New, free design books deliver inside story on EV charging
More manufacturers focus their design efforts on developing electric vehicle supply equipment, or EVSE. The International Energy Agency estimates around half a million new public chargers were installed globally in 2021, with many more needed. That figure is increasing every year, and demand is set to remain high for some years to come.
Recognizing that Avnet has the resources to help manufacturers make informed design decisions, Avnet Abacus, EBV Elektronik and Avnet Embedded have collaborated on a series of new publications. They cover power, control and connectivity, and are available free here.
The EV Charging Infrastructure Designbook: Volume 1 focuses on the requirements of the power stage in EVSE.
The power stage is critical in EVSE. Most EV charge points will comply with just one of several profiles. This includes the power level they supply and the interface they provide. Manufacturers need to evaluate the cost and opportunity of EVSE design. Efficiency is a high priority. Understanding the technologies available is crucial.
What you will learn from the EV Charging Infrastructure Designbook
As well as explaining the types of EV connectors, chargers and their power architectures, the design book covers both AC and DC EVSE. There are deeper dives into several areas of design, including:
- Energy flow
- Power factor correction
- Conversion
- Isolation
- Filtering
The information available in the design guide also covers standards and specifications. For example, the designbook provides an explanation of the over-voltage categories as they apply to EV chargers.
Due to their nature, EV chargers must comply with a number of standards before connecting to the public infrastructure. Source: The EV Charging Infrastructure Designbook: Volume 1, from Avnet Embedded, EBV Elektronik and Avnet Abacus
AC charging is at the core
Access to EV charging falls into two broad categories: public and private. The public EV charging infrastructure is expanding daily and has the potential to offer faster charging for many. Private EV charging is limited in power but becoming simpler for consumers to install.
Both types of AC charging are discussed in the designbook. As well as the amount of power they deliver, other features that differentiate public and private EV charge points include the need of galvanic isolation, and the requirement for a payment system.
Do you know that the level of transient suppression needed varies by charge mode? Do you know which over-voltage category your EVSE needs? These design requirements are covered, along with how they vary between domestic chargers that are either fixed or plug-in.
Engineers reading the design book can discover the role of advanced features such as scheduled charging. Subsequent design books will go into more detail about EVSE communications, both wired and wireless, and the technologies available.
Realizing DC fast charging
Vehicle OEMs also see the demand for faster charging. This is achieved through bypassing the AC on-board charging circuit and delivering a direct current to the vehicle’s battery. The design book goes into more detail about DC charging and includes a discussion about developing three-phase power circuits. It also explains how OEMs and vehicle owners need to think about DC charging as a separate part of the overall charging infrastructure, due to compatibility differences between manufacturers.
Due to the cost and complexity, and the need for a three-phase supply, the majority of DC chargers are likely to be in the public infrastructure. Importantly, there are limitations imposed on DC chargers whether they are fitted in a pubic or domestic setting. The designbook covers these in more detail.
Energy efficiency leads to savings
A more efficient power conversion stage delivers energy savings. But a more efficient design also reduces the bill of materials cost. In an EV charger, the consumer is paying for those loses. A more efficient EVSE design will not only reduce the BoM cost but also reduce the customer’s bill. This could be an important part of building brand value and customer loyalty.
The design book provides useful insights into efficiency. These include using bridgeless rectification, with reference to Totem-Pole PFC, Active Front End and Vienna Rectifier designs.
Various converter topologies are available to the EVSE designer, depending on the power rating. Source: The EV Charging Infrastructure Designbook: Volume 1, from Avnet Embedded, EBV Elektronik and Avnet Abacus
The use of capacitors and inductors on the DC stage are also discussed. This provides some smoothing from the PFC output stage. The position and configuration of the passives are as important as their type and selection.
Manufacturers will also need to consider lifetime, maintenance, and replacement of larger passives. The EVSE design will need to accommodate servicing, particularly when the equipment is installed in areas that experience high levels of use.
Wide bandgap in EV charging
The advantage of wide bandgap semiconductor devices, including silicon carbide (SiC) MOSFETs and diodes, is already appreciated in the EV sector. This extends to both the on-board chargers in the vehicle, and EVSE design. The design book delivers engineering wisdom on how and when to use SiC.
The main power conversion stage is perhaps the first thing engineers discuss when talking about EVSE. This important stage is, of course, also covered in the designbook. The requirements here include the power level, the direction of energy flow (uni- or bi-directional power) and isolation.
All these important aspects are discussed in the designbook. Avnet’s engineers provide advice on what topology to use based on the requirements outlined above. It also outlines the benefits of operating at high switching frequencies, such as smaller components and higher efficiency. This needs to be balanced with the power semiconductors selected. The design trade-offs are outlined, with the appropriate recommendations.
For any manufacturer now developing EVSE or investigating the opportunity of moving into the EVSE market, the EV Charging Infrastructure Designbook: Volume 1, from Avnet Embedded, EBV Elektronik and Avnet Abacus is a valuable resource that could save you many engineering hours. Download your free copy today.
Also available:
The EV Charging Infrastructure Designbook: Volume 2 – Control
The EV Charging Infrastructure Designbook: Volume 3 – Connectivity