Mode control method and system of four-switch converter

Abstract

The invention relates to the technical field of electrical control, and discloses a mode control method and system for a four-switch converter. The method comprises the following steps: obtaining a theoretical output current of the four-switch converter; establishing a mathematical model according to the topological structure of the four-switch converter, determining the switching states of the four-switch converter in four different switching modes, and obtaining the relationship between the theoretical inductive current and the theoretical output current of the four-switch converter so as to determine the theoretical inductive current of the four-switch converter; discretizing to form a discrete mathematical model of the four-switch converter in each switching mode so as to predict the actual inductive current of the four-switch converter in the corresponding switching mode and the actual duty ratio of a switching tube; the target switching mode corresponding to the discrete mathematical model with the predicted actual inductive current having the minimum offset relative to the theoretical inductive current is selected, and the four-switch converter is controlled to be switched to the target switching mode by adopting the correspondingly predicted actual duty ratio of the switching tube, so that the mode switching control effect is better.

Description

Technical Field

[0001] The present invention relates to the field of electrical control technology, and in particular to a mode control method and system for a four-switch converter. Background Art

[0002] Since the traditional power supply system with a single type of power supply is difficult to effectively cope with the broadband and strong pulsation characteristics of the load, combining the advantages of different types of power supplies, and connecting multiple energy storage units with different dynamic response characteristics on the basis of the original power supply system, it can transform from the traditional single type of power supply centralized power supply to multi-type power supply distributed power supply, forming a multi-source hybrid power supply system, such as Figure 1 When a multi-source hybrid power system needs to output pulse load power, since the dynamic characteristics and peak power of the main power supply in the multi-source hybrid power system cannot adapt to the dynamic characteristics of the pulse load, an electrolytic capacitor with fast dynamic characteristics can be used as a pulse energy storage device connected to the power supply system to compensate for the pulse power, so that the main power supply only bears the average power.

[0003] The dynamic phase of pulse load is divided into the following parts, such as Figure 2 As shown in the figure: the first stage: pulse operation stage, the electrolytic capacitor and the main power supply work together to supply power to the pulse load, in which the capacitor will bear most of the pulse power output; the second stage: energy regeneration stage, once the pulse load ends, regenerative energy is generated, which is caused by the braking of the servo system, and the regenerative energy should be absorbed by the electrolytic capacitor; the third stage: electrolytic capacitor charging stage, the electrolytic capacitor is charged until the electrolytic capacitor is full and the terminal voltage reaches the maximum value; the fourth stage: pulse preparation stage, the electrolytic capacitor stops working due to being fully charged and is ready to provide pulse load power for the next round.

[0004] The analysis of pulsed load power compensation above shows that if power output and absorption are required within a short period of time, the capacitor voltage will rapidly drop and recover. To ensure overall system stability and efficient energy transmission, the interface converter for the pulsed energy storage unit in a multi-source hybrid system must possess a wide voltage gain range and the ability to rapidly switch power flow. The four-switch Buck-Boost converter features a low number of passive components and high power density, which is sufficient to ensure the efficiency and reliability of switching power supplies over a wide input and output voltage range. Traditional mode determination methods for four-switch Buck-Boost converters select the operating mode of the four-switch converter by comparing the input and output voltages. However, since the converter's on-state voltage drop is ignored, the presence of the on-state voltage drop can easily cause erroneous mode switching when the input and output voltages are close. Therefore, the mode determination criteria for the four-switch Buck-Boost converter need to be redesigned.

[0005] The current mode determination method for a four-switch Buck-Boost converter incorporates the inductor current into the mode recognition process. By detecting the inductor current, the mode is selected based on a pre-determined correspondence between the inductor current and the mode. Furthermore, because mode switching causes output voltage instability, which leads to frequent mode switching, it is necessary to incorporate the current operating mode determination into the mode recognition process. For example, the addition of hysteresis control can avoid frequent mode switching near the mode switching boundary.

[0006] However, the above mode judgment method cannot accurately track the required current when the pulse load changes. When the converter switches modes, the sudden change in gain may cause a large drop or surge in the output current, resulting in a poor effect when switching modes. Summary of the Invention

[0007] An object of the present invention is to provide a mode control method and system for a four-switch converter, which can improve the system dynamic performance during mode switching of the four-switch converter.

[0008] To solve the above technical problems, an embodiment of the present invention provides a mode control method for a four-switch converter, comprising the following steps: Obtaining the pulse load current required when the pulse load frequency changes, and using the pulse load current as the theoretical output current of the four-switch converter; A mathematical model is established according to the topological structure of the four-switch converter, and the switching states of the four-switch converter in four different switching modes are determined by using the mathematical model and the ratio between the output voltage and the input voltage of the four-switch converter; Determine the relationship between the theoretical inductor current and the theoretical output current of the four-switch converter according to the switching state in each switching mode, and determine the theoretical inductor current of the four-switch converter through the relationship between the theoretical inductor current and the theoretical output current and the theoretical output current; Discretizing the mathematical model to form a discrete mathematical model of the four-switch converter in each switching mode, wherein the discrete mathematical model is used to predict an actual inductor current and an actual duty cycle of the switch tube of the four-switch converter in the corresponding switching mode; The target switching mode corresponding to the discrete mathematical model with the smallest deviation of the predicted actual inductor current relative to the theoretical inductor current is selected, and the actual duty cycle of the corresponding predicted switch tube is used to control the four-switch converter to switch to the target switching mode.

[0009] Optionally, the mathematical model is: ; Where, is the inductor, for The inductor current at time is the total stray resistance of the inductor current path, It is the switch tube of the Buck unit in the four-switch converter. is the switch tube of the Boost unit, and It is the main switch tube of the Buck unit. It is the main switch tube of the Boost unit.

[0010] Optionally, the ratio between the output voltage and the output voltage of the four-switch converter is: ; Where, Switching tube Duty cycle; by For the switch tube The maximum duty cycle allowed, For the switch tube The minimum duty cycle allowed, the switching states of the four-switch converter in four different switching modes are as follows: when When the four-switch converter is in Buck mode, , switch tube Alternating conduction, switch tube conduction, switch tube Shutdown, corresponding to state 1 and state 2 in the mathematical model; when When the four-switch converter is in E-Buck mode, , switch tube Alternating conduction, switch tube Alternating conduction corresponds to state 1 and state 2 in the mathematical model; when When the four-switch converter is in E-Boost mode, , switch tube Alternating conduction, switch tube Alternating conduction corresponds to state 3 and state 1 in the mathematical model; when When the four-switch converter is in Boost mode, , switch tube Alternating conduction, switch tube conduction, switch tube Shutdown, corresponding to state 3 and state 1 in the mathematical model; Among them, the switch tube The duty cycle of the switch tube The duty cycle of .

[0011] Optionally, the relationship between the theoretical inductor current and the theoretical output current of the four-switch converter is: ; Where, is the theoretical inductor current, is the theoretical output current.

[0012] Optionally, the discrete mathematical model in the Buck mode is: ; The discrete mathematical model in the Boost mode is: ; The discrete mathematical model in the E-Buck mode is: ; The discrete mathematical model in the E-Boost mode is: ; Where, is the sampling period, For the switch tube The variable duty cycle predicted in the discrete mathematical model is recorded as , are the duty cycle, output voltage, and input voltage at the current moment, respectively. is the inductor current and duty cycle at the next moment.

[0013] Optionally, selecting a target switching mode corresponding to a discrete mathematical model that minimizes the deviation of the predicted actual inductor current relative to the theoretical inductor current includes: With the goal of minimizing the deviation of the actual inductor current of the four-switch converter relative to the theoretical inductor current, an objective function corresponding to each discrete mathematical model is constructed. Constraints are set such that the cost function value of the duty cycle affected by the dead zone is positive infinity and the actual inductor current is less than or equal to the preset inductor current. The objective function is solved to obtain a discrete mathematical model when the objective function value is minimum, and the corresponding switching mode is used as the target switching mode.

[0014] Optionally, the objective function and constraints are: ; Where, is the objective function value under four switching modes, is the objective function value of the minimum duty cycle constraint, is the objective function value of the overcurrent protection constraint, The maximum current allowed by the system.

[0015] An embodiment of the present invention further provides a mode control system for a four-switch converter, comprising: an output current determination module, for obtaining the pulse load current required when the pulse load frequency changes, and using the pulse load current as the theoretical output current of the four-switch converter; a switch state determination module, configured to establish a mathematical model according to the topology of the four-switch converter and determine the switch states of the four-switch converter in four different switching modes using the mathematical model and a ratio between the output voltage and the input voltage of the four-switch converter; an inductor current determination module, configured to determine a relationship between a theoretical inductor current and a theoretical output current of the four-switch converter according to the switching state in each switching mode, and to determine the theoretical inductor current of the four-switch converter based on the relationship between the theoretical inductor current and the theoretical output current and the theoretical output current; A model discretization module is used to discretize the mathematical model to form a discrete mathematical model of the four-switch converter in each switching mode. The discrete mathematical model is used to predict the actual inductor current and the actual duty cycle of the switch tube of the four-switch converter in the corresponding switching mode; The mode control module is used to select the target switching mode corresponding to the discrete mathematical model with the smallest deviation of the predicted actual inductor current relative to the theoretical inductor current, and use the corresponding predicted actual duty cycle of the switch tube to control the four-switch converter to switch to the target switching mode.

[0016] The mode control method of the four-switch converter provided by the present invention has at least the following beneficial effects: By utilizing a mathematical model established for a four-switch converter, the theoretical inductor current of the four-switch converter is determined. The mathematical model is then discretized into discrete mathematical models for each switching mode to predict the actual inductor current and the actual duty cycle of the switch tube at a given moment in each switching mode. This allows the switching mode corresponding to the discrete mathematical model with the smallest deviation between the predicted actual inductor current and the theoretical inductor current to be selected for mode switching, accurately tracking the theoretical inductor current required by pulsed loads. This reduces output current mutations during mode switching and improves output current stability. Furthermore, by controlling mode switching based on the predicted actual duty cycle of the switch tube, smooth and rapid switching of the switching modes of the four-switch converter can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] One or more embodiments are exemplarily described by the figures in the corresponding drawings, and these exemplified descriptions do not constitute limitations on the embodiments.

[0018] Figure 1is a schematic diagram of a multi-element hybrid power system provided according to an embodiment of the present invention; Figure 2 is a schematic diagram of a dynamic phase of a pulse load provided according to an embodiment of the present invention; Figure 3 is a flow chart of a mode control method for a four-switch converter provided according to an embodiment of the present invention; Figure 4 is a flow chart for calculating a pulse load current according to an embodiment of the present invention; Figure 5 1 is a schematic diagram of a topological structure of a four-switch converter provided according to an embodiment of the present invention; Figure 6 is a schematic diagram of a mode control method for a four-switch converter provided according to an embodiment of the present invention; Figure 7 1 is a schematic diagram of simulation results when pulse load amplitudes are the same, provided according to an embodiment of the present invention; Figure 8 1 is a schematic diagram of simulation results when pulse load amplitudes are different according to an embodiment of the present invention. DETAILED DESCRIPTION

[0019] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, it will be understood by those skilled in the art that in the embodiments of the present invention, many technical details are provided to enable the reader to better understand the present invention. However, even without these technical details and the various changes and modifications based on the following embodiments, the technical solutions claimed in the present invention can be implemented. The division of the following embodiments is for convenience of description and should not constitute any limitation on the specific implementation of the present invention. The various embodiments can be combined with each other and referenced to each other under the premise that there is no contradiction.

[0020] One embodiment of the present invention relates to a mode control method for a four-switch converter, namely a four-switch Buck-Boost converter. The implementation details of the mode control method for the four-switch converter of this embodiment are specifically described below. The following content is only the implementation details provided for ease of understanding and is not necessary for implementing this solution.

[0021] The specific process of the mode control method of the four-switch converter in this embodiment is as follows: Figure 3 As shown, including: Step 301 : Obtain the pulse load current required when the pulse load frequency changes, and use the pulse load current as the theoretical output current of the four-switch converter.

[0022] Specifically, the calculation method of pulse load current can refer to Figure 4 , which includes four main detection or control units, namely pulse detection unit, energy feedback detection unit and storage capacitor Charge and discharge control unit. For the pulse detection unit, by With the set current threshold ( Represents constant load current and pulse current peak) to achieve comparison: When the capacitor discharge control unit is entered, Enter the energy feedback detection unit; for the capacitor discharge unit, by comparing the supercapacitor voltage and capacitor voltage minimum Implementation: When When the pulse load current ,in is the pulsating power distribution ratio of the active capacitor, when When the load is cut off; the energy feedback detection unit is used to detect Is it greater than 0 and enter the capacitor charging unit; in the capacitor charging unit, by comparing and the maximum value of the capacitor voltage Implementation: If and hour ,like and hour ,like and hour ,like and hour .

[0023] The output current of the four-switch converter is With pulse load current The relationship is as follows. Therefore, in this embodiment, the pulse load current is used as the theoretical output current of the four-switch converter: .

[0024] Step 302 : Establish a mathematical model based on the topology of the four-switch converter, and determine the switching states of the four-switch converter in four different switching modes based on the mathematical model and the ratio between the output voltage and the input voltage of the four-switch converter.

[0025] Specifically, the topology of the four-switch converter is as follows: Figure 5 As shown, based on this, the mathematical model of the four-switch converter is established as follows: ; Where, is the inductor, for The inductor current at time is the total stray resistance of the inductor current path, It is the switch tube of the Buck unit in the four-switch converter. is the switch tube of the Boost unit, and It is the main switch tube of the Buck unit. It is the main switch tube of the Boost unit.

[0026] The ratio between the inductor current and the output current of the four-switch converter (i.e., the voltage gain) is: ; Where, Switching tube duty cycle.

[0027] by For the switch tube The maximum duty cycle allowed, For the switch tube The minimum duty cycle allowed, the switching states of the four-switch converter in four different switching modes are as follows: when When the four-switch converter is in Buck mode, , switch tube Alternating conduction, switch tube conduction, switch tube Shutdown, corresponding to state 1 and state 2 in the mathematical model; when When the four-switch converter is in E-Buck mode, , switch tube Alternating conduction, switch tube Alternating conduction corresponds to state 1 and state 2 in the mathematical model; when When the four-switch converter is in E-Boost mode, , switch tube Alternating conduction, switch tube Alternating conduction corresponds to state 3 and state 1 in the mathematical model; when When the four-switch converter is in Boost mode, , switch tube Alternating conduction, switch tube conduction, switch tube Shutdown, corresponding to state 3 and state 1 in the mathematical model; Among them, the switch tube The duty cycle of the switch tube The duty cycle of .

[0028] Step 303: Determine the relationship between the theoretical inductor current and the theoretical output current of the four-switch converter according to the switching state in each switching mode, and determine the theoretical inductor current of the four-switch converter through the relationship between the theoretical inductor current and the theoretical output current and the theoretical output current.

[0029] The relationship between the theoretical inductor current and the theoretical output current of a four-switch converter is: ; Where, is the theoretical inductor current, is the theoretical output current.

[0030] Step 304 : discretize the mathematical model to form a discrete mathematical model of the four-switch converter in each switching mode. The discrete mathematical model is used to predict the actual inductor current and the actual duty cycle of the switch tube of the four-switch converter in the corresponding switching mode.

[0031] Specifically, based on the mathematical model of the four-switch converter, the discrete mathematical models under the four switching modes are derived using the state space averaging method to predict the actual inductor current and the actual duty cycle of the switch tube in each switching mode. The concept of deadbeat control is used to predict the key control variables (i.e., the switching tube Duty cycle ) to make the instantaneous value of the inductor current equal to the theoretical value:

[0032] .

[0033] Then, the discrete mathematical model in Buck mode, that is, the prediction model is: ; The prediction model in Boost mode is: ; The prediction model in E-Buck mode is: ; The prediction model in E-Boost mode is: ; Where, is the sampling period, For the switch tube The duty cycle, are the duty cycle, output voltage, and input voltage at the current moment, respectively. is the inductor current and duty cycle at the next moment, and the variable duty cycle predicted by the model is recorded as , which facilitates the setting of the second minimum duty cycle constraint function value in the subsequent objective function.

[0034] Step 305 : Select the target switching mode corresponding to the discrete mathematical model with the smallest deviation of the predicted actual inductor current relative to the theoretical inductor current, and use the corresponding predicted actual duty cycle of the switch to control the four-switch converter to switch to the target switching mode.

[0035] Specifically, with the goal of minimizing the offset of the actual inductor current of the four-switch converter relative to the theoretical inductor current, an objective function corresponding to each discrete mathematical model is constructed, and constraints are set such that the cost function value of the duty cycle affected by the dead zone is positive infinity and the actual inductor current is less than or equal to the preset inductor current; the objective function is solved to obtain the discrete mathematical model with the minimum objective function value, and the corresponding switching mode is used as the target switching mode to achieve mode switching.

[0036] In the specific implementation, the objective function is designed for the three control objectives of the maximum deviation of the inductor current trajectory from the theoretical value during the switching cycle of the four-switch converter, the minimum duty cycle constraint, and the cycle-by-cycle overcurrent protection constraint. The objective function and constraints are as follows: ; Where, is the objective function value under four switching modes, is the objective function value of the minimum duty cycle constraint, is the objective function value of the overcurrent protection constraint, The maximum current allowed by the system.

[0037] Among them, the first constraint aims to give priority to the combination that is closer to the theoretical value of the inductor current, so as to reduce the core loss and improve the efficiency of the converter; the second constraint sets the cost function value of the duty cycle affected by the dead zone to positive infinity, making this state impossible to be selected; the third constraint sets the cost function value of the inductor current exceeding the maximum current to positive infinity to ensure that the inductor current does not exceed the maximum limit, thereby ensuring the normal operation of the system.

[0038] In one embodiment, the mode control method of the four-switch converter of the present invention can be achieved by Figure 6 The control block diagram shown is used to implement: S1, obtains the load current when the pulse load frequency changes; S2, model the four-switch converter and obtain the switch states and output voltages in the four switching modes With input voltage Voltage gain; S3, get the theoretical value of inductor current in four modes The theoretical value of the output current relationship; S4, derive the prediction model of the four-switch converter and design the objective function.

[0039] Simulations of this four-switch converter mode control method were conducted in MATLAB / Simulink to verify its effectiveness. All simulations were performed with the four-switch converter operating under pulsed load conditions. Key controller parameters used in the simulations included a bus voltage of 270V and a converter input voltage of 500V.

[0040] First, verify the case where the pulse load amplitude changes are the same. Figure 7 As shown in Figure 2, the output current of the four-switch converter can still track the theoretical current well during mode switching.

[0041] Then we verified the situation of different pulse load amplitude changes. Figure 8 As shown in Figure 2, the output current of the four-switch converter can still track the theoretical current well during mode switching.

[0042] The steps of the above methods are divided only for clarity of description. When implemented, they can be combined into one step or some steps can be split and decomposed into multiple steps. As long as they include the same logical relationship, they are all within the scope of protection of the present invention.

[0043] Another embodiment of the present invention relates to a mode control system for a four-switch converter. The following describes implementation details of the mode control system for the four-switch converter of this embodiment. The following content is provided only for ease of understanding and is not essential for implementing this solution. The mode control system for the four-switch converter of this embodiment includes: an output current determination module, for obtaining the pulse load current required when the pulse load frequency changes, and using the pulse load current as the theoretical output current of the four-switch converter; a switch state determination module, configured to establish a mathematical model according to the topology of the four-switch converter and determine the switch states of the four-switch converter in four different switching modes using the mathematical model and a ratio between the output voltage and the input voltage of the four-switch converter; an inductor current determination module, configured to determine a relationship between a theoretical inductor current and a theoretical output current of the four-switch converter according to the switching state in each switching mode, and to determine the theoretical inductor current of the four-switch converter based on the relationship between the theoretical inductor current and the theoretical output current and the theoretical output current; A model discretization module is used to discretize the mathematical model to form a discrete mathematical model of the four-switch converter in each switching mode. The discrete mathematical model is used to predict the actual inductor current and the actual duty cycle of the switch tube of the four-switch converter in the corresponding switching mode; The mode control module is used to select the target switching mode corresponding to the discrete mathematical model with the smallest deviation of the predicted actual inductor current relative to the theoretical inductor current, and use the corresponding predicted actual duty cycle of the switch tube to control the four-switch converter to switch to the target switching mode.

[0044] It is not difficult to find that this embodiment is a system embodiment corresponding to the above-mentioned method embodiment, and this embodiment can be implemented in conjunction with the above-mentioned method embodiment. The relevant technical details and technical effects mentioned in the above-mentioned embodiment are still valid in this embodiment, and to reduce repetition, they are not repeated here. Accordingly, the relevant technical details mentioned in this embodiment can also be applied to the above-mentioned embodiment.

[0045] It is worth noting that all modules involved in this embodiment are logical modules. In actual applications, a logical unit can be a physical unit, a part of a physical unit, or a combination of multiple physical units. In addition, to highlight the innovations of the present invention, this embodiment does not include units that are not closely related to solving the technical problems proposed by the present invention. However, this does not mean that other units do not exist in this embodiment.

[0046] Those skilled in the art will appreciate that the above-described embodiments are specific embodiments for implementing the present invention, and that in actual applications, various changes in form and detail may be made thereto without departing from the spirit and scope of the embodiments of the present invention. Any person skilled in the art may make various changes and modifications without departing from the spirit and scope of the embodiments of the present invention. Therefore, the scope of protection of the embodiments of the present invention shall be subject to the scope defined in the claims.

Claims

1. A mode control method for a four-switch converter, characterized in that: include: Obtaining the pulse load current required when the pulse load frequency changes, and using the pulse load current as the theoretical output current of the four-switch converter; A mathematical model is established according to the topological structure of the four-switch converter, and the switching states of the four-switch converter in four different switching modes are determined by using the mathematical model and the ratio between the output voltage and the input voltage of the four-switch converter; Determine the relationship between the theoretical inductor current and the theoretical output current of the four-switch converter according to the switching state in each switching mode, and determine the theoretical inductor current of the four-switch converter through the relationship between the theoretical inductor current and the theoretical output current and the theoretical output current; Discretizing the mathematical model to form a discrete mathematical model of the four-switch converter in each switching mode, wherein the discrete mathematical model is used to predict an actual inductor current and an actual duty cycle of the switch tube of the four-switch converter in the corresponding switching mode; The target switching mode corresponding to the discrete mathematical model with the smallest deviation of the predicted actual inductor current relative to the theoretical inductor current is selected, and the actual duty cycle of the corresponding predicted switch tube is used to control the four-switch converter to switch to the target switching mode.

2. The mode control method of the four-switch converter according to claim 1, wherein: The mathematical model is: ； Where, is the inductor, for The inductor current at time is the total stray resistance of the inductor current path, It is the switch tube of the Buck unit in the four-switch converter. is the switch tube of the Boost unit, and It is the main switch tube of the Buck unit. It is the main switch tube of the Boost unit.

3. The mode control method of the four-switch converter according to claim 2, wherein: The ratio between the output voltage and input voltage of the four-switch converter is: ； Where, Switching tube Duty cycle; by For the switch tube The maximum duty cycle allowed, For the switch tube The minimum duty cycle allowed, the switching states of the four-switch converter in four different switching modes are as follows: when When the four-switch converter is in Buck mode, , switch tube Alternating conduction, switch tube conduction, switch tube Shutdown, corresponding to state 1 and state 2 in the mathematical model; when When the four-switch converter is in E-Buck mode, , switch tube Alternating conduction, switch tube Alternating conduction corresponds to state 1 and state 2 in the mathematical model; when When the four-switch converter is in E-Boost mode, , switch tube Alternating conduction, switch tube Alternating conduction corresponds to state 3 and state 1 in the mathematical model; when When the four-switch converter is in Boost mode, , switch tube Alternating conduction, switch tube conduction, switch tube Shutdown, corresponding to state 3 and state 1 in the mathematical model; Among them, the switch tube The duty cycle of the switch tube The duty cycle of .

4. The mode control method of the four-switch converter according to claim 3, wherein: The relationship between the theoretical inductor current and the theoretical output current of the four-switch converter is: ； Where, is the theoretical inductor current, is the theoretical output current.

5. The mode control method of the four-switch converter according to claim 4, wherein: The discrete mathematical model in the Buck mode is: ； The discrete mathematical model in the Boost mode is: ； The discrete mathematical model in the E-Buck mode is: ； The discrete mathematical model in the E-Boost mode is: ； Where, is the sampling period, For the switch tube The variable duty cycle predicted in the discrete mathematical model is recorded as , are the duty cycle, output voltage, and input voltage at the current moment, respectively. is the inductor current and duty cycle at the next moment.

6. The mode control method of the four-switch converter according to claim 5, wherein: The selecting of the target switching mode corresponding to the discrete mathematical model that minimizes the deviation of the predicted actual inductor current relative to the theoretical inductor current includes: With the goal of minimizing the deviation of the actual inductor current of the four-switch converter relative to the theoretical inductor current, an objective function corresponding to each discrete mathematical model is constructed. Constraints are set such that the cost function value of the duty cycle affected by the dead zone is positive infinity and the actual inductor current is less than or equal to the preset inductor current. The objective function is solved to obtain a discrete mathematical model when the objective function value is minimum, and the corresponding switching mode is used as the target switching mode.

7. The mode control method of the four-switch converter according to claim 6, wherein: The objective function and constraints are: ； Where, is the objective function value under four switching modes, is the objective function value of the minimum duty cycle constraint, is the objective function value of the overcurrent protection constraint, The maximum current allowed by the system.

8. A mode control system for a four-switch converter, characterized in that: include: an output current determination module, for obtaining the pulse load current required when the pulse load frequency changes, and using the pulse load current as the theoretical output current of the four-switch converter; a switch state determination module, configured to establish a mathematical model according to the topology of the four-switch converter and determine the switch states of the four-switch converter in four different switching modes using the mathematical model and a ratio between the output voltage and the input voltage of the four-switch converter; an inductor current determination module, configured to determine a relationship between a theoretical inductor current and a theoretical output current of the four-switch converter according to the switching state in each switching mode, and to determine the theoretical inductor current of the four-switch converter based on the relationship between the theoretical inductor current and the theoretical output current and the theoretical output current; A model discretization module is used to discretize the mathematical model to form a discrete mathematical model of the four-switch converter in each switching mode. The discrete mathematical model is used to predict the actual inductor current and the actual duty cycle of the switch tube of the four-switch converter in the corresponding switching mode; The mode control module is used to select the target switching mode corresponding to the discrete mathematical model with the smallest deviation of the predicted actual inductor current relative to the theoretical inductor current, and use the corresponding predicted actual duty cycle of the switch tube to control the four-switch converter to switch to the target switching mode.

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