Theory Based Design Of Unified Power Quality Conditioner

A Power system is an connection of generators to load centres. Through H.V. electrical lines & in general is controlled mechanically. It can be divided into 3 subsystems: Generation, X’mission and Distribution-systems. The electric power demand is Growing and building of new generating units & transmission circuits is becoming difficult because of environmental & economic reasons. So, power utilities are forced to depend on utilization of existing generating units and to load existing lines close to their heating limits.

The innovative inverter technology produces safe, smooth power, protecting your sensitive electronics (computers, smartphones, etc.) from damage.

There two ways to stabilize power supply, first approach is a Corrective approach, where new power stations are built, existing infrastructures are upgraded and new maintenance plans are developed and followed. This approach is a

Power electronics circuits convert electric power from one form to other using electronic devices. By using semiconductor devices as switches power electronics circuits function, thereby controlling or modifying a voltage or current.Power electronics application range from high-power conversion equipment such as dc power transmission to everyday appliances, such as cell phone chargers, cordless screwdrivers, power supplies for computers, and hybrid automobiles. Power electronics includes applications in which circuits process miliwatts or megawatts.Power electronics include conversion of an unregulated dc voltage to a regulated dc voltage conversion of ac to dc, conversion of dc to ac, and conversion of an ac power source from one amplitude and frequency to another amplitude and frequency. These power converters are classified as rectifiers, AC voltage controllers, DC choppers and inverters, which covers wide area of residential, commercial and industrial applications, including computers, transportation and power utilizes [1].

As industries expand, utilities become more interconnected and the use of electricity rises, power quality becomes essential to insure a smooth industrial process. The main problem that severely affects the power’s quality is the presence of the harmonics, which affects the performance of the system. Some of the problem caused by the harmonics are metal parts’ overheating, increasing noises in motors, decreasing the efficiency of the motors, etc. some corrective methods can be used to reduce its effect.

Induction Motor tolerate a level of unbalance. The variable speed drive are also affected as a result of the voltage unbalance which consist of three phase rectifier system. Unbalanced voltage is caused by mismatch of reactive power between generating and industrial stations, hence it can be classified BOV (Balanced Overvoltage), phase voltages greater than rated voltage. BUV (Balanced Under voltage), phase voltages lesser than rated voltage. UBOV (Unbalanced Overvoltage), phase voltage not equal to each other, therefore the positive sequence component is greater than rated voltage and finally UBUV (Unbalanced Under voltage), voltages are not equal, and hence the positive sequence component is lesser

Large scale cascaded photovoltaic systems is contributing renewable energy world wide due to its unique features like reliability, power quality ,amount of energy harvested and so on. However cascaded PV system is facing one of the tough challenges like reactive power control due to varied power distribution over different PV modules. This paper addresses the issue of effects due to reactive power on system reliability ,power quality and reactive power compensation strategy for optimal operation of system. A photovoltaic system consisting of three 5W, 10V solar modules with converters are used and proposed control strategy is implemented in laboratory. experimental results are presented to demonstrate the effectiveness of proposed reactive power control strategy.

protection are designed to achieve required discrimination by sensing that large second harmonic content [1]. The level of second harmonic component of the inrush current has been reduced due to improving in transformer core material and occur power system changes. Additionally, a large second harmonic can also be found in transformer internal fault currents if a shunt capacitor is connected to a transformer in a long extra high voltage transmission line. Therefore, the methods based on the measurement of the second harmonic are not sufficiently effective for differential protective relays [2].

The iterative techniques are used to solve the power flow equations such as Gauss-Seidel, Newton-Raphson and Decoupled Newton-Raphson methods. Each method has its equations and principle to reach the solution. The difference between them appeared in which method is more accurate and fast to get the results.

BACKGROUND: The power system, built on century-old technology and approaches, was designed to deliver electricity from large, remote power plants across significant distances to the cities and towns where electricity is used. For that reason, there is great need for an effective Protection and Control of the System to complete the chain of Generation, Transmission and Distribution to the users.

Feed forward control is a reliable for rejecting fast and dynamic voltage disturbances in the phase grid. Mainly in this scheme implemented in phase voltages of the Wyes connected configuration. Under this unbalanced and distorted grid conditions, the online conversion of line - to - line values into the phase value is unworkable. In order to an exploit full advantages of feed forward controller is a most appropriate modulator is needed. In this article the feed forward of grid line-to-line voltages is used in phase voltages. The introduced feed forward method is implemented in Implicit Zero Sequence Discontinuous Pulse Width Modulation (IZDPWM) technique that is compatible for grid connected inverters. Regarding in the IZDPWM grid topologies distorted the harmonics of the grid voltages. Hence, a sinusoidal current is injected to the grid. Moreover, the measuring grid line-to-line voltages two sensors are required; hence an overall system costs is reduced and control system reliability is increased. The time-domain simulations in MATLAB/Simulink and experimental results from a Hardware based laboratory prototypes are in good agreements,

This paper deals with a Cuk Topology for Power Factor Correction (PFC). Most of the front-end PFC converters are designed using diode bridge and has lower efficiency due to losses with reduced power factor.The current flow, during each intervals of the switching cycle reduces the conduction losses compared to the conventional Cuk PFC Rectifier. The converter also provides protection against inrush current occurring at start-up, decreases input current ripple and reduces Electromagnetic Interference (EMI).It works in the Discontinuous Conduction Mode (DCM) to provide almost unity power factor and low distortions in the input current. To analyse the performance of this converter, a model based on the CUK topology has been designed by using MATLAB/ SIMULINK software and implemented with Proportional-Integral (PI) and Fuzzy logic controller.

Over the years, variant strategies have been proposed in the literature for the control of the three-phase voltage (AFE) rectifier. All these strategies aim to achieve the same objectives, namely: a high power factor (close to one) and a quasi-sinusoidal waveform of the currents absorbed. They are differentiated by the nature of the servo loop used. The latter may be either current or power. For this purpose, two classes can be distinguished: VOC (Voltage Oriented Control): using a current loop, developed by analogy with the vector control of electrical machines. It consists in orienting the current vector in the same direction as that of the voltage vector [8], DPC (Direct Power Control): developed by analogy with the direct torque control (DTC) of induction motors. It is to control the instantaneous power, active and reactive, instead of the torque and flux through two inner loops [9].

There are a number of publications on droop based control for facilitating high reliability and avoiding complexity of a supervisory control system [6, 12]. The droop based control algorithms are popular due to their coordination capability among various power rating units together with flexibility and reliability. The concept of droop based power control is valid for the both high voltage (HV) transmission line and low voltage (LV) distribution line, although it has some limitations.

Key words – i) Effect of series resistance ii) i-v characterstics iii) Power region iv) Power Plane Analysis v)Maximum Power Point Tracking.