Novel synchronous rectification control method of phase-shifted full-bridge converter

Abstract

The invention relates to the technical field of synchronous rectification control, in particular to a novel synchronous rectification control method for a phase-shifted full-bridge converter, which comprises the following steps of: constructing a controller; calculating a duty ratio parameter of the converter; judging the working mode of the converter by using the current sampling signal; calculating the conduction duration of a synchronous rectifier tube by using the working mode signal of the converter, the duty ratio parameter of the converter, the output voltage sampling signal and the input voltage sampling signal; the method comprises the following steps of: performing synchronous updating on a signal according to a pulse width modulation (PWM) signal, realizing synchronous adjustment on duty ratios of leading and lagging bridge arm switch tubes in the converter, updating the conduction duration of a synchronous rectifier tube, and controlling the on-off of the switch tubes in a discontinuous current mode by utilizing a PWM (Pulse-Width Modulation) wave. The synchronous rectification control method of the discontinuous current mode is improved on the basis of an existing multi-mode control method, so that the synchronous rectification control method can be suitable for all phase-shifted full-bridge converters with the discontinuous current mode.

Description

Technical Field

[0001] The present invention relates to the technical field of synchronous rectification control, and in particular to a novel synchronous rectification control method for a phase-shifted full-bridge converter. Background Art

[0002] The development of new energy vehicles has put forward higher requirements on power electronics technology; DC-DC converter, as one of the key components in the peripheral power supply system of new energy vehicles, undertakes the important task of converting electrical energy; however, in traditional full-bridge converters, the efficiency under light load conditions is often not high, and there is a problem of large energy loss; therefore, a reliable and uncomplicated method is needed to reduce the loss of the converter under light load.

[0003] The phase-shifted full-bridge converter has been widely used in vehicle power supplies due to its zero-voltage switching characteristics, simple structure, easy control, and input-output electrical isolation. The phase-shifted full-bridge converter with synchronous rectification often operates in forced current continuous mode or current discontinuous mode under light load, among which it is more difficult to achieve zero-voltage switching of the switch tube in the forced current continuous mode.

[0004] The patent publication number is CN118554769, which solves the problem that zero-voltage switching of the switch tube is difficult under light load; however, the multi-mode control method adopts traditional synchronous rectification control under light load, and uses the body diode rectification of the switch tube part of the time, causing unnecessary conduction loss and reducing the light-load efficiency of the converter. Summary of the invention

[0005] In view of the shortcomings of the existing methods, the present invention improves the synchronous rectification control method of the current discontinuous mode on the basis of the existing multi-mode control method, so that the synchronous rectification control method can be applicable to all phase-shifted full-bridge converters with current discontinuous mode.

[0006] The technical solution adopted by the present invention is: a novel synchronous rectification control method of a phase-shifted full-bridge converter comprises the following steps:

[0007] Step 1: Build a controller based on a voltage loop control unit, an adaptive synchronous rectification control unit, and a digital ePEM unit;

[0008] Step 2: The voltage loop control unit compares the output voltage sampling signal with the output voltage reference value, and calculates the converter duty cycle parameter using a PID controller;

[0009] Step 3: The adaptive synchronous rectification control unit uses the current sampling signal to determine the working mode of the converter; and uses the working mode signal of the converter, the duty cycle parameter of the converter, the output voltage sampling signal and the input voltage sampling signal to calculate the conduction time of the synchronous rectifier tube;

[0010] Step 4. The controller of the digital ePEM unit uses the on-time of the synchronous rectifier tube and the duty cycle parameters of the converter to control the duty cycle, and synchronously updates the signal to achieve synchronous adjustment of the duty cycle of the leading and lagging bridge arm switches in the converter, as well as updating the on-time of the synchronous rectifier tube, and uses the PWM wave to control the on and off of the switch tube in the current discontinuous mode.

[0011] As a preferred implementation manner of the present invention, the conduction time length of the synchronous rectifier is when the converter operates in the current discontinuous mode, and a synchronous rectifier current model is constructed.

[0012] As a preferred embodiment of the present invention, the construction of the synchronous rectifier current model includes:

[0013] Using the volt-second balance principle, the peak value of the output filter inductor current peak and the output filter inductor current peak are obtained;

[0014] When the peak value of the filter inductor current peak is equal to the output filter inductor current peak value, a boundary load current condition between the current continuous mode and the current discontinuous mode is obtained;

[0015] Calculate the voltage gain and average output filter inductance in DCM;

[0016] Obtain the mathematical model of synchronous rectifier current when the converter works in current discontinuous mode;

[0017] The conduction time of the synchronous rectifier is calculated using the mathematical model of the synchronous rectifier current.

[0018] As a preferred implementation of the present invention, the calculation formula for the conduction time of the synchronous rectifier is:

[0019]

[0020] Among them, D DCM is the duty cycle of the converter operating in DCM, ΔD DCM is the equivalent duty cycle of the inductor current fall time, T s is the converter switching period, n is the transformer primary-to-secondary turns ratio, V in is the converter input voltage, V o is the converter output voltage.

[0021] As a preferred embodiment of the present invention, the control of the adaptive synchronous rectification control unit includes:

[0022] Determine the output voltage reference value V ref , switching frequency f s , get the input voltage sampling value V in_samp , output current sampling value I o_samp And the output voltage sampling value Vo_samp ,

[0023] According to the output voltage sampling value V o_samp Determine whether the converter is soft-started;

[0024] As a preferred implementation of the present invention, determining whether the converter is soft-started includes:

[0025] If the output voltage sampling value V o_samp Less than the output voltage reference value V ref , then the phase shift angle φ decreases by 1°;

[0026] If the output voltage sampling value V o_samp Greater than or equal to the output voltage reference value V ref , the soft start ends.

[0027] According to the output current sampling value I o_samp Perform the i-th judgment on the working mode of the converter;

[0028] As a preferred implementation of the present invention, the i-th determination of the working mode of the converter includes:

[0029] If the number of judgments i>=2, then i=0;

[0030] If I o_samp >=I o,boundary , then the current continuous mode flag CCM_Flag[i]=1;

[0031] If I o_samp >=I o,boundary , and CCM_Flag[0]=1, then CCM_Flag[i]=1.

[0032] The working mode flag CCM_Flag[2] is judged and the corresponding working mode is selected: if CCM_Flag[0] is equal to 1 and CCM_Flag[1] is equal to 1, the converter enters the current continuous mode and sets the switching timing of the synchronous rectifier tubes SR1 and SR2 to the current continuous mode: SR1 is turned on when Q1 is turned on and turned off when Q4 is turned off; SR2 is turned on when Q2 is turned on and turned off when Q3 is turned off.

[0033] As a preferred implementation of the present invention, the switching timing of the synchronous rectifier tubes SR1 and SR2 is set to a current discontinuous mode: SR1 and SR2 are turned on when Q4 and Q3 are turned on, respectively.

[0034] As a preferred embodiment of the present invention, a new synchronous rectification control system of a phase-shifted full-bridge converter includes: a memory for storing instructions executable by a processor; and a processor for executing instructions to implement a new synchronous rectification control method for a phase-shifted full-bridge converter.

[0035] As a preferred embodiment of the present invention, a computer readable medium stores a computer program code, and when the computer program code is executed by a processor, a novel synchronous rectification control method of a phase-shifted full-bridge converter is implemented.

[0036] Beneficial effects of the present invention:

[0037] 1. Compared with the conventional synchronous rectification control of the phase-shifted full-bridge converter, the novel synchronous rectification control method of the phase-shifted full-bridge converter of the present invention can realize the synchronous rectification tube control of the full-channel conduction of the switch tube without adding additional auxiliary circuits, thereby prolonging the device life, improving the energy conversion efficiency and reducing the cost;

[0038] 2. Compared with the conventional synchronous rectification control of the phase-shifted full-bridge converter, the novel synchronous rectification control method of the phase-shifted full-bridge converter of the present invention can calculate the optimal turn-on time of the synchronous rectifier tube according to the synchronous rectifier tube timing model, realize the precise control of the switch state of the switch tube, reduce the conduction loss, realize the zero current turn-off of the synchronous rectifier tube, and improve the system stability;

[0039] 3. Compared with the traditional synchronous rectification control of the phase-shifted full-bridge converter, the novel synchronous rectification control method of the phase-shifted full-bridge converter of the present invention can significantly improve the working efficiency of the phase-shifted full-bridge converter under light load conditions and reduce the energy loss of the converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic diagram of the structure of the phase-shifted full-bridge converter of the present invention;

[0041] Figure 2 A schematic diagram of a novel synchronous rectification control method for a phase-shifted full-bridge converter according to an embodiment of the present invention;

[0042] Figure 3 It is a control flow block diagram of the adaptive synchronous rectification unit, the voltage loop unit and the digital ePWM unit in the controller of the present invention;

[0043] Figure 4 A program flow chart of a synchronous rectification control unit for improving the light-load efficiency of a phase-shifted full-bridge;

[0044] Figure 5 It is the simulation waveform diagram of the new synchronous rectification control method of the phase-shifted full-bridge converter;

[0045] Figure 6 This is the experimental waveform diagram of the new synchronous rectification control of the phase-shifted full-bridge converter. DETAILED DESCRIPTION

[0046] The present invention is further described below in conjunction with the accompanying drawings and embodiments. This figure is a simplified schematic diagram, which only illustrates the basic structure of the present invention in a schematic manner, and therefore it only shows the components related to the present invention.

[0047] like Figure 1 The controller of the present invention is different from the CN118554769 patent in that an adaptive synchronous rectification control unit is adopted, and the phase-shifted full-bridge circuit is the same as that of CN118554769, which will not be described again.

[0048] A novel synchronous rectification control method for a phase-shifted full-bridge converter comprises the following steps:

[0049] Based on the switching timing of Q1 to Q4, the working mode of the phase-shifted full-bridge converter working in the current discontinuous mode is analyzed; the phase-shifted full-bridge converter is referred to as the converter;

[0050] When the converter works in the discontinuous current mode, it can be divided into 6 working modes. To study the conduction time of the synchronous rectifier, only 4 of the working modes need to be analyzed.

[0051] like Figure 2 As shown, the time [t0-t1] is the rising stage of the converter output filter inductor current; and the time [t1-t4] is the falling stage of the converter output filter inductor current.

[0052] 1. Working mode 1 [t0-t1];

[0053] At t1, the Q3 drive signal is set high, Q3 is turned on, and the power transmission stage begins. The primary current of the transformer increases from 0A in the reverse direction. The loop formed by Q2, Q3 and the primary winding of the transformer transfers energy to the secondary side. The two ends of the output filter inductor are subjected to positive voltage, and the output filter inductor current begins to rise. At t2, the Q2 drive signal is set low, and Q2 is turned off, indicating that the energy transmission of the converter ends and the output filter inductor current stops rising.

[0054] 2. Working mode 2 [t1-t2]:

[0055] The moment [t1-t2] is the process of the drain-source voltage of the leading bridge arm Q2 decreasing. At moment t1, the driving signal of the switch tube Q1 is set low, and Q1 is turned off. At this time, the parasitic capacitance of Q1 and Q2 begins to charge and discharge; the voltage of the primary winding of the transformer gradually decreases. According to Faraday's law of electromagnetic induction, the voltage of the secondary winding of the transformer decreases accordingly, forcing the parasitic capacitance of SR1 to discharge.

[0056] 3. Working mode 3[t2-t3]:

[0057] At time t2, the drive signal of the switch tube Q1 is set high, Q2 is turned on, and the primary current of the transformer circulates between the loop formed by Q2, Q4 and the primary winding of the transformer, causing the transformer to be clamped and unable to transfer energy. The load current relies on the output filter inductor current to continue to flow, and the excitation inductor current and the primary current remain unchanged.

[0058] 4. Working mode 4 [t3-t4]:

[0059] At t3, the SR1 body diode is turned off, and SR2 provides a freewheeling loop for the load current to ensure the continuity of the load current. In addition, the primary current decreases as the output filter inductor current decreases until the output filter inductor current decreases to 0A at t3, at which time the output filter inductor current decrease phase ends.

[0060] From the above analysis, it can be seen that body diode rectification phenomenon will occur in the traditional phase-shifted full-bridge synchronous rectifier control.

[0061] When the converter operates in the discontinuous current mode, the method for establishing the synchronous rectifier current model includes:

[0062] According to the volt-second balance principle, the peak value of the output filter inductor current peak is obtained as follows:

[0063]

[0064] Among them, V in is the converter input voltage, n is the transformer primary-to-secondary turns ratio, V o is the converter output voltage, D eff is the effective duty cycle of the converter operating in the continuous current mode, T s is the converter switching period, L f Output filter inductor for the converter.

[0065] Similarly, the peak value of the output filter inductor current can be obtained:

[0066]

[0067] Among them, I o is the converter output current.

[0068] When I Lf,pp Equal to its peak value I Lf,peak When , the boundary load current condition between the continuous current mode and the discontinuous current mode appears:

[0069]

[0070] Assume that the dead time between Q1 and Q2 is ignored and L at [t4-t6] f During the resonance period, L fVoltage across the terminals V Lf The average value of is zero; according to L f According to the volt-second balance principle, the following equation can be obtained:

[0071]

[0072] Among them, D DCM is the duty cycle of the converter operating in DCM, ΔD DCM is the equivalent duty cycle of the inductor current fall time.

[0073] From equation (4), the voltage gain in DCM is:

[0074]

[0075] The average value of the output filter inductance is equal to I o , then I o With D DCM The relationship is expressed as:

[0076]

[0077] Combining equations (5) and (6), the mathematical model of the synchronous rectifier current when the converter works in the current discontinuous mode is:

[0078]

[0079] Perform synchronous rectification control of the converter; determine the conduction time t of the synchronous rectifier according to the mathematical model of the synchronous rectifier current SR,con , that is, the sum of the rise time and fall time of the filter inductor current is:

[0080]

[0081] The adaptive synchronous rectification control method of the converter specifically includes:

[0082] Step 1: Determine the output voltage reference value V ref , switching frequency f s , the input voltage sampling value V is obtained through the input voltage sampling unit and ADC in_samp ; Obtain the output current sampling value I through the output voltage and current sampling unit and ADC o_samp And the output voltage sampling value V o_samp , and transmitted to the controller;

[0083] Step 2: The converter performs soft start, and the controller starts the converter according to the output voltage sampling value V o_samp Determine whether the converter has completed the soft start action;

[0084] If the output voltage sampling value V o_samp Less than the output voltage reference value Vref , then the phase shift angle φ decreases by 1°;

[0085] If the output voltage sampling value V o_samp Greater than or equal to the output voltage reference value V ref , the soft start ends;

[0086] Step 3: The controller samples the output current according to the value I o_samp Perform the i-th judgment on the working mode of the converter;

[0087] If the number of judgments i>=2, then i=0;

[0088] If I o_samp >I o,boundary , then the current continuous mode flag CCM_Flag[i]=1;

[0089] If I o_samp >I o,boundary , and CCM_Flag[0]=1, then CCM_Flag[i]=1;

[0090] Step 4. The controller determines the working mode flag CCM_Flag[2] and selects to enter the corresponding working mode: if CCM_Flag[0] is equal to 1 and CCM_Flag[1] is equal to 1, the converter enters the current continuous mode and sets the switching timing of the synchronous rectifier tubes (SR1, SR2) to the current continuous mode: SR1 is turned on when Q1 is turned on and turned off when Q4 is turned off; SR2 is turned on when Q2 is turned on and turned off when Q3 is turned off; if CCM_Flag[0] is equal to 0 and CCM_Flag[1] is also equal to 0, the converter enters the current discontinuous mode and sets the switching timing of the synchronous rectifier tubes (SR1, SR2) to the current discontinuous mode: SR1 and SR2 are turned on when Q4 and Q3 are turned on, respectively, and the on time is t SR,con ; Finally, clear the current mode flag and repeat step 3.

[0091] Compared with the CN118554769 patent, the adaptive synchronous rectification control method only involves two-mode control of the converter, namely the current continuous mode and the current discontinuous mode, and optimizes the switching timing of the synchronous rectifier tube in the current discontinuous mode on this basis. By calculating the conduction time t of the synchronous rectifier tube, the adaptive synchronous rectification control method can be used to optimize the switching timing of the synchronous rectifier tube in the current discontinuous mode. SR,con , eliminating the body diode conduction time of the synchronous rectifier in the current discontinuous mode, thereby further improving the energy conversion efficiency of the converter and weakening the voltage spike caused by the shutdown of the synchronous rectifier.

[0092] like Figure 3 As shown, the converter includes: a voltage loop control unit, a synchronous rectification control unit and a digital ePWM unit; an output current sampling signal I o_samp, output voltage sampling signal V o_samp And the input voltage sampling signal V in_samp The ADC peripheral of the controller is passed to the mode recognition module by reading I o_samp Determine the working mode that the phase-shifted full-bridge converter should be in, where the working modes include DCM and CCM; and transmit the working mode signal to t SR,con Calculation module; at the same time, the voltage loop control unit reads V o_samp , and the output voltage reference value V ref After comparison, the converter duty cycle parameter D is calculated by the PI controller; finally, t SR,con The calculation module reads the working mode signal, D, V o_samp and V in_samp , and calculates the optimal conduction timing of the synchronous rectifier tube under the current load conditions in real time, and inputs this value into the duty cycle control module of the digital ePWM module.

[0093] The duty cycle control module in the digital ePWM module receives the t SR,con signal and duty cycle parameter D signal; then, the duty cycle control module sends a synchronous update signal to the signal generation module to realize the synchronous adjustment of the duty cycle of the leading and lagging bridge arm switches in the converter, and the update of the conduction time of the synchronous rectifier tube, so as to generate a reasonable PWM waveform, control the switching of the switch tube in the current discontinuous mode, realize adaptive synchronous rectification control, reduce the turn-off loss and conduction loss of the rectifier tube, and improve the overall energy conversion efficiency.

[0094] like Figure 5 As shown in FIG. 1 , the simulation waveform of the novel synchronous rectification control of the phase-shifted full-bridge converter according to the embodiment of the present invention is shown; the driving waveforms of the leading and lagging bridge arm switches of the phase-shifted full-bridge circuit, the driving waveforms of the synchronous rectifier tubes of the full-wave rectifier circuit, and the filtering inductor current I Lf Waveform and filter inductor voltage V Lf Waveform; From the figure, we can see that in I Lf During the rise and fall times, the synchronous rectifier uses its channel rectification instead of its body diode, which can reduce the rectifier conduction loss.

[0095] like Figure 6 As shown in Figure 1, the experimental waveform of the new synchronous rectification control of the phase-shifted full-bridge converter; among them, channel 1 is the leading bridge arm switch tube drive waveform V GS1 ; Channel 2 is the lagging bridge arm switch tube drive waveform V GS4 ; Channel 3 is the synchronous rectification drive waveform V GS_SR2 ; Channel 4 is the output filter inductor current waveform I Lf ;Depend on Figure 6It can be seen that the synchronous rectification control method of the present invention can eliminate the conduction loss of the body diode during the decline of the inductor current in the traditional synchronous rectification control; compared with the traditional control that turns off the synchronous rectifier tube when the inductor current rises to the peak value, the proposed new synchronous rectification control turns off the synchronous rectifier tube when it drops to 0A, which greatly reduces the turn-off loss of the switch tube, suppresses the parasitic oscillation caused by the parasitic parameters of the switch tube, and improves the EMI performance of the converter; finally, Figure 6 The synchronous rectification control experimental waveforms and Figure 5 The synchronous rectification control simulation waveforms shown are consistent, and the invented new synchronous rectification control method is practically feasible.

[0096] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A novel synchronous rectification control method for a phase-shifted full-bridge converter, characterized in that: The following steps are involved: Step 1: construct a controller based on a voltage loop control unit, an adaptive synchronous rectification control unit, and a digital ePEM unit; Step 2: The voltage loop control unit compares the output voltage sampling signal with the output voltage reference value, and calculates the converter duty cycle parameter using a PID controller; Step 3: The adaptive synchronous rectification control unit uses the current sampling signal to determine the working mode of the converter; The conduction time of the synchronous rectifier is calculated by using the working mode signal of the converter, the duty cycle parameter of the converter, the output voltage sampling signal and the input voltage sampling signal; Step 4: The controller of the digital ePEM unit uses the conduction time of the synchronous rectifier tube and the duty cycle parameters of the converter to control the duty cycle, and synchronously updates the signal to achieve synchronous adjustment of the duty cycle of the leading and lagging bridge arm switches in the converter, as well as updating the conduction time of the synchronous rectifier tube, and using the PWM wave to control the on and off of the switch tube in the current discontinuous mode.

2. The novel synchronous rectification control method of the phase-shifted full-bridge converter according to claim 1 is characterized in that: The conduction time of the synchronous rectifier is to build a synchronous rectifier current model when the converter works in the current discontinuous mode.

3. The novel synchronous rectification control method of the phase-shifted full-bridge converter according to claim 2 is characterized in that: The construction of the synchronous rectifier current model includes: Using the volt-second balance principle, the peak value of the output filter inductor current peak and the output filter inductor current peak are obtained; When the peak value of the filter inductor current peak is equal to the output filter inductor current peak value, a boundary load current condition between the current continuous mode and the current discontinuous mode is obtained; Calculate the voltage gain and average output filter inductance in DCM; Obtain the mathematical model of synchronous rectifier current when the converter works in current discontinuous mode; The conduction time of the synchronous rectifier is calculated using the mathematical model of the synchronous rectifier current.

4. The novel synchronous rectification control method of the phase-shifted full-bridge converter according to claim 3 is characterized in that: The calculation formula for the conduction time of the synchronous rectifier is: Among them, D DCM is the duty cycle of the converter operating in DCM, ΔD DCM is the equivalent duty cycle of the inductor current fall time, T s is the converter switching period, n is the transformer primary-to-secondary turns ratio, V in is the converter input voltage, V o is the converter output voltage.

5. The novel synchronous rectification control method of the phase-shifted full-bridge converter according to claim 1 is characterized in that: The control of the adaptive synchronous rectification control unit includes: Determine the output voltage reference value V ref , switching frequency f s , get the input voltage sampling value V in_samp , output current sampling value I o_samp And the output voltage sampling value V o_samp , According to the output voltage sampling value V o_samp Determine whether the converter is soft-started; According to the output current sampling value I o_samp Perform the i-th judgment on the working mode of the converter; The working mode flag CCM_Flag[2] is judged and the corresponding working mode is selected: if CCM_Flag[0] is equal to 1 and CCM_Flag[1] is equal to 1, the converter enters the current continuous mode and sets the switching timing of the synchronous rectifier tubes SR1 and SR2 to the current continuous mode: SR1 is turned on when Q1 is turned on and turned off when Q4 is turned off; SR2 is turned on when Q2 is turned on and turned off when Q3 is turned off.

6. The novel synchronous rectification control method of the phase-shifted full-bridge converter according to claim 5 is characterized in that: The switching timing of the synchronous rectifiers SR1 and SR2 is set to the current discontinuous mode: SR1 and SR2 are turned on when Q4 and Q3 are turned on, respectively.

7. The novel synchronous rectification control method of the phase-shifted full-bridge converter according to claim 5 is characterized in that: Determining whether the converter is soft-started includes: If the output voltage sampling value V o_samp Less than the output voltage reference value V ref , then the phase shift angle φ decreases by 1°; If the output voltage sampling value V o_samp Greater than or equal to the output voltage reference value V ref , the soft start ends.

8. The novel synchronous rectification control method of the phase-shifted full-bridge converter according to claim 5 is characterized in that: The i-th judgment of the working mode of the converter includes: If the number of judgments i>=2, then i=0; If I o_samp >=I o,boundary , then the current continuous mode flag CCM_Flag[i]=1; If I o_samp >=I o,boundary , and CCM_Flag[0]=1, then CCM_Flag[i]=1.

9. A novel synchronous rectification control system for a phase-shifted full-bridge converter, characterized in that: include: a memory for storing instructions executable by a processor; A processor, used for executing instructions to implement a novel synchronous rectification control method for a phase-shifted full-bridge converter as described in any one of claims 1 to 8.

10. A computer readable medium storing computer program code, characterized in that: When the computer program code is executed by a processor, the computer program code implements a novel synchronous rectification control method for a phase-shifted full-bridge converter as claimed in any one of claims 1 to 8.

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