Xiang Zhang

With the electrification trend of future aircraft, high-speed permanent magnet starters/generators (PMSs/Gs) will potentially be widely used in onboard generation systems due to their high power density and high efficiency. However, the per-unit reactance of such high-speed machines is normally designed to be very low due to limited onboard power supply voltage and large electrical power demand, which can result in large current ripples in the machine and thus large torque ripples especially when the machine is fed with a semiconductor-based inverter of a lower switching frequency. The torque ripples may further lead to speed oscillation and generate severe vibrations and noises that are harmful to the mechanical system and human beings around. In this article, a speed/torque ripple reduction method for high-speed PMS/Gs with a low inductance is proposed to improve their performance within a wide speed range. An active damping technique is applied to the speed loop to increase the anti-disturbance capability and generate a smoother reference for the current loop, whereas an adaptive output voltage saturation limit is utilized for the current loop to limit the peak value of current to prevent overcurrent and torque spikes. The parameter tuning criteria are derived through a thorough analysis. Finally, the proposed method is validated on a high-speed PMS/G with an inductance of 99 $\mu \text{H}$ . The results show that the speed ripples and torque ripples are reduced by over 50% within a speed range of 2–14 krpm.

A dual-loop current control method (grid current loop and inverter-side current loop) is promising for digitally-controlled LCL-type shunt active power filters (APFs), due to its inherent active damping effect for LCL resonance. However, the damping region is only up to one sixth of the sampling frequency (fs/6), which leads to a limited system robustness against grid impedance variation at the point of common coupling (PCC). Hence, in this study, the robustness of such control is discussed through mathematic derivations and diagram analysis, which reveals that both the system delays and PCC voltage feedforward affect the system robustness. On the basis of theoretical analysis, a systematic approach via infinite impulse response (IIR) filters has been proposed for enhancing the robustness to grid impedance. Thereof, a second-order IIR filter-based inverter-side current feedback is proposed to widen the damping region up to almost the Nyquist frequency (fs/2), while a band-stop IIR filter-based PCC voltage feedforward is proposed to achieve the superior stability margins under a large grid impedance in comparison with unit feedforward. Finally, experimental results on a 30 kVA APF prototype have verified the effectiveness of the proposed approach.

High-speed Permanent-Magnet Synchronous Motors/Generators (PMSMs/Gs) in a Flywheel Energy Storage System (FESS) are faced with high cross-coupling voltages and low switching-to-fundamental frequency ratios. High cross-coupling voltages between d-q axis current loops lead to transient current errors, which is more serious at lower switching-to-fundamental-frequency ratios. If the delays are not properly considered during the current controller design in a digital control system, the low switching-to-fundamental-frequency ratios may result in oscillatory or unstable responses. In this study, an accurate discrete current controller for high-speed PMSMs/Gs is proposed based on an accurate discrete model that takes the phase and magnitude errors generated during the sampling period into consideration, and an Extended State Observer (ESO) is applied to estimate and compensate the back EMF error. The cross-coupling problem is well settled, and the current loop dynamic at lower switching-to-fundamental frequency ratios is improved. Finally, the proposed discrete controller is validated on a 12,000 rpm PMSM/G prototype.

This paper presents a DC-link voltage fast control strategy for high-speed Permanent Magnet Synchronous Motor/Generator (PMSM/G) of Flywheel Energy Storage System (FESS) to ensure fast dynamic performance within its wide operation range. Instead of the conventional strategy with cascaded outer DC-link voltage loop and inner current loop, the proposed strategy is a direct voltage control (DVC) strategy without an intermediate current loop. The nonlinear DC-link voltage loop model is globally linearized by treating the square of DC-link voltage as the state variable and lumping the nonlinear and uncertain terms in the power balance equation as the total disturbance. An Extended State Observer (ESO) is designed to observe the total disturbance, and a control law which compensates the speed variation and the total disturbance is proposed. The inner dynamic of the proposed ESO is analyzed, and the tracking performance and anti-disturbance capability of the proposed strategy is hereby derived. Finally, the proposed strategy is validated on a high-speed FESS test bench.