Browsing by Subject "Power factor correction"
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Item Development of an algorithm for detection and classification of capacitor switching events(2015-12) Furlani Bastos, Alvaro; Santoso, Surya; Baldick, RossShunt capacitor banks are widely used to improve power system operation by injecting reactive power into predominantly inductive systems. These banks may be continuously energized or switched according to the load levels. The primary goal of this work is to develop an algorithm for detection of capacitor switching events, both energizing and de-energizing. This identification allow us to assess the capacitor performance and detection of an unsuccessful energization, restrikes during the de-energizing operation, blown fuses, or even failed capacitors in one of the phases. The identification algorithms are developed based on the unique features associated to capacitor switching events, such as wavelet transform coefficients, voltage gradient at the switching instant, inrush current, steady-state voltage rise, and reactive power support. Moreover, a library with common range of values for these parameters is used to improve the algorithm accuracy. For each identified capacitor switching event, the following parameters are computed: peak voltage and current, voltage phase angle at the switching instant, duration and frequency of the transient, reactive power support in each phase, steady-state voltage rise, relative location of the switched bank, variation of power factor, voltage total harmonic distortion, and RMS line current. This capacitor switching identification module is tested with data from a power quality monitor, including different types of events. The results show that both energizing and de-energizing algorithms provide high accuracy levels. Moreover, using the scores assignment improves the performance of the capacitor energizing identification algorithm. As an application, these algorithms are used to evaluate the power factor over compensation in a distribution utility.Item Direct torque control of permanent magnet synchronous motors with non-sinusoidal back-EMF(2009-05-15) Ozturk, Salih BarisThis work presents the direct torque control (DTC) techniques, implemented in four- and six-switch inverter, for brushless dc (BLDC) motors with non-sinusoidal back- EMF using two and three-phase conduction modes. First of all, the classical direct torque control of permanent magnet synchronous motor (PMSM) with sinusoidal back-EMF is discussed in detail. Secondly, the proposed two-phase conduction mode for DTC of BLDC motors is introduced in the constant torque region. In this control scheme, only two phases conduct at any instant of time using a six-switch inverter. By properly selecting the inverter voltage space vectors of the two-phase conduction mode from a simple look-up table the desired quasi-square wave current is obtained. Therefore, it is possible to achieve DTC of a BLDC motor drive with faster torque response while the stator flux linkage amplitude is deliberately kept almost constant by ignoring the flux control in the constant torque region. Third, the avarege current controlled boost power factor correction (PFC) method is applied to the previously discussed proposed DTC of BLDC motor drive in the constant torque region. The test results verify that the proposed PFC for DTC of BLDC motor drive improves the power factor from 0.77 to about 0.9997 irrespective of the load. Fourth, the DTC technique for BLDC motor using four-switch inverter in the constant torque region is studied. For effective torque control in two phase conduction mode, a novel switching pattern incorporating the voltage vector look-up table is designed and implemented for four-switch inverter to produce the desired torque characteristics. As a result, it is possible to achieve two-phase conduction DTC of a BLDC motor drive using four-switch inverter with faster torque response due to the fact that the voltage space vectors are directly controlled.. Finally, the position sensorless direct torque and indirect flux control (DTIFC) of BLDC motor with non-sinusoidal back-EMF has been extensively investigated using three-phase conduction scheme with six-switch inverter. In this work, a novel and simple approach to achieve a low-frequency torque ripple-free direct torque control with maximum efficiency based on dq reference frame similar to permanent magnet synchronous motor (PMSM) drives is presented.