blanking time

Blanking Time: A Crucial Element in Inverter Bridge Design

In the realm of power electronics, inverters are essential for converting DC power into AC power. These devices utilize semiconductor switches, usually MOSFETs or IGBTs, to control the flow of current. A critical aspect of inverter design is ensuring the safety and efficient operation of the switching process, which is where the concept of "blanking time" comes into play.

The Short Circuit Threat

An inverter bridge typically comprises two switches in each leg, arranged in a complementary configuration. This means that while one switch is on, the other is off, and vice versa. The problem arises when these switches cannot transition instantaneously from on to off or vice versa. This non-ideal switching behavior introduces a brief window of time when both switches in a leg are momentarily off, potentially creating a direct path for the DC input voltage to flow to ground, causing a short circuit.

Blanking Time to the Rescue

To mitigate this short circuit risk, a "blanking time" is implemented. This is a carefully determined time interval during which both switches in a leg remain off. This interval follows the turn-off of one switch and precedes the turn-on of its complement. During this blanking time, the DC input is effectively isolated, preventing any unwanted current flow.

Why Blanking Time is Essential

• Safety: By preventing short circuits, blanking time ensures the safe operation of the inverter and protects components from damage.
• Efficiency: By eliminating short circuit events, blanking time contributes to improved efficiency by reducing energy loss.
• Reliability: Ensuring that the switching process is controlled and safe enhances the reliability of the inverter system.

Factors Influencing Blanking Time

The duration of blanking time is a critical parameter that is influenced by various factors, including:

• Switch characteristics: The switching speed and rise/fall times of the semiconductor devices play a significant role in determining blanking time. Faster switching devices allow for shorter blanking times.
• Circuit parameters: The inductance and capacitance of the circuit affect the rate of current change and the duration of the transient period, influencing the required blanking time.
• Operating conditions: Factors like temperature and load current can influence switch performance and therefore impact the necessary blanking time.

Designing for Blanking Time

Inverter designers carefully consider blanking time during the design phase. The choice of switching devices, the circuit layout, and the control algorithm all play a crucial role in determining and optimizing the blanking time. It is crucial to ensure that the blanking time is sufficient to prevent short circuits while being short enough to minimize performance degradation.

Conclusion

Blanking time is a vital concept in inverter bridge design. It addresses the inherent limitations of non-ideal switches by preventing short circuits, thereby ensuring safe, efficient, and reliable operation. Understanding blanking time is essential for anyone working with inverters, enabling them to design and operate these critical devices effectively.