Active power filter (APF) has become an effective approach to suppress harmonic and compensating the reactive power of a power grid. In this paper, the topological structure of the single-phase APF is T-type three-level which can suppress harmonic. For the traditional dual-loop PI control of APF, the voltage loop has poor disturbance rejection performance and long response time under nonlinear load and load mutation. To eliminate the impact on the reduction of power quality of the power grid, this paper uses a PI control of the current loop and a linear active disturbance rejection control (LADRC) of voltage loop. The first-order LADRC controller, which uses a linear extended state observer (ESO) and a linear state error feedback (SEF), does not depend on an explicit mathematical model of the controlled object. In this paper, a 2kVA experimental prototype with a processor of TMS320F28335 is designed to testify the performance and effectiveness of the presented method. The results of simulation and experiments show that the LADRC has better disturbance rejection performance and faster dynamic response than PI control under nonlinear load and load mutation.INDEX TERMS Active power filter, dc side voltage, linear active disturbance rejection control, linear extended state observer, T-type three-level.

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Recently, the permanent magnet linear synchronous motor (PMLSM) servo control technology has become a research hotspot. However, the control performance under the traditional PID control is not ideal, which usually has the problems of slow response speed, large overshoot and poor anti-interference performance. In addition, adding nonlinear links with certain characteristics purposefully can greatly improve the performance of the system and achieve the expected effect that the traditional linear controllers cannot achieve. Based on this, this paper introduces the nonlinear PID control strategy into the field of servo control, and proposes a nonlinear control strategy of the three-loop of the servo system to improve the above problems. Firstly, the proposed structure is explained and the rule of nonlinear parameters selection is discussed. Secondly, the conditions for the structural stability of the proposed nonlinear control strategy are analyzed. Finally, experiments on the servo system platform are carried out and the results verify the fast dynamic response, precise positioning and good anti-disturbance performance.

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