Optimized regenerative braking control of electric motors using look-up tables
A regenerative braking controller for an AC motor. To determine an electromagnetic torque for slowing or stopping the motor, the regenerative braking controller accesses a lookup table to retrieve a braking torque value corresponding to a current estimate of rotor velocity. The retrieved braking torque may correspond to a maximum or minimum torque level at which regenerative braking will occur at the current rotor velocity, or to a torque level at which charging current during regenerative braking will be maximized. If an external mechanical brake is present, the regenerative braking controller can forward an external braking torque signal to a controller so that the mechanical brake can apply the remainder of the braking force beyond that indicated by the regenerative braking torque. A method for establishing the braking torques to be stored in the lookup table is also disclosed.
1 . A system, comprising:
a memory configured to store data representing a set of regenerative braking torque over a range of velocity of a motor; and
a processor configured to:
receive a first signal indicating a desired velocity;
receive a second signal indicating a current velocity;
determine a desired torque in an opposite direction from the current velocity based on the desired velocity and the current velocity;
access the data to determine a regenerative braking torque associated with the current velocity;
determine whether the current velocity is greater than a threshold velocity for which regenerative braking is to be applied; and
provide a signal to control the motor based on a comparison of the regenerative braking torque with the desired torque and a determination whether the current velocity is greater than the threshold velocity.
2 . The system of claim 1 , wherein the data includes values of a set of maximum regenerative braking torque and values of a set of minimum regenerative braking torque over the range of velocity.
3 . The system of claim 1 , wherein the data includes values of a set of optimum regenerative braking torque over the range of velocity at which a current output by an energy storage system is minimized.
4 . The system of claim 3 , further comprising:
an inverter configured to:
control the motor based on the signal to generate a current to charge the energy storage system.
5 . The system of claim 1 , wherein the processor is configured to:
receive a third signal indicating measurement of a current of the motor;
receive a fourth signal indicating measurement of a voltage of the motor; and
determine the current velocity based on the current and the voltage of the motor.
6 . The system of claim 1 , wherein the processor is configured to utilize field-oriented control (FOC) to determine the desired torque based on the desired velocity and the current velocity.
7 . The system of claim 1 , wherein the motor is a permanent magnet electric motor.
8 . The system of claim 1 , wherein the processor is configured to:
determine that the desired torque exceeds the regenerative braking torque based on the comparison of the regenerative braking torque with the desired torque; and
based on determining that an external brake is available,
provide the signal to control the motor to produce the regenerative braking torque; and
provide another signal to cause the external brake to produce a difference between the regenerative braking torque and the desired torque.
9 . The system of claim 1 , wherein the processor is configured to:
determine that the desired torque exceeds the regenerative braking torque based on the comparison of the regenerative braking torque with the desired torque; and
based on determining that an external brake is not available,
determine whether compromise of a braking distance is acceptable; and
based on determining that compromise of the braking distance is acceptable, provide the signal to control the motor to produce the regenerative braking torque.
10 . The system of claim 1 , wherein the processor is configured to:
determine that the desired torque exceeds the regenerative braking torque based on the comparison of the regenerative braking torque with the desired torque; and
based on determining that an external brake is not available,
determine whether compromise of a braking distance is acceptable; and
based on determining that compromise of the braking distance is not acceptable, provide the signal to control the motor to produce the desired torque.
11 . A non-transitory computer readable medium storing instructions that when executed by a processor cause the processor to:
receive a first signal indicating a desired velocity of a motor;
receive a second signal indicating a current velocity of the motor;
determine a desired torque in an opposite direction from the current velocity based on the desired velocity and the current velocity;
retrieve data, which represents a set of regenerative braking torque over a range of velocity of the motor, to determine a regenerative braking torque associated with the current velocity;
determine whether the current velocity is greater than a threshold velocity for which regenerative braking is to be applied; and
provide a signal to control the motor based on a comparison of the regenerative braking torque with the desired torque and a determination whether the current velocity is greater than the threshold velocity.
12 . The non-transitory computer readable medium of claim 11 , wherein the data includes values of a set of maximum regenerative braking torque and values of a set of minimum regenerative braking torque over the range of velocity.
13 . The non-transitory computer readable medium of claim 11 , wherein the data includes values of a set of optimum regenerative braking torque over the range of velocity at which a current output by an energy storage system is minimized.
14 . The non-transitory computer readable medium of claim 13 , wherein the signal is provided to an inverter to drive the motor to generate a current to charge the energy storage system.
15 . The non-transitory computer readable medium of claim 11 , wherein the programs cause the processor to:
receive a third signal indicating measurement of a current of the motor;
receive a fourth signal indicating measurement of a voltage of the motor; and
determine the current velocity based on the current and the voltage of the motor.
16 . The non-transitory computer readable medium of claim 11 , wherein the programs cause the processor to:
utilize field-oriented control (FOC) to determine the desired torque based on the desired velocity and the current velocity.
17 . The non-transitory computer readable medium of claim 11 , wherein the motor is a permanent magnet electric motor.
18 . The non-transitory computer readable medium of claim 11 , wherein the programs cause the processor to:
determine that the desired torque exceeds the regenerative braking torque based on the comparison of the regenerative braking torque with the desired torque; and
based on determining that an external brake is available,
provide the signal to control the motor to produce the regenerative braking torque; and
provide another signal to cause the external brake to produce a difference between the regenerative braking torque and the desired torque.
19 . The non-transitory computer readable medium of claim 11 , wherein the programs cause the processor to:
determine that the desired torque exceeds the regenerative braking torque based on the comparison of the regenerative braking torque with the desired torque; and
based on determining that an external brake is not available,
determine whether compromise of a braking distance is acceptable; and
based on determining that compromise of the braking distance is acceptable, provide the signal to control the motor to produce the regenerative braking torque.
20 . The non-transitory computer readable medium of claim 11 , wherein the programs cause the processor to:
determine that the desired torque exceeds the regenerative braking torque based on the comparison of the regenerative braking torque with the desired torque; and
based on determining that an external brake is not available,
determine whether compromise of a braking distance is acceptable; and
based on determining that compromise of the braking distance is not acceptable, provide the signal to control the motor to produce the desired torque.
21 . A system comprising:
a motor;
a brake for the motor;
power drivers coupled to the motor; and
a controller unit coupled to the power drivers, to the motor, and to the brake the controller unit configured to:
obtain a goal rotor speed of the motor;
receive sense data from the motor;
determine a current rotor speed of the motor based on the sense data;
determine a goal torque associated with the brake based on the current rotor speed and the goal rotor speed;
obtain braking torque data based on a look-up table that includes a set of regenerative braking torque values over a range of rotor speeds;
determine a set of data signals based on a comparison of the braking torque data and the goal torque; and
transmit the set of data signals to the power drivers; and
wherein the power drivers are configured to control the motor based on the set of data signals.