Multi-modal control-based multi-target unified optimization modulation method for Semi-DAB converter

Abstract

The invention relates to a multi-modal control-based multi-target unified optimization modulation method for a Semi-DAB converter, and the method comprises the following steps: dividing the working mode of the Semi-DAB converter into a low-power mode and a high-power mode, combining with a cost function, optimizing the backflow power and the current stress, and carrying out the optimization of the backflow power and the current stress. And through a closed-loop control system based on multi-mode control, the converter can automatically switch working modes according to working states. After the input voltage Vin and the output voltage Vo of the Semi-DAB converter are sampled, the output reference voltage and the output voltage are input into a subtractor for subtraction, the obtained error amount is input into a PI controller, p is obtained through corresponding operation, the current working state of the Semi-DAB converter is judged according to the range of the obtained p, seamless switching between the two modes is automatically achieved, and therefore the semi-DAB converter can be switched automatically. And corresponding PWM signals are generated through D0 and D1 given in each mode, and the corresponding switching tubes are driven to be switched on and switched off, so that the converter always operates in the optimal efficiency state in different power intervals.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics, and in particular relates to a multi-objective unified optimization modulation method for a Semi-DAB converter based on multi-mode control. Background Art

[0002] Dual Active Bridge (DAB) converters are widely used in power transmission, industrial automation, energy conversion and management due to their high efficiency, good electrical isolation, bidirectional power transmission and other advantages. Since DAB can flexibly realize energy transmission between different voltage levels and adapt to a variety of application scenarios, DAB converters have obvious advantages in terms of bidirectional power transmission. However, in some specific application scenarios, such as DC-DC conversion in photovoltaic power generation systems, power adapters, DC power supply systems, etc., only unidirectional power transmission is usually required. At this time, the use of DAB converters may result in excess performance, thus affecting the cost-effectiveness of the system.

[0003] There are many common topologies for isolated DC-DC converters with unidirectional power transmission. Semi-DAB converter is one of them. It replaces the two switches with the same potential in the secondary full-bridge circuit of DAB converter with diodes. It also has the advantages of high efficiency and good electrical isolation. The entire topology has 6 switches. Using fewer switching elements can reduce the overall material and manufacturing costs. Fewer components make the overall volume and weight of the converter lower, which helps save space. Since diodes cannot be controlled to turn on and off like switches, the operating waveform of Semi-DAB converter will be different from that of DAB converter.

[0004] Similar to DAB converters, Semi-DAB also has modulation methods such as single phase shift modulation (SPS) and double phase shift modulation (DPS). However, under traditional single phase shift modulation and double phase shift modulation, Semi-DAB converters may have problems of excessive reflux power and current stress during operation, resulting in unnecessary power loss and reducing the overall efficiency of the converter. Summary of the invention

[0005] The present invention provides a multi-objective unified optimization modulation method for a Semi-DAB converter based on multi-modal control, which is significantly innovative. Traditional modulation methods usually use a fixed modulation mode, while the present invention divides the working mode of the Semi-DAB converter into two modes, low power and high power, and optimizes the return power and current stress in combination with the cost function, thereby ensuring that the converter can achieve efficient and stable operation in both low power and high power ranges. In addition, the present invention adopts a closed-loop control system based on multi-modal control, so that the Semi-DAB converter can automatically switch seamlessly between low power mode and high power mode according to different power requirements, realizing dynamic switching of low power and high power working modes, so that the converter always operates in the optimal efficiency state in different power ranges.

[0006] The Semi-DAB converter consists of an active H-bridge and a semi-active H-bridge, where the active H-bridge is the primary side, and each bridge arm of the primary side contains two fully controlled switches, and the semi-active H-bridge is the secondary side, and each bridge arm of the secondary side contains a diode and a fully controlled switch; the upper and lower switch signals of the same bridge arm of the converter are complementary, the transformer ratio is n:1, and the voltage gain ratio is M=nV o / V in In the present invention, M>1; two shift ratios are defined as D 0 , D 1 , where D 0 For S 1 With S 6 Compared with the shift between 1 For S 1 With S 4 Compared with the shift between.

[0007] In the solution of the present invention, in order to optimize power transmission and control efficiency, all power and current stress calculations are performed using per-unit values. Using per-unit value calculations can standardize parameters in different power ranges, making it easier to compare and optimize under different working conditions. Taking the maximum transmission power of the DAB converter under SPS modulation and the input current at this time as the reference value, the formula is as follows:

[0008]

[0009] Among them, P N ,I N are the reference values ​​of power and current, respectively, s is the switching frequency and L is the inductance value.

[0010] The calculation formulas for the transmission power, return power and current stress per unit value are as follows:

[0011]

[0012] Among them, P, Q, and I are transmission power, return power, and current stress, respectively. * , Q * and I * They are the per-unit value of transmission power, per-unit value of return power and per-unit value of current stress respectively.

[0013] The technical solution of the present invention is as follows:

[0014] The Semi-DAB converter of the present invention works at 0≤D 1 ≤D 0 ≤1, the working mode is divided into low power and high power. 1 The start of a cycle is when the inductor current reaches 0 for the first time and is greater than 0 and less than D 1 T hs When the inductor current reaches 0 for the first time, it is greater than D 1 T hs and less than D 0 T hs In the two modes, the transmission power per unit value, return power per unit value, and current stress per unit value of the Semi-DAB converter are as follows:

[0015] Low Power Mode:

[0016]

[0017] High Power Mode:

[0018]

[0019] In the above formula, They are the per-unit value of transmission power, per-unit value of return power, and per-unit value of current stress in low-power mode. They are the per-unit value of transmission power, per-unit value of return power and per-unit value of current stress in high-power mode respectively.

[0020] On this basis, in order to optimize the operating performance of the converter, the present invention introduces a cost function λ. The cost function aims to optimize the return power and current stress, thereby minimizing the return power and current stress while ensuring system efficiency. The specific definition is as follows:

[0021]

[0022] Among them, F is the optimized variable; i represents the control variable, that is, D i represents the displacement ratio; j represents the working mode, that is, F j , P j Represents the optimized variables and their transmission power under different modes.

[0023] When using the cost function to achieve optimization, the optimal solution is as follows:

[0024] λ(0,j)=λ(1,j)

[0025] The two working modes are combined with the cost function to optimize the current stress of the low-power mode and the return power of the high-power mode. The calculation formula is as follows:

[0026]

[0027] According to the above formula, the modulation obtained after optimizing the low power mode and high power mode is as follows:

[0028]

[0029] According to the above formula, the transmission power per unit value, return power per unit value, and current stress per unit value of the optimized low power mode and the optimized high power mode are calculated as follows:

[0030] Optimized for low power:

[0031]

[0032] Optimized high power:

[0033]

[0034] After the cost function is optimized, the return power of both low power and high power is 0, realizing the zero return power operation of the Semi-DAB converter.

[0035] In order to further optimize the operation of the Semi-DAB converter, the present invention adopts a closed-loop control system based on multi-modal control, including a sampling unit, a PI control unit and a modulation unit. The sampling unit has two signal input terminals, namely, the input voltage V in and output voltage V o ; Input the output reference voltage and the output voltage into the subtractor for difference calculation, and input the difference into the PI controller. After relevant operations, p is obtained. The calculation formula is as follows:

[0036] p=k p (V ref -V o )+k i ∫(V ref -V o )dt

[0037] where k p , k i is the PI controller parameter, V refis the output reference voltage.

[0038] In the modulation unit, the current working state of the Semi-DAB converter is determined according to the range of p, and the corresponding mode is automatically switched according to the current working state. When , switch to low power; when When the power is high, switch to high power.

[0039] According to the calculation formula of the transmission power per unit value of low power and high power, the D in the optimized low power mode and the optimized high power mode is obtained. 0 , D 1 The values ​​are:

[0040] i) Low power after optimization

[0041]

[0042] ii) High power after optimization

[0043]

[0044] Among them, f 1 (p), f 2 (p) is a function of p, according to the D 0 , D 1 , generate the corresponding PWM signal to drive the corresponding switch tube to turn on and off.

[0045] It can be seen from the above technical solution that the advantages of the present invention are: first, the working mode of the Semi-DAB converter is divided into low power and high power, and the two working modes are combined with the cost function, which realizes the optimization of return power and current stress without affecting the transmission power; second, through a closed-loop control system based on multi-modal control, the Semi-DAB converter automatically switches seamlessly between the two working modes according to different power requirements, realizing dynamic switching of the two working modes of low power and high power, so that the converter always operates in the optimal efficiency state in different power ranges, significantly improving the power transmission efficiency of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is the main topology diagram of the Semi-DAB converter.

[0047] Figure 2 It is the main working waveform of the Semi-DAB converter when it operates in low power mode and high power mode.

[0048] Figure 3These are the main working waveforms of the Semi-DAB converter when operating in the optimized low power mode and the optimized high power mode.

[0049] Figure 4 P is the P of the Semi-DAB converter optimized by the optimization method proposed in the present invention when M=1.441, M=2, and M=3 compared with that under traditional SPS modulation. * -I * Relationship diagram.

[0050] Figure 5 It is the closed-loop control system of the present invention. DETAILED DESCRIPTION

[0051] The present invention will be further described below in conjunction with the accompanying drawings, but the protection scope of the present invention shall not be limited thereto.

[0052] like Figure 1 As shown in FIG. 1 , the Semi-DAB converter consists of an active H-bridge, a semi-active H-bridge, a high-frequency inductor and a high-frequency isolation transformer, wherein the active H-bridge is the primary side, and each bridge arm of the primary side includes two fully-controlled switches; the semi-active H-bridge is the secondary side, and each bridge arm of the secondary side includes a diode and a fully-controlled switch; L is the high-frequency inductor, C in and C o are the input side capacitor and the output side capacitor respectively, V in is the input voltage, and R is the output resistance.

[0053] Figure 2 The main working waveforms of the Semi-DAB converter in low power mode and high power mode are shown in Figure 2. 1 For S 1 With S 4 Compared with the shift between 0 For S 1 With S 6 Compared with the shift between Figure 2 The shaded area in (b) is the return power in the high-power mode, and there is no return power in the low-power mode.

[0054] In order to optimize the operating performance of the converter, the present invention introduces a cost function λ, which aims to optimize the return power and current stress, thereby minimizing the return power and current stress while ensuring system efficiency. The specific definition is as follows:

[0055]

[0056] Among them, F is the optimized variable; i represents the control variable, that is, D i represents the displacement ratio; j represents the working mode, that is, F j , P jRepresents the optimized variables and their transmission power under different modes.

[0057] When D 0 With D 1 When the impact on the cost function is not equal, the return power can be further reduced through adjustment. Therefore, when using the cost function to achieve optimization, in order to minimize the optimized variable, the optimal solution is as follows:

[0058] λ(0,j)=λ(1,j)

[0059] The two working modes are combined with the cost function to optimize the current stress of the low-power mode and the return power of the high-power mode. The calculation formula is as follows:

[0060]

[0061] According to the above formula, the modulation obtained after optimizing the low power mode and the high power mode is as follows:

[0062]

[0063] Figure 3 The main working waveforms of the Semi-DAB converter in the optimized low power mode and the optimized high power mode. According to the optimized modulation of low power and high power calculated by the cost function and the transmission power per unit value, return power per unit value, and current stress per unit value of low power and high power before optimization, the transmission power per unit value, return power per unit value, and current stress per unit value of low power and high power after optimization are calculated as follows:

[0064] Optimized for low power:

[0065]

[0066] Optimized high power:

[0067]

[0068] After the cost function is optimized, the return power of both low power and high power is 0, realizing the zero return power operation of the Semi-DAB converter.

[0069] Figure 4 P is the P of the Semi-DAB converter optimized by the optimization method proposed in the present invention when M=1.441, M=2, and M=3 compared with that under traditional SPS modulation. * -I * Compared with SPS modulation, the Semi-DAB converter has a wider transmission power range and smaller current stress after being optimized by the optimization method proposed in the present invention.

[0070] like Figure 5 As shown, the present invention adopts a closed-loop control system based on multi-modal control, and the closed-loop control system includes the following sequential steps:

[0071] 1) In the S of the Semi-DAB converter 1 ~S 6 Before the switch tube drives the signal, the input voltage V in and output voltage V o Sampling is performed and the voltage gain ratio is calculated;

[0072] 2) The output reference voltage and the output voltage are input into the subtractor to obtain the error, and the obtained error is input into the PI controller. The appropriate PI parameters are set for compensation. After the corresponding operation, p is obtained. The operation is as follows:

[0073] p=k p (V ref -V o )+k i ∫(V ref -V in )dt

[0074] 3) According to the range of p, the current working state of the Semi-DAB converter is judged, and the corresponding mode is automatically switched according to the current working state. When , it switches to low power mode; when Switch to high power mode.

[0075] According to the calculation formula of the transmission power per unit value of low power and high power, the D in the optimized low power mode and the optimized high power mode is obtained. 0 , D 1 The values ​​are:

[0076] i) Optimized low power:

[0077]

[0078] ii) High power after optimization:

[0079]

[0080] Among them, f 1 (p), f 2 (p) is a function of p, according to the D 0 , D 1 , generate the corresponding PWM signal to drive the corresponding switch tube to turn on and off.

Claims

1. A multi-objective unified optimization modulation method for Semi-DAB converter based on multi-mode control, characterized in that: The working modes of the Semi-DAB converter are divided into low-power and high-power modes, and the return power and current stress are optimized in combination with the cost function to ensure that the converter can achieve efficient and stable operation in both low-power and high-power ranges. In addition, the present invention adopts a closed-loop control system based on multi-modal control, so that the Semi-DAB converter can automatically switch seamlessly between low-power mode and high-power mode according to different power requirements, realizing dynamic switching of low-power and high-power working modes, so that the converter always operates in the optimal efficiency state in different power ranges.

2. The Semi-DAB converter according to claim 1, characterized in that: The Semi-DAB converter consists of an active H-bridge and a semi-active H-bridge, where the active H-bridge is the primary side, and each bridge arm of the primary side contains two fully controlled switches, and the semi-active H-bridge is the secondary side, and each bridge arm of the secondary side contains a diode and a fully controlled switch; the upper and lower switch signals of the same bridge arm of the converter are complementary, the transformer ratio is n:1, and the voltage gain ratio is M=nV o / V in In the present invention, M>1; two shift ratios are defined as D0 and D1, where D0 is the shift ratio between S1 and S6, and D1 is the shift ratio between S1 and S4.

3. The two operating modes of the Semi-DAB converter according to claim 1 are combined with a cost function, characterized in that: The Semi-DAB converter of the present invention works in the state of 0≤D1≤D0≤1, and its working mode is divided into low power and high power. Taking S1 as the start of a cycle, when the inductor current reaches 0 for the first time, it is greater than 0 and less than D1T hs When the inductor current reaches 0 for the first time, it is greater than D1T. hs And less than D0T hs In the two modes, the transmission power per unit value, return power per unit value, and current stress per unit value of the Semi-DAB converter are as follows: Low Power Mode: High Power Mode: In the above formula, They are the per-unit value of transmission power, per-unit value of return power, and per-unit value of current stress in low-power mode. They are the per-unit value of transmission power, per-unit value of return power and per-unit value of current stress in high-power mode respectively. On this basis, in order to optimize the operating performance of the converter, the present invention introduces a cost function λ. The cost function aims to optimize the return power and current stress, thereby minimizing the return power and current stress while ensuring system efficiency. The specific definition is as follows: Among them, F is the optimized variable; i represents the control variable, that is, D i represents the displacement ratio; j represents the working mode, that is, F j , P j Represents the optimized variables and transmission power under different modes. When using the cost function for optimization, the formula is as follows: λ(0,j)=λ(1,j) The two working modes are combined with the cost function to optimize the current stress of the low-power mode and the return power of the high-power mode. The calculation formula is as follows: According to the above formula, the modulation obtained after optimizing the low power mode and high power mode is as follows: According to the above formula, the transmission power per unit value, return power per unit value, and current stress per unit value of the optimized low power mode and the optimized high power mode are calculated as follows: i) Optimized low power: ii) High power after optimization:

4. P as claimed in claim 3 * , Q * and I * peak All are per-unit values, characterized in that: The use of per-unit value calculation can standardize the parameters of different power ranges, which is convenient for comparison and optimization under different working conditions. Taking the maximum transmission power of the DAB converter under SPS modulation and the input current at this time as the reference value, the formula is as follows: Where P N ,I N are the power reference value and current reference value respectively, P, Q, and I are the transmission power, return power, and current stress respectively, and f s is the switching frequency, and L is the inductance value.

5. The closed-loop control system based on multi-modal control according to claim 1, characterized in that: The control process specifically includes the following steps: Step 1: Before giving the drive signal to the S1~S6 switches of the Semi-DAB converter, the input voltage V in and output voltage V o Sampling is performed and the voltage gain ratio is calculated. Step 2: Subtract the output reference voltage from the output voltage input into the subtractor to obtain the error, input the error into the PI controller, set appropriate PI parameters for compensation, and obtain p through corresponding calculations. The calculation is as follows: p=k p (V ref -V o )+k i ∫(V ref -V o )dt where k p , k i is the PI controller parameter, V ref is the output reference voltage. Step 3: Determine the current working state of the Semi-DAB converter according to the range of p obtained in step (2) and automatically switch to the corresponding mode. When , it switches to low power mode; when When , switch to high power mode; after optimization, the values ​​of D0 and D1 in low power mode and high power mode are: i) Optimized low power: ii) High power after optimization: Among them, f1(p) and f2(p) are functions about p, and according to D0 and D1, corresponding PWM signals are generated to drive the corresponding switch tube to be turned on and off.

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