Coordinated Self-Tuning Implementation of Repetitive Control and Active Damping for 400 Hz Inverter against Filter Inductance Fluctuation

The 400 Hz inverter plays an important role in connecting shipborne electric devices with the medium voltage bus. Due to the small ratio of the control frequency to the fundamental frequency f₀, the plugged-in repetitive control (RC) is more qualified for suppressing harmonics than other methods. However, the filter inductance variation resulting from the sustainability of overload may cause the drift of the resonant frequency f_r, which challenges the harmonic and stability of RC system. In this article, the resonance peak is damped by introducing an inner active damping loop, which results in a moderate magnitude/phase-frequency (MPF) response of the plant. The damping ability provided over the entire varied range of f_r is further enhanced by an elaborated configuration of the delay and the phase-lead compensation. The damping ratio and an inserted zero are coordinately adjusted to maintain the MPF response of the plant within a limited range, which takes a benchmark of the plant at triple overload. Additionally, the RC compensator is constructed by incorporating a biquad filter and a fractional-order notch filter, where the former is beneficial for 0 dB approximation, and the latter enhances high-frequency (HF) stability. The internal model gain is flexibly reshaped by the elaborated damping-based zero-phase-shift filter, which provides not only high modulus at selected nf₀ but also rapid roll-off over HF band. Finally, experiments on a scaled-down prototype validates that the proposed control strategy is qualified for enhancing stability and providing ability to suppress harmonics when the inductance fluctuates.