Advanced Materials Research Vols. 732-733

Abstract: As the dynamic response of the traditional direct power control using space vector modulation (DPC-SVM) is slow, an improved DPC-SVM for the three-phase grid-connected inverter is proposed. The feed-forward reference powers are used to improve the dynamic response. The operating principles of the traditional and improved DPC-SVMs are illustrated. Experimental results of a 15-kVA three-phase grid-connected inverter with the traditional and improved control methods verify the theoretical analysis.

Abstract: An investigation of gate degradation characteristics of AlGaN/GaN HEMTs under PWM stress is proposed in this paper. The device under testing features double source-connected field plates to reshape the surface electric field. A PWM signal with the operation frequency varied from 10 kHz to 1 MHz was applied to the gate electrode while the source was shorted to ground. HP 4155B was used to measure the gate characteristic of the device by every 30 minutes. The value of on-resistance shows an increase of 12.9 % after the device has been under stress for 30 minutes with the switching frequency of 10 kHz and the degradation is improved with higher switching frequency, while the threshold voltage and gate leakage current do not change significantly during the test.

Abstract: An improved control strategy for three-phase grid-connected inverters with space vector pulse width modulation (SVPWM) is proposed. When the grid current contains harmonics, the d-and q-axes grid currents is interacted in the traditional control method, and the waveform quality of the grid current is poor. As the reference output voltage cannot directly reflect the change of the reference grid current with the traditional control strategy, the dynamic response of the grid-connected inverter is slow. In order to solve the aforementioned problems, the d-and q-axes grid currents in the decoupled components of the grid current controller are substituted by the d-and q-axes reference grid currents, respectively. The operating principles of the traditional and proposed control methods are illustrated. Experimental results show that the grid-connected inverter with the improved control strategy has high waveform quality of the grid current and fast dynamic response.

Abstract: This paper first introduced the SVG main circuit and the basic principles of SVG, then finished SVG modeling in dq coordinate process. Then an SVG direct current control method was proposed as well. Considering stability requirement to the DC side voltage, the paper designed voltage and current dual closed-loop PWM control system. Finally, SVG system was simulated using the Matlab/simulink. Results show that SVG has a good dynamic performance, verifying the correctness and validity of the dual closed-loop control.

Abstract: A unified control structure for two-stage power converter system (PCS) is proposed which incorporates both charging and discharging modes within the same controller. Detailed modeling process is presented using sub-system approach. Power feed-forward compensation with direct battery current reference is engaged to enable fast response to power change on battery side, thus reducing DC bus voltage fluctuation during transients. Simulation and experiments show that the proposed control structure can effectively improve dynamic response without compromising steady-state performance.

Abstract: In this paper, a method of distributed state estimation in dispatch center based on ripe data and bus topology information of substation is proposed. Substation state estimation solves the reliability issues of basic data by means of processing the redundant information in substation side. By using a large amount of data source information of substation, state estimation can be performed efficiently in substation. On the basis of the unified data standard between master center and substation, uploading ripe data and calculation nodes topology structure are acquired in dispatch center level. Data rationality and consistency check of substation improve the state estimation accuracy of topology identification in dispatch master system. And also it provides reliable data for the online analysis software.

Abstract: A robust communication infrastructure, which consists of different network components, such as Home Area Networks (HANs), Feighborhood Area Networks (FANs) and Wide Area Networks (WANs), is the touchstone of a smart grid. However, the existing communications network is insufficient due to the factor that it does not cover the distribution side where the major changes are expected to occur. Field area networks form the communication facility for the electricity distribution systems and act as a bridge between customer premises and substations with collectors, access points and data concentrators. This paper focuses on design aspect of communication system for FANs of smart grid. The communication infrastructure using Ethernet Passive Optical Networks (EPONs) is discussed. And based on the power system applications operating in the distribution domain, communication systems for field based application are presented.

Abstract: The comprehensive fuzzy evaluation method for transmission network planning scheme has the drawback that relying more on the subjectivity. To solve this problem, gray theory is introduced into comprehensive fuzzy evaluation method. Gray correlation analysis method is used to calculate gray correlation coefficient as the membership of evaluation index to get fuzzy evaluation matrix. Then, the fuzzy weight vector is determined by the subjective and objective empowerment by integrating AHP and entropy method. Comprehensive fuzzy evaluation vector is obtained by using composite operator to synthesis evaluation matrix and fuzzy weight vector. The obtained result is used to evaluate transmission network planning scheme. Therefore, the problem that judger definate membership function based on subjective view is solved by combining the two methods. Calculation results show that the proposed method has a certain practical value.

Abstract: In order to reduce pollutant emissions to improve environmental protection, and maintain microgrid stability during real-time operation, a distributed energy optimization scheduling and stability control strategy was proposed. According to the distributed nature of the microgrid, as well as operational objectives of different microsources, an optimal scheduling model for microgrid environmental protection was designed. Based on the proposed model, the tasks of each unit in optimal scheduling and stability control were described. Genetic algorithm (GA) and user datagram protocol (UDP) were used to implement distributed optimization and control of the microgrid. The simulation indicates that, compared with the traditional centralized optimization and control, the proposed distributed optimization and control strategy can clearly show the characteristics of each unit, and have a faster computation speed. Meanwhile, it can timely response once the voltage fluctuates due to power imbalance, so as to keep microgrid stability in real-time operation.

Abstract: This article builds an efficiency evaluation model. Using AHP method, an evaluation indicator system is established, and the weights of the indicators are calculated. This paper applies Fuzzy Evaluation method to determine the membership function of qualitative and quantitative indicators, and then synthesizes the indicator weights and the evaluation matrix to get the fuzzy comprehensive evaluation result. Finally, a case of a certain power transmission & transformation project is studied, and the comprehensive evaluation result of its economic benefit is moderate.