Location

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

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

Description

Model

In this example model, a two-level three-phase converter is used to inject active and reactive power to a stiff AC voltage source that symbolizes the main grid. The following figure shows the high-level block diagram of the example model, which is separated to represent the grid with disturbances in one subsystem and the smart inverter with the solar PV system in another subsystem:

On the DC side of the two-level converter, a 5kW PV array is used as a primary energy source. To emulate maximum power point tracking (MPPT) of the PV array, a PV Controller block is implemented. The obtained output from the PV Controller block generates a normalized duty cycle signal which is fed to the boost converter. Following the boost converter circuit, a DC voltage chopper is used. The DC-link capacitor at the output of the chopper provides a smooth DC input to the two-level converter. The voltage in the DC link capacitor is controlled by the Primary Control block, which modifies the power injection on the AC side to maintain the DC link voltage at a certain reference value.

Based on the functionality, the controller is divided into four subsystems. The first subsystem corresponds to the Signal Conditioning unit, which measures the signals of interest, and conditions them to per-unit values as required by the controller. Consequently, the Secondary Control block generates the active and reactive power references, necessary to implement the grid support functions presented in the IEEE std. 1547-2018 [1]. Next, the Primary Control block generates the reference signals corresponding to active and reactive components of the output current. At last, the Wave Reference block is used to generate the reference signal to drive the two-level converter. In this example, an average converter model is used, and therefore, the reference signal is the duty ratio.

At the output of the two-level converter, an LCL filter is used to reduce high-order harmonics generated by the switching dynamics of the conversion process. The output of the filter is then connected to the main grid. The main grid is connected to a 10 kW load. The grid supply is emulated using a set of controlled voltage sources which have a subsystem introducing dynamic changes to the grid voltage as shown in the following figure:

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 control blocks. The Secondary Control block is configured to regulate the constant power factor to be at a reference value of 0.95 and to have a priority for reactive power injection. 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 grid conditions:

1. At t= 5 seconds, a 0.05 pu voltage step rise on the grid voltage from the nominal value .
2. At t= 8 seconds, a 0.05 pu voltage step down on the grid voltage.
3. At t= 11 seconds, PV irradiance change from 1000 to 500 W/m2.
4. At t= 14 seconds, PV irradiance change from 500 to 700 W/m2.
5. At t= 18 seconds, 3-Ph-g fault is introduced on the load which is connected to the grid. The fault resistance is set at 1e-6 ohm.
6. At t= 18.0916 seconds, the fault is cleared by tripping the circuit breaker. At this instant, the control system is disabled.
7. At t= 18.2 seconds, the control system is enabled again.

Simulation and Results

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

At the beginning of the simulation, the active power is slightly curtailed to maintain the apparent power at 1pu. This curtailment occurs because an increase of reactive power is produced by the CPF function. At t=5s, the change in the grid voltage causes a slight disturbance in power injection and power factor. However, the power factor is tracked adequately at 0.95. At t=11s and t=14s, the changes in irradiance create a higher disturbance in the power factor. However, it is noted that the power factor returns to the reference value adequately. Note that, although the irradiance decreases, the Pr signal remains at the rated value of 1pu. This is because the Pr signal is used as a limiting value for the MPPT and the power injection is subject to the available irradiance.

At t=18s, a fault occurs in the grid side. This causes that the converter is disabled by 0.1 second. After the fault is cleared, the converter returns to its regular operation. Instantaneous grid voltage and output currents during the fault event are shown in the figure below. It can be noticed that the converter is disabled 0.0916 seconds after the fault occurs. Then, the output current becomes zero until the fault and disable signal are cleared.

References

Intellectual Property Disclaimer

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