Primary Frequency Control of Multiple ON/OFF Load Clusters Considering Capacity Uncertainty and Lock-Time Constraint

In modern power systems, load-side controllable resources, especially ON/OFF type controllable loads, have emerged as promising reserves for providing fast frequency support. This article presents a three-layer hierarchical control framework enabling multiple ON/OFF load clusters to actively participate in primary frequency control (PFC) with their control characteristics well considered. At the cluster-layer, the probability distribution of aggregate regulation capacity is estimated by state evolution model with no underlying information needed. At the aggregator-layer, optimal droop coefficient allocation for multiple clusters is achieved by minimizing the comprehensive cost objective with capacity chance constraints. At the device-layer, a self-governing mechanism is designed for each individual load to timely formulate and correctly conduct its own response plan according to upper-layer broadcast instructions. Consequently, the reliability of PFC with ON/OFF loads is significantly enhanced by taking capacity uncertainty and inherent lock-time constraint into account. Meanwhile, the communication requirements and user privacy damage are minimized while ensuring the final control accuracy. Steady-state and transient simulations further validate the effectiveness of the proposed upper-layer and device-layer PFC method respectively.