Robust Fast Current Control for LCL-Equipped High-Speed PMSMs With Reduced Delay

For an inductor-capacitor–inductor (LCL) equipped high-speed permanent magnet synchronous machine (LCL-HSPMSM) with the inverter current feedback (ICF), the resonance frequency of the LCL filter is typically designed higher than one-sixth of the sampling frequency to accommodate the high electrical frequency. However, this design inherently poses a challenge to system stability in a digital system, primarily due to the presence of computation delays. This article proposes a two-degree-of-freedom (2DOF) current control strategy with reduced delay. Employing the proposed method, the system achieves strong stability, eliminating the need for active damping (AD). First, a mathematical model of the LCL-HSPMSM is formulated, which serves as the foundation for analyzing the stability concerning delays. Subsequently, a 2DOF control strategy is introduced, specifically tailored to the system with reduced delay. The additional DOF is provided by a feedforward controller to achieve dynamic decoupling. The delay-reducing method for the proposed control strategy is then described. In general, the whole controller design is independent of the resonance frequency, thereby exhibiting robust stability and resilience to a broad range of resonance frequency variations. Finally, the proposed method is verified in experiments, even with a carrier ratio as low as 8 and a resonance frequency close to the Nyquist frequency.