Location

The example model can be found in the Artemis installation folder:

C:\OPAL-RT\ARTEMIS\[ARTEMIS version]\common\Examples\

Description

Model

In this example model, two Synchronverter control based three-phase, two-level grid forming (GFM) inverters are connected in parallel in an islanded microgrid. The GFM inverters are required to maintain the voltage and frequency of the islanded microgrid by dispatching the required active and reactive power demanded by the loads. The high-level block diagram of the example model is depicted in Figure below. In the figure, the green block represents one of the grid forming inverter driven distributed generation unit (DG1), the block in Magenta represents DG2 having similar functionalities to DG1, and the Cyan block represents the loads. The two DGs shares power proportionally as DG 2 has twice the capacity of that of DG 1.

Open

The grid-forming inverter of the Distributed Generation (DG) unit-1 is shown in Figure below. A dispatchable DC source feeds the GFM inverter; therefore, with varying operating conditions, the DG can instantly adjust its active and reactive power dispatch in proportion to its nominal capacity. As Synchronverter does not require any inner synchronization, no Inner Control Loop has been adopted.

Open

Based on the functionality, the controller is divided into three subsystems. The first subsystem corresponds to the Signal Conditioning unit, which measures the signals of interest, filters and conditions them to per-unit values, and transforms the signals into d-q coordinates, as the subsequent controllers require. Afterward, the Primary Control Loop block estimates the phase angle and generates the reference control signal in the d-q coordinate. At last, the Reference Generation block is used to condition the reference control signal generated by its preceding control block according to the DGs nominal DC voltage and the GFM inverter’s operating voltage. In this example, an average two-level three-phase inverter model is used; therefore, the reference signal is directly connected to the Uref port of the inverter.

At the output of the two-level converter, an LC filter is used to reduce high-order harmonics generated by the switching dynamics of the conversion process. The two DGs are connected together at the Point of Inter Connection (POI) via distribution lines. Loads are connected with the DGs at POI through the distribution line.    

Scenarios

The example model is intended to introduce different dynamic changes to the system presented in the previous section to show the effectiveness of the Smart Inverter toolbox and its associated control blocks. The control blocks are supposed to maintain the microgrid’s voltage and frequency at the nominal value by injecting necessary active and reactive power, respectively. Refer to the supplementary MATLAB code to obtain the control parameters and nominal values used in the example model. The following dynamic changes are introduced to the example model to observe the effectiveness of the controller under varying operating conditions:

1. At t= 1.5 second, a new load is connected at the POI.

2. At t= 3 seconds, the newly connected load got detached from the microgrid.

Simulation and Results

The following figure shows the simulation results of the example model at the POI:

The Figure depicts the measured voltage, frequency, and combined dispatch of active and reactive power at POI. Although the primary controllers respond with varying operating conditions and adjust dispatch of power accordingly, however, due to the absence of Secondary controller, voltage and frequency deviates from nominal conditions.

The following figure shows the simulation results of the example model at the DG terminal:

The above figure represents the generation of active and reactive power by individual DGs. As frequency is a universal parameter, therefore, active power sharing between the two DGs is accurate. However, voltage is a local parameter and due to the absence of virtual impedance loop, reactive power sharing is not accurate. At t=1.5s, a new load gets connected with the microgrid. The two DG controllers sense the momentary deviation in voltage and frequency and immediately increase their active and reactive power dispatch. As in this example model, DG 2 has twice the capacity of DG 1; therefore, they maintain proportional contribution of power with varying operating conditions. Afterward, at t=3s, the newly connected load got disconnected from the system, and both DGs reduce their power dispatch to cope with the new operating conditions.

Intellectual Property Disclaimer

Natural Resources Canada owns all intellectual property rights in the Smart Inverter Modelling Toolbox software and related products.