Military electric land vehicles technology requirements and breakthroughs

Rajesh Uppal January 2, 2021 Army, Energy & Propulsion Comments Off on Military electric land vehicles technology requirements and breakthroughs 368 Views

The US Army is looking into the possibility of adding electric vehicle technology to its fleet of wheeled vehicles. The subject of a draft white-paper proposal by the Army Futures and Concepts Center (FCC), the hope is to simplify maintenance while reducing the logistical problems connected with fossil fuels.

Currently, the US Army is dependent on large vehicles powered by internal combustion engines to move personnel and materials to the battlefield. But such engines are extremely complex with many parts that could become more expensive as the demand for fossil fuel engines falls and production is cut back. In addition, such complex engines are difficult to maintain. Worst of all, conventional engines mean moving tonnes of fossil fuels across the globe and to the battlefield – putting commanders at the mercy of very long and very vulnerable logistics chains.

The hope is that electrification could be one way to overcome these limitations. Electric motors have few components, are relatively easy to maintain, and battery ranges have improved significantly. Unfortunately, the technology also has its drawbacks. Batteries take a long time to recharge and have a short service life. Worse, while fossil fuels cease to be a problem, electric vehicles still need a power source that is reliable and within a reasonable distance.

The technologies involved in EVs are multidiciplinary, which include electrical and electronics engineering, mechanical and automotive engineering, and chemical engineering. Many new technologies are being introduced in EVs. Mechanical, pneumatic and hydraulic parts, silicon power components and dumb structures are on the way out. In come merged parts often radically different components such as SiC, GaN and GaAs based ones including added systems for electrical input such as regeneration, induction and external energy harvesting. New electrical loads proliferate and merge. Improved performance, fuel economy and emissions reduction result. Even conventional powertrains will avoid illegality under new emissions laws by being reinvented as mild hybrids. These will evolve into vehicles with many pure electric modes so the total EV market rockets to nearly one trillion dollars in ten years.

The lack of appropriate technologies has been an important barrier for Electric Vehicles to become mainstream particularly the technologies that could help cut costs and significantly increase battery life. Changing to a vehicle which may need several hours charging before it can go anywhere and may only be able to travel 200 miles before it needs to be plugged in again, a challenge. To deal with the problem, the Army says that the Office of the Secretary of Defense is looking at several alternatives, including the development of mobile nuclear power plants to generate electricity. Meanwhile, the battery problem could be overcome by new capacitors that could extend battery life and reduce charge times.

One way to extend EVs’ range is to reduce their weight, therefore EV design concepts should include the consistent weight saving design, optimum safety concept, low drag coefficient- body design, and low rolling resistance concept. Automakers are seeking higher stiffness, better occupant safety and superior crash performance all at an optimized cost. HBPO offers plastic-metal hybrids with either metal or organic fiber “over-molded” with plastic.

With increasing vehicle content and safety requirements, weight reduction continues to escalate as a priority for all vehicles regardless of propulsion type. The design, materials and processes as each having the potential to save vehicle weight through better optimisation and emphasises the need for new approaches to design and analysis that allow full advantage to be taken of developments in materials and joining technologies.

EV Propulsion

Military vehicles are often loaded with energy-hungry mission electronics, such as navigation, communications and survivability systems. On-board devices such as sensors or communication and weapon systems require a continuous power supply. Militaries have traditionally solved this by hauling larger, heavier diesel generators around on a trailer. Some equipment may use a special generator to provide electricity, but some systems, such as Threat Detection, Active Protection Systems and data communications are operating continuously, draining the vehicle’s energy reserve. In order to meet this demand, vehicle designers integrate more powerful alternators, auxiliary power units, energy generation systems and high capacity batteries to increase the energy available on board.

OBVP refers to providing an alternative source of AC power on the battlefield that is generated from the vehicle itself which can solve many technical and logistical problems. For example, by providing the HMMWV with a 10 -KW OBVP system supplying continuous AC power, the need to trailer a diesel generator is reduced significantly. In addition, now the HMMWV can negotiate terrain that it could not previously engage while towing a generator, thus leading back to the more agile concept.

Electric propulsion is to interface electric supply with vehicle wheels, transferring energy in either direction as required, with high efficiency, under control of the driver at all times. Instead of using a single motor, the use of multiple motors has also been used. Likewise, costs are forecast to decline from $10 per kW to $4.5 per kW by 2035, while power density is expected to quadruple from the current 7kW/l to 30kW/l by 2035. Key to this, the APC says, is the introduction of alternative winding materials, while additive manufacturing has the potential to remove the need for dedicated winding processes.

Very high levels of integration are also predicted in electric drives, with the e-machine, transmission and power electronics coming together to create a single, light-weight, tightly-packaged and lower cost unit with greatly reduced complexity.

Open systems

After military systems can generate sufficient electrical power, the next challenge is controlling that power efficiently and economically. One way to that goal is open-systems architectures like the emerging Sensor Open Systems Architecture (SOSA) standard, administered by the Open Group in San Francisco. SOSA seeks to specify a limited number of established industry standards for power control, embedded computing, communications, and software to promote interoperability among components from different vendors to enable military systems designers to achieve economies of scale, while enabling suppliers to capitalize on their value-added technologies.

SOSA also seeks to settle on 12-volt power systems to make it less likely that systems designers will need custom-designed power conditioning and control. It’s the hope that standardized 12-volt power systems will provide sufficient power to satisfy the needs of high-performance computing and sensors, while promoting systems interoperability. “12 volts can deliver more power, as opposed to 5-volt systems,” says Joseph Pozzolano, vice president of sales and marketing at Behlman Electronics Inc. in Hauppauge, N.Y. “The military wants to standardize on a certain number of voltages, and there is a transition in industry to get away from 5-volt devices,” says “The driving force from the military is open systems such as MOSA, SOSA, HOST, and all those open systems.

SOSA also seeks to blend digital and analog power electronics in a way to create interoperable, affordable smart power. “The military wants intelligence on these power devices,” Behlman’s Pozzolano says. “This is all part of the SOSA technical standard. Intelligence enables an embedded computer to send a signal to whatever power device it wants, and get a response back. From the power perspective, the system can query for input power and output power, and monitor for temperatures; if it’s outside the normal range, there might be something wrong.”

Motors

Traditionally DC motors, have been prominent in EV propulsion. Their control principle is simple. However, the principle problem of DC motors arises from their commutators and brushes, which makes them less reliable and unsuitable for maintenance-free operation.

Recent technological developments have pushed AC motors to a new era, leading to take definite advantages over DC motors: higher efficiency, higher power density, lower cost, more reliable, and almost maintenance free. As high reliability and maintenance-free operation are prime considerations in EV propulsion, AC induction motors are becoming attractive.

The use of conventional gearing as the transmission device can no longer satisfy the needs of EVs. Recently, planetary gearing has been accepted as the transmission device of latest EVs, such as the GM Impact 4, Nissan FEV, BMW Elm2 and U2001, because it offers high gear ratio and high transmission efficiency. On the other hand, by abandoning the transmission device or gearing, these motorized wheels can be realized directly using outer-rotor wheel motors.

In the past few years, power device technology has made tremendous progress. The selection of power devices for EV propulsion is generally based on the requirements of the voltage rating, current rating, switching frequency, power loss, and dynamic characteristic. Among the available power devices, the GTO, BJT, MOSFET, IGBT and MCT are particularly suitable for EV propulsion.

In addition to converter topologies, another important aspect of power converters is switching schemes. Starting from the last decade, numerous PWM switching schemes have been developed for battery-fed inverters, focusing on harmonic suppression, better utilization of DC-link voltage, suitability for real-time and microcontroller-based implementation, and tolerance of DC-link voltage fluctuation.

Conventional linear control such as PID can no longer satisfy the stringent requirements placed on high- performance EVs. In recent years, many modern control strategies, such as model-referencing adaptive control (MRAC), self-tuning control (STC), variable structure control (VSC), fuzzy control and neural network control (NNC), have been proposed. Both MRAC and STC have been applied to EV propulsion. In order to implement the aforementioned modem control strategies, powerful microelectronic devices are necessary.

Batteries

The battery is among the most expensive elements of any electric vehicle, with the cost increasing significantly as storage capacity grows. The challenge of batteries is its low energy density, energy density for the lead-acid batteries, at about 90 watt-hours per kilogram (wh/kg), is so low, compared with 8,600 wh/kg for gasoline. Likewise, the energy density is only 240 wh/kg for lithium batteries, which are considered to be more advanced batteries for EVs. Lithium-ion batteries also degrade over time, which means an electric car will never travel as far as it can when it’s brand new.

Because the specific energy and specific power of electrochemical batteries are generally much smaller than those of gasoline, a large number of batteries are required to assure a desired level of power performance. However, mounting a vehicle with a large number of batteries suffers from several shortcomings: the reduction of interior and luggage spaces, the increase in vehicle weight and cost, and the degradation of vehicle performances

Therefore, to expand the use of EVs, new technologies are also needed to increase the battery’s efficiency. Complete set of criteria including the specific energy, specific power, energy efficiency, charging rate, cycle life, operating environment, cost, safety and recycling must be considered. APC foresees power density quadrupling from the current baseline of 3kW/kg to 12kW/kg by 2025. Similarly, energy density will nearly quadruple from its current level of 280Wh/l to 1,000Wh/l by 2035. These performance improvements are expected to be accompanied by a fall in price from $280kWH to $100kWh by 2035. However, to deliver these targets, battery chemistry will have to change with the development of new anode and cathode technologies.

Until now, the most mature battery suitable for EVs has been lead-acid (Pb-Ac). In recent years, the introduction of Lithium-based batteries has provided higher capacities and power management capabilities, enabling users to better support combat missions. Li-ion batteries suitable for powering combat vehicles were introduced in 2015. The new batteries contain hundreds of standard rechargeable lithium cells interconnected in multiple groups to deliver the required voltage and current. Designed to maintain a safe operating environment through physical isolation and using battery management systems to monitor and regulate electrical voltage, currents and temperature on charging and discharge, batteries are designed to prevent user abuse as well as meet harsh operating conditions. Among various advanced batteries, nickel-based batteries, such as nickel-iron (Ni-Fe), nickel- cadmium (Ni-Cd), and nickel-metal hydride (Ni-MH), have received heightened interest.

Another promising battery type is solid state battery, in which electrolyte and electrodes on the battery terminals are both solid. This creates a smaller, lighter and higher capacity battery with a longer lifecycle. Solid-state batteries are less likely to catch fire than lithium-ion batteries. In lithium-ion batteries, the motion of the liquid electrolytes generates heat, and in certain situations, this can slip into a “runaway” effect that results in a fire. Solid-state batteries, then, would let you make it safer to quickly draw power from (or add it back to) the battery, meaning you could theoretically charge a battery-powered car faster. It also could mean, structurally, less room has to be devoted to temperature control, which could allow companies to squeeze more battery cells into the same size pack. Carmakers like Tesla, Dyson, BMW and Toyota are looking into this technology. The UK government is also on board and has pledged part of a £42 million grant for electric car development for progress in solid state battery research.

There is also issue of battery recycling, currently there is still no environmentally safe way of recycling lithium-ion batteries. If these batteries are not recycled, then millions of them will become an environmental disaster. Improvements in recycling, innovation, and the greening of battery factories can go a long way towards reducing the impacts of battery production.

Many researchers are excited by the idea of coupling electrochemical batteries with electric flywheels or ultracapacitors, which can deliver surges of power. Recently, an ultrahigh-speed flywheel has been reported to deliver a whooping 5000-10000 Wkg, which is orders of magnitude higher than anything achievable by an electrochemical battery or even an intemal Combustion engine.

Super capacitors have the advantage of providing fast charging / discharging of only a few minutes and a dense energy source with a long life of 3,000 – 5,000 charging cycles. Because of this, already commonly used when starting a car or to harvest energy from braking. The main drawback of a supercapacitor is the inability to hold onto a charge for longer than a few minutes. Superdielectrics has provided a major breakthrough. The polymer produced by Superdielectrics is very good at holding a charge. Together with Bristol and Surrey Universities, this polymer has been used in supercapacitors to increase energy storage.

Materials

Cobalt, a key component of the lithium-ion batteries in electric cars, is linked to reports of child labour. The nickel used in those same batteries is toxic to extract from the ground. And there are environmental concerns and land use conflicts connected with lithium mining in countries like Tibet and Bolivia.

BATTERY CHARGING

The challenge of transforming EVs from concept to reality is to make it safe, convenient and easy for consumers to charge batteries. In order to improve convenience and increase charging efficiency, a number of charging schemes have been proposed: home charge, regenerative charge, solar charge, park-and-charge (PAC), and move-and-charge (MAC).

The most ideal situation for charging EV batteries is to perform charge while the vehicle is cruising on the road – so- called MAC. Thus, the driver does not need to find a charging station, park the vehicle, and spend relatively long time to charge up batteries. This MAC system is embedded on the surface of a section of highway, the charging zone, and does not need any additional space. Both contact and inductive types of MAC can be implemented.

Intelligent Energy Management

Maximizing energy usage and monitoring energy capacity are critical to attaining acceptable performance in EVs. The energy management system (EMS) making use of sensory inputs from sub-systems of the vehicle predicts range for standardized driving profiles, controls the energy usage of vehicle sub-systems, suggests more energy efficient driving behavior, directs regenerated energy to batteries, and selects battery charging algorithm based on battery state-of-charge and cycle life his

Optimal Battery Charging

As the power delivered by such batteries quickly degrades in cold temperatures, built-in heaters are used to maintain an optimal operating environment under extreme temperatures. Discharging a lead-acid battery to less than half of its capacity is not recommended because it might cause internal damage to the battery. Ideally, a 100Ah battery should not be discharged below 50Ah.

Therefore, measuring the battery State of Charge (SoC) and State of Health (SoH) are key indicators for effective power management on board. SoC is often thought of as the equivalent of a fuel gauge for a battery bank. Unlike lead-acid batteries, smart battery features enable communication with the end user, which provides information about the battery SoH, SoC, and other functions. In this analogy, SoH would be the size of the fuel tank.

Batteries of this type integrate into modern vehicles communicating with vehicle systems over the CAN BUS, relaying vital information, including SoC, SoH, cell voltages, temperatures and battery diagnostics. Since some Li-ion chemistries are more flammable than others, users and manufacturers opt to use 6T packs utilising Lithium Iron Phosphate (LFP) that are non-flammable. Li-ion batteries provide higher capacity but require special containers to protect the vehicle and crew from fire hazard in case of a battery failure or combat damage.

Power Steering

In order for power steering to be feasible in EVs, extremely efficient high-power controllers are necessary to provide needed performance without sapping precious battery reserves. Recently, an adaptable inverter fitting most 3-phase AC induction motors has been developed for power steering. A DSP is employed to perform VVVF control. The input power of this unit is about 900 W.

Safety and High Quality

“The market for electric vehicles is booming,” says Thomas Parker, Inficon’s North American automotive sales manager. “But to maintain a positive reputation for EVs, it is critically important for automakers to not only offer extended driving ranges and short charging times but also safe, high-quality drive technology.” Consumers definitely do not want their vehicle to catch fire

“Auto manufacturers and suppliers need to incorporate suitable leak-detection processes into their production operations,” the Inficon executive says. “Battery-cell electrolytes must never be allowed to escape or come into contact with water or humidity.”

References and Resources also include:

https://newatlas.com/military/us-army-future-electric-vehicles-battlefield/