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In this paper, a generalized multiband hysteresis modulation and its characterization have been proposed for the sliding-mode control of cascaded H-bridge multilevel-inverter (CHBMLI)-controlled systems. A frequency-domain method is proposed for the determination of net hysteresis bandwidth for a given desired maximum switching frequency of the inverter. The switching transition concept of Tsypkin's method and the describing function of nonlinear relay have been used for the derivation of results. A hierarchical switching algorithm has been suggested for the modular cells of the cascaded multilevel inverter. The hierarchy of each cell is swapped sequentially to provide the self-balancing capability in case the dc-link voltage is supported by the capacitors. The simulation and experimental verification of the derived results are provided through a single-phase distribution static compensator (DSTATCOM) model. The application in the three-phase system has been shown through simulation studies on a 3.3-kV distribution-system compensation using DSTATCOM. Verification on both single- and three-phase systems is obtained using a five-level cascaded-multilevel-inverter topology. [ABSTRACT FROM AUTHOR]

In this paper, a fixed-switching-frequency closed-loop modulation of a voltage-source inverter (VSI), upon the digital implementation of the modulation process, is analyzed and characterized. The sampling frequency of the digital processor is considered as an integer multiple of the modulation switching frequency. An expression for the determination of the modulation design parameter is developed for smooth modulation at a fixed switching frequency. The variation of the sampling frequency, switching frequency, and modulation index has been analyzed for the determination of the switching condition under closed loop. It is shown that the switching condition determined based on the continuous-time analysis of the closed-loop modulation will ensure smooth modulation upon the digital implementation of the modulation process. However, the stability properties need to be tested prior to digital implementation as they get deteriorated at smaller sampling frequencies. The closed-loop modulation index needs to be considered maximum while determining the design parameters for smooth modulation. In particular, a detailed analysis has been carried out by varying the control gain in the sliding-mode control of a two-level YSI. The proposed analysis of the closed-loop modulation of the VSI has been verified for the operation of a distribution static compensator. The theoretical results are validated experimentally on both single- and three-phase systems. [ABSTRACT FROM AUTHOR]

In this paper, the method of triangular carrier switching control of two-level inverters is extended to cascaded multilevel inverters using phase-shifted multicarrier unipolar pulsewidth modulation (PWM). The condition for smooth modulation is obtained using the Bessel's function representation of the PWM output and the switching condition of the multilevel- inverter-controlled system. A method is proposed for the determination of the minimum amplitude of the triangular carrier for smooth modulation at fixed switching frequency. It is shown that the multilevel modulation based on the phase-shifted carriers significantly reduces the ripple magnitude in the switching function and allows the use of a smaller carrier amplitude under closed loop. This increases the forward gain and, hence, improves the tracking characteristics. The proposed cascaded multilevel inverter control is implemented for the operation of a distribution static compensator (DSTATCOM) in the voltage control mode. The experimental verification of the theoretical and simulation results is provided through a field-programmable gate array (FPGA) based control of a laboratory model of a single-phase DSTATCOM. [ABSTRACT FROM AUTHOR]