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A novel frequency changing conversion scheme using three cascade multilevel converters in a \Pi topology is presented. The scheme resembles a direct frequency converter using the cascade converter in its simplest form (series strings of H-bridge modules equipped with a dc link capacitor) as the building block of the overall converter. This yields a highly modular implementation approach which may be attractive for large power applications such as intertie connections and variable speed drives. Frequency conversion takes place in a cascade converter which connects the input and output ports. Two other converters are placed, respectively, in parallel to the input, to remove unwanted current components from the input, and the output to regulate output voltage. Operation of this topology is explained and a scheme to control all the converters is developed, including control of converter currents, capacitor voltages, and output voltage. Experimental results, using a low-power prototype, confirm the foundations of the topology and verify its overall performance operating as a power supply at typical output frequencies (25 Hz, 16^2/3\ \Hz and dc) while being fed from a 50-Hz system. Additionally, PowerSIM simulations demonstrate that the topology may be suitable for implementing high-performance, high-power ac drive systems using vector control techniques. [ABSTRACT FROM PUBLISHER]

Matrix Converters (MCs) have some advantages when compared to conventional back-to-back PWM voltage source converters. The converter may be considered more reliable and it can be smaller because the bulky dc capacitors are eliminated from the topology. For ac to ac power conversion, the size and weight of the whole generation system can be much reduced when back-to-back converters are replaced by MCs. To supply electrical energy to an unbalanced 3\Phi stand-alone load, a fourth leg is required to provide a path for the zero-sequence load current. To regulate the load voltage, closed-loop control is required. In this paper, the application of d–q controllers and resonant controllers to four-leg MCs is addressed. The design and performance issues of the controllers, for operation with balanced, highly unbalanced loads and nonlinear loads are discussed in this paper. Experimental results obtained from a small prototype are presented and analysed in detail. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the control systems for the operation of a Doubly-Fed Induction Generator (DFIG), feeding an unbalanced grid/stand-alone load, are presented. The scheme uses two back-to-back PWM inverters connected between the stator and the rotor, namely the rotor side and stator side converters respectively. The stator current and voltage unbalances are reduced or eliminated by injecting compensation currents into the grid/load using the stator side converter. The proposed control strategy is based on two revolving axes rotating synchronously at ±ω e. From these axes, the d–q components of the negative and positive-sequence currents, in the stator and grid/load, are obtained. The scheme compensates the negative-sequence currents in the grid/load by supplying negative-sequence currents via the stator side converter. Experimental results obtained from a 2-kW experimental prototype are presented and discussed in this work. The proposed control methodology is experimentally validated for stand-alone and weak grid-connected conditions and the results show the excellent performance of the strategy used. [Copyright &y& Elsevier]