Open Charge Point Protocol (OCPP)
Overview
Open Charge Point Protocol (OCPP) is an application protocol for communication between Charge Points (Electric vehicle (EV) charging stations) and a central management system, also known as a charging station network. OCPP is a standard defined by The Open Charge Alliance and goal is to offer a uniform solution for the method of communication between charge point and central system. With this protocol it is possible to connect any central system with any charge point, regardless of the vendor.
Zephyr provides an OCPP Charge Point (CP) library built on top of websocket API
with payload in json format. The library can be enabled with
CONFIG_OCPP Kconfig option. Currently OCPP 1.6 with basic
core profile is supported.
OCPP charge point (CP) require a Central System (CS) server to connect, an open source SteVe server shall be setup locally for devlopment purpose, See SteVe server for more information about the setup.
The Zephyr OCPP CP library implements the following items:
engine to process socket connectivity and events
OCPP core functions to frame/parse payload, user notification for OCPP events, heartbeat notification
Sample usage
Init ocpp library with overall CP and CS information. Prior to init an OCPP library, a network interface should be ready using ethernet or wifi or modem. A filled CP, CS structure and user callback needs to be passed in ocpp_init.
static int user_notify_cb(ocpp_notify_reason_t reason,
ocpp_io_value_t *io,
void *user_data)
{
switch (reason) {
case OCPP_USR_GET_METER_VALUE:
...
break;
case OCPP_USR_START_CHARGING:
...
break;
...
...
}
/* OCPP configuration */
ocpp_cp_info_t cpi = { "basic", "zephyr", .num_of_con = 1};
ocpp_cs_info_t csi = {"192.168.1.3", /* ip address */
"/steve/websocket/CentralSystemService/zephyr",
8180,
AF_INET};
ret = ocpp_init(&cpi, &csi, user_notify_cb, NULL);
A unique session must open for each physical connector before any ocpp transcation API call.
ocpp_session_handle_t sh = NULL;
ret = ocpp_session_open(&sh);
idtag is EV user’s authentication token which should match with list on CS. Authorize request must call to ensure validity of idtag (if charging request originate from local CP) before start energy transfer to EV.
ocpp_auth_status_t status;
ret = ocpp_authorize(sh, idtag, &status, 500);
On successful, authorization status is available in status.
Apart from local CP, charging request may originate from CS is notified to user in callback with OCPP_USR_START_CHARGING, here authorize request call is optional. When the CS is ready to provide power to EV, a start transaction is notified to CS with meter reading and connector id using ocpp_start_transaction.
const int idcon = 1;
const int mval = 25; //meter reading in wh
ret = ocpp_start_transaction(sh, mval, idcon, 200);
Once the start transaction is success, user callback is invoked to get meter readings from the library. callback should be not be hold for longer time.