The global energy system is undergoing a fundamental transformation. With an increasing reliance on renewable sources, such as solar and wind, managing the flow and storage of electricity has become crucial. At the heart of this shift lies a technology set to change how we interact with energy: bidirectional charging (BDC). More than just charging a battery, BDC allows electricity to flow in both directions. This capability is turning battery systems from passive storage units into active participants in the energy network. Traditional power systems often require separate components for charging (AC/DC) and discharging (DC/AC). BDC streamlines this process with a single circuit that handles both operations. This inherent efficiency leads to significant advantages, including lower space, weight, power, and cost (SWaP-C), reduced complexity, and easier scalability.
Enabling this two-way flow at high power levels requires sophisticated power electronics. Silicon Carbide (SiC) technology enables the design of power systems that operate at significantly higher voltages, with designs using 1200 V SiC MOSFETs, compared to other semiconductor technologies, such as traditional silicon MOSFETs.
The impact of BDC and advanced wide bandgap power electronics extends across numerous applications, particularly when combined with battery energy storage systems (BESS) that use lithium-ion (Li-Ion) batteries. Some of the applications are:
The Multifaceted Role of BDC in EV Charging
In the context of EV charging, BDC’s role is multifaceted. Electric vehicles (EVs) equipped with BDC capabilities can act as mobile power sources, providing power to a home in a Vehicle-to-Home (V2H) setup, powering external devices in a Vehicle-to-Load (V2L) scenario, or even transferring energy to other electric vehicles through Vehicle-to-Vehicle (V2V) connections. This also extends to Vehicle-to-Grid (V2G), where EVs can supply power back to the grid. These interactions exemplify the dynamic nature of BDC, where EVs serve not just as energy consumers but also as active participants in energy distribution and management.
SiC is particularly well-suited for these BDC applications due to its ability to handle modern battery systems, such as the 800 V batteries found in many EVs.
Residential and Commercial/Industrial
DC bidirectional wall boxes can be installed in private homes or semi-public parking areas, allowing EVs to both charge and discharge energy.
V2G and V2H bidirectional charging diagram. Source: https://www.cleanenergyreviews.info/blog/bidirectional-ev-charging-v2g-v2h-v2l
BESS, typically between 5 kWh and 20 kWh, is widely used in these residential settings for purposes such as backup power, load shifting, and energy optimisation. Designs using 1200 V SiC MOSFETs can achieve power levels of 11 kW (3-phase, 16 A feed), a popular choice in residential wallboxes, and newer versions are moving towards 22 kW (32 A). In commercial and industrial applications, larger BESS, ranging from 100 kWh to several MWh, support energy arbitrage, demand response, and backup power.
Beyond wall boxes, the modular nature of advanced power designs, featuring two-stage solutions, is being seen in industrial DC bus systems for factories, where PFC stages can be separated from DC/DC stages. This enables the distribution of DC power throughout a factory, potentially simplifying wiring and application efforts.
Grid Infrastructure
At the grid management and utility-scale level, BESS provides services such as load balancing and peak shaving by storing excess energy during low demand and releasing it during peak demand. This bidirectional capability enables grid operators to maintain grid stability and helps prevent brownouts or power outages caused by excessive load.
Related to load balancing, BDC facilitates time shifting and renewable energy integration. BESS are often integrated locally to store excess energy generated during periods of high production from sources like solar or wind power. This allows for the energy to be shifted and provided back to the grid when production is low, ensuring a consistent power supply. The demand from large solar inverters, some running at 150 kW, is driving the need for higher voltage levels. SiC technology is particularly suited for this due to its current capabilities at 1200 V, 1500 V, and even 2200 V, which helps reduce losses for the same power.
Static/Mobile Off-Grid
Space is often at a premium in static power systems. Shipping container battery systems are frequently used in remote locations for various applications, such as power backup. Here, space is limited, and engineers need to maximise the energy density. BDC eliminates the need for separate power import and export systems, thereby saving space and reducing complexity. This space-saving allows for the installation of more battery cells, increasing the overall energy capacity of the shipping container.
Technology
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POWERING CHARGINGBeyond static applications, batteries with BDC can store and reuse kinetic energy. For example, energy generated by cranes lowering freight containers can be stored and reused to improve fuel economy. Similarly, hybrid trucks can recover energy going downhill to assist with climbs or power onboard systems when the vehicle is idling.
Furthermore, BDC is being specifically developed for the maritime sector. Vessel-to-Grid (V2G) infrastructure allows electric boats to not only charge efficiently but also discharge surplus energy back to the grid. This capability can help address challenges faced by harbours and marinas in providing sufficient power without costly grid upgrades.
New Design Challenges
The design of BDC systems using advanced wide bandgap power electronics introduces a new set of challenges for engineers. Both SiC and GaN enable exceptionally high switching speeds, sometimes exceeding 100 Volts per nanosecond, which means engineers will often require test equipment with capabilities far beyond traditional lab scopes. Furthermore, achieving the required power density and form factors, especially for mass-produced units such as server power supplies, calls for a shift from 2D PCB designs to more complex 3D or vertical structures. This transition introduces challenges related to mechanical constraints, manufacturing processes, and the need for sophisticated simulation tools covering electrical, thermal, mechanical, and even finite element analysis.
Conclusion
BDC is more than just a charging method; it’s a foundational technology that empowers batteries to actively interact with the energy grid, which will become increasingly prevalent as BDC progresses toward a seamlessly integrated and sustainable energy ecosystem. For engineers, the use of high-voltage SiC technology with microprocessor control can enable the development of new and innovative BDC designs. However, this presents a new set of challenges in testing, mass production, and complex 3D designs. Leveraging its expertise in powering the shift, Avnet Silica is at hand to help engineers design and develop reliable systems, benefiting from the superior performance and efficiency gains offered by high-voltage SiC technology.
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