Enabling DER-Rich power electronics-dominated power systems: a constant-frequency grid-forming control strategy based on voltage magnitude–active power droop

Conventional power systems dominated by synchronous generators are rapidly evolving into power electronics-dominated power systems (PEDPSs). Mainstream non-constant-frequency grid-forming control inherits the “active power–frequency and reactive power–voltage regulation” logic, causing inherent mutual coupling among voltage, power, and frequency. Meanwhile, existing constant-frequency strategies still exhibit strong coupling among reactive power, voltage, and active power, and fail to support flexible droop base point configuration and precise active power flow regulation. To address these limitations, this paper proposes a constant-frequency grid-forming control strategy based on voltage magnitude–active power ( U s – P ) droop enabled by time synchronization technology. The strategy decouples power from frequency at the control mechanism level and achieves unidirectional steady-state decoupling of reactive power from voltage and active power at the converter terminals. The constant-frequency grid-forming (CF-GFM) converter supports flexible setting of the droop base point and, with an active power dispatch method, enables precise regulation of system active power flow. The equivalent circuit model of the CF-GFM converter reveals its core operating mechanism of “constant frequency, active power–voltage regulation with internal reactive power compensation”: the voltage magnitude is uniquely determined by the linear U s – P droop, while the d-axis component E d of the internal voltage automatically accommodates reactive power variations, thereby internally absorbing the impact of reactive disturbances on the terminal voltage. Small-signal stability analysis is performed, and the control mechanism, controller performance, and feasibility are verified through simulations and hardware-in-the-loop experiments. Finally, the constant-frequency power system is discussed and summarized, and future research directions are outlined. This work offers a new approach for constructing future PEDPSs with high penetration of DERs and embodies the shift in grid-forming control philosophy from “emulating the physical characteristics of synchronous generators” to “actively shaping superior electrical terminal characteristics”.