DAB converter control method based on minimum current stress and finite set model prediction

Abstract

The invention discloses a DAB converter control method based on minimum current stress and finite set model prediction, and relates to the technical field of converter control, and the method comprises the steps: obtaining a phase shift ratio constraint formula of a DAB converter working in a target working mode according to a constraint condition, the constraint condition comprises that the DAB converter works at the minimum current stress; and constructing a prediction model in a finite set model prediction control algorithm by using the phase shift ratio constraint formula, and obtaining a phase shift ratio control group of the DAB converter working in the target working mode through the finite set model prediction control algorithm. According to the control method, the current stress of the power device in the DAB converter can be effectively reduced, so that the power loss is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of converter control, and in particular to a control method for a Dual Active Bridge (DAB) converter based on minimum current stress and finite set model prediction. Background Art

[0002] The Dual Active Bridge (DAB) converter is a topology widely used in power electronic conversion systems, especially in fields such as high-efficiency power transmission, conversion between DC and AC power supplies, and electric vehicle charging systems. The DAB converter topology can achieve wide voltage range transmission by adjusting the turns ratio of the transformer, and the presence of the transformer can also provide electrical isolation between the input and output terminals.

[0003] Current stress refers to the peak current of the power devices in the converter topology. Higher current stress will cause excessive heat generation in the power components (such as switching devices, inductors, capacitors, etc.) in the converter, increasing the system losses, and may lead to shortened device life and even failures. Therefore, how to minimize the current stress while ensuring the system performance has become a key issue that must be considered when designing and controlling the DAB converter.

[0004] Currently, most of the minimum current stress optimization control methods for DAB converters are based on the PID control method. This method is simple to control but has a slow dynamic response speed. Although the traditional model predictive control method has great advantages in dynamic control performance, its computational complexity is relatively high. Especially in the case of high-frequency switching and high-power transmission, both the PID control method and the traditional model predictive control method may cause delays in the implementation of the control strategy and reduce the system response speed. In addition, due to the difficulty in solving the optimal phase shift ratio of the DAB converter under triple-phase shift modulation, there is relatively little research on the control of the DAB converter under triple-phase shift modulation currently. Summary of the Invention

[0005] In view of the above problems and technical requirements, the inventor of the present invention has proposed a control method for a DAB converter based on minimum current stress and finite set model prediction. The technical solution of the present invention is as follows:

[0006] A control method for a DAB converter based on minimum current stress and finite set model prediction, characterized by comprising:

[0007] Obtaining a phase shift ratio constraint formula when the DAB converter operates in a target operating mode according to the constraint conditions, where the constraint conditions include making the DAB converter operate with minimum current stress;

[0008] Construct a prediction model in the finite set model predictive control algorithm using the phase shift ratio constraint, and obtain the phase shift ratio control group when the DAB converter operates in the target operating mode through the finite set model predictive control algorithm.

[0009] A further technical solution thereof is that when obtaining the phase shift ratio constraint when the DAB converter operates in the target operating mode under the constraint conditions, it includes:

[0010] Construct a Lagrangian function E and solve the constructed Lagrangian function E to obtain the phase shift ratio constraint. The constructed Lagrangian function E is:

[0011] E = i p + λ(p - p * )

[0012] where λ is the Lagrange multiplier, i p is the per-unit value of current stress, p is the per-unit value of transmission power, and p * is the expected transmission power.

[0013] A further technical solution thereof is that the target operating mode is the first operating mode or the second operating mode of the DAB converter under triple phase-shift modulation;

[0014] In the first operating mode, the first phase shift ratio D1, the second phase shift ratio D2, and the third phase shift ratio D3 in the DAB converter satisfy: D1 ≤ D2 ≤ D3 ≤ 1;

[0015] In the second operating mode, the first phase shift ratio D1, the second phase shift ratio D2, and the third phase shift ratio D3 in the DAB converter satisfy: D2 ≤ D1 ≤ D3 ≤ 1;

[0016] The per-unit value of transmission power p in the first operating mode and the second operating mode is:

[0017]

[0018] where P is the actual value of transmission power, P N is the maximum value of transmission power under single-phase shift modulation. The maximum value of transmission power P N under single-phase shift modulation is:

[0019]

[0020] where f s is the switching frequency of the DAB converter, L r is the sum of the auxiliary inductor and the leakage inductance of the transformer in the DAB converter, n is the turns ratio of the primary and secondary sides of the transformer in the DAB converter, V1 is the input voltage, and V2 is the output voltage;

[0021] The per-unit value of current stress ip In the first operating mode and the second operating mode:

[0022]

[0023] where i P is the actual value of the peak inductor current, and i N is the maximum value of the inductor current under single-phase-shift modulation. T s is the switching period of the DAB converter, and k is the voltage conversion ratio of the DAB converter.

[0024] A further technical solution thereof is that the phase-shift ratio constraint formula of the obtained DAB converter in the first operating mode and the second operating mode is:

[0025]

[0026] Under the phase-shift ratio constraint formula, the first phase-shift ratio D1 satisfies:

[0027]

[0028] A further technical solution thereof is that when constructing a prediction model in a finite set model predictive control algorithm by using the phase-shift ratio constraint formula, it includes:

[0029] Construct a reduced-order model of the DAB converter, and obtain a dynamic equation of the output voltage of the DAB converter according to the reduced-order model of the DAB converter. The dynamic equation of the output voltage of the DAB converter is:

[0030]

[0031] where C2 is the output capacitor of the DAB converter, V2 is the output voltage, I2 is the output current, and I load is the load current;

[0032] Express the output current I2 according to the phase-shift ratio constraint formula under the reduced-order model:

[0033]

[0034] where is the phase shift between the primary port voltage v ab and the secondary port voltage v cd of the transformer in the DAB converter;

[0035] Discretize the dynamic equation of the output voltage of the DAB converter to construct a prediction model. The constructed prediction model is:

[0036]

[0037] Among them, V2[d] is the output voltage at time d, V2[d+2] is the predicted output voltage at time d+2, I2[d] is the output current at time d, I2[d+1] is the output current at time d+1, and I load [d] is the load current at time d.

[0038] A further technical solution thereof is that when obtaining the phase shift ratio control group of the DAB converter operating in the target operating mode through the finite set model predictive control algorithm, it includes:

[0039] Obtain the moving discrete control set of and set the cost function ct, where the is the phase shift between the primary port voltage v ab and the secondary port voltage v cd of the DAB converter at time d+1, the moving discrete control set of includes multiple candidate phase shifts;

[0040] According to the prediction model and the cost function ct, calculate the cost function value corresponding to each candidate phase shift in the target operating mode, and use the candidate phase shift with the minimum cost function value among all candidate phase shifts as the phase shift ab between the primary port voltage v cd and the secondary port voltage v of the DAB converter at time d+1, and ab according to the phase shift cd between the primary port voltage v and the secondary port voltage v of the DAB converter at time d+1, calculate the phase shift ratio control group at time d+1 in the target operating mode;

[0041] The phase shift ratio control group at time d+1 in the target operating mode includes the first phase shift ratio D1[d+1], the second phase shift ratio D2[d+1], and the third phase shift ratio D3[d+1] of the DAB converter at time d+1 in the target operating mode.

[0042] A further technical solution thereof is that the moving discrete control set of is:

[0043]

[0044] Among them, Δ adp [d] is the adaptive step size at time d, is the phase shift between the primary port voltage v ab and the secondary port voltage v cd of the DAB converter at time d, and μ is the discrete parameter;

[0045] The adaptive step size Δ at time dadp [d]Adjust the resolution Δ according to the phase shift value f and the output voltage error V at time d Δ [d]Determined

[0046] A further technical solution thereof is that the adaptive step size Δ at time d adp [d]is:[[]]

[0047]

[0048] where λ is the voltage error gain, V 2_ref is the reference voltage, V m is the saturated voltage error

[0049] A further technical solution thereof is that when calculating the cost function value corresponding to each candidate phase shift in the target operating mode according to the prediction model and the cost function ct, it includes:

[0050] Calculate the predicted output voltage V2[d + 2] at time d + 2 corresponding to each candidate phase shift according to the prediction model, and substitute the predicted output voltage V2[d + 2] at time d + 2 corresponding to each candidate phase shift into the cost function ct to calculate the cost function value corresponding to each candidate phase shift in the target operating mode

[0051] A further technical solution thereof is that the cost function ct is:

[0052]

[0053] where G1 is the first function term, G2 is the second function term, α1 is the first weight factor, and α2 is the second weight factor

[0054] The beneficial technical effects of the present invention are:

[0055] (1) Aiming at the two operating modes of the DAB converter under triple phase shift modulation, the present invention calculates the phase shift ratio constraint formula that can achieve the minimum current stress through the Lagrange multiplier method, and uses this phase shift ratio constraint formula to control the converter, effectively reducing the current stress of the power devices in the dual active bridge converter, thereby reducing power loss, extending the service life of the devices, and significantly improving the overall efficiency of the converter. In addition, this method can also optimize the dynamic performance of the converter, making the system operation more stable and reliable

[0056] (2) A prediction model is established based on the phase shift ratio constraint, and the constraint of minimum current stress is applied to the finite set model predictive control method. The finite set model predictive control method can transform complex control problems into optimal selections in a discrete control set, avoiding the large computational requirements for continuous control variables in traditional optimization methods. It not only simplifies the control algorithm but also improves the real-time performance and response speed of the system, making it more suitable for scenarios with rapid dynamic changes, such as new energy power generation and electric vehicle charging. Brief Description of the Drawings

[0057] Figure 1 It is a schematic diagram of the DAB converter topology provided by the present invention.

[0058] Figure 2 It is a flowchart of an embodiment of the control method provided by the present invention.

[0059] Figure 3 It is a schematic diagram of the reduced-order model of the DAB converter provided by the present invention.

[0060] Figure 4 It is a modulation timing diagram in the first working mode of the triple phase shift modulation provided by the present invention.

[0061] Figure 5 It is a modulation timing diagram in the second working mode of the triple phase shift modulation provided by the present invention.

[0062] Figure 6 It is a program flowchart of the finite set model predictive control algorithm provided by the present invention.

[0063] Figure 7 It is a simulation waveform diagram of the DBA converter when the per-unit value of the transmission power p = 0.24.

[0064] Figure 8 It is a simulation waveform diagram of the DBA converter when the per-unit value of the transmission power p = 0.5.

[0065] Figure 9 It is a simulation waveform diagram of the DBA converter when the per-unit value of the transmission power p = 0.8.

[0066] Figure 10 It is the simulation waveform diagram of the output voltage V2, the load current I load and the inductor current i L when the load has a step change. Detailed Embodiments

[0067] The following further describes the detailed embodiments of the present invention with reference to the drawings. It can be understood that the described detailed embodiments are only used to explain the relevant content and do not limit the present invention.

[0068] To minimize current stress, reduce system losses and thermal stress, and thus improve the conversion efficiency and reliability of the DAB converter, the present invention proposes a control method for the DAB converter based on minimum current stress and finite set model prediction, including:

[0069] Obtain the phase shift ratio constraint equation when the DAB converter operates in the target operating mode according to the constraint conditions, where the constraint conditions include making the DAB converter operate with minimum current stress;

[0070] Use the phase shift ratio constraint equation to construct a prediction model in the finite set model predictive control algorithm, and obtain the phase shift ratio control group when the DAB converter operates in the target operating mode through the finite set model predictive control algorithm.

[0071] Specifically, Figure 1 The topology of the DAB converter is shown, as Figure 1 shown. The DAB converter includes a primary H-bridge and a secondary H-bridge. The primary H-bridge and the secondary H-bridge are connected through an auxiliary inductor and a transformer. The sum of the auxiliary inductor and the leakage inductance of the transformer is denoted as L r . The primary H-bridge includes an input capacitor C1, MOS transistors S1, S2, S3, and S4. The arm one formed by the series connection of MOS transistors S1 and S2 is connected in parallel with the arm two formed by the series connection of MOS transistors S3 and S4. Both ends of the arm one are connected in parallel with the input capacitor C1, and the input voltage V1 is applied across both ends of the arm one. The secondary H-bridge includes an output capacitor C2, MOS transistors S5, S6, S7, and S8. The arm three formed by the series connection of MOS transistors S5 and S6 is connected in parallel with the arm four formed by the series connection of MOS transistors S7 and S8. Both ends of the arm four are connected in parallel with the output capacitor C2, and the voltage across both ends of the arm four is the output voltage V2. The first end and the second end of the primary coil of the transformer are respectively connected to the midpoints of the arm one and the arm two. The first end and the second end of the secondary coil of the transformer are respectively connected to the midpoints of the arm three and the arm four. The voltage between the midpoints of the arm one and the arm two is the primary port voltage v ab , and the voltage between the midpoints of the arm three and the arm four is the secondary port voltage v cd .

[0072] The DAB converter usually adopts phase shift modulation. By controlling the conduction states of the MOS transistors in the primary H-bridge and the secondary H-bridge, the primary port voltage v ab and the secondary port voltage v cdThe phase shift between them is used to control the magnitude and direction of the transmission power. According to different control freedoms, the phase-shift modulation methods of the DAB converter can be divided into single-phase-shift modulation (SPS), extended-phase-shift modulation (EPS), dual-phase-shift modulation (DPS), and triple-phase-shift modulation (TPS). In the prior art, there is little research on the optimization of the phase-shift ratio in triple-phase-shift modulation. To improve the control effect of the DAB converter under triple-phase-shift modulation, in an embodiment of the present invention, the DAB converter adopts triple-phase-shift modulation.

[0073] Under triple-phase-shift modulation, the DAB converter has three key control freedoms: the first phase-shift ratio D1, the second phase-shift ratio D2, and the third phase-shift ratio D3. Specifically, the first phase-shift ratio D1 refers to the phase-shift angle between MOS transistor S1 and MOS transistor S4 in the primary H-bridge. The second phase-shift ratio D2 refers to the phase-shift angle between MOS transistor S1 in the primary H-bridge and MOS transistor S5 in the secondary H-bridge. The third phase-shift ratio D3 is the phase-shift angle between MOS transistor S5 and MOS transistor S8 in the secondary H-bridge.

[0074] Figure 2 The schematic block diagram of the control method provided by the present invention is shown. In the present invention, the phase-shift ratio constraint formula for the DAB converter operating in the target operating mode is obtained according to the constraint conditions. Specifically, in the target operating mode of triple-phase-shift modulation, with the minimum current stress of the DAB converter as the constraint condition, the relationship between the first phase-shift ratio D1, the second phase-shift ratio D2, and the third phase-shift ratio D3 is described, that is, the phase-shift ratio constraint formula. A prediction model is constructed using the phase-shift ratio constraint formula, and the phase-shift ratio control group for the DAB converter operating in the target operating mode is obtained through the finite set model predictive control algorithm (FCS-MPC), that is, the first phase-shift ratio D1, the second phase-shift ratio D2, and the third phase-shift ratio D3 used to control the DAB converter, so as to effectively reduce the current stress of the power devices in the DAB converter, reduce power loss, and improve the overall efficiency. Those skilled in the art know that PWM signals corresponding to controlling MOS transistors S1 - S8 can be generated according to the first phase-shift ratio D1, the second phase-shift ratio D2, and the third phase-shift ratio D3 using the prior art, and the operation of the DAB converter is controlled by controlling the on-off states of MOS transistors S1 - S8. Among them, the specific methods for obtaining the phase-shift ratio constraint formula and obtaining the phase-shift ratio control group through the prediction model can refer to the following description.

[0075] Under triple-phase-shift modulation, the DAB converter has 12 operating modes. In this embodiment, two operating modes for the DAB to perform forward power transmission are selected as the target operating modes, that is, the target operating modes are the first operating mode or the second operating mode of the DAB converter under triple-phase-shift modulation. In the first operating mode, the first phase-shift ratio D1, the second phase-shift ratio D2, and the third phase-shift ratio D3 in the DAB converter satisfy: D1 ≤ D2 ≤ D3 ≤ 1;

[0076] In the second operating mode, the first phase-shift ratio D1, the second phase-shift ratio D2, and the third phase-shift ratio D3 in the DAB converter satisfy: D2 ≤ D1 ≤ D3 ≤ 1;

[0077] Furthermore, in specific implementation, obtaining the phase-shift ratio constraint formula when the DAB converter operates in the target operating mode according to the constraint conditions includes the following steps:

[0078] S1.1. Obtain the per-unit value p of the transmission power and the per-unit value i of the current stress in the first operating mode and the second operating mode of the DAB converter in triple-phase-shift modulation p , where

[0079] The per-unit value p of the transmission power in the first operating mode and the second operating mode is:

[0080]

[0081] where P is the actual value of the transmission power, and P N is the maximum value of the transmission power under single-phase-shift modulation. The maximum value P of the transmission power under single-phase-shift modulation N is:

[0082]

[0083] where f s is the switching frequency of the DAB converter, L r is the sum of the auxiliary inductor and the leakage inductance of the transformer in the DAB converter, n is the turns ratio of the primary and secondary sides of the transformer in the DAB converter, V1 is the input voltage, and V2 is the output voltage. Those skilled in the art know that the switching frequencies of the MOS transistors S1 - S8 in the DAB converter are the same and are all the switching frequency f of the DAB converter s .

[0084] The per-unit value i of the current stress p in the first operating mode and the second operating mode is:

[0085]

[0086] where i P is the actual value of the peak inductor current, i N is the maximum value of the inductor current under single-phase-shift modulation, T s is the switching period of the DAB converter, and k is the voltage conversion ratio of the DAB converter.

[0087] S1.2. Construct the Lagrangian function E. The constructed Lagrangian function E is:

[0088] E = i p+λ(p - p * )(4)

[0089] where λ is the Lagrange multiplier, i p is the per-unit value of the current stress, and p * is the expected transmission power. The expected transmission power p * can be set according to the actual application requirements.

[0090] S1.3. Solve the constructed Lagrangian function E to obtain the phase-shift ratio constraint equation. Specifically, take the partial derivatives of the Lagrangian function E with respect to D1, D2, and D3 respectively:

[0091]

[0092] Solving the above equations can obtain the phase-shift ratio constraint equations of the DAB converter in the first operating mode and the second operating mode as:

[0093]

[0094] Substitute the above phase-shift ratio constraint equations into Equation (1), and the first phase-shift ratio D1 can be expressed as:

[0095]

[0096] Furthermore, in specific implementation, when constructing a prediction model using the phase-shift ratio constraint equation, it specifically includes the following steps:

[0097] S2.1. Construct a reduced-order model of the DAB converter;

[0098] Figure 3 shows the reduced-order model of the DAB converter. Specifically, the reduced-order model equivalently represents the primary H-bridge and the secondary H-bridge of the DAB converter as a controlled current source respectively.

[0099] S2.2. According to the reduced-order model of the DAB converter, the dynamic equation of the output voltage of the DAB converter can be obtained:

[0100]

[0101] where I load is the load current;

[0102] The output current I2 under the reduced-order model can be expressed as:

[0103]

[0104] where i2 represents the instantaneous value of the output current of the secondary controlled current source.

[0105] Figure 4Shows the modulation timing diagram in the first operating mode of triple-phase-shift modulation, Figure 5 Shows the modulation timing diagram in the second operating mode of triple-phase-shift modulation. Figure 4 And Figure 5 Shows the waveforms of the transformer primary port voltage v ab 、the transformer secondary port voltage v cd And the inductor current i L In a switching period of the corresponding operating mode, i2 = ni L The inductor current i L Is the current flowing through the auxiliary inductor. From Figure 4 And Figure 5 It can be seen that the inductor current i L Has half-cycle symmetry. Therefore, the instantaneous value of the output current i2 of the secondary controlled current source also has half-cycle symmetry. The expression of the instantaneous value of the output current i2 of the secondary controlled current source in the first operating mode (D1 ≤ D2 ≤ D3 ≤ 1) within half of the switching period T s Is:

[0106]

[0107] The expression of the instantaneous value of the output current i2 of the secondary controlled current source in the second operating mode (D2 ≤ D1 ≤ D3 ≤ 1) within half of the switching period T s Is:

[0108]

[0109] According to Equation (9), Equation (10), and Equation (11), combined with the half-cycle symmetry of the inductor current i L , the output current I2 can be obtained by integrating in segments using the existing technology:

[0110]

[0111] According to Equation (12), combined with the phase-shift ratio constraint equation and the expression of the first phase-shift ratio D1 with respect to the per-unit value of the transmission power p and the voltage conversion ratio k, the output current I2 can be expressed as:

[0112]

[0113] Among them, Is the phase shift between the transformer primary port voltage v ab And the secondary port voltage v cd .

[0114] S2.3. Build a prediction model;

[0115] By discretizing the dynamic equation of the output voltage of the DAB converter, i.e., Equation (8), using the forward Euler method, the predicted output voltage V2[d + 1] at time d + 1 can be obtained:

[0116]

[0117] where V2[d] is the output voltage at time d, I2[d] is the output current at time d, and I load [d] is the load current at time d.

[0118] Similarly, the predicted output voltage V2[d + 2] at time d + 2 can be obtained as:

[0119]

[0120] It should be noted that times d, d + 1, and d + 2 are within the same switching period. Generally, it can be assumed that the load current does not change drastically within a switching period, i.e., I load [k] = I load [k + 1]. Then the predicted output voltage V2[d + 2] at time d + 2 is:

[0121]

[0122] Substituting Equation (13) into Equation (15) can obtain the prediction model:

[0123]

[0124] where V2[d + 2] is the predicted output voltage at time d + 2, I2[d + 1] is the output current at time d + 1, and I load [d] is the load current at time d.

[0125] Furthermore, when obtaining the phase shift ratio control group for the DAB converter to operate in the target operating mode through the finite set model predictive control algorithm, the following steps are included:

[0126] S3.1. Obtain the moving discrete control set;

[0127] The is the phase shift between the primary port voltage v ab and the secondary port voltage v cd of the DAB converter at time d + 1. The moving discrete control set of includes multiple candidate phase shifts.

[0128] As known to those skilled in the art, in the first and second operating modes of triple phase shift modulation, the primary port voltage v ab and the secondary port voltage vcd Phase shift between The available value range of is [0, 0.5], that is can vary continuously within the range of [0, 0.5], but in actual digital control, it is necessary to Adjust the resolution Δ according to the phase shift value f That is, the minimum phase shift adjustment value that can be achieved by the digital platform is discretized. After the discretization process

[0129] Generally, the candidate phase shift can be based on the primary port voltage v of the transformer at the current d moment ab and the secondary port voltage v cd Phase shift between And the phase shift value adjustment resolution Δ f Determined, but in order to further improve the dynamic response speed of the DAB converter control, in this embodiment, according to the phase shift value adjustment resolution Δ f The adaptive step size Δ at the d moment is calculated in real time adp [d], and according to the adaptive step size Δ adp Calculate Multiple candidate phase shifts in the moving discrete control set of

[0130] Specifically, the adaptive step size Δ at the d moment adp [d] is:

[0131]

[0132] Among them, λ0 is the voltage error gain, V 2_ref Is the reference voltage, V m Is the saturation voltage error. V 2_ref The reference voltage is the expected output voltage of the DAB converter, and the saturation voltage error V m Can be selected according to the actual situation

[0133] It can be seen from Equation (17) that Δ adp [d] changes with the difference between the output voltage V2[d] at the current d moment and the reference voltage value V 2_ref . The greater the deviation of the output voltage at the current d moment from the reference value, the greater the adaptive step size Δ at the d moment adp [d] is

[0134] According to the adaptive step size Δ adp Defined The moving discrete control set of is:

[0135]

[0136] Among them, μ is the discrete parameter, and the number of candidate phase shifts in the moving discrete control set is 2μ + 1. The discrete parameter μ can be set according to actual needs. For example, when μ = 2, the moving discrete control set is:

[0137]

[0138] S3.2. Set the cost function ct:

[0139]

[0140] Among them, G1 is the first function term, G2 is the second function term, α1 is the first weight factor, and α2 is the second weight factor. The first function term G1 is related to the difference between the predicted output voltage and the reference voltage, and its purpose is to modulate the predicted output voltage to the reference voltage. The second function term G2 is related to the difference between the predicted output voltage and the current actual output voltage, and its purpose is to increase the convergence speed of the algorithm. The smaller the cost function value, the closer the predicted output voltage is to the reference voltage and the actual output voltage. The first weight factor α1 and the second weight factor α2 can be set according to actual needs.

[0141] S3.3. Calculate the cost function value corresponding to each candidate phase shift in the target operating mode;

[0142] For any candidate phase shift, substitute the candidate phase shift into Equation (13) to calculate the output current I2[d + 1] at the d + 1th moment in the first / second operating mode. Given the output current I2[d] at the current moment d, the load current I load [d] and the output voltage V2[d], substitute them into Equation (17) to obtain the predicted output voltage V2[d + 2] at the d + 2th moment corresponding to the candidate phase shift in the first / second operating mode;

[0143] Substitute the output voltage V2[d] at the current moment d and the predicted output voltage V2[d + 2] at the d + 2th moment corresponding to the candidate phase shift in the first / second operating mode into the cost function ct, and the cost function value corresponding to each candidate phase shift in the first / second operating mode can be calculated.

[0144] S3.4. Obtain the phase shift control group at the d + 1th moment in the target operating mode;

[0145] Take the candidate phase shift with the smallest cost function value among all candidate phase shifts as the phase shift ab between the primary port voltage v cd of the transformer in the DAB converter at the d + 1th moment in the first / second operating mode

[0146] According to Equation (6), Equation (7), and Equation (13), the phase shift ab between the primary port voltage v cd and the secondary port voltage v of the transformer in the DAB converter at time d + 1 can be used to calculate the phase shift ratio control group at time d + 1; the phase shift ratio control group at time d + 1 includes the first phase shift ratio D1[d + 1], the second phase shift ratio D2[d + 1], and the third phase shift ratio D3[d + 1] in the DAB converter at time d + 1.

[0147] In specific implementation, the finite set model predictive control algorithm is implemented in the form of a software program. Figure 6 FIG. shows the program flow block diagram when the finite set model predictive control algorithm is actually running. It should be noted that only a brief description of the program flow block diagram is given below. The specific implementation methods of each step in the block diagram are the same as the corresponding implementation methods described in the above embodiments, and can be understood by referring to the relevant content in the above embodiments. Details are not repeated below.

[0148] As Figure 6 shown, when performing finite set model predictive control, first calculate the current adaptive step size Δ adp value, and then calculate the moving discrete control set according to the current output value . The moving discrete control set is represented by list. Let the loop variable i start counting from 0. When the loop variable i is less than the total number 2μ + 1 of candidate phase shifts in the moving discrete control set list, calculate the corresponding cost function value ct(list[i]) according to the i-th candidate phase shift list[i] in the moving discrete control set list to traverse and calculate the corresponding cost function values of all candidate phase shifts. If ct(list[i]) is less than the currently calculated minimum cost function value min, then let min = ct(list[i]), and at the same time let the output value Otherwise, directly let i = i + 1, and the initial value of min can be set to a relatively large value.

[0149] When the loop variable i is greater than or equal to 2μ + 1, let the phase shift ab between the primary port voltage v cd and the secondary port voltage v of the transformer in the DAB converter at time d + 1, and calculate the phase shift ratio control group at time d + 1 according to . If it is necessary to continue to obtain the phase shift ratio control group at time d + 2, then update let and repeat the above process.

[0150] To verify the control effect of the control method proposed by the present invention, a simulation control experiment on the DAB converter was carried out based on the control method proposed by the present invention.Figures 7 - 9 is the reference voltage V 2_ref This is the simulation waveform of the DBA converter at 50V. Figures 7 - 9 The transmission power per unit value p of the DBA converter is equal to 0.24, 0.5 and 0.8 respectively. Figure 7 The DBA converter works in the second working mode. Figure 8 and Figure 9 The DBA converter operates in the first operating mode. The simulation waveform diagram includes the primary port voltage v ab The waveform of the secondary port voltage v cd The waveform of the inductor current i L The inductor current is the current flowing through the auxiliary inductor. Figure 10 It shows that when the load changes step, the output voltage V2 and the load current I load and the inductor current i L The simulation waveform is given by Figures 7 - 10 It can be seen that the control method proposed in the present invention has good control capability and response speed.

[0151] It should be noted that the words "first" and "second" used in the above description are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. The above is only a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the scope of protection of the present invention.

Claims

1. A DAB converter control method based on minimum current stress and finite set model prediction, characterized in that: include: Obtaining a shift phase constraint formula when the DAB converter operates in a target operating mode according to the constraint conditions, wherein the constraint conditions include making the DAB converter operate in a minimum current stress; The phase shift constraint formula is used to construct a prediction model in a finite set model predictive control algorithm, and a phase shift control group when the DAB converter works in a target working mode is obtained through the finite set model predictive control algorithm.

2. The DAB converter control method based on minimum current stress and finite set model prediction according to claim 1, characterized in that: When obtaining the shift ratio constraint formula when the DAB converter works in the target working mode under the constraint condition, it includes: Construct the Lagrangian function E and solve the constructed Lagrangian function E to obtain the shift phase constraint formula. The constructed Lagrangian function E is: E−i p +λ(pp * ) Where λ is the Lagrange multiplier, i p is the per-unit value of current stress, p is the per-unit value of transmission power, and p * is the expected transmission power.

3. The DAB converter control method based on minimum current stress and finite set model prediction according to claim 2, characterized in that: The target operating mode is the first operating mode or the second operating mode of the DAB converter under triple phase shift modulation; In the first working mode, the first shift phase D1, the second shift phase D2 and the third shift phase D3 of the DAB converter satisfy the following conditions: D1≤D2≤D3≤1; In the second working mode, the first shift phase D1, the second shift phase D2 and the third shift phase D3 of the DAB converter satisfy the following conditions: D2≤D1≤D3≤1; The transmission power per unit value p in the first working mode and the second working mode is: Where P is the actual value of the transmission power, P N is the maximum value of the transmission power under single phase shift modulation. N for: Among them, f s is the switching frequency of the DAB converter, L r is the sum of the auxiliary inductance and the transformer leakage inductance in the DAB converter, n is the primary-to-secondary turns ratio of the transformer in the DAB converter, V1 is the input voltage, and V2 is the output voltage; The current stress per unit value i p In the first working mode and the second working mode: Among them, i P is the actual value of the inductor current peak, i N is the maximum value of the inductor current under single phase shift modulation, T s is the switching period of the DAB converter, and k is the voltage conversion ratio of the DAB converter.

4. The DAB converter control method based on minimum current stress and finite set model prediction according to claim 3, characterized in that: The obtained phase shift constraint formula of the DAB converter in the first working mode and the second working mode is: Under the shift phase constraint, the first shift phase D1 satisfies:

5. The DAB converter control method based on minimum current stress and finite set model prediction according to claim 3, characterized in that: When the prediction model in the finite set model predictive control algorithm is constructed using the shift phase constraint formula, it includes: A reduced-order model of the DAB converter is constructed, and the dynamic equation of the output voltage of the DAB converter is obtained according to the reduced-order model of the DAB converter. The dynamic equation of the output voltage of the DAB converter is: Where C2 is the output capacitor of the DAB converter, V2 is the output voltage, I2 is the output current, and I load is the load current; The output current I2 is expressed according to the shift phase constraint in the reduced-order model: in, is the transformer primary port voltage v in the DAB converter ab and the secondary port voltage v cd The phase shift between The dynamic equation of the output voltage of the DAB converter is discretized to construct a prediction model, and the constructed prediction model is: Where V2[d] is the output voltage at time d, V2[d+2] is the predicted output voltage at time d+2, I2[d] is the output current at time d, I2[d+1] is the output current at time d+1, and I load [d] is the load current at time d.

6. The DAB converter control method based on minimum current stress and finite set model prediction according to claim 5, characterized in that: When the phase shift control group of the DAB converter working in the target working mode is obtained by the finite set model predictive control algorithm, it includes: Get The mobile discrete control set and set the cost function ct, is the transformer primary port voltage v in the DAB converter at time d+1 ab and the secondary port voltage v cd The phase shift between The mobile discrete control set includes multiple candidate phase shifts; The cost function value corresponding to each candidate phase shift in the target working mode is calculated according to the prediction model and the cost function ct, and the candidate phase shift with the smallest cost function value among all the candidate phase shifts is used as the transformer primary port voltage v in the DAB converter at time d+1 ab and the secondary port voltage v cd The phase shift between And according to the transformer primary port voltage v in the DAB converter at time d+1 ab and the secondary port voltage v cd The phase shift between Calculate the shift ratio of the target working mode at time d+1 compared with the control group; The phase shift control group at time d+1 in the target working mode includes a first phase shift D1[d+1], a second phase shift D2[d+1] and a third phase shift D3[d+1] in the DAB converter at time d+1 in the target working mode.

7. The DAB converter control method based on minimum current stress and finite set model prediction according to claim 6, characterized in that: Said The mobile discrete control set is: Among them, Δ adp [d] is the adaptive step size at time d, is the transformer primary port voltage v in the DAB converter at time d ab and the secondary port voltage v cd The phase shift between them, μ is a discrete parameter; The adaptive step size Δ at the time d adp [d] Adjust the resolution Δ according to the phase shift value f And the output voltage error V at time d Δ [d] OK.

8. The DAB converter control method based on minimum current stress and finite set model prediction according to claim 7, characterized in that: The adaptive step size Δ at the time d adp [d] is: Where λ is the voltage error gain, V 2_ref is the reference voltage, V m is the saturation voltage error.

9. The DAB converter control method based on minimum current stress and finite set model prediction according to claim 6, characterized in that: When calculating the cost function value corresponding to each candidate phase shift in the target working mode according to the prediction model and the cost function ct, it includes: The predicted output voltage V2[d+2] at time d+2 corresponding to each candidate phase shift is calculated according to the prediction model, and the predicted output voltage V2[d+2] at time d+2 corresponding to each candidate phase shift is substituted into the cost function ct to calculate the cost function value corresponding to each candidate phase shift under the target operating mode.

10. The DAB converter control method based on minimum current stress and finite set model prediction according to claim 9, characterized in that: The cost function ct is: Among them, G1 is the first function term, G2 is the second function term, α1 is the first weight factor, and α2 is the second weight factor.

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