Depot Edge Compute

control loops · protocols · OT security

Protection, inverter and charger control run faster than a cloud round trip. A depot needs its own industrial control computer, not just a data appliance.

Log-scale chart of depot control loops by timescale: relay protection trips over IEC 61850 GOOSE in 3-10 milliseconds; inverter and grid-forming control acts within one AC cycle, 16.7 milliseconds at 60 Hz; charger power setpoints over OCPP change every few seconds; the utility demand-charge window is 15 minutes; the day-ahead charge plan covers 24 hours. A dashed line at about 0.1 seconds marks a typical cloud round trip: the faster loops must run on site, and the slower ones must keep running when the wide-area link drops. DEPOT CONTROL LOOPS BY TIMESCALE (LOG SCALE) Relay trip (GOOSE)3-10 ms Inverter control loopone AC cycle Charger setpoint (OCPP)seconds Demand-charge window15 min Day-ahead charge plan24 h 1 ms 1 s 1 min 1 h 1 d Dashed line: a typical cloud round trip of about 0.1 s. Loops left of it must run on site; loops right of it must keep running when the WAN drops.
Relay trip
3-10 ms
Demand window
15 min
Charger protocol
OCPP 2.0.1
OT security
IEC 62443
Hub
Charging

Finding

A depot's control loops run from milliseconds to minutes, faster than a cloud round trip and through network outages, so the control computer has to sit on site

Relays trip over IEC 61850 GOOSE messages in 3-10 ms, grid-forming battery inverters regulate voltage and frequency within an AC cycle, and the charger management system reallocates power among stalls every few seconds to hold the site under its utility import limit. A cloud service a tenth of a second away cannot close those loops, and a depot that stops charging when its fiber is cut misses the morning dispatch.

A depot therefore runs two kinds of edge computer. The control computer - microgrid controller, energy management system (EMS) and charger gateway - is a hardened industrial system with deterministic timing, from Schneider Electric, Siemens, ABB, Hitachi Energy or, in China, NARI and Huawei Digital Power. The data computer ingests vehicle logs, stages over-the-air (OTA) updates and runs analytics; for autonomous fleets it is usually an appliance supplied by the AV developer, covered on Fleet Autonomy Edge Compute.

The control computer is also a protocol translator. Chargers speak OCPP (2.0.1 today, 2.1 adds bidirectional charging) and talk to vehicles over ISO 15118-20; batteries, inverters and meters use Modbus TCP or IEC 61850; the utility reaches the site through IEEE 2030.5, OpenADR or DNP3. Inverters must meet IEEE 1547-2018 and UL 1741 SB to interconnect. Keeping all of that on one site controller, with the cloud setting targets rather than issuing commands, is what lets a depot island, ride through faults and hold its demand peak when the wide-area link is down.

Control loops

What runs where

Fast loops stay local; the cloud sets plans and targets.

Depot control loops
LoopTimescaleRuns onProtocol
Protection and fault clearing3-10 msProtection relaysIEC 61850 GOOSE
Grid-forming inverter controlSub-cycleBESS power conversion systemVendor firmware
Islanding and resynchronization100 ms to secondsMicrogrid controllerIEC 61850, Modbus TCP
Charger power allocationSecondsCharger management gatewayOCPP 2.0.1 smart-charging profiles
Vehicle-charger sessionSecondsCharger and vehicleISO 15118-20, DIN 70121
Demand-peak control15-minute windowEMSMeter data, Modbus
Utility signals and grid servicesMinutes to hoursEMS and utility gatewayIEEE 2030.5, OpenADR 2.0b, DNP3
Charge and dispatch planningHours to a dayEMS with fleet management systemVendor APIs

Edge stack

The depot edge stack

A small industrial control room plus a small data room, usually in one prefabricated enclosure.

Depot edge compute stack
LayerComponentsDepot note
PhysicalRacks, UPS, cooling, enclosure, access controlOften a prefabricated IT or electrical room beside the switchgear
Control hardwareMicrogrid controller, protection relays, PLCs, revenue metersHardened, deterministic; keeps running without the WAN
NetworkIndustrial switches, firewalls, private LTE or 5G, Wi-Fi, redundant fiber and cellular backhaulSeparate OT, vehicle, IT and guest networks
Data compute and storageServers, GPUs where autonomy logs are triaged, storage arraysSized for ingest bursts at shift change
PlatformContainers, orchestration, monitoringSame image across sites so updates roll out uniformly
ApplicationsEMS, charger management, OTA staging, fleet and yard management adaptersBusiness logic; the cloud sets targets, the site executes

Security

Network zones and conduits

OT security for depots follows IEC 62443 zones and conduits. Bulk-grid NERC CIP rules generally do not reach a depot, but the utility interconnection agreement and UL 2900 or IEC 62443 certification of chargers increasingly do.

Depot network zones
ZoneDevicesRule
Protection and powerRelays, inverters, microgrid controllerNo direct internet path; changes only through engineering workstation
ChargingChargers, charger gatewayOCPP over TLS to the gateway; vendor cloud access through a broker
VehicleDepot Wi-Fi and wired offload portsAuthenticated by vehicle certificate; isolated from OT
Enterprise ITFleet, yard and maintenance systemsReads OT data through a historian or DMZ, never writes directly
Guest and contractorDriver lounge, vendor laptopsInternet only; vendor remote access is logged and time-limited

Sources

Sources and scope

Scope
Fleet Depot Edge Compute
Sources
IEC 61850; IEC 62443; Open Charge Alliance (OCPP); ISO 15118; IEEE 1547 and 2030.5; UL 1741 SB
Updated
October 2026