controlled multimotor drive for crawler transport … site/radovi_tr33016/2012... · spreader ars...

Международна научна конференция “УНИТЕХ’12” – Габрово I-92

‘

12

INTERNATIONAL SCIENTIFIC CONFERENCE 16 – 17 November 2012, GABROVO

CONTROLLED MULTIMOTOR DRIVE FOR CRAWLER TRANSPORT IN

EXTREME OPERATING CONDITIONS

Saša Štatkić Faculty of Technical Sciences, Kosovska Mitrovica

Neša Rašić, Dragan Jevtić, Milan Bebić, Leposava Ristić, Borislav Jeftenić Faculty of Electrical Engineering, Belgrade

Abstract This paper presents the application of control algorithm for multi-motor crawler drive on an ARs2000 Spreader.

The drive consists of three controlled drives with cage induction motors supplied from the frequency converters. The algorithm is based on control of average speed of the individual crawler drives. The presented concept of control of multi-motor crawler drive is tested in extreme operating conditions during the transport of the heavy mining machine on an incline. During the functional tests performed during commissioning, on both rectilinear and curved paths, it was experimentally verified that the average speed corresponds to the reference value, along with the uniform load distribution among the drives. The influence of the crawler tumbler on the motor load is identified from the recorded diagrams of the instantaneous motor speed estimated by the frequency converter.

Keywords: multi-motor drives, crawler, mining machine, control algorithm, induction motor and frequency converter.

Crawler Bridge

Crawler 1 Crawler 2

Crawler Spreader

Spreader ARs 2000

Angle of inclinationof the construction

Slope of terrain

Direction of travelduring the second experiment

Direction of travelduring the first experiment

TerrainTerrain

Crawler 3

Inclination sensor

Fig. 1. Spreader ARs 2000 on OPM Drmno near Kostolac, Serbia

INTRODUCTION

Mining machines on open pit mines (OPM) is usually supported by the crawler mechanisms due to their heavy weight, and the instability of the terrain. On OPM Drmno, near Kostolac, Serbia, a spreader ARs2000 [1] is in use as part of Excavator-Conveyors-Spreader (ECS) system. The spreader is supported by two crawler mechanisms, one for the main part of the spreader, and the other for the bridge, as shown in Fig. 1.

The crawler mechanism of the main part consists of three crawlers propelled by three individually controlled motors. The main requirement for this controlled multi-motor drive is the transport of the spreader with

given common reference speed, regardless of the individual motor speed on each crawler.

During the relocation of the spreader from one point of operation to another, both crawler mechanisms (on main part and on the bridge) operate simultaneously. If the relocation includes the change of altitude, the transport on an inclined path is imminent. If the spreader moves downhill, the bridge crawler precedes the main crawler; during uphill transport of the spreader the bridge crawler follows the main crawler. The inclination sensor is placed on the horizontal plate in the base of spreader to measure the angle referred to the horizontal plane as shown in Fig. 1. Information of the inclination in two axes (x-y)


is introduced to the control system via PROFIBUS communication protocol, for protection purpose (to disable the transport if inclination exceeds 5%). The operator of the spreader uses the information displayed on the SCADA screens to avoid such situations, whenever possible.

DESCRIPTION OF THE DRIVE The photograph of lower part (substructure)

of the spreader ARs 2000 form OPM Drmno is shown in Fig. 2. The spreader is supported on three crawlers, over which the transport of the machine is accomplished.

Fig. 2. Substructure of the spreader ARs 2000 with

crawlers used for transport

The arrangement of three crawlers of the spreader ARs 2000, together with the associated drives is shown in Fig. 3.

M3

M1 M2

Crawller 1 Crawller 2

Crawller 3

Fig. 3. The arrangement of the crawlers in the main crawler mechanism of the spreader ARs2000

The basic technical data of the motor-gear group are: Cage induction motors 1.RZKT 315M-6 Rated motor speed 974 rpm Rated motor power 75 kW Rated motor torque 735.7 Nm Gear ratio 945.6 Speed of the drive tumbler 1.03 rpm Cogs number of the drive tumbler 9 Width of the crawler track 0.65 m

Figure 4 shows the motor-gear group coupled to the drive tumbler of a single crawler (Crawler 2).

Fig. 4. Motor and the gear coupled to the drive

tumbler of a single crawler

Motor speed of the crawler drive has the oscillatory shape as a consequence of torque transmission from the drive gear to the rectilinear movement of the crawler chain. This mechanical transmission is accomplished by the drive tumbler (Fig. 5) on which flange is cogged, carrying out the coupling of two adjacent plates [2]. Number of cogs and tread of cogged is known (9) and this has the dominant influence on the frequency of the oscillations. During the movement, one cog begins the coupling with two adjacent plates, while another cog at the same moment begins the decoupling with its own two adjacent plates.

Fig. 5. Drive tumbler of a single crawler

Instants of coupling and decoupling on the

different crawler chains are never the same, and depend on many factors. The main factors are speed of movement, kind of terrain, slope of terrain, way of travel movement (curved or strait path), tension of the crawler chain, lubrication, and many others.

The multi-motor crawler travel drive of the Spreader ARs 2000 consists of three cage induction motors supplied from three frequency


converters with independent rectifier and inverter unit in single enclosure (singe drive configuration).

The transport drives on mining machines should have electrical breaking capabilities, to be able to operate during the downhill transport.

The crawler travel drive has been designed with common intermediate DC circuits for three converters. One chopper (CH), with one breaking resistor (R) is also connected to the common DC bus, as shown in Fig. 6.

М 3~

~ ~

M1 690 V 79 A 75 kW 974 rpm

FC1

М 3~

~ ~ FC2

M2 690 V 79 A 75 kW 974 rpm

690 V, 50 Hz

М 3~

~ ~ FC3

R

= =

M3 690 V 79 A 75 kW 974 rpm

CH

Fig. 6. Single line diagram of the transport drive of the ARs2000 spreader

The frequency converters which were used,

in addition to PROFIBUS communication, also support an optical interface for measurement and acquisition of available values on one drive. Frequency converters have factory implemented Direct Torque Control algorithm [3]. The control subsystem of the converters uses estimated values for motor speed. The speed estimation accuracy without an encoder is 10% nominal slip, while torque estimation accuracy is 1% nominal torque. The aforementioned estimation accuracy is completely acceptable for both controlling this drive and the analysis of its behavior.

In normal running conditions, all drives use the external torque reference (Teref) to operate with uniform load distribution. If the drive’s speed differs from the speed reference over the defined limits marked as IZP and IZN in Figure 7, then the output of the internal speed regulator, the internal torque reference (Teint) will be added to the external, common torque reference (Teref), to bring the drive’s speed to the desired range. The block diagram in Fig. 7 shows the structure of the control system for each drive, integrated in the frequency

converter’s control section. Controlled multi-motor drives such as the

crawler travel drive of the Spreader must have two levels: the superior control level which controls the multi-motor drive as a whole, and the subordinate control level for controlling individual drives [4]. The structure of the control system for multi-motor crawler travel drive of the Spreader ARs 2000 on OPM Drmno, is with the control of the average speed of all drives, and is realized in the supervisory PLC control system, as shown in Figure 8.

e refT

eintT

+ eiT

+ -Reg. ω

av refω

iω

IZP

IZN*eTe refT

iω

Insensitivity Zoneof the speed regulator

DTC

+

Fig. 7. Block diagram of the internal control system integrated in the frequency converters The Operator sets the speed reference (ωset)

with selector switch, which is processed through the soft start block, to be used as a speed reference (ωav ref) for the complete travel drive. The controller, marked as “Reg. ωav” in Fig. 8, compares the calculated average speed with this signal, and based on the difference, calculates the torque reference for all drives. The calculated torque reference Te ref and ωav ref are distributed to all frequency converters equally, over the PROFIBUS communication protocol. Therefore, all converters in the system are equal, having the same purpose in the system [2, 4].

EXPERIMENTAL RESULTS

The performance test of the crawler drive with multi-motor drive for main transport of the spreader was performed in different operating regimes. The path for the tests was designed to include both leveled and inclined sections, to enable the test for downhill and uphill transport. The performed tests, supported by the shown results recorded form the control system, verified the proper


dimensioning of the drives, and the correct structure of the control system.

The results recorded during the transport of the spreader on the leveled terrain, followed by the period of downhill transport are shown in Fig. 9. The recorded results show approximately 16 minutes of the transport. At the beginning of the record (the first 30 seconds) the reference speed for the drives was 400 rpm. Following the brief operation at the steady state, the spreader was accelerated to 600 rpm, which was the operating point used during the remaining of the experiment.

The oscillatory character of the individual drive speeds and average speed is the consequence of the nature of the mechanical mechanism, used to transfer the drive torque from the gear output shaft to the linear movement of the crawler.

The motion on leveled terrain can be identified on diagrams shown in Fig. 9 (time t < 100 s) during which the motor torques oscillate around the constant average value. The inclination angle of the construction of the spreader, Fig. 9.b is approximately constant. For the transport on leveled terrain, only frictional torque component exists, i.e. motion resistances, therefore all drives operate in motoring regime.

Due to the described distribution of weight of the Spreader, vertical component of force from the bridge supported by the main crawler structure is decreased when the auxiliary crawler enters the sloped part of the path. The decrease of weight is proportional to the length of path covered by the auxiliary crawler. This causes the decrease of the average value of torque around which the motor torques oscillate.

The angle of inclination of the spreader structure starts to change significantly after the main crawler structure enters the sloped part of the path, at time t =550 s on diagrams shown in Fig. 9. The change of inclination angle effectively increases the gravitational component of the load, and reduces the frictional component. At the end of the recorded experiment the gravitational and frictional component are approximately equal (but opposite in signs) resulting in total load near zero, i.e. the operating point of motors is at the boundary between the 1st and the 4th quadrant.

The recorded results during the transport of the spreader ARs 2000 along the sloped path in an uphill direction are shown in Fig. 10. The change of inclination angle during the transport is shown on diagram (b) of the same figure. The reference speed during the complete transport was 80% of nominal speed; all motors operate with positive torque. During the experiment shown in Fig. 10, the main crawler (the crawler that supports the Spreader) precedes the bridge crawler (the crawler that supports the Bridge). For this reason, when the Spreader enters the leveled terrain, the bridge is still on the inclined terrain.

The transition form sloped to level terrain for the bridge crawler can be noted in the recorded inclination angle shown in Fig. 10. (b), and starts from t = 300 s, until the end of experiment.

The inclination angle of the spreader construction at the end of the second experiment (Fig. 10) is approximately the same as the recorded angle at the beginning of the first experiment (Fig. 9). On the leveled terrain, only the frictional component of the load torque exists, and is shared equally among all drives of the crawler mechanism.

Reg. ωav+

−

31

1ωSOFT

START

Superior control level Subordinate control level

setω

av refω

avω

IZP

IZNe refT

IZP

IZN

av refω

ω

T

+

+ -Reg. ω


DTC

+

e refT

eintT

+eiT

+ -Reg. ω

iω*eT


DTC

+


The oscillation of individual drive speeds, notable in both experiments causes the oscillation of average speed, resulting in oscillatory component in the reference torque.

Variable mechanical transmission is consequence of coupling crawler chain that is discontinuous construction (compound from crawler plates (shoes) which is hingedly connected) and drive tumbler on which flange is cogged with variable radius.

Given the variable transmission, the load torque on the drive tumbler possesses the

component which is random in nature and cannot be explicitly defined. However, the period of this oscillatory component can be identified, since it is the result of engaging the drive tumbler teeth with crawler plates, during the single turn of the tumbler. The period during which all nine cogs engage into coupling with crawler plates corresponds to a period of revolution of the output shaft of the drive gear, and is defined by the instantaneous motor speed and transfer ratio of the gearbox.

Time [s]0 60 120 180 240 300 360 420 480 540 600 660 720 780 840 900 960

-20

0

20

40

60

80Ref. Speed [rpm] x 0.1,Ref. Torque [%] x 1,Speed Motor 1 [rpm] x 0,1 Torque Motor 1 [%] x 1,

Time [s]0 60 120 180 240 300 360 420 480 540 600 660 720 780 840 900 960

-20

0

20

40

60

80

Ref. Speed [rpm] x 0.1,Ref. Torque [%] x 1,Speed Motor 2 [rpm] x 0,1 Torque Motor 2 [%] x 1

Time [s]0 60 120 180 240 300 360 420 480 540 600 660 720 780 840 900 960

-20

0

20

40

60

80


a)

Time [s]

0 60 120 180 240 300 360 420 480 540 600 660 720 780 840 900 9600,00,51,01,52,02,53,0

Inclination [%]b)

Fig. 9. Measured results during transport of the Spreader ARs 2000 on leveled terrain

followed by transport on inclined path – downhill


CONCLUSION The application of the described control

algorithm for controlled multi-motor drive of the main crawler mechanism on the Spreader provided the coordinated motion of all drives. The average speed control is suitable for both rectilinear and curved path of travel of mining machines.

The algorithm provides uniform load distribution among all drives of the crawler mechanism, regardless of instantaneous changes in load torque, caused by mechanical coupling.

The presented results were recorded during the functional tests of the realized crawler drive of the Spreader. The drive performed well during travel on leveled terrain, as well as on inclined path, both uphill- with increased load, and downhill- with electrical breaking. The successful application of the control algorithm verifies its applicability to other mining machines with crawler mechanisms.

ACKNOWLEDGEMENT

The paper is the result of research on the Project TR 33016, which is financially supported by the Ministry of Education and Science.

REFERENCES [1] S.Stojićević, “Investment is Justified by the

Results – Three years of successful operation of the most modern mining system on OPM Drmno”, kWh Magazine, Electric Power Industries of Serbia - EPS, June 2012, ISSN 1452-8452, pp. 37-38,

[2] S. Štatkić, N. Rašić, B. Jeftenić, M. Bebić, “Controlled multi-motor crawler travel drives on open pit mining machines“, ACEMP 2007. Bodrum Turkey, 10-12 Sept. 2007, Page(s):812 – 817, IEEE Conferences.

[3] ABB Industry Dives, "Direct Torque Control", Technical Guide No1, EN 30.6.1999, 3BFE 58056685 R0125 REV B.

[4] Jeftenic Borislav, Bebic Milan, Sasa Statkic: “Controlled Multi-Motor Drives“, International Symposium on Power Electronics, Electrical Drives, Automation and Motion, SPEEDAM 2006. 23. - 26.5.2006, pp.1392 – 1398.

[5] W. Durst, W. Vogt, “Bucket Wheel Excavator”, TRANS TECHPUBLICATIONS, 1988.

[6] G. Kunze, H. Göring, K. Jacob: “Baumaschinen, Erdbau-und Tagebau-Maschinen”, Technische Universität Dresden, Vieweg+Teubner, Wiesbaden

Time [s]0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510 540

-200

20406080

100Ref. Speed [rpm] x 0.1,Ref. Torque [%] x 1,Speed Motor 1 [rpm] x 0,1 Torque Motor 1 [%] x 1,

Time [s]0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510 540

-200

20406080

100


Time [s]0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510 540

-200

20406080

100120


a)

Time [s]

0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510 5400,00,51,01,52,02,53,0

Inclination [%]

b)

Fig. 10. Measured results during transport of the Spreader ARs 2000, uphill on an inclined path

controlled multimotor drive for crawler transport … site/radovi_tr33016/2012... · spreader ars...

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