DAB optimization control method for single-phase power electronic conversion system

Abstract

The invention 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: acquiring system operation data, and calculating an optimization value of an intermediate DC bus voltage reference value of the single-phase power electronic conversion system; calculating a second harmonic generation power amplitude optimization value and an optimization value of an intermediate DC bus voltage ripple value; setting a maximum withstand voltage value of the system, and calculating a maximum allowable intermediate DC bus voltage ripple value; calculating an optimized feed-forward compensation value of the double-frequency power of the DAB converter according to the double-frequency power amplitude optimization value and the optimization value; calculating a reference value of the output power of the DAB converter according to the optimized feed-forward compensation value, converting the reference value into a direction-moving angle, and taking the direction-moving angle as a control instruction of the DAB converter; controlling the DAB converter according to the control instruction; according to the invention, high-efficiency optimized operation and control of the DAB converter under the condition of small intermediate DC bus capacitance are realized.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics, and in particular relates to a DAB optimization control method for a single-phase power electronic conversion system. Background Art

[0002] In the field of power electronics technology, 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 and other fields. This system is generally composed of a front-stage DC / DC converter + a rear-stage single-phase inverter. The topology composed of a front-stage dual full-bridge DC / DC converter (Dual Active Bridge, DAB) + a rear-stage H-bridge (H-Bridge) inverter is one of the very typical single-phase AC / DC ( / AC) power electronic conversion systems. Improving power density and improving work efficiency are the two core goals that the development of power electronic conversion system technology has always pursued. In order to improve the power density of the power electronic conversion system, significantly reducing the amount of DC bus capacitors is an effective method. However, in a single-phase power electronic conversion system, there is an inherent instantaneous power flow with double frequency. On the one hand, this will inevitably lead to a large double frequency ripple in the DC bus voltage, affecting the safe and stable operation of the subsequent H-bridge inverter and the power quality; on the other hand, the double frequency fluctuation will propagate into the previous DC / DC converter, causing the current fluctuation of the DC / DC converter, significantly reducing its working efficiency. Therefore, reducing the intermediate DC bus capacitance value and improving the system working efficiency are two contradictory goals.

[0003] In the prior art, there are still many problems in the control method of the single-phase AC / DC power electronic conversion system. An additional active filter circuit is connected in parallel at both ends of the DC bus to absorb the double frequency power fluctuation in the system. This type of method can effectively reduce the DC bus capacitance value and suppress the DC bus voltage ripple. However, this type of method requires additional devices to be added to the system, resulting in the complexity of the entire system structure, the complexity of control, and the decrease in reliability. Therefore, how to achieve the reduction of DC bus capacitance and the stable control of the power electronic conversion system under the premise of only using specific control technology and without adding any additional devices is an urgent problem to be solved. Several different closed-loop control strategies are proposed in the prior art, using the front-stage DC / DC converter to transmit the double frequency power from the DC bus side to the other side, thereby achieving the suppression of the DC bus voltage ripple and the reduction of the DC bus capacitance value. In the above methods, the front-stage DC / DC converter needs to transmit a large amount of double frequency power, which will cause the current of the front-stage DC / DC converter to produce a large low-frequency fluctuation, causing the system power loss to increase and the work efficiency to decrease. Therefore, how to improve the working efficiency of the single-phase two-stage power electronic conversion system is another problem that needs to be solved urgently.

[0004] The above-mentioned existing technologies either use the front-stage DC / DC converter to compensate for all the double frequency power to reduce the intermediate DC bus capacitance and improve the system power density, but this leads to larger low-frequency fluctuations of the DC / DC converter current and a decrease in working efficiency; or aim to suppress the low-frequency fluctuations of the DC / DC converter current to improve the working efficiency of the power electronic conversion system, but this leads to a larger amount of DC bus capacitance and a decrease in power density. Therefore, the above-mentioned existing technologies cannot coordinate and optimize the two goals of reducing the DC bus capacitance value and suppressing DC / DC current fluctuations to improve the system working efficiency, and are difficult to adapt to the current technical development requirements of the power industry for high power density and high efficiency power electronic conversion systems. Summary of the invention

[0005] In order to solve the above problems in the prior art, the present invention proposes a DAB optimization control method for a single-phase power electronic conversion system, the method comprising:

[0006] S1. Real-time acquisition of operating data of a single-phase power electronic conversion system;

[0007] S2. Calculate the optimized value V of the intermediate DC bus voltage reference value of the single-phase power electronic conversion system based on the collected operating data 2ref,aopt ;

[0008] S3, according to the optimized value V 2ref,aopt Calculate the optimal value P of the double frequency power amplitude DABf,aopt and the optimized value of the intermediate DC bus voltage ripple value V2f,aopt ;

[0009] S4. Set the system maximum withstand voltage value V BR , calculate the maximum allowable intermediate DC bus voltage ripple value V according to the system maximum withstand voltage value 2f,mav ;

[0010] S5. Set the DC voltage ripple redundancy coefficient ε to determine V 2f,aopt and εV 2f,mav If V 2f,aopt Greater than or equal to εV 2f,mav , then execute step S6, otherwise execute step S7;

[0011] S6, the optimization value P of the double frequency power amplitude DABf,aopt and the optimized value of the intermediate DC bus voltage ripple value V 2f,aopt make corrections;

[0012] S7, according to the double frequency power amplitude optimization value P DABf,aopt and the optimized value V 2f,aopt Calculation of the optimal feed-forward compensation value p of the double frequency power of the DAB converter f ;

[0013] S8, calculating a reference value of the output power of the DAB converter according to the optimized feedforward compensation value, converting the reference value into a shift angle, and using it as a control instruction of the DAB converter;

[0014] S9. Control the DAB converter according to the control instruction.

[0015] Beneficial effects of the present invention:

[0016] A novel control technology proposed in the present invention can always ensure the stable operation of the subsequent inverter under the condition of high ripple intermediate DC bus voltage and control the current low-frequency fluctuation amplitude of the previous DAB converter to the minimum, that is, it realizes the high-efficiency optimized operation and control of the DAB converter under the condition of small intermediate DC bus capacitance, so as to improve the power density and operation efficiency of the single-phase power electronic conversion system at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the overall flow chart of the present invention;

[0018] Figure 2 A topological structure diagram of a single-phase power electronic conversion system of the present invention;

[0019] Figure 3 It is the principle diagram of the control method of the present invention;

[0020] Figure 4 This is a diagram showing the optimization effect of the present invention on DAB low-frequency current fluctuations;

[0021] Figure 5 It is an experimental waveform diagram of the control method of the present invention;

[0022] Figure 6 This is a diagram showing the optimization effect of the present invention on the reduction of intermediate DC bus capacitance. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] This patent invents a DAB optimization control method for a single-phase power electronic conversion system. It solves the problem that the existing control technology is difficult to simultaneously take into account and optimize the control when facing the two goals of reducing the DC bus capacitance and suppressing DC / DC current fluctuations, and realizes the optimized control of the front-stage DC / DC converter under the reduced DC bus capacitance and higher intermediate DC bus voltage ripple. On the one hand, this method allows a higher amplitude of double-frequency DC bus voltage ripple to significantly reduce the DC bus capacitance value; on the other hand, it proposes an optimized control strategy to suppress the low-frequency current fluctuations in the DAB converter while ensuring the safe and stable operation of the subsequent inverter. This method takes into account the two goals of suppressing the low-frequency fluctuations of the current of the front-stage DC / DC converter and reducing the intermediate DC bus capacitance value, and achieves coordinated optimization of the two goals.

[0025] A DAB optimization control method for a single-phase power electronic conversion system, such as Figure 1 As shown, the method includes:

[0026] S1. Starting from the current control cycle, real-time acquisition of operating data of the single-phase power electronic conversion system;

[0027] S2. Calculate the optimized value V of the intermediate DC bus voltage reference value of the single-phase power electronic conversion system based on the collected operating data 2ref,aopt ;

[0028] S3, according to the optimized value V 2ref,aopt Calculate the optimal value P of the double frequency power amplitude DABf,aopt and the optimized value of the intermediate DC bus voltage ripple value V 2f,aopt ;

[0029] S4. Set the system maximum withstand voltage value V according to the device data sheet. BR , calculate the maximum allowable intermediate DC bus voltage ripple value V according to the system maximum withstand voltage value2f,mav ;

[0030] S5. Considering sampling error, circuit parameter error and noise interference, V 2f,mav There is a certain error between the actual value of and the theoretical calculated value in S4. Therefore, the DC voltage ripple redundancy coefficient ε range is set to [0,1] according to the actual hardware situation. When ε is closer to 0, the ripple redundancy is greater, and a larger V 2f,mav The calculation error of ε is smaller when ε is closer to 1, which means the ripple margin is smaller, and a smaller V is allowed. 2f,mav Calculation error. Determine V 2f,aopt and εV 2f,mav If V 2f,aopt Greater than or equal to εV 2f,mav , then execute step S6, otherwise execute step S7;

[0031] S6, the optimization value P of the double frequency power amplitude DABf,aopt and the optimized value of the intermediate DC bus voltage ripple value V 2f,aopt make corrections;

[0032] S7, according to the double frequency power amplitude optimization value P DABf,aopt and the optimized value V 2f,aopt Calculation of the optimal feed-forward compensation value p of the double frequency power of the DAB converter f ;

[0033] S8, calculating a reference value of the output power of the DAB converter according to the optimized feedforward compensation value, converting the reference value into a shift angle, and using it as a control instruction of the DAB converter;

[0034] S9. Control the DAB converter according to the control instruction.

[0035] In this embodiment, the operating data includes the AC output voltage v of the single-phase H-bridge inverter s The effective value U s , AC output current i of single-phase H-bridge inverter s The effective value of I s 、i s Ahead of v s The power factor angle The DC voltage at the input of the DAB converter is v1, and the intermediate DC bus voltage is v2.

[0036] The optimal value for calculating the intermediate DC bus voltage reference value is:

[0037]

[0038] Among them, V 2ref,aoptis the optimized value of the intermediate DC bus voltage reference value, v1 is the DC voltage at the input end of the DAB converter, A1 is the optimized parameter, U s is the AC output voltage v of the single-phase H-bridge inverter s The effective value of I s is the AC output current i of the single-phase H-bridge inverter s The effective value of is the power factor angle.

[0039] In this embodiment, the expression of the optimization parameter A1 is:

[0040] A1=0.0225·π 4 ω s 2 L 2 / v1

[0041] Among them, π is the coefficient of pi, which is approximately equal to 3.1415926, ω s is the switching angular frequency of the DAB converter, and L is the auxiliary inductance.

[0042] Calculate the optimal value P of the double frequency power amplitude DABf,aopt and the optimized value of the intermediate DC bus voltage ripple value V 2f,aopt for:

[0043]

[0044] Among them, P DABf,aopt is the optimized value of the double frequency power amplitude, A1 is the optimization parameter, ω is the grid voltage angular frequency, C is the intermediate DC bus capacitance value, V 2ref,aopt is the optimized value of the intermediate DC bus voltage reference value, V 2f,aopt is the optimized value of the intermediate DC bus voltage ripple.

[0045] Calculate the maximum allowable intermediate DC bus voltage ripple value V 2f,mav for:

[0046]

[0047] Here, min(x,y) represents the smaller of the two numbers x and y.

[0048] In this embodiment, when V 2f,aopt <ε·V 2f,mav When not targeting P DABf,aopt and V 2f,aopt The value of DABf,aopt and V 2f,aopt The value of is given according to the result in step S3; when V 2f,aopt ≥ε·V 2f,mav When P DABf,aoptand V 2f,aopt The value should be corrected to:

[0049] V 2f,aopt =εV 2f,mav

[0050] P DABf,aopt =U s I s -2εωCV 2,ref V 2f,max

[0051] Among them, V 2f,mav is the maximum allowable intermediate DC bus voltage ripple value, V 2,ref is the optimized value of the intermediate DC bus voltage ripple.

[0052] Calculating the optimal feed-forward compensation value of the double frequency power of the DAB converter includes:

[0053]

[0054] Where t is time, k p is the proportional coefficient in the voltage closed-loop PI controller G1.

[0055] In this embodiment, calculating the reference value of the output power of the DAB converter includes: 2ref,aopt The value after the difference with the intermediate DC bus voltage v2 is sent to the proportional integral controller G1 to obtain the output signal p o ; The signal p o The feedforward compensation value p f Add together to get the DAB converter power reference value p ref . Its expression is:

[0056] p o =k p (V 2ref,aopt -v2)+k i ∫(V 2ref,aopt -v2)dt

[0057] p ref =p o +p f

[0058]

[0059] Among them, ω s is the switching frequency of the DAB converter, L is the auxiliary inductor, v1 is the DC voltage at the input of the DAB converter, v2 is the intermediate DC bus voltage, p ref is the DAB converter power reference value.

[0060] In this embodiment, a single-phase power electronic system topology, such as Figure 2 As shown in the figure, the system consists of a single-phase H-bridge inverter and a DAB converter (Dual Active Bridge, DAB); the AC side of the single-phase H-bridge inverter is connected to the single-phase AC grid, and the voltage of the single-phase AC grid is e. The single-phase H-bridge inverter consists of four power electronic fully controlled switching devices (MOSFET or IGBT) from S1 to S4. s It is the grid-connected filter inductor of the single-phase H-bridge inverter. s and i s are the AC output voltage and grid-connected current of the single-phase H-bridge inverter. The DAB converter consists of the primary H-bridge (Q1~Q4), the secondary H-bridge (Q5~Q8), the high-frequency transformer T and the auxiliary inductor L. Q1~Q4 and Q5~Q8 are all fully controlled power electronic switching devices (MOSFET or IGBT). C is the intermediate DC bus capacitor. v2 and v1 are the intermediate DC bus voltage and the DAB input voltage respectively. i L is the current of the DAB transformer T.

[0061] After the above calculations are completed, the current control cycle ends, and the ten steps S1 to S9 are repeated until the next control cycle begins. This process is repeated over and over again to achieve real-time optimization control of the power electronic system. Figure 3 shown.

[0062] In this embodiment, the parameters of the single-phase power electronic system include: grid-connected filter inductance L s =4mH, auxiliary inductor L = 63uH, transformer T turns ratio is 1, DAB switching frequency is 20kHz, DC bus capacitor C = 220uF, grid voltage e effective value is 60V, grid frequency is 50Hz, single-phase H-bridge inverter AC output voltage v s and current i s The effective value U s and I s 60V and 6.7A respectively, the power factor is The DC voltage v1 at the DAB input terminal varies between -π / 2 and +π / 2, and is 100V.

[0063] Traditional control methods are generally divided into two categories. Traditional method 1: That is, using the front-stage DC / DC converter to transfer all the doubled frequency power in the system from the intermediate DC bus side to the input end. Therefore, the intermediate DC bus voltage ripple and the amount of capacitors used can be effectively reduced. However, this type of method will cause the current of the front-stage DC / DC converter to fluctuate greatly at a low frequency. Traditional method 2: That is, suppressing the doubled frequency power in the system from entering the front-stage DC / DC converter. Therefore, the low-frequency fluctuations of the current of the front-stage DC / DC converter can be effectively reduced. However, this type of method often requires the use of a larger intermediate DC bus capacitor to suppress the intermediate DC bus voltage ripple. The following is a detailed explanation combined with the experimental waveform diagram:

[0064] DAB current i L The square of the effective current in a double frequency cycle is I 2 Lrms.2ω , I 2 Lrms.2ω It can be used to directly characterize the power loss and low-frequency oscillation amplitude of the DAB converter. The control method proposed by the present invention and the traditional method 1 and the traditional method 2 have the following effects on suppressing the DAB low-frequency current fluctuation: Figure 4 As shown. When the experimental waveforms of the three control methods are as follows Figure 5 As shown. Figure 4 It can be seen that compared with the proposed method, the I 2 Lrms.2ω Increased by 35% and 150% This will lead to a significant increase in the power loss of the system in the traditional method 1; 2 Lrms.2ω At different power factor angles The following are all minimum, so the efficiency of the system in the proposed method will be higher; Figure 5 The experimental waveforms also show that in the traditional methods 1 and 2, the DAB current i L It fluctuates violently and at a low frequency around ±11.6A. In the proposed method, the DAB current i L It only fluctuates at a low frequency of about ±9V, which is significantly smaller than the traditional method. The results show that the control method proposed in the present invention has a good optimization effect on suppressing the low-frequency fluctuation of DAB current.

[0065] The control method of the present invention has the following optimization effect on the reduction of the intermediate DC bus capacitance: Figure 6 Conventional method 1 generally requires that the intermediate DC voltage ripple is no more than 10%, and the intermediate DC capacitor ripple value is C tran =640uF. Figure 6It can be seen that the method proposed in the present invention allows a 50% reduction in the intermediate DC bus capacitance with only an 8% increase in the effective current; or allows 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 the present 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.

[0066] The above embodiments further illustrate the purpose, technical solutions and advantages of the present invention in detail. It should be understood that the above embodiments are only preferred implementation modes 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 in 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 a 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 conversion system based on the collected operating data 2ref,aopt ; S3, according to the optimized value V 2ref,aopt Calculate the optimal value P of the double frequency power amplitude DABf,aopt and the optimized value of the intermediate DC bus voltage ripple value V 2f,aopt ; S4. Set the system maximum withstand voltage value V BR , calculate the maximum allowable intermediate DC bus voltage ripple value V according to the system maximum withstand voltage value 2f,mav ; S5. Set the DC voltage ripple redundancy coefficient ε to determine V 2f,aopt and εV 2f,mav If V 2f,aopt Greater than or equal to εV 2f,mav , then execute step S6, otherwise execute step S7; S6, the optimization value P of the double frequency power amplitude DABf,aopt and the optimized value of the intermediate DC bus voltage ripple value V 2f,aopt make corrections; S7, according to the double frequency power amplitude optimization value P DABf,aopt and the optimized value V 2f,aopt Calculation of the optimal feed-forward compensation value p of the double frequency power of the DAB converter f ; S8, calculating a reference value of the output power of the DAB converter according to the optimized feedforward compensation value, converting the reference value into a shift angle, and using it as a control instruction of the DAB converter; S9. Control the DAB converter according to the control instruction.

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

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

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

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

6. A DAB optimization control method for a single-phase power electronic conversion system according to claim 1, characterized in that: The optimized values ​​of the double frequency power amplitude and the intermediate DC bus voltage ripple are corrected to: V 2f,aopt =εV 2f,mav P DABf,aopt =U s I s -2εωCV 2,ref V 2f,mav Among them, V 2f,mav is the maximum allowable intermediate DC bus voltage ripple value, V 2,ref is the optimized value of the intermediate DC bus voltage ripple.

7. A DAB optimization control method for a single-phase power electronic conversion system according to claim 1, characterized in that: Calculating the optimal feed-forward compensation value of the double frequency power of the DAB converter includes: Where t is time, k p is the proportional coefficient in the voltage closed-loop PI controller G1.

8. A 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: taking the optimized intermediate DC bus voltage reference value V 2ref,aopt The value after the difference with the intermediate DC bus voltage v2 is sent to the proportional integral controller G1 to obtain the output signal p o ; The signal p o The feedforward compensation value p f Add together to get the DAB converter power reference value p ref .

9. A 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 displacement angle: Among them, ω s is the switching frequency of the DAB converter, L is the auxiliary inductor, v1 is the DC voltage at the input of the DAB converter, v2 is the intermediate DC bus voltage, p ref is the DAB converter power reference value.

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