Say Hello to Bidirectional Topologies in EV Charging

The average gas station fill-up for vehicles only takes two minutes. With more electric vehicles (EVs) hitting the road every day, drivers’ expectations of similar conveniences remain unequivocally strong, driving the need for DC fast charging capabilities and infrastructure. To facilitate this paramount and monumental undertaking, recent government initiatives aim to enable this infrastructure growth and pave the way for increased commercial and consumer EV usage.

Pain Points of Current EV Infrastructure

While electric vehicles yield many sustainability and convenience benefits, one significant pain point of current EV infrastructure is existing local grid limitations. As the number of electric vehicles on the road continues to rise, local power grids will be tested like never before. These grids were not designed to charge scores of EVs at once, and – as a result – could reach the limit of or exceed their capabilities. Additionally, power quality of the grid could suffer because of increased inductive loads on it.

On top of grid challenges, the unavailability of chargers due to downtime or other issues is another pain point for EV drivers. As it stands today, EV charging infrastructure is unable to keep up with the goal of uptime as outlined by the Biden Administration, which recently approved $100 million in an effort to achieve 97% charger network reliability. Given these large-scale goals, as EV adoption continues to grow it is essential that the challenges with grid stability and power availability are addressed through intelligent designs of the EV charging infrastructure.

Though projections of how much electricity will be consumed by EVs in the coming years vary, it’s generally agreed upon that the United States has sufficient power generation capacity, especially due to the increased usage of renewable sources such as wind and solar power. However, to ensure local grid stability, the distribution and allocation of power needs to be augmented.

Nuanced Challenges

Organizations are currently combating the pain points of grid stability with on-site energy storage, but these energy storage systems need to be sized for varying use cases while considering traffic and grid support needs. For example, there will be fewer drivers looking to gas up at 2 a.m. than at 2 p.m. and the installed infrastructure will need to be able to support both instances. Additionally, traffic patterns change over time as new facilities and roads are developed, and energy storage installations must be able to adapt to these shifts. This need requires on-site batteries and infrastructure to be scalable in order to accommodate the shifting traffic patterns and increased charging density needs.

There are many nuanced challenges when designing a resilient power topology. When any new multiuse commercial zone is developed, the grid will need to be sized for future planned EV charging installations as well. In order to support multiple facilities within an area that draw from the same power source, this grassroots design would need to be significantly more robust than previous designs lacking EV charging loads. Furthermore, power design engineers may consider leveraging a grid interactive system with distributed energy sources (DES) in these new design approaches – which can be enabled by bidirectional topologies.

It’s Time to Buy in on Bidirectional Topologies

While bidirectional technology has been around for a while, applying it to electric vehicle charging infrastructure is a relatively new concept. When an EV is plugged into a standard, one-way charging station, it only receives energy from the electrical grid to charge its batteries. With bidirectional topologies, however, EVs can do more than just store and use energy – they can take unused or surplus energy from their previous charge and send electricity back to a home or to the grid. The same is true for on-site battery-based energy storage.

If the charging infrastructure and power grid are connected by a bidirectional converter, the overall charging hub functions as a source of power that can support the grid as necessary (See Figure 1). In turn, this helps protect and stabilize grid demand from ebbs and flows in charging traffic, which could have severe consequences if not accounted for, such as region-wide blackouts.

Without bidirectional systems, two separate power solutions would be required to both charge the vehicle and discharge excess battery power back to a home or grid. This equates to added expense to achieve the two-way energy transfer. With bidirectional-enabled systems, there is a lower cost of implementation since the technology utilizes fewer components to facilitate two-way charging.

Implementation of a bidirectional converter into existing EV charging infrastructure would not be a complex endeavor for power engineers. The technology and power topology already exist, so making the switch to bidirectional converters would not be much of a challenge. Especially as technology and standards continue to evolve, integrating these converters would become more accessible for EV owners and charging infrastructure providers.

The Benefits of DC Fast Charging                                                   

While alternating current (AC) power is more common for at-home and overnight charging at workplaces and residential areas, direct current (DC) charging is gaining traction due to its higher voltages, resulting in faster charging. Using DC power can enable much higher power to be delivered in much less time – potentially meeting EV drivers’ high expectations for fast charging (See Figure 2).

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Figure 2: DC power can enable much higher power to be delivered in significantly less time for EV charging

According to the U.S. Department of Transportation, DC fast chargers can charge a battery electric vehicle (BEV) to 80% in just 20 minutes to one hour. Shortened vehicle charge times can deliver more convenient and flexible travel for EV drivers. For the United States to reach its sustainability goals through the increased adoption of electric vehicles, taking driver convenience into consideration is a must.

Additionally, DC fast charging tends to be more energy-efficient compared to AC. Due to the higher voltages used in DC charging, it results in lower current losses for an equivalent amount of power delivered.

Sitewide Distribution of DC Power instead of AC Power

When it comes to utilizing DC fast chargers, they can be installed on a site power infrastructure that already has the capability to distribute AC power. If power design engineers are keen on yielding the benefits of both DC power and bidirectional topologies, it’s worth noting that it is more complex to implement a bidirectional topology with multiple energy sources to sitewide grid distributing AC than DC.

With the continued increase in EV adoption, DC fast charging networks will need to be more accessible, robust, and augmented to be suitable for integrating DES while leveraging the advantages of lower losses and higher voltages. This is accomplished by implementing a DC power distributed network at voltages of 800Vdc and higher. With voltages almost double that of a comparable AC distributed installation, the losses are expected to be up to 75% lower.

It’s Smart to Leverage Smart Metering Systems

A notable concern rising with the adoption of electric vehicles is that their increased draw on the grid will result in demand surges. Another way to help offset this risk is encouraging electric vehicle owners to participate in smart metering and other smart energy management programs. With bidirectional-enabled charging topologies able to discharge unused power from the electric vehicle back to the grid, smart energy management and metering systems can help ensure grid stability and efficiency. The most important aspect of this will be grid interoperability, which assists with managing power distribution and the quality of the system.

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Figure 3: Bidirectional power converters allow electric vehicles and battery-supported charging locations to become more versatile and helpful in managing critical energy needs

Charging the Future of EVs

As electric vehicle adoption rises, power design engineers are turning toward power solutions that can meet availability, reliability, and charge speed challenges while also helping to offset grid surges and protect power quality. Overall, bidirectional power converters allow electric vehicles and battery supported charging locations to become more versatile and helpful in managing energy needs, whether it's supporting the grid or lowering implementation costs (See Figure 3). In conjunction with DC power and smart metering systems, bidirectional topologies have the potential to address some of today’s most pressing EV infrastructure challenges.

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