Power grid stability-oriented three-port current type three-active bridge grid-connected converter cooperative control method and storage medium

Abstract

The invention discloses a three-port current type three-active bridge grid-connected converter cooperative control method for power grid stability, and belongs to the technical field of electric energy conversion control. The method comprises the following steps: acquiring preset output voltages and load condition ranges of secondary high-voltage and low-voltage ports; based on a switching loss model of the CF-TAB converter, constructing an optimization objective function taking the minimum sum of currents flowing through the switching tube in the hard switching-on period as an objective; considering a power transmission requirement and a ZVS required condition, and determining a constraint condition for optimizing the objective function; performing optimization solution on the optimization objective function to obtain an optimal degree-of-freedom combination under different working conditions, and storing the optimal degree-of-freedom combination as a lookup table; when online cooperative control is carried out, the corresponding optimal degree-of-freedom combination is obtained from the lookup table according to the needed output voltage and output power, and PWM control of the converter is achieved. According to the invention, optimization of the switching loss of the CF-TAB converter system and widening of the ZVS range of the switching tube can be realized under the condition of full-range voltage and load power, so that the CF-TAB converter system can be suitable for relatively wide voltage and load power conditions, and the grid-connected stability is improved.

Description

Technical Field

[0001] This invention belongs to the field of power conversion control technology, and specifically relates to a collaborative control method for a three-port current-type three-active-bridge grid-connected converter oriented towards grid stability. Background Technology

[0002] Compared to the traditional independent operation of on-board chargers (OBC) and auxiliary power modules (APM) in electric vehicles, the integrated solution of the three-port current-type three-active bridge (CF-TAB) converter successfully integrates the OBC and APM modules by sharing the full-bridge circuit, high-frequency transformer, and control circuitry on the primary side. This integrated solution allows for the simultaneous charging of both the power battery and the low-voltage auxiliary power supply within a single converter, significantly improving the overall system efficiency and power density while reducing system size and cost.

[0003] Currently, there is considerable research on the working principle, power transfer characteristics, efficiency optimization strategies, soft-switching range extension control strategies, and power decoupling techniques of CF-TAB converter topologies. However, the current application of this topology in the integration of electric vehicle OBCs and APMs is still limited to verifying the effectiveness of topology power transfer, lacking research on closed-loop control strategies for optimizing system efficiency between ports. Furthermore, research on CF-TAB converter topology control strategies is incomplete, and most studies on its integration with electric vehicle OBCs and APMs remain at the open-loop verification and theoretical analysis stage.

[0004] Therefore, a control strategy needs to be studied that can optimize the efficiency of the CF-TAB converter topology system applied to the integration of OBC and APM in electric vehicles while extending its soft-switching range. Summary of the Invention

[0005] The purpose of this invention is to provide a collaborative control method for a three-port current-mode three-active-bridge grid-connected converter oriented towards grid stability. This method optimizes system switching losses and expands the ZVS range of the switching transistors under a full range of voltage and load power conditions, enabling the converter to be applicable to a wider range of voltage and load power conditions, thereby improving grid stability. The technical solution adopted in this invention is as follows.

[0006] On one hand, the present invention provides a cooperative control method for a three-port current-mode three-active-bridge grid-connected converter, comprising:

[0007] Obtain the preset output voltage and output power range of the secondary high voltage port and the secondary low voltage port;

[0008] Based on the switching loss model of a three-port current-source three-active-bridge grid-connected converter, an optimization objective function is constructed with the goal of minimizing the total current flowing through the switch during hard turn-on.

[0009] by As the control degrees of freedom, considering power transmission requirements and ZVS requirements, the constraints of the optimization objective function are determined during the solution process, resulting in the optimization mathematical model; where... These represent the duty cycles of the PWM within the full-bridge unit at the primary-side port, the secondary-side high-voltage port, and the secondary-side low-voltage port, respectively. Compared to the shift between the primary side port and the secondary side high-voltage port, The shift ratio between the primary side port and the secondary side low-voltage port;

[0010] Within the range of output voltage and output power, different combinations of system parameters for output voltage and output power are defined with a set step size. For any given combination of system parameters, the optimal combination of degrees of freedom is obtained by solving the optimization objective function and its constraints. ;

[0011] Store the optimal combination of degrees of freedom corresponding to all system parameter combinations as a lookup table;

[0012] When performing online coordinated control of a three-port current-type three-active-bridge grid-connected converter, the optimal combination of degrees of freedom is obtained from the lookup table according to the required output voltage and output power, and the PWM control of the converter is performed according to the obtained optimal combination of degrees of freedom.

[0013] Optionally, the switching loss model of the three-port current-source three-active-bridge grid-connected converter is expressed as follows:

[0014]

[0015] in, and These are the turn-on loss and turn-off loss of the switching transistor, respectively. The switching frequency of the switching transistor. and These represent the time when the switching transistor starts conducting and the time when it is fully turned on, respectively. and These are the start and complete turn-off times of the switching transistor, respectively. This is the drain-source voltage of the switching transistor. Let be the current value at the moment the switching transistor is turned on, and we have:

[0016]

[0017] In the formula, and These are the drive current during the turn-on phase and the drive current during the turn-off phase of the switching transistor, respectively. This refers to the voltage-current crossover time during the turn-on period of the switching transistor. This refers to the voltage-current crossover time during the turn-off period of the switching transistor. and These are the turn-on and turn-off drive resistors for the switching transistor, respectively, and VGS is the drive voltage. The total gate charge of the switching transistor. This is the Miller plateau voltage.

[0018] Based on the above switching loss model, it can be deduced that the shift ratio and duty cycle determine the instantaneous power of the switch at the moment of conduction, and also determine the current at the moment the switch starts to conduct. Therefore, by optimizing the combination of duty cycle and shift ratio, and reducing the current flowing through the switch during hard turn-on, the power consumption of the switch can be reduced.

[0019] Optionally, the optimization objective function is expressed as:

[0020]

[0021] In the formula, , These are the required output voltages for the secondary high-voltage port and the secondary low-voltage port, respectively. For the switching transistor in the converter The current value at the moment of conduction. Characterizing the switching transistor Whether soft switching is implemented is a 0 / 1 variable, which can be set to: when the switching transistor... When implementing ZVS, the switching transistor will be characterized. Whether or not soft switching is implemented Define it as 0, otherwise, Defined as 1. The objective function aims to reduce switching losses by decreasing the current flowing through the switching transistor during hard turn-on.

[0022] Optionally, for any combination of output voltage and load conditions of the CF-TAB converter. The optimized mathematical model is expressed as follows:

[0023]

[0024] In the formula, and These represent the port power required for the secondary high-voltage port and the secondary low-voltage port, respectively; constraints. and constraints This indicates that the combination of control degrees of freedom for the secondary high-voltage port and the secondary low-voltage port can meet their power transmission requirements, specifically expressed as follows:

[0025]

[0026]

[0027] constraint and constraints The two inequality constraints other than those are freedom range constraints.

[0028] Optionally, for any combination of system parameters, the optimal combination of degrees of freedom is obtained by solving the objective function and its constraints. ,include:

[0029] S1, within the preset duty cycle combination range, initialize the duty cycle. ;

[0030] S2, based on the current duty cycle, obtains the shift ratio by solving according to constraints C1 and C2 in the optimization mathematical model. ;

[0031] S3, Calculate the objective function value based on the current duty cycle and the current shift ratio obtained from the solution. ;

[0032] S4, set the current objective function value Assign to ;

[0033] S5, update duty cycle Proceed to step S2 to obtain the new move comparison;

[0034] S6. Determine whether the current duty cycle and shift ratio meet the degree of freedom range constraints. If they do, proceed to step S7; otherwise, proceed to step S5.

[0035] S7, Calculate the new objective function value based on the current duty cycle and shift ratio. Determine if it is less than the current value. If yes, proceed to step S5; otherwise, update using the objective function value. Then, it determines whether the preset duty cycle combination has been traversed. If it has been traversed, it outputs the optimal degree of freedom combination based on the current duty cycle.

[0036] Through the above technical solutions, the optimal combination of degrees of freedom can be obtained for different combinations of output voltage and transmission power. The preset duty cycle combination can be obtained by varying the values ​​of different degrees of freedom types with appropriate gradients according to the range of degrees of freedom values, and arranging and combining the different values ​​of each degree of freedom type to obtain multiple duty cycle combinations.

[0037] Optionally, the operation of solving for the optimal combination of degrees of freedom using the optimization objective function and its constraints for any of the system parameter combinations is performed offline in Python before being actually applied to the coordinated control of a three-port current-type three-active-bridge grid-connected converter.

[0038] The obtained lookup table is stored in a DSP, such as a TMS320F28388D. For its two-dimensional LUT in FLASH storage space, 110 sampling points are set for each dimension, and the two-dimensional table has a total of 110*110 storage units. Each storage unit stores a set of optimal degree of freedom combinations. For each degree of freedom type, all data of the same degree of freedom type are stored in the same area to facilitate linear interpolation calculation to obtain the optimal control degree of freedom under actual output voltage and load conditions.

[0039] In some possible embodiments, the offline solution of the above-mentioned optimal degree-of-freedom combination can be achieved by using the particle swarm optimization algorithm to initialize and update the duty cycle, and the duty cycle combination corresponding to the global optimal solution that satisfies the iteration termination condition and its corresponding shift ratio combination is taken as the optimal degree-of-freedom combination.

[0040] Optionally, storing the optimal degree-of-freedom combination corresponding to all system parameter combinations as a lookup table includes:

[0041] Output voltage of the port Combination and output power With one component fixed in the combination, a two-dimensional lookup table is obtained using the other component as an index. This results in either a data table of optimal degrees of freedom combinations indexed by output power for different port output voltage combinations, or a data table of optimal degrees of freedom combinations indexed by port output voltage combinations for different output power combinations.

[0042] Optionally, when performing online coordinated control of the three-port current-type three-active-bridge grid-connected converter, the optimal combination of degrees of freedom is obtained from the lookup table according to the required output voltage and output power, and the PWM control of the converter is performed according to the obtained optimal combination of degrees of freedom, including:

[0043] Obtain the real-time values ​​of the secondary high-voltage port voltage and the secondary low-voltage port output voltage, as well as the given reference values ​​of the secondary high-voltage port voltage, the secondary low-voltage port output voltage, and the port power.

[0044] The real-time values ​​of the secondary high-voltage port voltage and the secondary low-voltage port output voltage are respectively subtracted from the corresponding output voltage reference values. The resulting difference is then processed by a PI controller to obtain the shift ratio (φ). 12 , φ 13 );

[0045] Based on the given reference values ​​of the secondary high-voltage port voltage and the secondary low-voltage port power, the optimal degree of freedom table corresponding to the given combination of output voltage reference values ​​is found. The current output voltage and load condition combination is then obtained by matching the given combination of port power reference values. The optimal duty cycle combination Alternatively, find the optimal degree of freedom table corresponding to the given combination of port power reference values, and match the current output voltage and load condition combination according to the given combination of output voltage reference values. The optimal duty cycle combination ;

[0046] Will and As input to the PWM generator, the PWM signals output by the PWM generator are obtained to control the switching transistors in the current-mode three-active-bridge grid-connected converter.

[0047] In a second aspect, the present invention provides a collaborative control method for a three-port current-mode three-active-bridge grid-connected converter based on the method described in the first aspect, comprising:

[0048] Obtain the voltage at the secondary high-voltage port and real-time output voltage value of the secondary low-voltage port and the given secondary high-voltage port voltage Output voltage of the secondary low-voltage port Reference value of secondary high voltage port power and secondary low-voltage port power reference value ;

[0049] The real-time values ​​of the secondary high-voltage port voltage and the secondary low-voltage port output voltage are respectively subtracted from the corresponding output voltage reference values. The resulting difference is then processed by a PI controller to obtain the shift ratio between the primary port and the secondary high-voltage port. Compared to the shift between the primary side port and the secondary side low-voltage port ;

[0050] Based on the given secondary high-voltage port power Port power reference value of the secondary low-voltage port Find a given combination of output voltage reference values. The corresponding optimal degree of freedom table is used to match the current output voltage and load conditions. The optimal duty cycle combination Alternatively, based on the given secondary high-voltage port voltage... Output voltage of the secondary low-voltage port Find a combination of power reference values ​​for a given port. The corresponding optimal degree of freedom table is used to match the current output voltage and load conditions. The optimal duty cycle combination ;

[0051] Will and As input to the PWM generator, the PWM signals output by the PWM generator are obtained to control the switching transistors in the current-mode three-active-bridge grid-connected converter.

[0052] Thirdly, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the three-port current-type three-active-bridge grid-connected converter cooperative control method described in the second aspect.

[0053] Beneficial effects

[0054] The present invention provides a collaborative control method for a three-port current-mode three-active-bridge grid-connected converter. Based on a lookup table method, this method employs a control strategy with multiple degrees of control freedom and multiple optimization objectives to optimize system switching losses and expand the soft-switching range.

[0055] Compared to traditional DPS control strategies, this invention can significantly reduce the switching losses of the system at each operating point under a full range of voltage and load power conditions, including the secondary high-voltage port and the low-voltage port. It can also maintain a low loss value over a wide operating range and broaden the ZVS range of the switching transistor, making it applicable to a wider range of voltage and load power conditions, thereby improving grid connection stability. Attached Figure Description

[0056] Figure 1 The diagram shows the topology of a three-port current-mode three-active-bridge converter (CF-TAB).

[0057] Figure 2 The diagram shown is the three-port delta-type equivalent circuit diagram of the CF-TAB converter.

[0058] Figure 3 The diagram shows the current reference flow direction of the CF-TAB converter.

[0059] Figure 4 The figure shows a waveform diagram of the switching process of the switching transistor in the CF-TAB converter.

[0060] Figure 5 The diagram shown is a flowchart of the optimization control algorithm used in this invention.

[0061] Figure 6 The diagram shown is a block diagram of the optimized control strategy used in this invention.

[0062] Figure 7 The figure shows the objective function for optimizing switching losses under different control strategies. A three-dimensional graph showing the relationship between load power and output voltage;

[0063] Figure 8 The figure shows the objective function for optimizing switching losses under different control strategies. A two-dimensional graph showing the relationship between load power and output voltage rate;

[0064] Figure 9 As shown = 12V, = Comparison of ZVS range under different control strategies at 100W;

[0065] Figure 10 As shown = 350V, = Comparison of ZVS range under different control strategies at 300W. Detailed Implementation

[0066] The following description, in conjunction with the accompanying drawings and specific embodiments, provides further details.

[0067] In new energy combined power supply systems and new energy vehicles, the energy transferred between the ports of a three-port DC converter is closely related. Energy can be transferred between the three ports, and at least one port can transfer energy bidirectionally. Figure 1 The three-port DC-DC converter structure shown consists of multiple full-bridge units connected via a DC bus, plus 12 switching transistors and one three-winding transformer. It is suitable for high-power charging applications in electric vehicles. Because the three ports are electrically isolated, it is suitable for applications with different voltage levels at each port. In some applications, the primary port is the high-voltage DC bus side of the power grid, the secondary high-voltage port is the OBC (On-Board Battery) side port, and the secondary low-voltage port is the low-voltage auxiliary power supply side port. in This is the input voltage of the converter, connected to the output of the preceding PFC stage; V oH This is the output voltage at the secondary high-voltage port; V oL This is the output voltage at the low-voltage port of the secondary side. S1~S4, S5~S8 and S9~S 12 These are MOSFETs for three full-bridge units.

[0068] Example 1

[0069] This embodiment, based on the above three-port DC-DC converter, introduces a collaborative control method for a three-port current-mode three-active-bridge grid-connected converter, which includes:

[0070] Obtain the preset output voltage and output power range of the secondary high voltage port and the secondary low voltage port;

[0071] Based on the switching loss model of a three-port current-source three-active-bridge grid-connected converter, an optimization objective function is constructed with the goal of minimizing the total current flowing through the switch during hard turn-on.

[0072] by As the control degrees of freedom, considering power transmission requirements and ZVS requirements, the constraints of the optimization objective function are determined during the solution process, resulting in the optimization mathematical model; where... These represent the duty cycles of the PWM within the full-bridge unit at the primary-side port, the secondary-side high-voltage port, and the secondary-side low-voltage port, respectively. Compared to the shift between the primary side port and the secondary side high-voltage port, The shift ratio between the primary side port and the secondary side low-voltage port;

[0073] Within the range of output voltage and output power, different combinations of system parameters for output voltage and output power are defined with a set step size. For any given combination of system parameters, the optimal combination of degrees of freedom is obtained by solving the optimization objective function and its constraints. ;

[0074] Store the optimal combination of degrees of freedom corresponding to all system parameter combinations as a lookup table;

[0075] When performing online coordinated control of a three-port current-type three-active-bridge grid-connected converter, the optimal combination of degrees of freedom is obtained from the lookup table according to the required output voltage and output power, and the PWM control of the converter is performed according to the obtained optimal combination of degrees of freedom.

[0076] The three-port current-source three-active-bridge grid-connected converter collaborative control method described in this embodiment forms the basis for realizing real-time collaborative control of CF-TAB converters in practical applications. The research process specifically involves the following content.

[0077] (I) Derive mathematical models of switching losses for instantaneous port current, effective port current, and instantaneous output interleaved parallel inductor current of a current-type three-active-bridge converter;

[0078] (II) Derive the conditions required to achieve zero-voltage switching (ZVS) of the converter switching transistor;

[0079] (III) Based on the derivation in (I) and (II), we construct the optimization objective function F, which is defined as the sum of the current flowing through the switch during hard turn-on. By reducing the current of the switch during hard turn-on, we can reduce the switching loss.

[0080] Five control degrees of freedom are used in optimizing the objective function. This is to ensure that the system can meet the power transmission requirements during the optimization process;

[0081] Based on the optimization objective function, the following derivation is made for any combination of output voltage and load conditions of the CF-TAB converter. An optimized mathematical model that is applicable to all;

[0082] (iv) Based on the optimization mathematical model, the offline execution control degrees of freedom are optimized to obtain the optimal control degrees of freedom under each working condition and store them in the form of a lookup table;

[0083] (v) In practical collaborative control applications, based on the obtained lookup table and the given control parameters, the optimal duty cycle combination under the given control parameters is obtained, thereby completing the PWM control of the switching transistors in the CF-TAB converter.

[0084] The above Part (a) involves the following content when deriving the current expression.

[0085] Figure 2 The diagram shows the three-port delta-type equivalent circuit of a CF-TAB converter, with three square wave voltage sources u. p u H and u L This represents the square wave voltage at the midpoint of the three full-bridge units. L1, L2, and L3 are the power transfer inductors in the three active bridge circuits. The three square wave voltages act together on inductors L1, L2, and L3, and a corresponding current i is induced based on the voltage difference across the inductors. L1 i L2 i L3 This enables power transfer.

[0086] For the traditional piecewise linear method, due to the shift ratio and duty cycle The different combinations determine a large number of operating modes, and each operating mode needs to be divided into multiple operating modes according to the order of the rising and falling edges of each three-level square wave voltage. The solution calculation process is complex and prone to errors and omissions. The Fourier decomposition method can only consider harmonic components of a finite number of levels, and a trade-off needs to be made between calculation accuracy and calculation complexity.

[0087] Therefore, a method based on the superposition theorem to derive the transient current of transformer windings can be used to analyze the current. According to the three-port delta-type equivalent circuit, the following current relationship exists:

[0088]

[0089] Therefore, we first analyze the current in the Δ-type equivalent circuit. The expression is derived, and the transformer winding current can be obtained from the above formula.

[0090] The content involved in the derivation of Part (II) above is as follows.

[0091] First, clarify the conditions required to achieve zero-voltage switching (ZVS) of the converter's switching transistors: before the switching transistors are turned on, their drain-source voltage... The voltage has been reduced to zero and remains at zero during the turn-on process until fully turned on. For MOSFETs, this condition requires that the drain-source current be zero before the switch is turned on. Reverse the direction to turn on the anti-parallel diode and maintain a zero-voltage state.

[0092] according to Figure 3 The reference direction of the switching transistor current is shown. To satisfy the ZVS condition, the current flowing through the switching transistor at the moment of turn-on should be negative. When the switching transistor... Drain current When the value is negative, current flows through its anti-parallel diode at the moment of its turn-on, and the switching transistor... Achieving zero-voltage turn-on; conversely, the switching transistor... It was activated through a hard reset.

[0093] Table 1 below shows the turn-on times of each switch. Value, of which Corresponding switching transistor .

[0094] Table 1

[0095]

[0096] According to the turn-on times of each switch in Table 1 value, Figure 4 The converter current reference direction is shown, and the converter current expression derived earlier is used. The ZVS conditions for each switch are as follows:

[0097]

[0098] According to the ZVS conditions for each switch in the above formula, when the switch... When implementing ZVS, the switching transistor will be characterized. The expression ZVS(x) that enables soft switching is defined as 0; otherwise, ZVS(x) is defined as 1.

[0099] The specific content covered in Part (III) above is as follows.

[0100] First, under light load conditions, switching losses are the main component of system losses.

[0101] refer to Figure 4 It shows the voltage and current waveforms of the MOSFET during the turn-on and turn-off processes, where Corresponding activation process, The corresponding switch is in the ON state. Corresponding shutdown process.

[0102] During the switching process, This is the turn-on threshold of the MOSFET. This is the Miller plateau voltage of the MOSFET. This is the drain-source voltage of the switching transistor. This represents the current value at the moment the MOSFET is turned on. In reality, the process from the start of MOSFET conduction to full conduction is... The interval, from the start of shutdown to complete shutdown, is Interval.

[0103] The activation loss can be calculated as follows:

[0104] The turn-off loss can be calculated as follows:

[0105] in, This refers to the voltage-current crossover time during the turn-on period of the switching transistor. The voltage-current crossover time during the turn-off period of the switching transistor is related to the drive circuit design and the total gate charge of the switching transistor. Related.

[0106]

[0107] in, and These are the drive current during the turn-on phase and the drive current during the turn-off phase of the switching transistor, respectively. and These are the turn-on and turn-off drive resistors for the switching transistor, respectively, and VGS is the drive voltage.

[0108] Thus, the switching loss model is obtained. It can be deduced that the shift ratio and duty cycle determine the instantaneous power of the switch at the moment of conduction, and also determine the current at the moment the switch starts to conduct. Therefore, by optimizing the combination of duty cycle and shift ratio, the current flowing through the switch during hard turn-on can be reduced, thereby reducing the power consumption of the switch.

[0109] Therefore, this embodiment optimizes the objective function. Defined as the sum of currents flowing through the switching transistor during hard turn-on, this objective function aims to reduce switching losses by decreasing the current flowing through the switching transistor during hard turn-on.

[0110]

[0111] In the formula, , These are the required output voltages for the secondary high-voltage port and the secondary low-voltage port, respectively. For the switching transistor in the converter The current value at the moment of conduction. Characterizing the switching transistor Whether soft switching is implemented is a 0 / 1 variable, as described in Part (II) above, set to: when the switching transistor... When implementing ZVS, the switching transistor will be characterized. Whether or not soft switching is implemented Define it as 0, otherwise, Defined as 1.

[0112] To achieve the optimization objective, the system uses five degrees of freedom for control: Two degrees of freedom The remaining three degrees of freedom are used to satisfy the power transfer constraints. Used to optimize the objective function F.

[0113] For any combination of output voltage and load conditions of the CF-TAB converter The optimized mathematical model is expressed as follows:

[0114]

[0115] In the formula, and These represent the port power required for the secondary high-voltage port and the secondary low-voltage port, respectively; constraints. and constraints This indicates that the combination of control degrees of freedom for the secondary high-voltage port and the secondary low-voltage port can meet their power transmission requirements, specifically expressed as follows:

[0116]

[0117]

[0118] constraint and constraints The two inequality constraints other than those are freedom range constraints.

[0119] The specific content covered in Part (IV) above is as follows.

[0120] Based on the aforementioned optimized mathematical model, switching losses can be significantly reduced and system efficiency improved while meeting power transmission requirements. In practical implementation, the design can be optimized by considering the actual operating conditions of the circuit, such as output voltage range and load variations, and the optimization effect can be verified through simulation and experiments.

[0121] Because the optimization process is computationally complex, real-time optimization calculations consume significant memory resources. In some possible implementations, the objective function is first solved offline in Python to obtain the optimal control degrees of freedom under various possible operating conditions. These degrees of freedom are then stored in the DSP as a lookup table, where the index of the lookup table can be the output voltage. or load power .

[0122] For details, please refer to Figure 5 As shown, for any combination of system parameters, the optimal combination of degrees of freedom can be obtained by solving the optimization objective function and its constraints. ,include:

[0123] S1, within the preset duty cycle combination range, initialize the duty cycle. ;

[0124] S2, based on the current duty cycle, obtains the shift ratio by solving according to constraints C1 and C2 in the optimization mathematical model. ;

[0125] S3, Calculate the objective function value based on the current duty cycle and the current shift ratio obtained from the solution. ;

[0126] S4, set the current objective function value Assign to ;

[0127] S5, update duty cycle Proceed to step S2 to obtain the new move comparison;

[0128] S6. Determine whether the current duty cycle and shift ratio meet the degree of freedom range constraints. If they do, proceed to step S7; otherwise, proceed to step S5.

[0129] S7, Calculate the new objective function value based on the current duty cycle and shift ratio. Determine if it is less than the current value. If yes, proceed to step S5; otherwise, update using the objective function value. Then, it determines whether the preset duty cycle combination has been traversed. If it has been traversed, it outputs the optimal degree of freedom combination based on the current duty cycle.

[0130] The offline solution for the above optimal degree-of-freedom combination can be achieved by using the particle swarm optimization algorithm to initialize and update the duty cycle. The duty cycle combination corresponding to the global optimal solution that satisfies the iteration termination condition and its corresponding shift ratio combination are taken as the optimal degree-of-freedom combination.

[0131] Through the above technical solutions, the optimal combination of degrees of freedom can be obtained for different combinations of output voltage and transmission power. The preset duty cycle combination can be obtained by varying the values ​​of different degrees of freedom types with appropriate gradients according to the range of degrees of freedom values, and arranging and combining the different values ​​of each degree of freedom type to obtain multiple duty cycle combinations.

[0132] The lookup table obtained by the above optimization algorithm is a four-dimensional table. If calculated with 20 sampling points per dimension, it would require 160,000 data sets. Each data set contains five control variables, totaling 800,000 data points, requiring 1600K of storage space, far exceeding the controller's storage capacity. Reducing the number of sampling points per dimension would result in too low segmentation accuracy, affecting control performance. Therefore, considering storage space and segmentation accuracy, in some possible embodiments, after obtaining the optimal combination of degrees of freedom for different combinations of output voltage and transmission power, the output port voltage condition... Fixed, causing a four-dimensional table to degenerate into a two-dimensional table, correspondingly, the index size of the lookup table is the output power. Or set the port power condition The number of indexes in the lookup table is fixed. Assuming 110 sampling points are set for each dimension, a controller with a data storage capacity of 256KB is required to meet this requirement.

[0133] Specifically, storing the optimal degree-of-freedom combination corresponding to all system parameter combinations as a lookup table includes:

[0134] Output voltage of the port Combination and output power With one component fixed in the combination, a two-dimensional lookup table is obtained using the other component as an index. This results in either a data table of optimal degrees of freedom combinations indexed by output power for different port output voltage combinations, or a data table of optimal degrees of freedom combinations indexed by port output voltage combinations for different output power combinations.

[0135] Furthermore, since the sampled output voltage data in actual operation often does not completely overlap with the data at the sampling points in the lookup table, linear interpolation is required in the DSP to obtain the optimal control degrees of freedom under actual operating conditions. To facilitate obtaining the optimal combination of control degrees of freedom under actual output voltage and load conditions through linear interpolation, all data of the same degree of freedom type are stored in the same area, such as all... The data needs to be stored in the same region. Similarly.

[0136] The specific content covered in Part (V) above is as follows.

[0137] refer to Figure 6 As shown, in practical applications, before the online control of the CF-TAB converter, the duty cycle corresponding to (P2, P3) across the full power range is obtained by optimizing the objective function algorithm described in Part IV above. The voltage is then processed and stored in a lookup table in the controller. The difference between the secondary high-voltage port voltage and the secondary low-voltage port voltage is then calculated with respect to the given value, and the difference is processed by the PI controller to obtain the shift ratio. Based on the given reference values ​​of the secondary high-voltage port voltage and the secondary low-voltage port voltage. Matching with A two-dimensional table with an index. Port power setpoint By performing an online table lookup, the optimized duty cycle combination can be obtained. .

[0138] Example 2

[0139] Refer again Figure 6 This embodiment introduces a collaborative control method for a three-port current-source three-active-bridge grid-connected converter, which is an online control method. The method includes:

[0140] Obtain the voltage at the secondary high-voltage port and real-time output voltage value of the secondary low-voltage port and the given secondary high-voltage port voltage Output voltage of the secondary low-voltage port Reference value of secondary high voltage port power and secondary low-voltage port power reference value ;

[0141] The real-time values ​​of the secondary high-voltage port voltage and the secondary low-voltage port output voltage are respectively subtracted from the corresponding output voltage reference values. The resulting difference is then processed by a PI controller to obtain the shift ratio between the primary port and the secondary high-voltage port. Compared to the shift between the primary side port and the secondary side low-voltage port ;

[0142] Based on the given secondary high-voltage port power Port power reference value of the secondary low-voltage port Find a given combination of output voltage reference values. The corresponding optimal degree of freedom table is used to match the current output voltage and load conditions. The optimal duty cycle combination Alternatively, based on the given secondary high-voltage port voltage... Output voltage of the secondary low-voltage port Find a combination of power reference values ​​for a given port. The corresponding optimal degree of freedom table is used to match the current output voltage and load conditions. The optimal duty cycle combination The optimal degree-of-freedom table is obtained in advance by solving the optimization objective function in Example 1 offline.

[0143] Will and As input to the PWM generator, the PWM signals output by the PWM generator are obtained to control the switching transistors in the current-mode three-active-bridge grid-connected converter.

[0144] Example 3

[0145] This embodiment describes a computer-readable storage medium storing a computer program. When executed by a processor, the computer program implements the steps of the three-port current-type three-active-bridge grid-connected converter collaborative control method described in Embodiment 2, and is used to realize online control of the CF-TAB converter.

[0146] In summary, to verify the superiority and feasibility of the present invention, a simulation model of a CF-TAB converter was built, and the traditional DPS control and the optimized control strategy of the present invention were used respectively. The differences between the two control strategies in terms of switching losses and soft-switching range were compared, and the advantages of the optimized control strategy of the present invention were explained.

[0147] Test Example 1:

[0148] Using the multi-degree-of-freedom control method of the three-port current-source three-active-bridge converter in this embodiment, the following simulation verification is performed using a CF-TAB converter simulation model. Different control strategies are employed under different operating conditions to observe the optimization objective function. By comparing the changes in the proposed optimized control strategy with the traditional DPS control strategy, the significant effects of the proposed optimized strategy under various operating conditions can be clearly seen. (See attached diagram.) Figure 5 , 6 The simulation results are explained in sections 7 and 8 as follows:

[0149] 1) Appendix Figure 7 Figure (a) shows the power P2ref at port 2 being constant at 300W, with different combinations of low-voltage port voltage and power. Optimize the objective function under different control strategies under the given conditions. The output voltage VoH at port 2 varies across the entire range.

[0150] 2) Appendix Figure 7 Figure (b) shows the power P3ref at port 3 being constant at 100W, under different combinations of high-voltage port voltage and power. Optimize the objective function under different control strategies under the given conditions. The output voltage VoL at port 3 varies across the entire range.

[0151] 3) Appendix Figure 7 Figure (c) shows the output voltage VoH at port 2 being constant at 300V, with different combinations of low-voltage port voltages and power. Optimize the objective function under different control strategies under the given conditions. The power P2ref at port 2 varies across the entire range.

[0152] 4) Appendix Figure 7 Figure (d) shows the output voltage at port 3. Constant at 12V, with different high-voltage port voltage and power combinations Optimize the objective function under different control strategies under the given conditions. The power P3ref at port 3 varies across the entire range.

[0153] comprehensive Figure 7 Figures (a) to (d) show that, compared with the traditional DPS control strategy, the optimized control strategy adopted in this invention significantly reduces the objective function value related to switching losses under the full range of voltage and load power conditions at both the high-voltage and low-voltage ports on the secondary side.

[0154] To further verify the effectiveness of the proposed optimization algorithm, Figure 8 The objective function for optimizing switching losses was compared under two different control strategies. With load power or output voltage The proposed optimization scheme can optimize the objective function across the entire range of voltage or power variations, compared to traditional DPS control. With the complete reduction of losses, the switching losses of the system at each operating point can be effectively suppressed, and compared with traditional control strategies, it can maintain a low loss value over a wider operating range.

[0155] The impact of the proposed switching loss minimization optimization algorithm on the implementation range of ZVS is shown in the appendix. Figure 9 and attached Figure 10 As shown. (Attached) Figure 9 for = 12V, Comparison of ZVS range under two different control strategies at 100W; Appendix Figure 10 for =350V, At 300W, a comparison of the ZVS range under two different control strategies is presented. It can be seen that although the control strategy proposed in this invention aims to minimize the objective function related to switching losses, compared with the DPS control strategy, it also extends the ZVS range of the switching transistor, making it suitable for a wider range of voltage and load power conditions.

[0156] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0157] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0158] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0159] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0160] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A collaborative control method for a three-port current-mode three-active-bridge grid-connected converter, characterized in that, include: Obtain the preset output voltage and output power range of the secondary high voltage port and the secondary low voltage port; Based on the switching loss model of a three-port current-source three-active-bridge grid-connected converter, an optimization objective function is constructed with the goal of minimizing the total current flowing through the switch during hard turn-on. by As the control degrees of freedom, considering power transmission requirements and ZVS requirements, the constraints of the optimization objective function are determined during the solution process, resulting in the optimization mathematical model; where... These represent the duty cycles of the PWM within the full-bridge unit at the primary-side port, the secondary-side high-voltage port, and the secondary-side low-voltage port, respectively. Compared to the shift between the primary side port and the secondary side high-voltage port, The shift ratio between the primary side port and the secondary side low-voltage port; Within the range of output voltage and output power, different combinations of system parameters for output voltage and output power are defined with a set step size. For any given combination of system parameters, the optimal combination of degrees of freedom is obtained by solving the optimization objective function and its constraints. ; Store the optimal combination of degrees of freedom corresponding to all system parameter combinations as a lookup table; When performing online coordinated control of a three-port current-type three-active-bridge grid-connected converter, the optimal combination of degrees of freedom is obtained from the lookup table according to the required output voltage and output power, and the PWM control of the converter is performed according to the obtained optimal combination of degrees of freedom.

2. The method according to claim 1, characterized in that, The switching loss model of the three-port current-source three-active-bridge grid-connected converter is expressed as follows: in, and These are the turn-on loss and turn-off loss of the switching transistor, respectively. The switching frequency of the switching transistor. and These represent the time when the switching transistor starts conducting and the time when it is fully turned on, respectively. and These are the start and complete turn-off times of the switching transistor, respectively. This is the drain-source voltage of the switching transistor. Let be the current value at the moment the switching transistor is turned on, and we have: In the formula, and These are the drive current during the turn-on phase and the drive current during the turn-off phase of the switching transistor, respectively. This refers to the voltage-current crossover time during the turn-on period of the switching transistor. This refers to the voltage-current crossover time during the turn-off period of the switching transistor. and These are the turn-on and turn-off drive resistors for the switching transistor, respectively, and VGS is the drive voltage. The total gate charge of the switching transistor. This is the Miller plateau voltage.

3. The method according to claim 1 or 2, characterized in that, The optimization objective function is expressed as: In the formula, , These are the required output voltages for the secondary high-voltage port and the secondary low-voltage port, respectively. For the switching transistor in the converter The current value at the moment of conduction characterizes the switching transistor. Whether to implement soft switching is a 0 / 1 variable.

4. The method according to claim 3, characterized in that, variable The value is: when the switching transistor When implementing ZVS, Define it as 0, otherwise, Defined as 1.

5. The method according to claim 3, characterized in that, For any combination of output voltage and load conditions of the CF-TAB converter The optimized mathematical model is expressed as follows: In the formula, and These represent the port power required for the secondary high-voltage port and the secondary low-voltage port, respectively; constraints. and constraints This indicates that the combination of control degrees of freedom for the secondary high-voltage port and the secondary low-voltage port can meet their power transmission requirements, specifically expressed as follows: 。 6. The method according to claim 3 or 5, characterized in that, for The optimal combination of degrees of freedom can be obtained by solving for any of the system parameter combinations using the objective function and its constraints. ,include: S1, within the preset duty cycle combination range, initialize the duty cycle. ; S2, based on the current duty cycle, obtains the shift ratio by solving according to constraints C1 and C2 in the optimization mathematical model. ; S3, Calculate the objective function value based on the current duty cycle and the current shift ratio obtained from the solution. ; S4, set the current objective function value Assign to ; S5, update duty cycle Proceed to step S2 to obtain the new move comparison; S6. Determine whether the current duty cycle and shift ratio meet the degree of freedom range constraints. If they do, proceed to step S7; otherwise, proceed to step S5. S7, Calculate the new objective function value based on the current duty cycle and shift ratio. Determine if it is less than the current value. If yes, proceed to step S5; otherwise, update using the objective function value. Then, it determines whether the preset duty cycle combination has been traversed. If it has been traversed, it outputs the optimal degree of freedom combination based on the current duty cycle.

7. The method according to claim 6, characterized in that, The operation of solving for the optimal combination of degrees of freedom using the optimization objective function and its constraints for any of the system parameter combinations is executed offline in Python before being actually applied to the coordinated control of a three-port current-type three-active-bridge grid-connected converter. The obtained lookup table is stored in the DSP. For the two-dimensional LUT in its FLASH storage space, 110 sampling points are set for each dimension, and each storage unit stores a set of optimal degree-of-freedom combinations. For each degree-of-freedom type, all data of the same degree-of-freedom type are stored in the same area.

8. The method according to claim 5, characterized in that, The step of storing the optimal degree-of-freedom combination corresponding to all system parameter combinations as a lookup table includes: Output voltage of the port Combination and output power With one component fixed in the combination, a two-dimensional lookup table is obtained using the other component as an index. This results in either a data table of optimal degrees of freedom combinations indexed by output power for different port output voltage combinations, or a data table of optimal degrees of freedom combinations indexed by port output voltage combinations for different output power combinations.

9. The method according to claim 1, characterized in that, When performing online coordinated control of a three-port current-type three-active-bridge grid-connected converter, the optimal combination of degrees of freedom is obtained from the lookup table according to the required output voltage and output power. The converter's PWM control is then performed based on this optimal combination of degrees of freedom, including: Obtain the voltage at the secondary high-voltage port and real-time output voltage value of the secondary low-voltage port and the given secondary high-voltage port voltage Output voltage of the secondary low-voltage port Reference value of secondary high voltage port power and secondary low-voltage port power reference value ; The real-time values ​​of the secondary high-voltage port voltage and the secondary low-voltage port output voltage are respectively subtracted from the corresponding output voltage reference values. The resulting difference is then processed by a PI controller to obtain the shift ratio between the primary port and the secondary high-voltage port. Compared to the shift between the primary side port and the secondary side low-voltage port ; Based on the given secondary high-voltage port power Port power reference value of the secondary low-voltage port Find a given combination of output voltage reference values. The corresponding optimal degree of freedom table is used to match the current output voltage and load conditions. The optimal duty cycle combination Alternatively, based on the given secondary high-voltage port voltage... Output voltage of the secondary low-voltage port Find a combination of power reference values ​​for a given port. The corresponding optimal degree of freedom table is used to match the current output voltage and load conditions. The optimal duty cycle combination ; Will and As input to the PWM generator, the PWM signals output by the PWM generator are obtained to control the switching transistors in the current-mode three-active-bridge grid-connected converter.

10. A collaborative control method for a three-port current-mode three-active-bridge grid-connected converter based on the method described in any one of claims 1-9, characterized in that it comprises: Obtain the voltage at the secondary high-voltage port and real-time output voltage value of the secondary low-voltage port and the given secondary high-voltage port voltage Output voltage of the secondary low-voltage port Reference value of secondary high voltage port power and secondary low-voltage port power reference value ; The real-time values ​​of the secondary high-voltage port voltage and the secondary low-voltage port output voltage are respectively subtracted from the corresponding output voltage reference values. The resulting difference is then processed by a PI controller to obtain the shift ratio between the primary port and the secondary high-voltage port. Compared to the shift between the primary side port and the secondary side low-voltage port ; Based on the given secondary high-voltage port power Port power reference value of the secondary low-voltage port Find a given combination of output voltage reference values. The corresponding optimal degree of freedom table is used to match the current output voltage and load conditions. The optimal duty cycle combination ; Alternatively, based on the given secondary high-voltage port voltage Output voltage of the secondary low-voltage port Find a combination of power reference values ​​for a given port. The corresponding optimal degree of freedom table is used to match the current output voltage and load conditions. The optimal duty cycle combination ; Will and As input to the PWM generator, the PWM signals output by the PWM generator are obtained to control the switching transistors in the current-mode three-active-bridge grid-connected converter.

11. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the three-port current-mode three-active-bridge grid-connected converter collaborative control method as described in claim 10.

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