maximum half resonance period possibly exists between the actual switching period and the theoretically calculated switching period, the current on the inductor is unstable compared with a power supply system which is not conducted by the valley bottom switch, and meanwhile, the power supply of the structure belongs to a structure with discontinuous output current, the structure has a right plane zero point, which brings phase delay of a compensation loop and finally causes the problem of large output voltage ripple under the condition of stable output load.
Disclosure of Invention
In order to overcome the limitations and the disadvantages of the prior art, the invention provides a control method for improving the output precision of a switching power supply, belongs to steady-state regulation, and provides a corresponding algorithm aiming at the problems of large output ripple and low precision of a system under a stable output load, so that the overshoot and the undervoltage of the output voltage can be limited within a certain range, the output ripple is reduced, the output precision is improved, the instability of the system can not be caused in multi-mode control, and the output precision performance of a circuit is more excellent.
In order to achieve the purpose, the invention adopts the technical scheme that: a control method for improving the output precision of a switching power supply is characterized in that: based on a control system consisting of a sampling module, a precision control module, an error calculation module, a PID module and a PWM module, the control system is connected with a controlled switching power supply to form a closed loop;
the sampling module comprises a sampling circuit and a sampling calculation module, the sampling circuit obtains output voltage information through output voltage division of the switching power supply, and the sampling calculation module calculates a sampling voltage Vo corresponding to the output voltage information according to the output voltage information and simultaneously outputs the sampling voltage Vo to the error calculation module and the precision control module;
the precision control module comprises a voltage monitoring module and a mode switching module, wherein the voltage monitoring module receives the output of the sampling moduleJudging whether mode switching is adopted or not according to the relation between the magnitude of the sampled voltage Vo and the set magnitude of the upper limit value Vomax and the set magnitude of the lower limit value Vomin of the sampled voltage Vo, and selecting whether a CCM mode or a DCM mode is adopted; the voltage monitoring module comprises two comparators and a logic unit, wherein one comparator is used for comparing the sampling voltage Vo with the set upper limit value Vomax of the sampling voltage Vo, the other comparator is used for comparing the sampling voltage Vo with the set lower limit value Vomin of the sampling voltage Vo, the outputs of the two comparators are respectively connected to the logic unit, the logic unit outputs a mode selection result mode _ F to the mode switching module according to the comparison result of the two comparators, and when Vo is less than Vomin, the logic unit outputs mode _ F which is 1 and is in a CCM mode; when Vo is larger than Vomax, the logic unit outputs mode _ F which is 0 and is in a DCM mode; when Vo is between Vomin and Vref, the mode selection result mode _ F keeps the currently selected mode unchanged; the mode switching module receives a mode selection result mode _ F output by the voltage monitoring module and output voltage information Vsense obtained by outputting voltage division, compares the output voltage information Vsense with a zero level signal GND, and generates a signal ZCMP reflecting that the inductive current is reduced to zero, wherein the signal ZCMP is a signal for determining the conduction of the power tube in a DCM mode, an internal clock Fclk is a signal for determining the conduction of the power tube in a CCM mode, and the signals for turning off the power tubes in the DCM mode and the CCM mode are output by the PID module to form a signal VPIDetermining; the ZCMP signal and the internal clock Fclk pass through an alternative logic combination gate circuit, and a mode switching result control signal mode _ ctl is generated to a PWM module according to different values of a mode selection result mode _ F;
the error calculation module receives the sampling voltage Vo output by the sampling module, subtracts the difference of the sampling voltage Vo from the reference voltage Vref to obtain the current sampling voltage error e1, and outputs the current sampling voltage error e1 to the PID module, and the PID module outputs the current sampling voltage error e1 through a proportional parameter Kp and an integral parameter KiDifferential parameter KdPerforming PID operation to obtain compensation result VPIThe peak current value is output to a PWM module and used for determining the peak current value of the next period;
the PWM module comprises a PWM unit and a drive unit, and the input of the PWM unit is a mode switchMode switching result control signal mode _ ctl output by switching module and compensation result V output by PID modulePIObtaining a switching period Ts and a peak current Ipeak through calculation, outputting a duty ratio waveform through a driving unit, realizing loop control on a grid electrode of a power tube of a switching power supply, determining the conduction of the power tube according to a mode switching result mode _ ctl, and compensating a result VPIDetermining the turn-off of the power tube;
and repeating the process, sampling the output voltage of the switching power supply again, and circularly controlling the on and off of the power tube of the switching power supply so as to enable the system to be more stable and obtain higher output precision.
When the sampling voltage Vo is smaller than the lower limit voltage Vomin, the voltage monitoring module outputs a signal mode _ F to control the mode switching module to change the mode into a CCM mode with constant frequency, under the mode, the conduction of the power tube is determined by the rising edge of an internal clock, and the disconnection of the power tube is determined by the output signal V of the PID modulePIDetermining that the system inputs high power to enable the sampling voltage Vo to quickly rise to the reference voltage Vref, and keeping the mode to work until the sampling voltage Vo is larger than the upper limit voltage Vomax, and the system is switched to the DCM mode;
when the sampling voltage Vo is larger than the upper limit voltage Vomax, the voltage monitoring module outputs a signal mode _ F to control the mode switching module to change the mode into a DCM mode, in the DCM mode, after the conduction of the power tube needs to be equal to the zero of the inductor current, the power tube is conducted at the next valley bottom of the drain-source voltage Vds of the power tube, and the power tube is turned off by outputting a signal V by the PID modulePIAnd determining that the system inputs low power to enable the sampling voltage Vo to quickly drop to the reference voltage Vref in the mode, and keeping the mode to work until the sampling voltage Vo is smaller than the lower limit voltage Vomin, and switching the system to the CCM mode.
Two comparators COMP1 and COMP3 in the voltage monitoring module are provided, the positive end of the comparator COMP1 is connected with Vomax, the negative end is connected with Vo, the positive end of the comparator COMP3 is connected with Vo, the negative end is connected with Vomin, an output signal SMAX of the comparator COMP1 and an output signal SMIN of the comparator COMP3 are both connected with a logic unit, and the logic unit outputs a mode selection result mode _ F.
The mode switching module comprises a comparator COMP, an inverter INV, an AND gate AND AND two NOR gates NOR1 AND NOR2, wherein a positive input end of the comparator COMP is connected with a zero level signal GND, a negative input end of the comparator COMP is connected with output voltage information Vsense obtained by voltage division, an output of the comparator COMP is connected with one input end of a NOR gate NOR1, the other input end of the NOR gate NOR1 is connected with a mode selection result mode _ F AND one input end of the AND gate AND, the other input end of the AND gate AND is connected with an output of the inverter INV, an input of the inverter INV is connected with an internal clock Fclk, an output of the AND gate AND is connected with one input end of the NOR gate NOR2, the other input end of the NOR gate NOR2 is connected with an output of a NOR gate NOR1, AND the NOR gate NOR2 outputs a mode switching result control signal mode _ ctl.
The invention has the advantages and obvious effects that:
1. the control method for improving the output precision of the switching power supply can enable the circuit to immediately enter a DCM mode through mode switching when the output voltage exceeds the upper limit voltage, reduce the input energy, enable the output to be stable in a regulation range, enable the circuit to immediately enter a CCM mode through mode switching when the output voltage is lower than the lower limit voltage, increase the input energy, and enable the output voltage to be quickly recovered in the regulation range. In the normal regulation process, the change of the output voltage is limited between the upper limit voltage and the lower limit voltage, the voltage output ripple is reduced, and the precision is improved.
2. The control method for improving the output precision of the switching power supply can solve the problem of overlarge output ripple caused by large single-step energy change due to low regulation precision by detecting the switching of the output voltage control mode under the condition of low circuit regulation precision.
3. The invention belongs to steady state regulation, and is characterized in that a new algorithm is additionally added on the basis of dynamic regulation, a control method for improving dynamic response is still reserved, and a circuit for specifically implementing the algorithm is shown in figure 1 c.
4. The invention is suitable for various switch power supply circuit structures with discontinuous output current and small load output, namely the small load means that the difference between the average current of the inductor in a CCM mode and the average current of the inductor in a DCM mode cannot be too large.
Drawings
FIG. 1a is a block diagram of a system architecture of the control method of the present invention; FIG. 1b is a block diagram of the voltage monitoring module of FIG. 1 a; FIG. 1c is a block diagram of an embodiment of the mode switching module of FIG. 1 a;
FIG. 2 is a schematic diagram of the application of determining the switching mode according to Vo;
FIG. 3 is a block diagram embodiment of a closed loop circuit having a single tube resonant converter of the present invention;
FIG. 4 is a simulation of the relationship of the output voltage, resonant voltage and primary current of the structure of FIG. 3 at steady state;
FIG. 5 is a graph showing the relationship between the output voltage ripple, the resonant voltage and the primary side current of the structure of FIG. 3 at steady state;
FIG. 6 shows the output voltage ripple in steady state when the algorithm of this patent is not used in the dynamic regulation patent;
fig. 7 shows the output voltage ripple in steady state when the algorithm of the present patent is used in the dynamic regulation patent.
Detailed Description
Referring to fig. 1a, the present invention is based on a control system comprising a sampling module, a precision control module, an error calculation module, a PID module and a PWM module, which is connected to a controlled switching power supply to form a closed loop.
The sampling module comprises a sampling circuit and a sampling calculation module, the sampling circuit obtains information of output voltage through output voltage division, the sampling calculation module obtains sampling voltage Vo reflecting the current output voltage through a sampling algorithm according to the information of the output voltage and outputs the sampling voltage Vo to the precision control module and the error calculation module, the sampling can be direct sampling or indirect sampling, and the sampling result can be analog quantity or digital quantity.
The precision control module comprises a voltage monitoring module and a mode switching module, and the voltage monitoring module judges which mode is adopted according to the sampling voltage Vo. The voltage monitoring module receives the sampling voltage Vo output by the sampling module and judges whether mode switching is adopted according to the relationship between the magnitude of Vo and the set magnitude of the Vo upper limit value Vomax and the Vo lower limit value Vomin, wherein the Vomin and the Vomax are narrower than the acceptable range of Vo, namely a certain margin is reserved. The mode switching means that when the variation of the sampling voltage Vo exceeds an acceptable range, the single-cycle energy transmission is changed through mode conversion, so that the sampling voltage Vo is adjusted within a set range, and high-precision output is realized. The mode switching here refers to switching between CCM and DCM, and the mode switching module outputs the result as mode _ ctl.
As shown in fig. 1b, the voltage monitoring module includes two comparators COMP1 and COMP3 and a logic unit for determining which mode is adopted. The two comparators respectively judge the sampling voltage Vo and the lower limit voltage Vomin, the sampling voltage Vo and the upper limit voltage Vomax, and the logic unit outputs a mode selection result mode _ F according to the comparator result. mode _ F is used as an input of the mode switching module, the CCM mode is set when mode _ F is 1, the DCM mode is set when mode _ F is 0, the DCM mode is started when Vo is greater than Vomax, the DCM mode is started when Vo is less than Vomin, the CCM mode is started when Vo is greater than 1, and the mode _ F keeps the current mode unchanged when Vo is between Vomin and Vref.
As shown in FIG. 1c, the mode switching module receives the voltage monitoring module output signal mode _ F and the signal Vsense reflecting the magnitude of the output voltage. The Vsense signal is compared with a zero-level signal GND by a comparator COMP to generate a signal ZCMP reflecting that the inductor current drops to zero, which is passed through a NOR gate NOR1 with mode _ F to obtain a DCM _ ON signal, which is ZCMP _ B (ZCMP inverse signal) when mode _ F is 0; when mode _ F is 1, ZCMP is masked and DCM _ ON is 0. The internal clock signal Fclk passes through an inverter INV to obtain FclkB, which passes through an AND gate AND with mode _ F to output a CCM _ ON signal. When mode _ F is 1, CCM _ ON is FclkB; when mode _ F is 0, fcclkb is masked and CCM _ ON is 0. The CCM _ ON and DCM _ ON pass through a NOR gate NOR2 to obtain a signal mode _ ctl for finally controlling the power tube to be turned off. The mode _ ctl signal is passed to the PWM module. In two modes (CCM and DCM), the turn-off signal of the power tube is output by the PID module to form a signal VPIAnd (6) determining. In short, when Mode _ F is 1, the internal clock Fclk determines Mode _ ctl, and at this time, the system operates in CCM Mode, the system on is determined by the internal clock, and the system off is determined by the output of the PID. When Mode _ F is equal to 0, the voltage is controlled by Vsense and zero levelThe comparison result determines the Mode _ ctl, where Vsense is the voltage reflecting the inductor current, and may be equal to IL × Rsense, IL is the inductor current, Rsense is the sampling resistor, and comparator COMP is a zero current comparator.
When Vo is less than Vomin, the logic unit outputs mode _ F to be 1, the logic unit outputs a CCM mode with constant frequency in mode switching, in the mode, the power tube is switched on and off according to the rising edge of an internal clock, the PID module outputs signals, the system inputs high power to enable Vo to rise to the reference voltage Vref quickly, and the mode is kept to work until Vo is larger than the upper limit voltage Vomax. When Vo is smaller than the lower limit voltage Vomin, the logic unit outputs mode _ F to be 1, the logic unit outputs a CCM mode with constant frequency in mode switching, in the mode, the power tube is switched on and off according to the rising edge of an internal clock, the PID module outputs signals, the system inputs high power to enable Vo to rise to the reference voltage Vref rapidly, the mode is kept to work, and the system is switched to the DCM mode until Vo is larger than the upper limit voltage Vomax.
When Vo is larger than Vomax, the output mode of the logic unit is 0, the logic unit outputs a DCM mode in the mode switching, and in the mode, after the conduction of the power tube needs to wait for the current of the inductor to become zero, the power tube is conducted at the next valley bottom of Vds (the drain-source voltage of the main power tube); the power tube is turned off according to the output signal of the PID module. In this mode, the system inputs a small power to make Vo drop to the reference voltage Vref quickly, and the mode is kept working until Vo is smaller than the lower limit voltage Vomin, and the system is switched to the CCM mode. When Vo is larger than the upper limit voltage Vomax, the logic unit outputs a DCM mode in the mode switching, and in the mode, the power tube is conducted at the next valley bottom of Vds after the inductor current is required to be zero; the power tube is turned off by a PID module output signal VPIAnd (6) determining. The output is rapidly dropped to the reference voltage Vref by inputting a small power and the mode operation is maintained until Vo is smaller than the lower limit voltage Vomin.
The error calculation module calculates the current voltage errorThe input of the calculation module is the output Vo of the sampling module, the difference of the sampling voltage Vo subtracted from the calculation reference voltage Vref is the current sampling error, which is marked as e1 and is output to the PID module; the PID module carries out compensation operation according to the input error e1 signal, and carries out compensation operation according to a proportional parameter Kp and an integral parameter KiDifferential parameter KdPerforming PID operation to compensate the result VPIAnd inputting the peak current value into a PWM module for determining the peak current value of the next period.
The PWM module comprises a PWM unit and a driving unit, wherein the input of the PWM unit is a mode switching result mode _ ctl output by the mode switching module and a compensation result V output by the PID modulePIAfter the information of a switching period Ts and peak current Ipeak during control is obtained through calculation, a duty ratio waveform is output through a driving unit, loop control is realized on a grid electrode of a power tube of a switching power supply, the switching result mode _ ctl controls the switching tube to be conducted, and V isPIThe signal determines that the switching tube is turned off, and the driving unit should select a circuit with a small delay time as far as possible. And then sampling the output voltage of the switching power supply again, and repeating the process to circularly control the on and off of the power tube of the switching power supply so as to make the system more stable and obtain higher output precision.
Referring to fig. 2, when the load is large, for the switching power supply with discontinuous output current, due to the existence of the right half-plane zero point, when the circuit operates in CCM mode, the change of the input current and the change of the energy received by the output have phase lag, and even if a PID compensation scheme is adopted, the ripple is still large. Therefore, when the sampling voltage Vo is larger than Vomax, the system works in the DCM mode through mode switching, so that the transmitted energy is reduced, and Vo can be reduced as soon as possible. And when the sampling voltage Vo is lower than Vomin, the system works in a CCM mode through mode switching, so that the transmission energy is rapidly increased, and Vo is regulated to be within a preset range. It can be seen from the figure that the sampled voltage Vo exceeds Vomax and Vomin, because the energy obtained by the switching power supply structure with intermittent output and the energy stored in the inductor current are separated in the on state of the power tube, so that the obtained output energy has a certain lag with the change of the inductor current, and finally the output voltage exceeds the set range. The output voltage is therefore set to a smaller range than the permitted range of regulation, with a certain margin.
Fig. 3 is an embodiment targeting a flyback circuit. The method and system used by the present invention can also be used for other types of switching power supply circuit configurations. Here, a single-tube quasi-resonant circuit fed back by a primary side is taken as an example. The input of the single-tube quasi-resonant converter is 90-265V, the output is 20V, the maximum current is 4A, the size of the inductor is 1.6mH, the turn ratio of the transformer is 104/24, and the output is constant voltage. In the figure, Vin is the input voltage Csn, Rsn, D2Respectively, a capacitor, a resistor and a diode of the clamping circuit, Isn is a current flowing through the clamping resistor Rsn, and L islk、LpRespectively a leakage inductance and an excitation inductance, M1Is a power transistor, Imos is a current flowing through the power transistor M1Rs is a sampling resistor, Vs is a sampling voltage, Np, Ns and Na respectively correspond to the number of turns of a primary side, a secondary side and an auxiliary coil of the transformer, and D1Is secondary freewheeling diode, Is current flowing through secondary, Cl、RlRespectively an output capacitor and an output resistor, R1And R2The voltage dividing resistor is an auxiliary winding.
The following examples and corresponding test waveforms are given to increase the working method for optimizing the output accuracy performance in this example.
The flyback converter obtains a sampling voltage Vo by sampling the output voltage, the sampling voltage Vo is compared with a set Vomax and Vomin by using the precision control module, when Vo is larger than the Vomax, the output mode _ F is 0, the mode switching module starts a DCM mode, when Vo is smaller than the Vomin, the output mode _ F is 1, the mode switching module starts a CCM mode, and when Vo is between the Vomin and the Vref, the mode _ F keeps the current mode unchanged. When Vsense is 0, ZCMP is 1, indicating that the inductor current energy is fully discharged, which is the current zero current point, Vo is compared with the zero level signal to generate a valley-start signal, and the switch tube re-conduction time is determined in DCM mode, while in CCM mode, ZCMP signal is masked by mode _ F1, and the switch tube conduction is determined by the internal clock. Meanwhile, the error detection module detects an error e1 and sends the error e1 into the PID module to obtain a proper V through a PID algorithmPIThis value determines the next cycle peak current valueFinally, the result V is compensated by a PID modulePIAfter the control signal mode _ ctrl given by the mode switching module is calculated to obtain the information of the switching period and the peak current during control, the duty ratio waveform is output through the driving unit, and the loop control is realized on the grid electrode of the switching power supply power tube; then, the output voltage of the switching power supply is sampled again, and the process is repeated to circularly control the on and off of the power tube of the switching power supply, so that the system is more stable, and higher output precision is obtained, and the corresponding simulation waveform is shown in fig. 4.
Fig. 4 is a graph showing the simulated output waveforms of the flyback circuit of fig. 3 under different loads according to the present invention. Vo, Vcr, Ip respectively refer to output voltage (the sampling circuit samples and holds the output voltage, the sampling voltage Vo reflects the output voltage, and the sampling voltage Vo is equal to the output voltage without considering sampling delay, so that Vo here represents the output voltage, the same below), resonant voltage, and primary current. The CCM and DCM are uniformly and crossly distributed under the ideal condition that the output voltage rises as soon as possible and Vo is higher than 20V, the output voltage ripple is minimum, otherwise, the CCM and DCM work unevenly without any control and the output ripple is very large.
Fig. 5 shows a test waveform with a high-precision low-ripple control algorithm, an output voltage of 12V and a corresponding load of 1.2A, where the system operates in CCM and DCM switching state, and the output voltage ripple is within 100 mV.
Fig. 6 shows the output voltage ripple in steady state when the algorithm of the present patent is not used in the dynamic regulation patent, and the average value is 17.3V, and the output ripple reaches 2V.
Fig. 7 shows the output voltage ripple waveform in a steady state when the algorithm of the present invention is used in the same structure, the peak value of the output ripple is 500mV, and the comparison shows that the effect is obvious, and the ripple is reduced to 1/4 before.
While the invention has been described in further detail with reference to specific preferred embodiments thereof, it will be understood that the invention is not limited to the details of construction and the particular embodiments disclosed, as such may vary, without departing from the spirit and scope of the present invention. Accordingly, all changes which would be obvious to one skilled in the art are intended to be included within the scope of this invention as defined by the claims.

Claims (4)

1. A control method for improving the output precision of a switching power supply is characterized in that: based on a control system consisting of a sampling module, a precision control module, an error calculation module, a PID module and a PWM module, the control system is connected with a controlled switching power supply to form a closed loop;
the sampling module comprises a sampling circuit and a sampling calculation module, the sampling circuit obtains output voltage information through output voltage division of the switching power supply, and the sampling calculation module calculates a sampling voltage Vo corresponding to the output voltage information according to the output voltage information and simultaneously outputs the sampling voltage Vo to the error calculation module and the precision control module;
the precision control module comprises a voltage monitoring module and a mode switching module, wherein the voltage monitoring module receives the sampling voltage Vo output by the sampling module, judges whether mode switching is adopted according to the relation between the magnitude of the sampling voltage Vo and the set magnitude of the upper limit value Vomax and the lower limit value Vomin of the sampling voltage Vo, and selects a CCM mode or a DCM mode; the voltage monitoring module comprises two comparators and a logic unit, wherein one comparator is used for comparing the sampling voltage Vo with the set upper limit value Vomax of the sampling voltage Vo, the other comparator is used for comparing the sampling voltage Vo with the set lower limit value Vomin of the sampling voltage Vo, the outputs of the two comparators are respectively connected to the logic unit, the logic unit outputs a mode selection result mode _ F to the mode switching module according to the comparison result of the two comparators, and when Vo is less than Vomin, the logic unit outputs mode _ F which is 1 and is in a CCM mode; when Vo is larger than Vomax, the logic unit outputs mode _ F which is 0 and is in a DCM mode; when Vo is between Vomin and Vref, the mode selection result mode _ F keeps the currently selected mode unchanged; the mode switching module receives a mode selection result mode _ F output by the voltage monitoring module and an output obtained by outputting a partial voltageThe voltage information Vsense compares the output voltage information Vsense with a zero level signal GND to generate a signal ZCMP reflecting that the inductor current is reduced to zero, the signal ZCMP is a signal for determining the conduction of the power tube in the DCM mode, the internal clock Fclk is a signal for determining the conduction of the power tube in the CCM mode, and the signals for turning off the power tubes in the DCM mode and the CCM mode are output by the PID module to output a signal VPIDetermining; the ZCMP signal and the internal clock Fclk pass through an alternative logic combination gate circuit, and a mode switching result control signal mode _ ctl is generated to a PWM module according to different values of a mode selection result mode _ F;
the error calculation module receives the sampling voltage Vo output by the sampling module, subtracts the difference of the sampling voltage Vo from the reference voltage Vref to obtain the current sampling voltage error e1, and outputs the current sampling voltage error e1 to the PID module, and the PID module outputs the current sampling voltage error e1 through a proportional parameter Kp and an integral parameter KiDifferential parameter KdPerforming PID operation to obtain compensation result VPIThe peak current value is output to a PWM module and used for determining the peak current value of the next period;
the PWM module comprises a PWM unit and a driving unit, wherein the input of the PWM unit is a mode switching result control signal mode _ ctl output by the mode switching module and a compensation result V output by the PID modulePIObtaining a switching period Ts and a peak current Ipeak through calculation, outputting a duty ratio waveform through a driving unit, realizing loop control on a grid electrode of a power tube of a switching power supply, determining the conduction of the power tube according to a mode switching result mode _ ctl, and compensating a result VPIDetermining the turn-off of the power tube;
and repeating the process, sampling the output voltage of the switching power supply again, and circularly controlling the on and off of the power tube of the switching power supply so as to enable the system to be more stable and obtain higher output precision.
2. The control method for improving the output accuracy of the switching power supply according to claim 1, wherein: when the sampling voltage Vo is smaller than the lower limit voltage Vomin, the voltage monitoring module outputs a signal mode _ F to control the mode switching module to change the mode into a CCM mode with constant frequency, and in the mode, the conduction of the power tube is determined by the rising edge of an internal clockThe rate tube is turned off by a PID module output signal VPIDetermining that the system inputs high power to enable the sampling voltage Vo to quickly rise to the reference voltage Vref, and keeping the mode to work until the sampling voltage Vo is larger than the upper limit voltage Vomax, and the system is switched to the DCM mode;
when the sampling voltage Vo is larger than the upper limit voltage Vomax, the voltage monitoring module outputs a signal mode _ F to control the mode switching module to change the mode into a DCM mode, in the DCM mode, after the conduction of the power tube needs to be equal to the zero of the inductor current, the power tube is conducted at the next valley bottom of the drain-source voltage Vds of the power tube, and the power tube is turned off by outputting a signal V by the PID modulePIAnd determining that the system inputs low power to enable the sampling voltage Vo to quickly drop to the reference voltage Vref in the mode, and keeping the mode to work until the sampling voltage Vo is smaller than the lower limit voltage Vomin, and switching the system to the CCM mode.
3. The control method for improving the output accuracy of the switching power supply according to claim 1, wherein: two comparators COMP1 and COMP3 in the voltage monitoring module are provided, the positive end of the comparator COMP1 is connected with Vomax, the negative end is connected with Vo, the positive end of the comparator COMP3 is connected with Vo, the negative end is connected with Vomin, an output signal SMAX of the comparator COMP1 and an output signal SMIN of the comparator COMP3 are both connected with a logic unit, and the logic unit outputs a mode selection result mode _ F.
4. The control method for improving the output accuracy of the switching power supply according to claim 1, wherein: the mode switching module comprises a comparator COMP, an inverter INV, an AND gate AND AND two NOR gates NOR1 AND NOR2, wherein a positive input end of the comparator COMP is connected with a zero-level signal GND, a negative input end of the comparator COMP is connected with output voltage information Vsense obtained by voltage division, an output of the comparator COMP is connected with one input end of the NOR gate NOR1, the other input end of the NOR gate NOR1 is connected with a mode selection result mode _ F AND one input end of the AND gate AND, the other input end of the AND gate AND is connected with an output of the inverter INV, an input of the inverter INV is connected with an internal clock Fclk, an output of the AND gate AND is connected with one input end of the NOR gate NOR2, the other input end of the NOR gate NOR2 is connected with an output of the NOR gate NOR1, AND the NOR gate NOR2 outputs a mode switching result control signal mode _ ctl.
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