PLL Simulink 3 phase grid

Hi everybody,

I've found a Simulink model for a PLL for 3 phase grid. It works very well, but I don't understand the purpose of a block called 'actual amplitude detection'. It computes the followings: square of the magnitude, low pass filter the result (this is done for all the 3 phases), and then the maximum between the 3 signals. This value is then used to normalize the signals that represent the input grid. Can you please tell me why is this done, why I cannot normalize the input grid with a fixed value (for example 400V)? Why is this method better, I don't understand the principle, the theory behind this?

Many thanks, Monica

[sivakumar SL]

can u please help me by giving the simulink model..thank you

Answer 1

[Samar]

Hi @Monica,

The block referred to, 'actual amplitude detection', adjusts the normalization of the input grid signals based on real-time conditions. This method has several advantages over using a fixed normalization value like 400V. Here's why this method is used:

1. Adaptability to Grid Variations: The grid voltage can vary due to several factors such as load changes, line impedance, or faults. By dynamically detecting the actual amplitude, the system can adapt to these variations in real-time.
2. Improved Accuracy: Normalizing using the actual amplitude ensures that the PLL receives input signals that are consistently scaled, leading to more accurate phase detection and synchronization.
3. Noise Reduction: The low-pass filtering step helps in smoothing out any high-frequency noise or transient disturbances in the voltage measurements. This results in a more stable and reliable normalization factor.
4. Scalability: This method allows the system to be used in different grid environments without needing to adjust the normalization factor manually. Whether the grid operates at 380V, 400V, or some other level, the system can automatically adapt.

There are several other factors as well. Overall, the block adds flexibility and robustness to the model.

Hope this helps!