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Integrating smart charging applications is crucial to managing and optimizing charging of EV fleets. However, a fundamental question arises: which protocol should be used for building these advanced applications, OCPP or OCPI?
Understanding OCPI and OCPP
The Open Charge Point Interface (OCPI) primarily supports connections between eMobility Service Providers, who cater to EV drivers, and Charge Point Operators (CPOs) who manage charging stations. Meanwhile, the Open Charge Point Protocol (OCPP) aims to standardize communication between a charging point and a central system.
Why OCPI is Not Ideal for Building Smart Charging Applications
Relying solely on OCPI can be limiting for fleet electrification providers attempting to build smart charging applications, especially for those who own or operate charging hardware. This is because the OCPI protocol doesn't offer the comprehensive control and monitoring necessary for a CPO to manage power delivery effectively.
The Necessity for a Reliable, Scalable Smart Charging Solution
A reliable and scalable smart charging solution that aims to work across multiple EVSE vendors must have awareness of the state of every charger in the depot. These states include physical, connectivity, and energy aspects.
Physical State: Delays in receiving connector StatusNotifications will cause smart charging algorithms to be delayed in their response to changes in the physical environment. For example, re-conditioning existing charging sessions on connector plug-ins is not possible with delayed or missing connector state notifications.
Connectivity State: Real-world chargers often experience connectivity issues. A smart charging application must constantly be aware whether or not a charger is online.
Energy State: Smart charging applications require real-time energy readings (MeterValues in OCPP) from each ongoing charging session for their calculations. These readings must be:
Ubiquitous. Every charger in the depot must report MeterValues to the application otherwise the smart charging application cannot calculate and apply power limits.
Regular. All chargers should report MeterValues with the same time interval. One charger with intermittent energy reports can negatively affect the application.
Data-complete. Every charger has to be configured correctly to report the right “measurands” (for e.g. Current.Import - the current in Amps the EV is importing at the time of the measurement). Missing measurands will reduce the effectiveness of the smart charging application.
However, not all chargers automatically report power or energy consumption, necessitating manual configuration by the CPO. Depending on the algorithm complexity, more information may be required than factory standard (e.g. Power offered to the EV per phase).
How OCPP Enhances Smart Charging Applications
For a smart charging application to be interoperable across EVSE vendors, a set of common configurations and insurance mechanisms for energy measurements on all chargestations must be enforced. This is where OCPP stands out, providing the following operations to support this:
Get/ChangeConfiguration. Allows checking and setting MeterValue sample intervals and reported measurands.
TxDefaultProfile. Presets a charging session start state to avoid power limit violations during application downtime.
ChargePointMaxProfile. Sets a power ceiling per charge station, ensuring offline chargers do not receive smart charging signals and adhere to power limits.
TxProfile. Adjusts power limits for ongoing sessions. Can be used if there is a change in the available power conditions (e.g. an onsite battery is charged and ready to distribute power).
GetCompositeSchedule. Requests all active schedules and potential local limits at the Charge Point. Useful to check active schedules on a connector.
Trigger Message. Requests connector state and last MeterValue on demand. This is utilized when the current state of a charging session or connector is unknown (e.g. after an application restart).
Limitations of Implementing Smart Charging via OCPI
With OCPI, your application does not have direct access to the charging station. Instead, all OCPI requests are translated by the Charging Station Management System (CSMS) or to the appropriate OCPP charging profiles for power management. OCPI’s scope is confined to power management for ongoing charging sessions, which means that the smart charging application is then limited to only two OCPP operations: TxProfile and GetCompositeSchedule. This restriction is a drawback for applications that require detailed control and monitoring of charging stations. In contrast, direct and full unrestricted access to OCPP's comprehensive suite of operations offers a more robust framework for managing a wide variety of charging scenarios for power management.
For EV fleet operators and CPOs seeking to develop advanced smart charging applications, the choice between OCPI and OCPP is clear. While OCPI has its merits in specific scenarios, OCPP offers a more detailed and control-oriented approach necessary for managing complex EV charging infrastructure. By leveraging the comprehensive functionalities of OCPP, fleet operators can ensure efficient, reliable, and scalable charging solutions for their EV fleets.
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