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The control performance of reluctance actuator maglev system is seriously affected by inherent nonlinearities (e.g., hysteresis, eddy current, flux leakage, etc.) and external disturbances. To this end, this paper proposes an enhanced unknown system dynamics estimator (USDE)-based sliding mode control (USDE-SMC) method by a novel predictive-adaptive switching (PAS) controller (USDE-SMC-PAS). First, a USDE is incorporated into SMC to compensate for the uncertainties; Second, an adaptive switching (AS) controller is used to reduce chattering; Finally, the switching controller is modified by PAS to enhance the dynamic response ability and disturbance rejection ability with reduced chattering. In the PAS controller, the switching gain comprises a filtered estimate error part and a residual part, which are obtained by a first-order filter and an adaptive law, respectively. Consequently, the strong disturbance compensation ability, high levitation accuracy, high dynamic response, and reduced chattering property can be achieved simultaneously. The stabilities of USDE-SMC, USDE-SMC with an AS controller (USDE-SMC-AS), and USDE-SMC-PAS in the closedloop system are analyzed by the Lyapunov theorem.

In order to coordinate automatic voltage control (AVC) systems of a large interconnected system, a multi-level multi-area hybrid automatic voltage control (MLMA-HAVC) system was constructed. This system began its trial operation in the Northeast China Grid in January 2010, and for the first time in China and abroad it realized automatic close-loop control of multi-area and multi-level interconnected power grid and multi-objective self-approaching optimization in aspects of security, high quality and economic operation. This system has three breakthroughs in theory and engineering application: 1) Established the MLMA-HAVC theory to solve multi-objective optimization of large-scale system; 2) proposed reactive power/voltage coordination control method to inhibit or further eliminate regional oscillations; 3) presented advanced state estimation algorithm to guarantee acquisition of high reliability data. This paper summarizes the basic principle of MLMA-HAVC, and reports engineering realization of MLMA-HAVC system in the Northeast China Grid. hybrid automatic voltage control, coordinated control, advanced state estimation Citation: Zhang X M, Mei S W, Su X Y, et al. Multi-level multi-area hybrid automatic voltage control system and its trial operation in Northeast China Grid.