The objective of the Protection Elements (PE) of the Smart Inverter library is to generate a trip signal that disables the converter and all the control layers when abnormal conditions in the main grid are detected. The PE comprises four blocks as shown in the following figure:
Each of the blocks is explained as follows:
Frequency Protection: Generates a trip signal if the frequency is above or below limits for a certain amount of time. It also generates a trip signal if the magnitude of the Rate-of-Change-of-Frequency (ROCOF) is above limits.
Voltage Protection (Three-phase):Generates a trip signal if the voltage is above or below limits for a certain amount of time. This block can also indicate if the converter must cease to energize, have a momentary cessation, or operate during abnormal conditions, depending on the user configuration.
Bridge Protection (Three-phase):Generates a trip signal when there is an over-current event in the DC or AC side of the converter after a specified interval of time.
Protection Latch: Used to enable the protections and holds the trip output until a clear signal is received.
In addition, the release of the PE blocks includes the update of the Wave Reference block to support anti-islanding functions and momentary cessation mode. The momentary cessation mode is also included in the primary control block.
An example of the interconnection of the PE is shown in the following figure:
The bridge, frequency, and voltage protection blocks are directly connected to the Protection Latch block, which holds the output when a trip event occurs. The Islanding Detection is inside the Wave Reference block to configure the parameters of the islanding active detection algorithms. When no abnormal conditions are detected, a Clear signal is used to reset the output of the Protection Latch block.
The validation of the PE is performed according to the IEEE 1547-2018 and IEEE 1547.1-2020 standards  .
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