Consider this scenario:
- A 3-phase permanent-magnet generator is being driven by a strong force and at varying speeds e.g. 1000-6000 RPM
- Its output is rectified via a 3-phase bridge rectifier
- The resulting DC is fed to a DC-DC converter which powers something (e.g. charges a battery) - consider it a constant power load.
You'd have some capacitance in front of the DC-DC converter (e.g. it may be needed for stability). In this case the classical conduction angle issue of bridge rectifiers emerge, especially if the capacitance is large, and this setup specifically exacerbates this:
- when you increase the generator speed, the amplitude of its output voltage increases (so the amplitude of peaks and valleys of the rectified waveform increases)
- the period between peaks is smaller
- higher voltage = less current drawn by the DC-DC, thus the capacitor can hold out for longer
- the three dim traces are the phases of the generator
- the red trace is the rectifier output (what it would look like if it were unloaded)
- the cyan trace is the capacitor voltage
- the yellow trace is the generator current
I'm simulating winding resistance and cap ESR, but not winding inductance. Values taken from a specific application I was considering.
I'm worried that this pulsating current causes uneven load to the generator, and may cause issues with the generator itself - e.g. vibrations, uneven load to the bearings, or similar. On the other hand, rotor inertia may be capable of smoothing things out. Is my concern well founded, or I'm worried about the wrong thing?