Search

This paper analyzes and proposes technical considerations for the selection and design of passive filter schemes rated at several mega VARs to compensate reactive power and current harmonics in mining power distribution systems. The paper includes technical information and analysis required to select the most adequate passive filter topology, to select the tuning frequency for each unit, to calculate filter parameters, and to distribute reactive power between passive filters. Passive filter schemes analyzed in this paper are used to compensate mining power distribution systems, especially when high-power grinding mill drives energized from 12-pulse cycloconverters are used in conjunction with several other nonlinear loads. This paper also analyzes technical limitations that passive filters present in the attenuation of low-frequency current harmonics. Finally, two power distribution systems with different passive filters schemes are evaluated, and the limitations in the attenuation of low-frequency current harmonics generated by cycloconverters are demonstrated with measured results. [ABSTRACT FROM AUTHOR]

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]

Modular current source converters (MCSCs) have been proposed as an alternative method for increasing the power range of medium voltage PWM AC drives. MCSCs are built by stacking parallel current source converters. Two advantages that make MCSCs attractive are: (a) extended current/voltage ratings beyond the device ratings and (b) simplicity in balancing the DC link current in each module. This can be accomplished using two optimized modulating patterns that have been proposed for such topologies: (a) multilevel selective harmonic elimination (MSHE) and (b) displaced selective harmonic elimination (DSHE). Both techniques are based on SHE patterns but there are slight differences in their digital implementation due to the way they generate the harmonic cancellation. Furthermore, when these techniques are used in the rectifier stage, it is reported that MSHE and DSHE do not eliminate all the unwanted harmonics due to practical issues such as changes in the modulating indexes to control the DC link currents. This work compares the operation of DSHE and MSHE when used in rectifiers of an MCSC in terms of execution time, robustness to poor sampling frequency, and quality of harmonic profiles on AC input currents under different operating conditions. Experimental results are presented to validate the theoretical considerations. [ABSTRACT FROM PUBLISHER]