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Electrical System Analysis Of Hybrid Electric VehicleIntroduction

The trend to save the environment for future generations while at the same time maintain our current lifestyle has proved to be a constant struggle. One of the most discussed and debated issue of modern time is the increased use of petroleum based products for automobiles. Cars are considered consumer goods. Automobiles are run using an internal combustion (IC) engine that burn hydrocarbons to generate energy that helps move the vehicle. Currently, the two most commonly used hydrocarbons are gasoline and diesel.

The growing dependence on imported oil, along with a heightened concern about the environment, has led to our increased interest in electric cars as an alternative to traditional gas-powered automobiles. Battery systems for electric vehicles are improving, but with their limited range of travel, they are still not feasible for most people. In addition, we believe that the average person making the decision to purchase environmentally friendly vehicles would demand that those vehicles be comfortable, attractive, convenient, and affordable to purchase and maintain. Newly available automotive technology, known as hybrid electric vehicles (HEV), appears to meet these requirements. Hybrid power systems were conceived as a way to compensate for the shortfall in battery technology (Office of Transportation Technologies, HEV program). Hybrid electric vehicles recharge as it is driven, get approximately double the miles per gallon of gas than current vehicles (Toyota, technology) and can be refueled at any gas station. Each hybrid vehicle will produce thousands fewer pounds of pollutants than the vehicles currently on the road. According to Department of Energy estimates, a hybrid car driven 12,000 miles per year will cut carbon dioxide emissions by 4,700 pounds over its predecessor, says the National Resources Defense Council article on earth smart cars.

Hybrids will allow drivers to get between 20 and 30 miles per gallon more than standard automobiles. With this kind of savings, it won't take long to make up the additional cost of the hybrid. Hybrids save on gas in a number of ways. All hybrids shut off the gas engine automatically when the car is stopped. The engine turns back on when the driver presses the gas pedal. The gas engine will also come on to start charging the batteries when they become low on power.

Typically, when a consumer buys products to help the environment the consumer pays more. Hybrids are a refreshing exception where the consumer actually saves money by doing something good for the environment. Not only does fuel efficiency save the drive money, burning less gasoline means that there is less pollution causing emissions released into the atmosphere. There is also a lower level of carbon dioxide, a major contributor to global warming, released into the atmosphere.

HEVs are growing leaders in transportation technology development. Hybrids have great potential for growth in improving the automotive industry, while also reducing serious resource consumption, reliance on foreign oil, air pollution, and traffic congestion. The hybrid's complexity, and the fact that some of the best storage and conversion systems have yet to be fully developed, ignites varied opinions on hybrids' ultimate impact in the marketplace.

In conclusion, hybrid cars are better than traditional gasoline powered vehicles, however they still have problems. Currently hybrid cars seem to be the best solution in combating the devastating global effects of exhaust emissions. With lower emissions and improved fuel economy, hybrids are a great way to travel. However, these lightweight cars are more vulnerable to traffic fatalities and still give off some emissions. They also accelerate at a slower pace than conventional vehicles. Hybrids have a short battery life, and their parts are expensive and not easily accessible, but hopefully as hybrids become more popular, this will change. Overview

Hybrid Systems

The hybrid system is the wave of the future. In its simplest form, a hybrid system combines the best operating characteristics of an internal combustion engine and an electric motor. More sophisticated hybrid systems recover energy otherwise lost to heat in the breaks and use it to supplement the power of its fuel-burning engine. These sophisticated techniques allow the hybrid system to achieve superior fuel efficiency. On continuum that is hybrid technology, we typically break things down into full or strong, mild and micro hybrids which are also known as simply stop-start engine hybrid. A mild hybrid relies on the internal combustion engine to provide constant power for moving the vehicle but is incapable of propelling the vehicle alone. Full hybrids use a gasoline engine as the primary source of power like solar, fuel cells, battery etc; and electric motor provides additional power when needed. All these have been in chapter 1.

Battery Technology

Central to the discussion regarding the relative merits of the various hybrids is the big box that stores the energy to propel the electric motorthe battery. The battery is responsible for 25 - 75% of the increased weight, volume, and cost associated with the various hybrid configurations. Today most hybrid car batteries are Nickel metal hydride or Lithium-ion; both are regarded as more environment friendly then lead-based batteries which constitutes the bulk of car batteries today. The Lithium-ion battery has attracted attention due to its potential for use in hybrid electric vehicles. In addition its smaller size and lighter weight, Lithium-ion batteries deliver performance that helps to protect the environment with features such as improved charge efficiency without memory effect. The battery industry is currently working on the development of better performing and more sophisticated technology that costs less. In chapter 2, all the battery aspects are elaborated.

Electrical and Thermal management

The battery charger is a bidirectional ac-dc converter, recharge mode is ac to dc conversion and inverter mode is dc to ac conversion. To implement the plug-in function a single phase bidirectional ac-dc converter interfacing with the grid is essential. A dc-dc converter balances the voltage between the electric motor and the energy storage device, in a hybrid, boosting or reducing the voltage as necessary, which provides more of the energy under braking and under acceleration.

Regenerative braking means capturing the vehicles momentum (kinetic energy) and turning it into electricity that recharges the on board battery as the vehicle is slowing down or stopping. The super capacitor is an electro-chemical capacitor that has usually high energy density compared to common capacitors. These can quickly store large amount of electricity and discharge the electricity on demand to batteries.

The thermal management system delivers a battery pack an optimum average temperature with only small variations between the modules and within the pack. An ideal thermal management system should be able to maintain the desired uniform temperature in pack by rejecting heat in hot climates, adding heat in cold climates and providing ventilation if the battery generates potentially hazardous gases. The entire chapter 3 is about electrical and thermal management of the hybrid system.Chapter 01

Hybrid System

1.1 Stop-Starts Hybrids

A stop-start hybrid is the simplest kind, but this minimal technology may become the most common within a few years.

Figure 01: Start-stop hybridIt is composed simply of an energy storage devicelike a batteryand a beefed-up starter-motor that can also act as a generator.

Stop-Start systems are also called idle-stopbecause it puts an end to burning fuel and emitting pollutants when a conventional car would be idling.

In practice, the cars engine control unit shuts off the engine when the car slows down or comes to a stop. As soon as the driver puts in the clutch, moves the shift lever, or accelerates, the battery powers the starter motor, which quickly switches on the engine

Start-stop systems are the lowest-cost hybrid alternative, but if fitted to large numbers of cars, they could substantially reduce fuel consumption and air pollution from idling vehicles, especially in crowded city centers.

1.2 Mild Hybrid

A mild hybrid is a type of gasoline-electric hybrid that uses an internal combustion engine to power the vehicle at all times. An electric motor is incorporated only as a power booster of sorts, as a starter-generator, or both. While some mild hybrids use an electric drive motor to provide a gasoline engine with extra power, it cannot ever propel the vehicle on its own. Mild hybrids save fuel by shutting engine power off under most circumstances when the vehicle is stopped, braking, or coasting. The engine restarts seamlessly and efficiently. Electric accessories like the radio or GPS navigation continue to function with the engine off.

How They Are Different

All mild hybrids are less expensive than full hybrid systems because they require less sophisticated components and less battery power. Some, but not all, mild hybrids use regenerative braking to recharge the battery. Different mild hybrid configurations exist including Integrated Starter-Generator (ISG) and Belt Alternator Starter (BAS) systems.

The basic premise of the mild hybrid is same as the strong hybrid. An electric motor/generator operates in parallel with the internal combustion engine to provide additional drive torque as well as regenerative braking. The primary difference lies in the power and energy capacity of the electrical side of the system.

Figure 02: Next genera


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