ISOP-DAB converter three-ring decoupling control and zero backflow power modulation cooperative regulation and control method

Abstract

The invention discloses an ISOP-DAB converter three-loop decoupling control and zero backflow power modulation cooperative regulation and control method. The method comprises the following steps: S1, constructing a regulation and control system; the regulation and control system comprises a control stage and a modulation stage. S2, the control stage deconstructs a multivariable coupling control loop of the ISOP-DAB converter into a relatively independent control loop through a modular decoupling control strategy, and the DAB sub-modules are decoupled by aiming at each decoupled DAB sub-module; the phase shift duty ratio generated by the input grading ring and the phase shift duty ratio generated by the output voltage-current loop are subjected to fine tuning correction, and then an intermediate variable phase shift duty ratio is generated; s3, according to the intermediate variable phase shift duty ratio generated by each DAB sub-module, the modulation stage adopts a zero backflow power modulation algorithm to generate a zero backflow power modulation instruction, and each DAB sub-module is controlled to operate; according to the invention, zero backflow power modulation is carried out on the modulation stage, so that the backflow power of each sub-module of the ISOP-DAB converter is completely eliminated, and the power loss of the whole regulation and control system is effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of ISOP-DAB converter control strategies, and more specifically to a coordinated control method of triple-loop decoupling control and zero reverse power modulation for ISOP-DAB converters. Background Art

[0002] With the development of power electronics technology and new energy technology, as an energy routing interface converter, the dual active bridge DC-DC converter (DAB), due to its high power density, electrical isolation, bidirectional power transmission, fast dynamic response, easy implementation of soft switching and other characteristics, has been widely used in new energy power generation systems, energy management systems, AC-DC hybrid microgrids, DC distribution systems, electric vehicles and other fields. Taking the DAB converter as the basic power conversion unit and adopting the input-series-output-parallel (ISOP) connection method can improve the voltage level and power level of the whole system and be used in fields such as medium-voltage DC distribution networks. However, during certain periods within a switching cycle, the AC square-wave voltages on the primary and secondary sides of the high-frequency transformer and the inductor current are in opposite directions, resulting in power flowing back to the power supply side instead of flowing to the load, thus forming reverse power, which will greatly increase power loss and reduce system efficiency.

[0003] Regarding the ISOP-DAB converter, current research mainly focuses on input voltage balancing to achieve power balancing among DAB sub-modules. For example: (1) Chinese invention patent: "Input voltage equalization control method for modular combined DC converter" disclosed in CN 104993694 A; (2) Chinese invention patent: "Voltage and current equalization control method for ISOP modular DC / DC converter" disclosed in CN 115800754 A; (3) "An input-series output-parallel dual-active bridge converter input voltage self-balancing structure" in "Power System Protection and Control", 2023, 51(23): 141-150; (4) "Stability Analysis and Design of Common Phase Shift Control for Input-Series Output-Parallel Dual Active Bridge With Consideration of Dead-Time Effect", Z. Lu, G. Xu, M. Su, Y. Liao, Y. Liu and Y. Sun, "IEEE Journal of Emerging and Selected Topics in Power Electronics", vol. 10, no. 6, pp. 7721-7732, Dec. 2022; (5) "A 10kV / 400V SiC Based DC-DC Converter With Input-Series-Output-Parallel Configuration and Three-Loop Control", Shanglong Li, Zijian Wang, Xibo Yuan, Yonglei Zhang, Lijing Sun, Kai Wang, and Xiaojie Wu, "IEEE Transactions on Industry Applications", vol. 60, no. 5, pp. 7013-7029, Sept.-Oct. 2024. The main control objective of the above literature is to achieve power balancing among ISOP-DAB sub-modules, and the modulation strategies of each sub-module are not optimized. That is, the SPS modulation strategy is usually adopted for each sub-module in the ISOP-DAB converter.

[0004] Only a few papers have used TPS modulation strategy to optimize the submodules of ISOP-DAB converter, such as: (1) entitled “Multi-module Optimization Power Balance Control Method for Input Series and Output Parallel Dual Active Full-bridge DC-DC Converter”, Transactions of China Electrotechnical Society, 2018, 33(16): 3732-3742; however, the analytical expression of triple phase shift duty cycle obtained in the paper contains square root operation, which will increase the complexity of the algorithm and increase the computational burden of the controller; (2) entitled “Autonomous Input Voltage Sharing Control and Triple Phase Shift Modulation Method for ISOP-DABConverter in DC Microgrid: A Multiagent Deep Reinforcement Learning-Based Method”, Yu Zeng, Josep Pou, Changjiang Sun, Suvajit Mukherjee, Xu Xu, Amit KumarGupta, and Jiaxin Dong, IEEE Transactions on Power Engineering, 2018, 33(16): 3732-3742; Electronics》,vol.38,no.3,pp.2985-3000,March 2023;However, the deep learning algorithm used in the literature is very complex, which will increase the burden of the solver, especially when the number of ISOP-DAB converter sub-modules is large, the algorithm complexity will further increase.

[0005] In addition, none of the above literatures optimizes the return power of the ISOP-DAB converter, nor obtains the zero return power constraint condition, and cannot realize the zero return power modulation of the ISOP-DAB converter.

[0006] In summary, for the ISOP-DAB converter, under the premise of realizing multi-coupling loop decoupling control, the TPS modulation strategy is used to optimize the return power of each sub-module, explore the constraints of zero return power under step-down conversion (k>1) and step-up conversion (k<1), realize zero return power modulation of the ISOP-DAB converter, and then improve the efficiency of the entire system, which has very important practical significance. Summary of the invention

[0007] The purpose of the present invention is to provide a coordinated control method of three-loop decoupling control and zero reflux power modulation of an ISOP-DAB converter, which eliminates the reflux power of the ISOP-DAB converter through the coordinated action of three-loop decoupling control and zero reflux power modulation to achieve efficient operation of the control system.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A method for cooperative regulation of three-loop decoupling control and zero reverse current power modulation of an ISOP-DAB converter, comprising the following steps:

[0010] S1. Construct a regulation system; wherein, the regulation system includes a control stage and a modulation stage; the control stage includes an input voltage equalization loop control unit, an output voltage loop control unit, and an output current loop control unit; the modulation stage includes a phase-shift modulation unit, and the control stage and the modulation stage are communicatively connected, and the control stage is the basis of the modulation stage;

[0011] S2. The control stage uses a modular decoupling control strategy to decompose the multi-variable coupling control loop of the ISOP-DAB converter into relatively independent control loops. For each DAB sub-module after decoupling, the phase-shift duty ratio generated by the input voltage equalization loop is finely adjusted and corrected for the phase-shift duty ratio generated by the output voltage-current loop to generate an intermediate variable phase-shift duty ratio;

[0012] S3. The modulation stage uses the zero reverse current power modulation algorithm according to the intermediate variable phase-shift duty ratio generated by each DAB sub-module to generate a zero reverse current power modulation command to control the operation of each DAB sub-module.

[0013] Further, the input voltage equalization loop control unit specifically includes: an input voltage equalization loop controller and a first limiter;

[0014] The output voltage loop control unit specifically includes: an output voltage loop controller and a second limiter;

[0015] The output current loop control unit specifically includes: an output current loop controller and a third limiter.

[0016] Further, in S2, the control stage uses a modular decoupling control strategy to decompose the multi-variable coupling control loop of the ISOP-DAB converter into relatively independent control loops, including the following process:

[0017] For the regulation system formed by connecting the input ends of m DAB sub-modules in series and the output ends in parallel in the ISOP-DAB converter, the actual value of the input voltage of the first m-1 DAB sub-modules is collected, compared with the average value of the input voltage, and the difference is sent into the input voltage equalization loop controller to generate the input voltage equalization loop phase-shift duty ratio of the first m-1 DAB sub-modules and limit it; then the phase-shift duty ratios generated by the input voltage equalization loop controllers of the first m-1 DAB sub-modules after limiting are summed and the opposite value is taken as the phase-shift duty ratio generated by the input voltage equalization loop controller of the mth DAB sub-module to achieve the decoupling control of each DAB sub-module;

[0018] In S2, for each decoupled DAB sub-module, the phase-shifted duty cycle generated by the input voltage equalizing ring is finely adjusted and corrected with respect to the phase-shifted duty cycle generated by the output voltage-current loop to generate an intermediate variable phase-shifted duty cycle, including the following process:

[0019] The voltage on the parallel output side of the m DAB sub-modules is used as the actual value of the output voltage loop of the control system. After comparing and taking the difference with the output voltage reference value, it is sent into the output voltage loop controller to generate and limit the phase-shifted duty cycle of the output voltage loop controller, which serves as the reference value for the output current loop controller of each DAB sub-module. Then, the actual value of the output current of each DAB sub-module is collected, and after comparing and taking the difference with the reference value of the output current loop controller of each DAB sub-module, it is sent into the output current controller to generate and limit the phase-shifted duty cycle of the output current loop controller; the phase-shifted duty cycle generated by the input voltage equalizing ring controller is finely adjusted and corrected with respect to the phase-shifted duty cycle generated by the output current loop controller to generate the intermediate variable phase-shifted duty cycle d of each DAB sub-module j .

[0020] Furthermore, in S3, according to the intermediate variable phase-shifted duty cycles generated by each DAB sub-module, the modulation stage uses the zero reverse current power modulation algorithm to generate zero reverse current power modulation commands to control the operation of each DAB sub-module, including the following process:

[0021] According to the intermediate variable phase-shifted duty cycle d j generated by each DAB sub-module, using the zero reverse current power modulation algorithm, the final phase-shifted duty cycles (D 0 , D 1 , D 2 ) of the DAB sub-module under the triple phase-shifted modulation strategy are solved and obtained. Then, the final phase-shifted duty cycles are sent into the modulator for modulation to generate drive pulses acting on the front and rear bridge switching devices of the DAB sub-module, so as to achieve zero reverse current power modulation of each DAB sub-module

[0022] Furthermore, the zero reverse current power modulation algorithm is specifically:

[0023] Under buck conversion, the intermediate variable phase-shifted duty cycle d j output by the control stage is:

[0024] d j = 1 - D 1 ;

[0025] where: D 1 is the phase-shifted duty cycle between the diagonal switching devices of the front bridge in the ISOP-DAB converter;

[0026] D 1 has a value range of:

[0027]

[0028] According to D 1 's value range, the values of D 0 and D 2 are as follows:

[0029]

[0030] Among them, D 0 is the phase-shifted duty cycle between the front-bridge switching device and the rear-bridge switching device in the ISOP-DAB converter; D 2 is the phase-shifted duty cycle between the diagonal switching devices of the rear bridge in the ISOP-DAB converter;

[0031] According to the value range of D 1 , the value range of the phase-shifted duty cycle d j of the intermediate variable under buck conversion is:

[0032] 0 ≤ d j ≤ 1 / k;

[0033] where: j = 1, 2,..., m;

[0034] Under boost conversion, the phase-shifted duty cycle d j of the intermediate variable output by the control stage is expressed as:

[0035] d j = 1 - D 2 ;

[0036] Among them, the value range of D 2 is:

[0037] 1 - k ≤ D 2 ≤ 1;

[0038] According to the value range of D 2 , the values of D 0 and D 1 are as follows:

[0039]

[0040] According to the value range of D 2 , the value range of the phase-shifted duty cycle d j of the intermediate variable under boost conversion is:

[0041] 0 ≤ d j ≤ k, j = 1, 2,..., m.

[0042] Furthermore, the limit values of the phase-shifted duty cycle limiters generated by the input voltage equalizing loop control unit, the output voltage loop control unit, and the output current loop control unit are all [-0.5, 0.5].

[0043] Furthermore, the input voltage equalizing loop controller, the output voltage loop controller, and the output current loop controller are all PI controllers.

[0044] According to the specific embodiments provided by the present invention, the following technical effects are disclosed:

[0045] (1) By performing zero reverse power modulation on the modulation stage, the reverse power of each sub-module of the ISOP-DAB converter is completely eliminated, effectively reducing the power loss of the entire control system and improving the control system efficiency;

[0046] (2) By adopting the decoupling control strategy, not only can the modular expansion of the ISOP-DAB converter be realized, but also the independent design of each DAB sub-module can be achieved;

[0047] (3) The control method in the present invention can take into account the high efficiency, high-voltage high-power transmission characteristics, and overload current limiting ability of the ISOP-DAB converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0049] The following further illustrates the coordinated control method of three-loop decoupling control and zero reverse power modulation of the ISOP-DAB converter of the present invention with reference to the drawings;

[0050] Figure 1 is a schematic diagram of the topology structure of the ISOP-DAB converter in the coordinated control method of three-loop decoupling control and zero reverse power modulation of the ISOP-DAB converter of the present invention;

[0051] Figure 2 is a schematic diagram of the driving pulses, voltage, current, and reverse power waveforms of the j-th sub-module of the ISOP-DAB converter in the step-down conversion (k > 1) using the SPS modulation strategy in the present invention;

[0052] Figure 3 is a schematic diagram of the driving pulses, voltage, current, and reverse power waveforms of the j-th sub-module of the ISOP-DAB converter in the step-up conversion (k < 1) using the SPS modulation strategy in the present invention;

[0053] Figure 4 It is a schematic diagram of the inductor current path when the j-th sub-module of the ISOP-DAB converter in the present invention adopts the SPS modulation strategy in the time period from 0 to t 0 time period;

[0054] Figure 5 It is a schematic diagram of the inductor current path when the j-th sub-module of the ISOP-DAB converter in the present invention adopts the SPS modulation strategy in the time period from t 0 to t 1 time period;

[0055] Figure 6 It is a schematic diagram of the driving pulses, voltage and current, and reflux power waveforms when the j-th sub-module of the ISOP-DAB converter in the present invention adopts the TPS modulation strategy under step-down conversion (k>1);

[0056] Figure 7 It is a schematic diagram of the driving pulses, voltage and current, and reflux power waveforms when the j-th sub-module of the ISOP-DAB converter in the present invention adopts the TPS modulation strategy under step-up conversion (k<1);

[0057] Figure 8 It is a schematic diagram of the structure of the ISOP-DAB converter in the present invention adopting the existing control method; where, G vin is a control unit including an input voltage equalization loop controller and a first limiter; G vo is a control unit including an output voltage loop controller and a second limiter; G io is a control unit including an output current loop controller and a third limiter;

[0058] Figure 9 It is a schematic diagram of the structure of the ISOP-DAB converter in the present invention adopting the control method proposed in this application; in the figure, G vin is a control unit including an input voltage equalization loop controller and a first limiter; G vo is a control unit including an output voltage loop controller and a second limiter; G io is a control unit including an output current loop controller and a third limiter;

[0059] Figure 10 It is a schematic diagram of the equivalent decoupling structure of the ISOP-DAB converter in the present invention adopting the control method proposed in this application; where, G vin is a control unit including an input voltage equalization loop controller and a first limiter; G vo is a control unit including an output voltage loop controller and a second limiter; G io is a control unit including an output current loop controller and a third limiter;

[0060] Figure 11 These are the experimental waveforms of the primary - side AC square - wave voltage, inductor current, and instantaneous transmission power of the first DAB sub - module in the buck - conversion (k > 1) of the present invention. Among them, (a) is the experimental result using the existing control method, and (b) is the experimental result using the control method proposed in the present invention.

[0061] Figure 12 These are the experimental waveforms of the secondary - side AC square - wave voltage, inductor current, and instantaneous transmission power of the first DAB sub - module in the buck - conversion (k > 1) of the present invention. Among them, (a) is the experimental result using the existing control method, and (b) is the experimental result using the control method proposed in the present invention.

[0062] Figure 13 These are the experimental waveforms of the primary - side AC square - wave voltage, inductor current, and instantaneous transmission power of the second DAB sub - module in the buck - conversion (k > 1) of the present invention. Among them, (a) is the experimental result using the existing control method, and (b) is the experimental result using the control method proposed in the present invention.

[0063] Figure 14 These are the experimental waveforms of the secondary - side AC square - wave voltage, inductor current, and instantaneous transmission power of the second DAB sub - module in the buck - conversion (k > 1) of the present invention. Among them, (a) is the experimental result using the existing control method, and (b) is the experimental result using the control method proposed in the present invention.

[0064] Figure 15 These are the experimental waveforms of the primary - side AC square - wave voltage, inductor current, and instantaneous transmission power of the first DAB sub - module in the boost - conversion (k < 1) of the present invention. Among them, (a) is the experimental result using the existing control method, and (b) is the experimental result using the control method proposed in the present invention.

[0065] Figure 16 These are the experimental waveforms of the secondary - side AC square - wave voltage, inductor current, and instantaneous transmission power of the first DAB sub - module in the boost - conversion (k < 1) of the present invention. Among them, (a) is the experimental result using the existing control method, and (b) is the experimental result using the control method proposed in the present invention.

[0066] Figure 17 These are the experimental waveforms of the primary - side AC square - wave voltage, inductor current, and instantaneous transmission power of the second DAB sub - module in the boost - conversion (k < 1) of the present invention. Among them, (a) is the experimental result using the existing control method, and (b) is the experimental result using the control method proposed in the present invention.

[0067] Figure 18These are the experimental waveforms of the secondary side AC square wave voltage, inductor current, and instantaneous transmission power of the second DAB sub-module under boost conversion (k < 1) in the present invention; among them, (a) is the experimental result using the existing control method, and (b) is the experimental result using the control method proposed in the present invention.

[0068] Figure 19 This is a schematic diagram comparing the experimental efficiencies of the ISOP-DAB converter in the present invention under buck conversion (k > 1) using the existing control method and the control method proposed in the present invention.

[0069] Figure 20 This is a schematic diagram comparing the experimental efficiencies of the ISOP-DAB converter in the present invention under boost conversion (k < 1) using the existing control method and the control method proposed in this application. Detailed implementation manners

[0070] The following combines the accompanying drawings and embodiments to further describe in detail the specific implementation manners of the present invention. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0071] To better understand the purpose, structure, and function of the present invention, the following further describes the present invention in detail with reference to the accompanying drawings.

[0072] The present invention provides a coordinated control method for triple-loop decoupling control and zero reverse current power modulation of an ISOP-DAB converter, including the following steps:

[0073] S1. Construct a control system; among them, the control system includes a control stage and a modulation stage; the control stage includes an input voltage equalization loop control unit, an output voltage loop control unit, and an output current loop control unit; the modulation stage includes a phase-shift modulation unit, and the control stage and the modulation stage are communicatively connected, and the control stage is the basis of the modulation stage;

[0074] S2. The control stage deconstructs the multi-variable coupling control loop of the ISOP-DAB converter into relatively independent control loops through a modular decoupling control strategy. For each DAB sub-module after decoupling, the phase-shift duty ratio generated by the input voltage equalization loop is finely adjusted and corrected for the phase-shift duty ratio generated by the output voltage-current loop to generate an intermediate variable phase-shift duty ratio;

[0075] S3. The modulation stage generates a zero reverse current power modulation command according to the intermediate variable phase-shift duty ratios generated by each DAB sub-module, and controls the operation of each DAB sub-module.

[0076] The solution in the present invention is based on an ISOP-DAB converter composed of m DAB sub-modules, as Figure 1 shown, where each DAB sub-module is a DAB converter.

[0077] To completely eliminate the reverse power of the ISOP-DAB converter and improve the efficiency of the control system, the present invention introduces the TPS modulation strategy. On this basis, a zero reverse power modulation algorithm is also proposed. The TPS modulation strategy is based on the SPS modulation strategy, and a phase-shifted duty ratio is also added inside the front and rear bridges, and the phase-shifted duty ratios of the front and rear bridges are not equal.

[0078] To solve the zero reverse power constraint conditions of each sub-module of the ISOP-DAB converter under step-down conversion (k>1) and step-up conversion (k<1), it is first necessary to derive the analytical expressions of the inductor current and reverse power of each sub-module. Since the operating state of the DAB converter is symmetric between the first half cycle and the second half cycle without DC bias, it is only necessary to solve the reverse power expression for half a cycle, as Figure 2 shows the schematic diagrams of the driving pulses, voltage, current, and reverse power waveforms of the j-th sub-module of the ISOP-DAB converter under step-down conversion (k>1) using the SPS modulation strategy. Figure 3 shows the schematic diagrams of the driving pulses, voltage, current, and reverse power waveforms of the j-th sub-module of the ISOP-DAB converter under step-up conversion (k<1) using the SPS modulation strategy. As Figure 2 and Figure 3 shown, under SPS modulation of the DAB converter, there is only one phase-shifted duty ratio D 0 , that is, the phase-shifted duty ratio between the switching devices of the front bridge and the rear bridge. When the DAB converter uses the SPS modulation strategy under step-down conversion (k>1) and step-up conversion (k<1), there will always be moments when the AC square wave voltages on the primary and secondary sides and the inductor current are in opposite directions, so reverse power inevitably exists, as Figure 2 and Figure 3 shown by the shaded parts. Figure 4 shows the schematic diagram of the inductor current path of the j-th sub-module of the ISOP-DAB converter under step-down conversion (k>1) or step-up conversion (k<1) using the SPS modulation strategy during the time period from 0 to t 0 , as Figure 4 shown, the inductor current on the primary side flows in from the positive pole of the power supply, and at this time, there is reverse power on the primary side of the DAB converter. Figure 5 shows the schematic diagram of the inductor current path of the j-th sub-module of the ISOP-DAB converter using the SPS modulation strategy during the time period from t 0 to t 1 , at this time, the AC square wave voltage v cdj (t) is equivalent to a voltage source on the secondary side, as Figure 5 shown, the inductor current on the secondary side flows in from the positive pole of the power supply, and at this time, there is reverse power on the secondary side of the DAB converter.

[0079] Figure 6 Schematic diagrams of drive pulses, voltage, current, and reflux power waveforms of the j-th sub-module of the ISOP-DAB converter under buck conversion (k > 1) using the TPS modulation strategy; Figure 7 Schematic diagrams of drive pulses, voltage, current, and reflux power waveforms of the j-th sub-module of the ISOP-DAB converter under boost conversion (k < 1) using the TPS modulation strategy. As Figure 6 and Figure 7 shown, the phase-shifted duty cycle between the diagonal switch devices of the front bridge is defined as D 1 , and the phase-shifted duty cycle between the diagonal switch devices of the rear bridge is defined as D 2 . Then, the AC square-wave voltage, inductor current, and reflux power of each sub-module of the ISOP-DAB converter can all be determined by (D 0 , D 1 , D 2 ).

[0080] Therefore, using the method of piecewise analysis and solution, the inductor current expression of the DAB sub-module under buck conversion (k > 1) using the TPS modulation strategy in the Figure 6 time period t 0 ~t 4 is obtained, as shown in Table 1; the inductor current expression of the DAB sub-module under boost conversion (k < 1) using the TPS modulation strategy in the Figure 7 time period t 0 ~t 4 is shown in Table 2.

[0081] Table 1 Inductor current expression of the DAB sub-module under buck conversion (k > 1) using the TPS modulation strategy in the Figure 6 time period t 0 ~t 4

[0082]

[0083] Table 2 Inductor current expression of the DAB sub-module under boost conversion (k < 1) using the TPS modulation strategy in the Figure 7 time period t 0 ~t 4

[0084]

[0085] Therefore, according to the inductor current expression and the piecewise integration method, the expression of the primary-side reflux power within half a switching period of the DAB sub-module under buck conversion (k > 1) using the TPS modulation in Figure 6 is:

[0086]

[0087] Figure 6 When the DAB sub-module adopts TPS modulation under step-down conversion (k>1), the expression of the secondary side reflux power within half a switching period is

[0088]

[0089] Using the same method, it can be obtained that Figure 7 When the DAB sub-module adopts TPS modulation under boost conversion (k<1), the expression of the primary side reflux power within half a switching period is

[0090]

[0091] Figure 7 When the DAB sub-module adopts TPS modulation under boost conversion (k<1), the expression of the secondary side reflux power within half a switching period is:

[0092]

[0093] Therefore, according to the expressions of the primary and secondary side reflux powers within half a switching period when the DAB sub-module adopts TPS modulation under step-down conversion (k>1), the constraint condition for zero reflux power is:

[0094]

[0095] Phase-shift duty cycle D 0 and D 2 can be expressed in terms of D 1 as:

[0096]

[0097] where the range of the phase-shift duty cycle D 1 is:

[0098]

[0099] According to the expressions of the primary and secondary side reflux powers within half a switching period when the DAB sub-module adopts TPS modulation under boost conversion (k<1), the constraint condition for zero reflux power is:

[0100]

[0101] Therefore, the phase-shift duty cycle D 0 and D 1 can be expressed in terms of D 2 as:

[0102]

[0103] where the range of the phase-shift duty cycle D 2 is:

[0104] 1 - k ≤ D 2 ≤ 1

[0105] After obtaining the zero - reverse - current power constraint conditions of the ISOP - DAB converter under step - down conversion (k > 1) and step - up conversion (k < 1), the control process of the entire control system is analyzed below to achieve the goal of zero - reverse - current power operation of the system.

[0106] In the control stage, both the input voltage equalization loop control unit and the output voltage loop control unit include a voltage controller and a limiter; the output current loop control unit includes a current controller and a limiter. For a control system with input series and output parallel composed of m DAB sub - modules, the actual input voltage values of the first (m - 1) DAB sub - modules are collected and compared with the average input voltage (V in / m). After taking the difference, it is sent into the input voltage equalization loop controller to generate the phase - shift duty ratio of the input voltage equalization loop of the first (m - 1) DAB sub - modules and limit it. Then, the limited phase - shift duty ratios of the input voltage equalization loops of the first (m - 1) DAB sub - modules are used to generate phase - shift duty ratios, sum them up and take the opposite value as the phase - shift duty ratio generated by the input voltage equalization loop of the m - th DAB sub - module, so as to achieve the decoupled control of each DAB sub - module. The voltage on the parallel output side of the system is collected as the actual value of the output voltage loop of the entire system. After comparing it with the output voltage reference value and taking the difference, it is sent into the output voltage loop controller to generate the phase - shift duty ratio of the output voltage loop and limit it, which is used as the reference value of the output current loop of each DAB sub - module. Then, the actual output current values of each DAB sub - module are collected, compared with it and the difference is sent into the output current controller to generate the phase - shift duty ratio of the output current loop and limit it. After the phase - shift duty ratio generated by the input voltage equalization loop finely adjusts and corrects the phase - shift duty ratio generated by the output current loop, the intermediate variable phase - shift duty ratio d j (j = 1, 2, …, m) is generated to realize the connection between the control stage and the modulation stage.

[0107] Figure 8 is the structural schematic diagram of the ISOP - DAB converter adopting the existing control strategy; Figure 9 is the structural schematic diagram of the ISOP - DAB converter adopting the control strategy of this application. In Figure 8 and Figure 9 G vin includes an input voltage equalization loop PI controller and a first limiter, G vo includes an output voltage loop PI controller and a second limiter, G io includes an output current loop PI controller and a third limiter. Compared with Figure 8Compared with the existing control strategies of the ISOP-DAB converter, the control strategy proposed by the present invention mainly optimizes the modulation stage. In the existing control strategies of the ISOP-DAB converter, the intermediate variable phase-shifted duty cycle d j (j = 1, 2, …, m) output by the control stage is input into the modulation stage, and then d j = D 0 is used for SPS modulation.

[0108] As shown in the control strategy proposed by the present invention Figure 9 , in the modulation stage, according to the intermediate variable phase-shifted duty cycle d j (j = 1, 2, …, m) generated by each DAB sub-module, the zero reverse power modulation algorithm is adopted to solve and obtain the final phase-shifted duty cycle (D 0 , D 1 , D 2 ) of the DAB sub-module under the TPS modulation strategy, and then it is sent into the modulator for modulation to generate drive pulses acting on the front and rear bridge switching devices of the DAB sub-module, so as to realize the zero reverse power modulation of each DAB sub-module.

[0109] The present invention further provides the specific calculation process of the zero reverse power modulation algorithm:

[0110] Under step-down conversion (k > 1), the intermediate variable phase-shifted duty cycle d j (j = 1, 2, …, m) output by the control stage can be expressed as:

[0111] d j = 1 - D 1

[0112] where the value range of D 1 is:

[0113]

[0114] According to the value of D 1 and the zero reverse power constraint condition of the DAB sub-module under step-down conversion (k > 1), the values of D 0 and D 2 can be obtained as:

[0115]

[0116] According to the value range of D 1 , the value range of the intermediate variable phase-shifted duty cycle d j under step-down conversion (k > 1) can be obtained as:

[0117] 0 ≤ d j ≤ 1 / k, j = 1, 2, …, m

[0118] Under the boost conversion (k < 1), the phase-shifted duty cycle d of the intermediate variable output by the control stage j (j = 1, 2, …, m) can be expressed as:

[0119] d j = 1 - D 2

[0120] where D 2 has a value range of:

[0121] 1 - k ≤ D 2 ≤ 1

[0122] According to the value of D 2 and the zero reverse power constraint condition of the DAB sub-module under the boost conversion (k < 1), the values of D 0 and D 1 can be obtained as:

[0123]

[0124] According to the value range of D 2 the phase-shifted duty cycle d of the intermediate variable under the boost conversion (k < 1) can be obtained j and its value range is:

[0125] 0 ≤ d j ≤ k, j = 1, 2, …, m

[0126] Therefore, through the zero reverse power constraint conditions of the DAB sub-module under the buck conversion (k > 1) and the boost conversion (k < 1), its zero reverse power operation under the TPS modulation can be realized.

[0127] As Figure 9 shown, the sum of the output quantities of the input voltage equalization loop control units of the first (m - 1) DAB sub-modules can be expressed as:

[0128]

[0129] Therefore, the zero reverse power regulation strategy block diagram of the ISOP-DAB converter proposed by the present invention can be equivalent to the equivalent decoupling control form as Figure 10 shown.

[0130] Through the decoupling of multiple control loops at the control stage, the relative independence of m DAB sub-modules is achieved, and through the phase-shifted duty cycle d of the intermediate variable j (j = 1, 2, …, m), an effective link between the control stage and the modulation stage is realized. Then, in the modulation stage, the zero reverse power modulation algorithm proposed in this application is adopted for each DAB sub-module to eliminate the reverse power of the entire ISOP-DAB converter, thereby improving the system efficiency.

[0131] Comparative analysis:

[0132] Experimental results of the comparative study between the triple-loop decoupling control and zero reverse power modulation collaborative regulation method of the ISOP-DAB converter provided by the present invention and the existing regulation strategies:

[0133] Compared with the existing regulation strategies, the regulation strategy proposed by the present invention does not add additional equipment and costs. By simply optimizing the modulation algorithm, the reverse power of the entire ISOP-DAB converter can be eliminated and the system efficiency can be improved.

[0134] To verify the effectiveness of the proposed regulation strategy of the present invention, an experiment was conducted on an ISOP-DAB converter composed of two DAB sub-modules. The experimental parameters are shown in Table 3, and the experimental results are as Figures 11 - 18 shown.

[0135] Table 3 Experimental parameters of the ISOP-DAB converter

[0136]

[0137] Among them, Figures 11 - 14 presents the experimental results under step-down conversion (k>1); Figures 15 - 18 presents the experimental results under step-up conversion (k<1). In the following experiments, P j_1 (t) is the instantaneous transfer power on the primary side of the DAB converter sub-module, which can be expressed as P j_1 (t) = v abj (t)·i Lj_1 (t); P j_2 (t) is the instantaneous transfer power on the secondary side of the DAB converter sub-module, which can be expressed as P j_2 (t) = v cdj (t)·i Lj_2 (t).

[0138] Figure 11 In (a) and Figure 11 in (b) respectively show the waveforms of the primary side AC square wave voltage, inductor current, and instantaneous transfer power of the first DAB sub-module when k = 1.6667 and P o = 36 W, respectively, when using the existing regulation method and the regulation method proposed by the present invention. The experimental results show that when the ISOP-DAB converter uses the existing regulation method, a large amount of reverse power will be generated, while when using the regulation method proposed by the present invention, the reverse power can be completely eliminated.

[0139] Figure 12 In (a) and Figure 12 in (b) respectively show the waveforms of the primary side AC square wave voltage, inductor current, and instantaneous transfer power of the first DAB sub-module when k = 1.6667 and P oWaveforms of the secondary side AC square-wave voltage, inductor current, and instantaneous transmission power when the existing control method and the control method proposed in the present invention are respectively adopted at P = 36W. The experimental results show that when the existing control method is adopted for the ISOP-DAB converter, a large amount of reverse power will be generated, while when the control method proposed in the present invention is adopted, the reverse power can be completely eliminated.

[0140] Figure 13 In (a) and Figure 13 In (b), the waveforms of the primary side AC square-wave voltage, inductor current, and instantaneous transmission power of the second DAB sub-module when k = 1.6667 and P o Waveforms of the primary side AC square-wave voltage, inductor current, and instantaneous transmission power when the existing control method and the control method proposed in the present invention are respectively adopted at P = 36W. The experimental results show that when the existing control method is adopted for the ISOP-DAB converter, a large amount of reverse power will be generated, while when the control method proposed in the present invention is adopted, the reverse power can be completely eliminated.

[0141] Figure 14 In (a) and Figure 14 In (b), the waveforms of the secondary side AC square-wave voltage, inductor current, and instantaneous transmission power of the second DAB sub-module when k = 1.6667 and P o Waveforms of the secondary side AC square-wave voltage, inductor current, and instantaneous transmission power when the existing control method and the control method proposed in this application are respectively adopted at P = 36W. The experimental results show that when the existing control method is adopted for the ISOP-DAB converter, a large amount of reverse power will be generated, while when the control method proposed in this application is adopted, the reverse power can be completely eliminated.

[0142] Figure 15 In (a) and Figure 15 In (b), the waveforms of the primary side AC square-wave voltage, inductor current, and instantaneous transmission power of the first DAB sub-module when k = 0.8333 and P o Waveforms of the primary side AC square-wave voltage, inductor current, and instantaneous transmission power when the existing control method and the control method proposed in the present invention are respectively adopted at P = 144W. The experimental results show that when the existing control method is adopted for the ISOP-DAB converter, a large amount of reverse power will be generated, while when the control method proposed in the present invention is adopted, the reverse power can be completely eliminated.

[0143] Figure 16 In (a) and Figure 16 In (b), the waveforms of the secondary side AC square-wave voltage, inductor current, and instantaneous transmission power of the first DAB sub-module when k = 0.8333 and P o Waveforms of the secondary side AC square-wave voltage, inductor current, and instantaneous transmission power when the existing control method and the control method proposed in the present invention are respectively adopted at P = 144W. The experimental results show that when the existing control method is adopted for the ISOP-DAB converter, a large amount of reverse power will be generated, while when the control method proposed in the present invention is adopted, the reverse power can be completely eliminated.

[0144] Figure 17 In (a) and Figure 17 In (b), the waveforms of the primary-side AC square-wave voltage, inductor current, and instantaneous transmission power of the second DAB sub-module at k = 0.8333 and P o = 144 W are respectively given when the existing control method and the control method proposed in the present invention are adopted. The experimental results show that when the existing control method is adopted for the ISOP-DAB converter, a large amount of reverse power will be generated, while when the control method proposed in the present invention is adopted, the reverse power can be completely eliminated.

[0145] Figure 18 In (a) and Figure 18 In (b), the waveforms of the secondary-side AC square-wave voltage, inductor current, and instantaneous transmission power of the second DAB sub-module at k = 0.8333 and P o = 144 W are respectively given when the existing control method and the control method proposed in the present invention are adopted. The experimental results show that when the existing control method is adopted for the ISOP-DAB converter, a large amount of reverse power will be generated, while when the control method proposed in the present invention is adopted, the reverse power can be completely eliminated.

[0146] Figure 19 FIG. is a schematic diagram of the experimental efficiency comparison of the ISOP-DAB converter adopting the existing control method and the control method proposed in the present invention under step-down conversion (k>1). The experimental results show that adopting the control method proposed in the present invention under step-down conversion (k>1) can effectively improve the system efficiency.

[0147] Figure 20 FIG. is a schematic diagram of the experimental efficiency comparison of the ISOP-DAB converter adopting the existing control method and the control method proposed in the present invention under boost conversion (k<1). The experimental results show that adopting the control method proposed in the present invention under boost conversion (k<1) can effectively improve the system efficiency.

[0148] The above experimental results prove that compared with the traditional control method, the control method proposed in the present invention can completely eliminate the reverse power of the ISOP-DAB converter under step-down conversion (k>1) and boost conversion (k<1), and improve the system efficiency.

[0149] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for coordinated control of three-loop decoupling control and zero-return power modulation of ISOP-DAB converter, characterized in that: The following steps are involved: S1. Construct a control system; wherein the control system includes a control stage and a modulation stage; the control stage includes an input voltage-sharing loop control unit, an output voltage loop control unit, and an output current loop control unit; the modulation stage includes a phase-shift modulation unit, and the control stage is connected to the modulation stage in communication, and the control stage is the basis of the modulation stage; S2, the control stage deconstructs the multivariable coupling control loop of the ISOP-DAB converter into relatively independent control loops through a modular decoupling control strategy, and for each decoupled DAB sub-module, fine-tunes and corrects the phase-shift duty ratio generated by the input voltage-sharing loop to the phase-shift duty ratio generated by the output voltage-current loop to generate an intermediate variable phase-shift duty ratio; S3, the modulation stage uses a zero-return power modulation algorithm to generate a zero-return power modulation instruction according to the intermediate variable phase shift duty ratio generated by each DAB sub-module, and controls the operation of each DAB sub-module.

2. The method for coordinated control of three-loop decoupling control and zero-return power modulation of ISOP-DAB converter according to claim 1 is characterized in that: The input voltage grading ring control unit specifically includes: an input voltage grading ring controller and a first limiter; The output voltage loop control unit specifically includes: an output voltage loop controller and a second limiter; The output current loop control unit specifically includes: an output current loop controller and a third limiter.

3. The method for coordinated control of three-loop decoupling control and zero-return power modulation of ISOP-DAB converter according to claim 2 is characterized in that: In S2, the control stage deconstructs the ISOP-DAB converter multivariable coupling control loop into relatively independent control loops through a modular decoupling control strategy, including the following processes: For the control system composed of m DAB submodules in the ISOP-DAB converter, the input ends are connected in series and the output ends are connected in parallel. The actual value of the input voltage of the first m-1 DAB submodules is collected and compared with the average value of the input voltage, and then the difference is sent to the input voltage balancing ring controller to generate the input voltage balancing ring phase shift duty ratio of the first m-1 DAB submodules and limit it; then the phase shift duty ratios generated by the input voltage balancing ring controller of the first m-1 DAB submodules after limiting are summed and the inverse thereof is taken as the phase shift duty ratio generated by the input voltage balancing ring controller of the mth DAB submodule, so as to realize the decoupling control of each DAB submodule; In S2, for each decoupled DAB submodule, the phase shift duty ratio generated by the input voltage balancing loop is fine-tuned and corrected to the phase shift duty ratio generated by the output voltage-current loop to generate an intermediate variable phase shift duty ratio, including the following process: The voltage on the parallel output side of m DAB submodules is used as the actual value of the output voltage loop of the control system, and is compared with the output voltage reference value and subtracted, and then sent to the output voltage loop controller to generate the phase-shift duty ratio of the output voltage loop controller and limit it as the reference value of the output current loop controller of each DAB submodule. Then, the actual value of the output current of each DAB submodule is collected and compared with the reference value of the output current loop controller of each DAB submodule, and then the difference is sent to the output current controller to generate the phase-shift duty ratio of the output current loop controller and limit it; the phase-shift duty ratio generated by the input voltage balancing loop controller is fine-tuned and corrected to the phase-shift duty ratio generated by the output current loop controller, and the intermediate variable phase-shift duty ratio d generated by each DAB submodule is generated. j .

4. The method for coordinated control of three-loop decoupling control and zero-return power modulation of ISOP-DAB converter according to claim 3 is characterized in that: In S3, the modulation stage uses a zero-return power modulation algorithm to generate a zero-return power modulation instruction according to the intermediate variable phase shift duty ratio generated by each DAB submodule, and controls the operation of each DAB submodule, including the following process: According to the intermediate variable phase shift duty ratio d generated by each DAB submodule j , using the zero-return power modulation algorithm, the final phase-shift duty cycle (D0, D1, D2) of the DAB sub-module under the triple phase-shift modulation strategy is solved, and then the final phase-shift duty cycle is sent to the modulator for modulation to generate driving pulses acting on the front and rear bridge switching devices of the DAB sub-module to achieve zero-return power modulation for each DAB sub-module.

5. The method for coordinated control of three-loop decoupling control and zero-return power modulation of ISOP-DAB converter according to claim 4 is characterized in that: The zero-return power modulation algorithm is specifically: Under step-down conversion, the intermediate variable phase shift duty ratio d output by the control stage j : d j =1-D1; Where: D1 is the phase shift duty ratio between the diagonal switch devices of the front bridge in the ISOP-DAB converter; The value range of D1 is: According to the value range of D1, the values ​​of D0 and D2 are obtained as follows: Wherein, D0 is the phase shift duty ratio between the front bridge switch devices and the rear bridge switch devices in the ISOP-DAB converter; D2 is the phase shift duty ratio between the diagonal switch devices of the rear bridge in the ISOP-DAB converter; According to the value range of D1, the intermediate variable phase shift duty ratio d under step-down conversion is obtained. j The value range of is: 0≤d j ≤1 / k; Where: j = 1, 2, ..., m; Under boost conversion, the intermediate variable phase shift duty ratio d output by the control stage j , expressed as: d j =1-D2; The value range of D2 is: 1-k≤D2≤1; According to the value range of D2, the values ​​of D0 and D1 are obtained as follows: According to the value range of D2, the intermediate variable phase shift duty ratio d under boost conversion is obtained. j The value range of is: 0≤d j ≤k,j=1,2,…,m。 6. The method for coordinated control of three-loop decoupling control and zero-return power modulation of ISOP-DAB converter according to claim 5 is characterized in that: The limiting values ​​of the phase-shift duty cycle limiters generated by the input voltage-sharing loop control unit, the output voltage loop control unit and the output current loop control unit are all [-0.5, 0.5].

7. The method for coordinated control of three-loop decoupling control and zero-return power modulation of ISOP-DAB converter according to claim 2 is characterized in that: The input voltage-sharing loop controller, the output voltage loop controller and the output current loop controller are all PI controllers.

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