Design considerations for high-efficiency EV chargers

Introduction

Electric vehicles (EVs) may be charged using electric vehicle service equipment (EVSE) many of which operate at different charging speeds. As EVs continue to gain popularity in the transportation sector, it is vital to have an in-depth understanding of the optimal charging procedure. An EVSE is made of several components, the build quality and construction of these components determine the "efficiency" of the energy transfer from the grid to the battery. An EVSE must have the maximum possible charging efficiency. This article aims to provide insights into the detailed aspects of designing high-efficiency EV chargers, from technical intricacies to user experience and safety concerns.

Types of EV chargers

Numerous EV chargers exist, including Level 1, Level 2, and DC rapid chargers. Regardless of the charger type, obtaining high efficiency is critical. Efficient chargers reduce energy waste when charging, lowering overall electricity usage and environmental effects.

• AC level 1: This is the standard in most houses, such as a 110V wall outlet. It would take 20 hours to charge an EV completely.
• AC level 2: Equivalent to an upgraded home charger that uses a 200-240V circuit (often used for an electric clothes dryer) and typically requires a 50-amp breaker for each charger. It takes around five hours to recharge an EV completely. Frequently found at shopping malls.
• DC level 3 fast charging: A substantially greater grid connection is necessary to convert AC electricity to DC. The battery management system of an EV must be capable of handling the fast flow of power, which is now as high as 350 kW. It takes 15-20 minutes to charge most DCFC-ready automobiles from 10% to 80%.

EV charging level	Diagram	Connector type	Typical output power	Supply and interface	Estimated charge time(40kWh)	Estimated range per hour for charging	User case
Level 1		J1772	1kW – 1.8kW	AC, non-dedicated	22 – 40 hours	3 – 7 miles	Home / backup
Level 2		J1772 (North America) Mennekes (Europe)	3kW – 22kW	AC, Dedicated (IEC62196 – 2)	2 – 13 hours	10 – 75 miles	Workplace, hotels, overnight charging
Level 3		CCS 1 (North America) CCS 2 (Europe) CHAdeMO (Japan)	30kW – 360kW	DC, dedicated (IEC 62196-3)	15 min – 1.5 hours *Depending on charge acceptance rate	120 – 140+ miles	Fleets, Highway services, Car dealerships, Logistics hubs and Distribution centre

Table: Charging modes and power levels in line with standard

Design considerations for high-efficiency

EV charging solutions have several components; thus, there is no one-size-fits-all solution. Whilst charging stations installed in homes and at gas stations may have different layouts, they share many components. Employing effective components whilst designing a user-friendly, efficient, and visually beautiful charging station is critical.

Given the growing importance of fast-charging stations, the desire for higher power levels, and the significant investment required to supply both, EV charging system designers must plan for enhanced efficiency, dependability, and safety.

• Efficiency - Carbon emissions were the primary motivator for the shift from fossil-fuel-powered automobiles to electric vehicles (EVs). EVs not only reduce pollution but also enhance efficiency and overall performance. However, suitable infrastructure and a well-organised charging station solution are required to appropriately capitalise on this technology. The potential advantages may be lost if these factors are not present. One might wonder why an EV owner would bother traveling to a charging station when they can charge at home at the same rate. The answer is how long it takes to charge at home, often overnight. In contrast, DC charging stations may significantly speed up the charging process for EVs. These stations give the car batteries the most power by minimising power conversion losses, resulting in substantially quicker charging speeds.
  Power semiconductors convert alternating (AC) electricity into direct (DC) power, which is required to recharge a vehicle's batteries. The power semiconductor device manages the charge by switching to match the charge level to what the vehicle's battery demands, which naturally incurs power losses in the form of heat. In an EV charging application, the heat might pose technical issues. That is why sophisticated devices based on SiC and GaN technologies make sense for power conversion; compared to silicon devices, they provide ultra-fast switching, resulting in lower power losses.
• Reliability - Installing a DC charger requires a significant time commitment and financial expenditure. It is critical to guarantee that these chargers can survive extreme weather conditions and have a long lifespan. The key to tackling dependability issues is to use high-quality components in the equipment and to put preventative measures in place. For example, including fuses to protect power converters from overcurrent can improve the charging system's overall dependability.
  Semiconductors are primarily made of silicon or silicon carbide and have a poor thermal withstand capacity, making them particularly vulnerable to electrical dangers. Fuses must safeguard them from overcurrent.
  Whilst regular fuses can protect most devices, specialised high-speed DC fuses are necessary to safeguard the MOSFETs, IGBTs, thyristors, and diodes used in power converters (rectifiers, inverters, and so on). These fuses have a unique time-current characteristic and work much faster than typical AC input fuses.
  A further threat to sensitive semiconductors is overvoltage. For example, an EV charger near an industrial facility with enormous motors may encounter voltage spikes in the power supply due to the motors' on-and-off switching. Furthermore, lightning strikes near the charging station generate electromagnetic radiation, which can cause a voltage spike on the power lines in the neighborhood, which can then propagate into the charger through the AC power input lines. To absorb such energy, the charging station must utilise overvoltage protection to prevent harm to the charger's delicate components.
• Safety - The fundamental worry with electric car technology is safety, especially given that charging stations in residential contexts run at voltages higher than 120V. When it comes to DC charging, there is a higher danger of electric shock, because voltage levels might range between 400V and 1000V. Electric shock can occur due to unintentional contact with conductors and grounding. Insulation degradation due to dust or moisture on the circuit might contribute to this problem. However, the installation of a ground-fault protection system can avoid such events. This device protects drivers against electrocution in case of a faulty 1000-volt charging nozzle. When it senses an earth leak, it instantly shuts power to the output side, assuring the user's safety.
• In DC charging, make circuit protection essential rather than a last-minute consideration - Circuit protection devices span a wide range of technologies, each with its application options. Whilst many devices may function, choosing a component with the best technology for the application is preferable. High-power Transient Voltage Suppressor (TVS) diodes or metal oxide varistors (MOVs) often provide the optimum suppression type in a DC charging system. Other kinds of protectors are frequently mentioned, such as gas discharge tubes (GDTs), protection thyristors, multi-layered varistors (MLVs), or combinations of suppression devices. When shielding sensitive circuits, it is critical to understand how long a transient suppressor takes to activate. For example, suppose the suppressor is slow-acting and a fast-rising transient emerges. In that case, the voltage across the protected load might grow and inflict severe damage before the suppression can kick in.
• Future communication standards and grid integration - EVs act as energy consumers and potential energy suppliers, returning stored energy to the grid during high demand or power outages. This technology is characterised as a system allowing the bi-directional flow of electric energy between a vehicle and the power grid. The vehicle-to-grid system refers to integrating electric cars into the electrical grid.
  

  Figure 1: Schematic representation of V2G technology

  
  Robust communication systems in EV charging stations enable safe and secure data interchange between the car, the grid, and the cloud. The International Organisation for Standardisation (ISO) 15118 standard specifies a bidirectional communication protocol for automobile identification, charge control, and status. Adherence to ISO 15118 standards assures grid integration compliance and long-term design flexibility.
  Furthermore, finding the best connectivity option for EV chargers requires considering the use case, installation environment, and grid integration. Commercial chargers require cloud connectivity for invoicing and data insights, whereas residential chargers should interface with existing networks in smart houses.
  The Open Charge Point Protocol (OCPP) is a communication protocol for charging stations and networks that allows data interchange over Ethernet, cellular, Wi-Fi®, or Sub-1 GHz signals.
  Chargers should provide various connecting choices to fulfill the OCPP flexibility criteria. Wi-Fi allows for integration with infrastructure or local connectivity, whereas Sub-1 GHz is dependable in difficult RF situations. Flexibility is critical for commercial or residential chargers to provide robust connections and network compatibility even in harsh conditions.
  

Future trends and innovations

The landscape of EV charger design is changing as technology advances. Wireless charging and solid-state transformers are emerging technologies that promise even higher efficiency advantages. AI-driven charging process optimisation guarantees that chargers respond to user demands and grid circumstances. The advancement of charging standards and interoperability will affect the future of high-efficiency charging even more.

Conclusion

The journey to sustainable mobility is dependent upon an adequate charging infrastructure. High-efficiency EV chargers are a technological achievement and an essential facilitator for a greener future. We pave the path for an ecologically aware and user-centric electric mobility revolution by carefully addressing energy efficiency, charging speed, power output, interoperability, and safety. By embracing these design concerns, we can all help to make the world a cleaner and more sustainable environment.

Farnell has partnered with many different suppliers catering to a wide range of EV charging portfolio, such as EV charging connectors and cables, EV charging connector accessories, EV charging stations, EV charging station accessories, charging technology sets, interface / communications development kits, battery management development kits.