svpwm speed governing system of im based on dsp
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8/14/2019 SVPWM Speed Governing System of IM Based on DSP
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SVPWM Speed Governing System of Induction
Motor Based on DSP
Zhiyong Du,Xianfang WangCollege of Henan Mechanical and Electrical Engineering, Xinxiang, China,453002,e-mail:zhydu@163.comDepartment of Information Engineering/Henan Institute of Science and Technology,Xinxiang,China,453003
e-mail: 2wangfang@163.com, xfwang11@sina.comSchool of Communication and Control Engineering/Southern Yangtze University, Wuxi, China, 214122
Abstract Vector control technology is regard as a kindof controlling manner of AC asynchronous motor, and it isalready become the first method of the high-performancevariable-frequency speed regulating system. Compared withSPWM, SVPWM (Space Vector Pulse Width Modulation)
has been used widely because it has better performance. Thispaper introduced the basic principle of voltage SVPWM andvector control. A full-digital solution with TMS320LF2407using simplified SVPWM control method is presented.Through the experiment of controlling to a practical motor,the resulted shows that this method is feasible, the control-ling system has better dynamic and static performances andcontrolling effect, it would have a prospect widely used.
KeywordsSVPWM, Vector control, Variable-frequency
speed governing system, Dynamic and static performances,
DSP.
I. INTRODUCTION
The development and the application of Pulse Width
Modulation (PWM) technology have optimized perfor-mance of the frequency converter device, and it is applied
to all kinds of AC speed regulating system. In the special
way of vector modulation, the technology of SVPWM
modulation considers the motor and the PWM inverter as
an integer, on the base of the ideal magnetic linkage round
of AC motor of three-phase symmetrical sine voltage
supplied its power, use the effective magnetic linkage
vector produced in different switch modes of inverter to
come close to the criterion circle, that is, use a polygon to
approximate a circle[1]. The SVPWM control method has
some advanced merits compared with classical SPWM
controlling method, for example, direct physical signifi-cance, simple mathematic model, easy computer real-time
controlling, and small torque wave, low noise, simple
control, low cost of power, high effect of utilization of
DC voltage. At present time, this technology would be
applied widely whether in open loop or closed loop speed
governing system.
The traditional SVPWM algorithm adopts largely
trigonometric functions and other nonlinearity functions.
When realized, it would need compute the vector effect
time and store a mass of data in advance [2]. But these
compute is complex, the processing is also very difficult,
therefore, it would be not easy to realize the digital real-
time controlling especially.In this paper, we introduced a simplified SVPWM al-
gorithm, which can realize a conversion speed regulation
system of influence motor. The theoretical analysis and
the experiment results show that this system has some
characteristics, such as realized simply, high utilization
ratio of voltage and small harmonic current, and so on.
Therefore, if adopted this system, the operation quality
of the induction motor would be improved greatly, these
results illustrate that this system would have some higher
practical values.
II . WORKING PRINCIPLES OF SVPWM
A. The Relationship Between Voltage Vector and Mag-
netic Linkage Vector
Where, we suppose that the AC induction motors
power is supplied from an ideal three-phase symmetrical
sine voltage, these stators phase voltage USA , USB , USCis add on three-phase coils respectively, their direction is
always on the axis of each coil, and its value is exchanged
in sine rule following on the time. That is
USA = UA UNUSB = UB UNUSC = UC UN
(1)
In this formula, UA, UB, UC are the three-phase phasevoltage of the inverter output; The Un is the voltages
of the midpoint O that relative to negative potential of
the inverter DC side when the stator winding is star
connection.
The US which is synthesized with the voltage spacevector of the stator winding is as follows
US = USA + USB + USC= 2
3(USA + USB ej
2
3 + USC ej
4
3)
= 23
(UA + UB ej 23 + UC e
j 43)
(2)
The above formula indicated: (1) The voltage space
vector Us that synthesized by three phase voltage space
vectors addition is a space vector rotating with power
source angle frequency speed. (2) In the PWM inverter-
motor system, the analysis of motor stator voltage space
vector can change into the analysis of inverter space
vector [3].
In the same way, we can define the magnetic linkage
space vector S is
S = SA + SB + SC (3)
EUROCON 2007 The International Conference on Computer as a Tool Warsaw, September 9-12
1-4244-0813-X/07/$20.00 2007 IEEE. 45
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If ignoring the effect of resistant motor stator, then Scan be obtained by integral the voltage space vector to
time.
When the inverter outs put a voltage space vector
Ui(i = 0 7), the magnetic linkage space vectors S canbe expressed as follows:
S = S0 + Ui t (4)
In this form, S0 is an initial magnetic linkage spacevector, is the action time of Ui .
When Ui is a nonzero voltage vector, the magnetic link-age space vector sets off from initial location, whirligig
with the radius
2
3Ul
along the corresponding voltage
space vector direction. While Ui is zero voltage vector,S = S0, the magnetic linkage space vector motion isrestricted. Therefore, chose the operator order and work
time of six nonzero voltage space vector rationally, that
would make the space vectors head turning in clockwise
or in anticlockwise, and would become the certain shape
trace. Choose the different form, being the different
magnetic linkage locus. In general, it makes the magnetic
linkage locus approach a regular polygon or circular.
B. Mathematic Model of Voltage Form PWM Inverter
The power circuit adopted topology structure of the
three-phase voltage class inverter, as show in Fig.1 .The
Up and down switch component s of the inverter bridge
arm cant pass at any the same time. These switch would
be reciprocal state when we dont consider the died area,
Sa, Sb, Sc express three bridge arms state respectively,
1 indicated that the up-bridge arm pass, and 0 in-dicated that the down-bridge arm pass. UA, UB, UC arethe three-phase voltage outputs,Take pursuing negative
voltage shown by Fig.1 as a reference point, We canobtain:
UA = SaUdc, UB = SbUdc, UC = ScUdc
o
A
B
CS c
1 3 5
264
7
+
--
U dc Sa
Sb
Fig. 1. PWM inverter circuit.
Change the three-phase voltage to two-phase dq axissystem according to Clark Transform:
UdUq
=
2
3
1 1
2
1
2
03
2
3
2
UAUB
UC
(5)
The inverter has 8 kinds switch patterns, which
are 000, 001, 010, 011, 100, 101, 110 and 111. So,
we could obtain the 8-voltage space vectors:U0, U60, U120, U180, U240, U300, O000, O111. In thesevectors, O000 and O111 are zero vectors. The Fig.2 isinverters spatial distribution of the eight voltage space
vectors.
d
q
O 000
O 111
U 60 (110)
U 0(100)
U 120 (010)
U180(011)
U 240 (001) U 300 (101)
Fig. 2. Voltage space vectors.
C. Control of Magnetic Linkage Track
While the inverter output the basic voltage space vector
U0 alone, the arrow of the stator linkage vector wouldmove from A to B alone the direction of parallel U0,as show in Fig.3. When moving to B, if we changethe basic voltage space vector into U60, then the vectorarrow of the stator linkage vector also moving fromB to C in correspondingly. In this way, when 6 nonzerovoltage space vectors export alone in turns respectively,
the moving track of the head of stator linkage vector is a regular hexagon, as show in Fig.3.
U 0
U60U120
U180
U240 U300
01
2
34
5
A B
C
DE
F
Fig. 3. Regular hexagon magnetic linkage track.
But there are only six basic nonzero voltage space
vectors, if we want obtain polygon rotating magnetic field
as more as possible, it must has more switch states. One
commonly method is that it can obtain more switch states
use the linearity time combination of these six nonzero
basic voltage space vectors. The basic control principle
was shown as follows.
In Fig.4, Ux and Ux+60 are represent two adjacentbasic vectors of voltage space, Uout is the reference phasevoltage vector of the output, whose amplitude represents
the phase voltage amplitude, whose revolution angular
velocity is to export sine voltage angle frequency. Uoutwas come from the linearity time composed by Ux andUx+60, it is equal to vector sum of
t1TPWM
times Ux
and t2TPWM times Ux+60. Of which, t1 and t2 is the operatetime ofUx and Ux+60 respectively, TPWM is effect timeofUout.
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600
xPWM
UT
t 1
602
+x
PWM
U
T
t
d
q
U x
U x+ 60
U out
Fig. 4. The linearity combination of the voltage space vectors.
D. Calculation of the Voltage Vector Operating Time
As mentioned above, the voltage space vector of lin-
earity time combination is
Uout =t1
TPWMUx +
t2TPWM
Ux+60 (6)
In above formula, we projected Uout, Ux and Ux+60to coordinate system 0dq[4]. This formula may be wrotedown:
t1t2
= TPWM
Uxd Ux+60dUxq Ux+60q
1 UoutdUoutq
(7)
After when we would have
obtained Uxd Ux+60dUxq Ux+60q
1
,then can ascertain t1
and t2 right away.In Fig.3, when the inverter alone output zero vectors
O000 and O111, the magnetic linkage vector of themotor stator would be fixedly. According to theses char-
acteristic, intervene the zero vector effects t0 in TPWMperiod, make
TPWM = t1 + t2 + t3 (8)
By such method, it can adjust the angle frequency , andobtain frequency conversions purpose.
E. Ascertain Sector Number
We apart the Fig.3 into six sectors, every sector has asector No.(as show in Fig.3, 0, 1, 2, 3, 4, 5). Only whenwe have known which sector that Uout is located in, thencan ascertain which pair of adjacent basic voltage space
vector would be used to compose Uout.After Uoutd and Uoutq were given, we should calculate
B0, B1, B2 at first.
B0 = UoutqB1 = sin 60
0Uoutd sin 300UoutqB2 = sin60
0Uoutd sin 300Uoutq
(9)
Then calculate the P value
P = 4sign(B2) + 2sign(B1) + sign(B0) (10)
In the form, the sign(x) is a sign function. If x > 0,sign(x) = 1; x < 0,sign(x) = 0.
Finally, according to P value table and look-up TableI,then we can ascertain sector number.
TABLE I
P VALUE AND SECTOR NUMBER RELATION
P
Sector
654321
1 5 0 3 2 1
If we adopt above algorithm, it only needs the plus
minus and logical computation simply, then can ascertain
the location sector where the reference voltage vector be
in, and avoided calculating the complicated nonlinearity
function, this feature have an actual meaning for simpli-
fied the calculation and improve the response speed of
the system. Not only it can decrease the requirement for
controller calculation speed, but also the real time controlcan be realized easily.
III. REALIZATION OF SVPWM ARITHMETIC
THROUGH DSP
A. Event Manager of TMS320LF2407A DSP [5]
Event manager (EV) is a special module, which was
designed for controlling the motor. It can produce all
kinds of PWM waves, and these waves can adjust the
blind area. It can measure the rotating speed, divert and
angle displacement of the motor by the interface of the
increment photo-electricity coder, and measure the pulse
width by capture the power.There are 2 Event mangers in TMS320LF2407A DSP,
which are EVA and EVB. Every event manger has 2 gen-eral timers of16bit, has 8 pulse width modulation passesPWM of 16bit. 3 comparing units with programmingbead area control can produce 3 pairs of absolutely PWMwaves (ie.6 outputs), these 2 timers can produce 2 kindsabsolutely PWM waves. They could be realized: output
the symmetrical and asymmetric PWM wave; avoid out-
put pulse at the same time in up and gown bridges. During
the application of the motor controlled, the PWM circuit
could reduce the CPU overhead for producing PWM
wave and the workload of the user, also could simplifythe control soft for produce the symmetrical pulse width
modulation and symmetrical hardware.
B. Method of Output PWM Wave
We designed the method for produced PWM wave use
the periodic value of the periodic register and the com-
pared value of the comparator based on TMS320LF2407A
DSP. The periodic value is used to produce PWM wave
frequency (or period), the compare value is mainly used
to produce PWM wave pulse width.
According to using different comparator, there are two
methods to produce PWM wave: One use the timer
and the comparison register to realized, another use thecomparison unit to come true. The PWM wave that the
latter produced can add a blind spot.
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For obtained an output Wave with ideal form, it is
necessary not only set the value of control correctly, but
also need adopt the correct algorithm. For output the
space vector PWM wave, the consumer need sets up
the following register (choose the EVB module): 1)Setthe comparative form control register ARCTRB to define
output form of the compare output part. 2) If enablethe blind port, then must setup the blind port control
register DBT-CONB. 3) Setup the register of timer no.3speriod T3PR, that is the period of stipulating the PWM
waveform. 4) Initialize the comparison register CMPR4 6. 5) Set the comparison control register COMCONBto enable to the compare operation and the pattern of
the space vector PWM. 6) Set the timer no.3 to controlregister T3CON working in continuing increasing/ the
subtraction pattern [6, 7].
C. Seven Sections of Voltage Space Vector SVPWM Wave
To obtain a certain voltage of output, in a on-off cycle,whether how the switch order of the 3 switches state,it is OK if only the relation that was kept between the
switchs state in time was satisfied (7) and (8), this is
not limited for the precedence order of 3 kinds switchstates and the start time, so the optimized control may be
realized that reduced the number of these switch action
and the harmonic wave.
We may arrange the change order of 8 switch states inevery fan sector according the Table II when for making
the inverter change from a switch state to another switch
state, only change a bridge arm switch state, so that to
cut down the number of on/off times in the inverter.
TABLE II
THE STATE ALTERNATION ORDER OF SYMMETRICAL SVPWM
SWITCHES
Time
Sector
0
1
000
5
4
2
3
000
000
000
000
000
011001
011010
111110010
000100110111110100
110
111
111
111
111
101
101
100
001 101
011
101
011
001
000
000
010
010
000
000
000
100
001
T0 /4 T
0/4T
2 /2 T
2/2T
0 /2 T
0/4T
1/2
From Table II, we could know that the 3phase PWMwaves, which produced by symmetrical voltage space
vector, have some features as follows:
(1) Every phase and every PWM waves output only
makes the switch power tube switch one times.
(2) The positive and negative rotate of the motor is only
related to the choice of the fan sector.
(3) Every PWM wave all start and end at the zero
vectors O000, the zero vectors O111inserts in center, andthe zero vectors O000 and O111have the same effects
time.(4) The program of the motor revolution magnetic field
approaches circular is determined by the choice of the
sector TPWM. TPWM would be smaller, the magnetic
field would be more approached circular, but the Tzdecrease is limited by the allowed switch frequency of
the switch component.
(5) Compared with SPWM, its DC voltage utility factor
should be high 0.15, while the output voltage regulatingand controlling, the harmonic wave can be cut down in
an output voltage.
Adopted the control of the voltage space vector PWM,
could avoid unnecessary switch action, reduce switch
frequency, it could cut down the depreciation of the switch
by arranged the zero vectors meticulously.
D. DSP Software Designs of SVPWM Wave
In the program design of the SVPWM wave that
controlled by DSP, the modulation wave frequency was
input by exterior, the carrier frequency and the sampling
frequency are all 20 MHz. The function of frequency (its
domain:0
50HZ) and blind spot would be designed andrealized. The blind spot time is 1.6s, the crystal frequencyof the DSP is 10 MHz, 2 tomes frequency inside, the clockfrequency is 20 MHz, and the counting period is 50ns.
The program is composed of the main program and
the subprogram of the timer underflow interruption. The
task of the main program is initialization, and change
the adjusted ratio of the outside entering frequency into
angle frequency. According to U/F, determine amplitude
of the reference voltage. The function of the interruption
subprogram is work out the value of three comparison
registers in next PWM period during every PWM period,
and is send these values to the comparison register.
For this purpose, t0, t1 and t2 must be calculated outaccording to form (7) and (8).
Save scene
Compute the cornerincrease and reference
voltage phase angle
In the secondquadrant
In the first quadrant
In the third quadrant
SS=1,SC=1
SS=1,SC=-1
SS=-1,SC=-1
SS=-1,SC=1
Lookup table of sinand cos ,
And add the signal symbol
ComputeUoutd andUout according to
amplitud and phase angle
Computesector value
Compute address
of the inverse matrix
lable
Compute the head
address of the inverse
matrix lable
Compute the comparative value
0.5C1CMP- 1
0.5C2CMP- 20.25C0CMP-0
Send CMP- 0 to the firs t
Comparative register
Send CMP-0+CMP-1 to the first
Comparative register
to the firstComparative register
Restore scene
Y
N
N
N
Y
Y
Send CMP-0 +CMP-1+CMP-2
Fig. 5. The program flow graph of the timer interruption subprogram.
For programming easily, the period value of the peri-
odic register is equal to TPWM/2, and the Form (7) can
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be simplified:
0.5C10.5C2
=
Uxd Ux+60dUxq Ux+60q
1 UoutdUoutq
(11)
Where,C1 =t1
TPWM/2, C2 =
t2
TPWM/2.
The program flow graph of the timer interruption
subprogram as show in Fig.5
IV. EXPERIMENT RESULTS
Adopting the system designed in this paper, an exper-
iment was carried on with for a 1KW induction motor.These parameters are as the following: the carry frequency
is 20KH z, and the DC bus voltage is 70V.
(a) 30 Hz
(a) 50 Hz
Fig. 6. Current waves of each coil in different frequency.
When the DC bus voltage is 70V, In Fig.6, it shows thecurrent wave of the coil in different frequencies. From this
figure, it is seen clearly that the current wave of the coil
approaches the sin wave. Fig.7 shows the voltage wave
of the coil in different frequencies. From the figure, it isseen clearly the mutual difference of these line voltage of
coil is 1200.
V. CONCLUSION
In this paper, we adopted TMS320F2407 to design a
frequency speed control system of induction motor based
on SVPWM controlling. This is a new method to realize
the Variable-frequency speed governing system. Through
the experiments, it is indicated that this system could
improved the performance of the produced PWM wave in
the condition of non-increase the switch depreciation. At
the same time, it showed that square wave was output by
the wave generator of TMS320LF2407DSP event managemodule, this method simplified the development of soft
and hardware. And the quality and the robust of the
(a) 30 Hz
(a) 50 Hz
Fig. 7. Line voltage waves of each coil in different frequency.
SVPWM wave were also very good. These results illus-
trated that the system has a high control precision and has
good performances of dynamic and static. So, the above
method would have a certain value of popularization and
application..
REFERENCES
[1] Wang Xiao Ming et al, The electric motor DSP is controlled,Press of Beijing University of Aerospace, Beijing, China, 2004.
[2] B.K.Bose, Modern Power Electronics and AC Drives, Mechan-ical industry Press, Beijing, China, 2005.
[3] Huade Li, AC Speed Governing Controlling System, Press of electronic industry, Beijing, China, 2003.
[4] TI Company, AC Speed Governing Controlling System,TMS320LF2407A,TMS320LF2406A, DSP Controllers2002.
[5] Tiezhu Xu, Guoqing Xu, The AC speed regulation controls systembased on the DSP, Electric system and Automatic Proceedings,China, 2002, 14 (6).
[6] li Lin , Xiaojing Li, Yunfeng Jiang, SVPWM vector controls digiti-zation frequency speed regulating system base on DSP, Middle-Mini-type electric motor, China, 2004, 31 (5).
[7] [7] Yang-Gui Jie, Space vector pulse broad modulation methodresearch, Proceedings of the Chinese Society of ElectricalEngineering, China, 2001, 21 (5).
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