The recent public interest in using alternative fuels to power the automobile has created investment in a huge variety of technologies that could reduce the planets dependence on oil for transportation. Unfortunately, these technologies are diverse and disjointed, and while each one shows promise they need to be focused on working together to produce a system level solution that actually saves energy and reduces Green House Gas (GHG).
Fuel cells, fed by hydrogen and producing electricity and only water as a byproduct, have been in development for two decades and although the technology has improved tremendously the economic and safety aspects of producing and transporting hydrogen have not.
A recent joint study by the Electric Power Research Institute (EPRI) and the Natural Resources Defense Council (NRDC) concluded that Plug-in Hybrid Electric Vehicles (PHEV) have the potential to improve air quality and substantially contribute to meeting long term goals of reducing GHG to 80% below 1990 levels by 2050.
The PHEV presents a suitable system approach that has the potential to be the most appropriate investment to have an impact on reducing our dependence on oil and reducing GHG. Genovation Cars exists to produce a PHEV product that makes best use of the latest technologies that are safe on the road, not experimental and do no harm to the environment. We are building a vehicle for the average family that cares about protecting the environment.
Powering the vehicle is not the only aspect of being green that we consider. All other materials such as composite body panels made from soy based resins and natural fibers such as jute, bamboo or basalt are considered for application in the vehicle.
We keep six factors in mind when considering whether a technology is ready for our car. Those are Safety, Cost, Weight, Availability, Reliability and Ease of use/maintenance. Using the initials we call these our SCWARE factors.
The major components that make up a PHEV car are:
- The electric traction motor that moves the car.
- The controller that manages the power flow from the batteries to the traction motor.
- The battery pack that stores the energy.
- The charger that refills the energy store.
- The battery regulators that prevent the individual batteries from damage by either overcharging or overdraining.
- The Range Extender that produces electricity while driving to recharge the battery pack.
- The auxiliary 12V system to power all standard vehicle subsystems.
- The energy recovery system that captures energy that would normally be dissipated as heat when braking.
- The safety management system that makes sure all systems work in harmony and do not allow dangerous situations to exist.
The traction motor is what provides the power to the vehicle’s wheels. Traction motors have been around for a long time and have been deployed in electric trains, trams and buses for a hundred years. The technology needed in these applications has been very high power with easy access to electric power (overhead lines or power rails). When looking at the family car the power comes from batteries and is a limited resource. Also the weight of the vehicle has the biggest impact on efficiency.
Small, lightweight, efficient traction motors are available but at a high cost. They tend to be either inductance motors requiring sophisticated, custom designed controllers or permanent magnet DC motors using expensive materials in the magnet design. There are many other types of motors each with their own unique benefits and drawbacks. Until recently, traction motors for vehicle applications have been adaptations of motors originally designed for something else, such as fork lift trucks. Today, there are motors available for specific vehicle applications that are efficient, light weight and powerful over a wide speed range. For our G2 car we are using an AC induction motor.
The motor controller (often called inverter) is the brain of the car. It controls the power going to the traction motor in response to the throttle pedal. Presently, motors and controllers have to be purchased from the same vendor to ensure reliable efficient operation. An induction motor must provide feedback to the controller about its precise position for the controller to operate the motor efficiently. Also, energy recovery under braking and making the motor operate seamlessly with the hydraulic brakes requires a design synergy. Until there is an open industry collaboration focused on controller design there will never be a competitive market for all the various peripherals.
Battery technology did not change for decades. The lead acid battery was the state of the art for as long as we can remember until the advent of the personal computer and other personal devices. Then a rapid evolution from lead acid to Nickel Cadmium (NiCad) then to Nickel Metal Hydride (NiMH) and finally to Lithium-ion (Li-ion) chemistries happened. In each step of the evolution the batteries became more powerful by weight and by volume plus they could be recharged faster.
Li-ion is now the battery of choice for laptop computers and cell-phones, however, many of us remember the early scares caused by battery fires in laptops. Several variations of Li-ion chemistry are competing in this industry and we have chosen Lithium Iron Phosphate (LiFePO4). This is because, in our judgment, the LiFePO4 chemistry is the only Li-ion chemistry now ready for use in family cars and meet our SCWARE factors. Our car has a high voltage string of batteries to power the traction motor and a 12V auxiliary battery to power all the normal 12V circuits of a family car such as the radio and windshield wipers.
Battery chargers are either very heavy or very expensive. For a pure electric vehicle the charger can be left out of the car as was the case with the EV-1 built by General Motors. The EV-1 charger was a very clever and safe design but was also extremely heavy. However, weight was not an issue as it stayed in the owner’s garage. A PHEV needs an on board charger that can provide the performance needed by the charging capability of the batteries. Li-ion batteries can absorb a charge very quickly but each cell in the stack must be managed individually for safety reasons.
Genovation is using a sophisticated light-weight charger that has a higher cost than we would like but out of all our SCWARE factors, cost is the only factor that is compromised in this case.
A DC to DC converter is used to charge the 12V auxiliary battery from the high voltage traction pack.
All batteries of a type are not created equal; each has a slightly different capacity, especially when new. The best way to make sure that each battery is charged to its maximum would be to charge them individually. Unfortunately, they are connected in series to power the motor and therefore must be charged in series. Consequently, one battery will reach full charge before the rest and as the charger treats the whole series chain as one entity for charging it is inevitable that the first batteries to reach full charge will be overcharged before the charger cuts back the current. To avoid this we equip each battery with a regulator that monitors the state of charge and bypasses the current when full charge is reached. All regulators communicate with the charger and thus the charger “knows” when the whole string has reached full charge.
Our cars feature an on board range extender (also called a Genset) that is a small internal combustion engine coupled to an electric generator. The range extender starts either automatically or when desired by the driver to begin charging the batteries. The automatic function activates when the batteries have drained to a set level. The driver may activate the range extender any time he or she feels it is appropriate based on present and predicted driving conditions.
Range extenders may be fitted to run from a variety of fuels including regular gasoline, bio-ethanol, bio-butanol, diesel, biodiesel and liquid petroleum gas.
The auxiliary 12V system powers all the standard 12V systems in a vehicle. Pumps of various types are needed for power steering, brakes and air conditioning, entertainment, lights, wipers, etc. are all standard 12V systems. The system is powered by the auxiliary battery which is continually charged from the traction battery.
It is possible to have the traction motor become a generator under braking. This allows us to recover energy and reduce wear and tear and maintenance costs on the mechanical brakes. However, the power generated during braking is much higher than the batteries can absorb in the time available. Therefore, we are investigating several technologies to store recovered energy that can react fast enough and meet our SCWARE factors. Such ideas include ultra capacitors and compressed air or hydraulics.
Just connecting the power to the motor via a controller and a throttle pedal will make a car move. However, there is a need for multiple safety interlocks to avoid dangerous situations such as trying to drive off when the car is plugged in for charging. Genovation has multiple custom designed safety modules installed in the car thus having multiple ways to break the current feed to the motor that ensures no single failure will put the car’s occupants in danger. For example, if the throttle and brake pedals are pressed at the same time, drive current will be removed from the traction motor.