A DAB optimized control method for single-phase power electronic conversion systems

Abstract

The application belongs to the technical field of power electronics, and relates to a DAB optimization control method for a single-phase power electronic conversion system, which comprises the following steps: obtaining system operation data, calculating an optimization value of a middle direct-current bus voltage reference value of the single-phase power electronic conversion system; calculating an optimization value of a double-frequency power amplitude and an optimization value of a middle direct-current bus voltage ripple value; setting a maximum withstand voltage value of the system and calculating a maximum allowed middle direct-current bus voltage ripple value; calculating an optimized feedforward compensation value of double-frequency power of a DAB converter according to the optimization value of the double-frequency power amplitude and the optimization value; calculating a reference value of output power of the DAB converter according to the optimized feedforward compensation value, converting the reference value into a shift angle, and taking the shift angle as a control instruction of the DAB converter; and controlling the DAB converter according to the control instruction. The application realizes efficient optimization operation and control of the DAB converter under the condition of a small middle direct-current bus capacitor.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power electronics, and particularly relates to a DAB optimization control method for a single-phase power electronic conversion system. BACKGROUND

[0002] In the field of power electronics, single-phase AC / DC( / AC) power electronic conversion systems are widely used in many practical fields, such as electric vehicle charging, battery energy storage, power electronic transformers, renewable energy generation, etc. Such a system is generally composed of a front-stage DC / DC converter + a rear-stage single-phase inverter. The topology structure composed of a front-stage dual full-bridge DC / DC converter (Dual Active Bridge, DAB) + a rear-stage H-bridge inverter is one of the most typical single-phase AC / DC( / AC) power electronic conversion systems. Improving power density and improving operating efficiency are two core goals that the development of power electronic conversion system technology has been pursuing. In order to improve the power density of the power electronic conversion system, significantly reducing the amount of DC bus capacitor is an effective method. However, in the single-phase power electronic conversion system, there is an inherent instantaneous power flow at twice the frequency. On the one hand, this will inevitably cause a large amount of twice-frequency ripple in the DC bus voltage, affecting the safe and stable operation of the rear-stage H-bridge inverter and the power quality; on the other hand, this twice-frequency fluctuation will propagate into the front-stage DC / DC converter, causing current fluctuation of the DC / DC converter and significantly reducing its operating efficiency. Therefore, reducing the intermediate DC bus capacitor value and improving the system operating efficiency are two mutually contradictory goals.

[0003] In existing technologies, there are still many problems with the control methods of single-phase AC / DC power electronic conversion systems. One approach is to connect additional active filter circuits in parallel across the DC bus to absorb second-harmonic power fluctuations in the system. This method can effectively reduce the DC bus capacitance and suppress DC bus voltage ripple. However, this method requires additional components to be added to the system, leading to increased system complexity, control complexity, and decreased reliability. Therefore, how to achieve both DC bus capacitance reduction and stable control of the power electronic conversion system using only specific control techniques without adding any additional components is a pressing problem. Several different closed-loop control strategies have been proposed in existing technologies, utilizing a front-stage DC / DC converter to transfer second-harmonic power from the DC bus side to the other, thereby suppressing DC bus voltage ripple and reducing DC bus capacitance. In these methods, the front-stage DC / DC converter needs to transfer a large amount of second-harmonic power, which will cause large low-frequency fluctuations in the current of the front-stage DC / DC converter, leading to increased system power loss and decreased efficiency. Therefore, how to improve the working efficiency of a single-phase two-stage power electronic conversion system is another problem that urgently needs to be solved.

[0004] The aforementioned existing technologies either utilize a front-end DC / DC converter to compensate for all double-frequency power to reduce intermediate DC bus capacitance and increase system power density, but this results in significant low-frequency current fluctuations in the DC / DC converter and a decrease in operating efficiency; or they aim to suppress low-frequency current fluctuations in the DC / DC converter to improve the operating efficiency of the power electronic conversion system, but this leads to a large amount of DC bus capacitance and a decrease in power density. Therefore, these existing technologies cannot simultaneously reduce the DC bus capacitance and suppress low-frequency current fluctuations.

[0005] Coordinating and optimizing the control of DC / DC current fluctuations to improve system efficiency is insufficient to meet the current technological development requirements of the power industry for high power density and high efficiency power electronic conversion systems. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention proposes a DAB optimization control method for single-phase power electronic conversion systems, the method comprising:

[0007] S1. Real-time acquisition of operating data of single-phase power electronic conversion system;

[0008] S2. Calculate the optimized value V of the intermediate DC bus voltage reference value of the single-phase power electronic converter system based on the collected operating data. 2ref,aopt ;

[0009] S3, based on the optimized value V 2ref,aopt Calculate the optimized value P of the second harmonic power amplitude.DABf,aopt The optimized value V of the intermediate DC bus voltage ripple. 2f,aopt ;

[0010] S4. Set the system's maximum withstand voltage value V BR Calculate the maximum allowable intermediate DC bus voltage ripple value V based on the system's maximum withstand voltage. 2f,mav ;

[0011] S5. Set the DC voltage ripple redundancy coefficient ε and determine V. 2f,aopt and εV 2f,mav The size of V 2f,aopt Greater than or equal to εV 2f,mav If yes, proceed to step S6; otherwise, proceed to step S7.

[0012] S6, Optimization value P for second harmonic power amplitude DABf,aopt The optimized value V of the intermediate DC bus voltage ripple. 2f,aopt Make corrections;

[0013] S7. Based on the optimized value P of the second harmonic power amplitude DABf,aopt and optimized value V 2f,aopt Calculate the optimized feedforward compensation value p for the second harmonic power of the DAB converter. f ;

[0014] S8. Calculate the reference value of the DAB converter output power based on the optimized feedforward compensation value, convert the reference value into a steering angle, and use it as the control command for the DAB converter.

[0015] S9. Control the DAB converter according to the control instructions.

[0016] The beneficial effects of this invention are:

[0017] The control technology proposed in this invention can ensure the stable operation of the downstream inverter and minimize the low-frequency fluctuation amplitude of the current of the upstream DAB converter under the condition of high ripple intermediate DC bus voltage. In other words, it realizes the high-efficiency optimized operation and control of the DAB converter with a small intermediate DC bus capacitance, thereby improving the power density and operating efficiency of the single-phase power electronic conversion system at the same time. Attached Figure Description

[0018] Figure 1 This is an overall flowchart of the present invention;

[0019] Figure 2 This is a topology diagram of the single-phase power electronic conversion system of the present invention;

[0020] Figure 3 This is a schematic diagram of the control method of the present invention;

[0021] Figure 4 This diagram illustrates the optimization effect of the present invention on low-frequency current fluctuations in DAB.

[0022] Figure 5 The experimental waveform diagram is shown for the control method of the present invention.

[0023] Figure 6 This diagram illustrates the optimized effect of the present invention on reducing the intermediate DC bus capacitor. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] This patent invention discloses an optimized control method for DAB (Digital-Induced Block) converters in single-phase power electronic converter systems. It solves the problem of existing control technologies struggling to simultaneously and optimally control both the DC bus capacitance reduction and DC / DC current fluctuation suppression objectives. This method achieves optimized control of the front-stage DC / DC converter under conditions of reduced DC bus capacitance and relatively high intermediate DC bus voltage ripple. On the one hand, this method allows for higher amplitude second-harmonic DC bus voltage ripple to significantly reduce the DC bus capacitance; on the other hand, it proposes an optimized control strategy to suppress low-frequency current fluctuations in the DAB converter while ensuring the safe and stable operation of the downstream inverter. This method achieves coordinated optimization of both objectives: suppressing low-frequency current fluctuations in the front-stage DC / DC converter and reducing the intermediate DC bus capacitance.

[0026] A DAB optimization control method for single-phase power electronic conversion systems, such as Figure 1 As shown, the method includes:

[0027] S1. Starting from the current control cycle, acquire the operating data of the single-phase power electronic conversion system in real time;

[0028] S2. Calculate the optimized value V of the intermediate DC bus voltage reference value of the single-phase power electronic converter system based on the collected operating data. 2ref,aopt ;

[0029] S3, based on the optimized value V 2ref,aopt Calculate the optimized value P of the second harmonic power amplitude. DABf,aopt The optimized value V of the intermediate DC bus voltage ripple. 2f,aopt ;

[0030] S4. Set the system maximum withstand voltage V according to the device datasheet. BRCalculate the maximum allowable intermediate DC bus voltage ripple value V based on the system's maximum withstand voltage. 2f,mav ;

[0031] S5. Considering factors such as sampling error, circuit parameter error, and noise interference, V 2f,mav There is a certain error between the actual value and its theoretical calculation value in S4. Therefore, the DC voltage ripple redundancy coefficient ε is set to a range of [0,1] according to the actual hardware conditions. The closer ε is to 0, the greater the ripple redundancy, and at this time a larger V is allowed. 2f,mav The calculation error; the closer ε is to 1, the smaller the ripple redundancy, and at this time a smaller V is allowed. 2f,mav The calculation error. Determine V. 2f,aopt and εV 2f,mav The size of V 2f,aopt Greater than or equal to εV 2f,mav If yes, proceed to step S6; otherwise, proceed to step S7.

[0032] S6, Optimization value P for second harmonic power amplitude DABf,aopt The optimized value V of the intermediate DC bus voltage ripple. 2f,aopt Make corrections;

[0033] S7. Based on the optimized value P of the second harmonic power amplitude DABf,aopt and optimized value V 2f,aopt Calculate the optimized feedforward compensation value p for the second harmonic power of the DAB converter. f ;

[0034] S8. Calculate the reference value of the DAB converter output power based on the optimized feedforward compensation value, convert the reference value into a steering angle, and use it as the control command for the DAB converter.

[0035] S9. Control the DAB converter according to the control instructions.

[0036] In this embodiment, the operating data includes the AC output voltage v of the single-phase H-bridge inverter. s Effective value U s The AC output current i of a single-phase H-bridge inverter s Effective value I s i s ahead of v s Power factor angle

[0037] The input DC voltage of the DAB converter is v1, and the intermediate DC bus voltage is v2.

[0038] The optimized value for calculating the intermediate DC bus voltage reference value is:

[0039]

[0040] Among them, V 2ref,aopt The optimized value is the reference value for the intermediate DC bus voltage, v1 is the DC voltage at the input of the DAB converter, A1 is the optimized parameter, and U... s The AC output voltage V of a single-phase H-bridge inverter s The effective value of I s i is the AC output current of the single-phase H-bridge inverter. s The effective value, The power factor angle.

[0041] In this embodiment, the expression for the optimization parameter A1 is:

[0042] A1 = 0.0225 π 4 ω s 2 L 2 / v1

[0043] Where π is the coefficient of pi, approximately equal to 3.1415926, and ω s ω is the switching angular frequency of the DAB converter, and L is the auxiliary inductance.

[0044] Calculate the optimized value P of the second harmonic power amplitude. DABf,aopt The optimized value V of the intermediate DC bus voltage ripple. 2f,aopt for:

[0045]

[0046] Among them, P DABf,aopt Here, A1 is the optimized value for the second harmonic power amplitude, ω is the grid voltage angular frequency, C is the intermediate DC bus capacitance, and V is the optimized parameter. 2ref,aopt The optimized value for the intermediate DC bus voltage reference value, V 2f,aopt This is the optimized value for the intermediate DC bus voltage ripple.

[0047] Calculate the maximum allowable intermediate DC bus voltage ripple value V 2f,mav for:

[0048]

[0049] Here, min(x,y) represents the smaller of the two numbers x and y.

[0050] In this embodiment, when V 2f,aopt <ε·V 2f,mav At that time, not targeting P DABf,aopt and V 2f,aopt The value of P is corrected at this time. DABf,aopt and V 2f,aopt The value is given according to the result in step S3; when V 2f,aopt≥ε·V 2f,mav At that time, P DABf,aopt and V 2f,aopt The value should be corrected to:

[0051] V 2f,aopt =εV 2f,mav

[0052] P DABf,aopt =U s I s -2εωCV 2,ref V 2f,mav

[0053] Among them, V 2f,mav The maximum permissible intermediate DC bus voltage ripple value, V 2,ref This is the optimized value for the intermediate DC bus voltage ripple.

[0054] The calculation of the optimized feedforward compensation value for the second harmonic power of the DAB converter includes:

[0055]

[0056] Where t is time, k p This is the proportional coefficient in the voltage closed-loop PI controller G1.

[0057] In this embodiment, the reference value for calculating the output power of the DAB converter includes: using the optimized intermediate DC bus voltage reference value V. 2ref,aopt The value obtained by subtracting the intermediate DC bus voltage v2 is fed into the proportional-integral controller G1 to obtain the output signal p. o ; will signal p o With the feedforward compensation value p f The summation yields the power reference value p of the DAB converter. ref Its expression is:

[0058] p o =k p (V 2ref,aopt -v2)+k i ∫(V 2ref,aopt -v2)dt

[0059] p ref =p o +p f

[0060]

[0061] Where, ω s V is the switching angular frequency of the DAB converter, L is the auxiliary inductance, v1 is the DC voltage at the input of the DAB converter, v2 is the intermediate DC bus voltage, and p is the switching angular frequency of the DAB converter. refThis is the power reference value for the DAB converter.

[0062] In this embodiment, a single-phase power electronic system topology is described, such as... Figure 2 As shown, the system consists of one single-phase H-bridge inverter and one DAB converter (Dual Active Bridge, DAB). The AC side of the single-phase H-bridge inverter is connected to a single-phase AC power grid, and the voltage of the single-phase AC power grid is e. The single-phase H-bridge inverter consists of four fully controlled power electronic switching devices (MOSFETs or IGBTs) S1 to S4. s This is the grid-connected filter inductor for a single-phase H-bridge inverter. s and i s These represent the AC output voltage and grid-connected current of a single-phase H-bridge inverter, respectively. The DAB converter consists of a primary-side H-bridge (Q1-Q4), a secondary-side H-bridge (Q5-Q8), a high-frequency transformer T, and an auxiliary inductor L. Q1-Q4 and Q5-Q8 are all fully controlled power electronic switching devices (MOSFETs or IGBTs). C is the intermediate DC bus capacitor. V2 and V1 are the intermediate DC bus voltage and the DAB input voltage, respectively. L Let T be the current in the transformer T of DAB.

[0063] After the above calculations are completed, the current control cycle ends, and the process continues until the next control cycle begins. Then, steps S1 to S9 are repeated, and this process is repeated continuously to achieve real-time optimized control of the power electronic system. The block diagram of the controller proposed in this invention is as follows: Figure 3 As shown.

[0064] In this embodiment, the parameters of the single-phase power electronic system include: grid-connected filter inductor L s =4mH, auxiliary inductance L = 63uH, transformer T turns ratio is 1, DAB switching frequency is 20kHz, DC bus capacitance C = 220uF, grid voltage e RMS value is 60V, grid frequency is 50Hz, single-phase H-bridge inverter AC output voltage v s and current i s Effective value U s and I s 60V and 6.7A respectively, power factor angle It varies between -π / 2 and +π / 2, and the DC voltage v1 at the DAB input terminal is 100V.

[0065] Traditional control methods are generally divided into two categories. Traditional Method 1: This method utilizes a front-stage DC / DC converter to transfer all the second-harmonic power in the system from the intermediate DC bus side to the input. This effectively reduces the intermediate DC bus voltage ripple and capacitor usage. However, this method causes significant low-frequency fluctuations in the current of the front-stage DC / DC converter. Traditional Method 2: This method suppresses the second-harmonic power from entering the front-stage DC / DC converter. This effectively reduces the low-frequency fluctuations in the current of the front-stage DC / DC converter. However, this method often requires a large intermediate DC bus capacitor to suppress the intermediate DC bus voltage ripple. The following section provides a detailed explanation using experimental waveforms:

[0066] DAB current i L The square of the effective current within one harmonic cycle is I. 2 Lrms.2ω I 2 Lrms.2ω This can be directly used to characterize the power loss and low-frequency oscillation amplitude of the DAB converter. The control method proposed in this invention, as well as traditional methods 1 and 2, demonstrate the following suppression effects on low-frequency current fluctuations in the DAB converter: Figure 4 As shown. Among them, in The experimental waveforms for the three control methods are shown below. Figure 5 As shown. From Figure 4 As can be seen, compared to the proposed method, the traditional method 1 under I 2 Lrms.2ω They increased by 35% respectively and 150% This will lead to a significant increase in the power loss of the system in the traditional method 1; the proposed method I 2 Lrms.2ω At different power factor angles All of the following are minimum values, therefore the system efficiency in the proposed method will be higher; from Figure 5 The experimental waveforms also show that in traditional methods 1 and 2, the DAB current i L It fluctuates drastically at low frequencies around ±11.6A; in the proposed method, the DAB current i L The voltage fluctuates only at a low frequency of around ±9V, significantly less than that of traditional methods. The results show that the control method proposed in this invention has a better optimization effect in suppressing low-frequency fluctuations in DAB current.

[0067] The control method of the present invention has the following optimization effect on the reduction of intermediate DC bus capacitor: Figure 6 As shown. Traditional method 1 generally requires the intermediate DC voltage ripple to be no greater than 10%, at which point the intermediate DC capacitor ripple value is C. tran =640uF. For example... Figure 6As can be seen, the method proposed in this invention allows for a 50% reduction in the intermediate DC bus capacitance with only an 8% increase in the effective current; or allows for a 70% reduction in the intermediate DC bus capacitance with only a 20% increase in the effective current. The results show that the control method proposed in this invention can effectively suppress the fluctuation of the DAB low-frequency current while significantly reducing the intermediate DC bus capacitance, ensuring the high-efficiency operation of the system.

[0068] The above-described embodiments further illustrate the purpose, technical solution, and advantages of the present invention. It should be understood that the above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A DAB optimization control method for a single-phase power electronic conversion system, characterized in that, include: S1. Real-time acquisition of operating data of single-phase power electronic conversion system; S2. Calculate the optimized value V of the intermediate DC bus voltage reference value of the single-phase power electronic converter system based on the collected operating data. 2ref,aopt ; S3, based on the optimized value V 2ref,aopt Calculate the optimized value P of the second harmonic power amplitude. DABf,aopt The optimized value V of the intermediate DC bus voltage ripple. 2f,aopt ; S4. Set the system's maximum withstand voltage value V BR Calculate the maximum allowable intermediate DC bus voltage ripple value V based on the system's maximum withstand voltage. 2f,mav ; S5. Set the DC voltage ripple redundancy coefficient ε and determine V. 2f,aopt and εV 2f,mav The size of V 2f,aopt Greater than or equal to εV 2f,mav If yes, proceed to step S6; otherwise, proceed to step S7. S6, Optimization value P for second harmonic power amplitude DABf,aopt The optimized value V of the intermediate DC bus voltage ripple. 2f,aopt Make corrections; S7. Based on the optimized value P of the second harmonic power amplitude DABf,aopt and optimized value V 2f,aopt Calculate the optimized feedforward compensation value p for the second harmonic power of the DAB converter. f ; S8. Calculate the reference value of the DAB converter output power based on the optimized feedforward compensation value, convert the reference value into a steering angle, and use it as the control command for the DAB converter. S9. Control the DAB converter according to the control instructions.

2. The DAB optimization control method for a single-phase power electronic conversion system according to claim 1, characterized in that, Operating data includes: AC output voltage V of the single-phase H-bridge inverter. s Effective value U s The AC output current i of a single-phase H-bridge inverter s Effective value I s i s ahead of v s Power factor angle The input DC voltage v1 and the intermediate DC bus voltage v2 of the DAB converter.

3. The DAB optimization control method for a single-phase power electronic conversion system according to claim 1, characterized in that, The optimized value for calculating the intermediate DC bus voltage reference value is: Among them, V 2ref,aopt The optimized value is the reference value for the intermediate DC bus voltage, v1 is the DC voltage at the input of the DAB converter, A1 is the optimized parameter, and U... s The AC output voltage V of a single-phase H-bridge inverter s The effective value of I s i is the AC output current of the single-phase H-bridge inverter. s The effective value, The power factor angle.

4. The DAB optimization control method for a single-phase power electronic conversion system according to claim 1, characterized in that, The optimized values ​​for the second harmonic power amplitude and the intermediate DC bus voltage ripple are calculated as follows: Among them, P DABf,aopt U is the optimized value for the second harmonic power amplitude. s The AC output voltage V of a single-phase H-bridge inverter s The effective value of I s i is the AC output current of the single-phase H-bridge inverter. s The effective value, A1 is the optimized parameter, ω is the grid voltage angular frequency, C is the intermediate DC bus capacitance value, V 2ref,aopt The optimized value for the intermediate DC bus voltage reference value, V 2f,aopt This is the optimized value for the intermediate DC bus voltage ripple.

5. The DAB optimization control method for a single-phase power electronic conversion system according to claim 1, characterized in that, The maximum permissible intermediate DC bus voltage ripple value is calculated as follows: Among them, V BR V is the maximum withstand voltage of the system. 2ref,aopt U is the optimized value of the intermediate DC bus voltage reference value. s The AC output voltage V of a single-phase H-bridge inverter s The effective value, The power factor angle.

6. The DAB optimization control method for a single-phase power electronic conversion system according to claim 1, characterized in that, The optimized values ​​for the second harmonic power amplitude and the intermediate DC bus voltage ripple are corrected as follows: V 2f,aopt =εV 2f,mav P DABf,aopt =U s I s -2εωCV 2,ref V 2f,mav Among them, V 2f,mav The maximum permissible intermediate DC bus voltage ripple value, V 2,ref This is the optimized value for the intermediate DC bus voltage ripple; U s The AC output voltage V of a single-phase H-bridge inverter s The effective value of I s i is the AC output current of the single-phase H-bridge inverter. s The effective value of ω is the angular frequency of the grid voltage, and C is the capacitance of the intermediate DC bus.

7. The DAB optimization control method for a single-phase power electronic conversion system according to claim 1, characterized in that, The calculation of the optimized feedforward compensation value for the second harmonic power of the DAB converter includes: Where t is time, k p ω is the proportional coefficient in the voltage closed-loop PI controller G1; ω is the angular frequency of the grid voltage. The power factor angle.

8. The DAB optimization control method for a single-phase power electronic conversion system according to claim 1, characterized in that, The reference value for calculating the output power of the DAB converter includes: the optimized intermediate DC bus voltage reference value V. 2ref,aopt The value obtained by subtracting the intermediate DC bus voltage v2 is fed into the proportional-integral controller G1 to obtain the output signal p. o ; will signal p o With the feedforward compensation value p f The reference value p of the DAB converter output power is obtained by adding them together. ref .

9. The DAB optimization control method for a single-phase power electronic conversion system according to claim 1, characterized in that, Convert the reference value to the heading angle: Where, ω s V is the switching angular frequency of the DAB converter, L is the auxiliary inductance, v1 is the DC voltage at the input of the DAB converter, v2 is the intermediate DC bus voltage, and p is the switching angular frequency of the DAB converter. ref This is a reference value for the output power of the DAB converter.

Images