In an AC microgrid, harmonic distortion is mainly caused by power electronic equipment and nonlinear loads. In this paper, linear active disturbance rejection control (LADRC) is used to control the fundamental current at the point of common coupling (PCC). Meanwhile, an active power filter (APF) is added to eliminate the harmonic current generated by the nonlinear loads. The tracking differentiator (TD) in active disturbance rejection control (ADRC) serves as a low-pass filter (LPF) in the harmonic detection algorithm of APF. Compared to traditional harmonic detection algorithms, the improved strategy solves the contradiction between rapidity, accuracy, and overshoot of filtering. LADRC has good performance of disturbance rejection, internal decoupling, and accessible parameters tuning. It can observe the internal uncertainty and external disturbance of the system as the total disturbance through the extended state observer (ESO), and compensate it in time through state feedback to make the system achieve the desired performance. The abilities of resonance suppression for LCL-type filter and internal decoupling of LADRC demonstrates its advantages through frequency domain analysis and simulation. The proposed strategy was simulated in MATLAB/SIMULINK and realized in the experimental hardware platform, and the effectiveness of the proposed strategy is approved.

This paper proposes a harmonic compensation control with disturbance rejection function for a standalone inverter. Due to the LC type three-phase three-leg inverter is connected to nonlinear loads, low-order harmonic components appears in the inverter output current. These harmonic current generate harmonic voltage drops when flowing through the filter inductor and the feeder impedance, which causes the output voltage of the inverter distorted. In order to compensate harmonics and produce sinusoidal voltage without additional compensation devices, virtual harmonic impedance method can be added to the fundamental voltage control. Due to the compensation effect of virtual harmonic impedance are very sensitive to the fluctuation of filter inductance. Therefore, inductance variation, as a disturbance in physical system, should be considered. In this paper, linear active disturbance rejection control (LADRC) is proposed in the fundamental voltage control loop to reduce the sensitivity of virtual harmonic impedance and decouple the model. Compared with traditional dual-loop PI control, the proposed strategy has faster dynamic response in control performance and fewer acquisition modules in engineering applications. The whole design process of virtual harmonic impedance and stability analyses of this strategy are provided. The simulation and experiment results show the good performance of the proposed strategy.

Permanent-Magnet Linear Synchronous Motor (PMLSM) transforms electric energy into linear mechanical kinetic energy without transmission mechanism which is widely used in rail transmit due to its merits of high efficiency, relatively low losses and simple mechanism. In the field oriented control of the linear motor, high-precision speed and position information are required. However, the installation of the linear grating increases the cost and complexity of the system, reduces anti-disturbance ability for mechanical structures, which may directly affect the control performance. In this paper, based on the sensorless control method, a modified linear extended state observer (MLESO) is proposed and utilized to estimate the back electromotive force. Then, the linear active rejection disturbance control (LADRC) is used to estimate and compensate system dynamics and disturbances to enhance disturbance rejection and stability of the PMLSM system. Moreover, the feedforward controller (FFC) is introduced to improve the response speed of the PMLSM. The simulation results certify that the proposed strategy has the superiority to the conventional sensorless control method.

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The permanent magnet linear synchronous motor (PMLSM) is a promising motor to drive cordless elevator, computer numerical control machines due to its high force density and zero transmission. In the presence of rapidly varying loads, however, the conventional control methods of PMLSM cannot guarantee the precise-velocity and highdynamic operation. In this work, a large signal stabilization scheme, which comprises high order slide mode (HOSM) observer and a finite-time controller (FTC), is proposed. Firstly, a finite-time observer is introduced to accurately observe the varying loads in finite time. Secondly, the FTC exactly offsets the estimated values and stabilizes all system states at their designated points in finite time. Finally, numerical simulation results show that the proposed controller provides a stronger adaptability and better performance in precision and speed to rapidly varying loads than the traditional PI controller.