Deciding when to upgrade legacy power electronics depends on several factors including:

1. Performance: If the legacy power electronics are no longer meeting the required performance standards or if there are new technological advancements that can significantly enhance performance, it might be time to upgrade.
2. Reliability: As power electronics age, they may become less reliable, leading to increased downtime and maintenance costs. If the reliability of the system is compromised, upgrading may be necessary to ensure uninterrupted operation.
3. Efficiency: Newer power electronics often offer improved efficiency, which can result in energy savings and reduced operating costs over time. If the existing system is inefficient, upgrading to newer technology could be beneficial.
4. Obsolete Components: If the components used in the legacy power electronics are no longer available or supported by manufacturers, it may become increasingly difficult and costly to maintain the system. Upgrading to newer components can mitigate this risk.
5. Safety: Safety standards and regulations may evolve over time, and older power electronics may not meet current safety requirements. Upgrading to compliant equipment can help ensure the safety of personnel and equipment.
6. Integration with Modern Systems: If the legacy power electronics are incompatible with newer systems or technologies that are being implemented within the organization, upgrading may be necessary to facilitate integration and improve overall system functionality.
7. Cost Considerations: While upgrading may offer benefits in terms of performance, reliability, efficiency, and safety, it's essential to consider the upfront costs of upgrading compared to the potential savings and benefits gained over time.

In summary, it's important to regularly assess the performance, reliability, efficiency, safety, and compatibility of legacy power electronics systems to determine when an upgrade is warranted. This decision should be based on a careful evaluation of the specific needs and circumstances of the organization.