Power Electronics

List different application of power electronics devices

• Resistance Fan Regulator - Uses variable resistor; required large space

• Electronic Fan Regulator - Uses power semiconductor devices; remarkably smaller

• CFL - Uses mercury (hazardous); requires ballast to regulate current; longer warmup time to reach full brightness

• LEDs - Energy efficient and long lifespan; environmentally friendly; instant start with full brightness; Power electronics for efficient and safe operation, also enabling features like dimming

• Linear power supply - Dissipates excess power as heat; large transformers, heat sinks and capacitors make it bulkier

• Switched mode power supply - High-frequency switching for efficient power conversion; Smaller, lighter components due to advanced semiconductor technology

Why power electronics is highly efficient?

30V input → 5V output

• Using a resistor causes heat dissipation

• Replacing resistor with transistor still wastes power as heat

• Operate the transistor as switch

• The switch operates by quickly turning ON and OFF

• Since it doesn’t waste energy as heat, the system is highly efficient

With a neat block diagram, explain power electronic system

Power converter: Uses semiconductor devices to convert power to the desired output levels

Control unit: Regulates the power converter for efficient, stable operation

Explain power semiconductor devices

• Building blocks of power electronics

• Highly efficient in handling large voltages and currents

• Act as switches in power conversion units, enabling efficient energy management

• They operate in two states:

  • ON (Conducting state): Switch closed

  • OFF (Blocking state): Switch opened

Explain the difference between ideal & practical states of power electronic devices?

Ideal Power Electronic switch: Features

• Zero ON State resistance - No voltage drop; 0 conduction loss

• Infinite OFF state resistance - No current flow; 0 blocking loss

• Instantaneous Switching: Transition between ON and OFF occurs in no time; switching loss is 0

Practical Power Electronic switch: Features

• Finite ON State resistance - voltage drop; power loss

• Finite OFF state resistance - current leakage; power dissipation

• Switching - Transition between ON and OFF takes a finite amount of time; turn on and turn off times results in switching losses

Give the classification of Power Semiconductor devices

1. Uncontrolled switches (Diode): Only allows current flow in one direction

2. Semi-controlled switches (Thyristors): Can be turned ON by a control signal and naturally turns OFF when current turns to zero

3. Fully-controlled switches (Power transistors [Power MOSFET,IGBT]) - Can be turned ON and OFF by control signals

What are the different semiconductor devices used in power electronics?

Give classification of power electronic converters.

Give applications of different power electronic converters. 

Explain rectifiers (AC-DC) along with their types. Give their applications also

or

Explain the operation of single-phase half-wave and full-wave rectifiers with the help of circuit diagrams and waveforms.

• Converts AC from mains to DC

• Types:

  • Single phase Half-wave rectifiers

  • Single phase Full-wave rectifiers

  • Three phase rectifiers

• Applications: Power supplies for computers and other electronic devices

  

Explain choppers (DC-DC) along with their types. Give their applications also.

• A DC-DC converter is an electronic device that converts direct current (DC) electrical power from one voltage level to another

• Used to regulate voltage, improve efficiency and performance in various electronic devices

• Types:

  • Buck Converters: Steps down the voltage.

  • Boost Converters: Steps up the voltage.

  • Buck-Boost Converters: Can step-up or step-down voltage

• Applications:

  • Consumer electronics: Smartphones, LED lightnings, laptops, SMPS

  • Electric vehicles: Power management systems

  • Renewable energy systems: Solar inverters and battery chargers

Explain AC voltage regulators and cycloconverters (AC-AC). Give applications also.

• Convert alternating current (AC) of one voltage level to another and/or modify its frequency

• Types:

  • AC Voltage regulators: Converts fixed AC input voltage to variable AC output voltage but with constant frequency

  • Cycloconverters: Converts fixed AC input to variable AC output

• Applications: Motor Drives

Explain Inverters (DC-AC) along with their types. Give applications also.

• Converts AC back to DC

• Types:

  • Square wave inverter: Generates a square wave output signal

  • PWM inverter (pulse width modulation): Modulates the width of the pulses to approximate a sine wave output.

• Applications: Used in solar power systems, uninterruptible power supply (UPS) and electric vehicle

Describe power stages in Laptop and Desktops with diagram.

• Power source (Laptop):

  • AC Adapter: Converts AC power to DC for the laptop

  • Battery: Provides portable power with management to control battery life

• Power source (Desktop)

  • Power Supply Unit (PSU): Converts AC to multiple DC voltages

  • No battery backup: Relies on AC power, with an optional external UPS for outages

• Power management unit (Laptop):

  • Manages power between AC adapter and battery

  • Optimizes power usage to conserve battery. Eg: lowers CPU speed when on battery power

• Power management unit (Desktop):

  • No dedicated PMU

  • Power management is less critical due to no battery; focuses more on performance

• DC-DC Converters and Voltage Regulation

  • Both use buck converter to step down voltage required by components

  • Voltage regulators provide stable power to components like CPU, GPU, and RAM.

  • Laptops use advanced power management to save energy, while desktops focus on delivering stable power.

Describe Linear Power Supply (LPS) with block diagram

Power supplies convert AC (Alternating Current) to DC (Direct Current) required by electronic devices

Linear Power Supply: It uses linear regulators (transistors operating in linear regions) to regulate the voltage

1. Step down transformer: Reduces AC voltage

2. Rectifier: Converts AC to DC

3. Filter: Smoothens the rectified DC

4. Regulator: Maintains constant output voltage regardless of variations in input voltage or load conditions

Commonly used linear voltage regulators include:

• LM7805 - Provides a fixed +5V output

• LM7812 - Provides a fixed +12V output

• LM317 - Provides an adjustable voltage regulator

Describe Switch Mode Power Supply (SMPS) with block diagram

A Switch Mode Power Supply converts AC input into regulated DC output using high-frequency switching. The main blocks are:

1. AC Input: The supply receives AC from the mains.

2. Input Rectifier and Filter: The AC is converted into pulsating DC and filtered to reduce ripples.

3. High-Frequency Switch: A transistor turns ON and OFF at a very high frequency using PWM control to regulate how much energy is sent forward.

4. Power Transformer: The high-frequency pulses pass through a small transformer which steps the voltage up or down.

5. Output Rectifier and Filter: The transformer output is rectified again and filtered to produce smooth, stable DC.

6. Control Circuit: It senses the output voltage and adjusts the PWM duty cycle to maintain a constant, regulated output.

An SMPS is highly efficient because the switching device operates mostly in ON/OFF states, reducing power loss as heat.

Difference between LPS &SMPS

LPS:

• Advantages:

  • Simple design

  • Low noise

  • Good regulation with minimal ripple

• Disadvantages:

  • Inefficient (high heat dissipation)

  • Heavy and bulky due to transformers

• Applications (used in low noise applications):

  • Audio equipment

  • Laboratory instruments

  • Medical devices

SMPS:

• Advantages

  • High efficiency (less heat)

  • Compact and lightweight

  • Suitable for high power applications

• Disadvantages:

  • Complex design

  • Higher noise due to switching

  • High EMI

• Applications:

  • Computers and servers

  • Consumer electronics (TVs, laptops)

  • Telecommunication equipment

  • Industrial automation

Describe Uninterrupted Power Supply (UPS) with block diagram

• A device that provides emergency power to the load when the main power fails

• Serves to protect electronic equipment and systems from power interruptions and/or fluctuations.

• Eg: V-Gaurd, Eaton, Sorotek

• Layout of a UPS:

  • Rectfier: Converts AC to DC to charge the battery

  • Battery: Stores energy to be used during power outage

  • Inverter: Converts stored DC back to AC to power the load

  • Switch: Transfers input power source

Explain different types of UPS.

Offline:

• Stand by UPS: Offers basic protection with quick switchover to battery power.

• Line-Interactive UPS: Corrects minor power fluctuations without switching to battery.

Online:

• Double conversion UPS: 

  • Offers highest protection

  • Continously powers the load from inverter ensuring clean and consistent power

Cost:

• Offline - low to medium running cost

• Online - high cost

Power rating:

• Offline UPS: 1 kVA to 3 kVA

• Online UPS: Upto 10 kVA (single-phase)

• Online UPS: 0 kVA – several MW (three-phase)

What are the applications of a UPS

• Computer and servers: Protects data and ensures smooth operation during power interruptions.

• Telecommunication equipment: Maintains communication services during power outages

• Medical equipment: Ensures uninterrupted operation of critical medical devices.

• Industrial Control systems: Prevents downtime in manufacturing processes.

• Home and office electronics: Provides backup for personal computers, modems, and other essential devices.

What are the advantages of EVs?

• Reduced greenhouse gas emission

• Energy efficiency

• Increased use of renewable energy

• Energy conservation through efficient battery management & regenerative braking

Explain EV with the help of block diagram.

1. Battery Charging Unit (AC-DC): Converts the AC power from charging stations into DC power to store in the battery

2. Battery Pack: The battery pack is the main energy source of the EV. It stores DC power and supplies it to the motor, auxiliaries, and other systems

3. Battery Management System: Monitors voltage, temperature and ensures safe operation

4. DC-DC converter: Converts high battery voltage DC to lower voltage levels for auxiliary systems like lighting, sensors, dashboard electronics etc. and power the controller

5. DC–AC Inverter (Traction inverter): Converts battery DC to controlled AC for the traction motor; sets torque and speed.

6. Motor/Generator: Drives the vehicle during motoring; during braking it acts as a generator and sends energy back through the inverter to the battery (regeneration), under BMS limits.

7. Controller: The controller manages the inverter and coordinates the motor’s operation. It regulates power flow during driving.

8. Mechanical transmission with differential gears: Matches motor output to the wheels and splits torque to left/right.

List the types of EVs

List the challenges associated with EVs

• Charging stations

• Consumer perception

• Initial cost

• Maintenance and repairs

• Battery technology and range

• Supply chain issues

• Battery disposal and recycling

• Safety and reliability

• Policy and regulation

Government support in EV

• FAME India scheme: Provides subsidies for EV purchases and supports charging infrastructure.

• State Level Incentives

• Charging Infrastructure Development

• Production-Linked Incentive (PLI)

• Registration relaxations (Do not require Registration):

  • Bicycles and E-bikes (up to 250 Watts & 25km/h)

  • Electric Scooters & Electric Skateboards (under a certain speed or power limit)

  • Personal Mobility Devices (electric unicycles or hoverboards)

• India aims for EVs to comprise 30% of total vehicle sales by 2030

List the Emerging EV Technologies.

• Wheel hub motors: Motors placed inside the wheels for direct drive and improved efficiency

• Solid-state batteries: Safer batteries with higher energy density and faster charging.

• Vehicle-to-Grid (V2G) technology: Allows EVs to send power back to the grid when needed.

• Wireless charging: Charges the EV through electromagnetic induction without cables.

• Autonomous driving: Uses sensors and AI to enable self-driving functions in EVs.

• Smart charging solutions: Adjust charging based on grid load, electricity price, and user needs.