Output Power Increase at Idle Speed in Alternators

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                                                                                       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
                                                                                                                                                                                                                                                           π                                                   2π

      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
                                                                                                                                                                                                                                                                                                                                                                                    Experimental Results
                                                                                                                                                                     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
                                                                                                                                                                                                                                                                                                                                                                                    the current.
• 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).
                                                                                                                                                                                                                                                                                                                                                                                                                                                           Simulated                                 10
                                                                                                            Field Current

                                                                                                                                                                     •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

                                                                                                                        Rs               ia

                                                                                                                                                                                                                                                                                                                                                                                                        0                                                                                                     RMS Current Increase at Idle speed VBASE=14V Vov=20V

                                                                                                                                                                                                                                                                                                                                                                                                                                                                             %inc. in RMS phase Current
                                                                                                                             Rs          ib
                                                                                                                                                               Vo                                                                                                                                                                                                                                                                                                                                    20
                                                                                                                                  Rs     ic

                                                                                                                                                                     •Parameters we can now control:
                                                                                        Vsa                                                           c

                                                                                                    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
                                                                                                                                                                                                                                                                                                                                                                                                                               Time [ms]
                                                                                                                                                                    •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.
                                        ib                      b
                                   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
                                                                                                                                                                                                   δ (degs)
                                                                                                                                                                                                                                                      Φ (degs)
                                                                                                                                                                                                                                                                                                            δ(degs)                                 Φ(degs)
                                                                                                                                                                                                                                                                                                                                                                                    MIT/Industry Consortium on Advanced Automotive Electrical/Electronic Components and