CN111251941B - Pre-charging device of high-voltage bus capacitor of new energy automobile - Google Patents

Pre-charging device of high-voltage bus capacitor of new energy automobile Download PDF

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Publication number
CN111251941B
CN111251941B CN202010238241.5A CN202010238241A CN111251941B CN 111251941 B CN111251941 B CN 111251941B CN 202010238241 A CN202010238241 A CN 202010238241A CN 111251941 B CN111251941 B CN 111251941B
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voltage
switching tube
capacitor
bus capacitor
voltage bus
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CN111251941A (en
Inventor
闵晨
阳彩
王洪宝
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Keboda Technology Co ltd
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Keboda Technology Co ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
    • B60L58/00—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles
    • B60L58/10—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
    • B60L3/00—Electric devices on electrically-propelled vehicles for safety purposes; Monitoring operating variables, e.g. speed, deceleration or energy consumption
    • B60L3/0023—Detecting, eliminating, remedying or compensating for drive train abnormalities, e.g. failures within the drive train
    • B60L3/0046—Detecting, eliminating, remedying or compensating for drive train abnormalities, e.g. failures within the drive train relating to electric energy storage systems, e.g. batteries or capacitors
    • 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
    • H02M3/1582—Buck-boost converters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/60—Other road transportation technologies with climate change mitigation effect
    • Y02T10/70—Energy storage systems for electromobility, e.g. batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/60—Other road transportation technologies with climate change mitigation effect
    • Y02T10/72—Electric energy management in electromobility

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Sustainable Development (AREA)
  • Sustainable Energy (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

A pre-charging device of a high-voltage bus capacitor of a new energy automobile comprises the high-voltage bus capacitor, a capacitor voltage sampling circuit, a bidirectional DC-DC conversion circuit, a charging power supply and a controller. The two ends of the high-voltage bus capacitor are respectively connected with the positive electrode and the negative electrode of the direct current bus of the new energy automobile. The output end of the capacitor voltage sampling circuit is coupled with the input end of the controller. The bidirectional DC-DC conversion circuit is coupled between the DC bus capacitor and the charging power supply and comprises a Buck-Boost circuit, an inductor Lpre, a freewheel element Dpre, a switching tube Q safe and a capacitor Csafe. The controller charges the high-voltage bus capacitor in a step-down mode when the bidirectional DC-DC conversion circuit is in a precharge mode, and charges the high-voltage bus capacitor in a step-up mode when the voltage of the high-voltage bus capacitor reaches a preset threshold. The invention has simple structure, light weight, safety and reliability.

Description

Pre-charging device of high-voltage bus capacitor of new energy automobile
Technical Field
The invention relates to the field of new energy automobiles, in particular to a pre-charging device for a high-voltage bus capacitor of a new energy automobile.
Background
As shown in fig. 1, the electrical system of the hybrid vehicle generally comprises a 48V high-voltage Battery pack 91, a Battery Management System (BMS) MANAGEMENT SYSTEM, a junction box 93, a 48V high-voltage electric device 94, and the like, and when the vehicle is started, the Battery management system 92 controls the junction box 93 to switch on the 48V high-voltage Battery pack 91 and the 48V high-voltage electric device 94, and the 48V high-voltage electric device 94 is charged by the 48V high-voltage Battery pack 91. The 48V high voltage electrical device 94 may be various high voltage electrical devices such as a high voltage DC-DC converter, an inverter, an on-board charger, and the like. The high-voltage electric equipment is connected in parallel with a 48V high-voltage direct-current bus, and a 48V high-voltage bus capacitor C1 is usually arranged at the direct-current input end of the high-voltage electric equipment. In a 48V system of a hybrid electric vehicle, there are usually BSG controllers and other electric devices, which cause a very large capacitance on a 48V high-voltage dc bus, and in order to ensure the safety of the power consumption at the moment of switching on the 48V high-voltage battery, a precharge circuit for precharging the 48V high-voltage bus capacitor is required.
The conventional precharge circuit mainly consists of a precharge contactor 95 (typically a relay) and a precharge resistor 96, and the precharge resistor 96 limits the rush current when the 48V high voltage battery is connected to the 48V high voltage bus capacitor, but this causes heat loss from the resistor and contactor, consumes battery energy, and also causes a potential thermal failure risk for the components. In the prior art, although a pre-charging device for a high-voltage bus capacitor is disclosed for a pure electric vehicle, a pre-charging resistor is not needed, but because the voltage of a high-voltage battery of the pure electric vehicle is larger than 60V, a DC-DC converter of the pure electric vehicle is isolated, and the topological structure of the pre-charging device is different from that of a 48V DC-DC converter of a hybrid electric vehicle shown in fig. 2, so that a pre-charging scheme for the high-voltage bus capacitor cannot be applied to the hybrid electric vehicle. For a common 48V DC-DC converter, compared with an electric system of a hybrid electric vehicle, the capacitor at the 48V side is smaller, the risk of pre-charging is small, and a pre-charging circuit is not needed.
Disclosure of Invention
The technical problem to be solved by the invention is to provide the pre-charging device of the high-voltage bus capacitor of the new energy automobile, which has the advantages of simple structure, low energy loss, safety and reliability.
The embodiment of the invention provides a pre-charging device of a high-voltage bus capacitor of a new energy automobile, wherein the new energy automobile is provided with a direct-current bus and a charging power supply, one end of the high-voltage bus capacitor is connected with the positive electrode of the direct-current bus of the new energy automobile, and the other end of the high-voltage bus capacitor is connected with the negative electrode of the direct-current bus of the new energy automobile; the pre-charging device comprises a bidirectional DC-DC conversion circuit, a capacitor voltage sampling circuit and a controller; the bidirectional DC-DC conversion circuit is coupled between the high-voltage bus capacitor and the charging power supply, so that the charging power supply can charge the high-voltage bus capacitor through the bidirectional DC-DC conversion circuit; the output end of the capacitor voltage sampling circuit is coupled with the input end of the controller, and the capacitor voltage sampling circuit is used for collecting the voltage of the high-voltage bus capacitor; the bidirectional DC-DC conversion circuit is characterized by comprising a Buck-Boost circuit, an inductor Lpre, a follow current element Dpre, a switching tube Q safe and a capacitor Csafe; the first input/output end of the Buck-Boost circuit is connected with the high-voltage bus capacitor in parallel, and the positive electrode of the second input/output end of the Buck-Boost circuit is connected with one end of the inductor Lpre; the other end of the inductor Lpre is connected with a second conducting end of the switching tube Q safe; the first conducting end of the switching tube Q safe is connected with the anode of the charging power supply; the negative terminal of the follow current element Dpre is connected to the common connection point of the other end of the inductance Lpre and the second conducting terminal of the switching tube Q safe, and one end of the capacitor Csafe is connected to the common connection point of the first conducting terminal of the switching tube Q safe and the positive electrode of the charging power supply; the negative electrode of the second input/output end of the Buck-Boost circuit, the positive electrode of the follow current element Dpre and the negative electrode of the charging power supply are respectively connected with the negative electrode of the direct current bus; the controller is respectively connected with the control end of the Buck-Boost circuit and the control end of the switching tube Q safe; the controller can control the bidirectional DC-DC conversion circuit to work in a pre-charging mode, the bidirectional DC-DC conversion circuit firstly charges the high-voltage bus capacitor in a voltage-reducing mode in the pre-charging mode, and the bidirectional DC-DC conversion circuit charges the high-voltage bus capacitor in a voltage-increasing mode after the voltage of the high-voltage bus capacitor reaches a preset threshold value until the voltage of the high-voltage bus capacitor reaches a preset charging voltage value.
The invention has at least the following technical effects:
1. According to the pre-charging device, a branch circuit of an inductance Lpre and a follow current element Dpre is added to a basic topological structure of a high-voltage DC-DC converter of an existing new energy automobile, so that a two-stage pre-charging function is realized; the first stage is converted into a Buck circuit, a basic voltage is established on a high-voltage bus capacitor, after the basic voltage is established, the second stage is switched into a Boost circuit, so that the high-voltage bus capacitor is charged to a final target voltage, the generation of impact current during charging is avoided, and the safety and reliability of a charging process are improved;
2. The precharge device according to the embodiment of the invention has small change to the basic topology structure of the high-voltage DC-DC converter, and the circuit structure and the control process are simpler;
3. according to the pre-charging device provided by the embodiment of the invention, the pre-charging resistor is not arranged, so that the energy loss is low, and the charging efficiency is improved.
Drawings
Fig. 1 shows a schematic block diagram of an electrical system of a conventional hybrid vehicle.
Fig. 2 shows a schematic diagram of a 48V DC-DC converter circuit of a conventional hybrid vehicle.
Fig. 3 shows a schematic circuit diagram of an embodiment of the precharge device of the present invention.
Fig. 4 illustrates an operation principle of the precharge device in the buck mode according to an embodiment of the present invention.
Fig. 5 shows a timing diagram of the operation of the switching tube of the precharge device in the buck mode according to an embodiment of the present invention.
Fig. 6 illustrates an operation principle of the precharge device in the boost mode according to an embodiment of the present invention.
Fig. 7 shows an operation timing diagram of a switching tube of a precharge device in a boost mode according to an embodiment of the present invention.
Detailed Description
The invention will now be described in detail with reference to the drawings and specific examples.
Please refer to fig. 3. The invention relates to a pre-charging device for a high-voltage bus capacitor of a new energy automobile, which comprises a capacitor voltage sampling circuit 2, a bidirectional DC-DC conversion circuit 3 and a controller 4.
The capacitor voltage sampling circuit 2 is used for collecting the voltage of the high-voltage bus capacitor C48, and an output end of the capacitor voltage sampling circuit 2 is coupled with an input end of the controller 4 so as to send the collected voltage signal of the high-voltage bus capacitor C48 to the controller 4. One end of the high-voltage bus capacitor C48 is connected with the positive electrode of the direct current bus of the new energy automobile, and the other end of the high-voltage bus capacitor C is connected with the negative electrode of the direct current bus of the new energy automobile.
The bidirectional DC-DC conversion circuit 3 is coupled between the high voltage bus capacitor C48 and the charging power source V 12_bat, so that the charging power source V 12_bat can charge the high voltage bus capacitor C48 through the bidirectional DC-DC conversion circuit 3. R LD in the figure represents a load. The bidirectional DC-DC conversion circuit 3 includes a Buck-Boost circuit 31, an inductance Lpre, a freewheel element Dpre, a switching tube Q safe, and a capacitor Csafe.
The first input/output end of the Buck-Boost circuit 31 is connected in parallel with the high-voltage bus capacitor C48, and the positive electrode of the second input/output end of the Buck-Boost circuit 31 is connected with one end of the inductor Lpre; the other end of the inductor Lpre is connected with the second conducting end of the switching tube Q safe, and the first conducting end of the switching tube Q safe is connected with the positive electrode of the charging power supply V 12_bat; the negative terminal of the follow current element Dpre is connected to the common contact point of the other end of the inductance Lpre and the second conducting terminal of the switching tube Q safe, and one end of the capacitor Csafe is connected to the common contact point of the first conducting terminal of the switching tube Q safe and the positive electrode of the charging power supply V 12_bat; the negative electrode of the second input/output terminal of the Buck-Boost circuit 31, the positive electrode of the freewheel element Dpre, the other end of the capacitor Csafe, and the negative electrode of the charging source V 12_bat are connected to the negative electrode of the dc bus, respectively.
The controller 4 is respectively connected with the control end of the Buck-Boost circuit 31 and the control end of the switching tube Q safe. The controller 4 may control the bidirectional DC-DC conversion circuit 3 to operate in a precharge mode, in which the bidirectional DC-DC conversion circuit 3 charges the high voltage bus capacitor C48 in a buck mode first, and after the voltage of the high voltage bus capacitor reaches a predetermined threshold, the bidirectional DC-DC conversion circuit 3 charges the high voltage bus capacitor C48 in a boost mode until the voltage of the high voltage bus capacitor C48 reaches a preset charging voltage value.
In this embodiment, as shown in fig. 3, the Buck-Boost circuit 31 includes a bridge arm, an inductance Lf, and a capacitance C12.
The bridge arm comprises a switching tube Qh and a switching tube Ql, the switching tube Qh and the switching tube Ql are provided with body diodes, a first conduction end of the switching tube Qh is connected with one end of the high-voltage bus capacitor C48, a second conduction end of the switching tube Qh is connected with the first conduction end of the switching tube Ql, and the second conduction end of the switching tube Ql is connected with the other end of the high-voltage bus capacitor C48. One end of the inductor Lf is connected to a common contact point of the second conduction end of the switching tube Qh and the first conduction end of the switching tube Ql, and the other end of the inductor Lf is connected with one end of the inductor Lpre; one end of the capacitor C12 is connected to a common junction between the other end of the inductor Lf and one end of the inductor Lpre. The other end of the capacitor C12 is connected with the negative electrode of the direct current bus.
The controller 4 is respectively connected with the control end of the switching tube Qh and the control end of the switching tube Ql, and the controller 4 is used for controlling the switching tube Qh and the switching tube Ql to be normally disconnected and controlling the capacitor Csafe, the switching tube Q safe, the freewheel element Dpre, the inductor Lpre and the capacitor C12 to form a Buck circuit so as to enable the bidirectional DC-DC conversion circuit 3 to work in a step-down mode; the controller 4 is used for controlling the switching tube Q safe to be normally on, and controlling the capacitor C12, the inductor Lf, the switching tube Qh, the switching tube Ql and the high-voltage bus capacitor C48 to form a Boost circuit, so that the bidirectional DC-DC conversion circuit 3 works in a Boost mode.
In the present embodiment, the freewheel element Dpre is a diode. In other implementations, the freewheel element Dpre may also use a MOS transistor.
In this embodiment, the new energy automobile is a hybrid automobile, the charging power supply is a rechargeable battery, the output voltage of the charging power supply is 12V, the high-voltage power supply is a high-voltage battery, the output voltage of the high-voltage power supply is 48V, and the high-voltage bus capacitor C48 is 48V bus capacitor. Since the low voltage side is typically provided with an EMI differential mode filter inductance, the inductance Lpre can multiplex the EMI differential mode filter inductance. If the low voltage side is not provided with an EMI differential mode filter inductance, an additional inductance Lpre is required.
Optionally, the switch tube Qh, the switch tube Ql and the switch tube Q safe are all NMOS tubes, the gate of each NMOS tube is a control end, the drain of each NMOS tube is a first conduction end, and the source of each NMOS tube is a second conduction end. The diode Dh and the capacitor Ch are respectively a body diode and a parasitic capacitor of the switching tube Qh, and the diode Dl and the capacitor Cl are respectively a body diode and a parasitic capacitor of the switching tube Ql. In the present embodiment, a precharge contactor 95 is connected in series between the positive electrode of the high-voltage power supply V 48_bat connected in parallel with the high-voltage bus capacitor C48 and one end of the high-voltage bus capacitor C48.
In this embodiment, the pre-charging of the high-voltage bus capacitor C48 by the bidirectional DC-DC conversion circuit 3 is divided into two phases, the first phase is a step-down mode phase, the output voltage of the charging power supply V 12V_bat is charged to a predetermined threshold value, which is close to the output voltage of the charging power supply V 12_bat, by the Buck circuit; the second stage is a Boost mode stage, in which the high voltage bus capacitor C48 is continuously charged in current mode or voltage mode by a conventional Boost circuit until the voltage reaches the final target voltage (near the output voltage of the high voltage supply V 48_bat).
In the first stage, as shown in fig. 4, the capacitor Csafe, the switching tube Q safe, the freewheel element Dpre, the inductance Lpre, and the capacitor C12 constitute a Buck circuit (see a dotted box area in fig. 4) for the first stage precharge. At this stage, as shown in fig. 5, the switching transistor Qh and the switching transistor Ql are always in an off state, and the high-voltage bus capacitor C48 is charged by controlling the duty ratio of the switching transistor Qsafe. The duty cycle of the switching tube Q safe is gradually increased from 0% to 100%, according to the Buck circuit principle, a slowly rising voltage with a value equal to the voltage of the capacitor Csafe multiplied by the duty cycle is obtained on the capacitor C12, meanwhile, the capacitor C12 charges the high-voltage bus capacitor C48 through the inductor Lf and the body diode Dh of the switching tube Qh, the high-voltage bus capacitor C48 also obtains the same slowly rising voltage, and the charging path is shown by a dashed arrow in fig. 4, so that the problem of the surge current is eliminated. When the voltage V C48 of the high-voltage bus capacitor C48 is charged to a predetermined threshold (the output voltage of the charging power supply V 12_bat in this embodiment), the high-voltage power supply V 48_bat has already obtained the base voltage necessary for the boosting topology. The first stage can adopt open loop control or closed loop control, and the method adopts a voltage signal on the high-voltage bus capacitor C48 to carry out voltage mode control, or adopts an average current on the high-voltage side as a feedback signal to carry out current mode control. Finally, when the voltage on the high voltage bus capacitor C48 reaches a predetermined threshold, it switches to the second phase of pre-charge.
In the second stage, as shown in fig. 6, the control capacitor C12, the inductance Lf, the switching tube Qh, the switching tube Ql, and the high-voltage bus capacitor C48 constitute a Boost circuit (see a dotted frame area in fig. 6). In this stage, the switching tube Q safe is always in the normally-on state as shown in fig. 7, the duty ratio of the switching tube Ql is gradually increased from 0% according to the principle of the Boost circuit (V 48V_bat-V12V_bat)/V48V_bat, the voltage of the high-voltage bus capacitor is gradually increased without generating large voltage and current overshoots), the switching tube Qh and the switching tube Ql are complementarily output, the charging path is shown by the dashed arrow in fig. 6, and charging is finished until the voltage V C48 of the high-voltage bus capacitor C48 is charged to the final target voltage (the output voltage of the high-voltage power supply V 48_bat in this embodiment), a dead time is provided between the driving edges of the switching tube Ql and the switching tube Qh, so that the through is prevented.
The precharge device of the high-voltage bus capacitor of the new energy automobile according to the embodiment of the invention can also work in a forward Buck (Buck) mode and a reverse Boost (Boost) mode.
In the forward buck mode, the switching tube Qh is controlled to chop the output dc of the high-voltage power supply V 48_bat into PWM voltage, and the PWM voltage is freewheeled through the switching tube Ql, filtered by the inductor Lf and the capacitor C12, and the dc with a lower voltage (for example, 12V) is obtained at the low-voltage side.
In the reverse boost mode, the charging power supply V 12V_bat supplies auxiliary power to the high-voltage side. The inductor Lf, the switching tube Ql and the switching tube Qh form a Boost circuit, and Boost the output voltage of the low-voltage side charging power supply V 12_bat. The low-voltage side charging power supply V 12_bat stores energy for the inductor Lf through the switching tube Ql to generate voltage, the output voltage of the charging power supply V 12_bat and the voltage of the inductor Lf are supplied to the high-voltage side through the switching tube Qh, and the high-voltage side obtains direct current with higher voltage through filtering of the high-voltage bus capacitor C48.
If the precharge contactor between the high voltage power supply (e.g., 48V battery) and the high voltage electrical appliance (e.g., 48V high voltage electrical appliance) is directly engaged, since the high voltage side capacitance is typically 10mF or more, a large rush current is generated, so that the low voltage side charging power supply (e.g., 12V battery) is required to precharge the capacitance of the high voltage electrical appliance first. If the switching tube Q safe is directly closed on the low-voltage side, similarly, the charging power supply on the low-voltage side is close to being directly connected in parallel with the high-voltage bus capacitor, a very large impact current is caused, and the switching tube Q safe and the switching tube Qh are possibly failed, so that other potential failures are caused. According to the invention, through the thought of topology conversion, a low-voltage side charging power supply and a high-voltage bus capacitor are not directly connected in parallel, a group of inductance Lpre and a follow current element Dpre are added through a multiplexing switch tube Q safe, a Buck sub-circuit is generated in the first stage of pre-charging, the characteristics of small impact current during soft start of the Buck circuit are utilized to gradually charge the capacitor C12 and the high-voltage bus capacitor C48 to a basic voltage (for example, 12V) from 0V, current impact is solved, and the high-voltage bus capacitor C48 is further charged through a Boost circuit in the second stage of pre-charging, so that the overall pre-charging function is realized. Compared with the prior art, the circuit structure of the pre-charging device saves pre-charging resistance, so that the pre-charging device is environment-friendly and energy-saving, and reduces the cost.

Claims (9)

1. The pre-charging device of the high-voltage bus capacitor of the new energy automobile comprises a direct-current bus and a charging power supply, one end of the high-voltage bus capacitor is connected with the positive electrode of the direct-current bus of the new energy automobile, and the other end of the high-voltage bus capacitor is connected with the negative electrode of the direct-current bus of the new energy automobile; the pre-charging device comprises a bidirectional DC-DC conversion circuit, a capacitor voltage sampling circuit and a controller; the bidirectional DC-DC conversion circuit is coupled between the high-voltage bus capacitor and the charging power supply, so that the charging power supply can charge the high-voltage bus capacitor through the bidirectional DC-DC conversion circuit; the output end of the capacitor voltage sampling circuit is coupled with the input end of the controller, and the capacitor voltage sampling circuit is used for collecting the voltage of the high-voltage bus capacitor; the bidirectional DC-DC conversion circuit is characterized by comprising a Buck-Boost circuit, an inductor Lpre, a follow current element Dpre, a switching tube Q safe and a capacitor Csafe;
The first input/output end of the Buck-Boost circuit is connected with the high-voltage bus capacitor in parallel, and the positive electrode of the second input/output end of the Buck-Boost circuit is connected with one end of the inductor Lpre; the other end of the inductor Lpre is connected with a second conducting end of the switching tube Q safe; the first conducting end of the switching tube Q safe is connected with the anode of the charging power supply; the negative terminal of the follow current element Dpre is connected to the common connection point of the other end of the inductance Lpre and the second conducting terminal of the switching tube Q safe, and one end of the capacitor Csafe is connected to the common connection point of the first conducting terminal of the switching tube Q safe and the positive electrode of the charging power supply; the negative electrode of the second input/output end of the Buck-Boost circuit, the positive electrode of the follow current element Dpre, the other end of the capacitor Csafe and the negative electrode of the charging power supply are respectively connected with the negative electrode of the direct current bus;
The controller is respectively connected with the control end of the Buck-Boost circuit and the control end of the switching tube Q safe; the controller can control the bidirectional DC-DC conversion circuit to work in a pre-charging mode, the bidirectional DC-DC conversion circuit firstly charges the high-voltage bus capacitor in a voltage-reducing mode in the pre-charging mode, and the bidirectional DC-DC conversion circuit charges the high-voltage bus capacitor in a voltage-boosting mode after the voltage of the high-voltage bus capacitor reaches a preset threshold value until the voltage of the high-voltage bus capacitor reaches a preset charging voltage value; the controller is used for controlling the duty ratio of the switching tube Q safe to be gradually increased when the bidirectional DC-DC conversion circuit is in the step-down mode.
2. The precharge device of the high voltage bus capacitor of the new energy automobile as set forth in claim 1, wherein the Buck-Boost circuit comprises a bridge arm, an inductance Lf and a capacitor C12;
The bridge arm comprises a switching tube Qh and a switching tube Ql, the switching tube Qh and the switching tube Ql are provided with body diodes, a first conducting end of the switching tube Qh is connected with one end of the high-voltage bus capacitor, a second conducting end of the switching tube Qh is connected with the first conducting end of the switching tube Ql, and the second conducting end of the switching tube Ql is connected with the other end of the high-voltage bus capacitor;
One end of the inductor Lf is connected to a common contact point of the second conduction end of the switching tube Qh and the first conduction end of the switching tube Ql, and the other end of the inductor Lf is connected with one end of the inductor Lpre; one end of the capacitor C12 is connected to a common contact point between the other end of the inductor Lf and one end of the inductor Lpre, and the other end of the capacitor C12 is connected to the negative electrode of the direct current bus;
The controller is respectively connected with the control end of the switching tube Qh and the control end of the switching tube Ql, and is used for controlling the switching tube Qh and the switching tube Ql to be normally disconnected and controlling a capacitor Csafe, a switching tube Q safe, a follow current element Dpre, an inductance Lpre and a capacitor C12 to form a Buck circuit so that the bidirectional DC-DC conversion circuit works in the step-down mode; the controller is used for controlling the switching tube Q safe to be normally on, and controlling the capacitor C12, the inductor Lf, the switching tube Qh, the switching tube Ql and the high-voltage bus capacitor to form a Boost circuit, so that the bidirectional DC-DC conversion circuit works in the Boost mode.
3. The precharge device of a high voltage bus capacitor of a new energy vehicle according to claim 2, wherein said controller is configured to control the duty ratio of the switching transistor Ql to be gradually increased when said bidirectional DC-DC converter circuit is in said boost mode.
4. The precharge device of a high voltage bus capacitor of a new energy vehicle according to claim 2, wherein the controller is configured to control the duty ratio of the switching transistor Ql to gradually increase from 0 to (V 48V_bat -V12V_bat）/V48V_bat, where V 12V_bat is the output voltage of the charging power supply and V 48V_bat is the output voltage of a high voltage power supply connected in parallel with the high voltage bus capacitor when the bidirectional DC-DC converter circuit is in the boost mode.
5. The pre-charging device for the high-voltage bus capacitor of the new energy automobile according to claim 4, wherein the new energy automobile is a hybrid electric automobile, the output voltage of the charging power supply is 12V, the output voltage of the high-voltage power supply is 48V, and the high-voltage bus capacitor is 48V bus capacitor.
6. The precharge device of a high voltage bus capacitor of a new energy automobile according to claim 1, wherein the inductance Lpre is an EMI differential mode filter inductance.
7. The precharge device of the high-voltage bus capacitor of the new energy automobile according to claim 2, wherein the switching tube Qh, the switching tube Ql and the switching tube Q safe are all NMOS tubes, the gate of the NMOS tube is a control end, the drain of the NMOS tube is a first conduction end, and the source of the NMOS tube is a second conduction end.
8. The precharge device of the high voltage bus capacitor of the new energy automobile of claim 1, wherein the freewheel element is a diode or a MOS tube.
9. The precharge device of a high voltage bus capacitor of a new energy vehicle according to any one of claims 1 to 8, wherein a precharge contactor is connected in series between a positive electrode of a high voltage power supply connected in parallel with the high voltage bus capacitor and one end of the high voltage bus capacitor.
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