CN117353586A - Digital synchronous rectification control method of CLLC converter - Google Patents
Digital synchronous rectification control method of CLLC converter Download PDFInfo
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- CN117353586A CN117353586A CN202311326075.4A CN202311326075A CN117353586A CN 117353586 A CN117353586 A CN 117353586A CN 202311326075 A CN202311326075 A CN 202311326075A CN 117353586 A CN117353586 A CN 117353586A
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Classifications
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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
- H02M3/33569—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 having several active switching elements
- H02M3/33576—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 having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
- H02M3/33592—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 having several active switching elements having at least one active switching element at the secondary side of an isolation transformer having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/0048—Circuits or arrangements for reducing losses
- H02M1/0054—Transistor switching losses
- H02M1/0058—Transistor switching losses by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero
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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
- H02M3/01—Resonant DC/DC converters
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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
- H02M3/33515—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 digital control
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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
- H02M3/33569—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 having several active switching elements
- H02M3/33573—Full-bridge at primary side of an isolation transformer
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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
- H02M3/33569—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 having several active switching elements
- H02M3/33576—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 having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
- H02M3/33584—Bidirectional converters
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Dc-Dc Converters (AREA)
Abstract
The invention discloses a digital synchronous rectification control method of a CLLC converter. The method adopts a DSP chip to control the CLLC converter, and comprises the steps of sampling output voltage and output current in real time through an ADC module; calculating the voltage and current sampling signals; calculating the synchronous rectification enabling of the secondary side of the output power control; processing the secondary side resonant current sampling signal using a high speed comparator module; and outputting a secondary synchronous rectification control signal through an algorithm, and controlling the on-off of a secondary switching tube through a secondary driving circuit. The invention determines the working state through the switching frequency of the CLLC converter, carries out different delay treatments on the turn-on of the secondary side switching tube, ensures the ZVS turn-on of the secondary side switching tube, avoids the current backflow problem caused by the false turn-on, and improves the efficiency and the reliability of the system.
Description
Technical Field
The invention belongs to the technical field of power electronics, and particularly relates to a digital synchronous rectification control method of a CLLC converter.
Background
With the development of renewable energy sources, electric automobiles, power electronic transformers, energy storage systems and other fields, the bidirectional isolation type DC-DC converter is widely applied and is also a current research hot spot. High power density and high efficiency have been the focus of research on DC-DC converters, and particularly for resonant converters, how to improve the efficiency of the converter during operation and reduce the energy loss of the converter has been one of the efforts of research.
In order to reduce conduction loss of the secondary side network, synchronous rectification control is often adopted for the secondary side switching tube, so that when current flows through the corresponding switching tube, a driving signal is applied to the gate electrode of the secondary side switching tube to enable the secondary side switching tube to be conducted, a current flowing path of the current is changed into a channel from a body diode of the switching tube, and loss caused by the current flowing through the switching tube is reduced. The synchronous rectification control method commonly used at present comprises analog control and digital control. The analog control requires additional analog circuits, such as a comparator, to process signals, such as current, and the like, thereby increasing the cost of the circuit; the digital control does not need an extra analog circuit, and is more economical. The traditional synchronous rectification method does not carry out delay treatment when being switched on, so that a secondary side switching tube is hard to be switched on, and the switching loss is larger; the scholars also put forward to perform delayed turn-on processing in the under-resonance working state, but the influences of dead time and parasitic parameters are not considered in the resonance working state, so that the problem of current backflow caused by synchronous rectification and false turn-on exists in the CLLC converter.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a digital synchronous rectification control method of a CLLC converter, which enables the synchronous rectification ZVS of the CLLC converter to be turned on and avoids the problem of secondary side energy backflow. The invention adopts the DSP chip to control the CLLC converter, and comprises the steps of sampling output voltage and output current in real time through an ADC module; calculating the voltage and current sampling signals; calculating the synchronous rectification enabling of the secondary side of the output power control; processing the secondary side resonant current sampling signal using a high speed comparator module; and outputting a secondary synchronous rectification control signal through an algorithm, and controlling the on-off of a secondary switching tube through a secondary driving circuit. The invention determines the working state through the switching frequency of the CLLC converter, carries out different delay treatments on the turn-on of the secondary side switching tube, ensures the ZVS turn-on of the secondary side switching tube, avoids the current backflow problem caused by the false turn-on, and improves the efficiency and the reliability of the system.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a digital synchronous rectification control method of a CLLC converter is realized through the CLLC converter and a control circuit; the CLLC converter consists of a primary network, a secondary network and a resonant cavity; the control circuit comprises an output voltage sampling circuit, an output current sampling circuit, a secondary side resonance current sampling circuit, a DSP controller, a primary side driving circuit and a secondary side driving circuit, and the method comprises the following steps:
step 1: the ADC module of the DSP chip collects output signals of the output voltage sampling circuit and the output current sampling circuit in real time;
step 2: processing the signals acquired by the ADC module, calculating output power, and judging whether synchronous rectification enabling is started or not;
step 3: judging the working state of a circuit according to the switching frequency of the CLLC converter, wherein the working state of the circuit comprises a state A and a state B;
when CLLC converter switching frequency f s Less than or equal to the resonant frequency f r When the device is in the state A, the device is operated;
when CLLC converter switching frequency f s Greater than the resonant frequency f r When the device is in the state B;
step 4: according to the working state of the CLLC converter, selecting the synchronous rectification signal on delay time to obtain the on time of the synchronous rectification signal;
step 5: the high-speed comparator module of the DSP chip processes the output signal of the secondary side resonance current sampling circuit and compares the output signal with a threshold value to obtain the turn-off time of the synchronous rectification signal;
step 6: and according to the on time and the off time of the synchronous rectification signal, the DSP chip sends out a synchronous rectification control signal, and the on-off of the secondary side switching tube is controlled by the secondary side driving circuit.
Further, the output voltage sampling circuit and the output current sampling circuit convert the output voltage and the output current into weak current signals of 0-3.3V through a voltage sensor and a current sensor respectively.
Further, the ADC module of the DSP chip collects output signals of the output voltage sampling circuit and the output current sampling circuit, and converts the simulated weak current signals into digital signals for processing and calculation of the DSP chip.
Further, before the signal collected by the ADC module is calculated, the signal is filtered, the magnitude of the voltage and the current value is restored, and then the real-time output power is calculated by adopting a power calculation formula.
Further, in the step 2, determining whether to turn on synchronous rectification enabling includes:
when the output power is smaller than the power threshold value P th1 Synchronous rectification enable signal SR EN When the value is 0, synchronous rectification is not started, and a secondary side switching tube does not act;
when the output power is greater than the power threshold P th2 Synchronous rectification enable signal SR EN 1, representing the start of synchronous rectification, secondary side switching tube action, wherein the power threshold P th1 Less than the power threshold P th2 。
Further, in the step 4, selecting the synchronous rectification signal on delay time includes:
the opening delay is delayed based on the opening time of the corresponding primary side switching tube;
when the CLLC converter works in the state A, the turn-on delay time is fixed at t o ；
When the CLLC converter works in the state B, the turn-on delay time is at t according to the switching frequency o On the basis of stepped increment, when the switching frequency is maximum, the delay time reaches the maximum t n I.e. t n Is the maximum delay time, which, among other things,n represents the number of steps.
Further, in the step 5, the processing of the high-speed comparator module includes:
output signal V of secondary side resonance current sampling circuit by high-speed comparator in high-speed comparator module I_Sec Comparing, wherein the comparison comprises the turn-off time treatment of positive and negative half cycles; the high-speed comparator module comprises a high-speed comparator CMPSS_H and a high-speed comparator CMPSS_L;
the high-speed comparator CMPSS_H performs comparison and judgment in the positive half period, when V I_Sec ＜V th1 When the output of the high-speed comparator is 0, the high-speed comparator indicates a switching-off signal of a corresponding switching tube of the secondary network;
the high-speed comparator CMPSS_L performs comparison and judgment in the negative half period, when V I_Sec ＞V th2 When the output of the high-speed comparator is 0, the high-speed comparator indicates a switching-off signal of a corresponding switching tube of the secondary network;
wherein V is I_Sec Is the output signal of the secondary resonance current sampling circuit, V th1 And V th2 Is the two thresholds corresponding to when the secondary resonance current is close to 0.
Further, t o Is set according to the circuit characteristics, t n Is set according to dead time, circuit characteristics and worst working condition.
Compared with the prior art, the technical scheme of the invention has the beneficial effects that:
1. the invention adopts a digital synchronous rectification control method, and adopts a DSP high-speed comparator to process sampling signals by sampling secondary side resonance current in real time, so that no additional analog circuit is added, the applicability is strong, the control circuit is simplified, and the circuit cost is reduced.
2. According to the invention, aiming at the switching frequency of the CLLC converter, the working states of the CLLC converter are distinguished, synchronous rectification is carried out in the state A to fix the switching-on delay, the oscillation process of the drain-source voltage of the secondary side switching tube is avoided, so that the switching tube ZVS is switched on, and the switching loss is reduced; in the state B, the dead time and the influence of parasitic parameters of the circuit are considered, the switching-on delay time is set in a step mode according to the switching frequency, synchronous rectification time is widened as much as possible, and meanwhile, the secondary side current is ensured to be reversed when the synchronous rectification time is switched on, so that the problem of secondary side energy backflow caused by false switching-on is avoided.
Drawings
FIG. 1 is a control block diagram of a method of digitized synchronous rectification of a CLLC converter in accordance with the present invention;
FIG. 2 is a schematic diagram of the steps of a method for controlling digital synchronous rectification of a CLLC converter according to the present invention;
FIG. 3 is a diagram of a digitized synchronous rectification enabling control of a CLLC converter in accordance with the present invention;
FIG. 4 is a graph of the digitized synchronous rectification on delay of the CLLC converter of the present invention;
FIG. 5 is a timing diagram of the digitized synchronous rectification control drive of the CLLC converter of the present invention;
FIG. 6 is a graph of the digitized synchronous rectification test results of the CLLC converter in the invention; wherein, (a) is an experimental result diagram of the CLLC converter operating in the state A, and (B) is an experimental result diagram of the CLLC converter operating in the state B.
Detailed Description
In order to make the technical scheme of the invention more clear, the invention is further described below with reference to the accompanying drawings and the embodiments.
The embodiment provides a digital synchronous rectification control method of a CLLC converter, and the application topology and the control circuit of the method are shown in figure 1. The topology of the CLLC converter consists of a primary side network, a secondary side network and a resonant cavity, wherein the primary side network consists of a primary side switching tube S 1 -S 4 Composition; the secondary side network is formed by a secondary side switch tube S 5 -S 8 Composition; the resonant cavity is formed by primary side resonant inductance L r1 Primary side resonance capacitor C r1 Secondary side resonant inductance L r2 Secondary side resonance capacitor C r2 And a high frequency transformer. The control circuit comprises an output voltage sampling circuit, an output current sampling circuit, a secondary side resonance current sampling circuit, a DSP controller, a primary side driving circuit and a secondary side driving circuit.
Specifically, as shown in fig. 2, a digital synchronous rectification control method of a CLLC converter according to the present embodiment includes the following steps:
step 1: the ADC module of the DSP chip collects output signals of the output voltage sampling circuit and the output current sampling circuit in real time;
the output voltage sampling circuit and the output current sampling circuit respectively convert the output voltage and the output current into weak current signals of 0-3.3V through a voltage sensor and a current sensor, and the ADC module collects the signals and converts the analog weak current signals into digital signals for processing and calculation of the DSP chip.
Step 2: processing the signals acquired by the ADC module, calculating output power, and judging whether synchronous rectification enabling is started or not;
before the signal acquired by the ADC module is calculated, filtering processing is carried out on the signal, then the magnitude of the voltage and the current value is restored, and then the real-time output power is calculated by adopting a power calculation formula (1);
P o ＝U o I o (1)
wherein U is o Is the output voltage, I o Is the output current, P o Is the output power.
The synchronous rectification enabling determination performs hysteresis setting to prevent system oscillation, as shown in fig. 3, when the output power is smaller than the power threshold P th1 Synchronous rectification enable signal SR EN Is 0, which indicates that synchronous rectification is not started, and the secondary side switching tube S 5 -S 8 Does not act; when the output power is greater than the power threshold P th2 Synchronous rectification enable signal SR EN 1, the synchronous rectification is started, and the secondary side switching tube S 5 -S 8 Action, wherein the power threshold P th1 Less than the power threshold P th2 。
Step 3: judging the working state of a circuit according to the switching frequency of the CLLC converter, wherein the working state comprises a state A and a state B;
when CLLC converter switching frequency f s Less than or equal to the resonant frequency f r When the device is in the state A, the device is operated;
when CLLC converter switching frequency f s Greater than the resonant frequency f r When the device is in the state B;
wherein the resonant frequency f r Obtained according to a formula (2);
wherein L is r1 Is primary side resonance inductance, C r1 Is the primary side resonant capacitance.
Step 4: according to the working state of the CLLC converter, the turn-on delay time of the synchronous rectification signal is selected to obtain the turn-on time of the synchronous rectification signal, as shown in figure 4, wherein f 1 Is a first switching frequency threshold, f 2 Is a second switching frequency threshold, f max Is the maximum switching frequency;
when the CLLC converter works in the state A, the turn-on delay time is fixed at t o ；
When the CLLC converter works in the state B, the turn-on delay time is at t according to the switching frequency o On the basis of stepped increment, when the switching frequency is maximum, the delay time reaches the maximum t n I.e. t n Is the maximum delay time, where n represents the number of steps.
Wherein t is o Is set according to the circuit characteristics, t n Is set according to dead time, circuit characteristics and worst working condition.
In this embodiment, the resonant frequency is 120kHZ, the switching frequency range is 70-200kHZ, and when the CLLC converter works in state B, i.e., the switching frequency is 120-200kHZ, in order to ensure that the synchronous rectification time is as long as possible, a first-order delay is performed every 10kHZ, as shown in formula (3);
wherein t is the turn-on delay time, t 1 Is a first delay time, t 2 Is the second delay time, t n Is the maximum delay time.
Step 5: the high-speed comparator module of the DSP chip processes the output signal of the secondary side resonance current sampling circuit and compares the output signal with a threshold value to obtain the turn-off time of the synchronous rectification signal; the high-speed comparator module comprises a high-speed comparator CMPSS_H and a high-speed comparator CMPSS_L;
the high-speed comparator CMPSS_H performs comparison and judgment in the positive half period, when V I_Sec ＜V th1 When the output of the high-speed comparator is 0, the high-speed comparator indicates a switching-off signal of a corresponding switching tube of the secondary network;
the high-speed comparator CMPSS_L performs comparison and judgment in the negative half period, when V I_Sec ＞V th2 When the output of the high-speed comparator is 0, the high-speed comparator indicates a switching-off signal of a corresponding switching tube of the secondary network;
wherein V is I_Sec Is the output signal of the secondary resonance current sampling circuit, V th1 And V th2 Is the two thresholds corresponding to when the secondary resonance current is close to 0.
Step 6: according to the on-off time of synchronous rectification signal, DSP chip sends out synchronous rectification control signal, and utilizes secondary side driving circuit to control secondary side switching tube S 5 -S 8 Is provided.
As shown in FIG. 5, a synchronous rectification control driving timing chart is shown, the secondary side switching tube S 5 And S is 7 The driving signals are the same, S 6 And S is 8 The driving signals are the same, and delay is provided when the driving signals are turned on relative to the primary side switching tube.
Fig. 6 is a graph of experimental results of the present embodiment, in which (a) of fig. 6 is a graph of experimental results of the CLLC converter operating in state a, and (B) of fig. 6 is a graph of experimental results operating in state B. As can be seen from fig. 6, the secondary side switching tube is turned on with a delay relative to the primary side and turned off with a certain advance. The off-advance is due to threshold V th1 And V th2 The values of the resonance current are respectively corresponding to a value slightly larger than 0 and a value slightly smaller than 0 so as to avoid the problem of current zero crossing sampling inaccuracy caused by interference. The invention can effectively realize ZVS opening of the synchronous rectification switch tube and prevent the secondary side energy from flowing backwards.
Claims (8)
1. A digital synchronous rectification control method of a CLLC converter is realized through the CLLC converter and a control circuit; the CLLC converter consists of a primary network, a secondary network and a resonant cavity; the control circuit comprises an output voltage sampling circuit, an output current sampling circuit, a secondary resonance current sampling circuit, a DSP controller, a primary side driving circuit and a secondary side driving circuit, and is characterized by comprising the following steps:
step 1: the ADC module of the DSP chip collects output signals of the output voltage sampling circuit and the output current sampling circuit in real time;
step 2: processing the signals acquired by the ADC module, calculating output power, and judging whether synchronous rectification enabling is started or not;
step 3: judging the working state of a circuit according to the switching frequency of the CLLC converter, wherein the working state of the circuit comprises a state A and a state B;
when CLLC converter switching frequency f s Less than or equal to the resonant frequency f r When the device is in the state A, the device is operated;
when CLLC converter switching frequency f s Greater than the resonant frequency f r When the device is in the state B;
step 4: according to the working state of the CLLC converter, selecting the synchronous rectification signal on delay time to obtain the on time of the synchronous rectification signal;
step 5: the high-speed comparator module of the DSP chip processes the output signal of the secondary side resonance current sampling circuit and compares the output signal with a threshold value to obtain the turn-off time of the synchronous rectification signal;
step 6: and according to the on time and the off time of the synchronous rectification signal, the DSP chip sends out a synchronous rectification control signal, and the on-off of the secondary side switching tube is controlled by the secondary side driving circuit.
2. The method for digitally controlling synchronous rectification of a CLLC converter of claim 1, wherein said output voltage sampling circuit and said output current sampling circuit are respectively configured to convert an output voltage and an output current into weak current signals of 0-3.3V via a voltage sensor and a current sensor.
3. The method for controlling digital synchronous rectification of CLLC converter as claimed in claim 1, wherein said ADC module of said DSP chip collects output signals of output voltage sampling circuit and output current sampling circuit, and converts analog weak current signal into digital signal for processing calculation of DSP chip.
4. The method for controlling digital synchronous rectification of CLLC converter as claimed in claim 1, wherein before calculating the signal collected by ADC module, filtering the signal, then reducing the magnitude of voltage and current values, and then calculating the real-time output power by using a power calculation formula.
5. The method according to claim 1, wherein in the step 2, determining whether to turn on synchronous rectification enabling comprises:
when the output power is smaller than the power threshold value P th1 Synchronous rectification enable signal SR EN When the value is 0, synchronous rectification is not started, and a secondary side switching tube does not act;
when the output power is greater than the power threshold P th2 Synchronous rectification enable signal SR EN 1, representing the start of synchronous rectification, secondary side switching tube action, wherein the power threshold P th1 Less than the power threshold P th2 。
6. The method according to claim 1, wherein in the step 4, selecting the synchronous rectification signal on delay time includes:
the opening delay is delayed based on the opening time of the corresponding primary side switching tube;
when the CLLC converter works in the state A, the turn-on delay time is fixed at t o ；
When the CLLC converter works in the state B, the turn-on delay time is at t according to the switching frequency o On the basis of stepped increment, when the switching frequency is maximum, the delay time reaches the maximum t n I.e. t n Is the maximum delay time, where n represents the number of steps.
7. The method of claim 1, wherein in step 5, the processing of the high-speed comparator module comprises:
output signal V of secondary side resonance current sampling circuit by high-speed comparator in high-speed comparator module I_Sec Comparing, wherein the comparison comprises the turn-off time treatment of positive and negative half cycles; the high-speed comparator module comprises a high-speed comparator CMPSS_H and a high-speed comparator CMPSS_L;
the high-speed comparator CMPSS_H performs comparison and judgment in the positive half period, when V I_Sec ＜V th1 When the output of the high-speed comparator is 0, the high-speed comparator indicates a switching-off signal of a corresponding switching tube of the secondary network;
the high-speed comparator CMPSS_L performs comparison and judgment in the negative half period, when V I_Sec ＞V th2 When the output of the high-speed comparator is 0, the high-speed comparator indicates a switching-off signal of a corresponding switching tube of the secondary network;
wherein V is I_Sec Is the output signal of the secondary resonance current sampling circuit, V th1 And V th2 Is the two thresholds corresponding to when the secondary resonance current is close to 0.
8. The method of claim 6, wherein t is o Is set according to the circuit characteristics, t n Is set according to dead time, circuit characteristics and worst working condition.
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| CN117767766B (en) * | 2024-02-01 | 2024-07-09 | 深圳市优优绿能股份有限公司 | Synchronous rectification control system and power supply system of bridge rectification power circuit |
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