Model predictive control method for three-port converter and three-port converter

Abstract

The present application relates to a model predictive control method for a three-port converter and the three-port converter, the method comprising the following steps: step S1, for each output of the converter, based on the load current, the secondary side full-bridge output current corresponding to a plurality of candidate phase shift angles, and the output voltage at the current time, the output voltage at the next time corresponding to the plurality of candidate phase shift angles is predicted; step S2, based on the output voltage at the next time corresponding to the plurality of candidate phase shift angles and the preset target output voltage, the optimal phase shift angle is obtained, the power electronic switch is controlled to be turned on alternately based on the optimal phase shift angle, the square wave voltage of the input and the output is phase shifted, and the voltage control of the output side is realized. Compared with the prior art, the present application has the characteristics of high stability and strong reliability.

Description

Technical Field

[0001] This invention relates to the field of power electronics, and in particular to a model predictive control method for a three-port converter and a three-port converter. Background Technology

[0002] Electricity is a key factor for the power sector to reduce carbon dioxide emissions and achieve carbon neutrality. On the generation side, a new power system needs to be built that primarily relies on renewable energy sources such as wind, solar, and hydropower. On the consumption side, electricity has become the main mode of consumption. With the large-scale development of new energy sources and the increase in power terminal equipment, DC-DC converters, as highly efficient power conversion devices, are being used in various applications, such as electric vehicles, power systems, renewable energy integration, battery management systems, and distributed power sources.

[0003] With the development of power electronics technology, traditional single-port DC-DC converters are gradually failing to meet the increasingly complex requirements of power systems. In multi-voltage power systems, multi-port DC-DC converters have emerged to improve energy efficiency and reduce system size. Three-port DC-DC converters, as a typical type of multi-port converter, enable bidirectional power flow between three different ports, support various input / output combinations, and are widely used in battery charging, energy storage systems, and multi-power supply applications. However, in practical applications, three-port DC-DC converters face some technical challenges, particularly in terms of control strategies.

[0004] Most existing control methods for three-port DC-DC converters rely on traditional control techniques such as PID control and PWM control. While these methods can operate effectively in simple control tasks, in multi-port systems, due to the mutual coupling and complex dynamic characteristics between multiple ports, traditional control methods often struggle to achieve globally optimal control. This results in lower system stability, response speed, and efficiency under conditions of load changes, power fluctuations, or significant system disturbances.

[0005] Especially in multi-port DC-DC converter applications, coordinated control of different ports is often required to ensure that each port can adjust its output power in a timely manner according to load demands. However, traditional control methods often lack flexibility and global optimization capabilities. Specifically, traditional control methods typically employ local control strategies, adjusting each port independently, failing to effectively consider the coupling effects between multiple ports and the global state of the system, thus failing to achieve optimal power distribution.

[0006] When the load or input voltage of a DC-DC converter changes, it usually faces problems such as slow response speed, low control accuracy and poor stability.

[0007] In summary, there is currently a lack of control methods to solve or partially solve the aforementioned problems. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art by providing a model predictive control method and a three-port converter, so as to solve or partially solve the problems of slow response speed, low control accuracy and poor stability when the output load or input voltage of the converter changes.

[0009] The objective of this invention can be achieved through the following technical solutions:

[0010] One aspect of the present invention provides a model predictive control method for a three-port converter, comprising the following steps:

[0011] Step S1: For each output terminal of the converter, based on the load current, the current output through the full bridge on the secondary side corresponding to multiple candidate phase shift angles, and the output voltage at the current moment, predict the output voltage corresponding to multiple candidate phase shift angles at the next moment.

[0012] Step S2: Based on the output voltage corresponding to multiple candidate phase shift angles at the next moment and the preset target output voltage, the optimal phase shift angle is obtained. Based on the optimal phase shift angle, the power electronic switch is controlled to conduct alternately, so that the square wave voltage at the input and output ends is phase-shifted, thereby realizing voltage control on the output side.

[0013] As a preferred technical solution, the following steps are also included:

[0014] Step S3: Based on the current optimal phase shift angle, update multiple candidate phase shift angles and execute step S1.

[0015] As a preferred technical solution, the method of updating multiple candidate phase shift angles involves selecting multiple candidate phase shift angles within the adjustable range of the predicted phase shift control on both sides, with the current optimal phase shift angle as the center.

[0016] The predicted output voltage corresponding to multiple candidate phase shift angles at the next moment is obtained using the following formula:

[0017]

[0018] in, , These are the predicted output voltage value at the next moment and the current output voltage at the output port, respectively. The capacitor connected in parallel at the output terminal. For switching frequency, , These are the load current and the current output from the secondary side via the full bridge corresponding to multiple candidate phase shift angles, respectively.

[0019] As a preferred technical solution, the current output from the secondary side via the full bridge corresponding to the multiple candidate phase shift angles is calculated using the following formula:

[0020]

[0021] in, The current output from the secondary side via the full bridge is the current. The primary input voltage, For switching frequency, This represents the optimal phase shift angle at the previous time step.

[0022] As a preferred technical solution, in step S2, the phase shift angle corresponding to the lowest cost is selected as the optimal phase shift angle by calculating the cost function of each candidate phase shift angle, wherein the cost function is:

[0023]

[0024]

[0025] in, , These are the preset target output voltage and the predicted output voltage value of the output port at the next moment, respectively. For cost, These are the weighting coefficients.

[0026] As a preferred technical solution, the model predictive control method is executed in response to a sudden change in the output load.

[0027] In another aspect, the present invention provides a three-port converter for implementing the aforementioned model predictive control method for a three-port converter, the three-port converter comprising:

[0028] Input full bridge;

[0029] First output terminal full bridge;

[0030] Second output terminal full bridge;

[0031] The medium-to-high frequency isolation transformer is connected to the input full bridge, the first output full bridge, and the second output full bridge, respectively.

[0032] As a preferred technical solution, a power inductor is included for any one of the input full-bridge, the first output full-bridge, and the second output full-bridge.

[0033] As a preferred technical solution, the input full-bridge, the first output full-bridge, and the second output full-bridge are H-bridges.

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

[0035] To mitigate the negative impacts of load variations or input voltage variations at the converter output: Model predictive control is employed, which includes candidate phase shift angle selection, voltage prediction, and cost function calculation. When the input voltage and load change, the phase difference between the input and output voltage square waves is dynamically adjusted, allowing the output voltage to recover to the set value in a very short time. When a pulsed load is connected to the three-port converter, the output voltage can operate smoothly and stably. Compared with existing control methods, it has the characteristics of high stability and high reliability. Attached Figure Description

[0036] Figure 1 This is a flowchart of the model predictive control method for a three-port converter in the embodiment;

[0037] Figure 2 This is a circuit diagram of the three-port converter in the embodiment;

[0038] Figure 3 The voltage waveforms of the two output ports of the three-port DC-DC converter under load fluctuations (the load of port 1 changes abruptly from 10Ω to 20Ω at 0.3s, and the load of port 2 changes abruptly from 40Ω to 20Ω at 0.5s).

[0039] Figure 4 The voltage waveforms of the two output ports of the three-port DC-DC converter under pulse load fluctuations are shown (port 1 alternates between loads of 10Ω and 20Ω in a 0.2s cycle, and port 2 alternates between loads of 40Ω and 20Ω in a 0.2s cycle).

[0040] Figure 5 The voltage waveforms of the two output ports of the three-port DC-DC converter during the periodic fluctuation of the input voltage (the input port voltage alternates between 100V and 120V in a period of 0.2s). Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0042] Example 1

[0043] To address the problems existing in the prior art, this embodiment provides a model predictive control method for a three-port converter, aiming to improve the stability of the output voltage under conditions of load abrupt changes and input voltage fluctuations, thereby ensuring the constancy of the output voltage. This method is particularly suitable for distribution network environments, achieving precise and stable control of the output voltage under complex operating conditions of load and input voltage fluctuations. The model predictive control method mainly includes three key parts: control set selection, voltage prediction, and cost function calculation. See also... Figure 1 The method includes the following steps:

[0044] Step S1, Control Set Selection: The phase shift in the three-port DC-DC converter has a control margin of 0-0.5. This invention divides 0-0.5 into steps of 0.0001 and calculates five points within a control set. The most suitable point is selected from these five points as the midpoint for the next cycle and substituted into the calculation for that cycle. For example, if the first control set is (0, 0.0001, 0.0002, 0.0003, 0.0004, 0.0005), and the model predicts the control cost function, substituting 0.0005 as the minimum point for this control set, then the control set for the next cycle is selected as (0.0003, 0.0004, 0.0005, 0.0006, 0.0007), and so on.

[0045] Step S2, Voltage Prediction: Analyze the current across the output capacitor using Kirchhoff's laws.

[0046]

[0047] This refers to the current output from the secondary side via the full bridge. The current in the capacitor, The load current and capacitor current can be converted into the following over one cycle:

[0048]

[0049]

[0050] Discretize the capacitor current using a forward Euler:

[0051]

[0052] in The phase shift angle from the previous moment is used to obtain:

[0053]

[0054] Step S3, Cost Function Calculation:

[0055]

[0056] The set voltage reference value, This is the real-time voltage prediction value. This is to ensure that the predicted value is close to the voltage setpoint.

[0057] The cost function is:

[0058]

[0059] These are the weighting coefficients of the cost function, which can be tuned according to specific circumstances.

[0060] The control strategy described above can respond more quickly to sudden changes in load and input voltage.

[0061] Step S4: The G1 values ​​corresponding to the five candidate phase shift angles are calculated using step S3. The phase shift angle corresponding to the smallest G1 value is selected as the optimal phase shift angle and used as the control input for the current control cycle. This optimal phase shift angle will be carried back to the control set selection as one of the candidate control points for the next control cycle, further participating in the optimization calculation of subsequent cycles.

[0062] Step S5 involves controlling the drive pulses of the two H-bridges at the input and output sides, causing a phase shift in the square wave voltage generated on the input and output sides to achieve voltage control on the output side. Specifically, by alternately switching on and off the power electronic switches, a square wave with a certain phase shift is generated at the input and output sides to control the output voltage.

[0063] See Figure 3 The figure shows the voltage waveforms of the two output ports of a three-port DC-DC converter under load fluctuations. In the figure, the load of port 1 changes abruptly from 10Ω to 20Ω at 0.3s, and the load of port 2 changes abruptly from 40Ω to 20Ω at 0.5s.

[0064] See Figure 4 The figure shows the voltage waveforms of the two output ports of a three-port DC-DC converter under pulse load fluctuations. In the figure, port 1 alternates between loads of 10Ω and 20Ω in a cycle of 0.2s, and port 2 alternates between loads of 40Ω and 20Ω in a cycle of 0.2s.

[0065] See Figure 5 The voltage waveforms of the two output ports of a three-port DC-DC converter during the periodic fluctuation of the input voltage are shown. The input port voltage alternates between 100V and 120V in a period of 0.2s.

[0066] according to Figures 3-5As can be seen from the examples, compared with the existing technology, this method can achieve rapid control of the output side, improve dynamic response capability, and enhance system stability.

[0067] Example 2

[0068] Based on Example 1, this example provides a three-port converter to implement the model predictive control method for a three-port converter described in Example 1. (See also...) Figure 2 This includes load surge response and input voltage surge response. When the load and input voltage change abruptly, the drive pulses of the two H-bridges at the input and output sides are controlled to cause a phase shift in the square wave voltage generated on the input and output sides, thereby achieving voltage control on the output side. Specifically, a combination of three stacked H-bridges is connected to a medium-to-high frequency isolation transformer. Through the alternating conduction of power electronic switches, a square wave with a certain phase shift is generated at the input and output sides to control the output voltage.

[0069] Preferably, each full-bridge is equipped with a power inductor to ensure waveform quality and the stable operation of the high-frequency transformer, the core component of the three-port DC-DC converter. The output voltages of the two ports are independently controlled, allowing for separate control of the output voltages of the two output ports. Therefore, the two ports operate independently when faced with load fluctuations at different ports.

[0070] In summary, this invention employs a predictive control strategy based on a simplified model, aiming to significantly reduce the computational burden through single-step prediction while maintaining similar control effects. This optimized scheme significantly reduces the computational requirements of the prediction part, enabling the control system to be better applied to the control of three-port DC-DC converters while maintaining high efficiency, thus improving control accuracy and real-time performance.

[0071] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A model predictive control method for a three-port converter, characterized in that, Includes the following steps: Step S1: For each output terminal of the converter, based on the load current, the current output through the full bridge on the secondary side corresponding to multiple candidate phase shift angles, and the output voltage at the current moment, predict the output voltage corresponding to multiple candidate phase shift angles at the next moment. Step S2: Based on the output voltage corresponding to multiple candidate phase shift angles at the next moment and the preset target output voltage, the optimal phase shift angle is obtained. Based on the optimal phase shift angle, the power electronic switches are controlled to alternately conduct, causing the square wave voltage at the input and output terminals to shift phase, thereby achieving voltage control on the output side. The predicted output voltage corresponding to multiple candidate phase shift angles at the next moment is obtained using the following formula: in, , These are the predicted output voltage value at the next moment and the current output voltage at the output port, respectively. The capacitor connected in parallel at the output terminal. For switching frequency, , These represent the load current and the secondary side output current through the full bridge corresponding to multiple candidate phase shift angles, respectively. The current output from the secondary side via the full bridge corresponding to the multiple candidate phase shift angles is calculated using the following formula: in, The current output from the secondary side via the full bridge is the current. The primary input voltage, For switching frequency, This represents the optimal phase shift angle at the previous time step. In step S2, the phase shift angle with the lowest cost is selected as the optimal phase shift angle by calculating the cost function of each candidate phase shift angle. The cost function is: in, The preset target output voltage, For cost function, These are weighting coefficients. This is to ensure that the predicted value is close to the voltage setpoint.

2. The model predictive control method for a three-port converter according to claim 1, characterized in that, It also includes the following steps: Step S3: Based on the current optimal phase shift angle, update multiple candidate phase shift angles and execute step S1.

3. The model predictive control method for a three-port converter according to claim 2, characterized in that, The method of updating multiple candidate phase shift angles involves selecting multiple candidate phase shift angles within the adjustable range of the predicted phase shift control on both sides, with the current optimal phase shift angle as the center.

4. The model predictive control method for a three-port converter according to claim 1, characterized in that, In response to a sudden change in the output load, the model predictive control method is executed.

5. A three-port converter, characterized in that, For implementing the model predictive control method for a three-port converter as described in any one of claims 1-4, the three-port converter includes: Input full bridge; First output terminal full bridge; Second output terminal full bridge; The medium-to-high frequency isolation transformer is connected to the input full bridge, the first output full bridge, and the second output full bridge, respectively.

6. A three-port converter according to claim 5, characterized in that, For any one of the input full-bridge, the first output full-bridge, and the second output full-bridge, including the power inductor.

7. A three-port converter according to claim 5, characterized in that, The input full-bridge, the first output full-bridge, and the second output full-bridge are H-bridges.

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