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A single-objective predictive control method that deals with four main control objectives applied to a multivariable single-phase three-level neutral-point-clamped converter operating as an active power filter is proposed in this paper. The four control objectives are to self-support the dc-bus voltage under load variations, to compensate the reactive power and the current harmonics, and to balance the dc capacitor voltages by using a predefined combination of the redundant switching states of the converter. The main contribution of the proposed method is that these objectives are accomplished without using weighting factors in the cost function, which eliminates problems such as multiobjective optimization or additional empirical procedures for determination of these factors. As a result, the method is easy to implement and rapidly selects the optimal voltage to improve the dynamic-state performance. Experimental results from a 2-kVA prototype are presented to prove that the method is valid for single-phase compensation. The well-known effect of model parameter errors' issue, which is inherent in predictive control methods, is also tested to confirm that the harmonic distortion in the grid current is below 5% even when the predictive model has a 25% error between actual and theoretically estimated grid impedance values. [ABSTRACT FROM PUBLISHER]

This paper presents practical aspects related with the operation, compensation, and protection of high-power cycloconverters used in the mining industry. Practical recommendations related with startup, compensation requirements, operational characteristics, and unexpected shutdown process are described. Fuseless characteristics of modern cycloconverters are also discussed. Relevant current waveforms associated with the operation of a 20-MW synchronous motor semiautogenous grinding mill drive are presented, as well as current and voltage waveforms under fault operating conditions. [ABSTRACT FROM AUTHOR]

A modular and decoupled approach to achieve harmonic cancellation in a multilevel Static Compensator (STATCOM) is presented in this paper. This work shows that it is possible to split the compensation tasks depending on the frequency components present on the line current that is intended to be compensated by using the superposition principle and the modular features of an H-bridge based multilevel STATCOM. This approach allows the implementation of the topology with dedicated modules in order to decouple and simplify the control algorithms. The H-bridge modules can be implemented with two different kinds of semiconductors: (i) slow switches for fundamental frequency compensation modules and (ii) fast switches for harmonic frequency compensation modules. As the modules meant for harmonic cancellation can self-regulate its dc voltage, they can follow the load requirements and thus operate with minimum power. The theoretical analysis is validated in a laboratory prototype. [ABSTRACT FROM AUTHOR]

A discrete-time linear control strategy for a multilevel three-phase unified power quality conditioner (UPQC) based on single-phase power cells is presented. The multi-variable, nonlinear, and coupled features of these topologies make the control strategy design a difficult task. Controlling this kind of system with single-variable linear controllers—as proposed in this work—presents significant advantages compared with other approaches as simplicity in the design steps due to the large amount of tools developed for this kind of schemes. Particularly, a classic design method based on the root locus approach is used to choose the controllers parameters in order to achieve a given dynamical behavior. Compensation of reactive power and fundamental frequency disturbances is presented in this paper as part of a general control strategy for multilevel active power filters. The proposed control strategy is implemented on the TMS320C6713 DSP-based system for a low-power laboratory prototype, and thus the controllers design is carried out on the discrete-time and -frequency domain. Also, due to the inherent asymmetries among the power cells in a modular topology, a dedicated local control strategy is proposed to ensure a symmetrical distribution of the power among the power cells. This feature allows the semiconductor devices of each module to operate under the same voltage and current ratings. Simulated and experimental results showing stationary and transient conditions demonstrate the feasibility of the control scheme. [ABSTRACT FROM PUBLISHER]