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Research on electro-hydraulic
composite drive winch and energy
recovery system for mobile crane
Xianggen Xu
1
,
2
, Tianliang Lin
1
,
2
*, Haoling Ren
1
,
2
, Tong Guo
1
,
2
,
Zhongshen Li
1
,
2
and Cheng Miao
1
,
2
1
College of Mechanical Engineering and Automation, Huaqiao University, Xiamen, China,
2
Fujian Key
Laboratory of Green Intelligent Drive and Transmission for Mobile Machinery, Xiamen, China
Owing to the high power consumption and limited control precision of traditional
hydraulic drive winch systems, this study proposes hydraulic and electric-type
energy recovery systems. The accumulator used in the hydraulic type has low
energy density, which makes it difficult to store a large amount of energy.
Meanwhile, the electric motor/generator used in the electric type cannot solve
the secondary slip because of oil leakage, which leads to low controllability and
high-power consumption under near-zero speed and high torque conditions.
Thus, based on electric construction machinery with high-pressure, energy-
dense electric energy storage units, this study proposes an electro-hydraulic
composite drive winch and energy recovery system and control strategy for
mobile cranes. Considering the good control characteristics of the electric
motor/generator and the high-power density of the hydraulic accumulator,
this hydroelectric composite drive and energy recovery system may solve the
secondary sliding challenge and ensure large torque output at near-zero speed. A
simulation model of the mobile crane is established to verify the feasibility of the
proposed system and control strategy. The research results showed that the
system is more efficient at recovering energy when the weight is lowered by a
greater distance.
KEYWORDS
winch system, engineering machinery, secondary slip, mobile crane, electro-hydraulic
composite drive, energy recovery efficiency
1 Introduction
With global warming, rising oil prices, and the energy crisis, the importance of energy
saving and emission reduction has been gradually increasing in numerous guiding
frameworks (Zhang et al., 2017;Liu, 2019). Construction machinery often has a large
amount of negative load during movement. Reducing carbon emissions and implementing
electrification to achieve energy saving and environmental protection are of current interest
worldwide (Lin et al., 2020). The types of winch energy-saving drives are divided according
to their components into hydraulic drive, electro-hydraulic composite drive, and direct
electric motor/generator drive. Similarly, according to the energy storage components, winch
energy recovery can be divided into hydraulic recovery, electric recovery, and composite
recovery.
The winch systems of traditional construction machinery are primarily hydraulic drives.
Central South University proposed an energy-saving system for the recovery of the potential
energy of the main lowering winch of rotating drilling rigs, in which the secondary element
OPEN ACCESS
EDITED BY
Yang Yang,
Yangzhou University, China
REVIEWED BY
Wang Hongliang,
Changzhou Institute of Technology,
China
Weixuan Jiao,
Yangzhou University, China
Leilei Ji,
Jiangsu University, China
*CORRESPONDENCE
Tianliang Lin,
ltlkxl@163.com
RECEIVED 16 March 2023
ACCEPTED 01 June 2023
PUBLISHED 19 June 2023
CITATION
Xu X, Lin T, Ren H, Guo T, Li Z and Miao C
(2023), Research on electro-hydraulic
composite drive winch and energy
recovery system for mobile crane.
Front. Energy Res. 11:1187558.
doi: 10.3389/fenrg.2023.1187558
COPYRIGHT
© 2023 Xu, Lin, Ren, Guo, Li and Miao.
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under the terms of the Creative
Commons Attribution License (CC BY).
The use, distribution or reproduction in
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original author(s) and the copyright
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comply with these terms.
Frontiers in Energy Research frontiersin.org01
TYPE Original Research
PUBLISHED 19 June 2023
DOI 10.3389/fenrg.2023.1187558
hydraulic pump/motor was mechanically connected to the engine in a
coaxial manner, and the accumulator recovered the residual potential
energy (Zhu et al., 2018). Fang at Central South University designed a
hybrid oil-electric winch system based on the hydraulic system for the
main winch of rotary drilling rigs, in which the hydraulic motor/
generator was used to recover the potential energy into electric energy
stored in the supercapacitor when the main winch was lowered (Fang
et al., 2012). Bolonne, at the University of Molétouvo, proposed a
hybrid system for RTG cranes that included a lithium battery, a
supercapacitor, and a diesel generator, in which the supercapacitor
and lithium battery worked together to recover the crane’s regenerable
energy (Bolonne and Chandima, 2019). Kim at the Korean
Classification Society proposed a hybrid system using diesel
generators in combination with supercapacitors and lithium-ion
batteries and assessed energy recovery into lithium batteries and
supercapacitors under different operating conditions. The results
showed that the system could significantly reduce harmful emissions
(Kim et al., 2019). Corral-Vega of the University of Cadiz proposed an
RTG drive scheme using a fuel cell as the energy source and a
supercapacitor as the energy storage system. The simulation results
demonstrated the high energy efficiency of the hybrid system. Direct-
drive winches are primarily used in stationary machinery, such as tower
cranes, shovels, and elevators. Huang from Beijing Jiaotong University
proposed a supercapacitor-based power compensation and energy
recovery system for mine hoisting equipment, in which the energy
of the shaft grid and the potential energy of the shaft repair machine
were stored in the supercapacitor through a converter (Huang Pu,
2015). The results showed that the system was more practical at
obtaining power and the load was lower. Li from ZOOMLION
researched a purely electric truck crane energy recovery device and
system strategy in unplugged and plugged operation conditions, and
verified the effectiveness of the crane winch energy recovery device and
control strategy (Li et al., 2022). Research on electric winches has
focused on electrical control devices (Premkumar and Manikandan,
2014;Kodkin and Anikin, 2020). A control device was used to prevent
backlash due to slack in the traction component (Lee et al., 2019;
Caporali, 2021). In addition, there are control algorithms that
compensate for the loss of torque in the low-speed area of the
motors (Li and Wang, 2019;Roman et al., 2021), and mechanical
methods to improve the structure and stability to provide ordered
coiling of strings, etc. Electro-hydraulic composite drive winch systems
have used electric motor-hydraulic pumps/motors to supplement the
composite drive and the power regeneration system. Liu of the Taiyuan
University of Technology proposed an electro-hydraulic hybrid drive
winch potential energy recovery system, which used an electric motor
as the main drive to reduce throttling losses, combined with a hydraulic
pump/motor and accumulator as the energy recovery unit. The results
showed that the electro-hydraulic composite drive winch system had
good energy recovery (Liu et al., 2022). Zhao of the Taiyuan University
of Technology applied the composite electric motor-hydraulic pump/
motorcompositedrivesystemtoanelevatorsystem,whichrecovered
energy from the traction machine’s power generation state through the
accumulator, and released the energy from the accumulator when the
traction machine needed to be in the electric state for energy recovery
(Zhao et al., 2016;Zhang et al., 2020). Wang Xthe at the Taiyuan
University of Technology proposed a hybrid electro-hydraulic drive
electric excavator hoist system, which utilized the engine as the main
drive and the accumulator-hydraulic pump/motor as the auxiliary
drive. The potential energy of the hoist system was mainly stored in
the accumulator through the hydraulic pump/motor when the hoist
system was lowered. The energy was released by the accumulator when
it was lifted (Wang et al., 2020). The hydraulic pump/motor and the
electric motor worked together to complete the lifting. The simulation
results showed that the system reduced the power consumption by
approximately 30% compared to the traditional system. Zhang of the
Dalian University of Technology proposed a composite electro-
hydraulic drive hoist system, in which the speed was controlled by a
hydraulic system and the torque was controlled by an electric motor.
The hydraulic motor was connected to the two ends of the bobbin to
drag the load together. The results showed that the system energy
recovery efficiency was approximately 60% (Zhang, 2019).
To recover the potential energy of the mobile crane winch
system and reduce engine pollution, considering the good control
characteristics of the electric motor/generator and the high power
density of the hydraulic accumulator, this study proposes a hydro-
electric composite drive and energy recovery system to solve the
challenge of secondary sliding and ensure the large torque output at
near-zero speed. A control strategy is also proposed to integrate
energy recovery and regeneration for the proposed composite winch
system.
2 Working principles of the winch
system
The scheme of the proposed entity electro-hydraulic composite
drive winch system is shown in Figure 1. The system mainly contains
an electrical component, a hydraulic drive component, and a
mechanical drive component.
2.1 Electric drive component
The pressure signal from the hydraulic system, the speed and
torque signal from the motor controller, and the artificially desired
weightlifting speed signal are collected by the vehicle control unit
(VCU). The control unit in the hydraulic system, the electric motor
controller unit (MCU), and the lithium battery management system
(BMS) receive the control signals from the VCU via the controller
area network (CAN) bus and input and output (IO) port. The
closed-loop enables cooperative control in multiple quadrants of the
electric motor/generator-variable displacement hydraulic pump/
motor output speed, angle, torque, and other parameters. The
weight is driven to lift and lower to achieve the desired movement.
2.2 Hydraulic drive component
The hydraulic drive component is shown in Figure 2. In addition to
storing energy, the high-pressure and low-pressure accumulators provide
hydraulic energy to the variable displacement hydraulic pump/motor.
Each 2-position, 2-way electromagnetic valve receives control signals
from the VCU depending on the different working conditions. Hydraulic
oil in both the high-pressure and low-pressure accumulators is transferred
tothevariabledisplacementhydraulic pump/motor. The oil is pressurized
or depressurized and then returned to the high-pressure and low-pressure
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accumulators via the 2-position, 2-way electromagnetic valve to
complete the energy recovery. The differential pressure between
the two ends of the variable-displacement hydraulic pump/
motor changes continuously with changes in the pressure of
the high-pressure and low-pressure accumulators. The variable-
displacement hydraulic pump/motor receives control signals
from the VCU to change the displacement to meet the
required output torque, while the high-pressure and low-
pressure accumulators satisfy the pressure conditions.
2.3 Mechanical drive component
The mechanical drive component consists of coaxial mechanical
coupling among the variable-displacement hydraulic pump/motor,
electric motor/generator, and winch reducer. The weight is wound
onto the winch reducer using a wire string. The winch reducer is
driven by the electric motor/generator-variable-displacement
hydraulic pump/motor controlled by the VCU. The weightlifting
and lowering motion is determined by the VCU.
3 Control strategy and implementation
process of the winch system
3.1 Analysis of the winch system control
strategy
The signals of the pressure, displacement, torque, and SOC are
input to the VCU through various sensors. The weightlifting and
lowering motion mode differs depending on the load weight, the
pressure difference between the high-pressure and low-pressure
accumulators, the low-pressure accumulator pressure, and the
SOC. During the movement of the weight, the speed of the
electric motor/generator is directly controlled by the handle
opening. The displacement of the variable-displacement hydraulic
pump/motor adapts itself to the speed. When a constant torque
output of the variable-displacement hydraulic pump/motor is
required, the VCU sends a corresponding control signal to each
2-position, 2-way electromagnetic valve and variable-displacement
hydraulic pump/motor. The flow direction of the oil circuit and the
displacement of the displacement hydraulic pump/motor change to
achieve a constant torque output of the variable-displacement
hydraulic pump/motor. The electric motor/generator for adaptive
torque compensation and control strategy are shown in Figure 3,
where Y
P
is the handle opening (divided into positive and negative
sides); Y
min
is the positive and negative minimum handle opening;
Y
max
is the positive and negative maximum handle opening; SOC is
the state of charge of the lithium battery; S
max
is the maximum SOC
value when potential energy recovery is performed; Fis the negative
load weight; F
min
is the negative load weight when switching from
purely electric motor/generator drive to electro-hydraulic composite
drive; D
17
,D
18
,D
19
,D
20
, and D
21
correspond to the first, second,
third, fourth, and fifth 2-position, 2-way electromagnetic valve,
respectively; Δpand Δp
min
are the differential pressure and
minimum differential pressure between the high-pressure and
low-pressure accumulators, respectively; p
1
is the high-pressure
accumulator pressure; p
2
is the low-pressure accumulator
pressure; p
2min
is the minimum threshold pressure of the low-
pressure accumulator; and p
BA
is the differential pressure
between B-port pressure p
B
and A-port pressure p
A
of the
variable-displacement hydraulic pump/motor, i.e., the differential
pressure between the two ends of the variable displacement
hydraulic pump/motor.
FIGURE 1
Schematic diagram of the proposed winch system.
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According to the aforementioned, the control strategy is as
follows:
(1) If the load weight satisfies F<Fmin or the battery satisfies
SOC ≥Smax, the handle opening satisfies Ymin <|Yp|<Ymax ;
the system is in the pure electric motor/generator drive and
energy recovery mode. The electric motor/generator is in an
electric motor state when the weight is lifting and in the electric
generator state when it is lowering.
(2) If the load weight satisfies F≥Fmin and the battery satisfies
SOC <Smax, the handle opening satisfies Ymin <Yp<Ymax and
the differential pressure between the high-pressure and low-
pressure accumulators satisfies Δp≥Δpmin; the system is in the
electro-hydraulic composite drive mode. The electric motor/
generator is working as the electrical motor. The variable-
displacement hydraulic pump/motor is in a hydraulic motor
state to allow the electro-hydraulic composite drive to lift the
weight.
(3) If the load weight satisfies F≥Fmin and the battery satisfies
SOC <Smax, the handle opening satisfies −Ymax <Yp<−Ymin
and the low-pressure accumulator pressure satisfies p2≥p2min;
the system is in the recovery mode of the electro-hydraulic
composite drive. The electric motor/generator is in the electric
generator state. The variable-displacement hydraulic pump/
motor is in the hydraulic pump state to allow the electro-
hydraulic composite drive to lower the weight.
3.2 Implementation process for the winch
system
If the load is light (F<Fmin or SOC ≥Smax), the winch drive
system operates in a purely electric motor/generator drive mode
with an energy recovery mode and the electric motor/generator in an
electric motor or power production state.
If the load is heavy (F≥Fmin and SOC <Smax), the winch drive
system initially operates in electro-hydraulic composite drive mode,
in which the electric motor/generator is in the electric motor state
and the variable-displacement hydraulic pump/motor is in the
hydraulic motor state. D
17
,D
19
, and D
20
are energized and in a
fully open state. D
18
and D
21
are de-energized. The hydraulic oil in
the high-pressure accumulator reaches port B of the variable-
displacement hydraulic pump/motor through D
17
and D
19
. The
variable-displacement hydraulic pump/motor is then in the
hydraulic-motor state. After depressurization, the oil is returned
to the low-pressure accumulator from D
20
and the second check
valve. The pressures in both the high-pressure accumulator and the
low-pressure accumulator, as well as the pressure at both ends of the
FIGURE 2
Hydraulic schematic of the winch system.
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variable displacement hydraulic pump/motor, change with the
above process. The displacement of the variable-displacement
hydraulic pump/motor must be controlled to ensure that its
output torque is constant and, thus, outputs a certain amount of
power, as well as to control the motor controller to power the lithium
battery to drive the electric motor/generator synergy to output the
remaining power. If the differential pressure between the high-
pressure and low-pressure accumulators cannot meet the constant
torque output of the variable displacement hydraulic pump/motor;
namely, Δp<Δpmin during the weight lifting, D
17
,D
18
, and D
20
are
de-energized and D
19
and D
21
are energized and in a fully open state.
The electric motor/generator alone outputs power to drive the winch
reduction gear to lift the weight and drive the variable-displacement
hydraulic pump/motor in the idle state. The first and second check
valves and all four direct-acting relief valves work as required. In the
work process described earlier, the speed of the electric motor/
generator is directly controlled by the handle opening to achieve the
target velocity of the weightlifting and complete the lifting motion.
If the load is heavy (F≥Fmin and SOC <Smax), the winch drive
system initially operates in the electro-hydraulic composite drive
mode. The electric motor/generator is in the electric generator state
and the variable displacement hydraulic pump/motor is in the
hydraulic pump state. D
18
,D
19
, and D
20
are energized and in a
fully open state. D
17
and D
21
are de-energized. The hydraulic oil in
the low-pressure accumulator reaches port A of the variable
displacement hydraulic pump/motor through D
18
and D
19
. After
pressurization, the oil is returned to the high-pressure accumulator
from D
20
and the first check valve. The pressures in both the high-
pressure and low-pressure accumulators, as well as the pressure at
both ends of the variable displacement hydraulic pump/motor,
change during the above process. The displacement of the
variable-displacement hydraulic pump/motor is controlled by the
VCU to ensure a constant power output of the variable-
displacement hydraulic pump/motor. The lithium is treated as a
power source to ensure the remaining power output of the electric
motor/generator. If the fluid pressure in the low-pressure
accumulator is insufficient to keep the reverse towing torque
formed by the variable-displacement hydraulic pump/motor at a
certain value during the weight lowering; namely, p2<p2min,D
17
,
D
18
, and D
20
will be de-energized. D
19
and D
21
will be energized and
in a fully open state. The motor/generator alone outputs power to
drive the winch reduction gear to lower the weight and make the
variable-displacement hydraulic pump/motor in the idle state, and
the first check valve, the second check valve, and all four direct-
FIGURE 3
Control strategy for the winch system.
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acting relief valves work as required. In the working process
described above, the speed of the electric motor/generator is
directly controlled by the handle opening to achieve the target
lowering velocity of the weight.
When the winch must be stopped during the weight-lowering
process, the handle opening should be reduced to below the minimum
threshold. All the 2-position, 2-way electromagnetic valves are
controlled in the de-energized state. The electric motor/generator is
FIGURE 4
Simulation model of the winch system.
TABLE 1 Main simulation parameters of the winch system.
Parameter Parameter value
Rated power of the motor 50 kW
Rated speed of the motor 3,600 r/min
Rated torque of the motor 130 N·m
Battery capacity 6.5 Ah
Initial battery charge 90% SOC
Winch gear ratio 55.2
Diameter of the winch reducer reel 0.44
Maximum velocity of the weight movement 1 m/s
Load weight range 1–4t
Maximum displacement of the variable displacement hydraulic pump/motor 500 mL/r
Rated speed of the variable displacement hydraulic pump/motor 3,600 r/min
Opening pressure of the first direct-acting relief valve 20 MPa
Opening pressure of the second direct-acting relief valve 5 MPa
Opening pressure of the third direct-acting relief valve 20 MPa
Opening pressure of the fourth direct-acting relief valve 20 MPa
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controlled by the VCU in the blocked condition to stop the movement
of the weight. The first check valve, the second check valve, and all four
direct-acting relief valves work as required.
The system makes full use of the high energy density of the
electrical energy storage unit and the good control characteristics of
the electric motor/generator. The system also provides a solution to
the problem of secondary sliding of heavy loads as well as the low
energy density of the accumulator. The proposed closed hydraulic
system using the accumulator-variable displacement hydraulic
pump/motor can achieve high power density and high torque
output at near-zero speed and solve the problem of high energy
consumption of the electric motor/generator drive winch and part of
the energy loss in the balance and multiple directional control valves.
4 Winch system modeling and
simulation model
4.1 Winch system modeling
After the load weight Fand the desired lifting and lowering
speed vhave been determined, the output power of the electric
motor/generator-variable displacement hydraulic pump/motor is
determined using Eq. 1.
PF·v
1000 2πn·T
6000 (1)
where P,n, and Tare the output power, speed, and output torque of
the electric/generator-variable hydraulic pump/motor, respectively.
The output power Pincludes two components: output torque T
and output speed n. For the electric motor/generator-variable-
displacement hydraulic pump/motor, the required output torque
Tis determined by the load weight F, the diameter of winch reducer
reel D, and the winch reducer transmission ratio r, as shown in Eq. 2.
T30F·v
π·nF·D
2r (2)
In the case of the electric motor/generator-variable-
displacement hydraulic pump/motor, the desired velocity ncan
be determined by the desired lift and lowering velocity vof the
weight, the diameter of the winch reducer reel D, and the winch
reducer transmission ratio r, as shown in Eq. 3.
n60v·r
πD(3)
The variable-displacement hydraulic pump/motor is designed to
deliver a constant proportional torque. The displacement Vof the
variable displacement hydraulic pump/motor can be determined by
Δp, as shown in Eq. 4
V2πT
Δp·k(4)
where Vis the displacement of the variable displacement hydraulic
pump/motor, and kis the displacement influencing factor, the value
of which is directly related to the output power assumed by the
artificially desired variable displacement hydraulic pump/motor. T/k
denotes the amount of output torque that must be assumed by the
variable-displacement hydraulic pump/motor.
After the electric motor/generator speed has been controlled at
the desired value and the displacement of the variable-displacement
hydraulic pump/motor has been calculated, the required flow rate of
the high-pressure accumulator q
1
and low-pressure accumulator q
2
can be calculated by Eq. 5.
qn·V(5)
where qis the high-pressure and low-pressure accumulator
flow rate.
The maximum pressures of the high-pressure and low-pressure
accumulators are limited by the setting pressures of the first and
second direct-acting relief valves, respectively. The setting pressures
of the third and fourth direct-acting relief valves are determined by
the system operating pressure. The first check valve, the second
check valve, the first charge check valve, and the second charge
check valve are not set to an initial pressure. Each 2-position 2-way
electromagnetic valve has a fully open and a fully closed state. In the
fully open state, the flow rate restriction or pressure drop at the inlet
and outlet of the valve is as small as possible. Therefore, the
differential pressure between the high-pressure and low-pressure
accumulators can be approximated as that of the two ends of the
variable displacement hydraulic pump/motor. The hydraulic system
may not be capable of delivering constant proportional power due to
the capacity limitations of the high-pressure and low-pressure
accumulators. Thus, movement of the weight requires the electric
motor/generator alone.
4.2 Winch system simulation model
According to the scheme presented in Figure 1 and the control
strategy illustrated in Figure 3, the simulation model of the
electro-hydraulic composite drive winch system is shown in
Figure 4. The main components of the simulation model are the
hydraulic system model, the signal control system model, and the
mechanical system model.
FIGURE 5
Variation in accumulator state parameters.
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The heavy-load mass, the light-load mass, the winch reductionratio
r, the reel diameter, and the maximum lifting and lowering velocity of
the weight are defined as 3 t, 1 t, 55.2, 0.44 m, and 1.5 m/s respectively.
Calculated using Eq. 1, the maximum output powers required by
the electric motor/generator-variable-displacement hydraulic pump/
motor for heavy and light loads are 45 kW and 15 kW, respectively.
Calculated using Eq. 2,the maximum output torques required by the
electric motor/generator-variable-displacement hydraulic pump/motor
for the heavy and light loads are 120 N·mand40N·m, respectively.
Calculated using Eq. 3,the maximum weight-lowering speed
required by the electric motor/generator-variable-displacement
hydraulic pump/motor is 3,594 r/min.
The Δp
min
is controlled at around 1.2 MPa. The minimum kis
set at 5/3, which means that 3/5 of the torque required by the system
must be carried by the variable-displacement hydraulic pump/
motor. The maximum Vrequired by the variable-displacement
hydraulic pump/motor for the heavy and light loads can be
calculated using Eq. 4as 450 mL/r and 150 mL/r, respectively.
FIGURE 6
Dynamic characteristics of the system under different conditions. (A) Different p
3
.(B) Different k.
FIGURE 7
Pressure and flow rate characteristic of the system at different p
3
.(A) High-pressure and low-pressure accumulator pressure variation. (B)
Differential pressure variation of the high-pressure and low-pressure accumulators. (C) Flow rates of the high-pressure and low-pressure accumulators.
(D) Variation in the output torque of the electric motor/generator-variable hydraulic pump/motor.
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Therefore, the variable-displacement hydraulic pump/motor with a
maximum Vof 500 mL/r is used in the system.
The rated power, the rated torque, and the rated speed of the
electric motor/generator should be greater than the values calculated
above. The initial state of charge of the lithium battery is set to 90%,
and the capacity of the lithium battery is set to 6.5 Ah.
The main technical parameters required for the simulation of
the electro-hydraulic composite drive winch system are shown in
Table 1.
5 System simulation analysis
The simulation analysis focuses on the dynamic characteristics
of the lifting cycle of the weight at different variable-displacement
hydraulic pump/motor output proportional torques and initial
pressures of the high-pressure accumulator, as well as the energy
recovery efficiency of the system during the lowering of the weight.
5.1 Dynamic characteristics of the weight
under different conditions
The cycle time in the simulation is set to 12.5 s, where 0–6 s is the
lifting condition, 6 s–6.5 s is the stop condition, and 6.5 s–12.5 s is
the lowering condition. The expected lifting and lowering velocity is
0.2 m/s. The speed of the electric motor/generator-variable-
displacement hydraulic pump/motor is controlled by the PID at
480 r/min. The dynamic characteristics of the weight lifting and
lowering are studied under a different initial pressure of the high-
pressure accumulator and output torque of the variable-
displacement hydraulic pump/motor, respectively. As the Δpcan
be approximated as p
BA
, it is set to Δp
min
(1.2 MPa) when the weight
is lifting (F1t) and to p
2min
(1.3 MPa) when the weight is lowering
(F2t). If the movement is not completed, the variable-
displacement hydraulic pump/motor is put into an idle state by
the VCU and no more power is outputted, while the remaining
power is outputted by the electric motor/generator alone. During the
simulation, SOC and Fare set to F≥Fmin and SOC ≥SOC min, and
the system in the electro-hydraulic composite drive and energy
recovery mode.
Owing to the advantages of good oil and gas isolation, high
specific volume, and tightness, airbag accumulators are used for both
high-pressure and low-pressure accumulators in the system. The
high-pressure accumulator is set to 5 L with a pre-charge pressure of
2 MPa, while the low-pressure accumulator is set to 10 L with a pre-
charge pressure of 0.5 MPa. The relationship between the volume V
1
of the accumulator gas chamber and pressure is shown in Eq. 6.
pV1mW(6)
where Wis constant and mis the state index varying between
1 and 1.4.
FIGURE 8
Pressure and flow rate characteristics of the system at different kvalues. (A) High-pressure and low-pressure accumulator pressure variation. (B)
Differential pressure variation for high-pressure and low-pressure accumulators. (C) Flow rate for high-pressure and low-pressure accumulators. (D)
Variation of the output torque of the electric motor/generator-variable-hydraulic pump/motor.
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The trend of the accumulator state parameters during the
charging and discharging of the accumulator can be obtained
from Figure 5. Where the charging and discharging process
curves do not coincide, the general expansion process of the gas
(discharging process) is faster than the compression process
(charging process).
5.1.1 Different initial pressures of the high-pressure
accumulator
The purpose of this study was to investigate the dynamic
characteristics of weight lifting and lowering under different
initial high-pressure accumulator pressures from p
3
to 4 MPa,
5.5 MPa, and 7 MPa. The initial pressure p
2
is the same 1.5 MPa
under different conditions. Moreover, the lift condition is such that
k3, i.e., 1/3 of the total torque at a constant output of the variable-
displacement hydraulic pump/motor. As shown in Figure 6A, the
weight can quickly and more stably reach the target velocity loaded
from a stop condition (t6.2 s) and suddenly started from a stop
condition to a lowering condition (t6.5 s) with different p
3
. This
indicates that the proposed winch system has good dynamic
characteristics.
When the weight is in the lifting condition (0–6 s), the lower the
p
3
, the smaller the initial Δpand p
BA
ends of the variable-
displacement hydraulic pump/motor. In cases with the same
required torque and speed, according to Eq. 4; Eq. 5, the larger
the initial Vrequired, the larger the initial q
1
. Accordingly, a larger q
will flow into the low-pressure accumulator with the same initial p
2
(1.5 MPa). For the system with lower p
3
, as shown in Figures 5,7A
and Eq. 6show that p
2
rises faster. The faster that p
BA
falls, the faster
that Vwill rise. As shown in Figure 7C, the q
1
will rise faster, the flow
rate into the corresponding high-pressure and low-pressure
accumulators will also rise, and the pressure will rise faster. As
shown in Figures 7B,D, the faster the differential pressure reaches
Δp
min
(1.2 MPa), the faster the variable-displacement hydraulic
pump/motor will be in an idle state without output torque, and
the motor/generator will output torque separately during the lifting
condition.
When the weight is in the stop condition (6 s–6.5 s), the load
weight is lifted from 1 t to 2 t at 6.2 s and changed from the stop
condition to the lower condition at 6.5 s. As shown in Figures 6A,
7B, D and Eq. 10, no sliding down of twice the weight occurs owing
to the instantaneous high torque provided by the electric motor/
generator and variable-displacement hydraulic pump/motor. The
Δpis always 1.2 MPa during this period.
When the weight is in the lowering condition (6.5 s–12.5 s), for
the system with a different p
3
, the Δpis initially the same at 1.2 MPa.
When the required torque and speed are the same, according to Eq.
4; Eq. 5, the required Vand q
2
are also the same. For the system with
higher p
3
, as shown in Figure 7B shows that in the lowering
condition, the faster that the Δprises, the faster the pressure
difference between the two ends of the variable-displacement
hydraulic pump/motor rises, and the faster that V will fall. As
shown in Figure 7C,q
2
will fall faster. It is reasonable to say that in
the system with a higher p
3
, the slower that the pressure of the
corresponding high-pressure accumulator will rise and the slower
that the pressure of the low-pressure accumulator will fall during the
lowering process. For the system with a higher p
3
, the initial p
1
and
p
2
are higher. Combined with Figure 5;Figure 7B; Eq. 6show that in
the system with the higher p
3
, the faster the Δpand the pressure
difference between the two ends of the variable-displacement
hydraulic pump/motor will rise during the entire lowering
process. As shown in Figures 7A,D, the faster the p
2
reaches
p
2min
(1.3 MPa), the faster the variable-displacement hydraulic
pump/motor will be in an idle state without output torque, and
the motor/generator will output torque separately during the
lowering condition.
5.1.2 Different variable-displacement hydraulic
pump/motor output proportional torque
For k3, k2, and k5/3, we expect 1/3, 1/2, and 3/5 of the
total torque at a constant output of the variable-displacement
hydraulic pump/motor and observe the dynamic characteristics
of the lifting and lowering of the mass. When p
3
is 7 MPa, the
initial p
2
is 1.5 MPa. As shown in Figure 6B, the dynamic
characteristics of this winch system are all good for different k
values. The weight can quickly and more stably reach the target
velocity when loaded from a stop condition (t6.2 s) and when
suddenly starting from a stop condition to a down
condition (t6.5 s).
When the weight is in the lifting condition (0–6 s), the initial
pressures of the high-pressure and low-pressure accumulators are
the same for systems with different kvalues. The initial Δpis the
same. The initial differential pressure between the two ends of the
variable-displacement hydraulic pump/motor is the same. For the
system with larger proportional torque output, in the case of the
same required speed according to Eq. 4, the larger the required initial
V, the larger the initial q
1
. According to Eq. 5and as shown in
Figure 5 and Eq. 6, the faster the p
1
falls and p
2
rises, the faster the
pressure difference between the two ends of the variable-
displacement hydraulic pump/motor falls and the faster the V
will rise. As shown in Figure 8C, the q
1
will rise faster. The
corresponding q
2
and p
2
will also rise faster. As shown in Figures
8B, D, the faster the differential pressure reaches Δp
min
(1.2 MPa),
the faster the variable displacement hydraulic pump/motor will be in
FIGURE 9
Variations in the pressures of the accumulators and hydraulic
pump/motor.
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Xu et al. 10.3389/fenrg.2023.1187558
an idle state without torque output and the motor/generator will
separately output torque during the lifting condition.
When the weight is in the stop condition (6 s–6.5 s), the load
weight is lifted from 1 t to 2 t at 6.2 s and changed from the stop
condition to the lower condition at 6.5 s. As shown in Figures 6B,
Figures 8B,D and Eq. 10, no sliding down of twice the weight occurs
owing to the instantaneous high torque provided by the electric
motor/generator and variable-displacement hydraulic pump/motor.
The Δpis always 1.2 MPa during this period.
When the weight is in the lowering condition (6.5 s–12.5 s), for
the different kin the system, the initial Δpis always 1.2 MPa. For the
system with larger k, in the case of the same required speed
according to Eq. 4; Eq. 5shows that the required initial Vand
initial q
2
are larger. Figure 5 and Eq. 6show that the faster the p
2
falls
and the p
1
rises, the faster p
BA
rises, and the faster the Vwill fall. As
shown in Figure 8C, the q
2
will fall faster; thus, it is reasonable to say
that the higher the k, the slower the corresponding p
1
will rise and
the corresponding p
2
will fall during the lowering process. The
system with the higher proportional torque output of the variable-
displacement hydraulic pump/motor during the whole lower
process can still rely on its higher torque required to maintain
the qat a higher level even when the qfalls, as shown in Figure 8C.
The combination of Figures 5,8A, B, and Eq. 6shows that the higher
the proportional torque of the variabledisplacement hydraulic
pump/motor outputs during the whole lower process, the faster
p
1
rises, the faster p
2
falls, and the faster Δprises. As shown in
Figures 8B,D, the faster that p
2
reaches p
2min
(1.3 MPa), the faster
the variable-displacement hydraulic pump/motor will be in an idle
state without output torque, and the motor/generator will output
torque separately during the lowering condition.
5.2 Analysis of the efficiency of the system
energy recovery
The energy recovery efficiency of the winch system is discussed
in terms of the power of the high-pressure accumulator, the power of
the low-pressure accumulator, the power of the electric motor/
generator, and the power consumption of the lowering weight.
The energy can be obtained by integrating the corresponding
power of each component. The system is in the recovery mode
of the electro-hydraulic composite drive during the descent,
i.e., p2≥p2min. The Δpin the simulation process can be treated
as p
BA
. The whole simulation system is first in the electro-hydraulic
composite drive and energy recovery mode. The battery SOC and the
load weight Fare treated as F≥Fmin and SOC ≤Smax, respectively.
The power of the high-pressure accumulator P
1
and the low-
pressure accumulator P
2
are determined using Eq. 7and Eq. 8.
P1p1·q(7)
P2p2·q(8)
FIGURE 10
Variation in the displacement of the hydraulic pump/motor and
the flow rate of the accumulators.
FIGURE 11
Variation in the torque of the hydraulic pump/motor and electric
motor/generator.
FIGURE 12
Variation in the busbar current of the electric motor/generator
and the SOC of the battery.
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Xu et al. 10.3389/fenrg.2023.1187558
The power of the electric motor/generator P
3
can be calculated
from Eq. 9.
P3U·I(9)
where Uand Irepresent the busbar voltage and current of the
electric motor/generator, respectively. The electric motor/generator
is in the electric motor state when I>0 and in the electric generator
state when I<0.
The power of the lowering weight P
4
can be determined by the
weight lowering height sand F, as shown in Eq. 10.
P4F·s(10)
The energy recovery efficiency of the system P
5
is determined
using Eq. 11.
P5P1−P2+P3
P4
·100% (11)
After setting F0.5t, k3, and v0.2m/s, the energy
recovery efficiency of the system is investigated for a weight-
lowering height of 1 m (s1m). All the 2-position 2-way
electromagnetic valves are controlled in the de-energized
state before lowering the weight. As shown in Figure 9,no
pressure is built up at the two ends of the variable-
displacement hydraulic pump/motor, i.e., pBA 0att0s.
Combined with Figure 10 and Eq. 4, these results show that
the variable-displacement hydraulic pump/motor must adapt
itself to rapidly increase Vto deliver a certain torque when the
weight suddenly starts to lower. As shown in Figure 10 and Eq. 5,
the higher the V,thehighertheq.AsshowninFigure 13A,P
1
and P
2
both are large at the initial moment according to Eq. 7
and Eq. 8. The higher the q
1
and q
2
,thegreaterthechangesinthe
gas volumes of the high-pressure and low-pressure
accumulators. As shown in Figure 5 and Eq. 6,thegreater
the changes in the gas volume of the high-pressure and low-
pressure accumulators, the higher the changes in p
1
and p
2
.As
shown in Figure 9,p
1
,Δp,andp
BA
rise, while p
2
falls quickly after
the weight has been lowered. As shown in Figure 10,Vcannot be
reduced in time due to the delay in system control after a rapid
increase in p
BA
.AccordingtoEq.4and as shown in Figure 11,
the variable-displacement hydraulic pump/motor output torque
momentarily exceeds its required output by 1/3 proportional
torque in the hydraulic pump state. At the same time, as shown
in Figure 11,Figure 12,andEq.9, the positive torque output of
the electric motor/generator ensures that the system outputs a
constant torque; the busbar current Iis >0 meaning that the
electric motor/generator is in theelectricmotorstate;i.e.,the
SOC of the battery is consumed. Combined with Figure 13A,
Figure 13B,Figure 14,andEq.11, the electric motor/generator is
in the electric motor state, which means that P3<0isthemain
reason why P5<0 at the initial moment. As shown in Figure 10,
Figure 11,andFigure 12, the variable-displacement hydraulic
pump/motor and the electric motor/generator can output a
constant proportional torque respectively; I<0andP3>0
means the electric motor/generatorisintheelectricgenerator
state; i.e., the SOC of the battery is stored after Vhas returned to
its normal range of variation. As shown in Figure 9,Figure 10,
Figure 13A,Eq.7,andEq.8,asp
1
increases, so does P
1
; similarly,
as p
2
increases, so does P
2
.AsshowninFigure 14 and Eq. 11,the
longer the weight is lowered, the greater the P
5
.
FIGURE 13
Variation in the power and energy of each component. (A) Variation in the power of each component. (B) Variation in the energy of each
component.
FIGURE 14
Energy recovery efficiency at different distances of weight
descent.
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Xu et al. 10.3389/fenrg.2023.1187558
6 Conclusion
To recover the gravitational potential energy and avoid
secondary sliding, this study proposed an electro-hydraulic
composite drive winch and energy recovery system for mobile
cranes. The problems of secondary sliding of the weight and the
limited energy recovery of the accumulator can be solved effectively
by the high energy density of the lithium batteries and the good
control characteristics of the electric motor/generator. The problem
of high energy consumption of the electric motor/generator drive
winch and most of the energy consumption of the liquid drive winch
in the balance and multiple directional control valves can be
alleviated by instantaneous high-power density and large torque
output at the near-zero speed of the accumulator-variable
displacement hydraulic pump/motor.
Thefeasibilityofthecontrolstrategy of the electro-hydraulic
composite drive winch and potential energy recovery system was
verified through the study of the dynamic characteristics of the
weight lifting and lowering under different conditions. We studied
the pressure variations of the high-pressure and low-pressure
accumulators (p
1
and p
2
), as well as the pressure difference (Δp),
flow rate (q), and output torque of the electric motor/generator-
variable displacement hydraulic pump/motor (T). When p
3
or kis
at different values in this electro-hydraulic composite drive winch
system, the weight lifting and lowering dynamic characteristics differ.
The energy recovery efficiency of the electro-hydraulic composite
drive winch and potential energy recovery system control strategy was
higher for weights lowered a greater distance. Although the energy
recovery efficiency of the system was high in the final results, the
magnitude of the final recovery efficiency could be influenced by
changing the initial pressure and volume of the high-pressure and
low-pressure accumulators as well as the fixed voltage of the lithium
battery. The specificenergyrecoveryefficiency is for reference only and
must be considered in conjunction with the actual situation. The system
control strategy is mainly based on the detection of load weight F,
battery SOC, high-pressure and low-pressure accumulator pressure, etc.,
to determine the drive mode of the weight. The electro-hydraulic
composite drive mode can reasonably use the motor speed active
control to achieve variable-displacement hydraulic pump/motor
adaptive speed. Automatic adjustment of the displacement of the
variable-displacement hydraulic pump/motor is used to actively
control the torque and, thus, achieve adaptive torque compensation
of the electric motor/generator.
The energy recovery efficiency of the system in this study may
vary considerably under different initial conditions. The basis for the
high efficiency of the energy recovery of the system is the selection of
suitable initial conditions in the actual working process. The
efficiency of the energy recovery is not considered in this system
when the initial pressure (p
1
and p
2
) and volume of the high-
pressure and low-pressure accumulators and the performance
parameters of the lithium battery are changed. The results of this
study lay a foundation for further experimental research.
7 Research ethics
The study does not involve animal or human subjects and does
not contain identifiable human data.
Data availability statement
The raw data supporting the conclusion of this article will be
made available by the authors, without undue reservation.
Author contributions
XX and TL contributed to the direction of the research content,
study design, manuscript writing, data processing, and data analysis.
HR and TG contributed to the literature searches and data
collection. ZL and CM were mainly responsible for data analysis
and project management. All authors contributed to the article and
approved the submitted version.
Funding
This work was supported by the National Key Research and
Development Program (2020YFB2009900), the National Natural
Science Foundation of China (Grant No. 52275055), Key Projects of
the Natural Science Foundation (Grant No. 2021J02013).
Acknowledgments
We thank all the authors for completing the study and
acknowledge the valuable comments and constructive suggestions
of the editor and reviewers.
Conflict of interest
The authors declare that the research was conducted in the
absence of any commercial or financial relationships that could be
construed as a potential conflict of interest.
Publisher’s note
All claims expressed in this article are solely those of the authors
and do not necessarily represent those of their affiliated
organizations, or those of the publisher, the editors, and the
reviewers. Any product that may be evaluated in this article, or
claim that may be made by its manufacturer, is not guaranteed or
endorsed by the publisher.
References
Bolonne, S. R. A., and Chandima, D. P. (2019). Sizing an energy system for hybrid Li-
ion battery-supercapacitor RTG cranes based on state machine energy controller. Ieee
Access 7, 71209–71220. doi:10.1109/access.2019.2919345
Caporali,R.P.L.(2021).Anti-swaymethodforreducingvibrationsonatower
crane structure. Int. J. Nonlinear Sci. Numer. Simul. 24, 171–184. doi:10.1515/
ijnsns-2021-0046
Frontiers in Energy Research frontiersin.org13
Xu et al. 10.3389/fenrg.2023.1187558
Corral-Vega, P. J., Garcia-Trivino, P., and Fernandez-Ramirez, L. M. (2019). Design,
modelling, control and techno-economic evaluation of a fuel cell/supercapacitors
powered container crane. Energy 186, 115863. doi:10.1016/j.energy.2019.115863
Fang, X., Zhao, H., and Liu, P. (2012). Simulation study of main winch system
geopotential energy recovery in rotary driller. Eng. J. Wuhan Univ. 45, 241–245+272.
Huang Pu, H. (2015). Study of ultracapicator-based power compensation and energy
Rocovery system for mine lifting equipment. Beijing: Beijing Jiaotong University.
Kim, K., An, J., Park, K., Roh, G., and Chun, K. (2019). Analysis of a supercapacitor/
battery hybrid power system for a bulk carrier. Appl. Sciences-Basel 9. doi:10.3390/
app9081547
Kodkin, V. L., and Anikin, A. S., (2020) The reflection mode of the moment loads by
an asynchronous electric drive with vector control and the features of this mode in the
rotation drive of the tower crane", in: International Ural Conference on Electrical Power
Engineering, 22-24 September 2020, Russia.
Lee, J.-G., Yeo, H.-K., Jung, H.-K., Kim, T.-K., and Ro, J.-S. (2019). Electromagnetic
and thermal analysis and design of a novel-structured surface-mounted permanent
magnet motor with high-power-density. Iet Electr. Power Appl. 13, 472–478. doi:10.
1049/iet-epa.2018.5322
Li, K., and Wang, Y. (2019). Maximum torque per ampere (MTPA) control for
IPMSM drives using signal injection and an MTPA control law. Ieee Trans. Industrial
Inf. 15, 5588–5598. doi:10.1109/tii.2019.2905929
Li, X., Cao, S., Luo, M., and Sun, L. (2022). Design and control strategy of energy
recovery device for pure electric vehicle crane. Constr. Mach. Equip. 53, 104–108+113.
Lin, T., Lin, Y., Ren, H., Chen, H., Chen, Q., and Li, Z. (2020). Development and key
technologies of pure electric construction machinery. Renew. Sustain. Energy Rev. 132,
110080. doi:10.1016/j.rser.2020.110080
Liu, H., Quan, L., Hao, Y., Huang, J., Li, Y., and Liu, Y. (2022). Fabrication of
superhydrophobic coating based on waterborne silicone-modified polyurethane
dispersion and silica nanoparticles. Chin. Hydraulics Pneumatics 46, 22–29. doi:10.
3390/polym15010022
Liu, J. (2019). China’s renewable energy law and policy: A critical review. Renew.
Sustain. Energy Rev. 99, 212–219. doi:10.1016/j.rser.2018.10.007
Premkumar, K., and Manikandan, B. V. (2014). Adaptive neuro-fuzzy inference
System based speed controller for brushless DC motor. Neurocomputing 138, 260–270.
doi:10.1016/j.neucom.2014.01.038
Roman, R.-C., Precup, R.-E., and Petriu, E. M. (2021). Hybrid data-driven fuzzy active
disturbance rejection control for tower crane systems. Eur. J. Control 58, 373–387.
doi:10.1016/j.ejcon.2020.08.001
Wang, X., Ge, L., Zhao, B., Hao, Y., Quan, L., and Mu, X. (2020). Energy efficiency
characteristics of cable shovel lifting system driven by hydraulic-electric hybrid system.
Trans. Chin. Soc. Agric. Mach. 51, 418–426. [In Chinese].
Zhang, H. (2019). Research on energy saving technology of hydraulic truck crane.
Dalian: Dalian Ligong University. [master’s thesis].
Zhang, J., Zhao, B., Hao, Y., Yu, H., Wang, J., Lei, A., et al. (2020). Pluripotent stem
cell-derived CAR-macrophage cells with antigen-dependent anti-cancer cell functions.
Chin. Hydraulics&Pneumatics 13, 153–160. [In Chinese]. doi:10.1186/s13045-020-
00983-2
Zhang, Y.-J., Peng, Y.-L., Ma, C.-Q., and Shen, B. (2017). Can environmental
innovation facilitate carbon emissions reduction? Evidence from China. Energy
Policy 100, 18–28. doi:10.1016/j.enpol.2016.10.005
Zhao, B., Quan, L., and Hao, Y. (2016). Research of operating characteristics and
energy efficiency of traction elevator with hybrid electric-hydraulic drive. J. Mech. Eng.
52, 192–198. doi:10.3901/jme.2016.04.192
Zhu, J., Wang, P., Wu, H., and Zhu, Z. (2018). Guan (Care/Control): An ethnographic
understanding of care for people with severe mental illness from shanghai’s urban
communities. Mach. Des. Manuf. 42, 92–111. doi:10.1007/s11013-017-9543-x
Frontiers in Energy Research frontiersin.org14
Xu et al. 10.3389/fenrg.2023.1187558
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