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Microgrid architecture — grid-connected vs islanded, IEEE 2030.7

DOE/IEEE 2030.7 definition: bounded local DERs + loads + PCC, with islanding capability. Components: PV/battery/gas-gen/fuel-cell + tiered loads + PCC + static transfer switch + MEMS controller. Two modes: grid-connected (utility V/f) vs islanded (grid-forming DER self-regulates). Hierarchical control: primary droop / secondary MEMS / tertiary economic. AC vs DC vs hybrid architectures. IEEE 2030.7/2030.8/1547; FERC 2222. Examples: Princeton, Borrego Springs, DoD bases.

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Step 1 — Microgrid definition (DOE/IEEE): autonomous local power system

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Reference notes

A microgrid is a group of interconnected loads and distributed energy resources within clearly defined electrical boundaries that acts as a single controllable entity with respect to the grid (DOE / IEEE Std 2030.7 definition). The defining feature is islanding capability: it can operate grid-connected (utility sets V and f) or autonomously (microgrid sets its own V and f). Typical size: 500 kW to 50 MW.

Essential characteristics

Defined boundaries — clear electrical boundary; typically a single Point of Common Coupling (PCC).
Local generation + load — DERs and the loads they serve all within the boundary.
Islanding capability — can disconnect from grid and operate autonomously.

Components

Component	Role
PV solar	Day-time generation; inverter-based (per L107 pv-system-design)
Battery (Li-ion)	Energy time-shifting, V/F support, fast frequency response. 1-4 hr duration.
Gas generator (NG)	Firm capacity for low-renewable / long islanded events. 100 kW - 5 MW.
Fuel cells	NG or hydrogen, quiet/clean/efficient (Bloom Energy dominant)
Diesel backup	Emergency only (air-quality permits often restrict use)
CHP (cogeneration)	Heat + power at universities, hospitals
Critical loads	Hospitals, data centers, water/wastewater pumps, signaling, comms
Priority loads	Lighting, labs
Non-critical loads	HVAC, EV charging (can shed during emergency)
PCC + static transfer switch	Single utility connection; opens to island, closes to reconnect
Microgrid controller (MEMS)	Central management per IEEE 2030.7
Communication network	Fiber/wireless, < 100 ms latency for critical control

Two operating modes

Mode	Behavior
Grid-connected (parallel)	Utility grid sets V and f; microgrid follows. DERs operate at economic optimum or utility signal. Power flows either direction across PCC.
Islanded (autonomous)	PCC open. Microgrid maintains own V and f via at least one grid-forming DER (typically battery or generator). Other DERs grid-following.

Mode transitions

Planned islanding: scheduled in advance. Microgrid ramps up backup gen, charges battery, then opens PCC smoothly. Loads see minimal disturbance.
Unplanned islanding: utility outage forces sudden disconnection. Controller detects outage (PMU/RTU/local sensing) and rapidly switches grid-following DERs into grid-forming mode. May involve load shedding of non-critical loads.
Black start: restoring microgrid from fully de-energized state without grid support. Requires at least one DER capable of energizing the bus (grid-forming battery, genset with starting battery).
Resynchronization: when utility returns, microgrid synchronizes V/phase/frequency before closing PCC. ANSI 25 sync-check relay verifies magnitude (within ±5%), slip Δf < 0.05 Hz, angle difference Δθ (delta theta) < 20°. Target soft transition < 100 ms glitch.

Hierarchical control architecture

Layer	Timescale	Function
Primary	< 100 ms	Local droop control (P-f and Q-V) at each DER. Decentralized, no communication needed.
Secondary	100 ms - seconds	MEMS restores nominal V and f after primary; restores correct DER sharing. Centralized.
Tertiary	5-15 minutes	Economic dispatch: minimize fuel cost while meeting load. Considers SOC, weather, market.

Microgrid architectures — AC / DC / Hybrid

AC microgrid: traditional, AC bus at standard voltage (480 V / 12.47 kV / etc.). Compatible with all existing AC equipment and protective relays. Multiple AC-DC-AC conversion stages reduce efficiency.
DC microgrid: emerging, DC bus (380 V data centers, 1500 V solar farms, 750 V EV charging). Eliminates conversion stages; higher efficiency. Limited code support (NEC 712 emerging). DC arc faults harder to interrupt.
Hybrid AC/DC: combines both buses via back-to-back converter. Flexibility for mixed load types.

Standards

IEEE 2030.7 — Standard for the Specification of Microgrid Controllers
IEEE 2030.8 — Standard for the Testing of Microgrid Controllers
IEEE 1547 — DER Interconnection (each DER individually)
NEC 705 + state interconnection rules
FERC Order 2222 (2020) — aggregated DER participation in wholesale markets
IEEE P2800.2 — grid-forming inverter requirements (in development)

Economic value stack

Avoided outage costs: $100-10,000/kWh for critical loads (hospitals, data centers, military, food cold-chain).
Demand charge reduction: peak shaving with battery (commercial demand charges 30-50% of total bill).
Energy arbitrage: charge cheap night, discharge expensive day. Round-trip efficiency 85-90%.
Ancillary services: regulation, spinning reserve via aggregated DER.
Capacity market participation per FERC Order 2222.
Resilience value: state policies (California SGIP resilience adder) monetize avoided-outage benefit.
Solar ITC: 30% federal ITC (IRA 2022) if PV-equipped.
Capital cost: $2-5/W typical, dominated by battery line item.

Example deployments

Princeton University — 15 MW microgrid (gas turbine + PV + battery). Islanded during Hurricane Sandy 2012.
Borrego Springs, California — SDG&E utility-owned community microgrid serving 2,800 customers. Islanded during wildfire PSPS events.
Sendai, Japan — Tohoku University microgrid maintained power during 2011 earthquake and tsunami.
Bronzeville, Chicago — ComEd utility community microgrid pilot.
Department of Defense — dozens of microgrids on US military bases for energy security.
Tau Island, American Samoa — 100% solar + battery microgrid (no fossil backup).

Regulatory frameworks

California CPUC microgrid framework (2020-2024) — interconnection, tariff design, multi-customer microgrids per SB 1339.
New York REV proceeding — microgrid pilots since 2014; NY Prize competition.
Massachusetts, Hawaii, Colorado, Arizona — state programs aligned with renewable integration and resilience.
Department of Defense procurement frameworks since 2010.

Future trends

All-renewable microgrids (100% PV + battery) emerging on islands and remote areas.
Grid-forming inverter deployment enables 100%-IBR islanding (see L122 in roadmap).
Multi-customer / community microgrids (California SB 1339, etc.).
Vehicle-to-grid (V2G) — parked EVs as microgrid storage during outages.
AI / ML-based forecasting and dispatch.

Vendors

Microgrid controllers: Eaton (Power Xpert), Schneider (EcoStruxure), Siemens (SICAM), ABB (Microgrid Plus), GE (Microgrid Control System), Spirae, Heila Technologies.
Static transfer switches: Cummins, Russelectric, ASCO, Generac.
Battery integrators: Fluence, Tesla, Wartsila, BYD, Powin.

Take-away. Microgrid (DOE / IEEE 2030.7) = bounded local generation + load + PCC, with islanding capability. Components: DERs (PV/BAT/GEN/FC) + tiered loads + PCC with static transfer switch + MEMS controller + comm. Two modes: grid-connected (utility sets V/f) vs islanded (microgrid self-regulates with at least one grid-forming DER). Transitions: planned, unplanned, black start, resynchronize (ANSI 25 sync-check). Hierarchical control: primary droop < 100 ms; secondary MEMS; tertiary economic dispatch 5-15 min. Architectures: AC (mature), DC (efficient, data center / EV growing), hybrid. Standards: IEEE 2030.7/2030.8/1547, FERC 2222. Value stack: avoided outage + demand-charge cut + arbitrage + ancillaries + capacity market + resilience.