Frequency–Temperature Droop Control of Grid–Interactive Electric Water Heaters for Decentralized Grid Support

Abstract

The increasing penetration of converter-interfaced renewable generation reduces system inertia and heightens the need for fast primary frequency response (PFR). This paper proposes a device-level frequency-temperature droop control framework that enables legacy electric water heaters (EWHs) to provide autonomous PFR using only local frequency and temperature measurements. Unlike centralized or direct-load-control approaches, the proposed method preserves native thermostat operation while adapting each unit’s droop response according to its thermal headroom. A physics-based EWH model is integrated with the IEEE European Low-Voltage Test Feeder with 55 residential customers and evaluated under low-inertia disturbances, adaptive droop operation, and control-loop latency. Results show that grid-interactive EWH droop raises frequency nadir from below 47 Hz to about 49.2–49.5 Hz in representative cases, while the adaptive strategy improves nadir by about 1 Hz over static droop, substantially reduces delayed-response oscillations, and provides a practical communication-free solution for decentralized grid support.