Bidirectional power supply for electric vehicles (EV): practical and innovative power module use opportunities

400V and 800V electric vehicles coexist. How to coordinate these two different architectures?

It’s no secret that the race to electrify vehicles is already underway, whether spurred by government regulations and incentives or driven by consumer demand for green transportation solutions with higher performance, longer range and more features. All major automakers are actively participating in this competition. With auto brands such as General Motors publicly stating that all cars produced by GM will be zero-emission by 2035, automakers appear to be responding aggressively to the electrification of vehicles.

Bidirectional power conversion creates a unique opportunity for innovation for all power system designers. This concept, combined with intensive R&D work around electrification, results in practical and innovative application scenarios.

Fast charging infrastructure is an issue. The initial electric vehicle platform design uses 400V batteries, supported by 400V charging infrastructure and 400V auxiliary systems. However, long before the first 400V EVs were launched, the industry had begun developing 800V platforms, effectively splitting the entire EV market into two voltage categories.

Industry insiders predict that most electric vehicles launched between 2027 and 2030 will use 800V battery architecture. However, based on past experience, Vicor believes that this transition will be slower than expected, so we will continue to support 400V battery designs for the foreseeable future.

Bidirectional power supply module allows more freedom in design

In the past, power system designers designed power delivery networks (PDNs) from left to right, from source to point of load. This is a traditional practice that designers have followed for decades. In essence, we have always been "right-handed." Imagine a world where we could shoot left and right, with both hands, from left to right or right to left.

Currently, modular power components available to designers have two key attributes:

• They are effective and efficient "DC transformers" - that is, they provide a fixed ratio DC-to-DC conversion ratio

• They natively support bidirectional power supply

To realize the potential of bidirectional power networks, it is important to explore the core enabling technology and understand how sinusoidal amplitude converters (SACs) work. Say goodbye to left-to-right thinking and let's start in the middle; here you have a transformer and a series capacitor that resonates with the leakage inductance of the transformer.

There is a switching bridge on one side, which would normally be thought of as a chopper DC input to the DC bus, while the other side has essentially the same layout and could be called a synchronous rectifier. As long as these two paths switch in sync with the resonant waveform of the central "storage", the entire device is symmetrical and acts like a DC transformer.

The voltage increases and the current decreases based on the turns ratio of the magnetic element - and vice versa.

A change in impedance on one port is reflected on the other port, and current flows accordingly. Resonance, zero voltage and zero current switching ensure low losses. Minimal energy is stored in the resonant tank, producing good transient response through the converter, while MHz switching makes the required inductors and capacitors small and light.

Figure 1: Vehicle-to-grid (V2G) energy flow diagram using a DC bidirectional charger (Image source: Clean Energy Reviews).

How do 400V and 800V electric vehicles coexist?

Given that 400V and 800V electric vehicles are likely to coexist for some time, the industry must effectively resolve the following challenges: achieve a hybrid of the two architectures to ensure sufficient interoperability, while avoiding consumer confusion and causing potential buyers to reject electric vehicles. car.

So, what do we do next?

Ensuring interoperability between 400V and 800V systems, or conversely, between 800V and 400V battery architectures, requires industry support for all charging interfaces to ensure drivers’ cars are compatible with any charging station . At the same time, we need to find new ways to repurpose legacy 400V batteries, even as we improve the efficiency of 400/800V systems and expand and enhance vehicle-to-vehicle (V2V) and vehicle-to-other (V2X) charging ability. Mixing these two voltages can be complicated. Connecting a 400V battery to an 800V charger requires a boost; connecting an 800V battery to a 400V auxiliary system requires a step-down, and different V2V and V2X applications may require a combination of boost and buck conversion and regulation. .

Vicor believes that these power systems require high-voltage bidirectional voltage conversion, from 400V to 800V, or from 800V to 400V. Electric vehicle charging stations are a good example that clearly illustrate this point. The vast majority of charging infrastructure in the United States is 400V, which means the industry will need to complement charging stations by upgrading or installing 800V charging facilities - which will require significant investment. Installing a car-mounted two-way converter can easily solve this charging problem. After plugging in the charging plug, the system automatically detects whether the power supply needs to step down or step up to achieve seamless charging.

Figure 2: Basic energy flow diagram of a DC bidirectional charger when using a V2H system to power a home, and a CT meter used to measure grid energy flow (Image source: Clean Energy Reviews).

Bidirectional power supply innovation in V2X and other fields

Today, new concepts such as “Vehicle to Grid” (V2G) and “Vehicle to Home” (V2H) are becoming increasingly popular. Most cases require varying degrees of conditioning, but distribution networks (PDNs) are not very complex. In the V2G scenario, the benefits of bidirectional power supply are manifold. V2G paves the way to improve grid stability and resilience. Electric vehicles can be connected to the grid and used as mobile energy storage units. During periods of peak energy demand or unplanned outages, these vehicles can in turn supply power to the grid, acting as a buffer and taking the pressure off traditional power sources.

Figure 3: Basic energy flow diagram for an electric vehicle with an AC outlet, known as vehicle-to-load or V2L (Image source: Clean Energy Reviews).

This ensures uninterrupted power supply and reduces the need for auxiliary power stations (which usually come into operation during peak demand periods), resulting in significant cost savings. Additionally, allowing EV owners to sell excess electricity back to the grid has given rise to a new economic model. Electric vehicle owners can monetize stored energy, offsetting part of the cost of purchasing a car, and promoting the further popularity of electric vehicles.

Looking at V2H applications, bidirectional power supply heralds a new model for achieving home energy independence and security. As extreme weather conditions and power outages increase in frequency, having a V2H-enabled electric vehicle can be a lifeline. In this case, households can draw their power supply from electric vehicles to ensure the normal operation of essential systems such as heating or cooling. In this way, electric vehicles become a backup power source that can reduce a household's reliance on a central grid or independent generators that typically run on fossil fuels. In addition to emergencies, in daily life, V2H allows owners to draw power from electric vehicle batteries during peak hours and then charge the cars during off-peak hours, thereby optimizing power costs and achieving cost savings.

Another use case is Vehicle-to-Load (V2L), which opens up even more possibilities. V2L further demonstrates the versatility of bidirectional power supply. In this case, the electric vehicle becomes a portable power source capable of powering external devices, appliances or systems. This is particularly useful in remote areas where conventional power sources are difficult to access. Imagine setting up a campsite in a secluded spot and using an electric car to power lighting and cooking equipment. Merchants and event organizers can also use V2L to power their equipment on-site, freeing them from the constraints of fixed power sources and no longer having to haul bulky generators. The potential applications of V2L are vast: everything from entertainment to business.

Bidirectional power opens up a variety of possibilities. Solving the 400/800V charging problem is the top priority today. However, other concepts represent more than just technological innovation, but are a critical step towards a more integrated, sustainable energy landscape. By increasing grid resiliency, delivering economic benefits to EV owners, ensuring household energy security, and making power supplies more portable, bidirectional power technology harnesses the potential of EVs, transforming them from mere transportation into the energy foundation of the future. key points of the facility.

Figure 4: The sinusoidal amplitude converter (SAC) topology provides isolation and voltage conversion functions, allowing you to deploy these functions where needed, separate from the voltage regulation device.

Bidirectional power supply module brings new possibilities

The huge potential of bidirectional power supply is being discovered in the automotive field. Two series of power components make the most efficient use of the bidirectional power supply capability. One is the Vicor Bus Converter Module, or BCM, which provides isolated, fixed-ratio conversion between two voltage rails. The other is a non-isolated version, called NBM, which is otherwise similar to BCM. The latter is easier to use in a bidirectional power supply environment because it can be "primed" (established and stabilized resonant switching) using power from either port. If isolation is required, use a BCM®, but this requires a small amount of additional circuitry to provide the bias needed to start it from the "secondary side" device supply.