02-01-2013, 10:35 AM
HYBRID ELECTRIC VEHICLES
1HYBRID ELECTRIC.pdf (Size: 723.94 KB / Downloads: 65)
INTRODUCTION
By the time, the commercialization of the next-generation car comes around, advanced power electronics and motor drives will have already established themselves as prime components of advanced vehicular drive trains. Advanced power electronic converters and traction motor drives will be responsible for a major part of the vehicle‘s energy usage. As of now, the automotive market is making rapid developments in case of the hybrid electric vehicles (HEVs).
Commercially available HEVs include the Toyota Prius, Toyota Highlander Hybrid, Toyota Camry Hybrid, Lexus RX 400 h, Honda Insight, Honda Civic Hybrid, Honda Accord Hybrid, and Ford Escape Hybrid. In the case of future HEVs, power electronic converters and associated motor drives, which control the flow of electrical energy within the HEV power system, promise to be the keys to making HEVs more fuel efficient and emit lower harmful pollutants.
As is well known, in the first half of the past century, the 6-V electrical system in automobiles served the purpose of ignition, cranking, and a satisfying few lighting loads. Since then, there has been a constant rise in vehicular power requirement. Performance loads, such as electric steering, that were traditionally driven by mechanical, pneumatic, and hydraulic systems, are now increasingly being replaced by the electrically driven systems, in order to increase the performance and efficiency of operation. Furthermore, luxury loads have also increased over time, imposing a higher demand of electrical power[1].
CONVENTIONAL AUTOMOTIVE POWER SYSTEMS
During the mid 1950s, the automotive industry decided to opt for 12-V electrical power systems for vehicles, since the then popular 6-V system was rapidly becoming plagued by the increasing vehicular load demands[2]. The battery became a six cell module instead of three cells, at approximately the same energy rating. The electrical system demand had risen from the 100Wof the early 1900s to typically about 1 kW by the 1990s, as more and more electrically powered devices were installed. The conventional electrical system in an automobile can essentially be divided into the architectural elements of energy storage, generation, starting, and distribution. The distribution system of a conventional 14-V power system satisfies vehicular loads such as, interior/exterior lighting, electric motor driven fans/pumps/compressors, and instrumentation subsystems. A simple rendition of the conventional 14-V electric power system architecture is shown in Fig. 1. As from Fig. 1, the conventional power system arrangement has a single 14-V dc voltage level, with the vehicular loads being controlled by manual switches and relays. As mentioned earlier, the present average power demand in an automobile is approximately 1 kW. The voltage in a 14-V system actually varies between 9 and 16 V at the battery terminals, depending on the alternator output current, battery age, state of charge, and various other minor factors. This results in overrating the loads at nominal system voltage.
Battery Electric Vehicle (EV) Drive Train Topology
A purely electric drive system principally replaces the internal combustion engine (ICE) and the various transmission systems with an all-electric system. As is well known, rechargeable chemical batteries are the traditional option as energy sources for EVs. But they tend to be heavy and expensive to replace over their limited lifetimes. In addition to traditional batteries like lead–acid, nickel metal–hydride (Ni–MH), and nickel–cadmium (Ni–Cd), there are advanced technologies like lithium–polymer (Li-polymer) and lithium–ion (Li–ion) batteries. Despite the popularity that these advanced batteries have gained for portable electronic applications.
Series HEV Drive Train Topology
In a series design, the internal combustion engine is not directly connected to the drive train at all, but powers an electrical generator instead. This is similar to the operation of diesel-electric train locomotives. A series hybrid vehicle is basically an electric vehicle with an on-board battery charger. An ICE is generally run at an optimal efficiency point to drive the generator and charge the propulsion batteries on-board the vehicle, as shown in Fig. 2.4. When the state of charge (SOC) of the battery is at a predetermined minimum, the ICE is turned on to charge the battery.
Series-Parallel HEV Drive Train Topology
The series-parallel HEV is a combination of the series and parallel hybrids. There is an additional mechanical link between the generator and the electric motor, compared to the series configuration, and an additional generator compared to the parallel hybrid, as shown in Fig. 2.6. With this design, it is possible to combine the advantages of both the series and parallel HEV configurations. It must be highlighted here that the series-parallel HEV is also relatively more complicated and expensive. There are many possible combinations of the ICE and traction motor.
FCV Drive Train Topology
The potential for superior efficiency and zero (or near zero) emissions has long attracted interest to fuel cells as the potential automotive engine of the future. However, systematic
efforts to realize the efficiency and emissions benefits of fuel cells in the transportation sector have materialized only in the last 10 years. The overall goal of ongoing fuel cell research and development programs is to develop a fuel cell engine that will give vehicles the range of conventional cars, while attaining environmental benefits comparable to those of battery-powered electric vehicles. Although the technology is currently quite expensive, fuel cells offer benefits including high overall efficiency and quiet operation due to few moving parts. A typical fuel cell based propulsion system is shown in Fig.2.8.
POWER SYSTEM ARCHITECTURES FOR HEVS
Advanced Electrical Features in Future HEV Technologies
As mentioned earlier, there is a trend in the automotive industry to replace more engine driven mechanical and hydraulic loads with electrical loads, due to higher efficiency, safety requirements, and driver‘s comfort. All of these new functions require the application of power electronics. In most of the cases, the cost of the power electronics dominates the argument of introducing such functions. Many of these functions will only appear in concept vehicles in the projected future. Some of these include luxury loads, such as information and entertainment that have received lots of hype recently. The other class of features is x-by wire, where ―x‖ stands for an advanced function such as, ―steer‖ or ―brake.‖ Another class of advanced electrical features includes power steering pump, electric active suspension system, electromechanical valve control, electrically heated catalytic converter, air-conditioning systems, and water/oil/fuel pumps. There are also other loads such as throttle actuation, ride-height adjustment, rear-wheel steering, which are proposed to be driven electrically in the future. Fig. 3.1 depicts a summary of some of the future electrical features automotive power systems. It is virtually mandatory that most of the proposed future electric loads will indeed require power electronic controls of some sort[4].
1HYBRID ELECTRIC.pdf (Size: 723.94 KB / Downloads: 65)
INTRODUCTION
By the time, the commercialization of the next-generation car comes around, advanced power electronics and motor drives will have already established themselves as prime components of advanced vehicular drive trains. Advanced power electronic converters and traction motor drives will be responsible for a major part of the vehicle‘s energy usage. As of now, the automotive market is making rapid developments in case of the hybrid electric vehicles (HEVs).
Commercially available HEVs include the Toyota Prius, Toyota Highlander Hybrid, Toyota Camry Hybrid, Lexus RX 400 h, Honda Insight, Honda Civic Hybrid, Honda Accord Hybrid, and Ford Escape Hybrid. In the case of future HEVs, power electronic converters and associated motor drives, which control the flow of electrical energy within the HEV power system, promise to be the keys to making HEVs more fuel efficient and emit lower harmful pollutants.
As is well known, in the first half of the past century, the 6-V electrical system in automobiles served the purpose of ignition, cranking, and a satisfying few lighting loads. Since then, there has been a constant rise in vehicular power requirement. Performance loads, such as electric steering, that were traditionally driven by mechanical, pneumatic, and hydraulic systems, are now increasingly being replaced by the electrically driven systems, in order to increase the performance and efficiency of operation. Furthermore, luxury loads have also increased over time, imposing a higher demand of electrical power[1].
CONVENTIONAL AUTOMOTIVE POWER SYSTEMS
During the mid 1950s, the automotive industry decided to opt for 12-V electrical power systems for vehicles, since the then popular 6-V system was rapidly becoming plagued by the increasing vehicular load demands[2]. The battery became a six cell module instead of three cells, at approximately the same energy rating. The electrical system demand had risen from the 100Wof the early 1900s to typically about 1 kW by the 1990s, as more and more electrically powered devices were installed. The conventional electrical system in an automobile can essentially be divided into the architectural elements of energy storage, generation, starting, and distribution. The distribution system of a conventional 14-V power system satisfies vehicular loads such as, interior/exterior lighting, electric motor driven fans/pumps/compressors, and instrumentation subsystems. A simple rendition of the conventional 14-V electric power system architecture is shown in Fig. 1. As from Fig. 1, the conventional power system arrangement has a single 14-V dc voltage level, with the vehicular loads being controlled by manual switches and relays. As mentioned earlier, the present average power demand in an automobile is approximately 1 kW. The voltage in a 14-V system actually varies between 9 and 16 V at the battery terminals, depending on the alternator output current, battery age, state of charge, and various other minor factors. This results in overrating the loads at nominal system voltage.
Battery Electric Vehicle (EV) Drive Train Topology
A purely electric drive system principally replaces the internal combustion engine (ICE) and the various transmission systems with an all-electric system. As is well known, rechargeable chemical batteries are the traditional option as energy sources for EVs. But they tend to be heavy and expensive to replace over their limited lifetimes. In addition to traditional batteries like lead–acid, nickel metal–hydride (Ni–MH), and nickel–cadmium (Ni–Cd), there are advanced technologies like lithium–polymer (Li-polymer) and lithium–ion (Li–ion) batteries. Despite the popularity that these advanced batteries have gained for portable electronic applications.
Series HEV Drive Train Topology
In a series design, the internal combustion engine is not directly connected to the drive train at all, but powers an electrical generator instead. This is similar to the operation of diesel-electric train locomotives. A series hybrid vehicle is basically an electric vehicle with an on-board battery charger. An ICE is generally run at an optimal efficiency point to drive the generator and charge the propulsion batteries on-board the vehicle, as shown in Fig. 2.4. When the state of charge (SOC) of the battery is at a predetermined minimum, the ICE is turned on to charge the battery.
Series-Parallel HEV Drive Train Topology
The series-parallel HEV is a combination of the series and parallel hybrids. There is an additional mechanical link between the generator and the electric motor, compared to the series configuration, and an additional generator compared to the parallel hybrid, as shown in Fig. 2.6. With this design, it is possible to combine the advantages of both the series and parallel HEV configurations. It must be highlighted here that the series-parallel HEV is also relatively more complicated and expensive. There are many possible combinations of the ICE and traction motor.
FCV Drive Train Topology
The potential for superior efficiency and zero (or near zero) emissions has long attracted interest to fuel cells as the potential automotive engine of the future. However, systematic
efforts to realize the efficiency and emissions benefits of fuel cells in the transportation sector have materialized only in the last 10 years. The overall goal of ongoing fuel cell research and development programs is to develop a fuel cell engine that will give vehicles the range of conventional cars, while attaining environmental benefits comparable to those of battery-powered electric vehicles. Although the technology is currently quite expensive, fuel cells offer benefits including high overall efficiency and quiet operation due to few moving parts. A typical fuel cell based propulsion system is shown in Fig.2.8.
POWER SYSTEM ARCHITECTURES FOR HEVS
Advanced Electrical Features in Future HEV Technologies
As mentioned earlier, there is a trend in the automotive industry to replace more engine driven mechanical and hydraulic loads with electrical loads, due to higher efficiency, safety requirements, and driver‘s comfort. All of these new functions require the application of power electronics. In most of the cases, the cost of the power electronics dominates the argument of introducing such functions. Many of these functions will only appear in concept vehicles in the projected future. Some of these include luxury loads, such as information and entertainment that have received lots of hype recently. The other class of features is x-by wire, where ―x‖ stands for an advanced function such as, ―steer‖ or ―brake.‖ Another class of advanced electrical features includes power steering pump, electric active suspension system, electromechanical valve control, electrically heated catalytic converter, air-conditioning systems, and water/oil/fuel pumps. There are also other loads such as throttle actuation, ride-height adjustment, rear-wheel steering, which are proposed to be driven electrically in the future. Fig. 3.1 depicts a summary of some of the future electrical features automotive power systems. It is virtually mandatory that most of the proposed future electric loads will indeed require power electronic controls of some sort[4].