Active/reactive power-balancing principle governing the dynamical evolution of increments on frequency/amplitude operating points in converter interfaced systems

In the oscillation analysis of today’s AC power electronic systems, the determination of DC operating point has long remained a fundamental challenge due to alternating trajectories. In conventional DC signal system analysis, the determination of states and operating points is always closely related to energy-driven dynamics. Similarly, for AC signal systems, establishing the energy types driving AC system dynamics and their conservation mechanisms are the irrefutable physical basis for identifying the DC operating point of AC systems, and the fundamental for understanding oscillation mechanisms. While existing research inherited certain knowledge about electric power and energy balance, this understanding remains experiential rather than rational. This is directly reflected in three aspects: the operating point remains under discussion; prevailing methods have not yet correlated power balance with the oscillatory evolution of electrical variables; and the oscillation mechanisms still unclear. Thus, this paper aims to reveal the power balance principles in AC systems and their connection to dynamics. It indicates that the dynamics of AC internal voltage of converter interfaced device and AC current of network are determined by frequency and amplitude (F/A) evolution. Meanwhile, F/A evolution is driven by active/reactive power imbalances. Consequently, F/A serve as system states, and their incremental dynamic evolution on operating points is governed by two independent balance constraints: active power balance and reactive power balance. Simulations further deepen this rational understanding. Finally, we extend the discussion to propose a comprehensive framework for analyzing oscillations in converter interfaced systems and demonstrate advantages, laying a foundation for related research.