TECHNICAL FIELD
5
[001] The present invention described herein, in general, relates to a water
pumping system and more particularly to a solar photovoltaic (PV) based water pumping
system using brushless DC (BLDC) motor drive.
10 BACKGROUND
[002] A solar photovoltaic (PV) generation is emerging as one of the best
alternative of conventional sources for various appliances. With reference to this, the
water pumping has gained a broad attention in last few decades as a crucial application
15 of PV energy. An innumerable researches have been carried out on electric motor drives
to improve the performance and efficiency of PV fed pumping systems with cost benefit.
A permanent magnet brushless DC (BLDC) motor, due to its high efficiency, high power
density, no maintenance, log service life, low electromagnetic interference (EMI) issues
and small size, is being opted from last decade. It has been determined that introducing
20 this motor reduces the cost and size of PV panels in addition to improved performance
and maintenance free operation.
[003] Being a grid-isolated or standalone system, the existing BLDC motor
driven water pumps fed by a PV array rely only on solar PV energy. Due to its
intermittency, the solar PV generation exhibits its major drawback which results in an
25 unreliable water pumping system. In the course of bad climatic condition, the water
pumping is severely interrupted, and the system is underutilized as the pump is not
operated at its full capacity. Moreover, an unavailability of sunlight (at night) leads to
shutdown of an entire water pumping system. These shortcomings are required to be
incorporated in order to acquire a reliable PV based pumping system.
3
[004] So far, few attempts in this connection are made, although not with BLDC
motor drive, which deploy a battery as an energy storage. Associated with a bidirectional
control, the battery is charged and discharged during full and poor solar radiation (or no
radiation) respectively, thus it ensures a full water delivery continuously. 5 Contrary to it,
introducing a battery energy storage in PV based water pumping not only increases the
overall cost and maintenance but also reduces its service life. A lead acid battery which
is mostly used, has a useful life of only 2-3 years.
10 [005] Reference is made to Indian Patent No. 201611002791 (Pending), as filed
on January 25, 2016, namely ‘Water Pumping System with Solar Photovoltaic Array Fed
Brushless DC Motor and a Method Thereof’. The proposed topology discloses a single
stage PV based water pumping using a BLDC motor drive. Being a grid-isolated or
standalone system, the developed system leads to an unreliable water pumping. The
15 system is useful only for the isolated areas where utility grid is not accessible, or where a
continuous water pumping is not required.
[006] Reference is made to CN 204131142 U, namely ‘Photovoltaic Water
Pumping and Residual Electricity Grid-Connected System’, discloses a utility model, in
20 which a power allocation system decides whether to draw power form PV array or from
the utility grid (when PV array is insufficient to power the pump). A water pump along
with a pump controller, is connected at the common DC bus of PV array and grid
connected inverter. However, the developed control enables only a unidirectional power
flow i.e. an excess power or an unutilized power (when pumping is not required) of PV
25 array is not returned to the utility grid. Therefore, the PV installation is not fully utilized
and a consumer must pay an electricity bill.
[007] Reference is made to CN 202455296 U namely, ‘Photovoltaic Pumping
System Using Power Grid as Energy Storage Device’, discloses that the PV energy is fed
30 into the utility grid through a grid inverter and a water pump is then fed by that utility
4
grid through a pump inverter. Although being a grid connected PV pumping system, it
appears as a system operated by utility grid only.
[008] Reference is made to CN 203884338 U namely, ‘High-Efficiency
Photovoltaic Pump System’ discloses a kind of hybrid PV water 5 pumping, wherein a
battery is first charged by the PV array through a charge controller and then it is
discharged to feed the water pump via an inverter. The pump is also supported by a utility
interface through an option switch. The entire system becomes expensive due to an added
manufacturing and maintenance cost of the battery storage.
10
[009] Reference is made to CN 203859717 U, namely ‘Photovoltaic
Agricultural Power Generating Unit’ discloses a utility model which relates to a system
wherein a part of the PV installation is engaged in water pumping and the remaining part
in feeding power to the grid. The proposed system is not reliable as the pumping is
15 dependent only on the PV energy and no power is drawn from the utility grid.
[0010] However, all these aforementioned prior arts of a PV based pumping
systems presents a unidirectional power flow control which either feeds the grid or draws
power from the grid. A multifunctional system which may enable a bi-directional power
flow depending on the operating circumstances such that both PV installation and
20 pumping system are fully utilized, is not described in any of the prior arts.
[0011] Therefore, there exists a dire need to provide a more reliable and low cost
PV array fed water pumping system and method that can provide an uninterrupted water
pumping with full capacity regardless of the climate condition and that is capable of
25 utilizing the installed resources fully.
SUMMARY OF THE INVENTION
[0012] The following presents a simplified summary of the invention in order to
30 provide a basic understanding of some aspects of the invention. This summary is not an
5
extensive overview of the present invention. It is not intended to identify the key/critical
elements of the invention or to delineate the scope of the invention. Its sole purpose is to
present some concept of the invention in a simplified form as a prelude to a more detailed
description of the invention presented later.
5
[0013] The objective of the present invention is to provide a low cost and reliable
solution for PV array fed water pumping system employed for farm irrigation, drinking
water supply to the households and livestock, swimming pool, fish farms, fountain, water
supply to the industries, and the like.
10
[0014] Another objective of the present invention is to provide a grid interactive
PV based water pumping using a BLDC motor drive which leads to an enhanced
reliability by ensuring an uninterrupted water pumping regardless of the climatic
condition.
15
[0015] Yet another objective of the present invention is the maximum utilization
of resources, and continuous water pumping with full capacity.
[0016] Yet another objective of the present invention is to enable a bi-directional
20 power flow between the single phase utility grid and a common DC bus using a simple
unit vector template (UVT) generation technique.
[0017] Yet another objective of the present invention is to provide a battery
storage-less solar PV fed reliable water pumping in order to avoid high installation cost
25 and maintenance, and to enhance the service life.
[0018] Yet another objective of the present invention is to provide a source of
earning to the consumers by sale of electricity to the utility when the water pumping is
not required.
6
[0019] Yet another objective of the present invention is to manifest a power
quality improvement on the utility grid.
[0020] Still another objective of the present invention is the 5 validation of soft
starting and speed control of BLDC motor without any additional sensors or control, and
a fundamental frequency operation of the voltage source inverter (VSI) which feeds a
BLDC motor-pump.
10 [0021] In one aspect, there is provided a grid interactive photovoltaic (PV) based
water pumping system comprising: an array of solar photovoltaic (SPV) modules; at least
one brushless DC (BLDC) motor controller driven by said solar photovoltaic modules by
means of a boost converter and a three phase voltage source inverter (VSI); at least one
single phase utility grid adapted to support said voltage source inverter (VSI) for driving
15 said BLDC motor by means of a single phase voltage source converter (VSC), wherein
said voltage source converter (VSC) enables a bi-directional power flow; at least one unit
vector template (UVT) generation module communicably coupled to said single phase
voltage source converter (VSC), and adapted to control said bi-directional power flow on
said VSC.
20
[0022] In another aspect, there is provided a method for operating a grid
interactive photovoltaic (PV) based water pumping system as mentioned above, wherein
said method comprising:
• receiving, by means of an array of solar photovoltaic (SPV) modules, power for
25 driving a brushless DC (BLDC) motor during water pumping through a boost
converter and a three phase voltage source inverter (VSI);
• transferring, by means of a DC bus of said VSI, said power from said SPV
modules to a single phase utility grid through a single phase voltage source
converter (VSC), when water pumping is stopped, and thereby
7
• enabling, by means of said single phase voltage source converter (VSC), flow of
power from said single phase utility grid to drive a BLDC motor during a night
time and/or insufficient SPV power;
• controlling, by means of unit vector template (UVT) generation module, bidirectional
power flow control on said single phase voltage 5 source converter
(VSC).
[0023] Other aspects, advantages, and salient features of the invention will
become apparent to those skilled in the art from the following detailed description, which,
taken in conjunction with the annexed drawings, discloses exemplary embodiments of the
10 invention.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The above and other aspects, features, and advantages of certain exemplary embodiments
15 of the present invention will be more apparent from the following description taken in
conjunction with the accompanying drawings in which:
[0024] Figure 1 shows a Schematic diagram of the grid interactive PV array based
water pumping system using a BLDC motor drive according to one implementation of
20 the present invention.
[0025] Figure 2 shows UVT based bi-directional power flow control of VSC
(Voltage Source Converter)according to one implementation of the present invention.
25 [0026] Figure 3(a) depicts starting and steady state performances of PV array,
when only PV array feeds BLDC motor-pump according to one implementation of the
present invention.
8
[0027] Figure 3(b) depicts starting and steady state performances of BLDC
motor-pump, when only PV array feeds BLDC motor-pump according to one
implementation of the present invention.
[0028] Figure 4(a) depicts starting and steady state performances 5 of utility grid,
when only utility grid feeds water pump according to one implementation of the present
invention.
[0029] Figure 4(b) depicts starting and steady state performances of BLDC
10 motor-pump, when only utility grid feeds water pump according to one implementation
of the present invention.
[0030] Figure 5(a) depicts steady state response of PV array, when water pumping
is not required according to one implementation of the present invention.
15
[0031] Figure 5(b) depicts steady state response of utility grid, when water
pumping is not required according to one implementation of the present invention.
[0032] Figure 6(a) depicts dynamic response of PV array, under a transition from
20 grid feeding pump to PV array feeding grid according to one implementation of the
present invention.
[0033] Figure 6(b) depicts dynamic response of utility grid, under a transition
from grid feeding pump to PV array feeding grid according to one implementation of the
25 present invention.
[0034] Figure 6(c) depicts dynamic response of BLDC motor-pump, under a
transition from grid feeding pump to PV array feeding grid according to one
implementation of the present invention.
9
[0035] Figure 7(a) depicts dynamic performance of PV array, under a transition
from PV array feeding pump to both PV array and grid feeding pump according to one
implementation of the present invention.
5
[0036] Figure 7(b) depicts dynamic performance of utility grid, under a transition
from PV array feeding pump to both PV array and grid feeding pump according to one
implementation of the present invention.
10 [0037] Figure 7(c) depicts dynamic performance of BLDC motor-pump, under a
transition from PV array feeding pump to both PV array and grid feeding pump according
to one implementation of the present invention.
[0038] Figure 8 depicts dynamic performance of BLDC motor-pump when only
15 PV array feeds BLDC motor-pump according to one implementation of the present
invention.
[0039] Figure 9(a) depicts total harmonic distortion (THD) and harmonic
spectrum of supply current when the water pump is fed by utility grid only according to
20 one implementation of the present invention.
[0040] Figure 9(b) depicts THD and harmonic spectrum of supply current when
the water pump is fed by both utility grid and PV array according to one implementation
of the present invention.
25
[0041] Persons skilled in the art will appreciate that elements in the figures are
illustrated for simplicity and clarity and may have not been drawn to scale. For example,
10
the dimensions of some of the elements in the figure may be exaggerated relative to other
elements to help to improve understanding of various exemplary embodiments of the
present disclosure. Throughout the drawings, it should be noted that like reference
numbers are used to depict the same or similar elements, features, and structures.
5
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0042] The following description with reference to the accompanying drawings
is provided to assist in a comprehensive understanding of exemplary embodiments of the
10 invention. It includes various specific details to assist in that understanding but these are
to be regarded as merely exemplary.
[0043] Accordingly, those of ordinary skill in the art will recognize that various
changes and modifications of the embodiments described herein can be made without
15 departing from the scope of the invention. In addition, descriptions of well-known
functions and constructions are omitted for clarity and conciseness.
[0044] The terms and words used in the following description and claims are not
limited to the bibliographical meanings, but, are merely used by the inventor to enable a
20 clear and consistent understanding of the invention. Accordingly, it should be apparent to
those skilled in the art that the following description of exemplary embodiments of the
present invention are provided for illustration purpose only and not for the purpose of
limiting the invention as defined by the appended claims and their equivalents.
25 [0045] It is to be understood that the singular forms “a,” “an,” and “the” include
plural referents unless the context clearly dictates otherwise.
[0046] By the term “substantially” it is meant that the recited characteristic,
parameter, or value need not be achieved exactly, but that deviations or variations,
30 including for example, tolerances, measurement error, measurement accuracy limitations
11
and other factors known to those of skill in the art, may occur in amounts that do not
preclude the effect the characteristic was intended to provide.
[0047] Features that are described and/or illustrated with respect to one
embodiment may be used in the same way or in a similar way in 5 one or more other
embodiments and/or in combination with or instead of the features of the other
embodiments.
[0048] It should be emphasized that the term “comprises/comprising” when used
10 in this specification is taken to specify the presence of stated features, integers, steps or
components but does not preclude the presence or addition of one or more other features,
integers, steps, components or groups thereof.
[0049] Accordingly, in one implementation, the present invention deals with the
15 development of a bi-directional power flow control in a grid interactive solar PV fed water
pumping system using a BLDC motor drive, enabling the flow of power from PV array
to the single phase utility grid in case a water pumping is not required, and from grid to
BLDC motor-pump in case the PV array power is not sufficient (or at night) so as to run
the pump at its full capacity. The array of PV modules can feed the grid only when a
20 water pumping is not required.
[0050] In one implementation, there is provided a unit vector template generation
module, which due to its simplicity can perform a bi-directional power transfer. A single
phase voltage source converter (VSC) enables a bi-directional power transfer from the
25 solar photovoltaic modules to the single phase utility grid and/or from said single phase
utility grid to said BLDC motorthrough a DC bus capacitor.
[0051] In one implementation, grid interactive solar PV based water pumping
using BLDC motor drive is illustrated in Figure 1. In one example, a 6-pole, 3000 rpm
30 @ 310 V (DC) BLDC motor drives a 5.18 kW water pump. A PV array of 6.4 kW peak
power capacity under standard test conditions (1000W/m², 25°C, AM 1.5), a sufficient
12
power to run the water pump in case a utility grid is not available, feeds a BLDC motorpump
via a boost converter and Voltage Source Inverter (VSI). The DC bus of VSI can
be supported by a single phase, 180 V, 50 Hz utility grid through a Voltage Source
Converter (VSC). The subsequent Unit Vector Template (UVT) based bi-directional
power flow control is 5 shown in Figure 2.
[0052] In one implementation, Figure 1 shows the detailed schematic diagram of
a grid interactive solar PV based water pumping using a BLDC motor drive (7). The boost
converter (2) may be adapted to perform maximum power point tracking (MPPT) of PV
10 array through an incremental conductance (InC) mechanism while the three-phase VSI
(3) performs an electronic commutation of BLDC motor (7). A single phase VSC (4)
enables a bi-directional power transfer through a DC bus capacitor. An interfacing
inductor can be placed in the line to allow power flow between the single phase utility
grid (6) and single phase VSC (4), and to limit the harmonics current into the supply. An
15 R-C ripple filter can be provided to limit the harmonics in supply voltage.
[0053] In one implementation, Figure 2 shows a bi-directional power control
based on a UVT generation module (5). A single phase Phase Locked Loop (PLL) can be
used to synchronize the utility grid voltage and current values. It can generate a sinusoidal
20 unit vector of supply voltage (sin θ) at fundamental frequency. On the other hand, an
amplitude of fundamental component of supply current, (Isp) can be extracted by
regulating the DC bus voltage, (vdc). The filtered (vdc) can be subsequently compared with
a set value, (Vdc
*). A fundamental component of supply current, (is
*) can be extracted by
multiplying (Isp) and (sin θ) using a multiplier. A sensed supply current, (is) may be
compared with extracted (is
*25 ) and the current error may be processed through a hysteresis
current controller to generate plurality of gating pulses for VSC.
[0054] In one exemplary embodiment, Figure 3 shows the various starting and
steady state performances of PV array (1) and BLDC motor-pump when only a PV array
30 feeds the BLDC motor-pump. As shown in Figure 3(a), PV array is operated at its MPP
under the radiation level of 1000 W/m2. Therefore, the BLDC motor-pump can be
13
operated at its full capacity and it runs at rated speed i.e. 3000 rpm, as shown in Figure
3(b). No power grid is required as the PV array may generate a sufficient power to run
the pump at its full capacity. The various indices refer to back-EMF, (ea), stator current,
(isa), speed, (N), electromagnetic torque, (Te), and load torque, (TL). These results
demonstrate a soft starting along with the successful steady state operation 5 of the motorpump.
[0055] In one exemplary embodiment, Figure 4 shows the various starting and
steady state performances of utility grid and BLDC motor-pump when only utility grid
10 feeds the BLDC motor-pump. This operating condition occurs when a water pumping
may be required at night. Figure 4(a) depicts that an in-phase sinusoidal supply current of
33 A (rms) can be drawn and DC bus voltage can be maintained at 310 V. The motorpump
draws a sufficient power from utility to run at full capacity, as shown in Figure
4(b). A soft starting and full utilization of pumping system are demonstrated in this case
15 also.
[0056] In one exemplary embodiment, Figure 5 shows the various starting and
steady state performances of PV array and utility grid when the water pumping may be
not required. In this case, the pump is not operated and power generated by the PV array
20 can be fed to the utility grid. Figure 5(a) shows the MPP operation of PV array at 1000
W/m2. Figure 5(b) exhibits an out-of-phase sinusoidal supply current which indicates that
the utility can be fed by a PV array and the power flow can be reversed while maintaining
the DC voltage at 310 V.
25 [0057] In one exemplary embodiment, Figure 6 shows the various dynamic
performances of PV array, utility grid and BLDC motor-pump when a transition from the
grid feeding pump to PV array feeding grid takes place. This analysis assumes that the
water pump can be operated initially through the utility grid when the PV array power is
not available. The mode of operation can be suddenly changed by considering that the
30 water pumping is no more required but the PV array power is available. Therefore, it may
be desired to feed the power to the utility grid by the PV array. The mode of operation
14
can be changed at 0.4 s. Figures 6(a), 6(b) and 6(c) respectively present the PV array
indices, utility grid indices and BLDC motor-pump indices. As shown in Figure 6(b), the
direction of current flow reverses within a cycle while regulating the DC bus voltage
almost at 310 V. A reduction in the speed starts at 0.4 s and motor-pump reaches at
standstill after a while as shown 5 in Figure 6(c).
[0058] In one exemplary embodiment, Figure 7 shows the various dynamic
performances of PV array, utility grid and BLDC motor-pump when a transition from PV
array feeding pump to both PV array and grid feeding pump may take place. It may be
10 assumed that only the PV array (1) may be feeding the pump initially as it is sufficient to
run the water pump at its full capacity. A reduction in radiation level from 1000 W/m2 to
600 W/m2may be observed at 0.4 s. Since the PV array alone is unable to run the water
pump at its full capacity at 600 W/m2, it is desired to draw the remaining power from the
utility grid. As shown in Figure 7(a), the maximum PV array power may be reduced
corresponding to a radiation level of 600 W/m215 . Prior to 0.4 s, no power may be drawn
from the utility as shown by is in Figure 7(b). From 0.4 s onwards, the remaining power
may be drawn from the utility resulting in a flow of in-phase supply current of 14.5 A
(RMS). Figure 7(c) depicts that the motor-pump can be operated at its full capacity
regardless of climatic conditions. The motor may run at 3000 rpm as the DC bus voltage
20 can be regulated at 310 V.
[0059] In one exemplary embodiment, Figure 8 shows the various dynamic
performances of BLDC motor-pump when only the PV array feeds the pump under the
reduction in radiation level from 1000 W/m2 to 100 W/m2. When a utility grid is not
25 available and the radiation level is reduced, the water pump cannot operated at its full
capacity. However, the PV array can still be able to feed power to the water pump as per
the availability of sunlight which enables a less volume of water delivery. The motorpump
attains a speed of 1100 rpm at 100 W/m2 which is a sufficient speed to pump some
amount of water. Therefore, the capability of present system in grid-isolated mode can be
30 demonstrated.
15
[0060] In one exemplary embodiment, Figure 9 demonstrates a power quality
improvement on the utility grid in terms of power factor and total harmonic distortion
(THD). Figure 9(a) presents the THD and harmonics spectrum of supply current, (is)
shown in Figure 4(a), in case the water pump can be fed by utility grid (6) only. Similarly,
Figure 9(b) presents the THD and harmonics spectrum of (is) shown 5 in Figure 7(b), in
case the radiation level is 600 W/m2 and remaining power is required to be fed by the
utility grid. Under both conditions, THD of supply current can be observed below 5%
which meets the IEEE-519 standard. Moreover, a unity power factor operation can be
ensured under the various operating conditions.
10
[0061] Although system and method for grid interactive solar photovoltaic based
water pumping using brushless dc (BLDC) motor drive have been described in language
specific to structural features and/or methods, it is to be understood that the embodiments
disclosed in the above section are not necessarily limited to the specific features or
15 methods or devices described. Rather, the specific features are disclosed as examples of
implementations of the system and method for grid interactive solar photovoltaic based
water pumping using brushless dc (BLDC) motor drive.

WE CLAIM:
1. A grid interactive photovoltaic (PV) based water pumping 5 system comprising:
an array of solar photovoltaic (SPV) modules;
at least one brushless DC (BLDC) motor controller driven by said solar
photovoltaic modules by means of a boost converter and a three phase voltage
source inverter (VSI);
10 at least one single phase utility grid adapted to support said voltage source
inverter (VSI) for driving said BLDC motor by means of a single phase
voltage source converter (VSC), wherein said voltage source converter (VSC)
enables a bi- directional power flow;
at least one unit vector template (UVT) generation module communicably coupled
15 to said single phase voltage source converter (VSC), and adapted to control said bidirectional
power flow on said VSC.
2. The system as claimed in claim 1, wherein said single phase VSC enables a bidirectional
power transfer from said solar photovoltaic modules to said single phase utility
grid and/or from said single phase utility grid to said BLDC motor.
20 3. The system as claimed in claim 2, wherein said single phase VSC enables a bidirectional
power transfer through a DC bus capacitor.
4. The system as claimed in claim 1, further comprises: an interfacing inductor adapted
to allow power flow between said single phase utility grid and said VSC, and an R-C filter
adapted to limit the harmonics into the supply.
25 5. The system as claimed in claim 1, wherein said unit vector template (UVT) generation
module comprises:
17
a single phase Phase Locked Loop (PLL) to synchronize the utility grid voltage
and current and generate a sinusoidal unit vector of supply voltage (sin θ) at
fundamental frequency as output;
a voltage regulator to regulate the DC voltage so as to extract an amplitude of
fundamental component of supply current 5 (Isp) as output;
a multiplier coupled to said PLL and said voltage regulator, to receive output from
said PLL and said voltage regulator respectively, and to generate a fundamental
component of a supply current;
a current controller, adapted to compare said generated supply current with sensed
10 current from said utility grid to measure errors, and thereby adapted to generate a
plurality of gating pulses for said VSC by processing said error.
6. A method for operating a grid interactive photovoltaic (PV) based water pumping
system as claimed in claims 1-5, wherein said method comprising:
receiving, by means of an array of solar photovoltaic (SPV) modules, power for
15 driving a brushless DC (BLDC) motor during water pumping through a boost
converter and a three phase voltage source inverter (VSI);
transferring, by means of a DC bus of said VSI, said power from said SPV
modules to a single phase utility grid through a single phase voltage source converter
(VSC), when water pumping is stopped, and thereby
20 enabling, by means of said single phase voltage source converter (VSC), flow of
power from said single phase utility grid to drive a BLDC motor during a night
time and/or insufficient SPV power;
controlling, by means of unit vector template (UVT) generation module, bidirectional
power flow control on said single phase voltage source converter (VSC).
25 7. The method as claimed in claim 6, wherein the step of controlling, by means of unit
vector template (UVT) generation module, said bi-directional power flow control on said
single phase voltage source converter (VSC), comprises:
18
receiving, by means of a single phase PLL, voltage value from a single phase
utility grid as inputs, and generating a sinusoidal unit vector of supply voltage (sin θ) at
fundamental frequency as output;
regulating, by means of a voltage regulator, a DC bus voltage (Vdc) and thereby
extracting an amplitude of fundamental component of supply 5 current (Isp);
multiplying, by means of a multiplier, said sinusoidal unit vector of supply voltage
(sin θ) and said supply current (Isp) to generate an output corresponding to a supply
current (is
*);
comparing, by means of a current controller, said supply current (is
*) with a
10 current value sensed from said single phase utility grid to measure errors;
generating, by means of said current controller, plurality of gate pulses for
controlling said VSC by processing said errors.