**4. Switching to the backup power supply, in the case of a lowvoltage smart microgrids using an electric generator set and the photovoltaic panels**

**1.** The situation where ATS intervention is required.

grid using two transformers and an electric generator [1].

tain time period, called ATS time delay (tATS).

given, the ATS should not work again.

conditions simultaneously:

minimum value.

supply.

88 Smart Microgrids

generator, **Figure 6**.

**2.** The situation where ATS intervention is unnecessary.

For the ATS facility to distinguish between these two situations, it must meet the following

**Figure 6.** Single-line diagram of force for switching to the backup power supply in the case of a low-voltage symmetrical

**a.** To get into action when the voltage level on the consumers' bars drops below a certain

**b.** The automatic action of the reserve should not be made immediately, but only after a cer-

**c.** Switching the backup path to achieve only after the disconnection of the normal power

**d.** It operates once, so that if after the operation of the ATS a new activation command is

When the condition of minimum voltage on the station's bars is not satisfied in accordance to the abovementioned conditions, (a)–(d), the power supply is ensured by the M1 electric In the case of modern residential buildings that use an electric generator set and the photovoltaic panels, the functions that are provided by the ATS regard the following:


The automatic switching is necessary between the two types of users, critical and noncritical ones to the available sources, in this case the three-phase public grid, an electric generator set, and photovoltaic panels that are shown in **Figure 7**.

and photovoltaic source time. These functions are performed through a software program [9] which is implemented on an AL 2–24 MR-D, Alpha Mitsubishi programmable micro-

Unconventional Backup Structures Used in Smart Microgrids

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• When the public grid is not available, the triggering delay timing of the electric generator set is initiated; if the voltage grid does not reappear during this delay timing, the startup

• Several connecting attempts are possible, their number being set by the user. The duration of the connecting command and the related pause between the attempts can also be estab-

• When the electric generator set is connected and the output voltage is detected, the connecting command is maintained for another short period of time in order to avoid its

• After switching on the electric generator set and expiring the timer entry (also set by the user), critical and noncritical users are switched to the electric generator set circuit.

• Upon reappearance of the voltage on the public grid and after the end of the public grid stabilization (user settable), the users are disconnected from the electric generator and re-

• Simultaneously for the electric generator set, the stopping procedure is initiated with the

• In the case of public grid and group unavailability, vital consumers are supplied by the

• Fault and nonconfirmation conditions are stored and remain active even if the system is disconnected and then reconnected; resetting requires operator intervention to repair the

fuel shutdown and timed with the activation of the group shutdown command.

**5. The implementation of recloser devices for autoconfiguration and automatic connecting/disconnecting decisions, in order to switch on** 

As smart grids are composed of sensitive equipment at voltage interruptions in increasing proportion, higher-power-quality issues have become increasingly important. In order to reduce the rate of long-term interruptions and thus improve the quality of energy, for medium voltage (MV) distribution networks, it is proposed to use the recloser devices. Thus, it can prevent long outages by eliminating temporary malfunctions, before the fuses are operating in the system. Reclosers also offer control, measurement, automation, and telecommunication capabilities. This makes it possible to control in real time the intelligent network that now allows maneuvers for various purposes. Reclosers also provide consecutive automatic

In this case, the ATS automation must work in the following way:

procedure of the electric generator set will be initiated.

automat, **Figure 3**.

lished by the user.

disconnection.

connected to the public grid.

**the backup power supply**

photovoltaic panels' energy generation.

causes that triggered them and press the reset button.

**Figure 7.** Electric power diagram for switching to backup power supply in the case of a low-voltage smart microgrid using an electric generator set and the photovoltaic panels (courtesy of Sirius Trading & Services srl, Romania).

To implement the above basic functions and the control algorithm, the system also integrates the following additional functions:


and photovoltaic source time. These functions are performed through a software program [9] which is implemented on an AL 2–24 MR-D, Alpha Mitsubishi programmable microautomat, **Figure 3**.

In this case, the ATS automation must work in the following way:

