advanced scada systems for energy management of electric … ems white paper en.pdf ·...

Advanced SCADA systems for Energy Management of electric buses

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Advanced SCADA systems for

Energy management of electric buses

White paper

Balancing fleet charging for minimum

consumption

The management of charging of electric bus fleets requires using Energy Management Systems (EMS) aimed to balance charges on the basis of user priority criteria, in order to control load peaks on the grid and optimize energy costs.

The EMS are embedded in SCADA systems that control different subsystems (buses, charging stations, etc.) and manage the automation of charging operations for an optimal modulation of the charging power of each vehicle.

Development plans of municipalities estimate a progressive replacement of traditional vehicles with electric ones: SCADA systems must therefore be expandable, guaranteeing the performance optimization also when the number of vehicles of the fleet increases.

It is thus essential to identify an optimal SCADA architecture and advanced Energy Management algorithms for fleets.


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1. Traditional EMS Within a depot, buses are generally grouped into clusters served by substations and equipped with local monitoring systems for collecting data from individual vehicles and charging stations, performing diagnosis and generating possible alarms.

A cluster generally includes up to 25 buses charged by power stations of the order of 100 kW. Typical depots host up to 3-4 clusters, with the possibility of expanding the vehicle fleet even reaching 10 clusters within the same parking area.

It is understandable that in such a situation, charging vehicles without a coordination system could result in unsustainable peak loads. For this reason, the energy management of a depot is usually delegated to a SCADA system that embeds an EMS for balancing vehicle charge.

The EMS obtains from the charging stations data about the battery state of charge, the energy consumption during charging process, etc. and sends to the charging stations the voltage and current set-points to be used instantaneously for each vehicle, in order to modulate the vehicles charging power and control the peak loads, respecting the maximum available power constraints and the priority criteria set by users.

Static modulation Centralized EMS architecture


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However, this kind of static modulation does not consider the strong relationship between charging power and efficiency for each specific battery/charging station set, which varies during the life of the vehicle due to component aging and also every day during the charging process, because of the continuous variation of the battery state of charge.

This leads to energy waste and a poor care of vehicle batteries.

Traditional EMSs modulate the charging power by deferring the charging start time for the different vehicles and/or "spreading" the charge of each vehicle on the available time window, using power values lower than the maximum allowable one for the specific vehicle, implementing predetermined charging curves.

HANDICAPS OF TRADITIONAL EMS

High energy consumption and battery life reduction Comunication overhead

Poor expandability

Problem 1: Static modulation

Problem 2: Centralized EMS architecture

In traditional SCADAs, a central EMS controls charging processes by directly interfacing with each charging station of the clusters, thus centralizing the exchange of data from the clusters to a central node and the computational load on a single processing unit.

This architecture, conceived for the control of few nodes using basic energy management algorithms, leads however to a communication overhead and a poor expandability of the software of the EMS with the increase of the number of vehicles and the complexity of the algorithm of Energy Management.


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2. CalBatt EMS

CalBatt has developed a patented technology for the dynamic analysis of specific characteristics of the specific battery/charging station set in terms of energy efficiency when operating parameters change during vehicle charging.

Benefit 1: Dynamic modulation

Thanks to NomoStor unique features of characterization and optimization, CalBatt EMSs are able to perform a dynamic modulation of the charging power of each vehicle, updating in real time the charging profile parameters on the basis of the instantaneous characteristics of the specific battery/charging station set.

This allows to achieve perfectly tailored charging profiles leading to optimize really every day charging costs through an optimal combination, in terms of efficiency and battery care, of the priority criteria set by the user and related for example to:

the usage of vehicles in the depot (charging times, scheduled service, autonomy required at the departure, position priority);

possible variable electricity tariffs, which can make it convenient to concentrate the charge at specific times of the day;

the production profiles of renewable sources used to supply the charging stations.

This dynamic analysis is performed by NomoStor, the add-on processor embedded in the EMS, able to synthesize the information coming from the vehicle into simple indications about the instantaneous optimal values of voltage and current to be supplied to the battery during charging process (for more information see the NomoStor datasheet).


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Benefit 2: Modular and expandable EMS architecture

EMS are based on a modular distributed architecture in which:

each cluster is equipped with a Cluster EMS which locally optimizes the charging management for the vehicles of the same cluster;

Cluster EMSs communicate with the Depot EMS, which monitors and manages, thanks to a dedicated PC, the overall energy consumption of the clusters.

Dynamic modulation Distributed EMS architecture

Each Cluster EMS integrates a PC connected on one side to the charging stations and on the other one to a number of NomoStor cards equal to the number of vehicles parked inside the cluster, each NomoStor being a coprocessor dedicated to the dynamic analysis of the charging station/battery set of a given vehicle.


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In this manner, the computational load is distributed along the nodes of the architecture:

The Depot EMS sets the maximum instantaneous power that can be absorbed by each cluster based on the available power and the priority criteria set by the users, and communicates it to the Cluster EMS;

Each NomoStor of a Cluster EMS performs a complex algorithm of characterization and prediction of the charging performance of a single vehicle in the cluster and sends data to the Cluster EMS;

Each Cluster EMS sets instantaneous charging current and voltage parameters of vehicles in the cluster based on data received from the Depot EMS and the NomoStor present within the cluster.

Furthermore, the largest amount of data is exchanged locally in the cluster between NomoStor and the Cluster EMS, thus minimizing communication overhead towards the Depot EMS.

This makes the architecture intrinsically more robust and expandable than that of a traditional EMS, allowing to add a single vehicle simply by adding a NomoStor card in a DIN guide inside a Cluster EMS, and a whole cluster adding a Cluster EMS, without needing to modify the hardware and software of the Depot EMS.

BENEFITS OF CALBATT EMS

Cost optimization and battery life maximization Robustness

Expandability

White paper

FOR MORE INFORMATION Website: www.calbatt.com

Email: [email protected] Phone: +39 0984 494273

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