Abstract
Today's power systems have been extended due to interconnections with the neighboring systems. Energy cost is increasing due to greater sensitivity of new transmission lines. These have demanded the search of new controllers. These objectives were met by reactive power control on transmission lines. Hence, FACTS controllers are becoming an important part of the modern power transmission systems. Different control techniques are in use with STATCOM to generate control signals. But the conventional controllers like P; PI provide a slow dynamic response during the fault condition. This chapter creates an awareness of control issues and proposes an observer-based state feedback controller for STATCOM. The mathematical explanation of the observer-based state feedback controller for STATCOM is presented. Simulations have been carried out with one case study in MATLAB/SIMULINK environment. The simulation results show that the observer-based state feedback controller gives better performance than conventional PI controller during contingency condition.
TopIntroduction
Voltage Instability or transient instability and voltage collapse can cause the major blackout in the power system. Installation of FACTS Devices in existing transmission line is a way to strengthen power and voltage stability. Voltage collapse typically occurs on power systems which are heavily loaded, faulted and has reactive power shortages. Voltage collapse is system instability in that it involves many power system components and their variables at once. Indeed, voltage collapse often involves an entire power system, although it usually has a relatively larger involvement in one particular area of the power system. The present scenario of power stations of India demonstrates that the stress on transmission systems is increasing considerably because of the large population, modernization and vibrant economic growth. This growing demand for electricity and restriction on the set up of new transmission lines results in huge loss, even many existing transmission systems operate below their normal rating due to some limits. To tackle these problems now-a-days more advanced technologies have been developed for better control and reliable operation of power systems. In 1980s, the Electric Power Research Institute (EPRI) has introduced a new approach for increasing power transmission capability of existing power systems. The proposed concept is known as Flexible AC Transmission Systems (FACTS). Flexible AC Transmission System (FACTS) are Power Electronics based devices which have been developed for improving the utilization and capability of power transfer of the existing power systems. STATCOM is one of the most effective FACTS devices for providing dynamic compensation of ac transmission systems and also to improve the stability of the system. STATCOM can control various parameters of the transmission line .It has the capability to control both the real and reactive power flow through the line. Hence it brings new scopes in power electronics and power system design. During voltage instability reactive power support is so important. Now to control the amount of reactive power it requires a fast response and well designed controller. Controller of FACTS devices plays an important role to compensate the system in different system conditions. Different control techniques are in use with STATCOM to generate control signal. But the conventional controllers like P; PI provides slow dynamic response during the fault condition. This chapter presents with a new approach to design an Observer Based State Feedback Controller of VSI based STATCOM for improving transient stability of the system. Full order state feedback controller for VSI-STATCOM has been proposed. This chapter also presents detailed analysis to compare the performance of STATCOM with conventional PI and proposed Observer Based State Feedback Controller.
Key Terms in this Chapter
FACTS Devices: Flexible alternating current transmission system (FACTS) is static equipment used for the AC transmission of electrical energy. It is meant to enhance controllability and increase power transfer capability. It is generally a power electronics-based device.
Pole Placement Method: Pole placement method is a controller design method in which you determine the places of the closed loop system poles on the complex plane by setting a controller gain.
PI Controller: A proportional-integral controller (PI controller) is a control loop feedback mechanism widely used in industrial control systems and a variety of other applications requiring continuously modulated control.
Instability: Lack of stability.
Voltage Collapse: Voltage collapse is a system instability involving many power system components. In fact, a voltage collapse may involve an entire power system. Voltage collapse is typically associated with reactive power demand of load not being met due to shortage in reactive power production and transmission.
VSI (Voltage Source Inverter): The simplest dc voltage source for a VSI may be a battery bank, which may consist of several cells in series-parallel combination.
LQR (Linear Quadratic Regulation): The theory of optimal control is concerned with operating a dynamic system at minimum cost.
Contingency: A future event or circumstance which is possible but cannot be predicted with certainty.