CN113765394B

CN113765394B - Primary side feedback converter and switch control method

Info

Publication number: CN113765394B
Application number: CN202110967598.1A
Authority: CN
Inventors: 王冲; 姚宇; 孙大鹰
Original assignee: Nanjing University of Science and Technology
Current assignee: Nanjing University of Science and Technology
Priority date: 2021-08-23
Filing date: 2021-08-23
Publication date: 2024-04-23
Anticipated expiration: 2041-08-23
Also published as: CN113765394A

Abstract

The invention discloses a primary side feedback converter and a switch control method, comprising a primary side feedback controlled switch power supply structure and a controller forming a closed loop with the primary side feedback controlled switch power supply structure; the controller comprises a sampling module, an error calculation module, a PID module and a PWM module; the sampling module obtains the time quantity related to the output voltage and the working mode of the converter according to the output voltage of the switching power supply structure, calculates the digital quantity of the output voltage in the current period based on the time quantity and the working mode, outputs the digital quantity to the error calculation module, and obtains a switching mode control variable to be input to the PWM module; the error calculation module calculates a voltage error and outputs the voltage error to the PID module; the PID module calculates a switch control variable and outputs the switch control variable to the PWM module; the PWM module performs switching control of the switching power supply structure based on the switching mode variable and the switching control variable. The invention can adaptively compensate the sampling error in the CCM mode, and improves the sampling precision and the constant voltage precision.

Description

Primary side feedback converter and switch control method

Technical Field

The invention belongs to the field of switching power supplies, and particularly relates to a primary side feedback converter and a switching control method.

Background

Compared with the traditional linear power supply, the switching power supply has the advantages of high efficiency, small volume and the like, and is widely applied to a power system. The AC-DC switching power supply is widely applied to household appliances and consumer electronics at present. The primary side feedback flyback converter is a very superior solution for a low-and-medium-power AC-DC converter, compared with the traditional secondary side feedback flyback converter based on an optical coupler, the primary side feedback flyback converter removes the optical coupler and a corresponding circuit, has the advantages of simple circuit, high stability, low volume and cost and the like, is widely applied to mobile phone chargers, has charging power within 36W generally, and is controlled by adopting an intermittent current mode (DCM mode).

Due to the continuous development of fast charging technology, USB PD and other technologies, the power of the charging equipment is required to be at least 65W stably, and meanwhile, the charging equipment still needs to meet the requirement of consumer electronic products on the portability of the adapter. In order to maintain circuit cost and limit the volume of the charger, when the output power is large, a continuous current mode (CCM mode) is adopted, so that the increase of the volume of the transformer can be limited, so that the volume increase of the whole power supply is limited. However, when introducing the CCM mode, sampling the output voltage of the CCM mode is a problem to be considered. In the DCM mode, when the current of the output diode linearly drops to zero, the voltage of the output diode is zero, and the voltage of the auxiliary winding at the moment is sampled, so that the voltage on the output capacitor, namely the output voltage Vo, can be accurately obtained; in the CCM mode, the output diode current does not drop to zero, the sum of the output capacitor voltage Vo and the diode turn-on voltage Vf obtained by sampling the auxiliary winding voltage is smaller than Vo and can be ignored approximately, but the Vf can bring about a voltage deviation of 0.3-0.6V, and the output voltage in the actual CCM mode is lower, so that the stability and the service life of the load are affected.

For the sampling precision error of the CCM mode, two error correction methods are mainly available at present. The first idea is to mainly compensate the on-voltage Vf of the diode, which is to mainly calculate the diode current If at the sampling time, and consider the diode as an equivalent small resistance Rf, where the voltage Vf of the diode is the product of If and Rf. The method has the problems that the voltage Vf of the diode and the current If thereof are in nonlinear relation, the relation changes along with the temperature change, the accurate value of Vf under different working conditions cannot be accurately calculated by using the resistor Rf, and the compensation effect cannot reach high output precision. The second method is to output a rapidly-changing ramp voltage by using a DAC, and sample the ramp voltage in a single period through multiple ramp voltages in a DCM (digital-analog converter) mode to obtain an inflection point voltage, so as to obtain an accurate output voltage; in the CCM mode, a single slope sampling method is adopted, a DCM mode is inserted after every other a plurality of periods to obtain accurate output voltage, so that sampling errors in the CCM mode sampling can be corrected, the method can better compensate the sampling voltage of a diode in the CCM sampling, but the method has the problems that a high-speed DAC and a high-precision high-speed comparator are required, in addition, the sampling algorithm is quite complex, and the practical difficulty is quite high.

In summary, the existing primary side feedback flyback converter has sampling errors in the CCM mode, and the existing method has the problems that the error compensation accuracy is not high enough or the compensation algorithm is too complex. Therefore, aiming at the primary side feedback flyback converter, a CCM sampling control method with simple realization and high precision compensation is necessary.

Disclosure of Invention

The invention aims to provide a primary side feedback converter and a switch control method, which can accurately sample to obtain output voltages of DCM and CCM modes, adaptively obtain sampling compensation errors in the CCM modes, improve the accuracy of the output voltages in the CCM modes and have simple implementation method.

The technical scheme for realizing the purpose of the invention is as follows:

A primary side feedback converter comprises a switching power supply structure controlled by primary side feedback and a controller forming a closed loop with the switching power supply structure; the controller comprises a sampling module, an error calculation module, a PID module and a PWM module; the sampling module obtains the time quantity related to the output voltage and the working mode of the converter according to the output voltage of the switching power supply structure, calculates the digital quantity of the output voltage in the current period based on the time quantity and the working mode, outputs the digital quantity to the error calculation module, and obtains a switching mode control variable to be input to the PWM module; the error calculation module calculates a voltage error and outputs the voltage error to the PID module; the PID module calculates a switch control variable based on the voltage error and outputs the switch control variable to the PWM module; the PWM module performs switching control of the switching power supply structure based on the switching mode variable and the switching control variable, and simultaneously feeds back a switching duty ratio to the sampling module.

Further, the sampling module comprises a sampling circuit module and a sampling control module; the sampling circuit module is used for calculating comparison values of output voltage V _sense, zero voltage and V _ref1、V_ref2 of the switching power supply structure, V _ref1、V_ref2 is a first following voltage and a second following voltage output by the sampling control module respectively, the second following voltage V _ref2 is lower than the first following voltage V _ref1 by a fixed voltage of delta V, and delta V is a set voltage quantity; the sampling control module is used for calculating the time length deltat of the voltage V _sense between V _ref1 and V _ref2, judging the working Mode, defining a Counter, and calculating the output voltage V _o, the first following voltage V _ref1, the second following voltage V _ref2 and the switch Mode control variable mode_s based on the working Mode.

Further, the sampling circuit module comprises a zero comparator, a first comparator and a second comparator; the input of the zero comparator is the output voltages V _sense and 0 of the switching power supply structure, when V _sense is higher than 0, the output zero comparison value V _{zvs_comp} is 1, otherwise, V _{zvs_comp} is 0; the input of the first comparator is an output voltage V _sense and a first following voltage V _ref1, when V _sense is higher than V _ref1, the output of the first comparator is a first comparison value V _{ref_comp1} of 1, otherwise, the output of the first comparator is a first comparison value of 0; the input of the second comparator is an output voltage V _sense and a second following voltage V _ref2, when V _sense is higher than V _ref2, the output of the second comparator is a second comparison value V _{ref_comp2} of 1, otherwise, the output of the second comparator is a second comparison value of 0; the first comparison value V _{ref_comp1}, the second comparison value V _{ref_comp2}, and the zero comparison value V _{zvs_comp} are input to the sampling control module.

Further, the method for judging the working mode comprises the following steps: when V _{zvs_comp} is switched from 1 to 0 for the first time in the current period, if the duty ratio duty is 0 at this time, the DCM mode is adopted; if the duty cycle is 1, the CCM mode is established.

Further, the calculation method of the time length Δt is as follows: after the switch is turned off and vzvs_comp is 1, the length of time, i.e., Δt, for V _{ref_comp1} to be 0 and V _{ref_comp2} to be 1 is calculated.

Further, when the working mode is DCM mode, the sampling control method of the sampling control module specifically includes:

Setting a time reference value Deltatref, and calculating a current output voltage value Vo as follows:

Vo＝V_ref1+C*(Δtref-Δt)

Wherein C is a correction coefficient, and V _ref1 is a first following voltage of the current period;

the method comprises the steps of obtaining a first following voltage V _ref1 and a second following voltage V _ref2 of the following switching periods:

V_ref1*＝Vo

V_ref2*＝V_ref1*-ΔV

the value of the switch Mode control variable Mode _ s is zero.

Further, when the working mode is a CCM mode, the sampling control method of the sampling control module specifically includes:

Defining a Counter, wherein the Counter starts counting once every period, and after counting from 1 to N, the Counter sets 1 and re-counts;

Vo=v _ref1-ΔV_err +c (Δtref- Δt), 1+.ltoreq.counter+.n-2 or counter=n

Vo＝Vo′，Counter＝N-1

Wherein, C is a correction coefficient, V _ref1 is the first following voltage of the current period, and Vo' is the voltage of the previous period; the method comprises the steps of obtaining a first following voltage V _ref1 and a second following voltage V _ref2 of the following switching periods:

V _ref1*＝Vo+ΔV_err; 1 +.counter +.N-2 or counter=N

V_ref1*＝VREF；Counter＝N-1

V_ref2*＝V_ref1*-ΔV；

Wherein VREF is a set voltage reference value, deltaV _err is a sampling compensation error of the current period, and DeltaV _err is kept unchanged when 1 is less than or equal to Counter is less than or equal to N-2 or counter=N, namely DeltaV _err＝ΔV_err ', deltaVerr' is a sampling compensation error of the previous period; when counter=n-1, it is corrected by the following formula:

ΔV_err＝ΔV_err′+ΔVstep；Δt<Δtref

ΔV_err＝ΔV_err′；Δt＝Δtref

ΔV_err＝ΔV_err′-ΔVstep；Δt>Δtref

Wherein DeltaVstep is a fixed step voltage, and the quantization voltage of the DAC can be taken in digital control; determining a switch Mode control variable mode_s, and taking 0 when Counter is less than or equal to N-2; when counter=n-1, mode_s takes 1; when counter=n, mode_s takes 2.

Further, the PWM module performs switching control of the switching power supply structure based on the switching mode control variable and the switching control variable, including three cases:

(1) The switching Mode control variable mode_s= 0, the switch is controlled according to two parameters of the switch on time Ton and the switch period Ts calculated by the switching control variable V _pi, and the switch-off time tr_x of the switch tube in the period is recorded;

(2) The switch Mode control variable mode_s= 1, when the switch is turned on and the calculated switch on time Ton is reached, the switch is turned off, the turn-off time of the current switch tube is prolonged until the voltage V _sense is detected to be lower than 0V, the switch tube is turned on, and the current period is ended;

(3) The switching Mode control variable mode_s= 2, the calculated switch on time Ton is prolonged, so that the peak current of the period reaches the peak current when the peak current reaches the steady state, the off time of the switch is tr_x, and the converter directly enters the CCM steady state.

Further, the switching power supply structure is a primary side feedback flyback circuit, and the output voltage Vsense of the switching power supply structure is the auxiliary winding voltage division.

A switch control method based on the primary side feedback converter comprises the following steps:

Step 1, a sampling circuit module outputs comparison values of a voltage V _sense, a zero voltage, a first following voltage V _ref1 and a second following voltage V _ref2 to a sampling control module;

Step 2, the sampling control module firstly judges whether the working mode is a DCM mode or a CCM mode according to the output value of the sampling circuit module and the duty ratio output by the PWM module; then, calculating a voltage value Vo, a first following voltage V _ref1, a second following voltage V _ref2 and a switch Mode control variable mode_s according to the working Mode, outputting the first following voltage V _ref1 and the second following voltage V _ref2 to a sampling circuit module, outputting the output voltage Vo to an error calculation module, and inputting the mode_s to a PWM module;

step 3, the error calculation module subtracts the voltage Vo from the set voltage reference value VREF to obtain an actual output voltage error of the current period and outputs the actual output voltage error to the PID module;

step4, the PID module calculates a current control variable Vpi according to the actual output voltage error and outputs the current control variable Vpi to the PWM module;

step 5, the PWM module calculates the on-time Ton of the switch according to the switch Mode variable Mode_s and the switch control variable V _pi, so as to control the on-off of the switch;

and 6, repeating the period from the step 1 to the step 5, and controlling the switch to output stable voltage.

Compared with the prior art, the invention has the remarkable effects that:

(1) The voltage sampling method in the CCM mode can accurately compensate the sampling errors delta Verr in the CCM mode, the delta Verr can be continuously corrected by inserting the DCM mode, adjusting the following voltages Vref1 and Vref2 and the like, the accurate value is finally obtained, and high-precision voltage output is realized;

(2) When counter=n-1, the following voltages Vref1 and Vref2 are respectively equal to Vref, vref- Δv, Δt at the moment is sampled, the error voltage Δvrr sampled in the CCM mode is corrected according to the relationship between Δt and Δtref, and after multiple corrections, the Δvrr reaches an accurate value and remains stable;

(3) In the invention, one DCM mode is inserted into N CCM modes, and the DCM mode and the following CCM modes are adjusted in a switching mode, so that the stability of output voltage and control is not affected due to the voltage stabilizing effect of the output capacitor;

(4) In the DCM mode, by setting the proper DeltaV time reference Deltatref, the following voltage Vref1 can be equal to the accurate voltage sampling value of the auxiliary winding (the moment when the current of the output diode is reduced to zero) when the voltage is stable, and the DCM mode and the CCM mode can realize accurate output sampling;

(5) The invention is applicable to various primary side feedback control switch power supply circuit structures, has universality, reusability and portability, and has simple realization method and easy popularization.

Drawings

Fig. 1 is a block diagram of a controller according to the present invention.

Fig. 2 is a typical circuit configuration diagram of a primary-side feedback flyback converter.

Fig. 3 (a) is a signal diagram of the sampling circuit module in DCM, and fig. 3 (b) is a signal diagram of the sampling circuit module in CCM.

Fig. 4 is a specific control flow diagram of the sampling control module.

Fig. 5 is a specific operation method and waveform diagram of the PWM module.

FIG. 6 (a) is a waveform diagram illustrating the operation of DCM when a primary feedback flyback power supply is used as an example; fig. 6 (b) is a diagram of an operation waveform corresponding to the switching period when the CCM mode overall waveform and counter=n-1 when the primary feedback flyback power supply is used as an example; FIG. 6 (c) is a diagram of the corresponding operating waveforms in CCM mode with Counter < N-1, using a primary feedback flyback power supply as an example.

Fig. 7 (a) is an output waveform diagram when the load is switched from 24.6Ω to 6.15Ω when the CCM sampling error Δv _err is not compensated for at the 100VAC ac input; fig. 7 (b) is an output waveform diagram when the load is switched from 24.6Ω to 6.15Ω when the CCM sampling error Δv _err is compensated for at 100VAC ac input.

FIG. 8 (a) is a simulation graph of voltage accuracy output when the CCM sampling error DeltaV _err is not compensated for at different AC inputs and loads; fig. 8 (b) is a simulation diagram of the voltage accuracy output when compensating for CCM sampling error Δv _err for different ac inputs and loads.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

Referring to fig. 1, the controller of the present invention includes a sampling module, an error calculation module, a PID module, and a PWM module. The auxiliary winding voltage V _sense is input to a sampling module, the sampling module outputs the output voltage V _o to an error calculation module, and the switching Mode variable mode_s is output to a PWM module; the error calculation module calculates an output voltage error err and outputs the output voltage error err to the PID module; the PID module calculates a switch control variable V _pi based on the sampling error err and outputs the switch control variable V _pi to the PWM module; the PWM module performs switching control based on the switching Mode variable mode_s and the control switch control variable V _pi. The sampling module comprises a sampling circuit module and a sampling control module, the sampling circuit module compares the auxiliary winding voltage V _sense with zero voltage V _ref1,V_ref2, V _ref1 and V _ref2 are two follow voltages output by the sampling control module, and the comparison results V _{zvs_comp},V_{ref_comp1} and V _{ref_comp2} are input to the sampling control module; the sampling control module calculates an output voltage V _o based on the three comparator results, and outputs a switch Mode variable Mode_s to the PWM module.

Fig. 2 shows a typical circuit of a switching power supply main structure, in which a primary-side feedback flyback converter is used. The transformer has three windings, wherein the auxiliary winding voltage V _sense is input to a feedback circuit, which gets the output voltage based on V _sense and performs switching control, duty represents the on and off signals of the switch.

The signals of the sampling circuit module in the DCM mode and the CCM mode are shown in fig. 3, in which the input waveform and the output waveform of the sampling circuit module are shown, and I _s is the current of the output diode. V _ref1 and V _ref2 are two follow voltages output by the sampling control module, where V _ref2 is a fixed voltage that is Δv lower than V _ref1. In the sampling circuit module, V _{ref_comp1} sets "1" when V _sense is higher than V _ref1, otherwise sets "0"; v _{ref_comp2} sets "1" when V _sense is higher than V _ref2, otherwise sets "0"; v _{zvs_comp} sets "1" when V _sense is above zero volts, otherwise "0". The sampling control module calculates the time period Δt between V _ref1 and V _ref2 for V _sense, i.e., the time period for V _{ref_comp1} to be "0" and V _{ref_comp2} to be "1".

The specific control method of the sampling control module can be shown in fig. 4, where the input signal of the sampling control module is V _{ref_comp1},V_{ref_comp2},V_{zvs_comp}, i.e. the switching duty ratio duty, the output is the following voltages V _ref1 and V _ref2, the output voltage V _o, and the switching control Mode mode_s. The circuit works in DCM or CCM and can be obtained by V _{zvs_comp} and duty signals, when V _{zvs_comp} is switched from "1" to "0" for the first time, if the duty ratio duty is "0" at this time, the DCM mode is adopted; if the duty cycle is "1", the CCM mode is defined. The sampling control Mode first defines a Counter, then calculates an output voltage V _o, a following voltage V _ref1,V_ref2, an error voltage Δv _err, and a switching Mode control variable mode_s, respectively.

In DCM mode, the Counter is set to 0, when Δt is detected, the current output voltage V _o is calculated according to the relationship between Δt and Δt _ref, V _o remains unchanged when Δt is equal to Δt _ref, V _o increases when Δt is smaller than Δt _ref, V _o decreases when Δt is larger than Δt _ref, and the function f (Δt _ref - Δt) can be modified to calculate the adjustment amount of the output voltage V _o, and f (Δt _ref - Δt) =c (Δtref- Δt), where C is a correction coefficient set empirically. After the updated output voltage V _o is obtained, the following voltage V _ref1 in the next period is updated to the new output voltage V _o, and V _ref2 can be further calculated after V _ref1 is obtained. In DCM Mode, the value of the switch Mode control variable Mode_s is zero, i.e. the working Mode of the switch is not affected.

V_o＝V_ref1+f(Δt_ref-Δt)＝Vref1+C*(Δtref-Δt)

V_ref1*＝Vo

V_ref2*＝V_ref1*-ΔV

In CCM mode, the Counter counts once per cycle, and after counting from 1 to N, counter sets 1 and repeats the above-described accumulating manner, when Δt generation is detected, output voltage V _o is calculated, when 1+ counter+.n-2 or counter=n, output voltage needs to compensate sampling error Δv _err,V_ref1, when counter=n-1, default output voltage V _o remains unchanged, being the last cycle voltage Vo'.

V _o＝V_ref1-ΔV_err+f(Δt_ref - Δt), 1+.counter+.n-2 or counter=n

V_o＝Vo′；Counter＝N-1

Secondly, calculating a first following voltage V _ref1 and a second following voltage V _ref2 of the next switching period, and when 1+ counter+.n-2 or counter=n, determining V _ref1 by the new sampling result V _o and the sampling error Δv _err; when counter=n-1, V _ref1 is equal to the reference voltage V _REF corresponding to the output voltage.

V _ref1*＝V_o+ΔV_err; 1 +.counter +.N-2 or counter=N

V_ref1*＝V_REF；Counter＝N-1

V_ref2*＝V_ref1*-ΔV

Furthermore, the sampling compensation error DeltaV _err is calculated, when 1 is less than or equal to Counter is less than or equal to N-2 or counter=N, deltaV _err is kept unchanged, when counter=N-1, if Deltat is less than Deltat _ref at this time, the sampling compensation error DeltaV _err 'of the previous period is smaller, deltaV _err' increases the voltage of DeltaV _step, deltaV _step is a small fixed step voltage, and the quantized voltage of the DAC can be taken in digital control; if delta t is equal to delta t _ref,ΔV_err', the method is accurate and unchanged; if at this time Δt is greater than Δt _ref,ΔV_err ' and Δv _err ' is greater, Δv _step ' is reduced in voltage. After several corrections, when counter=n-1, Δt is equal to Δt _ref,ΔV_err and remains approximately unchanged, so that the problem error of the CCM mode can be adaptively and accurately compensated.

ΔV_err＝ΔV_err′+ΔV_step;Δt<Δt_ref

ΔV_err＝ΔV_err′;Δt＝Δt_ref

ΔV_err＝ΔV_err′-ΔV_step;Δt>Δt_ref

Finally, confirming the value of a switch Mode control variable mode_s, and outputting the switch Mode control variable mode_s to be 0 when the Counter is less than or equal to N-2; when counter=n-1, mode_s takes 1, and the turn-off time of the switch needs to be prolonged, namely the time for duty to be set to "0" needs to be prolonged; when counter=n, mode_s takes 2, and it is necessary to lengthen the on time of the switch, i.e. the time during which duty is set to "1". V _ref1,V_ref2 is output to the sampling circuit module, output voltage V _o is output to the error calculation module, and the mode_s signal is input to the PWM module.

The input of the error calculation module is output voltage V _o, and in the error calculation module, the output voltage reference value V _REF is subtracted by V _o to obtain the current sampling error err, and the error is output to the PID module; the PID module calculates a current control variable V _pi from the sampling error err and inputs the control variable V _pi to the PWM module.

The specific operation of the PWM module can be illustrated in fig. 5. The PWM module calculates the on-time Ton and the switching period Ts of the switch according to V _pi, and the calculation method is common knowledge in the art, and will not be described here; based on the input switch Mode control variable mode_s, three cases are divided:

(1) Mode_s= =0, in normal DCM or CCM sampling Mode, the switch is controlled by two parameters of switch on time Ton and switch period Ts, and the switch tube turn-off time of the period is recorded as t _{r_x}.

(2) Mode_s= 1, when the switch is turned on and the switch is turned off after the on time reaches Ton, the turn-off time of the current switching tube is prolonged until the current period is ended when the V _sense is detected to be lower than 0V, namely, the vzvs_comp is changed from '1' to '0'.

(3) Mode_s= =2, the on time Ton of the switch is prolonged, so that the peak current in the period reaches the peak current I _pp in the steady state, the off time of the switch is defined as t _{r_x}, and the system directly enters the CCM steady state without causing additional oscillation.

The PWM module controls the switch in the mode, outputs a switch duty ratio signal duty, and realizes sampling and control of output voltage in the primary feedback flyback converter.

Step 6, repeating the period from step 1 to step 5, and controlling the switch to output stable voltage;

The technical characteristics shared by the method and the primary side feedback converter are not described any more, and the method can obtain good sampling precision and constant voltage precision in both a DCM mode and a CCM mode.

Examples

The invention can also be used for other types of primary feedback switching power supply circuit structures, and only a primary feedback flyback circuit is taken as an example. Fig. 6 is an operational waveform of an embodiment of a primary side feedback flyback power supply. The flyback converter has the input of 90-265V, the output constant voltage of 20V, the maximum current of 3.25A, the inductance of 730uH and the turn ratio of the primary winding, the secondary winding and the secondary winding of the transformer of 48/8/4. The switching frequency is set to a constant frequency of 100 kHz. When the input voltage is low and the load power is high, the circuit is easier to enter the CCM mode, and when the load power is reduced, the circuit is easy to enter the DCM mode. Fig. 6 (a) shows the operating waveform when the load is 24.6Ω and 100V ac input, and at this time, the load is 25%, the circuit operates in DCM mode, V _ref1,V_ref2 follows the "knee" voltage, i.e. the voltage when the diode current drops to zero, and the output voltage can be accurately sampled, and at this time, the output voltage is 19.34V. As shown in fig. 6 (b), when the load changes to 6.15Ω, the circuit enters CCM mode, where N is 50, i.e. the sampling error Δv _err of CCM is corrected every 50 cycles, when counter=49, V _ref1 is reduced to V _REF, the switch off time is prolonged, the switch is turned on after ensuring that the voltage of V _sense is lower than zero volt, and the output voltage error Δv _err is corrected by Δt and Δt _ref; when counter=50, the conduction of the switch is prolonged, ensuring that the peak current reaches the value at steady state; when Counter <49, the sampling is as shown in fig. 6 (c), after the switch is turned off, V _sense is sampled by V _ref1 and V _ref2, and V _ref1 minus the sampling error Δv _err represents the output voltage V _o when it is stable.

Fig. 7 is an output waveform when the load is switched from 24.6Ω to 6.15Ω at 100VAC ac input, the circuit is operating in DCM mode when the load is 24.6Ω, and the circuit is operating in CCM mode when the load is 6.15Ω. In fig. 7 (a), Δv _err is constant to 0, and V _ref1 is used as the output voltage V _o in the steady state of the CCM mode, and at this time, there is an error in the CCM sampling, and the output is reduced from 19.900V to 19.510V. In fig. 7 (b), Δv _err is adjustable, the sampling error Δv _err is corrected every 50 cycles, the output voltage of CCM in steady state is 19.925V, and it is seen that the accuracy of the output voltage in steady state in CCM mode is improved. FIG. 8 is a comparison of the overall accuracy of the output voltage, in FIG. 8 (a), ΔV _err is constant at 0, V _ref1 represents the output voltage V _o at steady state, the maximum deviation of the output voltage from the 20V target voltage is 0.49V, and it is apparent that the larger the load or the lower the input voltage, i.e. the larger the output diode current at the switch on time, the larger the turn-on voltage of the output diode, the larger the steady state accuracy error of the CCM mode; in fig. 8 (b), the maximum deviation of the final output is 0.14V when Δv _err can be adaptively adjusted using the proposed method. The accuracy of the output voltage is greatly improved.

It can be seen from the above embodiments that, by adopting the method of the present invention, especially for the primary side feedback system with DCM and CCM modes, the circuit can adaptively compensate the sampling error in the CCM mode and improve the accuracy of the output voltage after adopting the proposed sampling scheme.

While the invention has been described in detail in connection with specific preferred embodiments thereof, it is not to be construed as limited to the specific embodiments of the invention, but rather as many variations of the invention are possible without departing from the spirit and scope of the invention. Accordingly, all changes which become apparent to those skilled in the art are intended to be included within the scope of the following claims.

Claims

1. A primary side feedback converter comprises a switching power supply structure controlled by primary side feedback and a controller forming a closed loop with the switching power supply structure; the method is characterized in that: the controller comprises a sampling module, an error calculation module, a PID module and a PWM module; the sampling module obtains the time quantity related to the output voltage and the working mode of the converter according to the output voltage of the switching power supply structure, calculates the digital quantity of the output voltage in the current period based on the time quantity and the working mode, outputs the digital quantity to the error calculation module, and obtains a switching mode control variable to be input to the PWM module; the error calculation module calculates a voltage error and outputs the voltage error to the PID module; the PID module calculates a switch control variable based on the voltage error and outputs the switch control variable to the PWM module; the PWM module performs switching control of the switching power supply structure based on the switching mode variable and the switching control variable, and simultaneously feeds back a switching duty ratio to the sampling module;

The sampling module comprises a sampling circuit module and a sampling control module; the sampling circuit module is used for calculating comparison values of output voltage V _sense, zero voltage and V _ref1、V_ref2 of the switching power supply structure, V _ref1、V_ref2 is a first following voltage and a second following voltage output by the sampling control module respectively, the second following voltage V _ref2 is lower than the first following voltage V _ref1 by a fixed voltage of delta V, and delta V is a set voltage quantity; the sampling control module is used for calculating the time length deltat of the voltage V _sense between V _ref1 and V _ref2, judging the working Mode, defining a Counter, and calculating the output voltage V _o, the first following voltage V _ref1, the second following voltage V _ref2 and a switch Mode control variable mode_s based on the working Mode;

The sampling circuit module comprises a zero comparator, a first comparator and a second comparator; the input of the zero comparator is the output voltages V _sense and 0 of the switching power supply structure, when V _sense is higher than 0, the output zero comparison value V _{zvs_comp} is 1, otherwise, V _{zvs_comp} is 0; the input of the first comparator is an output voltage V _sense and a first following voltage V _ref1, when V _sense is higher than V _ref1, the output of the first comparator is a first comparison value V _{ref_comp1} of 1, otherwise, the output of the first comparator is a first comparison value of 0; the input of the second comparator is an output voltage V _sense and a second following voltage V _ref2, when V _sense is higher than V _ref2, the output of the second comparator is a second comparison value V _{ref_comp2} of 1, otherwise, the output of the second comparator is a second comparison value of 0; the first comparison value V _{ref_comp1}, the second comparison value V _{ref_comp2} and the zero comparison value V _{zvs_comp} are input to the sampling control module;

The method for judging the working mode comprises the following steps: when V _{zvs_comp} is switched from 1 to 0 for the first time in the current period, if the duty ratio duty is 0 at this time, the DCM mode is adopted; if the duty ratio is 1, the CCM mode is adopted;

The calculation method of the time length delta t comprises the following steps: after the switch is turned off and vzvs_comp is 1, calculating the time length of V _{ref_comp1} being 0 and V _{ref_comp2} being 1, which is Δt;

When the working mode is a DCM mode, the sampling control method of the sampling control module comprises the following steps:

Vo＝V_ref1+C*(Δtref-Δt)

V_ref1*＝Vo

V_ref2*＝V_ref1*-ΔV

the value of the switch Mode control variable Mode_s is zero;

when the working mode is CCM mode, the sampling control method of the sampling control module comprises the following steps:

Vo=v _ref1-ΔV_err +c (Δtref- Δt), 1+.ltoreq.counter+.n-2 or counter=n

Vo＝Vo′，Counter＝N-1

V _ref1*＝Vo+ΔV_err; 1 +.counter +.N-2 or counter=N

V_ref1*＝V_REF；Counter＝N-1

V_ref2*＝V_ref1*-ΔV

Wherein V _REF is a set voltage reference value, Δv _err is a sampling compensation error of the current period, and when 1+.ltoreq.counter+.n-2 or counter=n, Δv _err remains unchanged, i.e. Δv _err＝ΔV_err ', Δvrr' is a sampling compensation error of the previous period; when counter=n-1, it is corrected by the following formula:

ΔV_err＝ΔV_err′+ΔVstep；Δt<Δtref

ΔV_err＝ΔV_err′；Δt＝Δtref

ΔV_err＝ΔV_err′-ΔVstep；Δt>Δtref

wherein DeltaVstep is a fixed step voltage, and the quantization voltage of the DAC can be taken in digital control;

Determining a switch Mode control variable mode_s, and taking 0 when Counter is less than or equal to N-2; when counter=n-1, mode_s takes 1; when counter=n, mode_s takes 2.

2. The primary side feedback converter of claim 1, wherein: the PWM module performs switching control of the switching power supply structure based on the switching mode control variable and the switching control variable, including three cases:

3. A primary side feedback converter according to any of claims 1-2, characterized in that: the switching power supply structure is a primary side feedback flyback circuit, and the output voltage V _sense of the switching power supply structure is the partial voltage of the auxiliary winding.

4. A method of switching control based on the primary-side feedback converter of claim 3, comprising the steps of:

Step 3, the error calculation module subtracts the voltage Vo from the set voltage reference value V _REF to obtain an actual output voltage error of the current period and outputs the actual output voltage error to the PID module;