An adaptive frequency control strategy for four-switch buck-boost converter

Abstract

The application relates to the field of power electronics, in particular to an adaptive frequency conversion control strategy of a four-switch Buck-Boost converter, which comprises the following steps: the conduction time sequence of a switching tube is controlled, the direction of an inductor current is changed, and thus the zero-voltage turn-on of four power switching tubes is realized; the zero-voltage turn-on characteristics of VT1 and VT2 need to meet the condition that the inductor current is negative; under a light load working condition, the four-switch Buck-Boost converter works in a pseudo-inductor current discontinuous conduction state; under a heavy load working condition, the four-switch Buck-Boost converter works in a pseudo-inductor current continuous conduction state; when the input voltage is not equal to the output voltage, the critical current of the four-switch Buck-Boost converter under the light load working condition and the heavy load working condition can be obtained according to the lowest switching period. The control strategy can ensure that VT1, VT2, VT3 and VT4 work in the zero-voltage turn-on state in the full load range, further reduces the switching loss of the semiconductor device, and effectively compresses the variation range of the switching frequency. 1S 2S The switching frequency is effectively compressed.​

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, specifically to an adaptive frequency conversion control strategy for a four-switch Buck-Boost converter. Background Technology

[0002] In recent years, fields such as photovoltaic energy storage, on-board charging, and USB PD fast charging have placed demands on DC-DC converters for wide-range voltage conversion. Traditional Buck converters can only step down, and Boost converters can only step up; a single topology is insufficient to handle scenarios with large input voltage fluctuations. Although buck-boost can be achieved through cascading or reverse-polarity Buck-Boost topologies, these often suffer from issues such as inverted output voltage, numerous passive components, and large size. The four-switch Buck-Boost converter, as a non-isolated topology, can achieve buck-boost functionality with in-phase output, offering significant advantages over a wide input voltage range. However, in practical applications, this converter still faces challenges such as complex control strategies, easily fluctuating output voltage during mode switching, and difficulties in optimizing efficiency across the entire load range, hindering its widespread adoption in high-power-density scenarios.

[0003] Four-switch Buck-Boost converters can adapt to voltage conversion requirements over a wide input voltage range; however, the zero-voltage turn-on of their power switches leads to increased inductor current ripple, limiting energy conversion efficiency under high load current conditions. To address this issue and achieve soft switching of semiconductor devices under wide load current conditions, various efficiency optimization strategies have been proposed. Currently, efficiency optimization strategies for four-switch Buck-Boost converters mainly fall into two categories: fixed switching frequency control and variable switching frequency control. Fixed switching frequency control has certain advantages in applications with narrow load current ranges; however, in wide load current applications, it cannot simultaneously achieve high efficiency under heavy and light loads. Furthermore, high current output can easily lead to the loss of the zero-voltage turn-on characteristic of the power switches. Variable switching frequency control ensures zero-voltage turn-on of the power switches across the entire load range by controlling the switching frequency to decrease with increasing load, but this results in an excessively large switching frequency variation range, affecting the stable operation of the converter and hindering EMI circuit design. Summary of the Invention

[0004] To address the problems mentioned in the background section, the present invention provides the following technical solution.

[0005] To address the challenge of simultaneously achieving high converter efficiency, zero-voltage turn-on of all power switches, and a narrow switching frequency range in four-switch Buck-Boost converters operating over wide load current ranges, this invention provides an adaptive frequency conversion control strategy. This control strategy ensures that VT1 and VT2 can operate within a wide load current range.1S VT2, VT 2S Operating at zero voltage turn-on across the full load range further reduces switching losses in semiconductor devices; it also effectively compresses the frequency variation range, which helps improve the efficiency of the four-switch Buck-Boost converter.

[0006] An adaptive frequency conversion control strategy for a four-switch Buck-Boost converter is disclosed. The four-switch Buck-Boost converter includes a Buck arm, a power inductor, a Boost arm, and a filter circuit. The Buck arm includes power switches VT1 and VT2. 1S The Boost bridge arm includes the power switch VT. 2S And VT2; the filter circuit includes input filter capacitor C in and C o The drain of VT1 is connected to the positive terminal of the power supply, and the source of VT1 is connected to VT... 1S Drain connected, VT 1S The source is connected to the negative terminal of the power supply; VT 2S The drain is connected to the positive output terminal, and the source of VT1 is connected to VT. 1S The drains of VT2 are connected, and the source of VT2 is connected to the negative terminal of the power supply; one end of the power inductor is connected to the source of VT1, and the other end is connected to VT2. 2S Source-to-source connection; VT 1S The source region VT2 is connected to the source; the input filter capacitor C in One end is connected to the positive terminal of the power supply, and the other end is connected to the negative terminal of the power supply; output filter capacitor C o One end is connected to the positive terminal of the load, and the other end is connected to the negative terminal of the load;

[0007] The specific steps of the control strategy are as follows:

[0008] Step 1: By controlling the turn-on timing of the switching transistors, the direction of the inductor current is changed, thereby achieving zero-voltage turn-on of the four power switching transistors;

[0009] Step 2: Zero-voltage turn-on characteristics of VT1 and VT2 require that the inductor current is negative, and the negative current I... zvs The formula for determining the value of is:

[0010] (2)

[0011] Step 3: Under light load conditions, the four-switch Buck-Boost converter operates in a pseudo-inductor current discontinuous conduction state;

[0012] Step 4: Under heavy load conditions, the four-switch Buck-Boost converter operates in a pseudo-inductor current continuous conduction state;

[0013] Step 5: When the input voltage is not equal to the output voltage, the critical current of the four-switch Buck-Boost converter under light load and heavy load conditions can be obtained based on the minimum switching cycle:

[0014] (6)

[0015] Step 6: When the input voltage equals the output voltage, control the switching period T of the converter. s The input voltage is at its highest value and remains constant; when the input voltage equals the output voltage, the durations of Mode 1 (T1) and Mode 3 (T3) are the same; under light load conditions, the converter operates in a pseudo-discontinuous inductor current mode, keeping the duration of Mode 1 (T1) constant and ensuring that the second peak value of the inductor current is slightly greater than the absolute value of the negative current; the duration of Mode 2 (T2) increases with the increase of the load current.

[0016] (7)

[0017] Step 7: Under heavy load conditions, the converter operates in the pseudo-inductor current continuous conduction mode; the duration of control mode 1 T1 and mode 3 increases with the increase of load current; the duration of mode 2 T2 is reduced by half the duration of mode 1 T1 or mode 3 T3 based on the longest duration.

[0018] (8)

[0019] (9).

[0020] In some implementations, step 1 is divided into four modes within one switching cycle. During the first operating mode T1, VT1 and VT2 are turned on, and during the second operating mode T2, VT1 and VT2 are turned on. 2S On, in the third operating mode T3, VT 1S With VT2 conducting, VT in the fourth operating mode T4 1SVT2 is on; in the first operating mode T1, the voltage across the inductor current is the input voltage; in the second operating mode T2, the voltage across the inductor current is the difference between the input and output voltages; in the third operating mode T3, the voltage across the inductor current is the output voltage; in the fourth operating mode T4, the voltage across the inductor current is zero; based on the magnitude of the voltage across the inductor in the second operating mode T2, the peak value of the inductor current appears at different switching points. When the input voltage is greater than the output voltage, the peak value of the inductor current appears at the beginning of the third operating mode T3, and the current value at the beginning of the third operating mode T3 is called the second peak value of the inductor current; when the input voltage is less than the output voltage, the peak value of the inductor current appears at the beginning of the second operating mode T2, and the inductor current value at the beginning of the third operating mode T3 is called the second peak value of the inductor current; when the input voltage equals the output voltage, the inductor current has a peak plateau during the second operating mode T2, and the inductor current value at the beginning of the second operating mode T2 is called the peak value under this condition; the expression for the inductor current in each mode is:

[0021] (1).

[0022] In some implementations, in step 3, when the input voltage is higher than the output voltage, the duration of mode 1 T1 remains unchanged and the second peak value of the inductor current is slightly greater than the absolute value of the negative current. The duration of mode 3 T3 can be obtained according to the voltage gain formula of the four-switch Buck-Boost converter. When the input voltage is lower than the output voltage, the duration of mode 3 T3 remains unchanged and the second peak value of the inductor current is slightly greater than the absolute value of the negative current. The duration of mode 1 T1 can be obtained according to the voltage gain formula of the four-switch Buck-Boost converter. The duration of mode 2 T2 is the highest switching period T. s The conduction time corresponding to the lowest output current condition; the switching period decreases with increasing load current, and shows a clear proportional relationship with the minimum switching period, the critical current under light load and heavy load conditions, and the output current:

[0023] (3).

[0024] In some implementations, in step 4, when the input voltage is higher than the output voltage, the duration of control mode 1 T1 remains unchanged and the second peak value of the inductor current is slightly greater than the absolute value of the negative current. The duration of mode 3 T3 can be obtained according to the voltage gain formula of the four-switch Buck-Boost converter. When the input voltage is lower than the output voltage, the duration of control mode 3 T3 remains unchanged and the second peak value of the inductor current is slightly greater than the absolute value of the negative current. The duration of mode 1 T1 can be obtained according to the voltage gain formula of the four-switch Buck-Boost converter. The switching period is the highest switching period T. sThe reference value increases with the increase of load current; the second mode, T2 stage, can be derived from the power conservation formula of the four-switch Buck-Boost converter and the corresponding switching cycle under this load current condition:

[0025] (4)

[0026] (5).

[0027] In some implementations, VT1, VT 1S VT2, VT 2S Zero-voltage turn-on is achieved under full load conditions; the switching frequency exhibits a trajectory of first increasing and then decreasing as the load current increases under conditions where the input voltage and output voltage are not equal.

[0028] This invention provides an adaptive frequency conversion control strategy for a four-switch Buck-Boost converter, which has the following significant advantages compared with the prior art:

[0029] (1) VT1, VT 1S VT2, VT 2S It enables zero-voltage turn-on under wide load current conditions. This helps reduce switching losses under high current conditions.

[0030] (2) The switching cycle shows a trajectory of first increasing and then decreasing with the increase of load current. This is beneficial for balancing energy conversion efficiency under both light and heavy load conditions, and at the same time effectively compresses the range of switching frequency variation of the converter under variable frequency control in wide load current applications. Attached Figure Description

[0031] Figure 1 This is the circuit topology diagram of a four-switch Buck-Boost converter.

[0032] Figure 2 This refers to the switching timing of the semiconductor device corresponding to the adaptive frequency conversion control proposed in this invention.

[0033] Figure 3 For extremely light load conditions, in the examples VT1 and VT 1S Simulation waveforms of drive and drain voltage during the conduction phase.

[0034] Figure 4 For extremely light load conditions, in the examples VT2 and VT 2S Simulation waveforms of drive and drain voltage during the conduction phase.

[0035] Figure 5 For extremely light load conditions, in the examples VT1 and VT 1S Simulation waveforms of drive and inductor current during the conduction phase.

[0036] Figure 6 For full-load operation, in the example, VT1 and VT 1S Simulation waveforms of drive and drain voltage during the conduction phase.

[0037] Figure 7 For full-load operation, in the examples VT2 and VT 2S Simulation waveforms of drive and drain voltage during the conduction phase.

[0038] Figure 8 For full-load operation, in the example, VT1 and VT 1S Simulation waveforms of drive and inductor current during the conduction phase. Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0040] Example 1: Figure 1 This is a diagram of the four-switch Buck-Boost converter topology used in this invention. The topology includes an input-side DC power supply V. in Input filter capacitor C in Buck bridge arm, power inductor L, Boost bridge arm, output filter capacitor C o and load R;

[0041] The Buck arm includes power semiconductor devices VT1 and VT2. 1S ;

[0042] The Boost bridge arm includes power semiconductor devices VT2 and VT2. 2S ;

[0043] The specific connection method is that the drain of VT1 is connected to the positive terminal of the power supply, and the source of VT1 is connected to VT... 1S Drain connected, VT 1S The source is connected to the negative terminal of the power supply;

[0044] VT 2S The drain is connected to the positive output terminal, and the source of VT1 is connected to VT. 1S The drains are connected, and the source of VT2 is connected to the negative terminal of the power supply.

[0045] One end of the power inductor is connected to the source of VT1, and the other end is connected to VT. 2S Source and pole connected;

[0046] VT 1S Source-pole domain VT2 source poles are connected;

[0047] Input filter capacitor C inOne end is connected to the positive terminal of the power supply, and the other end is connected to the negative terminal of the power supply;

[0048] Output filter capacitor C o One end is connected to the positive terminal of the load, and the other end is connected to the negative terminal of the load;

[0049] Figure 2 This is a schematic diagram of the switching transistor turn-on timing and inductor current waveforms for an adaptive frequency conversion control strategy for a four-switch Buck-Boost converter according to the present invention. The implementation steps of this method are as follows:

[0050] Step 1: Output of a four-switch Buck-Boost converter with adaptive frequency conversion control. The input voltage is higher than the output voltage, and the on-time of control mode T1 is fixed and minimized to a value of T. min Under the lowest output current condition, the corresponding preset minimum switching frequency f s The conduction time of mode 2 (T2) corresponds to the lowest output current condition and the lowest switching frequency mode. The conduction time of mode 3 (T3) can be derived from the voltage gain formula of the converter.

[0051] (10)

[0052] Under light load conditions, the inductor current operates in a pseudo-discontinuous conduction state, and the output current gradually increases from the lowest value. The switching frequency increases with the increase of the output current, and its value can be obtained by reverse calculation based on the formula for solving the output current.

[0053] (11)

[0054] Step 2: Under heavy load conditions, the inductor current operates in a pseudo-continuous conduction state, and the switching frequency decreases as the output current continues to increase. For ease of control, the switching frequency is converted into the switching period T. s Its step size as the output current increases is Δt;

[0055] (12)

[0056] The duration of mode 1 T1 remains unchanged, while the durations of mode 2 T2 and mode 3 T3 can be derived from the switching cycle under the output current using the voltage gain formula.

[0057] (13)

[0058] Step 3: When the input voltage is higher than the output voltage, the critical currents of the inductor current in the pseudo-discontinuous conduction mode and pseudo-continuous conduction mode, that is, the critical currents under light load and heavy load conditions, correspond to the state where the duration of mode 4 (T4) is 0. At this time, the critical current is:

[0059] (14)

[0060] The formula for calculating the switching cycle of the converter under light load conditions can be directly simplified by using the critical current expression and the output current value;

[0061] (15)

[0062] Example 2: This example is based on Figure 1 The simulation circuit of the four-switch Buck-Boost converter topology shown is constructed, and the control strategy proposed in this invention is adopted. The circuit parameters are: input voltage V... in =14.5V, power inductor L=0.25μH, input filter capacitor C in =3600uF, output filter capacitor C o =3600uF, output voltage V o =12V. Control switching frequency f s The variation range is [50kHz, 200kHz], and the dead time t dead =150ns.

[0063] Figure 3 For the Buck bridge arm MOSFETs VT1 and VT2 of the converter 1S The drive and drain-source voltage waveforms can be seen from the figure, VT1 and VT 1S It can have zero-voltage turn-on characteristics under extremely light load conditions.

[0064] Figure 4 For the Buck arm MOSFETs VT2 and VT of the converter 2S The drive and drain-source voltage waveforms can be seen from the figure, VT2 and VT 2S It can have zero-voltage turn-on characteristics under extremely light load conditions.

[0065] Figure 5 The figure shows the drive and inductor current waveforms of VT1 and VT2S under extremely light load conditions. As can be seen from the figure, the inductor current operates in a pseudo-discontinuous conduction state.

[0066] At this time, the converter switching frequency is 50kHz, the input power is 65.966W, the output power is 61.04W, and the operating efficiency is 92.53%.

[0067] Figure 6 The figure shows the drive and drain-source voltage waveforms of the Buck bridge arm MOSFETs VT1 and VT1S in the converter. As can be seen from the figure, VT1 and VT1S can have zero-voltage turn-on characteristics under full load conditions.

[0068] Figure 7 For the Buck arm MOSFETs VT2 and VT of the converter2S The drive and drain-source voltage waveforms can be seen from the figure, VT2 and VT 2S It can have zero-voltage turn-on characteristics under full-load conditions.

[0069] Figure 8 The figure shows the waveforms of VT1, VT2S drive and inductor current under full load conditions. As can be seen from the figure, the inductor current operates in a pseudo-continuous conduction state.

[0070] At this time, the converter switching frequency is 100kHz, the input power is 526.93W, the output power is 513.7W, and the operating efficiency is 97.4%.

[0071] The same proportion is based on Figure 1 The simulation circuit for the four-switch Buck-Boost converter topology shown is constructed with input voltages of 12V and 10.5V respectively. The remaining circuit parameters and control parameters are the same as in the embodiment. Figure 2 The conduction timing is shown. When using this adaptive frequency converter control strategy, VT1, VT1S, VT2, and VT2S all have zero-voltage turn-on characteristics across the entire load range.

[0072] At this point, the converter has an extremely light load input power of 72.464W and an output power of 67.33W with an efficiency of 92.92% when the input voltage is 12V; and a full load input power of 522.6W and an output power of 513.7W with an efficiency of 98.29%. At an input voltage of 10.5V, the converter has an extremely light load input power of 73.74W and an output power of 68.11W with an efficiency of 92.36%; and a full load input power of 529.035W and an output power of 513.4W with an efficiency of 97.04%.

[0073] Based on the above results, it can be seen that, under the same circuit parameters and control conditions, the modulation method proposed in this invention can enable the converter to achieve a peak efficiency of 98.29% and an efficiency higher than 92% under extremely light load conditions.

[0074] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. An adaptive frequency conversion control strategy for a four-switch Buck-Boost converter, based on a four-switch Buck-Boost converter, wherein the four-switch Buck-Boost converter includes a Buck arm, a power inductor, a Boost arm, and a filter circuit, wherein, The Buck bridge arm includes power switching transistors VT1 and VT2. 1S The Boost bridge arm includes the power switch VT. 2S And VT2; the filter circuit includes input filter capacitor C in and C o The drain of VT1 is connected to the positive terminal of the power supply, and the source of VT1 is connected to VT... 1S Drain connected, VT 1S The source is connected to the negative terminal of the power supply; VT 2S The drain is connected to the positive output terminal, and the source of VT1 is connected to VT. 1S The drains of VT2 are connected, and the source of VT2 is connected to the negative terminal of the power supply; one end of the power inductor is connected to the source of VT1, and the other end is connected to VT2. 2S Source-to-source connection; VT 1S The source region VT2 is connected to the source; the input filter capacitor C in One end is connected to the positive terminal of the power supply, and the other end is connected to the negative terminal of the power supply; output filter capacitor C o One end is connected to the positive terminal of the load, and the other end is connected to the negative terminal of the load; The control strategy is characterized by the following specific steps: Step 1: By controlling the turn-on timing of the switching transistors, the direction of the inductor current is changed, thereby achieving zero-voltage turn-on of the four power switching transistors; Step 2: Zero-voltage turn-on characteristics of VT1 and VT2 require that the inductor current is negative, and the negative current I... zvs The formula for determining the value of is: (2) Step 3: Under light load conditions, the four-switch Buck-Boost converter operates in a pseudo-inductor current discontinuous conduction state; Step 4: Under heavy load conditions, the four-switch Buck-Boost converter operates in a pseudo-inductor current continuous conduction state; Step 5: When the input voltage is not equal to the output voltage, the critical current of the four-switch Buck-Boost converter under light load and heavy load conditions can be obtained based on the minimum switching cycle: (6) Step 6: When the input voltage equals the output voltage, control the switching period T of the converter. s The input voltage is at its highest value and remains constant; when the input voltage equals the output voltage, the durations of Mode 1 (T1) and Mode 3 (T3) are the same; under light load conditions, the converter operates in a pseudo-discontinuous inductor current mode, keeping the duration of Mode 1 (T1) constant and ensuring that the second peak value of the inductor current is slightly greater than the absolute value of the negative current; the duration of Mode 2 (T2) increases with the increase of the load current. (7) Step 7: Under heavy load conditions, the converter operates in the pseudo-inductor current continuous conduction mode; the duration of control mode 1 T1 and mode 3 increases with the increase of load current; the duration of mode 2 T2 is reduced by half the duration of mode 1 T1 or mode 3 T3 based on the longest duration. (8) (9)。 2. The adaptive frequency conversion control strategy for a four-switch Buck-Boost converter according to claim 1, characterized in that: In step 1, one switching cycle is divided into four modes. During the first operating mode T1, VT1 and VT2 are turned on. During the second operating mode T2, VT1 and VT2 are turned on. 2S On, in the third operating mode T3, VT 1S With VT2 conducting, VT in the fourth operating mode T4 1S VT2 is on; in the first operating mode T1, the voltage across the inductor current is the input voltage; in the second operating mode T2, the voltage across the inductor current is the difference between the input and output voltages; in the third operating mode T3, the voltage across the inductor current is the output voltage; in the fourth operating mode T4, the voltage across the inductor current is zero; based on the magnitude of the voltage across the inductor in the second operating mode T2, the peak value of the inductor current appears at different switching points. When the input voltage is greater than the output voltage, the peak value of the inductor current appears at the beginning of the third operating mode T3, and the current value at the beginning of the third operating mode T3 is called the second peak value of the inductor current; when the input voltage is less than the output voltage, the peak value of the inductor current appears at the beginning of the second operating mode T2, and the inductor current value at the beginning of the third operating mode T3 is called the second peak value of the inductor current; when the input voltage equals the output voltage, the inductor current has a peak plateau during the second operating mode T2, and the inductor current value at the beginning of the second operating mode T2 is called the peak value under this condition; the expression for the inductor current in each mode is: (1)。 3. The adaptive frequency conversion control strategy for a four-switch Buck-Boost converter according to claim 1, characterized in that: In step 3, when the input voltage is higher than the output voltage, the duration of mode 1 (T1) remains unchanged, and the second peak value of the inductor current is slightly greater than the absolute value of the negative current. The duration of mode 3 (T3) can be obtained from the voltage gain formula of the four-switch Buck-Boost converter. When the input voltage is lower than the output voltage, the duration of mode 3 (T3) remains unchanged, and the second peak value of the inductor current is slightly greater than the absolute value of the negative current. The duration of mode 1 (T1) can be obtained from the voltage gain formula of the four-switch Buck-Boost converter. The duration of mode 2 (T2) is the highest switching period T. s And the on-time corresponding to the lowest output current operating condition; The switching period decreases with increasing load current, and exhibits a clear proportional relationship with the minimum switching period, the critical current under light load and heavy load conditions, and the output current. (3)。 4. The adaptive frequency conversion control strategy for a four-switch Buck-Boost converter according to claim 1, characterized in that: In step 4, when the input voltage is higher than the output voltage, the duration of control mode 1 T1 remains unchanged, and the second peak value of the inductor current is slightly greater than the absolute value of the negative current. The duration of mode 3 T3 can be obtained according to the voltage gain formula of the four-switch Buck-Boost converter. When the input voltage is lower than the output voltage, the duration of control mode 3 T3 remains unchanged, and the second peak value of the inductor current is slightly greater than the absolute value of the negative current. The duration of mode 1 T1 can be obtained according to the voltage gain formula of the four-switch Buck-Boost converter. The switching period is based on the highest switching period T. s The reference value increases with the increase of load current; the second mode, T2 stage, can be derived from the power conservation formula of the four-switch Buck-Boost converter and the corresponding switching cycle under this load current condition: (4) (5)。 5. The adaptive frequency conversion control strategy for a four-switch Buck-Boost converter according to claim 1, characterized in that: VT1, VT 1S VT2, VT 2S Zero-voltage turn-on is achieved under full load conditions; the switching frequency exhibits a trajectory of first increasing and then decreasing as the load current increases under conditions where the input voltage and output voltage are not equal.

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