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Currently, the scale of dc distributed power systems (DPSs) is experiencing a sustained high-speed growth, which makes stability analysis become a complicated but essential problem. This paper has proposed decentralized impedance specifications for small-signal stability of a dc DPS which contains one voltage source subsystem, multiple power controlled source subsystems and multiple load subsystems. The proposed method defines invariant impedance specifications for each subsystem of the DPS, which only depend on the rated dc bus voltage and the rated capacity of each subsystem. The decentralized invariant impedance specifications make it possible that each subsystem is designed individually and the small-signal stability of the DPS is guaranteed at the same time. The proposed method can be applied to both large-scale and plug-and-play dc DPSs, whose stability analyses with conventional approaches would suffer from the curse of dimensionality and changing parameters. The proposed method is verified by hardware-in-loop tests.

The DC microgrid is connected to the AC utility by parallel bidirectional power converters (BPCs) to import/export large power, whose control directly affects the performance of the grid-connected DC microgrid. Much work has focused on the hierarchical control of the DC, AC, and hybrid microgrids, but little has considered the hierarchical control of multiple parallel BPCs that directly connect the DC microgrid to the AC utility. In this paper, we propose a hierarchical control for parallel BPCs of a grid-connected DC microgrid. To suppress the potential zero-sequence circulating current in the AC side among the parallel BPCs and realize feedback linearization of the voltage control, a d-q-0 control scheme instead of a conventional d-q control scheme is proposed in the inner current loop, and the square of the DC voltage is adopted in the inner voltage loop. DC side droop control is applied to realize DC current sharing among multiple BPCs at the primary control level, and this induces DC bus voltage deviation. The quantified relationship between the current sharing error and DC voltage deviation is derived, indicating that there is a trade-off between the DC voltage deviation and current sharing error. To eliminate the current sharing error and DC voltage deviation simultaneously, slope-adjusting and voltage-shifting approaches are adopted at the secondary control level. The proposed tertiary control realizes precise active and reactive power exchange through parallel BPCs for economical operation. The proposed hierarchical control is applied for parallel BPCs of a grid-connected DC microgrid and can operate coordinately with the control for controllable/uncontrollable distributional generation. The effectiveness of the proposed control method is verified by corresponding simulation tests based on Matlab/Simulink, and the performance of the hierarchical control is evaluated for practical applications.

Aiming at the problems of low control precision and complex control process in electrical engineering automation control, this paper proposes a kind of intelligent electrical engineering automation control technology based on DeviceNet. This paper focuses on the development process, communication protocol and object modeling method of DeviceNet universal I / O interface based on microprocessor. At the same time, this paper designs the application layer software, and gives the detailed hardware circuit and software design process. The experimental results show that the method can reduce the complexity of the control process and improve the control accuracy.

In this paper, we have used magnetron sputtering to grow the high-quality GeSn layer on Ge (100) with Sn compositin up to 7%. The crystallinity of the GeSn layer is pretty good, and the strain relaxation degree of the GeSn layer is evaluated to be approximately 50%. The root mean square (RMS) value is 0.8 nm, and the averaged TDDs in the GeSn layer is 8.7×109 cm-2, which is obtained from the rocking curve of GeSn layer along (004) plane. PL measurement result shows the significant optical emission from the deposited high-quality GeSn layer, which also means that magnetron sputtering is an optional way to achieve the higher Sn composition GeSn luminescent material. To verify whether our deposited GeSn can used for optoelectronic devices, we fabricate the simple vertical p-i-n diode, and the room temperature current-voltage (I-V) characteristic was obtained. This result paves the way for future sputtered-GeSn optimization, which is critical for the optoelectronic application.

This study introduces an advanced decentralised control method for DC microgrids which can be adopted both in the grid-connected mode and the islanded mode with a small change. Compared with the conventional droop control methods, there are three improvements in this proposed control method. First, in the grid-connected mode, the proposed control method can output the specified current, which is useful for the economic dispatch of the microgrid. Second, in the islanded mode, the proposed control method can realise accurate current sharing among distributed generations (DGs). Third, in the islanded mode, the proposed control method can directly restore the average voltage of the bus without the extra secondary control, which can ensure the power quality and reduce the complexity of the control system. The high reliability of the proposed control method is illustrated by the analysis of the stability. Also, the time-delay effect caused by the finite bandwidth of the communication network is analysed and the limited bandwidth of the communication network can be calculated out. All the conclusions are verified by the corresponding simulation tests based on MATLAB/Simulink, also the real-time hardware-in-loop tests are conducted to evaluate the performance of the control method when applied practically.

This paper describes the design principles of damped proportional-resonant (PR) controllers used for the grid-connected inverters. Previous works focused on the frequency domain analysis to select parameters, which can't reflect the time domain performance directly. This paper presents a mathematical model of grid-connected inverter connected with a LC filter and isolation transformer in the stationary reference frame, whose order is reduced by weighted current feedback. Based on the reduced-order model, the principles for designing damped PR controllers in the frequency domain are presented in details. The optimized design of damped PR controller through genetic algorithm using the cumulative amount of current tracking error as indicator of the time-domain performance is proposed. Compared with traditional system, the system with the optimized damped PR controller achieves not only better stability in the frequency domain, but also more excellent performances of current tracking and lower total harmonic distortion in the time domain. Simulation results are presented to verify the feasibility and effectiveness of the proposed approach.

Conventional proportional-resonant controller is widely accepted and adopted in micro-grid applications. However, it's hard to design a satisfactory conventional proportion-resonant controller due to the contradictory nature of the inverter's stability, dynamic response speed and static tracking accuracy. Therefore, some trade-off strategies proposed in previous works are usually favored. This paper proposes a novel fuzzy proportional-resonant control strategy for a three-phase inverter, which can obtain better outcomes of three contradictory performance characteristics simultaneously. The detailed mathematical models and design procedure of the controller for the studied inverter are also presented. Compared with conventional proportional-resonant control strategy, the superiority of the proposed fuzzy proportional-resonant control strategy is significant for its better system stability, faster dynamic response speed and higher static tracking accuracy. Results from simulation are provided to verify the feasibility and effectiveness of the proposed approach.