Power Management for electric and hybrid electric vehicles
With the ever increasing number of Internal Combustion Engine (ICE) vehicles on the roads, the demand for fossil-fuels is rising steeply leading to increased CO2 emissions that are harmful to the environment. Also, as the world reels under a supply crunch of fossil fuels, their prices are touching all-time highs making them an unattractive option for vehicles. By Ravi Kadabi, Practice Head Powertrain and Vehicle Electronics Applications, Automotive Group, Wipro Technologies As a result of this scenario, Governments world over are introducing legislations to curtail emissions, provide incentives for more fuel efficient vehicles and reduce dependency on fossil fuels. Also, as the automotive industry faces competition and cost pressure, technological innovations in this area are becoming inevitable. The Electric Vehicle (EV)/Hybrid Electric Vehicles (HEV) are industry innovations addressing this issue. The required infrastructure which include Vehicle-To-Grid (V2G) and Grid-To-Vehicle (G2V), Home Energy Management, Smart Metering, Timed Energy Transfer, Charging and Bill Payment Services as well as Telematics Services, are drivers for the advancement of technologies including power management. As the existing power demand from domestic/ industrial sectors is increasing and with EV/HEV vehicles' requirement of additional electrical energy, grid-power management has to work in a more stringent environment. It is estimated that the world energy consumption will grow by 49 percent from 2007 to 2035. In this paper, we will discuss the current status and future trends for various energy sources that are going to be used in the automotive industry. The related challenges in automotive power electronics will also be discussed.
Automotive segment is one of the largest consumers for power management devices, as it forms the key component for EV/HEV. The key semiconductor power devices include smart IGBT/BJT, Power MOSFET, Power ICs as well as SiC that is expected to reach a $5 billion market in 2020. Automotive vehicles are classified into Micro-Hybrid (~6kW, also called as Start-Stop), Mild-Hybrid (~10kW), Full-Hybrid (~20kW), Plug-in-Hybrid (~30kW) and Electric Vehicles (~75kW). The HEVs are classified into Serial-Hybrid (Range Extender), where the drive-shaft gets driven by electric motor and Parallel Hybrid where the drive-shaft shares the load between ICE & electric motor. Among hybrid vehicles, Micro-Hybrid will have the highest growth due to its low cost and easy integration. Mild and Full-Hybrid vehicles will continue their strong penetration in the automotive market. Plug-in-Hybrid vehicles and Electric vehicles use the same technology for high voltage range and plug-to-grid for recharge. A typical configuration is illustrated in the block diagram:
The key subsystems of EV/HEV vehicles are illustrated in the above block diagram. The Inverter/ Converter is the main power house of a vehicle and manages the power according to the load-demand and stores sufficient energy from different power sources. Permanent magnet motors are widely used in the vehicles because of their high torque density, potentially wide constant power range, and relatively small required inverter rating. Also the kinetic energy generated in the motor during braking is used as re-generative electrical energy. A relatively small ICE is used in serial-hybrid vehicles as a Range Extender while the energy of the battery gets depleted.
As the BMS is an integral part of a vehicle, Wipro has developed a generic BMS framework which can be customized according to the requirements of Battery Manufacturers, Tier1/Tier2 & OEMs. The key features of this BMS include plug-and-play of battery-pack, energy management via smart algorithms, scalable battery capacity which depends on vehicle type, energy storage via regenerative braking, power line communication, safety and redundancy as well as battery analyzer including tell-tale of the battery health parameters. It also includes communication interfaces to other electronic control units like instrument cluster for displaying battery data, PC for reconfiguring BMS software for a given battery-pack and telematics for remote monitoring with LCD.
Automotive power electronics industry started to focus on the integration of inverter/converter and BMS with electric motor functionalities that has the ‘power' to reduce the cost of hybrid vehicles. Currently, Li-Ion batteries and ultra-capacitors are power storage devices with the greatest development potential. A combination of ultra-capacitors and battery optimizes the vehicle's power resources.
As power electronics for the automotive industry is a relatively new development, there are multiple challenges that need to be addressed, some of which are illustrated here: The functional and non-functional requirements of vehicles (key cases as mentioned in the table) bring in new challenges and opportunities for design engineers in power management areas.
The challenges faced for these requirements including EMC/EMI can be addressed through technical innovations. The EV/HEV technologies provide an opportunity to address the above design challenges.
To succeed in the 21st Century, the automotive industry has started to focus more on energy efficient vehicles so that they can contribute to new environment-friendly vehicles including EV/HEV vehicles. Power management in the automotive industry is a fast growing segment. Wipro has developed the BMS solution that enables these environment-friendly vehicles and can be extended to various renewable-energy sources. www.wipro.com
