A four-tube buck-boost converter ZVS dynamic control method

Abstract

The application discloses a four-tube Buck-Boost converter ZVS dynamic control method, and obtains a ZVS dynamic control core algorithm according to the relationship between the duty ratio and the power curve under the variable soft switching condition. On the basis of feedback closed-loop control of inductance current, input voltage and output voltage, the circuit working mode is judged according to the voltage conversion ratio and the output of the compensator, and the duty ratio required for the circuit to enter a steady state is calculated according to the working mode of the circuit, so that the circuit enters the steady state by controlling the phase shift duty ratio and the duty ratio of the switching tube. On the basis of the variable soft switching condition, the application considers the influence of the circuit resonance in the dead time on the inductance current, and proposes a corresponding compensation strategy; the application can judge the maximum power output point of the circuit according to the change of the input and output voltages, and improves the conversion efficiency and dynamic response speed of the converter.

Description

Technical Field

[0001] This invention belongs to the field of power converter control, and specifically relates to a ZVS dynamic control method for a four-transistor Buck-Boost converter. Background Technology

[0002] With the continuous development of power electronics technology, power electronic converters have been widely used in various fields. For applications with wide input voltage ranges and output voltages within the input voltage range, such as intermediate bus converters in distributed power systems, fuel cell systems, and two-stage active power factor correctors, DC-DC converters with buck-boost characteristics are required. There are four common non-isolated buck-boost converters: single-transistor Buck-Boost, Cuk, Zeta, and SEPIC. Among them, Buck-Boost and Cuk converters have opposite input and output voltage polarities. Cuk, Zeta, and SEPIC, due to their numerous passive components, are not conducive to improving the converter's power density. The four-transistor Buck-Boost converter is derived from the two-transistor Buck-Boost converter using synchronous rectification technology. For the four-transistor Buck-Boost converter, existing soft-switching control methods include dual-mode control and quadrilateral inductor current control. Dual-mode control has relatively high losses under light load conditions. To address the problems of dual-mode control, quadrilateral inductor current control was proposed. There are several different implementation schemes for quadrilateral inductor current control: some establish a mathematical model of the inductor current, and control is achieved through a lookup table method, which is a constant soft-switching control method. The higher the required control accuracy and the larger the range, the more storage resources are required, increasing the system complexity. Others propose simplified digital control strategies by optimizing the control method. Although they adopt a variable soft-switching control method, they have problems such as too large a soft-switching margin and non-minimum inductor current ripple, which affect the converter efficiency and maximum transmission power. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of the prior art by providing a ZVS dynamic control method for a four-transistor Buck-Boost converter. The main idea is to establish the relationship between the transformer ratio and various parameters, improve the converter's efficiency and maximum transmission power by softening the switching conditions, and enhance the circuit's dynamic response.

[0004] The technical solution to achieve the purpose of this invention is as follows:

[0005] A ZVS dynamic control method for a four-transistor Buck-Boost converter is disclosed. Based on feedback closed-loop control of inductor current, input voltage, and output voltage, the ZVS dynamic control method determines the circuit operating mode according to the transformer ratio and the compensator output. It then calculates the duty cycle required for the circuit to reach steady state based on the operating mode, and controls the phase shift duty cycle and the duty cycle of the switching transistors to bring the circuit into steady state. The specific steps are as follows:

[0006] Step S1: Parameter initialization;

[0007] Step S2: Sample the input voltage V in With output voltage V o Determine the circuit operating mode, calculate the transformer ratio k and the current reference I. zvs ;

[0008] Step S3: Determine the circuit combination mode by the transformer ratio and calculate the boundary duty cycle D. T2_b and D T2_Pmax ;

[0009] Step S4: Sample the output voltage V o and with a given voltage reference V ref By comparing the error signals and using a compensator with closed-loop regulation to stabilize the output voltage, the duty cycle D is obtained. c ;

[0010] Step S5: Using the boundary duty cycle D T2_b and D T2_Pmax For D c After constraint transformation, we get D T2 And determine the circuit's operating mode;

[0011] Step S6: Using the circuit operating mode, transformer ratio k, and D... T2 Calculate the phase shift duty cycle D T1 and the duty cycle D of the switching transistor Q1 x ;

[0012] Step S7: Sample the inductor current i L And with the negative current reference -I required to achieve soft switching of switching transistors Q1 and Q4 zvs Compare, when i L Linear decrease to -I zvs When switch Q3 is turned off, the duty cycle D of switch Q3 is obtained. y ;

[0013] Step S8, using duty cycle D x The switching action of switch Q1 is controlled by its inverted signal, which in turn controls the switching action of switch Q2; the duty cycle D is used to control the switching action of switch Q1. yThe switching action of switch Q3 is controlled by its inverted signal, which in turn controls the switching action of switch Q4; this is achieved through the phase shift angle D. T1 The phase difference between the turn-on times of control switches Q1 and Q3;

[0014] Step S9: Repeat steps S2 to S8 to enter the next cycle.

[0015] Furthermore, the four-transistor Buck-Boost converter consists of four switching transistors Q1, Q2, Q3, and Q4, and an inductor L. The two ends of the inductor L are connected to the midpoints of the bridge arms of switching transistors Q1 and Q2, and the midpoints of the bridge arms of switching transistors Q3 and Q4, respectively. Switches Q1 and Q2 are complementary in conduction, and switches Q3 and Q4 are complementary in conduction.

[0016] Furthermore, the parameter initialization calculation formula in step S1 is as follows:

[0017]

[0018] In the formula, V in Input voltage, V o Where L is the output voltage, C is the inductance, and L is the output voltage. oss f is the parasitic capacitance of the switching transistor. s D is the switching frequency. d This represents the dead-time duty cycle of the switching transistor.

[0019] Furthermore, in step S2, the circuit operating mode is determined, the transformer ratio k and the current reference I are calculated. zvs The specific criteria are:

[0020] When V in ≥V o At this time, the circuit operates in buck mode. I ZVS =λ·V in ;

[0021] When V in <V o At this time, the circuit operates in buck mode. I ZVS =λ·V o ;

[0022] When k > k b1 And V o <V ref At that time, it enters the constant duty cycle open-loop working mode and establishes a small voltage on the load side.

[0023] Furthermore, in step S3, the boundary duty cycle D T2_b and D T2_Pmax The calculation formula is:

[0024]

[0025]

[0026] Furthermore, in step S5, D T2 The specific criteria for determining the operating mode of the circuit are as follows:

[0027] When D c When <0, D T2 =0, the circuit enters PDCM operating mode;

[0028] When 0≤D c ≤D T2_b At that time, D T2 =D c The circuit enters the PDCM operating mode;

[0029] When D T2_b <D c <2D T2_b -D T2_Pmax At that time, D T2 =2D T2_b -D c The circuit enters the PCRM working mode;

[0030] When 2D T2_b -D T2_Pmax ≤D c At that time, D T2 =D T2_Pmax If k > k b2 The circuit enters the PDCM operating mode; if k≤k b2 The circuit then enters the PCRM working mode.

[0031] Furthermore, in step S6, the phase shift duty cycle D T1 and the duty cycle D of the switching transistor Q1 x The specific calculation formula is as follows:

[0032] When the circuit operates in buck mode (PDCM):

[0033]

[0034] When the circuit is in buck mode, PCRM operating mode:

[0035]

[0036] When the circuit is in boost mode (PDCM operating mode):

[0037]

[0038] When the circuit is in boost mode, PCRM operating mode:

[0039]

[0040] The selection of the compensation parameter δ must satisfy the following:

[0041]

[0042] In the formula:

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] 1. This invention provides a soft-switching condition (I) zvs The control method was proposed, and corresponding compensation was made for the nonlinearity of inductor current caused by soft switching.

[0045] 2. This invention provides a control method with a wide voltage range, capable of adapting to wide voltage input and output;

[0046] 3. This invention can determine the maximum power output point of the circuit according to the changes in input and output voltage, thereby improving the conversion efficiency and dynamic response speed of the converter;

[0047] 4. The control method of the present invention is adaptable to different switching frequencies and has good adaptability. Attached Figure Description

[0048] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0049] Figure 1 This is a circuit topology and control schematic diagram of a four-transistor Buck-Boost converter ZVS dynamic control method according to the present invention.

[0050] Figure 2a , 2b This is a schematic diagram showing the converter operating in different modes when the input and output voltages remain constant in this invention. Figure 2a China V in <V o , Figure 2b China V in >V o .

[0051] Figure 3aThis is a simulation waveform diagram of the full load when the input voltage is 60V and the output voltage is 100V.

[0052] Figure 3b This is a simulation waveform diagram of the present invention under half-load conditions when the input voltage is 60V and the output voltage is 100V.

[0053] Figure 3c This is a simulation waveform diagram of the light load when the input voltage is 60V and the output voltage is 100V in this invention.

[0054] Figure 4a This is a simulation waveform diagram of the output voltage switching from 20% load to full load and back to 20% load when the input voltage is 60V and the output voltage is 100V.

[0055] Figure 4b This is a simulated waveform diagram of the input voltage jumping from 60V to 150V and back to 60V when the output voltage is 100V under full load in this invention.

[0056] Figure 5 This invention establishes a simulation waveform diagram of the output voltage starting from zero when the input voltage is 60V and the output voltage is 100V under light load. Detailed Implementation

[0057] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0058] Please see Figures 1 to 5 The present invention provides an embodiment:

[0059] like Figure 1 This is a circuit topology and control schematic diagram of a four-transistor Buck-Boost converter ZVS dynamic control method according to the present invention. The four-transistor Buck-Boost converter consists of four switching transistors Q1, Q2, Q3, and Q4 and an inductor L. The two ends of the inductor L are connected to the midpoints of the bridge arms of switching transistors Q1 and Q2, and the midpoints of the bridge arms of switching transistors Q3 and Q4, respectively. Switches Q1 and Q2 are complementary in conduction, and switching transistors Q3 and Q4 are complementary in conduction. The converter also includes an input capacitor C. in and output capacitor C oThis is used to filter out the ripple of the switching frequency. Based on feedback closed-loop control of inductor current, input voltage, and output voltage, the controller determines the circuit's operating mode according to the transformer ratio and the compensator's output. It then calculates the duty cycle required for the circuit to reach steady state based on the operating mode. By controlling the phase-shift duty cycle and the duty cycle of the switching transistor, the circuit enters steady state. The specific steps of the control method are as follows:

[0060] Step S1: Based on the inductance L, the parasitic capacitance C of the switching transistor oss Switching frequency f s Dead zone duty cycle D d Calculate the initialization parameters λ, α, β, and k. b1 and k b2 The calculation formulas for each initialization parameter are as follows:

[0061]

[0062] Step S2: Sample the input voltage V in Output voltage V o Determine the circuit operating mode, calculate the transformer ratio k and the current reference I. zvs .

[0063] When V in ≥V o At this time, the circuit operates in buck mode. I ZVS =λ·V in ;

[0064] When V in <V o At this time, the circuit operates in buck mode. I ZVS =λ·V o ;

[0065] When k > k b1 And V o <V ref At this time, it will enter the constant duty cycle open-loop operating mode to establish a small voltage on the load side.

[0066] Step S3: Determine the circuit combination mode by the transformer ratio and calculate the boundary duty cycle D. T2_b and D T2_Pmax ;

[0067]

[0068]

[0069] The above formula can be optimized according to specific circuit parameters to ensure that k ≤ k b2 hour:

[0070] D T2_Pmax ≈a1k+b1

[0071] Where a1 and b1 are constants.

[0072] Step S4: Sample the output voltage V o and with a given voltage reference V ref By comparing the error signals and using a compensator with closed-loop regulation to stabilize the output voltage, the duty cycle D is obtained. c ,like Figure 1 As shown.

[0073] Step S5: Using the boundary duty cycle D b and D max For D c After constraint transformation, we get D T2 And determine the circuit's operating mode;

[0074] When D c When <0, D T2 =0, the circuit enters the PDCM (Pseudo Discontinuous Conduction Mode) operating mode;

[0075] When 0≤D c ≤D T2_b At that time, D T2 =D c The circuit enters the PDCM (Pseudo Critical Continuous Current Mode) operating mode;

[0076] When D T2_b <D c <2D T2_b -D T2_Pmax At that time, D T2 =2D T2_b -D c The circuit enters the PCRM working mode;

[0077] When 2D T2_b -D T2_Pmax ≤D c At that time, D T2 =D T2_Pmax If k > k b2 When the circuit enters the PDCM operating mode, if k≤k b2 The circuit enters the PCRM working mode.

[0078] Step S6: Using the circuit operating mode, transformer ratio k, and D... T2 Calculate the phase shift duty cycle D T1 and the duty cycle D of the switching transistor Q1x ;

[0079] When the circuit operates in buck mode (PDCM):

[0080]

[0081] When the circuit is in buck mode, PCRM operating mode:

[0082]

[0083] When the circuit is in boost mode (PDCM operating mode):

[0084]

[0085] When the circuit is in boost mode, PCRM operating mode:

[0086]

[0087] The selection of the compensation parameter δ must satisfy the following:

[0088]

[0089] In the formula:

[0090] The above formula can be optimized according to specific circuit parameters to achieve the following:

[0091] δ≈a2V in +b2V o +c

[0092] Where a2, b2, and c are constants.

[0093] Step S7: Sample the inductor current i L And with the negative current reference -I required to ensure soft switching of switching transistors Q1 and Q4. zvs When comparing, when i L Linear decrease to -I zvs When switch Q3 is turned off, the duty cycle D of switch Q3 is obtained. y .

[0094] Step S8, using duty cycle D x The switching action of switch Q1 is controlled by its inverted signal, which is used to control the switching action of switch Q2; the duty cycle D is used to control the switching action of switch Q2. y The switching action of switch Q3 is controlled by its inverted signal, which is used to control the switching action of switch Q4; this is achieved through the phase shift angle D. T1 The phase difference between the turn-on times of control switches Q1 and Q3.

[0095] Step S9: Repeat steps S2 to S8 to enter the next cycle.

[0096] Through the above control methods, the following can be achieved: Figure 2a , 2b The waveforms shown are for different operating modes.

[0097] To further illustrate the superiority of this control method, a simulation example of the present invention is given below.

[0098] Based on the parameters of the 300W four-transistor Buck-Boost converter shown in Table 1, a simulation circuit was built using Simulink simulation software. Figures 3a-3c Simulation waveforms of a four-transistor Buck-Boost converter with an input voltage of 300V and different load currents are presented. Figure 3a The simulation waveform is shown under full load with an input voltage of 60V. Figure 3b The simulation waveform is shown under half-load with an input voltage of 60V.

[0099] Figure 3c The simulation waveform diagram is shown under a light load with an input voltage of 60V. It can be seen that all switching transistors can achieve ZVS and the inductor current ripple is small. Figure 4a , 4b Simulation waveforms for load transition and input voltage transition are given, where, Figure 4a The middle image shows the simulated waveform of the load switching when the input voltage is 60V; Figure 4b The simulation waveform of the input voltage jump under full load shows that the output voltage can be stabilized at 100V. During the jump, the voltage drop and overshoot are small, and the dynamic response speed is fast. Figure 5 With an input voltage of 60V and an output voltage of 100V under light load, a simulation waveform diagram of the output voltage starting from zero is established. It can be seen that the circuit can adapt to a wide range of input and output voltages and can determine the maximum power output point of the circuit according to the changes in input and output voltages, thereby improving the conversion efficiency and dynamic response speed of the converter.

[0100] Table 1. Simulation parameters of the 1300W four-transistor Buck-Boost converter

[0101] parameter symbol numerical values Input voltage <![CDATA[V in ]]> 60V-150V Output voltage <![CDATA[V o ]]> 100V Output power <![CDATA[P o ]]> 300W Switching frequency <![CDATA[f s ]]> 500kHz inductance L 5μH Output capacitor <![CDATA[C o ]]> 47μF Dead zone duty cycle <![CDATA[D d ]]> 1.5％ Parasitic capacitance of switching transistor <![CDATA[C oss ]]> 106pF

[0102] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0103] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A ZVS dynamic control method for a four-transistor Buck-Boost converter, characterized in that, The ZVS dynamic control method, based on feedback closed-loop control of inductor current, input voltage, and output voltage, determines the circuit operating mode according to the transformer ratio and the compensator output. It then calculates the duty cycle required for the circuit to reach steady state based on the operating mode, and controls the phase-shift duty cycle and the duty cycle of the switching transistor to bring the circuit into steady state. The specific steps are as follows: Step S1: Parameter initialization. The parameter initialization calculation formula is: In the formula, V in Input voltage, V o Where L is the output voltage, C is the inductance, and L is the output voltage. oss f is the parasitic capacitance of the switching transistor. s D is the switching frequency. d This refers to the dead-time duty cycle of the switching transistor. Step S2: Sample the input voltage V in With output voltage V o Determine the circuit operating mode, calculate the transformer ratio k and the current reference I. zvs ; Step S3: Determine the circuit combination mode by the transformer ratio and calculate the boundary duty cycle D. T2_b and D T2_Pmax ; Step S4: Sample the output voltage V o and with a given voltage reference V ref By comparing the error signals and using a compensator with closed-loop regulation to stabilize the output voltage, the duty cycle D is obtained. c ; Step S5: Using the boundary duty cycle D T2_b and D T2_Pmax For D c After constraint transformation, we get D T2 And determine the circuit's operating mode; Step S6: Using the circuit operating mode, transformer ratio k, and D... T2 Calculate the phase shift duty cycle D T1 and the duty cycle D of the switching transistor Q1 x The specific calculation formula is as follows: When the circuit operates in buck mode (PDCM): When the circuit is in buck mode, PCRM operating mode: When the circuit is in boost mode (PDCM operating mode): When the circuit is in boost mode, PCRM operating mode: The selection of the compensation parameter δ must satisfy the following: In the formula: , ; Step S7: Sample the inductor current i L And with the negative current reference -I required to achieve soft switching of switching transistors Q1 and Q4 zvs Compare, when i L Linear decrease to -I zvs When switch Q3 is turned off, the duty cycle D of switch Q3 is obtained. y ; Step S8, using duty cycle D x The switching action of switch Q1 is controlled by its inverted signal, which in turn controls the switching action of switch Q2; the duty cycle D is used to control the switching action of switch Q1. y The switching action of switch Q3 is controlled by its inverted signal, which in turn controls the switching action of switch Q4; this is achieved through the phase shift angle D. T1 The phase difference between the turn-on times of control switches Q1 and Q3; Step S9: Repeat steps S2 to S8 to enter the next cycle.

2. The ZVS dynamic control method for a four-transistor Buck-Boost converter according to claim 1, characterized in that: The four-transistor Buck-Boost converter consists of four switching transistors Q1, Q2, Q3, and Q4, and an inductor L. The two ends of the inductor L are connected to the midpoints of the bridge arms of switching transistors Q1 and Q2, and the midpoints of the bridge arms of switching transistors Q3 and Q4, respectively. Switches Q1 and Q2 are complementary in conduction, and switches Q3 and Q4 are complementary in conduction.

3. The ZVS dynamic control method for a four-transistor Buck-Boost converter according to claim 1, characterized in that, In step S2, the circuit operating mode is determined, the transformer ratio k is calculated, and the current reference I is determined. zvs The specific criteria are: when At this time, the circuit operates in buck mode. , ; when At this time, the circuit operates in buck mode. , ; when and At that time, it enters the constant duty cycle open-loop working mode and establishes a small voltage on the load side.

4. The ZVS dynamic control method for a four-transistor Buck-Boost converter according to claim 1, characterized in that, In step S3, the boundary duty cycle D T2_b and D T2_Pmax The calculation formula is: 。 5. The ZVS dynamic control method for a four-transistor Buck-Boost converter according to claim 1, characterized in that, In step S5, D T2 The specific criteria for determining the operating mode of the circuit are as follows: when hour, The circuit enters the PDCM operating mode; when hour, The circuit enters the PDCM operating mode; when hour, The circuit enters the PCRM working mode; when hour, ,like The circuit enters the PDCM operating mode; if The circuit then enters the PCRM working mode.

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