Motor Control & PWM Techniques

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iLabTek Team

April 2025

40 min read

Advanced

1. Introduction to Motor Control

Motor control refers to controlling:

Speed
Direction
Torque
Position
Acceleration

of electric motors using electronic circuits and embedded software.

Motor control systems are widely used in:

Robotics
Electric vehicles
Drones
CNC machines
Industrial automation
Smart appliances
Medical devices

2. Types of Motors

Different applications use different motor types.

Motor Type	Applications
DC Motor	Robots, toys, conveyors
Servo Motor	Position control
Stepper Motor	CNC, 3D printers
BLDC Motor	Drones, EVs
AC Induction Motor	Industrial systems

3. What is PWM?

PWM stands for Pulse Width Modulation.

PWM controls average voltage delivered to a motor by rapidly switching power ON and OFF.

Instead of changing analog voltage directly, PWM changes:

Pulse width
Duty cycle

4. PWM Fundamentals

PWM waveform consists of:

ON time
OFF time
Period
Frequency

PWM Duty Cycle

Duty cycle determines motor power.

Duty\ Cycle = \frac{T_{ON}}{T_{TOTAL}} \times 100\%

Where:

T_ON = ON duration
T_TOTAL = Total PWM period

Duty Cycle	Motor Speed
0%	Motor OFF
25%	Low speed
50%	Medium speed
100%	Full speed

5. PWM Frequency

PWM frequency affects:

Motor smoothness
Noise
Efficiency
Heating

Typical PWM frequencies:

Application	Frequency
DC Motor	1–20 kHz
Servo Motor	50 Hz
BLDC Motor	10–50 kHz

6. PWM Generation in Microcontrollers

PWM is generated using hardware timers.

Popular PWM-capable MCUs:

STMicroelectronics STM32
Espressif Systems ESP32
Microchip Technology AVR/PIC
NXP Semiconductors LPC Series

7. PWM Using STM32 Timers

STM32 timers are widely used for PWM generation.

Features:

Multiple channels
Complementary outputs
Dead-time insertion
Center-aligned PWM
Encoder support

8. Basic PWM Generation Example (STM32 HAL)

Timer PWM Initialization

TIM_HandleTypeDef htim2;

void MX_TIM2_Init(void)
{
    TIM_OC_InitTypeDef sConfigOC = {0};

    htim2.Instance = TIM2;
    htim2.Init.Prescaler = 83;
    htim2.Init.Period = 999;
    htim2.Init.CounterMode = TIM_COUNTERMODE_UP;

    HAL_TIM_PWM_Init(&htim2);

    sConfigOC.OCMode = TIM_OCMODE_PWM1;
    sConfigOC.Pulse = 500;

    HAL_TIM_PWM_ConfigChannel(&htim2, &sConfigOC, TIM_CHANNEL_1);
    HAL_TIM_PWM_Start(&htim2, TIM_CHANNEL_1);
}
                            

9. Understanding PWM Timer Calculation

PWM frequency formula:

PWM\ Frequency = \frac{Timer\ Clock}{(Prescaler+1)(Period+1)}

Duty Cycle Calculation

Duty\ Cycle = \frac{Pulse}{Period+1} \times 100\%

10. DC Motor Control

DC motors are commonly controlled using:

H-Bridge drivers
PWM speed control
Direction pins

Popular drivers:

L298N
BTS7960
DRV8871
TB6612FNG

11. H-Bridge Motor Driver

An H-Bridge controls:

Forward rotation
Reverse rotation
Braking

IN1	IN2	Motor Direction
1	0	Forward
0	1	Reverse
0	0	Stop
1	1	Brake

12. DC Motor PWM Speed Control Example

__HAL_TIM_SET_COMPARE(&htim2, TIM_CHANNEL_1, 750);

This sets:

75% duty cycle
Higher motor speed

13. Servo Motor Control

Servo motors use PWM pulses for angle control.

Typical servo signal:

Parameter	Value
Frequency	50 Hz
Pulse Width	1–2 ms

Pulse Width	Angle
1 ms	0°
1.5 ms	90°
2 ms	180°

Servo PWM Example

__HAL_TIM_SET_COMPARE(&htim3, TIM_CHANNEL_1, 75);

14. Stepper Motor Control

Stepper motors move in discrete steps.

Applications:

CNC machines
3D printers
Robotics
Precision positioning

15. Stepper Motor Types

Type	Description
Unipolar	Simple control
Bipolar	Higher torque

16. Stepper Motor Driving Methods

Method	Feature
Full Step	Maximum torque
Half Step	Smoother movement
Microstepping	High precision

17. BLDC Motor Control

BLDC motors are highly efficient and widely used in:

Drones
Electric vehicles
Industrial systems

Advantages:

High efficiency
Low maintenance
High speed
Long life

18. BLDC Motor Control Methods

Six-Step Commutation: Simple method using Hall sensors
Sensorless Control: Uses back-EMF detection
Field-Oriented Control (FOC): Advanced high-performance control technique

19. Field-Oriented Control (FOC)

FOC provides:

Smooth torque
High efficiency
Precise speed control

Used in:

EVs
Drones
Industrial robotics

FOC Mathematical Concept

FOC transforms motor currents into rotating reference frames.

Common transforms:

Clarke Transform
Park Transform

Clarke Transform

i_\alpha = i_a

i_\beta = \frac{1}{\sqrt{3}}(i_a + 2i_b)

Park Transform

i_d = i_\alpha \cos\theta + i_\beta \sin\theta

i_q = -i_\alpha \sin\theta + i_\beta \cos\theta

20. PID Motor Speed Control

PID control is widely used in motor systems.

PID stands for:

Proportional
Integral
Derivative

PID Control Equation

u(t) = K_p e(t) + K_i \int e(t)dt + K_d \frac{de(t)}{dt}

21. Motor Feedback Systems

Feedback devices include:

Sensor	Purpose
Encoder	Position/speed
Hall Sensor	BLDC commutation
Current Sensor	Torque/current
IMU	Robot balancing

22. Encoder-Based Speed Control

Encoders provide pulses proportional to rotation.

Speed formula:

RPM = \frac{Pulses \times 60}{PPR \times Time}

23. PWM Dead Time

Dead time prevents shoot-through in MOSFET drivers.

Important in:

Inverters
BLDC drivers
Power electronics

24. Center-Aligned PWM

Advantages:

Reduced harmonics
Lower EMI
Better motor smoothness

Widely used in advanced motor control systems.

25. Current Control Techniques

Motor current control protects:

Motors
Drivers
Power supplies

Methods:

Current sensing resistor
Hall current sensor
Hardware comparators

26. Robotics Motor Control Applications

Motor control is essential in robotics.

Differential Drive Robots

Uses two independently controlled motors.

Applications:

Line followers
Autonomous robots

Robotic Arm Control

Uses:

Servo motors
Stepper motors
PID positioning

Drone Motor Control

Uses high-speed BLDC motors and ESCs.

27. PWM in Embedded Robotics

PWM controls:

Motor speed
LED brightness
Servo positioning
Audio generation

28. Real-Time Motor Control Challenges

Challenges include:

Timing precision
Interrupt latency
EMI noise
Thermal management
Power efficiency

29. Motor Driver Protection Features

Important protections:

Protection	Purpose
Overcurrent	Prevent damage
Thermal shutdown	Avoid overheating
Undervoltage lockout	Stable operation
Reverse polarity	Hardware safety

30. Advanced Motor Control Features in STM32

Advanced timers support:

Complementary PWM
Dead-time insertion
Encoder mode
Break input
Synchronization

STM32 is widely used in industrial motor control applications.

31. ESP32 PWM Features

ESP32 provides LEDC PWM module.

Features:

Multiple channels
Variable resolution
High frequency support

ESP32 PWM Example

ledcSetup(0, 5000, 8);
ledcAttachPin(18, 0);
ledcWrite(0, 128);
                            

32. Motor Control Communication Interfaces

Industrial motor systems often use:

CAN Bus
RS485
EtherCAT
Modbus
UART

33. AI and Smart Motor Control

Modern systems use AI for:

Predictive maintenance
Vibration analysis
Fault detection
Adaptive control

34. Industrial Applications

Factory Automation

Conveyor systems
CNC machines
Packaging systems

Automotive

Electric steering
EV traction motors
Cooling systems

Medical Devices

Surgical robots
Precision pumps

Consumer Electronics

Washing machines
Drones
Smart fans

35. Common Motor Control Problems

Problem	Cause
Motor jitter	Poor PWM timing
Overheating	Excess current
Noise	Wrong PWM frequency
Vibration	PID tuning issue

36. Best Practices for Motor Control Design

Use hardware PWM
Add flyback diodes
Use proper grounding
Implement current limiting
Tune PID carefully
Use EMI filtering

37. Recommended Development Tools

Hardware

STM32 Discovery Boards
ESP32 Dev Boards
Motor Driver Modules
Oscilloscope
Logic Analyzer

Software

STM32CubeIDE
Keil MDK
Arduino IDE
MATLAB

38. Future Trends in Motor Control

Emerging trends:

AI-based control
Sensorless FOC
Wide-bandgap semiconductors
Smart predictive diagnostics
High-efficiency EV systems

39. Conclusion

PWM and motor control techniques form the foundation of modern robotics, industrial automation, electric vehicles, and embedded control systems.

By understanding:

PWM generation
H-Bridge control
PID algorithms
BLDC commutation
Field-Oriented Control (FOC)

developers can design advanced and efficient motor control systems.

Microcontrollers like STM32 and ESP32 provide powerful hardware peripherals that simplify implementation of real-time motor control applications.

Mastering these concepts enables engineers to build:

Autonomous robots
Smart industrial machines
Electric mobility systems
Precision automation platforms
High-performance embedded control systems

Next Steps

Ready to implement motor control in your project? Start with basic DC motor PWM control and gradually move to advanced BLDC FOC algorithms. Check out our STM32 GPIO tutorial for hardware setup basics.