There is a method known as Switch mode rectification method which I have read in one of the papers shared on the research gate. How does the SMR technique improve the output power and efficiency as well?
http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=1296737&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D1296737
Hi again.
The question fits, thus I'll add a thought...
Regarding alternator efficiency (concentrating exclusively on the alternator):
- Increasing the stator winding copper cross-section will reduce ohmic losses.
- Working on the excitation circuit will also be able to improve efficiency (as the excitation current is pure 'loss'). Think about number of windings and active free-wheeling (a MOSFET shorting the diode) ...
- Full bridge rectification (replacing the high-side diodes by MOSFETs) is capable to reduce rectification losses.
- Not to forget: a hybrid design with permanent magnets in the slots between the claws improve the magnetic field - reducing field 'losses' due to a significant part of the field generated being directly between the claws instead of reaching the stator.
Just be aware that all these techniques add significantly to cost and complexity. And may show effects that could also be considered negative like a larger time constant regarding excitation current control. Thus you may have to add additional circuitry to overcome the drawbacks resulting originally from improving alternator efficiency.
Regards
Dear Shounak
SMR, also "Synchronous Mode Rectification" is a method to use the MOSFET channel instead of the paralleled freewheeling diode.
The diode features a forward voltage, losses are Uf*I.
The MOSFET channel has a resistance Rdson, losses thus are Rdson*i².
Depending on the values, losses in the channel can be smaller than the losses in the diodes.
Also paralleling MOSFETS will lead to smaller resistance, while paralleling diodes does not reduce the forward voltage in a similar way.
Regards - Martin
Present Lundell Alternators suffer from low efficiency < 50% at the expense of added fuel 0.1 L/100k or so. Most of the losses are copper conduction losses while most of the failures are diodes from excessive operating Tj temps near 200'C worst case, Since the load is a fixed voltage with very high capacitance (battery) currents will peak only twice in each cycle. Although we know from linear systems maximal power transfer occurs at 50% efficiency when the load matches the source impedance, this is not the most efficient. By interleaving pulses of synchronous rectification , more pulses per rev can be performed to lower the peak currents while increasing the RMS current substantially. This is not ideal however considering the RPM can vary over a 10:1 range, so added complexity of series/parallel crossover at mid-RPM is one of many solutions.
Much lower RdsOn of MOSFETs can reduce thermal issues in rectification reliability issues but at some added cost. Bulk Schottky diodes have conduction losses from their ESR which can be determined from the package power dissipation. It is generally (like all diodes) inverse with it's Pmax limit design, such that ESR=x/W_rated for X=0.5 to 1 unlike RdSOn. This also applies to Silicon and LED's from my own personal experience.
More details on actual design philosophies here. http://cdn.intechopen.com/pdfs/38166/intech-power_electronic_solutions_to_improve_the_performance_of_lundell_automotive_alternators.pdf
- Badges
- Science topic
- Similar topics
- Engineering
- Control Theory
- Control Systems
- Control Systems Engineering