A wide gain resonant converter based on the rectifier side and its hybrid modulation method

Abstract

The present invention belongs to the technical field of resonant converters, and specifically relates to a wide-gain resonant converter based on a rectifier side and a hybrid modulation method thereof, comprising an inverter side circuit, a rectifier side circuit, and a resonant tank circuit for connecting the inverter side circuit and the rectifier side circuit; wherein the rectifier side circuit comprises a rectifier circuit and a bidirectional switch, the bidirectional switch adopts two switch tubes connected in reverse series, the rectifier circuit is a full-bridge rectifier circuit composed of a first filter capacitor, a second filter capacitor, a third filter capacitor, a fourth filter capacitor, a first diode, a second diode, a third diode and a fourth diode; the rectifier topology of the rectifier circuit is adjusted by adjusting the on and off states of the bidirectional switch, and the rectifier topology of the rectifier circuit comprises a voltage doubling rectifier circuit and a quadruple voltage rectifier circuit.

Description

Technical Field

[0001] The present invention belongs to the technical field of resonant converters, and in particular relates to a wide-gain resonant converter based on a rectifier side and a hybrid modulation method thereof. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] New energy represented by wind power and solar energy is gradually replacing traditional energy represented by coal and oil; photovoltaic power generation system is one of the main forms of new energy utilization. The photovoltaic array in the photovoltaic power generation system can be connected to the DC distribution network through a DC converter. The DC converter can transform the voltage level to meet the power requirements of different loads. Since the photovoltaic array is affected by light and temperature, the output voltage range is large, so the required DC / DC converter should have a wide gain characteristic. The resonant converter LLC has the characteristics of high efficiency, high power density, low electromagnetic interference and soft switching, and can be widely used in photovoltaic power generation systems. However, the resonant converter under variable frequency modulation is difficult to adapt to the characteristics of large output voltage fluctuation of the photovoltaic array. In order to achieve wide voltage input and maintain stable output voltage, efficiency is often sacrificed. In order to meet the needs of resonant converters for wide voltage gain at high efficiency, new topologies continue to emerge.

[0004] According to the inventors, improvements to the wide gain resonant converter related structures can be divided into three categories: primary side topology improvement, secondary side topology improvement and resonant tank improvement:

[0005] (1) Primary side topology improvement, the core of which is to transform the primary side full-bridge or half-bridge circuit. By recombining the chopper unit, the amplitude of the chopper unit output waveform is adjusted according to the gain requirements and the network composition is changed. A related study proposed a dual-bridge resonant converter design, in which a bidirectional switch located at the midpoint of the input capacitor is added before the primary side switch network. The frequency is kept unchanged during operation. By adjusting the duty cycle of the front bridge arm and the bidirectional switch combined with frequency modulation, the amplitude component of the chopper output unit can be adjusted to adjust the gain. A related study proposed a cascade converter design combining Buck-Boost and resonant converter, cascading the traditional Buck-Boost circuit with the resonant converter, and adjusting the duty cycle of the Buck-Boost switch tube to adjust the half-bridge LLC equivalent input DC voltage to widen the voltage gain.

[0006] (2) Secondary side topology transformation, that is, by introducing active devices in the secondary side rectification link, the part that originally did not have the voltage regulation function is transformed into a power electronic conversion module with gain adjustment capability. By improving the structure of the resonant converter, a new LLC resonant converter based on four-fold voltage rectification and two-phase secondary side interleaving is proposed. By adding additional switching elements to the secondary side and using PWM modulation technology, the voltage gain is effectively increased by 2 times, while reducing the switching frequency variation. A related study has designed a voltage doubler rectifier unit. When the secondary switch is in the off state, the rectifier unit works in the same way as the traditional full-bridge rectifier circuit; when the secondary switch is closed, one end of the transformer is directly connected to the series midpoint of the output capacitor, turning the topology into a full-wave voltage doubler rectifier circuit; through simple operations, two different rectification modes are realized to meet different circuit gain requirements. A rectifier unit SA-VAR with voltage doubling rectification and voltage quadruple rectification can be designed. When both switches on the secondary side are turned off, the SA-VAR is transformed into a two-times-voltage rectification topology. When the load capacitance is alternately charged and discharged by modulating the two switches, it can operate in a four-times-voltage rectification mode, thereby further expanding its application range and performance.

[0007] (3) Improvement of the resonant tank, that is, changing the resonant parameters. An auxiliary LC resonant circuit that can change the equivalent excitation inductance according to the switching frequency is added to the third winding of the transformer. When the switching frequency decreases, the equivalent excitation inductance also decreases, thereby obtaining a steeper gain curve. The resonant tank is constructed into an LCLC structure, and an additional capacitor is connected in series with the excitation inductance to adjust the resonant characteristics of the resonant tank itself, so that when the converter operates at a lower operating frequency, the equivalent inductance of the excitation inductance decreases accordingly, changing the gain curve of the converter; however, it is a difficult task to connect the auxiliary capacitor in series with the excitation inductance without affecting the original transformer excitation characteristics. Summary of the invention

[0008] To solve the above problems, the present invention proposes a wide gain resonant converter based on the rectifier side and a hybrid modulation method thereof. On the basis of the traditional resonant converter, the secondary side rectifier network is replaced with a new voltage doubler rectifier network; according to the size of the input voltage, different circuit topologies and corresponding modulation strategies are adopted respectively, and under the conditions of achieving zero voltage turn-on (ZVS) of the primary side switch and zero current turn-off (ZCS) of the secondary side diode, the input voltage range of the converter is widened and the operating range of the resonant converter frequency is reduced.

[0009] According to some embodiments, a first solution of the present invention provides a wide gain resonant converter based on the rectifier side, using the following technical solution:

[0010] A wide gain resonant converter based on the rectifier side, comprising an inverter side circuit, a rectifier side circuit, and a resonant tank circuit for connecting the inverter side circuit and the rectifier side circuit; wherein the rectifier side circuit comprises a rectifier circuit and a bidirectional switch, the bidirectional switch adopts two switch tubes connected in reverse series, the rectifier circuit is a full-bridge rectifier circuit composed of a first filter capacitor, a second filter capacitor, a third filter capacitor, a fourth filter capacitor, a first diode, a second diode, a third diode and a fourth diode; the rectifier topology of the rectifier circuit is adjusted by adjusting the on and off states of the bidirectional switch, and the rectifier topology of the rectifier circuit comprises a voltage doubling rectifier circuit and a voltage quadruple rectifier circuit.

[0011] As a further technical limitation, the inverter side circuit is a full-bridge circuit consisting of a first power switch tube, a second power switch tube, a third power switch tube and a fourth power switch tube; wherein the duty cycles of the first power switch tube, the second power switch tube, the third power switch tube and the fourth power switch tube are all consistent.

[0012] As a further technical limitation, the resonant tank circuit includes a high-frequency transformer and a resonant inductor, an excitation inductor and a resonant capacitor arranged on the primary side of the high-frequency transformer.

[0013] Furthermore, the wide gain resonant converter based on the rectification side also includes a secondary side load connected in parallel across the third filter capacitor and the fourth filter capacitor.

[0014] According to some embodiments, the second solution of the present invention provides a hybrid modulation method based on a wide gain resonant converter on the rectifier side, adopting the wide gain resonant converter based on the rectifier side provided by the first solution, and adopting the following technical solution:

[0015] A hybrid modulation method for a wide-gain resonant converter based on the rectifier side adopts a modulation method that mixes variable frequency modulation and phase shift modulation to achieve a wide gain of the resonant converter; the output voltage of the resonant converter is adjusted by adjusting the switching frequency and the phase shift angle;

[0016] When the switching frequency f s is the series-parallel resonant frequency f of the resonant tank circuit m When the switching frequency f s When the switching frequency of the resonant converter reaches the maximum, the rectifier circuit is in a four-fold voltage rectifier circuit; when the switching frequency of the resonant converter is f s Reduced to the series resonant frequency f of the resonant tank circuit r When the resonant converter switches from variable frequency modulation to phase shift modulation under the same working topology, the operating frequency under phase shift modulation is kept at f r ;

[0017] By changing the phase shift angle between the power switches in the inverter circuit, the output voltage of the secondary load is adjusted to reduce the gain of the resonant converter so that the switching frequency f s The minimum frequency value when the rectifier circuit is in the voltage doubler rectifier circuit is reached, that is, the series-parallel resonant frequency f of the resonant tank circuit. m , the bidirectional switch is disconnected, the rectification topology of the rectification circuit is switched from the quadruple voltage rectification circuit to the double voltage rectification circuit, the phase shift value is reset to zero, and the minimum frequency of the resonant converter working under the double voltage rectification circuit is obtained. When the switching frequency f s Reaching the series resonant frequency f r When , the resonant converter performs phase shift modulation.

[0018] As a further technical limitation, the series resonant frequency f of the resonant tank circuit is r The resonant inductor L r and resonant capacitor C r The common resonance of the two forms The series-parallel resonant frequency f of the resonant tank circuit m The resonant inductor L r , resonant capacitor C r and the magnetizing inductance L m The three are resonated together, that is,

[0019] As a further technical definition, according to the series-parallel resonant frequency f m , series resonant frequency f r and the switching frequency f s The size between, that is, f s >f r 、f m >f s >f r or r =f s , determine the working mode of the resonant converter; when f m >f s >f r When the resonant converter has a resonant inductance L r , resonant capacitor C r and the magnetizing inductance L m In the common resonant mode of the three, the secondary current of the high-frequency transformer flows intermittently through the diode in the rectifier circuit.

[0020] As a further technical limitation, when the resonant converter is in a high input voltage or light load condition, the gain needs to be reduced by increasing the switching frequency. However, when the operating frequency of the resonant converter is high, the gain curve is flat, and phase shift modulation is introduced to adjust the switching frequency of the resonant converter.

[0021] Furthermore, during the phase shift modulation process of the resonant converter, the first power switch tube and the second power switch tube are both delayed behind the third power switch tube and the fourth power switch tube. By blocking the input voltage of the resonant converter and adjusting the average voltage entering the resonant tank circuit within one cycle, the phase shift modulation of the resonant converter is realized.

[0022] As a further technical limitation, the modulation switching point of the variable frequency modulation and phase shift modulation of the resonant converter needs to meet the switching frequency f s With the series resonant frequency f r Consistent.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] Based on the traditional resonant converter, the present invention replaces the secondary side rectification network with a new voltage doubling rectification network; according to the size of the input voltage, different circuit topologies and corresponding modulation strategies are adopted respectively, so as to broaden the input voltage range of the converter and reduce the operating range of the resonant converter frequency under the conditions of achieving zero voltage turn-on of the primary side switch and zero current turn-off of the secondary side diode.

[0025] The present invention improves the circuit topology and designs its modulation method to maintain the stability of the output voltage when the input voltage changes over a wide range; the voltage gain variation law of the two structures under different modulation methods and the conditions for realizing soft switching are derived through the fundamental wave analysis method; in terms of modulation strategy, a hybrid modulation method based on the combination of variable frequency modulation and phase shift modulation is adopted to effectively widen the range of input voltage and gain while maintaining the stability of the output voltage; under the hybrid modulation, the primary side switch of the converter can achieve zero voltage turn-on and the secondary side diode can achieve zero current turn-off. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings in the specification that constitute a part of this embodiment are used to provide a further understanding of this embodiment. The schematic embodiments of this embodiment and their descriptions are used to explain this embodiment and do not constitute improper limitations on this embodiment.

[0027] Figure 1 Schematic diagram of the topological structure of a wide gain resonant converter based on the rectifier side in an embodiment of the present invention;

[0028] Figure 2 Schematic diagram of the working mode of the quadruple voltage rectifier circuit structure under variable frequency modulation in an embodiment of the present invention;

[0029] Figure 3 Schematic diagram of the working mode of the voltage doubler rectifier circuit structure under phase shift modulation in an embodiment of the present invention;

[0030] Figure 4Schematic diagram of a gain curve of a wide gain resonant converter based on the rectifier side in an embodiment of the present invention;

[0031] Figure 5 It is a waveform diagram of a wide gain resonant converter based on the rectifier side when the input voltage is 22V in an embodiment of the present invention;

[0032] Figure 6 It is a waveform diagram of a wide gain resonant converter based on the rectifier side when the input voltage is 227 in an embodiment of the present invention;

[0033] Figure 7 It is a waveform diagram of a wide gain resonant converter based on the rectifier side when the input voltage is 37V in an embodiment of the present invention;

[0034] Figure 8 It is a waveform diagram of a wide gain resonant converter based on the rectifier side when the input voltage is 52V in an embodiment of the present invention;

[0035] Fig. 9 It is a schematic diagram of the efficiency curve of the wide gain resonant converter based on the rectification side in an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0037] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0038] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0039] In the present invention, terms such as "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "side", "bottom", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are relational words determined only for the convenience of describing the structural relationships of the various parts or elements of the present invention, and do not specifically refer to any part or element in the present invention and should not be understood as limitations on the present invention.

[0040] In the present invention, terms such as "fixed connection", "connected", "connection", etc. should be understood in a broad sense, indicating that it can be fixedly connected, integrally connected or detachably connected; it can be directly connected or indirectly connected through an intermediate medium. For relevant scientific research or technical personnel in this field, the specific meanings of the above terms in the present invention can be determined according to specific circumstances, and they cannot be understood as limitations on the present invention.

[0041] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0042] Example

[0043] The embodiment of the present invention introduces a wide gain resonant converter based on the rectifier side. On the basis of the traditional resonant converter, the secondary side rectifier network is replaced with a new voltage doubler rectifier network. The converter adopts different circuit topologies and corresponding modulation strategies according to the size of the input voltage. Under the conditions of achieving zero voltage switching (ZVS) of the primary side switch and zero current switching (ZCS) of the secondary side diode, it can not only effectively widen the input voltage range of the converter, but also significantly reduce the operating range of the resonant converter frequency. When applied to photovoltaic power generation systems, it can improve the overall efficiency of the system and better adapt to the characteristics of large output voltage fluctuations of photovoltaic arrays.

[0044] The wide gain resonant converter based on the rectifier side proposed in this embodiment is as follows Figure 1 As shown, it includes an inverter side circuit, a rectifier side circuit, a resonant tank circuit and a secondary side load; the inverter side is composed of a power switch Q 1 ~Q 4 The full bridge circuit, Q 1 ~Q 4 The duty cycle is 0.5, and a certain dead time is reserved; the resonant tank is composed of the resonant inductor L r , magnetizing inductance L m , resonant capacitor C r And high frequency transformer T r Composition; the rectifier side consists of filter capacitor C 1 ~C 4 、Diode D 1 ~D 4 A new voltage doubler rectifier circuit and a bidirectional switch Q composed of two MOSFET tubes connected in series 5 According to the bidirectional switch Q 5 By turning on or off the rectifier, two different rectifier topologies can be constructed, namely the voltage doubler rectifier circuit (VDR) and the voltage quadruple rectifier circuit (VQR). On this basis, the frequency conversion and phase shift mixed modulation method can better achieve a wide gain range while maintaining high efficiency.

[25] The voltage doubler rectifier circuit on the secondary side can reduce the turns ratio of the transformer secondary side. At the same time, the VDR and VQR structures also have the advantage of balancing the voltage stress on the capacitor and diode.

[0045] Modal Analysis under Variable Frequency Modulation

[0046] In this embodiment, the resonant tank circuit contains three resonant elements, so the resonant converter has two different resonant frequencies when working: one is caused by C r and L r Determine the series resonant frequency, denoted as f r ; Second, by C r , L r and L m The series-parallel resonance frequency f formed by the common resonance of the three m ;Right now

[0047]

[0048] According to the converter switching frequency f s With f r and f m The converter has three different working modes: f s >f r , f m >f s >f r and f r =f s When the converter is at f m >f s >f r When C r , L r , L m In the common resonant mode, the secondary current flows intermittently through the diode, and this working mode includes all the modes of the other two working modes.

[0049] like Figure 2 As shown, the VQR structure is at f m >f s >f r Take the time as an example to perform modal analysis:

[0050] Working mode 1[t 0 Before]: In t 0 Before the time, corresponding to Figure 2 (a), at this time switch Q 1 and Q 4 On, Q 2 and Q 3 Turn off, the resonant circuit C r , L r and L mCommon resonance, excitation current i Lm With the resonant current i Lr Similarly, no current flows through the primary and secondary sides of the transformer, and the load is supplied by the filter capacitor C 3 and C 4 powered by.

[0051] Working mode 2[t 0 -t 1 ]:correspond Figure 2 (b) At t 0 At this moment, turn off Q 1 and Q 4 , at this time the resonant current i Lr Give Q 1 and Q 4 Side parasitic capacitance C oss1 and C oss4 Charge and give Q 2 and Q 3 Side parasitic capacitance C oss2 and C oss3 Discharge, due to the buffering effect of parasitic capacitance, the switch tube Q 1 and Q 4 It is zero voltage shutdown. Due to the large resonant current, this process is short. The secondary side load is still provided by capacitor C 3 and C 4 Provide power supply.

[0052] Working mode 3[t 1 -t 2 ]:correspond Figure 2 (c) at t 1 At this moment, the parasitic capacitance C oss1 and C oss4 The voltage has risen to U in , C oss2 and C oss3 has dropped to 0, at which point the resonant current i Lr Flow through the power switch Q 2 and Q 3 The internal freewheeling diode turns on Q at zero voltage 2 and Q 3 Be prepared. 2 and Q 3 After opening, the voltage between the primary bridge arms is the power supply voltage U in , current i Lm and i Lr Starts to increase, the diode D in the rectifier network 4 The transformer secondary voltage is clamped, so the magnetizing inductance L m Does not participate in resonance, inductor L r and capacitor C r Resonant operation, excitation current iLm The electric energy is transferred from the primary side of the transformer to the secondary side, and the filter capacitor C 2 Through diode D 4 and the bidirectional switch Q 5 Give C 4 and load power supply.

[0053] Working mode 4[t 2 -t 3 ]:correspond Figure 2 (d) at t 2 Moment, L r and C r Continue to resonate, the transformer secondary voltage reaches U C1 So the diode D 1 conduction, giving C 1 Charging, preparing to charge the load in the negative half cycle. Lr Continue to increase in the opposite direction and change polarity to negative. At this time, the voltage on the secondary side of the transformer is still the same as C 2 Give C 4 and load charging.

[0054] Working mode 5[t 3 -t 4 ]:correspond Figure 2 (e), at t 3 At this moment, L in the resonant tank r and C r Continue to resonate, the transformer secondary capacitor C 1 The voltage is greater than the transformer secondary voltage, so it flows through the diode D 1 The current decays to 0 to achieve zero current shutdown. In addition, the excitation current i Lm Change the polarity to negative and flow, the secondary current all passes through the diode D 4 and the bidirectional switch Q 5 C 2 Discharge to C 4 Charge.

[0055] Working mode 6[t 4 -t 5 ]:correspond Figure 2 (f), at t 4 At this moment, the resonant current i Lr and the excitation current i Lm Equal, excitation inductance L m The output voltage is no longer clamped. The primary current of the transformer decreases to 0. During this period, L m , L r and C r Working in common resonance, the power stops entering the transformer to transfer energy to the secondary side, and the diode D in the rectifier side circuit 4The current in the circuit also decays to 0 naturally, achieving zero current shutdown, and the load is powered by the output capacitor. 5 At this moment, turn off Q 2 and Q 4 , the second half cycle starts. The principle is the same as that of the first half cycle mode, so it will not be repeated here.

[0056] Modal Analysis under Phase Shift Modulation

[0057] When the converter is in high input voltage or light load condition, it is necessary to reduce the gain by increasing the switching frequency. However, when the converter operating frequency is high, the gain curve is flatter and insensitive to frequency changes, which means that to make a large change in the converter gain, the switching frequency needs to be adjusted significantly. Therefore, phase shift modulation is introduced as part of the modulation strategy. Phase shift modulation is to make the switch tube Q 1 , Q 2 Lag behind Q 3 , Q 4 , by blocking the input voltage for a period of time to modulate the average voltage entering the resonant network within a cycle.

[0058] like Figure 3 As shown, taking the VQR structure as an example, the improved converter operates at the resonant frequency f r When , the modal analysis using phase shift modulation is:

[0059] Working mode 1[t 0 Before]: t 0 Before the time, corresponding to Figure 3 (a), Q 1 and Q 2 On, Q 3 and Q 4 Turn off. The voltage between the primary bridge arms is U AB is 0. Where L r , L m and C r The resonant current i Lr Equal to the excitation current i Lm There is no current flowing through the primary and secondary sides of the transformer, and the load is provided by capacitor C 3 and C 4 powered by.

[0060] Working mode 2[t 0 -t 1 ]:t 0 Time, corresponding Figure 3 (b), turn off Q 2 , at this time the resonant current i Lr Give switch Q 2 The parasitic capacitance on the side is charged, and Q 4The parasitic capacitance on the side is discharged, leaving a certain dead time, and the switch Q 2 The voltage at the primary bridge arm is U AB starts to rise, where the resonant current i Lr Decision AB The rising speed of this process is relatively short, so it can be considered that L r , L m and C r The load continues to be powered by the output capacitor.

[0061] Working mode 3[t 1 -t 3 ]:In t 1 Time, corresponding Figure 3 (c), at this time Q 4 The parasitic capacitance on the side has been fully discharged, and the switch Q 4 Zero voltage turn-on. Q in the switch network 1 and Q 4 Open, Q 2 and Q 3 Turn off, then L r and C r The resonance begins, but the magnetizing inductance L m is clamped and does not participate in resonance, the resonant current i Lr increases faster, while the excitation current i Lm It starts to increase slowly and linearly, and energy begins to transfer between the primary and secondary sides of the transformer. The secondary current flows through D 3 and Q 5 Switch pair C 1 Discharge to C 3 and load charging. At t 2 Time, corresponding Figure 3 (d), the transformer secondary voltage reaches U C2 As a result, diode D2 is turned on, and part of the energy of the secondary current of the transformer is given to C 2 The other part of the energy continues to flow through the diode D 3 , is the load capacitance C 3 and load power supply.

[0062] Working mode 4[t 3 -t 4 ]:t 3 Time, corresponding Figure 3 (e), switch Q 2 Turn off, the resonant current i Lr Start giving Q 1 The parasitic capacitance on the side is charged, and at the same time Q 3 The parasitic capacitor on the side is discharged, and the secondary side of the transformer is still connected to C 2 , C 3and load charging, for C 1 Discharge.

[0063] Working mode 5[t 4 -t 6 ]:In t 4 Time, corresponding Figure 3 (f), Q 1 The voltage of the parasitic capacitance on the side rises to U in , Q 3 The voltage of the parasitic capacitor on the side drops to 0, and the anti-parallel diode is turned on, and the switch Q 1 Zero voltage turn-on. 5 Time, corresponding Figure 3 (g), the transformer secondary voltage is lower than U C2 , so that the diode D 2 Zero current shutdown, the secondary current all passes through D 3 and Q 5 C 1 Discharge to C 3 Charge.

[0064] Working mode 6[t 6 -t 7 ]:In t 6 Time, corresponding Figure 3 (h), at this time the resonant current i Lr and the excitation current i Lm equal, at this time the transformer primary current is reduced to 0, the rectifier side circuit diode D 3 The current in the output capacitor C 3 and C 4 Power supply, Lr , U Cr ,i Lm The expression is as follows. The second half cycle is similar to the first half cycle and will not be described here.

[0065] Gain Characteristics of Frequency Modulation Down-Converter

[0066] This embodiment adopts the fundamental wave analysis method to achieve linearization by ignoring high-order harmonics, thereby simplifying the analysis process. The resonant converter is divided into three main parts: a switch network, a resonant network, and a rectifier network.

[0067] Switching network input voltage U in By alternately opening and closing the front and rear bridge arms of the switch network, a square wave voltage u can be obtained. AB , for the square wave u AB Perform Fourier series expansion to obtain u AB The fundamental voltage RMS value U AB1 :

[0068]

[0069] This embodiment uses the VQR structure as an example to simplify the rectifier network. When the converter works in the positive half cycle of the VQR structure, the capacitor C 2 The discharge current is only supplied to capacitor C 4 , so the transformer secondary voltage u res for:

[0070]

[0071] When in the negative half cycle, the capacitor C 2 Charged by the secondary voltage of the transformer, we can get:

[0072] u res =U C2 (5)

[0073] According to the volt-second balance principle, the above two equations can be combined to obtain:

[0074] U 0 =4u res (6)

[0075] The voltage fundamental component U can be obtained by Fourier series expansion of the transformer secondary voltage: res1 :

[0076]

[0077] Different from VQR, when working in the positive half cycle of VDR, the capacitor C 2 Discharge only to C 3 and C 4 , so the transformer secondary voltage u res =U 0 -U C2 , when the converter is operating in the negative half cycle of VDR, u res =U C2 According to the volt-second balance, U 0 =2u res .

[0078] The input-output voltage transfer ratio M of the resonant converter refers to the ratio of the output voltage converted to the primary side of the transformer to the input voltage. The voltage gain M under the VQR structure can be obtained as:

[0079]

[0080] in, R ac Is the equivalent resistance. k=L m / L r , Q=Z r / R ac , f n =f s / f r .

[0081] Similarly, the voltage gain M under the VDR structure can be obtained:

[0082]

[0083] Soft Switching Characteristics of Frequency Modulated Down-Converter

[0084] To ensure the converter achieves soft switching, the switch parasitic capacitance should be fully charged and discharged within a certain period of time, and a dead time must be set between the modulation signals of the switch tubes on the same bridge arm. 1 and Q 4 After shutdown, Q 2 and Q 3 The parasitic capacitance starts to discharge. Before the driving signal comes, the parasitic capacitance C oss2 and C oss3 It needs to be fully discharged, so the dead time t dead greater than the discharge time t f In addition, to ensure that the primary switch can achieve zero voltage switching (ZVS), sufficient excitation current peak must be ensured during the switch off period to facilitate the junction capacitance on the switch to commutate. Therefore, the excitation current peak needs to meet:

[0085] I Lm_pk t dead ≥2C oss U in (10)

[0086] Among them, I Lm_pk is the excitation current peak value, t dead is the dead time, C oss is the output capacitance of the primary switch tube, U in is the input voltage.

[0087] The peak value of the excitation current is expressed as:

[0088]

[0089] The peak value expression of excitation current under VQR structure can be obtained:

[0090]

[0091] Combining equation (10) and equation (12) we can get the value of dead time:

[0092] t dead >t f =32C oss Lm f s / M (13)

[0093] Similarly, the peak value expression of excitation current under VDR structure can be obtained:

[0094]

[0095] Dead time must meet:

[0096] t dead >t f =16C oss L m f s / M (15)

[0097] Gain Characteristics of Phase-Shift Modulation Down-Converter

[0098] When the VQR structure adopts phase shift modulation, the U AB The fundamental component of the power is blocked from entering the resonant tank, so the switch network port voltage U AB It is a square wave less than 0.5.

[0099] Voltage U at the switch network port AB Perform Fourier series expansion:

[0100]

[0101] Wherein, θ is the phase shift angle, and its value range is 0°≤θ≤180°.

[0102] The fundamental component in phase-shift modulation is cos(θ / 2) times the fundamental component in variable frequency modulation mentioned above. Similarly, when the VQR structure is in phase-shift modulation, the normalized voltage gain M is:

[0103]

[0104] From formula (17), we can get that when f s =f r When f n =1. At this time, the gain M has nothing to do with the k value and the Q value, but only with the value of the phase shift angle θ. Therefore, when the VQR structure operates at the resonant frequency f r The voltage gain M under is:

[0105] M=4cos(θ / 2) (18)

[0106] Similarly, the voltage gain M under the VDR structure under phase shift modulation is:

[0107]

[0108] When the VDR structure operates at the resonant frequency f r The voltage gain M under is:

[0109] M=2cos(θ / 2) (20)

[0110] Soft Switching Characteristics of Phase-Shift Modulated Down-Converter

[0111] When the phase shift angle increases to a certain value, the inductance L r , L m and capacitor C r The common resonance time is too long, resulting in the resonance current i Lr The charge of the switch tube of the lagging bridge arm cannot be completely released before it is turned on, so the switch tube of the lagging bridge arm cannot reach the soft switching condition. To achieve soft switching, the resonant current i Lr During the dead time, the parasitic capacitance on the switch side is fully charged and discharged. Lm Greater than the minimum current for complete charge and discharge during the dead time, that is, it satisfies:

[0112] I Lm_pk t dead ≥2C oss U in (twenty one)

[0113] The peak value expression of excitation current under phase shift modulation is:

[0114]

[0115] Wherein, D = (π-θ) / π is the equivalent duty cycle of the primary switch tube.

[0116] The value of the dead time under phase shift modulation is similar to that under variable frequency modulation. In order to achieve soft switching characteristics in the VQR structure, the dead time must meet the following requirements:

[0117]

[0118] Similarly, under the VDR structure, the dead time must satisfy:

[0119]

[0120] By reasonably selecting the values ​​of the excitation inductance and the dead time and satisfying the above conditions under phase-shift modulation, zero voltage turn-on can be achieved.

[0121] Modulation strategy

[0122] By adopting a hybrid modulation strategy and using different modulation methods in different gain regions, the advantages of each modulation method can be maximized and its disadvantages can be avoided. n<1, the variable frequency modulated LLC converter can not only achieve zero voltage turn-on (ZVS) of the switch tube on the primary side, but also achieve zero current turn-on (ZCS) of the diode on the secondary side, thereby improving the converter efficiency; and the voltage gain curve has a large slope in this area, so variable frequency modulation can effectively adjust the voltage gain of the LLC converter. When the input voltage continues to rise, the converter gain needs to be reduced to stabilize the output voltage. However, as the switching frequency f s As f increases, the slope of the converter gain curve decreases gradually, causing a sharp increase in switching frequency, thereby increasing converter losses. n >1, the secondary diode cannot achieve ZCS, thus increasing power loss. At this time, if phase shift modulation is adopted, the secondary diode can not only achieve ZCS, but also the slope of the voltage gain curve of the LLC converter gradually increases with the increase of the phase shift angle θ, indicating that when f n <1, phase shift modulation can more effectively adjust the voltage gain of the converter. Since the converter works most efficiently at the series resonant frequency, the modulation switching point between variable frequency modulation and phase shift modulation should be selected as f s =f r , θ=0°.

[0123] The operation mode of the modulation system is selected according to the input and output voltages. The initial operation mode of the converter is the VQR structure under variable frequency modulation, such as Figure 4 As shown in Figure 1. Frequency modulation is first used to adjust the output voltage of the load. The switching frequency first works at f in the VQR structure. m At this time, the converter gain is the largest, and as the switching frequency slowly increases, until the switching frequency reaches f r When the modulation system switches from variable frequency modulation to phase shift modulation under the same working topology, the working frequency under phase shift modulation remains at f r The output voltage is adjusted by changing the phase shift angle between the two bridge arm switches in the front switch network. By further reducing the converter gain, the converter gain reaches the maximum value under the VDR structure, that is, the switching frequency is f m At the same time, the phase shift value under the VQR structure also reaches the upper limit. At this time, the bidirectional switch Q 5 The circuit topology switches from the VQR structure to the VDR structure, where the phase shift value returns to zero and the converter operates at the minimum frequency under the VDR structure. As the converter gain further decreases, the switching frequency reaches f r When , the modulation system performs phase shift modulation at this operating frequency to realize the modulation strategy of high efficiency wide gain converter.

[0124] Case Analysis

[0125] In order to verify the applicability of the proposed converter to a wide voltage input range and the feasibility of practical application, a 400W experimental prototype was built for verification, and experiments were carried out under different input voltage and load conditions. The main parameters of the prototype are shown in Table 1. The modulation signal is generated by TMS320F28335.

[0126] Table 1 Main parameters and models of experimental prototype

[0127]

[0128] Figure 5 This is the experimental waveform of the converter when the input voltage is 22V. At this time, the converter is in a VQR structure under variable frequency modulation, and the voltage gain is maximum. Figure 6 This is the experimental waveform of the converter when the input voltage is 27V. At this time, the converter is in a VQR structure and uses phase shift modulation. It can be seen that the voltage U between the two bridge arms AB The output voltage is regulated by blocking a portion of the electrical energy from entering the resonant tank during a cycle. Figure 7 This is the experimental waveform of the converter when the input voltage is 38V. At this time, the converter adopts variable frequency modulation and is in the VDR structure. It can be seen that the current flowing through the secondary rectifier diode D 1 The current naturally crosses zero within one cycle, realizing ZCS of the diode on the rectifier side. Figure 8 This is the experimental waveform of the converter when the input voltage is 52V. At this time, the converter is in the VDR structure and uses phase-shift modulation. At this time, the voltage gain is the minimum.

[0129] When the converter works at light load, half load and full load, the experimental data and theoretical analysis are highly consistent. Converters with different structures can maintain stable output voltage in a wide range of input voltages according to the required gain requirements. The U of the switch tube in different working modes of the converter can be DS and U GS The experimental waveform shows that all switches are turned on at zero voltage, but after the power switch is turned off, U DS There is a small voltage oscillation, which is due to the resonance between the capacitor and the inductor. This resonance does not affect the normal operation of the circuit. In one cycle, the excitation inductor current i Lm and the resonant inductor current i Lr The phenomenon of being equal indicates that the excitation inductance L m Not clamped by the load on the rectifier side, diode D 1 and D 2 The current is discontinuous, which means that the rectifier diode has also reached the zero current switching (ZCS) state.

[0130] The efficiency of the prototype under different input voltages is shown in Fig. 9As shown in the figure, within the input voltage range of 20V-60V, the conversion efficiency is always maintained above 90%, and the efficiency reaches the highest at the resonant frequency under the VQR structure, which is 94.8%. When using variable frequency modulation, the system reaches the highest efficiency at the resonant frequency. At this time, not only can the ZVS of the switch tube and the ZCS of the diode be achieved, but the circulating current is relatively small; the phase-shift modulation strategy is applicable within the voltage range of 25V-35V and 50V-60V. When using phase-shift modulation, the frequency is maintained at the resonant frequency, which is convenient for the design of magnetic components. Although it will cause a slight increase in switching losses, the parameter optimization design will become simple. The efficiency curve is consistent with the analysis results in the second part, verifying the effectiveness of the hybrid modulation strategy under different structures and the converter's efficient conversion capability over the entire voltage range.

[0131] In view of the fact that the voltage gain range of the traditional LLC resonant converter is narrow and it is difficult to cope with the large output voltage fluctuation in the photovoltaic power generation system, this embodiment designs a wide-input LLC resonant converter based on the improvement of the rectifier side under hybrid modulation. There are two structures of the converter. When the required gain is large, the converter works in the VQR structure. When the required converter gain is small, the converter works in the VDR structure. At the same time, a hybrid modulation strategy combining frequency conversion and phase shifting is adopted to more effectively expand the range of voltage gain. Compared with the traditional LLC resonant converter, the proposed converter not only has the characteristics of ZVS and ZCS, but also can achieve a larger voltage gain range within a narrow switching frequency. The above performance of the proposed resonant converter is confirmed through theoretical analysis and experimental verification.

[0132] The above description is only a preferred embodiment of the present embodiment and is not intended to limit the present embodiment. For those skilled in the art, the present embodiment may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present embodiment shall be included in the protection scope of the present embodiment.

Claims

1. A hybrid modulation method based on a wide gain resonant converter on the rectifier side, characterized in that: A modulation method that combines variable frequency modulation and phase shift modulation is used to achieve a wide gain of the resonant converter; the output voltage of the resonant converter is adjusted by adjusting the switching frequency and the phase shift angle; When the switching frequency f s is the series-parallel resonant frequency f of the resonant tank circuit m When the voltage gain reaches the maximum, the rectifier circuit is in a four-fold voltage rectifier circuit; when the resonant converter switching frequency f s Increase to the series resonant frequency f of the resonant tank circuit r When the resonant converter switches from variable frequency modulation to phase shift modulation under the same working topology, the operating frequency under phase shift modulation is kept at f r ; By changing the phase shift angle between the power switches in the inverter circuit, the output voltage of the secondary load is adjusted to reduce the gain of the resonant converter so that the switching frequency f s The minimum frequency value when the rectifier circuit is in the voltage doubler rectifier circuit is reached, that is, the series-parallel resonant frequency f of the resonant tank circuit m , the bidirectional switch is disconnected, the rectification topology of the rectification circuit is switched from the quadruple voltage rectification circuit to the double voltage rectification circuit, the phase shift value is reset to zero, and the minimum frequency of the resonant converter working under the double voltage rectification circuit is obtained. When the switching frequency f s Reaching the series resonant frequency f r When , the resonant converter performs phase shift modulation; A wide gain resonant converter based on the rectifier side includes an inverter side circuit, a rectifier side circuit, and a resonant tank circuit for connecting the inverter side circuit and the rectifier side circuit; wherein the rectifier side circuit includes a rectifier circuit and a bidirectional switch, the bidirectional switch uses two switch tubes connected in reverse series, and the rectifier circuit is a full-bridge rectifier circuit composed of a first filter capacitor, a second filter capacitor, a third filter capacitor, a fourth filter capacitor, a first diode, a second diode, a third diode and a fourth diode; the rectifier topology of the rectifier circuit is adjusted by adjusting the on and off states of the bidirectional switch, and the rectifier topology of the rectifier circuit includes a voltage doubling rectifier circuit and a quadruple voltage rectifier circuit.

2. The hybrid modulation method based on the wide gain resonant converter on the rectifier side as described in claim 1, characterized in that: The series resonant frequency f of the resonant tank circuit r The resonant inductor L r and resonant capacitor C r The common resonance of the two forms The series-parallel resonant frequency f of the resonant tank circuit m The resonant inductor L r , resonant capacitor C r and the magnetizing inductance L m The three are resonated together, that is, 3. The hybrid modulation method based on the wide gain resonant converter on the rectifier side as described in claim 1, characterized in that: According to the series-parallel resonant frequency f m , series resonant frequency f r and the switching frequency f s The size between, that is, f s >f r 、f m <f s <f r or r =f s , determine the working mode of the resonant converter; when f m <f s <f r When the resonant converter has a resonant inductance L r , resonant capacitor C r and the magnetizing inductance L m In the common resonant mode of the three, the secondary current of the high-frequency transformer flows intermittently through the diode in the rectifier circuit.

4. The hybrid modulation method based on the wide gain resonant converter on the rectifier side as described in claim 1, characterized in that: When the resonant converter is in high input voltage or light load condition, the gain needs to be reduced by increasing the switching frequency. However, when the operating frequency of the resonant converter is high, the gain curve is flat. Phase shift modulation is introduced to adjust the switching frequency of the resonant converter.

5. The hybrid modulation method based on the wide gain resonant converter on the rectifier side as described in claim 4, characterized in that: During the phase shift modulation process of the resonant converter, the first power switch tube and the second power switch tube are both delayed behind the third power switch tube and the fourth power switch tube. By blocking the input voltage of the resonant converter and adjusting the average voltage entering the resonant tank circuit within one cycle, the phase shift modulation of the resonant converter is realized.

6. The hybrid modulation method based on the wide gain resonant converter on the rectifier side as described in claim 1, characterized in that: The modulation switching point of the variable frequency modulation and phase shift modulation of the resonant converter needs to meet the switching frequency f s With the series resonant frequency f r Consistent.

7. A hybrid modulation method based on a wide gain resonant converter on the rectifier side as claimed in claim 1, characterized in that: The inverter side circuit is a full-bridge circuit consisting of a first power switch tube, a second power switch tube, a third power switch tube and a fourth power switch tube; wherein the duty cycles of the first power switch tube, the second power switch tube, the third power switch tube and the fourth power switch tube are all consistent.

8. A hybrid modulation method based on a wide gain resonant converter on the rectifier side as claimed in claim 1, characterized in that: The resonant tank circuit includes a high-frequency transformer and a resonant inductor, an excitation inductor and a resonant capacitor arranged on the primary side of the high-frequency transformer.

9. A hybrid modulation method based on a wide gain resonant converter on the rectifier side as claimed in claim 1, characterized in that: It also includes a secondary side load connected in parallel across the third filter capacitor and the fourth filter capacitor.

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