Real Time Simulation of an LC output Filter Grid Connected Gas Turbine under Voltage Sag Operation
| Originally published |  |
| in the December 2009 | |
| issue of Planet-RT |
The liberalization of electricity markets and the rapid growth of the Distributed Generation sector, due to the trend towards large-scale integration of renewable energy sources with existing electrical power systems, provide impetus to highly reliable good-quality electrical power generation.
Three-phase voltage inverters have been widely used in these power systems. Consequently, it is necessary to achieve a high level of power quality with minimal output distortion. To reach this goal, filters are used to interface these inverters with the grid in order to attenuate the harmonics injection into the grid.
In power systems with distributed energy production, low voltage distributed energy sources, such as gas micro turbines, photovoltaic arrays and wind turbines, as well as storage devices such as flywheels, supercapacitors, batteries and controllable load, form an energy system structure commonly known as a microgrid. A microgrid can operate either in parallel with the utility grid or in a stand-alone or islanded mode; in this case, the microgrid is an islanded system.
In grid-connected mode, L and LCL filters are usually used to connect inverters with the main grid. According to the previous operation mode, the generator operates as a current injector to the main grid, while the main grid imposes voltage to the micogrid’s generators. In islanded mode, the loads connected to the microgrid can only receive power from local microsources. The microgrid must also have at least one voltage generator which controls microgrid voltage during islanded operation mode. Thus, three-phase voltage inverters must be equipped with LC output filters, which are usually used to fix output voltage and attenuate voltage harmonics.
This paper and presentation discuss the design, test and validation of an inverter based on an LC output filter using real-time simulation and the Power Hardware-in-the-Loop (PHIL) methodology. The focus is primarily on the inverter stage. Testing and validation are performed only on passive load. Research studies are underway to connect this kind of inverter to a microgrid or an existing power grid and to designed robust LC output filter grid connected inverter.
In this paper and presentation, an overview of the design of a voltage source inverter including an LC output filter is presented. The parameters of the filter are chosen to minimize output voltage harmonics. A robust LC filter controller based resonant controller is suggested instead of using vector control with a synchronous PI controller. Vector control with synchronous PI controllers is used for regulating sinusoidal parameters in three-phase systems. However, if a non-sinusoidal command is applied and/or non-linear disturbances are introduced in the control system, resonant controllers offer better performance. In addition, synchronous d-q coordinate transformation isn't relevant in single-phase systems. A stationary reference frame control method is therefore proposed. It introduces a cosine transfer function with a specified resonant frequency in the voltage compensator. Hence, this controller is generally made up of a proportional and a resonance term, which contains two imaginary poles that aimed to obtain an infinite gain at the resonance frequency.
The designed inverter is first tested and validated using real-time simulation based on an RT-LAB simulator (Pulse Width Modulation (PWM) is simulated using Opal-RT’s RT-Events interpolator). Universite de Lille’s technological facility is equipped with a power stage directly connected to the real-time simulator, allowing testing of this inverter with real loads and to carry out PHIL validation.
Author(s):
Frederic Colas,
Narrator:
Frederic Colas,
Download Video : FredColas.mp4
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