Inverter short circuit protection precautions - Solutions - Huaqiang Electronic Network

The short-circuit protection function refers to the ability of a device connected between the power source and the load to effectively isolate the short circuit from the power supply when a fault occurs on the load side. This feature is crucial for preventing damage to the system and limiting the spread of the fault. The short-circuit breaking capability, on the other hand, describes the device's capacity to safely interrupt the short-circuit current without being damaged itself. While these two concepts are closely related, they are not entirely the same. For example, an air circuit breaker (ACB) may have a short-circuit protection function, but if the actual short-circuit current exceeds its breaking capacity, it might not be able to fully disconnect the circuit, leading to damage. This can happen due to improper selection of the circuit breaker or limitations in the grid’s capacity. The short-circuit current is calculated based on the system parameters, including the power supply capacity and line impedance, which are essential considerations during design. It's important to note that if an inverter is damaged after a short circuit, it doesn’t necessarily mean it lacked short-circuit protection. It could indicate an issue elsewhere in the system, such as a faulty component or improper configuration. In many cases, the inverter’s internal IGBT modules are designed to resist short circuits by automatically locking out current flow. This built-in protection helps prevent damage to the power devices. In some systems, especially older ones, fast-melting fuses were used to protect the DC bus. However, modern designs often rely on output reactors to limit short-circuit currents. These reactors help reduce the risk of damage to the inverter’s output stage. That said, the output side of the inverter typically lacks direct hardware protection because the IGBTs themselves are capable of withstanding short circuits for a short period. IGBTs are designed to handle short-circuit events by quickly shutting down the current flow. However, if the load suddenly opens during operation, the resulting high dv/dt voltage can cause the IGBT to fail. This is similar to a sudden dam closure in a river, causing a powerful reverse surge that can overwhelm the system. Overload and short-circuit conditions are different. Short-circuit currents are much larger than overload currents, and IGBTs respond rapidly to them. However, prolonged overloads can lead to thermal stress and eventual failure. Therefore, frequency converters are usually equipped with both short-circuit and overload protection mechanisms. In summary, while short-circuit protection and breaking capability are closely linked, they serve different purposes. Modern IGBT-based systems are designed to handle short circuits internally, reducing the need for external protection on the output side. However, proper system design, component selection, and protection settings remain critical to ensuring reliable operation.

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