In this work, a novel technique based on adaptive filtering is proposed for the control of three-phase universal active power filter with a solar photovoltaic array integrated at its DC bus. Two adaptive filters along with a zero crossing detection technique are used to extract the magnitude of fundamental active component of distorted load currents, which is then used in estimation of reference signal for the shunt active filter. This technique enables extraction of active component of all three phases with reduced mathematical computation. The series active filter control is based on synchronous reference frame theory and it regulates load voltage and maintains it in-phase with voltage at point of common coupling under conditions of voltage sag and swell. The performance of the system is evaluated on an experimental prototype in the laboratory under various dynamic conditions such as sag and swells in voltage at point of common coupling, load unbalancing and change in solar irradiation intensity.
- Power quality
- Universal active power filter
- Adaptive filtering
- Photovoltaic system
- Maximum power point tracking
- Quadrature signal generation
Fig.1 System Configuration of Solar Photovoltaic Integrated Unified Active Power Filter
EXPECTED SIMULATION RESULTS
Fig.2 Salient Signals in Series Active Filter Control
Fig.3. Salient Signals in Extraction of Fundamental Positive Sequence Load Current using Adaptive Filter
Fig. 4. Steady State Per Phase Signals of PCC and Load Side in a PV-UAPF Compensated System
Fig. 5. Performance of PV-UAPF Under Three Phase Short Circuit Fault
The performance of adaptive filter based PV-UAPF system under both steady state and dynamic conditions have been analyzed in detail. The method of sampling the fundamental component of load current obtained through adaptive filter enables fast extraction of fundamental active component of nonlinear load currents for all phases in one sampling. Only two adaptive filters are required to extract magnitude of active component of three phase load currents. This technique requires reduced computational resources while achieving good dynamic and steady state performance in extraction of fundamental active component of nonlinear load current. The system performance has been found to be satisfactory under various disturbances in load current, PCC voltage and solar irradiation. The series active filter is able to regulate load voltage at 220 V under variations of PCC voltage from 170 V to 270 V. The grid current THD is maintained at approximately 3% even though the THD of load current is 28% thus meeting requirement of IEEE-519 standard. The PV-UAPF system has been able to maintain the grid currents balanced under unbalanced loading condition. The proposed topology and algorithm are suited for employing in conditions where PCC voltage sags/swells and load current harmonics are major power quality issues. Certain power quality issues not addressed include voltage distortions, flicker, neutral current compensation etc. This power quality issues can be addressed by modification of topology and control algorithm according to the requirements in the distribution system. The PV-UAPF system provides dual benefit of distributed generation as well as improving power quality of the distribution system.
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