SEP 2.0 DER Support

Version 1.0

Smart Energy Profile 2.0 (SEP2, IEEE 2030.5) specifies a REST architecture built around the core HTTP verbs: GET, HEAD, PUT, POST and DELETE. A specification for the SEP2 protocol can be found here.

SEP2 EndDevices (clients) POST XML resources representing their state, and GET XML resources containing command and control information from the server. The server never reaches out to the client unless a “subscription” is registered and supported for a particular resource type. This implementation does not use SEP2 registered subscriptions.

The SEP2 specification requires HTTP headers, and it explicitly requires RESTful response codes, for example:

  • 201 - “Created”
  • 204 - “No Content”
  • 301 - “Moved Permanently”
  • etc.

SEP2 message encoding may be either XML or EXI. Only XML is supported in this implementation.

SEP2 requires HTTPS/TLS version 1.2 along with support for the cipher suite TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8. Production installation requires a certificate issued by a SEP2 CA. The encryption requirement can be met by using a web server such as Apache to proxy the HTTPs traffic.

SEP2 discovery, if supported, must be implemented by an xmDNS server. Avahi can be modified to perform this function.

Function Sets

SEP2 groups XML resources into “Function Sets.” Some of these function sets provide a core set of functionality used across higher-level function sets. This implementation implements resources from the following function sets:

  • Time
  • Device Information
  • Device Capabilities
  • End Device
  • Function Set Assignments
  • Power Status
  • Distributed Energy Resources

Distributed Energy Resources

Distributed energy resources (DERs) are devices that generate energy, e.g., solar inverters, or store energy, e.g., battery storage systems, electric vehicle supply equipment (EVSEs). These devices are managed by a SEP2 DER server using DERPrograms which are described by the SEP2 specification as follows:

Servers host one or more DERPrograms, which in turn expose DERControl events to DER clients. DERControl instances contain attributes that allow DER clients to respond to events that are targeted to their device type. A DERControl instance also includes scheduling attributes that allow DER clients to store and process future events. These attributes include start time and duration, as well an indication of the need for randomization of the start and / or duration of the event. The SEP2 DER client model is based on the SunSpec Alliance Inverter Control Model [SunSpec] which is derived from IEC 61850-90-7 [61850] and [EPRI].

EndDevices post multiple SEP2 resources describing their status. The following is an example of a Power Status resource that might be posted by an EVSE (vehicle charging station):

<PowerStatus xmlns="http://zigbee.org/sep" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" href="/sep2/edev/96/ps">
    <batteryStatus>4</batteryStatus>
    <changedTime>1487812095</changedTime>
    <currentPowerSource>1</currentPowerSource>
    <estimatedChargeRemaining>9300</estimatedChargeRemaining>
    <PEVInfo>
        <chargingPowerNow>
            <multiplier>3</multiplier>
            <value>-5</value>
        </chargingPowerNow>
        <energyRequestNow>
            <multiplier>3</multiplier>
            <value>22</value>
        </energyRequestNow>
        <maxForwardPower>
            <multiplier>3</multiplier>
            <value>7</value>
        </maxForwardPower>
        <minimumChargingDuration>11280</minimumChargingDuration>
        <targetStateOfCharge>10000</targetStateOfCharge>
        <timeChargeIsNeeded>9223372036854775807</timeChargeIsNeeded>
        <timeChargingStatusPEV>1487812095</timeChargingStatusPEV>
    </PEVInfo>
</PowerStatus>

Design Details

../_images/volttron_sep2.jpg

VOLTTRON’s SEP2 implementation includes a SEP2Agent and a SEP2 device driver, as described below.

VOLTTRON SEP2Agent

SEP2Agent implements a SEP2 server that receives HTTP POST/PUT requests from SEP2 devices. The requests are routed to SEP2Agent over the VOLTTRON message bus by VOLTTRON’s MasterWebService. SEP2Agent returns an appropriate HTTP response. In some cases (e.g., DERControl requests), this response includes a data payload.

SEP2Agent maps SEP2 resource data to a VOLTTRON SEP2 data model based on SunSpec, using block numbers and point names as defined in the SunSpec Information Model, which in turn is harmonized with 61850. The data model is given in detail below.

Each device’s data is stored by SEP2Agent in an EndDevice memory structure. This structure is not persisted to a database. Each EndDevice retains only the most recently received value for each field.

SEP2Agent exposes RPC calls for getting and setting EndDevice data.

VOLTTRON SEP2 Device Driver

The SEP2 device driver is a new addition to VOLTTRON MasterDriverAgent’s family of standard device drivers. It exposes get_point/set_point calls for SEP2 EndDevice fields.

The SEP2 device driver periodically issues SEP2Agent RPC calls to refresh its cached representation of EndDevice data. It issues RPC calls to SEP2Agent as needed when responding to get_point, set_point and scrape_all calls.

Field Definitions

These field IDs correspond to the ones in the SEP2 device driver’s configuration file, sep2.csv. They have been used in that file’s “Volttron Point Name” column and also in its “Point Name” column.

Field ID SEP2 Resource/Property Description Units Type
b1_Md
device_information
mfModel
 Model (32 char lim).   string
b1_Opt
device_information
lfdi
 Long-form device identifier (32 char lim).   string
b1_SN
abstract_device
sfdi
 Short-form device identifier (32 char lim).   string
b1_Vr
device_information
mfHwVer
 Version (16 char lim).   string
b113_A
mirror_meter_reading
PhaseCurrentAvg
 AC current. A float
b113_DCA
mirror_meter_reading
InstantPackCurrent
 DC current. A float
b113_DCV
mirror_meter_reading
LineVoltageAvg
 DC voltage. V float
b113_DCW
mirror_meter_reading
PhasePowerAvg
 DC power. W float
b113_PF
mirror_meter_reading
PhasePFA
 AC power factor. % float
b113_WH
mirror_meter_reading
EnergyIMP
 AC energy. Wh float
b120_AhrRtg
der_capability
rtgAh
 Usable capacity of the battery. Maximum charge minus minimum charge. Ah float
b120_ARtg
der_capability
rtgA
 Maximum RMS AC current level capability of the inverter. A float
b120_MaxChaRte
der_capability
rtgMaxChargeRate
 Maximum rate of energy transfer into the device. W float
b120_MaxDisChaRte
der_capability
rtgMaxDischargeRate
 Maximum rate of energy transfer out of the device. W float
b120_WHRtg
der_capability
rtgWh
 Nominal energy rating of the storage device. Wh float
b120_WRtg
der_capability
rtgW
 Continuous power output capability of the inverter. W float
b121_WMax
der_settings
setMaxChargeRate
 Maximum power output. Default to WRtg. W float
b122_ActWh
mirror_meter_reading
EnergyEXP
 AC lifetime active (real) energy output. Wh float
b122_StorConn
der_status
storConnectStatus
 CONNECTED=0, AVAILABLE=1, OPERATING=2, TEST=3.   enum
b124_WChaMax
der_control
opModFixedFlow
 Setpoint for maximum charge. This is the only field that is writable with a set_point call. W float
b403_Tmp
mirror_meter_reading
InstantPackTemp
 Pack temperature. C float
b404_DCW
PEVInfo
chargingPowerNow
 Power flow in or out of the inverter. W float
b404_DCWh
der_availability
availabilityDuration
 Output energy (absolute SOC). Calculated as (availabilityDuration / 3600) * WMax. Wh float
b802_LocRemCtl
der_status
localControlModeStatus
 Control Mode: REMOTE=0, LOCAL=1.   enum
b802_SoC
der_status
stateOfChargeStatus
 State of Charge %. % WHRtg float
b802_State
der_status
inverterStatus
 DISCONNECTED=1, INITIALIZING=2, CONNECTED=3, STANDBY=4, SOC PROTECTION=5, FAULT=99.   enum

Revising and Expanding the Field Definitions

The SEP2-to-SunSpec field mappings in this implementation are a relatively thin subset of all possible field definitions. Developers are encouraged to expand the definitions.

The procedure for expanding the field mappings requires you to make changes in two places:

  1. Update the driver’s point definitions in services/core/MasterDriverAgent/master_driver/sep2.csv
  2. Update the SEP2-to-SunSpec field mappings in services/core/SEP2Agent/sep2/end_device.py and __init__.py

When updating VOLTTRON’s SEP2 data model, please use field IDs that conform to the SunSpec block-number-and-field-name model outlined in the SunSpec Information Model Reference (see the link below).