1.1 General
Over the past few years, the gain in the use of nonlinear power electronics loads, like static rectifiers, adjustable speed drives, dc/ac converter, has caused many electric power quality problems like high current harmonics, poor power factor and more neutral current, etc. problems caused by power quality can have an adverse economic impact on utilities and customers. These power quality problems can be resolved by the use of unified power quality conditioners (UPQCs). The UPQC, which is combination of the shunt and series active filters, is able to mitigate most of the power quality problems. This project is to design a UPQC for improvement of power quality in a power distribution system. A new control using pulse width modulation (PWM) technique will be designed to improve the power quality problems.
The first name of UPQC was universal power quality conditioning system (UPQS) named after unified power quality conditioner (UPQC) , which is continued by adding a shunt active filter at the load side[1].
In recent years, Power engineers are increasingly disturbed over the quality of the electrical energy. In present-day industries, load appliances uses electronic controllers which are delicate to poor voltage quality and will shut down if the supply voltage is depressed and may mal-operate in other ways if harmonic Distortion of the supply voltage is maximum. Most of this current load equipment uses electronic switching devices which can commit to poor network voltage duality. The competition in electrical power supply has created greater commercial alertness of the issues of power quality while equipment is readily available to measure the quality of the voltage waveform and so compute the problem [2].
Along with advance technology, the organization of the worldwide economy has derive towards globalization and the profit margins of many activities tend to decays. The increased in sensitivity of the ample major of processes such as (industrial, other services and even residential areas) to power quality disturbancesturn the availability of electric power with quality a crucial factor for competitiveness in each sector. The regular process industry and the information technology services are most difficult area. Due to some variation, a large amount of financial losses may occur, with the consequent loss of productivity and competitiveness.
Many attempts have been taken by utilities to fulfill customer’s fulfillment and some consumers require a higher level of power quality than the level provided by modern network of electrical supply. This mentions that some measures must be taken so that higher levels of power quality can be obtained.
The FACTS devices and Custom power devices are introduced to electrical system to improve the power quality of the electrical power system network. DVR, DSTATCOM, ACTIVE POWER FILTERs and UPQC etc. are some of the equipments used toimprove the power quality of the voltage profile and current profile. For using FACTS devices to reduce the problems related to power quality.
Although all devices can improve the power quality but in this the proposed is on Unified Power Quality Conditioner.UPQC is a custom power device consist of both DVR and D-STATCOM, departed is connected in series and recent is connected in parallel to protect the sensitive load from all disturbances.
Reliability of supply and power quality (PQ) is two most important facets of any power delivery system today [3]. Not so long ago, the main concern of consumers of electricity was the required continuity of power supply. Forever now-days, consumers want not only continuity of supply, but the quality of power is very imperative to them too. The power quality problems in distribution and transmission power systems are not new, but customer awareness of these problems has recently increased. The power quality at the point of common coupling (PCC) with the utility grid is governed by the various standards and the IEEE-519 standard is widely accepted.
Utilities and researchers all over the world have for decades worked on the improvement of power quality. There are sets of conventional solutions to the power quality problems, which have continue for a long time. For this conventional result use passive elements and do not always respond correctly as the nature of the power system conditions change. The increased power capabilities, ease of control, and reduced price of modern semiconductor devices have made power electronic converters economical in a large number of uses. New adjustable solutions too many power quality problems have become possible with the aid of these power electronic converters.
The power electronic based power conditioning devices can be effectively utilized to improve the quality of power supplied to customers [3].One most effective solution that deals with both load current and supply voltage defect is the Unified Power Quality Conditioner (UPQC) [4], which was first presented in 1995 by Hirofumi Akagi. Such a solution can overcome for different power quality phenomena, such as: sags, swells, voltage fluctuations, flicker, harmonics and reactive currents etc.
UPQC is a combination of series and shunt active filters connected in cascade via a common dc link capacitor. The series active filter injects a voltage, which is added at the point of the common coupling (PCC) such that the load ends voltage remains unaffected by any voltage disturbance. The main objectives of the shunt active filter are to overcome for the load reactive power demand and fluctuations to cancel the harmonics from the supply current, and to control the common dc link voltage.
A unified power quality conditioner (UPQC) [6], is another mitigating device that is similar in construction to a unified power flow controller (UPFC). A UPFC is used in power transmission system where as a UPQC is employed in a power distribution power system, to perform the shunt and series compensation together. But a UPFC only require providing balance shunt and/or series compensation, since an electrical power transmission system generally operates with balanced, distortion free environment. The primary objective of a UPFC is to control the flow of power at fundamental frequency only. On the other hand, a power distribution system may contain distortion, dc components and unbalance. Therefore, a UPQC must operate under these environments while performing shunt and/or series compensation.
Quality of power supply has become an important issue with the increasing demand of distributed generation systems either connected to the conventional grid, smart grid or micro-grid. Power quality has become a research topic in power distribution system due to a significant increase of harmonic pollution caused by generation of nonlinear loads, use of rectifiers, switching power supplies and other line connected power converters. So to improve the voltage profile, stability of system, improvement of power quality, reliability of power and reduction in THD etc. The various ductile alternating currenttransmission systems (FACTS) are come in electrical network. The FACTS based application of power electronic devices effective for the power distribution systems to enhance the quality and the reliability of power delivered to the consumers. The core of FACTS technology contains high power electronics drives; a variety of thyristor based devices, micro-electronics, communications and advanced control actions. By FACTS, operator governs the phase angle, the voltage profile at positive buses and line impedance.Power flow is composed and it flows bythe control actions using FACTS devices, which include (i) Static VAR Compensators (SVC), (ii) Thyristor Controlled Series Capacitors (TCSC), (iii) Static Compensators (STATCOM), (iv) Static Series Synchronous Compensators (SSSC), (v) Unified Power Flow Controllers (UPFC) and (vi) Unified Power Quality Conditioner system (UPQC) etc.
According to the basic idea of UPQC, it consists of back-to-back connection of two three phase active filters (AFs) with a common dc link. UPQC is to minimize grid voltage and load current disturbances along with reactive and harmonic power compensation. UPQC is a versatile device that can compensate almost all power quality problems such as voltage harmonics, voltage fluctuations’, voltage flickers; voltagedips, voltage swells, current harmonics, current unbalance, reactive current, etc.
1.2 Necessity/Need
Power quality is the quality of the electrical power supplied to electrical appliance. For poor power quality the operation of the equipment are in mal-operation. The electrical utility may define power Quality as reliability and state that the system is 99.5% reliable. For poor power quality many power related problems are created there is no better utilization of electrical energy.Nowadays the power quality has most important factor in modern society’s developing dependence on electricity and the fact that poor power quality may generate significant economic losses in some moments. Some poor power quality problems are, such as harmonics, flicker, voltage sag and supply voltage interruptions. Improving in power quality by using filters and compensators. Custom Power (CP) devices that overcome these power quality problems have gained more attention in the recent decades. Unified Power Quality Conditioner (UPQC) is one of the CP devices which mitigate both load current and supply voltage problems simultaneously. For avoid this problems we use the power electronics based facts devices to minimize these problems.
1.3 Objective
This project work proposes the MATLAB SIMULINK model of unified power quality conditioner which is used for the improvement of power quality at distribution level.
In an electrical power system one of the biggest problems in power quality condition is the harmonic contents in the electrical power system. There are two types of harmonics such as: i) voltage harmonics and ii) current harmonics. Current harmonics are occurred by harmonics contained in voltage supply and depend on the type of load. Harmonics generated due to different types of loads in the supply system can cause the overheating of the magnetic cores of all types’ transformer and induction motors. The source harmonics are mainly generated by power supply with non-sinusoidal voltage waveform. To study and overcome the above problems related to power quality issues,
The some objectives are described as follows:
Study the model of UPQC.
To explore the performance of Unified Power Quality Conditioner (UPQC) using the shunt active power filter and series active power filter.
To look the performance of Unified Power Quality Conditioner (UPQC) using the sinusoidal pulse width modulation technique.
By using (UPQC) to improve the system performance like voltage sag, voltages swell and compensate THD etc.
1.4 Theme
When a UPQC is used for power quality improvement, common practice is to design the multilevel converter base UPQC by using shunt active power filter and series active power filter. The shunt active power filter (APF) is usually connectedacross the loads to overcome for all current-related problems such as the reactive power compensation, improvement in power factor, compensation of current harmonics, and compensation of load unbalance, whereas the series active power filter is connected in a series with a line through series connected transformer. It acts as controlled voltage sourceand can overcome all voltage-related problems, such as voltage harmonicscompensation, voltage dips, over voltage, etc.
Fig.1.1: Multi-level Converter based UPQC Structure
1.5 Outline of Dissertation
Having been discussed various factors to complete the project has been organized follows:
Chapter 1: Introduction
This chapter contains the introduction of Unified power Quality Conditioner (UPQC). This chapter also deals with objective of proposed system and theme of the system.
Chapter 2: Literature Survey
In this chapter proposed an historical back-ground of Unified Power Quality Conditioner and also contain the summary of work carried out by various researches.
Chapter 3: Power Quality
In this chapter brief explanation of power quality, different kind of power quality problems and the various solutions that can be implemented to improve the quality of power in transmission and distribution network.
Chapter 4: Custom power device
This chapter contain the concept of custom power devices was introduced to improve the power quality and the detail introduction of different kinds of custom power device and also explain why use the unified power quality conditioner in proposed system.
Chapter 5: Unified Power Quality Conditioner
In this chapter describe the unified power quality system in detail and also explain the function performed by UPQC in proposed system.
Chapter 6: System Development
This chapter contains the overall system development for this purpose use the modulation method developed for this family of converter sinusoidal pulse width modulation (SPWM) and PWM technique. the multicarrier technique as phase disposition (PD) are used for the generation of gate pulse for triggering the semiconductor device .this chapter also deals with describe the UPQC controller for proposed system and use the synchronous reference frame theory.
Chapter 7: Simulation and Result
In this chapter describe the project work simulation and their result of simulation which have been done. The Unified Power Quality Conditioning system is modeled in Mat lab- simulink using power system black set. The corresponding % THD value is measured using FFT analysis and they are shown in tables.
Chapter 8: Conclusion and Future Scope
This chapter contains the conclusion of the overall work of dissertation. It also represents the future work of proposed system.