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This paper presents a dual voltage source inverter (DVSI) scheme to enhance the power quality and reliability of the microgrid system. The proposed scheme is comprised of two inverters, which enables the microgrid to exchange power generated by the distributed energy resources (DERs) and also to compensate the local unbalanced and nonlinear load. The control algorithms are developed based on instantaneous symmetrical component theory (ISCT) to operate DVSI in grid sharing and grid injecting modes. The proposed scheme has increased reliability, lower bandwidth requirement of the main inverter, lower cost due to reduction in filter size, and better utilization of microgrid power while using reduced dc-link voltage rating for the main inverter. These features make the DVSI scheme a promising option for microgrid supplying sensitive loads. The topology and control algorithm are validated through extensive simulation and experimental results. � 2010-2012 IEEE.

Voltage sag remains a serious power-quality (PQ) problem by being the most common and causing more economic losses. The dynamic voltage restorer (DVR) is a definitive solution to address the voltage-related PQ problems. Conventional topologies operate with a dc link, which makes them bulkier and costlier; it also imposes limits on the compensation capability of the DVR. Topologies with the same functionality, operating without the dc link by utilizing a direct ac-ac converter, are preferable over the conventional ones. Since no storage device is employed, these topologies require improved information on instantaneous voltages at the point of common coupling and need flexible control schemes depending on these voltages. Therefore, a control scheme for DVR topologies with an ac-ac converter, based on the characterization of voltage sags is proposed in this paper to mitigate voltage sags with phase jump. The proposed control scheme is tested on an interphase ac-ac converter topology to validate its efficacy. Detailed simulations to support the same have been carried out in MATLAB, and the results are presented. The results of real-time testing of the scheme on a single-phase model of the topology to compensate various sag types using DSPF28335 are also presented. � 2014 IEEE.

This paper proposes a modified four-leg distribution static compensator (DSTATCOM) topology for compensation of unbalanced and nonlinear loads in three-phase four-wire distribution system. DSTATCOM, connected in parallel to the load, supplies reactive and harmonic powers demanded by unbalanced nonlinear loads. In this proposed topology, the voltage source inverter (VSI) of DSTATCOM is connected to point of common coupling (point of interconnection of source, load, DSTATCOM) through interface inductor and series capacitance, unlike the conventional topology which consists of interface inductor alone. Load compensation with a lower value of input DC link voltage of VSI is possible in this modified topology compared to conventional topology. A comparative study on modified and conventional topologies in terms of voltage rating of inverter power switches, switching losses in VSI and power rating of input DC capacitor of VSI is presented. The detailed design aspects of DC link capacitor and interface series capacitor are also presented. The reference filter currents are generated using instantaneous symmetrical component theory and are tracked using hysteresis current control technique. A detailed simulation study is carried out, to compare the compensation performances of conventional, modified topologies using PSCAD simulator and experimental studies are done to validate the simulation results.

Multilevel neutral point clamped (NPC) inverter systems are increasingly used in load compensation applications. However, the most significant problem associated with these compensators is the capacitor voltage imbalances and drift due to dc components in the zero sequence current, resulting in degradation of tracking performance of the voltage source inverter. This paper proposes a carrier-based pulsewidth modulation control for an inverter-chopper circuit in order to regulate the capacitor voltages to their reference values. To demonstrate the simplicity and effectiveness of the aforementioned control scheme, a three-phase four-wire three-level NPC compensator system is taken as an example. Detailed simulation has been carried out in PSCAD 4.2.1. Experiments are conducted to validate the proposed control scheme. � 2006 IEEE.

In this paper, load compensation techniques under unbalanced and distorted voltages have been discussed. Two kinds of compensation methods are considered. In the first category, synchronous detection and modified equal current strategies are used under the unbalanced but sinusoidal source voltages. In the second method, load compensation based on instantaneous symmetrical component theory with positive sequence extraction is proposed and is shown to work under unbalanced and the non-sinusoidal source voltages. To support the proposed method, a 440 V (L-L) three-phase, four-wire distribution system is considered. The compensator is realized using a three-phase voltage source inverter (VSI) operated in the current control mode. Detailed digital simulation and experimental results are presented to validate the approach. � 2006 IEEE.

In this paper, the theory of instantaneous symmetrical components is applied to explore various control strategies of load compensation, under different supply voltages. When the supply voltages are balanced and sinusoidal, all of these strategies converge to the same compensation characteristics. However, when the supply voltages are not balanced sinusoids, these control strategies result in different degrees of compensation in harmonics, power factor, neutral current, and compensator ratings. These control strategies are discussed in detail and a comparative study of their performance in terms of the rms value, total harmonic distortion, power factor of source currents, and compensator ratings is presented. Based on this study, it is possible to select the best strategy to meet the required load compensation characteristics for available supply voltages. A three-phase four-wire distribution system supplying an unbalanced and nonlinear load is considered for simulation study. The detailed simulation results using MATLAB are presented to support the proposed compensation strategies. � 2008 IEEE.