A control method and system of a four-switch buck-boost converter

Abstract

The application discloses a control method and system of a four-switch Buck-Boost converter, adopts a control parameter lookup table mode to replace a traditional negative current sampling control mode, simultaneously realizes ZVS of a switching tube, reduces unnecessary negative current detection circuits and simplifies PCB layout. The application proposes a control method of changing control parameters, can realize smooth switching between PDCM and PCRM two working modes, guarantees reliable operation of the four-switch Buck-Boost converter, and is suitable for being applied to bidirectional direct-current power conversion occasions such as a photovoltaic system, a battery system, an electric automobile and a fuel cell automobile.

Description

TECHNICAL FIELD

[0001] The present application relates to a power electronic converter, in particular to a control method and system of a four-switch Buck-Boost converter. BACKGROUND

[0002] In applications such as photovoltaic systems, battery systems, electric vehicles and fuel cell vehicles, DC-DC converters with wide input or output voltage range are essential. Among many DC-DC converters, four-switch Buck-Boost (FSBB) converters have received extensive attention due to their ability to boost and buck, low device voltage stress, and few passive components. Four-switch Buck-Boost converters not only can realize bidirectional power conversion between different voltages, but also can optimize real-time energy management, improve system reliability and availability.

[0003] The FSBB circuit topology is shown in FIG. 1. In the four-switch Buck-Boost converter topology, there are Q1, Q2 bridge arms, Q3, Q4 bridge arms, and an inductor. There are four control parameters, which are the duty cycle D1 of Q1, the duty cycle D2 of Q3, the phase difference Figure 1 between Q1 and Q3 The switching frequency f of Q1, Q2, Q3, Q4 s .

[0004] Currently, the control strategies of four-switch Buck-Boost converters mainly include hard switching and soft switching. The hard switching control strategy is relatively simple to implement, but it has high switching loss and cannot make the switching frequency higher, so the size of the converter is large.

[0005] In the soft switching control strategy, the four degrees of freedom are T1, T2, T3, T4, and their relationship with the four control parameters is as follows:

[0006]

[0007] Four-switch Buck-Boost converters generally use pseudo continuous conduction mode (PCCM). According to the different inductor currents, four-switch Buck-Boost converters have two working modes: PDCM (pseudo discontinuous current mode) and PCRM (pseudo critical continuous current mode). When the output power is small, the converter is in PDCM, and the four control parameters satisfy the following expression:

[0008]

[0009] As the output power increases, the four-switch Buck-Boost converter operating mode gradually changes from PDCM to PCRM, and when the converter is in PCRM, the four control parameters satisfy the following expression:

[0010]

[0011] During the operation of the converter, the digital processor cannot solve the equation in real time, so the inductor negative current detection method is usually used to close the loop of the converter, such as Figure 2 The schematic diagram of the negative current detection circuit used in the closed loop.

[0012] The control method using negative current detection requires additional sampling resistors and operational amplifiers in the circuit, which not only increases the size of the converter, but also increases the complexity of the PCB layout. Moreover, if the negative current detection is inaccurate, the switch tube cannot achieve ZVS, thereby affecting the efficiency of the converter.

[0013] As the output power gradually increases, the four-switch Buck-Boost converter operating mode gradually changes from PDCM to PCRM, as shown in Figure 3 The transmission power changes significantly at the switching moment, thereby making it difficult for the converter to be stably closed. SUMMARY

[0014] The present application provides a control method and system for a four-switch Buck-Boost converter, which is not only an alternative to the existing negative current detection for mode switching, but also enables smooth switching between PDCM and PCRM operating modes for the four-switch Buck-Boost converter.

[0015] The technical solution adopted by the present application is a control method for a four-switch Buck-Boost converter. In a four-switch Buck-Boost converter without a negative current detection circuit module, the control parameters T1 or T3 are obtained by looking up the table according to the input voltage, output voltage and output power of the four-switch Buck-Boost converter, and other control parameters of the PWM module are calculated according to the constraint conditions in different operating modes. The PWM module is controlled according to the obtained T1, T2, T3 and T4 control parameters, thereby achieving the replacement of the negative current detection circuit module. The control parameters T1 or T3 are obtained by looking up the table, which includes: judging the size of the input voltage and the output voltage, when the input voltage is greater than the output voltage, the control parameter T3 is obtained by looking up the table, and when the input voltage is less than the output voltage, the control parameter T1 is obtained by looking up the table.

[0016] In a four-switch Buck-Boost converter adopting a pseudo-continuous mode, switching between the two working modes of pseudo-critical continuous mode and pseudo-discontinuous mode includes: in the pseudo-discontinuous mode, according to the input voltage, output voltage and output power of the four-switch Buck-Boost converter, a control parameter T1 or T3 is obtained by looking up a table, the control parameter output by the voltage loop is used as the control parameter T2, and other control parameters of the PWM module are calculated according to the constraints in different working modes; in the pseudo-critical continuous mode, according to the input voltage, output voltage and output power of the four-switch Buck-Boost converter, a control parameter T1 or T3 is obtained by looking up a table, according to the control parameter output by the voltage loop and the working mode judgment value T 2max The control parameter T2 is calculated, and other control parameters of the PWM module are calculated according to the constraints in different working modes.

[0017] Among them, in the pseudo critical continuous mode, according to the control parameters of the voltage loop output and the working mode judgment value T 2max The control parameter T2 is calculated as follows:

[0018] T2=T 2max -(T u -T 2max )

[0019] in,

[0020] Where, T u Represents the control parameter of the voltage loop output, T 2max Indicates the working mode judgment value, V in Indicates the input voltage, V o represents the output voltage, T represents the period, I zvs It represents the expected negative current value to achieve ZVS, and L represents the inductance.

[0021] In order to achieve smooth switching between the two modes, in the pseudo critical continuous mode, according to the control parameters of the voltage loop output and the working mode judgment value T 2max The control parameter T2 is calculated as follows:

[0022]

[0023] in,

[0024] Where, T u Represents the control parameter of the voltage loop output, T 2max Indicates the working mode judgment value, V in Indicates the input voltage, V o represents the output voltage, T represents the period, I zvsindicates the negative current expectation value for realizing ZVS, L indicates inductance;

[0025] k is a ratio, and the ratio k is calculated as follows: the output power of the four-switch Buck-Boost converter in pseudo-discontinuous mode and pseudo-critical continuous mode is calculated, and the intersection of the output power in the two modes is calculated, and the ratio of dP o / dT2 in pseudo-discontinuous mode and dP o / dT2 in pseudo-critical continuous mode is taken as the value of k.

[0026] The calculation formula of the ratio k is:

[0027]

[0028] In the formula, f s indicates the switching frequency.

[0029] Further, in pseudo-discontinuous mode, when the input voltage is greater than the output voltage, the constraint condition is:

[0030] T1=2LI zvs / V in

[0031] T1+T2+T3+T4=T

[0032] When the input voltage is less than or equal to the output voltage, the constraint condition is:

[0033] T3=2LI zvs / V o

[0034] T1+T2+T3+T4=T

[0035] In the formula, V in indicates the input voltage, V o indicates the output voltage, T indicates the period, I zvs indicates the negative current expectation value for realizing ZVS, L indicates inductance.

[0036] In pseudo-critical continuous mode, the constraint condition is:

[0037] T4=0

[0038] T1+T2+T3+T4=T

[0039] In the formula, T indicates the period.

[0040] The control parameter T1 or T3 is obtained by looking up a table, and the table is obtained by establishing the relationship between the negative current amplitude and T1, T3 of the four-switch Buck-Boost converter under different input voltages, output voltages and output powers.

[0041] The application further provides a control system of the four-switch Buck-Boost converter, which comprises a memory, a processor and a computer program stored in the memory and executable on the processor, and the control method of the four-switch Buck-Boost converter is realized when the processor executes the computer program.

[0042] Beneficial effects: Compared with the prior art, the application has the following advantages: according to the input voltage, the output voltage and the output power of the four-switch Buck-Boost converter, the control parameter T1 or T3 is obtained by table lookup, and then T1, T2, T3 and T4 are calculated to control the PWM module output, so as to realize the replacement of the negative current detection circuit module. Therefore, the application realizes the ZVS of the switching tube while reducing unnecessary negative current detection circuits and simplifying the PCB layout. On this basis, the proportional coefficient k is introduced in the calculation of the control parameter T2, and the converter can be smoothly switched between the PDCM and PCRM working modes by changing the proportional coefficient k. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 is the FSBB circuit topology;

[0044] Figure 2 is the FSBB circuit and its negative current detection circuit topology;

[0045] Figure 3 is the instantaneous transmission power of PDCM and PCRM under the control of the negative current detection circuit;

[0046] Figure 4 is the intention of the degree of freedom lookup table for realizing ZVS according to the application;

[0047] Figure 5 is the relationship between the output power P in of the FSBB circuit and the output parameter T u of the PI loop at different input voltages V o ;

[0048] Figure 6 is the relationship between the output power P o of the FSBB circuit and the output parameter T u of the PI loop after the control parameter is corrected;

[0049] Figure 7 is the closed-loop control block diagram of the control system of the four-switch Buck-Boost converter according to the application. DETAILED DESCRIPTION

[0050] The technical solutions of the application will be further described below with reference to the drawings and examples.

[0051] The control method for a four-switch Buck-Boost converter according to the present invention is directed to a four-switch Buck-Boost converter that uses a pseudo continuous conduction mode (PCCM) and includes four control parameters, T1, T2, T3, and T4, and implements ZVS through a negative current detection circuit. In a four-switch Buck-Boost converter that does not include a negative current detection circuit module, the control parameter T1 or T3 is obtained by table lookup based on the input voltage, output voltage, and output power of the four-switch Buck-Boost converter. Other control parameters of the PWM module are calculated based on constraints in different operating modes. The PWM module output is controlled based on the obtained four control parameters, T1, T2, T3, and T4, thereby replacing the negative current detection circuit module.

[0052] This method replaces the traditional negative current detection with a table lookup of control parameters, making the converter smaller and simpler in layout. Furthermore, by varying the coefficients between the two operating modes, the four-switch Buck-Boost converter can smoothly switch between them.

[0053] To facilitate quantitative illustration of the technical solution of this invention, a 3kW four-switch bidirectional DC converter with a 210-330V input and a 270V output is used as an example. This quantitative description maintains the general applicability of the technical method. Under different operating conditions, a table lookup is performed for control parameters T1 and T3, replacing the original negative current detection circuit. During circuit operation, the four control parameters satisfy the two constraints of Equation 7:

[0054]

[0055] The other two control parameters are defined as degrees of freedom, namely the degrees of freedom used to optimize the effective value of the inductor current C v1 and the degree of freedom C used to achieve ZVS v2 The degree of freedom C v1 Different control parameters are assigned values ​​under different working conditions. The calculation formula is as shown in Equation 8:

[0056]

[0057] like Figure 4 As shown, the degree of freedom C used to achieve ZVS is obtained by looking up the table. v2 . At input voltage V in Less than the output voltage V o When T1 is obtained by looking up the table, the input voltage V in Greater than or equal to the output voltage V oT3 is obtained by table lookup method.

[0058] In PDCM and PCRM, P o

[0059]

[0060] In PDCM, T2 increases with the increase of P o ; while in PCRM, T2 decreases with the increase of P o . Therefore, the relationship between T2 and T u is defined as formula 10, and the method of obtaining the control parameter T u is different in different modes.

[0061]

[0062] At this time, P o and the control parameter T u are related as shown in formula 8. Figure 5 As the control parameter T u passes through the transition area between PDCM and PCRM, the output power changes sharply, which will cause the instability of the closed loop of the converter.

[0063] After the relationship between P o and T u in PDCM and PCRM is solved, the ratio k of the slopes between PDCM and PCRM can be obtained as formula 11:

[0064]

[0065] Therefore, a control method for smooth switching between the two working modes is proposed, and its expression is shown as formula 12:

[0066]

[0067] In PDCM, the original controller parameters are still used, while in PCRM, the controller parameters are modified according to the size relationship between the input voltage and the output point through formula 12 to realize smooth switching between the two working modes, and the problem of mismatching of the control parameters will not affect the stability of the closed loop of the converter. Its effect is shown as formula 13. Figure 6

[0068] The following will be introduced respectively.

[0069] After substituting the circuit parameters into formula 5, the values of the control parameters in different working conditions can be obtained, and then the control parameters T1 and T3 in different working conditions are formed into a table as shown in formula 6 and sent to the MCU. Figure 4 ​​​

[0070] In the PDCM and PCRM working mode o After the expression of T2, the derivative of T2 is obtained, and the slope ratio of PCRM and PDCM is as shown in formula 11.

[0071] The control system of the four-switch Buck-Boost converter comprises a memory, a processor, and a computer program stored in the memory and capable of running on the processor, and the processor implements the control method of the four-switch Buck-Boost converter when executing the computer program. The closed-loop control block diagram of the system is as shown in the accompanying Figure 7 The intermediate control quantity T u The control parameter C v2 is output through the input voltage and output current, and then the frequency constraint in formula 7 is substituted and calculated to obtain T1, T2, T3 and T4, which are output to the MOSFET to realize ZVS, and when the output power continuously changes, the converter will not be unstable due to the switching of the working mode.

Claims

1. A control method of a four-switch Buck-Boost converter, characterized by: In the four-switch Buck-Boost converter without the negative current detection circuit module, according to the input voltage, output voltage and output power of the four-switch Buck-Boost converter, the control parameter T1 or T3 is obtained by table lookup, and other control parameters of the PWM module are calculated according to constraint conditions in different working modes; the four control parameters T1, T2, T3 and T4 obtained are used to control the PWM module output, so as to realize the replacement of the negative current detection circuit module; In the four-switch Buck-Boost converter in pseudo-continuous mode, for the switching of pseudo-critical continuous mode and pseudo-discontinuous mode, including: in the pseudo-critical continuous mode, according to the input voltage, output voltage and output power of the four-switch Buck-Boost converter, the control parameter T1 or T3 is obtained by table lookup, according to the control parameter output by the voltage loop and the working mode determination value T 2max The control parameter T2 is calculated, and other control parameters of the PWM module are calculated according to the constraint conditions in different working modes; wherein, according to the control parameter output by the voltage loop and the working mode determination value T 2max The control parameter T2 is calculated, and other control parameters of the PWM module are calculated according to the constraint conditions in different working modes; wherein, according to the control parameter output by the voltage loop and the working mode determination value T ； In the formula, T u represents the control parameter of the voltage loop output, T 2max represents the working mode determination value, k is a ratio, and the calculation formula of the ratio k is: ； In the formula, f s represents the switching frequency, V in represents the input voltage, V o represents the output voltage, T represents the period, I zvs represents the negative current expectation value for realizing ZVS, and L represents the inductance Operation mode determination value T 2max The calculation formula is: ； In the formula, T u represents a control parameter of a voltage loop output, T 2max represents a working mode determination value, V in represents an input voltage, V o represents an output voltage, T represents a period, I zvs represents a negative current expectation value for realizing ZVS, and L represents an inductance.

2. The control method of a four-switch Buck-Boost converter according to claim 1, characterized in that: In the four-switch Buck-Boost converter adopting the pseudo continuous mode, for the switching between the pseudo critical continuous mode and the pseudo discontinuous mode, the method further comprises: in the pseudo discontinuous mode, according to the input voltage, output voltage and output power of the four-switch Buck-Boost converter, the control parameter T1 or T3 is obtained by table lookup, and the control parameter output by the voltage loop is used as the control parameter T2, and other control parameters of the PWM module are calculated according to constraint conditions in different working modes.

3. The control method of the four-switch Buck-Boost converter according to claim 1, characterized in that: The control parameter T1 or T3 is obtained by table lookup, which comprises: judging the size of the input voltage and the output voltage, when the input voltage is greater than the output voltage, the control parameter T3 is obtained by table lookup, and when the input voltage is less than the output voltage, the control parameter T1 is obtained by table lookup.

4. The control method of a four-switch Buck-Boost converter according to claim 2, characterized in that: In the pseudo discontinuous mode, when the input voltage is greater than the output voltage, the constraint condition is: ； ； When the input voltage is less than or equal to the output voltage, the constraint condition is: ； ； In the formula, V in represents the input voltage, V o represents the output voltage, T represents the period, I zvs represents the negative current value expected to achieve ZVS, and L represents the inductance.

5. The control method of a four-switch Buck-Boost converter according to claim 1, characterized in that: In the pseudo critical continuous mode, the constraint condition is: ； ； In the formula, T represents a period.

6. The control method of a four-switch Buck-Boost converter according to claim 1, characterized in that: The control parameter T1 or T3 is obtained by table lookup, and the table is obtained by establishing the relationship between the negative current amplitude and T1, T3 of the four-switch Buck-Boost converter under different input voltages, output voltages and output powers.

7. A control system for a four-switch Buck-Boost converter, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, wherein the control system is configured to: The processor implements the control method of the four-switch Buck-Boost converter according to any one of claims 1 to 6 when executing the computer program.

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