CN112865538A

CN112865538A - High-voltage-reduction-ratio dual-resonance three-level LLC resonant converter and control method thereof

Info

Publication number: CN112865538A
Application number: CN202110058301.XA
Authority: CN
Inventors: 马红波; 卢松; 徐帅东; 易俊宏
Original assignee: Southwest Jiaotong University
Current assignee: Southwest Jiaotong University
Priority date: 2021-01-15
Filing date: 2021-01-15
Publication date: 2021-05-28

Abstract

The invention discloses a high step-down ratio double resonance three-level LLC resonant converter and a control method thereof. The converter includes a flying capacitor C _FLY , a three-level bridge arm, a flying capacitor C _MID , a first resonance network, a first isolation transformer, a second resonance network, a second isolation transformer and a rectifier circuit. Among them, the three-level bridge arm is connected to the positive and negative ends of the input by connecting the first switch tube, the second switch tube, the third switch tube, and the fourth switch tube in series in sequence, and the flying capacitor C _FLY is connected across the first switch. The source of the tube and the source of the third switch tube, and the flying capacitor C _MID is connected across the source of the second switch tube and the source of the fourth switch tube. The invention has higher step-down capability, which is reflected in the fact that the peak-to-peak value of the input voltage of the resonant cavity from the inverter of the three-level bridge arm is half of the input voltage V _IN , and it is also beneficial to reduce the number of turns of the transformer, thereby reducing the loss of a single transformer. Especially when the primary current of the transformer is large and the number of turns is large, the overall efficiency and power density of the converter can be greatly improved.

Description

High-voltage-reduction-ratio dual-resonance three-level LLC resonant converter and control method thereof

Technical Field

The invention relates to the technical field of double-resonance converters, in particular to a high-voltage-reduction-ratio double-resonance three-level LLC resonance converter and a control method thereof.

Background

LLC resonant converters have received extensive attention in academia and industry due to advantages such as simple topology and superior soft switching characteristics. The double-resonance LLC converter is provided with two resonant cavities and an isolation transformer, so that the double-resonance LLC converter is high in efficiency, good in heat dissipation characteristic, easy to realize double-path output and the like, and is widely applied.

A widely used half-bridge dual-resonant LLC resonant converter in industry and industry is shown in fig. 1a, 1 b. The structure shown in fig. 1a is a structure in a two-path output scene, and the structure shown in fig. 1b is a structure in a one-path output scene. Each of the half-bridge dual-resonant LLC resonant converters shown in fig. 1a and 1b is composed of a switching inverter bridge arm circuit, a resonant circuit, a transformer, a rectifier circuit, and the like, where the switching inverter bridge arm circuit is composed of two switching tubes Q₁、Q₂The series connection is used for inverting the direct current voltage into a square wave; the resonant circuit helps to realize the soft switching characteristic of the switching tube; the transformer and the rectifying circuit are used for transmitting energy to a load end. The control strategy of the half-bridge double-resonant LLC resonant converter shown in FIG. 1a and FIG. 1b is shown in FIG. 2, and the switching tube Q in the topology₁Driven by a 50% duty cycle control signal, and switching transistor Q₂Driven by another complementary 50% duty ratio control signal, so that the peak-to-peak value of the input voltage of the two resonant cavities inverted by the bridge arms is equal to the input voltage V_IN. In practical application, dead time is required between the driving signals of the two tubes for preventing the tubes from being connected in a straight-through manner and realizing zero-voltage conduction of the switching tubes.

With the development of modern industrial systems, the disadvantages of the two half-bridge LLC dual-resonant converter topologies shown in fig. 1a and 1b are gradually revealed. Under high-voltage input occasion or high-voltage reduction ratio scene, the problem of insufficient voltage reduction capability exists in the existing double-resonance half-bridge LLC converter, the number of turns of the primary side of the transformer is increased, extra loss and volume of the two transformers are increased, and the efficiency and the power density of the converter are not improved favorably.

Disclosure of Invention

The invention aims to provide a high step-down ratio dual-resonance three-level LLC resonant converter and a control method thereof.

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

a high voltage reduction ratio double-resonance three-level LLC resonance converter comprises a three-level bridge arm; the three-level bridge arm comprises a first switch tube, a second switch tube, a third switch tube and a fourth switch tube which are sequentially connected in series, and further comprises a first flying capacitor bridged between the source electrode of the first switch tube and the source electrode of the third switch tube and a second flying capacitor bridged between the source electrode of the second switch tube and the source electrode of the fourth switch tube, wherein the drain electrode of the first switch tube is connected to the positive electrode of a power supply, and the source electrode of the fourth switch tube is connected to the negative electrode of the power supply; the first resonant network, the first isolation transformer and the first rectifying circuit are sequentially connected; the positive input end of the first resonant network is connected to the drain electrode of the first switch tube, and the negative input end of the first resonant network is connected to the source electrode of the first switch tube; the second resonant network, the second isolation transformer and the second rectifying circuit are sequentially connected; and the positive input end of the second resonant network is connected to the source electrode of the third switching tube, and the negative input end of the second resonant network is connected to the source electrode of the fourth switching tube.

The further technical scheme is as follows: the output end of the first rectifying circuit is used for being connected with a first load, and the output end of the second rectifying circuit is used for being connected with a second load. Or the number of turns of the first isolation transformer is equal to that of the second isolation transformer, and the output end of the first rectifying circuit is connected with the output end of the second rectifying circuit in parallel and then used for connecting a load.

According to the control method of the high step-down ratio double-resonance three-level LLC resonant converter, a first group of driving signals with 50% duty ratio are simultaneously applied to a first switching tube and a third switching tube, and a second group of driving signals with 50% duty ratio are simultaneously applied to a second switching tube and a fourth switching tube; the first set of drive signals and the second set of drive signals are complementary; a dead time is provided between the first set of drive signals and the second set of drive signals.

Compared with the prior art, the invention has the advantages that,

1. the converter has higher voltage reduction capability, and is embodied in that the peak-to-peak value of the resonant cavity input voltage inverted by the three-level bridge arm is the input voltage V_INAnd half of the high buck ratio characteristics make the converter more suitable for high voltage input or high buck ratio applications.

2. The high step-down ratio characteristic of the converter is beneficial to reducing the turns of the transformer, thereby reducing the loss of a single transformer, and particularly greatly improving the overall efficiency and power density of the converter under the condition that the primary current of the transformer is large and the number of turns is large.

3. The four switching tubes on the primary side of the converter are driven by two pairs of control signals with 50% duty ratio, and the control strategy is simple and easy to implement.

Drawings

Fig. 1a is a diagram of a conventional half-bridge dual-resonant LLC resonant converter in a two-way output scenario.

Fig. 1b shows a conventional half-bridge dual-resonant LLC resonant converter in a single-output scenario.

Fig. 2 is a schematic diagram of a control strategy of a conventional half-bridge dual-resonant LLC resonant converter.

Fig. 3a is a double-resonance half-bridge three-level LLC topology under a two-way output scenario of the present invention.

Fig. 3b is a double-resonant half-bridge three-level LLC topology under the single-output scenario of the present invention.

Fig. 4 is a waveform diagram of steady-state operation of the dual-resonant half-bridge three-level LLC at single-path output of the present invention.

FIG. 5a is the equivalent circuit diagram of the single output operating mode I of the present invention.

Fig. 5b is an equivalent circuit diagram of the present invention in the operating state II when outputting one-way.

Fig. 5c is an equivalent circuit diagram of the working state III when the single output is performed according to the present invention.

Fig. 5d is an equivalent circuit diagram of the present invention in a single output operating state IV.

Fig. 6a and 6b are operation waveform diagrams of actual measurement key signals of a single-path output prototype.

The labels in the figure are: v_INThe power supply voltage is input. Q₁、Q₂、Q₃、Q₄And a switch tube. C_Q1、C_Q2、C_Q3、C_Q4And the parasitic capacitance of the switching tube. D_Q1、D_Q2、D_Q3、D_Q4A switching body diode. C_FLY、C_MIDA flying capacitor. L is_r1A resonant inductance in the first resonant network. L is_m1And exciting an inductor in the first resonant network. C_r1A resonant capacitor in the first resonant network. TR1, first isolation transformer. L is_r2And a resonant inductance in the second resonant network. L is_m2And exciting an inductance in the second resonant network. C_r2A resonant capacitor in the first resonant network. TR2, second isolation transformer. D₁、D₂、D₃、D₄And a secondary side rectifying diode. C₀And outputting a filter capacitor. R_LAnd a single output load. R_L1And the first path of load is output by two paths. R_L2And the second load is loaded when the two paths output. V₀And outputting the voltage in a single way. V₀₁And the first path outputs voltage when the two paths output. V₀₂And the second path outputs voltage when the two paths output. V_ABAnd the voltage between the point A and the point B is the input voltage of the first resonant network. V_CDAnd the voltage between the point C and the point D is the input voltage of the second resonant network. V_CFLYFlying capacitor C_FLYA steady state operating voltage. V_CMIDFlying capacitor C_MIDA steady state operating voltage. V_{gs_Q1}、V_{gs_Q2}、V_{gs_Q3}、V_{gs_Q4}And four switching tube driving waveforms. V_{ds_Q1}、V_{ds_Q2}、V_{ds_Q3}、V_{ds_Q4}And the voltage waveform between the drain electrode and the source electrode when the four switching tubes work. i.e. i_Lr1The resonant current waveform in the first resonant network. i.e. i_Lr2The resonant current waveform in the second resonant network. i.e. i_D1、i_D2、i_D3、i_D4And a secondary side rectifying diode current waveform. n, the number of turns of the isolation transformers TR1 and TR2 when the single output is obtained. n is₁Isolation in two-way outputTransformer TR1 turns. n is₂And the number of turns of the isolation transformer TR2 is two-way output.

Detailed Description

The invention provides a novel double-resonance half-bridge three-level LLC resonance converter with a high step-down ratio and a control method thereof. The main advantages of this topology are: compared with a traditional half-bridge three-double resonance LLC converter, the input voltage of the two resonant cavities is reduced by half, namely the square wave inverter bridge arm has higher voltage reduction capability, which means that the number of turns of the primary sides of the two transformers can be reduced by half, and the transformer loss and the size of the converter are reduced.

The high step-down ratio double-resonance three-level LLC resonance converter is characterized by comprising a flying capacitor C_FLYThree-level bridge arm and flying capacitor C_MIDThe resonant circuit comprises a first resonant network (first resonant cavity), a first isolation transformer, a second resonant network (second resonant cavity), a second isolation transformer and a rectifying and filtering circuit.

The three-level bridge arm is composed of a first switching tube, a second switching tube, a third switching tube and a fourth switching tube which are sequentially connected in series and then connected to the positive end and the negative end of an input, wherein the four switching tubes respectively comprise parasitic body diodes and parasitic capacitors of the four switching tubes. Flying capacitor C_FLYA flying capacitor C connected between the source electrode of the first switching tube and the source electrode of the third switching tube_MIDAnd the source electrode of the second switching tube is connected with the source electrode of the fourth switching tube in a bridging mode.

For a single-path output scene and a two-path scene, the dual-resonance three-level LLC resonant converter of the present invention has two application structure forms, as shown in fig. 3a and fig. 3b, respectively. It is noted that, in the scenario of dual output application, the number of turns n of the isolation transformers TR1 and TR2₁、n₂The voltages of the two paths of outputs can be equal or unequal, depending on whether the voltages of the two paths of outputs are required to be equal, but when the actual closed loop carries out output control, only one path of outputs is selected as the main control, and the other path of outputs works in an open loop state; in the single-output application scenario, the numbers of turns of the isolation transformers TR1 and TR2 must be equal, and are both n.

The converter regulates output power by changing the frequency of the control signal of the switching tubeAnd (6) pressing. Moreover, the converter proposed by the present invention can adopt the same control strategy as the existing half-bridge dual-resonant LLC converter, namely: for the first switch tube Q₁And a third switching tube Q₃Applying a set of driving signals with 50% duty ratio to the second switching tube Q₂And a fourth switching tube Q₄Another set of complementary 50% duty cycle drive signals is applied, but with a dead band between the two sets of drive signals. The closed-loop control of the topology provided by the invention is simple to operate and easy to realize.

Fig. 3a and 3b are schematic diagrams of the basic structure of the present invention. Fig. 3a shows a structure in a double-resonance half-bridge three-level LLC topology two-way output application scenario, and fig. 3b shows a structure in a double-resonance half-bridge three-level LLC topology one-way output application scenario. The specific circuit is composed of a flying capacitor C_FLYThree-level bridge arm and flying capacitor C_MIDThe first resonant network, the first isolation transformer, the second resonant network, the second isolation transformer and the rectifying and filtering circuit. The secondary side of the two isolation transformers can adopt a full-wave rectification mode or a full-bridge rectification mode, wherein the full-wave rectification mode is taken as an example, D₁、D₂、D₃、D₄Are four rectifying diodes. The two resonant networks are used for realizing zero-voltage switching of the switching tube and zero-current switching of the rectifier diode.

The specific control mode of the converter provided by the invention is as follows: for the first switch tube Q₁And a third switching tube Q₃Applying a set of driving signals with 50% duty ratio to the second switching tube Q₂And a fourth switching tube Q₄Another set of complementary 50% duty cycle drive signals is applied with a dead band between the two sets of drive signals. The converter for single-path and double-path output application can adjust output voltage by changing the switching frequency of a driving signal of a switching tube, wherein one path of output is selected to be used as a main control under the application of double-path output, and the other path of output works in an open-loop mode. Since the two topology principles shown in fig. 3a and fig. 3b are similar, the analysis is performed by taking the single-output application scenario shown in fig. 3b as an example. Before performing a detailed modal analysis, the following assumptions are made:

1. the output filter capacitor is large enough to make the output voltage as a constant value in one switching period;

2. the resonant parameters in the two resonant cavities being identical, i.e. resonant capacitance C_r1、C_r2Are all equal to C_rResonant inductance L_r1、L_r2Are all equal to L_rExcitation inductance L_m1、L_m2Are all equal to L_m；

3. Flying capacitor C_FLYAnd C_MIDThe resonance capacitance is large enough not to affect the resonance frequency of the resonance network.

So that f can be used_rRepresenting the resonant capacitance C_rAnd a resonant inductor L_rResonant frequency of both, by f_mRepresenting the resonant capacitance C_rResonant inductor L_rAnd an excitation inductance L_mResonant frequency of the three, and_r>f_m. Due to the magnitude relationship between the switching frequency fs and the resonant frequency fr, the operating mode of the converter is divided into three modes, namely, the under-resonant mode (fs)<fr), quasi-resonant mode (fs ═ fr), and over-resonant mode (fs)>fr). The operation principle of the converter in different modes is slightly different, but the LLC converter has the highest efficiency when operating in a quasi-resonant mode (fs ═ fr). Therefore, the present description only deals with the case of fs ═ fr to analyze the working principle, and the other two analysis methods are similar. In the quasi-resonant mode (fs ═ fr) mode, one switching period of the converter can be divided into 4 working modes, and in the steady-state operation, the waveforms of each key voltage and current are as shown in fig. 4.

The specific working principle is as follows:

(1) operating state I, as shown in fig. 5 a: t is t₀<t<t₁And (5) stage. At t₀Time, Q₁And Q₃Zero voltage conduction, input voltage V of the first resonant cavity and the second resonant cavity_ABAnd V_CD0 and 0.5V respectively_IN. In the first resonant network, L_r1And C_r1Series resonance, reverse resonance of resonant current, secondary side rectifier diode D₁On, the primary side voltage of the first isolation transformer is clamped to-nV₀With excitation current starting from a maximum value at-nV₀/L_mIs linearly decreased and stored in the resonant capacitor C_r1The energy in (b) is transferred to the load through the first isolation transformer as a difference between the resonant current and the excitation current. In the second resonant network, L_r2And C_r2Series resonance, forward resonance of resonant current, secondary side rectifier diode D₄On, the primary side voltage of the second isolation transformer is clamped to nV₀With excitation current starting from a minimum value at nV₀/L_mThe slope of the resonant current and the excitation current are linearly increased, and the difference between the resonant current and the excitation current transfers energy to the load through the second isolation transformer. In this stage, the source of the resonant current in the second resonant network is divided into two parts, half of the resonant current is from the input and flows through the flying capacitor C_FLYAnd to flying capacitor C_FLYCharging, the other half of resonant current is driven by flying capacitor C_MIDProviding, i.e. flying capacitors C_MIDAnd (4) discharging.

(2) Operating state II, as shown in fig. 5 b: t is t₁<t<t₂And (5) stage. At t₁Time, Q₁And Q₃Simultaneously turn off and flow through the secondary side rectifier diode D₁、D₄The current just resonates to 0, the primary side resonant current in the first resonant network and the secondary side resonant current in the second resonant network are respectively equal to the minimum value and the maximum value of the excitation current, the input voltage of the first resonant network is reversed from 0, and the input voltage of the second resonant network is reversed from 0.5V_INThe commutation is started. In the first resonant network, L_r1、L_m1、C_r1The three elements resonate together and, because of the long resonant period of the three elements, the resonant current in the first resonant cavity, which may remain approximately within the dead time, is approximately constant, equal to its excitation current. Similarly, in the second resonant network, L_r2、L_m2、C_r2The three elements resonate together in this phase, the resonant current being approximately equal to the excitation current. In this stage, the exciting currents of the two resonant networks are commonly supplied to the switching tube Q₁、Q₃Output capacitor C_Q1、C_Q3Charging while supplying Q to the switch tube₂、Q₄Output capacitor C_Q2、C_Q4Discharge of Q₂、Q₄The zero voltage conduction creates conditions.

(3) Operating state III, as shown in fig. 5 c: t is t₂<t<t₃And (5) stage. At t₂Time of day, V_{ds_Q1}And V_{ds_Q3}Has been charged to 0.5V_IN，V_{ds_Q2}And V_{ds_Q4}Is discharged to 0, at which time Q₂And Q₄Zero voltage conduction, the first resonant network input voltage has been commutated to 0.5V_IN，L_r1And C_r1Starting series resonance, the input voltage of the second resonance network has been commutated to 0, L_r2And C_r2The series resonance is started. Similar to the operating state I, since the secondary side rectifier diode D is in this stage₂And D₃Is turned on, so that the primary side voltage of the first isolation transformer is clamped to nV₀With excitation current starting from a minimum value at nV₀/L_mThe slope of the second isolation transformer is linearly increased, and the primary side voltage of the second isolation transformer is clamped to-nV₀With excitation current starting from a maximum value at-nV₀/L_mThe slope of (a) decreases linearly and the resonant current in the two resonant networks is always greater than the excitation current, the difference between the two transferring energy to the load through the two transformers.

(4) Operating state IV, as shown in fig. 5 d: t is t₃<t<t₄And (5) stage. At t₃Time, Q₂And Q₄Is turned off simultaneously and flows through a secondary side rectifier diode D similar to the working state II₂、D₃The current just resonates to 0, the primary side resonant current in the first resonant network and the secondary side resonant current in the second resonant network are respectively equal to the maximum value and the minimum value of the exciting current, and the input voltage of the first resonant network is controlled to be 0.5V_INThe commutation is started and the input voltage of the second resonant network commutates from 0. Similarly, in both resonant networks, the resonant inductor, the excitation inductor and the resonant capacitor resonate together, so that both resonant currents can be considered to be approximately constant and equal to the excitation currents. In this stage, the exciting currents of the two resonant networks are commonly supplied to the switching tube Q₂、Q₄Output capacitor C_Q2、C_Q4Charging while supplying Q to the switch tube₁、Q₃Output capacitor C_Q1、C_Q3Discharge of electricityIs Q₁、Q₃The zero voltage conduction creates conditions.

In order to verify the correctness of the theoretical analysis of the circuit, a 48V input and 6V output double-resonance half-bridge three-level LLC two-way output prototype is set up in a laboratory, and the maximum output current is 40A. When the output current of the prototype is 40A, the steady-state operating voltage waveform of the prototype is shown in fig. 6a and 6b, wherein each channel in fig. 6a sequentially comprises: fourth switch tube Q₄Driving voltage, fourth switching tube Q₄The resonant current in the first resonant network and the resonant current in the second resonant network. The first and second channel waveforms in FIG. 6b are changed to the first flying capacitor C_FLYAnd a second flying capacitor C_MIDThe other two channels still have two resonant current waveforms. According to experimental results and actually measured waveforms, after circuit parameters are reasonably designed, zero voltage conduction can be realized by four main switches in the topology, and the steady-state voltage and the resonant cavity input voltage of the two flying capacitors are half of the input voltage, so that the correctness of theoretical analysis is proved.

In conclusion, the two-way output and one-way output application topologies of the novel double-resonance half-bridge three-level LLC resonant converter with the high voltage reduction ratio provided by the invention keep the zero-voltage conduction and zero-current turn-off characteristics of the LLC resonant converter, but have the high voltage reduction ratio characteristic, so that the novel double-resonance half-bridge three-level LLC resonant converter with the high voltage reduction ratio is more suitable for high-voltage input or high voltage reduction ratio application occasions. The high voltage reduction ratio characteristic relieves the requirement on the number of turns of the transformer, can reduce the number of turns of the transformer, effectively reduces the loss of a single transformer, and can greatly improve the integral efficiency and power density of the converter particularly under the condition that the primary side current of the transformer is large and the number of turns is large. In addition, the four switching tubes on the primary side are driven by two pairs of control signals with 50% duty ratio, and the four switching tubes on the primary side have the characteristics of simple control strategy and easiness in implementation.

Claims

1. a high step-down ratio dual-resonance three-level LLC resonant converter, is characterized in that, comprises three-level bridge arm; Described three-level bridge arm comprises the first switch tube, the second switch tube that are connected in series successively, The third switch tube and the fourth switch tube also include a first flying capacitor connected across the source electrode of the first switch tube and the source electrode of the third switch tube, and a first flying capacitor connected across the source electrode of the second switch tube and the source electrode of the fourth switch tube The second flying capacitor of the pole, the drain of the first switch tube is connected to the positive pole of the power supply, and the source of the fourth switch tube is connected to the negative pole of the power supply; it also includes a first resonant network, a first isolation transformer and a first rectifier circuit connected in sequence; The positive input end of the first resonant network is connected to the drain of the first switch tube, and the negative input end is connected to the source electrode of the first switch tube; it also includes a second resonant network, a second isolation transformer and a second rectifier circuit connected in sequence; The positive input terminal of the two resonant networks is connected to the source of the third switch, and the negative input is connected to the source of the fourth switch.

2. a kind of high step-down ratio double resonance three-level LLC resonant converter as claimed in claim 1 is characterized in that, the output end of the first rectifier circuit is used to connect the first load, and the output end of the second rectifier circuit is used for connecting the first load. Used to connect a second load.

3. a kind of high step-down ratio double resonance three-level LLC resonant converter as claimed in claim 1 is characterized in that, the first isolation transformer and the second isolation transformer have equal turns, and the output end of the first rectifier circuit is equal to the number of turns of the second isolation transformer. The output ends of the second rectifier circuit are connected in parallel and used for connecting the load.

4. The control method of a high step-down ratio dual-resonance three-level LLC resonant converter according to claim 1, 2 or 3, wherein the first switch tube and the third switch tube are simultaneously applied with the first A group of driving signals of 50% duty cycle is applied to the second switch tube and the fourth switch tube simultaneously with a second group of driving signals of 50% duty cycle; the first group of driving signals and the second group of driving signals are complementary; the first group Dead time is set between the driving signal and the second group of driving signals.