A redundant control AC motor braking system and control method thereof

Abstract

The present application provides a redundant control AC motor braking system and a control method thereof, wherein the redundant control AC motor braking system includes: a brake, an MCU, a VCU and a motor step-down circuit. The brake is used to provide braking torque for the vehicle, the MCU is used to control the drive motor and the brake, the VCU is used to detect the voltage of the electric control bus and control the on and off of the motor step-down circuit, and the motor step-down circuit is used to consume the back electromotive force generated by the drive motor. When the voltage of the electric control bus is higher than the first threshold, the VCU determines that the MCU is faulty and the back electromotive force generated by the motor rotation cannot be consumed normally. The VCU turns on the motor step-down circuit and consumes the back electromotive force generated by the drive motor to reduce the voltage of the electric control bus, protect the drive motor and the control system, realize dual redundant control of the braking system, and improve the safety of the braking system.

Description

Technical Field

[0001] The present invention relates to the technical field of scanning devices, and in particular to a redundant control AC motor braking system and a control method thereof. Background Art

[0002] With the widespread use of electric forklifts, users are increasingly concerned about the safety of their brakes. The braking system of an electric forklift is typically controlled by an MCU (motor control unit). When the driver presses the brake pedal, the drive motor is de-energized, and the MCU controls the braking mechanism. The piston in the master brake cylinder moves, compressing the brake fluid, causing the piston in the wheel cylinder to expand outward, pushing the brake shoe into contact with the brake drum, generating braking torque. A malfunction in the MCU not only prevents the brake mechanism from operating properly and the electric forklift from stopping, but also causes the wheels to continue rotating due to vehicle inertia, generating back electromotive force (EMF) that causes the voltage of the electronic control bus to continuously increase, potentially damaging the drive motor and the entire control system. Therefore, if an electric forklift relies solely on an MCU to control the braking system, there is insufficient safety redundancy, and an MCU failure can lead to serious safety accidents. Summary of the Invention

[0003] In order to solve the technical problem of insufficient safety redundancy caused by controlling the braking system only by the MCU, the present application provides a redundantly controlled AC motor braking system and a control method thereof.

[0004] The redundantly controlled AC motor braking system includes a brake, an MCU, a VCU (vehicle control unit), and a motor step-down circuit. The brake provides braking torque for the vehicle, the MCU controls the drive motor and the brake, the VCU detects the voltage of the electrical control bus and controls the brake, and the motor step-down circuit dissipates the back EMF generated by the drive motor. When the electrical control bus voltage exceeds a first threshold, the VCU activates the motor step-down circuit, dissipating the back EMF generated by the drive motor and reducing the voltage of the electrical control bus.

[0005] When the driver applies the brake pedal, the drive motor loses power, the MCU controls brake application, the electronic control bus connects to the motor's step-down circuit, and the VCU monitors the bus voltage. If the MCU is functioning properly, the bus voltage should be below a first threshold due to the connection between the bus and the motor's step-down circuit. If the bus voltage exceeds the first threshold, indicating that the MCU is not functioning properly, the VCU activates the bus voltage, dissipating the back EMF generated by the drive motor and reducing the bus voltage.

[0006] Specifically, the motor step-down circuit includes a power resistor and a power switch connected in series. The power switch receives control signals from the VCU to connect or disconnect the circuit between the power resistor and the electrical control bus. The power resistor effectively dissipates the induced electrical energy generated by the drive motor's rotation, reducing the voltage of the electrical control bus and ensuring the safety of the drive motor and control system.

[0007] Furthermore, the motor step-down circuit further includes a rectifier bridge and a current detection unit. The rectifier bridge is connected in series between the power switch and the drive motor and is configured to convert the three-phase AC power generated by the drive motor into DC power. The current detection unit is configured to detect the current flowing through the power resistor. By detecting the current flowing through the power resistor, the current detection unit can determine whether the vehicle has completed braking, allowing the VCU to stop sending control signals to the brake and the motor step-down circuit.

[0008] Specifically, the current detection unit includes a micro resistor and an operational amplifier circuit. The micro resistor is connected in series with the power resistor, and the operational amplifier circuit is used to transmit the current signal in the micro resistor to the VCU. Considering that the power resistor is typically used to consume the inductive power generated by the drive motor and is not suitable for direct current sampling and detection, a micro resistor is connected in series with the power resistor. By measuring the current in the micro resistor, it is determined whether there is still current flowing in the power resistor, thereby determining whether the vehicle has completed braking.

[0009] Furthermore, the redundant control AC motor braking system also includes a CAN communication module for transmitting control signals between the VCU and the MCU.

[0010] Furthermore, the VCU is also used to control the brake to perform a braking action when the voltage of the electric control bus is higher than the first threshold.

[0011] The present application also provides a brake system control method for controlling the redundant control AC motor brake system, comprising the following steps:

[0012] S1, the VCU receives a braking signal and starts to obtain the voltage value of the electric control bus;

[0013] S2. The VCU compares the voltage value with the first threshold;

[0014] S3. If the voltage value is greater than the first threshold, the VCU turns on the motor step-down circuit.

[0015] Furthermore, the control method further includes:

[0016] S4: Detecting the current of the motor step-down circuit;

[0017] S5: comparing the current of the motor step-down circuit with a second threshold;

[0018] S6: According to the comparison result of step S5, if the current of the motor step-down circuit is greater than or equal to the second threshold, the VCU sends an action instruction to the brake to enable the brake to continue to perform the braking action; if the current of the motor step-down circuit is less than or equal to the second threshold, the VCU stops sending the action instruction to the brake, the brake stops the braking action, and the VCU disconnects the motor step-down circuit.

[0019] In some embodiments, the first threshold is 150% of the rated voltage of the drive motor.

[0020] Furthermore, the step of comparing the voltage value with the first threshold value also includes: after the VCU receives the braking signal for a first time, if the voltage value is greater than the first threshold value, the VCU controls the brake to operate and turns on the motor step-down circuit.

[0021] Technical effects and advantages of the present invention:

[0022] 1. By having the VCU monitor the voltage of the electric control bus and timely determine whether the MCU can perform the braking action normally, when the MCU cannot perform the braking action normally, the VCU will connect the motor step-down circuit to consume the back electromotive force generated by the drive motor to reduce the voltage of the electric control bus, protect the drive motor and control system, realize dual redundant control of the braking system, and improve the safety of the braking system;

[0023] 2. By setting a current detection unit in the motor step-down circuit to detect the current of the power resistor, it is possible to determine whether the vehicle has completed braking, so that the VCU stops sending control signals to the brake and the motor step-down circuit, thereby realizing closed-loop control of the braking system by the VCU. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the braking system circuit provided in Example 1 of the present invention.

[0025] Figure 2 This is a flow chart of the control method provided in the third embodiment of the present invention. DETAILED DESCRIPTION

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] Example 1

[0028] refer to Figure 1 A first embodiment of the present invention provides a redundantly controlled AC motor braking system, comprising a brake, an MCU, a VCU (vehicle control unit), and a motor step-down circuit. The brake provides braking torque for the vehicle, the MCU controls the drive motor and brake, the VCU detects the voltage of the electric control bus and controls the brake, and the motor step-down circuit dissipates the back electromotive force generated by the drive motor. When the voltage of the electric control bus exceeds a first threshold, the VCU activates the motor step-down circuit, dissipating the back electromotive force generated by the drive motor and reducing the voltage of the electric control bus.

[0029] During normal braking, when the driver steps on the brake pedal, the drive motor is powered off, the MCU sends a brake command to the power drive circuit, and the power drive circuit controls the power circuit to slow down or stop the drive motor. At the same time, the MCU controls the brake action and connects the electric control bus to the motor step-down circuit. The VCU detects the voltage of the electric control bus to determine whether the MCU is working properly. If the MCU is working properly, since the electric control bus is connected to the motor step-down circuit, the back electromotive force generated by the drive motor is small, the time is very short, and the voltage rise is not obvious. The voltage in the electric control bus should be less than the first threshold. If the voltage of the electric control bus exceeds the first threshold, it means that the MCU is not working properly. At this time, the VCU connects the motor step-down circuit to consume the back electromotive force generated by the drive motor and reduce the voltage of the electric control bus.

[0030] Specifically, if Figure 1 As shown, the motor step-down circuit includes a power resistor R1 and a power switch Q7 connected in series. Power switch Q7 is connected to pin 5 of the VCU and receives control signals from the VCU to open or close the circuit between power resistor R1 and the electrical control bus. Power resistor R1 effectively dissipates the induced electrical energy generated by the drive motor's rotation, reducing the voltage of the electrical control bus and ensuring the safety of the drive motor and control system.

[0031] The power switch Q7 can be either a MOS transistor or an IGBT switch. Both switches can be switched on and off at high speed by sending PWM signals through the VCU to control the on and off of the motor buck circuit and control the current and voltage of the motor buck circuit.

[0032] Specifically, control signals can be transmitted between the VCU and the MCU through the CAN communication module. Pins 1 and 2 of the CAN communication module are connected to pins 8 and 7 of the MCU respectively, and pins 7 and 8 of the CAN communication module are connected to pins 2 and 1 of the VCU respectively.

[0033] Furthermore, if Figure 1 As shown, the motor step-down circuit also includes a rectifier bridge and a current detection unit. The rectifier bridge is connected in series between the power switch Q7 and the drive motor. The rectifier bridge is used to convert the three-phase AC power generated by the drive motor into DC power. The current detection unit is used to detect the current flowing through the power resistor R1 to determine whether the vehicle has completed braking, so that the VCU stops sending control signals to the power switch Q7 and controls the on and off of the motor step-down circuit.

[0034] Furthermore, considering that the power resistor R1 is usually used to consume the induced electric energy generated by the drive motor and is not suitable for direct current sampling and detection, a current detection unit is connected in series with the power resistor R1, including a micro resistor R2 and an operational amplifier circuit. The micro resistor R2 is used to sample the current flowing through the power resistor R1. The operational amplifier circuit transmits the amplified sampling signal MCU_ADC to the VCU. The VCU determines whether the vehicle has completed the braking action based on the sampling signal MCU_ADC.

[0035] Furthermore, the VCU can be set to take over the brake when the voltage of the electric control bus is higher than the first threshold, that is, when the MCU fails, the VCU controls the brake to perform the braking action, so as to achieve redundant control of the brake and further improve the safety of the braking system.

[0036] Example 2

[0037] In the field of electric vehicles, energy regenerative braking is a commonly used braking method. During braking, the induced electrical energy generated by the drive motor is transmitted to the energy storage unit through the rectifier and voltage regulator. When the vehicle is driving normally, the energy storage unit can use the stored electrical energy to power the drive motor, thereby achieving the purpose of energy recovery and utilization.

[0038] The motor step-down circuit of the present application can also be provided with an energy storage unit, a rectifier and a voltage stabilizer. The rectifier is used to convert the AC power in the electric control bus into DC power, the voltage stabilizer is used to stabilize the voltage output by the rectifier, and the energy storage unit is used to store the electrical energy in the electric control bus and power the drive motor.

[0039] Example 3

[0040] This embodiment provides a braking system control method for controlling the redundant control AC motor braking system. Figure 2 As shown, the following steps are included:

[0041] S1, VCU receives the brake signal and starts to obtain the voltage value of the electric control bus;

[0042] S2, VCU compares the voltage value with the first threshold;

[0043] S3. If the voltage value is greater than the first threshold, the VCU turns on the motor step-down circuit.

[0044] Specifically, the allowable reverse voltage of the electric control bus varies depending on the braking state. During normal MCU braking, a reverse voltage of less than 10% of the rated voltage is allowed within the electric control bus. When the MCU is abnormal and braking is impossible, a reverse voltage of less than 150% of the rated voltage is allowed within the electric control bus. Therefore, the first threshold can be set to 150% of the rated voltage of the drive motor. During energy regenerative braking, a reverse voltage of less than 110% of the rated voltage is allowed within the electric control bus. Therefore, it is necessary to adopt different first thresholds depending on the braking state of the electric forklift.

[0045] Furthermore, during normal braking, the back electromotive force generated by the inertia of the drive motor causes the voltage of the electronic control bus to rise briefly, usually for no more than 2 seconds. Of course, the specific time varies depending on the circuit and vehicle design. Therefore, a time limit can be added when comparing the voltage value with the first threshold:

[0046] After the VCU receives the brake signal for a first time, if the voltage value of the electric control bus is greater than the first threshold, the VCU controls the brake to operate and connects the electric control bus to the motor step-down circuit.

[0047] Furthermore, in order to achieve closed-loop control of the brake by the VCU, the following steps can be added:

[0048] S4: Detect the current of the motor step-down circuit;

[0049] S5: comparing the current of the motor step-down circuit with a second threshold;

[0050] S6: Based on the comparison result in step S5, if the current in the motor step-down circuit is greater than or equal to the second threshold, the VCU continues to send action commands to the brake, causing the brake to continue braking. The VCU continues to send PWM control commands to power switch Q7 to maintain the connection between the electrical control bus and the motor step-down circuit. If the current in the motor step-down circuit is less than or equal to the second threshold, the VCU stops sending action commands to the brake, causing the brake to cease braking. The VCU also stops sending PWM control signals to power switch Q7, disconnecting the motor step-down circuit, and completing the braking process.

[0051] When detecting the current of the motor step-down circuit, the second threshold value can be set to 0 or a very small value to prevent the micro-current fluctuation in the circuit from affecting the detection result.

[0052] Finally: The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A redundant control AC motor braking system, characterized in that: include: Brakes, used to provide braking torque for the vehicle; MCU, used to control the drive motor and the brake; VCU, used to detect the voltage of the electric control bus and control the on / off of the motor step-down circuit; A motor step-down circuit, used to consume the back electromotive force generated by the drive motor; When the voltage of the electric control bus is higher than a first threshold, the VCU controls the motor step-down circuit to be turned on, so that the motor step-down circuit consumes the back electromotive force generated by the drive motor to reduce the voltage of the electric control bus; The motor step-down circuit comprises a power resistor (R1) and a power switch (Q7) connected in series, wherein the power switch (Q7) is used to receive a control signal from the VCU to connect or disconnect the circuit between the power resistor (R1) and the electric control bus; The motor step-down circuit further includes a rectifier bridge and a current detection unit, wherein the rectifier bridge is connected in series between the power switch (Q7) and the drive motor, the rectifier bridge is used to convert the three-phase alternating current generated by the drive motor into direct current, and the current detection unit is used to detect the current flowing through the power resistor (R1); The current detection unit comprises a micro resistor (R2) and an operational amplifier circuit, wherein the micro resistor (R2) is connected in series with the power resistor (R1), and the operational amplifier circuit is used to transmit the current signal in the micro resistor (R2) to the VCU.

2. The redundant control AC motor braking system according to claim 1, characterized in that: The redundant control AC motor braking system further includes a CAN communication module for transmitting control signals between the VCU and the MCU.

3. The redundant control AC motor braking system according to claim 1, characterized in that: The VCU is further configured to control the brake to perform a braking action when the voltage of the electric control bus is higher than the first threshold.

4. A braking system control method for controlling the redundant control AC motor braking system according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1, the VCU receives a braking signal and starts to obtain the voltage value of the electric control bus; S2. The VCU compares the voltage value with the first threshold; S3. If the voltage value is greater than the first threshold, the VCU turns on the motor step-down circuit; S4: Detecting the current of the motor step-down circuit; S5: comparing the current of the motor step-down circuit with a second threshold; S6: According to the comparison result of step S5, if the current of the motor step-down circuit is greater than or equal to the second threshold, the VCU sends an action instruction to the brake to enable the brake to continue to perform the braking action; if the current of the motor step-down circuit is less than or equal to the second threshold, the VCU stops sending the action instruction to the brake, the brake stops the braking action, and the VCU disconnects the motor step-down circuit.

5. The brake system control method according to claim 4, characterized in that: The first threshold is 150% of the rated voltage of the drive motor.

6. The brake system control method according to claim 4, characterized in that: The step of comparing the voltage value with the first threshold value further comprises: After a first time has passed since the VCU received the brake signal, if the voltage value is greater than the first threshold, the VCU controls the brake to actuate and turns on the motor step-down circuit.

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