Why do you use amplitude ratings instead of RMS?
A very good question! We use amplitude ratings because they offer a more intuitive approach to understanding current in power systems. While RMS values work well for constant frequency AC (to obtain DC-equivalent Joule losses), they become misleading in electronic commutation where frequency varies or drops to zero.
A further reasoning breakdown behind this choice:
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Intuitive Understanding: Amplitude ratings show the actual peak current - seeing a 100A rating immediately tells you the maximum current without calculations. With RMS, you'd multiply by √2 to find the peak.
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Unified AC/DC Approach: Amplitude ratings maintain consistency across both AC and DC operation - a 100A rating means the same thing in either mode.
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Simplified Control System Design: The DC current exactly matches the AC amplitude current at 100% controller output, creating a direct relationship that simplifies system design and troubleshooting.
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Direct Mathematical Correspondence: In D-Q transformations, amplitude values retain their meaning across reference frames, reducing calculation errors.
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Real-World Protection: During motor stalls when all current flows through one phase, RMS values can be dangerously misleading for wire ratings.