Current Sharing Method and Device for Interleaved Parallel LLC Resonant Converter

Abstract

In view of the deficiencies of the existing current sharing technology, the present invention proposes a novel current sharing method and device for a multi-phase interleaved LLC resonant converter. The multi-phase interleaved LLC resonant converter device includes: a multi-phase interleaved LLC resonant converter composed of N half-bridge LLC resonant converter modules, N*(N-1) / 2 active impedance balancing units, and a controller, where N is equal to 2 or 3. The active impedance balancing units are respectively connected in series between every two-phase LLC resonant converter modules. The first end and the second end of the active impedance balancing unit form a loop with the resonant capacitors of the two-phase LLC resonant converter modules connected thereto and the primary ground. By changing the equivalent impedance of the active impedance balancing unit connected in series between each phase LLC resonant converter module, the output current of each phase LLC resonant converter module is not affected by the parameter deviation of the resonant elements, and the output current sharing of the multi-phase interleaved LLC resonant converter can be realized.

Description

Technical Field

[0001] The present invention belongs to the switching power supply technology in the field of power electronics, and relates to a current sharing method and device for a novel multi-phase interleaved parallel LLC resonant converter. Background Art

[0002] LLC resonant converters have been widely used in applications where high converter efficiency, power density, etc. are required due to their advantages such as high efficiency, low EMI, and high power density. In applications with high power and large current, converters are required to have larger capacity, higher power density, and lower losses. Obviously, single-phase LLC resonant converters can no longer meet the requirements. Therefore, multi-phase interleaved parallel LLC resonant converters are usually adopted to reduce the output current ripple and increase the output power.

[0003] However, since the voltage gain of LLC resonant converters is closely related to the parameters of resonant devices, in a multi-phase parallel system in practical applications, due to problems such as manufacturing process deviations and parameter changes caused by environmental variations, there will inevitably be differences among the resonant elements, which will in turn lead to large deviations in the voltage gain among the parallel phases, resulting in different magnitudes of load currents output by each phase of the resonant converter, which will seriously affect the efficiency, reliability, and service life of the entire system.

[0004] To effectively solve the problem of uneven current sharing among the phases of multi-phase interleaved parallel LLC resonant converters and at the same time improve the conversion efficiency and reliability of the entire system, proposing an effective solution to the current sharing problem of multi-phase LLC resonant converters is a very practical and challenging task. Summary of the Invention

[0005] In view of the deficiencies of the existing current sharing technology, the present invention proposes a current sharing method and device for a novel interleaved parallel LLC resonant converter.

[0006] The steps of the current sharing method for the interleaved parallel LLC resonant converter of the present invention are as follows:

[0007] Step 1: During the startup process of the converter, by detecting and comparing the magnitudes of the output currents of each phase, determine the leading and lagging relationships between the modules through the control circuit: successively take the module with a larger output current as the leading phase and the module with a smaller output current as the lagging phase, and control the phase difference of each phase of the LLC resonant converter module to obtain a better current output ripple cancellation effect: that is, when the number of parallel modules N = 2, control the phase difference of the LLC resonant converter module to be 90°, and when the number of parallel modules N = 3, control the phase difference of the LLC resonant converter module to be 60° or 120°.

[0008] Step 2: After the converter enters the steady state, adjust the frequencies of each phase LLC resonant converter module synchronously according to the output voltage feedback information or the output total current information to achieve output voltage regulation or output total current regulation. At the same time, adjust the equivalent impedance of the corresponding active impedance balancing unit according to the output current deviation of every two-phase LLC resonant converter modules to achieve current sharing among the output currents of each phase LLC resonant converter module.

[0009] The implementation device obtained by the current sharing method of the multi-phase interleaved parallel LLC resonant converter proposed by the present invention includes:

[0010] A multi-phase interleaved parallel LLC resonant converter composed of N half-bridge LLC resonant converter modules, N*(N - 1) / 2 active impedance balancing units, and a controller, where N is equal to 2 or 3. The active impedance balancing units are respectively connected in series between every two-phase LLC resonant converter modules. The first end and the second end of the active impedance balancing unit form a loop with the resonant capacitors of the two-phase LLC resonant converter modules connected thereto and the primary ground.

[0011] Preferably, the active impedance balancing unit includes an auxiliary inductor, an auxiliary capacitor, and a bidirectional switch composed of two MOS transistors. The first end of the auxiliary inductor is the first end of the active impedance balancing unit. The second end of the auxiliary inductor is connected to the first end of the auxiliary capacitor. The second end of the auxiliary capacitor is connected to the first end of the bidirectional switch. The second end of the bidirectional switch is the second end of the active impedance balancing unit.

[0012] The controller controls each phase LLC resonant converter module and the active impedance balancing unit: According to the detection and comparison of the magnitudes of the output currents of different phases during the startup process, determine the leading and lagging relationships between the modules, that is, sequentially take the module with the larger output current as the leading phase and the module with the smaller output current as the lagging phase, and control the phase difference of each phase LLC resonant converter module to obtain an optimized current output ripple cancellation effect. After the converter enters the steady-state operation, adjust the frequencies of each phase LLC resonant converter module synchronously according to the output voltage feedback information or the output total current information to achieve output voltage regulation or output total current regulation. At the same time, adjust the phase difference between the driving signal of the bidirectional switch in the corresponding active impedance balancing unit and the voltage across the active impedance balancing unit according to the output current deviation of every two-phase LLC resonant converter modules to achieve current sharing among the output currents of each phase LLC resonant converter module.

[0013] Preferably, the active impedance balancing unit includes a coupling inductor and a controllable current source; two ends of the first winding of the coupling inductor form the first end and the second end of the active impedance balancing unit, and the controllable current source and the second winding of the coupling inductor form a loop; the controller controls each phase LLC resonant converter module and the active impedance balancing unit: according to the detected and compared magnitudes of the output currents of different phases during the startup process, determine the leading and lagging relationships between the modules, that is, sequentially take the module with the larger output current as the leading phase and the module with the smaller output current as the lagging phase, and control the phase difference of each phase LLC resonant converter module to obtain an optimized current output ripple cancellation effect; after the converter enters the steady-state operation, adjust the frequencies of each phase LLC resonant converter module synchronously according to the output voltage feedback information or the output total current information to achieve output voltage regulation or output total current constant current, and at the same time, respectively adjust the magnitudes of the controllable current sources in the corresponding active impedance balancing units according to the output current deviations of every two-phase LLC resonant converter modules to achieve equal current sharing of the output currents of each phase LLC resonant converter module.

[0014] Specifically, the basic principle of the present invention is: when there is a situation where the resonant parameters in the N-phase interleaved parallel LLC resonant converter are inconsistent, the control circuit is used to change the equivalent impedance of the active impedance balancing unit connected in series between each phase LLC resonant converter module, so that the equivalent resonant parameters of each phase LLC resonant converter module return to be consistent again, thereby eliminating the current sharing error caused by the deviation of the resonant element parameters between each phase and realizing current sharing of the output of the multi-phase interleaved parallel LLC resonant converter.

[0015] The beneficial effects of the present invention are as follows: By changing the equivalent impedance of the active impedance balancing unit connected in series between each phase LLC resonant converter module, the output current of each phase LLC resonant converter module is not affected by the deviation of the resonant element parameters, and current sharing of the output of the multi-phase interleaved parallel LLC resonant converter can be realized. The active impedance balancing unit is independently controlled, does not affect the normal operation of each phase converter and the original phase shift angle, and can achieve an optimized output current ripple cancellation effect. The active impedance balancing unit processes a small amount of energy and has little impact on the converter efficiency. Description of the Drawings

[0016] Figure 1 Shows the flowchart of the current sharing method of the interleaved parallel LLC resonant converter of the present invention;

[0017] Figure 2 Shows the schematic diagram of the interleaved parallel LLC resonant converter device of the present invention;

[0018] Figure 3 Shows the simplified AC circuit model of the two-phase LLC resonant converter of the present invention based on the fundamental wave approximation method;

[0019] Figure 4 Shows the simplified AC circuit model of the two-phase LLC resonant converter of the present invention after the △->Y transformation;

[0020] Figure 5 Shows the voltage gain curve of a traditional two-phase interleaved LLC resonant converter when the resonant parameters of the two-phase modules are asymmetric;

[0021] Figure 6 Shows the voltage gain curve of the two-phase interleaved LLC resonant converter of the present invention when the resonant element parameters of the two-phase modules are asymmetric;

[0022] Figure 7 Shows the first specific embodiment of the active impedance balancing unit adopted by the present invention;

[0023] Figure 8 Shows Figure 7 The key waveforms in the active impedance balancing unit shown;

[0024] Figure 9 Shows based on Figure 7 The controller of the interleaved LLC resonant converter of the present invention with the active impedance balancing unit shown;

[0025] Figure 10 Shows the second specific embodiment of the active impedance balancing unit adopted by the present invention;

[0026] Figure 11 Shows the equivalent impedance L of the active impedance balancing unit of the second specific embodiment of the active impedance balancing unit adopted by the present invention sci Following the controllable current source IDC i The curve of the amplitude change;

[0027] Figure 12 Shows based on Figure 10 The controller of the interleaved LLC resonant converter of the present invention with the active impedance balancing unit shown. Detailed implementation mode

[0028] The well-known implementation modes and operation means are not described in detail herein to avoid confusing the various technical implementation schemes of the present invention. However, for those skilled in the art, the lack of one or more specific details or components does not affect the understanding and implementation of the present invention.

[0029] Refer to Figure 1 , the steps of the current sharing method of the multi-phase interleaved LLC resonant converter of the present invention are as follows:

[0030] Step 1: During the startup process of the converter, by detecting and comparing the magnitudes of the output currents of each phase, the leading-lagging relationship between the modules is determined through the control circuit: the module with the larger output current is sequentially taken as the leading phase, and the module with the smaller output current is taken as the lagging phase, and the phase difference of each phase LLC resonant converter module is controlled to obtain an optimized current output ripple cancellation effect: that is, when the number of parallel modules N = 2, the phase difference of the LLC resonant converter module is controlled to 90°, and when the number of parallel modules N = 3, the phase difference of the LLC resonant converter module is controlled to 60° or 120°.

[0031] Step 2: After the converter enters the steady state, the frequencies of each phase LLC resonant converter module are synchronously adjusted according to the output voltage feedback information or the output total current information to achieve output voltage regulation or output total current regulation. At the same time, the equivalent impedance of the corresponding active impedance balancing unit is adjusted respectively according to the output current deviation of every two-phase LLC resonant converter modules fed back, so as to achieve equal current sharing of the output currents of each phase LLC resonant converter module.

[0032] According to the current sharing method of the present invention described above, the schematic diagram of the implementation device of the multi-phase interleaved parallel LLC resonant converter of the present invention can be obtained as Figure 2 shown in the following, including:

[0033] A multi-phase interleaved parallel LLC resonant converter composed of N half-bridge LLC resonant converter modules, N*(N - 1) / 2 active impedance balancing units and a controller, where N is equal to 2 or 3, and the active impedance balancing units are respectively connected in series between every two-phase LLC resonant converter modules; further, the first end and the second end of the active impedance balancing unit form a loop with the resonant capacitors of the two-phase LLC resonant converter modules connected thereto and the primary ground.

[0034] The controller controls each phase LLC resonant converter module and the active impedance balancing unit: during the startup process, by detecting and comparing the magnitudes of the output currents of each phase, the leading-lagging relationship between the modules is determined, that is, the module with the larger output current is sequentially taken as the leading phase, and the module with the smaller output current is taken as the lagging phase, and the phase difference of each phase LLC resonant converter module is controlled to obtain an optimized current output ripple cancellation effect, that is, when the number of parallel modules N = 2, the phase difference of the LLC resonant converter module is controlled to 90°, and when the number of parallel modules N = 3, the phase difference of the LLC resonant converter module is controlled to 60° or 120°; during steady-state operation, the frequencies of each phase LLC resonant converter module are synchronously adjusted according to the output voltage feedback information or the output total current information to achieve output voltage regulation or output total current regulation. At the same time, the equivalent impedance of the corresponding active impedance balancing unit is adjusted respectively according to the output current deviation of every two-phase LLC resonant converter modules fed back, so as to achieve equal current sharing of the output currents of each phase LLC resonant converter module.

[0035] To illustrate the basic principle of the present invention, a two-phase LLC resonant converter module with an active impedance balancing unit is taken as an example. Figure 3 Its simplified AC circuit model based on the fundamental wave approximation method is shown. Among them, one phase of the module leads the other phase by 90° to obtain a better output current ripple cancellation effect, and the equivalent impedance of the active impedance balancing unit is represented by a variable inductor L. sc It is represented.

[0036] By observing Figure 3 it can be seen that the resonant capacitors C r1 , C r2 and the variable inductor L sc constitute a triangular impedance network. To further simplify the analysis, a Δ->Y transformation is performed on this impedance network, as Figure 4 shown. Through derivation, the impedances Z C , Z D and Z G of the corresponding branches after the Δ->Y transformation can be obtained, and their corresponding expressions are shown in formulas (1)-(3) respectively.

[0037]

[0038]

[0039]

[0040] Applying Kirchhoff's first law of current to the center point Z, formula (4) can be obtained:

[0041]

[0042] Among them, and are the relative equivalent AC input voltages of module one and module two respectively;

[0043] and are the equivalent AC output resistances of each module respectively, is the voltage of the center point Z. According to formula (4), the expression of can be solved as shown in formula (5):

[0044]

[0045] Furthermore, according to the equivalent circuit shown in Figure 4 , the equivalent AC output voltage expressions of module one and module two are obtained as shown in formulas (6) and (7) respectively:

[0046]

[0047]

[0048] Substitute ands = j2πf s into expressions (6) and (7), and the input-output voltage gain expressions G z1 (f s , L sc , I o1 , I o2 ) and G z2 (f s , L sc , I o1 , I o2 ) of Module 1 and Module 2 of the interleaved LLC resonant converter with an active impedance balancing unit according to the present invention can be derived, as shown in (8) and (9).

[0049]

[0050]

[0051] For comparison, Figure 5 shows the voltage gain curves of a traditional two-phase interleaved LLC resonant converter when the resonant parameters of the two-phase modules are asymmetric, where G1 is the voltage gain curve of Module 1, G2 is the voltage gain curve of Module 2, and G c is the target voltage gain. It can be seen that at the target voltage gain, there is no intersection between the two voltage gain curves G1 and G2, which means that the traditional two-phase interleaved LLC resonant converter cannot achieve current sharing when the resonant parameters of the two phases are asymmetric.

[0052] Figure 6 shows the voltage gain curves of the two-phase interleaved LLC resonant converter according to the present invention obtained based on formulas (8) and (9) when the resonant element parameters of the two-phase modules are asymmetric, where G Z1 is the voltage gain curve of Module 1, and G Z2 is the voltage gain curve of Module 2. It can be seen that after introducing the active impedance balancing unit, the equivalent impedance of the two-phase modules is changed, thereby changing the voltage gains of the two-phase modules, so that the gain curves of the two can intersect at the target voltage gain, thus achieving current sharing between the two-phase modules.

[0053] Figure 7 shows the first specific embodiment of the active impedance balancing unit adopted by the present invention, including an auxiliary inductor L ai , an auxiliary capacitor C ai , MOS transistors Q ai1 and MOS transistor Q ai2A bidirectional switch is formed. Here, i represents the sequence, that is, the i-th active impedance balancing unit. The auxiliary inductor L ai The first end of is used as the first end IN of the active impedance balancing unit i and its second end is connected to the first end of the auxiliary capacitor C ai The second end of the auxiliary capacitor C ai is connected to the drain of the MOS transistor Q ai1 The source of the MOS transistor Q ai1 is connected to the source of the MOS transistor Q ai2 The drain of the MOS transistor Q ai2 is used as the second end OUT of the active impedance balancing unit i ;

[0054] Figure 8 shows Figure 7 the key waveforms in the active impedance balancing unit shown in ai where i cdi is the current flowing through the active impedance balancing unit, e ai1 is the voltage across the active impedance balancing unit, VG_Qai1 and VG_Qai2 are the control signals of the MOS transistors Q ai2 and MOS transistor Q cdi respectively, VG_Qai1 and VG_Qai2 are complementary signals with a duty cycle close to 50%, and their frequencies are the same as the switching frequency of the LLC resonant converter module. α is the phase difference between VG_Qai1 and e

[0055] In actual operation, the capacitor C ai mainly plays a role in blocking direct current and has no effect on impedance. The approximate relationship between the equivalent inductance L sci of the active impedance balancing unit and the original inductance L ai is shown in Equation (10).

[0056]

[0057] It can be seen from (10) that changing α can change L sci and thus change the impedance and voltage gain of the connected LLC resonant converter module, thereby achieving current sharing. In order to make L sci change monotonically, the change range of α is set within [90°, 180°]. Within this range, the larger α is, the larger L sci is.

[0058] Figure 9 shows based on Figure 7The controller of the interleaved parallel LLC resonant converter of the present invention with an active impedance balancing unit as shown. The controller controls each phase LLC resonant converter module and the active impedance balancing unit: during the startup process of the converter, it detects and compares the magnitudes of the output currents of different phases to determine the leading-lagging relationship between the modules, that is, successively taking the module with the larger output current as the leading phase and the module with the smaller output current as the lagging phase, and controls the phase difference of each phase LLC resonant converter module to obtain an optimized current output ripple cancellation effect: that is, when the number of parallel modules N = 2, the phase difference of the LLC resonant converter module is controlled to be 90°, and when the number of parallel modules N = 3, the phase difference of the LLC resonant converter module is controlled to be 60° or 120°; after the converter enters the steady-state operation, according to the output voltage feedback information V o_FB or the output total current information I o_FB it adjusts and synchronously regulates the frequencies of each phase LLC resonant converter modules to achieve output voltage regulation or output total current constant current. At the same time, according to the output current deviation of every two-phase LLC resonant converter modules fed back, it respectively adjusts the phase difference between the bidirectional switch drive signal in its corresponding active impedance balancing unit and the voltage across the active impedance balancing unit to achieve equal current sharing of the output currents of each phase LLC resonant converter modules: the greater the current deviation, the smaller the phase difference, and vice versa. Among them, VGi1~VGi2 are the drive signals of the primary switch bridge arm of the i-th phase LLC resonant converter module, and I oi_FB is the output current feedback signal of the i-th phase LLC resonant converter module.

[0059] When the number of parallel modules N = 3, the basic principle is the same and will not be elaborated here.

[0060] Figure 10 Figure 13 shows the second specific embodiment of the active impedance balancing unit adopted by the present invention, including a coupled inductor T i and a controllable current source IDC i ; the two ends of the first winding of the coupled inductor T i constitute the first end INi and the second end OUTi of the active impedance balancing unit, and the controllable current source IDC i forms a loop with the second winding of the coupled inductor T i ; by changing the amplitude of the controllable current source IDC i , the inductance L i on the first winding side of the coupled inductor T mi can be changed, that is, the equivalent impedance L sci of the active impedance balancing unit, as shown in Figure 11 .

[0061] Figure 12 Figure 14 shows based on Figure 10The controller of the interleaved parallel LLC resonant converter of the present invention for the active impedance balancing unit shown. The controller controls each phase LLC resonant converter module and the active impedance balancing unit: based on detecting and comparing the magnitudes of the output currents of different phases during the startup process, determining the leading-lagging relationship between the modules, that is, successively taking the module with the larger output current as the leading phase and the module with the smaller output current as the lagging phase, and controlling the phase difference of each phase LLC resonant converter module to obtain an optimized current output ripple cancellation effect: that is, when the number of parallel modules N = 2, controlling the phase difference of the LLC resonant converter module to be 90°, and when the number of parallel modules N = 3, controlling the phase difference of the LLC resonant converter module to be 60° or 120°; after the converter enters the steady-state operation, according to the output voltage feedback information V o_FB or the output total current information I o_FB to adjust and synchronously adjust the frequencies of each phase LLC resonant converter modules to achieve output voltage regulation or output total current constant current. At the same time, according to the output current deviation of each two-phase LLC resonant converter module feedback, through the C IDCi signal to adjust the magnitude of the controllable current source IDC i to achieve equal current sharing of the output currents of each phase LLC resonant converter modules: the larger the current deviation, the larger the magnitude of the controllable current source, and vice versa. Among them, C IDCi is the control signal of the controllable current source IDC i in the i-th active impedance balancing unit.

[0062] The specific embodiments described above have further elaborated on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. Current sharing method for interleaved parallel resonant converter, characterized in that Including the following steps: Step 1: During the startup process of the converter, by detecting and comparing the magnitudes of the output currents of each phase, determine the leading-lagging relationship between the modules through the control circuit: successively take the module with the larger output current as the leading phase and the module with the smaller output current as the lagging phase, and control the phase difference of each phase LLC resonant converter module to obtain a better current output ripple cancellation effect: that is, when the number of parallel modules N = 2, control the phase difference of the LLC resonant converter module to be 90°, and when the number of parallel modules N = 3, control the phase difference of the LLC resonant converter module to be 60° or 120°; Step 2: After the converter enters the steady state, synchronously adjust the frequencies of each phase LLC resonant converter module according to the output voltage feedback information or the output total current information to achieve output voltage regulation or output total current constant current. At the same time, respectively adjust the equivalent impedance of the corresponding active impedance balancing unit according to the output current deviation of every two-phase LLC resonant converter module, so that the output currents of each phase LLC resonant converter module are equal; The first end and the second end of the active impedance balancing unit form a loop with the resonant capacitor of every two-phase LLC resonant converter module connected thereto and the primary ground; The active impedance balancing unit includes: an auxiliary inductor, an auxiliary capacitor, and a bidirectional switch composed of two MOSs; The first end of the auxiliary inductor is the first end of the active impedance balancing unit. The second end of the auxiliary inductor is connected to the first end of the auxiliary capacitor. The second end of the auxiliary capacitor is connected to the first end of the bidirectional switch. The second end of the bidirectional switch is the second end of the active impedance balancing unit.

2. Interleaved parallel LLC resonant converter device, characterized in that, Using the current sharing method of the interleaved parallel resonant converter described in claim 1, including: A multi-phase interleaved parallel LLC resonant converter composed of N half-bridge LLC resonant converter modules, N*(N - 1) / 2 active impedance balancing units, and a controller, where N is equal to 2 or 3, and the active impedance balancing units are respectively connected in series between every two-phase LLC resonant converter modules; The controller receives the output voltage or the total output current signal and the output current signals of each phase half-bridge LLC resonant converter module, and outputs the control signals of the primary side switch bridge arm of each half-bridge LLC resonant converter module and the control signals of the active impedance balancing unit.

3. The interleaved parallel LLC resonant converter device according to claim 2, characterized in that: The control signal of the bidirectional switch in the active impedance balancing unit corresponding to every two-phase LLC resonant converter module is a square wave signal with a duty cycle close to 50%. Its frequency is the same as the switching frequency of the LLC resonant converter module, and the phase difference between it and the voltage across the active impedance balancing unit is adjusted within the range of [90°, 180°] according to the output current deviation of the two-phase LLC resonant converter module: the larger the current deviation, the smaller the phase difference, and vice versa.

4. The interleaved parallel LLC resonant converter device according to claim 2, wherein The active impedance balancing unit includes: a coupled inductor and a controllable current source; the two end points of the first winding of the coupled inductor form the first end and the second end of the active impedance balancing unit, and the controllable current source forms a loop with the second winding of the coupled inductor.

5. The interleaved parallel LLC resonant converter device according to claim 4, characterized in that, The amplitude of the controllable current source is adjusted by a control signal generated by the controller according to the output current deviation of each two-phase LLC resonant converter module in the feedback: the greater the current deviation, the greater the amplitude of the controllable current source, and vice versa.

Images