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Management of Operation modes

The ordinary grid-connected mode and P/Q control 

In this connection mode, a P/Q control strategy is implemented. In particular, the micro sources are operated in MPP control mode and the storage energy devices are controlled to improve the economic dispatch or to smooth the output power oscillation of non-programmable renewable energy sources (i.e. wind turbine and PV system).

  • Voltage control system, aimed at optimizing the nodal voltage profile of the μG by managing the reactive power provided by all micro-sources connected to it.
  • Optimization algorithm, aimed at regulating the active power of dispatchable sources in order to implement an economic dispatch algorithm or to match the electric load with the minimum possible error . 

Transition from grid-connected to isolated mode  

  • Master-slave control: the SCADA will use as a master generator the CHP or the battery banks or the micro-turbine.The SCADA will select the resource depending on its availability and on its regulating reserve. The master generator will promptly change its operation mode from current control to voltage control mode, providing thus the reference for voltage and frequency. Other sources will continue to operate under the current control mode.
  • Droop control the SCADA will switch into voltage control mode two or more controllable sources (i.e. gas-fuelled CHP system, battery banks and micro-turbine). In this case, the regulation burden will be shared among the selected sources on the basis on their droop control.

Transition from isolated to grid-connected mode operation

 

The voltage of the μG should be synchronized to the main grid voltage before re-connection.

 

The SCADA monitors the voltages at both sides of the switch-disconnector.

 

The SCADA regulates active and reactive powers of all micro sources of the μG, until magnitude and phase errors are lower than predefined thresholds. When this condition is achieved, the SCADA sends an enabling command to the synchrocheck relay and then the reclosing of the switch-disconnector can be done. 

 

Black start mode operation

 

In this case, the SCADA should give to the operator the possibility to decide what kind of black start procedure would execute.  

By-pass converter as voltage regulator

In this case, the SCADA sends a command to this device to start it in the voltage control mode, enabling it to provide the reference of voltage and frequency. Subsequently, the SCADA sends a command to switch on the other generators. When all available generators are connected also the loads will be activated and the system will be operated as in Isolated mode.    

Master control mode

In this case, the SCADA will select one of the controllable micro sources to act as a master. The SCADA will send an enable command to the selected master unit to operate in the voltage control mode. All available generators will be connected and operated in the current control mode. As in the previous, the SCADA will activate a load sharing procedure to ensure the balance power within the microgrid. 

 

 


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