A vehicle-mounted DC / DC reverse precharging device and control method

Abstract

The present invention discloses an on-vehicle DC / DC reverse pre-charging device and control method. The reverse pre-charging device includes a low-voltage switching circuit connected to a low-voltage battery, a high-voltage switching circuit connected to a high-voltage battery, and a DC / DC transformer connecting the low-voltage switching circuit and the high-voltage switching circuit. The reverse pre-charging device also includes an anti-backfeed circuit disposed between the low-voltage switching circuit and the low-voltage battery. The anti-backfeed circuit includes a MOS transistor connected in series between the low-voltage switching circuit and the low-voltage battery. The reverse pre-charging device implements a reverse pre-charging function by adjusting the driving voltage of the MOS transistor. Compared with the prior art, the present invention, by adding an anti-backfeed circuit, can simultaneously implement both the reverse anti-backfeed function and the reverse pre-charging function.

Description

Technical Field

[0001] The present invention relates to a vehicle-mounted DC / DC, and in particular to a vehicle-mounted DC / DC reverse precharging device and a control method. Background Art

[0002] With the advancement of energy conservation and emission reduction, new energy vehicles, including pure electric, hybrid, and plug-in hybrid vehicles, are becoming increasingly popular in the market. New energy vehicles contain high-voltage batteries and corresponding high-voltage electrical equipment. High-voltage electrical equipment generally has large capacitance at the high-voltage port and cannot be directly connected to the high-voltage battery. Otherwise, large pulse currents will be generated, damaging components. Traditional solutions require adding a pre-charge circuit between the high-voltage battery and the high-voltage electrical equipment. Initially, the high-voltage capacitor is charged through a pre-charge resistor to limit the current. After the voltage difference between the capacitor voltage and the battery voltage reaches a reasonable range, the relay is energized to complete the pre-charge process. This solution uses the high-voltage battery to pre-charge the high-voltage end. The pre-charge circuit is separated from the on-board DC / DC circuit, requiring the addition of additional components and detection circuits, resulting in large size, high cost, and complex control.

[0003] Existing solutions for reverse precharging using on-board DC / DC circuits include adding a winding with secondary-side inductance and connecting a diode to the high-voltage busbar for reverse precharging, and adding a diode to the output end to form a reverse buck circuit, which is then reverse precharged through the DC / DC. However, these solutions require additional components to the existing on-board DC / DC circuit. While reverse precharging can be achieved, it also increases costs.

[0004] Automotive DC / DC converters are frequently used throughout vehicles, necessitating high reliability and safety requirements. This often requires an external port capable of connecting a low-voltage battery to the DC / DC in the event of an internal short circuit. This is typically achieved by adding an external fuse for overcurrent protection or by adding an anti-backflow circuit (ORing circuit) to the DC / DC output.

[0005] Therefore, how to propose an on-vehicle DC / DC reverse pre-charging device and control method that can achieve both anti-backflow function and reverse pre-charging function is a technical problem that needs to be solved urgently in the industry. Summary of the Invention

[0006] In view of the problem in the prior art that a reverse pre-charging device and an anti-backflow circuit need to be provided separately, which increases costs, the present invention proposes an on-vehicle DC / DC reverse pre-charging device and a control method.

[0007] The technical solution of the present invention is to propose an on-vehicle DC / DC reverse pre-charging device, which includes a low-voltage switching circuit connected to a low-voltage battery, a high-voltage switching circuit connected to a high-voltage battery, and a DC / DC transformer connecting the low-voltage switching circuit and the high-voltage switching circuit. It also includes an anti-backflow circuit arranged between the low-voltage switching circuit and the low-voltage battery. The anti-backflow circuit includes a MOS tube connected in series between the low-voltage switching circuit and the low-voltage battery. The reverse pre-charging device realizes the reverse pre-charging function by adjusting the driving voltage of the MOS tube.

[0008] Furthermore, the anti-backfeed circuit includes four working modes:

[0009] Pass-through mode: The driving voltage is continuous and higher than the threshold voltage, and the MOS tube operates in the saturation region, which is used for forward and reverse charging of on-board DC / DC;

[0010] Current limiting mode: The driving voltage is continuous and lower than the threshold voltage, and the MOS tube operates in the linear region, which is used for forward and reverse current limiting of vehicle-mounted DC / DC;

[0011] PWM mode: The driving voltage is lower than the threshold voltage and is adjusted by the PWM signal. The MOS tube operates between the linear region and the cut-off region, which is used for reverse current limiting of the vehicle-mounted DC / DC.

[0012] Blocking mode: The driving voltage is zero, and the MOS tube operates in the cut-off region, which is used to block the reverse energy transmission of the vehicle DC / DC.

[0013] Furthermore, the reverse pre-filling device includes three pre-filling stages, namely:

[0014] Soft start stage: the anti-backfeed circuit operates in PWM mode, and the duty cycle of the PWM signal increases successively to reduce the inrush current;

[0015] Current limiting stage: the anti-backflow circuit operates in PWM mode or current limiting mode to limit the inductor current in the low-voltage switching circuit and perform reverse pre-charging;

[0016] Boost stage: the anti-backfeed circuit operates in a pass-through mode to charge the capacitor on the high-voltage switch circuit side.

[0017] Furthermore, when the capacitance on the low-voltage switch circuit side is lower than a first preset voltage, the reverse pre-charging device operates in a soft start phase;

[0018] When the capacitance on 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 operates in a current limiting stage;

[0019] When the capacitance on the low-voltage switch circuit side is higher than a second preset voltage, the reverse pre-charging device operates in the Boost stage.

[0020] Furthermore, the low-voltage switching circuit and the high-voltage switching circuit adopt one of a half-bridge circuit, a full-bridge circuit, a current doubler rectifier circuit, and a full-wave rectifier circuit.

[0021] Furthermore, the low-voltage switching circuit adopts a full-wave rectifier circuit, which includes a switching tube SR1, a switching tube SR2, an inductor Lf, and a capacitor Co. The DC / DC transformer is a transformer with a center tap on the low-voltage side. One end of the inductor Lf is connected to the center tap end of the low-voltage side of the DC / DC transformer, and the other end is connected in series with the anti-backfeed circuit and then connected to the positive electrode of the low-voltage battery. One end of the switching tube SR2 is connected to the second end of the low-voltage side of the DC / DC transformer, and the other end is connected to the negative electrode of the low-voltage battery. One end of the switching tube SR1 is connected to the first end of 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 switching tube SR2. One end of the capacitor Co is connected between the inductor Lf and the anti-backfeed circuit, and the other end is connected between the switching tube SR2 and the negative electrode of the low-voltage battery.

[0022] Furthermore, the high-voltage switching circuit adopts a full-bridge circuit, which includes a switching tube Q1, a switching tube Q2, a switching tube Q3, a switching tube Q4, and a capacitor Chv. The switching tubes Q1 and Q2 are connected in series and connected to both ends of the high-voltage battery. The switching tubes Q2 and Q4 are connected in series and connected to both ends of the high-voltage battery. The first end of the high-voltage side of the DC / DC transformer is connected between the switching tubes Q1 and Q2, and the second end is connected between the switching tubes Q3 and Q4. The capacitor Chv is connected in parallel to both ends of the high-voltage battery.

[0023] Furthermore, the current ripple frequency of the inductor Lf is twice the switching frequency of the switch tubes SR1 and SR2, and the equivalent impedance of the low-voltage switch circuit is: Where N is the turns ratio of the primary and secondary sides of the DC / DC transformer, and D is the proportion of the time when the switch tubes SR1 and SR2 are simultaneously turned on to half of the switching period.

[0024] The present invention also proposes a control method for a vehicle-mounted DC / DC reverse pre-charging device, comprising:

[0025] When the vehicle-mounted DC / DC is reversely precharged, the anti-backflow circuit is adjusted to operate in a current limiting mode or a PWM mode;

[0026] When the on-board DC / DC reverse pre-charging is completed, the on-board DC / DC forward transmission is started, and the anti-backflow circuit is controlled to operate in a pass-through mode;

[0027] When a backfeed current is detected, the anti-backfeed circuit is controlled to operate in a blocking mode.

[0028] Furthermore, before the on-board DC / DC enters reverse pre-charging, it is necessary to detect the output of the on-board DC / DC. If it is determined that there is an internal fault in the on-board DC / DC output, the anti-backflow circuit is controlled to operate in blocking mode, otherwise it enters reverse pre-charging.

[0029] Compared with the prior art, the present invention has at least the following beneficial effects:

[0030] By adding an anti-backflow circuit and corresponding control, the reverse backflow prevention function and reverse precharge function can be simultaneously realized, eliminating the need to set up multiple additional devices for implementing the reverse backflow prevention function and reverse precharge function, thereby reducing design costs. At the same time, the reverse charging speed and state can be adjusted by adjusting the driving voltage of the MOS tube in the present invention, which has simple control logic and can also realize forward and reverse current limiting and buffering functions. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 This is a block diagram of the high-voltage pre-charging connection system for traditional new energy vehicles;

[0033] Figure 2 This is a block diagram of the connection system of the vehicle-mounted DC / DC reverse pre-charging device of the present invention;

[0034] Figure 3 This is a circuit diagram of an embodiment of a vehicle-mounted DC / DC reverse pre-charging device of the present invention;

[0035] Figure 4 This is a schematic diagram showing the operation of the MOS tube in the anti-backfeed circuit of the present invention;

[0036] Figure 5 This is a driving timing diagram of the switch tube SR1 and the switch tube SR2 in the present invention;

[0037] Figure 6 This is a system block diagram of an embodiment of a vehicle-mounted DC / DC reverse pre-charging device of the present invention;

[0038] Figure 7 This is an equivalent circuit diagram of the vehicle-mounted DC / DC reverse pre-charging device of the present invention;

[0039] Figure 8The waveform diagram of the pre-charge voltage, duty cycle and pre-charge current of the present invention;

[0040] Figure 9 This is a diagram of the reverse pre-charging stage according to an embodiment of the present invention;

[0041] Figure 10 A block diagram of a dual-loop control method according to an embodiment of the present invention;

[0042] Figure 11 This is the forward safe working area diagram of the MOS tube;

[0043] Figure 12 This is a flow chart of a reverse pre-charging device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0044] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, 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 only used to explain the present invention and are not intended to limit the present invention.

[0045] Thus, a feature indicated in this specification is intended to illustrate one of the features of one embodiment of the present invention, rather than to imply that every embodiment of the present invention must have the described feature. In addition, it should be noted that this specification describes many features. Although certain features can be combined together to illustrate possible system designs, these features can also be used in other, not explicitly described, combinations. Thus, unless otherwise noted, the described combinations are not intended to be limiting.

[0046] The principle and structure of the present invention are described in detail below with reference to the accompanying drawings and embodiments.

[0047] In the prior art, on-board DC / DC circuits generally require an anti-backfeed circuit to prevent the generation of reverse current to ensure safety. Furthermore, to implement the reverse pre-charge function, an additional reverse pre-charge circuit is also required, increasing circuit costs. The present invention proposes an on-board DC / DC reverse pre-charge device that can achieve both anti-backfeed and reverse pre-charge functions without requiring additional circuitry, thereby reducing circuit design costs.

[0048] See Figure 1 and Figure 2In the prior art, the high-voltage pre-charging method generally connects the high-voltage electrical equipment 110 and the high-voltage battery 130 respectively through the high-voltage pre-charging device 120, which can only realize the reverse pre-charging function between the high-voltage equipment. In the present invention, the anti-backflow circuit 140 is set in the on-board DC / DC 140, and the low-voltage battery 150, the high-voltage electrical equipment 110 and the high-voltage battery 130 are respectively connected through the on-board DC / DC 140 to realize the reverse pre-charging function between high and low voltages.

[0049] For details, see Figure 3 In one embodiment of the present invention, the reverse pre-charging device includes a low-voltage switching circuit 142 connected to a low-voltage battery 150, a high-voltage switching circuit 144 connected to a high-voltage battery 130, a DC / DC transformer 143 connecting the low-voltage switching circuit 142 and the high-voltage switching circuit 144, and an anti-backflow circuit 141 connected in series between the low-voltage battery 150 and the low-voltage switching circuit 142. The anti-backflow circuit 141 is a MOS transistor connected in series between the low-voltage switching circuit 142 and the low-voltage battery 150. The MOS transistor is an Oring MOS transistor and can implement an anti-backflow function through its conduction characteristics. In the present invention, the reverse pre-charging function of the reverse pre-charging device can be implemented by controlling the driving voltage of the MOS transistor.

[0050] Without a MOS transistor for reverse pre-charging, the high-voltage bus capacitance during vehicle-mounted DC / DC operation can cause the input voltage to remain higher than the output voltage for extended periods. This can cause the current in inductor Lf in low-voltage switching circuit 142 to continue to rise, ultimately leading to inductor Lf saturation and affecting reverse pre-charging. Therefore, to prevent inductor Lf saturation, the reverse pre-charging input current must be controlled to ensure that inductor Lf does not over-current saturate, thus enabling reverse pre-charging.

[0051] For details, see Figure 3In the present invention, the low-voltage switching circuit 142 adopts a full-wave rectifier circuit, which includes a switching tube SR1, a switching tube SR2, an inductor Lf, and a capacitor Co. Among them, the DC / DC transformer 143 is a transformer with a center tap on the low-voltage side. One end of the inductor Lf is connected to the center tap end of the DC / DC transformer 143, and the other end is connected to the anti-backfeed circuit 141, and is connected to the positive electrode of the low-voltage battery 150 through the anti-backfeed circuit 141. One end of the switching tube SR2 is connected to the second end of the DC / DC transformer 143, and the other end is connected to the negative electrode of the low-voltage battery 150. One end of the switching tube SR1 is connected to the first end of the low-voltage side of the DC / DC transformer 143, and the other end is connected between the negative electrode of the low-voltage battery 150 and the switching tube SR2. The capacitor Co One end is connected between the inductor Lf and the anti-backfeed circuit 141, and the other end is connected between the switch tube SR2 and the negative electrode of the low-voltage battery 150. It acts as a bus capacitor, can receive the voltage of the low-voltage battery 150, and transmit it to the low-voltage switch circuit 142.

[0052] In the first embodiment of the present invention, the low-voltage switching circuit 142 adopts a full-wave rectifier circuit, and its current fluctuation amplitude is small. In other embodiments of the present invention, the low-voltage switching circuit 142 can also adopt one of a half-bridge circuit, a full-bridge circuit, and a current doubler rectifier circuit, all of which can achieve a rectification effect by controlling the operation of its switching tube.

[0053] Furthermore, in this embodiment, the high-voltage switching 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 form a bridge rectifier circuit, the capacitor Chv is connected in parallel at both ends of the high-voltage battery for charging the bus capacitor, the switch tube Q1 and the switch tube Q2 form one bridge arm, the switch tube Q3 and the switch tube Q4 form another bridge arm, and the two ends of the high-voltage side of the DC / DC transformer 143 are respectively connected to the midpoints of the two bridge arms. The current after DC / DC conversion can be rectified by the full-bridge circuit and output to the high-voltage battery.

[0054] Compared with the full-wave rectifier circuit, the full-bridge rectifier circuit has a better rectification effect, and the utilization rate of the transformer is higher than that of the full-wave rectifier circuit. In other embodiments of the present invention, the high-voltage switch circuit 144 can also 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 used for rectification of the low-voltage side and the high-voltage side respectively. In theory, the settings of the low-voltage switch circuit 142 and the high-voltage switch circuit 144 can be arbitrarily combined under the adjustment that meets the rectification requirements.

[0055] The working principle of the present invention is described below using a low-voltage switch circuit 142 employing full-wave rectification and a high-voltage switch circuit 144 employing 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. To ensure the operation of the reverse pre-charge function of the circuit, it is necessary to prevent the inductor Lf from overcurrent saturation. In the present invention, the current limiting function is achieved by controlling the working mode of the Oring MOS tube, thereby preventing the inductor Lf from overcurrent saturation. For details, please refer to Figure 4 According to the change of driving voltage, the anti-backfeed circuit has four different working modes:

[0056] Pass-through mode: The drive voltage is continuous and higher than the threshold voltage. The MOS transistor operates in the saturation region. At this time, the MOS transistor is in the on state, its resistance is very small, and the voltage drop across the two ends is very small. After the voltage is boosted by the switch transistors SR1 and SR2, it can charge the high-voltage side capacitor for the forward charging of the on-board DC / DC. (The continuous drive voltage mentioned in this article refers to a continuous voltage signal. In contrast to the PWM signal, there is no moment when the voltage signal is 0).

[0057] Current-limiting mode: The drive voltage remains constant and below the threshold voltage, and the MOS transistor operates in the linear region. At this point, the MOS transistor has a certain resistance. Although it can conduct, the voltage across the MOS transistor is divided, reducing the back-end voltage and current. This is used for forward and reverse current limiting in automotive DC / DC systems. In this case, the low current prevents overcurrent saturation of the inductor Lf, thereby achieving a reverse pre-charge function.

[0058] PWM mode: The drive voltage is lower than the threshold voltage and is regulated by the PWM signal. The MOS transistor operates between the linear region and the cutoff region. In this case, the MOS transistor is equivalent to having a large resistance and the back-end current is small. It can be used for reverse current limiting of automotive DC / DC. At the same time, due to the small current in this case, it can prevent the inductor Lf from overcurrent saturation, thereby realizing the reverse pre-charge function. Compared with the current limiting mode, the current in the circuit is smaller in PWM mode, and the charging speed is slower. It is generally used in the startup phase to prevent large current overshoot.

[0059] Blocking mode: The drive voltage is zero and the MOS transistor operates in the cutoff region. At this point, the MOS transistor is equivalent to an open circuit or infinite resistance. The current flowing through the MOS transistor is zero, making it unusable for reverse pre-charging. However, it can prevent reverse energy transmission from the on-board DC / DC, thus preventing backflow.

[0060] Among them, the threshold voltage of the MOS tube is the minimum voltage for its direct conduction, which is determined according to the selection of the MOS tube. When the driving voltage is higher than the threshold voltage, the MOS tube is in the direct conduction mode, and the voltage drop across it is small. Conversely, when the driving voltage is lower than the threshold voltage, the MOS tube will be in the non-direct conduction mode, and there will be a certain voltage drop across it.

[0061] According to the startup process of the on-board DC / DC, the reverse pre-charging device can be divided into three pre-charging stages: the soft start stage: the anti-backflow circuit works in PWM mode, and the duty cycle of the PWM signal increases successively to reduce the inrush current;

[0062] Current limiting stage: The anti-backflow circuit works in PWM mode or current limiting mode to limit the inductor current in the low-voltage switching circuit and perform reverse pre-charging;

[0063] Boost stage: The anti-backfeed circuit works in the pass-through mode to charge the capacitor on the high-voltage switching circuit side;

[0064] Specifically, when the on-board DC / DC begins pre-charging, after the switches SR1 and SR2 are turned on, the voltage Vco across capacitor Co is very low. At this time, if a linearly turned-on Oring MOS transistor is used, a large inrush current will be generated. Therefore, when the on-board DC / DC is first started, it is necessary to enter the soft-start phase to reduce the inrush current. Since the charging current is proportional to the PWM duty cycle, the PWM duty cycle needs to be increased to gradually increase the charging current. As the pre-charging process progresses, the voltage across capacitor Co gradually increases until it reaches the first preset voltage. At this time, the voltage in the high-voltage switching circuit is low, and the voltage of capacitor Chv is low, allowing reverse pre-charging. To achieve reverse pre-charging of the on-board DC / DC, it is necessary to prevent the inductor Lf from being saturated due to excessive current. Therefore, the current limiting phase is entered at this time to prevent the inductor Lf from being saturated due to excessive current, and reverse pre-charging is performed. After a certain period of reverse precharging, when the voltage across capacitor Chv is higher than a second preset voltage, the input voltage of the on-board DC / DC converter is lower than the output voltage, and there is no risk of the current in inductor Lf continuing to increase. If the Oring MOS tube is operated in the linear region at this time, its current loss will be large. Therefore, it is necessary to operate the anti-backfeed circuit in direct-flow mode and boost the voltage to charge the high-voltage switching circuit by adjusting the duty cycle of switch tubes SR1 and SR2.

[0065] In other embodiments of the present invention, the soft-start stage and the current-limiting stage may be combined. Since the anti-backfeed circuit can play a current-limiting role 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-backfeed circuit. In this case, it is no longer necessary to determine whether the voltage is higher than the first preset voltage to switch the mode. Instead, it is only necessary to determine whether the voltage across the capacitor Chv is higher than the second preset voltage, so that the input voltage of the on-board DC / DC is lower than the output voltage. This makes the overall control logic simpler and the operation more convenient.

[0066] The first preset voltage is a threshold voltage set based on the circuit components and determined by circuit selection. When the voltage across capacitor Co is higher than the first preset voltage, the inrush current in the circuit is small or zero, allowing reverse precharging. The second preset voltage is the product of the voltage across capacitor Co and the transformer primary-to-secondary turns ratio N. When the voltage across capacitor Chv is higher than the second preset voltage, the input voltage of the on-board DC / DC converter is lower than the output voltage, and the current in inductor Lf does not continue to increase.

[0067] Furthermore, the present invention can also adjust the impedance of the ORING MOS tube after it is connected by adjusting the open-loop duty cycle of the switch tube SR1 and the switch tube SR2, thereby adjusting the charging time. Figure 5 The current ripple frequency on the inductor Lf is twice the switching frequency of the switch tubes SR1 and SR2. The proportion of the time that the switch tubes SR1 and SR2 are simultaneously turned on to half of the switching period is defined as the duty cycle D. The entire circuit can be regarded as a Boost circuit. The differences between it and the Boost circuit are: 1. The circuit of the present invention requires a transformer to transfer energy. Therefore, the switch tubes SR1 and SR2 need to be turned on alternately and symmetrically to ensure the positive and negative excitation balance of the transformer; 2. The circuit of the present invention cannot be completely shut down when the current is continuous. The inductor has no freewheeling circuit, which will cause overvoltage on the switch tube SR1 or the switch tube SR2 to damage the device. However, the input energy can be adjusted by the Oring MOS tube, so that the switch tube SR1 or the switch tube SR2 can quickly reach the shutdown regulation, thereby improving the dynamic performance of the reverse control.

[0068] See Figure 6, which is a system block diagram of an embodiment of reverse pre-charging of an Oring MOS tube. In the system, the low-voltage side current ILV, the low-voltage side voltage VLV, the voltage across the capacitor Co Vco, the high-voltage side transformer current Ict, and the high-voltage side voltage Vhv are sampled. These samples are the sampling signals required for forward DC / DC operation and can be used exactly for the reverse pre-charging process without repeated sampling. After the internal loop is controlled, the switch tubes SR1 and SR2 are switched on and off, and the driving voltage and driving PWM of the OringMOS are controlled to achieve current limiting reverse pre-charging and shutdown functions. Among them, after small-signal modeling of the circuit behind the switch tubes SR1 and SR2, the input impedance transfer function under CCM can be obtained as follows:

[0069]

[0070] Where N is the turns ratio of the primary to secondary sides of the DC / DC transformer, and D is the defined duty cycle (the ratio of the time that switches SR1 and SR2 are simultaneously on to half of their cycle time). The formula shows that the equivalent impedance of the circuitry behind switches SR1 and SR2 is inversely proportional to the duty cycle D. A larger duty cycle D results in a smaller equivalent impedance. Therefore, the input impedance Zin, and thus the pre-charge speed, can be adjusted by adjusting the duty cycle D in an open-loop manner.

[0071] See Figure 7 , which is the circuit after the input impedance of the subsequent stage is equivalent. The switch tube SR1, the switch tube SR2, the capacitor Chv in the high-voltage switch circuit and other active devices are equivalent to the capacitor Cz. The subsequent circuit of the Oring MOS tube can be regarded as the inductor Lf and the capacitor Cz in series, and then in parallel with the capacitor Co. The relationship of the capacitor Cz can be calculated as follows:

[0072]

[0073] When the Oring MOS tube is controlled in the linear region, it can be regarded as a constant current source. The s-domain function of the voltage Vco across the capacitor Co can be obtained by calculation as follows:

[0074]

[0075] After the inverse Laplace transform, Vco is converted to Vhv, and the time domain expression of Vhv can be obtained as follows (ignoring parasitic parameters, the waveform will have oscillations):

[0076]

[0077] In addition to being related to the device parameters of the circuit itself, the speed at which the pre-charge voltage rises is also related to the input current and the duty cycle controlled by the switch tubes SR1 and SR2.

[0078] For details, see Figure 8 The left figure shows the relationship between the duty cycle controlled by switches SR1 and SR2 and the voltage of capacitor Chv. The horizontal axis is time, the vertical axis is voltage, and the slope is the ratio of voltage to time, that is, the rate of voltage rise. The higher the slope, the faster the charging speed. As can be seen from the left figure, the line with a duty cycle of 0.3 is above the line with a duty cycle of 0.5. In other words, the line with a duty cycle of 0.3 has a higher slope and a faster charging speed. Therefore, it can be determined that the smaller the duty cycle controlled by switches SR1 and SR2, the faster the charging speed. The right figure shows the relationship between the input current and the voltage of capacitor Chv. The horizontal axis is time, the vertical axis is voltage, and the slope is the ratio of voltage to time. As can be seen from the right figure, the line with input current I = 200A is above the line with input current I = 100A, that is, the charging speed is faster when the input current is 200A. Therefore, it can be determined that the larger the input current I, the faster the charging speed.

[0079] Generally, high-voltage pre-charging is required to be completed within 150ms. Depending on the battery voltage, the input current and the duty cycle of the switch tubes SR1 and SR2 can be set according to the above relationship to meet the pre-charging requirements while reducing current shock.

[0080] See Figure 9 , which is a reverse pre-charge stage diagram of the present invention. The first stage is the soft start stage, which is used for pre-charging at the beginning. Pre-charging is performed by increasing the PWM duty cycle from small to large, reducing the initial inrush current. When the voltage across the capacitor Co is higher than the first preset voltage, the second stage is entered. This stage is the current limiting pre-charging stage. In this stage, the current limiting value of the current source is adjusted by adjusting the driving voltage or the PWM duty cycle, thereby ensuring that the current of the inductor Lf does not continue to increase and the current of the control circuit is within the tolerable current range. After charging for a certain period of time, the voltage across the capacitor Chv reaches the second preset voltage, and the third stage is entered. This stage is the Boost stage. At this time, the Oring MOS tube works in the through state, and the switch tube SR1 and the switch tube SR2 can be adjusted to boost the voltage to charge the capacitor Chv. This stage can adopt the form of open-loop drive to adjust the duty cycle, or add closed-loop control.

[0081] See Figure 10This is a block diagram of the dual-loop control approach proposed in the present invention. The error between the high-voltage voltage reference Vhvref and the voltage sample Vhv passes through a first-stage PI controller and then a limiter, before being fed into the inner current loop as the low-voltage side current reference ILVref. If operating in the three-stage precharge mode, Vhvref is set to the product of the low-voltage voltage VLV and the transformer turns ratio N. Otherwise, it can be set to the target precharge voltage. The limiter's limit value can be gradually increased, ultimately setting an acceptable input charging current. The error between the low-voltage current reference ILVref and the low-voltage current sample ILV passes through the inner-loop PI controller and then through the limiter. The limiter's amplitude is determined by detecting the MOSFET voltage difference and looking up the corresponding limit value based on the safe operating area. This limiter can be used to control the duty cycle of the ORing MOSFET, or its drive amplitude is controlled to drive the ORing MOSFET, ultimately achieving a closed high-voltage voltage loop and soft-starting and limiting the input charging current. The driving control of the switch tube SR1 and the switch tube SR2 can be reasonably adjusted in an open-loop manner according to the specific parameters of the circuit and the requirements of the pre-charge time.

[0082] See Figure 11 Because the ORing MOS transistor operates in the linear region during the pre-charge process, significant losses are generated. Therefore, it is necessary to assess the safety of the MOS transistor operation. Loss verification can be performed for different low-voltage ranges and high-voltage battery range boundaries. Taking one of these states as an example, the voltage and current relationship across the ORing MOS transistor during the pre-charge process can be obtained using the aforementioned voltage relationship function or through simulation. This allows the ORing MOS transistor losses for the entire pre-charge time to be calculated. The equivalent thermal resistance is calculated using the equivalent thermal resistance curve in the data sheet, and the instantaneous junction temperature is calculated to determine safety. The operating current, voltage, and duration of the MOS transistor operating in the linear region should be designed, referring to the forward safe operating area in the device data sheet. By monitoring the ORing MOS transistor voltage, an appropriate upper limit for the ORing MOS transistor duty cycle and drive level can be set to ensure that the MOS operates within the safe area.

[0083] See Figure 12, which is a control flow chart of the reverse pre-charge device of the present invention. After the system is initialized, it enters the standby working mode. After the ECU sends the power-on command, the DC / DC converter enters the reverse pre-charge mode. First, the DC / DC converter will perform a self-test to determine whether there is an internal fault in the output. If an internal short circuit occurs, the ORing MOS transistor operates in the blocking mode. If the self-test is successful, it enters the reverse pre-charge mode. The ORing MOS transistor operates in the current limiting mode or PWM mode. The duty cycle can be gradually adjusted as needed, and the soft start is performed from small to large to control the capacitor voltage at the back end of the MOS. The DC / DC converter then operates in the reverse direction to charge the capacitor Chv. After the reverse pre-charge is completed, the system will determine whether the BMS relay is energized. If it is, it means that the reverse pre-charge is complete and the high-voltage battery has been connected to the high-voltage equipment. Otherwise, it will re-enter the reverse pre-charge mode. After the high-voltage battery is connected, the system will start the DC / DC converter forward transmission. Based on the detected MOS transistor current or voltage, a certain threshold is set. If the forward transmission conditions are met, the ORing MOS transistor will operate in the pass-through mode to reduce the DC / DC forward transmission loss.

[0084] The operating principle of the present invention is to adjust the driving voltage of the ORing MOS transistor to enable it to operate in different modes, thereby achieving reverse pre-charging and blocking functions. When reverse pre-charging is required, the driving voltage is adjusted to operate the ORing MOS transistor in the linear region, limiting the current in the circuit and preventing saturation of the inductor Lf, thereby achieving the reverse pre-charging function. When the blocking function is required, the driving voltage is adjusted to operate the ORing MOS transistor in the cutoff region, effectively disconnecting the ORing MOS transistor and achieving the blocking function.

[0085] Compared with the prior art, the present invention can simultaneously realize the anti-backflow function and the reverse pre-charge function, without setting up multiple devices for the anti-backflow and reverse pre-charge functions respectively, reducing the complexity of the circuit and reducing the circuit design cost.

[0086] The above embodiments are only used to illustrate the specific implementation of the present invention. It should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the concept of the present invention, and these modifications and variations should all fall within the scope of protection of the present invention.

Claims

1. A vehicle-mounted DC / DC reverse pre-charging device, comprising a low-voltage switching circuit connected to a low-voltage battery, a high-voltage switching circuit connected to a high-voltage battery, and a DC / DC transformer connecting the low-voltage switching circuit and the high-voltage switching circuit, characterized in that: It also includes an anti-backflow circuit provided between the low-voltage switch circuit and the low-voltage battery, the anti-backflow circuit includes a MOS 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; The anti-backfeed circuit includes 4 working modes: Through mode: The driving voltage is continuous and higher than the threshold voltage, and the MOS tube operates in the saturation region, which is used for forward and reverse charging of the on-board DC / DC; Current limiting mode: The driving voltage is continuous and lower than the threshold voltage, and the MOS tube operates in the linear region, which is used for forward and reverse current limiting of vehicle-mounted DC / DC; PWM mode: The driving voltage is lower than the threshold voltage and is adjusted by the PWM signal. The MOS tube operates between the linear region and the cut-off region, which is used for reverse current limiting of the vehicle-mounted DC / DC. Blocking mode: The driving voltage is zero, and the MOS tube operates in the cut-off region, which is used to block the reverse energy transmission of the vehicle DC / DC; The reverse pre-charging device includes three pre-charging stages, namely: Soft start stage: the anti-backfeed circuit operates in PWM mode, and the duty cycle of the PWM signal increases successively to reduce the inrush current; Current limiting stage: the anti-backflow circuit operates in PWM mode or current limiting mode to limit the inductor current in the low-voltage switching circuit and perform reverse pre-charging; Boost stage: the anti-backfeed circuit operates in a pass-through mode to charge the capacitor in the high-voltage switching circuit; The low-voltage switching circuit adopts a full-wave rectifier circuit, which includes a switching tube SR1, a switching tube SR2, an inductor Lf, and a capacitor Co. The DC / DC transformer is a transformer with a center tap on the low-voltage side. One end of the inductor Lf is connected to the center tap end of the low-voltage side of the DC / DC transformer, and the other end is connected in series with the anti-backfeed circuit and then connected to the positive electrode of the low-voltage battery; The current ripple frequency of the inductor Lf is twice the switching frequency of the switch tubes SR1 and SR2. The equivalent impedance of the low-voltage switch circuit is: ; Where N is the primary-to-secondary turns ratio of the DC / DC transformer, and D is the proportion of the time when the switch tube SR1 and the switch tube SR2 are simultaneously turned on to half of the switching cycle. L f is the inductance of the inductor Lf, C hv is the capacitance Chv of the high-voltage switching circuit.

2. The vehicle-mounted DC / DC reverse pre-charging device according to claim 1, characterized in that: When the capacitance on the low-voltage switch circuit side is lower than a first preset voltage, the reverse pre-charging device operates in a soft-start phase; When the capacitance on 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 operates 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 operates in the Boost stage.

3. The vehicle-mounted DC / DC reverse pre-charging device according to claim 1, characterized in that: The high-voltage switching circuit adopts any one of a half-bridge circuit, a full-bridge circuit, a current doubler rectifier circuit, and a full-wave rectifier circuit.

4. The vehicle-mounted DC / DC reverse pre-charging device according to claim 1, characterized in that: One end of the switch tube SR2 of the low-voltage switching circuit is connected to the second end of the low-voltage side of the DC / DC transformer, and the other end is connected to the negative electrode of the low-voltage battery. One end of the switch tube SR1 is connected to the first end of 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. One end of the capacitor Co is connected between the inductor Lf and the anti-backfeed circuit, and the other end is connected between the switch tube SR2 and the negative electrode of the low-voltage battery.

5. The vehicle-mounted DC / DC reverse pre-charging device according to claim 4, characterized in that: The high-voltage switching circuit adopts a full-bridge circuit, which includes a switching tube Q1, a switching tube Q2, a switching tube Q3, a switching tube Q4, and a capacitor Chv. The switching tubes Q1 and Q2 are connected in series to the two ends of the high-voltage battery, and the switching tubes Q2 and Q4 are connected in series to the two ends of the high-voltage battery. The first end of the high-voltage side of the DC / DC transformer is connected between the switching tubes Q1 and Q2, and the second end is connected between the switching tubes Q3 and Q4. The capacitor Chv is connected in parallel to the two ends of the high-voltage battery.

6. A control method using the vehicle-mounted DC / DC reverse pre-charging device according to any one of claims 1 to 5, characterized in that: include: When the vehicle-mounted DC / DC is reversely precharged, the anti-backflow circuit is adjusted to operate in a current limiting mode or a PWM mode; When the on-board DC / DC reverse pre-charging is completed, the on-board DC / DC forward transmission is started, and the anti-backflow circuit is controlled to work in the direct-through mode; When a backfeed current is detected, the anti-backfeed circuit is controlled to operate in a blocking mode.

7. The control method according to claim 6, characterized in that: Before the on-board DC / DC enters reverse pre-charging, it is also necessary to detect the output of the on-board DC / DC. If it is determined that there is an internal fault in the on-board DC / DC output, the anti-backflow circuit is controlled to operate in blocking mode, otherwise it enters reverse pre-charging.

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