Redundant control AC motor braking system and control method thereof

Abstract

The invention provides a redundancy control AC motor braking system and a control method thereof, and the system comprises a brake, an MCU, a VCU, and a motor voltage reduction circuit. The brake is used for providing braking torque for a vehicle, the MCU is used for controlling the driving motor and the brake, the VCU is used for detecting the voltage of the electric control bus and controlling the on-off of the motor step-down circuit, and the motor step-down circuit is used for consuming back electromotive force generated by the driving motor. When the voltage of the electric control bus is higher than a first threshold value, the VCU judges that the MCU breaks down and the counter electromotive force generated by rotation of the motor cannot be normally consumed, the VCU switches on a motor voltage reduction circuit to consume the counter electromotive force generated by the driving motor so as to reduce the voltage of the electric control bus, protect the driving motor and the control system and achieve dual redundancy control of the braking system. The safety of the braking system is improved.

Description

Technical Field

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

[0002] With the wide application of electric forklifts, users pay more and more attention to the safety of electric forklift braking. The braking system of an electric forklift is usually controlled by an MCU (motor controller). When the driver steps on the brake pedal, the drive motor is powered off, and the MCU controls the braking device to brake. The piston of the master cylinder moves, compresses the brake fluid, so that the piston in the wheel cylinder expands outwards, pushing the brake shoe into contact with the brake drum to generate a braking torque. When the MCU fails, it will not only cause the braking device to malfunction and the electric forklift cannot stop moving, but due to the inertia of the vehicle, the wheels will continue to rotate with the motor, and the motor generates a back electromotive force, resulting in a continuous increase in the voltage of the electric control bus, damaging the drive motor and the entire control system. Therefore, if only the MCU is used to control the braking system of an electric forklift, there is a problem of insufficient safety redundancy, and serious safety accidents will occur once the MCU fails. Summary of the Invention

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

[0004] Among them, the redundant control AC motor braking system includes: a brake, an MCU, a VCU (vehicle controller), and a motor buck circuit. The brake is used to provide a 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 brake, and the motor buck 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 controls the motor buck circuit to be turned on, so that the motor buck circuit consumes the back electromotive force generated by the drive motor to reduce the voltage of the electric control bus.

[0005] When the driver steps on the brake pedal, the drive motor is powered off, the MCU controls the brake to act, the electric control bus is connected to the motor buck circuit, and the VCU detects the voltage of the electric control bus. If the MCU works normally, since the electric control bus is connected to the motor buck circuit, 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 does not work normally, and the VCU will control the electric control bus to be connected to consume the back electromotive force generated by the drive motor to reduce the voltage of the electric control bus.

[0006] Specifically, the motor buck circuit includes a power resistor and a power switch connected in series. The power switch is used to receive the control signal from the VCU to connect or disconnect the circuit between the power resistor and the electric control bus. The power resistor can effectively consume the induced electric energy generated by driving the motor to rotate, so as to reduce the voltage of the electric control bus and ensure the safety of the driving motor and the control system.

[0007] Further, the motor buck circuit further includes a rectifier bridge and a current detection unit. The rectifier bridge is connected in series between the power switch and the driving motor. The rectifier bridge is used to convert the three-phase alternating current generated by the driving motor into direct current. The current detection unit is used to detect the current flowing through the power resistor. By detecting the current flowing through the power resistor with the current detection unit, it can be judged whether the vehicle has completed braking, so that the VCU stops sending control signals to the brake and the motor buck 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. The operational amplifier circuit is used to transmit the current signal in the micro resistor to the VCU. Considering that the power resistor is usually used to consume the induced electric energy generated by the driving motor and is not suitable for directly sampling and detecting the current, a micro resistor is connected in series with the power resistor. By measuring the current in the micro resistor, it is judged whether there is still current passing through the power resistor to judge whether the vehicle has completed braking.

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

[0010] Further, the VCU is further 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 braking system control method for controlling the above redundant control AC motor braking system, including the following steps: 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 buck circuit.

[0012] Further, the control method further includes: S4: Detect the current of the motor buck circuit. S5: Compare the current of the motor buck circuit with a second threshold. S6: According to the comparison result in step S5, if the current of the motor buck circuit is greater than or equal to the second threshold, the VCU sends an action instruction to the brake to make the brake continue to perform the braking action. If the current of the motor buck 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 buck circuit.

[0013] In some embodiments, the first threshold is 150% of the rated voltage of the drive motor.

[0014] Further, the step of comparing the voltage value with the first threshold further includes: after the VCU receives the braking signal for a first time, if the voltage value is greater than the first threshold, the VCU controls the brake to act and turns on the motor buck circuit.

[0015] Technical effects and advantages of the present invention: 1. By enabling the VCU to monitor the voltage of the electric control bus to timely determine whether the MCU can normally perform the braking action. When the MCU cannot normally perform the braking action, the VCU turns on the motor buck circuit to consume the back electromotive force generated by the drive motor, so as to reduce the voltage of the electric control bus, protect the drive motor and the control system, realize the dual redundant control of the braking system, and improve the safety of the braking system. 2. By setting a current detection unit in the motor buck circuit to detect the current of the power resistor to determine whether the vehicle has completed braking, so that the VCU stops sending control signals to the brake and the motor buck circuit, realizing the closed-loop control of the VCU on the braking system. Description of the drawings

[0016] Figure 1 It is a schematic circuit diagram of the braking system provided by Embodiment 1 of the present invention.

[0017] Figure 2 It is a flowchart of the control method provided by Embodiment 3 of the present invention. Detailed implementation manners

[0018] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0019] Embodiment 1 Refer to Figure 1, Embodiment 1 of the present invention provides a redundant control AC motor braking system, including: a brake, an MCU, a VCU (vehicle controller), 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 brake, 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 controls the motor step-down circuit to be turned on to consume the back electromotive force generated by the drive motor to reduce the voltage of the electric control bus.

[0020] During a normal braking process, when the driver steps on the brake pedal, the drive motor is powered off, the MCU sends a braking instruction to the power drive circuit, and the power drive circuit controls the power circuit to make the drive motor decelerate or stop rotating. At the same time, the MCU controls the brake to act and connects the electric control bus to the motor step-down circuit, and 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 increase 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 turns on 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.

[0021] Specifically, as Figure 1 shown, the motor step-down circuit includes a power resistor R1 and a power switch Q7 connected in series. The power switch Q7 is connected to pin 5 of the VCU and is used to receive the control signal of the VCU to connect or disconnect the circuit between the power resistor R1 and the electric control bus. The power resistor R1 can effectively consume the induced electric energy generated by the rotation of the drive motor to reduce the voltage of the electric control bus and ensure the safety of the drive motor and the control system.

[0022] The power switch Q7 can be either a MOS transistor or an IGBT switch. Both switches can be turned on and off at high speed by the VCU sending a PWM signal to control the on and off of the motor step-down circuit and control the current and voltage of the motor step-down circuit.

[0023] Specifically, control signals can be transmitted between the VCU and the MCU through a CAN communication module. Pin 1 and pin 2 of the CAN communication module are respectively connected to pin 8 and pin 7 of the MCU, and pin 7 and pin 8 of the CAN communication module are respectively connected to pin 2 and pin 1 of the VCU.

[0024] Further, as Figure 1As shown in the figure, the motor buck circuit further 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 alternating current generated by the drive motor into direct current. 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 as to facilitate the VCU to stop sending control signals to the power switch Q7 and control the on / off of the motor buck circuit.

[0025] Further, 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 directly sampling and detecting the current, a current detection unit including a micro resistor R2 and an operational amplifier circuit is connected in series with the power resistor R1. The micro resistor R2 is used to sample the current flowing through the power resistor R1, and 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 according to the sampling signal MCU_ADC.

[0026] Further, the VCU can also 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 to achieve redundant control of the brake and further improve the safety of the braking system.

[0027] Embodiment 2 In the field of electric vehicles, regenerative braking is a commonly used braking method. During braking, the induced electric energy generated by the drive motor is transmitted to the energy storage unit through a rectifier and a voltage regulator. When the vehicle is driving normally, the energy storage unit can use the stored electric energy to supply power to the drive motor to achieve the purpose of recovering and utilizing electric energy.

[0028] The motor buck circuit of the present application can also be provided with an energy storage unit, a rectifier, and a voltage regulator. The rectifier is used to convert the alternating current in the electric control bus into direct current, the voltage regulator is used to stabilize the voltage output by the rectifier, and the energy storage unit is used to store the electric energy in the electric control bus and supply power to the drive motor.

[0029] Embodiment 3 This embodiment provides a braking system control method for controlling the redundant control alternating current motor braking system as Figure 2 shown, including the following steps: 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 buck circuit.

[0030] Specifically, according to different braking states, the allowable reverse voltage of the electronic control bus is different. During the braking process when the MCU is working normally, a reverse voltage below 10% of the rated voltage is allowed to exist in the electronic control bus. When the MCU is abnormal and cannot brake normally, a reverse voltage below 150% of the rated voltage is allowed to exist in the electronic control bus. Therefore, the first threshold can be set to 150% of the rated voltage of the drive motor. During the braking process of energy feedback, a reverse voltage below 110% of the rated voltage is allowed to exist in the electronic control bus. Therefore, different first thresholds need to be adopted according to the braking state of the electric forklift.

[0031] Furthermore, during the normal braking process, the back electromotive force generated by the drive motor due to inertia will cause the voltage of the electronic control bus to rise briefly, usually for no more than 2s. Of course, the specific time varies due to different circuit and vehicle designs. Therefore, when comparing the voltage value with the first threshold, a time limit can also be added: After the VCU receives the braking signal and after the first time, if the voltage value of the electronic control bus is greater than the first threshold, the VCU controls the brake to act and connects the electronic control bus to the motor step-down circuit.

[0032] Furthermore, in order to achieve the closed-loop control of the VCU over the brake, the following steps can also be added: S4: Detect the current of the motor step-down circuit; S5: Compare the current of the motor step-down circuit with the 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 continues to send an action instruction to the brake to make the brake continue to perform the braking action, and the VCU continues to send a PWM control instruction to the power switch Q7 to keep the electronic control bus connected to the motor step-down circuit. If the current of the motor step-down circuit is less than or equal to the second threshold, the VCU stops sending an action instruction to the brake, the brake stops the braking action, and the VCU stops sending a PWM control signal to the power switch Q7 to disconnect the motor step-down circuit, completing the braking process.

[0033] When detecting the current of the motor step-down circuit, the second threshold can be set to 0 or a small value to avoid the influence of micro-current fluctuations in the circuit on the detection result.

[0034] Finally: The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A redundant control AC motor braking system, characterized in that, Comprising: A brake for providing braking torque to a vehicle; An MCU for controlling a drive motor and the brake; A VCU for detecting the voltage of an electric control bus and controlling the on / off of the motor buck circuit; A motor buck circuit for consuming 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 buck circuit to be turned on, so that the motor buck circuit consumes the back electromotive force generated by the drive motor to reduce the voltage of the electric control bus.

2. The redundant control AC motor braking system according to claim 1, wherein The motor buck circuit includes a power resistor (R1) and a power switch (Q7) connected in series, and 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.

3. The redundant control AC motor braking system according to claim 2, wherein, The motor buck circuit further 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 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).

4. The redundant control AC motor braking system according to claim 3, wherein, The current detection unit includes a micro resistor (R2) and an operational amplifier circuit. 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.

5. 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 mutually transmitting control signals between the VCU and the MCU.

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

7. A braking system control method for controlling the redundant control AC motor braking system according to claim 6, characterized in that, Including the following steps: 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 buck circuit.

8. The braking system control method according to claim 7, wherein, The control method further includes: S4: Detect the current of the motor buck circuit; S5: Compare the current of the motor buck circuit with a second threshold; S6: According to the comparison result of step S5, if the current of the motor buck circuit is greater than or equal to the second threshold, the VCU sends an action instruction to the brake to make the brake continue to perform a braking action. If the current of the motor buck circuit is less than or equal to the second threshold, the VCU stops sending an action instruction to the brake, the brake stops the braking action, and the VCU disconnects the motor buck circuit.

9. The braking system control method according to claim 7, wherein, The first threshold is 150% of the rated voltage of the drive motor.

10. The braking system control method according to claim 7, wherein The step of comparing the voltage value with the first threshold further includes: After the VCU receives the braking signal for a first time, if the voltage value is greater than the first threshold, the VCU controls the brake to act and turns on the motor buck circuit.

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