Synchronization of Three Phase Inverter with Electrical Grid

Abstract

Phase, frequency, and amplitude of phase voltages are the most important and basic parameters need to be controlled or grid-connected applications. The aim of this paper is to present a review of various synchronization techniques for pulse width modulated voltage source inverter. This paper describes the estimation method and verifies its usefulness by extensive numerical experiments. Various synchronization algorithms are described here. The primary application of the proposed synchronization methods is for the distributed generation units with renewable energy sources, which utilize power electronic converters as an integral part of their systems. The synchronization is usually carried out with respect to the voltage, frequency and phase angle of voltage (or current) signal(s) of the utility system. The paper also describes the issues, challenges & solutions for. Index Terms-Microgrid, Inverter, Synchronization, Amplitude, frequency and phase control. I.INTRODUCTION A Microgrid is an aggregation of multiple distributed generators (DGs), such as renewable energy sources, conventional generators, and energy storage systems etc. Typically, a Microgrid operates in parallel with the main grid. However, in some situation a Microgrid need to operate in an islanded mode, or in a standalone state. Islanded distributed generators (DGs) in a Microgrid can change its operational mode to grid connected operation by reconnection to the grid, which is referred to as synchronization. A Microgrid or a portion of the power grid which consists of load and distributed generator (DG) system; it can be isolated from Grid. In this situation, it is important for the Microgrid to continue to provide adequate power to the load under standard supply conditions. In various circumstances, if fault conditions occur in the grid, then the Microgrid is expected to isolate from the main grid, each distributed generators (DGs) of inverter system must detect this islanding situation and must switch to a voltage control mode. However, the synchronization of Microgrids that operate with multiple distributed generators (DGs) and loads cannot be controlled by a traditional synchronizer. It is needed to control multiple generators and energy storage systems in a coordinated way for the Microgrid synchronization. In ideal condition, the output voltage parameters like amplitude, frequency and phase cannot be controlled for a grid together where multiple DGs are working in parallel; whereas the same parameters for sand alone inverter to be connected to grid, can be controlled by means of the various control strategies[1]-[8]. In order to provide the required load voltage, inverter system works in standalone mode or grid connected mode. In load scheduling condition or grid off condition, the inverters works in standalone mode and provide the required power to the load. Being major of the power available through renewable systems is in DC form, inverters are preferred instead of alternators. Parameters of the inverter such as voltage, frequency and phase can be controlled for the purpose of synchronization with the relevant parameters of the grid system. Synchronization of inverter parameters like voltage, frequency and phase with grid systems can be possible by specific control system with embedded controller. To meet the load sharing requirement, the output from the inverter system can be varied with synchronization of grid system. The system presented here is a DC to AC inverter controlled using a compact controller based on an embedded system and that can be synchronized with the grid system [9]-[12]. Various techniques of synchronization of the inverter are described in the second section named as literature review. Proposed system for synchronization of inverter with electrical grid is described in Methodology section. Experimentation and Results are discussed in next section. II.LITERATURE REVIEW In sinusoidal pulse width modulation, there are multiple pulses per half-cycle and the width of the each pulse is varied with respect to the sine wave magnitude. Pure sine wave DC/AC conversion will introduce the least amount of harmonics into an electrical system, but these methods are also expensive. Since the AC sine wave to come from a DC source, the static devices will be switched in a logical way such that the energy delivered to a load approaches that of a pure sine wave. This means that extra components and design considerations are involved in the control circuitry of a pure sine wave inverter, driving up cost. A more precise method of DC/AC conversion is the modified sine wave, which introduces a dead time in a normal square wave output so that higher peak voltages can be used to produce the same average voltage as a sinusoidal output. This method produces fewer harmonics than square wave generation, but it still is not quite the same as the AC power that comes from an AC