Load current feedforward control method of three-port DC-DC converter

Abstract

The invention relates to a load current feed-forward control method for a three-port DC-DC converter. The method comprises the following steps: acquiring output voltages Uo1 and Uo2 and load currents io1 and io2 of two output ports in the three-port DC-DC converter in real time; calculating a difference value between the output voltages Uo1 and Uo2 and an output voltage set value, and obtaining a virtual output voltage set value through a PI controller; and based on the output voltages Uo1 and Uo2 and the load currents io1 and io2, combining an output voltage set value and a virtual output voltage set value, calculating a phase-shift ratio D in real time so as to dynamically adjust the phase-shift ratio D and complete a control process. Compared with the prior art, the method has the advantages of high stability, high reliability and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of DC-DC converters, and in particular to a load current feedforward control method for a three-port DC-DC converter. Background Art

[0002] With the large-scale grid connection of renewable energy and the rapid development of smart grid technology, as a core device for energy conversion and management, the multi-port, high-efficiency, and intelligent requirements of power electronic converters are becoming increasingly prominent. In complex application scenarios such as photovoltaic-storage-load integrated systems, multi-source power supply for electric vehicles, and redundant power supplies for data centers, traditional single-port or dual-port DC-DC converters (such as Buck, Boost, dual-active bridge, etc.) gradually expose problems such as architecture redundancy, insufficient dynamic response, and difficulty in multi-port coordination, making it difficult to meet the requirements of modern power systems with high dynamics and multi-energy coordination. Therefore, the three-port DC-DC converter emerges as the times require. It can simultaneously connect multiple power sources, energy storage units, and loads to achieve efficient energy conversion and distribution between different ports. However, this also poses higher requirements on its control strategy to adapt to complex and changing energy inputs and load demands.

[0003] Existing controls for three-port DC-DC converters mostly draw on the control strategies of single-port or dual-port converters, such as classical PI control and the predictive control method and system for a three-port DC-DC converter proposed in patent application CN119134916A. This control method is designed based on a linear model and can achieve good control effects when the system parameters change little and the operating conditions are relatively stable. However, the three-port DC-DC converter has the characteristics of strong coupling and nonlinearity. Its internal state variables (such as voltage and current) affect each other, and the power flow relationships between different ports are complex. When the system operating conditions change greatly, such as sudden changes in the output power of new energy or sudden increases or decreases in the load, it is difficult for PI control to quickly and accurately adjust the control parameters, resulting in slow system dynamic response, poor stability, and even possible oscillation phenomena.

[0004] In addition, traditional control methods usually rely on accurate mathematical models. However, in the actual application of three-port DC-DC converters, due to the dispersion of component parameters, temperature changes, and the uncertainty of load characteristics, it is very difficult to establish an accurate mathematical model. This greatly limits the application of traditional control methods based on accurate models in actual applications. Summary of the Invention

[0005] The purpose of the present invention is to provide a load current feedforward control method for a three-port DC-DC converter that can improve the recovery speed and stability of the output voltage when the load changes suddenly.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A load current feedforward control method for a three-port DC-DC converter, comprising the following steps:

[0008] Obtain in real time the output voltages U o1 、U o2 and the load currents i o1 、i o2 ;

[0009] Calculate the differences between the output voltages U o1 、U o2 and the output voltage set values, and obtain the virtual output voltage set values through a PI controller;

[0010] Based on the output voltages U o1 、U o2 and the load currents i o1 、i o2 , in combination with the output voltage set values and the virtual output voltage set values, calculate in real time the phase shift ratio D to dynamically adjust the phase shift ratio D and complete the control process.

[0011] Further, the expression of the virtual output voltage set value is:

[0012]

[0013] In the formula, P is the output power, U v * is the virtual output voltage set value, i o * is the load current set value, U o * is the output voltage set value, U o is the actual output voltage value, and i o is the actual load current value.

[0014] Further, the relationship between the output power P and the phase shift ratio D satisfies:

[0015] P = U o (D - D 2 )

[0016] In the formula, U o is the actual output voltage value.

[0017] Further, the steps for obtaining the relationship between the output power P and the phase shift ratio D include:

[0018] According to the current flowing through the inductor in the three-port DC-DC converter, obtain the initial expression of the output power P as:

[0019]

[0020] In the formula, T S is the switching period, t0 is the starting time of a switching period, t4 is the ending time of a switching period, U ac (t) is the instantaneous voltage at the input end of the H-bridge circuit in the three-port DC-DC converter, and i L (t) is the instantaneous current of the input inductor;

[0021] Substituting the initial instantaneous value i0 at the starting moment of the inductor current cycle into Equation (1), the initial expression of the output power P becomes:

[0022]

[0023] In the formula, U DC is the actual value of the input voltage, f S is the switching frequency, n is the turns ratio of the transformer in the three-port DC-DC converter, and L is the inductance value;

[0024] Further simplifying Equation (2), the relational expression between the output power P and the phase shift ratio D is obtained.

[0025] Furthermore, the calculation expression of the phase shift ratio D is:

[0026]

[0027] In the formula, U o * is the set value of the output voltage, U v * is the set value of the virtual output voltage, i o is the actual value of the load current, and U o is the actual value of the output voltage.

[0028] Furthermore, the three-port DC-DC converter includes an input module, a first output module, a second output module, and a three-port high-frequency transformer. The input module is connected to the second output module through the three-port high-frequency transformer, and the first output module is connected to the second output module through the three-port high-frequency transformer.

[0029] Furthermore, the three-port high-frequency transformer adopts a three-winding design.

[0030] Furthermore, the input module includes an input DC voltage source DC, an input H-bridge circuit, a DC-side filter capacitor C1, and a power inductor L1. The input DC voltage source DC and the DC-side filter capacitor C1 are connected in parallel, and the power inductor L1 is connected between the input H-bridge circuit and the three-port high-frequency transformer.

[0031] Further, both the first output module and the second output module include an output-side voltage, a DC-side filter capacitor, an output H-bridge circuit, and a power inductor. Among them, in the first output module, the output-side voltage U o1 is connected in parallel with the DC-side filter capacitor C2, and the power inductor L2 is connected between the first output H-bridge circuit and the three-port high-frequency transformer.

[0032] In the second output module, the output-side voltage U o2 is connected in parallel with the DC-side filter capacitor C3, and the power inductor L3 is connected between the second output H-bridge circuit and the three-port high-frequency transformer.

[0033] Further, there are four switches in the input H-bridge circuit, the first output H-bridge circuit, and the second output H-bridge circuit. During the switching process of each H-bridge circuit, when the current flows into the inductor, the inductor converts electrical energy into magnetic energy for storage. When the switch state changes, the inductor releases the magnetic energy and converts it into electrical energy to be output to the circuit.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) By real-time monitoring the changes in the output voltage and load current of the output port, and using the change in the load current as a feedforward signal to dynamically adjust the phase shift ratio in real time, the present invention can improve the recovery speed and stability of the output voltage during load mutation through load current feedforward control when the load at the output side changes suddenly.

[0036] (2) The present invention is independent of circuit parameters such as inductors, and has good portability and generality because there is no need to establish an accurate mathematical model.

[0037] (3) The present invention has the characteristics of high stability and strong reliability, and is suitable for scenarios with strict dynamic response requirements such as new energy grid connection and electric vehicle charging. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a schematic diagram of the method flow of the present invention;

[0039] Figure 2 is the main circuit topology diagram of the three-port DC-DC converter of the present invention;

[0040] Figure 3 is the load current feedforward control block diagram of the present invention;

[0041] Figure 4 is the voltage waveforms of the two output ports of the three-port DC-DC converter during load mutation in the embodiment of the present invention;

[0042] Figure 5The voltage waveforms of two output ports of a three-port DC-DC converter when the duty cycle changes in the embodiments of the present invention. Detailed implementation manners

[0043] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and gives detailed implementation manners and specific operation processes, but the protection scope of the present invention is not limited to the following embodiments.

[0044] This embodiment provides a load current feedforward control method for a three-port DC-DC converter, as Figure 3 shown. This method dynamically adjusts the phase shift ratio by real-time monitoring the changes in the load currents of the two output ports and using them as feedforward signals, so as to improve the recovery speed and stability of the output voltage during load mutation. Specifically, as Figure 1 shown, this method includes the following steps:

[0045] S1. Real-time obtain the output voltages U o1 、U o2 and load currents i o1 、i o2 of two output ports in the three-port DC-DC converter.

[0046] This embodiment first needs to select the main circuit topology of the three-port DC-DC converter:

[0047] The main circuit topology of the three-port DC-DC converter can be divided into non-isolated type, partially isolated type, and fully isolated type according to whether there is electrical isolation between ports. The fully isolated type realizes complete electrical isolation between ports through transformers or magnetic coupling elements, effectively preventing the cross-port propagation of faults such as electric leakage and short circuits, reducing the risk of electric shock, and improving the operation safety of the system. At the same time, through topology optimization, the fully isolated type topology can flexibly realize the bidirectional flow of energy (such as energy storage charging and discharging) at each port, meet the dynamic energy scheduling requirements, and be applicable to more scenarios. The three-active-bridge (TAB) structure is one of the fully isolated types. With its high efficiency, high dynamic response, compactness, and bidirectional energy flow ability, it has become the mainstream choice for three-port DC-DC converters, especially suitable for new energy systems and high-dynamic load scenarios. Although its control complexity is relatively high, through advanced control and hardware integration technologies, its reliability and economy can be further improved. Therefore, this embodiment adopts the three-active-bridge (TAB) structure.

[0048] This embodiment uses Figure 2The three-port DC-DC converter topology shown is used as the object for feedforward control. By collecting the load currents of the two output ports in real time, the phase shift ratio is dynamically adjusted to optimize the output voltage response. This three-port DC-DC converter adopts a single-input dual-output structure, including an input module, a first output module, a second output module, and a three-port high-frequency transformer. The input module is used to connect to a renewable energy source or an energy storage unit. The first output module and the second output module are independent outputs, which can output different voltage values respectively and are connected to loads of different voltage levels. Electrical isolation is achieved through the high-frequency transformer. The input module, the first output module, and the second output module are coupled through the three-port high-frequency transformer to achieve bidirectional energy transfer. The input module includes an input DC voltage source DC and a DC-side filter capacitor C1 connected in parallel in sequence. A power inductor L1 is connected between the input H-bridge circuit and the three-port high-frequency transformer. The first output module includes an output-side voltage U o1 and a DC-side filter capacitor C2. A power inductor L2 is connected between the first output H-bridge circuit and the three-port high-frequency transformer. A resistor R1 is connected to the output-side voltage U o1 . The second output module includes an output-side voltage U o2 and a DC-side filter capacitor C3. A power inductor L3 is connected between the second output H-bridge circuit and the three-port high-frequency transformer. A resistor R2 is connected to the output-side voltage U o2 . The ratio of the three-port high-frequency transformer is N1:N2:N3. The inductors in the circuit play a role in energy buffering and transfer. The input H-bridge circuit, the first output H-bridge circuit, and the second output H-bridge circuit all contain four switches (S1-S 12 ). During the switching process of the H-bridge, when the current flows into the inductor, the inductor converts electrical energy into magnetic energy for storage; when the switch state changes, the inductor releases the stored magnetic energy and converts it into electrical energy to be output to the circuit. This process helps to smooth the energy transfer and reduce the fluctuations during the energy transmission process.

[0049] According to the selected three-port DC-DC converter, the output voltages U o1 , U o2 and the load currents i o1 , i o2 of the two output ports are collected in real time.

[0050] S2, calculate the differences between the output voltages U o1 , U o2 and the output voltage set values, and through a PI controller, obtain the virtual output voltage set values.

[0051] First calculate the difference between the output voltage set value and the actual output voltage, and then obtain the virtual output voltage set value after passing through the PI controller.

[0052] S3. Based on the output voltage U o1 、U o2 and the load current i o1 、i o2 , combined with the output voltage set value and the virtual output voltage set value, calculate the phase shift ratio D in real time to dynamically adjust the phase shift ratio D and complete the control process.

[0053] This step mainly substitutes the output voltage set value, the actual output voltage value, the actual load current value and the virtual output voltage set value into the calculation formula of the phase shift ratio D to obtain the phase shift ratio D, and dynamically adjusts the phase shift ratio D to quickly restore the output voltage on the load side to the set value.

[0054] Derivation of the phase shift ratio D of the load current feedforward control: According to the current flowing through the inductor, the expression of the output power can be obtained as:

[0055]

[0056] In the formula, T S is the switching period, t0 is the starting time of a switching period, t4 is the ending time of a switching period, U ac (t) is the instantaneous voltage at the input end of the H-bridge, and i L (t) is the instantaneous current of the inductor at the input end.

[0057] Substituting the initial instantaneous value i0 at the starting moment of the inductor current period, the expression of the output power P becomes:

[0058]

[0059] In the formula, U DC is the actual input voltage value, U o is the actual output voltage value, D is the phase shift ratio, f S is the switching frequency, n is the transformer turns ratio, and L is the inductor value.

[0060] Further simplify the expression of the output power P to:

[0061] P = U o (D - D 2 )

[0062] In the formula, U o is the actual output voltage value, and D is the phase shift ratio.

[0063] Further, the expression of the phase shift ratio D can be derived as:

[0064]

[0065] In the formula, P is the output power, and U o is the actual output voltage value.

[0066] The output power P can also be expressed as:

[0067]

[0068] where U v * is the virtual output voltage set value, and i o * is the load current set value.

[0069] Also, since i in the above formula o * can be expressed as:

[0070]

[0071] where U o * is the output voltage set value, U o is the actual output voltage, and i o is the actual load current.

[0072] According to the above formula, the expression of the phase shift ratio D can be further obtained as:

[0073]

[0074] where U o * is the output voltage set value, U v * is the virtual output voltage set value, i o is the actual load current, and U o is the actual output voltage.

[0075] The following experiments were carried out in this embodiment for verification:

[0076] The system switching frequency is set to 10 kHz, the input side power supply of the three-port DC-DC converter is set to 100 V, the output voltage set value of output port 1 is 50 V, and the output voltage set value of output port 2 is 60 V. Figure 4 It is the implementation result when the load of output port 1 suddenly increases from 5 ohms to 10 ohms at 0.4 s, and the load of output port 2 suddenly decreases from 15 ohms to 10 ohms at 0.7 s; Figure 5 It is the implementation result when the load of output port 1 changes between 5 ohms and 10 ohms with a period of 0.5 s, and the load of output port 2 changes between 10 ohms and 15 ohms with a period of 0.5 s.

[0077] Through the above load current feedforward control method, when a mutation occurs in the load on the output side, the load current feedforward control can be used to improve the recovery speed and stability of the output voltage during load mutation. Moreover, the present invention has no dependence on circuit parameters such as auxiliary inductors and has good portability and versatility.

[0078] If the above functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage medium includes: various media that can store program codes such as USB flash drives, mobile hard disks, read-only memories (ROM, Read-Only Memory), random access memories (RAM, Random Access Memory), magnetic disks, or optical discs.

[0079] Those skilled in the art should understand that the embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memories, CD-ROMs, optical memories, etc.) containing computer-usable program codes. The solutions in the embodiments of the present invention can be implemented in various computer languages. For example, object-oriented programming languages such as Java and interpreted scripting languages such as JavaScript.

[0080] The present invention is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowchart and / or block diagram, and the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the functions specified in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0081] These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means that implement the function specified in one or more of the procedures Figure 1 or steps and / or Figure 1 boxes or more boxes.

[0082] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, whereby the instructions executed on the computer or other programmable apparatus provide steps for implementing the function specified in one or more of the procedures Figure 1 or steps and / or Figure 1 boxes or more boxes.

[0083] Although the preferred embodiments of the present invention have been described, additional changes and modifications can be made by those skilled in the art once they learn of the basic inventive concept. Therefore, the appended claims are intended to be construed to cover the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0084] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A load current feedforward control method for a three-port DC-DC converter, characterized in that, It includes the following steps: Obtain the output voltages U o1 and U o2 of two output ports in a three-port DC-DC converter and the load current i o1 and i o2 in real time; Calculate the difference between the output voltage U o1 , U o2 and the output voltage set value, and obtain the virtual output voltage set value through a PI controller; Based on the output voltage U o1 , U o2 and the load current i o1 , i o2 , combining the output voltage set value and the virtual output voltage set value, calculate the phase shift ratio D in real time to dynamically adjust the phase shift ratio D and complete the control process.

2. The load current feedforward control method of a three-port DC-DC converter according to claim 1, wherein The expression of the virtual output voltage set value is: Wherein, P is the output power, U v * is the virtual output voltage set value, i o * is the load current set value, U o * is the output voltage set value, U o is the actual output voltage value, i o is the actual load current value.

3. The load current feedforward control method of a three-port DC-DC converter according to claim 2, wherein The relationship between the output power P and the phase shift ratio D satisfies: P = U o (D - D 2 ) Where U o is the actual value of the output voltage.

4. A load current feedforward control method for a three-port DC-DC converter according to claim 3, characterized in that, The steps for obtaining the relationship between the output power P and the phase shift ratio D include: According to the current flowing through the inductor in the three-port DC-DC converter, the initial expression of the output power P is obtained as: where T S is the switching period, t0 is the starting time of a switching period, t4 is the ending time of a switching period, U ac (t) is the instantaneous voltage at the input of the H-bridge circuit in the three-port DC-DC converter, and i L (t) is the instantaneous current of the input inductor; Substitute the initial instantaneous value i0 at the start of the inductor current period into Equation (1), and the initial expression of the output power P becomes: Where U DC is the actual value of the input voltage, f S is the switching frequency, n is the turns ratio of the transformer in the three-port DC-DC converter, and L is the inductance value; Further simplify Equation (2) to obtain the relationship expression between the output power P and the phase shift ratio D.

5. A load current feedforward control method for a three-port DC-DC converter according to claim 1, characterized in that, The calculation expression of the phase shift ratio D is: Wherein, U o * is the set value of the output voltage, U v * is the set value of the virtual output voltage, i o is the actual value of the load current, U o is the actual value of the output voltage.

6. The load current feedforward control method of a three-port DC-DC converter according to claim 1, characterized in that The three-port DC-DC converter includes an input module, a first output module, a second output module, and a three-port high-frequency transformer. The input module is connected to the second output module through the three-port high-frequency transformer, and the first output module is connected to the second output module through the three-port high-frequency transformer.

7. A load current feedforward control method for a three-port DC-DC converter according to claim 6, characterized in that, The three-port high-frequency transformer adopts a three-winding design.

8. A load current feedforward control method for a three-port DC-DC converter according to claim 6, characterized in that, The input module includes an input DC voltage source DC, an input H-bridge circuit, a DC-side filter capacitor C1, and a power inductor L1. The input DC voltage source DC and the DC-side filter capacitor C1 are connected in parallel, and the power inductor L1 is connected between the input H-bridge circuit and the three-port high-frequency transformer.

9. The load current feedforward control method of a three-port DC-DC converter according to claim 6, characterized in that, The first output module and the second output module both include an output-side voltage, a DC-side filter capacitor, an output H-bridge circuit, a power inductor, and a resistor. Among them, in the first output module, the output-side voltage U o1 is connected in parallel with the DC-side filter capacitor C2, the power inductor L2 is connected between the first output H-bridge circuit and the three-port high-frequency transformer, and the resistor R1 is connected to the output-side voltage U o1 and In the second output module, the output side voltage U o2 is connected in parallel with the DC side filter capacitor C3, and the power inductor L3 is connected between the second output H-bridge circuit and the three-port high-frequency transformer. The resistor R2 is connected to the output side voltage U o2 for connection.

10. A load current feedforward control method for a three-port DC-DC converter according to any one of claims 8-9, characterized in that, There are four switches in the input H-bridge circuit, the first output H-bridge circuit, and the second output H-bridge circuit. During the switching process of each H-bridge circuit, when the current flows into the inductor, the inductor stores electrical energy as magnetic energy. When the switch state changes, the inductor releases the magnetic energy and converts it into electrical energy to be output to the circuit.

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