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This article proposes a new control method for the synchronous rectifier (SR) of phase-shifted full-bridge (PSFB) converter to improve its efficiency in light-load condition. In general, the PSFB converter operates in the discontinuous conduction mode (DCM) in light-load condition to reduce the effective duty-ratio and core loss. However, the conventional control methods in the DCM cause undesirable conduction loss in SR because the output inductor current flows through the body-diode instead of the channel of SR. To figure it out, the proposed control method modulates the turn-on time of SR to eliminate the body-diode conduction. Moreover, it can be easily implemented without any auxiliary circuits. Therefore, it can improve the efficiency in light-load condition while keeping the advantages of DCM. The operating principle of PSFB converter in the DCM is first described. Thereafter, the proposed control method for SR is theoretically analyzed. Finally, its practical effectiveness is verified by experimental tests on the hardware implementation. [ABSTRACT FROM AUTHOR]

Recently, microgrids have faced a great challenge for the stable operation of converter-dominant system with very high renewable penetration. The converter-based-generator reduces inertia constant. In this case, very small power imbalance can cause large frequency variation. Therefore, the accurate load sharing between generators is important for the stable operation. This paper proposes the virtual multi-slack (VMS) droop control based on the power sensitivity analysis. In other words, one physical slack generator directly controls the magnitude and phase angle of its bus voltage. At the same time, the other generators indirectly control the magnitudes and phase angles of their bus voltages by using the VMS droop control. This results in the proper load sharing between the generators in the stand-alone microgrid. That is, all nonslack generators operate as virtual slacks so that they solve the power imbalances together with one physical slack generator. The proposed VMS control is realized with the multi-slack power flow analysis, which enables adaptive droop based power allocation between the generators. Then, its effectiveness is verified with several case studies on the practical stand-alone microgrid in South Korea by using the electromagnetic transient program. [ABSTRACT FROM PUBLISHER]

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]

In South Korea, the stand-alone microgrid on an island has synchronous diesel generators and multiple distributed generations (DG) based on renewable energy, and energy storage systems (ESS). According to the active policy of government to develop eco-friendly microgrids with zero carbon emission, many diesel generators in stand-alone microgrids are being replaced by the DGs. It brings challenges on the operation and control of multiple DGs because this causes the lack of inertia, which is originally provided from the diesel generators. [ABSTRACT FROM AUTHOR]

This paper proposes the new clamping angle control (CAC) pulse width modulation (PWM) method to restore its maximum linear modulation range of voltage source inverters (VSIs) reduced by the duty ratio limitation in hardware implementation, which makes the VSIs to operate nonlinearly in the high modulation range. The deadtime and the bootstrap gate driver circuit mainly cause this duty ratio limitation in practice. In particular, the bootstrap gate driver circuit is used in many industrial applications by avoiding the additional power supply to apply the gate-source voltage of power switches, and therefore making the VSIs to be small size with the low cost. First, the proposed CACPWM method is theoretically analyzed. Then, it is applied in the high modulation range to overcome the limitation of the duty ratio due to the use of the bootstrap gate driver circuit. Thereafter, its practical effectiveness is verified by both simulation and experimental tests. Also, the resulting harmonic distortions are compared with those by the conventional PWM methods. [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]

The kinetic energy stored in the rotating mass of wind turbine generators can provide the effective power quality solution to the inertia-free stand-alone (IFSA) microgrid by improving its stability. In conventional power systems, the power released from the inertia of synchronous generators regulates the system frequency. However, the frequency does not vary much even when a large disturbance or a load change occurs in the IFSA microgrid with only converter-based generators. This paper proposes a new inertia control method for a type-4 permanent magnet synchronous generator wind turbine system in the IFSA microgrid by utilizing the measurement of the dc-link voltage of the converter and its derivatives, not by the system frequency. Several case studies are carried out to evaluate the performance of the proposed inertia control in the IFSA microgrid with electromagnetic transients program-based simulation. Also, its effectiveness is verified with the experimental results from the hardware-in-the-loop test implemented by the controller interface with the digital signal processor, which is connected to the real-time digital simulator. [ABSTRACT FROM AUTHOR]

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 paper proposes a method to determine the optimal size of superconducting magnetic energy storage (SMES) to improve the stability of distribution power system with photovoltaic (PV) generation. The output power of PV system fluctuates according to changing weather conditions. Then, the system is subject to be unstable. In order to improve its stability, the SMES is applied. In general, the SMES is being considered as a strong candidate among energy storage devices in industry due to its high efficiency, fast response, and high energy density. [ABSTRACT FROM PUBLISHER]