Transactions on Engineering and Sciences
Vol. 2, Issue 5, May 2014
ISSN: 2347-1964 Online 2347-1875 Print
Power Factor Corrected (PFC) Zeta Converter Fed
BLDC Motor
M.B.Jyothi1
1PG
C.Gnanavel2
Scholar, Dept. of EEE, Vivekanandha Institute of Engineering and Technology for Women.
Professor, Dept. of EEE, Vivekanandha Institute of Engineering and Technology for Women.
2Assistant
Abstract—A power factor corrected (PFC) zeta converter feeding Brushless DC (BLDC) motor drive with
direct back emf detection is proposed in this paper. The voltage of a DC link capacitor which is lying
between zeta converter and Voltage Source Inverter (VSI) is controlled by a single phase power supply
followed by a uncontrolled bridge rectifier and zeta converter.
Index terms: PFC, BLDC Motor, Sensor Less, Back EMF, Voltage Control, VSI, Zeta Converter.
I.
INTRODUCTION
As imposed by the International PQ (Power Quality) standards like IEC 61000-3-2 the requirement of
improved power quality at the AC mains is becoming essential. The power factor above 0.9 and THD (Total
Harmonic Distortion) below 5% for Class-D (under 600 W, <16 A, single phase) applications recommends
the use of BLDC (Brush Less DC) motor drive. Brushless dc motors have been desired for small horsepower
control motors due to their high efficiency and low maintenance. The control complexity for variable speed
control and the high cost of the electric drive reduce the widespread use of brushless dc motor. There are
many AC-DC converters topologies reported to meet the recommended PQ standards.
BLDC motor is an ideal motor for low-medium power applications because of its high efficiency, high
torque/inertia ratio, low maintenance and wide range of speed control. Two stage PFC converters are
widely in practice in which first stage is used for the power factor correction which is preferably a boost
converter and second stage for voltage regulation which can be any converter topology depending upon the
requirement. The two stage topology used in conventional systems are complex and results in more losses
and higher cost which is undesirable; so a single stage Zeta converter is proposed here which perform DC
link voltage control and thus correcting the power factor. The operation is studied for a Zeta converter
working in DICM (Discontinuous Inductor Current Mode) hence a voltage follower approach is used.
II. BRUSHLESS DC (BLDC) MOTOR
Brushless dc motor is a permanent magnet synchronous motor, with permanent magnets on the rotor
also with back EMF with trapezoidal shape. The rotor position determines the switching sequence. The
phase current of BLDC motor, is synchronized with the back EMF to produce constant torque at a constant
speed. The electronic switches replaces the mechanical commutation of the brushed dc motor, which supply
current to the motor windings which is a function of the rotor position. This kind of ac motor is called
brushless dc motor, because it has similar performance as that of the traditional dc motor with
commutations. These motors are usually controlled using a three-phase inverter, which requires a rotor
position sensor which is required for starting and providing the proper commutation sequence to control
the inverter. Hall sensors can be used as these position sensors, resolvers, or absolute position sensors .
Figure 1: Proposed zeta converter fed BLDC motor drive
A. Equations for designing
The duty ratio D for the Zeta converter (buck-boost) is given as
52
Techscripts
Transactions on Engineering and Sciences
Vol. 2, Issue 5, May 2014
D=
where
ISSN: 2347-1964 Online 2347-1875 Print
Vdc
(Vdc + Vin )
(1)
V dc represents the DC link voltage of Zeta converter.
If the permitted ripple of current in input inductor Li and output inductor Lo is given as
and
∆i Lo respectively, then the inductor value Li and Lo are given as
Li =
LO =
where
D.Vin
{ f s .∆i Li }
(2)
(1− D) .V
{ f s .(∆iLo )} dc
(3)
f s the switching frequency. For the critical conduction mode,
∆ i Li = 2 .. I dc
LO (critical ) =
(4)
(1 − D).Vdc
{f
s
}
.(2.I dc )
The value of intermediate capacitor
Ci =
D.I dc
{f
s
.∆Vin
(5)
C i is given as
}
(6)
The value capacitor Cd is given as
Cd =
I dc
(2ω.∆Vdc )
(7)
The PFC converter and the sensor less BLDC motor drive are modeled for the proposed drive scheme.
The control scheme of the PFC converter consists of following three blocks.
B. Reference Voltage Generator
The speed of BLDC motor is proportional to the DC link voltage of the VSI, hence a reference voltage
generator is required to produces an equivalent voltage corresponding to the particular reference speed of
the BLDC motor. The reference voltage generator produces a voltage by multiplying the speed with a
constant value known as the voltage constant (Kb) of the BLDC motor.
C. Speed Controller
An error of the Vdc* and Vdc is given to a PI (Proportional Integral) speed controller which generates a
controlled output corresponding to the error signal. The error voltage Ve at any instant of time k is as,
Ve (k ) = Vdc ∗ (k ) − Vdc (k )
And the output
(8)
of the PI controller is given by,
VC (k ) = VC (k − 1) + K P (Ve (k ) − VC (k − 1) + K i .v(k ))
(9)
Where, Kp is the proportional gain and Ki the integral gain constant.
D. PWM Generator
The dynamic modeling of the BLDC motor is governed by the following equations given as
Van = Ra ia + pλa + ean
(10)
Vbn = Rb ib + pλb + ebn
(11)
Vcn = Rc ic + pλc + ecn
(12)
where p represents the differential operator,
,
and
are the per phase voltages,
,
represents back EMF and a, b, and c represents flux linkages,where Vao, Vbo, Vco are the three phase
voltages and Vno is the neutral voltage referred to the zero reference potential as shown in Figure.The flux
linkages are given as,
λa = Ls ia − M (ia + ic )
(13)
53
Techscripts
Transactions on Engineering and Sciences
Vol. 2, Issue 5, May 2014
ISSN: 2347-1964 Online 2347-1875 Print
λb = Ls ib − M (ia + ic )
(14)
λc = Ls ic − M (ia + ic )
(15)
Where, Ls is the self inductance per phase and M is the mutual inductance of the windings. Moreover
for star connected three phase windings of the stator,
i a + ib + i b = 0
(16)
The equation for torque is expressed as
(ean ia + ebn ib + ecn ic )
Te =
ωr
(17)
is the rotor speed in electrical rad/sec.
Where
III. SIMULATED PERFORMANCE OF PROPOSED BLDC MOTOR DRIVE
The performance of proposed BLDC motor drive is simulated in MATLAB-Simulink environment
using the Sim-Power-System toolbox. The performance evaluation of the proposed drive is categorized in
terms of performance of BLDC motor, zeta converter and the achieved power quality indices obtained at
AC mains.
The rotor speed, stator current, back emf voltage, supply voltage, torque of the BLDC motor are
clearly shown in the following graphs. Performance of SEPIC fed BLDC motor drive in DICM mode and
power quality performance with input AC voltage variation for zeta converter fed BLDC motor drive is
also evaluated on parameters such as supply voltage(VS),THD ,PF and Is .
Electromagnetic Torque
Stator current(A)
Rotor speed (rad/sec)
3
4000
2.5
3500
Back emf voltage
3
1000
800
2
600
3000
2
400
C u r r e n t( A )
S p eed (R p m )
1.5
2000
1
1500
V o lta g e (V )
T o rq u e(N m )
1
2500
200
0
-1
0.5
0
-200
-400
1000
-600
0
-2
500
-800
-0.5
0
2
4
6
8
Time (s)
10
12
14
4
x 10
0
0
2
4
6
8
Time(s)
10
12
-3
14
0
2
4
4
6
8
Time(sec)
x 10
10
12
14
4
x 10
-1000
0
2
4
6
8
10
12
Time(s)
14
4
x 10
(1)
(2)
(3)
(4)
Figure 1: Electromagnetic torque waveform, Figure 2: Rotor speed waveform, Figure 3: Stator current
waveform, Figure 4: Back emf voltage waveform
IV. CONCLUSION
Voltage control and power factor correction of a PFC Zeta converter fed BLDC motor drive is a simple
control using a voltage follower approach. A novel scheme of speed control using a single voltage sensor
has been proposed. Sensor less operation is used which eliminate the need of position sensor. The speed
control with improved power quality at the AC mains for a wide range of speed is achieved by the design of
single stage PFC converter system. Evaluation for varying input AC voltages are done and found
satisfactory performance details. The speed control and supply voltage variation have been obtained within
the limits which is set by International power quality standards.
ACKNOWLEDGMENT
I sincerely thank my guide for the complete support for my work. Also I thank all the members who
directly or indirectly helped me in completing this work.
REFERENCES
[1] R.W Erickson and D Maksimovic , “Fundementals of Power Electronics” ,2nd ed,Kluwer Academic
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
Publishers
“Limits for Harmonic current Emission , International standards IEC”.
M.H Rashid, “Power electronics handbook ,devices circuits and appliacations” 3rd edition.
PSIM, User Manual, 2004.
L. Dixon, “Average Current Mode Control of Switching Power Supplies,” Unitrode
Application Note U-140.
K. S. Fung, W. H. Ki, and P. K. T. Mok, “Analysis and Measurement of DCM Power Factor Correctors”
R. Zane and D. Maksimovic, “Nonlinear-Carrier Control for High- Power-Factor Rectifiers”
J. W. Kolar, H. Sree, N. Mohan, and F. C. Zach, “Novel Aspects of Power electronics”.
54
Techscripts