**2.1 Grid connected system requirements**

The fundamental requirements of interfacing with the grid are as follows, the voltage magnitude and phase must equal to that required for the desired magnitude and direction

cross coupling between active and reactive powers. Hysteresis current controller is used as inner current control loop to provide switching pulses to inverter, it has good dynamic response it is more suitable as inner current controller where we need fast acting inner current loop, but drawback of this hysteresis current controller is variation of switching frequency with parameters of grid voltage, filter inductor and output current is having lower order harmonics. In current regulated delta modulator switching frequency of inverter is limited by using latch circuit, but in this case also switching frequency is not maintaining constant during fundamental period. In Modified ramp type current controller switching frequency is limited, also maintain switching frequency constant. This controller ramp signal is generated at particular frequency to maintain switching frequency constant

The configuration of Distributed Power Generation System depends on input power sources (wind, solar etc) and different hardware configurations are possible. The basic structure of DPGS is shown in fig.1. The system consists of renewable energy sources, two back-to-back converters with conventional pulse width modulation techniques, grid filter, transformer

The input-side converter, controlled by an input side controller, normally ensures that the maximum power is extracted from the input power source and transmits the information

The main objective of the grid-side controller is to interact with the utility grid. The gridside controller controls active power sent to the grid, control of reactive power transferred between the DPGS and the grid, control of the DC-link voltage, control of power quality and grid synchronization. Gird filter and transformer eliminates harmonics is inverter output

The fundamental requirements of interfacing with the grid are as follows, the voltage magnitude and phase must equal to that required for the desired magnitude and direction

[4],[5],[6].

and utility grid [1].

**2. Configuration of DPGS and its control** 

about available power to the grid-side controller.

voltage and ensures proper synchronization of inverter with grid.

Fig. 1. General structure of distributed power generating system

**2.1 Grid connected system requirements** 

of the power flow. The voltage is controlled by the transformer turn ratio and/or the rectifier inverter firing angle in a closed-loop control system. The frequency must be exactly equal to that of the grid, or else the system will not work. To meet the exacting frequency requirement, the only effective means is to use the utility frequency as a reference for the inverter switching frequency.

Earlier, control and stabilization of the electricity system as taken care only by large power system like thermal, nuclear etc. due to large penetration of DPGS the grid operators requires strict interconnection called grid code compliance. Grid interconnection requirements vary from country to country. Countries like India where the wind energy systems increasing rapidly, a wind farm has to be able to contribute to control task on the same level as conventional power plants, constrained only by limitation of existing wind conditions. In general the requirements are intended to ensure that the DPGS have the control and dynamic properties needed for operation of the power system with respect to both short-term and long-term security of supply, voltage quality and power system stability. In this paper most significant requirement is power quality. The power quality measurement is mainly the harmonic distortion and unity power factor [2].
