Torque and speed control loop in EV Technology - Step-by-Step Execution

Concept Flow - Torque and speed control loop

Set desired speed

↓

Measure actual speed

↓

Calculate speed error

↓

Speed controller adjusts torque command

↓

Apply torque to motor

↓

Motor speed changes

↓

Loop back to measure actual speed

The control loop starts by setting a target speed, measures the actual speed, calculates the difference, adjusts torque accordingly, applies it to the motor, and repeats to maintain desired speed.

Execution Sample

EV Technology

desired_speed = 60  # km/h
actual_speed = 50
speed_error = desired_speed - actual_speed
torque_command = speed_controller(speed_error)
motor.apply_torque(torque_command)
actual_speed = motor.get_speed()

This code sets a target speed, measures actual speed, calculates error, adjusts torque, applies it, and updates speed.

Analysis Table

Step	desired_speed (km/h)	actual_speed (km/h)	speed_error (km/h)	torque_command (Nm)	Action
1	60	50	10	15	Calculate error and torque command; apply torque
2	60	55	5	8	Speed increased; recalculate error and torque
3	60	58	2	3	Speed closer to target; torque reduced
4	60	60	0	0	Target speed reached; torque command zero
5	60	60	0	0	Maintain speed; no torque change

💡 Loop stabilizes when actual speed equals desired speed and torque command is zero

State Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
desired_speed	60	60	60	60	60	60
actual_speed	50	50	55	58	60	60
speed_error	10	10	5	2	0	0
torque_command	0	15	8	3	0	0

Key Insights - 3 Insights

Why does the torque command decrease as the actual speed approaches the desired speed?

Because the speed error reduces, the controller lowers the torque command to avoid overshooting, as shown in steps 2 to 4 in the execution_table.

What happens if the actual speed is higher than the desired speed?

The speed error becomes negative, causing the controller to reduce or reverse torque to slow down the motor, though this is not shown in the current table but follows the same logic.

Why does the loop keep measuring actual speed after applying torque?

Measuring actual speed after applying torque allows the controller to update the error and adjust torque continuously, ensuring the motor speed stays close to the target, as seen in the loop flow.

Visual Quiz - 3 Questions

Look at the execution_table at Step 3, what is the speed_error value?

A 5 km/h

B 2 km/h

C 0 km/h

D 10 km/h

💡 Hint

Check the 'speed_error (km/h)' column at Step 3 in the execution_table.

At which step does the torque_command become zero?

A Step 2

B Step 1

C Step 4

D Step 3

💡 Hint

Look at the 'torque_command (Nm)' column in the execution_table to find when it reaches zero.

If the actual_speed was 65 km/h at Step 1, how would the speed_error change?

A It would be -5 km/h

B It would be +5 km/h

C It would be 0 km/h

D It would be +10 km/h

💡 Hint

Speed error = desired_speed - actual_speed; check variable_tracker for calculation logic.

Concept Snapshot

Torque and speed control loop:
- Set desired speed
- Measure actual speed
- Calculate speed error = desired - actual
- Controller adjusts torque based on error
- Apply torque to motor
- Motor speed changes
- Repeat loop to maintain speed

Full Transcript

The torque and speed control loop in electric vehicles works by first setting a desired speed. The system measures the actual speed of the motor and calculates the difference, called speed error. This error is used by the speed controller to adjust the torque command sent to the motor. Applying this torque changes the motor speed. The loop repeats by measuring the new speed, recalculating error, and adjusting torque again. This continuous process keeps the motor speed close to the desired speed. The torque command decreases as the actual speed approaches the target to avoid overshoot. If the motor goes faster than desired, the controller reduces torque to slow it down. This loop ensures smooth and accurate speed control.

Practice

1. What is the main role of the speed control loop in an electric vehicle motor system?

easy

A. To decide how much torque is needed based on speed error

B. To convert torque commands into motor current

C. To measure the battery voltage

D. To control the temperature of the motor

Solution

1. Step 1: Understand the speed control loop function

   The speed control loop compares the desired speed with the actual speed and calculates the difference called speed error.

2. Step 2: Determine the output of the speed control loop

   Based on the speed error, it decides the amount of torque needed to correct the speed.

3. Final Answer:

   To decide how much torque is needed based on speed error -> Option A

4. Quick Check:

   Speed control loop = torque decision [OK]

Hint: Speed loop sets torque based on speed difference [OK]

Common Mistakes:

• Confusing torque control with speed control
• Thinking speed loop measures battery voltage
• Assuming speed loop controls motor temperature

2. Which of the following correctly describes the torque control loop in an EV motor system?

easy

A. It converts torque commands into motor current

B. It measures the motor speed directly

C. It calculates speed error from desired and actual speed

D. It controls the battery charging rate

Solution

1. Step 1: Identify the function of the torque control loop

   The torque control loop takes the torque command from the speed control loop and converts it into the motor current needed to produce that torque.

2. Step 2: Eliminate incorrect options

   Measuring speed and calculating speed error are functions of the speed control loop, not torque control. Battery charging is unrelated.

3. Final Answer:

   It converts torque commands into motor current -> Option A

4. Quick Check:

   Torque loop = torque to current conversion [OK]

Hint: Torque loop changes torque command into current [OK]

Common Mistakes:

• Mixing speed error calculation with torque control
• Thinking torque loop measures speed
• Confusing battery charging with torque control

3. Consider this simplified control sequence:
speed_error = desired_speed - actual_speed
torque_command = Kp * speed_error
motor_current = torque_command * motor_constant
If desired_speed = 100, actual_speed = 80, Kp = 2, and motor_constant = 3, what is the motor_current?

medium

A. 40

B. 60

C. 360

D. 120

Solution

1. Step 1: Calculate speed error

   speed_error = 100 - 80 = 20

2. Step 2: Calculate torque command

   torque_command = 2 * 20 = 40

3. Step 3: Calculate motor current

   motor_current = 40 * 3 = 120

4. Final Answer:

   120 -> Option D

5. Quick Check:

   speed_error * Kp * motor_constant = 120 [OK]

Hint: Multiply error by Kp, then by motor constant [OK]

Common Mistakes:

• Multiplying in wrong order
• Using actual_speed instead of speed_error
• Forgetting to multiply by motor_constant

4. A control loop code snippet is:
speed_error = desired_speed - actual_speed
torque_command = Kp * speed_error
motor_current = torque_command / motor_constant
Why might this cause a problem in the torque control loop?

medium

A. Multiplying torque_command by Kp is wrong

B. Dividing by motor_constant reduces current incorrectly

C. Speed error should be added, not subtracted

D. motor_current should be zero always

Solution

1. Step 1: Analyze the motor_current calculation

   The torque control loop converts torque command to motor current by multiplying by motor_constant, not dividing.

2. Step 2: Understand the effect of division

   Dividing by motor_constant reduces the motor_current incorrectly, leading to insufficient torque output.

3. Final Answer:

   Dividing by motor_constant reduces current incorrectly -> Option B

4. Quick Check:

   Torque to current = multiply, not divide [OK]

Hint: Torque to current uses multiplication, not division [OK]

Common Mistakes:

• Confusing multiplication with division
• Misunderstanding speed error calculation
• Assuming motor_current should be zero

5. In an EV torque and speed control system, if the speed control loop outputs a negative torque command, what should the torque control loop do to maintain correct motor operation?

hard

A. Convert the negative torque command into a positive motor current to increase speed

B. Ignore the negative torque command and set motor current to zero

C. Convert the negative torque command into a negative motor current to reverse motor direction

D. Send an error signal and stop the motor immediately

Solution

1. Step 1: Understand negative torque command meaning

   A negative torque command means the motor should apply torque in the opposite direction, usually to slow down or reverse.

2. Step 2: Determine torque control loop response

   The torque control loop must convert this negative torque command into a negative motor current, which causes the motor to rotate in reverse or apply braking torque.

3. Final Answer:

   Convert the negative torque command into a negative motor current to reverse motor direction -> Option C

4. Quick Check:

   Negative torque = negative current for reverse [OK]

Hint: Negative torque means reverse current direction [OK]

Common Mistakes:

• Ignoring negative torque commands
• Converting negative torque to positive current
• Stopping motor unnecessarily on negative torque