WO2021120220A1 - 一种直流变换器 - Google Patents

一种直流变换器 Download PDF

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Publication number
WO2021120220A1
WO2021120220A1 PCT/CN2019/127191 CN2019127191W WO2021120220A1 WO 2021120220 A1 WO2021120220 A1 WO 2021120220A1 CN 2019127191 W CN2019127191 W CN 2019127191W WO 2021120220 A1 WO2021120220 A1 WO 2021120220A1
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WO
WIPO (PCT)
Prior art keywords
voltage
switching device
bus
intermediate node
diode
Prior art date
Application number
PCT/CN2019/127191
Other languages
English (en)
French (fr)
Inventor
陈东
石磊
王朝辉
Original Assignee
华为技术有限公司
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 华为技术有限公司 filed Critical 华为技术有限公司
Priority to PCT/CN2019/127191 priority Critical patent/WO2021120220A1/zh
Priority to AU2019478501A priority patent/AU2019478501B2/en
Priority to EP19956757.9A priority patent/EP3961896B1/en
Priority to CN201980020069.1A priority patent/CN113287253A/zh
Publication of WO2021120220A1 publication Critical patent/WO2021120220A1/zh
Priority to US17/548,963 priority patent/US11870346B2/en

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0095—Hybrid converter topologies, e.g. NPC mixed with flying capacitor, thyristor converter mixed with MMC or charge pump mixed with buck
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/36—Means for starting or stopping converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/06—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using resistors or capacitors, e.g. potential divider
    • H02M3/07—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using resistors or capacitors, e.g. potential divider using capacitors charged and discharged alternately by semiconductor devices with control electrode, e.g. charge pumps
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/4837—Flying capacitor converters

Definitions

  • This application relates to the field of energy technology, and in particular to a DC converter.
  • DC converters used to convert DC voltage to DC voltage are widely used in systems such as solar power generation, energy storage, and uninterrupted power supply (UPS).
  • UPS uninterrupted power supply
  • FIG. 1 shows a schematic structural diagram of a three-level direct current (DC)-DC conversion circuit.
  • the DC-DC conversion circuit includes an upper bridge arm, a lower bridge arm, a flying capacitor and an inductor.
  • the upper bridge arm includes two diodes (D1, D2) connected in series, and the two connected in series with D1 and D2 The ports are respectively connected to the positive terminal P and the reference terminal O of the bus, and the middle node is marked as SP; the lower bridge arm contains two IGBTs (T3, T4) connected in series and their anti-parallel diodes (D3, D4).
  • the two ports are respectively connected to the reference terminal O and the negative terminal N of the bus, the intermediate node is marked as SN; the positive terminal of the flying capacitor Cfly is connected to the intermediate node SP, and the negative terminal is connected to the intermediate node SN; the two ends of the inductor Lin are respectively connected to the low-voltage positive terminal L and Reference terminal O; the low-voltage negative terminal is directly connected to the negative terminal of the bus, which is also marked as N.
  • the voltage at the positive terminal P of the bus is Vbus, the voltage at the middle node M of the bus is Vbus/2, and the voltage at the negative terminal of the bus is 0.
  • the reference terminal O can have three level states, so this circuit is called a three-level DC-DC conversion circuit. By controlling the turn-on and turn-off time of each switching device in the circuit, the output DC voltage can be adjusted.
  • the voltage of the flying capacitor Cfly is charged to Vbus/2 through an additional pre-charging circuit.
  • the voltage across the flying capacitor Cfly (that is, the voltage between SP and SN) is approximately Vbus/2.
  • the reference terminal O is connected to the negative terminal N of the bus bar, and the voltage at the reference terminal O is 0; when D2 and T4 are turned on, the voltage at the reference terminal O is equal to the voltage Vbus/ across the flying capacitor Cfly.
  • the reference terminal O When T3 and D1 are turned on, the voltage of the reference terminal O is equal to the voltage of the positive terminal P of the bus bar minus the voltage across the flying capacitor Cfly, which is Vbus/2; when D2 and D1 are turned on, the reference terminal O is connected to the positive terminal of the bus. Terminal P, the voltage is Vbus. Therefore, the reference terminal O has three level states: 0, Vbus/2, and Vbus.
  • the three-level DC/DC conversion circuit shown in Figure 1 has the following problems: When some abnormal working conditions occur, some components in the circuit have the risk of overvoltage damage.
  • the low-voltage positive terminal L is incorrectly connected to a negative voltage (that is, the low-voltage positive terminal L and the low-voltage negative terminal N are connected reversely)
  • the low-voltage positive terminal L should be connected to a voltage of 1200V, but it was accidentally connected due to negligence- The voltage of 1200V.
  • the low voltage negative terminal N is 0V
  • D3 and D4 are turned on
  • the voltage of the intermediate node SN is 0V
  • the voltage on D1 is the difference between Vbus and the voltage on Cfly. If Cfly has not been precharged at this time , Then D1 will bear a larger voltage, resulting in the risk of overvoltage damage.
  • the three-level DC-DC conversion circuit provided in the prior art has a problem that it is difficult to deal with abnormal operating conditions.
  • the embodiment of the present application provides a DC converter to solve the problem that the three-level DC-DC converter circuit in the prior art is difficult to deal with abnormal operating conditions.
  • an embodiment of the present application provides a DC converter
  • the DC converter includes: a first switching device, a second switching device, a third switching device, a fourth switching device, a first capacitor, a second capacitor, a flywheel Transcapacitor and protection circuit; one end of the first capacitor is connected to the positive end of the bus, and the other end is connected to the intermediate node of the bus; one end of the second capacitor is connected to the intermediate node of the bus, and the other end is connected to the negative end of the bus; one end of the first switching device is connected to the positive end of the bus One end of the second switching device is connected to the first intermediate node, and the other end is connected to the reference terminal; one end of the third switching device is connected to the reference terminal, and the other end is connected to the second intermediate node; the fourth switching device One end of the flying capacitor is connected to the second intermediate node, and the other end is connected to the negative end of the bus; the positive end of the flying capacitor is connected to the first intermediate node, and the negative end is
  • the protection circuit includes a clamping unit and a buffer unit.
  • the clamping unit is used to clamp the first switching device to the voltage of the first capacitor when the voltage between the positive end of the bus bar and the negative end of the bus bar rises, and the fourth switch The device is clamped to the voltage of the second capacitor; the buffer unit is used to reduce the current flowing through the clamp unit and the flying capacitor when the voltage between the positive end of the bus and the negative end of the bus rises.
  • the voltage of the negative terminal of the bus is 0V
  • the positive terminal of the low voltage is the negative voltage
  • the third switching device and the fourth switching device are turned on, and the second The voltage of the intermediate node is 0V. Since the DC converter has not started to work and the flying capacitor has not been precharged, the voltage across the flying capacitor is 0V, and therefore the voltage of the first intermediate node is also 0V. If the first capacitor and the second capacitor already have voltage at this time, the flying capacitor will be charged by the bus intermediate node, through the protection circuit, the first intermediate node, and the second intermediate node, and finally charged to the same value as the second capacitor. Voltage; At the same time, the first switching device is clamped by the protection circuit to the voltage of the first capacitor, avoiding the risk of overvoltage damage.
  • the flying capacitor When the voltage of the positive terminal of the bus suddenly jumps high, the flying capacitor can be charged through the protection circuit.
  • the clamping unit in the protection circuit clamps the first switching device to the voltage of the first capacitor, and clamps the fourth switching device to the second
  • the voltage of the capacitor reduces the risk of overvoltage damage to the first switching device and the fourth switching device; at the same time, the buffer unit in the protection circuit reduces the current impact when the flying capacitor is charged, thereby improving the charging loop of each device Reliability.
  • the flying capacitor can also be adjusted by adjusting the turn-on and turn-off times of the first switching device, the second switching device, the third switching device, and the fourth switching device.
  • the voltage across the capacitor specifically, the voltage across the flying capacitor may be greater than the voltage of the first capacitor and greater than the voltage of the second capacitor.
  • the voltage across the flying capacitor is greater than the voltage of the first capacitor and greater than the voltage of the second capacitor, if there is an abnormal condition where the voltage of the positive terminal P of the bus suddenly jumps, then when the flying capacitor is charged, due to charging
  • the difference between the final voltage and the instantaneous voltage of the flying capacitor when an abnormal operating condition occurs is further reduced, so that the current impact of the flying capacitor charging can be reduced, and the reliability of each device in the charging circuit is further improved.
  • the protection circuit when the voltage across the flying capacitor is greater than the voltage of the first capacitor and greater than the voltage of the second capacitor, when the DC converter is working normally, the voltage of the bus intermediate node M is less than the voltage of the first intermediate node and greater than For the voltage of the second intermediate node, the clamping device in the protection circuit cannot be turned on, so the protection circuit does not participate in the normal operation of the DC converter. That is to say, the protection circuit only protects the components in the DC converter when abnormal operating conditions occur, and the protection circuit does not participate in the work when the DC converter is working normally.
  • the DC converter provided in the first aspect may further include a first inductor; wherein one end of the first inductor is connected to the low-voltage positive terminal, the other end is connected to the reference terminal, and the negative terminal of the bus bar is coupled with the low-voltage negative terminal; or, the first inductor One end of the bus is connected to the negative end of the low voltage, and the other end is connected to the reference end;
  • the low-voltage positive terminal and the low-voltage negative terminal are the input terminals of the circuit, and the positive terminal of the bus and the negative terminal of the bus are the output terminals of the circuit; or, the positive terminal of the bus and the negative terminal of the bus It is the input terminal of the circuit, and the low-voltage positive terminal and the low-voltage negative terminal are the output terminals of the circuit.
  • the DC converter provided in the first aspect may be a unidirectional converter or a bidirectional converter.
  • the DC converter is used to convert the DC voltage between the positive end of the bus and the negative end of the bus into The DC voltage between the low-voltage positive terminal and the low-voltage negative terminal.
  • the positive terminal of the bus and the negative terminal of the bus are used as output terminals.
  • the DC converter is used to convert the DC voltage between the low-voltage positive terminal and the low-voltage negative terminal into the positive terminal and the negative terminal of the bus. The DC voltage between the negative terminals of the bus.
  • the clamping unit may include a first clamping device and a second clamping device; wherein one end of the first clamping device is connected to the first intermediate node, and the first clamping device The other end of the device is connected to the second clamping device; one end of the second clamping device is connected to the second intermediate node, and the other end is connected to the first clamping device; one end of the buffer unit is connected to the first clamping device and the second clamping device Connect the node, and the other end is connected to the intermediate node of the bus.
  • first clamping device may be a first diode
  • second clamping device may be a second diode
  • first clamping device may be a first insulated gate bipolar transistor IGBT and its Anti-parallel diode
  • the second clamping device can be a second IGBT and a diode anti-parallel to it
  • first clamping device can be a first metal-oxide semiconductor field effect transistor MOSFET and its body diode
  • the second The clamping device may be a second MOSFET and its body diode; wherein the cathode of the diode in the first clamping device is connected to the first intermediate node, and the anode is connected to the cathode of the diode in the second clamping device; in the second clamping device The anode of the diode is connected to the second intermediate node.
  • each of the first clamping device and the second clamping device includes a diode (for example, the first clamping device includes a first diode, and the second clamping device includes a second diode, or
  • the first clamping device includes the anti-parallel diode of the IGBT
  • the second clamping device includes the anti-parallel diode of the IGBT
  • the first clamping device includes the body diode of the MOSFET
  • the second clamping device includes the body diode of the MOSFET.
  • Two diodes are connected in series between the first intermediate node and the second intermediate node, and the intermediate nodes of the two diodes are connected to the bus intermediate node M through the buffer unit.
  • the buffer unit includes at least one of the following: a first buffer resistor; a third IGBT and a diode anti-parallel to it, a fourth IGBT and a diode anti-parallel to it, the third IGBT and the fourth IGBT
  • the top connection; the third MOSFET and its body diode, the fourth MOSFET and its body diode, the third MOSFET and the fourth MOSFET are connected to the top; the second snubber resistor, the third snubber resistor, the fifth switching device, and the second snubber resistor It is connected in series with the third buffer resistor, and the fifth switch device is connected in parallel with the third buffer resistor.
  • the fifth switching device is any one of the following: a mechanical switching device; a fifth IGBT and a diode anti-parallel to it; a fifth MOSFET and a body diode thereof.
  • the main body of the buffer unit is a resistor, and its specific form can be a fixed resistance resistor, an adjustable resistance realized by an IGBT and an anti-parallel diode, or an adjustable resistance realized by a MOSFET and its body diode.
  • the resistance can also be an adjustable resistance adjusted by a switching device.
  • the first switching device, the second switching device, the third switching device, and the fourth switching device are all composed of an IGBT and its anti-parallel diode or a MOSFET and its body diode; or, the first switching device,
  • the second switching device is composed of an IGBT and its anti-parallel diode or a MOSFET and its body diode;
  • the third and fourth switching devices are composed of diodes; or the first and second switching devices are composed of diodes;
  • the third switch The device and the fourth switching device are composed of an IGBT and its anti-parallel diode or a MOSFET and its body diode.
  • the DC converter provided by the first aspect can It is a two-way converter.
  • the protection circuit is also used to precharge the flying capacitor when the circuit is started.
  • the flying capacitor can be pre-charged from the low-voltage positive terminal via the second switching device ⁇ protection circuit ⁇ bus intermediate node ⁇ bus negative terminal, so there is no need to configure an additional pre-charging circuit, which reduces the cost.
  • Fig. 1 is a schematic structural diagram of a three-level DC-DC conversion circuit provided in the prior art
  • Fig. 2 is a schematic structural diagram of another three-level DC-DC conversion circuit provided by the prior art
  • FIG. 3 is a schematic structural diagram of a first DC converter provided by an embodiment of the application.
  • FIG. 4 is a schematic structural diagram of a second type of DC converter provided by an embodiment of the application.
  • FIG. 5 is a schematic structural diagram of a third DC converter provided by an embodiment of the application.
  • FIG. 6 is a schematic structural diagram of a fourth type of DC converter provided by an embodiment of the application.
  • FIG. 7 is a schematic structural diagram of a fifth DC converter provided by an embodiment of the application.
  • FIG. 8 is a schematic structural diagram of a sixth DC converter provided by an embodiment of the application.
  • FIG. 9 is a schematic structural diagram of a seventh DC converter provided by an embodiment of the application.
  • FIG. 10 is a schematic structural diagram of an eighth DC converter provided by an embodiment of the application.
  • FIG. 11 is a schematic structural diagram of a ninth DC converter provided by an embodiment of the application.
  • FIG. 12 is a schematic structural diagram of a tenth DC converter provided by an embodiment of the application.
  • FIG. 13 is a schematic structural diagram of an eleventh DC converter provided by an embodiment of this application.
  • 15 is a schematic diagram of the working state of the DC converter provided by the embodiment of the application when it is started;
  • 16 is a schematic diagram of the working state of the DC converter provided by the embodiment of the application when charging the flying capacitor;
  • FIG. 17 is a schematic diagram of the working state of the DC converter provided by the embodiment of the application under abnormal working conditions.
  • the three-level DC-DC conversion circuit shown in FIG. 1 is improved, and the improved three-level DC-DC conversion circuit
  • the flat DC-DC conversion circuit can be shown in Figure 2.
  • the conversion circuit shown in Fig. 2 adds a switch S and a diode D6 to the topology of the conversion circuit shown in Fig. 1. Among them, the negative terminal of the flying capacitor Cfly is connected to the intermediate node SN through the switch S; at the same time, the negative terminal of the flying capacitor Cfly is connected to the intermediate node M of the bus through the diode D6.
  • the conversion circuit shown in Figure 2 can directly pre-charge the flying capacitor Cfly without an additional pre-charging circuit: when the conversion circuit is normally started from the low-voltage positive terminal L, the flying capacitor Cfly can be passed by the low-voltage positive terminal voltage.
  • the working principle is as follows: before the conversion circuit starts to work, the switch S remains off. If the low voltage positive terminal L is connected to a negative voltage, D3 and D4 are turned on, and the voltage of the intermediate node SN is 0; at this time, since the flying capacitor Cfly has not been charged, the voltage at both ends is 0, so the bus voltage Vbus Shared by D1 and switch S. That is to say, compared with the conversion circuit shown in Fig. 1, the additional switch S avoids the risk that the bus voltage Vbus is borne by D1 alone, which will cause its overvoltage damage. After the circuit starts normally, the switch S remains closed.
  • the working principle is as follows: After the conversion circuit works normally, if the bus voltage suddenly jumps to a higher voltage, the voltage across the flying capacitor Cfly has not yet been If a change occurs, when D1 is turned on, the flying capacitor Cfly is charged through diodes D6 and Cbus-; since S is closed and D6 is turned on, the voltage across T4 is the same as the voltage across Cbus- at this time. In other words, the increased diode D6 clamps T4 to the negative voltage source of the bus, thereby reducing the risk of T4 overvoltage damage.
  • the conversion circuit shown in Figure 2 is used, and T4 is clamped to 700V. Compared with the conversion circuit shown in Figure 1, the voltage that T4 bears It becomes smaller (950V ⁇ 700V), so the conversion circuit shown in Figure 2 is used to reduce the risk of T4 overvoltage damage.
  • the conversion circuit shown in Figure 2 can cope with abnormal operating conditions to a certain extent, the conversion circuit still has the following problems: First, the added switch S will introduce a certain conduction loss, and the addition of S will lead to circuit loops. The longer it will increase the voltage stress of the IGBT and diode. Second, the added diode D6, when clamping T4 to the negative voltage source of the bus, if the original voltage across the flying capacitor Cfly and the abrupt half bus voltage (ie Vbus/2) have a large difference in value, Then the charging process of the flying capacitor Cfly will produce a large current impact on the flying capacitor Cfly, diode D6, and Cbus-, which reduces the reliability of these devices.
  • the added switch S will introduce a certain conduction loss, and the addition of S will lead to circuit loops. The longer it will increase the voltage stress of the IGBT and diode.
  • the added diode D6 when clamping T4 to the negative voltage source of the bus, if the original voltage across the flying capacitor Cf
  • embodiments of the present application provide a DC converter to solve the problem that the three-level DC-DC conversion circuit in the prior art is difficult to deal with abnormal operating conditions.
  • the DC converter includes a first switching device S1, a second switching device S2, a third switching device S3, a fourth switching device S4, a first capacitor C1, a second capacitor C2, a flying capacitor Cfly, and Protection circuit; one end of the first capacitor C1 is connected to the positive terminal P of the bus, and the other end is connected to the intermediate node M of the bus; one end of the second capacitor C2 is connected to the intermediate node M of the bus, and the other end is connected to the negative terminal N of the bus; one end of the first switching device S1 The positive terminal P of the bus is connected, and the other end is connected to the first intermediate node SP; one end of the second switching device S2 is connected to the first intermediate node SP, and the other end is connected to the reference terminal O; one end of the third switching device S3 is connected to the reference terminal O, and the other end Connected to the second intermediate node SN; one
  • the protection circuit includes a clamping unit and a buffer unit.
  • the clamping unit is used to embed the first switching device S1 when the voltage between the positive terminal P of the bus and the negative terminal N of the bus rises.
  • the buffer unit is used to reduce the voltage flowing through when the voltage between the positive terminal P of the bus bar and the negative terminal N of the bus increases.
  • the current of the clamping unit and the flying capacitor Cfly is used to reduce the voltage flowing through when the voltage between the positive terminal P of the bus bar and the negative terminal N of the bus increases.
  • the reference terminal O can have a variety of electrical circuits. Therefore, the DC converter provided in the embodiment of the present application can be regarded as a multi-level DC-DC converter.
  • the DC converter shown in FIG. 3 is only an example.
  • the DC converter provided in the embodiment of the present application may also be as shown in FIG. 4.
  • the difference between the DC converter shown in FIG. 4 and the DC converter shown in FIG. 3 is that the distribution of the switching devices at the positive end of the bus bar and the negative end of the bus bar are different, and the connection relationship between the devices remains unchanged.
  • the DC converter provided by the embodiment of the present application may further include a first inductor.
  • a first inductor For the example of Fig. 3, one end of the first inductor L1 is connected to the low-voltage positive terminal L, the other end is connected to the reference terminal O, and the negative terminal N of the bus bar is coupled with the negative terminal N of the low voltage, as shown in Fig. 5;
  • the first One end of the inductor L1 is connected to the low-voltage negative terminal Q, and the other end is connected to the reference terminal O; the positive terminal P of the bus is coupled with the low-voltage positive terminal P, as shown in Figure 6.
  • the DC converter shown in FIG. 5 may be a unidirectional converter or a bidirectional converter.
  • the low-voltage positive terminal L and the low-voltage negative terminal N can be connected to the photovoltaic module, and the bus positive terminal P and the bus negative terminal N can be connected to the device.
  • the low-voltage positive terminal L and the low-voltage negative terminal N may be connected to the battery assembly, and the bus positive terminal P and the bus negative terminal N may be connected to the device.
  • the low-voltage positive terminal L and the low-voltage negative terminal N are used as output terminals.
  • the DC converter is used to connect the positive terminal P of the bus and the negative terminal N of the bus.
  • the intermediate DC voltage is converted into the DC voltage between the low-voltage positive terminal L and the low-voltage negative terminal N.
  • the device can be used to charge the battery assembly through the DC converter.
  • the positive terminal P of the bus and the negative terminal N of the bus are used as output terminals.
  • the DC converter is used to convert the DC voltage between the low-voltage positive terminal L and the low-voltage negative terminal N It is converted into a DC voltage between the positive terminal P of the bus and the negative terminal N of the bus.
  • the photovoltaic module/battery module can be used to supply power to the device through the DC converter.
  • the positive end P of the bus and the negative end N of the bus can be used as input ends, and the low voltage positive end L and the low voltage negative end N can be used as output ends.
  • the first switching device, the second switching device, the third switching device, and the fourth switching device are all made of IGBT and its anti-parallel diode or MOSFET and its Body diode composition.
  • the first switching device and the second switching device are composed of an IGBT and its anti-parallel diode or a MOSFET and its body diode.
  • the switching device and the fourth switching device are composed of diodes.
  • the DC converter can be regarded as a buck (BUCK) with the positive end P of the bus and the negative end N of the bus as the input end, and the low-voltage positive end L and the low-voltage negative end N as the output end.
  • BUCK buck
  • the first switching device and the second switching device are composed of diodes
  • the third and fourth switching devices are composed of IGBT and its anti-parallel diode or MOSFET and its body
  • the DC converter is composed of diodes.
  • the DC converter can be regarded as a BUCK circuit with the positive end P of the bus and the negative end N of the bus as the input end, and the low-voltage positive end P and the low-voltage negative end Q as the output end.
  • the protection circuit is also used to precharge the flying capacitor Cfly when the DC converter is started.
  • the flying capacitor Cfly can be pre-charged from the low-voltage positive terminal L via the second switching device S2 ⁇ protection circuit ⁇ bus intermediate node M ⁇ bus negative terminal N, thereby The problem that the DC-DC conversion circuit shown in FIG. 1 needs to be additionally configured with a pre-charge circuit is avoided, and the cost is reduced.
  • the voltage of the negative terminal N of the bus bar is 0V
  • the positive terminal L of the low-voltage is negative voltage
  • S3 and S4 are turned on
  • the voltage of the second intermediate node SN is 0V. Since the DC converter has not started to work and the flying capacitor Cfly has not been precharged, the voltage across Cfly is 0V, and therefore the voltage of the first intermediate node SP is also 0V.
  • the flying capacitor Cfly will be charged by the charging circuit of the bus intermediate node M ⁇ protection circuit ⁇ SP ⁇ SN ⁇ S4, and finally charged to the same voltage as C2; at the same time , S1 is clamped to the voltage of C1 by the protection circuit, avoiding the risk of overvoltage damage.
  • the flying capacitor Cfly can be charged through the protection circuit.
  • the clamping unit in the protection circuit clamps S1 to the voltage of the first capacitor C1 and clamps S4 to the second capacitor C2. Therefore, the risk of overvoltage damage to S1 and S4 is reduced; at the same time, the buffer unit in the protection circuit reduces the current impact when the flying capacitor Cfly is charged, thereby improving the reliability of each device in the charging loop.
  • the first switching device S1, the second switching device S2, the third switching device S3, and the fourth switch can also be adjusted.
  • the turn-on and turn-off time of the device S4 is used to adjust the voltage of the flying capacitor Cfly.
  • the voltage across the flying capacitor is greater than the voltage of the first capacitor C1 and greater than the voltage of the second capacitor C2.
  • the protection circuit when the voltage across the flying capacitor is greater than the voltage of the first capacitor and greater than the voltage of the second capacitor, when the DC converter is working normally, the voltage of the bus intermediate node M is less than the voltage of the first intermediate node SP and If the voltage is greater than the second intermediate node SN, the clamping device in the protection circuit cannot be turned on, so the protection circuit does not participate in the normal operation of the DC converter. That is to say, the protection circuit only protects the components in the DC converter when abnormal operating conditions occur, and the protection circuit does not participate in the work when the DC converter is working normally.
  • the clamping unit may include a first clamping device and a second clamping device; wherein, one end of the first clamping device is connected to the first intermediate node, and the other end of the first clamping device is connected to The second clamping device; one end of the second clamping device is connected to the second intermediate node, and the other end is connected to the first clamping device; one end of the buffer unit is connected to the connection node of the first clamping device and the second clamping device, and the other end Connect the intermediate node of the bus.
  • the first clamping device may be a first diode, and the second clamping device may be a second diode.
  • the first clamping device may be a first insulated gate bipolar transistor IGBT and a diode in anti-parallel with it, and the second clamping device may be a second IGBT and a diode in anti-parallel with it; or, the first clamping device
  • the device may be a first metal-oxide semiconductor field effect transistor MOSFET and its body diode, and the second clamping device may be a second MOSFET and its body diode; wherein the cathode of the diode in the first clamping device is connected to the first middle Node, the anode is connected to the cathode of the diode in the second clamping device; the anode of the diode in the second clamping device is connected to the second intermediate node.
  • each of the first clamping device and the second clamping device includes a diode (for example, the first clamping device includes a first diode, and the second clamping device includes a second diode, or The first clamping device includes the anti-parallel diode of the IGBT, the second clamping device includes the anti-parallel diode of the IGBT, or the first clamping device includes the body diode of the MOSFET, and the second clamping device includes the body diode of the MOSFET).
  • Two diodes are connected in series between the first intermediate node SP and the second intermediate node SN, and the intermediate nodes of the two diodes are connected to the bus intermediate node M through the buffer unit.
  • the specific composition of the protection circuit can be as shown in FIG. 7.
  • the buffer unit includes at least one of the following: a first buffer resistor; a third IGBT and a diode in anti-parallel with the third IGBT, a fourth IGBT and a diode in anti-parallel with the third IGBT, and the third IGBT and the fourth IGBT are connected to the top; Three MOSFET and its body diode, the fourth MOSFET and its body diode, the third MOSFET and the fourth MOSFET are connected to the top; the second snubber resistor, the third snubber resistor and the fifth switching device, the second snubber resistor and the third snubber resistor In series, the fifth switching device is connected in parallel with the third buffer resistor.
  • the fifth switching device is any one of the following: a mechanical switching device; a fifth IGBT and a diode anti-parallel to it; a fifth MOSFET and a body diode thereof.
  • the main body of the buffer unit is a resistor, and its specific form can be a fixed-resistance resistor, an adjustable resistance realized by an IGBT and an anti-parallel diode, or an adjustable resistance realized by a MOSFET and its body diode.
  • the resistance can also be an adjustable resistance adjusted by a switching device.
  • the buffer unit includes The first buffer resistor
  • a possible structural diagram of the DC converter may be as shown in FIG. 8.
  • T1 and D1 constitute the first switching device
  • T2 and D2 constitute the second switching device
  • T3 and D3 constitute the third switching device
  • T4 and D4 constitute the fourth switching device
  • D5 is the first switching device.
  • One diode, D6 is the second diode
  • R0 is the buffer unit.
  • the DC converter shown in FIG. 8 can be regarded as a specific example of the DC converter shown in FIG. 3 or FIG. 5.
  • the specific composition of the switching device is illustrated by taking an IGBT and a diode anti-parallel with it as an example.
  • the switching device can also be composed of a MOSFET and its body diode.
  • the MOSFET and its body diode have similar functions to the IGBT and its anti-parallel diode, and the two can be replaced with each other.
  • the buffer unit includes The first buffer resistor
  • a possible schematic diagram of the structure of the DC converter may be as shown in FIG. 9.
  • T1 and D1 constitute the first switching device
  • T2 and D2 constitute the second switching device
  • T3 and D3 constitute the third switching device
  • T4 and D4 constitute the fourth switching device
  • D5 is the first switching device.
  • One diode, D6 is the second diode
  • R0 is the buffer unit.
  • the DC converter shown in FIG. 9 can be regarded as a specific example of the DC converter shown in FIG. 4 or FIG. 6.
  • the DC converter provided by the embodiment of the present application is a unidirectional converter
  • the first clamping device is a first diode
  • the second clamping device is a second diode
  • the buffer unit includes The first buffer resistor
  • T1 and D1 constitute the first switching device
  • T2 and D2 constitute the second switching device
  • D3 is the third switching device
  • D4 is the fourth switching device
  • D5 is the first diode
  • D6 is the second diode
  • R0 is the buffer unit.
  • the DC converter shown in FIG. 10 can be regarded as a specific example of the DC converter shown in FIG. 3 or FIG. 5.
  • the first clamping device may also be composed of the first MOSFET and its body diode
  • the second clamping device may be composed of the second MOSFET and its body diode; or, the first clamping device may be composed of the second MOSFET and its body diode.
  • the bit device is composed of a first IGBT and a diode connected in anti-parallel with it
  • the second clamping device is composed of a second IGBT and a diode connected in anti-parallel with it.
  • the first clamping device can be a MOSFET and its body diode
  • the second clamping device can be an IGBT and a diode anti-parallel to it
  • the first clamping device can be an IGBT and a diode anti-parallel to it
  • the second clamping device is MOSFET and its body diode.
  • a possible structural schematic diagram of the DC converter may be as shown in FIG. 11.
  • the first clamping device is composed of an IGBT (ie T5) and a diode (ie D5) in anti-parallel with it
  • the second clamping device is composed of an IGBT (ie T6) and its reverse It is composed of parallel diodes (ie D6).
  • the buffer unit may also be composed of two top-connected MOSFETs and their body diodes, as shown in example a in FIG. 12, or the buffer unit may also be composed of two A pair of top-connected IGBTs and diodes connected in anti-parallel to them are formed, as shown in the example of b in Figure 12.
  • the buffer unit may also be composed of a second buffer resistor, a third buffer resistor, and a fifth switch device, wherein the second buffer resistor and the third buffer resistor are connected in series, and the fifth switch The device is connected in parallel with the third buffer resistor.
  • the fifth switching device may be a mechanical switching device, a fifth IGBT and a diode anti-parallel thereto, or a fifth MOSFET and its body diode.
  • a possible structural schematic diagram of the DC converter may be as shown in FIG. 13.
  • the second buffer resistor is R1
  • the third buffer resistor is R2
  • the fifth switching device is a mechanical switching device.
  • the working principles can be referred to each other.
  • the following takes the DC converter shown in FIG. 8 as an example to analyze the pre-charging, abnormal operating conditions and normal conditions of the DC converter provided in the embodiment of this application.
  • the working principle during work is introduced, and other examples can be referred to, and the details are not repeated in the embodiments of the present application.
  • Fig. 14 shows the working condition when the low-voltage positive terminal L of the DC converter shown in Fig. 8 is connected to a negative voltage, that is, the working condition in which the low-voltage positive terminal L and the low-voltage negative terminal N are reversely connected before the DC converter is started.
  • the voltage of the low-voltage negative terminal N is 0V
  • the low-voltage positive terminal L is a negative voltage
  • D3 and D4 are turned on
  • the voltage of the second intermediate node SN is 0V. Since the DC converter has not started to work and the flying capacitor Cfly has not been precharged, the voltage across Cfly is 0V, and therefore the voltage of the first intermediate node SP is also 0V.
  • the Cfly can be charged through the charging path of the bus intermediate node M ⁇ R0 ⁇ D5 ⁇ SP ⁇ Cfly ⁇ SN, as shown by the arrow direction in Figure 14, and finally Cfly is charged to the same voltage as C2 (the voltage at point SP changes from 0V to 600V); at the same time, T1 and D1 are clamped from R0 and D5 to the voltage across C1 (that is, 600V), thereby reducing the excess of T1 and D1. Risk of pressure damage.
  • the use of the DC converter shown in FIG. 8 can protect the switching device when the low-voltage positive terminal L is connected to a negative voltage, and reduce the risk of overvoltage damage to the switching device.
  • Figure 15 shows the normal working condition of the DC converter when it is started from the low voltage positive terminal L.
  • the voltage of the low-voltage negative terminal N is 0V
  • the voltage of the low-voltage positive terminal L gradually rises from 0V to a certain value, for example, 1200V.
  • D2 and D1 are turned on, the voltage of the first intermediate node SP follows the voltage of the low-voltage positive terminal L, and the low-voltage positive terminal L charges C1 and C2 through D2 and D1, that is, the voltage of the positive terminal P of the bus is also follow the L voltage.
  • the voltage of the bus intermediate node M is divided by C1 and C2 in series, for example, when the parameters of C1 and C2 are the same, the divided voltage is 600V.
  • the flying capacitor Cfly is charged through the low-voltage positive terminal L ⁇ L1 ⁇ D2 ⁇ SP ⁇ Cfly ⁇ SN ⁇ D6 ⁇ R0 ⁇ M, as shown in the direction of the arrow in Figure 15, and finally charged to The voltage equal to C1 completes the pre-charging of the flying capacitor Cfly.
  • the DC converter shown in FIG. 8 can be used to precharge the flying capacitor Cfly without actively driving the switching device, which is different from the conventional circuit shown in FIG. 1 Compared with the technical solution, the pre-charging circuit is saved and the cost is reduced.
  • the DC-DC conversion can be realized by adjusting the turn-on and turn-off time of each switching device in the DC converter.
  • the low-voltage positive terminal L and the low-voltage negative terminal N can be combined.
  • the smaller DC voltage is boosted, and a larger DC voltage is output between the positive terminal P of the bus and the negative terminal N of the bus.
  • Fig. 16 shows the normal working condition of the DC converter shown in Fig. 8.
  • the voltage of the negative terminal N of the bus is 0V
  • the voltage of the low-voltage positive terminal L is 800V
  • the voltage of the positive terminal P of the bus is 900V
  • the voltage of the intermediate node M of the bus when the parameters of C1 and C2 are the same is 450V.
  • the voltage of the flying capacitor Cfly can be higher than the voltages of C1 and C2, for example, it can be 500V.
  • the voltage of the second intermediate node SN is 0V
  • the voltage of the first intermediate node SP is 500V, as shown in the example of a in Fig. 16.
  • the first clamping device D5 in the protection circuit will not be turned on, and the protection circuit will not participate in the normal operation of the DC converter.
  • the voltage of the first intermediate node SP is 900V
  • the voltage of the second intermediate node SN is 400V, as shown in the example b in Figure 16, at this time, since the voltage of SN is lower than M Therefore, the second clamping device D6 in the protection circuit will not be turned on, and the protection circuit will not participate in the normal operation of the DC converter.
  • Figure 17 shows an abnormal working condition where the bus voltage of the DC converter suddenly increases.
  • the DC converter Before the abnormal working condition occurs, the DC converter is working in a normal working condition, for example, the working condition shown in FIG. 16.
  • the abnormal working condition that the bus voltage suddenly becomes higher occurs, the voltage at the positive terminal P of the bus suddenly changes to a higher value, for example, 1400V, and the intermediate node M of the bus follows the sudden change to 700V.
  • the voltage of the second intermediate node SN is 0V, as shown in the example of a in Figure 17; since the voltage of the flying capacitor Cfly has not undergone a sudden change, it remains the same as before the abnormal operating condition. 500V, so the voltage of the first intermediate node SP is 500V.
  • the two ends of T1 and D1 will bear the 900V voltage, which will cause overvoltage damage Risk; and after the protection circuit is added in the embodiment of this application, Cfly can be charged through the charging path of the bus intermediate node M ⁇ R0 ⁇ D5 ⁇ SP ⁇ Cfly ⁇ SN, as shown by the arrow direction in the example of a in Figure 17 Finally, the flying capacitor Cfly is charged to the voltage 700V equal to C2; at the same time, T1, D1 are clamped from R0, D5 to the voltage across C1 (ie 700V), thereby avoiding the risk of overvoltage damage.
  • a protection circuit ie, the circuit topology shown in Figure 1
  • the voltage of the first intermediate node SP is 1400V, as shown in the example b of Figure 17; since the voltage of the flying capacitor Cfly has not undergone abrupt change, it remains the same as before the abnormal operating condition. 500V, so the voltage of the second intermediate node SN is 900V.
  • the DC converter is not equipped with a protection circuit (that is, the circuit topology shown in Figure 1), the two ends of T4 and D4 will bear the 900V voltage, and there will be overvoltage damage Risk; and after the protection circuit is added in the embodiment of this application, Cfly can be charged through the charging path SP ⁇ Cfly ⁇ SN ⁇ D6 ⁇ R0 ⁇ M, as shown in the arrow direction in the b example of Figure 17, and Finally, the flying capacitor Cfly is charged to a voltage of 700V equal to C1; at the same time, T4 and D4 are clamped from D6 and R0 to the voltage across C2 (ie 700V), thereby avoiding the risk of overvoltage damage.
  • a protection circuit that is, the circuit topology shown in Figure 1
  • Cfly can be charged through the charging path SP ⁇ Cfly ⁇ SN ⁇ D6 ⁇ R0 ⁇ M, as shown in the arrow direction in the b example of Figure 17, and Finally, the flying capacitor Cfly is charged to a voltage of 700V equal to C
  • the use of the DC converter shown in FIG. 8 can protect the switching device when the bus voltage suddenly rises, and reduce the risk of overvoltage damage to the switching device.
  • the DC converter shown in FIG. 8 is adopted, and the protection circuit is provided with a buffer unit (that is, R0), which can effectively reduce the current impact when the flying capacitor Cfly is charged.
  • R0 a buffer unit
  • the size of the charging current can be changed by setting the resistance of R0; at the same time, because the voltage of the flying capacitor Cfly is set to be greater than the voltage across C1 and greater than the voltage across C2, the flying capacitor Cfly can be reduced under abnormal conditions.
  • the difference between the instantaneous voltage and the final charging voltage thereby further reducing the current impact when the flying capacitor is charged, and improving the reliability of each device in the charging loop.
  • the working state of the DC converter provided by the embodiment of the present application through the DC converter shown in FIG. 8 in the pre-charging, normal operating conditions and abnormal operating conditions (the low-voltage positive terminal L is connected to a negative voltage, and the bus voltage suddenly increases) It is introduced in detail.
  • the working state of other DC converters provided in the embodiments of the present application is similar to the working principle of the DC converter shown in FIG. 8, and the difference lies only in some subtle adjustments.
  • the difference between the DC converter shown in FIG. 9 and the DC converter shown in FIG. 8 is only the distribution of switching devices, and the working principles of the two are the same; the DC converter shown in FIG. 10 is a unidirectional converter, and The working state of the DC converter shown in Fig. 8 is the same when used as a BUCK circuit; the DC converter shown in Fig. 11 performs the first and second clamping devices on the basis of the DC converter shown in Fig. 8
  • the improvement, the only difference is that the conduction characteristics (such as the conduction voltage drop) of the first clamping device and the second clamping device in Figure 11 can be changed, which makes the adjustment of the DC converter more flexible and can meet different abnormal operating conditions
  • the buffer unit 12 improves the buffer unit on the basis of the DC converter shown in FIG. 8.
  • the conduction characteristics of the buffer unit in the DC converter can be changed, so that the DC converter
  • the adjustment is more flexible and can meet the adjustment needs under different abnormal working conditions;
  • the DC converter shown in Figure 13 makes the resistance of the buffer unit adjustable through a mechanical switch, so as to meet the adjustment needs under different abnormal working conditions.
  • the voltage at the negative terminal of the bus is 0V
  • the low voltage positive terminal is negative voltage
  • the third switching device and the fourth switching device conduct On
  • the voltage of the second intermediate node is 0V. Since the DC converter has not started to work and the flying capacitor has not been precharged, the voltage across the flying capacitor is 0V, and therefore the voltage of the first intermediate node is also 0V. If the first capacitor and the second capacitor already have voltage at this time, the flying capacitor will be charged by the bus intermediate node, through the protection circuit, the first intermediate node, and the second intermediate node, and finally charged to the same value as the second capacitor. Voltage; At the same time, the first switching device is clamped by the protection circuit to the voltage of the first capacitor, avoiding the risk of overvoltage damage.
  • the flying capacitor When the voltage of the positive terminal of the bus suddenly jumps high, the flying capacitor can be charged through the protection circuit.
  • the clamping unit in the protection circuit clamps the first switching device to the voltage of the first capacitor, and clamps the fourth switching device to the second
  • the voltage of the capacitor reduces the risk of overvoltage damage to the first switching device and the fourth switching device; at the same time, the buffer unit in the protection circuit reduces the current impact when the flying capacitor is charged, thereby improving the charging loop of each device Reliability.

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Abstract

一种直流变换器，包括：第一电容，两端分别连接母线正端和母线中间节点；第二电容，两端分别连接母线中间节点和母线负端；第一开关器件，两端分别连接母线正端和第一中间节点；第二开关器件，两端分别连接第一中间节点和参考端；第三开关器件，两端分别连接参考端和第二中间节点；第四开关器件，两端分别连接第二中间节点和母线负端；飞跨电容，两端分别连接第一中间节点和第二中间节点，第一中间节点和第二中间节点通过保护电路连接母线中间节点；保护电路，包含嵌位单元和缓冲单元，在母线正端与母线负端间电压升高时，嵌位单元将第一开关器件和第四开关器件分别嵌位至第一电容和第二电容的电压，缓冲单元减小流经嵌位单元和飞跨电容的电流。

Description

一种直流变换器 技术领域
本申请涉及能源技术领域，尤其涉及一种直流变换器。
背景技术
用于实现直流电压与直流电压转换的直流变换器，广泛应用于太阳能发电、储能、不间断电源(uninterrupted power supply，UPS)等系统中。
在直流变换器中，多电平电路由于可以提供多种电压值而受到关注。示例性地，图1示出了一种三电平直流(direct current，DC)-直流变换电路的结构示意图。该DC-DC变换电路包含一个上桥臂、一个下桥臂、一个飞跨电容和一个电感，其中，上桥臂包含两个串联的二极管(D1、D2)，D1、D2串联后的两个端口分别连接母线正端P和参考端O，中间节点记为SP；下桥臂包含两个串联的IGBT(T3、T4)及其反并联二极管(D3、D4)，T3、T4串联后的两个端口分别连接参考端O和母线负端N，中间节点记为SN；飞跨电容Cfly的正端连接中间节点SP，负端连接中间节点SN；电感Lin的两端分别连接低压正端L和参考端O；低压负端与母线负端直接相连，同样记为N。母线正端P的电压为Vbus，母线中间节点M的电压Vbus/2，母线负端的电压为0。在该电路正常工作时，参考端O可以有三种电平状态，因此该电路称为三电平DC-DC变换电路。通过控制该电路中各个开关器件的导通和关断时间，可以实现输出直流电压的调节。
在图1所示的DC/DC变换电路正常工作前，先通过一个额外的预充电电路将飞跨电容Cfly的电压充电至Vbus/2。DC/DC变换电路正常启动后，飞跨电容Cfly两端的电压(即SP、SN之间的电压)约为Vbus/2。具体地，T3、T4导通时，参考端O连接至母线负端N，参考端O的电压为0；D2、T4导通时，参考端O的电压等于飞跨电容Cfly两端的电压Vbus/2；T3、D1导通时，参考端O的电压等于母线正端P的电压减去飞跨电容Cfly两端的电压，为Vbus/2；D2、D1导通时，参考端O连接至母线正端P，电压为Vbus。因此，参考端O有0、Vbus/2、Vbus三种电平状态。
图1所示的三电平DC/DC变换电路存在如下问题：在发生一些异常工况时，电路中的某些器件存在过压损坏的风险。
比如，在低压正端L误接入负电压(即低压正端L与低压负端N接反)的情况下，假设低压正端L本应接入1200V电压，但是由于疏忽而误接入-1200V的电压，此时低压负端N为0V，故D3和D4导通，中间节点SN的电压为0V，D1承受的电压为Vbus与Cfly上电压的差值，若此时Cfly还未预充电，那么D1会承受较大的电压，产生过压损坏的风险。再比如，在该电路正常工作的情况下，若母线正端P突然跳变至更高电压，例如从900V跳变到1400V，那么由于Cfly两端的电压还未发生变化，仍为900V/2＝450V，在D1导通的情况下，T4承受的电压为母线正端P的电压减去飞跨电容Cfly两端的电压，即1400V-450V＝950V，从而造成T4管承受较大的电压，产生过压损坏的风险。
因此，现有技术提供的三电平DC-DC变换电路存在难以应对异常工况的问题。
发明内容
本申请实施例提供一种直流变换器，用以解决现有技术中存在的三电平DC-DC变换电路难以应对异常工况的问题。
第一方面，本申请实施例提供一种直流变换器，该直流变换器包括：第一开关器件、第二开关器件、第三开关器件、第四开关器件、第一电容、第二电容、飞跨电容，以及保护电路；第一电容的一端连接母线正端，另一端连接母线中间节点；第二电容的一端连接母线中间节点，另一端连接母线负端；第一开关器件的一端连接母线正端，另一端连接第一中间节点；第二开关器件的一端连接第一中间节点，另一端连接参考端；第三开关器件的一端连接参考端，另一端连接第二中间节点；第四开关器件的一端连接第二中间节点，另一端连接母线负端；飞跨电容的正端连接第一中间节点，负端连接第二中间节点；第一中间节点和第二中间节点通过保护电路连接至母线中间节点。
其中，保护电路包含嵌位单元和缓冲单元，嵌位单元用于在母线正端与母线负端之间的电压升高时将第一开关器件嵌位至第一电容的电压以及将第四开关器件嵌位至第二电容的电压；缓冲单元用于在母线正端与母线负端之间的电压升高时减小流经嵌位单元和飞跨电容的电流。
采用第一方面提供的直流变换器，当低压正端误接入负电压时，母线负端的电压为0V，低压正端为负电压，因而第三开关器件与第四开关器件导通，第二中间节点的电压为0V。由于该直流变换器还未启动工作，飞跨电容还未进行预充电，故飞跨电容两端的电压为0V，因此第一中间节点的电压也为0V。如果此时第一电容和第二电容已经具有电压，飞跨电容将由母线中间节点，经过保护电路、第一中间节点以及第二中间节点对其进行充电，并最终充电至与第二电容相等的电压；与此同时，第一开关器件由保护电路嵌位至第一电容的电压，避免了过压损坏风险。
当母线正端的电压突然跳高时，飞跨电容可以通过保护电路进行充电，保护电路中的嵌位单元将第一开关器件嵌位至第一电容的电压，将第四开关器件嵌位至第二电容的电压，从而降低了第一开关器件和第四开关器件过压损坏的风险；同时，保护电路中的缓冲单元减小了飞跨电容充电时的电流冲击，从而提高了充电回路中各器件的可靠性。
在直流变换器正常工作对飞跨电容进行电压均衡控制时，还可以通过调节第一开关器件、第二开关器件、第三开关器件和第四开关器件的导通和关断时间，来调节飞跨电容的电压，具体地，在飞跨电容两端的电压可以大于第一电容的电压，且大于第二电容的电压。
在飞跨电容两端的电压大于第一电容的电压且大于第二电容的电压的情况下，若出现母线正端P的电压突然跳高的异常工况，那么在对飞跨电容充电时，由于充电最终电压与发生异常工况时飞跨电容的瞬时电压之间的差值进一步减小，因而可以减小飞跨电容充电的电流冲击，进一步提高了充电回路中各器件的可靠性。此外，在飞跨电容两端的电压大于第一电容的电压且大于第二电容的电压的情况下，该直流变换器正常工作时，由于母线中间节点M的电压小于第一中间节点的电压且大于第二中间节点的电压，保护电路中的嵌位器件无法导通，因而保护电路不参与该直流变换器的正常工作。也就是说，保护电路仅在出现异常工况时对直流变换器中的器件起到保护作用，在直流变换器正常工作时保护电路不参与工作。
此外，第一方面提供的直流变换器中还可以包括第一电感；其中，第一电感的一端连接低压正端，另一端连接参考端，母线负端与低压负端耦合；或者，第一电感的一端连接 低压负端，另一端连接参考端；母线正端与低压正端耦合。
在一种可能的设计中，在该直流变换器中，低压正端与低压负端为电路的输入端，母线正端与母线负端为电路的输出端；或者，母线正端与母线负端为电路的输入端，低压正端与低压负端为电路的输出端。
应理解，第一方面提供的直流变换器可以为单向变换器，也可以为双向变换器。作为双向变换器时，若母线正端和母线负端作为输入端，则低压正端和低压负端作为输出端，该直流变换器用于将母线正端和母线负端之间的直流电压转换为低压正端和低压负端之间的直流电压。或者，若低压正端和低压负端作为输入端，则母线正端和母线负端作为输出端，该直流变换器用于将低压正端和低压负端之间的直流电压转换为母线正端和母线负端之间的直流电压。
具体地，在第一方面提供的直流变换器中，嵌位单元可以包括第一嵌位器件和第二嵌位器件；其中，第一嵌位器件的一端连接第一中间节点，第一嵌位器件的另一端连接第二嵌位器件；第二嵌位器件的一端连接第二中间节点，另一端连接第一嵌位器件；缓冲单元的一端连接第一嵌位器件与第二嵌位器件的连接节点，另一端连接母线中间节点。
进一步地，第一嵌位器件可以为第一二极管，第二嵌位器件可以为第二二极管；或者，第一嵌位器件可以为第一绝缘栅双极型晶体管IGBT以及与之反并联的二极管，第二嵌位器件可以为第二IGBT以及与之反并联的二极管；或者，第一嵌位器件可以为第一金属-氧化物半导体场效应晶体管MOSFET及其体二极管，第二嵌位器件可以为第二MOSFET及其体二极管；其中，第一嵌位器件中的二极管的阴极连接第一中间节点，阳极连接第二嵌位器件中的二极管的阴极；第二嵌位器件中的二极管的阳极连接第二中间节点。
也就是说，第一嵌位器件和第二嵌位器件中均各自包括一个二级管(例如第一嵌位器件包括第一二极管、第二嵌位器件包括第二二极管，或者第一嵌位器件包括IGBT的反并联二极管、第二嵌位器件包括IGBT的反并联二极管，或者第一嵌位器件包括MOSFET的体二极管、第二嵌位器件包括MOSFET的体二极管)，这两个二极管串联接在第一中间节点与第二中间节点之间，且这两个二极管的中间节点通过缓冲单元与母线中间节点M连接。
在一种可能的设计中，缓冲单元包括以下至少一种：第一缓冲电阻；第三IGBT以及与之反并联的二极管、第四IGBT以及与之反并联的二极管，第三IGBT与第四IGBT对顶连接；第三MOSFET及其体二极管、第四MOSFET及其体二极管，第三MOSFET与第四MOSFET对顶连接；第二缓冲电阻、第三缓冲电阻、第五开关器件，第二缓冲电阻和第三缓冲电阻串联，第五开关器件与第三缓冲电阻并联。
其中，第五开关器件为以下任一种：机械开关器件；第五IGBT以及与之反并联的二极管；第五MOSFET及其体二极管。
不难看出，缓冲单元的主体为电阻，其具体形式可以是固定阻值的电阻，可以是通过IGBT以及与之反并联的二极管实现的可调电阻，可以是MOSFET及其体二极管实现的可调电阻，也可以是通过开关器件进行调节的可调电阻。当缓冲单元包括电阻时，在异常工况下对飞跨电容进行充电时，可以减小对飞跨电容以及充电回路中其他器件的电流冲击，降低器件过压损坏的风险。
在一种可能的设计中，第一开关器件、第二开关器件、第三开关器件和第四开关器件均由IGBT及其反并联二极管或者MOSFET及其体二极管组成；或者，第一开关器件、第二开关器件由IGBT及其反并联二极管或者MOSFET及其体二极管组成，第三开关器件、 第四开关器件由二极管组成；或者，第一开关器件、第二开关器件由二极管组成；第三开关器件、第四开关器件由IGBT及其反并联二极管或者MOSFET及其体二极管组成。
采用上述方案，若第一开关器件、第二开关器件、第三开关器件和第四开关器件均由IGBT及其反并联二极管或者MOSFET及其体二极管组成，则第一方面提供的直流变换器可以为双向变换器。
在一种可能的设计中，保护电路还用于在电路启动时对飞跨电容进行预充电。
采用上述方案，飞跨电容可以由低压正端经由第二开关器件→保护电路→母线中间节点→母线负端这一回路进行预充电，因而不需要额外配置预充电电路，降低了成本。
附图说明
图1为现有技术提供的一种三电平DC-DC变换电路的结构示意图；
图2为现有技术提供的另一种三电平DC-DC变换电路的结构示意图；
图3为本申请实施例提供的第一种直流变换器的结构示意图；
图4为本申请实施例提供的第二种直流变换器的结构示意图；
图5为本申请实施例提供的第三种直流变换器的结构示意图；
图6为本申请实施例提供的第四种直流变换器的结构示意图；
图7为本申请实施例提供的第五种直流变换器的结构示意图；
图8为本申请实施例提供的第六种直流变换器的结构示意图；
图9为本申请实施例提供的第七种直流变换器的结构示意图；
图10为本申请实施例提供的第八种直流变换器的结构示意图；
图11为本申请实施例提供的第九种直流变换器的结构示意图；
图12为本申请实施例提供的第十种直流变换器的结构示意图；
图13为本申请实施例提供的第十一种直流变换器的结构示意图；
图14为本申请实施例提供的直流变换器在异常工况下的工作状态示意图；
图15为本申请实施例提供的直流变换器在启动时的工作状态示意图；
图16为本申请实施例提供的直流变换器在对飞跨电容充电时的工作状态示意图；
图17为本申请实施例提供的直流变换器在异常工况下的工作状态示意图。
具体实施方式
现有技术中，为了解决背景技术中提出的三电平DC-DC变换电路难以应对异常工况的问题，对图1所示的三电平DC-DC变换电路进行改进，改进后的三电平DC-DC变换电路可以如图2所示。
图2所示的变换电路在图1所示的变换电路拓扑上，增加了一个开关S和一个二极管D6。其中，飞跨电容Cfly的负端经过开关S连接中间节点SN；同时，飞跨电容Cfly的负端经过二极管D6连接母线的中间节点M。
图2所示的变换电路可以直接对飞跨电容Cfly进行预充电，而无需通过额外的预充电电路：该变换电路从低压正端L正常启动时，飞跨电容Cfly可以由低压正端电压经过电感Lin→二极管D2→二极管D6→Cbus-进行预充电，从而节省了传统的预充电电路。
图2所示的变换电路在应对低压正端L误接入负电压的情况时，工作原理如下：在该 变换电路开始工作之前，开关S保持断开。如果低压正端L接入了负电压，则D3、D4导通，中间节点SN的电压为0；此时，由于飞跨电容Cfly还未进行充电，其两端电压为0，故母线电压Vbus由D1和开关S共同承担。也就是说，与图1所示的变换电路相比，增加的开关S避免了母线电压Vbus由D1单独承担从而导致其过压损坏的风险。电路正常启动后，开关S保持闭合。
图2所示的变换电路在应对母线电压突然跳变的情况时，工作原理如下：变换电路正常工作后，如果母线电压突然跳变至更高电压，此时飞跨电容Cfly两端的电压还未发生变化，那么当D1导通时，飞跨电容Cfly经过二极管D6、Cbus-进行充电；由于S闭合且D6导通，此时T4两端的电压为与Cbus-两端的电压相同。也就是说，增加的二极管D6将T4嵌位至母线负电压源，从而降低T4过压损坏的风险。仍以背景技术中母线正端P从900V跳变到1400V为例，那么采用图2所示的变换电路，T4嵌位至700V，与采用图1所示的变换电路相比，T4承受的电压变小了(950V→700V)，因而采用图2所示的变换电路降低了T4过压损坏的风险。
采用图2所示的变换电路虽然可以在一定程度上应对异常工况，但是该变换电路还存在如下问题：第一，增加的开关S会引入一定的导通损耗，且S的加入导致电路回路变长，还会增加IGBT和二极管的电压应力。第二，增加的二极管D6，在将T4嵌位至母线负电压源时，如果飞跨电容Cfly两端的原电压与突变后的半母线电压(即Vbus/2)在数值上相差较大的话，那么飞跨电容Cfly的充电过程会对飞跨电容Cfly、二极管D6以及Cbus-等器件产生较大的电流冲击，降低这些器件的可靠性。
基于背景技术中提出的问题，本申请实施例提供一种直流变换器，用以解决现有技术中存在的三电平DC-DC变换电路难以应对异常工况的问题。
下面将结合附图对本申请实施例作进一步地详细描述。
需要说明的是，本申请实施例中，多个是指两个或两个以上。另外，在本申请的描述中，“第一”、“第二”等词汇，仅用于区分描述的目的，而不能理解为指示或暗示相对重要性，也不能理解为指示或暗示顺序。
参见图3，为本申请实施例提供的一种直流变换器的结构示意图。如图3所示，该直流变换器包括第一开关器件S1、第二开关器件S2、第三开关器件S3、第四开关器件S4、第一电容C1、第二电容C2、飞跨电容Cfly以及保护电路；第一电容C1的一端连接母线正端P，另一端连接母线中间节点M；第二电容C2的一端连接母线中间节点M，另一端连接母线负端N；第一开关器件S1的一端连接母线正端P，另一端连接第一中间节点SP；第二开关器件S2的一端连接第一中间节点SP，另一端连接参考端O；第三开关器件S3的一端连接参考端O，另一端连接第二中间节点SN；第四开关器件S4的一端连接第二中间节点SN，另一端连接母线负端N；飞跨电容Cfly的正端连接第一中间节点SP，负端连接第二中间节点SN；第一中间节点SP和第二中间节点SN通过保护电路连接至母线中间节点M。
在图3所示的直流变换器中，保护电路包含嵌位单元和缓冲单元，嵌位单元用于在母线正端P与母线负端N之间的电压升高时将第一开关器件S1嵌位至第一电容C1的电压以及将第四开关器件S4嵌位至第二电容C2的电压；缓冲单元用于在母线正端P与母线负端N之间的电压升高时减小流经嵌位单元和飞跨电容Cfly的电流。
在图3所示的直流变换器中，随着第一开关器件S1、第二开关器件S2、第三开关器件S3、第四开关器件S4的导通和闭合，参考端O可以具有多种电平状态，因而本申请实施例提供的直流变换器可以视为多电平DC-DC变换器。
需要说明的是，图3所示的直流变换器仅为一种示例，在另一种示例中，本申请实施例提供的直流变换器也可以如图4所示。图4所示的直流变换器与图3所示的直流变换器的区别在于开关器件在母线正端和母线负端的分布不同，各器件间的连接关系不变。
此外，本申请实施例提供的直流变换器中还可以包括第一电感。对于图3的示例，第一电感L1的一端连接低压正端L，另一端连接参考端O，母线负端N与低压负端N耦合，如图5所示；对于图4的示例，第一电感L1的一端连接低压负端Q，另一端连接参考端O；母线正端P与低压正端P耦合，如图6所示。
以上根据本申请实施例中各器件之间的连接关系给出了图3～图6几个直流变换器的示例。上述几个示例的区别仅在于第一电感L1的位置以及开关器件在母线正端和母线负端的分布，上述几个示例中的直流变换器的控制策略和工作原理相同，因此，在本申请实施例中，将重点以图5所示的直流变换器为例对本申请实施例提供的直流变换器的具体组成、控制策略和工作原理进行阐述，其他示例可以相应参照。
具体应用中，图5所示的直流变换器可以为单向变换器，也可以为双向变换器。在一个具体的示例中，低压正端L和低压负端N可以与光伏组件连接，母线正端P和母线负端N可以与设备连接。在另一个具体的示例中，低压正端L和低压负端N可以与电池组件连接，母线正端P和母线负端N可以与设备连接。
作为双向变换器时，若母线正端P和母线负端N作为输入端，则低压正端L和低压负端N作为输出端，该直流变换器用于将母线正端P和母线负端N之间的直流电压转换为低压正端L和低压负端N之间的直流电压，例如可以通过该直流变换器实现设备向电池组件充电。或者，若低压正端L和低压负端N作为输入端，则母线正端P和母线负端N作为输出端，该直流变换器用于将低压正端L和低压负端N之间的直流电压转换为母线正端P和母线负端N之间的直流电压，例如可以通过该直流变换器实现光伏组件/电池组件向设备供电。
作为单向变换器时，可以将母线正端P和母线负端N作为输入端，将低压正端L和低压负端N作为输出端。
具体地，本申请实施例中，若直流变换器为双向变换器，则第一开关器件、第二开关器件、第三开关器件和第四开关器件均由IGBT及其反并联二极管或者MOSFET及其体二极管组成。若直流变换器为单向变换器，则对于图3和图5所示的直流变换器，第一开关器件、第二开关器件由IGBT及其反并联二极管或者MOSFET及其体二极管组成，第三开关器件、第四开关器件由二极管组成，此时该直流变换器可以视为由母线正端P和母线负端N作为输入端、低压正端L和低压负端N作为输出端的降压(BUCK)电路；对于图4和图6所示的直流变换器，第一开关器件、第二开关器件由二极管组成；第三开关器件、第四开关器件由IGBT及其反并联二极管或者MOSFET及其体二极管组成，此时该直流变换器可以视为由母线正端P和母线负端N作为输入端、低压正端P和低压负端Q作为输出端的BUCK电路。
此外，本申请实施例中，保护电路还用于在直流变换器启动时对飞跨电容Cfly进行预充电。例如，直流变换器从低压正端L启动时，飞跨电容Cfly可以由低压正端L经由第 二开关器件S2→保护电路→母线中间节点M→母线负端N这一回路进行预充电，从而避免图1所示的DC-DC变换电路需要额外配置预充电电路的问题，降低了成本。
当低压正端L误接入负电压时，母线负端N的电压为0V，低压正端L为负电压，S3与S4导通，第二中间节点SN的电压为0V。由于该直流变换器还未启动工作，飞跨电容Cfly还未进行预充电，故Cfly两端的电压为0V，因此第一中间节点SP的电压也为0V。如果此时C1和C2已经具有电压，飞跨电容Cfly将由母线中间节点M→保护电路→SP→SN→S4这一充电回路对其进行充电，并最终充电至与C2相等的电压；与此同时，S1由保护电路嵌位至C1的电压，避免了过压损坏风险。
当母线正端P的电压突然跳高时，飞跨电容Cfly可以通过保护电路进行充电，保护电路中的嵌位单元将S1嵌位至第一电容C1的电压，将S4嵌位至第二电容C2的电压，从而降低S1和S4过压损坏的风险；同时，保护电路中的缓冲单元减小了飞跨电容Cfly充电时的电流冲击，从而提高了充电回路中各器件的可靠性。
此外，本申请实施例中，在直流变换器正常工作对飞跨电容Cfly进行电压均衡控制时，还可以通过调节第一开关器件S1、第二开关器件S2、第三开关器件S3和第四开关器件S4的导通和关断时间，来调节飞跨电容Cfly的电压。具体地，本申请实施例中，在直流变换器启动完成后，飞跨电容两端的电压大于第一电容C1的电压且大于第二电容C2的电压。
在飞跨电容两端的电压大于第一电容的电压且大于第二电容的电压的情况下，若出现母线正端P的电压突然跳高的异常工况，那么在对飞跨电容Cfly充电时，由于充电最终电压与发生异常工况时飞跨电容的瞬时电压之间的差值进一步减小，因而可以减小飞跨电容Cfly充电的电流冲击，进一步提高了充电回路中各器件的可靠性。此外，在飞跨电容两端的电压大于第一电容的电压且大于第二电容的电压的情况下，该直流变换器正常工作时，由于母线中间节点M的电压小于第一中间节点SP的电压且大于第二中间节点SN的电压，保护电路中的嵌位器件无法导通，因而保护电路不参与该直流变换器的正常工作。也就是说，保护电路仅在出现异常工况时对直流变换器中的器件起到保护作用，在直流变换器正常工作时保护电路不参与工作。
具体地，本申请实施例中，嵌位单元可以包括第一嵌位器件和第二嵌位器件；其中，第一嵌位器件的一端连接第一中间节点，第一嵌位器件的另一端连接第二嵌位器件；第二嵌位器件的一端连接第二中间节点，另一端连接第一嵌位器件；缓冲单元的一端连接第一嵌位器件与第二嵌位器件的连接节点，另一端连接母线中间节点。
其中，第一嵌位器件可以为第一二极管，第二嵌位器件可以为第二二极管。或者，第一嵌位器件可以为第一绝缘栅双极型晶体管IGBT以及与之反并联的二极管，第二嵌位器件可以为第二IGBT以及与之反并联的二极管；或者，第一嵌位器件可以为第一金属-氧化物半导体场效应晶体管MOSFET及其体二极管，第二嵌位器件可以为第二MOSFET及其体二极管；其中，第一嵌位器件中的二极管的阴极连接第一中间节点，阳极连接第二嵌位器件中的二极管的阴极；第二嵌位器件中的二极管的阳极连接第二中间节点。
不难看出，第一嵌位器件和第二嵌位器件中均各自包括一个二级管(例如第一嵌位器件包括第一二极管、第二嵌位器件包括第二二极管，或者第一嵌位器件包括IGBT的反并联二极管、第二嵌位器件包括IGBT的反并联二极管，或者第一嵌位器件包括MOSFET的体二极管、第二嵌位器件包括MOSFET的体二极管)，这两个二极管串联接在第一中间节点SP与第二中间节点SN之间，且这两个二极管的中间节点通过缓冲单元与母线中间节点 M连接。
以图5所示的直流变换器为例，保护电路的具体组成可以如图7所示。
具体地，缓冲单元包括以下至少一种：第一缓冲电阻；第三IGBT以及与之反并联的二极管、第四IGBT以及与之反并联的二极管，第三IGBT与第四IGBT对顶连接；第三MOSFET及其体二极管、第四MOSFET及其体二极管，第三MOSFET与第四MOSFET对顶连接；第二缓冲电阻、第三缓冲电阻和第五开关器件，第二缓冲电阻和第三缓冲电阻串联，第五开关器件与第三缓冲电阻并联。其中，第五开关器件为以下任一种：机械开关器件；第五IGBT以及与之反并联的二极管；第五MOSFET及其体二极管。
也就是说，缓冲单元的主体为电阻，其具体形式可以是固定阻值的电阻，可以是通过IGBT以及与之反并联的二极管实现的可调电阻，可以是MOSFET及其体二极管实现的可调电阻，也可以是通过开关器件进行调节的可调电阻。
在一个具体的示例中，若本申请实施例提供的直流变换器为双向变换器，且第一嵌位器件为第一二极管，第二嵌位器件为第二二极管，缓存单元包括第一缓存电阻，则该直流变换器的一种可能的结构示意图可以如图8所示。在图8所示的直流变换器中，T1和D1组成第一开关器件，T2和D2组成第二开关器件，T3和D3组成第三开关器件，T4和D4组成第四开关器件，D5为第一二极管，D6为第二二极管，R0为缓冲单元。图8所示的直流变换器可以视为图3或图5所示的直流变换器的一个具体示例。
需要说明的是，在图8的示例中，以IGBT以及与之反并联的二极管为例对开关器件的具体组成进行示意。实际应用中，开关器件也可以由MOSFET及其体二极管组成。此外，在本申请实施例的各示例中，MOSFET及其体二极管与IGBT及其反并联的二极管的功能类似，二者可以相互替换。
在一个具体的示例中，若本申请实施例提供的直流变换器为双向变换器，且第一嵌位器件为第一二极管，第二嵌位器件为第二二极管，缓存单元包括第一缓存电阻，则该直流变换器的一种可能的结构示意图可以如图9所示。在图9所示的直流变换器中，T1和D1组成第一开关器件，T2和D2组成第二开关器件，T3和D3组成第三开关器件，T4和D4组成第四开关器件，D5为第一二极管，D6为第二二极管，R0为缓冲单元。图9所示的直流变换器可以视为图4或图6所示的直流变换器的一个具体示例。
在一个具体的示例中，本申请实施例提供的直流变换器为单向变换器，且第一嵌位器件为第一二极管，第二嵌位器件为第二二极管，缓存单元包括第一缓存电阻，则该直流变换器的一种可能的结构示意图可以如图10所示。在图10所示的直流变换器中，T1和D1组成第一开关器件，T2和D2组成第二开关器件，D3为第三开关器件，D4为第四开关器件，D5为第一二极管，D6为第二二极管，R0为缓冲单元。图10所示的直流变换器可以视为图3或图5所示的直流变换器的一个具体示例。
进一步地，图8所示的直流变换器中，第一嵌位器件也可以由第一MOSFET及其体二极管组成，第二嵌位器件由第二MOSFET及其体二极管组成；或者，第一嵌位器件由第一IGBT以及与之反并联的二极管组成，第二嵌位器件由第二IGBT以及与之反并联的二极管组成。当然，实际应用中，第一嵌位器件可以为MOSFET及其体二极管、第二嵌位器件为IGBT以及与之反并联的二极管，或者第一嵌位器件可以为IGBT以及与之反并联的二极管、第二嵌位器件为MOSFET及其体二极管。在一个具体的示例中，该直流变换器的一种可能的结构示意图可以如图11所示。在图11所示的直流变换器中，第一嵌位器件由IGBT(即 T5)以及与之反并联的二极管(即D5)组成，第二嵌位器件由IGBT(即T6)以及与之反并联的二极管(即D6)组成。
进一步地，图8所示的直流变换器中，缓冲单元也可以由两个对顶连接的MOSFET及其体二极管组成，如图12的中的a示例所示，或者，缓冲单元也可以由两个对顶连接的IGBT以及分别与之反并联的二极管组成，如图12的b示例所示。
进一步地，图8所示的直流变换器中，缓冲单元也可以由第二缓冲电阻、第三缓冲电阻和第五开关器件组成，其中，第二缓冲电阻和第三缓冲电阻串联，第五开关器件与第三缓冲电阻并联。第五开关器件可以为机械开关器件、第五IGBT以及与之反并联的二极管，或者第五MOSFET及其体二极管。在一个具体的示例中，该直流变换器的一种可能的结构示意图可以如图13所示。在图13中，第二缓冲电阻为R1、第三缓冲电阻为R2，第五开关器件为机械开关器件。
对于本申请中直流变换器的各个示例，其工作原理均可以互相参照，下面以图8所示的直流变换器为例对本申请实施例提供的直流变换器的在预充电、异常工况以及正常工作时的工作原理进行介绍，其他示例可以参照，本申请实施例中不再赘述。
图14为图8所示的直流变换器的低压正端L接入负电压时的工作状况，即在该直流变换器启动前低压正端L与低压负端N接反的工况。此时，低压负端N的电压为0V，低压正端L为负电压，D3与D4导通，第二中间节点SN的电压为0V。由于直流变换器还未启动工作，飞跨电容Cfly还未进行预充电，故Cfly两端的电压为0V，因此第一中间节点SP的电压也为0V。如果此时C1和C2已经具有电压，例如均为600V，则母线正端P的电压为1200V。如果该直流变换器未设置保护电路(即如图1所示的电路拓扑)，则T1、D1两端的承压为母线正端P的电压减去第一中间节点SP的电压，即1200-0＝1200V，T1和D1存在过压损坏风险。而本申请实施例中增加了保护电路以后，可以通过母线中间节点M→R0→D5→SP→Cfly→SN这一充电路径对Cfly进行充电，如图14中的箭头方向所示，并最终将Cfly充电至与C2相等的电压(SP点的电压由0V变为600V)；与此同时，T1、D1由R0、D5嵌位至C1两端的电压(即600V)，从而降低了T1和D1过压损坏的风险。
因此，与图1所示的变换电路相比，采用图8所示的直流变换器能够在低压正端L接入负电压时对开关器件实现保护，降低开关器件过压损坏的风险。
图15为直流变换器从低压正端L启动时的正常工作状况。此时，低压负端N的电压为0V，低压正端L的电压从0V逐渐上升至一定值，例如1200V。在此过程中，D2、D1导通，第一中间节点SP的电压跟随低压正端L的电压，并且低压正端L经过D2、D1对C1、C2进行充电，即母线正端P的电压也跟随L电压。母线中间节点M的电压则由C1、C2串联进行分压，例如C1、C2参数一致时分压为600V。与此同时，飞跨电容Cfly通过低压正端L→L1→D2→SP→Cfly→SN→D6→R0→M这一充电路径进行充电，如图15中的箭头方向所示，并最终充电至与C1相等的电压，从而完成飞跨电容Cfly的预充电。
因此，与图1所示的变换电路相比，采用图8所示的直流变换器能够在不主动驱动开关器件的情况下完成对飞跨电容Cfly的预充电，与图1所示的现有技术方案相比节省了预充电电路，降低了成本。
在图8所示的直流变换器正常启动后，可以通过调节该直流变换器中各个开关器件的导通和关断时间来实现DC-DC变换，例如可以将低压正端L与低压负端N之间的较小的 直流电压升压，在母线正端P和母线负端N之间输出较大的直流电压。图16为图8所示的直流变换器正常工作的状况。此时，例如母线负端N的电压为0V，低压正端L的电压为800V，母线正端P的电压为900V，C1、C2参数一致时母线中间节点M的电压为450V。根据前述对飞跨电容Cfly进行电压均衡控制的设定，飞跨电容Cfly的电压可以高于C1、C2的电压，例如可以为500V。
在T4或D4导通的情况下，则第二中间节点SN的电压为0V，第一中间节点SP的电压为500V，如图16中的a示例所示，此时由于SP的电压高于M的电压，因而保护电路中的第一嵌位器件D5不会导通，保护电路不参与该直流变换器的正常工作。
在T1或D1导通的情况下，则第一中间节点SP的电压为900V，第二中间节点SN的电压为400V，如图16中的b示例所示，此时由于SN的电压低于M的电压，因而保护电路中的第二嵌位器件D6不会导通，保护电路不参与该直流变换器的正常工作。
通过以上分析可以看出，采用图8所示的直流变换器，由于飞跨电容Cfly电压的控制设定，使得在正常工作状况下保护电路不参与直流变换器的工作，从而使得该直流变换器可以保持未设置保护电路之前的原有性能。
图17为直流变换器的母线电压突然变高的异常工作状况。在异常工况发生前，该直流变换器工作在正常工况，例如图16所示的工作状况。当母线电压突然变高的异常工况发生时，母线正端P的电压突变为一个较高值，例如1400V，则母线中间节点M跟随突变为700V。
在T4或D4导通的情况下，第二中间节点SN的电压为0V，如图17的a示例所示；由于飞跨电容Cfly的电压还未发生突变，仍保持为异常工况发生前的500V，故第一中间节点SP的电压为500V，如果该直流变换器中未设置保护电路(即如图1所示的电路拓扑)，则T1、D1两端将承担900V电压，存在过压损坏风险；而本申请实施例中增加了保护电路以后，可以通过母线中间节点M→R0→D5→SP→Cfly→SN这一充电路径对Cfly进行充电，如图17的a示例中的箭头方向所示，并最终将飞跨电容Cfly充电至与C2相等的电压700V；与此同时，T1、D1由R0、D5嵌位至C1两端的电压(即700V)，从而避免了过压损坏风险。
在T1或D1导通的情况下，第一中间节点SP的电压为1400V，如图17的b示例所示；由于飞跨电容Cfly的电压还未发生突变，仍保持为异常工况发生前的500V，故第二中间节点SN的电压为900V，如果该直流变换器中未设置保护电路(即如图1所示的电路拓扑)，则T4、D4两端将承担900V电压，存在过压损坏风险；而本申请实施例中增加了保护电路以后，可以通过SP→Cfly→SN→D6→R0→M这一充电路径对Cfly进行充电，如图17的b示例中的箭头方向所示，并最终将飞跨电容Cfly充电至与C1相等的电压700V；与此同时，T4、D4由D6、R0嵌位至C2两端的电压(即700V)，从而避免了过压损坏风险。
因此，与图1所示的变换电路相比，采用图8所示的直流变换器可以在母线电压突然变高时实现对开关器件的保护，降低开关器件过压损坏的风险。
此外，与图2所示的变换电路相比，采用图8所示的直流变换器，由于保护电路中设置有缓冲单元(即R0)，因而可以有效降低飞跨电容Cfly充电时的电流冲击，例如可以通过设置R0的阻值来改变充电电流的大小；同时，由于飞跨电容Cfly的电压设定大于C1两端的电压且大于C2两端的电压，因而可以降低异常工况时飞跨电容Cfly的瞬时电压与充电最终电压之间的差值，从而进一步降低飞跨电容充电时的电流冲击，提高充电回路中 各器件的可靠性。
以上通过图8所示的直流变换器对本申请实施例提供的直流变换器在预充电、正常工况以及异常工况(低压正端L接入负电压、母线电压突然变高)时的工作状态进行了详细介绍。本申请实施例提供的其他直流变换器的工作状态与图8所示的直流变换器的工作原理类似，区别仅在于一些细微的调节。
例如，图9所示的直流变换器与图8所示的直流变换器的区别仅在于开关器件的分布，二者的工作原理相同；图10所示的直流变换器为单向变换器，与图8所示的直流变换器作为BUCK电路时的工作状态相同；图11所示的直流变换器在图8所示的直流变换器的基础上对第一嵌位器件和第二嵌位器件进行改进，区别仅在于图11中的第一嵌位器件和第二嵌位器件的导通特性(例如导通压降)可以改变，使得直流变换器的调节更为灵活，可以满足不同异常工况下的调节需求；图12所示的直流变换器在图8所示的直流变换器的基础上对缓冲单元进行改进，该直流变换器中的缓冲单元的导通特性可以改变，使得直流变换器的调节更为灵活，可以满足不同异常工况下的调节需求；图13所示的直流变换器通过机械开关使得缓冲单元的阻值可调，从而满足不同异常工况下的调节需求。
因此，本申请实施例中仅针对图8所示的直流变换器的工作状态进行详细分析，其他示例中直流变换器的工作状态可以参见图8中的相关描述，此处不再赘述。
综上，采用本申请实施例提供的直流变换器，当低压正端误接入负电压时，母线负端的电压为0V，低压正端为负电压，因而第三开关器件与第四开关器件导通，第二中间节点的电压为0V。由于该直流变换器还未启动工作，飞跨电容还未进行预充电，故飞跨电容两端的电压为0V，因此第一中间节点的电压也为0V。如果此时第一电容和第二电容已经具有电压，飞跨电容将由母线中间节点，经过保护电路、第一中间节点以及第二中间节点对其进行充电，并最终充电至与第二电容相等的电压；与此同时，第一开关器件由保护电路嵌位至第一电容的电压，避免了过压损坏风险。
当母线正端的电压突然跳高时，飞跨电容可以通过保护电路进行充电，保护电路中的嵌位单元将第一开关器件嵌位至第一电容的电压，将第四开关器件嵌位至第二电容的电压，从而降低了第一开关器件和第四开关器件过压损坏的风险；同时，保护电路中的缓冲单元减小了飞跨电容充电时的电流冲击，从而提高了充电回路中各器件的可靠性。
显然，本领域的技术人员可以对本申请实施例进行各种改动和变型而不脱离本申请实施例的范围。这样，倘若本申请实施例的这些修改和变型属于本申请权利要求及其等同技术的范围之内，则本申请也意图包含这些改动和变型在内。

Claims (10)

  1. 一种直流变换器，其特征在于，包括：第一开关器件、第二开关器件、第三开关器件、第四开关器件、第一电容、第二电容、飞跨电容，以及保护电路；所述第一电容的一端连接母线正端，另一端连接母线中间节点；所述第二电容的一端连接所述母线中间节点，另一端连接母线负端；所述第一开关器件的一端连接所述母线正端，另一端连接第一中间节点；所述第二开关器件的一端连接所述第一中间节点，另一端连接参考端；所述第三开关器件的一端连接所述参考端，另一端连接第二中间节点；所述第四开关器件的一端连接所述第二中间节点，另一端连接所述母线负端；所述飞跨电容的正端连接所述第一中间节点，负端连接所述第二中间节点；所述第一中间节点和所述第二中间节点通过所述保护电路连接至所述母线中间节点；
    其中，所述保护电路包含嵌位单元和缓冲单元，所述嵌位单元用于在所述母线正端与所述母线负端之间的电压升高时将所述第一开关器件嵌位至所述第一电容的电压以及将所述第四开关器件嵌位至所述第二电容的电压；所述缓冲单元用于在所述母线正端与所述母线负端之间的电压升高时减小流经所述嵌位单元和所述飞跨电容的电流。
  2. 如权利要求1所述的直流变换器，其特征在于，在所述电路启动完成后，所述飞跨电容两端的电压大于所述第一电容的电压，且大于所述第二电容的电压。
  3. 如权利要求1或2所述的直流变换器，其特征在于，还包括：
    第一电感；其中，所述第一电感的一端连接低压正端，另一端连接所述参考端，所述母线负端与低压负端耦合；或者，所述第一电感的一端连接低压负端，另一端连接所述参考端；所述母线正端与低压正端耦合。
  4. 如权利要求3所述的直流变换器，其特征在于，所述低压正端与所述低压负端为所述电路的输入端，所述母线正端与所述母线负端为所述电路的输出端；或者，所述母线正端与所述母线负端为所述电路的输入端，所述低压正端与所述低压负端为所述电路的输出端。
  5. 如权利要求1～4任一项所述的直流变换器，其特征在于，所述嵌位单元包括第一嵌位器件和第二嵌位器件；
    其中，所述第一嵌位器件的一端连接所述第一中间节点，所述第一嵌位器件的另一端连接所述第二嵌位器件；所述第二嵌位器件的一端连接所述第二中间节点，另一端连接所述第一嵌位器件；所述缓冲单元的一端连接所述第一嵌位器件与所述第二嵌位器件的连接节点，另一端连接所述母线中间节点。
  6. 如权利要求5所述的直流变换器，其特征在于，所述第一嵌位器件为第一二极管，所述第二嵌位器件为第二二极管；或者，所述第一嵌位器件为第一绝缘栅双极型晶体管IGBT以及与之反并联的二极管，所述第二嵌位器件为第二IGBT以及与之反并联的二极管；或者，所述第一嵌位器件为第一金属-氧化物半导体场效应晶体管MOSFET及其体二极管， 所述第二嵌位器件为第二MOSFET及其体二极管；
    其中，所述第一嵌位器件中的二极管的阴极连接所述第一中间节点，阳极连接所述第二嵌位器件中的二极管的阴极；所述第二嵌位器件中的二极管的阳极连接所述第二中间节点。
  7. 如权利要求1～6任一项所述的直流变换器，其特征在于，所述缓冲单元包括以下至少一种：
    第一缓冲电阻；
    第三IGBT以及与之反并联的二极管、第四IGBT以及与之反并联的二极管，所述第三IGBT与所述第四IGBT对顶连接；
    第三MOSFET及其体二极管、第四MOSFET及其体二极管，所述第三MOSFET与所述第四MOSFET对顶连接；
    第二缓冲电阻、第三缓冲电阻、第五开关器件，所述第二缓冲电阻和所述第三缓冲电阻串联，所述第五开关器件与所述第三缓冲电阻并联。
  8. 如权利要求7所述的直流变换器，其特征在于，所述第五开关器件为以下任一种：
    机械开关器件；
    第五IGBT以及与之反并联的二极管；
    第五MOSFET及其体二极管。
  9. 如权利要求1～8任一项所述的直流变换器，其特征在于，所述第一开关器件、所述第二开关器件、所述第三开关器件和所述第四开关器件均由IGBT及其反并联二极管或者MOSFET及其体二极管组成；或者，
    所述第一开关器件、所述第二开关器件由IGBT及其反并联二极管或者MOSFET及其体二极管组成，所述第三开关器件、所述第四开关器件由二极管组成；或者，
    所述第一开关器件、所述第二开关器件由二极管组成；所述第三开关器件、所述第四开关器件由IGBT及其反并联二极管或者MOSFET及其体二极管组成。
  10. 如权利要求1～9任一项所述的直流变换器，其特征在于，所述保护电路还用于在所述电路启动时对所述飞跨电容进行预充电。
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