Design of Dual-Output Alternators with Switched-Mode - MIT

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                                    Design of Dual-Output Alternators with Switched-Mode Rectification
                                                                            Gimba Hassan                        David J. Perreault                                                       Thomas A. Keim
                                                                   Massachusetts Institute of Technology, Laboratory for Electromagnetic and Electronic Systems

Abstract ---The push to introduce dual-voltage (42V/14V) automotive
electrical systems necessitates power generation solutions capable of
                                                                                  A New Dual-Output Alternator with SMR                                                                                                         Simulations and Experimental Results
supplying power to multiple outputs. A number of approaches for
                                                                                                                                                                                                                                                                  speed = 1800 rpm
implementing dual-voltage electrical systems have been proposed, but                                                                                                                                                                                              Ls = 105 uH                                                                                      speed = 6000 rpm
                                                                                                                                                                                                                                                                  Rs = 33 mOhm
most suffer from severe cost or performance limitations. This research                                                                                                                                                              i42(A)                        k = 0.004 V-s/rad-A
                                                                                                                                                                                                                                                                                                                                                                   Ls = 105 uH
                                                                                                                                                                                                                                                                                                                                                                   Rs = 33 mOhm
                                                                                                                                                                                                                                                                  vary r , h, if
explores the design of alternators incorporating dual-output switched-mode                                                                                                                                                                                                                                                                                         k = 0.004 V-s/rad-A
                                                                                                                                                                                                                                                                                                                                                                   vary r , h, if

rectifiers (SMR). The proposed approach enables the full load-matched
power capability of the alternator machine to be achieved, with power
delivered to the two outputs in any desired combination. A prototype
                                                                                                                                                                                                                                                        i14 (A)
system has been developed. Experimental results are presented that                                                                                              V14           V42
                                                                                                                                                                                                                                                    Simulated alternator output over the control range
demonstrate the feasibility and high performance of the approach.
                                                                                                                                                                                                                                                 (hatched regions represent achievable operating points)

                                                                                                                                  fsw = 100 kHz

DUAL-VOLTAGE ARCHITECTURES                                                                                                  Alternator with SMR                  .


                                                                                                         How the circuit works                                                                                                    SMR voltage and
                                                                                                                                                                                                                                  gating waveforms
          1.     dc/dc converter-based architecture                            The switching frequency is much                                                                               i42
                                                                                                                                                                                                                                  over a switching
                                                                               higher than the alternator electrical                                                                                                              cycle                                                                                         q1
Use of a dc/dc converter can                                                   frequency. Field control and duty ratio ifield                                         ix     D3                                                                                                                                                                  (inverted)
                                                                                                                                                                                        D2              i14
result in a system having very                                                 control of the SMR are used together
good performance, but:                                                         to regulate the outputs and achieve                                                                  +        Q2
                                                                               good machine utilization.                                                                     Q1                       V14                 V42
                                                                                                                                                                     q1(t)          vX        q2(t)
•dc/dc converters are expensive                                                During a switching cycle, the rectified
                                                                               alternator current ix is approximately
                                                                                                                                                                                     -                                                                                                         25
by automotive standards                                                                                                                                                                                                                                                                                 4.2A (field current)
                                                                               constant. Each switching cycle is                                        Alternative rectifier implementation
                                                                               broken up into three time segments:                                                  (Simplified)                                                                                                                        3.6A
•Size, packaging and cooling                                                                                                                                                                                                                                                                   20

are significant challenges                                                     •In the first segment, which we denote         v x(t)              42V                                                                                                                                                   2.81A

                                                                                                                                                                     14V                                                  A

                                                                                                                                                                                                                                                                        42V bus currents (A)
                                                                               as being hrT in length, the diode D3                                                                                                                                                                            15
                                                                               conducts delivering the current ix to the                                                                                      t
                                                                                                                                                          hrT                hT                T                                   Experimental                                                         2.33A
                                                                               42V bus.                                       Q1(t)                                                                                                alternator output
                                                                               •In the second time period, which lasts                                                                                                    B                                                                    10 1.94A

                                                                                                                                                                                                              t                    currents across
         2.     dual-wound alternator architecture                             for h(1-r)T, switch Q2 is on. In this                                                                                                               control range                                                        2.33A
                                                                               period diode D2 and switch Q2                  Q2(t)                                                                                       C        at 1800 rpm
                                                                               conduct, delivering the rectified                                                                                                  t                (idle speed )
Uses an alternator having a                                                    alternator current ix to the 14V bus.                                                                                                                                                                            0

separate set of stator windings to                                             •In the final time period, lasting (1-h)T,     i14                                                                                          D
                                                                                                                                                                                                                                                                                                    0           10        20        30      40        50
                                                                                                                                                                                                                                                                                                                                    14V bus currents (A)
                                                                                                                                                                                                                                                                                                                                                              60         70         80

supply each output                                                             switch Q1 conducts and the current ix                                                                                              t
                                                                               is shunted to the return bringing the
Limitations                                                                    voltage vx to zero. (See waveforms “A”          i42                                                                                         E                                                                        4.2A (field current)

•field control is common to both                                               “D” and “E”)                                                                                                                           t                                                                        80
outputs. This poses serious                                                                                                                                                                                                                                                                    70

difficulties in regulating both                                                Control Equations                                                                                                                                                                                               60

                                                                                                                                                                                                                                                                        42V bus currents (A)
                                                                                      4 Ls                             •   i*42 and i*14 are desired (reference) currents                                                                                                                           2.81A

                                                                                if        (V14i14  V42i42 )
                                                                                                *        *                                                                                                                                                                                     50
•utilization of alternator machine                                                   3k 
                                                                                                                       •   h, r are switching time controls                                                                       alternator output                                            40 2.33A

power capability is poor for                                                             *                             •   if is the field current                                                                                currents across                                              30 1.94A
some operating conditions                                                        r * *  42                            •   Ls is the armature synchronous inductance (per phase)                                                  control range
                                                                                   i14  i42
                                                                                                                                                                                                                                                                                               20 2.33A

                                                                                                                       •   k is the machine constant (Volt-sec per Amp-rad)                                                       at 6000 rpm
         3.     dual-rectified alternator architecture                                                                 •    is alternator ac electrical frequency
                                                                                                                                                                                                                                  (cruising speed )                                            10

                         (Phase-controlled rectifier)                                          ki f                                                                                                                                                                                               1.94A

                                                                                                                                                                                                                                                                                                    0                20        40           60           80          100            120

                                                                                     2 2(rV42  (1  r )V14 )                                                                                                                                                                                                                       14V bus currents (A)

 A dual-output phase-controlled
                                                                                                                                                                                                                                The simulation and experimental results demonstrate the ability to simultaneously
 rectifier is used
                                                                                                                                                                                                                                control power to both outputs

 •Machine utilization is poor for                                                                                                                                                                                               References:
 some loading conditions
                                                                                                                                                                                                                                D. J. Perreault and V. Caliskan. “A New Design for Automotive Alternators,” 2000 International
                                                                                                                                                                                                                                Congress on Transportation Electronics. (Convergence 2000), pp 583 – 594, October 2000,
 •Extremely large output filters                             V14      V42
                                                                                                                                                                                                                                SAE paper 2000 – 01 – C084.
 are required due to the large,
 low frequency current ripple                                                                                                                                                                                                    G. Hassan, D. J. Perreault, and T.A. Keim. “Design of Dual-Output Alternators with Switched-
                                                                                                                                                                                                                                 Mode Rectification,” 2003 IEEE Power Electronics Specialists Conference, June 2003.
 appearing at the outputs                                                                                         Experimental setup

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