Multi-phase input parallel output parallel dual active full-bridge converter and current sharing control method

Abstract

The present invention discloses an automatic current balancing method for a multi-phase input parallel output parallel dual active bridge converter. Each submodule in the multi-phase input parallel output parallel dual active bridge converter is composed of a first switch circuit, a series inductor, an isolation transformer, a second switch circuit and a DC port side capacitor. A cyclic disturbance parameter estimation algorithm is used to estimate the parameter mismatch of each module. Once the parameters of each module are estimated, the compensation shift ratio of each submodule of the parallel system to meet the current balancing can be calculated, thereby achieving system current balancing. The present invention realizes automatic current balancing of a multi-phase input parallel output parallel dual active bridge converter, so that the power of each submodule is evenly distributed; it can be used in high-power parallel switch power supply occasions such as new energy power generation, electric vehicles, aerospace, uninterruptible power supply, DC power distribution system, energy storage system, etc., and has many advantages such as reasonable method, convenient implementation, good versatility, small size, low cost, etc.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronic cascade, and in particular to a current sharing control method of a multi-phase input parallel output parallel dual active full-bridge converter. Background Art

[0002] In recent years, converters in power electronic systems are developing towards high power, integration, low cost, high power density and high efficiency. The dual active bridge converter has many advantages such as bidirectional power transmission, electrical isolation, high transformation ratio buck-boost, easy to realize soft switch control, etc., and can realize multiple modular solutions through parallel combination. It has developed into one of the core topologies of high-power parallel switching power supplies in new energy power generation, electric vehicles, aerospace, uninterruptible power supplies, DC distribution systems, energy storage systems and other occasions. The modular parallel solution can effectively improve the power capacity, reduce the stress of power tubes, and enhance the redundancy of the system. However, in the actual circuit, the parameters such as the series inductance of each submodule cannot be guaranteed to be completely consistent, which will lead to unbalanced currents of each submodule, thereby causing serious problems such as excessive current stress of some modules. Most of the existing solutions use current sensors to achieve current sharing of each submodule. Therefore, a large number of current sensors and sampling and conditioning circuits are required, which not only increases the cost and volume of the system, but also reduces the reliability of the system. In addition, the use of coupled inductors to achieve current sharing of each submodule is also a common method. However, the addition of coupled inductors also increases the volume, weight and cost of the system. Summary of the invention

[0003] The technical problem to be solved by the present invention is to address the defects of the background technology. The present invention estimates the parameter mismatch of each module through a cyclic disturbance parameter estimation algorithm. Once the parameters of each module are estimated, the compensation shift ratio of each sub-module of the parallel system to meet the current sharing can be calculated, thereby achieving system current sharing.

[0004] The present invention adopts the following technical solutions to solve the above technical problems:

[0005] A multi-phase input parallel output parallel dual active full-bridge converter, wherein the multi-phase input parallel output parallel dual active full-bridge converter is composed of two or more dual active full-bridge converter sub-modules, and the dual active full-bridge converter sub-modules are connected in parallel;

[0006] The dual-active full-bridge converter submodule P1 includes a first switch circuit S11, a first series inductor L1, a first isolation transformer T1, a second switch circuit S12, and capacitors C11 and C12 on the DC port side of the converter. The first series inductor L1 is connected in series with the primary winding of the first isolation transformer T1. The first switch circuit S11 has an input port 1-1 and an output port 1-2. The second switch circuit S12 has an input port 1-3 and an output port 1-4.

[0007] A current sharing control method for a multi-phase input parallel output parallel dual active full-bridge converter is used for the multi-phase input parallel output parallel dual active full-bridge converter mentioned above, comprising:

[0008] Step S1: Determine the conditions for achieving current sharing of the input parallel output dual active full-bridge converter;

[0009] Step S2: Estimate M based on the switching frequency perturbation scheme i / M1 value;

[0010] Step S3: Perform switching frequency compensation to achieve current sharing of the input parallel output dual active full-bridge converters.

[0011] Preferably, the specific method of step S1 is:

[0012] The output current equation of each submodule is derived based on the transmission power expression of the dual active full-bridge converter:

[0013]

[0014] Where: I 2i is the output current of the ith submodule; P i is the transmission power of the ith submodule; f si is the switching frequency of the ith submodule; n i is the turns ratio of the ith submodule; L i is the sum of the leakage inductance and auxiliary inductance of the i-th submodule transformer; D 1i and D 2i are the inner and outer phase shift angles of the i-th submodule;

[0015] For the dual active full-bridge converter, it can be seen from (1) that there are two controllable variables in the output current expression of each submodule, including: D 2i and f si ; When the circuit parameters of each submodule do not match, the parallel system can be controlled based on common phase shift control (D 21 =D 22 …=D 2m ), adjust the switching frequency f of each submodule siTo achieve current sharing in parallel systems; when achieving current sharing, the phase shift angle and switching frequency of each submodule have the following relationship:

[0016]

[0017] Among them, D 21 ~D 2m is the external shift phase angle from the first submodule to the mth submodule and is equal; Δf1~Δf m-1 The switching frequency of the first submodule is used as the reference, and the switching frequency compensation value of the second submodule to the mth submodule is used to achieve current sharing of each submodule; for the input parallel output parallel dual active full-bridge converter, the input voltage and output voltage of each submodule are equal; when the system achieves current sharing, the output current of each submodule must meet:

[0018] I 21 =I 22 =…I 2m (3)

[0019] Substituting (2) into formula (1) and combining it with (3), we can calculate:

[0020]

[0021] Where M1=n1 / L1, M i =n i / L i , define M1 as the internal parameter of the first submodule, M i is the internal parameter of the i-th submodule; according to (4), when we know M i / M1, the switching frequency compensation values ​​of each submodule Δf1~Δf m-1 , and then adjust the switching frequency of each submodule through formula (2) to achieve system current sharing; therefore, the next step is to estimate M i / The value of M1.

[0022] Preferably, the specific method of step S2 is:

[0023] Taking two submodules as an example, firstly, a set of common phase shift angles (using D M The external phase angle relationship of the two submodules is D 21 =D 22 =D M ; Then, subtract Δf from the switching frequency of the first submodule s The component implements the perturbation, at Δf s Under the disturbance of, when the system reaches a new steady state, the common external phase shift angle D generated by the output voltage closed loop of the parallel system M Will be adjusted to The common external shift phase angle of the two submodules before disturbance has the following relationship:

[0024]

[0025] Δd in (5) is the common external phase angle offset of the two submodules before and after the disturbance. Substituting (5) into (1), the output currents of the two submodules after the disturbance are I' 21 , I' 22 :

[0026]

[0027] According to (1) and (6), the changes in the output current of the two submodules before and after the disturbance can be expressed as:

[0028]

[0029] According to the law of conservation of energy, the sum of the current changes of the two submodules before and after the disturbance is 0, so:

[0030] ΔI 21 +ΔI 22 =0 (8)

[0031] Combining (6)-(8), the parameter ratio M2 / M1 between the first submodule and the second submodule is:

[0032]

[0033] Among them, Δd can be obtained by DSP controller in practice, D M is the common outward shift phase angle before the disturbance, and M2 / M1 can be estimated by the above formula;

[0034] Based on the two-submodule parameter estimation method, the first submodule is selected as the main module and the other m-1 submodules are selected as slave modules. By perturbing two submodules each time and fixing the external phase shift angle and switching frequency of other submodules, the two-submodule parameter estimation process can be extended to multiple submodules. By perturbing the two submodules in turn, after m-1 perturbations, M submodules can be estimated cyclically. i / M1 value, M i The parameter estimation expression of / M1 is:

[0035]

[0036] In the formula, Δd i When the first submodule and the i-th submodule are disturbed, the common external phase angle offset of the two submodules after the disturbance.

[0037] Preferably, the specific method of step S3 is:

[0038] When M i When / M1 is obtained, the switching frequency compensation value of each sub-module that satisfies the output current sharing is known by (4). Further, according to (2), the switching frequency of each sub-module is adjusted to achieve the current sharing of the system.

[0039] Compared with the prior art, the present invention adopts the above technical solution and has the following beneficial effects:

[0040] 1. The multi-phase input parallel output parallel dual active full-bridge converter current sharing control method provided by the present invention can estimate the parameter mismatch of each sub-module, and further calculate the external phase angle compensation value of each module, thereby realizing parallel system current sharing.

[0041] 2. The current balancing control method for the multi-phase input parallel output parallel dual active full-bridge converter provided by the present invention does not introduce any additional circuit devices, does not require any current sensors, and has a simple control method and good current balancing effect.

[0042] 3. The multi-phase input parallel output parallel dual active full-bridge converter current sharing control method provided by the present invention can save many advantages compared with traditional solutions, such as reasonable method, convenient implementation, small system size and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0044] Attached Figure 1 A multi-phase input parallel output parallel dual active full-bridge converter;

[0045] Attached Figure 2 It is a schematic diagram of a disturbance scheme of a two-phase input parallel output parallel dual active full-bridge converter according to an embodiment of the present invention;

[0046] Attached Figure 3 This is a disturbance scheme for a multi-phase input parallel output parallel dual active full-bridge converter according to embodiment 1 of the present invention;

[0047] Attached Figure 4 is the inductor current i of the three-phase input parallel output parallel dual active full-bridge converter when the method of the present invention is not adopted L1 、i L2 、i L3 Simulation waveform;

[0048] Attached Figure 5 When the method of the present invention is adopted, the inductor current i of the three-phase input parallel output parallel dual active full-bridge converter is L1 、i L2 、i L3 Simulation waveform;

[0049] The V in the attached figure p , V s is the DC side port voltage of the multi-phase input parallel output parallel dual active full-bridge converter. Figure 4 and attached Figure 5 in i L1 、i L2 、i L3 is the inductor current of each submodule of the three-phase input parallel output parallel dual active full-bridge converter. h1 、v h2 It is the AC voltage on the primary and secondary sides of the isolation transformer. DETAILED DESCRIPTION

[0050] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] A multi-phase input parallel output parallel dual active full-bridge converter, wherein the multi-phase input parallel output parallel dual active full-bridge converter is composed of two or more dual active full-bridge converter sub-modules, and the dual active full-bridge converter sub-modules are connected in parallel;

[0052] The dual-active full-bridge converter submodule P1 includes a first switch circuit S11, a first series inductor L1, a first isolation transformer T1, a second switch circuit S12, and capacitors C11 and C12 on the DC port side of the converter. The first series inductor L1 is connected in series with the primary winding of the first isolation transformer T1. The first switch circuit S11 has an input port 1-1 and an output port 1-2. The second switch circuit S12 has an input port 1-3 and an output port 1-4.

[0053] A current sharing control method for a multi-phase input parallel output parallel dual active full-bridge converter is used for the multi-phase input parallel output parallel dual active full-bridge converter mentioned above, comprising:

[0054] Step S1: Determine the conditions for achieving current sharing of the input parallel output dual active full-bridge converter;

[0055] Step S2: Estimate M based on the switching frequency perturbation scheme i / M1 value;

[0056] Step S3: Perform switching frequency compensation to achieve current sharing of the input parallel output dual active full-bridge converters.

[0057] As a specific implementation, the specific method of step S1 is:

[0058] The output current equation of each submodule is derived based on the transmission power expression of the dual active full-bridge converter:

[0059]

[0060] Where: I 2i is the output current of the ith submodule; P i is the transmission power of the ith submodule; f si is the switching frequency of the ith submodule; n i is the turns ratio of the ith submodule; L i is the sum of the leakage inductance and auxiliary inductance of the i-th submodule transformer; D 1i and D 2i are the inner and outer phase shift angles of the i-th submodule;

[0061] For the dual active full-bridge converter, it can be seen from (1) that there are two controllable variables in the output current expression of each submodule, including: D 2i and f si ; When the circuit parameters of each submodule do not match, the parallel system can be controlled based on common phase shift control (D 21 =D 22 …=D 2m ), adjust the switching frequency f of each submodule si To achieve current sharing in parallel systems; when achieving current sharing, the phase shift angle and switching frequency of each submodule have the following relationship:

[0062]

[0063] Among them, D 21 ~D 2m is the external shift phase angle from the first submodule to the mth submodule and is equal; Δf1~Δf m-1 The switching frequency of the first submodule is used as the reference, and the switching frequency compensation value of the second submodule to the mth submodule is used to achieve current sharing of each submodule; for the input parallel output parallel dual active full-bridge converter, the input voltage and output voltage of each submodule are equal; when the system achieves current sharing, the output current of each submodule must meet:

[0064] I 21 =I 22 =…I 2m (3)

[0065] Substituting (2) into formula (1) and combining it with (3), we can calculate:

[0066]

[0067] Where M1=n1 / L1, M i =n i / L i , define M1 as the internal parameter of the first submodule, M i is the internal parameter of the i-th submodule; according to (4), when we know M i / M1, the switching frequency compensation values ​​of each submodule Δf1~Δf m-1 , and then adjust the switching frequency of each submodule through formula (2) to achieve system current sharing; therefore, the next step is to estimate M i / The value of M1.

[0068] As a specific implementation, the specific method of step S2 is:

[0069] Taking two submodules as an example, firstly, a set of common phase shift angles (using D M The external phase angle relationship of the two submodules is D 21 =D 22 =D M ; Then, subtract Δf from the switching frequency of the first submodule s The component implements the perturbation, at Δf s Under the disturbance of, when the system reaches a new steady state, the common external phase shift angle D generated by the output voltage closed loop of the parallel system M Will be adjusted to The common external shift phase angle of the two submodules before disturbance has the following relationship:

[0070]

[0071] Δd in (5) is the common external phase angle offset of the two submodules before and after the disturbance. Substituting (5) into (1), the output currents of the two submodules after the disturbance are I' 21 , I' 22 :

[0072]

[0073] According to (1) and (6), the changes in the output current of the two submodules before and after the disturbance can be expressed as:

[0074]

[0075] According to the law of conservation of energy, the sum of the current changes of the two submodules before and after the disturbance is 0, so:

[0076] ΔI 21 +ΔI 22 =0 (8)

[0077] Combining (6)-(8), the parameter ratio M2 / M1 between the first submodule and the second submodule is:

[0078]

[0079] Among them, Δd can be obtained by DSP controller in practice, D M is the common outward shift phase angle before the disturbance, and M2 / M1 can be estimated by the above formula;

[0080] Based on the two-submodule parameter estimation method, the first submodule is selected as the main module and the other m-1 submodules are selected as slave modules. By perturbing two submodules each time and fixing the external phase shift angle and switching frequency of other submodules, the two-submodule parameter estimation process can be extended to multiple submodules. By perturbing the two submodules in turn, after m-1 perturbations, M submodules can be estimated cyclically. i / M1 value, M i The parameter estimation expression of / M1 is:

[0081]

[0082] In the formula, Δd i When the first submodule and the i-th submodule are disturbed, the common external phase angle offset of the two submodules after the disturbance.

[0083] As a specific implementation, the specific method of step S3 is:

[0084] When M i When / M1 is obtained, the switching frequency compensation value of each submodule to meet the output current sharing is known by (4). Further, according to (2), the switching frequency of each submodule is adjusted to achieve the current sharing of the system.

[0085] By the attached Figure 3 The simulation waveform of the disturbance phase of the three-phase input parallel output parallel dual active full-bridge converter shows that the disturbance scheme of disturbing two sub-modules in turn and fixing the other sub-modules to move outward is well implemented; Figure 4 and attached Figure 5 It can be seen that when the present invention is not adopted, the inductor current i of the three-phase input parallel output parallel dual active full-bridge converter is L1 、i L2 、i L3The simulated waveforms of the inductor current are very different and unbalanced, and the current sharing error reaches 11.7%. After adopting the present invention, the inductor current i of the three-phase input parallel output parallel circuit is L1 、i L2 、i L3 The difference in the simulated inductor current waveform is very small and very balanced, with a current sharing error of 0.5%. The simulation parameters are: Vp = 48V, Vs = 110V, L1 = 2.0μH, L2 = 1.9μH, L3 = 1.8μH, transmission power 6kW, switching frequency 50kHz, Δf p =5kHz.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A current sharing control method for a multi-phase input parallel output parallel dual active full-bridge converter, characterized in that: The multi-phase input parallel output parallel dual active full-bridge converter is composed of two or more dual active full-bridge converter sub-modules, and the dual active full-bridge converter sub-modules are connected in parallel; The dual-active full-bridge converter submodule P1 includes a first switch circuit S11, a first series inductor L1, a first isolation transformer T1, a second switch circuit S12, and capacitors C11 and C12 on the DC port side of the converter. The first series inductor L1 is connected in series with the primary winding of the first isolation transformer T1. The first switch circuit S11 has an input port 1-1 and an output port 1-2. The second switch circuit S12 has an input port 1-3 and an output port 1-4. A current sharing control method for a multi-phase input parallel output parallel dual active full-bridge converter, used for the multi-phase input parallel output parallel dual active full-bridge converter, comprises the following steps: Step S1: Determine the conditions for achieving current sharing of the input parallel output dual active full-bridge converter; Step S2: Estimate M based on the switching frequency perturbation scheme i / M1 value; Step S3: Perform switching frequency compensation to achieve current sharing of the input parallel output dual active full-bridge converter; The specific method of step S1 is: The output current equation of each submodule is derived based on the transmission power expression of the dual active full-bridge converter: Where: I 2i is the output current of the ith submodule; P i is the transmission power of the ith submodule; f si is the switching frequency of the ith submodule; n i is the turns ratio of the ith submodule; L i is the sum of the leakage inductance and auxiliary inductance of the i-th submodule transformer; D 1i and D 2i is the inner phase shift angle and outer phase shift angle of the ith submodule; V p is the input voltage of the ith submodule; V s is the output voltage of the ith submodule; For the dual active full-bridge converter, it can be seen from (1) that there are two controllable variables in the output current expression of each submodule, including: D 2i and f si ; When the circuit parameters of each submodule do not match, based on the common phase shift control of the parallel system (D 21 =D 22 …=D 2m ), adjust the switching frequency f of each submodule si To achieve current sharing in parallel systems; when achieving current sharing, the phase shift angle and switching frequency of each submodule have the following relationship: Among them, D 21 ~D 2m is the external shift phase angle from the first submodule to the mth submodule and is equal; Δf1~Δf m-1 The switching frequency of the first submodule is used as the reference, and the switching frequency compensation value of the second submodule to the mth submodule is used to achieve current sharing of each submodule; for the input parallel output parallel dual active full-bridge converter, the input voltage and output voltage of each submodule are equal; when the system achieves current sharing, the output current of each submodule must meet: I 21 =I 22 =…I2m (3) Substituting (2) into formula (1) and combining it with (3), we can calculate: Where M1=n1 / L1, M i =n i / L i , define M1 as the internal parameter of the first submodule, M i is the internal parameter of the i-th submodule; according to (4), when we know M i / M1, the switching frequency compensation values ​​of each submodule Δf1~Δf m-1 , and then adjust the switching frequency of each submodule through formula (2) to achieve system current sharing; therefore, the next step is to estimate M i / The value of M1.

2. The current sharing control method of a multi-phase input parallel output parallel dual active full-bridge converter according to claim 1, characterized in that: The specific method of step S2 is: There are two sub-modules. First, the system output voltage closed loop generates a set of common phase shift angles D M To control two sub-modules at the same time, the external phase shift angle relationship of the two sub-modules is D 21 =D 22 =D M ; Then, subtract Δf from the switching frequency of the first submodule s The component implements the perturbation, at Δf s Under the disturbance of, when the system reaches a new steady state, the common external phase shift angle D generated by the output voltage closed loop of the parallel system M Will be adjusted to The common external shift phase angle of the two submodules before disturbance has the following relationship: Δd in (5) is the common external phase angle offset of the two submodules before and after the disturbance. Substituting (5) into (1), the output currents of the two submodules after the disturbance are I' 21 , I' 22 : According to (1) and (6), the changes in the output current of the two submodules before and after the disturbance are expressed as: According to the law of conservation of energy, the sum of the current changes of the two submodules before and after the disturbance is 0, so: ΔI 21 +ΔI 22 =0 (8) Combining (6)-(8), the parameter ratio M2 / M1 between the first submodule and the second submodule is: Among them, Δd is obtained by DSP controller in practice, D M is the common outward shift phase angle before the disturbance, and M2 / M1 can be estimated by the above formula; Based on the two-submodule parameter estimation method, the first submodule is selected as the main module and the other m-1 submodules are selected as slave modules. By perturbing two submodules each time and fixing the external phase shift angle and switching frequency of other submodules, the two-submodule parameter estimation process can be extended to multiple submodules. By perturbing the two submodules in turn, after m-1 perturbations, M submodules can be estimated cyclically. i / M1 value, M i The parameter estimation expression of / M1 is: In the formula, Δd i When the first submodule and the i-th submodule are disturbed, the common external phase angle offset of the two submodules after the disturbance.

3. The current sharing control method of a multi-phase input parallel output parallel dual active full-bridge converter according to claim 1, characterized in that: The specific method of step S3 is: When M i When / M1 is obtained, the switching frequency compensation value of each sub-module that satisfies the output current sharing is known by formula (4). Further, according to formula (2), the switching frequency of each sub-module is adjusted to achieve the current sharing of the system.

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