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This paper proposes a novel automatic mode transition control strategy for multiple inverters to operate in grid-connected and standalone modes. When grid is available, these inverters feed power the grid by operating in current control mode. Upon grid failure, all inverters automatically shift to droop control mode for achieving proportional power sharing and shift back to current control mode when the grid becomes available. The synthesis of dual structure control algorithms of various inverters is achieved using novel state machines. These state machines are designed to facilitate smooth mode transition of the inverters. In this way, the control signals for mode transition are generated by state machines specific to each inverter. Unlike existing control methods, the proposed method neither requires communication-based supervisory control of inverters nor it requires dedicated storage facility for achieving smooth mode transition. The proposed control strategy is tested on a simulation model as well as an experimental prototype multi-inverter system. [ABSTRACT FROM PUBLISHER]

High efficiency and operating life of grid feeding solar photovoltaic (PV) inverters are demanded. Due to reduced dc-link capacitor requirement, current source inverter (CSI) offers higher reliability than the voltage source based solar inverter. However, conventional three-phase pulse width modulated (PWM) current source based solar inverter injects high earth leakage current into the grid. In order to suppress this current, an isolation transformer can be used. Use of this transformer increases the cost and size, and decreases overall efficiency. In order to address the aforementioned limitations, a modified CSI is proposed in this paper. The proposed inverter suppresses the earth leakage current without using an isolation transformer, thereby increasing the efficiency and reducing cost as compared to conventional current source based solar inverters. A mathematical model of the system is derived based on which controller for the operation of the inverter is designed. The effectiveness of the scheme is verified through detailed simulation study. To confirm the viability of the scheme, experimental studies are carried out on a scaled-down laboratory prototype. [ABSTRACT FROM PUBLISHER]

In this paper, a simple static var compensating scheme using a cascaded two-level inverter-based multilevel inverter is proposed. The topology consists of two standard two-level inverters connected in cascade through open-end windings of a three-phase transformer. The dc-link voltages of the inverters are regulated at different levels to obtain four-level operation. The simulation study is carried out in MATLAB/SIMULINK to predict the performance of the proposed scheme under balanced and unbalanced supply-voltage conditions. A laboratory prototype is developed to validate the simulation results. The control scheme is implemented using the TMS320F28335 digital signal processor. Further, stability behavior of the topology is investigated. The dynamic model is developed and transfer functions are derived. The system behavior is analyzed for various operating conditions. [ABSTRACT FROM AUTHOR]

A novel soft-switched quasi-resonant dc-link (QRDCL) inverter topology is derived using the concept of an auxiliary switch-assisted soft-switcher (AASS) employing the flying capacitor. This concept is known for its high efficiency at high power levels, and is used for soft-switching the boost switch in zero-voltage transition (ZVT) power factor correction (PFC) boost rectifiers. Also, an active clamp circuit configuration to clamp the dc-link and recover the energy stored in the clamp capacitor is introduced and is applied to the proposed inverter topology. The resultant inverter configuration gives high efficiency and is suitable for high power motor drive applications. The maximum dc-link voltage is clamped at around (1.05–1.1) times the input dc-source voltage. The proposed inverter is suitable for pulse width modulation (PWM) operation. A detailed analysis along with the design procedure of the proposed inverter is presented. Simulation and laboratory experiments are carried out to validate the analysis. [ABSTRACT FROM AUTHOR]

Presents a study which investigated a quasi-resonant direct current-link inverter. Description of the proposed circuit; Principle in power circuit configuration; Results of simulation experiments.