By Filip Jankun, Łukasz Czerniak, and Magdalena Pietrysko*
The need to reduce greenhouse gas emissions is one of the main factors driving the shift from conventional combustion engines to zero-emission and electric power systems. This is especially important for public transportation systems.
Electric power systems have excellent operating parameters, are quiet and highly efficient, and make it possible to recover energy while braking. Yet to make these electric power systems more available to the public transportation sector, there needs to be a better focus on extended range.
Current solutions make it possible to cover about 250 km (about 155 miles) per charge, which is often insufficient for public transportation needs. There are two solutions which are being developed in parallel:
- A solution aimed at boosting the capacity of traction batteries.
- A solution oriented towards rapid charging via a pantograph.
Both solutions show enormous potential, and they will soon come into widespread use across Europe.
Issues with Charging for Public Transportation Systems
Whatever method is used for charging an electric bus, slow charging mode at night or rapid charging mode via a pantograph, of key relevance for the traveling range is the electric energy consumption level expressed in kWh/100 km, which corresponds to the fuel consumption level in a combustion engine in litres/100 km.
Based on initial electric bus implementation efforts in several cities of Poland, it has been determined that the level of energy consumption varies widely, from 80 up to 140 kWh/100 km for a bus of 12 meters in length. In electric buses, the level of energy consumption is directly related to the traveling range and this is a fact of key importance.
The costs of operation are obviously just as important. However, they are a secondary concern. For example, a bus provided with a set of traction batteries with total capacity 240 kWh can cover a distance of 170 to 300 km. The first analyses demonstrated that the level of energy consumption depends on a number of factors, such as traffic density, temperature, time of day, or individual driving performance. A more in-depth analysis has been launched.
Analysis of Electric Solutions for Buses
All sub-distances of the bus trips were analyzed as autonomous units. Such an approach opened the way to exploring the impact of some elementary driving behaviours on the amount of energy consumed while driving. The studies focused on driving behaviours which are determined to the greatest degree by the individual driving style. The procedure has been the starting point for the final concept of algorithms used for rating the driver’s performance.
In total, there are three autonomous modules designed for processing, analyzing, and merging the available data. The modules have been developed by dividing the total distance covered by a bus into microtrips. First, it was necessary to identify three phases of movement: acceleration, travel at a constant speed, and braking action. These are intuitive components for a driver, and as such they can be improved, with a considerable impact on the amount of energy consumed by a vehicle.
It was necessary to analyze phases of movement:
The resulting rate takes into account the passenger’s comfort while allowing the driver to minimize the impact of this phase on the general level of consumption of electric power. The difference in the amount of energy consumed when a bus is properly accelerated and that which is used during less-than-optimum acceleration can be up to 33%.
Based on the relationship between the efficiency of energy recovery and the braking force. The correlation between this phenomenon and the increase in the energy in batteries in relation to the lost kinetic energy of a vehicle is used for determining the rate of braking efficiency. The analysis helped to determine the optimum braking force and style so as to enable energy recovery. The study also provided relevant information about what type of braking action has no impact on the level of energy accumulated in the batteries.
Traveling at a constant speed
It can be clearly identified that, just as expected, the lower the speed variability, the lower the energy consumption level during this phase, by up to 60%. As a result, a stable style of driving at a constant speed helps to reduce the energy consumed during longer trips. The driving style of drivers who often tend to push towards higher speeds and then to brake rapidly was classified in that analysis as absolutely negative.
Using statistical analysis and Big Data technology, it was possible to precisely define which driving behaviours help to reduce the general level of electric power consumption in vehicles. This provided the basis for a system which gives points for good driving style or alerts the driver to any inappropriate driving behaviours. The system enables the driver to learn good practices and consolidate his/her practical skills while driving.
The Economizer offers a solution for dealing with the problem of monitoring the driver’s performance. This tool enables real-time monitoring of the driver’s performance as well as displaying and analyzing historical scores with a view to secure improvement for the future.
The system is composed of two modules, a web-based application and a mobile application.
The mobile application includes an assistant which sends messages showing how a driver can improve the efficiency of his/her driving style, rates the driver’s performance on a scale of 1 to 6, and informs of energy increase if the driver follows the assistant’s recommendations.
The web-based application shows a detailed view of driving sessions, analyses, and graphs showing complex performance scores or a map of any of the recorded microtrips with related scores. The application also provides access to an extended functionality designed for managers only.
As a result, managers can generate reports and lists of drivers, as well as view selected sessions and adjust settings of the driving style optimization system. The Economizer, through the underlying algorithms, is based on the level of energy consumed by a driver, thus taking such factors as traffic density, urban infrastructure, or vehicle load out of the equation. Hence, it is possible to check to what extent a driver meets the economic recommendations and whether or not he/she has achieved the optimum level of energy consumption during a trip.
This type of information brings a number of advantages. Firstly, it is a valuable source of information for managers, showing how a vehicle is operated, which undoubtedly provides a way to monitor the driver’s performance and the bus operating parameters.
The other advantage is associated with the possibility of evaluating a driver’s performance specifically regarding their electric efficiency, using a variety of rates, graphs, and historical data.
The third advantage is that drivers are able to learn and consolidate good practices while driving a bus. The above features are considered to be beneficial both for the manager and the driver.
Additionally, the Economizer allows the driver to join a gamification platform. Such an additional function enables initiating sessions when drivers compete with each other based on their score for efficient driving. All the scores are recorded in a ranking list which makes it possible to identify the best driver. Drivers can win bonus points for extra-efficient performance. The bonus points are accounted for in the overall result. Not only does this function add variety to the application, but it also allows its users to interact with the system and reward the best drivers. These points are later used to grade the overall performance of the driver for a given period (e.g., one month) and then companies might base their bonus policies on that evaluation.
A more efficient driving style, achievable with the Economizer, helps to reduce the energy consumption level in vehicles operated under real conditions. The estimated level of savings varies according to traffic density, vehicle load, and terrain shaping. The energy consumption might be lowered by up to 30% if the driver follows the instructions.
The data also shows that, when monitored, overall wear and tear on vehicles operated in urban spaces using the Economizer can be reduced by up to 30%.
For a regular bus operated in urban areas, which covers about 75,000 km per year, this results in savings of about €3,500 per year based on the current prices of electric power.
Additionally, it is possible to review the drivers’ performance and to manage business-wide cost optimization processes on an ongoing basis. The Economizer is a clear benefit to fleet managers and city transportation managers who want to build a safer, more efficient driver workforce. The project was co-financed with EU funds.
About the Authors:
Filip Jankun, CEO: Filip conceived the idea of the product. He is a graduate of the Warsaw University of Technology. He has over 9 years of experience in developing of battery systems for electric buses. He has a solid background and know-how in implementing innovative solutions.
Łukasz Czerniak, Data Analyst: Łukasz has an economic background with work experience in Business Intelligence analysis and Big Data software development. He was working for financial and IT sectors.
Magdalena Pietrysko, COO/Product Owner: Magdalena has a strong background and hands-on expertise in running projects of mobile and web applications as a product owner and manager. Moreover, she participated in setting up various companies, running day-to-day operations and sales related tasks.
*This article was sponsored by INSOH; images from the company.
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