solution for both new elevator systems and retrofitting of existing ones. An interesting energy analysis of a SRE has been presented in [2], regarding specific ...
2014 International Symposium on Power Electronics, Electrical Drives, Automation and Motion
Energy Harvesting in Roped Elevators G. Nobile, A.G. Sciacca, M. Cacciato, C. Cavallaro, A. Raciti, G. Scarcella, G. Scelba Department of Electrical, Electronics Engineering and Computer Science University of Catania Italy Focusing on adding storage systems for energy recover from electrical motors, it is necessary to perform comprehensive energy analysis to evaluate the economic convenience of such solution for both new elevator systems and retrofitting of existing ones. An interesting energy analysis of a SRE has been presented in [2], regarding specific scenarios obtained considering real traffics data monitored in a short period of time; the sizing of storage system, based on super-capacitors, is performed considering the maximum energy capability for a single ride. Similar analysis are carried out in [3-5], [9] and [12]. In [6], a storage system for elevators based on supercapacitors is proposed including an optimal energy management strategy to achieve maximum savings in a certain number of rides, also by reducing the activation of braking resistor, normally operated when the energy storage system is fully-charged. In the present paper, a comprehensive study of a SRE is presented, including an accurate modeling of the system and energy analyses performed on different scenarios, also considering long time periods. Moreover, the possibility to use a simple regenerative electrical drive configuration including chemical batteries-based storage system has been evaluated. The latter can be considered as a tradeoff between the standard systems and new drives, using PMSM, in terms of investment costs and energy saving. The avoiding of use super-capacitors allows a relevant costs reduction. The activation of a breaking resistor is provided in case of fullycharged batteries or peak power too large for storage system. The proposed system configuration consists of a three phase inverter where a scalar control or a sensorless vector control is applied [15-17] and an energy storage system is connected through a bidirectional DC/DC converter to the inverter DC bus. This solution allows to recover part of the kinetic energy of the braking and deceleration phases of the elevator. Consequently, such energy can be stored in a battery pack and used during the motor phase of the lift duty cycle or to supply ancillary stand-by loads (lights inside the car, controller, etc.). Moreover, the energy stored in the battery pack can be also exploited to complete the lift trip in the case of electrical grid fault interruption during the ride, improving the security of the elevator in a simple way. Other solutions for backup supply system in elevators, using a combination of super-capacitors and fuel cells are presented in [13]. Finally, since the motor and elevator mechanics are not modified, the investment cost is limited with respect to system replacement with high performance ones. Thus, the payback time has been evaluated to confirm the feasibility of the investment.
Abstract— In civil buildings, large part of energy consumption of common service is related to lift apparatus operations. Considering the huge diffusion of roped elevators and their reciprocating operating mode, a critical evaluation of energy streams has been done using an accurate model specially developed. Thus, a retrofit kit has been studied and designed able to store the energy during the generating mode of the electrical machine and to recover it back in motor operation. Finally, a comprehensive evaluation of the saved energy parameterized with the numbers of passengers and lift duty cycle is presented, as well as the kit cost estimation and pay-back time. Keywords— Elevators; induction machine; energy storage systems; energy savings; bidirectional converters.
I.
INTRODUCTION
In last years, energy savings has become a particularly significant issue; in fact, energy efficiency policy in many countries has been established in order to mitigate the environmental effects of the conventional energy sources. Moreover, the reduction of electrical energy consumption is considered a key aspect to make the national energy systems robust enough to ensure the energy services needed for local and global economies. Among the several international and national action plans undertaken for energy saving, a considerable prominence has been given to the sustainability certifications of buildings and green building ratings. In the context of a sustainable development, the lift consumptions plays a key role as it strongly affects the energy use associated to the buildings. The Standard Roped Elevators (SRE) have been widely adopted from many years in several buildings and till now they are in service although they represent a relevant energy cost. A newer class of elevators is represented by hydraulic type but, due to their low efficiency due to the absence of the counterweight, such kind of lifts is not fashionably anymore. New elevator configurations are proposed nowadays from specialized industry in this sector, mainly based on the use of regenerative PMSM electrical drives, coupled to energy storage systems for regeneration and power peak shaving; such solutions show good service and energy saving capability, but the investment cost for systems modernization can be significant. An interesting analysis of energy efficiency potentials for existent elevators and escalators on a European scale is performed in [1], showing that relevant energy savings, up to 30% or more of the total consumptions, are possible by using components with high efficiency for running operation.
978-1-4799-4749-2/14/$31.00 ©2014 IEEE
533
II.
Table I – Technical specifications of the analyzed elevator
SYSTEM MODELING
number of floors maximum number of passengers maximum load cabin weight counterweight mass car nominal speed pulley mass pulley diameter R rope rails friction coefficient rg rope losses coefficient rf pivot point friction coefficient rc gears transmission ratio Wg transmission efficiency KT
The SRE system analyzed in this paper is mainly composed by a gear box, connecting the shaft of the electrical machine to other mechanical components, a three phase induction motor supplied by a three-phase Voltage Source Inverter (VSI), a three-phase diode rectifier bridge, a bidirectional DC/DC converter exploited to manage the power flow between the electrical drive and the battery pack; a scheme of the whole system is shown in Fig. 1.
R
RECTIFIER
INVERTER DC
AC
6 6 500 kg 300 kg 500 kg 0.7 m/s 70 kg 0.5 m 0.04 0.0015 0.09 1/53 0.5
M
S T 3- PHASE AC GRID
DC
AC
LCL FILTER
3
MECHANICAL LOAD (ELEVATOR)
DC/DC CONVERTER DC
TRT
1 1
W g KT
TRr Fi R M i M pd
(1)
where the torque TRr is calculated as:
DC
TRr
OPTIONAL PHOTOVOLTAIC SYSTEM FOR SUPPLEMENTARY CHARGE
REGENERATIVE MODULE
Tcs Ta
(2)
Tcs includes the torque load due to the difference of weights between the cabin and the counter weight, while Ta is the torque related to the friction losses occurring during the pulleys rotations:
Fig. 1. Block diagram of the analyzed roped elevator system.
A more detailed description of each component is given in the following.
Ta
( Fg F c F f ) R
(3)
where R indicates the pulley diameter while Fg, Fc and Ff are, respectively, the resisting forces produced by the friction of rails, friction of the pulleys on their pivot and bending stiffness of ropes. All these parameters are related to masses and forces values through coefficients rg, rc and rf depending by the geometrical and mechanical characteristics of rails, pulleys and ropes. Mi and Mpd represents the torque associated to the inertia of rotating masses and breakaway forces, while Fi is the inertial force related to translating masses. As the load torque TRT is applied to the rotor of the motor through the gear box, the gear ratio Wg is taken into account in (1). Theoretically, the regenerated energy would be equal to the motoring energy. However, losses due to the presence of friction in the guide rails and air resistance must be considered in an accurate modeling as well as the losses in the gearbox. All these losses are included in (1) by the coefficient KT.
A. Mechanical Load and Electrical Machine Basically, the mechanical part of the elevator is composed of a system of pulleys, ropes and gears, which are arranged in order to reduce the effort required by the lift for carrying people up and down. Moreover, the mechanical system includes the elevator car and the counterweight; the latter is frequently designed to be equal to 40% (or 50%) of the elevator maximum capacity and cabin weight. Both car and counterweight slide on steel mechanical guides to maintain a vertical trajectory and emergency breaking. The technical specifications of the analyzed mechanical system composing the elevator are listed in Tab. I. As widely described in the literature, the most suitable elevator displacement curves are composed by an uniformly accelerated motion of the car during the start-up, followed by a constant speed movement at steady state, while an equally decelerated motion is imposed to the elevator during the transient stop. According to these control laws, a low speed elevator system has been analyzed, whose speed range is between 0.6 and 0,8 m/s at steady state, with maximum acceleration equal to 0.5 m/s2 and maximum deceleration equal to -0.7 m/s2. An example of the speed profile of the lift car is shown in Fig. 2 in red, obtained considering a ride from the ground departure floor to the arrival 6th floor. To get high passengers comfort thus avoiding high jerk values, a smooth accelerationdeceleration are implemented during transients when no discernible bumps or vibration should be perceived. The same figure depicts the associated angular speed profile of the induction motor used to drive the elevator. The load torque TRT applied to the electrical motor during the whole working cycle is given by:
0.7
1500
0.6
0.5 1000 0.4
0.3 500 0.2
Rotor Speed [ rpm ]
0.1
Car Speed[m/s] 0
0
5
10
15
20
25
30
t [s]
Fig. 2. Example of speed profile during a working cycle.
534
35
0 40
Induction machines have been commonly used in the elevator installations over many past years. Motors with double windings, having different pole pairs, have been widely adopted in this application in order to achieve a soft transition from low to high speed but also standard induction machines were often used. In the following analysis, only the latter have been considered since they avoid the use of external contactors necessary in double winding motors, whose commutations could lead to inverter fault. This drawback can be mitigated by the use of a passive filter connected between the inverter and motor. The electrical motor used to drive the elevator is a threephase induction motor, whose main characteristics are summarized in Tab. II.
In particular, a significant percentage of the power is converted from the mechanical system to battery pack during rides from higher to lower floors with many passengers (high load) or in rides from lower to higher floors with few passengers (low load). Fig. 4 clearly shows the operating modes of the induction machine during two working cycles of the elevator where the elevator rides from ground to sixth floor and back at full load. Note that there is an inversion of the energy flow between the mechanical system and electrical machine during the second ride, which is related to the electromechanical torque inversion with respect to the motor speed. Basically, the regenerative module must manage the energy exchanging between the battery pack and motor by adopting a bidirectional DC/DC power converter shown in Fig. 5. The two low pass filters are designed to suitably limit the current ripple and let the converter to correctly operate in buck and boost modes. The battery pack is connected to the low voltage side at about 100V. If a lower voltage level for battery pack is required (for example 48 V) it is necessary to use a converter with a HF transformer to overdue the high difference between input and output voltage values, that, for buck converter would result in too low values of the duty cycle.
Table II – Nameplate data of the electrical motor Type IM squirrel cage Power 4,4 kW Frequency 50 Hz Voltage 400 V Current 10,5 A Speed 1440 rpm Torque 28 Nm
B. Regenerative Module As it is shown in Fig. 3, energy recovering periods in a SRE mainly occurs during two of the four motor operating modes.
Load Torque [Nm] 40
Motoring Operation Te 0
Zr 0
Te >0
Te >0
Zr >0
Zr
15
Energy Consumption
10 Ligh tly load car
Energy Regeneration
Full loaded car
5 SOC DOW N
SOC DOW N
0
0
10
20
30
40
50
60
70
80
t[s]
Zr > 0
Fig. 4. Torque load variation during two working cycles of the elevator.
Regenerative Operation Te< 0 Zr < 0
Te> 0
4 mH
GATE CONTROL People weight < Counterw eight Ligh tly load car
SOC UP
People weight > Counterw eight
V_INPUT
4 mH 2µF
VOLTAGE CURRENT SOC CONTROL
V_OUTPUT 2,5µF
Full loaded car
SOC UP
Fig. 5. DC / DC power converter scheme.
Fig. 3. Elevator operating modes.
535
III.
ENERGY ANALYSIS
Kinetic energy from the Elevator
The energy value has been calculated by integrating the active power Pist of the electrical machine and battery pack. During a working cycle time period T=t2-t1 the energy exchanged between the two components is given by:
Motor Losses 11%
t2
³ Pist dt
E
(4)
DC Bus Capacitors
t1
Converter and Battery Losses 6%
where Pist can be computed as:
CRT Zr
Pist
(5)
The quantity ωr indicates the rotor speed. Whenever Pist is transferred from the mechanical system to the battery pack, the DC bus voltage increases. When a specific voltage value is overtaken, the DC/DC converter starts to transfer such an energy to the battery pack. The aforementioned model has been used to analyze the energy flows of the SRE described in Tab. I. In order to determine the effective use of the elevators, the rides have been audited for a long period in a real case, monitoring the frequency of rides per day, week, month and year and monitoring the number of passengers as well. The audit has been performed for an elevator in a condominium with lowmedium traffic, with two offices placed at the 5 th and 6th floors, during working days and weekends in order to highlight possible different uses of the elevator during weekends. The number of rides in a generic week are shown in Fig. 6, where it is possible to note that higher frequencies are associated to the offices floors, although a significant number of rides occurs also in the third and fourth floors. The energy flows were calculated from the audited data including the losses of each part composing the system, as sketched in Fig. 7. Four significant regenerative rides are reported in Tab. III in which the time duration of working cycle, number of passengers, mechanical losses and energy delivered to the battery pack have been evaluated. It is worth to note that the percentage of mechanical losses considerably increase during the rides “2” and “4” because of the friction torques, which
Energy stored in the battery pack
Fig. 7. Power losses related with different components .
are related to the differences between the total car weight (car weight plus passengers) and counterweight. Moreover, the amount of the energy delivered to the battery pack during the energy recovering can reach 50% of the entire energy required, as for rides “1” and “3”. Of course, the rides described in Tab. III are the most significant in terms of energy regeneration but, during the year, the elevator will often operate in intermediated conditions. In order to verify the economic convenience of energy saving during regeneration in SRE and in consideration of previous works, a long term analysis of the elevator has been considered, including comparisons between energy savings and consumption [7,8,14]. It is obvious that the regeneration Table III Energy Recovering in four significant rides
Number of rides
90
Mechanical Losses 35 ÷ 40%
80
ride “1” Number of passengers Duration of working cycle Total mechanical energy involved Mechanical power losses Electrical energy at the motor output Stored energy in batteries
0 to 6 floor 0 29.9 s 0.0232 kWh 25% 0.0174 kWh 0.0146 kWh
ride “2” Number of passengers Duration of working cycle Total mechanical energy involved Mechanical power losses Electrical energy at the motor output Stored energy in batteries
0 to 6 1 29.9 s 0.0156 kWh 43% 0.0089 kWh 0.0074 kWh
ride “3” Number of passengers Duration of working cycle Total mechanical energy involved Mechanical power losses Electrical energy at the motor output Stored energy in batteries
6 to 0 6 29 s 0.0304 kWh 31% 0.0210 kWh 0.0174 kWh
ride “4” Number of passengers Duration of working cycle Total mechanical energy involved Mechanical power losses Electrical energy at the motor output Stored energy in batteries
6 to 0 5 29 s 0.0236 kWh 45% 0.0130 kWh 0.0105 kWh
70 60
50 40
30 20
10 0
6 6
2
1
4
5 0
0 6
→
0
→
0
1
→
0
3
→
0
2 2
→
rides
0
3 1
→
0
←
0
4
←
0
3
←
0
5 4
←
←
← 0
5
0
x ↕ y
Fig. 6. Frequency distribution of rides in a generic week.
536
shown in Fig. 8.a.It is possible to observe that long rides towards high floors provide the highest recovered energy levels, while minor regeneration level are achieved during elevator rides down. All intermediate ride combinations are grouped in the row indicated as (xly) and their contribution is not significant. The total amount of energy potentially stored in one year corresponds to 250 kWh, equal to the 20% of the estimated energy consumption. The stored energy could be potentially used to cover part of the consumptions providing an effective cost reduction which can be economically quantified in 20% discount on the energy component of the electric bill. In order to verify the effectiveness of the aforementioned analysis, the audited data have been mathematically readapted to a different scenario where the two offices are located on the 1st and 2nd floors, while the apartments are located on the other floors. The same trip frequencies and passengers number of previous scenario have been associated to the offices and flats. The results of this case are summarized in Fig. 8.b, where it is noticeable a significant reduction of the recovered energy; in fact, the total stored energy is about 150 kWh, which corresponds to the 12% of the total amount of energy consumption. The final scenario analyzed in this study has been achieved by manipulating the data related to the rides of the two offices of the first scenario and by considering offices in all six floors of the building, with the same traffic audited for the offices of the previous scenarios. The recovered energy in this case is four times higher compared to the first scenario, as clearly visible in Fig. 8.c. These three study cases clearly highlight that the economical convenience of using a regenerative system is essentially proven whenever scenarios with high traffic rides are present. Starting from this energy analysis it is possible to evaluate the technical characteristics of the regenerative module and the payback time of the system modernization. The battery pack is designed taking into account the input/output voltages of the DC/DC converter, the energy flows during charging and discharging cycles, the maintenance costs and life span. The main features regarding the operating conditions of the regenerative module are specified in Tab. IV. The charging and discharging current ratings depends on the technology adopted by the energy storage system, the working cycles and the duration of the cycles. By using the above criteria and including costs, a comparison has been performed in order to detect the energy storage system technology more suitable for the proposed regenerative module. The comparison was focused on standard technologies, evaluating the charging capacity, the energy stored, the energy density and the cost of the energy storage system associated to the case study.
[ kWh]
200
a ) scenario 1
180 160 140 120 100 80 60 40 20 0 6
4
3
2
1
1
2
3
5
0
6
→
rides
4
0
→
0
→
0
→
0
→
0
→
0
←
0
←
0
←
0
←
←
←
5
0
6 5 4 3 2 1 0 0
x ↕ y
[ kWh ]
200
b ) scenario 2
180 160 140 120 100 80 60 40 20 0 5
4
3
2
1
1
2
4
0
5
0
6
→
rides
3
0
→
0
→
0
→
0
→
0
→
←
0
←
0
←
0
←
0
←
←
6
6 5 4 3 2 1 0 0
x ↕ y
[ kWh]
200
c ) scenario 3
180 160 140 120 100 80 60 40 20 0 5
4
3
2
1
2
3
4
5
0
6
→
0
→
0
→
0
→
0
→
rides
1
0
→
0
←
0
←
0
←
0
←
0
←
←
6
6 5 4 3 2 1 0 0
x ↕ y
Fig. 8. Yearly energy recovered for the three considered scenario as a combination of ride and passengers number.
effectiveness associated to a specific elevator depends on many parameters such as the building category (condominium, offices, hospital, etc.), the number of floors and flats in each floor, the number of users per trip, etc.. These data have been included in the aforementioned models and estimation of the regenerated energy in one year has been calculated for each combination of ride and passengers number; the results are
Table IV – Operating conditions of the regenerative module Rated Input - Output DC/DC converter voltage Maximum charging current Maximum discharging current Maximum duration of each working cycle
537
600V - 100 V 25 A 30 A, 80 A for 2 s 30 s
Table V – Battery packs considered in the study specifications 12 V, 27 Ah 12 V, 75 Ah 3,2 V, 40 Ah
Technology sealed lead-acid VRLA Lead Deep Cycle Lithium Ions
the pictures of the experimental setup. The whole system is controlled by a single control unit, which must control the inverter supplying the induction machine, the AC/DC converter used to drive the DC motor; in addition, the same control unit implements the current and voltage control of the DC/DC converter. Fig. 12 shows some experimental results obtained by emulating a ride from 6th floor to ground with 4 passengers; during regeneration the DC bus voltage would tend to rapidly increase, but the activation of the DC/DC converter establishes a suitable current charging set maintaining the value of voltage into the band; extra regenerative energy goes towards the batteries. After motor startup, mechanical load balancing leads to regenerative scenario where the proposed topology allows to deliver energy (green area) towards the batteries. Energy recovery is about 0.002 kWh in this test, corresponding to approximately 40% of total energy involved in this scenario. In order to validate long term energy analyses, a certain sequence of rides can be automatically executed by the experimental setup . Fig. 13 shows an example, regarding a sequence of 10 different regenerative scenarios. In this test the energy recovered reaches about 15% of total energy. Experimental tests confirm the effectiveness of system and controls for a single ride and for a series of rides, obtaining amounts of energy recovery close to that theoretically calculated. Furthermore, experimental system allows to test a wide variety of elevators by modifying few parameters. The State of Charge (SOC) of the battery pack has been estimated by only measuring the voltage and exploiting a standard model. To obtain an accurate estimation of SOC, manufacturers of VRLA generally recommend to read voltage at least some minutes after last discharge (or more in case of charge).
configuration 8 in series 8 in series 31 in series
More information regarding the use of other technologies are included in [10]. The batteries considered in this study are listed in Tab V and the results of the comparison are displayed in Fig. 9, where for each technical criteria it has been assigned a 100% index value to the battery pack with maximum value and the other values calculated by using linear relationship. Looking at Fig. 9 it is possible to conclude that Lead Deep Cycle technology shows the best tradeoff for this application, since the cost of lithium ions batteries is inconsistent with the total investment cost. The economic investment is a key aspect affecting the feasibility of the elevator modernization solution presented in this study. Assuming that the cost of electricity remains constant at 0.3 euro/kWh for several years, the payback period of the investment can be evaluated in 4-5 years, only referring to the scenario with high traffic rides and considering estimated costs summarized in Tab. VI; in the other cases the investment is economically unacceptable. 120
%
Lead VRLA Lead Deep Cycle Lithium Ions
100
40A
102Wh/Kg
7.2kWh
2200€
80
60
40
4-quadrants chopper
AC/AC Converter R AC
20
AC
DC
IM
S T
0
charging current
energy storage
energy density
DC
AC
DC Motor DC
3 - PHASE AC GRID
costs
DC
Fig. 9. Comparison of battery technologies. DC
Table VI – Estimated breakeven costs of the regenerative module
CONTROL UNIT
8x VRLA 12V 27Ah
Fig. 10. Block diagram of the experimental setup.
Voltage and Current Sensors
IV.
EXPERIMENTAL TESTS
This section is devoted to the experimental validation of the proposed regenerative module. In particular, the elevator of Tab. I has been emulated by mechanically coupling a regenerative DC motor and a IM drives of Fig. 10. The experimental setup includes also the DC/DC converter and a battery pack consisting of 8 VRLA batteries. Fig. 11 shows
DC/DC Converter
Fig. 11. Test bench: IM and DC motor drives (left), DC/DC converter (right).
538
Although it would be preferable to follow this instructions , it was experimentally found that SOC estimation performed in a shortest span of time as for instance during floor stops or at zero-current state is fairly accurate for the purposes of this specific application. From this evidence SOC can be determined also during short dwell time between two or more rides for high traffic elevators. Depending on the actual SOC value, a specific control action is adopted by the control system in order to avoid unsafe operation for batteries and for the emulated elevator For instance, if actual SOC is close to its maximum value (100%), batteries charging operation is disable until SOC is lowered by a motor operation. On the contrary, if actual SOC is close to its minimum value, discharges must be temporarily inhibited. If SOC value is between its limits, four intermediate states are defined; in each state only some operations are allowed. In the lower state only recharging operations are permitted, in middle-low state also stand-by power consumption are covered, in middle-high all operations are allowed, finally, in high state recharging operations are banned.
store the energy of the regenerating mode of the electrical machine with the aim to recover it back during motor operations. In order to estimate the benefits of this solution, a comprehensive evaluation of the saved energy, parameterized with the number of passengers and lift duty cycle, have been presented considering different scenarios, as well as the kit cost estimation. As a result, the payback period for the best case is less than 4 years. The proposed recovering energy system is suitable to retrofit a wide variety of existent standard elevator as it does not require substantial modifications to the system, while ensures higher system reliability acting as a energy buck-up in case of grid fault. AKNOWLEDGEMENTS This work has been supported by the research project “POR FESR SICILIA 2007-2013 – LINEA 4.1.1.2 - RIgenerazione ELettrica EVOluta – RI.EL.EVO”. REFERENCES
BUS DC
[1]
Bus DC (V)
700 650 600 550 500 0
20
40
60 Time(s) Power
80
100
120
20
40
60 Time(s) Speed Feedback
80
100
120
[2]
Power(kW)
3 2 1
[3]
0 -1 0
Speed(rpm)
1500
[4]
1000 500
[5]
0 -500 0
20
40
60 Time(s)
80
100
120
Fig. 12. Mechanical and electrical quantities monitored during a single ride from 6 to ground floors with 4 passengers.
[6]
BUS DC
700
(V)
650
[7]
600 550 500
0
70
140
210
280
350
420
490
560
630
[8]
Time(s) Power
1.5
(kW)
1
[9]
0.5 0 - 0.5
0
70
140
210
280
350
420
490
560
630
[10]
Time(s) Speed Feedback
1000
(rpm)
500
[11]
0 -500
0
70
140
210
280
Time (s)
350
420
490
560
630
[12]
Fig. 13. Mechanical and electrical quantities monitored during a series of 10 different rides (various scenarios).
V.
[13]
CONCLUSIONS [14]
In this paper, an accurate evaluation of energy streams in roped elevators has been done using an accurate system model. Hence, a retrofit kit has been studied and designed to
539
A. De Almeidaa, S. Hirzelb, C. Patrãoa, J. Fonga, E. Dütschke, “Energy—efficient elevators and escalators in Europe: An analysis of energy efficiency potentials and policy measures”, Energy and Buildings Journal, vol. 47, 2012, pp. 151–158. E. Oyarbide, I. Elizondo, A. Martinez-Iturbe, C. Bernal, J. Irisarri, "Super-capacitor-based plug & play energy-recovery system for elevator retrofit" Proceedings of 2011 IEEE International Symposium on Industrial Electronics (ISIE), 27-30 June 2011, pp. 462,467. K. Sang-Min, S. Seung-Ki, “Control of rubber tyred gantry crane with energy storage based on super-capacitor bank” IEEE transactions on power electronics, vol. 21, no. 5, September 2006, pp. 1420-1427. T. Eilinger “Emergency power supply device for lift system” Patent US6938733 B2, March 2001. E. Aulanko, T. Syrman, S. Korvenranta, P. Jahkonen, KONE Corporation “Energy storage system for elevators” Patent US 7681694 B2, June 2008. E. Bilbao, P. Barrade, I. Etxeberria-Otadui, A. Rufer, S. Luri, I. Gil “Optimal Energy Management Strategy of an Improved Elevator With Energy Storage Capacity Based on Dinamic Programming”, IEEE transactions on industry applications, vol. 50, no. 2, March April 2014. M. Fatih Adak, N. Duru, H. Tarik Duru, “Elevator simulator design and estimating energy consumption of an elevator system”, Energy and Buildings 65, pp. 272–280, 2013. S. Ahmed, A. Iqbal, R. Sarwar, Md. Salam, “Modeling the energy consumption of a lift”, Energy and Buildings 71, pp. 61–67, 2014 A. Rufer, P.Barrade, “A super-capacitor-based energy storage system for elevators with soft commutated interface”, IEEE transactions on industry applications, vol. 38, no. 5, September October 2002 S. Tominaga, I. Suga, H. Araki, H. Ikejima, M.Kusuma, K. Kobayashi, “Development of energy-saving elevator using regenerated power storage system”, PCC Osaka, 0-7803-7156, IEEE, 2002. N. Mutoh, N. Ohnuma, A. Omiya, M. Konya, “A motor drive controller suitable for elevators”, IEEE transactions on power electronics, vol. 13, no. 6, pp. 1123-1134, November 1998. C. Attaianese, V. Nardi, G. Tomasso, “A high efficiency conversion system for elevators”, 1-4244-0632, IEEE, 2007. L. Zhou, Z. Dong, S. Wang, Z. Qi, “Design and analyis of a hybrid backup power system for a high-rise and high-speed elevator ”, 1-42442368, IEEE, 2008. J. Liu, F. Qiao, L. Chang, “The hybrid predictive model of elevator system for energy consumption”, Proceedings of the Internation Conference on Modelling, Identification and Control Okayama Japan, July 2010.
of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011), pp. 1-10, Aug. 30 - Sept. 1 2011 [17] G. Bottiglieri, G. Scelba, G. Scarcella, A. Testa, A. Consoli, “Sensorless speed estimation in induction motor drives”, Electrical Machines and Drive Conference, digital object identifier 10.1109 IEMDC.2003.1211327, pp. 624-630 vol. 1, 2003
[15] M. Cacciato, A. Consoli, G. Scarcella, G. Scelba, A. Testa, "Efficiency optimization techniques via constant optimal slip control of induction motor drives", Proc. of International Symposium on Power Electronics, Electrical Drives, Automation and Motion, SPEEDAM 2006, pp. 33-38, 23-26 May 2006. [16] A. Consoli, G. Scarcella, G. Scelba, M. Cacciato, "Energy efficient sensorless scalar control for full speed operating range IM drives", Proc.
540
