Minimum current stress modulation method for dual-active bridge DC-DC converter

Abstract

The invention discloses a minimum current stress modulation method for a dual-active bridge DC-DC converter, and belongs to the technical field of converters. The method comprises the following steps: calculating the relation between the output power and the phase-shift angle and the relation between the current stress and the phase-shift angle of the dual-active bridge DC-DC converter under a dual-phase-shift modulation strategy; solving the optimal phase shift angle in the step-down mode; judging the current working mode of the dual-active bridge DC-DC converter; at 0.95 lt; klt; and the 1.05 region constantly adopts a single phase shift modulation strategy. According to the invention, the current stress and the current ripple of the switching tube are reduced, the minimum current stress control is realized on the premise of meeting the output power requirement, the stability, the reliability and the service life of the system are improved, the system loss is reduced, the overall energy efficiency is improved, and the method has remarkable engineering application value and economic benefit.

Description

Technical Field

[0001] The invention relates to a minimum current stress modulation method for a dual active bridge DC-DC converter, belonging to the technical field of converters. Background Art

[0002] The dual active bridge DC-DC (DAB) converter achieves bidirectional power flow and improves system efficiency by precisely controlling the internal and external phase shift angles of the H-bridges on both sides. It is suitable for application scenarios with high power density and high efficiency requirements, such as electric vehicles and energy storage systems, and has significant engineering practicality. In order to further optimize the performance of the converter and reduce the current stress in the switch tube (i.e., the peak current in the high-frequency transformer), the industry has widely adopted a variety of multi-degree-of-freedom modulation schemes, including extended phase shift (EPS) modulation, dual phase shift (DPS) modulation, and triple phase shift (TPS) modulation.

[0003] Among the above modulation strategies, the TPS strategy has attracted much attention because it has the most degrees of freedom. However, its complex three control variables make analysis and control extremely cumbersome, which is not conducive to engineering application. In contrast, EPS and DPS modulation forms are more concise. In particular, DPS modulation not only has two control degrees of freedom, but also can avoid the exchange of control logic between the two H bridges, thus achieving a good balance between current stress optimization and control complexity.

[0004] However, when solving the DPS phase shift angle for minimum current stress, existing methods mainly rely on the Lagrange multiplier method (LMM). Although LMM is an effective optimization tool in theory, it has the following two problems in practical applications:

[0005] 1) The rationality of the LMM method is based on the premise that the feasible domain is a convex set. However, when the DAB converter adopts the DPS modulation strategy, due to the complex constraints between the output power and the phase shift angle, its feasible domain may be non-convex. Therefore, although the solution that satisfies the LMM is necessary, it is not a sufficient condition, which may lead to the inability to find the global optimal solution.

[0006] 2) The power ranges of DAB converters in different operating modes (defined by phase shift angle constraints) overlap. This means that for a given output power, there may be multiple different optimal phase shift angle combinations. Direct application of the LMM method may not fully consider these potential solutions, thus missing the true optimal solution.

[0007] Therefore, directly applying the LMM method may have potential defects in the DPS optimal solution process, which are not considered by existing methods. Summary of the invention

[0008] In order to solve the problems existing in the background technology, the present invention provides a minimum current stress modulation method for a dual active bridge DC-DC converter.

[0009] To achieve the above object, the present invention adopts the following technical solution: a dual active bridge DC-DC converter minimum current stress modulation method, the method comprising the following steps:

[0010] S1: Calculate the relationship between the output power and the phase shift angle of the dual active bridge DC-DC converter under the dual phase shift modulation strategy and the relationship between the current stress and the phase shift angle;

[0011] The dual active bridge DC-DC converter described in S1 is divided into two working modes according to the relationship between the phase shift angles under the dual phase shift modulation strategy modulation:

[0012] Mode 1: satisfy the constraints D1>D2 and D1+D2≤1;

[0013]

[0014] Mode 2: satisfying the constraints D1>D2 and D1+D2>1;

[0015]

[0016] In formula (1) and (2):

[0017] D1 represents the phase shift angle of the primary and secondary sides, i.e., the internal phase shift angle;

[0018] D2 represents the phase shift angle between the two H bridges, i.e., the outer phase shift angle;

[0019] k=U in / (nU o ) represents the voltage gain;

[0020] P n represents the normalized output power, Where: P represents the actual output power, P r It indicates the base value of output power, n indicates the ratio of primary and secondary turns of transformer, U in Indicates input voltage, U o represents the output voltage, f s Indicates the control frequency, L r Represents the leakage inductance of the high-frequency transformer;

[0021] I stn represents the normalized current stress, Where: I st Indicates the peak current of current stress, I str Indicates the reference value of current stress;

[0022] S2: Solve the optimal phase shift angle in buck mode;

[0023] For mode 1, the optimal internal and external phase shift angles are solved based on the power gradient optimization algorithm so that the current stress is minimized under a given output power. Specifically, the following steps are included:

[0024] S201: Under a given voltage gain k, determine that the gradient of the current stress is a constant value;

[0025] S202: Find the point where the gradient of the power contour line completely overlaps with the gradient of the current stress contour line, and obtain the optimal internal and external phase shift angle through the following formula, which is the minimum current stress point for a given power:

[0026]

[0027] In formula (3):

[0028] represents the optimal value of D1;

[0029] represents the optimal value of D2;

[0030]

[0031] For mode 2, the optimal internal and external phase shift angles are solved based on the power gradient optimization algorithm so that the current stress is minimized under a given output power. Specifically, the following steps are included:

[0032] S201: Under a given voltage gain k, determine that the gradient of the current stress is a constant value;

[0033] S202: Find the point where the gradient of the power contour line completely overlaps with the gradient of the current stress contour line, and obtain the optimal internal and external phase shift angle through the following formula, which is the minimum current stress point for a given power:

[0034]

[0035] In formula (4):

[0036] represents the optimal value of D1;

[0037] represents the optimal value of D2;

[0038]

[0039] S3: Determine the current working mode of the dual active bridge DC-DC converter; if the per-unit output power Then the dual active bridge DC-DC converter works in mode 1, otherwise, it works in mode 2;

[0040] S4: In the region of 0.95 < k < 1.05, the single-phase-shift modulation strategy is always adopted. When k = 1, the optimal phase-shift angle of the dual-active-bridge DC-DC converter is the same as the optimal phase-shift angle of the single-phase-shift modulation strategy.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] 1. By controlling different internal and external phase-shift angles, the present invention controls the voltages and currents at both ends of the high-frequency transformer, and further controls the output-port voltage and power transfer to achieve DC voltage conversion. It effectively reduces the current stress and current ripple of the switching tubes, realizes the minimum current stress control on the premise of meeting the output power requirements, improves the system stability, reliability and lifespan, reduces the system losses, enhances the overall energy efficiency, and has significant engineering application value and economic benefits.

[0043] 2. The present invention directly calculates the equal-gradient points of the power contour line and the current stress contour line, avoiding the potential problem of non-optimal solutions that may exist when using the Lagrange multiplier method, making the solution method more intuitive, concise and rigorous. It can directly calculate the unique and optimal internal and external phase-shift angles to achieve the stable and effective control of the DAB converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is a schematic diagram of the topological structure of the DAB converter of the present invention;

[0045] Figure 2 is a schematic diagram of the typical waveforms of the voltages and currents at both ends of the high-frequency transformer in two modes, where: (a) is a schematic diagram of the typical waveform in Mode 1, and (b) is a schematic diagram of the typical waveform in Mode 2;

[0046] Figure 3 is a schematic diagram of the waveforms of the voltages and currents at both ends of the high-frequency transformer under the control of the PGO-based modulation strategy when the output voltage is 80V, where: (a) is a schematic diagram of the experimental waveform under light load (load resistance 60Ω), and (b) is a schematic diagram of the experimental waveform under heavy load (load resistance 30Ω); The square-wave diagram is a schematic diagram of the voltage waveform at both ends of the high-frequency transformer, and the broken-line diagram is a schematic diagram of the current waveform inside the high-frequency transformer;

[0047] Figure 4 is a schematic diagram of the waveforms of the voltages and currents at both ends of the high-frequency transformer under the control of the PGO-based modulation strategy when the output voltage is 100V, where: (a) is a schematic diagram of the experimental waveform under light load (load resistance 60Ω), and (b) is a schematic diagram of the experimental waveform under heavy load (load resistance 30Ω);

[0048] Figure 5The voltage and current waveforms at both ends of the high-frequency transformer under the control of the PGO modulation strategy when the output voltage is 135V, where: (a) is a schematic diagram of the experimental waveform under light load (load resistance 60Ω), and (b) is a schematic diagram of the experimental waveform under heavy load (load resistance 30Ω); DETAILED DESCRIPTION

[0049] The technical solution of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0050] The present invention relates to a dual active bridge DC-DC converter (DAB) minimum current stress modulation algorithm based on a dual phase shift modulation strategy, that is, changing the phase shift angle between different bridge arms in two H-bridges and between two different H-bridges, so as to reduce the current stress of switching devices in a bidirectional energy conversion process, improve system efficiency and extend device life.

[0051] A dual active bridge DC-DC converter minimum current stress modulation method of the present invention comprises the following steps:

[0052] S1: Calculate the relationship between the output power and the phase shift angle of the dual active bridge DC-DC converter (DAB) under the dual phase shift modulation strategy (DPS) and the relationship between the current stress and the phase shift angle;

[0053] The two H bridges are connected to a high frequency transformer (HFT). The dual active bridge DC-DC converter described in S1 can be divided into two working modes according to the relationship (constraint) between the phase shift angles under the dual phase shift modulation strategy modulation:

[0054] Mode 1: satisfy the constraints D1>D2 and D1+D2≤1;

[0055]

[0056] Mode 2: satisfying the constraints D1>D2 and D1+D2>1;

[0057]

[0058] In formula (1) and (2):

[0059] D1 represents the phase shift angle of the primary and secondary sides, i.e., the internal phase shift angle;

[0060] D2 represents the phase shift angle between the two H bridges, i.e., the outer phase shift angle;

[0061] k=U in / (nUo ) represents the voltage gain, where: k>1 is the buck mode;

[0062] P n represents the normalized output power, Where: P represents the actual output power, P r It indicates the base value of output power, n indicates the ratio of primary and secondary turns of transformer, U in Indicates input voltage, U o represents the output voltage, f s Indicates the control frequency, L r Represents the leakage inductance of the high-frequency transformer;

[0063] I stn represents the normalized current stress, Where: I st Indicates the peak current of current stress, I str Indicates the reference value of current stress;

[0064] S2: Solve the optimal phase shift angle in buck mode;

[0065] For mode 1, the optimal internal and external phase shift angles are solved based on the power gradient optimization (PGO) algorithm to minimize the current stress at a given output power, which specifically includes the following steps:

[0066] S201: Under a given voltage gain k, determine that the gradient of the current stress is a constant value;

[0067] S202: Find the point where the gradient of the power contour line completely overlaps with the gradient of the current stress contour line, and obtain the optimal internal and external phase shift angle through the following formula, which is the minimum current stress point for a given power:

[0068]

[0069] In formula (3):

[0070] represents the optimal value of D1;

[0071] represents the optimal value of D2; since the output power of the DAB converter is symmetrical about the external phase shift angle D2 = 0.5 in the mode, it is assumed that the value range of D2 in the solution is 0 to 0.5.

[0072]

[0073] For mode 2, the optimal internal and external phase shift angles are solved based on the power gradient optimization (PGO) algorithm to minimize the current stress at a given output power, which specifically includes the following steps:

[0074] S201: Determine that the gradient of the current stress is a constant value under a given voltage gain k;

[0075] S202: Solve for the point where the gradient of the power contour is exactly coincident with the gradient of the current stress contour, and obtain the optimal inner and outer phase-shift angles through the following formula, which is the point of minimum current stress for a given power:

[0076]

[0077] In formula (4):

[0078] represents the optimal value of D1;

[0079] represents the optimal value of D2;

[0080]

[0081] S3: Determine the current operating mode of the dual-active-bridge DC-DC converter according to the relationship between the per-unit output power and the voltage gain; if the per-unit output power then the dual-active-bridge DC-DC converter operates in Mode 1, otherwise, it operates in Mode 2;

[0082] S4: Adopt a hysteresis control method to avoid the output voltage oscillation of the voltage gain near the boundary. Always adopt a single-phase-shift modulation strategy in the region of 0.95 < k < 1.05. When k = 1, the optimal displacement angle of the dual-active-bridge DC-DC converter is the same as the optimal phase-shift angle of the single-phase-shift modulation strategy.

[0083] Table 1 Optimal phase-shift angles in the full operating range

[0084]

[0085]

[0086] The present invention can be implemented in a standard digital control chip (such as a DSP or an FPGA) without additional hardware modification, and is applicable to the dual-active-bridge converter topology widely used.

[0087] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent conditions of the claims are intended to be encompassed within the present invention. Any reference signs in the claims should not be regarded as limiting the claims involved.

[0088] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A minimum current stress modulation method for a dual-active-bridge DC-DC converter, characterized in that: the method comprises the following steps: S1: Calculate the relationship between the output power and the phase-shift angle and the relationship between the current stress and the phase-shift angle of the dual-active-bridge DC-DC converter under the dual-phase-shift modulation strategy; S2: Solve the optimal phase-shift angle in the step-down mode; S3: Determine the current working mode of the dual active bridge DC-DC converter; if the per-unit output power Then the dual active bridge DC-DC converter works in mode 1, otherwise, it works in mode 2; S4: Always adopt the single-phase-shift modulation strategy in the region of 0.95 < k < 1.

05.

2. The minimum current stress modulation method for a dual-active-bridge DC-DC converter according to claim 1, characterized in that: The dual-active-bridge DC-DC converter in S1 is divided into two operating modes according to the relationship between the phase-shift angles under the dual-phase-shift modulation strategy: Mode 1: Satisfying constraint D 1 >D 2 And D 1 +D 2 ≤1; Mode 2: Satisfying Constraint D 1 >D 2 And D 1 +D 2 >1; In equations (1) and (2): D 1 It indicates the phase shift angle of the original secondary side, that is, the inner phase shift angle; D 2 Represents the phase shift angle between the two H bridges, that is, the external phase shift angle; k=U in / (nU o ) represents the voltage gain; P n represents the normalized output power, Where: P represents the actual output power, P r It indicates the base value of output power, n indicates the ratio of primary and secondary turns of transformer, U in Indicates input voltage, U o represents the output voltage, f s Indicates the control frequency, L r Represents the leakage inductance of the high-frequency transformer; I stn represents the normalized current stress, Where: I st Represents the peak current of current stress, I str Indicates the reference value of current stress.

3. The minimum current stress modulation method for a dual-active-bridge DC-DC converter according to claim 1, characterized in that: The said S2 comprises the following steps: For mode one, solve the optimal inner and outer phase-shift angles based on the power gradient optimization algorithm to minimize the current stress at a given output power, specifically including the following steps: S201: At a given voltage gain k, determine that the gradient of the current stress is a constant value; S202: Solve the point where the gradient of the power contour line coincides exactly with the gradient of the current stress contour line, and obtain the optimal inner and outer phase-shift angles through the following formula, which is the minimum current stress point for the given power: In equation (3): Indicates D 1 The optimal value of Indicates D 2 The optimal value of For mode two, solve the optimal inner and outer phase-shift angles based on the power gradient optimization algorithm to minimize the current stress at a given output power, specifically including the following steps: S201: At a given voltage gain k, determine that the gradient of the current stress is a constant value; S202: Solve the point where the gradient of the power contour line coincides exactly with the gradient of the current stress contour line, and obtain the optimal inner and outer phase-shift angles through the following formula, which is the minimum current stress point for the given power: In equation (4): Indicates D 1 The optimal value of Indicates D 2 The optimal value of

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