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

Abstract

The invention relates to a model predictive control method for a three-port converter and the three-port converter, and the method comprises the following steps: S1, aiming at each output end of the converter, carrying out the model predictive control on the output end of the converter based on a load current, a current which is output by a secondary side through a full bridge and corresponds to a plurality of candidate phase shift angles, and an output voltage at a current moment; predicting to obtain output voltages corresponding to a plurality of candidate phase shift angles at the next moment; and S2, based on the output voltage corresponding to the plurality of candidate phase shift angles at the next moment and a preset target output voltage, obtaining an optimal phase shift angle, and based on the optimal phase shift angle, controlling a power electronic switch to be switched on alternately, so that the square wave voltage of the input end and the output end generates phase shift, and voltage control of the output side is realized. Compared with the prior art, the system has the characteristics of high stability and high reliability.

Description

Technical Field

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

[0002] Electricity is a key factor for the power sector to reduce carbon dioxide emissions and achieve carbon neutrality. On the power generation side, a new power system with wind, solar, hydropower and other renewable energy as the main energy supply should be built, while on the energy consumption side, electricity has become the main consumption mode. With the massive development of new energy and the increase of power terminal equipment, DC-DC converters, as an efficient power conversion device, are used in various occasions, such as electric vehicles, power systems, renewable energy access, battery management systems and distributed power sources.

[0003] With the development of power electronics technology, traditional single-port DC-DC converters are gradually unable to meet the requirements of increasingly complex power systems. In multi-voltage power systems, multi-port DC-DC converters have emerged to improve energy efficiency and reduce system size. As a typical multi-port converter, the three-port DC-DC converter can carry out bidirectional flow of electric energy between three different ports, supports a variety of input and output combinations, and is widely used in battery charging, energy storage systems, and multi-power supply occasions. However, in practical applications, the three-port DC-DC converter faces some technical challenges, especially in terms of control strategy.

[0004] Most of the existing control methods for three-port DC-DC converters rely on traditional control technologies, such as PID control, PWM control, etc. Although these methods can work 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 have difficulty in achieving global optimal control. This leads to low system stability, response speed and efficiency in the case of load changes, power fluctuations or large system disturbances.

[0005] Especially in the application scenarios of multi-port DC-DC converters, it is often necessary to coordinate the control of different ports to ensure that each port can adjust the output power in a timely manner according to the load demand, but traditional control methods often lack flexibility and global optimization capabilities. Specifically, traditional control methods usually adopt local control strategies, and each port is adjusted independently, which fails to effectively consider the coupling effect between multiple ports and the global state of the system, and thus cannot achieve optimal power allocation.

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

[0007] In summary, there is currently a lack of a control method to solve or partially solve the above-mentioned problems. Summary of the invention

[0008] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a model predictive control method and a three-port converter for 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 converter output load changes or the input voltage changes.

[0009] The purpose of the present invention can be achieved by 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 end of the converter, based on the load current, the current outputted by the secondary side through the full bridge corresponding to the multiple candidate phase shift angles, and the output voltage at the current moment, predicting the output voltage corresponding to the multiple candidate phase shift angles at the next moment;

[0012] Step S2, based on the output voltages corresponding to the multiple candidate phase shift angles at the next moment and the preset target output voltage, the optimal phase shift angle is obtained, and based on the optimal phase shift angle, the power electronic switch is controlled to alternately conduct, so that the square wave voltages at the input and output ends are 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 updating of multiple candidate phase shift angles is to select multiple candidate phase shift angles within the adjustable range of phase shift control predicted on both sides, taking the current optimal phase shift angle as the center.

[0016] The prediction of the output voltage corresponding to the multiple candidate phase shift angles at the next moment is implemented by the following formula:

[0017]

[0018] Among them, V 2 (k+1), V 2 (k) are the predicted output voltage of the output port at the next moment and the output voltage at the current moment, respectively. 2 is the capacitor connected in parallel with the output terminal, f s is the switching frequency, I load ,I hv2They are respectively the load current and the current output by the secondary side through the full bridge corresponding to multiple candidate phase shift angles.

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

[0020]

[0021] Among them, I hv2 is the current output by the full bridge on the secondary side, V in is the primary input voltage, f s is the switching frequency, and D is the optimal phase shift angle at the previous moment.

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

[0023] G 1 =V ref -V p

[0024] ct=α 1 G 1

[0025] Among them, V ref 、V p are the preset target output voltage and the output voltage prediction value of the output port at the next moment, ct is the cost, α 1 is the weighting coefficient.

[0026] As a preferred technical solution, the model predictive control method for a three-port converter according to claim 1 is characterized in that the model predictive control method is executed in response to a sudden change in the output load.

[0027] Another aspect of the present invention provides a three-port converter for implementing the aforementioned model predictive control method for the three-port converter, wherein the three-port converter comprises:

[0028] Full bridge at input end;

[0029] First output full bridge;

[0030] The second output terminal is full bridge;

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

[0032] As a preferred technical solution, any one of the input end full bridge, the first output end full bridge, and the second output end full bridge includes a power inductor.

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

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

[0035] Alleviate the negative impact of load changes or input voltage changes on the converter output: adopt the model predictive control method, 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 voltage square waves on the input and output sides is dynamically adjusted so that the output voltage can be restored to the set value in a very short time. When the three-port converter is connected to a pulsed load, the output voltage can run smoothly and stably. Compared with the existing control methods, it has the characteristics of high stability and strong reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a flow chart of a model predictive control method for a three-port converter in an embodiment;

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

[0038] Figure 3 The voltage waveforms of the two output ports of the three-port DC-DC converter when the load fluctuates (the load of port 1 suddenly changes from 10Ω to 20Ω at 0.3s, and the load of port 2 suddenly changes 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 when the pulse load fluctuates (the load of port 1 alternates between 10Ω and 20Ω at a cycle of 0.2s, and the load of port 2 alternates between 40Ω and 20Ω at a cycle of 0.2s);

[0040] Figure 5 The voltage waveforms of the two output ports of the three-port DC-DC converter when the input voltage fluctuates periodically (the input port voltage alternates between 100V and 120V with a cycle of 0.2s). DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0042] Example 1

[0043] In view of the problems existing in the above-mentioned prior art, this embodiment provides a model predictive control method for a three-port converter, which aims to improve the stability of the output voltage of the converter under load mutation and input voltage fluctuation, thereby ensuring the constancy of the output voltage. This method is particularly suitable for distribution network environments, and can achieve accurate and stable control of the output voltage under complex working 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. Figure 1 , the method comprises 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. The present invention takes 0-0.5 as a step of 0.0001 and calculates five points in one control set. The most suitable point is selected from the five points as the midpoint of the next cycle and substituted into the calculation of the next cycle. For example, the first control set is (0, 0.0001, 0.0002, 0.0003, 0.0004, 0.0005). At this time, the model predictive control cost function part is substituted into 0.0005 as the minimum point of this control set, then the next cycle control set selection is (0.0003, 0.0004, 0.0005, 00006, 0.0007), and so on.

[0045] Step S2, voltage prediction: by analyzing the current on the output capacitor using Kirchhoff's law:

[0046] I hv2 =I c +I load

[0047] I hv2 is the current output by the full bridge on the secondary side, I c is the current on the capacitor, I load is the load current, and the capacitor current in one cycle can be converted into:

[0048]

[0049] Discretize the capacitor current using forward Euler:

[0050]

[0051] Among them I hv2 The phase shift angle at the previous moment is obtained:

[0052]

[0053] Step S3, cost function calculation:

[0054] G 1 =V ref -V p

[0055] V ref is the set voltage reference value, V p is the real-time voltage prediction value. 1 To ensure that the predicted value is close to the voltage set value.

[0056] The cost function is:

[0057] ct=α 1 G 1

[0058] α 1 is the weighting coefficient of the cost function and can be adjusted according to the detailed situation.

[0059] Facing sudden changes in load or input voltage, the control strategy can respond more quickly.

[0060] Step S4, calculate the G1 values ​​corresponding to the five candidate phase shift angles through step S3, select the phase shift angle corresponding to the smallest G1 value as the optimal phase shift angle, and use it as the control input of the current control cycle. The optimal phase shift angle will be brought back to the control set selection as one of the candidate control points of the next control cycle, and further participate in the optimization calculation of the subsequent cycle.

[0061] Step S5, control the driving pulses of the two H-bridges at the input and output sides so that the square wave voltage generated at the input and output sides is phase-shifted to achieve voltage control at the output side. Specifically, by alternately conducting the power electronic switches, a square wave with a certain phase shift is generated at the input and output sides to achieve the purpose of controlling the output side voltage.

[0062] See also Figure 3 Figure 2 is the voltage waveform of the two output ports of the three-port DC-DC converter when the load fluctuates. In the figure, the load of port 1 suddenly changes from 10Ω to 20Ω at 0.3s, and the load of port 2 suddenly changes from 40Ω to 20Ω at 0.5s.

[0063] See also Figure 4The voltage waveforms of the two output ports of the three-port DC-DC converter when the pulse load fluctuates. In the figure, the load of port 1 alternates between 10Ω and 20Ω with a cycle of 0.2s, and the load of port 2 alternates between 40Ω and 20Ω with a cycle of 0.2s.

[0064] See also Figure 5 The voltage waveforms of the two output ports of the three-port DC-DC converter when the input voltage fluctuates periodically, where the input port voltage alternates between 100V and 120V with a cycle of 0.2s.

[0065] according to Figure 3-Figure 5 It can be seen from the example that, compared with the prior art, this method can achieve rapid control of the output side, improve dynamic response capability, and enhance system stability.

[0066] Example 2

[0067] Based on Example 1, this embodiment provides a three-port converter to implement the model predictive control method for the three-port converter of Example 1. Figure 2 , including load mutation response and input voltage mutation response. When the load and input voltage suddenly change, the driving pulses of the two H-bridges on the input and output sides are controlled to shift the square wave voltage generated on the input and output sides to achieve voltage control on the output side. Specifically, the three stacked H-bridges are connected to the medium-high frequency isolation transformer and combined. Through the alternating conduction of the power electronic switches, a square wave with a certain phase shift is generated on the input and output sides to achieve the purpose of controlling the output side voltage.

[0068] Preferably, each full bridge is equipped with a power inductor to ensure waveform quality and stable operation of the high-frequency transformer, the core component of the three-port DC-DC converter. The output voltage of the two ports is independently controlled, and the output voltage of the two output ports can be controlled separately, so when facing load fluctuations of different ports, the two ports act independently.

[0069] In summary, the present invention adopts a predictive control strategy based on a simplified model, which aims to significantly reduce the computational burden through single-step prediction under the premise of similar control effects. This optimization scheme significantly reduces the computational requirements of the prediction part, so that the control system can be better applied to the control of the three-port DC converter while maintaining high efficiency, and improves the control accuracy and real-time performance.

[0070] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A model predictive control method for a three-port converter, characterized in that: The steps include: Step S1, for each output end of the converter, based on the load current, the current outputted by the secondary side through the full bridge corresponding to the multiple candidate phase shift angles, and the output voltage at the current moment, predicting the output voltage corresponding to the multiple candidate phase shift angles at the next moment; Step S2, based on the output voltages corresponding to the multiple candidate phase shift angles at the next moment and the preset target output voltage, the optimal phase shift angle is obtained, and based on the optimal phase shift angle, the power electronic switch is controlled to alternately conduct, so that the square wave voltages at the input and output ends are phase-shifted, thereby realizing voltage control on the output side.

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

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

4. A model predictive control method for a three-port converter according to claim 1, characterized in that: The prediction of the output voltage corresponding to the multiple candidate phase shift angles at the next moment is implemented by the following formula: Among them, V2(k+1) and V2(k) are the predicted output voltage of the output port at the next moment and the output voltage at the current moment, respectively. C2 is the capacitor connected in parallel to the output end. f s is the switching frequency, I load ,I hv2 They are respectively the load current and the current output by the secondary side through the full bridge corresponding to multiple candidate phase shift angles.

5. A model predictive control method for a three-port converter according to claim 4, characterized in that: The current outputted by the secondary side through the full bridge corresponding to the multiple candidate phase shift angles is calculated using the following formula: Among them, I hv2 is the current output by the full bridge on the secondary side, V in is the primary input voltage, f s is the switching frequency, and D is the optimal phase shift angle at the previous moment.

6. A model predictive control method for a three-port converter according to claim 1, characterized in that: In step S2, the cost function of each candidate phase shift angle is calculated, and the phase shift angle corresponding to the lowest cost is selected as the optimal phase shift angle, wherein the cost function is: G1=V ref -V p ct=α1G1 Among them, V ref 、V p are the preset target output voltage and the predicted output voltage of the output port at the next moment, ct is the cost, and α1 is the weighting coefficient.

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

8. A three-port converter, characterized in that: Used to implement the model predictive control method for a three-port converter according to any one of claims 1 to 7, the three-port converter comprising: Full bridge at input end; First output full bridge; The second output terminal is full bridge; The medium-high frequency isolation transformer is respectively connected to the input end full bridge, the first output end full bridge, and the second output end full bridge.

9. A three-port converter according to claim 8, characterized in that: Any one of the input end full bridge, the first output end full bridge, and the second output end full bridge comprises a power inductor.

10. A three-port converter according to claim 8, characterized in that: The input end full bridge, the first output end full bridge and the second output end full bridge are H bridges.

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