Integrated three-phase Boost-LLC topology and modulation method

Abstract

The invention discloses an integrated three-phase Boost-LLC topology and a modulation method. The integrated three-phase Boost-LLC topology comprises a transformer, a primary side circuit and a secondary side circuit, wherein the primary side circuit and the secondary side circuit are connected to the two sides of the transformer; the primary side circuit comprises a preceding-stage three-phase staggered Boost circuit and a backward-stage three-phase LLC resonant circuit, the preceding-stage three-phase Boost circuit comprises six switching tubes and three choking coil inductors, the three inductors are connected between the input and the midpoint of a three-phase bridge arm, the six switching tubes are located between the positive electrode and the negative electrode of a middle bus, and the backward-stage three-phase LLC resonant circuit is located between the positive electrode and the negative electrode of the middle bus. Meanwhile, the six switching tubes are multiplexed to serve as inversion bridge arms of a post-stage three-phase LLC, and the post-stage LLC resonant circuit is connected behind the three-phase bridge arms; the secondary side circuit comprises a three-phase rectifier bridge, is composed of six switching tubes and is connected to the secondary side of the transformer, and the direct current output is connected with an output filter capacitor and a load. According to the invention, the number of devices is reduced through bridge arm multiplexing, a wide voltage regulation range is realized, and synchronous rectification is convenient to realize.

Description

Technical Field

[0001] The invention belongs to the technical field of isolated DC-DC converters, and in particular relates to an integrated three-phase Boost-LLC topology and a modulation method. Background Art

[0002] In the prior art, in order to improve the power density of the system, the switching frequency of the device can usually be increased to reduce the size of the passive components. However, the higher the switching frequency, the greater the switching loss. In order to achieve high-efficiency and high-power density conversion, LLC is used because it can realize soft switching of primary and secondary devices. In order to increase power capacity and reduce current ripple, three-phase interleaved LLC is widely used. However, like the single-phase LLC, it also needs to adjust the gain by frequency conversion. Therefore, many studies use a two-stage structure to achieve voltage regulation. In the two-stage structure, the three-phase interleaved LLC usually works in a quasi-resonant state, the switching frequency is fixed, and a wide range of voltage regulation is achieved through the voltage regulation stage. However, the two-stage structure has many switching devices and many energy processing stages, which will greatly affect the system cost and efficiency, so it is difficult to achieve wide range voltage regulation. Therefore, it is urgent to propose an integrated three-phase Boost-LLC topology and modulation method. Summary of the invention

[0003] In order to solve the above technical problems, the present invention proposes an integrated three-phase Boost-LLC topology and modulation method, which reduces the number of devices by multiplexing bridge arms, while achieving a wider voltage regulation range and facilitating synchronous rectification.

[0004] On the one hand, to achieve the above-mentioned object, the present invention provides an integrated three-phase Boost-LLC topology, including: a transformer and a primary circuit and a secondary circuit connected on both sides of the transformer;

[0005] The primary circuit includes a front-stage three-phase interleaved Boost circuit and a rear-stage three-phase LLC resonant circuit, wherein the front-stage three-phase Boost circuit includes six switch tubes and three choke inductors, wherein the three inductors are connected between the input and the midpoint of the three-phase bridge arm, and the six switch tubes are located between the positive and negative poles of the intermediate bus, and the six switch tubes are reused as the inverter bridge arm of the rear-stage three-phase LLC, and the rear-stage LLC resonant circuit is connected after the three-phase bridge arm;

[0006] The secondary circuit includes a three-phase rectifier bridge, which is composed of six switching tubes and connected to the secondary side of the transformer. The DC output is connected to the output filter capacitor and the load.

[0007] Optionally, the connection form of the three-phase resonant capacitor in the three-phase interleaved LLC circuit is Y-connection, the connection form of the three-phase resonant inductor in the three-phase interleaved LLC circuit is Δ-connection, the primary winding of the transformer is connected in series with the resonant inductor of each phase, the connection form of the secondary winding of the transformer is Δ-connection, and the half-bridge midpoints of the secondary three-phase rectifier bridge are respectively connected to the three vertices of the secondary winding Δ connection.

[0008] Optionally, the upper and lower switch tubes of the same bridge arm are turned on complementary to each other, and the phase shift between different bridge arms is 120°.

[0009] Optionally, the three-phase Boost bridge arm of the primary circuit is reused with the three-phase LLC bridge arm, and the primary circuit uses six switching tubes to simultaneously complete the functions of Boost and LLC.

[0010] Optionally, the front-stage three-phase Boost circuit includes six switching tubes and three choke inductors, and the three inductors are connected between the input and the midpoint of the three-phase bridge arm.

[0011] Optionally, six switch tubes are located between the positive and negative poles of the intermediate bus, and the six switch tubes are reused as the inverter bridge arm of the rear-stage three-phase LLC, and the rear-stage LLC resonant circuit is connected after the three-phase bridge arm.

[0012] On the other hand, to achieve the above object, the present invention also provides a modulation method of an integrated three-phase Boost-LLC topology, comprising the following steps:

[0013] Calculate the required duty cycle based on the input voltage and output voltage;

[0014] Calculate the required switching frequency based on the duty cycle;

[0015] The secondary side synchronous rectification function is determined according to the range of the duty cycle.

[0016] Technical effects of the present invention:

[0017] (1) The length of the positive half-cycle or negative half-cycle of the three-phase interleaved LLC resonant current is always equal to half of the resonant period, and the sum of the two is always equal to the resonant period. This is equivalent to the three-phase interleaved LLC always working in a quasi-resonant state even if the switching frequency changes, so the efficiency is higher.

[0018] (2) Since the three-phase interleaved LLC operates in a quasi-resonant state, it is easy to implement secondary synchronous rectification. However, unlike the traditional LLC with integrated bridge arms, the secondary side can be directly driven by the same drive as the primary side, and the timing of the secondary synchronous rectification is different. The present invention also provides a switch timing function for the secondary synchronous rectification.

[0019] (3) The Boost operates in forced continuous conduction mode (FCCM) to achieve soft switching of the device using inductor current, enabling full-range zero-voltage turn-on without exciting current. Therefore, the transformer does not require an air gap, which can further reduce winding losses. Description of the Drawings

[0020] The drawings forming a part of this application are used to provide a further understanding of this application. The schematic embodiments and descriptions thereof are used to explain this application and do not constitute an improper limitation of this application. In the drawings:

[0021] Figure 1 It is a schematic structural diagram of an integrated three-phase Boost-LLC topology according to an embodiment of the present invention;

[0022] Figure 2 It is a key waveform diagram of a three-phase integrated Boost-LLC converter according to an embodiment of the present invention when 0 < D < 1 / 3;

[0023] Figure 3 It is a key waveform diagram of a three-phase integrated Boost-LLC converter according to an embodiment of the present invention when 1 / 3 < D < 1 / 2;

[0024] Figure 4 It is a key waveform diagram of a three-phase integrated Boost-LLC converter according to an embodiment of the present invention when 1 / 2 < D < 2 / 3;

[0025] Figure 5 It is a key waveform diagram of a three-phase integrated Boost-LLC converter according to an embodiment of the present invention when 2 / 3 < D < 1;

[0026] Figure 6 It is a schematic diagram showing the relationship between the duty cycle and frequency of a three-phase integrated Boost-LLC converter according to an embodiment of the present invention. Detailed Embodiments

[0027] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The following will refer to the drawings and combine with the embodiments to detail this application.

[0028] It should be noted that the steps shown in the flowchart of the drawings can be executed in a computer system such as a set of computer-executable instructions, and although the logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in a different order than here.

[0029] As Figure 1 shown, in this embodiment, an integrated three-phase Boost-LLC topology is provided, including: a transformer and a primary circuit and a secondary circuit connected to both sides of the transformer;

[0030] The primary circuit includes a front-stage three-phase interleaved Boost circuit and a rear-stage three-phase LLC resonant circuit. The front-stage three-phase Boost circuit includes six switch tubes and three choke inductors. The three choke inductors are connected between the input and the midpoint of the three-phase bridge arm. The six switch tubes are located between the positive and negative poles of the intermediate bus. At the same time, the six switch tubes are reused as the inverter bridge arm of the rear-stage three-phase LLC. The rear-stage three-phase LLC resonant circuit is connected after the three-phase bridge arm.

[0031] The secondary circuit includes a three-phase rectifier bridge, which is composed of six switching tubes and connected to the secondary side of the transformer. The DC output is connected to the output filter capacitor and the load.

[0032] Specifically, the primary circuit includes three chokes (L1 / L2 / L3), six switch tubes (S1 / S2 / S3 / S4 / S5 / S6) forming a three-phase half-bridge circuit, three resonant capacitors (Cr1 / Cr2 / Cr3), and three resonant inductors (Lr1 / Lr2 / Lr3). The chokes are connected in series with the resonant capacitors, and the three resonant inductors are connected in series with the primary winding of the three-phase transformer (T), and are connected in a triangle shape, with the three vertices of the triangle connection connected to the right sides of the three resonant capacitors. The secondary circuit includes six switch tubes forming a three-phase half-bridge circuit. The secondary winding of the transformer is connected in a triangle shape, with the three vertices of the triangle connected to the midpoints of the three half bridges.

[0033] Furthermore, the connection form of the three-phase resonant capacitor in the three-phase interleaved LLC circuit is Y-connection, the connection form of the three-phase resonant inductor in the three-phase interleaved LLC circuit is Δ-connection, the primary winding of the transformer is connected in series with the resonant inductor of each phase, the connection form of the secondary winding of the transformer is Δ-connection, and the half-bridge midpoints of the secondary three-phase rectifier bridge are respectively connected to the three vertices of the secondary winding Δ connection.

[0034] Furthermore, the upper and lower switch tubes of the same bridge arm are turned on complementary to each other, and the phase shift between different bridge arms is 120°.

[0035] Furthermore, the three-phase Boost bridge arm of the primary circuit is multiplexed with the three-phase LLC bridge arm, and the primary circuit uses six switching tubes to simultaneously complete the functions of Boost and LLC.

[0036] Furthermore, the front-stage three-phase Boost circuit includes six switch tubes and three choke inductors, and the three choke inductors are connected between the input and the midpoint of the three-phase bridge arm.

[0037] Furthermore, six switch tubes are located between the positive and negative poles of the intermediate bus, and the six switch tubes are reused as the inverter bridge arm of the subsequent three-phase LLC, and the subsequent three-phase LLC resonant circuit is connected after the three-phase bridge arm.

[0038] This embodiment also provides a modulation method for an integrated three-phase Boost-LLC topology, comprising the following steps:

[0039] Calculate the required duty cycle based on the input voltage and output voltage;

[0040] Calculate the required switching frequency based on the duty cycle;

[0041] The secondary side synchronous rectification function is determined according to the range of the duty cycle.

[0042] The modulation method is an adaptive variable frequency and variable duty cycle strategy. By adjusting the driving signal sent by the controller, the length of the positive half-cycle or negative half-cycle of the three-phase interleaved LLC resonant current is always equal to half of the resonant period, and the sum of the two is always equal to the resonant period, so that the three-phase interleaved LLC always operates in a quasi-resonant state with high efficiency, and synchronous rectification is achieved on the secondary side.

[0043] Take the duty cycle less than 0.5 as an example. Figure 2 As shown in the figure, when the duty cycle changes, the switching frequency changes accordingly to ensure that the high level time is equal to half the resonant period. s is the switching period, f r is the resonant frequency:

[0044]

[0045] Therefore, we can get Figure 6 The relationship between the switching frequency and the duty cycle is shown in Figure 1. When the duty cycle is 0.5, the switching frequency is equal to the resonant frequency, the three-phase interleaved LLC operates in a quasi-resonant mode, and the resonant element just has a complete resonant cycle. When the duty cycle is not equal to 0.5, the switching frequency can be changed so that the resonant element still has a complete resonant cycle. This means that even if the duty cycle changes, the three-phase interleaved LLC is still equivalent to operating in a quasi-resonant mode, which is beneficial to the realization of synchronous rectification on the secondary side. It can be seen that the proposed modulation is equivalent to inserting a certain length of zero-level time on the basis of the resonant period.

[0046] The difference between the proposed modulation and the three-phase interleaved LLC working in quasi-resonant mode is that a certain length of zero-level time is inserted. Therefore, the length of the zero level in each mode is calculated, and the secondary side on / off signal is adjusted based on this to achieve synchronous rectification. According to the different duty cycles, the driving signal of the secondary side switching device needs to be discussed in four cases: [0, 1 / 3], [1 / 3, 1 / 2], [1 / 2, 2 / 3], [2 / 3, 1]. The corresponding key waveforms in each case are as follows: Figure 2-Figure 5 To simplify the analysis, the following analysis is conducted by taking the duty cycle less than 1 / 3 and phase A as an example, ignoring the influence of the dead time.

[0047] Mode I(t0,t1): S1, S4, and S6 are turned on. Cr1 starts to charge. At the previous moment, Cr3 has already been charged. Since S4 is conducting, Cr3 starts to discharge. iCr1 = -iCr3. Therefore, there is no current in phase B, and the capacitor voltage remains at 0. Due to the change in the switching frequency, DTs = 0.5fr, so the resonant current in phase A has a complete half-resonant cycle.

[0048] Mode II(t1,t2): S2, S4, and S6 are turned on. The resonant current in phase A enters the discontinuous mode, and the capacitor voltage remains unchanged. The duration of the zero level in this stage is (1 / 3 - D)*Ts.

[0049] Mode III(t2,t3): S2, S3, and S6 are turned on. The resonant capacitor in phase A starts to discharge, and the resonant current enters the negative half-cycle. DTs = 0.5fr, so the resonant current in phase A has a complete half-resonant cycle.

[0050] Mode IV(t3,t4): S2, S4, and S6 are turned on. This mode is the same as Mode II. The resonant current enters the discontinuous mode, and the capacitor voltage remains unchanged. The duration of the zero level in this stage is (1 / 3 - D)*Ts.

[0051] Mode V(t4,t5): S2, S4, and S3 are turned on. This mode is similar to Mode I. Cr3 charges, Cr2 discharges, and their currents are equal. There is no current in phase A, and the capacitor voltage remains at 0. The duration of the zero level in this stage is D*Ts.

[0052] Mode VI(t5,t6): S2, S4, and S6 are turned on. This mode is similar to Mode II.

[0053] Therefore, the following synchronous rectification strategy can be given:

[0054] When 0 < D < 1 / 3:

[0055]

[0056] When 1 / 3 < D < 1 / 2:

[0057]

[0058] When 1 / 3 < D < 2 / 3:

[0059]

[0060] When 2 / 3 < D < 1:

[0061]

[0062] The time length of the positive half cycle or negative half cycle of the three-phase staggered LLC resonant current in the present invention is always equal to half of the resonant period, and the sum of the two is always equal to the resonant period. This is equivalent to that even if the switching frequency changes, the three-phase staggered LLC always operates in a quasi-resonant state, so the efficiency is higher. Since the three-phase staggered LLC operates in a quasi-resonant state, it is easy to realize secondary side synchronous rectification. However, unlike the LLC with traditional integrated bridge arms, the secondary side can be directly driven by the same drive as the primary side, and the timing of the secondary side synchronous rectification is different. The present invention also provides a switching timing function for the secondary side synchronous rectification. The Boost of the present invention operates in a forced continuous conduction mode (FCCM) and uses the inductor current to realize soft switching of the device, and full-range zero voltage opening can be achieved without the need for an excitation current. Therefore, the transformer does not require an air gap, which can further reduce winding losses.

[0063] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. An integrated three-phase Boost-LLC topology, characterized in that: It includes: a transformer and a primary circuit and a secondary circuit connected on both sides of the transformer; The primary circuit includes a front-stage three-phase interleaved Boost circuit and a rear-stage three-phase LLC resonant circuit, the front-stage three-phase Boost circuit includes six switch tubes and three choke inductors, the three choke inductors are connected between the input and the midpoint of the three-phase bridge arm, the six switch tubes are located between the positive and negative poles of the intermediate bus, and the six switch tubes are reused as the inverter bridge arm of the rear-stage three-phase LLC, and the rear-stage three-phase LLC resonant circuit is connected after the three-phase bridge arm; The secondary circuit includes a three-phase rectifier bridge, which is composed of six switching tubes and connected to the secondary side of the transformer. The DC output is connected to the output filter capacitor and the load.

2. The integrated three-phase Boost-LLC topology according to claim 1, characterized in that: The connection form of the three-phase resonant capacitor in the three-phase interleaved LLC circuit is Y-connection, the connection form of the three-phase resonant inductor in the three-phase interleaved LLC circuit is Δ-connection, the primary winding of the transformer is connected in series with the resonant inductor of each phase, the connection form of the secondary winding of the transformer is Δ-connection, and the half-bridge midpoint of the secondary three-phase rectifier bridge is respectively connected to the three vertices of the secondary winding Δ connection.

3. The integrated three-phase Boost-LLC topology according to claim 2, characterized in that: The upper and lower switch tubes of the same bridge arm are turned on complementary to each other, and the phase shift between different bridge arms is 120°.

4. The integrated three-phase Boost-LLC topology according to claim 2, characterized in that: The three-phase Boost bridge arm of the primary circuit is reused with the three-phase LLC bridge arm. The primary circuit uses six switching tubes to simultaneously complete the functions of Boost and LLC.

5. The integrated three-phase Boost-LLC topology according to claim 2, characterized in that: The front-stage three-phase Boost circuit includes six switch tubes and three choke inductors, and the three inductors are connected between the input and the midpoint of the three-phase bridge arm.

6. The integrated three-phase Boost-LLC topology according to claim 2, characterized in that: The six switch tubes are located between the positive and negative poles of the intermediate bus, and the six switch tubes are reused as the inverter bridge arm of the rear-stage three-phase LLC. The rear-stage LLC resonant circuit is connected after the three-phase bridge arm.

7. A modulation method of an integrated three-phase Boost-LLC topology according to any one of claims 1 to 6, characterized in that: The following steps are involved: Calculate the required duty cycle based on the input voltage and output voltage; Calculate the required switching frequency based on the duty cycle; The secondary side synchronous rectification function is determined according to the range of the duty cycle.

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