In many simulink models the switching of the grid tied inverter is controlled by a current reference. What is the need of such a reference current? and which current we are considering as a reference current, is it grid current, or load current? And can anyone explain the process of deriving such a reference current for the system?
Thanks in advance
Dear friend,
The necessity of current reference is to avoid the injection of harmonics in the grid.
and the grid or load current you are taking as reference is depend upon the operating mode of your machine....i.e. either it is in generating or motoring mode.
Generating- Grid current
Motoring- Load current
For a grid connected inverter, the terminal voltage and frequency will be taken care by the grid once the system is synchronized with the grid.
We need to control the power injected into the grid. Also, the current injected in the grid should be free form harmonics (in the acceptable limit).
Control of inverter involves inner current control and outer voltage control loops. For a grid tied inverter, only current control is sufficient.
If the control is performed in d-q domain. The reference commands for current in d-q is obtained from P and Q injected into the grid. (P=VdId+VqIq) and Q = (VqId-VdIq) for a power invariant d-q transformation with rotor axis d-component and q component leading d-axis.
Vd, Vq and w are obtained from PLL. Generate Id and Iq reference commands from P,Q, Vd and Vq.
I agree with the answer of Manjunath K . You may read section 11.2.3 of the following book for more details
Book Dynamic Security of Interconnected Electric Power Systems - ...
Detailed mathematical models are available at
Wang, L. (2012). Modeling and Control of Sustainable Power Systems. Springer
Dear Ajan,
it is so that the grid can be considered as a consonant voltage source. So, when we connect a power source to the grid and this source has much less power than the grid power then there is conditions for successful connection of the source to the grid. Since the pv source can not source any value of current when it is connected to the grid it is required to make it working as a constant current source. So, the controller limits the current supplied to the grid and so this current is the load current of the PV system. It is the current supplied to the grid. It is so that the controller controls the current from the PV to the grid.
Best wishes
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