Frequency-Modulated Wireless Direct-Drive Motor Control

Abstract

This paper proposes and implements a frequency-modulated wireless direct-drive motor control (WDMC) for a promising application of underground in-pipe pumping. Accordingly, a novel urban drainage scheme is conceived, which offers high robustness, mobility and flexibility. This scheme can help with the emergency response to prevent severe weather hazards, such as heavy rainfall. To power one energy-demanding unit of pumping network, a movable energy-carrying electric vehicle can park above the underground in-pipe pump and wirelessly drive the motor for accelerating the flow rate as required. Also, a pulse frequency modulation is newly used for wireless motor speed control with frequency-reduced zero-voltage switching. The system efficiencies can reach 87.6% and 83.9% with two tested power levels of 430 W at rated load and around 600 W at overload, respectively. Theoretical analysis, computer simulation and practical experimentation are given to verify the feasibility of proposed drainage system using the frequency-modulated WDMC.

Full text

IEEE TRANSACTIONS ON MAGNETICS
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Frequency-Modulated Wireless Direct-Drive Motor Control
Wei Liu1,Student Member, IEEE, K. T. Chau1,Fellow, IEEE, Christopher H. T. Lee2,Senior Member, IEEE,
Libing Cao1,Student Member, IEEE, and Chaoqiang Jiang3,Member, IEEE
1Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong, China
2School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore
3Department of Engineering, University of Cambridge, United Kingdom
This paper proposes and implements a frequency-modulated wireless direct-drive motor control (WDMC) for a promising
application of underground in-pipe pumping. Accordingly, a novel urban drainage scheme is conceived, which offers high robustness,
mobility and flexibility. This scheme can help with the emergency response to prevent severe weather hazards, such as heavy rainfall.
To power one energy-demanding unit of pumping network, a movable energy-carrying electric vehicle can park above the
underground in-pipe pump and wirelessly drive the motor for accelerating the flow rate as required. Also, a pulse frequency
modulation is newly used for wireless motor speed control with frequency-reduced zero-voltage switching. The system efficiencies can
reach 87.6% and 83.9% with two tested power levels of 430 W at rated load and around 600 W at overload, respectively. Theoretical
analysis, computer simulation and practical experimentation are given to verify the feasibility of proposed drainage system using the
frequency-modulated WDMC.
Index Terms—In-pipe pumping, underground drainage system, wireless direct-drive motor control, pulse frequency modulation.
I. INTRODUCTION
XPLORATION of magnetic resonant coupling has greatly
promoted the development progress of wireless power
transfer (WPT) technology. Due to its distinctive advantages
of security, flexibility and robustness, the WPT technology
has been promisingly applied in various industrial or
interdisciplinary areas [1], such as electric vehicle (EV)
wireless charging [2], wireless lighting [3], [4], magnetic field
focusing [5], and wireless energy-on-demand [6] and
encryption [7], [8]. Accordingly, to fully utilize its mobility
and flexibility, a wireless in-wheel motor scheme was studied
[9]. Actually, it is a pure in-wheel motor powered by the WPT
rather than controlled. For achieving motor drive, the
converter and inverter are still involved in its receiver, which
will make the whole system suffer from the drawbacks of high
cost and low reliability. Recently, a kind of wireless motor
drive scheme was revealed based on the WPT-controlled
direct motoring [10], which can be totally sealed for isolated
environment applications desiring spark-proof and mobility.
Nevertheless, both the potential application and the motoring
control of this wireless motor drive are not fully explored. 
The purpose of this paper is to conceive a promising
application of urban underground drainage system. Such a
new in-pipe pumping scheme can be wirelessly powered by an
energy-carrying EV based on the wireless direct-drive motor
control (WDMC). It aims to take immediate action in response
to emergencies for reducing the risk of severe weather
hazards, such as in heavy rainy season. Desiring to get rid of
annoying maintenances, the in-pipe pumping unit will be
sealed and mounted underground. Although plenty of
permanent-magnet (PM) brushless machines and hybrid-
excitation flux-switching machines advanced the EV
applications [11], [12], the use of inverter and controller for
Manuscript received March 31, 2020; revised August 6, 2020; accepted
August 31, 2020. Corresponding author: K. T. Chau (ktchau@eee.hku.hk).
Color versions of one or more of the figures in this paper are available
online at http://ieeexplore.ieee.org.
Digital Object Identifier ***
the motor drive will reduce system reliability and increase
maintenance requirements. Besides, the high-temperature
superconducting machine [13] is uneconomic and difficult to
implement in this new scheme comprising in-pipe pumping
networks. Finally, a PM brushed DC motor is chosen, and its
carbon brush is durable enough due to operating for only
emergency response. Significantly, none of active switches,
controllers and power cables are used in the underground in-
pipe pumping unit. This new wireless pumping scheme takes
the key advantages of good mobility, flexibility and
maintenance-free over its conventional wired counterparts.
Another research focus is the motor speed control. First, the
phase-shift control (PSC), as a typical pulse width modulation,
can be adopted with a varying duty ratio, but the initial zero-
voltage switching (ZVS) operation will be deteriorated unless
using a complicated ZVS angle adaptation. Besides, a scheme
of rapid pulse density modulation was experimentally demons-
trated in a bidirectional WPT system [14], but it inevitably
suffers from the low subharmonics and the need of inverter
modifications. Finally, a pulse frequency modulation (PFM)
was proposed for wireless power controllability, selectivity
and security with full-range soft-switching operation [15].
Such a high-efficiency PFM method can be flexibly extended
to derive a frequency-modulated WDMC for motor speed
regulation while maintaining a full-range ZVS.
Section II will discuss the conceived underground in-pipe
pumping drainage system based on the WDMC. Section III
will present the soft-switching PFM motor speed control. In
Section IV, both simulation and experimental results will be
given to verify the feasibility of proposed underground
drainage system. A conclusion will be drawn in Section V.
II. WIRELESS DIRECT-DRIVE MOTOR FOR IN-PIPE PUMPING
A. Underground Drainage System
The conceived underground in-pipe pumping drainage
system offers one of the most promising applications for the
wireless motor drive. The schematic view of the whole
drainage system is depicted in detail in Fig. 1. Generally, the
E

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depth of the drainage pipeline ranges from 1 m to 3 m. Both
one WPT receiver and one pump, driven by a PM brushed DC
motor, can be totally sealed and independently installed at
each critical node of a long drainage pipeline, thus forming an
in-pipe pumping network. The in-pipe pumping unit will take
action in response to only emergencies for preventing severe
weather hazards. Instead of using an electrically excited
brushed DC motor or PM brushless motor, the in-pipe
pumping system uses a PM brushed DC motor and contains no
controller, drivers, switches and power cables. Thus, it can
operate with both a robust structure and a reliable network
which enable to get rid of the annoying maintenances while
maintaining relatively high efficiency. To withstand the
extreme weather, such as the heavy rainy season, the flow rate
usually requires acceleration by activating the in-pipe
pumping at a particular point. Otherwise, the pump will be
idling standby. Correspondingly, based on a reserved
installation sign or an accurate position detection using
magnetoresistive sensors [16], the energy-carrying EV
integrating one WPT transmitter will park above that
particular point and wirelessly motoring the pump for
accelerating the flow rate.
Energy-carrying EV
Energy-demanding
in-pipe pumping
Drain Accelerating
Wireless motoring
Underground pipeline
Concrete pouring
1~3 m
Battery
bank GaN
inverter
Idling
Zoom in
Zoom in
Fig. 1. Schematic view of proposed underground in-pipe pumping drainage system using wireless motoring.
LCC network
Pumping
WPT transmitter
S2
uin
it
E
S1
S4
S3
GaN inverter
Batt ery bank
Lrp Lri
Uop
Cop
...
Lt
Ct
Uoi
Coi
Mtrp
Idling
ZVS-PFM
n(δd)
Drive signals
M
Motor
Motor
M
LCC network
WPT receiver Underground
δd
nLrpe
Cfp
Rrp
Lfp
T-circuits
Rfp
U
in
Rt
Ct
Lt
UCt
Mtrp
CMp
CMp
It
Irp
Ifp
(a) (b)
Fig. 2. Proposed frequency-modulated WDMC for the underground in-pipe pumping drainage scheme. (a) Topology and modulation. (b) Equivalent circuit.
B. Wireless Direct-Drive Motoring System
Both the system topology and the PFM strategy are shown
in Fig. 2(a), where the proposed WDMC system mainly
consists of one gallium-nitride (GaN) full-bridge inverter, one
series-compensated transmitter and multiple pump units
including the pumping and idling ones, and each of them
integrates one LCC-compensated receiver. Mounted at
different critical nodes in an underground pipeline, each pump
unit integrates one receiver and one PM brushed DC motor
without the need of power cables. In the energy-carrying EV,
the GaN inverter is served to dump the stored energy in the
battery bank to an energy-demanding pump via the WPT
transmitter. Since the equivalent motor load RL will vary
during the motor speed control, a high-order LCC
compensation network is designed to contribute to a load-
independent output [17]. With a controllable duty ratio δd, the
ZVS-PFM strategy is newly adopted to realize the motor
speed control for reducing both the switching frequency and
the switching loss, thus improving the system efficiency.
Besides, Fig. 2(b) shows the equivalent circuits of the S-
LCC compensated WPT system which involves two high-
order T-circuits. In Fig. 2, Rt, Lt,Ct,it, Rrx, Lrx,Crx and irx with
subscripts “t” and “r” denote the coil internal resistances,
resonant inductances, matched capacitances and resonant
currents of the transmitter and receiver circuits, respectively;
the subscript x is “p” or “i” representing the pumping or idling
unit, respectively; Lfx,Cfx and ifx are the receiver filter
inductor, capacitor and current, respectively; Mtrx is the mutual
inductance between the transmitter and one pumping or idling
receiver coils, and Mtri=0 due to the long distance; Cox,Uox and
Iox are the filter capacitor, motor voltage and current,
respectively. With two high-order T-circuits in Fig. 2(b), all
resonant parameters should be tuned as
t t f f re f re f r
22
r
11
,
xxxxxxx
x
LCLCLCLLL
C

   (1)
where an equivalent inductor Lrxe is used to represent the
receiver components Lrx and Crx. In Fig. 2(b), CMp=1/(ω2Mtrp)
is to represent a virtual inductor –Mtrp. The Kirchhoff’s
voltage law provides the general equations as given by

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rp rpe fp fp rp
M
fp fp fp fp Le fp
0
LCC
CCL
RZZZ
ZZZRR





 


I
E
I
(2)
t Mp trp trp t
in
trp rp Mp trp rp
0
CMM
MCM
RZZZ
ZZZZ





 


I
U
I
(3)
where EM is the induced electromotive force; RLe=8RL/π2 is the
equivalent AC load before the rectification; ZLrep=ZLfp=–ZCfp,
ZCMp=–ZMtrp, and they are the impedances of components
represented by their subscripts, such as ZCMp=1/(jωCMp) and
ZLfp=jωLfp; At the resonant frequency f, both the transmitter
and receiver input impedances Zin and Zrp can be derived as




22
trp fp
inM
in t rp rp
t rp rp fp Le
,
ML
ZR ZR
ZRR



UE
II
(4)
III. FREQUENCY-MODULATED MOTOR SPEED CONTROL
A. WPT-Based Pulse Frequency Modulation
Two alternative methods can be used for motor speed
control as shown in Fig. 3. Especially for a dynamic response
with a varying phase-shift angle θ, the PSC may fail to
maintain a ZVS unless using a complicated ZVS angle
adaption. In the PFM, N1 and N2 are the minimum modulated
numbers of high-frequency and low-frequency half-cycles,
respectively. The PFM can vary the duty ratio δd=N1/(N1+N2)
between two optimal modulated frequencies of f/(2n±1) so as
to realize a switching-frequency-reduced ZVS. The funda-
mental component of the piecewise PFM inverter output is
used to equivalently power the WPT system, which can be
expressed in an average Fourier series
 

in d1d2
14
( ) sin
1π
E
utt
nn


 (5)
where n1=2n–1 and n2=2n+1. As a rule, the root-mean-square
value Uin and the proportion factor δ of its nFth harmonic can
be generalized as given by

   
FF
in
d1 d2 d1 d2
22 π1
,
11
En n
U
nnnn

 

  (6)
δd=3/4
uin
itf
Modulated
sine wave
PFM
N1=3, fN2=1, f/3
uin it
f
S1
θ
PSC
S3
S2
S4
Fig. 3. Alternative motor speed control methods of PSC and PFM.
B. System Characteristic Analysis
With the S-LCC compensation, Fig. 4 shows the input
impedance (Zin) characteristics against operating frequency
with different loads, where Zin will become a complex number
unless at the zero-phase angle (ZPA) frequencies. The
resonant frequency and one specific ZPA are impervious to
this varying equivalent AC load of motor. The same ZPA
operation can also be achieved withstanding a varying
coupling coefficient due to displacement deviations. Besides,
to quantitatively assess the output fluctuations of proposed
WDMC using the PFM, Fig. 5 indicates that both the low
magnitudes in bode plots and the low amplitudes in step
responses can well verify the zero steady-state gains and the
low output fluctuations. Also, the smaller the load is, the lower
the output fluctuations become. Minimizing N1 and N2 can
further reduce the input fluctuations, thus outputting more
insignificant fluctuations at the receiver side.
65 75 85 95 105
-80
-40
0
40
80
Magnitude (dB)Phase (degree)
Frequency (kHz)
RLe=45
RLe=60
RLe=15
RLe=30
RLe=100
Operating
frequency
RLe decrease
2
6
10
14
10lg(|Zin|)


in
in
arctan Z
Z






ZPA
Fig. 4. Input impedance characteristics against operating frequency.
-40
-30
-20
-10
0Bode Plot
40 60 80 120 160 200
-90
-45
0
45
90
Frequency (kHz)
Magnitude (dB)Phase (degree)
100
RLe=15
RLe=30
RLe=45
RLe=60
Operating frequency
RLe decrease

 
2
fp
rp fpLe
20lg L
RRR







(a)
020 40 60 80 100
-2
-1
0
1
2
3
Amplitude (×10-2)
Time (µs)
Step Response
RLe=45
RLe=60
RLe=15
RLe=30
RLe decrease
(b)
Fig. 5. Characteristics of receiver T-circuit. (a) Bode plots. (b) Step responses.
TABLE I
DESIGN SPECIFICATIONS AND PARAMETERS
Parameter Symbol Value
Battery band voltage
E
50 V
Transmitter match
ed
capacitance
C
t
27.30
n
F
Transmitter coil inductance
L
t
128.44 μH
Transmitter coil
internal resistance
R
t
0.
18 Ω@
f
WPT
coil turns
n
t
,
n
rp
,
n
ri
15
Receiver matched capacitance
s
C
rp
,
C
ri
62.49
n
F
Receiver coil inductance
s
L
rp
,
L
ri
74.81 μH
Receiver coil
internal resistance
s
R
rp
,
R
ri
0.11 Ω@
f
Receiver filter
inductance
s
L
fP
,
L
fi
18.70 μH
Receiver filter inter
nal resistance
s
R
fp
,
R
fi
0.0
5 Ω@
f
Receiver filter capacitance
s
C
fp
,
C
fi
187.46
nF
Transfer distance
s
D
p
,
D
i
15
c
m,
∞
Mutual inductance
s
M
trp
,
M
tri
7.585, 0
μH
Nominal resonant
frequency
f
85.0 kHz

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IV. RESULTS AND VERIFICATIONS
To verify the feasibility of proposed underground in-pipe
pumping drainage scheme using the frequency-modulated
WDMC, the computational simulation and practical experi-
mentation are both performed. The design specifications and
parameters are listed in Table I. The GaN full-bridge inverter
is populated with GS66516B. The specification of Litz wire is
250×0.10 mm.
A. Simulation Results
(a) (b)
nrx = 15
Ø100mm
200mm
150mm
Ø50mm
37.5mm
nt = 15
200mm
300mm
37.5mm Ø80mm
Ø120mm
Transmitter coil 225mm
150mm
(c)
Receiver coil
125mm
Fig. 6. Geometries of coils. (a) Transmitter. (b) Receiver. (c) Displacements.
(A/mm2)
0
1
2
3
4
0
1
2
3
(mT)
Max: 0.107 T
(a) (b)
Flux density (mT)
0
0.4
0.8
1.2
1.6
0
0.4
0.8
1.2
1.6
150 100 200
50 100
00
-50 -100
-100 -200
-150
(mT)
Max: 1.624mT
(c)
Fig. 7. Magnetic field distributions. (a) Flux lines. (b) Flux densities along the
vertical plane. (c) Flux densities along the middle parallel plane.
Scaled-down geometries with detailed dimensions of WPT
coils are depicted in Fig. 6, where the distance is 15 cm. For
practical application, their dimensions and distance will
readily become ten times larger at least. By using the finite
element analysis, the current source is set as 30 A, and an
equivalent motor load RL=25 Ω is used. The magnetic field
distributions of proposed drainage system are shown in Fig. 7
in which the receiver is induced a stable resonance and
generates high current and flux densities, thus successfully
powering the energy-demanding in-pipe pump unit. By using
ferrite bars, the flux densities can reach 1.624 mT along the
middle parallel plane.
-15
0
15
-50
0
50
6.50 6.52 6.54 6.56
0
50
100
6.58
Time (ms)
Modulated
voltageuin (V)
Receiver
current irp (A)
Motor
voltageUop (V)
85 kHz 85/3 kHz
N2=1
d=4/5 with ZVS
Controllable output
Currentit (A)
N1=4
(a)
020 40 60 80 100
65
70
75
80
85
90
95
Equivalent load RLe (Ω)
Transmission efficiency (%)
kc=0.10
kc=0.05
kc=0.075
Varying motor load
(b)
Fig. 8. System performances of proposed WDMC-based drainage scheme
using the PFM. (a) Simulated waveforms. (b) Transmission efficiencies.
With a duty ratio δd=4/5, Fig. 8(a) shows the simulated
waveforms of proposed WDMC-based drainage system using
the PFM, including the input voltage uin, transmitter current it,
receiver current irp and motor voltage Uop. To maintain the
ZVS, two switching frequencies of 85 kHz and 85/3 kHz are
involved and modulated to energize the WPT with
insignificant output fluctuations, thus reducing the average
switching frequency. By regulating the duty ratio, the motor
voltage can be readily adjusted, and thus the motor speed is
controllable. With different coupling coefficients kc, Fig. 8(b)
shows the transmission efficiencies of proposed WDMC
scheme against the increasing equivalent AC load RLe. Since
both the motor speed and load torque may vary in the practical
operation, the equivalent load will accordingly change. The
designed system should maintain a high-efficiency operation
within a wide load range. Also, the system transmission
efficiency can reach up to 92.8% with kc=0.075, which can be
further improved in practical applications with the increasing
WPT coil sizes and power level. These characteristics well
confirm that the energy-carrying EV can wirelessly drive the
underground energy-demanding in-pipe pump unit to
accelerate the flow rate for emergency responses while
realizing a frequency-reduced ZVS.
B. Experiential Results
A prototype is built for experimental verification as shown
in Fig. 9. The two modulated switching frequencies are 85.4
kHz and 85.4/3 kHz. With different output torques – no load

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(0 Nm), rated load (2.3 Nm) and overload (3.5 Nm), Figs.
10(a), 10(b) and 10(c) show the measured waveforms of
proposed WDMC-based in-pipe pumping scheme using the
PFM with various duty ratios (δd=1, 2/3, 4/5 and 6/7),
respectively, including the modulated input voltage uin,
transmitter current it, motor voltage Uop, motor current Iop and
receiver current irp. By energizing the transmitter current
slightly before its zero-crossing points, the PFM can realize a
frequency-reduced ZVS while maintaining insignificant output
fluctuations. Due to the effect of back electromotive force, the
DC motor should be modeled as a DC power source rather
than a simple DC load resistor [18], especially outputting a
torque or rotating at a higher speed. By adding the LCC-
compensated network to from a T-circuit, a variable but tiny
inductance will be generated in the equivalent AC load and
transformed to the transmitter side. As a result, the phase
angle, by which the inverter output leads the transmitter
current, may vary with different motor loads, thus always
guaranteeing a robust zero-voltage-switching operation.
PM DC motor
Magnetic
powder brake
Spee d & torque
transducer
Oscilloscope
DC power source
Power
supply
GaN inverter
High-precision
power su pply
Lfp
Cfp
Crp Lt
Lrp
Ct
Controller
(TMS320F28335) Sensor
amplifier
15cm
Fig. 9. Experimental setup.
Uop (50V/div)
uin (50V/div)
t (5μs/div)
it(10A/div)
Iop (2A/div)
δd=1
Uop (50V/div )
uin (50V/div)
t (10μs/div)
it(10A/div)
irp (10A/div)
δd=2/3
N2=1N1=2
Uop (50V/div)
uin (50V/div)
t (5μs/div)
it(10A/div)
Iop (2A/div)
δd=1
Uop (50V/div )
uin (50V/div)
t (10μs/div)
it(10A/div)
irp (10A/div )
δd=4/5
N2=1N1=4
Uop (50V/div )
u
in
(50V/div)
t (5μs/div)
i
t
(10A/div)
Iop (2A/div)
δ
d
=
1
Uop (50V/div )
uin (50V/div)
t (10μs/div)
it(15A/div)
irp (10A/div )
δd=6/7
N2=1N1=6
(a) (b) (c)
Fig. 10. Measured waveforms of the WDMC-based drainage system using the PFM. (a) No load (0 Nm). (b) Rated load (2.3 Nm). (c) Overload (3.5 Nm).
uin (50V/div)
t (200ms/div)
it(25A/div)
δd=1δd=4/5
Uop (50V/div)
t (20μs/div)
Iop (2A/div)
Zoom in
δddecrease
(a)
uin (50V/div)
t (200ms/div)
it(25A/div)
δd=4/5 δd=1
Uop (50V/div) t (20μs/div)
Iop (2A/div)
Zoom in
δdincrease
(b)
Fig. 11. Dynamic responses of proposed frequency-modulated WDMC system. (a) Step decrease of δd. (b) Step increase of δd.

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Furthermore, Figs. 11(a) and 11(b) show the dynamic
responses of proposed scheme with the suddenly decreasing
and increasing duty ratios, respectively. The measured
transient waveforms and their zoom-in ones are both shown in
Fig. 11, which indicates that the frequency-modulated WDMC
can flexibly conduct a dynamic motor speed regulation with a
suddenly varying duty ratio. Also, the ZVS can keep
impervious to these dynamic characteristics of the PM motor.
With no load (0 Nm), light load (0.5 Nm), rated load (2.3 Nm)
and overload (3.5 Nm), Figs. 12(a) and 12(b) show that motor
speed control characteristics using the PFM at the rated
voltage and undervoltage, respectively. It can be observed that
all motor speeds monotonically reduce with the decreasing
duty ratio. When lower switching frequencies, such as f/3 and
f/5, are chosen, the controllable motor speed will be further
reduced still with ZVS. The system electrical efficiencies from
the DC power supply to the motor terminal can reach 87.6%
and 83.9% with two tested power levels of 430 W (rated load,
1500 rpm) and around 600 W (overload, 1348 rpm),
respectively, at a 15-cm distance. They can readily be
improved further with a higher power level or a larger ratio of
WPT coil size to transfer distance. These measured results
well verify the feasibility of the PFM-WDMC and its in-pipe
pumping scheme for emergency responses.
2.3Nm0Nm
3.5Nm0.5Nm
0
0.5
1.0
1.5
2.0
020 40 60 80 100
Duty ratio (%)
Motor speed (rpm×103)
1500rpm
(a)
2.3Nm0Nm
3.5Nm0.5Nm
020 40 60 80 100
0
0.3
0.6
0.9
1.2
1.5
Duty ratio (%)
Motor speed (rpm×103)
1000rpm
(b)
Fig. 12. Motor speed control characteristics. (a) Using the rated voltage of
battery bank. (b) Using undervoltage of battery bank.
C. Discussion
The use of 85 kHz is to ensure that energy-carrying EV can
get wireless charging compatibly over the electrified roadways
or parking lots. The WPT coils and the transfer distance are
both scaled-down for better verification. Practically, a larger
transmitter coil can be installed on the chassis of electric
vehicles, and also a larger receiver coil can be buried beneath
the ground as shown in Fig. 1. Their coil sizes may enlarge
several or ten times, and thus the transfer distance may reach
the range of 1~3 m with an acceptable efficiency [19].
Another method is to deploy one or several underground
repeaters between the transmitter and receiver for transfer
distance extension [20]. Apart from using the enlarged coils
and multiple repeaters to maintain the high-efficiency
transmission, the WPT can adopt the MHz frequency band
[21]–[23] to achieve the wireless motoring drainage function
in practice. To balance the tradeoff between the required
power level and the desired system efficiency, the relatively
high efficiency can be realized to stabilize the system
performance against a long transfer distance. On the other
hand, the frequency-modulated WDMC is still effective
during the MHz operation. Significantly, to prevent the severe
weather hazards, the function of wireless motoring drainage
can outweigh the slightly reduced efficiency considering only
emergency responses.
V. CONCLUSION
A promising in-pipe pumping drainage system using the
frequency-modulated WDMC has been proposed and imple-
mented, which can take action in response to emergencies for
preventing severe weather hazards. With no underground
motor drivers and cables, it has the advantages of mobility,
flexibly and maintenance-free. The underground in-pipe pump
network can be wirelessly powered by a moveable energy-
carrying EV to accelerate the flow rate. The proposed WDMC
scheme newly adopts the ZVS-PFM method to conduct the
motor speed control up to 1500 rpm. Meanwhile, the system
electrical efficiency can reach 87.6% at rated load with a 430-
W output electric power and a 15-cm distance, while it can
still achieve 83.9% at overload with an around 600-W electric
power. Theoretical analysis, computer simulation and practical
experimentation are given to verify the feasibility of proposed
in-pipe pumping drainage system using frequency-modulated
WDMC.
ACKNOWLEDGMENT
This work was supported by a grant (Project No. 17207420)
from the Hong Kong Research Grants Council, Hong Kong
Special Administrative Region, China.
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