Tag Archives: Electric Vehicles

Standard Connectors for EV Charging

With EVs or electric vehicles becoming a trend for both individuals and commercial operations, more people are opting for them for commuting to work, school, and moving around the town. While there are tax benefits to using EVs, they also reduce our dependence on fossil fuels. Moreover, with the maturing of battery technologies, EV performance is comparable to those of vehicles with traditional internal combustion engines.

With the increasing number of EVs in use, their fundamental and foremost requirement is charging the battery. This aspect has led to a spurt in the growth of electric vehicle charging stations. Manufacturers of electric vehicles produce a range of vehicles that they base on their specific design specifications. However, charging devices need a uniform design so that any make or model of an electric vehicle can hook up for charging. At present, there are two categories of electric vehicle chargers—Level 1 and Level 2.

Level 1 chargers are available with the vehicle. They have adapters that the user can plug into a standard mains 120-Volt outlet. Manufacturers make these chargers common for use in home charging outlets.

Level 2 chargers are standalone types and separate from electric vehicles. They have adapters to plug into a 240-Volt outlet. These chargers are typically available in offices, parking garages, grocery stations, and other such locations. Homeowners may also purchase Level 2 chargers separately.

To allow any model or make of EV to connect to any Level 2 chargers, it is necessary for both the EV and the charger to use a standard connector. At present, the standard charger connector for Level 2 chargers is the SAR J1772. All the latest electric vehicles using plug-in charging use the standard SAE J1772 plug, while the charger connectors use the standard SAE J1772 adapters. These are also known as J plugs. J1772_201710 is the most current revision for the J plug specifications.

While SAE was originally an acronym for the Society of Automobile Engineers, presently they are known as SAE International. They often come up with recommended practices that the entire automobile industry accepts as standards. With the use of the standard SAE J1772 plugs, a customer purchasing an electric vehicle from any manufacturer can charge it using the same charging connector. Public electric charging stations also use the SAE J1772 chargers, and these are compatible with plugs in most vehicles from different manufacturers.

Each SAE J1772 charger has a standard coupler control system consisting of AC and DC residual current detectors, an off-board AC to DC high power stage, an auxiliary power stage, an isolation monitor unit, a two-way communication system over a single wire, contactors, relays, service and user interface, and an energy metering unit. Charging stations with J1772 connectors use a cable for charging the electric vehicle, and the rating of this cable is EVJE for 300 Volts or EVE for 600 Volts.

The EVJE/EVE cable consists of a thermoplastic elastomer jacket and insulation around a center conductor made of copper. The cable usually has two conductors of 18 AWG wire, one conductor of 10 AWG, and another conductor of 16 AWG.

Advanced Solutions for Electric Vehicles

Although EVs or electric vehicles have existed in some form or the other for many hundred years now, it is only in the past few decades that technology has advanced and companies have found success. With concern over the effects of air pollution, climate change, and an ever-diminishing supply of fossil fuel, more and more people are considering changing over to EVs.

Consumer demand constitutes the basis of the growing popularity of EVs. The role of governments also helps by tightening their regulations and mandates in reducing carbon emissions with an effort towards reducing global warming.

The rapidly increasing rate of growth of EVs is presenting a huge opportunity not only for EV manufacturers alone, but also for OEMs, and suppliers of aftermarket parts. Although there has been a significant advancement in EV technologies and solutions over the past few decades, there are still a few challenges that must be overcome, and which can quickly become hindrances. Manufacturers must develop new and innovative ways of addressing these challenges if they want to continue on the path to success.

At present, there are three important considerations that most consumers stipulate manufacturers must overcome—range anxiety, performance, and cost.

Even among modern EVs, many could not go very far without their batteries needing a recharge. For most people, this range was too small to seriously consider a changeover to fully electric vehicles. Although battery and motor technology have advanced significantly, range anxiety is still a factor.

Even two decades ago, EVs were struggling to match the performance and power of fossil-fuel-powered vehicles.

As with any new technology, EVs were initially expensive. Typically, modern EVs were far beyond the reach of most people, or what people were willing to pay for them.

Although car manufacturers are actively addressing the above challenges, an EV that is affordable enough for most consumers and does not compromise on performance, and one that requires only a single charge a month, is still only a mirage. Right now, manufacturers are busy balancing tradeoffs between range, performance, and cost. For instance, improving the performance affects range and cost, while cutting costs can severely compromise range and performance.

Fortunately, manufacturers are finding enhancing efficiency to be the key to the solution. For instance, the primary bottleneck to improving range is the capacity of the battery. Although the obvious solution is to use a bigger battery, that complicates matters further. Not only do bigger batteries cost more, but they also weigh more. Therefore, a bigger battery while increasing the vehicle’s cost can also decrease its performance.

Therefore, manufacturers are looking for ways to use the existing battery more efficiently. They are reducing the energy losses occurring naturally in the power-conversion system of the vehicle. This is mainly as lost energy in the form of heat in the EV’s motor, powertrain, and the power-electronics systems in the vehicle.

Weight is another factor affecting performance—a lightweight vehicle has superior performance. Therefore, manufacturers are trying for higher power density, where they add more power to the vehicle without increasing its weight. With lighter batteries and power-conversion systems, the vehicle can achieve better performance and speed.

Types of EV Connectivity

Technologies related to EVs or electric vehicles are undergoing enormous research and development efforts with the ultimate aim of achieving widespread EV adoption. Although at present, extending the driving range is occupying much of the direction of this effort, future benefits will ultimately extend beyond progressive battery and charging technologies.

For instance, for future EVs, there are exciting value propositions like the number of different connectivity technologies they will be featuring. This is the V2X or vehicle-to-everything connectivity that includes in-use technology like V2G or vehicle-to-grid, V2N or vehicle-to-network connectivity, and the emerging technology like V2V or vehicle-to-vehicle, which engineers expect will change the future working of EVs.

The recent production of EVs includes V2G or vehicle-to-grid connectivity. This refers to the EV’s ability to allow electricity to flow bidirectionally from the vehicle to the grid and back. The concept is that the batteries in the EV, being relatively large, can not only act as energy storage for the vehicle but also as energy storage for the grid and as V2H, energy storage for the home.

V2G, therefore, relies on a power electronics technology, bidirectional charging. Such an EV requires a versatile power conversion and control circuit, allowing conversion between the AC of the grid and the DC of the battery. There are innumerable benefits of V2G for both the vehicle owner and the grid.

The owner can use the EV not only as a vehicle but also as a backup generator for home use in case of a disaster like a blackout. The vehicle owner can offset their cost by selling excess energy in their EV to the grid.

For the infrastructure of the grid, V2G technology can supplement the grid stress when the demand is at its peak. During low demands, or when the energy generation is higher, the grid can recharge the EV.

V2N is another type of EV connectivity, and it refers to the ability of the vehicle to connect to the Internet and communicate with anything else on the network. This mostly refers to the vehicle connecting to the internal network and cloud service of its manufacturer. This allows the manufacturer to closely monitor the vehicle, update it dynamically, and thereby, ensure maximum performance.

Companies use V2N connectivity for extracting information related to performance from their vehicles. They gather metrics such as battery charge cycles, energy throughput, and range. With such feedback information from all vehicles connected to the V2N network, EV manufacturers conduct statistical analysis for understanding the real-time operating conditions of their vehicles and improve their performance. V2N-connected vehicles can also receive necessary updates for their software and firmware for introducing performance improvements.

However, V2V connectivity will bring the biggest impact of all these, although, currently it is far from being a reality. This connectivity is the interconnection of all connected vehicles on the road. V2V allows all vehicles to wirelessly communicate between themselves, information like position, speed, road conditions, and other important driving information. V2V-enabled vehicles can also share real-time road and traffic condition information for achieving the optimal path to their destination.

Dual Board Net Systems in Automobiles

Modern electric vehicles are increasingly using dual board net systems. These contain both a 12 VDC bus and a 48 VDC bus. One of the key building blocks in the architecture of these vehicles is the high-power, bidirectional 48 VDC to 12 VDC converter. Energy flows in either direction between the two batteries—48 V and 12 V. This helps to optimize the overall efficiency of the vehicle. The direction of the energy flow depends on the demands the vehicle’s electrical system places on the batteries and their state of health.

Vishay offers a complete 3 kW 48 V / 12 V buck-boost type DC/DC converter for electrical vehicles. The design has a standard FR-4 controller board mounted on an IMS or Insulated Metal Substrate that sports a heat sink for the power stage. As these converter designs do not operate at maximum efficiency over a wide power range, Vishay has designed them as six modular power stages operating at 500 W each.

It is possible to switch the protection MOSFETs on/off in each stage. This allows the system to activate or deactivate each power stage individually. Vishay uses this topology for maximizing efficiency under various operating conditions. Moreover, this also provides built-in redundancy, preventing a total breakdown in the event of any failure in an individual power stage.

The converter design from Vishay has another important detail—the half-bridge design uses different MOSFETs. As the high-side MOSFET operates at one-fourth the output current, its on-resistance is not essential. Instead, the gate-drain charge and the gate-source charge of the MOSFETs are more significant. Rather than use the regular low-power thick film resistors, Vishay uses thin-film MELF resistors for driving the gates.

Thin-film MELF resistors can handle large pulses, while not drifting over time and temperature. This prevents an increase in switching losses at frequencies of 100-150 kHz. Switching losses are the dominating power-loss factors at these frequencies. To minimize the drain-to-source resistance in the low-side MOSFET, Vishay connects two of them in parallel, as this resistance is the largest factor dominating the power loss.

The DC/DC converter has a primary storage inductor. This inductor must support both the DC output current and the ripple current. The inductance value and the switching frequency determine the ripple current amplitude. Although increasing the inductance value or the switching frequency helps in reducing the ripple current, it is necessary to consider a tradeoff in performance and size. The designer must ensure the inductor rating is adequate for the output current it must handle, without saturation and high self-heating.

Vishay uses IHDM inductors for primary storage. These have a good combination of low core loss (AC), low DC loss, and very good saturation performance. The IHDM series of inductors from Vishay cover a wide range of inductor values, ranging from 0.1 µH to 200  µH. Their current handling capacity ranges from a few amperes to several hundred amperes. The inductor series also comes in several materials, allowing efficient operation when the converter is operating between 100 kHz and 5 MHz.

Wireless Charging and Electric Vehicles

In our daily lives, we are increasingly using wireless products. At the same time, researchers are also working on newer trends in charging electric vehicles wirelessly. With more countries now implementing regulations for fuel economy and pushing initiatives for replacing fossil-fuel based vehicles with those driven by electricity, automotive manufacturers have focused their targets on development of electric vehicles. On one hand there are technological advancements on lithium-ion batteries and ultra-capacitors, while on the other, researchers are working on infrastructure and the availability of suitably fast charging systems that will lead to a smoother overall transition to the adoption of electric vehicles.

Charging the batteries of a vehicle requires charging systems using high power conversion equipment. They convert the AC or DC power available from the power supply sources into suitable DC power for charging. As of now, the peak power demand from chargers is of the order of 10-20 KW, but this is likely to climb up depending on the time available for charging, and the advancements made in capabilities for battery charging. Therefore, both governments and OEMs are gearing up for developing high-power charging systems to cater to the power needs of future electric vehicles.

Wireless charging systems transfer power from the source to the load without the need for a physical connection between the two. Commonly available schemes use an air-cored transformer—with power transfer taking place without any contact between the source and the load. Wireless power transfer technology is available in various ranges, starting from mobile power charger systems rated for 10s of watts, to high power fast chargers for electric vehicles rated for 10s of kilowatts.

Earlier, the major issues with wireless charging systems were their low efficiency and safety. The technology has now progressed to the stage where achieving efficiencies of over 80% is commonplace. Although this is on par with wired power charger systems, increasing the spacing between the primary and secondary coils allows the efficiency to drop exponentially, which means the efficiency improves as the spacing between the coils decreases. Researchers are also looking at adopting various other methods of constructing the coils to address the issue.

Likewise, smart power controls are taking care of safety, by detecting power transfers taking place spuriously and suspending power transmission directly. Manufacturers are ensuring safety at all stages by implementing regulatory guidelines such as SAE J2954.

Although several methods exist for wireless power transfer, most popular are the resonance and inductive transfer methods. The inductive method of power transfer uses the principles of the transformer, with the AC voltage applied to the primary side inducing a secondary side voltage through magnetic coupling, and thereby transferring power.

The inductive method of power transfer is highly sensitive to the coupling between the primary and secondary windings. Therefore, as the distance increases, the power loss also increases, reducing the efficiency. That restricts this method to low power applications alone.

Based on impedance matching between the primary and the secondary side, the design of a resonant method allows forming a tunnel effect for transferring magnetic flux. While minimizing the loss of power, this method allows operations at higher efficiency even when placing the coils far apart, making it suitable for transferring higher levels of power.