Test #5. Impact of microgrid

To prevent microgrid collapse due to a fault in utility grid it is necessary to:

• isolate the microgrid;

• maintain to voltage and frequency;

This characteristics are illustrated a control methods correspond for `

• AC microgrid system

• DC microgrid system

DC microgrids control strategy are formulated as follows:

• P/f and Q/V droop characteristics;

• P/V_DC droop characteristic only;

• P/V_DC and Q/V droop characteristics;

• P/f droop characteristic only.

Islanded microgrid operation is characterized by:

• Frequency and voltage are controlled by local generation under direction of a controller.

• Frequency and voltage are controlled by main grid via a microgrid controller.

• Frequency and voltage are not controlled.

• All of the above.

Which of the following statement in isolated mode is correct

• All the DGs operate in PQ mode

• All the Dgs operate in VF mode

• Some DGs in PQ mode and Some DGs in VF mode

• None of the above

Which of the following statement is correct:

• During the grid connected operation, all DGs and invertors in the microgrid use the voltage and frequency grid` signals as a reference for voltage and frequency.

• During the islanded operation, the Virtual Synchronous Generator can provide a primary voltage and frequency regulation.

• During the islanded operation of the microgrid, if local load changes, local DGs will either increase or reduce their output power to keep the energy balance constant as far as possible.

• All of the above.

List the voltages balancing approach in microgrid:

• introduction of special control loops to converter based DGs and energy storage units;

• using reactive support devices (simple switched capacitors, SVC, STATCOM);

• using simple switched capacitors;

• All of the above.

The microgrid synchronization criteria (according to IEEE standard 1547):

• voltage magnitude difference (ΔV < 0.03 pu), phase angle deviation (ΔФ < 100), frequency difference (Δf < 0.1 Hz);

• voltage magnitude difference (ΔV < 0.03 pu), phase angle deviation (ΔФ < 100);

• voltage magnitude difference (ΔV < 0.03 pu), frequency difference (Δf < 0.1 Hz);

• phase angle deviation (ΔФ < 100), frequency difference (Δf < 0.1 Hz).

Introduction of switched capacitor bank is used to meat the synchronization requirements via:

• Improvement the voltage at grid side;

• Improvement the voltage at microgrid side;

• Improvement the voltage at microgrid side and reduced the maximum voltage deviation;

• Improvement the voltage at microgrid side, reduced the maximum voltage deviation and voltage unbalance;

Active synchronization is characterized by:

• using inbuilt control mechanism to match the voltage, frequency, and phase angle of the island system to the utility grid;

• according to the synchroramps or synchroscope and the synchcheck relay the operator throws a switch close command to the static switch;

• before microgrid will reconnect to the grid loads and DGs in the island should be de-energized;

• none of the above.