Network current quality enhancement under nonlinear and unbalanced load conditions using a four-wire inverter-based active shunt filter

The flow of a large current in the neutral conductor of a transmission system is one of the major problems caused by harmonic pollution. This current can assume excessive values and even exceed the current flowing in the phases which can be extremely dangerous both for the equipment and the safety of the personnel. Currently, the parallel or shunt active filter (SAF) or parallel active filter is considered as the most effective solution to mitigate harmonic pollution and restore a sinusoidal current waveform in electrical distribution networks. The SAF can be used to compensate for harmonic currents, as well as that of the reactive power. This paper proposes a SAF circuit based on a four-arm inverter topology. The designed SAF is shown to lead to better harmonic compensation with a reduced THD (Total Harmonic Distortion) level in the presence of nonlinear and unbalanced loads in the network. The other goal of this study is to eliminate the neutral current caused by the unbalance in the polluting loads connected to the distribution network, achieve a near-sinusoidal current waveform and protect the electric network equipment

Improvement of power quality and reliability in the distribution system of petrochemical plants using active power filters

Variable speed drives (VSDs) are used extensively for pumping/compressor operations in petrochemical plants of the Jurong Island in Singapore. The VSDs draws harmonic current from the mains which causes power quality issues in the system. Passive harmonic mitigation techniques, 12-pulse/24-pulse transformers are being used in the petrochemical plant to minimize the voltage/current harmonics because of their lower cost and higher reliability, but these methods are less efficient. This paper investigates the power quality and reliability improvement in the petrochemical plants by using active power filters (APFs). The study has been conducted in the petrochemical plant distribution system by connecting an active front end (AFE) converter and shunt active power filter (SAF) with the 6-pulse drive system in place of conventional 12-pulse rectifier-drive system. Simulation were carried out in MATLAB/Simulink environment for 1 MW drive system with 12-pulse rectifier, 6-pulse rectifier with the SAF and the system with AFE. Subsequently, reliability assessment has been carried out for the three test systems under study in DIgSILENT Power Factory simulation software. Harmonic mitigation methodologies are verified through a down scale experimental laboratory setup of 7.5 kW motor drive system to check the effectiveness active harmonic mitigation methodologies