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This paper proposes a control strategy for a three-phase three-wire thyristor-controlled LC -coupling hybrid active power filter (TCLC-HAPF), which can balance active power and compensate reactive power and harmonic currents under unbalanced loading. Compared with TCLC-HAPF with conventional control strategy, active power filters and hybrid active power filters which either fail to perform satisfactory compensation or require high-rating active inverter part for unbalanced compensation, a control strategy was proposed for TCLC-HAPF to operate with a small rating active inverter part for a variety of loads with satisfactory performance. The control idea is to provide different firing angles for each phase of the thyristor-controlled LC-coupling part (TCLC) to balance active power and compensate reactive power, while the active inverter part aims to compensate harmonic currents. First, the required different TCLC impedances are deduced. Then, independent firing angles referenced to the phase angle of voltage across TCLC are calculated. After angle transformations, final firing angles referenced to phase angle of load voltages are obtained. In this paper, a novel controller for TCLC-HAPF under unbalanced loading is proposed. Simulation and experimental results are provided to verify the effectiveness of the proposed controller in comparison with a state-of-the-art controller. [ABSTRACT FROM PUBLISHER]

Motor current signature analysis (MCSA) based detection of rotor cage faults (RFs) in medium-high voltage induction motors has become common in the field due to its low-cost remote monitoring capability. However, low-frequency load oscillations (LOs) in applications that employ speed reduction couplings can induce frequency components in the vicinity of that of RFs. It has been reported that false-positive or -negative RF indications can be produced with the MCSA, if the frequency components produced by RF and LO overlap. There, recently, have been studies on discriminating RF and LO; however, the case where two harmonic components overlap at the same frequency, which is the most difficult and serious case, has not been investigated. In this paper, a spectrum analysis of instantaneous active and reactive power is applied, and it is shown that RF and LO can be separated for the case where the MCSA fails due to the overlap in the two spectral components. An experimental study performed on a 380 V motor with a speed reduction gear shows that RF and LO can be reliably detected and separated for avoiding false RF indications. [ABSTRACT FROM PUBLISHER]

In this paper, a multilayer control is proposed for inverters that are able to operate in parallel without intercommunications. The first control layer is an improved droop method that introduces power proportional terms into the conventional droop scheme, letting both active and reactive power to be shared among the inverters. The second layer is designed to compensate the voltage deviations caused by the aforementioned droop control, thus improving the load-voltage regulation of the system. The third layer is a quasi-synchronization control that roughly adjusts the angle of the inverter to be close to the common ac bus. This layer ensures that the phase difference of each inverter is inside a limited margin with the help of the phase signal sensed from the common ac bus. The principle of operation of the control scheme has been analyzed in detail. A small-signal model has been developed in order to study the system dynamics, which can be used for adjusting the main control parameters. A prototype consisting of a two 35-kVA-inverter system has been built and tested in order to verify the feasibility of the proposed approach. [ABSTRACT FROM AUTHOR]

Errors may creep in when measuring power by conventional methods due to the inductance and capacitance of the coils and the induced eddy current in the metal parts of the instruments through the alternating magnetic field of the current coil. Apart from these, if a fault occurs in any of the potential transformer secondary circuits or the potential coil of the measuring equipment, a conventional meter cannot detect it, which results in underregistration. In this paper, a microprocessor-based three-phase real, reactive, and apparent power measurement system is developed, which displays the power being fed to a load under both normal and faulty conditions. The microprocessor provides a simple, accurate, reliable, and economical solution to these problems. A framework of the hardware circuitry and the assembly language program for the evaluation of power values is given, and the problems to which attention should be paid to execute the proposed algorithm using the microprocessor are discussed. Illustrative laboratory test results confirm the validity and accurate performance of the proposed method in real-time. [ABSTRACT FROM AUTHOR]

This paper presents analytical details of how active and reactive power output of a stand-alone proton-exchange-membrane (PEM) fuel cell power plant (FCPP) is controlled. This analysis is based on an integrated dynamic model of the entire power plant including the reformer. The validity of the analysis is verified when the model is used to predict the response of the power plant to: 1) computer-simulated step changes in the load active and reactive power demand and 2) actual active and reactive load profile of a single family residence. The response curves indicate the load-following characteristics of the model and the predicted changes in the analytical parameters predicated by the analysis. [ABSTRACT FROM AUTHOR]