Search

The output voltage of renewable energy sources is influenced by environmental conditions. To compensate for the variations of voltage, a buck–boost power conditioning system can be used. This article presents a full-bridge single-inductor-based buck–boost inverter. Its output voltage can be greater or lower than the input voltage depending on the controllable duty ratio. This inverter features bidirectional and reactive power flow operations with no high-frequency common-mode voltage. The unique feature of the proposed inverter is using a single inductor in the power train, which enhances the power density. Moreover, only two switches can operate at high frequency. This enables the inverter to be made with the high efficiency and simple circuit configuration. Based on the proposed full-bridge inverter, a novel cascaded buck–boost inverter is also presented. It retains all the benefits of the proposed full-bridge inverter. The theoretical analysis of the proposed full-bridge inverter is first explained in detail. It is then extended to a cascaded inverter. Thereafter, the practical effectiveness of the proposed inverters is verified with the experimental tests by implementing the hardware prototypes of 110 Vrms, 60 Hz, and 500 W for full-bridge single-inductor-based buck–boost inverter, and 220 Vrms, 60 Hz, and 1000 W for the cascaded inverter. [ABSTRACT FROM AUTHOR]

The smart inverter (SI) is an emerging technology, which enables the effective integration of distributed energy resources (DERs). Nevertheless, the operation by the only single SI function is not sufficient to deal with various conditions in a distribution system. In other words, all DERs are required to rapidly update the proper mode of SI functions depending on the system conditions. In this article, we propose the new active distribution management system (ADMS) for photovoltaic (PV)/energy storage system (ESS) integrated system based on the SI functions. It effectively regulates the system voltage, and it solves the line congestion problem in a distribution system by adaptively controlling the mode of SI functions. This method enables DER to effectively regulate its generation without the additional controllers. The effectiveness of the proposed ADMS is verified by several case studies on a practical distribution system in South Korea with the real measurements of generation from PV and load consumption based on the electromagnetic transient program. Also, the PV/ESS integrated system prototype of 100 kW is implemented for the experimental verification of the proposed ADMS. [ABSTRACT FROM AUTHOR]

The inertia-free stand-alone (IFSA) microgrid is the new small power grid without synchronous generators equipped in conventional power systems. In other words, this system has the only converter-based generators (CBGs) based on energy storage devices and renewable energies. Therefore, it requires a new CBG control to provide strong voltage reference for the CBGs connected to the point of common coupling (PCC). This is because the IFSA microgrid is subject to a weak system such that it cannot maintain its rated frequency and/or bus voltage with the conventional real and reactive power controllers, which usually get their references from the PCC. This paper proposes the innovative conceptual approach for distributed coordination in the IFSA microgrid by applying the synchronized global positioning system time to the CBGs. Moreover, it is verified that the proposed physical structure of the IFSA microgrid makes it possible for all CBGs to share the real and reactive powers effectively. As the result, the proposed CBG control can provide the robustness, which is strongly required in the IFSA microgrid, based on timely outage management and restoration process. Several case studies are carried out with the microgrid of 36 MW to verify the effectiveness of the proposed CBG controller. The simulation and hardware-in-the loop tests are carried out using the power system computer-aided design/electromagnetic transient design and control (PSCAD/EMTDC) and the real-time digital power system simulator (RTDS), respectively. [ABSTRACT FROM AUTHOR]

This paper proposes a computationally effective method for optimal operation of multiple distributed generations (DGs) in dc distribution systems to improve their efficiency. There have been many research works to select the optimal sizes of multiple DGs. However, these optimal sizes are valid only in the particular operating point. For optimal operations of power systems, the DG sizes must be determined all the time according to the various load conditions. The proposed method can maintain the distribution system operating in its optimal condition with only single optimization process, without regard to load variations. Therefore, it can moderate the serious problems, derived from inaccurate load forecasting. To verify the performance of the proposed method, the dc system is first implemented with the real distribution system of Do-gok area in Seoul, Korea. Then, the real hourly-load data, acquired from SCADA system in Korea, are used to simulate the practical load variations. [ABSTRACT FROM PUBLISHER]

When the wind-turbine generator system (WTGS) is connected to a radial distribution system, it can improve reliability of system by achieving the appropriate voltage regulation via its suitable control action. In this case, protective relay coordination and voltage stability issues become important factors in determining the optimal size of the WTGS, and moreover in evaluating its maximum capacity. In this paper, the proposed algorithm for selecting the optimal size of WTGS is applied based on a power flow analysis by treating the WTGS as a regulated voltage source, which is added to the related utility substation. Also, it considers the coordination time interval (CTI) of existing relays to maintain their present settings, and therefore provides an efficient solution in power system restructuring process by connecting the WTGS with its optimal size. The case study is carried out to verify that the proposed method can effectively determine the optimal size of WTGS under tightly constrained conditions resulting from voltage regulation and required protective relay coordination problems. [ABSTRACT FROM PUBLISHER]

This article proposes a family of single-phase transformer based Z-source ac–ac converters (ZSACs). The proposed converters inherit all the benefits associated with the classical single-phase ZSAC, which are providing the buck–boost operation, maintaining or reversing the phase angle, and improving reliability. The proposed converters also have the improved input profile, continuous input current, and shared ground between input and output. Moreover, they use the turns ratio of transformers to produce the required voltage gain, which can be tuned by either increasing or decreasing the turns ratio of transformer depending on the configuration of Z-source structure. A safe-commutation strategy is also presented to achieve the soft commutation, which eliminates the voltage and current spikes without any additional snubber circuits. The features of proposed converters are comprehensively discussed with the detailed theoretical analysis. Thereafter, its performances are evaluated by both simulation and experimental tests. [ABSTRACT FROM AUTHOR]

The high penetration of distributed energy resources (DERs) in the distribution system brings new challenges related to voltage variations and reverse power flow. The sudden changes in electric power generation from the DERs due to climate conditions or their internal malfunction might cause high fluctuations in system voltage. To enhance the voltage stability when a disturbance occurs, this paper proposes a new reactive power management method to control each DER based on voltage sensitivity analysis. The voltage variation has the different features in both steady-state and transient conditions. In particular, its transient behavior depends on the type of DERs. Therefore, the particular optimal control for improving the dynamic response of voltage is difficult to apply for all types of DERs. In contrast, the voltage variation in steady-state can be controlled with the reactive power management by the sensitivity analysis between reactive power generation and system voltage. Even though this paper focuses on the reduction of voltage variation in steady-state, the relationship between the voltage variations in steady-state and transient conditions is also analyzed. The effectiveness of the proposed method is verified with several case studies on the practical distribution system in South Korea by using the time-domain simulation based on the PSCAD/EMTDC® software. The results show that the proposed reactive power management method can improve the dynamic voltage responses in both steady-state and transient conditions when the distribution system has the high penetration of renewables. [ABSTRACT FROM AUTHOR]

This paper proposes a computationally efficient technique for estimating the composite load model parameters based on analytical similarity of parameter sensitivity. When the model parameters are updated in the optimization procedure to best fit the actual load dynamics, i.e., measurements, parameters of similar sensitivity representation in the given mathematical model structure are updated in the same manner at every iterative step. This research allows for practically reducing the number of load model parameters to be identified in the estimation process and the overall computational cost while preserving the desired complexity and accuracy of the original model. This approach consequently facilitates the parameter estimation in the optimization process and helps manage increased number of parameters often criticized for adopting the dynamic composite load model via measurement-based approach. Case studies for the real power system demonstrate the computational efficiency and intact accuracy of the proposed method with reference to the existing methods of estimating all the parameters of the given composite load model independently. [ABSTRACT FROM AUTHOR]

This paper presents an effective optimization scheme for the measurement-based load modeling based on the sensitivity analysis of composite load model parameters. Each parameter of load model has different effects on its dynamic response. Moreover, some parameters are insensitive to the change of others. To estimate the dynamic interactions between parameters, their sensitivity is analyzed by using the eigenvalues of Hessian matrix used in the optimization algorithm. Also, the linear dependence between two load model parameters is then identified by examining the condition number of Jacobian matrix. With this parameter analysis, the performance of optimization process for measurement-based composite load modeling is improved by reducing the number of necessary parameters to consider. The performance of proposed method is verified with the practical data measured at a feeder in a real substation. [ABSTRACT FROM PUBLISHER]