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Electric Drives:
Assignment 2
Name– Alok Kumar
Roll No.- 2022UEE4585 Objective- Present a detailed case study of a real-world DC motor drive application, including design, implementation, and performance analysis.
Case Study for real-world DC motor drive:
This case study examines the design, implementation, and performance
analysis of a DC motor drive system specifically tailored for an electric vehicle (EV). DC motor drives play a critical role in the control and efficiency of EVs, enabling smooth propulsion and energy management. The study focuses on the implementation of a DC motor drive system to control a series wound DC motor, emphasizing the drive design and performance in real-world conditions. Brushless DC motor Drive used in EV
System Specifications Motor Type: Series Wound DC Motor Voltage: 72V DC Power: 15 kW (continuous) Torque: 50 Nm (max) Speed: 4000 RPM (max)
Design of the DC Motor Drive
1. Motor Drive Architecture The motor drive consists of the following key components: DC-DC Converter: Steps down the battery voltage to match the motor's voltage requirements while regulating the current. Pulse Width Modulation (PWM) Inverter: The core of the motor drive, responsible for controlling the motor speed by modulating the voltage supplied to the motor. Current Sensing Circuit: Measures the current supplied to the motor and provides feedback to the control system for accurate torque control. Closed-Loop Control System: Utilizes feedback from speed and current sensors to regulate the drive’s output, ensuring precise speed and torque control.
The PWM technique is used to efficiently control the motor by switching the DC voltage on and off at high frequencies (20 kHz) to create a variable average voltage, which directly controls motor speed and torque.
B lock diagram of DC motor drive Matlab Model for DC Motor Drive
2. Control Strategy The drive employs a closed-loop control strategy to manage the motor’s speed and torque: Speed Control: A Proportional-Integral (PI) controller adjusts the PWM duty cycle to regulate motor speed based on the desired setpoint. The system uses feedback from a tachometer to ensure accurate speed regulation, particularly under varying load conditions like inclines or sudden acceleration. Torque Control: The motor’s torque is controlled by regulating the current supplied to the motor. The current feedback loop monitors motor current using a sensor, and the controller adjusts the PWM signal to limit current when necessary, protecting the motor from overheating or overloading.
3. Regenerative Braking Integration
The motor drive also includes a regenerative braking system that enables the DC motor to function as a generator during braking. This allows the system to capture kinetic energy and convert it into electrical energy, which is fed back into the battery. The drive adjusts the current and voltage levels during regenerative braking to optimize energy recovery.
Implementation of the DC Motor Drive
1. Hardware Implementation The motor drive system was implemented with robust hardware: Power electronics: MOSFETs were used in the PWM inverter for fast switching and efficiency. Control Unit: A microcontroller-based system managed the closed-loop control, processing feedback from sensors and sending PWM signals to the motor. Cooling: The power electronics and motor drive components were air- cooled, ensuring thermal stability during operation. Power MOSFET in DC Drive
2. Software and Control Algorithms
PWM Generation: The control software generated PWM signals based on speed and current feedback. PI Controller Tuning: The PI controller was tuned to minimize overshoot and achieve fast response times for speed regulation, especially during transitions such as acceleration and deceleration. Protection Logic: The software included protection algorithms to prevent overcurrent and thermal overload conditions, automatically adjusting the drive output to protect the motor.
Performance Analysis 1. Speed Control The motor drive achieved precise speed control, maintaining the desired speed within ±2% of the setpoint across various load conditions. The closed-loop PI controller provided stable operation even during abrupt changes in speed demands, such as sudden acceleration or deceleration. The speed control equation for a DC motor is N = K (V – IaRa)/ ø, where K is a constant. This equation implies that: The motor's speed is directly proportional to the supply voltage The motor's speed is inversely proportional to the armature voltage drop The motor's speed is inversely proportional to the flux due to the field findings
2. Torque and Acceleration Performance
The series wound DC motor, controlled by the motor drive, exhibited high torque at low speeds, a critical requirement for EV applications. The drive maintained a consistent torque output, allowing the vehicle to accelerate smoothly. The motor was capable of delivering a maximum torque of 50 Nm, sufficient for typical urban driving scenarios.
3. Regenerative Braking Efficiency
The regenerative braking system allowed the motor to act as a generator, capturing 10-15% of the energy during braking events and feeding it back to the battery. This significantly improved the overall energy efficiency of the vehicle, extending its range by reducing energy wastage during deceleration.
4. Energy Consumption and Efficiency
The DC motor drive exhibited high efficiency, with energy consumption averaging 145 Wh/km during urban driving. This efficiency was primarily due to the optimized PWM control, which minimized switching losses, and the integration of regenerative braking. 5. Thermal Management and Reliability The cooling system ensured the motor drive components remained within safe operating temperatures. Under peak load conditions, the drive components reached a maximum temperature of 75°C, which was within the safe operating range. There were no instances of thermal shutdown or failure, demonstrating the reliability of the drive system under real-world conditions. Experimental Data for Series Wound DC Motor in Electric Vehicle
Here is some sample experimental data based on testing the performance of a
Series Wound DC Motor in an electric vehicle (EV) application. The data focuses on critical aspects such as speed, torque, current, voltage, and temperature under different load and operating conditions.
Motor Specifications: Voltage: 72V DC Power: 15 kW (continuous) Max Torque: 50 Nm Max Speed: 4000 RPM
Experimental Conditions: Vehicle weight: 1000 kg Ambient temperature: 25°C Driving scenario: Urban driving with accelerations, decelerations, and flat road cruising.
1. Speed vs. Torque at Different Voltages
Voltage (V) Motor Speed (RPM) Torque (Nm) Power Output (kW) 72 4000 30 12.56 60 3500 35 12.84 50 3000 40 12.56 Voltage (V) Motor Speed (RPM) Torque (Nm) Power Output (kW) 40 2500 45 11.77 10.47 30 2000 50
Observation: As voltage decreases, speed drops, but torque increases to meet
load demands. This is typical for series wound motors, which generate higher torque at lower speeds.
Observation: As the load increases, the current drawn by the motor increases to maintain the torque output. The motor is efficient at generating torque under load, but power consumption rises accordingly.
