Petri Korhonen, Chief Engineer, and Mikko Veikkolainen, CTO of Kempower discuss the benefits of dynamic charging of electric vehicles.
Kempower is a leading e-mobility charging technology provider in the Nordics, specialising in dynamic and scalable DC charging for electric vehicles and machines.
Fast-charging solutions for electric vehicles
Kempower designs and manufactures DC fast charging solutions for electric vehicles and machines. We’re a team of electric vehicles enthusiasts with a deep understanding of the charging market and a hands-on mentality. Our product development and production are rooted in Finland with over 90% of our materials and components sourced locally. We focus on all areas of transportation, from personal cars and commercial vehicles to mining equipment, boats, and motorsports. With 70 years of experience in perfecting power sources, we set the bar high in engineering and user-experience design.
Why do the electric passenger cars (EVs) need dynamic DC charging?
When an electric car is plugged to a DC charger, the car sends a message to the charger, requesting a specific amount of power. The charger starts the charging session based on this request.
The charging curves of electric passenger cars are strongly declining by nature. If the charging curves were more stable throughout the charging session, the need for dynamic charging would be smaller. In other words: if the cars would ask for a steady amount of power throughout the charging session, there would be no need for dynamic charging.
The charging curves of electric vehicles also massively differs model to model, with only a few electric cars have a steadily decreasing charging curve. There are also some electric car models on the market with very high charging capacity. The problem, however, is that there are only a few chargers providing equal charging power. Plus, even the most powerful electric cars attain maximum power only for a short period of time.
Thus, all electric cars on the market request a declining amount of power during a fast-charging session, creating the need for dynamic charging. In practice, the charging power requested by a car when starting the charging session can be over 10 times greater than by the end of the charging session. This means that the charger should be able to change the configuration during charging sessions.
In the DC charging solutions provided by Kempower, the charging set up is configured throughout the charging session to match with the declining power requested by the car.
The benefit of dynamic EV charging for the end-users: electric car drivers
In charging areas with several charging stations and charging outputs, the dynamic charging means that the power released from the charging session of the electric car A can be transferred to the electric car B. This transfer is made simultaneously as the electric car A asks less and less power towards the end of the charging session. The cars are set in the queue automatically when plugged to the charger and system knows in which order the released power will be distributed to other cars.
For example, if the car initially asks for e.g., 75kw at the beginning of the charging session, the charging power requested by the car drops under the below 75kw after a while. In dynamic charging, this released power is transferred to the next car in the queue as quickly and smoothly as possible. This is the reason why Kempower charging solutions’ power supplies are 25 kilowatts in size: it is a suitable resolution step for dynamic charging. With bigger power supplies, the dynamic charging would not be as smooth: the electric cars queuing for more power would need to wait for a longer amount of time.
Benefits of dynamic EV charging for the charging operators
The dynamic charging makes it easier to install multiple charging points in the same area, as the charging capacity can be shared. For charging sites operators, this means that a larger proportion of the kilowatts purchased is in use, thus the charging capacity ratio is better than with single chargers.
With dynamic charging the charging operator does not need to invest to the charging capacity that is needed at the busiest days of the year. Instead, the charging capacity needed at one charging station can be evaluated to serve an adequate power level for several electric cars most of the time. For example, at a charging station designed for e.g., 8 cars the cars never receive the ultimate maximum power asked by the cars simultaneously. Yet the cars will always get enough power to maintain a smooth and fast charging session.
Dynamic charging also allows the so-called priority charging. Priority can come in many ways. In cities, priority can be determined, for example, by vehicle category: electric buses may have higher priority than taxis, taxis have higher priority than passenger cars, and so on. Another way to determine the priority is so called “first in first out” model. The common factor is that the charging system controls the priority automatically.
We see that the need for dynamic DC charging sites with multiple charging stations is increasing as electric cars become mainstream. Charging operators want to provide the best possible charging experience for EV drivers, who in turn want to avoid charging queues and continue their journey as quickly as possible.
Petri Korhonen & Mikko Veikkolainen
Chief Engineer Kempower – CTO of Kempower