A control method for a four-switch buck-boost converter

Abstract

The present invention discloses a control method for a four-tube buck-boost converter, which belongs to the technical field of power generation, transformation or distribution. The present invention adopts a four-stage control method, which divides the load range into two sections and adopts different control strategies according to the critical load value corresponding to the optimal control. In the Boost mode, before the critical load, the load is kept constant. T 1 , T 2 constant, T 3 To achieve the minimum value of soft switching, T 4 As the load increases, it decreases; when it reaches the critical load, T 4 Drop to 0; after critical load, T 1 、 T 2 、T 3 、 T As the load increases. In Buck mode, before the critical load, keep T 2 , T 3 constant, T 1 To achieve the minimum value of soft switching, T 4 As the load increases, it decreases; when it reaches the critical load, T 4 Drop to 0; after critical load, T 1 、 T 2 、 T 3 、 T The present invention achieves low loss within the full load range by regulating the control quantities in four dimensions.

Description

Technical Field

[0001] The invention discloses a control method for a four-tube buck-boost converter, relates to a DC-DC converter technology of an electric energy conversion device, and belongs to the technical field of power generation, power transformation or power distribution. Background Art

[0002] With the advancement of various electronic products, DC power supplies are developing towards technical requirements such as higher efficiency, higher integration, and a wider input range. Currently, the dual-mode modulation scheme widely used in buck-boost DC-DC converters enables efficient voltage conversion under different operating conditions. However, when the input voltage approaches the output voltage, the presence of a dead zone causes increased voltage ripple and large inductor current ripple, leading to instability. Furthermore, during the dual-mode modulation process, one switch will always be unable to achieve soft start, which fails to improve converter efficiency.

[0003] As a common-mode buck-boost converter, the four-switch buck-boost converter has advantages such as a wide input range and bidirectional power flow, making it widely used in various applications. The quadrilateral inductor current control method is a control strategy that achieves zero-voltage switching (ZVS) of the power switches in the four-switch buck-boost converter over the full load range. The principle of the quadrilateral inductor current control method is to ensure that positive and negative inductor currents coexist within a cycle, thereby achieving ZVS of all power switches. However, since positive and negative inductor currents coexist within a cycle, the RMS value of the inductor current increases, and conduction losses also increase. To reduce the RMS value of the inductor current, some control methods operate the four-switch converter in critical conduction mode at all times, eliminating the inductor current holding phase of quadrilateral control. This increases the energy transfer ratio within a cycle, thereby reducing the RMS value of the inductor current. However, this efficiency optimization method is not effective at low loads. There are also some optimized quadrilateral inductor current control methods that take conduction loss as the optimization target and propose a fixed-frequency control method to adjust the four-stage duration of the converter. This fixed-frequency control method requires the calculation of the effective value of the inductor current, which is complex to calculate. In addition, this fixed-frequency control method ignores the impact of turn-off loss and drive loss on the working efficiency of the converter. Therefore, this fixed-frequency control method has limited effect on improving the efficiency of the converter.

[0004] In summary, prior art buck-boost converter control methods fail to optimize efficiency across the full load range, and low converter efficiency persists under certain operating conditions. During converter operation, the conduction, turn-off, and drive losses of the switching transistors constitute the vast majority of circuit losses. Reducing these losses is crucial for improving the stable operation of the switching devices, the conversion efficiency of the circuit topology, and the safety of the operating environment. This present invention proposes an improved quadrilateral inductor current control method for a four-transistor buck-boost converter. Summary of the Invention

[0005] The object of the present invention is to address the deficiencies of the above-mentioned background technology and provide a control method for a four-tube buck-boost converter. The method takes into account conduction loss, turn-off loss, and drive loss, takes the duration of the first three stages of quadrilateral current control and the operating frequency of the converter as control variables, establishes a loss analysis, determines the relationship between the loss and the control variable, and obtains a control method to achieve lower loss. Ultimately, the purpose of reducing the loss of the four-tube buck-boost converter and converting the voltage with high efficiency within the full load range is achieved, solving the technical problem that the existing quadrilateral inductor current control technology cannot control the four-tube buck-boost converter to convert the voltage with high efficiency within the full load range.

[0006] The present invention adopts the following technical solutions to achieve the above-mentioned purpose:

[0007] The present invention utilizes a control signal generator to achieve efficient full-load control of a four-tube buck-boost converter consisting of a first switching tube, a second switching tube, a third switching tube, a fourth switching tube, and an inductor. In the four-tube buck-boost converter, the first and second switching tubes are connected in series to form a first bridge arm, the third and fourth switching tubes are connected in series to form a second bridge arm, the inductor is connected between the midpoint of the first bridge arm and the midpoint of the second bridge arm, the input voltage source is connected between the drain of the first switching tube and the primary ground, and the port between the third switching tube and the secondary ground constitutes the converter output. The voltage at the converter output port is equivalent to the output voltage source. The primary-side inductor node is the midpoint of the first bridge arm, denoted as point a, and the secondary-side inductor node is the midpoint of the second bridge arm, denoted as point b. The positive direction of the inductor current is defined as from a to b.

[0008] The present invention controls four switching tubes to make the converter work in four stages within one working cycle:

[0009] Inductor charging stage: When the fourth switch tube is turned on and the second switch tube is turned off, the inductor charging stage begins. The reverse inductor current charges the junction capacitance between the first and second switch tubes, causing the voltage at the primary side inductor node to increase and eventually reach the input voltage, allowing the first switch tube to achieve zero voltage conduction. Energy is transferred from the input voltage source to the inductor. The magnitude of the inductor current is proportional to the time of this stage. The duration of the inductor charging stage is T 1 When the fourth switch is turned off, this phase ends.

[0010] Energy transfer phase: The fourth switch is turned off, and the inductor current begins to charge the junction capacitance between the third and fourth switches. When the voltage at the secondary inductor node increases to the output voltage, the third switch achieves zero voltage conduction, and energy is directly transferred from the input voltage source to the converter output port. The inductor current slope in this phase is determined by the difference between the input voltage and the output voltage. This phase ends when the first switch is turned off. The duration of the energy transfer phase is T 2 .

[0011] Inductor discharge phase: When the first switch is turned off, the junction capacitance between the first and second switches discharges into the inductor, causing the voltage at the primary inductor node to drop to 0. The second switch then conducts at zero voltage, and the energy stored in the inductor is transferred to the converter output port. This phase ends when the third switch is turned off. The duration of the inductor discharge phase is T 3 .

[0012] Inductor current holding stage: As soon as the third switch is turned off, the junction capacitance between the third and fourth switches discharges into the inductor, causing the voltage at the secondary inductor node to drop to 0. The fourth switch then achieves zero voltage conduction, and both ends of the inductor L are connected to ground. Therefore, the inductor current remains constant during this stage. This stage ends when the second switch is turned off. The duration of the inductor current holding stage is T 4 .

[0013] In the above circuit and working mode, in order to reduce losses and improve efficiency, the RMS value of the inductor current should not be too high. This requires reducing the difference between the maximum and minimum inductor currents in the same cycle. At the same time, in order to take into account the soft switching of all switches, it is necessary to ensure that the inductor currents in the inductor charging stage and the inductor discharging stage are the minimum values for achieving soft switching. Therefore, when the load is low and the circuit has not entered the continuous conduction mode, the inductor charging stage and the inductor discharging stage have a minimum working time limit. T 1_min , T 3_min .when V in < V out When in Boost mode, T 3 To achieve the minimum value of soft switching; when V in > V out In Buck mode, it is necessary to always keep T 1 To achieve the minimum value for soft switching.

[0014] Under the premise of realizing soft switching of all power switches, in order to achieve loss reduction in the full load range, the present invention will establish a loss model to find the control method corresponding to the minimum loss, that is, to find the control method corresponding to the minimum loss. T 1 、 T 2 、 T 3 and cycle T Therefore, first set the operating frequency f Set it as a variable, under the same input voltage, calculate the loss corresponding to different load currents in each cycle, draw the loss curve, and calculate the frequency value corresponding to the minimum loss under the same input voltage and different load currents f_ best Then we explore the relationship between the optimal frequency value and the load current, and get the optimal frequency under the same input voltage. f_ best As the load increases, it shows a trend of first increasing and then decreasing. The optimal frequency is f_ best The load current corresponding to the maximum value is the critical load under the input voltage.

[0015] The present invention adopts a current mode control circuit, which includes a voltage outer loop and a current inner loop. The sampling circuit collects information of input voltage, output voltage and load, and obtains the critical load value under the working condition according to the sampled input voltage. Then, according to different loads, the control signal generator generates corresponding information related to the input voltage, output voltage and load current value. T 1 、 T 2 、 T 3 and cycle T The specific control methods are as follows:

[0016] At critical load, the circuit efficiency reaches the highest, and the four-tube buck-boost converter works in continuous conduction mode. In Boost mode, T 3 Keep to the minimum value to achieve ZVS, T 2 Calculated by the energy formula, T 1 for i L When the value reaches 0, T 4 0. In Buck mode: T 1 Keep to the minimum value to achieve ZVS, T 2Calculated by the energy formula, T 3 for i L When the value reaches 0, T 4 is 0.

[0017] Under other load conditions, for T 1 、 T 2 、 T 3 、 T 4 and cycle T The control is described below.

[0018] Boost mode: When the load current is lower than the critical load, the operating frequency f It increases linearly with the load current, maintaining T 1 、T 2 、T 3 Take the value for the critical load location, that is, T 3 To achieve the minimum value of ZVS, T 2 is the value calculated according to the energy formula, T 1 for iL When the value reaches 0, it only decreases T 4 When the load current is higher than the critical load, the operating frequency f It has a quadratic decreasing relationship with the load current, and is determined according to different input conditions so that the current in each working cycle T 1 、T 2 、T 3 As the load current increases, the linear coefficient, under the same input conditions T 1 、T 2 、T 3 It has a linear growth relationship with the load current with different coefficients to meet the output conditions.

[0019] Buck mode: When the load current is lower than the critical load, the operating frequency f It increases linearly with the load current, maintaining T 1 、T 2、T 3 Take the value for the critical load location, that is, T 1 To achieve the minimum value of ZVS, T 2 is the value calculated according to the energy formula, T 3 for iL When the value reaches 0, it only decreases T 4 When the load current is higher than the critical load, the operating frequency f It has a quadratic decreasing relationship with the load current, and is determined according to different input conditions so that the current in each working cycle T 1 、T 2 、T 3 As the load increases, the linear coefficient, under the same input conditions T 1 、T 2 、T 3 It has a linear growth relationship with the load current with different coefficients to meet the output conditions.

[0020] The present invention adopts the above technical solution and has the following beneficial effects:

[0021] (1) The control method of the four-tube buck-boost converter proposed in the present invention uses the working time and frequency of the four stages of the converter as control variables, adjusts the working time of the inductor charging stage and the inductor discharging stage under the critical load condition, increases the working frequency and reduces the working time of the inductor current holding stage based on the real-time load under the condition below the critical load, and reduces the frequency and increases the working time of the inductor charging stage, energy transmission stage, and inductor discharging stage based on the real-time load under the condition above the critical load, and takes the minimum total loss including conduction loss, turn-off loss, and driving loss as the goal of optimizing the working mode of the four-tube buck-boost converter, not only realizes the soft switching of all power tubes of the four-tube buck-boost converter within the full load range, but also reduces various losses of the four-tube buck-boost converter within the full load range, thereby achieving the invention purpose of efficiently converting voltage.

[0022] (2) The present invention selects the four-stage working time and frequency of the converter reflecting the conduction loss, turn-off loss and driving loss as the control variables. When the real-time load reaches the critical load, the converter is controlled to have a fixed frequency and meet the ZVS control. When the real-time load does not reach the critical load or exceeds the critical load, the converter is controlled to have a variable frequency and meet the ZVS control. Compared with the traditional fixed-frequency control method, this method has the advantage of improving the converter efficiency and power density within the full load range. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the circuit diagram of the four-tube buck-boost converter.

[0024] Figure 2 (a) and Figure 2 (b) are the operating waveforms of the four-tube buck-boost converter under the four-stage current control mode in Boost mode and Buck mode.

[0025] Figure 3 This is a graph showing how the loss changes with frequency under different input conditions.

[0026] Figure 4 The waveform diagram shows the frequency corresponding to the minimum loss under various input conditions changing with load.

[0027] FIG5( a ) is a flow chart of controlling a four-tube buck-boost converter according to the present invention, and FIG5( b ) and FIG5( c ) are flow charts of algorithms for generating control signals in Boost mode and Buck mode respectively.

[0028] Figure 6 For example, the load condition is less than the critical load condition. As the load increases, the cycle T And the waveform diagram of the changes in working time in each stage.

[0029] Figure 7 For example, the load is greater than the critical load condition. As the load increases, the cycle T And the waveform diagram of the changes in working time in each stage.

[0030] Explanation of the numbers in the figure: S1~S4 are the first to fourth switch tubes, L is the inductor, Cin is the input capacitance, Co is the output capacitor. DETAILED DESCRIPTION

[0031] The technical solution of the invention is described in detail below with reference to the accompanying drawings.

[0032] like Figure 1 As shown, the four-tube buck-boost converter consists of a first switch tube S1, a second switch tube S2, a third switch tube S3, a fourth switch tube S4, an inductor L The switch tube drive signal generated by the four-tube buck-boost converter control method is generated by a control signal generator. The first switch tube S1 and the second switch tube S2 are connected in series to form the first bridge arm, and the input capacitor is connected between the two terminals of the first bridge arm. Cin The third switch tube S3 and the fourth switch tube S4 are connected in series to form a second bridge arm, and an output capacitor is connected between the two terminals of the second bridge arm. Co , the inductor L is connected between the midpoint a of the first bridge arm and the midpoint b of the second bridge arm, and the input voltage source VinConnected between the drain of the first switch tube S1 and the primary ground, the third switch tube S3 and the secondary ground form the converter output port, the converter output port output voltage Vo Equivalent to a current source connected to the output port Io , the inductor current is defined as i L , the positive direction of the inductor current is from a to b. The control method proposed in the present invention enables the four-tube buck-boost converter to operate in four working stages as shown in FIG2 .

[0033] Inductor charging stage: When the fourth switch tube S4 is turned on and the second switch tube S2 is turned off, the inductor charging stage begins. The reverse inductor current charges the junction capacitance between the first switch tube S1 and the second switch tube S2. V a Increase to eventually reach V in , so that the first switch tube S1 can realize zero voltage switching and conduction, and the energy is transferred from the input voltage source V in Transferred to the inductor L, the inductor current i L The size of is proportional to the time of this stage. The duration of the inductor charging stage is T 1 When the fourth switch tube S4 is turned off, this phase ends.

[0034] Energy transfer stage: When the fourth switch S4 is turned off, the inductor current i L Start charging the junction capacitance between the third switch tube S3 and the fourth switch tube S4, so that V b Increase reach V o When the third switch tube S3 is turned on by zero voltage switching, the energy is directly taken from the input voltage source. V in Transfer to V o The inductor current slope in this phase is determined by the difference between the input voltage and the output voltage. When the first switch S1 is turned off, this phase ends. The duration of the energy transfer phase is T 2 .

[0035] Inductor discharge stage: When the first switch tube S1 is turned off, the junction capacitance between the first switch tube S1 and the second switch tube S2 discharges to the inductor L, so that V a When the voltage drops to 0, the second switch S2 realizes zero voltage conduction, and the energy stored in the inductor is transferred to the output. When the third switch S3 is turned off, this stage ends. The duration of the inductor discharge stage is T3 .

[0036] Inductor current holding stage: When the third switch tube S3 is turned off, the junction capacitance between the third switch tube S3 and the fourth switch tube S4 discharges to the inductor L, so that V b When the voltage of the inductor is reduced to 0, the fourth switch tube S4 realizes zero voltage conduction, and both ends of the inductor L are connected to the ground. Therefore, the inductor current remains constant during this stage. When the second switch tube S2 is turned off, this stage ends. The duration of the inductor current holding stage is T 4 .

[0037] The high efficiency control method of the present invention in the full load range is to establish a loss model of the four-tube buck-boost converter and adjust the operating frequency to f Set as a variable, calculate the loss corresponding to the same input voltage and different load current in each cycle, and draw the loss curve, such as Figure 3 As shown. As the load current changes, there is a frequency value corresponding to the minimum loss. The frequency value corresponding to the minimum loss point under the input voltage is extracted, and the relationship between frequency and load current is drawn, as shown in Figure 4 As shown. Figure 4 It can be seen that under the same input voltage, as the load current increases, the optimal frequency value first increases and then decreases. There is a maximum frequency value. The load corresponding to the maximum frequency is taken as the critical load under the input voltage.

[0038] The present invention uses the working time of the four working stages of the four-tube buck-boost converter T 1， T 2， T 3， T 4 and cycle T A loss model is established by considering conduction loss, turn-off loss, and drive loss as variables. A loss curve is obtained for each input voltage and load condition. The frequency value corresponding to the low point of each loss curve is taken. For the optimal frequency under each input condition, the load corresponding to the maximum value of the optimal frequency is taken as the critical load under that operating condition. The load current value is detected by the voltage outer loop. Based on the critical load value, the load range of the four-switch converter is divided into two stages and different control methods are implemented to achieve a control method for high-efficiency voltage conversion over the full load range, as shown in Figures 5(a), 5(b), and 5(c).

[0039] Phase 1: When the load current reaches the critical load value, the circuit efficiency is the highest. Under this load condition, the four-tube buck-boost converter works in continuous conduction mode. T3 Keep to the minimum value to achieve ZVS, T 2 Calculated by the energy formula, T 1 for i L When the value reaches 0, T 4 0. In Buck mode: T 1 Keep to the minimum value to achieve ZVS, T 2 Calculated by the energy formula, T 3 for i L When the value reaches 0, T 4 is 0.

[0040] Phase 2: Under other load conditions, the duration and cycle changes of each working phase are summarized as follows:

[0041] In Boost mode, when the load current is less than the critical load I1 When the load current Io The increase in working time and working cycle of each stage T The changing process of Figure 6 As shown, the operating frequency f With load I O The relationship can be expressed as: f=kI O +q ,Keep T 3 To achieve the minimum value of soft switching while maintaining T 1 , T 2 No change, only reduced T 4 When the load current is greater than the critical load I1 Under the condition of load current increasing, the working time and working cycle of each stage T The changing process of Figure 7 As shown, this solution makes the operating frequency f by f=a 1 I O 2 +d 1 I O +c 1The relationship decreases with the load current and makes T 1 by T 1 =k 1 I O +b 1 relationship, and T 2 by T 2 =k 2 I O +b 2 , T 3 by T 3 =k 3 I O +b 3 As the load current increases ( k,q,k 1 ,k 2 ,k 3 ,b 1 ,b 2 ,b 3 , a 1 ,d 1 ,c 1 is the corresponding constant related to the input condition in Boost mode).

[0042] In Buck mode, when the load current is less than the critical load, the Io The increase in working time and working cycle of each stage T The changing process of Figure 6 As shown, the operating frequency f With load I O The relationship can be expressed as: f=mI O + nb ,Keep T 1 To achieve the minimum value of soft switching while maintaining T 2 ,T 3 No change, only reduced T 4 When the load current is greater than the critical load I1 Under the condition of T The changing process of Figure 7 As shown, this solution makes the operating frequency f by f=a 2 I O 2 +d 2 I O +c 2 The relationship decreases with load and makes T 1 by T 1 =m 1 I O +n 1 relationship, and T 2 by T 2 =m 2 I O +n 2 , T 3 by T 3 =m 3 I O +n 3 As the load current increases ( m,n,m 1 ,m 2 ,m 3 ,n 1 ,n 2 ,n 3 ,a 2, d 2, c 2 is the corresponding constant related to the input condition in Buck mode).

[0043] Compared to the fixed-frequency control method, the control method for the four-tube buck-boost converter proposed in this invention improves the converter's voltage conversion efficiency by more than 10% below the critical load range and by approximately 15% above the critical load range. This shows that the control method proposed in this invention not only improves the efficiency of the four-tube buck-boost converter over the full load range but also significantly improves its voltage conversion efficiency across different load ranges.

[0044] The above embodiments are only for illustrating the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A control method for a four-tube buck-boost converter, characterized in that: When the real-time load current of the four-tube buck-boost converter reaches the critical load under the current input voltage, the duration of the inductor charging phase and the duration of the inductor discharging phase are adjusted according to the principle of minimizing the soft switching time of each switch tube in the converter. The duration of the energy transfer phase is calculated according to the energy formula, and the duration of the inductor current holding phase is adjusted to zero. When the real-time load current of the four-tube buck-boost converter does not reach the critical load under the current input voltage, the operating frequency is increased according to the linear increasing relationship between the operating frequency and the real-time load current, the inductor charging phase duration, the energy transfer phase duration, and the inductor discharge phase duration are kept at the values at the critical load, and the inductor current holding phase duration is reduced. When the real-time load current of the four-tube buck-boost converter exceeds the critical load at the current input voltage, the operating frequency is reduced according to the quadratic decreasing relationship between the operating frequency and the real-time load, and the linear growth coefficients of the inductor charging phase duration, the energy transfer phase duration, and the inductor discharging phase duration in each working cycle are determined according to the real-time input voltage; Among them, the method for determining the critical load is: with the goal of minimizing the total loss including conduction loss, turn-off loss, and driving loss, a model is established to describe the relationship between the loss and frequency of the four-tube buck-boost converter under different input voltages, the operating frequency when the loss is lowest under different input voltages is obtained under the obtained model, the relationship between the operating frequency when the loss is lowest under different input voltages and the load current is fitted, and the load current corresponding to the highest frequency point under the same input voltage is used as the critical load under the input voltage. The specific method for establishing the model to describe the relationship between the loss and frequency of the four-tube buck-boost converter under different input voltages is: setting the operating frequency as a variable, solving the loss corresponding to different load currents under the same input voltage in each cycle, and drawing the loss curve of the four-tube buck-boost converter corresponding to different load currents under the same input voltage.

2. The control method of a four-tube buck-boost converter according to claim 1, characterized in that: When the four-tube buck-boost converter operates in Boost mode, the specific method for adjusting the duration of the inductor charging phase and the duration of the inductor discharging phase according to the principle of minimizing the soft switching time of each switch tube in the converter is as follows: adjusting the duration of the inductor discharging phase to the shortest time for each switch tube in the converter to achieve soft switching, and adjusting the inductor charging phase to end when the inductor current crosses the zero point.

3. The control method of a four-tube buck-boost converter according to claim 1, characterized in that: When the four-tube buck-boost converter operates in Buck mode, the specific method for adjusting the duration of the inductor charging phase and the duration of the inductor discharging phase according to the principle of minimizing the soft switching time of each switch tube in the converter is as follows: adjusting the duration of the inductor charging phase to the shortest time for each switch tube in the converter to achieve soft switching, and adjusting the inductor discharging phase to end when the inductor current crosses the zero point.

4. The control method of a four-tube buck-boost converter according to claim 1, wherein: When the four-tube buck-boost converter operates in the Boost mode, the linearly increasing coefficient and the quadratic decreasing coefficient are constants related to the input voltage in the Boost mode.

5. The control method of a four-tube buck-boost converter according to claim 1, characterized in that: When the four-tube buck-boost converter operates in Buck mode, the linearly increasing coefficient and the quadratic decreasing coefficient are constants related to the input voltage in Buck mode.

6. The control method of a four-tube buck-boost converter according to claim 1, characterized in that: When the four-tube buck-boost converter operates in Boost mode, the linear growth coefficients of the inductor charging phase duration, the energy transfer phase duration, and the inductor discharge phase duration in each working cycle are constants related to the input voltage in Boost mode, and the linear growth coefficients of the inductor charging phase duration, the energy transfer phase duration, and the inductor discharge phase duration in each working cycle are not equal.

7. The control method of a four-tube buck-boost converter according to claim 1, characterized in that: When the four-tube buck-boost converter operates in Buck mode, the linear growth coefficients of the inductor charging phase duration, the energy transfer phase duration, and the inductor discharge phase duration in each working cycle are constants related to the input voltage in Buck mode, and the linear growth coefficients of the inductor charging phase duration, the energy transfer phase duration, and the inductor discharge phase duration in each working cycle are not equal.

8. A control signal generator for a control method of a four-tube buck-boost converter, characterized in that: The invention comprises a voltage acquisition circuit, a current acquisition circuit, and a controller, wherein the voltage acquisition circuit acquires the real-time input voltage and real-time output voltage of the four-tube buck-boost converter, the current acquisition circuit acquires the real-time load current of the four-tube buck-boost converter, and the controller generates a drive signal for each switch tube in the four-tube buck-boost converter according to the real-time input voltage, real-time output voltage, and real-time load current of the four-tube buck-boost converter in accordance with the method described in any one of claims 1 to 7.

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