Week 4 Session 5

EV Fundamentals Week:4: Session:5 Challenge

Problems: -

Explain the various applications of Power converters in an Electric vehicle. For Example, what type of converter will you use for Horn which requires DC and less than 10V. Likewise come up with different applications.

Answers: -

Power electronic converters find numerous applications in electric vehicles (EVs) and are crucial for efficient energy management and system operation by efficiently converting and controlling electrical energy. The three major types of power converters that are used in EVs are: -

• DC-DC Converters: - DC-DC converters are widely employed in EVs for voltage regulation and power delivery. This converter converts an unregulated DC input to a regulated DC output. Based on the load requirement they can step up or step down the output voltage levels. They can further be classified into three categories:
  1. Non-isolated type converters: - The examples of this type of converter are Buck converter, Boost converter, Buck-Boost converter etc.
  2. Isolated type converters: - In this type of converters the input and the output side are electrically isolated by a transformer. The examples of this type of converter are Flyback converter, Forward converter, Half-bridge converter, Full-bridge converter, Push-Pull converter etc.
  3. Resonant converters: - This family of DC-DC converters is used for high power applications. The examples of this type of converter are Zero voltage switching (ZVS) converter, Zero current switching (ZCS) converter.

These converters are used for various purposes to regulate voltage levels within the EV system. They find application in:

• Acting as an interface between the charging station and the battery.
• Powering low-voltage accessories: - DC-DC Buck converters are used step down the high-voltage DC battery power to provide the required voltage for operating low-voltage auxiliary loads such as:
  • Horn: A DC-DC Buck converter can step down the high-voltage DC battery power to the required lower voltage (less than 10V) for operating the horn. In this case the DC-DC Buck converter would take the higher DC battery voltage (typically 12V or higher) and convert it to the desired lower voltage of less than 10V to power the horn. The converter's output voltage can be adjusted and regulated to meet the specific requirements of the horn.
  • Lighting systems: DC-DC converters can adjust the voltage to power different lighting systems in the vehicle, such as headlights, taillights, and interior lights, and for dimming purpose as well.
  • Onboard Accessories: DC-DC Converters can power and control various onboard accessories, including infotainment systems, instrument clusters, and HVAC (Heating, Ventilation, and Air Conditioning) systems, pumps, fans, and motors for various functions like coolant circulation, hydraulic fluid control, and windshield wipers.
• Charging auxiliary batteries: They convert the high-voltage battery power to the appropriate voltage for charging auxiliary batteries, such as those used for the 12V system.
• In some applications where low voltage battery packs are used for cost minimization purpose, DC-DC step up converters are used to interface this low voltage battery systems with high voltage motor systems.
• When we use multiple energy storage systems in EVs (battery, ultracapacitor, fuel cells, PV panels) to improve the energy reliability, each energy storage systems will generate different output voltages. Therefore, in order to accumulate the desired output, we need DC-DC converter.

• AC-DC Converters: - They are commonly called as rectifiers. In EVs, rectifiers are widely used in battery charging purpose. They convert the AC power from the charging infrastructure or an onboard generator to the DC power level required for charging the EV’s main traction battery systems. Also, the rectifiers are an essential component for the Onboard chargers. The Onboard Chargers in EVs utilize power converters to convert AC power from external charging sources to the appropriate DC voltage for charging the EV's battery. Recently rectifiers with power factor correction have found more popularity in the EV industry.
• DC-AC Inverters: - This power converter can control both the magnitude and the frequency of the output AC voltage. DC-AC inverters are used to convert the DC power stored in the traction battery systems to AC power for driving the electric motors. They provide variable frequency and voltage control to adjust the motor speed and torque. They can provide both single phase output or three phase output depending upon the application.

Other than the abovementioned converters and their applications, the power converters in EV system find their application in various other areas. Some important applications are discussed below:

• Battery Management System (BMS): - The power electronic converters are an integral part of the BMS, which manages the battery pack. They are used for:
  1. Balancing individual cells: The power converters redistribute the energy among individual battery cells to ensure that the individual cells in the battery pack are balanced in terms of voltage and state of charge, and ensures balanced charging and discharging, maximizing the overall performance and lifespan of the battery.
  2. Charging and discharging control: The Power converters regulate the charging and discharging process, ensuring safe and optimized operation of the battery.
  3. Monitoring and protection: Power converters monitor various parameters of the battery, such as temperature and voltage, and provide protection mechanisms to prevent overcharging, over-discharging, and thermal issues.
  4. State-of-Charge (SOC) estimation: The power converters help to provide accurate estimation of the battery's SOC, allowing the vehicle's control systems to effectively manage the battery's energy usage.
• Regenerative Braking: - Power electronic converters facilitate regenerative braking by converting the kinetic energy of the wheel during braking into electrical energy, which is then stored in the battery for later use, enhancing overall energy efficiency. For example we know that we can use a Two quadrant or a Four quadrant DC-DC chopper for the regenerative braking purpose of DC motors.
• Power Steering converters: - Electric power steering systems use power converters to convert electrical power into mechanical power for assisting the driver in steering the vehicle with reduced effort.
• Powertrain cooling system: - Power electronic converters are involved in controlling the cooling systems for various components, including the inverter and motor, to maintain their optimal operating temperatures.
• Motor Drive Control: - Power electronic converters like Inverters or DC-DC choppers are responsible for precise control of the electric motor's speed, torque, and direction. They regulate the power delivered to the motor, enhancing efficiency and performance ensuring efficient and optimized operation.
• Vehicle-to-Grid (V2G)/Grid-to-Vehicle (G2V) Converters: - In recent years the V2G/G2V converters are been used widely which are basically Bi-directional power converters where one side of the converter is connected to the AC power supply from the grid and the other side is connected to the DC battery traction pack of the vehicle. This converter enables bidirectional power flow, allowing the EV to supply energy back to the grid when it is in idle condition and the load demand in the grid is high. In many applications the On board chargers of the vehicles are inbuilt with Bi-directional converters. While charging (G2V operation) the converter takes AC power supply from the grid and charges the DC battery pack system. This time it works as a Rectifier. Whereas in Vehicle-to-Grid (V2G) power supply the converter converts the input DC power from the traction battery pack to suitable AC power to the grid. This time it operates like an Inverter.