Harmonic Compensation and Reactive Power Support Using Ultracapacitor with Shunt Active Filter in Distribution system

Abstract

Sustaining a quality of power supply is an important problems to the power Engineers. Owing to improvement in power quality a lot of power electronic devices and custom power devices are used in the industrial and commercial applications. Some of the non-linear loads and converters produces non-linear characteristics and create a flow of harmonic component in lines. Due to this effect, load voltages, load currents and the neutral current waveform due to unbalance gets distorted. In this project, the above effects are mitigated by neuro fuzzy Hysteresis Controller based ultracapacitor (UCAP) integration with an APF through a bi-directional dc-dc converter with in the phase conductor. By connecting filter in the line, load voltage becomes nearly sinusoidal and the distortion in the load and neutral current is reduced significantly. The MATLAB/Simulink model is used to verify this method. Index Terms: Neuro Fuzzy Logic, Hysteresis Controller, Phase Locked Loop, Active Filter, ultra capacitor (UCAP), Coupling Transformer. I. Introduction Ultra capacitor are made up of double layered electromechanical capacitors , have established a lot of considerations in power conversion application. They are widely used in controlled industrial electric drives, traction and automotive drives, uninterruptible power supplies (UPSs), and active filters. It energy storage devices and their advantages over the conventional capacitors and electrochemical batteries are high energy and power density, high efficiency, high cycling capability, and long life. The ac power system has viewed the problems concerning reactive power and unbalance . It has deteriorated with the increased use of power electronic converters as some of these converters not only increase reactive currents, but also generate harmonics in the source current. These power electronic converters are used in variable frequency AC motor drives, large power supplies, standby inverters and UPS, battery chargers, etc., which produces harmonics with large harmonic ranges. The current quality problem also concerned under unbalance. The increased reactive power, harmonics, and unbalance cause an increase in line losses, instability, and voltage distortion when harmonics increases and produce voltage drop across the line impedance, which spoils the power system. Conventionally, shunt passive filers are used to suppress the harmonics, and also provides reactive power compensation. An UCAP bank into a unified power quality conditioner (UPQC) system through dc-dc converter is also providing active and reactive power support for the grid through the shunt APF is an another applications. The grids are connected with distributed energy sources through a three-phase grid-tied inverter which can be controlled to supplying active power, reactive power, harmonic compensation, and frequency regulation. II. Three-Phase Grid Connected Inverter A system diagram of the proposed system is shown in Fig. 1. The APF-UCAP is connected between the source and load with coupling transformer in shunt with the system. This system consists of a UCAP , bi- directional dc-dc converter which acts as an interface between the UCAP and the grid tied inverter. The advantage of this system is that ,it has the capability to supply and absorb active power from the grid .In UCAP there will be some voltage profile changes during charges/discharges it can be controlled by bi-directional dc-dc converter while the inverter dc-link voltage has to stay constant for accurate control of inverter. Due this converter act as a boost converter while the UCAP is discharging energy into the grid and during charging the UCAP from the grid it acts as buck converter . A. Power Stage The power stage that consists of a three-phase inverter and its controller is shown in Fig. 2. This system includes of an insulated gate bipolar transistor (IGBT) module, its gate driver, LC filter, and an isolation transformer.The dc-link capacitor voltage has to be regulated for optimum performance of the converter such that