Bidirectional DC / DC Converter Switching Control Method for Electric Vehicle Discharge System

Abstract

Bidirectional DC / DC converter switching control method for an electric vehicle discharging system, used to realize the operation of the electric vehicle's power battery driving the motor and the energy feedback of the motor. It includes the following steps: Step 1, establish a switching system model of the bidirectional DC / DC converter with the bidirectional BUCK / BOOST converter as an example; Step 2, based on the switching model established in Step 1, design a switching controller to achieve direct switching control of the bidirectional BUCK / BOOST converter; it has a control strategy that can achieve bidirectional energy flow control in the electric vehicle discharging system; the switching model can accurately describe the working process of the converter; the switching controller is simple and does not require a complex control parameter tuning process, can directly output the switch state, and does not require a complex pulse width modulation process; it is insensitive to circuit parameters and has the advantage of strong robustness when the circuit parameters are uncertain or change.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy, and particularly relates to a switching control method for a bidirectional DC / DC converter in an electric vehicle discharging system. Background Art

[0002] The discharging system of an electric vehicle transmits the energy in the battery to the driving motor through an electric energy conversion circuit, thereby driving the electric vehicle to run, and is a key component of the electric vehicle operation. Conducting modeling and control research on the power electronic converter that realizes energy conversion and control in the electric vehicle discharging system, so as to improve the efficiency, stability and performance of the electric vehicle discharging system, is the key to improving the performance such as the cruising range and acceleration ability of the electric vehicle.

[0003] Currently, in order to save the energy consumption of the power battery of the electric vehicle and increase the cruising range of the electric vehicle, the discharging system of the electric vehicle usually has a regenerative braking function, that is, to realize the bidirectional flow of energy in the electric vehicle discharging system. When the discharging system operates normally, the battery outputs energy to the motor to drive the electric vehicle to travel. When the electric vehicle is in the braking process, the discharging system recovers the energy generated by braking into the power battery, so as to achieve the purpose of increasing the cruising range. Here, it is necessary for the electric vehicle discharging system to adopt a DC / DC converter capable of realizing bidirectional power flow to realize the functions of battery energy release and motor energy recovery.

[0004] Bidirectional DC / DC represented by the bidirectional BUCK / BOOST converter is widely used in the electric vehicle discharging system. Studying the modeling and control strategy of the bidirectional DC / DC converter to improve the efficiency and performance of the converter has always been a research hotspot. Due to the existence of power switching devices, the power electronic converter is a typical non-linear system. The traditional modeling method for the DC / DC converter establishes a linearized model of the influence of the low-frequency changes of system states such as duty cycle, voltage and current on the converter by averaging the system states within one switching period and ignoring the switching frequency characteristics of the system, and designs a controller based on the linear system theory for the linearized model. Therefore, the traditional linearized modeling method cannot accurately describe the working state of the converter. The traditional DC / DC converter control method based on the model obtained by the traditional linearized modeling method can only achieve good performance near the system linear operating point, and has problems such as instability, low modeling and control accuracy when disturbances occur or the system working state changes. In addition, the duty cycle control scheme usually adopted by the traditional control method requires a complex vector modulation process. Summary of the Invention

[0005] In order to overcome the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a switching control method for a bidirectional DC / DC converter of an electric vehicle discharge system, and to establish a switching control method for a bidirectional DC / DC converter in an electric vehicle discharge system. The method regards the working state of the bidirectional BUCK / BOOST converter in different switching states as different subsystems, and realizes an accurate description of the converter working process by establishing a switching model of the bidirectional BUCK / BOOST converter. At the same time, a switching controller is designed based on the switching model, and the switching controller directly generates the switching rules function in different working modes. (Discharge, feedback) The switching state of the bidirectional BUCK / BOOST converter realizes direct switching control of the bidirectional BUCK / BOOST converter.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a bidirectional DC / DC converter switching control method of an electric vehicle discharge system, comprising the following steps:

[0007] Step 1, establish a bidirectional BUCK / BOOST converter switching model;

[0008] In step 1, a bidirectional BUCK / BOOST converter switching model is established as shown in the following formula:

[0009]

[0010] In formula (1), x(t) = [I L ,U c1 ,U c2 ] T is the system state variable, is the derivative of the system state variable x(t), t is the time variable; d / dt is the derivative function with respect to time; R 1 is the low voltage side load resistance; R 2 is the internal resistance of the motor; C 1 is the low voltage side capacitance; C 2 is the high-voltage side capacitor; L is the inductor; I L is the inductor current; U C1 Represents capacitance C 1 Voltage across the terminals, U C2 Represents capacitance C 2 Voltage across the two ends; U 1 Indicates the voltage on the power supply side; U 2 Represents the motor side voltage; S is the switch function, representing the switch S 1 , S 2 When S 1 On, S 2 When cut off, S = 1; when S 2 On, S 1At the cut-off, S = 0; Q is a function of the current direction, representing the energy flow direction in the bidirectional BUCK / BOOST converter circuit. When the inductor current is in the positive direction, i.e., working in the Boost mode, Q = 1, and when the inductor current is in the negative direction, i.e., working in the Buck mode, Q = 0; respectively represent the system state parameter matrix and the input parameter matrix under different S and Q values. Since there are 4 combinations of the parameters of S and Q, the matrix A i , b i has 4 matrix value states, that is, its subscript i = {1, 2, 3, 4},

[0011] Equations (1) and (2) together constitute the switching model of the bidirectional BUCK / BOOST converter established in the present invention. According to the different values of the switching function S and the current direction function Q in Equation (2), the working process of the bidirectional BUCK / BOOST converter is divided into 4 subsystems (i = {1, 2, 3, 4}). The specific method is as follows: when the current direction function Q of the bidirectional DC / DC converter is 1 and the switching function S = 0, it is subsystem 1; when the current direction function Q of the bidirectional DC / DC converter is 1 and the switching function S = 1, it is subsystem 2; when the current direction function Q of the bidirectional DC / DC converter is 0 and the switching function S = 0, it is subsystem 3; when the current direction function Q of the bidirectional DC / DC converter is 0 and the switching function S = 1, it is subsystem 4;

[0012] Step 2, establish the switching model of the bidirectional BUCK / BOOST converter;

[0013] In the said Step 2, the design process of the switching controller based on the switching model is as follows:

[0014] Establish the Lyapunov function V() of the bidirectional BUCK / BOOST converter as:

[0015] V(e(t)) = e(t) T Pe(t) > 0 (3)

[0016] where e(t) = [I L - I Lr , U C1 - U C1r , U C2 - U C2r T is the difference between the system state variable and the expected value; e(t) T represents the transpose of e(t); I Lr is the expected value of the inductor current I L ; U C1r is the expected value of the voltage U c1 ; U C2r is the voltage U c2The expected value; P is a positive definite matrix, selected as:

[0017]

[0018] It can be obtained from Equation (1) that the derivative of the Lyapunov function in Equation (3) is:

[0019]

[0020] where is the derivative of the system state; min i represents the minimum value under the condition of selecting subsystem i;

[0021] According to the Lyapunov stability theorem, the conclusion of Equation (5) satisfies the Lyapunov stability condition, that is, the subsystem i based on the bidirectional BUCK / BOOST converter switching model and with the minimum derivative of the Lyapunov function is stable. Further, a switching controller can be designed, that is, the switching rule is expressed as:

[0022]

[0023] where σ(t) is the switching rule function; represents the operation of taking the minimum average value among the subsystems i = {1, 2, 3, 4}. It can be seen from Equation (6) that by designing the switching rule, that is, selecting the switch function S corresponding to the subsystem state with the minimum calculation result of formula (6) to act on the bidirectional BUCK / BOOST converter in the next control cycle, the control of the bidirectional BUCK / BOOST converter can be realized.

[0024] The beneficial effects of the present invention are:

[0025] The present invention provides a switching control method for a bidirectional DC / DC converter of an electric vehicle discharge system, having the following beneficial effects: By establishing a switching model of a bidirectional BUCK / BOOST converter, the present invention realizes an accurate description of the working process of the converter under the condition of considering bidirectional energy flow; at the same time, since the working process of the bidirectional BUCK / BOOST converter is regarded as a switching process between different subsystems, under the analysis of the Lyapunov stability condition of the system, a switching rule is designed to realize the direct switching control of the bidirectional BUCK / BOOST converter between different subsystems, having the advantages of simple controller design process, fast response speed, no control parameters to be adjusted, the controller directly outputting the switching states of the converter power switches, and no need for a complex pulse width modulation process. In addition, since the switching controller designed for the bidirectional BUCK / BOOST converter in the present invention is generated by a switching rule based on the Lyapunov stability theorem, its control performance has insensitivity to circuit parameters and can still achieve satisfactory control performance under the conditions of unknown or changing circuit parameters, that is, the system has strong robustness. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 FIG. is a circuit topology diagram of the bidirectional BUCK / BOOST converter of the present invention.

[0027] Figure 2 FIG. is a simulation comparison diagram of the bidirectional BUCK / BOOST converter working in Boost mode by using the switching control method of the present invention and the traditional PI control method.

[0028] Figure 3 FIG. is a simulation comparison diagram of the bidirectional BUCK / BOOST converter working in Buck mode by using the switching control method of the present invention and the traditional PI control method.

[0029] Figure 4 FIG. is a comparison diagram of the battery-side voltage U when the bidirectional BUCK / BOOST converter switches from Boost mode to Buck mode by using the switching control method of the present invention and the traditional PI control method. 1 SIMULATION RESULT COMPARISON DIAGRAM

[0030] Figure 5 FIG. is a comparison diagram of the motor-side voltage U when the bidirectional BUCK / BOOST converter switches from Buck mode to Boost mode by using the switching control method of the present invention and the traditional PI control method. 2 SIMULATION RESULT COMPARISON DIAGRAM DETAILED DESCRIPTION OF THE INVENTION

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] A bidirectional DC / DC converter switching control method for an electric vehicle discharging system includes the following steps:

[0033] Step 1, establish a bidirectional BUCK / BOOST converter switching model. The specific method is as follows:

[0034] The topology of the bidirectional BUCK / BOOST converter is as Figure 1 shown. In the figure, S 1 and S 2 are fully controlled power switch devices, C 1 is the low-voltage side capacitor, C 2 is the high-voltage side capacitor, L is the energy storage inductor, U 1 represents the power supply side voltage; U 2 represents the motor side voltage.

[0035] In the electric vehicle battery discharging system, the power supply side voltage U 1 is connected to the electric vehicle power battery, and the motor side voltage U 2 is connected to the drive motor circuit. When the electric vehicle is working in the state of the battery outputting energy to drive the motor, the power supply side voltage U 1 provides energy for the inductor L after being regulated by the low-voltage side capacitor C 1 . Define the direction of the current flowing through the inductor as positive from left to right. Then when S 1 is off and S 2 is on, the power supply side voltage U 1 charges the inductor L, and the value of the current I L flowing through the inductor increases. When S 1 is on and S 2 is off, the inductor L discharges, and the power supply side voltage U 1 and the inductor L supply power to the output capacitor C 2 together. At this time, the value of the current I L flowing through the inductor decreases. After the above operations, the control that the motor side voltage value U 2 is greater than the power supply side voltage U 1 can be achieved. Therefore, it is called the Boost mode, characterized in that the inductor current I L is always greater than or equal to 0, and the power supply side provides energy to the motor side. When the electric vehicle is working in the state of the motor feeding back energy to the battery, the motor side voltage U 2Since the motor of an electric vehicle operates in the braking mode, energy will be generated and fed back to the battery. At this time, the voltage U on the motor side 2 After being regulated by the high-voltage side terminal capacitor C 2 and through controlling the power switching device S 1 and S 2 to supply power to the inductor L and the low-voltage side capacitor C 1 to achieve the energy feedback operation. Similarly, it is defined that the direction of the current flowing through the inductor is positive from left to right. Then when S 1 is turned on and S 2 is turned off, the voltage U on the motor side 2 supplies power to the inductor L and the low-voltage side capacitor C 1 . At this time, the inductor L is charged, and the value of the current I flowing through the inductor L increases, but its current direction is from right to left, and the inductor current is negative. When S 1 is turned off and S 2 is turned on, the inductor L forms a loop through the low-voltage side capacitor C 1 and the switching device S 2 . The inductor discharges to the low-voltage side capacitor C 1 . The value of the current I flowing through the inductor L decreases, but its current direction is from right to left, and the inductor current is also negative. After the above operations, the control that the voltage U on the power supply side 1 is less than the voltage value U on the motor side can be achieved. Therefore, it is called the Buck mode, which is characterized in that the inductor current I 2 is always less than or equal to 0, and the motor side provides energy to the power supply side.

[0036] For Figure 1 the bidirectional BUCK / BOOST converter shown below, establish its switching model as shown in the following formula:

[0037]

[0038] where x(t) = [I L , U c1 , U c2 T is the system state variable, is the derivative of the system state variable x(t), t is the time variable; d / dt is the function of taking the derivative with respect to time; I L is the inductor current; U C1 represents the voltage across the capacitor C 1 , U C2 represents the voltage across the capacitor C 2 ; S is the switching function. When S 1 is turned on and S 2 is turned off, S = 1. When S 2 is turned on and S 1When it is disconnected, S = 0; Q is a function of the current direction, representing the direction of the inductor current of the bidirectional BUCK / BOOST converter. When Q = 1, the bidirectional BUCK / BOOST converter operates in Boost mode. When Q = 0, the bidirectional BUCK / BOOST converter operates in Buck mode; respectively represent the system state parameter matrix and the input parameter matrix under different S and Q values. Since there are 4 combinations of the parameters S and Q, the matrix A i , b i has 4 matrix value states, that is, its subscript i = {1, 2, 3, 4}.

[0039] Equations (1) and (2) together constitute the switching model of the bidirectional BUCK / BOOST converter established in the present invention. If the bidirectional BUCK / BOOST converter operating under different switching functions and current directions is regarded as different subsystems, then according to the different values of the switching function S and the current direction function Q in equations (1) and (2), the working process of the bidirectional BUCK / BOOST converter is divided into 4 subsystems (i = {1, 2, 3, 4}), as shown in Table 1:

[0040] Table 1 Subsystem Division of Bidirectional BUCK / BOOST Converter

[0041]

[0042] Step 2, design a switching controller based on the switching model. The specific method is as follows:

[0043] To achieve the purpose of accurately switching the working state of the system by controlling the switch state S of the bidirectional BUCK / BOOST converter, the bidirectional BUCK / BOOST converter under the action of different switching functions S and current direction functions Q is regarded as different subsystems, and the direct switching control of the switch state S of the bidirectional BUCK / BOOST converter is realized by designing a switching controller; to ensure the stability of the bidirectional BUCK / BOOST converter during the switching of different switch states (subsystems), it is necessary to conduct a stability analysis on its switching process;

[0044] Define the system state error of the bidirectional BUCK / BOOST converter as e(t) = x(t) - x eq , where x(t) = [I L , U C1 , U C2 T is the system state variable, and x eq = [I Lr , U C1r , U C2r T is the expected value of the system state variable x(t); I Lris the expected value of the inductor current I L ; U C1r is the expected value of the voltage U c1 ; U C2r is the expected value of the voltage U c2 ; Select the Lyapunov function V() as:

[0045] V(e(t)) = e(t) T Pe(t) > 0(3)

[0046] where P is a positive definite matrix, selected as:

[0047]

[0048] Suppose there is a stable subsystem, and we can get A i x eq + b i = 0. Take the derivative of the Lyapunov function as

[0049]

[0050] where, is the derivative of the system state; min i means to select the minimum value under the condition of subsystem i;

[0051] According to the Lyapunov stability theorem, if it can be ensured that in equation (5) then the bidirectional BUCK / BOOST converter is stable when switching under different switch states S (subsystems).

[0052] It can be seen from equation (5) that since A i P + PA i < 0, so then That is, it satisfies the Lyapunov stability theorem. That is, for any time t > 0, at the switching rate the bidirectional BUCK / BOOST converter is stable.

[0053] To sum up, for the bidirectional BUCK / BOOST converter, design its switching controller, that is, the switching rule is:

[0054]

[0055] where, σ(t) is the switching rule function; means to take the operation of the minimum average value among the i = {1, 2, 3, 4} subsystems.

[0056] For the actual bidirectional BUCK / BOOST converter, when selecting the first subsystem, there is

[0057]

[0058] When the second subsystem is selected, there is

[0059]

[0060] When the third subsystem is selected, there is

[0061]

[0062] When the fourth subsystem is selected, there is

[0063]

[0064] If in equations (7)-(10), the calculation result σ of equation (7) 1 is less than σ 2 , σ 3 , σ 4 , then according to Table 1, select the next control cycle bidirectional BUCK / BOOST converter switch state function S = 0, that is, control Figure 1 the bidirectional BUCK / BOOST converter switch S 2 to conduct, S 1 to cut off, and work in the battery discharge (Buck) mode. Other situations can be obtained similarly according to the above conclusions.

[0065] Simulation and experimental verification:

[0066] According to the above switching control method of the bidirectional BUCK / BOOST converter, build a Matlab / Simulink simulation model to achieve simulation verification. The parameters of each component in the simulation are shown in Table 2:

[0067] Table 2 Simulation component parameters

[0068] Input filter inductance L = 1mH Low - voltage side capacitor <![CDATA[C 1 = 2400 μF]]> High - voltage side capacitor <![CDATA[C 2 = 1200 μF]]> Motor internal resistance <![CDATA[R 2 = 10 Ω]]> Low - voltage side load <![CDATA[R 1 = 1 Ω]]> Sampling frequency 50kHz

[0069] Figure 2 Fig. is the simulation comparison diagram of the bidirectional BUCK / BOOST converter working in the Boost mode using the switching control method of the present invention and the traditional PI control method. Let the voltage U 1 on the power supply side be 110 V, the target voltage U 2 on the motor side be 540 V, and the simulation time be 0.3 s. As Figure 2 can be seen, under the two control methods, the system boosts the voltage and reaches the target stable voltage before 0.05 s and remains stable thereafter. However, there are large voltage fluctuations in the traditional PI control, while the entire boosting process in the switching control is smooth and there is no severe jitter phenomenon, which can reflect the good dynamic performance of the switching control.

[0070] Figure 3 This is a simulation comparison diagram of a bidirectional BUCK / BOOST converter operating in Buck mode using the switching control method of the present invention and the traditional PI control method. Assume the voltage U on the motor side 2 is 540 volts, and the target voltage U on the power supply side 1 is 110 volts, and the simulation time is 0.3 seconds. As can be seen from Figure 3 , in the Buck step-down mode, the motor generates a high voltage as the power source. Under the traditional PI control, the stepped-down voltage reaches the steady state after 0.06 seconds of adjustment, and there is an overshoot during this period. In the switching control, the system reaches stability within 0.02 seconds, and there is no voltage fluctuation and overshoot during this period, indicating that the switching control has a small adjustment time and strong reliability.

[0071] Figure 4 This is a comparison diagram of the battery-side voltage U when the bidirectional BUCK / BOOST converter using the switching control method of the present invention and the traditional PI control method switches from Boost mode to Buck mode. Assume the total simulation time is 0.6 seconds. The system operates in Boost mode for the first 0.3 seconds, and the target voltage U on the motor side 1 is 540 volts. The system operates in Buck mode for the next 0.3 seconds, and the target is the voltage U on the power supply side 2 110 volts. As can be seen from 1 , when the system operating mode changes, under the traditional PI control, the system reaches the stable state after 0.15 seconds of adjustment, and there are multiple oscillations during this period; under the switching control, the system reaches the steady state after 0.1 second, and there is only one voltage mutation. Figure 4 It can be seen that when the system operating mode changes, under the traditional PI control, the system reaches the stable state after 0.15 seconds of adjustment, and there are multiple oscillations during this period; under the switching control, the system reaches the steady state after 0.1 second, and there is only one voltage mutation.

[0072] Figure 5 This is a comparison diagram of the motor-side voltage U when the bidirectional BUCK / BOOST converter using the switching control method of the present invention and the traditional PI control method switches from Buck mode to Boost mode. Assume the total simulation time is 0.6 seconds. The system operates in Buck mode for the first 0.3 seconds, and the target voltage U on the motor side 2 is 540 volts. The system operates in Boost mode for the next 0.3 seconds, and the target is the voltage U on the motor side 2 is 960 volts. As can be seen from 2 , when the system operating mode changes, under the traditional PI control, the motor-side voltage U Figure 5 has strong oscillation, its convergence speed is slow, and there is a steady-state error between the motor-side voltage U 2 at steady state and the expected value; under the switching control, the change process of the motor-side voltage U 2 is stable, the convergence speed is fast, and there is no steady-state error. 2 The change process of the motor-side voltage U is stable, the convergence speed is fast, and there is no steady-state error.

Claims

1. Bidirectional DC / DC converter switching control method for an electric vehicle discharge system, comprising the following steps: Step 1, establish a bidirectional BUCK / BOOST converter switching model; In said Step 1, the specific approach is: Use Equation (1) and Equation (2) to form a bidirectional BUCK / BOOST converter switching model, In formula (1), x(t) = [I L , U c1 , U c2 T is the system state variable, is the derivative of the system state variable x(t), t is the time variable; d / dt is the derivative function with respect to time; R 1 is the low-voltage side load resistance; R 2 is the motor internal resistance; C 1 is the low-voltage side terminal capacitor; C 2 is the high-voltage side terminal capacitor; L is the inductor; I L is the inductor current; U C1 represents the voltage across the capacitor C 1 , U C2 represents the voltage across the capacitor C 2 ; U 1 represents the power supply side voltage; U 2 represents the motor side voltage; S is the switch function, representing the combination of switches S 1 , S 2 . When S 1 is on and S 2 is off, S = 1; when S 2 is on and S 1 is off, S = 0; Q is the current direction function, representing the energy flow direction in the bidirectional BUCK / BOOST converter circuit. When the inductor current is in the positive direction, that is, when working in the Boost mode, Q = 1, and when the inductor current is in the negative direction, that is, when working in the Buck mode, Q = 0; respectively represent the system state parameter matrix and input parameter matrix under different S and Q values. Since there are 4 parameter combinations of S and Q, the matrix A i , b i has 4 matrix value states, that is, its subscript i = {1, 2, 3, 4},​ Equation (1) and (2) together constitute the established bidirectional BUCK / BOOST converter switching model; In said Step 1, according to different values of the switching function S and the current direction function Q, the operating process of the bidirectional BUCK / BOOST converter is divided into 4 subsystems (i = {1, 2, 3, 4}). The specific approach is: when the current direction function Q of the bidirectional DC / DC converter is 1 and the switching function S is 0, it is Subsystem 1; when the current direction function Q of the bidirectional DC / DC converter is 1 and the switching function S is 1, it is Subsystem 2; when the current direction function Q of the bidirectional DC / DC converter is 0 and the switching function S is 0, it is Subsystem 3; when the current direction function Q of the bidirectional DC / DC converter is 0 and the switching function S is 1, it is Subsystem 4; Step 2, design a switching controller based on the switching model.

2. The bidirectional DC / DC converter switching control method for an electric vehicle discharge system according to Claim 1, characterized in that in said Step 2, the specific approach is: Establish the Lyapunov function V() of the bidirectional BUCK / BOOST converter as: V(e(t)) = e(t) T Pe(t) > 0(3) where \(e(t)=[I L -I Lr ,U C1 -U C1r ,U C2 -U C2r T is the difference state between the system state variable and the expected value; \(e^T(t) T represents the transpose of \(e(t)\); \(I Lr is the expected value of the inductor current \(I L ; \(U C1r is the expected value of the voltage \(U c1 ; \(U C2r is the expected value of the voltage \(U c2 ; \(P\) is a positive definite matrix, chosen as:​ It can be obtained from Equation (1) that the derivative of the Lyapunov function in Equation (3) is as follows: wherein, is the derivative of the system state; min i represents selecting the minimum value under the condition of subsystem i; According to the Lyapunov stability theorem, the conclusion of Equation (5) satisfies the Lyapunov stability condition, that is, the subsystem i based on the bidirectional BUCK / BOOST converter switching model and having the minimum derivative of the Lyapunov function is stable. Further, a switching controller can be designed, that is, the switching rule is expressed as: where, σ(t) is the switching rule function; denotes the operation of taking the minimum average value among i = {1, 2, 3, 4} subsystems. As can be seen from Equation (6), by designing the switching rule, that is, selecting the switching function S corresponding to the state of the subsystem with the smallest calculation result of Formula (6) to act on the bidirectional BUCK / BOOST converter in the next control cycle, the control of the bidirectional BUCK / BOOST converter can be realized.

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