Photovoltaic Solar Plant As A Statcom During Dark Periods In A Distribution Network

Abstract - Photovoltaic (PV) energy is supposed to be one of the cleanest forms of renewable energy. PV solar plants produce real power only during day time whereas in the nights they are completely idle. PV technology is expensive. Such an expensive asset thus remains entirely unutilized in the night time and brings no revenue to the solar plant owner. A key component of the PV solar plant is a voltage source converter which is also a core element of STATCOM. Using this fact we present a simple open-loop control method of using PV solar plant as STATCOM, in dark periods without sunlight, for load reactive power compensation and voltage control. The simulation work is carried out in MATLAB Simulink. The results show that the method is effective in mitigating voltage sags and swells with improved voltage regulation and power factor. further risk the stability of the system. Hence system Index Terms: Solar energy, PV cells, STATCOM, Power Quality I. INTRODUCTION Utilization of renewable energy comes from the perspective of environmental conservation and fossil fuel shortage. Recent studies suggest that in medium and long terms, photovoltaic (PV) generator will become commercially so attractive that large-scale implementation of this type can be seen in many parts of the world [1], [2]. A large-scale PV generation system includes photovoltaic array, DC/AC converter and the associated controllers. It is a multivariable and non-linear system, and its performance depends on environmental conditions. Recently, the increasing penetration levels of PV plants are raising concerns to utilities due to possible negative impacts on power system stability as speculated by a number of studies. Thus, the thorough investigation of power system stability with large-scale PV is an urgent task. Among stability issues, voltage instability has been a major concern for power system. Several major power interruptions have been linked to power system voltage instability in recent past. It has been proved that inadequate reactive power compensation during stressed operating condition can lead to voltage instability. Although large-scale PV is capable of generating reactive power, however, the operation of PV in terminal voltage mode has the potential for adverse interaction with other voltage controllers [8]. Therefore, grid code requires operation at power factors equal or greater than 0.95 for PV generators. Moreover, the size and position of large-scale PV generator can introduce detrimental effect on power system voltage stability as the level of PV penetration increased. Furthermore, the technical regulations or specific standards are trying to shape the conventional control strategies to allow the flawless integration of renewable energy based distributed generation (DG) in main grid. According to technical regulations or standards the post fault voltage recovery time at DG bus is crucial as it requires DG to trip, if recovery time exceeds certain limits [9], [10]. With increased penetration of renewable energy DG, early tripping of DG due to local disturbance can operator becomes responsible to maintain the voltage profile under all operating conditions. As a result, fault tolerant control algorithm based on dynamic VAr planning (e.g. placement of FACTS devices) is applied in DG integrated system. The most common, or preferred, dynamic VAr planning with multiple DGs is the placement of dynamic VAr device at the point of common coupling of DG. Nowadays solar energy using PV technology is becoming popular due to government subsidies. Obviously solar forms generate energy during sunny periods only. When sunlight is not bright enough they remain idle. To make the PV technology cost effective with higher utilization factor it is to be used throughout day and night. Efforts are being made in this direction [7,11]. Power quality is an important aspect of power distribution. Power is to be distributed with tolerable voltage sags and swells. Here Flexible AC Transmission Systems (FACTS) devices play a vital role. It is well known that STATic synchronous COMpensator (STATCOM) is a FACTS device which acts as a shunt compensating device. A key component of the PV solar plant is a voltage source inverter which is also a core element of STATCOM. Using this fact we present a simple open-loop control method of using PV solar plant as STATCOM, in dark periods without sunlight, for load reactive power compensation and voltage control. Due to improvement in power factor load current reduces. Also the