A system of three-phase interleaved CLLC resonant converter and phase-to-phase current sharing control method

Abstract

The application discloses a system of a three-phase interleaved CLLC resonant converter and a phase-to-phase current equalization control method, and belongs to the field of DC / DC converters. The method comprises the following steps: according to the operating state of the resonant converter, collecting the effective values of three-phase currents on the output side of the circuit structure; based on the effective values of the three-phase currents, calculating the phase difference between three-phase bridge arms on the input side by PI; fixing the turn-on and turn-off time of preset phase switches on the input side, and respectively calculating the turn-on and turn-off time of the other two phase switches on the input side according to the phase difference, so as to obtain the driving signals of six switches of the three-phase bridge arms on the input side; controlling the switches on the input side according to the driving signals, adjusting the phase difference of the current phase on the output side of the resonant cavity, and setting the included angle between the fundamental wave phase of the three-phase currents on the output side to 2pi / 3, so that the currents among the phases are balanced. The phase difference between the currents on the output side is indirectly controlled by adjusting the voltage of the input resonant cavity through phase shift control, so that the balance degree of the currents is adjusted.

Description

Technical Field

[0001] This invention belongs to the field of DC / DC converters, and more specifically, relates to a system of a three-phase interleaved CLLC resonant converter and a method for interphase current sharing control. Background Technology

[0002] In recent years, with the rapid development of new energy power generation, DC microgrids, electric vehicles, and energy storage systems, the demand for high-power-density and high-efficiency power conversion technologies has surged, leading to an increased demand for high-power isolated bidirectional DC / DC converters. Multiphase interleaved resonant converters, due to their advantages such as low switching losses and wide voltage regulation range, have become a research hotspot for high-power isolated bidirectional DC / DC converters.

[0003] Currently, multiphase interleaved resonant converters can be divided into three-phase interleaved LLC resonant converters and three-phase interleaved CLLC resonant converters. Among them, the three-phase interleaved CLLC resonant converter not only possesses the excellent soft-switching capability inherent in resonant converters, enabling ZVS turn-on of the primary-side switch and ZCS turn-off of the secondary-side switch, but also exhibits stronger bidirectional energy transfer capability and wider voltage range regulation capability due to the symmetrical primary and secondary structure. With these advantages, the three-phase interleaved CLLC resonant converter is gradually replacing the traditional three-phase interleaved LLC resonant converter topology, becoming the preferred solution for medium- and high-power applications.

[0004] Three-phase interleaved CLLC resonant converters reduce the current stress on each phase switching device and lower the output current ripple by employing a three-phase topology, thereby reducing the size and cost of filter components. However, in a multi-phase interleaved parallel architecture, considering the manufacturing tolerances, temperature drift, and circuit parasitic parameters of each phase resonance parameter, there is an imbalance in the phase current, and there is a risk of unbalanced phase power distribution, which can lead to safety hazards such as local overheating and excessive device stress. Therefore, current sharing technology is needed to balance the phase current.

[0005] Existing phase-to-phase current sharing techniques for resonant converters can be broadly categorized into passive and active current sharing techniques. Passive current sharing relies on improvements to the hardware circuitry itself to achieve self-current sharing, primarily depending on magnetic circuit design. However, this method requires specific design for particular parameters, leading to complex and cumbersome implementation. Furthermore, magnetic design often results in increased size and cost, contradicting current demands for high power density. Active current sharing, on the other hand, introduces additional adjustment degrees of freedom, such as variable inductors, variable capacitors, and phase shift angles, to regulate phase-to-phase current balance without major circuit modifications. However, this approach also increases the cost and size of the hardware circuitry.

[0006] Therefore, it is evident that the application of three-phase CLLC resonant converters in high-power applications still faces considerable challenges. The issue of interphase current balancing has become a key bottleneck restricting its large-scale commercialization, urgently requiring the support of critical interphase current sharing control strategies. Summary of the Invention

[0007] In view of the shortcomings of related technologies, the purpose of this invention is to provide a system and a phase-to-phase current sharing control method for a three-phase interleaved CLLC resonant converter, which aims to solve the problem of phase-to-phase current balance when the three-phase CLLC resonant converter is applied to high-power applications.

[0008] To achieve the above objectives, the present invention provides a phase-to-phase current sharing control method for a three-phase interleaved CLLC resonant converter, comprising: Based on the operating state of the resonant converter, the effective values ​​of the three-phase current on the output side of the circuit structure are collected; wherein, when the resonant converter is running in the forward direction, the secondary side is the output side, and the effective values ​​of the three-phase current on the secondary side are collected; when the resonant converter is running in the reverse direction, the primary side is the output side, and the effective values ​​of the three-phase current on the primary side are collected. The included angle between the fundamental phasors of the three-phase current on the output side is set to 2π / 3, and the phase difference between the three-phase bridge arms on the input side of the resonant cavity is obtained based on the effective value of the three-phase current. The turn-on and turn-off times of the preset phase switch transistors on the fixed output side are calculated based on the phase difference to obtain the turn-on and turn-off times of the other two phase switch transistors on the output side, thereby obtaining the drive signals of the six switch transistors of the three-phase bridge arm on the output side. The switching transistor on the output side is controlled according to the driving signal to adjust the phase difference of the phasor of the resonant cavity output current so as to balance the current between each phase.

[0009] Optionally, when the resonant converter is in forward operation, the effective value of the three-phase current is I D , I E and I F The angles between the three-phase current phasors on the secondary side are expressed as follows:

[0010] in, I D , I E and I F These represent the secondary currents, respectively. i D , i E and i F The magnitude of the fundamental phasor.α DE , α EF and α FD These represent the secondary currents, respectively. i D , i E between, i E , i F Between and i F , i D The angle between the fundamental phasors.

[0011] Optionally, when the included angles between the fundamental phasors of the three-phase currents are all set to 2π / 3, the following is also included: The triangle of the three-phase current phasors is an equilateral triangle, and the output current is balanced.

[0012] Optionally, obtaining the phase difference between the three-phase bridge arms on the input side based on the effective value of the three-phase current includes: When the resonant converter is in forward operation, drive pulses are applied sequentially to the three-phase bridge arms A, B, and C on the primary side, with turn-on and turn-off occurring in a sequentially delayed manner. β AB , β BC , β CA In the initial case β AB , β BC , β CA All are set to 2 / 3π; The corrected turn-on and turn-off phase differences of the three-phase bridge arms A, B, and C on the primary side are:

[0013] Where, Δ β AB and Δ β BC Δ α DE and Δ α EF The correction value after PI tuning, Δ α DE for α DE The difference between 2π / 3 and Δ α EF for α EFThe difference between 2π / 3 and 2π / 3.

[0014] Optionally, obtaining the phase difference between the three-phase bridge arms on the input side based on the effective value of the three-phase current includes: When the resonant converter is running in reverse, drive pulses are applied sequentially to the three-phase bridge arms D, E, and F on the secondary side, with turn-on and turn-off occurring in a sequentially delayed manner. β DE , β EF , β FD In the initial case β DE , β EF , β FD All are set to 2 / 3π; The corrected turn-on and turn-off phase differences of the three-phase bridge arms D, E, and F on the secondary side are:

[0015] Where, Δ β DE and Δ β EF Δ α AB and Δ α BC The correction value after PI tuning, Δ α AB for α BC The difference between 2π / 3 and Δ α CA for α CA The difference between 2π / 3 and 2π / 3.

[0016] In a second aspect, the present invention provides a system for a three-phase interleaved CLLC resonant converter, comprising: a controller, a primary side unit, a secondary side unit, and a resonant network unit; The primary side unit includes three half-bridge structures with clamping diodes. The midpoints A, B, and C of the three half-bridge arms are respectively connected to the resonant inductor and resonant capacitor of the primary side of the resonant network. The secondary side unit includes three half-bridge structures with clamping diodes. The midpoints D, E, and F of the three half-bridge arms are respectively connected to the resonant inductor and resonant capacitor of the secondary side of the resonant network. The transformer of the resonant network unit adopts a star connection on both sides, with the resonant inductors and resonant capacitors on both sides connected in series on the primary and secondary sides of the transformer, respectively. The controller is used to execute the phase-to-phase current sharing control method of the three-phase interleaved CLLC resonant converter as described in any one of claims 1-5, and to control the switching transistors in the primary side unit and the secondary side unit.

[0017] Optionally, the transformer of the resonant network unit includes a transformer. T ra ,transformer T rb and transformer T rc All of them are high-frequency isolation transformers; The turns ratio of the transformers are all n :1, the excitation inductances are respectively L ma , L mb and L mc .

[0018] Optionally, the A-phase bridge arm of the primary-side unit is connected to the primary-side resonant inductor of the resonant network. L a1 and resonant capacitor C a1 ; The B-phase bridge arm of the primary side unit is connected to the primary resonant inductor of the resonant network. L b1 and resonant capacitor C b1 ; The C-phase bridge arm of the primary-side unit is connected to the primary-side resonant inductor of the resonant network. L c1 and resonant capacitor C c1 .

[0019] Optionally, the D-phase bridge arm of the secondary-side unit is connected to the secondary-side resonant inductor of the resonant network. L a2 and resonant capacitor C a2 ; The E-phase bridge arm of the secondary side unit is connected to the secondary resonant inductor of the resonant network. L b2 and resonant capacitor C b2 ; The F-phase bridge arm of the secondary unit is connected to the secondary resonant inductor of the resonant network. L c2 and resonant capacitor C c2 .

[0020] Compared with the prior art, the above-described technical solutions conceived in this invention can achieve the following beneficial effects: 1. This invention provides a phase-to-phase current sharing control method for a three-phase interleaved CLLC resonant converter topology. It acquires the effective values ​​of the three-phase currents on corresponding sides, sets the included angle of the fundamental phasors of the three-phase currents on corresponding sides to 2π / 3, and indirectly controls the phase difference between the output currents by adjusting the voltage of the input resonant cavity through phase shift control, thereby adjusting the current balance. Phase-to-phase current sharing control can be achieved simply by adding a sampling circuit to sample the effective values ​​of the phase-to-phase currents, resulting in minimal increase in cost and size, but significantly improving the phase-to-phase current balance.

[0021] 2. The present invention provides a system with a three-phase interleaved CLLC resonant converter topology, including a controller and a three-phase interleaved CLLC resonant converter circuit structure. This circuit structure has both excellent soft-switching characteristics and bidirectional power transmission capability, as well as small output filter volume and cost, making it very suitable for high-power applications. Attached Figure Description

[0022] Figure 1 This is a topology diagram of the three-phase interleaved CLLC resonant converter in an embodiment of the present invention; Figure 2 This is a phasor diagram of the input voltage and output current of the resonant cavity in the forward operation of the three-phase interleaved CLLC topology proposed in the embodiments of the present invention; wherein, (a) is the phasor diagram of the input voltage and output current of the resonant cavity without current sharing control; and (b) is the phasor diagram of the input voltage and output current of the resonant cavity with current sharing control. Figure 3 This is a control block diagram of the flow sharing control method proposed in this invention under forward operation conditions; Figure 4 This is a schematic diagram of the flow sharing control method proposed in this invention under forward operation conditions; Figure 5 This is a schematic diagram showing the relationship between the phase difference between the phase shift angles of the inverter bridge arms in the current sharing control method proposed in this invention; wherein, (a) is a schematic diagram of the phase voltage when there is no phase shift at the midpoint voltage of the bridge arm; (b), (c), and (d) are respectively the phase shift Δ of the midpoint voltage of the A-phase bridge arm, the B-phase bridge arm, and the C-phase bridge arm. θ The effect on the phase difference of the interphase current phasors in the resonant cavity; Figure 6 This is a schematic diagram showing the phase difference between the output current phasors of the resonant cavity in the current sharing control method proposed in this invention; wherein, (a) is the phase difference between the three-phase current phasors on the output side. α DE , α EF and α FD Phase shift Δ with phase A bridge arm θ and normalized switching frequency ω n (a) Relationship diagram; (b) Phase difference of the three-phase current phasors on the output side. α DE , α EF and α FD Phase shift Δ with phase B bridge arm θ and normalized switching frequency ω n Relationship diagram; (c) shows the phase difference of the three-phase current phasors on the output side. α DE , α EF and α FD Phase shift Δ with phase C bridge arm θ and normalized switching frequency ω n Relationship diagram; Figure 7 The diagrams show the phase-to-phase current waveforms before and after applying the current sharing control method proposed in this invention under forward operation; (a), (b), (c), and (d) are schematic diagrams under different parameters. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0024] The following description, in conjunction with a preferred embodiment, illustrates the content involved in the above embodiments.

[0025] This invention provides a method for phase-to-phase current sharing control of a three-phase interleaved CLLC resonant converter, comprising: Based on the operating state of the resonant converter, the effective values ​​of the three-phase current on the output side of the circuit structure are collected; wherein, when the resonant converter is running in the forward direction, the secondary side is the output side, and the effective values ​​of the three-phase current on the secondary side are collected; when the resonant converter is running in the reverse direction, the primary side is the output side, and the effective values ​​of the three-phase current on the primary side are collected. The included angle between the fundamental phasors of the three-phase current on the output side is set to 2π / 3, and the phase difference between the three-phase bridge arms on the input side of the resonant cavity is obtained based on the effective value of the three-phase current. By fixing the turn-on and turn-off times of the preset phase switch transistors on the output side, and calculating the turn-on and turn-off times of the other two phase switch transistors on the output side based on the phase difference, the drive signals for the six switch transistors of the three-phase bridge arm on the output side are obtained. g 11 - g 32 ; The switching transistor on the output side is controlled according to the driving signal to adjust the phase difference of the phasor of the resonant cavity output current so as to balance the current between each phase.

[0026] The phase-to-phase current sharing control method provided in this embodiment of the invention is applied to a three-phase interleaved CLLC resonant converter. Specifically, refer to... Figure 1 The primary-side unit of the three-phase interleaved CLLC resonant converter topology consists of three half-bridge structures with clamping diodes. The midpoints A, B, and C of the three half-bridge arms are connected to the primary-side resonant inductor of the resonant network, respectively. L a1 and resonant capacitor C a1 Primary resonant inductor L b1 and resonant capacitor C b1 Primary resonant inductor L c1 and resonant capacitor C c1 The secondary-side unit consists of three half-bridge structures with clamping diodes. The midpoints D, E, and F of the three half-bridge arms are connected to the secondary-side resonant inductor of the resonant network, respectively. L a2 and resonant capacitor C a2 Secondary resonant inductor L b2 and resonant capacitor C b2 Secondary resonant inductor L c3 and resonant capacitor C c3 The primary and secondary units are connected by a resonant network unit. The transformer containing this resonant network unit uses a star connection on both sides. Simultaneously, the resonant inductors and capacitors on both sides are connected in series on the primary and secondary sides of the transformer, respectively. T ra , T rb and T rc It is a high-frequency isolation transformer with a turns ratio of [missing information]. n :1, the excitation inductances are respectively L ma ,L mb and L mc In a three-phase interleaved CLLC topology, the current stress of each phase switch is one-third of the total current, which is beneficial for device selection in high-power applications.

[0027] Due to the existence of resonant parameter tolerance, temperature drift differences, and circuit parasitic parameters (mainly leakage inductance of high-frequency transformers), three-phase interleaved CLLC resonant converters exhibit phase-to-phase current imbalance, which endangers the safe operation of the resonant converter. At this time, relying solely on frequency conversion control cannot adjust the phase-to-phase current, and other control degrees of freedom need to be introduced to balance the phase-to-phase current.

[0028] Depending on the operating state of the resonant converter, the specific operation of the phase-to-phase current sharing control method will also be different.

[0029] Figure 2 This is a phasor diagram of the input voltage and output current of the resonant cavity in the forward operation of the three-phase interleaved CLLC topology proposed in this invention. Figure 2 (a) is the phasor diagram of the input voltage and output current of the resonant cavity without current sharing control. At this time, due to the existence of resonant parameter tolerance, temperature drift difference and circuit parasitic parameters, the actual resonant parameters of each phase are not equal. This further leads to a serious phase deviation of the output current from 2 / 3π when the input voltage phase difference is maintained at 2 / 3π, resulting in a serious current imbalance. Figure 2 (b) is a phasor diagram of the input voltage and output current of the resonant cavity using current sharing control. At this time, the phase difference of the output current is indirectly adjusted by adjusting the phase difference of the input voltage, so that the phase difference of the output current is restored to 2 / 3π, thereby ensuring the current balance of the output current.

[0030] refer to Figure 1 Analyzing the forward operation, for a three-phase resonant unit, according to Kirchhoff's current theorem, the secondary current... i D , i E and i F Since the current flows into the same generalized node, the three are linearly correlated, and it's easy to see that they only have two independent components. Therefore, theoretically, current sharing control only requires two independent control degrees of freedom. The primary input voltage... v AB , v BC and v CAIt is easy to see that all three are linearly correlated, with only two independent components, which provides exactly two degrees of freedom for control. Therefore, current sharing control can be achieved by adjusting the phase-to-phase current through controlling the input voltage. In this embodiment of the invention, the primary-side input voltage is controlled by controlling the on- and off-time of the primary-side bridge arm. v AB , v BC and v CA The phase relationship is such that the midpoint of each bridge arm still outputs 50% of the square wave, but the phase difference between each bridge arm fluctuates around 2 / 3π, that is, the current sharing control is achieved through phase shift control.

[0031] When the resonant converter is operating in the forward direction, since the secondary currents flow into the same generalized node, the secondary current phasors can be connected end-to-end to form a phasor triangle. When the phasor triangle is an equilateral triangle, the secondary current phasors are equal in magnitude, and the angle between any two current phasors is 2 / 3π. Therefore, by controlling the angle between the primary voltage phasors, the angle between the secondary current phasors is indirectly controlled, thus achieving current sharing control.

[0032] According to the law of cosines, the effective value of the three-phase current on the secondary side is I D , I E and I F The angles between the secondary current phasors are respectively (1) In the formula, I D , I E and I F These represent the secondary currents, respectively. i D , i E and i F The magnitude of the fundamental phasor is used instead of its effective value in this invention. α DE Indicates secondary current i D and i E The angle between the fundamental phasors; α EF express i E and i F The angle between the fundamental phasors; α FD expressi F and i D The angle between the fundamental phasors; when α DE and α EF When both are 2π / 3, the phasor triangle of the secondary current is an equilateral triangle, and the secondary current must be in equilibrium.

[0033] Pick α DE and α EF The difference between 2π / 3 and Δ α DE and Δ α EF ; (2) Assume that switching pulses are applied sequentially to the primary side arms, causing the opening and closing of arms A, B, and C to be delayed sequentially. β AB , β BC , β CA When this switching sequence is followed, initially... β AB , β BC , β CA Both are 2 / 3π. After adopting PI control, the corrected turn-on and turn-off phase difference of the three-phase bridge arms A, B, and C on the primary side is: (3) In the formula, Δ β AB and Δ β BC Δ α DE and Δ α EF The correction value after PI tuning, Δ α DE for α DE The difference between 2π / 3 and Δ α EF for α EF The difference between 2π / 3 and 2π / 3. , , These are the corrected turn-on and turn-off phase differences of bridge arms A, B, and C, respectively. The turn-on and turn-off times of phase A are fixed. and Substitute the values ​​into the calculation to obtain the activation times of bridge arm B and bridge arm C, thereby realizing the active current sharing strategy.

[0034] Figure 3 This is the control block diagram of the current sharing control method proposed in this invention under forward operation. The current values ​​in the diagram are the sampled effective values, and the phase difference between the actual current phasors at this time is calculated using formula (1). α EF and α FD Then, subtract this phase difference from 2 / 3π to obtain the actual current phase difference Δ that needs to be compensated. α EF and Δ α FD After PI tuning, the result is obtained θ EF and θ FD Then, the phase difference of each phase loaded onto the primary side arm at this time is calculated by formula (3).

[0035] Figure 4 This is a schematic diagram of the current sharing control method proposed in this invention under forward operation. Without the current sharing control method, the input bridge arm phase difference remains at 2 / 3π. When the current sharing control method proposed in this invention is used, the on / off time of phase A bridge arm is fixed, and the phase difference between phase A and phase B bridge arms is changed to... The phase difference between phase B and phase C is At this time, the phase difference between phase C arm and phase A arm automatically changes. .

[0036] Figure 5 and Figure 6 This is a schematic diagram showing the relationship between the phase shift angle of the inverter bridge arm and the phase difference between the phasor of the resonant cavity output current in the current sharing control method proposed in this invention. Figure 5 Part (a) is a schematic diagram of the phase voltages when there is no phase shift at the midpoint of the bridge arm. Figure 5 Figures (b), (c), and (d) respectively examine the phase shift Δ of the midpoint voltage of phase A, phase B, and phase C bridge arms. θ The effect on the phase difference of the interphase current phasors in the resonant cavity. (See figure) β AB , β BC and β CA These represent the phase difference of the voltage at the midpoint between the bridge arms, which ideally are both 2 / 3π. , and Let Δ represent the phase difference between the voltages of the bridge arms after phase shifting. Simultaneously, define the leading shift of the voltage phasor at the midpoint of the bridge arm, i.e., when the voltage phasor at the midpoint of the bridge arm rotates counterclockwise, Δ... θ If positive, then Δ θ It is a negative value.

[0037] Figure 6 Part (a) shows the phase difference of the three-phase current phasors on the output side. α DE , α EF and α FD Phase shift Δ with phase A bridge arm θ and normalized switching frequency ω n The relationship can be seen α DE , α EF and α FD Basically does not depend on frequency ω n It changes with Δ. θ When changing from -π / 6 to π / 6 α DE Increase α EF Almost unchanged, α FD Decrease. Simultaneously, when Δ θ When changing from -π / 6 to π / 6 Gradually increase constant, Gradually decrease.

[0038] Figure 6 Part (b) provides the phase difference of the three-phase current phasors on the output side. α DE , α EF and α FD Phase shift Δ with phase B bridge arm θ and normalized switching frequency ω n The relationship shows that when the B-phase bridge arm shifts by Δθ, and Δθ changes from -π / 6 to π / 6, α DE Decrease α EF Increase α FD It remains almost unchanged. Meanwhile, when Δθ changes from -π / 6 to π / 6, Gradually decrease, Gradually increase constant.

[0039] Figure 6 Section (c) provides the phase difference of the three-phase current phasors on the output side. α DE , α EF and α FD Phase shift Δ with phase C bridge arm θ and normalized switching frequency ω n The relationship is as follows: when the C-phase bridge arm shifts by Δθ, and Δθ changes from -π / 6 to π / 6... α DE Almost unchanged, α EF Decrease α FD It increases. Simultaneously, as Δθ changes from -π / 6 to π / 6... constant, Gradually decrease, Gradually increase.

[0040] In one specific embodiment, the rated power of the circuit is 10kW, and the primary bus voltage is guaranteed to be... V =1=400V, secondary voltage is 300V~400V. Transformer turns ratio is 2, ideally the primary side resonant inductance of each phase is ( L a1 , L b1 , L c1 The size is 10μH, and the resonant capacitance is ( C a1 , C b1 , C c1 The value is 253nF, and the secondary resonant inductor ( L a2 , L b2 , L c2 The size is 10μH, and the resonant capacitance is ( C a2 , C b2 , C c2 The value is 253nF, and the transformer magnetizing inductance is ( L ma , L mb , L mc The size is 40μH, and the ideal resonant frequency is 100kHz.

[0041] Figure 7 The diagram shows the phase-to-phase current waveforms before and after applying the current sharing control method proposed in this invention under forward operation.

[0042] Figure 7 In (a) and (b), the parameters of the primary resonant inductance of phase A are considered. L a1 With a +20% tolerance, the secondary voltage is 400V, the average output current is 24A, and the switching frequency is... f s It is 80kHz. (By...) Figure 5 As can be seen in (a), when the current sharing control method is not used, the effective values ​​of the three-phase resonant currents are 20.0A, 17.1A, and 18.5A, respectively, with an output current ripple of 7A, indicating a severe imbalance in the phase-to-phase currents. Figure 5 As can be seen in (b), when the current sharing control method is adopted, the effective values ​​of the three-phase resonant currents are 18.4A, 18.4A and 18.6A, respectively, the output current ripple is reduced to 4A, and the phase current imbalance is effectively suppressed.

[0043] Figure 7 Considering the primary resonant inductance parameters of phase A in (c) and (d) of section 6 L a1 With a +20% tolerance, the secondary voltage is 300V, the average output current is 32A, and the switching frequency is... f s It is 120kHz. (By...) Figure 5 As can be seen in (c), when the current sharing control method is not used, the effective values ​​of the three-phase resonant currents are 22.0A, 24.3A and 24.5A, respectively, the output current ripple reaches 9A, and the phase current is seriously unbalanced.

[0044] Depend on Figure 5 As can be seen in (d), when the current sharing control method is adopted, the effective values ​​of the three-phase resonant currents are 23.5A, 23.5A and 23.6A, respectively, the output current ripple is reduced to 7A, and the phase current imbalance is effectively suppressed.

[0045] Furthermore, in an alternative embodiment, the effective values ​​of the three-phase currents on the primary side are acquired when the resonant converter is operating in reverse. Primary side currents i A , i B and i C If currents flow into the same generalized node, the primary-side current phasors can be connected end-to-end to form a phasor triangle. The secondary-side input voltage is controlled by adjusting the turn-on and turn-off times of the secondary-side bridge arms. v DE , vEF and v FD The size of the primary side current is adjusted accordingly. i A , i B and i C This enables phase-to-phase flow sharing control.

[0046] When the resonant converter is running in reverse, drive pulses are applied sequentially to the three-phase bridge arms D, E, and F on the secondary side, with turn-on and turn-off occurring in a sequentially delayed manner. β DE , β EF , β FD In the initial case β DE , β EF , β FD All are set to 2 / 3π; The corrected turn-on and turn-off phase differences of the three-phase bridge arms D, E, and F on the secondary side are:

[0047] Where, Δ β DE and Δ β EF Δ α AB and Δ α BC The correction value after PI tuning, Δ α AB for α BC The difference between 2π / 3 and Δ α CA for α CA The difference between 2π / 3 and 2π / 3.

[0048] , , These are the corrected turn-on and turn-off phase differences of bridge arms D, E, and F, respectively. The turn-on and turn-off times of phase D are fixed. and Substitute the values ​​into the calculation to obtain the activation times of bridge arm E and bridge arm F, thereby realizing the active current sharing strategy.

[0049] The current sharing control method described above, which indirectly controls the phase difference between currents by controlling the phase difference between the input side bridge arms, is simple and feasible. It can significantly improve the phase current balance of the converter, thereby improving the phase power balance characteristics.

[0050] The above control method only considers the application of three-phase two-sided star-connected interleaved CLLC resonant converters, but this control method can undoubtedly be extended to applications of three-phase two-sided delta-connected interleaved LLC resonant converters.

[0051] This invention, based on the operating state of the resonant converter, acquires the effective values ​​of the three-phase currents on the output side, sets the angle between the fundamental phasors of the three-phase currents on the output side to 2π / 3, and indirectly controls the phase difference between the currents on the output side by adjusting the voltage of the input resonant cavity through phase shift control, thereby adjusting the current balance. This solves the phase-to-phase current balance problem that exists when three-phase CLLC resonant converters are applied to high-power applications. Phase-to-phase current sharing control can be achieved simply by adding a sampling circuit to sample the effective values ​​of the phase-to-phase currents, resulting in a very small increase in cost and size, but significantly improving the phase-to-phase current balance.

[0052] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for phase-to-phase current sharing control of a three-phase interleaved CLLC resonant converter, characterized in that, include: Based on the operating state of the resonant converter, the effective values ​​of the three-phase current on the output side of the circuit structure are collected; wherein, when the resonant converter is running in the forward direction, the secondary side is the output side, and the effective values ​​of the three-phase current on the secondary side are collected; when the resonant converter is running in the reverse direction, the primary side is the output side, and the effective values ​​of the three-phase current on the primary side are collected. The included angle between the fundamental phasors of the three-phase current on the output side is set to 2π / 3, and the phase difference between the three-phase bridge arms on the input side of the resonant cavity is obtained based on the effective value of the three-phase current. The turn-on and turn-off times of the preset phase switch transistors on the fixed output side are calculated based on the phase difference to obtain the turn-on and turn-off times of the other two phase switch transistors on the output side, thereby obtaining the drive signals of the six switch transistors of the three-phase bridge arm on the output side. The switching transistor on the output side is controlled according to the driving signal to adjust the phase difference of the phasor of the resonant cavity output current so as to balance the current between each phase.

2. The method as described in claim 1, characterized in that, When the resonant converter is in forward operation, the effective value of the three-phase current is I D , I E and I F The angles between the three-phase current phasors on the secondary side are expressed as follows: in, I D , I E and I F These represent the secondary currents, respectively. i D , i E and i F The magnitude of the fundamental phasor; α DE , α EF and α FD These represent the secondary currents, respectively. i D , i E between, i E , i F Between and i F , i D The angle between the fundamental phasors.

3. The method as described in claim 1, characterized in that, When the angle between the fundamental phasors of the three-phase currents is set to 2π / 3, it also includes: The triangle of the three-phase current phasors is an equilateral triangle, and the output current is balanced.

4. The method as described in claim 1, characterized in that, The method of obtaining the phase difference between the three-phase bridge arms on the input side based on the effective value of the three-phase current includes: When the resonant converter is in forward operation, drive pulses are applied sequentially to the three-phase bridge arms A, B, and C on the primary side, with turn-on and turn-off occurring in a sequentially delayed manner. β AB , β BC , β CA In the initial case β AB , β BC , β CA All are set to 2 / 3π; The corrected turn-on and turn-off phase differences of the three-phase bridge arms A, B, and C on the primary side are: Where, Δ β AB and Δ β BC Δ α DE and Δ α EF The correction value after PI tuning, Δ α DE for α DE The difference between 2π / 3 and Δ α EF for α EF The difference between 2π / 3 and 2π / 3.

5. The method as described in claim 1, characterized in that, The method of obtaining the phase difference between the three-phase bridge arms on the input side based on the effective value of the three-phase current includes: When the resonant converter is running in reverse, drive pulses are applied sequentially to the three-phase bridge arms D, E, and F on the secondary side, with turn-on and turn-off occurring in a sequentially delayed manner. β DE , β EF , β FD In the initial case β DE , β EF , β FD All are set to 2 / 3π; The corrected turn-on and turn-off phase differences of the three-phase bridge arms D, E, and F on the secondary side are: Where, Δ β DE and Δ β EF Δ α AB and Δ α BC The correction value after PI tuning, Δ α AB for α BC The difference between 2π / 3 and Δ α CA for α CA The difference between 2π / 3 and 2π / 3.

6. A system of a three-phase interleaved CLLC resonant converter, characterized in that, include: Controller, primary side unit, secondary side unit, and resonant network unit; The primary side unit includes three half-bridge structures with clamping diodes. The midpoints A, B, and C of the three half-bridge arms are respectively connected to the resonant inductor and resonant capacitor of the primary side of the resonant network. The secondary side unit includes three half-bridge structures with clamping diodes. The midpoints D, E, and F of the three half-bridge arms are respectively connected to the resonant inductor and resonant capacitor of the secondary side of the resonant network. The transformer of the resonant network unit adopts a star connection on both sides, with the resonant inductors and resonant capacitors on both sides connected in series on the primary and secondary sides of the transformer, respectively. The controller is used to execute the phase-to-phase current sharing control method of the three-phase interleaved CLLC resonant converter as described in any one of claims 1-5, and to control the switching transistors in the primary side unit and the secondary side unit.

7. The system as described in claim 6, characterized in that, The transformer of the resonant network unit includes a transformer. T ra ,transformer T rb and transformer T rc All of them are high-frequency isolation transformers; The turns ratio of the transformers are all n :1, the excitation inductances are respectively L ma , L mb and L mc .

8. The system as described in claim 1, characterized in that, The A-phase bridge arm of the primary-side unit is connected to the primary-side resonant inductor of the resonant network. L a1 and resonant capacitor C a1 ; The B-phase bridge arm of the primary side unit is connected to the primary resonant inductor of the resonant network. L b1 and resonant capacitor C b1 ; The C-phase bridge arm of the primary-side unit is connected to the primary-side resonant inductor of the resonant network. L c1 and resonant capacitor C c1 .

9. The system as described in claim 1, characterized in that, The D-phase bridge arm of the secondary unit is connected to the secondary resonant inductor of the resonant network. L a2 and resonant capacitor C a2 ; The E-phase bridge arm of the secondary side unit is connected to the secondary resonant inductor of the resonant network. L b2 and resonant capacitor C b2 ; The F-phase bridge arm of the secondary unit is connected to the secondary resonant inductor of the resonant network. L c2 and resonant capacitor C c2 .

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