DAB output series voltage balancer voltage equalization control method and system

Abstract

The present invention discloses a voltage balancing control method and system for a DAB output series voltage balancer. Aiming at the DAB output series voltage balancer topology, the present invention proposes a dual-loop voltage balancing control method, which is composed of a series voltage outer loop and a voltage balancing inner loop. Among them, the outer loop uses the fundamental wave shift ratio of triple phase shift control as the control quantity, which can effectively reduce the current stress of the DAB while achieving a given value for the output voltage of two DABs in series; the inner loop adjusts the fundamental wave shift ratio of the two DABs through an integrator and a voltage comparator, thereby achieving equal output voltages. Under the control method proposed by the present invention, the output voltage of the DAB output series voltage balancer can be well balanced, and has high application value in bipolar DC power distribution systems.

Description

Technical Field

[0001] The invention relates to the control field of dual active full-bridge DC-DC converters, in particular to a voltage balancing control method for a DAB output series voltage balancer. Background Art

[0002] In recent years, the proportion of renewable energy power generation in electricity supply has continued to increase. The electric energy directly output by renewable energy sources such as photovoltaics, fuel cells, and energy storage is direct current. Therefore, if direct current is used in the distribution network, it can provide a simple and efficient access point for direct current power such as photovoltaics and energy storage. In a DC distribution system, a voltage balancer can be used to convert unipolar voltage into bipolar voltage, thereby providing users with more voltage levels and higher redundancy. In a bipolar DC distribution system, most of the electric energy needs to flow through a voltage balancer. Therefore, the efficiency, reliability and other performance of the voltage balancer will have a direct impact on the operation of the DC distribution system. It is of great significance to study the topology and control strategy of high-performance voltage balancers.

[0003] The dual active full bridge DC-DC converter has the advantages of high transmission power level, easy soft switching, and electrical isolation. In the bipolar DC distribution network, the voltage balancer (such as Figure 1 As shown, the DAB output series voltage balancer includes two DAB inputs connected in parallel and outputs connected in series. a and DAB b , output CLC filters C1L1C3 and C2L2C4. Two DAB a and DAB b Same structure, DAB a For example, it includes a first H-bridge module, a transformer and a second H-bridge module. The first H-bridge module and the second H-bridge module each include two parallel bridge arms. The midpoint of the first bridge arm of the first H-bridge module (including switch tubes S1 and S2 connected in series) is connected to one end of the primary side of the transformer through an auxiliary inductor La, and the midpoint of the second bridge arm of the first H-bridge module (including switch tubes S3 and S4 connected in series) is connected to the other end of the primary side of the transformer. The two ends of the secondary side of the transformer are respectively connected to the midpoints of the two bridge arms of the second H-bridge module. Figure 1 In the figure, V1 is the unipolar input voltage, C0 is the input filter capacitor, V 2a and V 2b is the bipolar output voltage, V s is the series output voltage, R 2a and R 2bThe two DABs use IGBT as the switching device, and the switching frequency is 10kHz. The two DABs are connected to the unipolar DC voltage V1 in parallel. The outputs of the two DABs are filtered by CLC to obtain the bipolar output voltage V 2a and V 2b , respectively R 2a and R 2b As a load, V s For the DAB output series voltage balancer, if two DABs are independently closed-loop controlled, two controllers and two sensors are required to measure the two output voltages respectively, which has the problem of high cost on the one hand and low reliability on the other.

[0004] Invention patent application CN110677048A discloses a bipolar DC transformer, and a control method and device thereof, but this solution cannot reduce the current stress of DAB. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a DAB output series voltage balancer voltage equalization control method and system in view of the shortcomings of the existing technology, which effectively reduces the current stress of the DAB, thereby reducing the switching loss of the DAB and the iron loss of the inductor and transformer, and improving the efficiency of the DAB.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a voltage balancing control method for a DAB output series voltage balancer, wherein the DAB output series voltage balancer comprises two DABs; the input sides of the two DABs are connected in parallel, and the output sides are connected in series; the method comprises:

[0007] S1. Obtain the fundamental shift ratio D of the two DABs fa and D fb ;

[0008] S2, using the fundamental wave shift ratio of each DAB, respectively obtain the internal shift ratios of the two DABs;

[0009] S3, using the fundamental wave shift ratio of each DAB and the inner shift ratio of the two DABs, respectively obtain the outer shift ratios of the two DABs;

[0010] S4. Perform triple phase shift control on each DAB according to the fundamental wave phase shift ratio, inner phase shift ratio and outer phase shift ratio of the DAB to obtain the output voltage of the DAB under the corresponding load.

[0011] The two DABs of the present invention both adopt triple phase shift control for current stress optimization (performing triple phase shift control on the DAB), which can effectively reduce the current stress of the DAB, thereby reducing the switching loss of the DAB and the iron loss of the inductor and transformer, and improving the efficiency of the DAB. At the same time, since the voltage balancer of the present invention includes two DABs, a larger power transmission can be achieved.

[0012] Before step S1 of the present invention, the present invention further includes: using an integrator to calculate the coefficient ΔD f or -ΔD f The output voltages of the two DABs are compared. When the output voltage V 2a Greater than the output voltage V of the second DAB 2b When the coefficient of the inner loop integration is ΔD f When the output voltage V 2a is less than the output voltage V of the second DAB 2b When -ΔD f Integrate; when entering the steady state, within two consecutive integration cycles, when the output of the integrator remains unchanged, V 2a Equal to V 2b The present invention does not need to measure the output voltages of the two DABs separately, and only needs one voltage comparator (to compare the output voltages of the two DABs) to ensure that the output voltages of the two DABs are equal, thus saving costs.

[0013] Get the fundamental shift ratio D of two DAB stations fa and D fb The specific implementation process includes:

[0014] 1) In each switching cycle, the series output voltage V s To sample, V s After passing through a low-pass filter, half of the filtered series output voltage is taken as the feedback value of the outer loop control;

[0015] 2) Compare half of the filtered series output voltage with the given value V 2r Subtract, the difference is used as the input of PI regulation, and the fundamental wave shift phase D is obtained after PI operation. f ;

[0016] 3) Shift the fundamental wave to D f Add D fI , minus D fI , the fundamental shift of the two DABs is D fa and D fb .

[0017] By comparing the two DAB fundamental wave shiftsfa and D fb The difference makes the output voltages of the two DABs equal under load imbalance. Compared with independently controlling the output voltages of the two DABs, the method of the present invention only needs to use one PI controller to control the output voltages of the two DABs, which has greater redundancy.

[0018] The calculation formula for the internal shift comparison of two DABs is:

[0019] when

[0020] when

[0021] Where x is a or b; d x is the voltage transfer ratio of DAB, d x =nV 2x / V1; n is the transformation ratio from the primary to the secondary winding of the DAB high-frequency transformer, V 2x is the output voltage of the xth DAB, and V1 is the input voltage of the DAB.

[0022] The inner shift phase obtained by this method can ensure that the current stress of DAB is smaller under the same transmission power.

[0023] The calculation formula for the external shift of two DABs is: 3x =0.5D 1x -0.5D 2x +D fx .

[0024] In the present invention, the transmission power calculation formula of two DABs is:

[0025] when hour,

[0026] when hour,

[0027] Among them, P x is the transmission power of DAB, f s is the switching frequency, L x Auxiliary inductor for DAB.

[0028] In the present invention, the specific implementation process of the triple phase shift control includes: obtaining 4 PWM signals ePWM1A, ePWM2A, ePWM3A, and ePWM4A with a duty cycle of 50%, a frequency of 10kHz, and different rising edge times, using the four PWM signals as the driving signals of the DAB upper bridge arm switch tubes, and using the complementary signals of the four PWM signals as the driving signals of the corresponding lower bridge arm switch tubes; the ratio of the time length of ePWM1A leading ePWM2A to the half cycle is the inner shift phase ratio. D1, the half-cycle proportion of ePWM3A leading ePWM4A is the inner phase shift ratio D2; the duration of ePWM1A leading ePWM3A is the outer phase shift ratio D3; the half-cycle proportion of the duration of the first switch tube in the first DAB leading the third switch tube is D1, the half-cycle proportion of the duration of the first switch tube in the second DAB leading the third switch tube in the second DAB is D2, and the half-cycle proportion of the duration of the first switch tube in the first DAB leading the first switch tube in the second DAB is D3. In the present invention, triple phase shift can be realized by using DSP to control four ePWM output signals, and the three phase shifts of DAB can be accurately controlled, thereby realizing triple phase shift, thereby reducing the current stress and reflux power of DAB under the same transmission power.

[0029] As an inventive concept, the present invention also provides a DAB output series voltage balancer voltage equalization control system, which includes a memory and a processor; the memory stores a computer program / instructions; when the processor executes the computer program / instructions, the steps of the above method of the present invention are implemented.

[0030] The control system of the present invention further includes a voltage sensor for collecting the series output voltage of the two DABs; the voltage sensor is connected to the processor. The voltage balancing control strategy of the DAB output series voltage balancer of the present invention only needs to use one controller and one voltage sensor, which increases the reliability of the system and reduces the cost.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows: the voltage equalization control strategy of the DAB output series voltage balancer of the present invention only needs to use one controller and one voltage sensor, which increases the reliability of the system and reduces the cost; both DABs adopt triple phase-shift control for current stress optimization, which can effectively reduce the current stress of the DAB; the designed outer loop directly controls the series output voltage, and the load connected to the series voltage has a faster dynamic response speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The circuit topology diagram of the DAB output series voltage balancer;

[0033] Figure 2This is a block diagram of a dual-loop control system of a DAB output series voltage balancer according to an embodiment of the present invention;

[0034] Figure 3 This is a schematic diagram of an output voltage comparison circuit according to an embodiment of the present invention;

[0035] Figure 4 It is a principle diagram of DAB triple phase shift control according to an embodiment of the present invention;

[0036] Figure 5 This is the specific implementation principle diagram of triple phase shift control in DSP chip;

[0037] Figure 6 The figure is a simulation waveform diagram of the bipolar output voltage of the DAB output series voltage balancer when starting and the load changes under the control method of the embodiment of the present invention;

[0038] Figure 7 The waveform diagrams of the DAB inductor current under the same load conditions are respectively shown in FIG. 1 and FIG. 2 , when the conventional single phase shift control and the triple phase shift control used in the embodiment of the present invention are used. DETAILED DESCRIPTION

[0039] Figure 2 The block diagram of the voltage balancing control system of a DAB output series voltage balancer according to an embodiment of the present invention is mainly composed of a series voltage outer loop control module, a voltage balancing inner loop control module, a triple phase shift current stress optimization algorithm module, and a voltage comparison module.

[0040] In the embodiment of the present invention, the voltage balancing control method of the DAB output series voltage balancer is as follows:

[0041] 1) In each switching cycle, the series output voltage V of the two DABs is measured using a voltage sensor. s After filtering by the low-pass filter, half of the filtered series output voltage is taken, that is, V s / 2 is used as the feedback value of the outer loop control;

[0042] 2) The controller converts the feedback value V obtained in step 1) s / 2 and the given quantity V 2r The difference is calculated by PI to obtain the fundamental wave shift phase D f , the transfer function G of PI control v The expression of (z) is:

[0043]

[0044] In the formula, k p is the proportional coefficient of the PI controller, and its value is 0.005; k iis the integral coefficient of the PI controller, which is 0.5; T S is the control cycle duration, which is 0.1ms; z is the operator of the discrete domain transfer function.

[0045] 3) Compare the output voltages of the two DABs, such as Figure 3 As shown; when the output voltage V 2a Greater than V 2b When the inner loop controller is f Integrate; when the output voltage V 2a Less than V 2b When the inner loop controller is -ΔD f When entering the steady state, the output of the integrator remains unchanged in two consecutive integration cycles, so that the output voltage V 2a Equal to V 2b ; ΔD f is the coefficient of the inner loop integral, and its value is 0.0002; the integral period is the switching period, and the D output of the integrator is fI is the deviation of the fundamental wave shift;

[0046] 4) Shift the fundamental wave output by the outer loop to D f Add D fI , minus D fI , the fundamental shift of the two DABs is D fa and D fb , where D fa As DAB a Compared with the fundamental shift of fb As DAB b Compared with the fundamental shift;

[0047] 5) According to the UTPS-IpOpt triple-phase shift current stress optimization algorithm (Huang J, Wang Y, Li Z, et al. Unified Triple-Phase-Shift Control to Minimize Current Stress and Achieve Full Soft-Switching of Isolated Bidirectional DC–DC Converter [J]. IEEE Transactions on Industrial Electronics, 2016, 63(7): 4169-4179.), the fundamental-phase shift current stress optimization algorithm D fa DAB can be calculated a The inward shift compared to D 1a and D 2a ; Compared with the fundamental wave, D fb DAB can be calculatedb The inward shift of D 1b and D 2b The required internal shift ratio is calculated as:

[0048] when

[0049] when

[0050] In the formula, the subscript x is a or b, which means that the physical quantity belongs to DAB. a or DAB b ;d x is the voltage transfer ratio of DAB, and its calculation formula is d x =nV 2x / V1; n is the transformation ratio from the primary to the secondary winding of the DAB high frequency transformer.

[0051] Under the above triple phase shift control method, the transmission power formula of DAB is:

[0052] when

[0053] when

[0054] 6) In the formula, P x is the transmission power of DAB, f s is the switching frequency, L x is the auxiliary inductor of DAB. fa , D 1a and D 2a DAB can be calculated a Compared with D 3a ; from D fb , D 1b and D 2b DAB can be calculated b Compared with D 3b ; The calculation formula for the outward shift ratio is:

[0055] D 3x =0.5D 1x -0.5D 2x +D fx , x=a or b.

[0056] 7) Under triple phase shift control mode, the internal phase shift of DAB is relative to D1, which means the primary full-bridge output AC voltage v H1 (t) ratio, internal shift ratio D2 refers to the secondary full-bridge output AC voltage v H2 (t) ratio, outward shift compared to D3 refers to vH1 (t)Advance v H2 (t) duration and half-cycle duration T h The ratio of Figure 4 As shown, the DSP controller outputs driving signals g1-g8 with a duty cycle of 50% to the eight switch tubes S1-S8 of DAB, wherein the half-cycle proportion of the time length of which g1 is controlled to be ahead of g3 is D1, the half-cycle proportion of the time length of which g5 is controlled to be ahead of g7 is D2, and the half-cycle proportion of the time length of which g1 is controlled to be ahead of g5 is D3, so that the triple phase shift control of DAB can be realized. The control method of the leading time length of the driving signals g1-g8 is as follows: Figure 5 As shown; according to the D obtained in the previous step 1a , D 2a and D 3a About DAB a Perform triple phase shift control, when the load R 2a The output voltage V 2a ; According to the obtained D 1b , D 2b and D 3b About DAB b Perform triple phase shift control, when the load R 2b The output voltage V 2b .

[0057] Figure 3 This is a schematic diagram of a bipolar output voltage comparison circuit according to an embodiment of the present invention. Figure 3 In the process, V 2a and V 2a +V 2b The voltage is divided into 1 / 50 and 1 / 100. When the voltage comparator outputs a high level, V 2a >V 2b ; When the voltage comparator outputs a low level, there is V 2a <V 2b The output of the voltage comparator is electrically isolated from the control circuit through an optocoupler.

[0058] Figure 4 It is a principle diagram of DAB triple phase shift control according to an embodiment of the present invention. Figure 4 In the figure, the inward shift ratio D1 and D2 are respectively the duty ratios of the square wave voltage output by the primary full bridge and the secondary full bridge of the DAB, and their value ranges are both [0,1]; the outward shift ratio D3 refers to the ratio of the time length that the primary full bridge output square wave voltage leads the secondary full bridge output square wave voltage to the half-cycle time length. In the embodiment of the present invention, its value is specified as -0.5≤D3≤0.5.

[0059] Figure 5This is the specific implementation schematic diagram of triple phase-shift control in DSP chip. The DSP chip used is TMS320F28335 from TI. The period value of PWM counter is assigned to 14999, and a 10kHz PWM signal can be obtained. In DSP, the value of PWM counter increases from 0 to 14999, then reset to 0, and repeats the above process. When the current value of PWM counter is greater than the value of comparison register, PWM pin outputs high level, otherwise it outputs low level. Therefore, in each switching cycle, the comparison registers CMP1A, CMP1B, CMP2A, CMP2B, CMP3A, CMP3B, CMP4A, and CMP4B of the ePWM1, ePWM2, ePWM3, and ePWM4 modules of the DSP can be assigned values ​​to obtain four PWM signals ePWM1A, ePWM2A, ePWM3A, and ePWM4A with a duty cycle of 50%, a frequency of 10kHz, and different rising edge times. These four PWM signals are respectively used as driving signals of the upper bridge arm switch tube of the DAB, and their complementary signals are used as driving signals of the corresponding lower bridge arm switch tubes; the ratio of the duration of ePWM1A leading ePWM2A to the half cycle is the inward shift ratio D1, and correspondingly, the half cycle ratio of ePWM3A leading ePWM4A is the inward shift ratio D2; the duration of ePWM1A leading ePWM3A is the outward shift ratio D3.

[0060] Figure 6 The bipolar output voltage simulation waveform of the DAB series output voltage balancer under the dual-loop control method of the embodiment of the present invention is shown in the figure when the bipolar load is unbalanced. In the startup stage, the output voltages of the two DABs are equal. After a dynamic adjustment process of about 0.04s, they converge to a given value of 190V. At t=0.1s, the positive and negative loads are unbalanced, and the positive load is smaller than the negative load, resulting in a positive output voltage V 2a Increase, negative output voltage V 2b After 0.04s of dynamic adjustment, the bipolar output voltage returns to balance and equals the given value of 190V. Figure 6 It can be seen that after the DAB output series voltage balancer adopts the control method of the embodiment of the present invention, its bipolar output voltage can be effectively kept balanced and equal to a given value.

[0061] Figure 7 The following are simulation waveforms of the DAB inductor current under the same load conditions, respectively using single phase shift control and current stress optimization triple phase shift control used in the embodiment of the present invention. Figure 7It can be seen that when single phase-shift control is adopted, the peak-to-peak value of the DAB inductor current is 43.13A, while after adopting triple phase-shift control, under the same load condition, the peak-to-peak value of the inductor current is reduced to 35.66A.

Claims

1. A voltage balancing control method for a DAB output series voltage balancer, wherein the DAB output series voltage balancer comprises two DABs; the input sides of the two DABs are connected in parallel, and the output sides are connected in series; the method is characterized in that: The method includes: S1. Obtain the fundamental shift ratio D of the two DABs fa and D fb ; S2, using the fundamental wave shift ratio of each DAB, respectively obtain the internal shift ratios of the two DABs; Get the fundamental shift ratio D of the two DABs fa and D fb The specific implementation process includes: 1) In each switching cycle, the series output voltage V s To sample, V s After passing through a low-pass filter, half of the filtered series output voltage is taken as the feedback value of the outer loop control; 2) Compare half of the filtered series output voltage with the given value V 2r Subtract, the difference is used as the input of PI regulation, and the fundamental wave shift phase D is obtained after PI operation. f ; 3) Shift the fundamental wave to D f Add D fI , minus D fI , the fundamental shift of the two DABs is D fa and D fb ; The calculation formula for the internal shift comparison of two DABs is: Where x is a or b; d x is the voltage transfer ratio of DAB, d x =nV 2x / V1; n is the transformation ratio from the primary to the secondary winding of the DAB high-frequency transformer, V 2x is the output voltage of the xth DAB, V1 is the input voltage of the DAB; S3. Using the fundamental wave shift ratio of each DAB and the inner shift ratio of the two DABs, respectively obtain the outer shift ratio of the two DABs; the calculation formula of the outer shift ratio of the two DABs is: <h2 style=";text-align:left;direction:ltr">D<h2 style=";text-align:left;direction:ltr"> 3x <h2 style=";text-align:left;direction:ltr"> <0.5D<h2 style=";text-align:left;direction:ltr"> 1x <h2 style=";text-align:left;direction:ltr"> -0.5D<h2 style=";text-align:left;direction:ltr"> 2x <h2 style=";text-align:left;direction:ltr"> +D<h2 style=";text-align:left;direction:ltr"> fx <h2 style=";text-align:left;direction:ltr"> ; S4, performing triple phase shift control on the DAB according to the fundamental wave phase shift, inner phase shift and outer phase shift of each DAB, and obtaining the output voltage of the DAB under the corresponding load; The specific implementation process of the triple phase-shift control includes: obtaining four PWM signals ePWM1A, ePWM2A, ePWM3A, and ePWM4A with a duty cycle of 50%, a frequency of 10kHz, and different rising edge times, and using the four PWM signals as driving signals for the upper bridge arm switch tube of the DAB respectively, and using the complementary signals of the four PWM signals as driving signals for the corresponding lower bridge arm switch tubes; the ratio of the time length and half cycle of ePWM1A leading ePWM2A is the inner shift phase ratio D1, and the half cycle ratio of ePWM3A leading ePWM4A is the inner shift phase ratio D2; the time length of ePWM1A leading ePWM3A is the outer shift phase ratio D3; the half cycle ratio of the time length of the first switch tube in the first DAB leading the third switch tube is controlled to be D1, the half cycle ratio of the time length of the first switch tube in the second DAB leading the third switch tube in the second DAB is controlled to be D2, and the half cycle ratio of the time length of the first switch tube in the first DAB leading the first switch tube in the second DAB is controlled to be D3.

2. The voltage balancing control method for a DAB output series voltage balancer according to claim 1, characterized in that: Before step S1, the process further includes: using an integrator to calculate the coefficient ΔD f or -ΔD f The output voltages of the two DABs are compared. When the output voltage V 2a Greater than the output voltage V of the second DAB 2b When the coefficient of the inner loop integration is ΔD f Integration is performed; when the output voltage V 2a is less than the output voltage V of the second DAB 2b When -ΔD f Integrate; when entering the steady state, within two consecutive integration cycles, when the output of the integrator remains unchanged, V 2a Equal to V 2b .

3. The voltage balancing control method of a DAB output series voltage balancer according to claim 1, characterized in that: The formula for calculating the transmission power of two DABs is: when hour; Among them, P x is the transmission power of DAB, f s is the switching frequency, L x Auxiliary inductor for DAB.

4. A DAB output series voltage balancer voltage control system, characterized in that: The invention comprises a memory and a processor; the memory stores a computer program / instruction; when the processor executes the computer program / instruction, the steps of the method according to any one of claims 1 to 3 are implemented.

5. The DAB output series voltage balancer voltage balancing control system according to claim 4, characterized in that: It also includes a voltage sensor for collecting the output voltage of two DABs connected in series; The voltage sensor is connected to the processor.

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