Direct-current conversion device, grid-connected inverter, and control method for direct-current conversion device thereof

Abstract

The application discloses a DC conversion device, a grid-connected inverter and a control method of the DC conversion device of the grid-connected inverter. The device comprises: an inductor unit arranged between a BUCK unit and a BOOST unit; and a capacitor unit arranged at the output side of the BOOST unit. The BUCK unit, the inductor unit, the BOOST unit and the capacitor unit are all three-phase and are staggered and connected in parallel to form a three-phase staggered double-tube BUCK-BOOST parallel circuit. The parallel circuit is arranged between the voltage input end and the voltage output end of the front-stage DC-DC converter of the grid-connected inverter. The parallel circuit can work in a BUCK asynchronous mode or a BOOST asynchronous mode. According to the scheme, the three-phase staggered double-tube BUCK-BOOST parallel circuit is arranged and works in the asynchronous mode, so that the double-tube switching tubes of each phase do not need to be turned on and turned off simultaneously, the switching tube loss is reduced, and the efficiency of the front-stage DC-DC converter is improved.

Description

Technical Field

[0001] This invention belongs to the field of grid-connected inverter technology, specifically relating to a DC-DC converter, a grid-connected inverter and a control method for the DC-DC converter, and particularly to a three-phase interleaved dual-transistor BUCK-BOOST parallel circuit, a control method for the three-phase interleaved dual-transistor BUCK-BOOST parallel circuit. Background Technology

[0002] The electrical energy generated by wind power generation units or solar photovoltaic power generation units is generally fed into the power grid through a grid-connected inverter. Since the input voltage range of the grid-connected inverter is relatively wide, the grid-connected inverter is generally composed of a DC-DC converter and a DC-AC converter. The front-end DC-DC converter converts the output voltage of the wind turbine or solar cell into the required constant DC voltage, and the back-end DC-AC inverter converts this DC voltage into AC voltage and feeds it into the power grid.

[0003] For wind power or solar photovoltaic power generation, the output voltage variation range is relatively wide. The front-end DC-DC converter obtains a stable output voltage Vo through a dual-transistor BUCK-BOOST parallel circuit. However, in the synchronous mode, the dual-transistor BUCK-BOOST converter in the dual-transistor BUCK-BOOST parallel circuit requires the two switching transistors to turn on and off simultaneously, resulting in severe switching transistor losses.

[0004] The above content is only used to help understand the technical solution of the present invention and does not represent an admission that the above content is prior art. Summary of the Invention

[0005] The purpose of this invention is to provide a DC-DC converter, a grid-connected inverter, and a control method for the DC-DC converter, to solve the problem that when the output voltage of a wind power generation system or a solar photovoltaic power generation system is converted into the required constant DC voltage by the front-stage DC-DC converter in the grid-connected inverter, the front-stage DC-DC converter passes through a dual-tube BUCK-BOOST parallel circuit. However, in synchronous mode, the dual-tube BUCK-BOOST converters in the parallel circuit need to turn on and off simultaneously, resulting in severe switching losses and reducing the efficiency of the front-stage DC-DC converter in the grid-connected inverter. The invention achieves the effect of reducing switching losses and improving the efficiency of the front-stage DC-DC converter in the grid-connected inverter by setting a three-phase interleaved dual-tube BUCK-BOOST parallel circuit and operating in asynchronous mode, so that the dual-tube switches of each phase do not need to turn on and off simultaneously.

[0006] This invention provides a DC-DC converter, which is applied to a grid-connected inverter as the front-stage DC-DC converter of the grid-connected inverter. The DC-DC converter includes a BUCK unit, an inductor unit, a BOOST unit, and a capacitor unit. The inductor unit is disposed between the BUCK unit and the BOOST unit. The capacitor unit is disposed on the output side of the BOOST unit. The BUCK unit, inductor unit, BOOST unit, and capacitor unit are all three-phase and are interleaved in parallel to form a three-phase interleaved dual-transistor BUCK-BOOST parallel circuit. The three-phase interleaved dual-transistor BUCK-BOOST parallel circuit is disposed between the voltage input terminal and the voltage output terminal of the front-stage DC-DC converter of the grid-connected inverter. The three-phase interleaved dual-transistor BUCK-BOOST parallel circuit can operate in either BUCK asynchronous mode or BOOST asynchronous mode.

[0007] In some implementations, when the deviation voltage between the actual output voltage and the target output voltage at the voltage output terminal of the pre-stage DC-DC converter of the grid-connected inverter is between the minimum and maximum carrier values ​​of the BUCK unit, the three-phase interleaved dual-transistor BUCK-BOOST parallel circuit operates in the BUCK asynchronous mode; when the deviation voltage between the actual output voltage and the target output voltage at the voltage output terminal of the pre-stage DC-DC converter of the grid-connected inverter is between the minimum and maximum carrier values ​​of the BOOST unit, the three-phase interleaved dual-transistor BUCK-BOOST parallel circuit operates in the BOOST asynchronous mode.

[0008] In some embodiments, the BUCK unit includes: a first QBUCK switching module, a second QBUCK switching module, and a third QBUCK switching module; the inductor unit includes: a first inductor module, a second inductor module, and a third inductor module; the BOOST unit includes: a first QBOOST switching module, a second QBOOST switching module, and a third QBOOST switching module; the capacitor unit includes: a first capacitor module, a second capacitor module, and a third capacitor module; wherein, in the BUCK unit, the first QBUCK switching module, the second QBUCK switching module, and the third QBUCK switching module are connected in parallel between the input voltage of the front-stage DC-DC converter and ground; the front-stage DC-DC converter of the grid-connected inverter... The voltage at the voltage input terminal of the inverter is the input voltage of the preceding DC-DC converter; in the inductor unit, the first inductor module, the second inductor module, and the third inductor module are arranged in parallel between the corresponding switching transistor modules in the BUCK unit and the BOOST unit; in the BOOST unit, the first QBOOST switching transistor module, the second QBOOST switching transistor module, and the third QBOOST switching transistor module are connected in parallel between ground and the first terminal of the capacitor unit; the second terminal of the capacitor unit is grounded; in the capacitor unit, the first capacitor module, the second capacitor module, and the third capacitor module are connected in parallel, and the voltage across the capacitor unit is the actual output voltage of the preceding DC-DC converter of the grid-connected inverter.

[0009] In some embodiments, in the first, second, and third QBUCK switching modules, each QBUCK switching module includes: a QBUCK switching transistor and a QBUCK diode; the input voltage of the front-end DC-DC converter is connected to the first terminal of the QBUCK switching transistor; the second terminal of the QBUCK switching transistor is connected to the cathode of the QBUCK diode on one side and to the first terminal of a corresponding inductor module among the first, second, and third inductor modules on the other side; in the first, second, and third QBOOST switching modules, each QBOOST switching module includes: a QBOOST switching transistor and a QBOOST diode; the first terminal of the QBOOST switching transistor is grounded; the second terminal of the QBOOST switching transistor is connected to the second terminal of a corresponding inductor module among the first, second, and third inductor modules on one side and to the anode of the QBOOST diode on the other side.

[0010] In some embodiments, both the QBUCK switch and the QBOOST switch are MOSFETs; the first terminal of the QBUCK switch is the drain of the MOSFET; the second terminal of the QBUCK switch is the source of the MOSFET; the first terminal of the QBOOST switch is the drain of the MOSFET; and the second terminal of the QBOOST switch is the source of the MOSFET.

[0011] In conjunction with the above-described device, the present invention further provides a grid-connected inverter, comprising: the DC-DC converter described above.

[0012] In conjunction with the aforementioned grid-connected inverter, this invention further provides a control method for the DC-DC converter of the grid-connected inverter, comprising: when the DC-DC converter of the grid-connected inverter is operating, acquiring the actual output voltage of the DC-DC converter and acquiring the target output voltage of the DC-DC converter; determining the voltage difference between the actual output voltage of the DC-DC converter and the target output voltage of the DC-DC converter, denoted as the deviation voltage; and controlling the DC-DC converter to operate in either BUCK asynchronous mode or BOOST asynchronous mode based on the deviation voltage.

[0013] In some embodiments, controlling the DC-DC converter to operate in either BUCK asynchronous mode or BOOST asynchronous mode based on the deviation voltage includes: determining the range of the deviation voltage; the range being between the minimum and maximum carrier values ​​of the BUCK unit, or between the minimum and maximum carrier values ​​of the BOOST unit; if the deviation voltage is between the minimum and maximum carrier values ​​of the BUCK unit, then controlling the DC-DC converter to operate in the BUCK asynchronous mode; if the deviation voltage is between the minimum and maximum carrier values ​​of the BOOST unit, then controlling the DC-DC converter to operate in the BOOST asynchronous mode.

[0014] In some embodiments, when the BUCK unit includes a first QBUCK switch module, a second QBUCK switch module, and a third QBUCK switch module, and the BOOST unit includes a first QBOOST switch module, a second QBOOST switch module, and a third QBOOST switch module, controlling the DC-DC converter to operate in the BUCK asynchronous mode includes: controlling the operating time of the first QBUCK switch module to be (V e –V L1The second QBUCK switch module is controlled to have a 120-degree phase difference with the first QBUCK switch module's PWM wave relative to the first QBUCK switch module's PWM wave. The operating time of the second QBUCK switch module is (V / Vsaw). e –V L1 The second QBOOST switch module is turned off; the PWM wave of the third QBUCK switch module is controlled to have a 240-degree phase difference with the PWM wave of the first QBUCK switch module; the operating time of the third QBUCK switch module is (V / Vsaw). e –V L1 ) / Vsaw, and control the third QBOOST switching module to turn off; wherein, V e V is the deviation voltage. L1 Vsaw is the minimum carrier value of the BUCK unit, and Vsaw is the peak-to-peak value of the carrier of the BUCK unit and the carrier of the Boost unit.

[0015] In some embodiments, when the BUCK unit includes a first QBUCK switch module, a second QBUCK switch module, and a third QBUCK switch module, and the BOOST unit includes a first QBOOST switch module, a second QBOOST switch module, and a third QBOOST switch module, controlling the DC-DC converter to operate in the BOOST asynchronous mode includes: controlling the operating time of the first QBUCK switch module to be 1, and controlling the operating time of the first QBOOST switch module to be (V e –V L2 ) / Vsaw; Control the phase difference between the PWM wave of the second QBUCK switch module and the PWM wave of the first QBUCK switch module to be 120 degrees, control the phase difference between the PWM wave of the second QBOOST switch module and the PWM wave of the first QBOOST switch module to be 120 degrees, the operating time of the second QBUCK switch module is 1, and control the operating time of the second QBOOST switch module to be (V e –V L2) / Vsaw; Control the PWM wave of the third QBUCK switch module to have a phase difference of 240 degrees relative to the PWM wave of the first QBUCK switch module, control the PWM wave of the third QBOOST switch module to have a phase difference of 240 degrees relative to the PWM wave of the first QBOOST switch module, the operating time of the third QBUCK switch module is 1, and control the operating time of the third QBOOST switch module to be (V e –V L2 ) / Vsaw; where V e V is the deviation voltage. L2 Vsaw is the minimum carrier value of the BOOS unit, and Vsaw is the peak-to-peak value of the carrier of the BUCK unit and the carrier of the Boost unit.

[0016] Therefore, the solution of the present invention, by setting a three-phase interleaved dual-transistor BUCK-BOOST parallel circuit, the parallel circuit includes a BUCK unit and a BOOST unit. The BUCK unit includes three switching transistors QBUCK arranged in parallel across three phases, and the BOOST unit includes three switching transistors QBOOST arranged in parallel across three phases. During control, the deviation voltage between the actual output voltage and the target output voltage of the parallel circuit is detected. Based on the range of the deviation voltage, the parallel circuit is controlled to operate in either BUCK asynchronous mode or BOOST asynchronous mode. Specifically, if the deviation voltage is between the minimum and maximum carrier values ​​of the BUCK unit, the parallel circuit is controlled to operate in BUCK asynchronous mode; if the deviation voltage is between the minimum and maximum carrier values ​​of the BOOST unit, the parallel circuit is controlled to operate in BOOST asynchronous mode. Thus, by setting a three-phase interleaved dual-transistor BUCK-BOOST parallel circuit and operating in asynchronous mode, the dual-transistor switching transistors of each phase do not need to be turned on and off simultaneously, reducing switching transistor losses and improving the efficiency of the front-end DC-DC converter in the grid-connected inverter.

[0017] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1 A schematic diagram of the structure of the solar power generation or wind power output side and the grid-connected inverter;

[0020] Figure 2 This is a schematic diagram of the dual-transistor BUCK-BOOST converter in the relevant scheme;

[0021] Figure 3 This is a schematic diagram of the structure of an embodiment of the DC-DC converter of the present invention;

[0022] Figure 4 This is a flowchart illustrating an embodiment of the control method for the DC-DC converter of the present invention;

[0023] Figure 5 This is a flowchart illustrating an embodiment of the method of the present invention for controlling the DC-DC converter to operate in BUCK asynchronous mode or BOOST asynchronous mode.

[0024] Figure 6 This is a flowchart illustrating an embodiment of the method of the present invention for controlling the DC-DC converter to operate in the BUCK asynchronous mode.

[0025] Figure 7 This is a flowchart illustrating an embodiment of the method of the present invention for controlling the DC-DC converter to operate in the BOOST asynchronous mode;

[0026] Figure 8 This is a schematic diagram of an embodiment of a three-phase interleaved dual-transistor BUCK-BOOST parallel main circuit according to the present invention;

[0027] Figure 9 This is a schematic diagram of an embodiment of a three-phase interleaved dual-transistor BUCK-BOOST parallel main circuit and controller according to the present invention;

[0028] Figure 10 This is a schematic diagram showing the time, duty cycle of the switching transistors, and voltage range curves of an embodiment of a three-phase interleaved dual-transistor BUCK-BOOST parallel main circuit according to the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0030] Figure 1 This is a schematic diagram of the structure of the output side of a solar power generation or wind power system and the grid-connected inverter, such as... Figure 1As shown, the output voltage of solar power or wind power is used as the input voltage Vin of the front-end DC-DC converter, which is then converted into the required constant DC voltage Vo. The constant DC voltage Vo is then converted into AC voltage by the rear-end DC-AC inverter and connected to the power grid.

[0031] Figure 2 This is a schematic diagram of the dual-transistor BUCK-BOOST converter in the relevant scheme. (See diagram below.) Figure 2 As shown, the positive terminal of the input voltage Vin is connected to the drain of switching transistor Q1; the source of switching transistor Q1 is connected to point A. Point A is connected to the cathode of diode D1 on one side and to point B via inductor Lf on the other. Point B is connected to the drain of switching transistor Q2 on one side and to the anode of diode D2 on the other. The anode of diode D1 is connected to the negative terminal of the input voltage Vin. The source of switching transistor Q2 is connected to the negative terminal of the input voltage Vin. The cathode of diode D2 is connected to the negative terminal of the input voltage Vin via capacitor Cf. The voltage across capacitor Cf is the output voltage Vo. Figure 2 The dual-tube BUCK-BOOST converter shown has advantages such as input and output polarity being the same and low stress on the switching transistors. However, in synchronous mode, the dual-tube switching transistors need to be turned on and off simultaneously, resulting in severe losses in the switching transistors.

[0032] Considering that when the output voltage of a wind power generation system or a solar photovoltaic power generation system is converted into the required constant DC voltage by the front-stage DC-DC converter in the grid-connected inverter, the front-stage DC-DC converter passes through a dual-transistor BUCK-BOOST parallel circuit. However, in synchronous mode, the two switching transistors in the dual-transistor BUCK-BOOST converter need to be turned on and off simultaneously, resulting in severe switching transistor losses.

[0033] To reduce switching losses, improve the efficiency of the front-stage DC-DC converter in a grid-connected inverter, and reduce output voltage ripple, this invention addresses the front-stage DC-DC converter in small-to-medium power wind power systems or photovoltaic power systems. This front-stage DC-DC converter typically employs a simple, non-isolated converter. The invention proposes a three-phase interleaved dual-transistor BUCK-BOOST parallel circuit and control strategy to reduce switching losses, improve the efficiency of the front-stage DC-DC converter in the grid-connected inverter, and reduce output voltage ripple.

[0034] According to an embodiment of the present invention, a DC-DC converter is provided. See also Figure 3The diagram shows a structural schematic of an embodiment of the device of the present invention. The DC-DC converter is applied to a grid-connected inverter, serving as the front-stage DC-DC converter of the grid-connected inverter. The DC-DC converter includes: a BUCK unit, an inductor unit, a BOOST unit, and a capacitor unit. The inductor unit is disposed between the BUCK unit and the BOOST unit. The capacitor unit is disposed on the output side of the BOOST unit. The BUCK unit, inductor unit, BOOST unit, and capacitor unit are all three-phase and are interleaved in parallel to form a three-phase interleaved dual-transistor BUCK-BOOST parallel circuit. The three-phase interleaved dual-transistor BUCK-BOOST parallel circuit is disposed between the voltage input terminal and the voltage output terminal of the front-stage DC-DC converter of the grid-connected inverter. The three-phase interleaved dual-transistor BUCK-BOOST parallel circuit can operate in either BUCK asynchronous mode or BOOST asynchronous mode.

[0035] Specifically, when the voltage deviation between the actual output voltage and the target output voltage at the voltage output terminal of the pre-stage DC-DC converter of the grid-connected inverter is between the minimum and maximum carrier values ​​of the BUCK unit, the three-phase interleaved dual-transistor BUCK-BOOST parallel circuit operates in the BUCK asynchronous mode. When the voltage deviation between the actual output voltage and the target output voltage at the voltage output terminal of the pre-stage DC-DC converter of the grid-connected inverter is between the minimum and maximum carrier values ​​of the BOOST unit, the three-phase interleaved dual-transistor BUCK-BOOST parallel circuit operates in the BOOST asynchronous mode.

[0036] The present invention provides a three-phase interleaved dual-transistor BUCK-BOOST parallel circuit. This three-phase interleaved dual-transistor BUCK-BOOST parallel circuit is an asynchronous circuit, which can reduce switching transistor losses, improve the efficiency of the DC-DC converter, and mitigate load voltage fluctuations. Furthermore, in the present invention, the dual-transistor BUCK-BOOST converter can operate in an interleaved control mode in asynchronous mode. The output voltage and input voltage of the dual-transistor BUCK-BOOST converter are in phase. The period of the dual-transistor BUCK-BOOST parallel asynchronous circuit is 2π, and the periods of each controller switching transistor differ by 2π / 3. The three-phase interleaved dual-transistor BUCK-BOOST parallel asynchronous circuit and... Figure 2 Compared to the dual-transistor BUCK-BOOST converter shown, the current ripple of the inductor Lf is effectively reduced, which can lower the output voltage ripple.

[0037] In some embodiments, the BUCK unit includes: a first QBUCK switching module, a second QBUCK switching module, and a third QBUCK switching module. The inductor unit includes: a first inductor module, a second inductor module, and a third inductor module, where the first inductor module is, for example, inductor L1, the second inductor module is, for example, inductor L2, and the third inductor module is, for example, inductor L3. The BOOST unit includes: a first QBOOST switching module, a second QBOOST switching module, and a third QBOOST switching module. The capacitor unit includes: a first capacitor module, a second capacitor module, and a third capacitor module, where the first capacitor module is, for example, capacitor C1, the second capacitor module is, for example, capacitor C2, and the third capacitor module is, for example, capacitor C3.

[0038] In the BUCK unit, the first QBUCK switching module, the second QBUCK switching module, and the third QBUCK switching module are connected in parallel between the input voltage of the front-stage DC-DC converter and ground; the voltage at the input terminal of the front-stage DC-DC converter of the grid-connected inverter is the input voltage of the front-stage DC-DC converter. In the inductor unit, the first inductor module, the second inductor module, and the third inductor module are connected in parallel between the corresponding switching modules in the BUCK unit and the BOOST unit. In the BOOST unit, the first QBOOST switching module, the second QBOOST switching module, and the third QBOOST switching module are connected in parallel between ground and the first terminal of the capacitor unit; the second terminal of the capacitor unit is grounded. In the capacitor unit, the first capacitor module, the second capacitor module, and the third capacitor module are connected in parallel, and the voltage across the capacitor unit is the actual output voltage of the voltage output terminal of the front-stage DC-DC converter of the grid-connected inverter.

[0039] Specifically, in the first, second, and third QBUCK switching modules, each QBUCK switching module includes: a QBUCK switching transistor and a QBUCK diode. The input voltage of the front-end DC-DC converter is connected to the first terminal of the QBUCK switching transistor. The second terminal of the QBUCK switching transistor is connected to the cathode of the QBUCK diode on one hand, and to the first terminal of a corresponding inductor module among the first, second, and third inductor modules on the other hand.

[0040] In the first, second, and third QBOOST switching modules, each QBOOST switching module includes: a QBOOST switching transistor and a QBOOST diode. The first connection terminal of the QBOOST switching transistor is grounded. The second connection terminal of the QBOOST switching transistor is connected to the second terminal of a corresponding inductor module in the first, second, and third inductor modules, and also connected to the anode of the QBOOST diode.

[0041] Preferably, both the QBUCK switch and the QBOOST switch are MOSFETs. The first terminal of the QBUCK switch is the drain of the MOSFET. The second terminal of the QBUCK switch is the source of the MOSFET. The first terminal of the QBOOST switch is the drain of the MOSFET. The second terminal of the QBOOST switch is the source of the MOSFET.

[0042] Specifically, Figure 8 This is a schematic diagram of an embodiment of a three-phase interleaved dual-transistor BUCK-BOOST parallel main circuit according to the present invention. Figure 8 As shown, the three-phase interleaved dual-transistor BUCK-BOOST parallel main circuit provided by the present invention includes: switching transistors QBUCK-1, QBUCK-2, and QBUCK-3; inductors L1, L2, and L3; diodes DBUCK-1, DBUCK-2, and DBUCK-3; switching transistors QBOOST1, QBOOST2, and QBOOST3; diodes DBOOST1, DBOOST2, and DBOOST3; and capacitors C1, C2, and C3. Inductors L1, L2, and L3 are energy storage inductors; switching transistors QBUCK-1, QBUCK-2, and QBUCK-3 are power MOSFETs; switching transistors QBOOST1, QBOOST2, and QBOOST3 are power MOSFETs; and capacitors C1, C2, and C3 are load energy storage capacitors.

[0043] exist Figure 8In the example shown, the input voltage Vin is connected to the drain of the switching transistor QBUCK-1. The source of the switching transistor QBUCK-1 is connected to the cathode of the diode DBUCK-1 and the first terminal of the inductor L1. The anode of the diode DBUCK-1 is grounded. The second terminal of the inductor L1 is connected to the source of the switching transistor QBOOST1 and the anode of the diode DBOOST1. The drain of the source of the switching transistor QBOOST1 is grounded. The cathode of the diode DBOOST1 is grounded through capacitors C1, C2, and C3 connected in parallel. The voltage across capacitors C1, C2, and C3 is the output voltage Vo.

[0044] exist Figure 8 In the example shown, the input voltage Vin is connected to the drain of the switching transistor QBUCK-2. The source of the switching transistor QBUCK-2 is connected to the cathode of the diode DBUCK-2 on one side and to the first terminal of the inductor L2 on the other. The anode of the diode DBUCK-2 is grounded. The second terminal of the inductor L2 is connected to the source of the switching transistor QBOOST2 on one side and to the anode of the diode DBOOST2 on the other. The drain of the source of the switching transistor QBOOST2 is grounded. The cathode of the diode DBOOST2 is grounded through capacitors C1, C2, and C3 connected in parallel.

[0045] exist Figure 8 In the example shown, the input voltage Vin is connected to the drain of the switching transistor QBUCK-3. The source of the switching transistor QBUCK-3 is connected to the cathode of the diode DBUCK-3 on one side and to the first terminal of the inductor L3 on the other. The anode of the diode DBUCK-3 is grounded. The second terminal of the inductor L3 is connected to the source of the switching transistor QBOOST3 on one side and to the anode of the diode DBOOST3 on the other. The drain of the source of the switching transistor QBOOST3 is grounded. The cathode of the diode DBOOST3 is grounded through capacitors C1, C2, and C3 connected in parallel.

[0046] The technical solution of this invention involves setting up a three-phase interleaved dual-transistor BUCK-BOOST parallel circuit. This parallel circuit includes a BUCK unit and a BOOST unit. The BUCK unit includes three QBUCK switches arranged in parallel across the three phases, and the BOOST unit includes three QBOOST switches arranged in parallel across the three phases. During control, the deviation voltage between the actual output voltage and the target output voltage of the parallel circuit is detected. Based on the range of this deviation voltage, the parallel circuit is controlled to operate in either BUCK asynchronous mode or BOOST asynchronous mode. Specifically, if the deviation voltage is between the minimum and maximum carrier values ​​of the BUCK unit, the parallel circuit is controlled to operate in BUCK asynchronous mode. If the deviation voltage is between the minimum and maximum carrier values ​​of the BOOST unit, the parallel circuit is controlled to operate in BOOST asynchronous mode. Therefore, by setting up a three-phase interleaved dual-transistor BUCK-BOOST parallel circuit and operating in asynchronous mode, the dual-transistor switches of each phase do not need to be turned on and off simultaneously, reducing switching losses and improving the efficiency of the front-end DC-DC converter in the grid-connected inverter.

[0047] According to an embodiment of the present invention, a grid-connected inverter corresponding to a DC-DC converter is also provided. This grid-connected inverter may include the DC-DC converter described above.

[0048] Since the processing and functions implemented by the grid-connected inverter in this embodiment are basically the same as those in the embodiments, principles and examples of the device, any details not covered in this embodiment can be found in the relevant descriptions in the foregoing embodiments, and will not be repeated here.

[0049] The technical solution of this invention employs a three-phase interleaved dual-transistor BUCK-BOOST parallel circuit. This parallel circuit includes a BUCK unit and a BOOST unit. The BUCK unit includes three QBUCK switches connected in parallel across three phases, and the BOOST unit includes three QBOOST switches connected in parallel across three phases. During control, the deviation voltage between the actual output voltage and the target output voltage of the parallel circuit is detected. Based on the range of this deviation voltage, the parallel circuit is controlled to operate in either BUCK asynchronous mode or BOOST asynchronous mode. Specifically, if the deviation voltage is between the minimum and maximum carrier values ​​of the BUCK unit, the parallel circuit is controlled to operate in BUCK asynchronous mode. If the deviation voltage is between the minimum and maximum carrier values ​​of the BOOST unit, the parallel circuit is controlled to operate in BOOST asynchronous mode. This improves the efficiency of the DC-DC converter and reduces output voltage ripple.

[0050] According to embodiments of the present invention, a control method for a DC-DC converter of a grid-connected inverter corresponding to a grid-connected inverter is also provided, such as... Figure 4 The diagram shows a flowchart of an embodiment of the method of the present invention. The control method of the DC-DC converter of the grid-connected inverter may include steps S110 to S130.

[0051] In step S110, when the DC-DC converter of the grid-connected inverter is working, the actual output voltage of the DC-DC converter is obtained, and the target output voltage of the DC-DC converter is obtained.

[0052] In step S120, the voltage difference between the actual output voltage of the DC-DC converter and the target output voltage of the DC-DC converter is determined and denoted as the deviation voltage.

[0053] In step S130, the DC-DC converter is controlled to operate in either BUCK asynchronous mode or BOOST asynchronous mode based on the deviation voltage.

[0054] Specifically, Figure 9 This is a schematic diagram of an embodiment of a three-phase interleaved dual-transistor BUCK-BOOST parallel main circuit and controller according to the present invention. Figure 9 As shown, the control system of the three-phase interleaved dual-transistor BUCK-BOOST parallel main circuit includes: a voltage regulator module, a digital main chip, and a drive module.

[0055] The control system of the three-phase interleaved dual-transistor BUCK-BOOST parallel main circuit detects the actual output voltage V of the three-phase interleaved dual-transistor BUCK-BOOST parallel main circuit. O Target output voltage V o-ref Deviation voltage V e =Target output voltage V o-ref -Actual output voltage V O Deviation voltage V e This serves as the output voltage or modulation signal of the voltage regulator module. The output voltage of the voltage regulator module is input to the digital main chip. Based on the output voltage of the voltage regulator module, the digital main chip outputs a drive signal to the drive module. The drive module can drive power MOSFETs QBUCK-1, QBUCK-2, and QBUCK-3, as well as power MOSFETs QBOOST1, QBOOST2, and QBOOST3.

[0056] In some embodiments, the specific process of controlling the DC-DC converter to operate in BUCK asynchronous mode or BOOST asynchronous mode according to the deviation voltage in step S130 is described in the following exemplary description.

[0057] The following is combined with Figure 5 The flowchart shown is a schematic diagram of an embodiment of the method of the present invention for controlling the DC-DC converter to operate in BUCK asynchronous mode or BOOST asynchronous mode. The specific process of controlling the DC-DC converter to operate in BUCK asynchronous mode or BOOST asynchronous mode in step S130 is further explained, including steps S210 to S230.

[0058] Step S210: Determine the range of the deviation voltage. This range is between the minimum and maximum carrier values ​​of the BUCK unit, or between the minimum and maximum carrier values ​​of the BOOST unit.

[0059] Step S220: If the deviation voltage is between the minimum carrier value and the maximum carrier value of the BUCK unit, then control the DC-DC converter to operate in the BUCK asynchronous mode.

[0060] Step S230: If the deviation voltage is between the minimum carrier value and the maximum carrier value of the BOOST unit, then control the DC-DC converter to operate in the BOOST asynchronous mode.

[0061] Specifically, Figure 10 This is a schematic diagram showing the time, duty cycle of the switching transistors, and voltage range curves of an embodiment of a three-phase interleaved dual-transistor BUCK-BOOST parallel main circuit according to the present invention. Switches QBUCK-1, QBUCK-2, and QBUCK-3 constitute the BUCK unit. Switches QBOOST1, QBOOST2, and QBOOST3 constitute the Boost unit. The sawtooth wave Vsaw_buck modulated by the software program in the digital main chip is the carrier wave of the BUCK unit, and its minimum value is V. L1 The maximum value is V H1 In the digital main chip, the sawtooth wave Vsaw_boost, modulated by the software program, is the carrier wave of the Boost unit, and its minimum value is V. L2 The maximum value is V H2 The maximum carrier value V of the BUCK cell H1 = Maximum carrier value V of the Boost cell L2 The two carrier waves have the same shape (see [reference]). Figure 10 (as shown in the example), and the peak-to-peak values ​​are all Vsaw.

[0062] The volt-second product balances as follows:

[0063] Vo = d1 / (1-d2)Vin.

[0064] d1=(V e –V L1 ) / Vsaw(V L1 ≤V e ≤V H1 ).

[0065] d1=1 (V L2 ≤V e ≤V H2 ).

[0066] d2=0 (V L1 ≤V e ≤V H1 ).

[0067] d2=(V e –V L2 ) / Vsaw(V L2 ≤V e ≤V H2 ).

[0068] Where Vo is the actual output voltage, d1 is the operating time of the switching transistor in the BUCK unit, d2 is the operating time of the switching transistor in the BOOST unit, Vin is the input voltage, and V e For the deviation voltage, V L1 V is the minimum carrier value of the BUCK cell. H1 V represents the maximum carrier value of the BUCK cell. L2 V is the minimum carrier value of the Boost cell. H2 Vsaw represents the maximum carrier value of the Boost unit, and Vsaw represents the peak-to-peak value of the carrier of the BUCK unit and the carrier of the Boost unit.

[0069] In some embodiments, when the BUCK unit includes a first QBUCK switch module, a second QBUCK switch module, and a third QBUCK switch module, and the BOOST unit includes a first QBOOST switch module, a second QBOOST switch module, and a third QBOOST switch module, the specific process of controlling the DC-DC converter to operate in the BUCK asynchronous mode in step S220 is described in the following exemplary description.

[0070] The following is combined with Figure 6 The flowchart shown is a schematic diagram of an embodiment of the method of the present invention for controlling the DC-DC converter to operate in the BUCK asynchronous mode. The specific process of controlling the DC-DC converter to operate in the BUCK asynchronous mode in step S220 is further explained, including steps S310 to S330.

[0071] Step S310, control the operating time of the first QBUCK switching module to be (V e –V L1 ) / Vsaw, and control the first QBOOST switching module to turn off.

[0072] Step S320: Control the PWM wave of the second QBUCK switching module to have a phase difference of 120 degrees relative to the PWM wave of the first QBUCK switching module; control the PWM wave of the second QBOOST switching module to have a phase difference of 120 degrees relative to the PWM wave of the first QBOOST switching module; the operating time of the second QBUCK switching module is (V e –V L1 ) / Vsaw, and control the second QBOOST switching module to turn off.

[0073] Step S330: Control the PWM wave of the third QBUCK switch module to have a phase difference of 240 degrees relative to the PWM wave of the first QBUCK switch module; control the PWM wave of the third QBOOST switch module to have a phase difference of 240 degrees relative to the PWM wave of the first QBOOST switch module; the operating time of the third QBUCK switch module is (V e –V L1 ) / Vsaw, and control the third QBOOST switching module to turn off.

[0074] Among them, V e V is the deviation voltage. L1 Vsaw is the minimum carrier value of the BUCK unit, and Vsaw is the peak-to-peak value of the carrier of the BUCK unit and the carrier of the Boost unit.

[0075] Specifically, in the asynchronous BUCK mode of the three-phase interleaved dual-transistor BUCK-BOOST parallel circuit:

[0076] Determine the given voltage (i.e., the target output voltage V) o-ref ) and actual output voltage V O Deviation voltage V e When the deviation voltage V e In V L1 ≤V e ≤V H1 Within the specified range, the three-phase interleaved dual-transistor BUCK-BOOST parallel circuit operates in the BUCK region, and the operating time d of the switching transistor QBUCK-1 is... 1＝ (V e –V L1 ) / Vsaw, the operating time d of the switching transistor QBOOST1 2＝0. Switch QBOOST1 is in the off state. The overall PWM waves of switches QBUCK-2 and QBOOST2 are 120 degrees out of phase with respect to the PWM waves of switches QBUCK-1 and QBOOST1. The operating time d of switch QBUCK-2 is... 1＝ (V e –V L1 ) / Vsaw, the operating time d of the switching transistor QBOOST2 2＝ 0. Switch QBOOST2 is in the off state. The PWM waves of switches QBUCK-3 and QBOOST3 are 240 degrees out of phase with respect to the PWM waves of switches QBUCK-1 and QBOOST1. The operating time d of switch QBUCK-3 is... 1＝ (V e –V L1 ) / Vsaw, the operating time d of the switching transistor QBOOST3 2＝ 0. Switch QBOOST3 is in the off state.

[0077] In some embodiments, when the BUCK unit includes a first QBUCK switch module, a second QBUCK switch module, and a third QBUCK switch module, and the BOOST unit includes a first QBOOST switch module, a second QBOOST switch module, and a third QBOOST switch module, the specific process of controlling the DC-DC converter to operate in the BOOST asynchronous mode in step S230 is described in the following exemplary description.

[0078] The following is combined with Figure 7 The flowchart shown is a schematic diagram of an embodiment of the method of the present invention for controlling the DC-DC converter to operate in the BOOST asynchronous mode. The specific process of controlling the DC-DC converter to operate in the BOOST asynchronous mode in step S230 is further explained, including steps S410 to S430.

[0079] Step S410: Control the operating time of the first QBUCK switching transistor module to 1, and control the operating time of the first QBOOST switching transistor to (V e –V L2 ) / Vsaw.

[0080] Step S420: Control the phase difference between the PWM wave of the second QBUCK switch module and the PWM wave of the first QBUCK switch module to be 120 degrees; control the phase difference between the PWM wave of the second QBOOST switch module and the PWM wave of the first QBOOST switch module to be 120 degrees; set the operating time of the second QBUCK switch module to 1; and control the operating time of the second QBOOST switch module to be (V... e –V L2 ) / Vsaw.

[0081] Step S430: Control the phase difference between the PWM wave of the third QBUCK switch module and the PWM wave of the first QBUCK switch module to be 240 degrees; control the phase difference between the PWM wave of the third QBOOST switch module and the PWM wave of the first QBOOST switch module to be 240 degrees; set the operating time of the third QBUCK switch module to 1; and control the operating time of the third QBOOST switch module to be (V... e –V L2 ) / Vsaw.

[0082] Among them, V e V is the deviation voltage. L2 Vsaw is the minimum carrier value of the BOOS unit, and Vsaw is the peak-to-peak value of the carrier of the BUCK unit and the carrier of the Boost unit.

[0083] Specifically, in the asynchronous BOOST mode of a three-phase interleaved dual-transistor BUCK-BOOST parallel circuit:

[0084] Determine the given voltage (i.e., the target output voltage V) o-ref ) and actual output voltage V O Deviation voltage V e When the deviation voltage V e In V L2 ≤V e ≤V H2 Within the specified range, the three-phase interleaved dual-transistor BUCK-BOOST parallel circuit operates in the BOOST region. The operating time of switch QBUCK-1 is d1 = 1, and switch QBUCK-1 is in the on state. The PWM waveform turn-on time of switch QBOOST1 is (V e –V L2 With Vsaw, switch QBOOST1 is in the ON state. The overall PWM waves of switches QBUCK-2 and QBOOST2 are 120 degrees out of phase with respect to the PWM waves of switches QBUCK-1 and QBOOST1. The operating time d of switch QBUCK-2 is... 1＝1. Switch QBUCK-2 is in the ON state, and the PWM waveform turn-on time of switch QBOOST2 is (V e –V L2 With Vsaw, switch QBOOST2 is in the ON state. The overall PWM waves of switches QBUCK-3 and QBOOST3 are 240 degrees out of phase with respect to the PWM waves of switches QBUCK-1 and QBOOST1. The operating time d of switch QBUCK-3 is... 1＝ 1. Switch QBUCK-3 is in the ON state, and the PWM waveform turn-on time of switch QBOOST2 is (V e –V L2 ) / Vsaw.

[0085] Since the processing and functions implemented by the method in this embodiment are basically the same as the embodiments, principles and examples of the grid-connected inverters described above, any parts not detailed in the description of this embodiment can be referred to the relevant descriptions in the aforementioned embodiments, and will not be repeated here.

[0086] The technical solution of this embodiment, by setting a three-phase interleaved dual-transistor BUCK-BOOST parallel circuit, includes a BUCK unit and a BOOST unit. The BUCK unit includes three QBUCK switches arranged in parallel across three phases, and the BOOST unit includes three QBOOST switches arranged in parallel across three phases. During control, the deviation voltage between the actual output voltage and the target output voltage of the parallel circuit is detected. Based on the range of the deviation voltage, the parallel circuit is controlled to operate in either BUCK asynchronous mode or BOOST asynchronous mode. Specifically, if the deviation voltage is between the minimum and maximum carrier values ​​of the BUCK unit, the parallel circuit is controlled to operate in BUCK asynchronous mode; if the deviation voltage is between the minimum and maximum carrier values ​​of the BOOST unit, the parallel circuit is controlled to operate in BOOST asynchronous mode. This reduces switching losses, improves the efficiency of the DC-DC converter, and mitigates load voltage fluctuations.

[0087] In summary, it is readily understood by those skilled in the art that, without conflict, the aforementioned advantageous methods can be freely combined and superimposed.

[0088] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A DC-DC converter, characterized in that, The DC-DC converter is applied to a grid-connected inverter as a front-end DC-DC converter of the grid-connected inverter; the DC-DC converter includes: a BUCK unit, a BOOST unit and a capacitor unit, and the BUCK unit and the BOOST unit share an inductor unit; the capacitor unit is located on the output side of the BOOST unit. The BUCK unit, the inductor unit, the BOOST unit, and the capacitor unit are all three-phase and are connected in parallel to form a three-phase interleaved dual-transistor BUCK-BOOST parallel circuit; the three-phase interleaved dual-transistor BUCK-BOOST parallel circuit can operate in either BUCK asynchronous mode or BOOST asynchronous mode. The BUCK unit includes three interleaved parallel switching transistors QBUCK, and the BOOST unit includes three interleaved parallel switching transistors QBOOST. During control, the deviation voltage between the actual output voltage and the target output voltage of the parallel circuit is detected. Based on the range of the deviation voltage, the parallel circuit is controlled to operate in either BUCK asynchronous mode or BOOST asynchronous mode. Specifically, if the deviation voltage is between the minimum and maximum carrier values ​​of the BUCK unit, the parallel circuit is controlled to operate in BUCK three-phase interleaved asynchronous mode; if the deviation voltage is between the minimum and maximum carrier values ​​of the BOOST unit, the parallel circuit is controlled to operate in BOOST three-phase interleaved asynchronous mode.

2. The DC-DC converter according to claim 1, characterized in that, The BUCK unit includes: a first QBUCK switching transistor module, a second QBUCK switching transistor module, and a third QBUCK switching transistor module; the inductor unit includes: a first inductor module, a second inductor module, and a third inductor module; the BOOST unit includes: a first QBOOST switching transistor module, a second QBOOST switching transistor module, and a third QBOOST switching transistor module; the capacitor unit includes: a first capacitor module, a second capacitor module, and a third capacitor module; wherein, In the BUCK unit, the first QBUCK switch module, the second QBUCK switch module, and the third QBUCK switch module are connected in parallel between the input voltage of the front-stage DC-DC converter and ground; the voltage at the voltage input terminal of the front-stage DC-DC converter of the grid-connected inverter is the input voltage of the front-stage DC-DC converter. In the inductor unit, the first inductor module, the second inductor module, and the third inductor module are arranged in parallel between the corresponding switching transistor modules in the BUCK unit and the BOOST unit; In the BOOST unit, the first QBOOST switch module, the second QBOOST switch module, and the third QBOOST switch module are connected in parallel between ground and the first terminal of the capacitor unit; the second terminal of the capacitor unit is grounded. In the capacitor unit, the first capacitor module, the second capacitor module, and the third capacitor module are connected in parallel, and the voltage across the capacitor unit is the actual output voltage of the voltage output terminal of the front-end DC-DC converter of the grid-connected inverter.

3. The DC-DC converter according to claim 2, characterized in that, In the first QBUCK switching module, the second QBUCK switching module, and the third QBUCK switching module, each QBUCK switching module includes: a QBUCK switching transistor and a QBUCK diode; the input voltage of the front-end DC-DC converter is connected to the first connection terminal of each QBUCK switching transistor; the second connection terminal of each QBUCK switching transistor is connected to the cathode of each QBUCK diode on one hand, and to the first terminal of a corresponding inductor module in the first, second, and third inductor modules on the other hand. In the first QBOOST switching module, the second QBOOST switching module, and the third QBOOST switching module, each QBOOST switching module includes: a QBOOST switching transistor and a QBOOST diode; the first connection terminal of each QBOOST switching transistor is grounded; the second connection terminal of each QBOOST switching transistor is connected to the second terminal of a corresponding inductor module in the first, second, and third inductor modules, and is also connected to the anode of each QBOOST diode.

4. The DC-DC converter according to claim 3, characterized in that, Both the QBUCK switch and the QBOOST switch are MOSFETs. The first connection terminal of the QBUCK switch is the drain of the MOSFET; the second connection terminal of the QBUCK switch is the source of the MOSFET. The first connection terminal of the QBOOST switch is the drain of the MOS transistor; the second connection terminal of the QBOOST switch is the source of the MOS transistor.

5. A grid-connected inverter, characterized in that, include: The DC-DC converter as described in any one of claims 1 to 4.

6. A control method for a DC-DC converter of a grid-connected inverter as described in claim 5, characterized in that, include: When the DC-DC converter of the grid-connected inverter is working, the actual output voltage of the DC-DC converter is obtained, and the target output voltage of the DC-DC converter is obtained. The voltage difference between the actual output voltage of the DC-DC converter and the target output voltage of the DC-DC converter is determined and denoted as the deviation voltage. Based on the deviation voltage, the DC-DC converter is controlled to operate in either BUCK asynchronous mode or BOOST asynchronous mode.

7. The control method for the DC-DC converter of the grid-connected inverter according to claim 6, characterized in that, Based on the deviation voltage, controlling the DC-DC converter to operate in either BUCK asynchronous mode or BOOST asynchronous mode includes: Determine the range in which the deviation voltage is located; this range is between the minimum and maximum carrier values ​​of the BUCK unit, or between the minimum and maximum carrier values ​​of the BOOST unit. If the deviation voltage is between the minimum and maximum carrier values ​​of the BUCK unit, the DC-DC converter is controlled to operate in the BUCK asynchronous mode. If the deviation voltage is between the minimum and maximum carrier values ​​of the BOOST unit, the DC-DC converter is controlled to operate in the BOOST asynchronous mode.

8. The control method for the DC-DC converter of the grid-connected inverter according to claim 6 or 7, characterized in that, When the BUCK unit includes a first QBUCK switch module, a second QBUCK switch module, and a third QBUCK switch module, and the BOOST unit includes a first QBOOST switch module, a second QBOOST switch module, and a third QBOOST switch module, controlling the DC-DC converter to operate in the BUCK asynchronous mode includes: The operating time of the first QBUCK switching module is controlled to be (V e –V L1 ) / Vsaw, and control the first QBOOST switching module to turn off; The PWM wave of the second QBUCK switch module is controlled to have a 120-degree phase difference with the PWM wave of the first QBUCK switch module, and the PWM wave of the second QBOOST switch module is controlled to have a 120-degree phase difference with the PWM wave of the first QBOOST switch module. The operating time of the second QBUCK switch module is (V e –V L1 ) / Vsaw, and control the second QBOOST switching module to turn off; The PWM wave of the third QBUCK switch module is controlled to have a phase difference of 240 degrees relative to the PWM wave of the first QBUCK switch module. The operating time of the third QBUCK switch module is (V... e –V L1 ) / Vsaw, and control the third QBOOST switching module to turn off; Among them, V e V is the deviation voltage. L1 Vsaw is the minimum carrier value of the BUCK unit, and Vsaw is the peak-to-peak value of the carrier of the BUCK unit and the carrier of the BOOST unit.

9. The control method for the DC-DC converter of the grid-connected inverter according to claim 6 or 7, characterized in that, When the BUCK unit includes a first QBUCK switch module, a second QBUCK switch module, and a third QBUCK switch module, and the BOOST unit includes a first QBOOST switch module, a second QBOOST switch module, and a third QBOOST switch module, controlling the DC-DC converter to operate in the BOOST asynchronous mode includes: The operating time of the first QBUCK switch module is controlled to be 1, and the operating time of the first QBOOST switch is controlled to be (V e –V L2 ) / Vsaw; The PWM wave of the second QBUCK switch module is controlled to have a phase difference of 120 degrees relative to the PWM wave of the first QBUCK switch module, and the PWM wave of the second QBOOST switch module is controlled to have a phase difference of 120 degrees relative to the PWM wave of the first QBOOST switch module. The operating time of the second QBUCK switch module is 1, and the operating time of the second QBOOST switch module is controlled to be (V e –V L2 ) / Vsaw; The PWM wave of the third QBUCK switch module is controlled to have a phase difference of 240 degrees relative to the PWM wave of the first QBUCK switch module, and the PWM wave of the third QBOOST switch module is controlled to have a phase difference of 240 degrees relative to the PWM wave of the first QBOOST switch module. The operating time of the third QBUCK switch module is 1, and the operating time of the third QBOOST switch module is controlled to be (V e –V L2 ) / Vsaw; Among them, V e V is the deviation voltage. L2 Vsaw is the minimum value of the carrier of the BOOST unit, and Vsaw is the peak-to-peak value of the carrier of the BUCK unit and the carrier of the BOOST unit.

Images