Bidirectional model predictive control method and system for DC converters used in V2G charging piles

Abstract

The present invention proposes a bidirectional model predictive control method and system for a DC converter for V2G charging piles, comprising: sampling the primary-side voltage, secondary-side voltage, and secondary-side output current of the DAB converter, and setting the secondary-side output reference voltage; a controller determines the power transmission direction based on the sampled data and calculates the optimal control quantity under bidirectional power transmission using a piecewise expression for the optimal control quantity applicable to bidirectional power transmission conditions; and a pulse width modulator performs phase shift modulation based on the obtained optimal control quantity to obtain control signals for each switching tube of the DC converter. The technical solution of the present invention is a model predictive control method for a dual-active full-bridge DC / DC converter (DAB) for V2G electric vehicle charging piles. This method has the advantages of fast dynamic response and bidirectional power control capability.

Description

Technical Field

[0001] The present invention belongs to the technical field of DC / DC converter model predictive control (MPC), and in particular relates to a bidirectional model predictive control method and system for a DC converter for a V2G charging pile. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] As the proportion of renewable energy generation continues to increase, the requirements for energy storage device capacity and performance in new power systems are also increasing. At the same time, electric vehicles are becoming more and more popular. V2G electric vehicle charging piles have gradually attracted the attention of scholars in recent years because they can fully utilize the energy storage batteries of idle electric vehicles to feed power to the grid. The DAB converter has become a common topology for the DC / DC link of charging piles due to its advantages such as bidirectional power flow, high voltage ratio, electrical isolation, and high power density. Its bidirectional power flow capability is also compatible with V2G technology. The dynamic performance of existing bidirectional power control schemes for DAB converters needs to be improved. Among them, MPC is an effective solution to improve its dynamic performance and is a hot topic of research among scholars.

[0004] While installed capacity of renewable energy has continued to increase in recent years, its discontinuity and volatility can easily lead to power generation fluctuations and energy waste, necessitating the use of extensive energy storage devices to smooth out peaks and fill valleys. Existing electric vehicle charging stations are mostly one-way, meaning the grid charges the vehicle, failing to fully utilize this valuable energy storage resource. Therefore, it is necessary to accelerate research on V2G charging station technologies to effectively utilize electric vehicle energy storage and enable vehicle-to-grid power feeds.

[0005] The DAB converter (direct current converter) is a common topology in the DC / DC link of charging piles. Traditional control strategies for this converter suffer from poor dynamic performance, limiting the overall performance of the charging pile system. MPC can be used to control the DAB converter to improve its dynamic performance. However, to implement MPC in V2G charging piles, the bidirectional power control issue of the DAB converter must be addressed.

[0006] In the existing technology, bidirectional power control of DAB converters is mostly based on PI controllers. In addition, the existing MPC method applied to DAB converters models the system power model of the converter's forward power transmission, which can realize the control of the converter under unidirectional power transmission.

[0007] It can be seen that since traditional control strategies are mostly based on PI controllers, the transient performance of the charging pile system is relatively poor.

[0008] In addition, the existing MPC method only models the system power model of the forward power transmission of the DAB converter, and does not consider the reverse power transmission. Therefore, it cannot achieve control under bidirectional power transmission and cannot be applied to V2G charging piles. Summary of the Invention

[0009] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a bidirectional model predictive control method for a DAB converter, which can realize model predictive control of the DAB converter under bidirectional power transmission.

[0010] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions:

[0011] In a first aspect, a bidirectional model predictive control method for a DC converter for a V2G charging pile is disclosed, comprising:

[0012] Sampling the primary side voltage, secondary side voltage and secondary side output current of the DAB converter, and setting the secondary side output reference voltage;

[0013] The controller determines the power transmission direction based on the sampled data and calculates the optimal control quantity under bidirectional power transmission using a piecewise expression for the optimal control quantity under bidirectional power transmission conditions.

[0014] The pulse width modulator performs phase shift modulation according to the obtained optimal control quantity to obtain the control signal of each switch tube of the DC converter.

[0015] As a further technical solution, a piecewise expression for obtaining the optimal control quantity under bidirectional power transmission conditions is also applicable, specifically:

[0016] The power model of the DAB converter is expressed as a first piecewise expression;

[0017] According to Kirchhoff's law, the voltage and current relationship on the secondary side of the DAB converter is expressed;

[0018] Substituting the first piecewise expression into the prediction expression of the secondary side voltage, the piecewise prediction expression of the secondary side voltage is obtained;

[0019] The valence function is replaced by a piecewise prediction expression based on the secondary voltage;

[0020] The piecewise prediction expression of the secondary side voltage and the cost function are combined, and the direction of power and the positive and negative of the control quantity are comprehensively considered. After calculation, a piecewise expression of the optimal control quantity that is applicable to both bidirectional power transmission conditions is obtained.

[0021] As a further technical solution, before expressing the power model of the DAB converter as the first segmented expression, it also includes: based on the topology of the DAB converter, under single phase-shift modulation, comprehensively considering the forward and reverse power transmission conditions, expressing its power model.

[0022] As a further technical solution, after expressing the voltage-current relationship on the secondary side of the DAB converter according to Kirchhoff's law, it includes: using the forward Euler method to discretize the expressed voltage-current relationship on the secondary side of the DAB converter within one control cycle to obtain a predicted expression for the secondary side voltage.

[0023] As a further technical solution, a piecewise expression for the optimal control quantity under bidirectional power transmission conditions is also applicable, specifically:

[0024]

[0025] Where D is the phase shift control amount and P is the transmission power.

[0026] As a further technical solution, the parameters in the phase shift control amount calculation formula are specifically:

[0027]

[0028] Among them, V1 is the primary side voltage; V2 is the secondary side voltage; f s is the switching frequency and control frequency of the DAB converter; L is the inductance of the power transmission inductor; n is the transformer ratio; C2 is the capacitance of the secondary side support capacitor; I2 is the secondary side output current; is the output reference voltage of the secondary side; T s is the switching period and the control period.

[0029] As a further technical solution, the pulse width modulator performs phase-shift pulse width modulation according to the phase-shift control amount to obtain four rectangular wave signals with certain duty cycles, which are respectively input to the eight switching tubes of the DAB converter to control one working cycle.

[0030] Secondly, a bidirectional model predictive control system for a DC converter used in a V2G charging pile is disclosed, including:

[0031] The data acquisition module is configured to: sample and obtain the primary side voltage, secondary side voltage and secondary side output current of the DAB converter, and set the output reference voltage of the secondary side;

[0032] The optimal control quantity calculation module is configured to: determine the power transmission direction according to the sampled data and calculate the optimal control quantity under bidirectional power transmission using a piecewise expression for the optimal control quantity under bidirectional power transmission conditions;

[0033] The phase-shift modulation module is configured as follows: the pulse width modulator performs phase-shift modulation according to the obtained optimal control amount to obtain the control signal of each switch tube of the DC converter.

[0034] One or more of the above technical solutions have the following beneficial effects:

[0035] The technical solution of the present invention comprehensively considers the system power model of the DAB converter under both forward and reverse power transmission, establishing a piecewise prediction expression. This is then used as a basis for designing a piecewise cost function. Finally, through mathematical calculations, the cost function is minimized to obtain a piecewise expression for the optimal control variable. This enables model predictive control of the DAB converter under bidirectional power transmission, suitable for V2G electric vehicle charging stations, and improves the system's dynamic performance.

[0036] The technical solution of the present invention is a model predictive control method for a dual-active full-bridge DC / DC converter (DAB) used in V2G electric vehicle charging piles. This method has the advantages of fast dynamic response and bidirectional power control capabilities.

[0037] Advantages of additional aspects of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0039] Figure 1 Schematic diagram of the topology of a DAB converter according to an embodiment of the present invention;

[0040] Figure 2 This is a flow chart of the bidirectional model predictive control of a DAB converter for a V2G charging pile according to an embodiment of the present invention. DETAILED DESCRIPTION

[0041] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0042] It should be noted that the terms used herein are for describing particular embodiments only and are not intended to limit the exemplary embodiments according to the present invention.

[0043] In the absence of conflict, the embodiments of the present invention and the features thereof may be combined with each other.

[0044] Glossary:

[0045] MPC: Model Predictive Control, Chinese: Model Predictive Control.

[0046] V2G: Vehicle-to-grid, Chinese: electric vehicles accessing the grid.

[0047] DAB: Dual Active Bridge, Chinese: Dual Active Bridge.

[0048] Example 1

[0049] See attached Figure 2 As shown, this embodiment discloses a bidirectional model predictive control method for a DC converter for a V2G charging pile, including:

[0050] Step 1: The sensor samples the converter primary side voltage V1, secondary side voltage V2 and secondary side output current I2, and sets the secondary side output reference voltage

[0051] Step 2: The controller determines the power transmission direction based on the data obtained in step 1 and calculates the optimal control quantity D under bidirectional power transmission according to equations (7) and (8).

[0052] Specifically, the power transmission direction is determined according to the measured current direction, see formula (7).

[0053] Step 3: The pulse width modulator performs phase shift modulation according to the optimal control quantity D obtained in step 2 to obtain the control signal of each switch tube.

[0054] By looping the above steps, model predictive control of the DAB converter under bidirectional power transmission can be realized, which is suitable for V2G electric vehicle charging piles and improves their dynamic performance.

[0055] The above technical solution has the characteristics of excellent MPC dynamic performance, can realize the control of DAB converter under bidirectional power transmission conditions, and is suitable for V2G electric vehicle charging piles.

[0056] To implement the above steps, the following description is made based on the topology structure:

[0057] Figure 1 The topology of the DAB converter is given. Under single phase-shift modulation, considering both forward and reverse power transmission, the system power model can be expressed as:

[0058]

[0059] Where V1 is the primary side voltage; V2 is the secondary side voltage; f sis the switching frequency and control frequency of the DAB converter; L is the inductance of the power transmission inductor; D is the phase shift control amount; n is the transformer ratio; P is the transmission power.

[0060] The establishment of this model takes into account the forward and reverse power transmission conditions. Therefore, the subsequent phase shift control quantity is suitable for controlling the DAB converter under bidirectional power transmission conditions.

[0061] Express (1) as a piecewise expression:

[0062]

[0063] According to Kirchhoff's law, the voltage and current relationship on the secondary side of the DAB converter can be expressed as:

[0064]

[0065] Where C2 is the capacitance value of the secondary side support capacitor; I c2 is the average output current of the full-bridge on the secondary side of the DAB converter; I2 is the secondary side output current.

[0066] Using the forward Euler method to discretize (3) within one control cycle, the prediction expression of the secondary side voltage can be obtained:

[0067]

[0068] Where k represents the working time, T s is the switching period and the control period.

[0069] Substituting the piecewise expression (2) of the system power model into (4) yields the piecewise prediction expression for the secondary side voltage:

[0070]

[0071] Replace the valence function J:

[0072]

[0073] in, is the output reference voltage of the secondary side. By minimizing the cost function and calculating the optimal control quantity D, the secondary side voltage can be controlled to be constant at the given reference voltage value. Here, for the case of bidirectional power transmission, equations (5) and (6) are combined to comprehensively consider the direction of power P and the positive and negative of the control quantity D. After mathematical calculation, a piecewise expression for the optimal control quantity applicable to both bidirectional power transmission conditions can be obtained:

[0074]

[0075] Among them: α is the intermediate quantity:

[0076]

[0077] Then the pulse width modulator performs phase shift pulse width modulation according to the phase shift control value D, and obtains four rectangular wave signals with a duty cycle of 50%, which are input to Figure 1 The eight switching transistors in each DAB module are controlled over a single duty cycle. This method enables model predictive control of the DAB converter under bidirectional power transmission. V2G electric vehicle charging stations require bidirectional power transmission, so the above method is applicable to V2G electric vehicle charging stations and improves the system's dynamic performance.

[0078] Example 2

[0079] The purpose of this embodiment is to provide a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above method when executing the program.

[0080] Example 3

[0081] The purpose of this embodiment is to provide a computer-readable storage medium.

[0082] A computer-readable storage medium stores a computer program, which, when executed by a processor, performs the steps of the above method.

[0083] Example 4

[0084] The purpose of this embodiment is to provide a bidirectional model predictive control system for a DC converter for a V2G charging pile, including:

[0085] The data acquisition module is configured to: sample and obtain the primary side voltage, secondary side voltage and secondary side output current of the DAB converter, and set the output reference voltage of the secondary side;

[0086] The optimal control quantity calculation module is configured to: determine the power transmission direction according to the sampled data and calculate the optimal control quantity under bidirectional power transmission using a piecewise expression for the optimal control quantity under bidirectional power transmission conditions;

[0087] The phase-shift modulation module is configured as follows: the pulse width modulator performs phase-shift modulation according to the obtained optimal control amount to obtain the control signal of each switch tube of the DC converter.

[0088] When the whole system is implemented, the hardware required includes data acquisition module, controller, pulse width modulator, and the data acquisition module includes voltage and current sensors. For the specific connection relationship, please refer to the attached Figure 2 shown.

[0089] The steps involved in the apparatuses of Examples 2, 3, and 4 above correspond to those of Method Example 1. For detailed implementations, please refer to the relevant description of Example 1. The term "computer-readable storage medium" should be understood to mean a single medium or multiple media containing one or more instruction sets; it should also be understood to include any medium capable of storing, encoding, or carrying an instruction set for execution by a processor and causing the processor to perform any method of the present invention.

[0090] Those skilled in the art will appreciate that the modules or steps of the present invention described above can be implemented using a general-purpose computer device. Alternatively, they can be implemented using program code executable by a computing device, which can then be stored in a storage device and executed by the computing device. Alternatively, they can be fabricated into separate integrated circuit modules, or multiple modules or steps can be fabricated into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0091] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without any creative work are still within the scope of protection of the present invention.

Claims

1. A bidirectional model predictive control method for a DC converter for a V2G charging pile, characterized by: include: Sampling the primary side voltage, secondary side voltage and secondary side output current of the DAB converter, and setting the secondary side output reference voltage; The controller determines the power transmission direction based on the sampled data and calculates the optimal control quantity under bidirectional power transmission using a piecewise expression for the optimal control quantity under bidirectional power transmission conditions. The pulse width modulator performs phase shift modulation according to the obtained optimal control quantity to obtain the control signal of each switch tube of the DC converter; Among them, the piecewise expression of the optimal control quantity under the bidirectional power transmission condition is also applicable, specifically: Where D is the phase shift control amount, P is the transmission power, and the parameters in the phase shift control amount calculation formula are as follows: Wherein, V1 is the primary side voltage; V2 is the secondary side voltage; L is the inductance of the power transmission inductor; n is the transformer ratio; C2 is the capacitance of the secondary side support capacitor; I2 is the secondary side output current; is the output reference voltage of the secondary side; T s is the switching period and control period, and k represents the working time.

2. The bidirectional model predictive control method for a DC converter for a V2G charging pile according to claim 1, wherein The method for obtaining the piecewise expression of the optimal control quantity under bidirectional power transmission conditions is as follows: The power model of the DAB converter is expressed as a first piecewise expression; According to Kirchhoff's law, the voltage and current relationship on the secondary side of the DAB converter is expressed; Substituting the first piecewise expression into the prediction expression of the secondary side voltage, the piecewise prediction expression of the secondary side voltage is obtained; The valence function is replaced by a piecewise prediction expression based on the secondary voltage; The piecewise prediction expression of the secondary side voltage and the cost function are combined, and the direction of power and the positive and negative of the control quantity are comprehensively considered. After calculation, a piecewise expression of the optimal control quantity that is applicable to both bidirectional power transmission conditions is obtained.

3. The bidirectional model predictive control method for a DC converter for a V2G charging pile according to claim 2, wherein: Before expressing the power model of the DAB converter as the first segmented expression, the method further includes: based on the topology of the DAB converter, comprehensively considering the forward and reverse power transmission conditions under single phase shift modulation, expressing its power model.

4. The bidirectional model predictive control method for a DC converter for a V2G charging pile according to claim 2, wherein: After expressing the voltage-current relationship of the secondary side of the DAB converter according to Kirchhoff's law, the method includes: discretizing the voltage-current relationship of the secondary side of the DAB converter within a control cycle using the forward Euler method to obtain a prediction expression of the secondary side voltage.

5. The bidirectional model predictive control method for a DC converter for a V2G charging pile according to claim 1, wherein: The pulse width modulator performs phase-shift pulse width modulation according to the phase-shift control amount to obtain four rectangular wave signals with a certain duty cycle, which are input to the eight switching tubes of the DAB converter respectively to control one working cycle.

6. A bidirectional model predictive control system for a DC converter used in a V2G charging pile, characterized by comprising: The data acquisition module is configured to: sample and obtain the primary side voltage, secondary side voltage and secondary side output current of the DAB converter, and set the output reference voltage of the secondary side; The optimal control quantity calculation module is configured to: determine the power transmission direction according to the sampled data and calculate the optimal control quantity under bidirectional power transmission using a piecewise expression for the optimal control quantity under bidirectional power transmission conditions; The phase-shift modulation module is configured to: perform phase-shift modulation on the pulse width modulator according to the obtained optimal control amount to obtain the control signal of each switch tube of the DC converter; Among them, the piecewise expression of the optimal control quantity under the bidirectional power transmission condition is also applicable, specifically: Where D is the phase shift control amount, P is the transmission power, and the parameters in the phase shift control amount calculation formula are as follows: Wherein, V1 is the primary side voltage; V2 is the secondary side voltage; L is the inductance of the power transmission inductor; n is the transformer ratio; C2 is the capacitance of the secondary side support capacitor; I2 is the secondary side output current; is the output reference voltage of the secondary side; T s is the switching period and control period, and k represents the working time.

7. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the steps of the method described in any one of claims 1 to 5 are implemented.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method described in any one of claims 1 to 5 are executed.

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