faces of this machine can be provided with a special damper winding, and the rotor is ... armature reaction harmonic fields which are not present in an induction ...
Furthermore, the description in this
paper can
not only to generators but also to motors.
be applied
In this paper, a brushless, exciterless, single-phase synchronous machine can be diverted from a three-phase machine. All phase parts of the armature winding which is arranged for a three-phase double-star connection are used as the stator winding in the single-phase synchronous machine, as shown in Fig. 1. One phase part of the above three-phase double-star armature winding is used as an auxiliary stator winding, and the other two phase parts are used as an armature winding. Two special features of the construction of the singlephase synchronous macine of this paper are that the pole faces of this machine can be provided with a special damper winding, and the rotor is provided with balanced two phase field windings [31, [4]. It has been shown theoretically and experimentally that the rotating electric machine made for a three-phase synchronous machine can be diverted as a brushless and exciterless, single-phase, sinusoidal wave synchronous machine having an auxiliary stator winding. It has been an important problem to be solved in this study that the wave forms of such a single-phase synchronous machines are to be sinusoidal. It has been confirmed experimentally in this study that the wave forms of the generator terminal voltage and of the motor current are almost completely sinusoidal. This will be understood when the wave forms shown by the oscillograms in Fig. 2 and Fig. 3 are compared with those shown in the prior paper [11. This is a result having been obtained by being provided with a special damper winding and a balanced two phase field winding in the rotor. It is naturally favourable for the loads that wave forms of generator terminal voltages are sinusoidal. On the other hand, it is favourable for increasing the motor efficiencies that wave forms of the motor currents are sinusoidal. Such single-phase synchronous machines can be used widely as portable generators supplying the small loads which require sinusoidal wave voltage with electric power and as domestic motors for driving the small loads. We consider further works necessary in this system about study of design of damper windings and simplifcation of rotor constructions.
References [11 F. Shibata, T. Kohrin, "A brushless, self-excited singlephase synchronous generator operating with load and exciting currents flowing in armature," IEEE. Trans. on Energy Conversion, vol. EC-2, No. 2, June, 1987, pp. 254-261. [21 F. Shibata, US. Patent No. 4656410. [31 F. Shibata, Japanese Patent Application S-61-85, 716. (Japanese). [41 F. Shibata, US. Patent Application No. 06/870, 621.
im
if
Fig. 1. A fundamental connection of a brushless, exciterless, single-phase, sinusoidal wave synchronous machine having an auxiliary stator winding.
Vm=181 [V]
\l~
".
0
Fig. 2. A
wave
/"-
ll
I11
'\
form of the generator terminal voltage.
Im=ll 9(Al \
\,/
\
Fig. 3. A
wave
\.~/
\1
form of the motor load current.
88 SM 615-7 June 1989
Core Loss in Buried Magnet Permanent Magnet Synchronous Motors Rich Schiferl and T. A. Lipo University of Wisconsin Madison, Wisconsin Permanent magnet synchronous motors with magnets buried below the rotor outer surface have been considered for constant and variable speed applications over the past decade due to the introduction of new magnet materials. In line start, constant speed motors the magnets are placed below a starting cage which lies near the rotor surface as shown in Figure 1. Here the added cost of magnet material must be justified by a reduction in steady state losses over that of an induction motor before mass market penetration will be realized. The stator core loss component of these losses in a permanent magnet motor will be a result of not only fundamental component fields but also magnet and
5454
IEEE Power Engineering Review, June June 1989 Engineering Review,
armature reaction harmonic fields which are not present in an
induction machine. Under variable speed operation the core loss is also important, especially at high speed where motor losses may limit output power. In this paper the measured and calculated stator core loss characteristics of a buried magnet synchronous motor are presented. Core Loss in a Line Start Motor The measured core loss characteristics for 60 Hz operation of a line start, 230 volt, 2 hp buried magnet synchronous motor are given for two constant load conditions in Figure 2. Sinusoidal terminal voltage was applied to the motor for all operating voltages. An increase in core loss with decreasing voltage is evident for both motor loads at low terminal voltage levels. Examination of the measured air gap field of the motor operating at low terminal voltage levels indicated a large amount of harmonic distortion. The penetration of these air gap harmonic fields in the stator core is the cause of the increased core loss under these operating conditions. Two dimensional finite element magnetic field modelling of the line start motor was used to calculate the stator core loss. Total core loss was calculated in each stator core finite element using the flux density waveforms obtained from multiple field solutions. Input 60 Hz hysteresis and eddy current loss data was utilized along with waveform distortion factors in order to accurately predict the core loss associated with each element. Total calculated stator core loss obtained from element flux density waveforms modelled with seven time harmonics is plotted in Figure 2. Also plotted are the calculated core loss characteristics derived from element flux density waveforms which include only the fundamental component. Notice that the stator harmonic fields act to increase the motor core loss by up to a factor of six at low voltage levels. Motor operation at these low fundamental flux levels will be realized if a buried magnet motor is run in the flux weakening, high speed operating mode of a variable speed drive.
Origin of the Stator Core Harmonic Fields Detailed analysis of the magnetic field distribution of the buried magnet motor suggests that the increase in air gap and stator core harmonic fields at low voltage levels are a direct result of the redistribution of rotor armature reaction flux due to localized iron saturation in the motor q axis. In particular, when armature currents act to decrease the magnet air gap flux the magnet leakage and armature reaction flux act to saturate the q axis rotor bridges causing armature reaction pole to pole flux to pass from one rotor pole face to the stator teeth and back to the other rotor pole face. This zigzag flux distorts the stator core flux density waveforms causing an increase in steady state core loss. At high motor flux levels the armature reaction fields aid the magnet and pull the q axis bridges out of saturation. Now the armature reaction pole to pole flux remains in the rotor and the air gap and core flux density remains sinusoidal.
field. Since buried magnet motors must have some form of nonmagnetic or saturating rotor q axis flux barriers the increased stator core loss due to this field distortion should be expected in all buried magnet motor designs at low fundamental air gap flux levels. flux barrIers
tarting
cage
d axis Fig. 1. One pole rotor cross section of a four pole, line start, buried magnet synchronous motor.
a) L
80 5
CClculated
x Inluing& 1Harm.)
0[> Including 7 Harm.
J
R
40
2320 -x R o680
20 b) '0
uie
x ~~x
1 M
ed asu lS0
Calculated
x
ex.. 200 250
acoe
Including 1 Harm.
to H&Vlarm. aIinldng
alclatd ad masuedacoredlos-f,hetw.h Fig.2. oo o 0 zoeain mantsnhoou ~ ~~7. ~ buried
Conclusion The presence of flux barriers to rotor magnet flux in the q axis prevents the armature reaction demagnetizing flux from staying in the rotor. The resulting pole to pole zigzag flux increases the harmonic distortion of the stator core magnetic
IEEE Power Engineering Review, June 19899
55
