High Frequency Passivity Properties of Grid-Connected Admittance with Double-Sampling Asymmetric Dual-Edge Modulator

Small-signal stability and dynamic interactions among power electronic converters (PECs) and electrical grids are widely analyzed using the impedance-based approach. To reduce such interactions, a desirable feature of PECs is that their admittance exhibits dissipative behavior. Due to control delays, the PEC admittance usually exhibits non-dissipative zones around and above the crossover frequency of the inner control loop, possibly reducing the stability margins of the contemporary electrical grids. This paper proposes the double-sampling asymmetric dual-edge digital pulse-width modulator (ADE-DPWM) as an effective way to improve the passivity properties of the PEC admittance. Even in the digital implementation, the ADE-DPWM features zero delay and almost unity magnitude up to half of the switching frequency. Moreover, this paper examines the influence of ADE-DPWM on the PEC admittance even at higher frequencies, where destabilization of poorly damped grid resonances may be influenced by sampling and pulse-width modulation sidebands. Due to an operating point dependent ADE-DPWM small-signal model, the high-frequency passivity properties highly depend on the steady-state operating point. The analytical predictions are shown to be in excellent agreement with the experimental admittance measurements up to twice the switching frequency for all tested steady-state operating points.