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The OCPP protocol provides a unified communication solution between charging stationswallbox electric car charger and any central management system. This protocol architecture supports the interconnection of any charging wallbox electric car charger service provider's central management system with all charging posts.

I. OCPP Protocol

1. The full name of OCPP is Open Charge Point Protocol, which is a free and open protocol developed by the OCA (Open Charge Alliance), an organisation based in the Netherlands. The Open Charge Point wallbox electric car charger Protocol (OCPP) is used for unified communication between charging stations (CS)wallbox electric car charger and any charging station management system (CSMS). This protocol architecture supports interconnection of any charging service provider's CSMS with all charging posts. Advantages of OCPP protocol: open and free to use, prevents lock-in to a single provider (charging platform), reduces integration time/effort and IT issues.

2、Main versions of OCPP protocol

OCPP1.2(SOAP) OCPP1.5(SOAP) OCPP1.6(SOAP/JSON)

OCPP2.0.1 (JSON)

SOAP is limited by its own protocol constraints, can not be a wide range of rapid promotion; JSON version of the WebSocket communication, can be in any network environment to send data to each other, the most used protocols on the market is the 1.6J version, OCPP2.0.1 is the 2018 out of the protocol is promoting the use of the direction of the future.

3, the differences between the various OCPP versions wallbox electric car charger

OCPP1.* is compatible with lower versions, OCPP1.6 is compatible with OCPP1.5, OCPP1.5 is compatible with OCPP1.2.

OCPP2.0.1 is not compatible with OCPP1.6, OCPP2.0.1 although some of the contents of OCPP1.6 also have, but the format of the data frame sent has been completely different, OCPP2.0.1 added a lot of OCPP1.6 does not have the function, for example.

(1) StartTransaction and StopTransaction in OCPP1.6 are replaced by TransactionEvent in OCPP2.0.1.

(2) Firmware update in OCPP2.0.1 adds digital signatures to prevent incomplete firmware downloads, leading to firmware update failures.

(3) The transactionId is guaranteed to be unique by the platform in OCPP1.6, and guaranteed to be unique by the charging postwallbox electric car charger in OCPP2.0.1.

(4) In OCPP1.6, the defective places have been optimised and upgraded, for example: in OCPP1.6, the transactionId data inside the StartTransaction is determined by the platform, but in OCPP2.0.1, it is the charging pile wallbox electric car charger that determines the transactionId value, which is advantageous because when there is a network failure, it is necessary to re-send the StartTransaction data when the charging pile wallbox electric car charger has to send the data again. The advantage of this is that when there is a network failure, need to re-send StartTransaction data, if it is OCPP1.6 version, the platform is very likely to save two copies of the same Transaction data, resulting in the deduction of the customer's money twice;

(5) OCPP 2.0.1 details and features than the 1.6 version of a lot more, the development of the difficulty has increased.

Second, OCPP 2.0.1 agreement

OCPP2.0.1 supports the use of JSON format data websockets communication, OCPP2.0.1 is not compatible with OCPP1.6.

Supports multiple security authorisation methods, ISO15118, smart charging, device management, charging management, etc. Features high compatibility, high security and high scalability.

OCPP Network Topology

1、OCPP2.0.1 Software Architecture

It mainly includes modules of data transmission, authorisation, security, configuration, diagnosis, firmware management, device management and charging management, etc. Functional module division (part) in OCPP2.0.1 protocol:

2、Data transmission (DataTransfer) module

Use the third-party library libwebsockets to establish a websockets connection with the remote CSMS through the network for data interaction; use the third-party library rapidjson for

3、Authorisation(Authorization) Module

Authorisation methods include RFID, start button, debit/credit card, PIN code, CSMS, local idToken, ISO15118, offline authorisation and so on.

Example: CSMS Authorisation Timing Chart

4、Security(Security) Module

Security module uses third-party library mbedtls RSA, ECC (Elliptic Curve) module to encrypt and decrypt data, and X509 module to manage certificates.

Example: Timing diagram for updating charging station certificates

5、Transactions(Transactions) Module

Transactions refers to the process of charging an electric vehicle by a charging device.

In OCPP2.0, all the transaction related messages are integrated in the message <TransactionEvent>, which replaces <StartTransaction>, <StopTransaction>, <StatusNotification >, <MeterValue > and other messages in OCPP1.6.

Timing Diagram: Start Transaction - Plug and Play

6、MeterValues module

During the transaction process, it needs to send local meter data to CSMS periodically, so that CSMS and users can understand the progress of the transaction in real time.

Timing diagram: transaction-related meter data

7、Cost Module

Billing module is a new software module in OCPP2.0, which is used to provide price and billing information to users. It mainly includes:

-Before charging, providing detailed price information of charging station wallbox electric car charger.

-During charging, providing real-time cost information.

-After charging, providing final charging information.

(1) Timing diagram of price information before charging:

(2) Timing chart of billing information during charging

(3) Timing diagram of charging information after charging

8、Reservation Module

Reservation is a reserved function, which can be set by the operator. Since there are not many charging stations wallbox electric car charger and the driving range of electric vehicles is limited, users need to secure the ownership of charging equipment in advance.

Timing diagram for reserving the designated charging equipment at a charging station wallbox electric car charger:

9、SmartCharging Module

Smart charging refers to the behaviour of dynamically adjusting the charging power as needed during the charging process. It mainly includes:

-Load balancing within the charging station -Central system control

-Local smart charging -Energy management system control

In OCPP smart charging wallbox electric car charger control is mainly reflected in the Charging profiles, which contain the energy transfer limits for the charging station at a specific point in time.

Charging profiles message content (JSON):

10、Diagnostics module

It is used to remotely diagnose the problems of the charging station by uploading a file containing diagnostic information from the charging station.

Diagnostic information file uploading sequence diagram:

Diagnostic file related code (part):

11、Firmware Management Module

When the charging station needs to update the firmware, CSMS will notify the charging station when it can start to download the new firmware, and the charging station should notify CSMS after each step of downloading and installing the new firmware.

Example: Firmware Update Timing Diagram (Partial)

Firmware update related code (part):

12、DisplayMessage module

Display message module is used by the charging station operator (CSO) to display charging related information to the user, the display message module is a new function in OCPP 2.0, mainly including

-Setup display message by CSO

-Charging station wallbox electric car charger uploading display message

Setting the display message timing diagram: