1. ANALYSIS AND SYNTHESIS OF AN ELECTROHYDRAULIC
CLOSED LOOP CONTROL SYSTEM FOR DRIVE
OF AN ELECTROGENERATOR DEVICE
Ilcho Angelov, Nikola Stanchev
TECHNICAL UNIVERSITY – SOFIA
Department of Hydroaerodynamics and hydraulic machines
Stanchev®
2014
The article presents energy analysis of аn electro-hydraulic closed
loop control system to power generators for production of electric
current trough а renewable source of energy - energy recovery wave.
Discussed are the syntheses of the structure of the hydraulic system and
the energy efficiency of tree types of hydraulic engineering solutions
under the same exploitation conditions.
ABSTRACT
HYDRAULIC DRAFT OF VARIANT 1 HYDRAULIC DRAFT OF VARIANT 2
HYDRAULIC DRAFT OF VARIANT 3
G G G
M1.2M1.1 M2.2M2.1 M3.2M3.1
U
p
U
p
U
p
P T
A B
b2P T
A B
b1
◄ Cylinders 7 ÷ 12
◄ Cylinders 13 ÷ 18
◄ Cylinders 1 ÷ 6
a1 a2 a3
pa1
qa1
pa2
qa2
pa3
qa3
b1 b2
а1 а2 а3
pa1
pa2
pa3
qa1
qa2
qa3
Uact.
ΔU
Ucom.
Uact.
ΔU
Uact.
ΔU
+ Cylinders 3 ÷ 18 ►
Hydrulic Cylinders
Pressure-relief valve,
pilot operated
Pressure filter
Controller,
closed loop
control
Controller,
functionality
Accumulator group
Flow meter and
pressure transducer
Directional valve ►
Reservoir
Check valve
G G G
M1.2M1.1 M2.2M2.1 M3.2M3.1
U
p
U
p
U
p
P T
A B
b2P T
A B
b1
G
b3P T
A B
G
A B
P T
G
A B
P Tb4 b5
a1 a2 a3
Ucom.
Uact.
ΔU
pa1
qa1
pa2
qa2
pa3
qa3
b1 b2
а1 а2 а3
pa1
pa2
pa3
qa1
qa2
qa3
Ucom.
Uact.
ΔU
Ucom.
Uact.
ΔU
Reservoir
Hydrulic Cylinders
◄ Cylinders 7 ÷ 12
◄ Cylinders 13 ÷ 18
◄ Cylinders 1 ÷ 6 + Cylinders 3 ÷ 18 ►
Pressure-relief valve,
pilot operated
Pressure filter
Controller,
closed loop
control
Controller,
functionality
Accumulator group
Flow meter and
pressure transducer
Directional valve ►
Proportional
directional valve
Check valve
+ Cylinders 3 ÷ 18 ►
M2.2 M2.1M1.2 M1.1
U
p
a1
pa1
qa1
b1 b2
а1 а2 а3
pa1
pa2
pa3
qa1
qa2
qa3
G
A
T2
B
M1
DU
Vg min
Vg max
U
n
G
A
T
2
B
M1
DU
Vg min
Vg max
U
n
G
A
T2
B
M1
DU
Vg min
Vg max
U
n
G
A
T2
B
M1
DU
Vg min
Vg max
U
n
P T
A B
b1 P T
A B
b2 P T
A B
b3 P T
A B
b4
Hydrulic Cylinders
Reservoir
◄ Pressure-relief valve, pilot operated
◄ Accumulator groups
Flow meter and
pressure transducer
Directional valve ►
Hydro motor
with variable
displacement
Pressure
filter
Controller,
closed loop
control
Controller,
functionality
The main hydraulic system parameters are set based on the terms of reference of the manager of the project as
follows: Drive three or four electric generator groups with output power P = 25 kW; Possibility for electric generator
groups to work in parallel or separately; Maintaining a constant rotational speed, respectively, for n = 500 rpm and
n = 1000 rpm; Required drive torque executive, M500 = 240 Nm, M1000 = 475 Nm; After analysis of the results by the
authors and by the manager of the project are defined as basic operating parameters of the system:
After analysis of the results [1] by the authors and by the manager of the project are defined as basic operating
parameters of the system: Maximum available flow in the system for the movement of a pendulum and thus a pair of
hydraulic cylinders, qmax = 75 l / min; Maximum working pressure in the system, pmax = 17,5 MPa; On this basis, defines
the basic design parameters of the components that construct the different variants of the hydraulic system.
Principal of operation

2. Stanchev®
2014
Energy analysis of the proposed three solutions is presented as loss of nominal power of the input of the system, trough by presents the effectiveness of each of the systems as the Structure efficiency.
In established flow stream pressure losses (linear losses) in pipes due to the resistance of the pipe wall friction is calculated by the formula:
Where:
ρ – Density of the working fluid;
ρ = 900 kg/m3;
ν – Kinematic viscosity, ν = 41,4.10-6 m2/s;
d - Diameter of the cross-sectional area of the pipeline, m;
l - Length of the pipeline, m;
Hydraulic losses due local resistances. In established flow stream at the locations of the pipeline connections, bends, branches, and other there is a pressure loss of local resistances. The local resistance is derived from both the tangential stresses
which are exerted on the walls of the fluid motion, and the vortex generating, wherein the kinetic energy of the fluid passes into the inner one of the heat resulting from friction. Pressure losses in local resistances of hydraulic systems are perceived to
be calculated by the formula:
Where:
ξ – Coefficient of local resistance, ξ = 1,6;
ρ – Density the working fluid, ρ = 900 kg/m3;
S – Area of the cross-sectional area of the local resistance;
Pressure losses in the flow of fluid through the individual hydraulic elements are defined by the graphical analysis of the real static characteristics, which are presented in the technical documentation from the manufacturer for the device.
Pressure losses in the system can be represented as a power loss, using the following mathematical relationship:
Where:
q – Flow, l/min;
p – Pressure, bar;
Table below shows the calculation of the hydraulic losses in the Variant 2 of the system with throttle speed control of the hydraulic actuators at maximum flow, in which realizes the set rotational speed of the adjustable hydraulic motor to drive the
electric generator. Analogously losses are calculated at the maximum and minimum flow in all three cases, with maximum power losses in the variant 1 are PLoss = 5,4 kW, in variant 2 PLoss = 1,6 kW and in variant 3 PLoss = 6,7 kW.
ENERGY ANALYSIS OF THE PROPOSED SOLUTIONS
Section L d q q RLi RLo ∆p ∆p
- m m l/min m3/s Pa.s/m3 Pa.s2/m6 Pa bar
1-7 2 0,019 37,5 0,000625 23297995 8856983326 18021,01 0,18021
2-7 2 0,019 37,5 0,000625 23297995 8856983326 18021,01 0,18021
3-7 2 0,019 37,5 0,000625 23297995 8856983326 18021,01 0,18021
4-7 2 0,019 37,5 0,000625 23297995 8856983326 18021,01 0,18021
5-7 2 0,019 37,5 0,000625 23297995 8856983326 18021,01 0,18021
6-7 2 0,019 37,5 0,000625 23297995 8856983326 18021,01 0,18021
7-8 11 0,04 225 0,00375 6523124 450879267 30802,21 0,308022
8-9 Filter 1
9-10 2 0,04 225 0,00375 1186023 450879267 10788,07 0,107881
10-11 Flow m. 0,6
11-12 1,5 0,04 225 0,00375 889517 450879267 9676,178 0,096762
12-13 Valve 0,4
13-14 1,5 0,04 225 0,00375 889517 450879267 9676,178 0,096762
14-15 P. Valve 10
15-16 1,5 0,04 225 0,00375 889517 450879267 9676,178 0,096762
17-18 5 0,06 675 0,01125 585690,2 89062571,3 17861 0,17861
18-19 Filter 0,5
Total pressure losses: 14,4661
Total energy losses In kW: 5,42477
Li Lip R .q, MPa 
Li 4 3
128. . .l Pa.s
R ,
.d m
 


2
Lo Lop R .q , MPa 
2
Lo 2 6
Pa.s
R ,
2S m

 
Loss
q.p
P ,kW
600

HYDRAULIC LOSSES IN THE VARIANT 2
1. Regardless of the comparison of the different options, if so specified energy efficiency refers to the maximum output power obtained at the
suitable option from this perspective proves the performance of the system as variant 1 or variant 3.
2. Energy efficiency results shown in Fig. 8 show that the difference between variant 2 and variant 3 is minimal (within 1%), which imposes
additional economic analysis, and here it should be noted that variant 3 rated power output is Pall = 100 kW, while variant 1 is Pall = 75 kW.
3. Final choice of variant of the hydraulic system can be made only after a thorough technical-economy analysis of the three variants
CONCLUSION
COMPARATIVE ANALYSIS AND EFFECTIVENESS OF THE PROPOSED SOLUTIONS
◄ The Figures shows graphically in scale
hydraulic losses at a minimum and
maximum flow, corresponding to variants
1, 2 and 3. Graphs illustrate visually how
much the available inlet pressure of the
system is lost to overcome the hydraulic
resistance of the examined specific
hydraulic systems.
▲ Energy efficiency of the proposed solutions
p,bar►
q, l/min ►0 225170
175
100
100
3,3
4,4
Δp
Δp
p,bar►
q, l/min ►
175
2251700 100
100
13,5
14,5
Δp
Δp
p,bar►
q, l/min ►0
175
675410100
100
200 300 500 600
4
5,94
Δp
Δp
78,4%
21,6%
Efficiency/LostEnergy
0
93,6% 93,3%
Var. 1
100%
6,4% 6,7%
Var. 2 Var. 3
VARIANT 1 VARIANT 2
VARIANT 3