American Journal of Engineering Research (AJER) 2016 American Journal of Engineering Research (AJER) e-ISSN: 2320-0847 p-ISSN : 2320-0936 Volume-5, Issue-10, pp-230-237 www.ajer.org Research Paper Open Access
Modeling and Control of Directly Connected and Inverter Interfaced Sources in a Micro-Grid Ammar Ajabnoor 1
(Electrical Engineering/ University of South Florida, USA)
ABSTRACT: There has been an intensive interest on Distributed Generation due to their restricted goals of meeting local loads and improving reliability of the overall system. In this project two DC power supply has been connected to micro-grid via VSC, the concept of micro grid, where all the distributed generators including the renewable energy sources can be operated and controlled at the distribution level itself, reduces the pressure on the main grid and hence the chance of a blackout is minimized. A micro grid may contain both directly connected and inverter-interfaced micro sources, including PQ control loop. The micro-grid has the ability to disconnect itself or island from the rest of the grid when a fault occurs and operate by itself. In this paper we are going to simulate and evaluate micro-grid operation during transition between grid-connected mode and islanding mode under different control strategies. A programhas been created that simulate the results using given formula for d-q axis. A complete scheme toget the output result has been implemented. Keywords: PQ control, voltage source converter, droop control
I.
INTRODUCTION
The islanding mode is a condition in which a micro-grid or a portion of the power grid, which Contains both load and distributed generation (DG), is isolated from the remainder of the utility system and continues to operate, the master-slave system control strategy is usually adopted when micro-grid is on islanded operation mode. In grid connected operation mode, all the controllable distributed generators adopt P/Q control strategy and their desired output values are given by economical operation plan. In islanding operation mode, there will be a master inverter which provides reference voltage and reference frequency for slave inverters. On the other hand , in connected operation mode during the grid-connected operation, each DG system is usually operated to provide or inject preset power to the grid, which is the current control mode in stiff synchronization with the gridThe introduction of the paper should explain the nature of the problem, previous work, purpose, and the contribution of the paper. The contents of each section may be provided to understand easily about the paper.
II.
PQ CONTROL OPERATION
As previously mentioned the micro-grid in this paper contains both directly connected and inverter interfaced micro-sources, their control scheme also varies. All the controllable inverter Interfaced micro-sources are operated with a PQ control strategy when grid-connected. In the PQcontrol of an inverter as shown in Fig.1, Park’s transformation is used to convert the three-phase voltages and currents at the grid side into the rotating reference frame components. The currentsin the rotating reference frame i.e. id and iq are proportional to the active and reactive power, hence by controlling the direct and quadrature axis components of current the active and reactive power through an inverter can be controlled. As the reference frame is synchronized with the grid voltage, the qudratrature voltage component, Vsq = 0 and hence the power equations at the grid side can be written: Ps = Vsd* id ……………... (1) Qs = - Vsd*iq …………..... (2) From (1) and (2) the reference currents for a current controlled inverter with predetermined power settings, Psref and Qsref are given by: Idref = Psref /Vsd................. (3) Iqref = -Qsref /Vsd ……….. (4)
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