An automatic discharge circuit for an on-board high-voltage DC bus capacitor with power-on self-locking function

Abstract

The application discloses an on-board high-voltage DC bus capacitor automatic discharge circuit with a power-on self-locking function, comprising an anti-backflow isolation unit, an auxiliary power supply voltage stabilizing and bus synchronous sampling unit, a comparator power supply filtering unit, a differential RC time sequence self-locking sampling unit, a comparator discrimination unit, a SiC-MOS gate drive unit and a high-voltage residual voltage discharge main circuit. The application utilizes two voltage division networks to match filter capacitors with different capacitance values, and realizes power-on self-locking through pure hardware by means of charge and discharge rate difference; during the power-off stage, C5 fast discharge makes A voltage lower than B, and the comparator flips to drive the SiC-MOS to conduct and discharge the bus residual voltage. The application adopts a single-comparator topology, is completely separated from the prior art of a double-capacitor triode time sequence scheme, and has the advantages of absolute safety during power-on, zero standby power consumption, adjustable under-voltage threshold and pure hardware high reliability.

Description

Technical Field

[0001] This invention relates to the field of airborne high-power high-voltage DC power electronics technology, specifically an airborne high-voltage DC bus capacitor automatic discharge circuit with power-on self-locking function. Background Technology

[0002] In high-power high-voltage DC power supply systems, large-capacity filter or energy storage capacitors are typically installed on the bus to smooth bus voltage fluctuations and provide instantaneous power support. Typical capacitance values ​​range from hundreds to thousands of microfarads. In applications such as airborne aircraft, eVTOL (electric vertical takeoff and landing) aircraft, and new energy vehicles, power-consuming units typically operate with frequent power-on and power-off cycles. When the power system is powered off, if the time interval between power-on and power-off is short, the charge stored in the bus capacitor cannot be completely released through the downstream load, leaving a high voltage residue across the bus capacitor. When the system is powered on again, this residual voltage will superimpose with the input voltage, potentially causing multiple serious hazards: downstream power semiconductor devices such as SiC-MOSFETs and IGBTs will be subjected to overvoltage stress and break down; the power supply startup sequence will be disrupted, leading to abnormal operation of the control chip; furthermore, if maintenance personnel touch the circuit while the residual voltage is not completely discharged, there is a risk of electric shock. Therefore, how to achieve safe, reliable, and efficient discharge of residual voltage from the bus capacitor has become a critical technical problem that urgently needs to be solved in the design of high-voltage DC power supply systems.

[0003] Currently, existing bus capacitor discharge solutions in the industry mainly fall into the following categories. The first category is a fixed resistor parallel discharge solution, where a fixed resistor is connected in parallel across the bus capacitor, continuously consuming the energy stored in the capacitor. This solution is simple in structure, but its drawbacks are also significant: the resistor continuously consumes energy during normal power-on, leading to a substantial increase in the system's static power consumption. Furthermore, the resistor is at risk of overheating and burning out under prolonged high voltage. The second category is an active discharge solution based on an MCU or processor. This solution uses a microcontroller to sample the bus voltage and controls the power switch to conduct upon detecting a power failure, thus achieving discharge. This solution offers high flexibility, but the MCU itself requires an auxiliary power supply, which may fail due to power instability during a high-voltage bus power failure. Additionally, the MCU software is prone to crashes or freezes, making it difficult to meet safety requirements in high-reliability applications such as aviation. Moreover, the introduction of the MCU solution increases system complexity and overall cost. The third type is a pure hardware discharge scheme based on optocouplers or transistors. While this scheme avoids the risk of single-point failure of the MCU, its detection logic is based on the presence or absence of auxiliary power supply rather than directly detecting the bus voltage itself. This results in the discharge trigger threshold being greatly affected by the characteristics of the auxiliary power supply, and the circuit structure is complex with a large number of components. The fourth type is a scheme based on single-point voltage comparison, which controls the discharge switch by comparing the bus voltage with a fixed reference voltage. Although this type of scheme has a relatively simple circuit, the bus voltage gradually rises from 0V during the power-on phase, inevitably passing through the discharge threshold point, causing the discharge switch to be falsely triggered during power-on. At this time, the discharge resistor connected to the bus will form a short-circuit load on the input power supply, which may cause the system to fail to power on normally, or even burn out the discharge resistor and power switch. Summary of the Invention

[0004] The purpose of this invention is to provide an airborne high-voltage DC bus capacitor automatic discharge circuit with power-on self-locking function, including an anti-backflow isolation unit, an auxiliary voltage regulation and bus synchronous sampling unit, a comparator power supply filtering unit, a differential RC timing self-locking sampling unit, a comparator U2, a SiC-MOS gate driving unit, a power switch and a discharge unit;

[0005] The backflow prevention isolation unit is used to block high-voltage backflow into the busbar.

[0006] The auxiliary voltage regulator and bus synchronous sampling unit outputs a driving voltage to power capacitor C1 of the comparator power supply filter unit, capacitor C3 and capacitor C5 of the differential RC timing self-locking sampling unit.

[0007] The comparator power supply and filtering unit supplies power to comparator U2 and filters the voltage.

[0008] When the airborne power supply V1 is disconnected, the differential RC timing self-locking sampling unit causes the comparator U2 to output a high level, which in turn enables the SiC-MOS gate drive unit to drive the power switch and discharge unit to conduct.

[0009] Furthermore, the backflow prevention isolation unit is a diode D2;

[0010] The anode of D2 is connected to the airborne input power supply V1, and the cathode is connected to the bus VIN node and the bus energy storage capacitor C2.

[0011] Furthermore, the auxiliary voltage regulator and bus synchronous sampling unit includes a voltage divider resistor R21, a voltage divider resistor R22, and a Zener diode D6;

[0012] One end of the voltage divider resistor R21 is connected to the bus VIN, and the other end is connected in series with R22 to ground.

[0013] Zener diode D6 is connected in parallel across R22 to form the VCC voltage regulation branch.

[0014] Furthermore, the comparator power supply filtering unit includes an isolation diode D1, an energy storage capacitor C1, and a filter capacitor C4;

[0015] The anode of the isolation diode D1 is connected to the VCC voltage regulator branch, and the cathode is connected to the power supply terminal of the comparator U2 after being connected in series with C1. The filter capacitor C4 is connected in parallel to the VCC voltage regulator branch.

[0016] Furthermore, the differential RC timing self-locking sampling unit includes an inverting sampling network A and a non-inverting sampling network B;

[0017] The inverting sampling network A includes resistor R15, resistor R17, and filter capacitor C5;

[0018] The resistors R15 and R17 are connected in series to divide the voltage, and then connected in parallel to filter capacitor C5, which is then connected to the inverting input of comparator U2.

[0019] The in-phase sampling network B includes resistors R1 and R2 and a filter capacitor C3;

[0020] The resistors R1 and R2 are connected in series to divide the voltage, and then connected in parallel to filter capacitor C3, which is connected to the non-inverting input of comparator U2.

[0021] Furthermore, the total resistance of resistors R15 and R17 is half the total resistance of resistors R1 and R2;

[0022] The capacitance of capacitor C5 is much smaller than that of capacitor C3.

[0023] Furthermore, when the airborne power supply V1 is powered on in steady state, the charging speed of capacitor C5 is greater than that of capacitor C3, the voltage of the inverting sampling network A is greater than that of the non-inverting sampling network B, and the comparator outputs a low level to lock M1 off.

[0024] When the airborne power supply V1 is powered off, capacitor C5 discharges rapidly, causing the voltage of the inverting sampling network A to be lower than the voltage of the non-inverting sampling network B. The comparator outputs a high level, driving M1 to conduct.

[0025] Furthermore, the SiC-MOS gate drive unit includes a pull-up resistor R19 and a gate current limiting resistor R3;

[0026] The output of comparator U2 is pulled up to the positive power supply via pull-up resistor R19, and the output is connected in series with gate current limiting resistor R3 to the gate of power switch and discharge unit SiC-MOS M1.

[0027] Furthermore, the power switch and discharge unit includes a SiC-MOSFET M1, a discharge resistor R5, a gate-source decoupling capacitor C6, and a gate-source bleeder resistor R20;

[0028] The decoupling capacitor C6 and the leakage resistor R20 are connected in parallel between the gate and source of the SiC-MOSM1.

[0029] The drain of the SiC-MOSFET M1 is connected to the output terminal OUT, and the source is connected to one end of the discharge resistor R5; the other end of the discharge resistor R5 is grounded.

[0030] An automatic discharge control method for airborne high-voltage DC bus capacitors based on the aforementioned circuit includes the following steps:

[0031] S1, the airborne power supply V1 is powered on, and the auxiliary voltage regulator and bus synchronous sampling unit charges capacitors C1, C3 and C5 respectively.

[0032] When the comparator outputs a low level, the SiC-MOS remains off, the discharge branch is hardware-locked, and there is zero static power consumption.

[0033] S2, input V1 is disconnected, load B1 consumes bus energy, and the drive voltage output of the auxiliary voltage regulator and bus synchronous sampling unit decreases synchronously; capacitor C5 discharges rapidly, making the voltage of the inverting sampling network A less than the voltage of the non-inverting sampling network B;

[0034] When comparator U2 flips to output a high level, the driving voltage is sent to the gate of SiC-MOS M1 through capacitor R3, and SiC-MOS M1 is saturated and turned on.

[0035] S3, the high voltage stored in the bus capacitor C2 is quickly discharged to ground through SiC-MOS M1 and power resistor R5 until the bus voltage drops to a safe value;

[0036] S4: After the residual voltage is completely released, power is applied again to re-establish the self-locking voltage difference where the voltage of the inverting sampling network A is greater than the voltage of the non-inverting sampling network B, and the system starts safely.

[0037] The technical effects of this invention are as follows:

[0038] The high-voltage bus capacitor automatic discharge circuit proposed in this invention has achieved significant technical effects in terms of functional reliability, engineering practicality, and system safety.

[0039] This invention implements a self-locking function during the power-on phase, eliminating the risk of false triggering. By introducing a dual RC timing differential mechanism, utilizing the difference in the rise rates of the two key node voltages VA and VB during power-on, it ensures that the comparator always outputs a low level throughout the entire power-on process, keeping the discharge switch reliably off. This power-on self-locking mechanism is one of the core innovations of this invention. It effectively overcomes the problem of false triggering and short circuits caused by the bus voltage crossing the threshold point during power-on in traditional single-point voltage comparison schemes, ensuring a smooth start-up of the system every time it is powered on.

[0040] This invention employs a pure hardware architecture, resulting in extremely high reliability. The entire discharge control logic is built entirely from analog circuits, requiring no MCU, software code, or complex digital logic. Compared to MCU solutions, which may experience failure modes such as software malfunction, clock drift, and power supply failure in harsh environments like high and low temperatures, strong vibrations, and strong electromagnetic interference, this invention's pure hardware solution possesses inherent anti-interference capabilities and failure safety, making it particularly suitable for aviation, aerospace, and high-reliability automotive-grade applications.

[0041] This invention, through the rational configuration of external voltage divider resistors and the selection of the Zener diode's voltage regulation value, can precisely set the bus voltage threshold for discharge initiation. This threshold can be directly correlated with the undervoltage protection characteristics of the downstream load, ensuring that the discharge circuit only initiates discharge when the bus voltage drops to a range where the load cannot operate normally. This avoids malfunctions under normal load conditions and achieves intelligent matching between the discharge logic and the system operating conditions.

[0042] This invention features extremely low static power consumption. During normal system power-on operation, the main discharge circuit is completely disconnected, eliminating the continuous current path. Only the voltage divider network and Zener diodes generate a tiny microamp-level static current, which has a negligible impact on the overall system efficiency. This characteristic is particularly important for airborne and vehicle-mounted high-voltage power supply systems with limited thermal design margins, significantly reducing the heat dissipation burden.

[0043] This invention is perfectly compatible with high-voltage SiC devices. By providing a stable low-voltage power supply to the comparator through a Zener diode, it simultaneously provides a gate drive voltage of approximately 18V to the SiC-MOSFET, enabling direct driving of 1200V-level SiC-MOSFETs and meeting the application requirements of 450V to 700V high-voltage DC buses. This allows for seamless integration with silicon carbide power modules rapidly being adopted in the current aerospace and new energy vehicle sectors, forming a complete system-level high-voltage safety protection solution.

[0044] The circuit structure of this invention is simple. All functions can be achieved with only one comparator, one SiC-MOSFET, and a small number of resistors and capacitors. The number of components is far less than that of existing optocouplers or multi-stage transistor solutions, which not only reduces material costs and PCB area, but also improves production yield and long-term operational reliability. Attached Figure Description

[0045] Figure 1 This is a circuit diagram of an automatic discharge circuit for an airborne high-voltage DC bus capacitor based on dual-capacitor energy storage timing control.

[0046] Figure 2 This is a waveform diagram for the working simulation. Detailed Implementation

[0047] The present invention will be further described below with reference to embodiments, but it should not be construed that the scope of the present invention is limited to the following embodiments. Various substitutions and modifications made based on ordinary technical knowledge and common practices in the art without departing from the above-described technical concept of the present invention should be included within the scope of protection of the present invention.

[0048] Example 1:

[0049] An airborne high-voltage DC bus capacitor automatic discharge circuit with power-on self-locking function includes an anti-backflow isolation unit, an auxiliary voltage regulation and bus synchronous sampling unit, a comparator power supply filter unit, a differential RC timing self-locking sampling unit, a comparator U2, a SiC-MOS gate drive unit, a power switch and a discharge unit.

[0050] The backflow prevention isolation unit is used to block high-voltage backflow into the busbar.

[0051] The auxiliary voltage regulator and bus synchronous sampling unit outputs a driving voltage to power capacitor C1 of the comparator power supply filter unit, capacitor C3 and capacitor C5 of the differential RC timing self-locking sampling unit.

[0052] The comparator power supply and filtering unit supplies power to comparator U2 and filters the voltage.

[0053] When the airborne power supply V1 is disconnected, the differential RC timing self-locking sampling unit causes the comparator U2 to output a high level, which in turn enables the SiC-MOS gate drive unit to drive the power switch and discharge unit to conduct.

[0054] Example 2:

[0055] An automatic discharge circuit for airborne high-voltage DC bus capacitor with power-on self-locking function, the technical content of which is the same as that of Embodiment 1, further wherein the anti-backflow isolation unit is a diode D2;

[0056] The anode of D2 is connected to the airborne input power supply V1, and the cathode is connected to the bus VIN node and the bus energy storage capacitor C2.

[0057] Example 3:

[0058] An airborne high-voltage DC bus capacitor automatic discharge circuit with power-on self-locking function, the technical content is the same as any one of embodiments 1-2, further, the auxiliary voltage stabilization and bus synchronous sampling unit includes voltage divider resistor R21, voltage divider resistor R22 and Zener diode D6;

[0059] One end of the voltage divider resistor R21 is connected to the bus VIN, and the other end is connected in series with R22 to ground.

[0060] Zener diode D6 is connected in parallel across R22 to form the VCC voltage regulation branch.

[0061] Voltage divider resistors R21 and R22 divide the bus voltage to obtain an auxiliary power supply, which is then used as the detection voltage.

[0062] Example 4:

[0063] An airborne high-voltage DC bus capacitor automatic discharge circuit with power-on self-locking function, the technical content is the same as any one of embodiments 1-3, further, the comparator power supply filter unit includes an isolation diode D1, an energy storage capacitor C1 and a filter capacitor C4;

[0064] The anode of the isolation diode D1 is connected to the VCC voltage regulator branch, and the cathode is connected to the power supply terminal of the comparator U2 after being connected in series with C1. The filter capacitor C4 is connected in parallel to the VCC voltage regulator branch.

[0065] Example 5:

[0066] An airborne high-voltage DC bus capacitor automatic discharge circuit with power-on self-locking function, the technical content of which is the same as any one of embodiments 1-4, further wherein the differential RC timing self-locking sampling unit includes an inverting sampling network A and a non-inverting sampling network B;

[0067] The inverting sampling network A includes resistor R15, resistor R17, and filter capacitor C5;

[0068] The resistors R15 and R17 are connected in series to divide the voltage, and then connected in parallel to filter capacitor C5, which is then connected to the inverting input of comparator U2.

[0069] The in-phase sampling network B includes resistors R1 and R2 and a filter capacitor C3;

[0070] The resistors R1 and R2 are connected in series to divide the voltage, and then connected in parallel to filter capacitor C3, which is connected to the non-inverting input of comparator U2.

[0071] Example 6:

[0072] An automatic discharge circuit for airborne high voltage DC bus capacitor with power-on self-locking function, the technical content is the same as any one of embodiments 1-5, further wherein the total resistance of resistors R15 and R17 is 1 / 2 of the total resistance of resistors R1 and R2.

[0073] The capacitance of capacitor C5 is much smaller than that of capacitor C3.

[0074] Example 7:

[0075] An automatic discharge circuit for airborne high-voltage DC bus capacitors with power-on self-locking function, the technical content of which is the same as any one of embodiments 1-6, further wherein when the airborne power supply V1 is powered on in a steady state, the charging speed of capacitor C5 is greater than that of capacitor C3, the voltage of the inverting sampling network A is greater than that of the non-inverting sampling network B, and the comparator outputs a low level to lock M1 off.

[0076] When the airborne power supply V1 is powered off, capacitor C5 discharges rapidly, causing the voltage of the inverting sampling network A to be lower than the voltage of the non-inverting sampling network B. The comparator outputs a high level, driving M1 to conduct.

[0077] Example 8:

[0078] An airborne high-voltage DC bus capacitor automatic discharge circuit with power-on self-locking function, the technical content is the same as any one of embodiments 1-7, further, the SiC-MOS gate drive unit includes pull-up resistor R19 and gate current limiting resistor R3;

[0079] The output of comparator U2 is pulled up to the positive power supply via pull-up resistor R19, and the output is connected in series with gate current limiting resistor R3 to the gate of power switch and discharge unit SiC-MOS M1.

[0080] Example 9:

[0081] An automatic discharge circuit for airborne high voltage DC bus capacitor with power-on self-locking function, the technical content is the same as any one of embodiments 1-8, further, the power switch and discharge unit includes SiC-MOSFET M1, discharge resistor R5, gate-source decoupling capacitor C6 and gate-source discharge resistor R20.

[0082] The decoupling capacitor C6 and the leakage resistor R20 are connected in parallel between the gate and source of the SiC-MOSM1.

[0083] The drain of the SiC-MOSFET M1 is connected to the output terminal OUT, and the source is connected to one end of the discharge resistor R5; the other end of the discharge resistor R5 is grounded.

[0084] Example 10:

[0085] An automatic discharge control method for airborne high-voltage DC bus capacitors based on the circuit described in any one of Embodiments 1-9 includes the following steps:

[0086] S1, the airborne power supply V1 is powered on, and the auxiliary voltage regulator and bus synchronous sampling unit charges capacitors C1, C3 and C5 respectively.

[0087] When the comparator outputs a low level, the SiC-MOS remains off, the discharge branch is hardware-locked, and there is zero static power consumption.

[0088] S2, input V1 is disconnected, load B1 consumes bus energy, and the drive voltage output of the auxiliary voltage regulator and bus synchronous sampling unit decreases synchronously; capacitor C5 discharges rapidly, making the voltage of the inverting sampling network A less than the voltage of the non-inverting sampling network B;

[0089] When comparator U2 flips to output a high level, the driving voltage is sent to the gate of SiC-MOS M1 through capacitor R3, and SiC-MOS M1 is saturated and turned on.

[0090] S3, the high voltage stored in the bus capacitor C2 is quickly discharged to ground through SiC-MOS M1 and power resistor R5 until the bus voltage drops to a safe value;

[0091] S4: After the residual voltage is completely released, power is applied again to re-establish the self-locking voltage difference where the voltage of the inverting sampling network A is greater than the voltage of the non-inverting sampling network B, and the system starts safely.

[0092] Example 11:

[0093] An automatic discharge circuit for airborne high-voltage DC bus capacitors with power-on self-locking function includes:

[0094] The backflow prevention isolation unit includes a first diode D2. The anode of the first diode is connected to an external high-voltage DC power supply V1, and the cathode is connected to the positive terminal of the bus capacitor C2 and the output terminal OUT, in order to prevent current backflow.

[0095] The auxiliary power supply voltage regulation and bus voltage monitoring unit includes a first voltage divider resistor R21, a second voltage divider resistor R22, and a Zener diode D6. The first and second voltage divider resistors are connected in series between the positive terminal of the bus capacitor and ground. The Zener diode is connected in parallel across the second voltage divider resistor. The connection node of the first and second voltage divider resistors forms a VCC network, which serves as the auxiliary power supply output and bus voltage monitoring signal.

[0096] The comparator power supply unit includes a second diode D1 and a first energy storage capacitor C1. The anode of the second diode is connected to the VCC network, the cathode is connected to the positive terminal of the first energy storage capacitor, the negative terminal of the first energy storage capacitor is grounded, and the positive terminal of the first energy storage capacitor serves as the power supply positive terminal of the comparator U2.

[0097] The first RC voltage divider filter network includes a third voltage divider resistor R15, a fourth voltage divider resistor R17, and a second filter capacitor C5. The third and fourth voltage divider resistors are connected in series between the VCC network and ground. The second filter capacitor is connected in parallel across the fourth voltage divider resistor. The connection node of the third and fourth voltage divider resistors forms a network A, which is connected to the inverting input terminal of the comparator.

[0098] The second RC voltage divider filter network includes a fifth voltage divider resistor R1, a sixth voltage divider resistor R2, and a third filter capacitor C3. The fifth and sixth voltage divider resistors are connected in series between the VCC network and ground. The third filter capacitor is connected in parallel across the sixth voltage divider resistor. The connection node of the fifth and sixth voltage divider resistors forms a B network, which is connected to the non-inverting input of the comparator.

[0099] Wherein, the time constant τA of the first RC voltage divider filter network is much smaller than the time constant τB of the second RC voltage divider filter network, that is, C5·(R15 / / R17) << C3·(R1 / / R2), and the steady-state voltage divider value of the A network is slightly higher than the steady-state voltage divider value of the B network, with a difference of 0.3V~0.5V;

[0100] The comparator output and drive unit includes a pull-up resistor R19 and a gate drive resistor R3. The pull-up resistor is connected between the positive power supply terminal of the comparator and the output terminal of the comparator, and one end of the gate drive resistor is connected to the output terminal of the comparator.

[0101] A power switch and discharge unit includes a SiC-MOSFET M1, a discharge resistor R5, a gate-source decoupling capacitor C6, and a gate-source bleeder resistor R20. The gate of the SiC-MOSFET is connected to the other end of the gate drive resistor. The gate-source decoupling capacitor and the gate-source bleeder resistor are connected in parallel between the gate and source of the SiC-MOSFET. The drain of the SiC-MOSFET is connected to the output terminal OUT, and the source is connected to one end of the discharge resistor. The other end of the discharge resistor is grounded.

[0102] The Zener diode D6 has a Zener voltage of not less than 18V to ensure that the SiC-MOSFET receives a sufficient gate drive voltage.

[0103] The resistance values ​​of the first voltage divider resistor R21 and the second voltage divider resistor R22 are configured such that when the bus voltage drops to 300V, the voltage of the VCC network is approximately 18V.

[0104] The total resistance of the third voltage divider resistor R15 and the fourth voltage divider resistor R17 is half the total resistance of the fifth voltage divider resistor R1 and the sixth voltage divider resistor R2.

[0105] The capacitance of the second filter capacitor C5 is much smaller than that of the third filter capacitor C3.

[0106] The first filter capacitor C4 has a capacitance of 100nF, and the first energy storage capacitor C1 has a capacitance of 4.7μF.

[0107] The working principle of this invention is as follows:

[0108] Power-on self-locking stage: When the external high-voltage DC power supply is connected, the bus voltage rises from 0V. The VCC network is established after voltage division by R21 and R22 and voltage regulation by D6. Since the time constant τA of the first RC voltage divider filter network is much smaller than the time constant τB of the second RC voltage divider filter network, the voltage rise rate of network A is significantly faster than that of network B. At the same time, the steady-state voltage division value of network A is slightly higher than that of network B. Therefore, during the power-on process, VA is always greater than VB, the comparator outputs a low level, the SiC-MOSFET remains in the off state, the discharge circuit is not connected, realizing the power-on self-locking function and ensuring normal system power-on.

[0109] During normal operation: The bus voltage stabilizes within the range of 450V~700V. The VCC network stabilizes at the clamping voltage of the Zener diode. Both networks A and B reach their respective steady-state voltage division values, VA > VB, the comparator continuously outputs a low level, the SiC-MOSFET is turned off, the discharge circuit is disconnected, and the system has no additional static power consumption.

[0110] Power-down trigger phase: When the external power supply is disconnected, the bus voltage begins to drop. Due to the presence of the downstream load simulated by B1, the bus voltage is first consumed by the load to approximately 300V, the undervoltage point of the downstream stage. When the bus voltage drops below 300V, the downstream load stops working, and residual charge begins to remain in the bus capacitor C2. At this time, the VCC network voltage drops synchronously with the bus voltage. Since τA << τB, the voltage drop rate of network A is much faster than that of network B. When VA drops below VB, the comparator output flips to a high level, pulling up through R19 and driving through R3, turning on the SiC-MOSFET. The bus capacitor C2 forms a discharge circuit through R5 and M1, and the residual voltage is quickly released.

[0111] Discharge completion stage: As the bus capacitor voltage continues to decrease, the VCC network voltage eventually drops below the comparator's minimum operating voltage, causing the comparator to stop working and the output to become uncertain. However, due to the decoupling effect of C6 and the bleedering effect of R20, the gate voltage of the SiC-MOSFET is reliably pulled down, ensuring that the MOSFET is eventually turned off and avoiding false turn-on.

[0112] Example 12:

[0113] An automatic discharge circuit for airborne high-voltage DC bus capacitors with power-on self-locking function is described below:

[0114] 1. Component selection and parameter design

[0115] This embodiment is applied to a 540V airborne high-voltage DC system, with the undervoltage discharge threshold set to 300V and the main switch selected as a 1200V SiC-MOS.

[0116] The devices are shown in Table 1, including:

[0117] Main discharge switch M1: Self-developed 1200V N-type SiC-MOS, with a standard gate drive voltage of 18V, low on-resistance, and able to withstand instantaneous large discharge current.

[0118] Auxiliary power supply: R21=150kΩ, R22=15kΩ, D6=18V / 1W. When VIN=300V, VCC≈18V, which meets the SiC-MOS drive requirements.

[0119] Differential RC network: Network A: R15 = 100kΩ, R17 = 100kΩ, C5 = 100nF; Network B: R1 = 200kΩ, R2 = 200kΩ, C3 = 4.7μF. The following conditions are met: R15 + R17 = (R1 + R2) / 2, C5 ≪ C3. In steady-state power-up, A is approximately 0.4V higher than B.

[0120] Comparator U2: Aerospace-grade rail-to-rail comparator, operating temperature -55℃~+125℃.

[0121] Power discharge resistor R5: 10Ω / 20W cement resistor, suitable for instantaneous power discharge of busbars.

[0122] Table 1: Circuit Components

[0123] label name label name V1 Onboard input power D2 Anti-backflow fast recovery diode R21, R22 Voltage divider resistor D6 18V Zener diode R15, R17 A network voltage divider resistor C5 A network fast filter capacitor R1, R2 B network voltage divider resistor C3 B network slow filter capacitor U2 Wide-temperature voltage comparator R19 Output pull-up resistor R3 Gate drive resistor R20 Gate pull-down resistor C6 Gate decoupling capacitor M1 High-voltage SiC-MOS discharge switch R5 Power discharge resistor B1 Airborne equivalent load C2 Busbar high voltage energy storage capacitor D1, C1 Comparator power supply branch

[0124] 2. Detailed description of the work process

[0125] Normal power-on self-locking phase: Upon system power-on, the bus voltage rises from 0V. After VCC is established, the charging speed of C5100nF is much faster than that of C34.7μF. The voltage of network A rises rapidly and stabilizes at approximately 9.2V, while the voltage of network B lags behind and stabilizes at approximately 8.8V, VA > VB. The comparator outputs a low level, there is no drive voltage at the gate of M1, M1 is turned off, the discharge branch is completely disconnected, achieving power-on self-locking with zero static power consumption.

[0126] Undervoltage release self-locking stage: The input power supply is disconnected, load B1 consumes bus energy, VIN drops below 300V, and VCC drops synchronously. The small-capacity C5 rapidly releases its charge, and the potential of network A drops rapidly; the large-capacity C3 discharges slowly, and the voltage drop of network B lags behind, forming a voltage difference of B > A, and the self-locking is released.

[0127] Discharge drive and discharge stage: Comparator U2 flips to output a high level, and the 18V drive voltage is sent to the gate of M1 via R3, causing M1 to saturate and conduct. The high voltage stored in the bus capacitor C2 is rapidly discharged to ground via M1 and power resistor R5 until the bus voltage drops to the safe low voltage range.

[0128] Repeated power-on protection: After the residual voltage is completely released and power is applied again, the two RC networks re-establish the A>B self-locking voltage difference, and there is no residual voltage impact on the power module, so the system starts safely.

Claims

1. An automatic discharge circuit for airborne high-voltage DC bus capacitors with power-on self-locking function, characterized in that: It includes an anti-backflow isolation unit, an auxiliary voltage regulator and bus synchronous sampling unit, a comparator power supply filter unit, a differential RC timing self-locking sampling unit, a comparator U2, a SiC-MOS gate drive unit, a power switch and discharge unit; The backflow prevention isolation unit is used to block high-voltage backflow into the busbar. The auxiliary voltage regulator and bus synchronous sampling unit outputs a driving voltage to power capacitor C1 of the comparator power supply filter unit, capacitor C3 and capacitor C5 of the differential RC timing self-locking sampling unit. The comparator power supply and filtering unit supplies power to comparator U2 and filters the voltage. When the airborne power supply V1 is disconnected, the differential RC timing self-locking sampling unit causes the comparator U2 to output a high level, which in turn enables the SiC-MOS gate drive unit to drive the power switch and discharge unit to conduct.

2. The airborne high-voltage DC bus capacitor automatic discharge circuit with power-on self-locking function according to claim 1, characterized in that: The backflow prevention isolation unit is a diode D2; The anode of D2 is connected to the airborne input power supply V1, and the cathode is connected to the bus VIN node and the bus energy storage capacitor C2.

3. The automatic discharge circuit for airborne high-voltage DC bus capacitors with power-on self-locking function according to claim 1, characterized in that: The auxiliary voltage regulator and bus synchronous sampling unit includes voltage divider resistor R21, voltage divider resistor R22 and voltage regulator diode D6; One end of the voltage divider resistor R21 is connected to the bus VIN, and the other end is connected in series with R22 to ground. Zener diode D6 is connected in parallel across R22 to form the VCC voltage regulation branch.

4. The airborne high-voltage DC bus capacitor automatic discharge circuit with power-on self-locking function according to claim 3, characterized in that: The comparator power supply filter unit includes an isolation diode D1, an energy storage capacitor C1, and a filter capacitor C4. The anode of the isolation diode D1 is connected to the VCC voltage regulator branch, and the cathode is connected to the power supply terminal of the comparator U2 after being connected in series with C1. The filter capacitor C4 is connected in parallel to the VCC voltage regulator branch.

5. The airborne high-voltage DC bus capacitor automatic discharge circuit with power-on self-locking function according to claim 1, characterized in that: The differential RC timing self-locking sampling unit includes an inverting sampling network A and a non-inverting sampling network B; The inverting sampling network A includes resistor R15, resistor R17, and filter capacitor C5; The resistors R15 and R17 are connected in series to divide the voltage, and then connected in parallel to filter capacitor C5, which is then connected to the inverting input of comparator U2. The in-phase sampling network B includes resistors R1 and R2 and a filter capacitor C3; The resistors R1 and R2 are connected in series to divide the voltage, and then connected in parallel to filter capacitor C3, which is connected to the non-inverting input of comparator U2.

6. The airborne high-voltage DC bus capacitor automatic discharge circuit with power-on self-locking function according to claim 5, characterized in that: The total resistance of resistors R15 and R17 is half the total resistance of resistors R1 and R2. The capacitance of capacitor C5 is much smaller than that of capacitor C3.

7. The airborne high-voltage DC bus capacitor automatic discharge circuit with power-on self-locking function according to claim 5, characterized in that: When the airborne power supply V1 is powered on in steady state, the charging speed of capacitor C5 is greater than that of capacitor C3, the voltage of the inverting sampling network A is greater than that of the non-inverting sampling network B, and the comparator outputs a low level to lock M1 off. When the airborne power supply V1 is powered off, capacitor C5 discharges rapidly, causing the voltage of the inverting sampling network A to be lower than the voltage of the non-inverting sampling network B. The comparator outputs a high level, driving M1 to conduct.

8. The automatic discharge circuit for airborne high-voltage DC bus capacitors with power-on self-locking function according to claim 1, characterized in that: The SiC-MOS gate drive unit includes a pull-up resistor R19 and a gate current limiting resistor R3; The output of comparator U2 is pulled up to the positive power supply via pull-up resistor R19, and the output is connected in series with gate current limiting resistor R3 to the gate of power switch and discharge unit SiC-MOS M1.

9. The automatic discharge circuit for airborne high-voltage DC bus capacitors with power-on self-locking function according to claim 1, characterized in that: The power switch and discharge unit includes a SiC-MOSFET M1, a discharge resistor R5, a gate-source decoupling capacitor C6, and a gate-source bleeder resistor R20; The decoupling capacitor C6 and the leakage resistor R20 are connected in parallel between the gate and source of the SiC-MOSM1. The drain of the SiC-MOSFET M1 is connected to the output terminal OUT, and the source is connected to one end of the discharge resistor R5; the other end of the discharge resistor R5 is grounded.

10. A method for automatic discharge control of an airborne high-voltage DC bus capacitor based on the circuit described in any one of claims 1-9, characterized in that, Includes the following steps: S1, the airborne power supply V1 is powered on, and the auxiliary voltage regulator and bus synchronous sampling unit charges capacitors C1, C3 and C5 respectively. When the comparator outputs a low level, the SiC-MOS remains off, the discharge branch is hardware-locked, and there is zero static power consumption. S2, input V1 is disconnected, load B1 consumes bus energy, and the drive voltage output of the auxiliary voltage regulator and bus synchronous sampling unit decreases synchronously; capacitor C5 discharges rapidly, making the voltage of the inverting sampling network A less than the voltage of the non-inverting sampling network B; When comparator U2 flips to output a high level, the driving voltage is sent to the gate of SiC-MOS M1 through capacitor R3, and SiC-MOS M1 is saturated and turned on. S3, the high voltage stored in the bus capacitor C2 is quickly discharged to ground through SiC-MOS M1 and power resistor R5 until the bus voltage drops to a safe value; S4: After the residual voltage is completely released, power is applied again to re-establish the self-locking voltage difference where the voltage of the inverting sampling network A is greater than the voltage of the non-inverting sampling network B, and the system starts safely.

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