Study on Flywheel-rotor Permanent-magnet Generator for Miniature
Tractor
ZHANG Xueyi SHI Liwei
School of Traffic & Vehicle Engineering, Shandong University of technology,
shiliwei@sdut.edu.cn
P.R.China, 610036
Abstract
The flywheel-rotor permanent-magnet generator, which combines the flywheel of the
engine and the outer rotor of the generator, has compact conformation and high stock utilization. When
the flywheel-rotor rotating, magnetic field rotates with it, the armature coil cuts magnetic-curve, and
produces electromotive force. The parallel electronic regulator with zero current blockade function is
designed, output voltage is stabilized when the speed of rotation is high, the problem of instable voltage
which generated by the miniature tractor’s permanent magnet generator at wide speed and wide load is
solved.
Key words flywheel-rotor; permanent-magnet generator; voltage-stabilized; tractor
1 Introduction
With the development of the rural economic of our nation, the production lot of the miniature
tractor increase continually, the yearly output upwards of two million, which facilitate the rural
economic greatly. At present most miniature tractor use the permanent-magnet alternator, which still has
the problem: At low speed light is dark; high speed damage the light. If the tractor run at night, road
surface condition is bad, especially when two tractors pass the same place at same time or steering, the
rotate speed of the engine is low, in the dark, traffic accident is easily to occur. So it’s very necessary to
develop a new kind of flywheel-rotor permanent-magnet generator, the conformation of which is
compact, and the light is bright no matter the engine rotate speed is low or high.
2 Ascertain of major parameter
2.1 Range of output power, rotate speed and regulated voltage
The generator produces direct current for the head lamp, direction signal light and klaxon of the
tractor. Miniature tractor needs about 120W electric quantity, so the output power is designed for 150W.
～
The engine’s power of the miniature tractor in our nation is about 5.9KW 13.2KW, the idle speed
is around 1000r/min, maximum speed is 2200r/min, considering the new designed generator install
between the engine body and flywheel, the rotate speed of the generator range from 1000r/min to
2200r/min.
According to the P.R.C. Mechanism Industry Standard on Generator for Agriculture Automobile
Appliance JB/T8582.6—2001, when the rotate speeds of the generator range from 1000r/min to
2200r/min the output voltage should between 8.0V and 14.5V. But the output voltage of the generator
～
used at present is only about 5V 6V when the engine is idling, which can’t satisfy the low speed
～
lighting of the miniature tractor, so the scope of voltage regulation should be 11.0V 14.5V when the
～
rotate speed of the generator is between 1000r/min 2200r/min.
2.2 Design of major parameter
The fly-wheel permanent-magnet generator composes of electronic regulator, rotor and stator. The
crankshaft, flywheel, permanent magnet and nonmagnetic fixing block compose the rotor; the stator
core, stator bracket and armature winding compose the stator. The permanent magnet material and the
nonmagnetic fixing block fixed on the internal surface of the flywheel with bolt alternately; the
generator combines the flywheel of the engine and the outer rotor of the generator; the stator fixed on
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the engine body with bolt. The generator has high stock utilization, low cost, and long life, the compact
conformation is on the safe side. The structure of the generator is shown in figure 1.
Figure 1 The structure of flywheel-rotor permanent magnet generator
1.engine body 2.insulating spacer 3.nonmagnetic fixing block 4.bolt 5.flywheel 6.stator core 7.armature
winding 8.threaded bolt 9.stator bracket 10.crankshaft 11.nut 12. permanent magnet
2.2.1 Calculating the circle amount of the winding
According to the electromagnetism principium formula, calculate the circle amount of the winding:
N=
E0
4k B fk wφ 0
Where E0——electromotive force of generator as empty load
kB——waveform factor when magnetic field in air gap obeys the sinusoidal functions kB =1.11
f——frequency,
，
f =
pn
60
，
，
，
p——number of pole pairs the permanent magnet generator is designed for 12 poles p=6;
n——rotate speed (r/min);
kW——winding factor kW =0.92;
Φ0 ——Effective magnetic flux through stator winding, (Weber)
，
Φ0 =
，
Φδ
σ0
Where σ 0 ——magnetic leakage coefficient, the radial rotor
here σ 0 =1.05
Φδ ——magnetic flux of per pole in air gap,
Φδ = αBδ S δ = αBδ τLδ
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～ ，
without pole shoes σ 0 =1.05 1.2
σ
0
，
Where α ——pole arc coefficient the radial rotor without pole shoes
selects α =0.65
Bδ ——magnetic induction on zero load, Bδ = (0.75 ~ 0.85)B r
α
B
B
α =0.6～0.7,
the design
δ
γ
Br ——remanence intensity, (T)
τ
τ
——pole pitch, (m);
τ=
πD
2p
D——outer stator diameter, (m)
Lδ ——axial length of air gap. (m)
2.2.2 Calculation of the Magnet Steel Dimension
Calculation of the magnet steel dimension is based on the formula:
L
δ
2
PσC k
k
V = N 0 F α . i ×10 − 2 ( m3 )
3.54k B fBδ H δ ki −1
Where PN ——apparent power of generator when its power factor equal to zero, namely
cos ϕ =0, (W), When cos ϕ >0, the function that magneto armature neutralize the magnetic field of
cos ϕ
permanent magnet is reduced, the volume of permanent magnet could shrink,
′
ΡΝ = ΡN cosϕ ——apparent power of generator when cos ϕ >0, W.
C F ——coefficient of magnetometive force, when magnetic domain is not in
saturation C F =1.1~1.15, the design selects C F =1.1
k a ——coefficient of longitudinal axial armature reaction
απ + sin απ
ka =
απ
4 sin
2
H δ ——short circuit magnetic field strength,
H δ =(0.6~0.7) H C ; H C ——coercive force of permanent magnet KA/m
ki ——short circuit current multiple, the design selects ki =2.
I n ——short circuit current, (A)
I N ——working current, (A)
（
I
）
n
3 Principle of Electronic Regulator
， ，
，
Electronic Regulator consists of circuit component PCB aluminum die-casting shell down-lead.
The welded PCB is fixed inside the aluminum shell, and then molded with unsaturated colophony. The
regular is dustproof, moistureproof, shakeproof and shock-resisting. So it adapt well to the worse
surroundings. Electronic regulator circuit diagram is shown in figure 2.
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M
SCR1
SCR1
D2
JF
C1
R2
A
T1
DW
R1
D1
D3
Figure 2 parallel electronic regulator circuit diagram
M—current transformer; D 1 ,D 2 ,D 3 —diode; T1 —audion; SCR 1 ,SCR 2 —silicon controlled rectifier;
D W—Zener diode; R1 ,R 2 —resistance; C1 —capacitance; JF 1 —alternator
When the speed of the generator is low, using the permanent magnet with high remanence intensity
and the optimization design of the generator—adding the poles and the number of armature winding to
ensure that the output voltage is high enough.
When the generator’s load is zero, there is no current pass through the circuit, so there is no output
signal in the secondary coil of the current transformer M, Silicon controlled rectifier SCR1 cut off,
SCR2 cut off either. Working in the daytime, the floodlit doesn’t work, there is no current in the circuit,
although the rotor of the generator rotates, generator has no output power, which not only reduce the
energy loss, but also ensure the reliability of electric regulator and generator, further more, it’s prolong
the service life of the generator.
When the generator has load, current pass through the circuit, there is output signal in the
secondary coil of the current transformer M, silicon controlled rectifier SCR1 turns on. When generator
starts, the rotate speed is low, so the output voltage is low, it is lower than the target stabilized voltage.
The voltage between the emitter of audion T 1 and A point is less than breakdown voltage of Zener diode
DW, T 1 is cut-off, it can’t provide ignition current for the grid of SCR2 , the silicon controlled rectifier
SCR2 doesn’t turn on, the output voltage of the electronic regulator is the voltage generated by the
generator.
With the rise of the rotate speed, the output voltage is ascending, when the voltage between the
emitter of audion T 1 and point A is high enough to break through Zener diode Dw, audion T 1 is thus turn
on. T 1 provide ignition current for the grid of silicon controlled rectifier SCR2 , SCR2 thus turn on,
which instantaneous short the generator, the voltage waveform is cut a part to reduce output voltage,
SCR2 cut-off when there is no forward voltage. The output voltage rise along with the SCR2 cut-off, the
voltage between the emitter of audion T 1 and point A is also ascending, when the voltage is high enough
to break through Zener diode Dw again, T 1 turn on, provide ignition current for the grid of silicon
controlled rectifier SCR2 , SCR2 thus turn on again, which short the generator again, output voltage
reduce, this go round and round, SCR2 repeat in the state of on and off, it’s steady the output voltage of
the electronic regulator. In addition, when silicon controlled rectifier SCR2 turn on, is produce induced
current with the short current property, the demagnetization and direct current magnetic action reduce
voltage amplitude value either, so the goal of voltage stabilizing is achieved. The output voltage
oscillograms before/after the regulation are shown in figure 3.
U
0
U
ωt
ωt
0
（ a） The output voltage before regulation （ b） The output voltage after regulation
Figure 3.The output voltage oscillogram before/after the regulation
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4 Performance test
Flywheel-rotor permanent-magnet generator for miniature tractor has a rotor of 12 star poles
without pole shoes, the rated voltage is 14V and the nominal power is 150W, nominal speed is
2000r/min. The magnetic material is Y30BH ferrite, its remanent magnetism density Br=0.41T (Tesla),
～
coercive force Hc=220 240KA/m (Oersted), maximum product of the magnetic energy (BH)max=27.1
~30.3KJ/m3. The test results of this new type generator on load of 150W, and from low rotary speed to
high speed are shown in table 1.
Table 1 The test results of the generator output voltage
Voltage Speed
Machine
1000r/min
2000r/min
2200r/min
1
12.0
14.1
14.2
2
12.2
14.2
14.3
3
12.1
13.9
14.1
4
5
11.9
11.7
13.8
14.0
14.0
14.2
From the chart above we can see that, as the rotate speed range from 1000r/min to 2200r/min, the
output voltage stays between 11.7V and 14.3V, this data achieves the design requirements, and surpasses
the national mechanical industry standard.
5 Conclusions
①The generator combines the flywheel of the engine and the outer rotor of the generator, which
has high stock utilization, low cost, and long life, and the compact conformation is on the safe side.
The electronic regulator adopts a current transformer with zero current blockade function, when
the generator has no load, the regulator doesn’t work, so the reliability of the generator was heightened.
As the rotate speed varies from 1000r/min to 2200r/min, the output voltage stays between 11.7V
and 14.3V, and performance of stabilizing the voltage is well. The illume problem of the miniature
tractor at low speed has solved.
②
③
References
～
[1] Chen Junfeng. Permanent Magnet Generator. Beijing: Chinese Machine Press,(1983), p1 70.
[2] Tang Renyuan. Modern Permanent Magnet Machine—Theory and Design.Beijing: Chinese Machine Press, 2000
p273 307.
[3] Hu Mingyi. Configuration Principle and Overhaul of The Generator for Vehicle, Tractor and Motorcycle.Beijing:
Beijing Institute of Technology Press, (1998), p128 185.
[4] Li Zhongming, Liu Weiguo and Liu Jinglin. Rare Earth Permanent Magnet Electrical Machines. National
Defense Industry Press (1997) p8 38
[5] Ma Youliang, Ding Weidong. Electric Appliance and Electronic Control System for Automobile. Beijing:China
Machine Press, 1,(2003), p486.
[6] Liu Jinglin, Li Zhongming. Analysis on Small Rare Earth PM Synchronous Generator and Its Application. S& M
Electric Machines,5(2001),p14 16.
[7] Zhang Xueyi, Du Qinjun, Tan Derong. Magneto and Voltage constant Generator with Tension Wheel for Farm
Transport Vehicles. Transactions of The Chinese Society of Agricultural Machinery, 6(2000),p98 100.
[8] Zhang Xueyi. Study on the Voltage-regulating Theory of Permanent Magnet Generating Set for Vehicles
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Transactions of the Chinese Society of Agriculture Machinery 1 (2005), p130 133.
[9] P.R.C. Mechanism Industry Standard on Generator for Agriculture Automobile Appliance JB/T8582.6—2001.
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