Output Power Increase at Idle Speed in Alternators
Juan Rivas David J. Perreault Thomas A. Keim
Massachusetts Institute of Technology, Laboratory for Electromagnetic and Electronic Systems
Increasing output power at Idle Prototype Implementation
•Objective: Improve Idle-speed Output power without cost increase. •An experimental setup has be developed to demonstrate the proposed
Abstract --- The use of a Switched-Mode Rectifier (SMR) allows modulation technique
automotive alternators to operate at a load-matched condition at •Using the Switched Mode Rectifier, introduce novel modulation techniques
all operating speeds, overcoming the limitation of optimum that increase in output power at Idle speed. •Using simple sensing based on the direction of the phase currents, the
performance at just one speed. While use of an SMR and load gating signals of the Mosfets can be easily implemented using an FPGA.
•By modulating the active switches individually, a position dependent
matching control enables large improvements in output power at modulation can be implemented enables enhanced performance at idle
cruising speed, no extra power is obtained at idle. This work speed.
investigates new SMR modulation strategies that improve
alternator output power at idle speed without violating alternator •The new modulation consists of the following parameters relative to the
thermal or current limits. The new modulation scheme may be positive zero crossing of the phase current:
implemented with simple control hardware, and without the use of
expensive current or position sensors. After introducing the new Φ
modulation method, we develop approximate analytical models Vag VOV
that establish the underlying basis for the approach.
Implementation considerations are addressed, and both Schematic illustration of gating signals
simulation and experimental results are provided that δ
demonstrate the advantages of the proposed control method. •The information needed for the new modulation can be easily acquired by
simple voltage measurements at the input of the SMR (only the direction of
Lundel Alternator Characteristics the current is employed).
•Conventional alternators in automotive applications are connected to a
full-wave diode bridge, and regulated by field control. •δ: The voltage at the input of the SMR is hold near ground, storing energy
in the machine inductances. •We validate the accuracy of the averaged circuit models used during
•In a Lundell alternator, the phase inductances are large, and dominate
simulation by comparing those results with experimental measurements of
the electrical performance of the machine. •Vbase: Nominal operating local average of the voltage at the input of the
• Parameters optimized for load-matched power delivery at idle speed Output Power Increase at Idle speed V BASE=14V Vov=20V
Phase Current ia(t) :
(~1800 rpm). •Φ: The duty cycled is changed in order to obtain a local average that δ = 15°, Φ = 53.8°,VOV = 18.7V , f = 180 Hz
% inc. in Output Power
exceeds the nominal local average by Vov volts (red curve).
•When the phase current goes negative, the back diode associated with the
Phase Current [A]
δ =0 δ =0 δ =0 δ =0 δ =0 δ =9 δ = 12
bottom Mosfet conducts, so no modulation can be applied during this 0
Φ=0 Φ = 26 Φ = 46 Φ = 55 Φ = 63 Φ = 55 Φ = 62
0 RMS Current Increase at Idle speed VBASE=14V Vov=20V
%inc. in RMS phase Current
•Parameters we can now control:
Vsc -50 δ =0 δ =0 δ =0 δ =0 δ =0 δ =9 δ = 12
|IL|= Current Magnitude 0
Φ=0 Φ = 26 Φ = 46 Φ = 55 Φ = 63 Φ = 55 Φ = 62
α= Phase between EMF and phase current -100 -10
Switched Mode Rectifier (SMR)
0 5 10 15 20
•We have control over the output power and the dissipation in the alternator
windings. Thermal boundaries of operation must be observed. •Experimental measurements shows that a 14% percent increase in power
•Replacing bottom diodes by controlled switches and modulating them
was obtained with an allowable increase of 12% in RMS phase current.
together at high frequency, load matching control is possible by selecting •Models suggest that 15% increase in RMS current at idle speed is
an appropriate duty cycle. acceptable.
•Load matching control does not improve power delivery at idle speed. •Simulation over parameter space predicts a significant increase in power at
References (partial list)
idle speed. •D.J. Perreault and V. Caliskan. “A new design for automotive alternators”. In IEEE/SAE
Field Current Output Power increase at Idle speed: V base =14, V ov=20V Phase Current Increase at Idle speed: V base =14V V OV =20V
International Congress on Transportation Electronics (Convergence), SAE paper 2000-01-C084,
Excessive d issipation!
RMS Current Increase (%)
•S.C. Tang, T. A. Keim, and D.J. Perreault. “Thermal analysis of Lundell alternators”. In IEEE
Output Power Increase [%]
No extra power at idle Transactions on Energy Conversion, Submitted.
•J.M. Rivas, D.J. Perreault, and T.A. Keim. “Performance Improvement of Alternators with Switched
Mode Rectifiers”, in IEEE Power Electronics Specialists Conference (PESC’03). To appear.
Ls Co oler op eratio n
Vsa ic c
Dz Pout (δ = 0 , Φ = 0 ) = 914 .2W Ia (δ = 0 , Φ = 0 ) = 48 .46 A
MIT/Industry Consortium on Advanced Automotive Electrical/Electronic Components and