A table-free closed-loop control method for four-switch buck-boost converter with optimal variable line

Abstract

The application discloses a table-free closed-loop control method of a four-switch Buck-Boost converter with an optimal variable load line, and belongs to the technical field of power generation, power transformation or power distribution. The method comprises an optimal variable load line control strategy, a driving signal trigger strategy and a quadrilateral inductor current modulation strategy. The optimal variable load line control strategy accurately calculates the time parameters of the quadrilateral inductor current meeting the soft switching condition in a given switching frequency range, the driving signal trigger strategy compensates the time parameters of the quadrilateral inductor current in each switching period to keep the minimum value of the quadrilateral inductor current at a given value, and the quadrilateral inductor current modulation strategy generates the driving signal of the switch in each switching period, so that the soft switching can be realized and the effective value of the quadrilateral inductor current is minimum in the full load range.

Description

TECHNICAL FIELD

[0001] The application discloses a non-table lookup closed-loop control method of a four-switch Buck-Boost converter with an optimal variable load line, relates to power electronic technology, and belongs to the technical field of power generation, power transformation or power distribution. BACKGROUND

[0002] In the field of photovoltaic energy storage, bidirectional non-isolated converters play an important role, and a four-switch Buck-Boost converter has comprehensive advantages compared with other non-isolated DC-DC converters, for example, the voltage and current stress of four switch tubes of the four-switch Buck-Boost converter is low, bidirectional voltage conversion can be realized, passive inductance and capacitance elements are few, the voltage and current polarities of input and output are the same, control variables are many, and a control method can be flexible and changeable.

[0003] In traditional four-switch Buck-Boost converter control, a multi-mode control method of three modes or four modes is mostly used, and there is a problem of switching in different modes. A four-edge inductance current modulation method proposed in 2013 solves the mode switching problem in multi-mode control, but in closed-loop control, continuous three-dimensional data is converted into discrete table data and stored in the memory of an MCU, so that the requirement of closed-loop control on the memory is increased, control cost is increased, and at the present stage, the method based on the four-edge inductance current modulation is realized based on frequency conversion, frequent frequency conversion leads to an increase in system control difficulty and an increase in the design difficulty of a front-stage EMC circuit. In addition, the existing four-edge inductance current modulation method cannot realize the minimum four-edge inductance current effective value in a full load range.

[0004] The application aims to propose a non-table lookup closed-loop control method of a four-switch Buck-Boost converter with an optimal variable load line to overcome the above defects. SUMMARY

[0005] The application aims to propose a non-table lookup closed-loop control method of a four-switch Buck-Boost converter with an optimal variable load line to overcome the above defects.

[0006] The application adopts the following technical scheme to solve the technical problems:

[0007] The four-switch Buck-Boost converter with optimal variable load line method for table-free closed-loop control comprises:

[0008] The optimal variable load line control strategy takes the minimum RMS value of the quadrangular inductor current as the control target in the frequency range determined by the maximum and minimum values of the set switching frequency, and calculates the time parameter of the quadrangular inductor current according to the peak value of the quadrangular inductor current in the frequency range on the premise that the time parameter of the quadrangular inductor current is clamped at a value meeting the zero voltage switching condition.

[0009] The drive signal triggering strategy compares the inductor current sampling value with the minimum value of the given inductor current, and compensates the inductor discharge phase duration parameter and the inductor current maintaining phase duration parameter calculated by the optimal variable load line control strategy according to the comparison result; and,

[0010] The quadrangular inductor current modulation strategy generates the drive signals of the four switches according to the inductor charging phase duration parameter, the energy transmission phase duration parameter, and the inductor discharge phase duration parameter and the inductor current maintaining phase duration parameter compensated by the drive signal triggering strategy.

[0011] As a further optimization scheme of the four-switch Buck-Boost converter with optimal variable load line method for table-free closed-loop control, when the four-switch Buck-Boost converter works in the Buck mode, the optimal variable load line control strategy takes the minimum RMS value of the quadrangular inductor current as the control target in the frequency range determined by the maximum and minimum values of the set switching frequency, and calculates the time parameter of the quadrangular inductor current according to the peak value of the quadrangular inductor current in the frequency range on the premise that the inductor charging phase duration parameter is clamped at a value meeting the zero voltage switching condition.

[0012] As a further optimization scheme of the four-switch Buck-Boost converter with optimal variable load line method for table-free closed-loop control, when the four-switch Buck-Boost converter works in the Boost mode, the optimal variable load line control strategy takes the minimum RMS value of the quadrangular inductor current as the control target in the frequency range determined by the maximum and minimum values of the set switching frequency, and calculates the time parameter of the quadrangular inductor current according to the peak value of the quadrangular inductor current in the frequency range on the premise that the inductor discharge phase duration parameter is clamped at a value meeting the zero voltage switching condition.

[0013] As a further optimization scheme of the table-free closed-loop control method of the four-switch Buck-Boost converter with the optimal variable load line, the inductor charging phase duration parameter is clamped at a value meeting the zero voltage switching condition, specifically: the inductor charging phase duration parameter is clamped at the minimum inductor charging phase duration or the minimum inductor charging phase duration meeting the zero voltage switching condition.

[0014] As a further optimization scheme of the table-free closed-loop control method of the four-switch Buck-Boost converter with the optimal variable load line, the inductor charging phase duration parameter is clamped at a value meeting the zero voltage switching condition, specifically: the inductor charging phase duration parameter is clamped at the minimum inductor charging phase duration or the minimum inductor charging phase duration meeting the zero voltage switching condition.

[0015] As a further optimization scheme of the table-free closed-loop control method of the four-switch Buck-Boost converter with the optimal variable load line, the inductor charging phase duration parameter is clamped at a value meeting the zero voltage switching condition, specifically: the inductor charging phase duration parameter is clamped at the minimum inductor charging phase duration or the minimum inductor charging phase duration meeting the zero voltage switching condition.

[0016] In the first stage, the converter operates at the maximum set switching frequency, and the inductor charging phase duration parameter is clamped at a value meeting the zero voltage switching condition, then T1=(2*I ZVS )*L / V in , T2=(V pi -I zvs )*L / (V in -V out ), T`3=(V pi +I zvs )*L / V out , T`4=1 / f max -T1-T2-T`3, wherein T1 is the inductor charging phase duration parameter, T2 is the energy transfer phase duration parameter, T3′ is the inductor discharging phase duration parameter, T′4 is the inductor current holding phase duration parameter, I zvs is the maximum value of the given inductor current, L is the inductance of the inductor in the converter, V in is the input voltage of the converter, V pi is the peak value of the quadrilateral inductor current, V out is the output voltage of the converter, and f max is the maximum set switching frequency.

[0017] In the second stage, the converter works at a set maximum switching frequency, and the inductor charging phase duration parameter is clamped at a value meeting the zero voltage switching condition; the inductor charging phase duration parameter, the energy transmission phase duration parameter, the inductor discharging phase duration parameter and the stage 1 value are the same, and the inductor current maintaining phase duration parameter is zero,

[0018] In the third stage, the converter working frequency is reduced, and the inductor charging phase duration parameter is clamped at a value meeting the zero voltage switching condition; T1=(2*I ZVS )*L / V in , T2=(V pi -I zvs )*L / (V in -V out ), f is a working frequency,

[0019] In the fourth stage, the converter working frequency is reduced to a set minimum switching frequency, and a value meeting the zero voltage switching condition is lifted; the inductor charging phase duration parameter is clamped at a minimum inductor charging phase duration meeting the zero voltage switching condition after being lifted, T'4=0, I a_const and I b_const are respectively a maximum value of the inductor current at the T1 end time when the converter working frequency reaches the set minimum switching frequency and a maximum value of the inductor current at the T'3 start time.

[0020] As a further optimization scheme of the four-switch Buck-Boost converter without table lookup closed-loop control method with an optimal variable load line, in the fourth stage, the expression of the minimum inductor charging phase duration meeting the zero voltage switching condition after being lifted is: Wherein, ΔIa is a lifting amount of the inductor current at the T1 end time, and ΔIb is a lifting amount of the inductor current at the T'3 start time.

[0021] As a further optimization scheme of the four-switch Buck-Boost converter without table lookup closed-loop control method with an optimal variable load line, the acquisition method of the quadrilateral inductor current peak value is: comparing an output voltage sampling value and an output voltage reference value, and performing PI regulation on the comparison result.

[0022] As a further optimization scheme of the four-switch Buck-Boost converter without table lookup closed-loop control method with an optimal variable load line, the inductor current at the start time of the inductor discharging phase duration parameter after compensation of the driving signal trigger strategy is equal to the minimum value of the given inductor current.

[0023] The present application has the following beneficial effects by adopting the above technical scheme:

[0024] (1)Cost advantage: Compared with the ordinary quadrilateral inductance current modulation, the control method does not need to query the three-dimensional table to obtain the four time parameters of the quadrilateral inductance current, the memory requirement of the MCU is lower, and the cost is reduced.

[0025] (2) Performance advantage: Compared with the ordinary quadrilateral inductance current modulation, the closed-loop control method proposed in the application accurately calculates the quadrilateral inductance current time parameters that meet the soft switching condition in the given switching frequency range through the optimal variable load line control strategy, compensates the quadrilateral inductance current time parameters in each switching cycle through the drive signal trigger strategy to keep the minimum value of the quadrilateral inductance current in the specified power range at a given value, and generates the drive signal of the switch tube in each switching cycle in the specified power range through the quadrilateral inductance current modulation strategy. In the full load range, soft switching can be realized, the effective value of the quadrilateral inductance current is minimized, the operating loss is reduced, and the efficiency is better.

[0026] (3) Easy to integrate: The control method does not need external injection signal, and the small range variable frequency control is friendly to the design of the front-stage EMC circuit. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a block diagram of a non-table lookup closed-loop control method of a four-switch Buck-Boost converter with an optimal variable load line proposed by the application.

[0028] Figure 2 is a quadrilateral inductance current waveform diagram of the four-switch Buck-Boost converter in the Buck mode.

[0029] Figure 3 is a quadrilateral inductance current waveform diagram of the four-switch Buck-Boost converter in the Boost mode.

[0030] Figure 4 is a flowchart of the control method proposed by the application.

[0031] Figure 5 is a schematic diagram of the optimal variable load line control strategy proposed by the application.

[0032] Figure 6 is a quadrilateral inductance current waveform diagram under the closed-loop control method proposed by the application.

[0033] Figure 7 is a quadrilateral inductance current waveform diagram after the variable load line is lifted I a .

[0034] Figure 8 T3 is an analog circuit part of the drive trigger circuit.

[0035] Figure 9 The digital circuit part of the T3 drive trigger circuit.

[0036] Figure 10 A relationship diagram of the quadrilateral inductance current effective value and the inductance charging phase duration parameter T1.

[0037] Explanation of the figure labels: S1, first switch tube, S2, second switch tube, S3, third switch tube, S4, fourth switch tube, L, inductance, C O , output filter capacitor, R L , load. DETAILED DESCRIPTION

[0038] The present application proposes a four-switch Buck-Boost converter without lookup table closed-loop control method with optimal variable load circuit. In order to make the purpose, technical scheme and effect of the present application more clear and explicit, the present application will be further described in detail below with reference to the accompanying drawings.

[0039] In view of the problems existing in the existing lookup table control method, the present application proposes a four-switch Buck-Boost converter without lookup table closed-loop control method with optimal variable load circuit as shown in the figure. Figure 1 The four-switch Buck-Boost converter includes: a first switch tube S1, a second switch tube S2, a third switch tube S3, a fourth switch tube S4, an inductance L, an output filter capacitor C O , a load R L , a first bridge arm composed of the first switch tube S1 and the second switch tube S2 in series connection is connected to an input voltage V in , a second bridge arm composed of the third switch tube S3 and the fourth switch tube S4 in series connection, the inductance L is connected between the midpoint of the first bridge arm and the midpoint of the second bridge arm, the output filter capacitor C O is connected in parallel across the second bridge arm, and the load R L is connected in parallel with the output filter capacitor C O .

[0040] The control method proposed by the present application performs PI operation on the difference between the output voltage V out and the given output voltage V ref , obtains a quadrilateral inductance current peak value V pi , the quadrilateral inductance current peak value V pi is I b in the Buck mode as shown in the figure Figure 2 , and is I a in the Boost mode as shown in the figure Figure 3 , follows the principle that the quadrilateral inductance current effective value is minimum in the load change process, and according to the quadrilateral inductance current peak value V pi , each time parameter meeting the soft switching condition can be obtained. Figure 4For the control flow chart of the method, the method is divided into digital control and analog control two parts, and the two parts are executed at the same time, and finally the driving signal generated according to the four-edge inductor current time parameters obtained by the digital control part and the analog control part is applied to the four switches in the four-switch Buck-Boost circuit. The method includes: optimal variable load circuit control strategy, driving signal trigger strategy and four-edge inductor current modulation strategy, and the control strategies of each part of the method are described below.

[0041] 1. Optimal variable load circuit control strategy

[0042] In most actual cases, the power P is in a variable range, which requires a discussion on how the four-edge inductor current changes within a certain power range to minimize its effective value. In the Buck mode, the optimal variable load circuit control strategy proposed is as shown in Figure 5 . Wherein Figure 5 There are four stages 1-4, which correspond to powers P1, P2, P3 and P4, respectively. The power of the four stages is P1 min <P2 max <P3 s <P4. During the process of increasing the load power, the frequency will also increase, and the change of the frequency is not conducive to the design and operation of the circuit, and the wider the frequency change, the more difficult it will be to design the front-end EMC circuit. Therefore, under the premise of ensuring that the effective value of the four-edge inductor current is minimized within a certain power range, the frequency is limited to a certain range [f min , f max ]. Wherein f s is the switching frequency, f max is the maximum value of the set switching frequency, and f min is the minimum value of the set switching frequency. This variable load circuit can keep the four-edge inductor current minimum in the wide power range of the FSBB converter and limit the change of the frequency to a certain extent to ensure stability.

[0043] In order to ensure the stability of the output voltage, PI control is required, in which the detected output voltage is compared with the set output voltage value, and the comparison value is considered as the peak value V pi of the four-edge inductor current after PI operation, as shown in Figure 6 . Wherein when T4 is not equal to 0, the four time parameters can be calculated by the following formula, corresponding to stage 1 in the optimal variable load circuit control strategy:

[0044] T1 = (2*I ZVS )*L / V in

[0045] T2 = (V pi -I zvs )*L / (V in -V out

[0046] T`3 = (V pi + I zvs )*L / V out

[0047] T`4 = 1 / f max -T1-T2-T`3

[0048] The inductance charging phase duration parameter T1, the energy transmission phase duration parameter T2, the inductance discharging phase duration parameter T'3 in the optimal variable load line control strategy phase 2 are the same as in phase 1, and the inductance current maintaining phase duration parameter T'4 = 0.

[0049] In the optimal variable load line control strategy phase 3, T1 maintains the optimal soft switching condition, and the power requirement is met by reducing the frequency, at this time, the three time parameters and the frequency can be obtained by the following formula:

[0050] T1 = (2*I ZVS )*L / V in

[0051] T2 = (V pi -I zvs )*L / (V in -V out )

[0052] T`3 = (V pi + I zvs )*L / V out

[0053]

[0054] In the optimal variable load line control strategy phase 4, the frequency has reached the minimum value, so it is necessary to lift the optimal soft switching clamp value, as shown in the following formula: Figure 7 T1 is greater than T 1_s at this time. The lifting relationship can be obtained through plane geometry, I a_const and I b_const are the maximum inductance current at the end of T1 and the maximum inductance current at the beginning of T3' when the frequency reaches the minimum value.

[0055]

[0056] The three time parameters in phase 4 can be calculated by the following formula:

[0057]

[0058] The above formulas are obtained in Buck mode, and Boost mode is similar, which is not described here. Since the logic is negative feedback, Vpi will be stable to the peak value of the corresponding quadrilateral inductor current.

[0059] 2. Drive signal trigger strategy

[0060] Since the above analysis is in the ideal case, and does not take into account the loss of the system, when the system has a certain loss, if the input power is fixed, the power delivered to the output side will decrease, resulting in a decrease in output voltage, that is, other equilibrium will be reached in open loop, which will result in the minimum value of the quadrilateral inductor current may not remain at -I zvs . In order to guarantee the minimum value of the quadrilateral inductor current and the soft switching of the switch tube, that is, the inductor current should be at -I zvs when T3 is turned on, the comparator circuit shown in Figure 8 can be used to amplify and compare the detected inductor current with the given -I zvs , and obtain the decision result Ti zvs whether the inductor current is equal to the minimum value of the quadrilateral inductor current -I L , through the drive signal trigger circuit shown in Figure 9 , combined with T3', T4' obtained by the optimal variable load circuit control strategy and the decision result Ti L , T3 and T4 are obtained, and the compensation waveform of the drive signal of the third switch tube S3 and the fourth switch tube S4 can be obtained according to T3 and T4, which can guarantee that the minimum value of the quadrilateral inductor current will not be less than or greater than -I zvs , which can guarantee the soft switching characteristics of the switch tube and make the output voltage stable at the given value in closed loop control.

[0061] 3. Quadrilateral inductor current modulation strategy

[0062] For a given frequency of quadrilateral inductor current, the four time parameters in quadrilateral inductor current modulation can be solved by the following formula:

[0063] V in (T1+T2)=V o (T2+T3)

[0064]

[0065] T1+T2+T3+T4=T s

[0066] V o *T3=2*L*I x

[0067] By solving the four time parameters of the quadrilateral inductor current, the duty cycles of the two bridge arms are respectively: D1=(T1+T2) / T sD2 = (T2 + T3) / T s The phase shift time of the two bridge arms is T1. The waveform of the quadrilateral inductor current in Buck mode is as follows: Figure 2 As shown, the waveform in Boost mode is as follows Figure 3 As shown.

[0068] Through the reasoning of the above formula, the relationship between the quadrilateral inductor current and T1 is obtained as follows: Figure 10 As shown, the switching frequency f = 300kHz, the inductance L = 10uH, and the input voltage is V. in =270V.

[0069] like Figure 10 As shown, the three different lines represent the output voltage V. out The waveforms of the effective value of the quadrilateral inductor current at 160V, 270V, and 200V show that the smaller T1 is, the smaller the effective value of the quadrilateral inductor current will be. Figure 9 The dashed line represents the minimum T required to achieve soft switching. 1_s If T1 is less than T 1_s Therefore, soft switching cannot be achieved. In summary, in Buck mode, T1 is clamped in the minimum inductor charging phase duration T that satisfies the zero-voltage switching condition. 1_s Alternatively, T1 can be taken as the minimum value of the inductor charging phase duration T. 1_min This is an effective method to ensure the soft-switching boundary conditions while achieving the minimum effective value of the quadrilateral inductor current. In Boost mode, clamping T3 to the minimum inductor discharge stage duration T that satisfies the zero-voltage switching condition is achieved. 3_s Alternatively, T3 can be taken as the minimum value of the inductor discharge phase duration T. 3_min It is an effective method to ensure the boundary conditions of soft switching while achieving the minimum effective value of quadrilateral inductor current.

[0070] Therefore, the quadrilateral inductor current modulation strategy precisely controls the turn-on and turn-off times of the four switching transistors, so that the inductor current forms a quadrilateral trajectory in each switching cycle, effectively improving the power supply efficiency and power density while reducing switching losses and electromagnetic interference.

[0071] The above embodiments are merely illustrative of the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solutions based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A lookup-free closed-loop control method for a four-switch Buck-Boost converter with optimal load-changing lines, characterized in that, include: The optimal load-changing line control strategy, within a frequency range defined by the maximum and minimum values ​​of the set switching frequency, takes minimizing the effective value of the quadrilateral inductor current as the control objective. While clamping the quadrilateral inductor current time parameter to a value satisfying the zero-voltage switching condition, the quadrilateral inductor current time parameter is calculated based on the peak value of the quadrilateral inductor current within the frequency range. Specifically, this calculation involves the converter sequentially experiencing output power within the frequency range... P 1. P 2. P 3 and P The four stages of 4 P 1< P 2< P 3< P 4, In the first stage, the converter operates at the maximum set switching frequency, clamping the inductor charging stage duration parameter to a value that satisfies the zero-voltage switching condition. , , , ,in, T 1 represents the duration parameter of the inductor charging phase. T 2 represents the duration parameter of the energy transfer phase. This is a parameter representing the duration of the inductor discharge phase. This is a parameter representing the duration of the inductor current holding phase. I zvs Given the maximum value of the inductor current, L The inductance value of the inductor in the converter. V in The input voltage of the converter. V pi The peak current of the quadrilateral inductor is... V out The output voltage of the converter. f max To set the maximum switching frequency, In the second stage, the converter operates at the maximum value of the set switching frequency, clamping the inductor charging stage duration parameter to a value that satisfies the zero-voltage switching condition. Therefore, the inductor charging stage duration parameter, energy transfer stage duration parameter, and inductor discharging stage duration parameter are the same as in stage 1, while the inductor current holding stage duration parameter is zero. In the third stage, the converter's operating frequency decreases, clamping the inductor charging stage duration parameter to a value that satisfies the zero-voltage switching condition. , , , , , f For operating frequency, In the fourth stage, the converter's operating frequency is reduced to the minimum set switching frequency, the value satisfying the zero-voltage switching condition is raised, and the inductor charging stage duration parameter is clamped to the minimum inductor charging stage duration satisfying the zero-voltage switching condition after the raising. , , , , I a_const and I b_const When the converter operating frequency reaches the minimum value of the set switching frequency T 1. The maximum value of the inductor current at the end time. The maximum value of the inductor current at the initial moment; The drive signal triggering strategy compares the sampled inductor current value with the minimum value of the given inductor current, and compensates for the inductor discharge stage duration parameter and the inductor current holding stage duration parameter calculated by the optimal load change line control strategy based on the comparison result; and, The quadrilateral inductor current modulation strategy generates drive signals for four switching transistors based on the inductor charging phase duration parameters, energy transfer phase duration parameters calculated by the optimal variable load line control strategy, the inductor discharging phase duration parameters compensated by the drive signal triggering strategy, and the inductor current holding phase duration parameters.

2. The lookup-free closed-loop control method for a four-switch Buck-Boost converter with optimal load-changing lines according to claim 1, characterized in that, When the four-switch Buck-Boost converter operates in Buck mode, the optimal variable load line control strategy aims to minimize the effective value of the quadrilateral inductor current within the frequency range determined by the maximum and minimum values ​​of the set switching frequency. Under the premise of clamping the inductor charging stage duration parameter to a value that satisfies the zero-voltage switching condition, the quadrilateral inductor current time parameter is calculated based on the peak value of the quadrilateral inductor current within the frequency range.

3. The lookup-free closed-loop control method for a four-switch Buck-Boost converter with optimal load-changing lines according to claim 1, characterized in that, When the four-switch Buck-Boost converter operates in Boost mode, the optimal variable load line control strategy aims to minimize the effective value of the quadrilateral inductor current within the frequency range determined by the maximum and minimum values ​​of the set switching frequency. Under the premise of clamping the inductor discharge stage duration parameter to a value that satisfies the zero-voltage switching condition, the quadrilateral inductor current time parameter is calculated based on the peak value of the quadrilateral inductor current within the frequency range.

4. The lookup-free closed-loop control method for a four-switch Buck-Boost converter with optimal load-changing lines according to claim 2, characterized in that, The specific meaning of clamping the inductor charging phase duration parameter to a value that satisfies the zero-voltage switching condition is: clamping the inductor charging phase duration parameter to the minimum inductor charging phase duration or the minimum inductor charging phase duration that satisfies the zero-voltage switching condition.

5. The lookup-free closed-loop control method for a four-switch Buck-Boost converter with optimal load-changing lines according to claim 3, characterized in that, The specific meaning of clamping the inductor discharge stage duration parameter to a value that satisfies the zero-voltage switching condition is: clamping the inductor discharge stage duration parameter to the minimum value of the inductor discharge stage duration parameter or the minimum inductor discharge stage duration that satisfies the zero-voltage switching condition.

6. The lookup-free closed-loop control method for a four-switch Buck-Boost converter with optimal load-changing lines according to claim 1, characterized in that, In the fourth stage, the expression for the duration of the minimum inductance charging stage that satisfies the zero-voltage switching condition is: Where, Δ Ia for T 1. The increase in inductor current at the end, Δ Ib for The amount of inductor current rise at the initial moment.

7. The lookup-free closed-loop control method for a four-switch Buck-Boost converter with optimal load-changing lines according to any one of claims 1 to 6, characterized in that, The method for obtaining the peak current of the quadrilateral inductor is as follows: compare the output voltage sample value and the output voltage reference value, and perform PI adjustment on the comparison result.

8. The lookup-free closed-loop control method for a four-switch Buck-Boost converter with optimal load-changing lines according to any one of claims 1 to 6, characterized in that, The duration parameter of the inductor discharge phase after compensation by the drive signal triggering strategy is that the inductor current at the beginning of the phase is equal to the minimum value of the given inductor current.

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