2014 IEEE Students’ Conference on Electrical, Electronics and Computer Science
Solar PV Stand-Alone Water Pumping System
Employing PMSM Drive
Menka Dubey, Shailendra Sharma, Member IEEE and Rakesh Saxena
Electrical Engineering Department
Shri G.S. Institute of Technology & Science
23 Park Road, Indore-452003, India
menkadubey@gmail.com, ssharma.iitd@gmail.com, rakeshsaxena@hotmail.com
Abstract - This paper deals with the stand alone solar PV
(Photo Voltaic) supplied PMSM (Permanent Magnet
Synchronous Motor) drive for water pumping system. An
interlink Boost converter is used between solar PV panel and DC
bus of PMSM drive. The DC bus voltage of PMSM drive is
maintained constant by controlling the duty cycle of boost
converter. Three phase VSI (Voltage Source Inverter) is
controlled to supply PMSM under change in solar irradiation to
regulate discharge of water. Solar PV stand–alone water
pumping system employing PMSM drive is modelled in
MATLAB/SIMULINK environment using the sim power system
toolboxes. The performance of the proposed system is obtained
under wide variation in PMSM speed with change in solar
irradiation.
Keywords- DC to DC boost converter; PMSM drive; photo
voltaic; vector control; water pumping system
I.
INTRODUCTION
Renewable energy penetrations are increased in power
sector to reduce dependency on fossil fuels [1]. Solar PV
(Photo-Voltaic) systems are now well recognized for trapping
solar energy. Solar energy has the greatest availability
compared to other energy sources. It has been estimated that
the amount of energy supplied to the earth in one day is
sufficient to cater energy needs of the earth of one year [2].
For such solar PV systems, maximum power point tracking
control is preferred for efficient operation [3]-[5]. Matsui et. al
have presented a MPPT control system for solar PV system by
utilizing steady state power balancing condition at DC link
[6]. It has further improved by Mikihiko for sensorless
application [7]. Integration of PV system with the grid fulfil
standard power quality requirements and it have been reported
in [8]-[10].
The solar PV system has found many potential
applications such as residential, vehicular, space air craft and
water pumping system [11]. PV water-pumping is highly
competitive compared to traditional energy technologies and
best suited for remote site applications that have small to
moderate power requirements. Most of the existing
photovoltaic irrigation systems offer a mechanical output
power from 0.85 kW up to 2.2 kW. The efficiency of
Induction motors are less compared to permanent magnet
motors, whereas DC machines are not suitable for submersible
978-1-4799-2526-1/14/$31.00©2014 IEEE
installations [12].
In recent years, the use of PMSM (Permanent Magnet
Synchronous Motors) are increased for drives applications due
to its high efficiency, large torque to weight ratio, longer life
and recent development in permanent magnet technologies
[13]-[15]. It need power processor for effective control [16].
PMSM become a serious challenger of induction motors in
hybrid electric vehicle applications [17]-[18].
This paper presents a stand alone solar PV supplied PMSM
drive for water pumping system. Pumping water is a universal
need for agriculture and the use of PV panels is a natural
choice for such applications. In the proposed system, duty
cycle of boost converter is controlled to maintain the DC link
voltage at required level. The speed of a PMSM drive is a
function of solar irradiation. Three phase VSI (Voltage Source
Inverter) is controlled to supply PMSM under change in
irradiation in vector oriented mode.
II.
SYSTEM CONFIGURATION AND PRINCIPLE
OF OPERATION
Fig.1 shows schematic diagram for the stand-alone solar
PV based PMSM drive for water pumping system. The
proposed system consists of solar PV panel, a boost converter,
a three phase VSI (Voltage Source Inverter)and a PMSM
coupled with a centrifugal water pump.
A PV or solar cell is the basic building block of a PV
system. An individual PV cell is usually quite small, typically
producing about 1 or 2W of power. To increase the power
output of PV cells, these cells are connected in series and
parallel to assemble larger unit called PV module. The PV
array is connected to the DC to DC boost converter to increase
the output voltage level. An IGBT (Insulated Gate Bipolar
Transistor) based VSI is used for DC to AC conversion and
connected to the PMSM drive. The constant DC voltage is
converted to the AC output using a VSI. Reference speed of
PMSM is a function of solar irradiation.
III.
DESIGN OF PV BASED PMSM DRIVE
The design of a PV based PMSM drive consists of PV
array, a DC to DC converter, a DC link capacitor and a VSI.
Ratings of selected parameters are given in Appendix. The
designs of various components of drive system are as follows,
+
Fig. 1 Schematic diagram of standalone solar PV based PMSM drive for water pumping system.
A. Design of PV Array
The PV panel is designed for a 1.5 kW peak power
capacity. According to design considerations, one solar
module consists of 36 cells in series. Each cell has an open
circuit voltage of 0.6V and short circuit current of 4 A. Its one
module has an open circuit voltage of 21.67 V and short
circuit current of 4 A. For the desired output voltage and
current, the proposed SPV power generating system consists
of 3 modules in parallel and 11 module in series to form a
SPV array. This PV array can produce maximum 1.5 kW
power.
It is obtained as 1500 VA. The rms current through a VSI
is given as,
B. Design of Boost Converter
The boost converter is used to feed the active power from
PV array to the DC link capacitor connected VSI fed PMSM.
The design parameters of the boost converter are given as,
Fig.1 shows the comprehensive control scheme for a stand
alone solar PV based PMSM drive. The control scheme is
discussed in two parts, i.e. control of boost converter to
maintain constant DC link voltage and control of VSI in
vector oriented mode to achieve fast dynamic response under
change in solar irradiances and load conditions. Basic Eq.
used in control algorithms are as follows,
The value of a boost inductor L is given as, [21]
L=
VPV D
2 * Δi * f sw
=2.67 mH
(1)
where D is duty cycle, Vpv is output voltage of PV array, fsw is
switching frequency, ∆i is ripple in output current of PV array.
Considering Vpv =198.99V, ∆i=10% of PV current and fsw =
15 kHz, the value of L is obtained as 2.67 mH.
The maximum current through boost converter IGBTs is
obtained as 1.25 (ipp+
Ipv) where ipp is peak to peak ripple
current considering 10% ripple 25 A, 600 V IGBT is used for
boost converter.
C. Voltage Source Inverter
The apparent power rating of a VSI is given as,
S
VSI
= P2 + Q2
I
VSI
=
kW * 10 3
3 Vm
=2.165A
where Vm is stator voltage of PMSM. The maximum current
through IGBTs is obtained as 1.25 (ipp+
IVSI) [20].
Considering 7.5% peak-peak ripple current, 25 A, 600 V
IGBTs are used in a VSI.
IV. CONTROL SCHEME
A. Control of Boost Converter
The DC bus voltage and the output of the DC PI controller
is used to estimate the DC voltage error at the kth sampling
instant is as,
* (k ) − V (k )
Vdce (k ) = Vdc
dc
(4)
where Vdc and V*dc are sensed and reference DC bus voltages
respectively.
The output of the DC PI controller at the kth sampling
instant is expressed as,
I*pv (k ) = I*pv (k − 1) + k pa [Vdce (k ) − Vdce (k − 1)] + k ia Vdce (k )
(2)
(3)
(5)
where kpa and kia are the proportional and integral gain
constants of the PI controller. Vdce (k) and Vdce (k-1) are the
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DC bus voltage errors in the kth and (k-1)th sampling instant
and I*pv (k) and I*pv (k-1) are output of DC PI controller in the
kth and (k-1)th instant needed for voltage control.
The reference and actual PV bus current are used to
estimate the PV bus current error at the kth sampling instant as,
I pve (k ) = I*pv (k ) − I pv (k)
(6)
The PV bus current error (Ipve) is amplified using gain K
and compared with fixed frequency carrier signal to generate
switching signals for IGBT used in boost converter.
B. Control of VSI
For the VSI, a VOC (Vector Oriented Control) scheme is
used. Two Hall effect current sensors are used to sense two
phase motor currents ia, ib and third phase source current ic is
estimated considering that instantaneous sum of three-phase
currents is zero. Reference motor speed (ω*r) is the function of
solar irradiation and used to track the maximum power.
Irradiation sensor transducer gives the output in the form of
voltage signal which is fed to the look up table. Reference
speed is compared with the measured rotor speed (ωr) and it
provided speed error ωe.
The speed error at the kth sampling instant is given as,
ω re (k ) = ω*r (k ) − ω r (k )
(7)
Speed error is processed using the speed PI controller,
which provide the reference electromagnetic torque (T*ref).
The reference torque (T*ref) is used to generate reference qaxis current (i*q) as follows,
i *q (k ) = i *q (k − 1) + k pa [ω e (k ) − ω e (k − 1)] + k ia ω e (k )
(8)
where kpa and kia are the proportional and integral gain
constants of the PI controller. ωe (k) and ωe (k-1) are the speed
errors in the kth and (k-1)th sampling instant and i*q (k) and i*q
(k-1) is the output of speed PI controller in the kth and (k-1)th
instant needed for speed control.
Similarly, from the sensed rotor speed of the PMSM,
magnitude of d-axis PMSM current (i*d) is obtained which is
consider zero below rated speed.
i *d = 0
(9)
For the estimation of three phase PMSM currents the
transformation angle (θre) is obtained as,
P
θr
2
where P is the number of poles of the PMSM.
θ re =
(10)
Three-phase reference PMSM currents (i*a, i*b, i*c) are
obtained using i*d and i*q and the rotor angular position in
electrical rad/sec by inverse park transformation.
Three-phase reference PMSM currents are as [13],
i*a = i*d cosθre − i*q sinθre
(11)
i*b = i*d cos(θre − 2π / 3) − i*q sin(θre − 2π / 3)
(12)
i *c
(13)
= i *d
cos(θ re + 2π / 3) − i *q
sin(θ re + 2π / 3)
Three phase reference currents (i*a, i*b, i*c) are compared
with sensed PMSM currents (ia, ib, ic) and resulting current
errors are fed to the PWM current controller for generating the
switching signals.
V.
RESULTS AND DISCUSSION
The model of stand-alone solar PV based PMSM drive
system for water pumping application is developed using
MATLAB/ SIMULINK R2010. The performance of the PV
based PMSM drive system for water pumping application is
evaluated under various operating conditions and observed in
terms of PV voltage (VPV), PV currents (IPV), PMSM currents
(Imabc), PMSM speed (N), electromagnetic torque and load
torque (T,Tl), DC link voltage (Vdc) and mechanical power
(Pm).
A. Performance of PV based PMSM Drive under Starting
Fig. 2 shows the performance of the PV based PMSM
drive under starting. During starting of a PMSM drive, it is
observed that the DC link voltage is maintained constant and
motor allows developing rated torque. The PMSM achieves
the reference speed in a 50 ms. The observed performance of
proposed drive establishes the efficacy of proposed system.
B. Transient Performance of PV based PMSM Drive
Fig. 3 shows the performance of solar PV based PMSM
drive under step change in irradiation. At 0.6s, a step change
in PV radiation from 1000 to 900 W/m2. It leads to
instantaneous change in electromagnetic torque of PMSM due
to which the PMSM starts deaccelerate and it is achieved the
desired speed within 20 ms.
The time require to achieve steady state point is reasonably
small. However under such transient conditions, the DC link
voltage remains fairly constant and necessary changes in stator
currents are also monitored to maintain power balance
between input supply and load.
C. Steady State Performance of the PV based PMSM Drive
Fig. 4 shows the performance of the solar PV based
PMSM drive under steady state operation at the rated
condition. The PMSM drive is running at 4000 rpm which is
the rated reference speed. The electromagnetic torque (Te)
developed by PMSM, coincides with the load torque (TL)
which is the function of speed as evident from obtained
results. A centrifugal pump load is considered in this study.
The DC link voltage is maintained at its reference value and
three phase PMSM stator currents are observed balanced and
sinusoidal.
Fig. 5 shows the graphical plot of PMSM speed, input and
output power under change in solar irradiances. It is observed
that as irradiance decreases, PMSM speed fall. It is also
observed that at very low value of radiation, input and output
power are also very less in accordance with characteristics of
solar PV.
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Fig. 2 Performance of PV based PMSM drive during starting.
Fig. 3 Performance of the PV based PMSM drive under change in solar irradiation.
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Fig. 4 Performance of the solar PV based PMSM drive under constant solar irradiation.
Fig. 5 Change in PMSM speed and input and output power respect to change in irradiation.
APPENDIX
VI. CONCLUSION
A stand alone solar PV system has been modelled for
the PMSM drive used in water pumping system. Solar PV
water-pumping systems are simple, reliable, conserve energy
and need less maintenance. It has been demonstrated that
proposed system provide satisfactory control on motor speed
for water pumping under wide change in solar irradiation.
Specification of
PMSM
Specification of
Boost Converter
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1.5kW, 400V, 50Hz, 4Pole, 4000 rpm,
3.6 Nm, Stator resistance-2.2 ohm,
Stator inductance-8.2 mH, Moment of
interia-0.000553 kgm2, Flux linkage0.1885 V.s
Interface inductor- 2.67 mH, DC link
capacitor- 1800µf, DC PI gain
Kp=0.289, Ki=1.8
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