For grid-connected LCL-filtered inverters, resonance yields instability and low bandwidth. As a result, careful designs are required. This paper presents a systematic current control structure, where pole assignment consisting of one or more feedbacks is the inner loop, and the outer loop is the direct grid current control. Several other issues are discussed, such as the inner-loop feedback choices, pole-assignment algorithms, robustness and harmonic rejection. Generally, this kind of strategy has three different types according to the inner-loop feedback choices. Among them, a novel pole-assignment algorithm has been proposed, where the inner control maintains four freely-assigned poles which are just two pairs of conjugated poles located at the fundamental and resonance frequencies separately. It has been found that with the different types, the steady-state and dynamic performances are quite different. Finally, simulations and experiments have been provided to verify the control and design of the proposed methods.

In the LCL-filtered grid-tied inverter, the classical low-cost control strategy which is composed of the single converterside current control and the unit grid voltage feedforward compensation, is commonly employed to inject the sinusoidal current into the utility. However, the inverter output admittance features the non-passive behaviour, which indicates that the harmonic currents may be amplified under the disturbances of the grid voltage and the grid impedance. Therefore, two dedicated current loops based on only the converter-side current feedback are proposed, which consist of the low-pass filter-based current regulation and the high-pass filter-based active damping (HFAD). The mixed asymmetrical regular sampling method is further used to reduce the control delay of the HFAD. Moreover, the low-pass filter-based feedforward is developed to make a compromise between the disturbance rejection and the stability. Fair comparisons with other typical control strategies are made through analysing the virtual resistor in parallel with the filter capacitor, which reveals that the positive virtual resistance at the frequency lower than half of the switching frequency is maintained. With the elaborated control parameters, the exhaustive experimental results finally verify the effectiveness of the proposed method in passivating the inverter output admittance.

With the development of computer technology, the concept of computer automatic control has gradually penetrated the research field of aircraft power control, and intelligent power control systems have become mainstream research. The present work aims to improve the performance of the broadband phase-locked loop (PLL) based on the linear Kalman filter. Specifically, this paper first introduces linear Kalman filter and second-order generalized integrator (SOGI). Then, SOGI is added to PLL based on the linear Kalman filter. The purpose is to use the infinite gain effect of SOGI at the central angular frequency to eliminate the time-varying angular frequency component in the error when the system inputs SOGI to achieve a better filtering effect. Then, the system’s stability analysis and parameter settings are carried out to establish an intelligent phase-locked method of aviation variable frequency power supply. Finally, simulation experiments are performed. The experimental results demonstrate that PLL via the linear Kalman filter with SOGI can solve the problem that the output phase angle contains high-frequency components when the power supply voltage distortion rate is 10%. This scheme has a strong anti-interference ability under power grid voltage imbalance. The accuracy of the Long and Short-term Memory network used here is about 80%, which can well realize the intelligent aviation power frequency conversion control method. The research reported here provides a reference for establishing smart phase-locked technology of aviation variable frequency power supply.

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