This paper presents a novel minimum entropy filter design for a class of stochastic nonlinear systems, which are subjected to non-Gaussian noises. Motivated by stochastic distribution control, an output entropy model is developed using a radial basis function neural network, while the parameters of the model can be identified by the collected data. Based upon the presented model, the filtering problem has been investigated, while the system dynamics have been represented. As the model output is the entropy of the estimation error, the optimal nonlinear filter is obtained based on the Lyapunov design, which makes the model output minimum. Moreover, the entropy assignment problem has been discussed as an extension of the presented approach. To verify the presented design procedure, a numerical example is given, which illustrates the effectiveness of the presented algorithm. The contributions of this paper can be summarized as follows: 1) an output entropy model is presented using a neural network; 2) a nonlinear filter design algorithm is developed as the main result; and 3) a solution of the entropy assignment problem is obtained, which is an extension of the presented framework.

This paper proposes a perturbation estimation based nonlinear adaptive power decoupling controller for doubly-fed induction generator based wind turbines (DFIG-WTs). Perturbation states are defined to include the nonlinearities, uncertainties of the system model, the cross-coupling between control loops, and external disturbances. Perturbation observers are designed to estimate the fast time-varying perturbation states. With perturbation estimation, the DFIG-WT system is fully decoupled and an output feedback control can be designed for the control of rotor currents. Rotor current references are calculated based on steady-state relation between active/reactive power and rotor current, and stator dynamic is ignored. The performance of the proposed controller is evaluated and verified via both simulation and experimental tests.

Inrush current with high amplitude is generated when the transformer is energized. On the one hand, it will have a negative impact on the safety of the transformer itself, and even cause the relay protection to malfunction. On the other hand, it may reduce operation speed of the protection when there is slight fault because of the protection restraint criteria. Both aspects will affect grid security. Based on the generation mechanism of inrush current, this paper proposes an inrush current reduction strategy that combines prefluxing and controlled switching technology. By constructing an equivalent magnetic circuit model of the large-capacity three-phase transformer with a universal core structure, the analytical formulas of the magnetic flux at each stage of implementing the strategy are obtained, and then the parameters design method of this strategy is proposed. The accuracy of the theoretical analysis of magnetic flux is verified through the accurate simulation. Compared with common inrush current reduction strategies, this strategy can reduce the inrush current to 0.5 times rated current below in any situation where the residual flux is unknown and the “core flux equalization” effect are not obvious, avoiding the problem of residual flux measurement. Finally, in the case of the transformer differential protection, the influence of this strategy on the protection is analyzed from the perspective of theory and simulation, and it shows that it can improve the performance of various protections effectively.

A distributed cooperative control (DCC) strategy based on the consensus protocol is proposed for providing frequency support through voltage source converter based multi-terminal direct current transmission (VSC-MTDC) systems. The DCC consists of a local P-V droop controller and a cooperative agent network for cooperation control. Each agent controller is composed of a frequency regulation subagent (FRA) for frequency support and a load ratio subagent (LRA) for balancing the power sharing amongst the stations connected to the same ac grid. Moreover, to reduce the impact of the communication link failure, a topology evaluating method is proposed to select the suitable topology of the communication network via graph theory. The small signal stability analysis and the steady-state analysis are performed to investigate the stability and the consensus performance of the VSC-MTDC systems with DCC. Compared with decentralized control, the DCC can simultaneously achieve better frequency support and power sharing without leading to a large dc voltage deviation. The effectiveness of the DCC is verified by simulations on a hybrid ac/dc grid with a 7-terminal VSC-MTDC in DIgSILENT/PowerFactory under the load step change event and communication failure event.

The hybrid distribution transformer (HDT) achieves a compromise between the low-frequency transformer (LFT) and the solid-state transformer. It combines the LFT's efficiency and reliability with the added advantage of partial power controllability via an integrated converter. However, the existing research on the HDT fault ride-through does not consider the coordination relationship with its own safe operation constraints, while few studies have considered capacity coordination between multiple converters. Therefore, this article proposes an improved hierarchical coordination control of integrated HDT (IHDT), considering grid fault and normal conditions. First, the IHDT topology is proposed, and the operation mechanism of IHDT to realize the voltage support and current compensation is clarified by analyzing the coupling mechanism between the converter and LFT. Furthermore, under complex conditions, the unified expressions of the IHDT winding voltage, current, and power are derived, the safe operation constraints of IHDT are analyzed, and a hierarchical coordination control strategy is proposed. Finally, the correctness and effectiveness of the IHDT topology and control strategy are demonstrated by simulation analysis and experimental verification.

High frequency reciprocating rig (HFRR) that utilises direct drive voice coil motor (VCM) is designed to perform pin-on-flat tribotest such as assessing the lubricity of fuel. In this paper, we propose direct amplitude control to maintain the amplitude of high frequency reciprocating motion of VCM on HFRR subjects to frictional load. First, the mathematical model of HFRR is developed, which takes the effect of frictional load into consideration. Subsequently, direct amplitude control is proposed, which takes the error of amplitude rather than position error as performance index. It consists of an amplitude regulator and an offset compensator. Analysis and simulations of the proposed control method are presented as well. Finally, the proposed control method is deployed to a digital signal processor on an HFRR prototype experimental platform. The experiment results indicate a significant improvement of the performance of VCM based HFRR in terms of amplitude accuracy in high frequency band compared with that given by traditional PI control. The results also suggest the instability of PR control in this case.