What is an OCPP CPMS?

What is an OCPP server (CPMS or CSMS)?

An OCPP server (Open Charge Point Protocol server), also known as a CPMS (Charge Point Management System) or CSMS (Charging Station Management System), is a central software system that manages and communicates with electric vehicle (EV) charging stations, known as charge points or EVSEs (Electric Vehicle Supply Equipment). It uses the OCPP standard, which is an open, standardized protocol for communication between charging stations and management systems.

Key functions of an OCPP server include:

• Monitoring and control: It can monitor the status of each charging station, start or stop charging sessions, and perform remote diagnostics.
• Data exchange: It facilitates the exchange of information such as energy consumption, station status, and transaction details.
• User authentication: It manages user authentication via token valdiation

How to connect a Charger to an OCPP server?

Although there are different options depending on the protocol version, the most common way that charge points connect to a CPMS using OCPP is via websockets, which provide real-time two-way communication between the server (CPMS) and client (ChargePoint).

The ChargePoint is pre-configured with a chargePointId and the address of the CPMS to connect to, as well as often being provided with a password. The charger attempts to establish a HTTP connection to the target CPMS, which if successful will be upgraded to a websocket connection.

The CPMS will determine if the connection attempt is valid by checking:

• The connection path is correct
• The provided chargePointId is valid for the server
• The charger provides a compatible protocol version in the SecWebsocketProtocol header
• The provided basic authentication password is correct for the charger

How does the OCPP protocol work?

Once a connection has been established between a charger and CPMS, messages are exchanged in a request-reply format. One side sends a request with a unique ID, and the other party will send a response with the same unique ID. Using this method each side can verify:

• It's message was correctly received by the other party
• The response can be associated with the initial request

Messages are sent in JSON format, as an array, where the first item is the message type, the unique ID, and then either the CALL followed by the payload for message type 2 (request), or simply the payload for message type 3 (response). An example of message exchange between a charger and server might look like the following:

    Charger: [2, "uuid-0001", "StatusNotification", { "connectorId":1, "status":"Available", "errorCode":"NoError" }]
    CPMS: [3, "uuid-0001", {}]
    CPMS: [2, "uuid-0002", "ChangeAvailability", { "connectorId":1, "type":"Inoperative" }]
    Charger: [3, "uuid-0002", { "status":"Accepted" }]
    Charger: [2, "uuid-0003", "StatusNotification", { "connectorId":1, "status":"Unavailable", "errorCode":"NoError" }]
    CPMS: [3, "uuid-0003", {}]