CN216146250U

CN216146250U - Vehicle-mounted DC/DC reverse pre-charging device

Info

Publication number: CN216146250U
Application number: CN202121833732.0U
Authority: CN
Inventors: 韩永杰; 刘钧; 冯仁伟; 杨乐军
Original assignee: Shanghai Weimeisi New Energy Co ltd
Current assignee: Shanghai Weimeisi New Energy Co ltd
Priority date: 2021-08-06
Filing date: 2021-08-06
Publication date: 2022-03-29
Anticipated expiration: 2031-08-06

Abstract

The utility model discloses a vehicle-mounted DC/DC reverse pre-charging device, which comprises a low-voltage switch circuit connected with a low-voltage battery, a high-voltage switch circuit connected with the high-voltage battery, a DC/DC transformer connected with the low-voltage switch circuit and the high-voltage switch circuit, and an anti-reverse pre-charging circuit arranged between the low-voltage switch circuit and the low-voltage battery, wherein the anti-reverse pre-charging circuit comprises an MOS (metal oxide semiconductor) tube connected in series between the low-voltage switch circuit and the low-voltage battery, and the reverse pre-charging device realizes a reverse pre-charging function by adjusting the driving voltage of the MOS tube. Compared with the prior art, the reverse pre-charging prevention device can realize the reverse pre-charging prevention function and the reverse pre-charging prevention function at the same time by adding the reverse pre-charging prevention circuit.

Description

Vehicle-mounted DC/DC reverse pre-charging device

Technical Field

The utility model relates to vehicle-mounted DC/DC, in particular to a vehicle-mounted DC/DC reverse pre-charging device.

Background

With the promotion of energy conservation and emission reduction, new energy automobiles including pure electric vehicles, hybrid vehicles, plug-in hybrid vehicles and the like have higher and higher popularization rate in the market. The new energy automobile is provided with a high-voltage battery and corresponding high-voltage electric equipment. High-voltage electric equipment generally has a large capacitor at a high-voltage port and cannot be directly connected with a high-voltage battery, otherwise, large pulse current can be generated to damage parts. The traditional scheme needs to add a pre-charging circuit between a high-voltage battery and high-voltage electric equipment, initially charges a high-voltage capacitor through pre-charging resistor current limiting, and attracts a relay to complete a pre-charging process after the voltage difference between the capacitor voltage and the battery voltage reaches a reasonable range. The scheme is characterized in that a high-voltage battery is used for pre-charging a high-voltage end, a pre-charging circuit is separated from a vehicle-mounted DC/DC circuit, additional devices and detection circuits are required, and the defects of large size, high cost and complex control are caused.

The existing scheme of utilizing a vehicle-mounted DC/DC circuit to carry out reverse pre-charging is a scheme of utilizing a secondary side inductor to add a winding and a diode to be connected to a high-voltage bus to carry out reverse pre-charging, and a scheme of adding a diode at an output end to form a reverse Buck circuit and then carrying out DC/DC reverse pre-charging is also provided. However, these solutions require additional devices to be added to the original on-board DC/DC circuit, and although the reverse precharge can be implemented, the cost is also increased.

Since the vehicle-mounted DC/DC is used in a high frequency in the entire vehicle, the reliability and safety requirements are high. It is often desirable to have the ability to port the low voltage battery externally to the DC/DC when the DC/DC is internally shorted. Generally, a fuse is added at an external end to perform overcurrent protection, or an anti-reverse-flow circuit (Oring circuit) is added at a vehicle-mounted DC/DC output end.

Therefore, how to provide a vehicle-mounted DC/DC reverse pre-charging device, which can realize both the reverse pre-charging and reverse pre-charging functions, is a technical problem to be solved in the industry.

SUMMERY OF THE UTILITY MODEL

The utility model provides a vehicle-mounted DC/DC reverse pre-charging device, aiming at the problem that in the prior art, a reverse pre-charging device and a reverse-charging prevention circuit are required to be arranged respectively, so that the cost is increased.

The technical scheme includes that the vehicle-mounted DC/DC reverse pre-charging device comprises a low-voltage switch circuit connected with a low-voltage battery, a high-voltage switch circuit connected with the high-voltage battery, a DC/DC transformer connected with the low-voltage switch circuit and the high-voltage switch circuit, and an anti-reverse pre-charging circuit arranged between the low-voltage switch circuit and the low-voltage battery, wherein the anti-reverse pre-charging circuit comprises an MOS (metal oxide semiconductor) tube connected between the low-voltage switch circuit and the low-voltage battery in series, and the reverse pre-charging device realizes a reverse pre-charging function by adjusting the driving voltage of the MOS tube.

Further, the anti-reverse-flow circuit comprises 4 working modes:

a through mode: the driving voltage is continuously higher than the threshold voltage, and the MOS tube works in a saturation region and is used for charging the vehicle-mounted DC/DC in the forward and reverse directions;

a current limiting mode: the driving voltage is continuous and lower than the threshold voltage, and the MOS tube works in a linear region and is used for vehicle-mounted DC/DC forward and reverse current limiting;

PWM mode: the driving voltage is lower than a threshold voltage and is regulated through a PWM signal, and the MOS tube works between a linear region and a cut-off region and is used for vehicle-mounted DC/DC reverse current limiting;

blocking mode: the driving voltage is zero, and the MOS tube works in a cut-off region and is used for blocking the reverse energy transmission of the vehicle-mounted DC/DC.

Further, the reverse pre-charging device comprises three pre-charging stages, which are respectively:

and (3) soft start stage: the reverse-filling prevention circuit works in a PWM mode, and the duty ratios of the PWM signals are sequentially increased to reduce the impact current;

and (3) current limiting stage: the reverse-filling prevention circuit works in a PWM mode or a current-limiting mode and is used for limiting the inductive current in the low-voltage switch circuit and carrying out reverse pre-charging;

and (3) Boost stage: the reverse-filling prevention circuit works in a direct-through mode and is used for charging a capacitor on the side of the high-voltage switch circuit.

Further, when the capacitance of the low-voltage switch circuit side is lower than a first preset voltage, the reverse pre-charging device works in a soft start stage;

when the capacitance at the side of the low-voltage switch circuit is higher than a first preset voltage and lower than a second preset voltage, the reverse pre-charging device works in a current-limiting stage;

when the capacitance on the low-voltage switch circuit side is higher than a second preset voltage, the reverse pre-charging device works in a Boost stage.

Further, the low-voltage switch circuit and the high-voltage switch circuit adopt one of a half-bridge circuit, a full-bridge circuit, a current-doubling rectifying circuit and a full-wave rectifying circuit.

Furthermore, the low-voltage switch circuit adopts a full-wave rectification circuit, which comprises a switch tube SR1, a switch tube SR2, an inductor Lf and a capacitor Co, the DC/DC transformer is a transformer with a central tap at the low-voltage side, one end of the inductor Lf is connected with the central tap end at the low-voltage side of the DC/DC transformer, the other end of the inductor Lf is connected with the positive electrode of the low-voltage battery after being connected with the reverse-filling prevention circuit in series, one end of the switching tube SR2 is connected with the second end of the low-voltage side of the DC/DC transformer, the other end is connected with the negative pole of the low-voltage battery, one end of the switch tube SR1 is connected with the first end of the low-voltage side of the DC/DC transformer, the other end of the switch tube SR1 is connected between the negative electrode of the low-voltage battery and the switch tube SR2, one end of the capacitor Co is connected between the inductor Lf and the reverse-flow prevention circuit, and the other end of the capacitor Co is connected between the switch tube SR2 and the negative electrode of the low-voltage battery.

Further, the high-voltage switch circuit adopts a full-bridge circuit, and comprises a switch tube Q1, a switch tube Q2, a switch tube Q3, a switch tube Q4 and a capacitor Chv, wherein the switch tube Q1 and the switch tube Q2 are connected in series and then connected to two ends of the high-voltage battery, the switch tube Q2 and the switch tube Q4 are connected in series and then connected to two ends of the high-voltage battery, a first end of a high-voltage side of the DC/DC transformer is connected between the switch tube Q1 and the switch tube Q2, a second end of the high-voltage side of the DC/DC transformer is connected between the switch tube Q3 and the switch tube Q4, and the capacitor Chv is connected in parallel and at two ends of the high-voltage battery.

Further, the current ripple frequency of the inductor Lf is twice the switching frequency of the switching transistors SR1 and SR2, and the equivalent impedance of the low-voltage switching circuit is:

n is the turn ratio of the primary side and the secondary side of the DC/DC transformer, and D is the proportion of the time of the simultaneous conduction of the switch tube SR1 and the switch tube SR2 in half of the switching period.

Compared with the prior art, the utility model has at least the following beneficial effects:

by additionally arranging the reverse-filling prevention circuit and corresponding control, the reverse-filling prevention function and the reverse pre-filling function can be realized at the same time, a plurality of devices are not required to be additionally arranged for realizing the reverse-filling prevention function and the reverse pre-filling function respectively, and the design cost is reduced. Meanwhile, the reverse charging speed and state can be adjusted by adjusting the driving voltage of the MOS tube, the control logic is simple, and forward and reverse current limiting and buffering functions can be realized.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise.

Fig. 1 is a block diagram of a conventional high-voltage pre-charging connection system of a new energy automobile;

FIG. 2 is a block diagram of a connection system of the on-board DC/DC reverse pre-charging device according to the present invention;

FIG. 3 is a schematic circuit diagram of an embodiment of the on-board DC/DC reverse pre-charging apparatus according to the present invention;

FIG. 4 is a schematic diagram of the operation of the MOS transistor in the anti-reverse-flow circuit according to the present invention;

FIG. 5 is a timing diagram illustrating the driving of the switch SR1 and the switch SR2 according to the present invention;

FIG. 6 is a system diagram of an embodiment of the on-board DC/DC reverse pre-charging apparatus according to the present invention;

FIG. 7 is an equivalent circuit diagram of the on-board DC/DC reverse pre-charging device according to the present invention;

FIG. 8 is a waveform diagram of the precharge voltage and duty cycle and precharge current of the present invention;

FIG. 9 is a diagram illustrating a reverse precharge phase according to an embodiment of the present invention;

FIG. 10 is a block diagram of a dual loop control scheme according to an embodiment of the present invention;

FIG. 11 is a diagram of a forward safety operation region of a MOS transistor;

FIG. 12 is a flow chart of a reverse priming apparatus according to an embodiment of the present invention.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the utility model and are not intended to limit the utility model.

Thus, a feature indicated in this specification will serve to explain one of the features of one embodiment of the utility model, and does not imply that every embodiment of the utility model must have the stated feature. Further, it should be noted that this specification describes many features. Although some features may be combined to show a possible system design, these features may also be used in other combinations not explicitly described. Thus, the combinations illustrated are not intended to be limiting unless otherwise specified.

The principles and construction of the present invention will be described in detail below with reference to the drawings and examples.

In the prior art, in order to ensure the safety of the vehicle-mounted DC/DC, an anti-reverse-filling circuit is generally required to be arranged to prevent the generation of reverse-filling current, and meanwhile, in order to realize the reverse pre-filling function, an additional reverse pre-filling circuit is required to be additionally arranged, so that the cost of the circuit is increased. The utility model provides a vehicle-mounted DC/DC reverse pre-charging device, which can realize the function of preventing reverse pre-charging and the function of reverse pre-charging, does not need to additionally arrange redundant circuits, and reduces the design cost of the circuit.

Referring to fig. 1 and 2, in the prior art, a high voltage pre-charging mode generally includes that a high voltage pre-charging device 120 is respectively connected to a high voltage electric device 110 and a high voltage battery 130, which can only achieve a reverse pre-charging function between the high voltage electric devices, in the present invention, an anti-reverse pre-charging circuit 140 is disposed in a vehicle-mounted DC/DC140, and is respectively connected to a low voltage battery 150, the high voltage electric device 110 and the high voltage battery 130 through the vehicle-mounted DC/DC140, so as to achieve the reverse pre-charging function between high voltage and low voltage.

Specifically, referring to fig. 3, in an embodiment of the present invention, the reverse pre-charging device includes a low-voltage switch circuit 142 connected to the low-voltage battery 150, a high-voltage switch circuit 144 connected to the high-voltage battery 130, a DC/DC transformer 143 connected to the low-voltage switch circuit 142 and the high-voltage switch circuit 144, and an anti-reverse-charging circuit 141 connected in series between the low-voltage battery 150 and the low-voltage switch circuit 142, wherein the anti-reverse-charging circuit 141 is a MOS transistor connected in series between the low-voltage switch circuit 142 and the low-voltage battery 150, and the MOS transistor is an Oring MOS transistor, which can implement an anti-reverse-charging function through its conduction characteristic.

If the MOS tube is not used for reverse pre-charging, during vehicle-mounted DC/DC operation, the input voltage is higher than the output voltage for a long time due to the large capacitance of the high-voltage bus, and the current of the inductor Lf in the low-voltage switch circuit 142 is continuously increased, so that the inductor Lf is saturated, and reverse pre-charging is affected. Therefore, to prevent the inductor Lf from being saturated, the input current of the reverse pre-charge needs to be controlled to ensure that the inductor Lf does not be over-saturated, so as to realize the reverse pre-charge function.

Specifically, referring to fig. 3, in the present invention, the low-voltage switch circuit 142 adopts a full-wave rectification circuit, which includes a switch SR1, a switch SR2, an inductor Lf, and a capacitor Co, wherein the DC/DC transformer 143 is a transformer with a center tap at a low-voltage side, one end of the inductor Lf is connected to the center tap end of the DC/DC transformer 143, the other end is connected to the anti-reverse-flow circuit 141, and is connected to the positive electrode of the low-voltage battery 150 through the anti-reverse-flow circuit 141, one end of the switch SR2 is connected to the second end of the DC/DC transformer 143, the other end is connected to the negative electrode of the low-voltage battery 150, one end of the switch SR1 is connected to the first end of the low-voltage side of the DC/DC transformer 143, the other end is connected to the negative electrode of the low-voltage battery 150 and the switch SR2, one end of the capacitor Co is connected between the inductor Lf and the anti-reverse-flow circuit 141, the other end is connected to the negative electrode of the switch SR2 and the negative electrode of the low-voltage battery 150, which functions as a bus capacitor capable of receiving the voltage of the low-voltage battery 150 and transmitting it to the low-voltage switching circuit 142.

In the first embodiment of the present invention, the low-voltage switching circuit 142 employs a full-wave rectifying circuit, and the current fluctuation amplitude of the full-wave rectifying circuit is small, and in other embodiments of the present invention, the low-voltage switching circuit 142 may also employ one of a half-bridge circuit, a full-bridge circuit, and a current-doubling rectifying circuit, which can achieve the rectifying effect by controlling the operation of the switching tube thereof.

Further, in this embodiment, the high-voltage switch circuit 144 adopts a full-bridge rectifier circuit, which includes a switch tube Q1, a switch tube Q2, a switch tube Q3, a switch tube Q4, and a capacitor Chv, wherein the switch tube Q1, the switch tube Q2, the switch tube Q3, and the switch tube Q4 constitute a bridge rectifier circuit, the capacitor Chv is connected in parallel to two ends of the high-voltage battery for charging the bus capacitor, the switch tube Q1 and the switch tube Q2 constitute a bridge arm, the switch tube Q3 and the switch tube Q4 constitute another bridge arm, two ends of the high-voltage side of the DC/DC transformer 143 are respectively connected to midpoints of the two bridge arms, and the current after DC/DC conversion can be rectified by the full-bridge circuit and then output to the high-voltage battery.

Compared with a full-wave rectification circuit, the full-bridge rectification circuit has a better rectification effect, and the utilization rate of the transformer is higher than that of the full-wave rectification circuit. In other embodiments of the present invention, the high voltage switch circuit 144 may further adopt one of a half-bridge circuit, a current doubler rectifier circuit, and a full-wave rectifier circuit. The low-voltage switch circuit 142 and the high-voltage switch circuit 144 have the same function and are respectively used for rectification of a low-voltage side and a high-voltage side, and theoretically, the low-voltage switch circuit 142 and the high-voltage switch circuit 144 can be freely combined under the condition of meeting the rectification requirement.

The working principle of the present invention is explained below when the low-voltage switch circuit 142 adopts full-wave rectification and the high-voltage switch circuit 144 adopts a full-bridge rectification circuit, it should be noted that the reverse transmission mentioned herein refers to transmission from low voltage to high voltage, and the forward transmission refers to transmission from high voltage to low voltage, in order to ensure the operation of the reverse pre-charging function of the circuit, it is necessary to prevent the over-current saturation of the inductor Lf, in the present invention, the current-limiting function is realized by controlling the operating mode of the Oring MOS transistor, thereby preventing the over-current saturation of the inductor Lf, specifically, referring to fig. 4, the anti-reverse-charging circuit has 4 different operating modes according to the change of the driving voltage, which are respectively:

a through mode: the driving voltage is continuously higher than the threshold voltage, the MOS tube works in a saturation region, the MOS tube is in a conducting state at the moment, the resistance is small, the voltage drop at two ends is small, the MOS tube can charge a high-voltage side capacitor after being boosted by the switching tube SR1 and the switching tube SR2, and the high-voltage side capacitor is used for vehicle-mounted DC/DC forward charging (the driving voltage is continuously a continuous signal which is opposite to a PWM signal, and the moment when the voltage signal is 0 does not exist);

a current limiting mode: the driving voltage is continuously lower than the threshold voltage, the MOS tube works in a linear region, the MOS tube has a certain resistance at the moment, and although the MOS tube can play a role in conduction, the two ends of the MOS tube can be subjected to voltage division, so that the voltage division at the rear end is reduced, the current is reduced, and the vehicle-mounted DC/DC forward and reverse current limiting device is used for vehicle-mounted DC/DC forward and reverse current limiting. In this case, since the current is small, the inductor Lf can be prevented from being saturated by overcurrent, and thus the reverse precharge function can be realized.

PWM mode: the driving voltage is lower than the threshold voltage and is regulated through the PWM signal, the MOS tube works between a linear region and a cut-off region, the MOS tube is equivalent to a resistor with a large resistance, the rear-end current is small, and the vehicle-mounted DC/DC reverse current limiting circuit can be used for vehicle-mounted DC/DC reverse current limiting. Meanwhile, in this case, since the current is small, the inductor Lf can be prevented from being saturated by overcurrent, so that the reverse pre-charging function is realized.

Blocking mode: the driving voltage is zero, and the MOS tube works in a cut-off region. At the moment, the MOS tube is equivalent to open circuit or infinite resistance, the current flowing through the MOS tube is zero at the moment, the MOS tube cannot be used for reverse pre-charging, but the vehicle-mounted DC/DC reverse energy transmission can be prevented, and the reverse filling prevention effect is achieved.

The threshold voltage of the MOS transistor is the minimum voltage of the direct connection of the MOS transistor, the threshold voltage is determined according to the type selection of the MOS transistor, when the driving voltage is higher than the threshold voltage, the MOS transistor is in a direct connection mode, the voltage drop of two ends of the MOS transistor is small, otherwise, when the driving voltage is lower than the threshold voltage, the MOS transistor is in a non-direct connection mode, and a certain voltage drop exists between the two ends of the MOS transistor.

According to the starting process of the vehicle-mounted DC/DC, the reverse pre-charging device can be divided into 3 pre-charging stages which are respectively a soft start stage: the reverse-filling prevention circuit works in a PWM mode, and the duty ratios of PWM signals are sequentially increased to reduce impact current;

and (3) Boost stage: the reverse-filling prevention circuit works in a direct-through mode and is used for charging a capacitor on the side of the high-voltage switch circuit;

specifically, when the vehicle-mounted DC/DC starts to be precharged, after the switching transistor SR1 and the switching transistor SR2 are turned on first, the voltage Vco at the two ends of the capacitor Co is very low, and if the Oring MOS transistor is linearly turned on at this time, a large impact current is generated, so that the soft start stage needs to be entered when the vehicle-mounted DC/DC starts to be started for reducing the impact current. With the advance of the pre-charging process, the voltage at the two ends of the capacitor Co gradually increases until the first preset voltage is reached, at this time, the voltage in the high-voltage switch circuit is lower, the voltage of the capacitor Chv is lower, and the reverse pre-charging can be performed. In order to realize the reverse pre-charging of the vehicle-mounted DC/DC, the current of the inductor Lf needs to be prevented from being saturated due to overlarge current, so that the current limiting stage is started, the current of the inductor Lf is prevented from being saturated due to overlarge current, and the reverse pre-charging is carried out. After the reverse pre-charging is carried out for a certain time, when the voltage at the two ends of the capacitor Chv is higher than a second preset voltage, the input voltage of the vehicle-mounted DC/DC is lower than the output voltage, the current of the inductor Lf is not in a risk of continuously increasing, if the Oring MOS tube works in a linear region at the moment, the current loss is large, the anti-reverse-charging circuit needs to work in a direct-connection mode, and the voltage is boosted to charge the high-voltage switching circuit by adjusting the duty ratios of the switching tube SR1 and the switching tube SR 2.

In other embodiments of the present invention, the soft start stage and the current limiting stage may be combined, and since the anti-reverse-flow circuit can play a role in current limiting when operating in both the PWM mode and the current limiting mode, the soft start stage and the current limiting stage may be combined through the PWM mode of the anti-reverse-flow circuit, in this case, it is not necessary to determine whether the voltage is higher than the first preset voltage to perform the mode switching, and it is only necessary to determine whether the voltage at the two ends of the capacitor Chv is higher than the second preset voltage to make the input voltage of the vehicle DC/DC lower than the output voltage, so that the overall control logic is simpler and the operation is convenient.

The first preset voltage is a threshold voltage set according to a circuit device, the voltage is determined by circuit type selection, and when the voltage at two ends of the capacitor Co is higher than the first preset voltage, the impulse current in the circuit is smaller or zero, and reverse pre-charging can be performed. The second preset voltage is the product of the voltage at the two ends of the capacitor Co and the turn ratio N of the primary side and the secondary side of the transformer, and when the voltage at the two ends of the capacitor Chv is higher than the second preset voltage, the input voltage of the vehicle-mounted DC/DC is lower than the output voltage at the moment, and the current on the inductor Lf cannot be continuously increased.

Furthermore, the utility model can also adjust the impedance of the Oring MOS transistor after being connected by adjusting the open-loop duty ratio of the switching transistor SR1 and the switching transistor SR2, so as to adjust the charging time, please refer to fig. 5, the current ripple frequency on the inductor Lf is twice the switching frequency of the switching transistor SR1 and the switching transistor SR2, the proportion of the time that the switching transistor SR1 and the switching transistor SR2 are simultaneously turned on in half of the switching period is defined as the duty ratio D, and the whole circuit can be regarded as a Boost circuit, which is different from the Boost circuit in that: 1. the circuit of the utility model needs a transformer to transfer energy, so that the switching tube SR1 and the switching tube SR2 need to be alternately and symmetrically conducted, and the positive and negative excitation balance of the transformer is ensured; 2. the circuit of the utility model can not be completely switched off when the current is continuous, the inductor does not have a follow current loop, an overvoltage is generated on the switch tube SR1 or the switch tube SR2 to damage the device, but the input energy can be adjusted through the Oring MOS tube, so that the switch tube SR1 or the switch tube SR2 can be quickly switched off and adjusted, and the dynamic performance of reverse control is improved.

Please refer to fig. 6, which is a system block diagram of an embodiment of reverse precharge of an Oring MOS transistor, in the system, a low-voltage side current ILV, a low-voltage side voltage VLV, a voltage Vco at two ends of a capacitor Co, a high-voltage side transformer current Ict, and a high-voltage side voltage Vhv are sampled, and these samples are sampling signals required by a forward DC/DC operation, and can be just used in a reverse precharge process without repeated sampling. After the internal access loop is controlled, the switching tube SR1 and the switching tube SR2 are switched, and the driving voltage and the driving PWM of the Oring MOS are controlled, so that the current-limiting reverse pre-charging and turn-off functions are realized. After small-signal modeling is performed on the circuits at the rear ends of the switching tube SR1 and the switching tube SR2, the transfer function of input impedance under CCM can be obtained as follows:

wherein, N is the primary and secondary side turn ratio of the DC/DC transformer, and D is the defined duty ratio (the ratio of the conduction time of the switching tube SR1 and the switching tube SR2 at the same time to half of the cycle time). It can be derived from the formula that the equivalent impedances of the switching tube SR1 and the switching tube SR2 back-end circuit are inversely proportional to the duty ratio D, and the larger the duty ratio D is, the smaller the equivalent impedance is, so that the input impedance Zin can be adjusted by adjusting the duty ratio D in an open loop manner, thereby adjusting the pre-charging speed.

Referring to fig. 7, the circuit after the rear-stage input impedance is equivalent, the switching tube SR1, the switching tube SR2, the capacitor Chv in the high-voltage switching circuit and other active devices are equivalent to a capacitor Cz, the rear-stage circuit of the Oring MOS transistor can be regarded as an inductor Lf connected in series with the capacitor Cz, and then connected in parallel with the capacitor Co, and the relationship of the capacitor Cz can be calculated as follows:

when the Oring MOS transistor is controlled in a linear region, that is, it can be regarded as a constant current source, the s-domain function of the voltage Vco at the two ends of the capacitor Co can be obtained by calculation as follows:

after inverse laplace transform, converting Vco to Vhv, and obtaining a Vhv time domain relational expression as follows (ignoring parasitic parameters, the waveform will oscillate):

in addition to the device parameters of the circuit itself, the speed of the pre-charge voltage rise is also related to the input current, the duty cycle controlled by the switch SR1 and the switch SR 2.

Specifically, referring to fig. 8, the left graph is a graph of a relationship between duty cycles controlled by the switching transistor SR1 and the switching transistor SR2 and a voltage of the capacitor Chv, an abscissa of the graph is time, an ordinate of the graph is voltage, and a slope of the graph is represented as a ratio of the voltage to the time, that is, a rising rate of the voltage, the higher the slope is, the faster the charging speed is, and it can be seen from the left graph that a straight line with a duty cycle of 0.3 is located above a straight line with a duty cycle of 0.5, that is, the higher the slope of the straight line with a duty cycle of 0.3 is, the faster the charging speed is, so it can be determined that the smaller the duty cycles controlled by the switching transistor SR1 and the switching transistor SR2 is, the faster the charging speed is. The right graph is a graph of the voltage relationship between the input current and the capacitor Chv, the abscissa is time, the ordinate is voltage, and the slope is represented as the ratio of voltage to time, and it can be seen from the right graph that the straight line of the input current I equal to 200A is located above the straight line of the input current I equal to 100A, that is, the charging speed is faster when the input current is 200A, and therefore, it can be determined that the charging speed is faster as the input current I is larger.

The high-voltage pre-charging requirement is generally completed within 150ms, and according to different battery voltages, the input current and the duty ratios of the switching tube SR1 and the switching tube SR2 can be set through the relationship, so that the pre-charging requirement is met, and the current impact is reduced.

Referring to fig. 9, which is a diagram of a reverse precharge stage of the present invention, a first stage is a soft start stage, and is configured to perform precharge in a manner of reducing a PWM duty ratio when the precharge is just started, so as to reduce an impact current at the start, enter a second stage when a voltage across a capacitor Co is higher than a first preset voltage, the second stage is a current-limiting precharge stage, and a current-limiting value of a current source is adjusted in the stage by adjusting a driving voltage or the PWM duty ratio, so as to ensure that a current of an inductor Lf is not continuously increased, control a circuit current is within a current-carrying range, after charging for a certain time, a voltage across a capacitor Chv reaches a second preset voltage, enter a third stage, the stage is a Boost stage, at which an Oring MOS transistor works in a through state, and a Boost can be performed to charge a capacitor Chv by adjusting a switching transistor SR1 and a switching transistor SR2, and the stage can adopt a form of open-loop driving to adjust the duty ratio, closed loop control may also be added.

Referring to fig. 10, which is a block diagram of a dual-loop control method proposed by the present invention, after an error between a high voltage reference Vhvref and a voltage sample Vhv passes through a first-stage PI controller and then through an amplitude limiter, the error is provided to a current inner loop as a reference ILVref of a low-voltage side current. If operating in the three-stage precharge mode, Vhvref is set to the product of the low voltage VLV and the transformer turns ratio N, otherwise it may be set to the target precharge voltage. The limiter limit may be gradually increased from small to large, eventually given an acceptable value of the input charging current. After the error of the low-voltage current reference ILVref and the low-voltage current sampling ILV passes through the inner-ring PI controller, the error passes through the amplitude limiter, the amplitude of the amplitude limiter detects the voltage difference of the MOS tube, a corresponding limit value is obtained by table look-up according to a safe working area, the error can be used as duty ratio control of the Oring MOS tube, or the duty ratio control of the Oring MOS tube is carried out after the drive amplitude control of the duty ratio control, and finally, the high-voltage closed loop is realized, and the soft start and the limitation of the input charging current are realized. The driving control of the switch tube SR1 and the switch tube SR2 can be reasonably adjusted through the open loop mode, the specific parameters of the circuit and the requirement of the pre-charging time.

Referring to fig. 11, in the pre-charging process, the Oring MOS transistor works in the linear region and generates a large loss, so whether the MOS transistor works safely must be checked, and the loss can be checked for boundaries of different low-voltage ranges and different high-voltage battery ranges. Taking one of the states as an example, the relationship between the voltage and the current at the two ends of the Oring MOS transistor in the pre-charging process can be obtained through the voltage relationship function or in a simulation mode, so that the loss of the Oring MOS transistor in the whole pre-charging time can be calculated, the equivalent thermal resistance can be calculated through the equivalent thermal resistance curve of the specification, and the instantaneous junction temperature can be calculated to judge whether the safety is ensured. And designing the working current, voltage and duration of the MOS tube working in the linear region, wherein the forward working safety working region in the specification of the device needs to be referred. By detecting the voltage of the Oring MOS tube, the duty ratio upper limit and the driving level of the Oring MOS tube are set properly, and the MOS works in a safe area.

Referring to fig. 12, it is a control flow chart of the reverse pre-charging device according to the present invention, and the system enters a standby mode after initialization. After the ECU sends a power-on instruction, the DC/DC transformer enters a reverse pre-charging mode, firstly, the DC/DC transformer carries out self-checking to judge whether internal faults exist in output, if the internal short circuit exists, the Oring MOS tube works in a blocking mode, if the self-checking is successful, the reverse pre-charging mode is entered, the Oring MOS tube works in a current-limiting mode or a PWM mode, duty ratio can be gradually adjusted according to requirements, the Oring MOS tube is softened from small to large to control the capacitor voltage at the rear end of the MOS tube, and then the DC/DC transformer carries out reverse work and charges the capacitor Chv. After the reverse pre-charging is completed, the system can judge whether the relay of the BMS is attracted, if the attraction is completed, the reverse pre-charging is completed, the high-voltage battery is connected with the high-voltage equipment, otherwise, the system can enter the reverse pre-charging mode again. After the high-voltage battery is connected, the system can start the forward transmission of the DC/DC of the transformer, a certain threshold value is set according to the current or voltage of the detected MOS tube, and if the forward transmission condition is met, the Oring MOS tube can work in a direct-through mode so as to reduce the forward transmission loss of the DC/DC.

The working principle of the utility model is that the drive voltage of the Oring MOS tube is adjusted to enable the Oring MOS tube to work in different modes, thereby realizing the reverse pre-charging and blocking functions. When reverse pre-charging is needed, the driving voltage is adjusted to enable the Oring MOS tube to work in a linear region, the current in the circuit is limited, and the inductor Lf is prevented from being saturated, so that the reverse pre-charging function is realized; when the blocking function needs to be realized, the drive voltage is adjusted to enable the Oring MOS tube to work in a cut-off region, and the Oring MOS tube is equivalent to open circuit at the moment, so that the blocking function is realized.

Compared with the prior art, the utility model can simultaneously realize the function of preventing reverse filling and the function of reverse pre-filling, does not need to be respectively provided with a plurality of devices for preventing reverse filling and reverse pre-filling, reduces the complexity of the circuit and reduces the design cost of the circuit.

The above examples are intended only to illustrate specific embodiments of the present invention. It should be noted that, for a person skilled in the art, several modifications and variations can be made without departing from the inventive concept, and these modifications and variations shall fall within the protective scope of the present invention.

Claims

1. The vehicle-mounted DC/DC reverse pre-charging device comprises a low-voltage switch circuit connected with a low-voltage battery, a high-voltage switch circuit connected with the high-voltage battery, and a DC/DC transformer connected with the low-voltage switch circuit and the high-voltage switch circuit, and is characterized by further comprising an anti-reverse-charging circuit arranged between the low-voltage switch circuit and the low-voltage battery, wherein the anti-reverse-charging circuit comprises an MOS (metal oxide semiconductor) tube connected between the low-voltage switch circuit and the low-voltage battery in series, and the reverse pre-charging device realizes a reverse pre-charging function by adjusting the driving voltage of the MOS tube.

2. The on-board DC/DC reverse pre-charging device of claim 1, wherein the anti-reverse-charging circuit comprises 4 operating modes:

3. The on-board DC/DC reverse pre-charging device of claim 2, wherein the reverse pre-charging device comprises three pre-charging stages, respectively:

and (3) soft start stage: the reverse-filling prevention circuit works in a PWM mode, and the duty ratio of the PWM signal

Sequentially increasing for reducing the impact current;

and (3) Boost stage: the reverse-filling prevention circuit works in a direct-through mode and is used for charging a capacitor in the high-voltage switch circuit.

4. The on-board DC/DC reverse pre-charge device according to claim 3, wherein the reverse pre-charge device operates in a soft start phase when the capacitance on the low voltage switch circuit side is lower than a first preset voltage;

when the capacitance of the low-voltage switch circuit side is higher than a first preset voltage and lower than a second preset voltage

The reverse pre-charging device works in a current limiting stage;

5. The on-board DC/DC reverse pre-charge apparatus according to claim 1, wherein the low-voltage switch circuit and the high-voltage switch circuit are one of a half-bridge circuit, a full-bridge circuit, a current-doubling rectifying circuit and a full-wave rectifying circuit.

6. The vehicle-mounted DC/DC reverse pre-charging device according to claim 5, wherein the low-voltage switch circuit adopts a full-wave rectification circuit, which includes a switch tube SR1, a switch tube SR2, an inductor Lf and a capacitor Co, the DC/DC transformer is a transformer with a center tap at a low-voltage side, the inductor Lf has one end connected to a center tap end at the low-voltage side of the DC/DC transformer and the other end connected to the positive electrode of the low-voltage battery after being connected in series with the anti-reverse charging circuit, one end of the switch tube SR2 is connected to the second end at the low-voltage side of the DC/DC transformer and the other end connected to the negative electrode of the low-voltage battery, one end of the switch tube SR1 is connected to the first end at the low-voltage side of the DC/DC transformer and the other end is connected between the negative electrode of the low-voltage battery and the switch tube SR2, and one end of the capacitor is connected between the inductor Lf and the anti-reverse charging circuit, The other end of the low-voltage battery is connected between the switching tube SR2 and the negative electrode of the low-voltage battery.

7. The vehicle-mounted DC/DC reverse pre-charging device according to claim 6, wherein the high voltage switch circuit adopts a full bridge circuit, and comprises a switch tube Q1, a switch tube Q2, a switch tube Q3, a switch tube Q4 and a capacitor Chv, the switch tube Q1 and the switch tube Q2 are connected in series and then connected to two ends of the high voltage battery, the switch tube Q2 and the switch tube Q4 are connected in series and then connected to two ends of the high voltage battery, a first end of a high voltage side of the DC/DC transformer is connected between the switch tube Q1 and the switch tube Q2, a second end of the high voltage side of the DC/DC transformer is connected between the switch tube Q3 and the switch tube Q4, and the capacitor Chv is connected in parallel and then connected to two ends of the high voltage battery.

8. The on-board DC/DC reverse pre-charge device of claim 7, wherein the electricity is

The current ripple frequency of the inductor Lf is twice the switching frequency of the switching tubes SR1 and SR2, and the equivalent impedance of the low-voltage switching circuit is:

wherein N is the primary and secondary turns ratio of the DC/DC transformer, and D isThe switching tube SR1 and the switching tube SR2 are simultaneously conducted for a half of the switching period.