A fuel cell system high-voltage bus active discharge method and system

Abstract

The application provides a fuel cell system high-voltage bus active discharge method, comprising the following steps: S1: an air compressor controller receives an active discharge instruction sent by a stack system controller; S2: a state of an input-output contactor is detected; S3: whether an active discharge condition is met is judged, if yes, the next step is performed, and if not, the contactor is disconnected and the step S2 is returned; S4: an active discharge mode is entered, and a switch action command after loss is improved is generated; S5: a power device executes the switch action command generated in the step S4; and S6: whether a voltage of a high-voltage bus meets a requirement is judged, if yes, the discharge is ended, and if not, the step S5 is returned. The method adopts open-loop control, does not involve a complex control algorithm, changes an air compressor controller working mode, improves switch loss and conduction loss of a controller power semiconductor device and power line loss, so as to achieve the purpose of consuming electric energy, and electric energy release of high-voltage components can be realized without increasing an additional discharge circuit.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell technology and relates to a method and system for active discharge of high-voltage bus in a fuel cell system. Background Technology

[0002] Currently, new energy electric vehicles require batteries to power the motor controller. The motor controller integrates a large bus capacitor to stabilize its bus voltage. When the vehicle stops operating, the battery disconnects from the motor controller. Due to the large bus capacitor, the entire controller remains at a high voltage. This high bus voltage can pose a life-threatening risk when the vehicle malfunctions or undergoes routine maintenance. Therefore, the motor controller needs an active discharge method to release residual charge on the film capacitors and Y capacitors, reducing the bus voltage to a safe range. The national standard GB / T 18488 requires that the voltage of high-voltage components in the vehicle's high-voltage system be released to below 60V within 3 seconds after stopping operation. This necessitates rapid high-voltage energy release equipment.

[0003] In existing technologies, the high-voltage components of fuel cells discharge via a switch and a discharge resistor connected in parallel to the DC bus. This requires an additional discharge circuit, specifically a discharge branch connected in parallel to the high-voltage bus, essentially a parallel discharge branch within the DC-DC converter. This discharge branch typically consists of a discharge branch switch K1 and its control circuit, a discharge resistor, and a temperature detection unit for the discharge resistor. When high-voltage discharge is required, the control circuit closes the switch of this discharge branch, thus connecting the discharge resistor in parallel to the high-voltage bus to achieve energy release. However, this additional discharge circuit increases cost and complicates the structural design. Summary of the Invention

[0004] The purpose of this invention is to solve the problem of increased costs caused by adding extra circuits to release excess electrical energy in the prior art.

[0005] To address the above objectives, the present invention provides a method for active discharge of a high-voltage bus in a fuel cell system, the method comprising the following steps:

[0006] S1: The air compressor controller receives the active discharge command sent by the fuel cell system controller;

[0007] S2: Detects the status of input / output contactors;

[0008] S3: Determine whether the active discharge conditions are met. If they are met, proceed to the next step. If they are not met, disconnect the contactor and return to S2.

[0009] S4: Enter active discharge mode and generate a switching action command with increased loss;

[0010] S5: The power device executes the switching action command generated by S4;

[0011] S6: Determine whether the voltage of the high-voltage bus meets the requirements. If it does, end the discharge; otherwise, return to S5.

[0012] The active discharge method for the high-voltage bus of the fuel cell system provided by the present invention also has the following feature: entering the active discharge mode in S4 further includes disabling the undervoltage protection of the bus voltage, the short-circuit protection of the drive board, and the undervoltage protection of the gate by the air compressor controller.

[0013] The active discharge method for the high-voltage bus of a fuel cell system provided by this invention also has the following feature: the switching action command includes the following steps:

[0014] S4.1: Reduce gate drive voltage;

[0015] S4.2: Increase switching frequency;

[0016] S4.3: Reduce dead time so that the power devices of the upper and lower bridge arms can operate in the non-saturation region.

[0017] The active discharge method for the high-voltage bus of the fuel cell system provided by this invention also has the following feature: the reduced gate drive voltage V drv as follows:

[0018]

[0019] Wherein, the V plt V is the Miller plateau voltage. s I is the instantaneous voltage across the power device. s Q is the instantaneous value of the current flowing through the power device. gd Q is the gate-drain charge. gs R is the gate-source charge. g f is the gate resistance. sw Q is the switching frequency. total This represents the decrease in gate voltage and the total energy of the bus.

[0020] The active discharge method for high-voltage bus of fuel cell system provided by the present invention also has the following feature: in step S4.2, the switching frequency is increased to no more than three times the switching frequency when not in discharge mode.

[0021] The active discharge method for the high-voltage bus of the fuel cell system provided by this invention also has the following feature: in S4.3, the dead time Td2:

[0022] Td2=(0.5-0.8)tdead

[0023] Wherein, the t dead Dead time is caused by the switching characteristics of power devices.

[0024] Another object of the present invention is to provide an active discharge system for a high-voltage bus of a fuel cell system, the system being used to implement the above-described discharge method.

[0025] The high-voltage bus active discharge system for fuel cell systems provided by this invention also has the following features: the system includes an on-board power supply, a voltage-adjustable power chip, an isolated drive power supply, a drive chip, a power device, and a main control chip connected in sequence. The main control chip is used to provide drive voltage commands to the voltage-adjustable power chip and drive signal commands to the drive chip.

[0026] The beneficial effects of this invention are:

[0027] The active discharge method for high-voltage bus of fuel cell system provided by this invention adopts open-loop control and does not involve complex control algorithms. By changing the working mode of air compressor controller, the switching loss and conduction loss of controller power semiconductor device, as well as power line loss, are increased to achieve the purpose of consuming electrical energy. The release of electrical energy of high-voltage components can be realized without adding an additional discharge circuit. Attached Figure Description

[0028] Figure 1 A flowchart of the active discharge method provided by the present invention;

[0029] Figure 2 This is a power supply structure diagram of the discharge system provided in an embodiment of the present invention;

[0030] Figure 3 This is a diagram showing the relationship between the drive signal command and the gate voltage after adjusting the gate voltage in the active discharge method provided in this embodiment of the invention.

[0031] Figure 4 This is a diagram showing the gate voltage setting in the active discharge method provided in this embodiment of the invention.

[0032] Figure 5 This is a diagram showing the relationship between the drive signal command and the gate voltage for adjusting the dead time when entering active discharge mode, as provided in an embodiment of the present invention.

[0033] Figure 6 This is a diagram showing the relationship between the drive signal command and the gate voltage for adjusting the dead time in the prior art.

[0034] Figure 7 This is a circuit diagram of a fuel high-pressure component in the prior art. Detailed Implementation

[0035] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0036] Traditional DC-DC active discharge involves closing K3 to connect the discharge resistor, which takes up cost and space.

[0037] The active discharge technology of the main drive system can realize the discharge of the main drive system. However, when the system is stopped, K2 is disconnected, and the DC side cannot be discharged. Moreover, it only uses normal switching losses, so the discharge capacity is limited and cannot meet the national standard requirement of reducing the bus voltage to below 60V within 3 seconds.

[0038] The power devices generate the following losses during operation:

[0039]

[0040] Among them, P loss Total power device losses, V s Instantaneous voltage value across the power device, I s The instantaneous value of the current flowing through the power device, R g Gate resistance, V drv Gate drive voltage, V plt Miller plateau voltage, Qgd gate-drain charge, Qgs gate-source charge, Rds(on) power device on-resistance, fsw switching frequency.

[0041] According to the above formula, it can be seen that the switching loss decreases with the increase of the gate drive voltage, increases with the increase of the switching frequency, and increases with the increase of the current.

[0042] Based on the above principles, embodiments of the present invention provide a method for active discharge of the high-voltage bus in a fuel cell system, such as... Figure 1 As shown, after the system shuts down, the fuel cell all-in-one system enters active discharge mode. The entire process is controlled by the operating software of the main control chip of the all-in-one controller. This method includes the following steps:

[0043] S1: The air compressor controller receives the active discharge command sent by the fuel cell system controller;

[0044] S2: Detects the status of input / output contactors;

[0045] S3: Determine whether the active discharge conditions are met. If they are met, proceed to the next step. If they are not met, disconnect the contactor and return to S2.

[0046] S4: Enter active discharge mode and generate a switching action command with increased loss;

[0047] S5: The power device executes the switching action command generated by S4;

[0048] S6: Determine if the voltage of the high-voltage bus meets the requirements. If it does, end the discharge; otherwise, return to S5. Meeting the requirements means the voltage is below 60V.

[0049] In some embodiments, entering the active discharge mode in S4 also includes disabling the air compressor controller's bus voltage undervoltage protection, drive board short circuit protection, and gate undervoltage protection.

[0050] In some embodiments, the switch action command includes the following steps:

[0051] S4.1: Reduce gate drive voltage;

[0052] S4.2: Increase switching frequency;

[0053] S4.3: Reduce dead time so that the power devices of the upper and lower bridge arms can operate in the non-saturation region.

[0054] In some embodiments, when the software running on the main control chip receives a message that the controller has entered active discharge mode, the main control chip sends a power supply voltage command to the voltage-adjustable power supply chip via communication. The output voltage of the power supply chip decreases, the output voltage of the isolation power supply decreases accordingly, and the voltage supplied to the driver chip also decreases.

[0055] The total energy stored on the high-voltage bus after the fuel cell system shuts down:

[0056] Q total =Q1+Q2+Q3

[0057] Q1 represents the charge of the low-voltage side capacitor, Q2 represents the charge of the high-voltage side capacitor, and Q3 represents the charge of the DC side capacitor controlling the air compressor.

[0058] The switching losses generated in the power circuit of the power device during operation are as follows:

[0059]

[0060] Among them, P sw-loss This represents the total power device losses, and active discharge requires consuming all the energy Q stored in the DC fuel cell system bus within 3 seconds. total Q must be satisfied total <3×P loss ,Right now

[0061]

[0062] The above formula shows that the decrease in gate voltage is related to the total bus energy Q. total Negative correlation, meaning the larger the total charge, the lower the gate voltage needs to be set. V drv The settings are based on the parameters of the power devices and the system charge, but must be greater than the Miller plateau voltage V. plt .like Figure 3-4 As shown, U1 is the gate voltage value during normal operation, and U2 is the gate voltage value during active discharge mode. Therefore, the reduced gate drive voltage V drv as follows:

[0063]

[0064] Wherein, the V plt V is the Miller plateau voltage. s I is the instantaneous voltage across the power device. s Q is the instantaneous value of the current flowing through the power device. gd Q is the gate-drain charge. gs R is the gate-source charge. g f is the gate resistance. sw Q is the switching frequency. total This represents the decrease in gate voltage and the total energy of the bus. Additionally, as the gate voltage decreases, the on-resistance R of the power device also decreases. ds(on) This will also increase, leading to increased conduction losses and faster energy consumption.

[0065] In some embodiments, the switching frequency can be set according to the load capacity of the hardware circuit. Power consumption of the power device's drive circuit:

[0066] P drv =Q g V drv f sw

[0067] Low-voltage power supplies are generally designed with a capacity of 2 to 3 times the rated load power consumption. Therefore, as shown in the above formula, the switching frequency in active discharge mode cannot exceed 3 times the switching frequency when not in discharge mode, ensuring it does not exceed the design capacity of the power supply circuit. Otherwise, it will cause the drive power supply to overload and be damaged. In addition, the maximum output switching frequency is limited by the PWM output capability of the main control chip and the switching capability of the power devices.

[0068] In some embodiments, the switching frequency is increased by 2 times.

[0069] In controller design, to prevent bridge arm shoot-through during normal operation, a dead time is added to the drive signal commands of the power devices. This dead time is typically longer than the dead time caused by the switching characteristics of the power devices. The dead time caused by the switching characteristics of the power devices is t. dead =t off -t don , where t off t is the power device turn-off delay time. don The turn-on delay time for the power device is specified. Therefore, the dead time Td1 of the drive signal command must be greater than t. dead This ensures that the bridge arm will not be straight through. For example... Figure 6-7 As shown.

[0070] In some embodiments, 3. The drive signal command generated in the main control chip will reduce the dead time from Td1 in the normal operating state to Td2, causing the drive signals of the power devices in the upper and lower bridge arms to overlap, resulting in bridge arm shoot-through. The dead time caused by the switching characteristics of the power devices is t. dead =t off -t don This can generally be obtained through a double-pulse test. To ensure the safe operation of the controller, Td1 is usually t dead 1.2 to 1.5 times (depending on the switching characteristics of the power device). To induce bridge arm shoot-through, Td2 should be less than Td1, but the selection of Td2 should not exceed the maximum short-circuit withstand time of the device. According to the double-pulse test calibration, Td2 = (0.5-0.8)t dead Thus, the gate signals of the two power devices in the upper and lower bridge arms will overlap. This invention utilizes this overlap to generate a short-time short circuit, thereby increasing the current I flowing through the power devices. s This will increase rapidly. Therefore, the switching losses of power devices will increase significantly, thereby increasing the discharge capability through the power devices, such as... Figure 5 As shown.

[0071] In some embodiments, such as Figure 2 As shown, a high-voltage bus active discharge system for a fuel cell system is provided. The system includes an on-board power supply, a voltage-adjustable power chip, an isolated drive power supply, a drive chip, a power device, and a main control chip connected in sequence. The main control chip is used to provide drive voltage commands to the voltage-adjustable power chip and drive signal commands to the drive chip.

[0072] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the protection scope of the present invention.

Claims

1. A method for active discharge of a high-voltage bus in a fuel cell system, characterized in that, The method includes the following steps: S1: The air compressor controller receives the active discharge command sent by the fuel cell system controller; S2: Detects the status of input / output contactors; S3: Determine whether the active discharge conditions are met. If they are met, proceed to the next step. If they are not met, disconnect the contactor and return to S2. S4: Enter active discharge mode and generate a switching action command with increased loss; S5: The power device executes the switching action command generated by S4; S6: Determine whether the voltage of the high-voltage bus meets the requirements. If it does, end the discharge. If it does not, return to S5. The switching action command includes reducing the gate drive voltage; the reduced gate drive voltage V drv as follows: Wherein, the V plt V is the Miller plateau voltage. s I is the instantaneous voltage across the power device. s Q is the instantaneous value of the current flowing through the power device. gd Q is the gate-drain charge. gs R is the gate-source charge. g f is the gate resistance. sw Q is the switching frequency. total The total energy of the busbar is the sum of the electrical quantities of the high-voltage side capacitor, the low-voltage side capacitor, and the DC-side capacitor controlling the air compressor.

2. The active discharge method for the high-voltage bus of a fuel cell system according to claim 1, characterized in that, Entering the active discharge mode in S4 also includes disabling the air compressor controller's undervoltage protection for the bus voltage, short-circuit protection for the drive board, and undervoltage protection for the gate.

3. The active discharge method for the high-voltage bus of a fuel cell system according to claim 1, characterized in that, The switch action command includes the following steps: S4.1: Reduce gate drive voltage; S4.2: Increase switching frequency; S4.3: Reduce dead time so that the power devices of the upper and lower bridge arms can operate in the non-saturation region.

4. The active discharge method for the high-voltage bus of a fuel cell system according to claim 3, characterized in that, In S4.2, increasing the switching frequency means increasing the switching frequency to no more than three times the switching frequency when not in the discharge mode.

5. The active discharge method for the high-voltage bus of a fuel cell system according to claim 3, characterized in that, In S4.3, the dead time Td2 is: Td2=(0.5-0.8)t dead Wherein, the t dead Dead time is caused by the switching characteristics of power devices.

6. A high-voltage bus active discharge system for a fuel cell system, characterized in that, The system is used to implement the discharge method as described in any one of claims 1-5.

7. The active discharge system for the high-voltage bus of the fuel cell system according to claim 6, characterized in that, The system includes an on-board power supply, a voltage-adjustable power chip, an isolated drive power supply, a drive chip and power devices, and a main control chip connected in sequence. The main control chip is used to provide drive voltage commands to the voltage-adjustable power chip and drive signal commands to the drive chip.

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