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In this paper, a model-predictive control of medium voltage, grid-tied four-level diode-clamped inverter for use in high-power wind energy conversion systems is presented. The control objectives such as regulation of net dc-link voltage, reactive power generation to meet the grid operator request, dc-link capacitor voltages balancing, and switching frequency minimization are included in the cost function. The latter objective is an important requirement for high-power converters, and this has been achieved without any modifications to the software or hardware configuration. The future behavior of the grid currents and dc-link voltages is predicted for all the possible switching states using the discrete-time model of the inverter, dc-link, inductive filter, and grid. The switching state that minimizes the cost function has been chosen and applied to the inverter directly. During different operating conditions, the switching frequency is regulated between 750 and 850 Hz with the help of a lookup-table-based weighting factor, and thus, the proposed methodology appears as a promising tool to control the high-power grid-tied inverters. The results obtained through the MATLAB simulations on 4 MVA/4000 V system and dSPACE DS1103-based experiments on 5 kW/208 V prototype are in a close relationship and thus validate the proposed control strategy. [ABSTRACT FROM AUTHOR]

Half-cycle symmetry selective-harmonic-elimination pulsewidth-modulation (SHE-PWM) problems may have a large number of valid solutions, which are beneficial to the optimization design. This paper proposes a novel generalized formulation of half-cycle symmetry SHE-PWM problems for multilevel inverters. The advantages of the proposed formulation include simplicity in format, flexibility in PWMwaveforms, and a broad solution space. A method to obtain initial values for the SHE-PWM equations according to the reference modulation index M and the initial phase angle of output fundamental voltage is proposed and investigated thoroughly. Take a five-level inverter with M = 0.75 as an example; six sets of solutions for two typical initial phase angles of 0°? and 90°? are presented. Simulations and experiments are carried out. It is demonstrated that the experimental results agree well with simulated ones, which proves the validity and practicability of the new method proposed. [ABSTRACT FROM AUTHOR]

This paper proposes an input power factor control strategy for a current-source drive with active front-end. The proposed strategy is realized without modification of the drive's pulsewidth modulation and speed control schemes through the collaborative use of two methods: a modulation index regulation method and a flux adjustment method. Specifically, the modulation index regulation method functions to directly control the dc-link current and voltage, and it can effectively correct a leading input power factor as long as the space vector modulation is used for the inverter. On the other hand, the flux adjustment method can improve the power factor when the power factor is lagging or when the selective harmonic elimination modulation is used for the inverter at high motor speeds. When implemented together, the two methods will complement each other's functionalities and improve the overall compensation performance. Experimental results are obtained from a 600-hp and an 1100-hp drive system. [ABSTRACT FROM AUTHOR]