Torque and speed control loop in EV Technology - Mini Project: Build & Apply

Torque and Speed Control Loop

📖 Scenario: You are designing a simple control loop for an electric vehicle (EV) motor. The goal is to maintain the motor speed by adjusting the torque based on the difference between the desired speed and the actual speed.This control loop helps the EV run smoothly and efficiently.

🎯 Goal: Build a basic torque and speed control loop that calculates the torque needed to reach a target speed by comparing it with the current speed.

📋 What You'll Learn

Create variables for target speed and current speed with exact values

Add a variable for speed error calculation

Calculate torque using a proportional control formula

Set a maximum torque limit to avoid overloading the motor

💡 Why This Matters

🌍 Real World

Electric vehicles use torque and speed control loops to maintain smooth acceleration and efficient energy use.

💼 Career

Understanding basic control loops is essential for engineers working on EV motor control systems and embedded software.

1

Set up speed variables

Create two variables called target_speed and current_speed. Set target_speed to 60 (km/h) and current_speed to 45 (km/h).

EV Technology

# Create variables for target_speed and current_speed
# Your code here

Hint

Use simple assignment to create the variables with the exact values.

2

Calculate speed error

Add a variable called speed_error that calculates the difference between target_speed and current_speed.

EV Technology

target_speed = 60
current_speed = 45
# Calculate speed_error as target_speed minus current_speed
# Your code here

Hint

Subtract current_speed from target_speed to find the error.

3

Calculate torque using proportional control

Create a variable called torque that calculates torque by multiplying speed_error by a proportional constant Kp. Set Kp to 2.

EV Technology

target_speed = 60
current_speed = 45
speed_error = target_speed - current_speed
# Set Kp to 2 and calculate torque as speed_error times Kp
# Your code here

Hint

Multiply the error by the proportional constant to get torque.

4

Limit torque to maximum safe value

Add a variable called max_torque set to 30. Then update torque so it does not exceed max_torque. If torque is greater than max_torque, set torque to max_torque.

EV Technology

target_speed = 60
current_speed = 45
speed_error = target_speed - current_speed
Kp = 2
torque = speed_error * Kp
# Set max_torque to 30 and limit torque to max_torque if it is higher
# Your code here

Hint

Use an if statement to check and limit the torque value.

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