hi

Nowadays, these renewable DG are required to equip with reactive power devices (such as static VAR compensators, capacitor banks, etc), to provide reactive power as well as to control the voltage at their terminal bus. So, the issues related to voltage control, voltage stability are no longer an issue

hope you find your answer and more in the following paper

Dear Mohammad,

There are many effects of DG on the network operational performance. Some of the important problems are: voltage control problem (due to less reactive support), instability (both transient and small signal), incorrect operation of protection settings due to varied short circuit levels, poor damping and inertia support, calls for more reserves, and at last harmonics......and all these, of course, affects the component reliability and then overall reliability .....

Impacts of distributed generation on power system depend on the type of generation to be connected to grid. However, common impact is voltage stability and control.

The impact of dispersed generation (DG) by adding an active power source to the distribution network is aiming mainly to reduce the active power loss in the distribution network and as a result improving the voltage profile at the network .

Mohammad,

As you know, DG includes not just renewable resources, like wind and solar, but also other dispatchable smaller types of generators, such as microturbines. But, most researchers would focus on renewable resources and treat them as DG. 

Nowadays, these renewable DG are required to equip with reactive power devices (such as static VAR compensators, capacitor banks, etc), to provide reactive power as well as to control the voltage at their terminal bus. So, the issues related to voltage control, voltage stability are no longer an issue (it is not an important research problem any more). 

Also, if you start to assume that your small system (be it micro-grid or mini-grid) has only renewable resources, many of the problems that we have in AC-based system will go away. Those issues include angular stability, frequency stability etc, because you have no more rotating synchronous generators. The system becomes just pure DC-system.

I hope this helps.

Jeremy

generally DG's are placed in distribution system to improve the voltage profile of the system.

DG's have various technical benefits such as voltage profile improvement, relief in feeder loading, power loss minimization, stability improvement if they are properly deployed i.e. size and location od DG's

Hi

I means the impact of DGs (ie: pv , wind ...) on the stability , reliability , economic cost

I need a thesis or paper that has analyzed these effects.

hi

in terms stability on power system ?

The impact of DG is associated with:

Control and regulation of voltage profiles.

Reactive power compensation and power factor improvement.

Increased load capacity that can assume the power system.

Minimizing power losses.

Generation without dependence on fossil fuels.

Meet energy demand increases.

Raises the reliability of the power system.

Reduction in greenhouse gas effects, noise pollution and environmental preservation.

Disadvantages:

bidirectional flow, may cause over voltages, harmonic distortion, can affect the system with connection and disconnection of generation centers fortuitously.

DG has several effects on power system:

Pros:

-           Locally feeds loads;

-           Reactive power support (voltage profiles);

-           Power losses reduction;

-           Environmentally friendly (i.e. less energy from “traditional” power plants based on fossil fuels);

Cons:

-           Stability issues due to smaller inertia;

-           Uncertainty of power production;

-           Undesired reverse power flows (i.e. from the distribution to the transmission network);

-           harmonic injection (DG is connected to the power system via converters);

-           Frequency regulation.

From a unidirectional energy flow (from large power plants to the final user) to a bidirectional energy flow (DG inject energy in the power system). Hence different power system controls may be necessary.

Most of influence of DG on power grid are already written above. I would mention one very important. Protection coordination setting need to be checked and performed carrefuly .

These fellows already pointed out the significant ones, What I can add to above is:

Changes in conventional control of Power systems from a larger grid to micro and nano grids where its possible to be islanded or grid connected, therefore improving the peak demands (also known as peak lopping/shaving), and respond energy management, etc. In this sense not only affecting the certainty adversely but also improving the system stability once a contingency event occurs. However, the system matrix would be variable and accordingly the dynamic stability control more complex.

Protection settings also have to be reviewed particularly for islanded operation.

HI

www.sciencedirect.com

Most of the thins already mentioned. Some more things I need to add

DG introduction leads to: reduced fault levels, reduced/lack of/improperly distributed inertia and damping. 

Damping and inertia leads to stability problems

Fault levels lead to improper protection operation, and in ability of passing through low voltage and frequency disturbance events......

hi

Nowadays, these renewable DG are required to equip with reactive power devices (such as static VAR compensators, capacitor banks, etc), to provide reactive power as well as to control the voltage at their terminal bus. So, the issues related to voltage control, voltage stability are no longer an issue

Hi

Most of invluence of DG on power grid are already written above. I would mention one very important. Protection coordination setting need to be checked and performed carrefuly .

Can any one throw some light on what challenges are there as of now in islanding detection methods for grid-connected PV systems?

Article Impact of Distributed Generation on Power System Protection