This paper is concerned with the power dispatch problem of distributed generators (DGs) for optimal operation of a microgrid. The objective is to minimize the fuel cost during the grid-connected operation, while ensuring stable operation after islanding. To achieve this goal, the economic dispatch (ED) problem and related constraints are formulated. The constraints considered in this study are: i) reserve for variation in load demand, ii) reserve for variation in the power outputs of non-dispatchable DGs, iii) flow limits between two adjacent areas, and iv) reserve for the stable islanded operation. The first three constraints, which have been employed in ED problem for conventional power systems, are modified to apply to Microgrids. We also provide a detailed formulation of the constraint for stable islanded operation in accordance with two power-sharing principles: i) fixed droop and ii) adjustable droop. The problem is solved using a modified direct search method, and the effect of the constraints on the operational cost is investigated via numerical simulations.

In this study, two topologies are presented for switched-inductor quasi-Z-source inverters, namely a ripple input current switched-inductor quasi-Z-source inverter (rSL-qZSI) and a continuous input current switched-inductor quasi-Z-source inverter (cSL-qZSI). The proposed inverters possess high boost voltage inversion ability and a lower voltage stress across the active switching devices. Compared with a conventional switched-inductor ZSI, the proposed SL-qZSIs for the same input and output voltage provide a continuous input current and a reduced voltage stress on the capacitors. Moreover, the proposed inverters can overcome the startup inrush current problem but a conventional SL-qZSI cannot overcome this. This study presents the operating principles and analysis, and compares them with the conventional ZSIs. In order, to verify the performance of the proposed converters, a 60 W scaled-down laboratory prototype was constructed and, to test both the configurations it employed a 36 V_dc input and an ac output line-to-line voltage of 83 V_rms. The peak-to-peak input current ripple of the rSL-qZSI and cSL-ZSI is 126.3 and 59.8%, respectively. The experiment results verified that the proposed inverters have high step-up inversion ability, lower voltage stress on the capacitors and lower input current ripple.

The integration of Distributed Energy Resources (DERs) into the future Smart Distribution Network (SDN) has challenging issues regarding the successful development of smart grids. The SDN offers new opportunities in the improvement of the efficiency of power distribution networks. The DERs will be distributed in the existing distribution networks, interconnected in customer areas and operated on its own schedule without communication to the control center of the existing distribution system. The DER units have both positive and negative effects regarding SDN operations. With the appropriate operation of the DER units in the SDN, losses can be reduced during normal operations and they can support local loads during abnormal conditions. Thus, the positive effects of the DER units need to be enabled in the SDN by adopting advanced operation schemes. In this paper, the smart control functions for the DER units in the SDN are defined and classified. In addition, the integration schemes for the SDN with DER units are introduced. The proposed operation strategies will be implemented into the Korean Smart Distribution Management System (KSDMS) as operation schemes used for loss reduction and service restoration. A sample case study shows the effectiveness of the proposed operation schemes to achieve smart operation functions for the SDN with DER units.

In this paper, a new isolated high step-up dc-dc converter is proposed based on the quasi-switched-boost network. The proposed converter has the following features: 1) continuous input current; 2) reduced turn ratio of the isolated transformer; 3) increased reliability, as it can operate in either short-circuit mode or open-circuit mode without causing damage to the power converter; and 4) unchanged primary and secondary voltage waveforms of the transformer, although the shoot-through duty cycle is variable. Compared to the quasi-Z-source-based isolated dc-dc converter, the proposed converter uses fewer passive components. The operating principles, analysis, parameter design guideline, and comparison with the quasi-Z-source-based isolated dc-dc converter are presented. A 450 W prototype is built to test the proposed converter. The proposed converter is applicable for distributed power generation applications where a varying low dc input voltage is converted to a high stabilized dc output voltage with a galvanic separation requirement.

Two high voltage gain quasi-switched boost inverters (HG-qSBIs) are introduced in this paper. The proposed HG-qSBIs has the following characteristics: 1) continuous input current with low ripple; 2) reduced voltage stress on the capacitor, switch and diodes; 3) shoot-through immunity; 4) achieved high voltage gain with single-stage conversion; and 5) improve the output voltage capability with using high modulation index. A novel PWM control technique is proposed for the introduced HG-qSBI. Operating principle, circuit analysis, and passive component design guideline of the HG-qSBI are addressed. Comparison analysis between the introduced HG-qSBI and other Z-source-based high voltage gain inverters is presented. A prototype is made to test the introduced HG-qSBI. Simulation and experimental verifications are shown to prove the accuracy of the theoretical analysis.

Conventional switched boost inverters (SBIs) employ a single LC‐pair in the impedance network to boost the input voltage by setting a shoot‐through interval in the inverter bridge switches. This study extends the concept of SBIs to the transformer‐based switched boost inverters (trans‐SBIs). By changing the turn ratio of the transformer, the proposed trans‐SBIs can produce a strong voltage gain. Compared with a tapped‐inductor Z‐source inverter with the same voltage gain at the same transformer turn ratio, the proposed trans‐SBIs have only one extra active switch but significantly fewer passive components. Compared with trans‐ZSI, the proposed trans‐SBIs use a transformer with a lower turn ratio to achieve a higher boost factor. The required current rating of the switches in the proposed trans‐SBI is lower than for the alternative ZSIs. The operating principles and the analyses and comparisons with the conventional transformer‐based ZSIs are presented. To verify the high boost capability of the proposed inverters, a laboratory prototype was built for both the single‐phase and three‐phase trans‐SBIs.