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Microgrid Model

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Microgrid Controller

This model demonstrates the implementation of a microgrid comprising four distributed energy resources and their controllers, all of which are part of the Microgrid Library . Additionally, the microgrid incorporates three different types of loads. The microgrid includes four distributed energy resource models: one Photovoltaic Generation System , one Type-3 Wind Turbine Block , one Diesel Generator , and one Battery Energy Storage System (BESS) . All of these components are connected to the common 6.6kV L-L Microgrid bus using step-up transformers and breakers. The common bus is linked to an infinite AC-Grid, emulating an external AC network, through a transformer and a component referred to as the 'PCC breaker.' This connection allows all the components to be connected to the infinite AC-Grid. Furthermore, this model employs diverse controllers that, in addition to the distributed energy resource controllers, endeavor to fulfill the model's criteria. During operation in the non-islanded mode, these controllers also strive to meet the network's criteria while ensuring a reliable power supply to the loads. These controllers include Active Power Controller , Reactive Power Controller , Curtailment Power Controller , Load Management Controller , and Islanded Controller . The Active Power Controller generates power references for DERs and manages power curtailment, load shedding, and grid import/export for RERs. This Reactive Power Controller handles the generation of reactive power references for DERs. If there's a non-zero reference for reactive power transmission to/from the external AC grid, the controller calculates the DERs' references based on their instantaneous reserve power in proportion to the required magnitude. The Islanded Controller manages the Microgrid's transition between grid-connected and islanded conditions, ensuring minimal dq-frame currents for islanded mode and minimizing voltage differences for Grid-Connected mode. It also generates PCC error references for power transmission and sets the Diesel Generator frequency reference to compensate for phase shifts across the PCC. The Curtailment Power Controller handles the logic for distributing curtailment power among the RERs based on their real power references. It also disconnects RERs from the Microgrid if their required curtailment exceeds a predefined limit. The Load Management Controller regulates active power flow through the Point of Common Coupling (PCC) when the microgrid is connected to an external AC grid. Users can adjust active power settings using this block.

Block settings

The signals feeding into the P ref and Q ref inputs of the PV system are sourced from the microgrid controller blocks. The PV system has two USER-defined input references, Ir ref (Irradiance (W/m2)) and T ref (Temperature (°C)), currently set as constant values of 500 and 25, respectively. However, it is important to note that these constants can be substituted with varying signals to represent changing profiles of irradiance and temperature. The signal to the Curtail enable input comes from Curtailment Power Controller .

Just like the PV system, the wind turbine block receives input signals for P ref and Q ref from the microgrid controller blocks. The wind turbine block also features a USER-defined input reference called Wind speed ref (m/s), which is currently maintained at a constant value of 12. However, it is important to note that this constant can be substituted with varying signals to represent changing profile of wind speed. And the signal to the Curtail enable input comes from Curtailment Power Controller .

The diesel generator and battery energy storage blocks receive input signals for P ref and Q ref from the microgrid controller blocks Each of the blocks also feature a USER-defined input reference called V ref, which is currently maintained at a constant value of 1 (pu).

In this example, the active power and reactive power references at the PCC have been adjusted to zero. This means that the microgrid is not currently injecting any active or reactive power into the external AC grid.

In the microgrid model, three distinct types of loads have been considered:

1. Critical Load: Normally with a 60kW maximum capacity, for this example, it has been adjusted to 40 kW. This load must always be fully serviced and cannot be partially shed.

2. Sheddable Load: Typically with a 60kW maximum capacity, for this example, it has been set to 20 kW. This load can be completely shed if necessary, but partial shedding is not allowed.

3. Demand Response (DR) Load: Normally with a 25kW maximum capacity, for this example, it has been set to 0 kW. This load has the potential to be reduced by up to 9kW through demand response measures, but for this case, it is not active

It is important to note that for these three loads, instead of using fixed values as references, load profiles that vary over time can also be considered as references.

Demonstration

In this simulation, a time step of 5 microseconds has been utilized, and the overall duration of the simulation is 35 seconds.

The figure below depicts the active powers generated by various Distributed Energy Resources (DERs): Battery Energy Storage System (BESS) , Photovoltaic Generation System , Diesel Generator , and Type-3 Wind Turbine Block . It also illustrates the active power being transferred to the grid through the PCC, the active power consumption of critical loads, sheddable loads, and demand response loads, along with the frequency of the AC grid.

The microgrid takes approximately 10 seconds to reach a stable state and synchronize with the external AC grid, achieving a frequency of 50 Hz. The Diesel Generator's synchronous machine and mechanical inertia make it suitable for frequency control in the Microgrid. In grid-connected mode, it assists the external AC grid by maintaining frequency and following the real power reference from the central controller.

The provided figure showcases the reactive powers of all Distributed Energy Resources (DERs): Battery Energy Storage System (BESS) Photovoltaic Generation System Diesel Generator and Type-3 Wind Turbine Block Additionally, it displays the reactive power transmitted to the grid through the PCC, along with the microgrid's voltage. In this example (grid-connected mode), the microgrid's voltage control is notably influenced by the external AC grid, while the DERs actively regulate voltage by absorbing or injecting reactive power.

The figure below showcases further information about the microgrid model. It presents the battery's state of charge, the curtailment activation signal, the demand response load reduction signal, the demand response load status, the sheddable loads status, the signal for microgrid islanding (where 0 denotes it is connected to the external grid), and the active and reactive power of the external AC grid connected to the microgrid.