High-voltage direct-current load power distribution constant-loss closed-loop pre-charging circuit and method for special vehicle

Abstract

The invention relates to the technical field of electronic control of new energy vehicles, in particular to a high-voltage direct-current load power distribution constant-loss closed-loop pre-charging circuit and method for a special vehicle, which can maintain the loss of a switching tube constant in the charging process, thereby avoiding the problem that the loss of a constant-current charging circuit is relatively large at the starting stage, and improving the charging efficiency. The constant-loss charging circuit and the constant-loss charging method have the advantages that a high-voltage load can be quickly charged, loss of the switch tube is kept constant during charging, risks of damage of the switch tube due to overheating are reduced, development of high-voltage power distribution technologies of special vehicles is promoted, and the constant-loss charging circuit and the constant-loss charging method are brand-new.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic control of new energy vehicles, in particular to a high-voltage DC load power distribution constant-loss closed-loop pre-charging circuit and method for special vehicles. BACKGROUND

[0002] With the vigorous development of electrification and intelligentization technologies, accompanied by the surge in power consumption of special vehicles, the DC bus of special vehicles is gradually changing from low voltage to high voltage. Meanwhile, high-voltage loads are often motor-actuated loads that need to be controlled by motor controllers. The front end of the motor controller usually has a pre-capacitor, which needs to be charged before work, otherwise a large inrush current will be generated, which can easily damage the device. Therefore, a special pre-charging circuit needs to be designed on the special vehicle to manage the pre-charging of high-voltage loads before power-up, and the rationality of its function design is particularly important in the implementation of the entire special vehicle function.

[0003] The most common method of pre-charging is to connect a resistor and a relay in series. When pre-charging, the pre-charging switch is turned on, and the power supply can charge the load capacitor through the pre-charging resistor. After the load voltage reaches the set value, the main switch is turned on and the pre-charging branch is cut off. This method is simple and practical, but the pre-charging resistor is large in size and belongs to a variable current charging mode. The charging current gradually decreases during the process of lifting the load voltage, and the charging current is small in the later stage. If the back-end load is leaking, it can easily lead to failure to complete the pre-charging. Pre-charging can also be achieved by using a switching power supply, for example, using a Buck method. By adjusting the duty cycle of the Buck switch tube, the charging current can be controlled, increasing the adaptability to the load. However, an additional filter inductor is needed, which is large in size and high in cost, and the switching operation will cause more electromagnetic interference. In addition, constant current charging can also be used, which controls the gate voltage of the switch tube to control the charging current. This method uses fewer components, but the switch tube will bear a large charging loss at the beginning of the charging stage. If the current is large, the switch tube is easy to overheat and damage. SUMMARY

[0004] Therefore, the present application provides a high-voltage DC load power distribution constant-loss closed-loop pre-charging circuit and method for special vehicles, which can maintain the loss of the switch tube constant during the charging process, thereby avoiding the problem of large loss at the beginning of the constant current charging circuit.

[0005] To achieve the above purpose, the technical scheme of the present application is as follows:

[0006] The application discloses a high-voltage direct-current load power distribution constant-loss closed-loop pre-charging circuit for a special vehicle, which comprises a control power module, a sampling module, a microcontroller module, a pre-charging drive module and a pre-charging power module; the control power module provides control power for the microcontroller module, the pre-charging drive module and the sampling module;

[0007] The sampling module is connected with a high-voltage direct-current bus and a load capacitor, is used for collecting bus voltage Vbus, charging current Ichg and load capacitor voltage Vcap in real time, and inputs the conditioned signals into the microcontroller module; the microcontroller module is internally provided with a constant-loss closed-loop PID algorithm, calculates power tube instantaneous loss Ploss in real time according to Vbus, Ichg and Vcap input by the sampling module, compares Ploss with a preset loss value Pset to generate a deviation signal, and outputs a high-frequency PWM signal through a PI controller; the pre-charging drive module receives the PWM signal output by the microcontroller module, converts the PWM signal into a smooth direct-current gate drive voltage Vgs through an isolation drive chip and an RC low-pass filter circuit; and the pre-charging power module comprises a charging power tube MOSFET and a discharging power tube, wherein the gate of the MOSFET receives the Vgs signal, and the MOSFET is caused to work in a variable resistance region by adjusting the Vgs, so as to dynamically control the on-resistance of the MOSFET to realize constant-loss pre-charging.

[0008] The microcontroller module dynamically adjusts the PWM duty cycle to maintain the same instantaneous loss of the power tube and the preset loss value by calculating the deviation of the instantaneous loss of the power tube and the preset loss value in real time.

[0009] The RC low-pass filter circuit of the pre-charging drive module converts the PWM signal into a direct-current voltage Vgs, so that the MOSFET continuously works in the linear region.

[0010] The pre-charging power module omits the filter inductor and the freewheeling diode in the Buck topology, and only realizes constant-loss control through impedance adjustment of the MOSFET in the variable resistance region.

[0011] The control power module adopts an isolation type DC-DC converter to convert the high-voltage direct-current bus voltage into multiple isolated low-voltage power supplies, and independently supplies power to each module.

[0012] The sampling module comprises a differential operational amplifier circuit, collects bus voltage Vbus through a resistance dividing network, and collects charging current Ichg through a high-side current sampling chip and an operational amplifier conditioning circuit.

[0013] The pre-charging power module comprises a discharging power tube MOSFET connected in parallel with the load capacitor, and the gate of the MOSFET is controlled by the microcontroller module, and is used for quickly discharging the load capacitor charge when pre-charging fails.

[0014] The circuit does not have a magnetic element.

[0015] The application also provides a high-voltage DC load power distribution constant-loss closed-loop pre-charging method for special vehicles, which is realized based on the circuit and comprises the following steps:

[0016] (a) acquiring the bus voltage Vbus, the charging current Ichg and the load capacitor voltage Vcap in real time through a sampling module;

[0017] (b) calculating the instantaneous loss Ploss of the power tube by the microcontroller module, i.e., Ploss = Ichg x (Vbus-Vcap), and comparing the result with a preset loss value Pset to generate a deviation signal;

[0018] (c) processing the deviation signal by a PI controller to dynamically adjust the duty cycle D of the output PWM signal;

[0019] (d) converting the PWM signal into a DC gate voltage Vgs through low-pass filtering by a pre-charging drive module, so that the charging power tube works in a variable resistance region; adjusting Vgs to make the MOSFET equivalent to a dynamically adjustable resistance to realize adaptive control of the charging current;

[0020] (e) maintaining Ploss ≈ Pset through closed-loop regulation until the main relay is closed and the pre-charging circuit is turned off when Vcap reaches a preset threshold.

[0021] In step (e), when there is a leakage current in the load, the closed-loop control automatically increases the charging current to ensure the completion of pre-charging.

[0022] Advantages:

[0023] 1. The high-voltage DC load power distribution constant-loss closed-loop pre-charging circuit for special vehicles realizes the function of fast charging of high-voltage loads, maintains the constant loss of the switch tube during the charging process, reduces the risk of damage of the switch tube due to overheating, promotes the development of high-voltage power distribution technology for special vehicles, and is a new constant-loss charging circuit that maintains the constant loss of the switch tube during the charging process, thereby avoiding the problem of large loss of the constant-current charging circuit at the beginning.

[0024] 2. The constant-loss closed-loop control algorithm ensures that the power loss of the pre-charging power tube (MOSFET) remains constant during the entire charging process, which effectively avoids the problems of high instantaneous loss and local overheating of the power tube caused by large current and large tube voltage drop at the initial stage of the traditional constant-current charging, significantly reduces the risk of damage of the power tube due to overheating, and improves the reliability and service life of the system.

[0025] 3、The circuit of the present application, closed-loop control strategy can be according to the load capacitor voltage and charging current real-time dynamic adjustment of the power tube working state (gate voltage). This makes the system can adapt to the changes of the load (such as different capacitor value), and even in the late charging there is a certain load leakage current, can maintain sufficient charging current to complete the pre-charge process, overcome the resistance type pre-charge later may be due to the current is too small to complete the defect.

[0026] 4、Compared with the pre-charge circuit using Buck converter and other switching power supply scheme, the present application eliminates the bulky, heavy weight of the filter inductor and other magnetic elements. Only need to use MOSFET, drive circuit, sampling circuit and control unit, significantly reduce the overall volume and weight of the pre-charge module, more in line with the harsh requirements of special vehicles on space and weight.

[0027] 5、Since there is no power inductor, freewheeling diode and related complex control in Buck topology, the circuit structure of the present application is more simple. The main core components are general MOSFET and standard microcontroller, the number of components is reduced, the manufacturing cost is significantly reduced, and about 40% of the cost can be saved compared with switching power supply scheme (such as Buck).

[0028] 6、The core control means of the present application is to convert the high-frequency PWM signal into a smooth DC gate drive voltage through low-pass filtering, so that the power tube continuously works in the variable resistance area (linear area), rather than in the high-frequency switching state. This fundamentally avoids the strong electromagnetic interference (EMI) caused by high-speed switching of the power tube in Buck and other switching power supply schemes. The system EMC performance is better, and the interference to other electronic equipment of the vehicle is smaller. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The present application is a special vehicle high-voltage DC load distribution constant loss closed-loop pre-charge circuit schematic diagram.

[0030] Figure 2 The control power module in the circuit of the present application is a schematic diagram.

[0031] Figure 3 The pre-charge drive module in the circuit of the present application is a schematic diagram.

[0032] Figure 4 The pre-charge power module in the circuit of the present application is a schematic diagram.

[0033] Figure 5 The microcontroller module in the circuit of the present application is a schematic diagram.

[0034] Figure 6 The sampling module in the circuit of the present application is a schematic diagram. DETAILED DESCRIPTION

[0035] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0036] This invention discloses a constant-loss closed-loop pre-charge circuit for high-voltage DC load distribution in special vehicles, such as... Figure 1 As shown, it includes: a control power supply module, a sampling module, a microcontroller module, a pre-charge drive module, and a pre-charge power module. The control power supply module provides control power. Based on the voltage and current information obtained from the sampling module, the microcontroller module implements a constant loss closed-loop PID algorithm to output a PWM signal. The pre-charge drive module obtains the PWM signal from the microcontroller module and converts it into the gate drive voltage of the power transistor to drive the pre-charge power module, thereby achieving constant loss control throughout the process.

[0037] Specifically, in this embodiment, the control power module provides control power D3.3V to the microcontroller module, control power D3.3V and P15V to the pre-charge drive module, and control power A3.3V and P5V to the sampling module. The principle of the control power module is as follows: Figure 2 As shown in the diagram; the sampling module is responsible for acquiring and conditioning the voltage and current, and outputting the conditioning results to the microcontroller module, which then performs the acquisition and calculation. The schematic diagram of the sampling module in this embodiment is shown below. Figure 3 As shown; based on the current and voltage information obtained from the sampling module, the microcontroller module uses a closed-loop PID algorithm to achieve constant loss control of the pre-charge power transistor and outputs a PWM wave. The schematic diagram of the microcontroller module in this embodiment is shown below. Figure 4 As shown, the microcontroller module uses GigaDevice's GD32F450ZIT6 chip. First, based on the sampled output voltage and current values, it calculates the deviation between the current MOSFET's heat loss and the preset value in real time. Then, through a PI controller, it changes the duty cycle of the high-frequency PWM output to generate a PWM digital signal, which is input to the pre-charge drive module. The pre-charge drive module, based on the acquired PWM wave, uses a filtering circuit to restore it to an analog signal, thereby controlling the gate voltage of the pre-charge power transistor. The schematic diagram of the pre-charge drive module in this embodiment is shown below. Figure 5 As shown, the microcontroller module generates a PWM digital signal Pre_H. After isolation by the driver chip, the output passes through a low-pass filter circuit of Rp8 and Cp4, converting the high-frequency PWM drive signal into a low-voltage DC signal. This drives the pre-charge MOSFET to operate in the variable resistance region, maintaining its constant loss operation. Under the action of the gate drive voltage, the pre-charge power module enables the power transistor to operate in the variable resistance region. The schematic diagram of the pre-charge power module in this embodiment is shown below. Figure 6As shown, wherein Q1 is a charging power tube, Q2 is a discharging power tube, Pre_G_H is a pre-charge power tube gate control voltage, BUS+ is a positive bus, BUS is a negative bus, the amplitude of the gate voltage controls the charging power tube to work in a variable resistance region, thereby realizing the current regulation function, and further realizing the constant-loss charging of the whole process. The circuit of the embodiment has undergone project bench integration test and can meet the use requirements of the vehicle.

[0038] The application also provides a special vehicle high-voltage DC load power distribution constant-loss closed-loop pre-charging method, which realizes fast, safe and low-heat-risk pre-charging by dynamically adjusting the MOSFET gate voltage to make it work in a variable resistance region and maintain constant loss, and comprises the following steps:

[0039] obtaining a bus voltage Vbus and a charging current Ichg;

[0040] calculating the MOSFET instantaneous loss: Ploss=Ichg×(Vbus-Vcap) (Vcap is the load capacitance voltage);

[0041] comparing Ploss with a preset loss value Pse to generate a deviation signal ΔP;outputting a PWM duty cycle D through a PI controller to dynamically adjust DD to maintain Ploss≈Pset, thereby avoiding heat accumulation in the initial stage. Through uniform loss distribution, the initial overheat problem of constant-current charging is solved, and through adaptive load change, the fault tolerance to leakage current is improved.

[0042] wherein the microcontroller outputs a high-frequency PWM signal (such as Pre_H);transmitted through an isolation driving chip (such as an optocoupler or a dedicated driver);the RC low-pass filter circuit converts the PWM into a smooth DC voltage Vgs, and Vgs directly drives the pre-charging MOSFET (Q1);by adjusting Vgs, Q1 is accurately controlled to work in a variable resistance region (linear region), which is equivalent to an adjustable resistor: the charging current is dynamically regulated by Vgs. The inductor element of the Buck circuit is omitted, thereby reducing the cost and volume;avoiding switching noise, and improving EMC performance.

[0043] The embodiment method is realized through the circuit of the application, and the specific process is as follows:

[0044] controlling the power supply module to supply power to each unit (D3.3V, P15V, A3.3V);

[0045] The sampling module obtains Vbus, Ichg and Vcap in real time;the microcontroller calculates PlossPloss, and outputs a PWM signal through a PI algorithm;the driving module filters the PWM into Vgs to control the on-resistance of Q1;when Vcap approaches Vbus (such as 90%), the main relay is closed, and the pre-charge circuit is turned off.

[0046] To sum up, the above is only the preferred embodiment of the present application, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A special vehicle high-voltage DC load power distribution constant-loss closed-loop pre-charge circuit, characterized in that, The circuit comprises a control power module, a sampling module, a microcontroller module, a pre-charge driving module and a pre-charge power module; the control power module provides control power for the microcontroller module, the pre-charge driving module and the sampling module; the sampling module is connected with a high-voltage DC bus and a load capacitor, and is used for collecting bus voltage Vbus, charging current Ichg and load capacitor voltage Vcap in real time, and inputting the conditioned signals into the microcontroller module; the microcontroller module is internally provided with a constant-loss closed-loop PID algorithm, and instant power tube loss Ploss is calculated in real time according to Vbus, Ichg and Vcap input by the sampling module, and compared with a preset loss value Pset to generate a deviation signal, and a high-frequency PWM signal is output through a PI controller; the pre-charge driving module receives the PWM signal output by the microcontroller module, and converts the PWM signal into a smooth DC gate driving voltage Vgs through an isolation driving chip and an RC low-pass filter circuit; and the pre-charge power module comprises a charging power tube MOSFET and a discharging power tube, wherein the gate of the MOSFET receives the Vgs signal, and the MOSFET is caused to work in a variable resistance region by adjusting the Vgs, so as to dynamically control the on-resistance of the MOSFET to realize constant-loss pre-charging.

2. The special vehicle high voltage DC load distribution constant loss closed loop pre-charge circuit of claim 1, wherein, The microcontroller module dynamically adjusts the PWM duty cycle to maintain the same instant power tube loss and preset loss value by calculating the deviation of the instant power tube loss and the preset loss value in real time.

3. The special vehicle high voltage DC load distribution constant loss closed loop pre-charge circuit of claim 1, wherein, The RC low-pass filter circuit of the pre-charge driving module converts the PWM signal into a DC voltage Vgs, so that the MOSFET continuously works in a linear region.

4. The special vehicle high voltage DC load distribution constant loss closed loop pre-charge circuit of claim 3, wherein, The pre-charge power module omits the filter inductor and freewheeling diode in the Buck topology, and only realizes constant-loss control through impedance adjustment of the MOSFET in the variable resistance region.

5. The special vehicle high voltage DC load distribution constant loss closed loop pre-charge circuit of claim 1, wherein, The control power module adopts an isolation type DC-DC converter to convert the high-voltage DC bus voltage into multiple isolated low-voltage power supplies to independently supply power to each module.

6. The special vehicle high voltage DC load distribution constant loss closed loop pre-charge circuit of claim 1, wherein, The sampling module comprises a differential operational amplifier circuit, collects the bus voltage Vbus through a resistance dividing network, and collects the charging current Ichg through a high-side current sampling chip and an operational amplifier conditioning circuit.

7. The special vehicle high voltage DC load distribution constant loss closed loop pre-charge circuit of claim 1, wherein, The pre-charge power module comprises a discharging power tube MOSFET connected in parallel with the load capacitor, and the gate of the MOSFET is controlled by the microcontroller module, and is used for quickly discharging the load capacitor charge when pre-charging fails.

8. The special vehicle high voltage DC load distribution constant loss closed loop pre-charge circuit according to any one of claims 1 to 6, characterized in that, The circuit does not have a magnetic element.

9. A method for high-voltage DC load power distribution constant-loss closed-loop pre-charge of special vehicles, characterized in that, The circuit is realized based on any one of claims 1-8, and comprises the following steps: (a) acquiring bus voltage Vbus, charging current Ichg and load capacitor voltage Vcap in real time through the sampling module; (b) the microcontroller module calculates power tube instant loss Ploss = Ichg × (Vbus-Vcap), and compares it with a preset loss value Pset to generate a deviation signal; (c) the PI controller processes the deviation signal to dynamically adjust the duty cycle D of the output PWM signal; (d) the pre-charge driving module converts the PWM signal into a DC gate voltage Vgs through a low-pass filter to drive the charging power tube to work in a variable resistance region; the MOSFET is equivalent to a dynamically adjustable resistance by adjusting the Vgs, so as to realize adaptive control of the charging current. (e) Ploss≈Pset is maintained by closed loop regulation until the main relay is closed and the pre-charge circuit is turned off after Vcap reaches a preset threshold.

10. The method of claim 9, wherein, The closed loop control automatically boosts the charging current when the load has a leakage current in step (e), ensuring that the pre-charge is completed.

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