Advanced Smart Charging for a Fleet of Electric Buses

INTRODUCTION

One of Bia's main functionalities is the dynamic optimisation of charging, also known as smart charging. This optimisation ensures that vehicles receive the necessary amount of energy to perform their service before their departure time, while also taking advantage of the most opportune moments for charging. Therefore, once a vehicle is connected to a charger, instead of starting to charge at nominal power, an optimal charging schedule will be followed, considering:

• The charging needs of the vehicle
• The electrical limitations of the depot
• The smart charging criteria selected by the Operator

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For smart charging, Bia leverages criteria and constraints such as: 

1. Peak Power: Reduction of the maximum consumption peak (in kW) required by all chargers in the depot to operate. This criterion can indirectly impact the fixed term of the depot's electricity bill.
2. Power Excesses: Reducing the number of times the power exceeds the agreed supply capacity in the energy contract. Through this criterion, power penalties are reduced, and they would only occur if the fleet's operation is compromised.
3. Variable Charging Costs: Direct reduction of charging costs by prioritising consumption during times when electricity is cheapest.
4. Vehicle Battery Degradation: Application of charging patterns that minimise battery degradation during the charging process.
5. Carbon Footprint: Direct reduction of CO2 emissions from charging energy by prioritising consumption during times when the energy mix is most decarbonised.

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BUS OPERATOR PRIORITIES

As discussed with the Bus Operator in January 2024, it was decided to combine criteria 3 and 4 of Bia's load optimization algorithm.

Variable charging costs

The Operator's depot has an indexed tariff, so the cost of electricity varies every hour of the day and month according to the conditions of the electricity market. 

The time windows when electricity is cheaper (sometimes with a negative price) are during the day, between 12-5 pm (when the Operator's buses are not in the depot) and during the early hours, between 1 and 6 am. 

The Bia platform is connected in real-time to these prices and therefore takes into account the actual cost of charging at all times.

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Vehicle battery degradation

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For this criterion, BYD, the bus manufacturer, recommends charging as slowly as possible to minimize the impact on battery degradation. This implies distributing the energy during the vehicle's connection period to the charger, also taking into account the previously mentioned energy cost. This co-optimization is configured in Bia so that the bus fleet charges according to these requirements.

Fleet schedule

Furthermore, the Bia platform takes into account the departure schedules of the vehicles by loading a CSV file with the days and hours at which each vehicle must be 100% charged. The Operator can consult these schedules through the Bia dashboard and, if necessary, update them. 

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In summary, Bia's optimization algorithm will manage the recharge of each vehicle automatically to ensure that:

1. The electrical limitations of the depot are respected.
2. The fleet is ready according to the schedules indicated by the operator.
3. Charging is prioritised when energy is cheapest.
4. Each bus is charged at the lowest possible power.

RESULTS

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• Reduced variable charging costs by nearly 25%
• Reduced the average charging power required for each vehicle by 24%

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