Sasa Statkic

Controlled multi-motor drives

Controlled multi-motor drives are used in a great number of industrial plants. The functioning of large and complex systems such as ironworks, paper mills, excavators, etc. depends on the performance of the controlled multi-motor drives. A systematic survey of multi-motor drives based on the method of coupling and mutual influence is presented in the paper. Following that, an overview of the appropriate control algorithms, sorted by the principle of operation and the means of realization, is given. The paper is illustrated with selected applications of controlled multi-motor drives from the authors practice

Controlled induction motor drives supplied by frequency converters on belt conveyors — modeling and commissioning

During the past two decades, drive and control system of belt conveyors on open pit lignite mines have seen significant advances. The main demand for new construction of belt conveyors was the increase of reliability, unit capacity, minimization of personal, reduction of maintenance cost, increase of safety, reduction of consumed energy, etc. The paper presents detailed mathematical model of the belt conveyor suitable for analyses of both static and transient operating regimes. The model includes electrical drive system of the conveyor, and the mechanical part, with the special attention given to the elastic nature of the belt. Simulation results of the developed model for the drive with frequency converter are presented. Experimental results from the field measurements confirm the validity of the model.

Optimal utilization of the bulk material transportation system based on speed controlled drives

The main demand for construction of new belt conveyors in open pit mines (OPM) is the increase of safety and system capacity, minimization of personal, reduction of maintenance cost, consumed energy, etc. The paper presents the algorithm for speed control of the system of belt conveyors, in terms of improved system efficiency. The algorithm is based on the principle of optimum utilization of the available material cross section on the belt. The algorithm is developed and tested on the detailed mathematical model of the drive system with the rubber belt, transporting variable capacity of the bulk material, measured at the input of the system. The simulation results are verified through performed measurements of characteristic values, which best illustrates the response of the system to the applied control strategy in the control center of the belt conveyor system with remote control.

Energy efficiency in transportation of bulk material with frequency controlled drives

The paper presents the algorithm for speed control of belt conveyors, in terms of optimal energy consumption. The algorithm is based on principle “minimal speed means minimum power”. The minimal speed is calculated as a ratio of transported capacity of bulk material and maximum possible material cross section on the belt.

Fuzzy speed control of belt conveyor system to improve energy efficiency

The paper presents a control strategy for the system of belt conveyors with adjustable speed drives based on fuzzy logic control. The proposed control structure is developed and tested on the detailed mathematical model of the drive system with the rubber belt. The presented algorithm is implemented on the new variable speed belt conveyor system with remote control on an open pit mine. Results of measurements on the system are used to compare the proposed algorithm with another approach to optimum speed determination based on the method of sequential quadratic programming. It is proved that both solutions provide minimum of electrical energy consumption of the drive under given constraints.

Control of the main working axes of bucket wheel excavators according to the criterion of desired capacity

The bucket wheel excavator is basic mining machine used on open pit mines with a continuous excavation process for soft and medium-hard materials. The increase in the need for ever greater quantities of excavated material has led to excavators being constructed today with a daily production capacity greater than 200,000 m3. Aside from the time and capacity availability of the excavators, to achieve efficient production, the manner in which they are controlled is also of great significance. The analysis of the technology for excavating massifs, as well as the structure and geometry of excavators, has led to the greatest number of applied solutions for control of excavators being through automatic operation: no/cos and P=const. Due to the non-homogenous structure of material and the inconsistent and unpredictable geometry of the excavated block, the aforementioned methods do not provide the necessary efficiency for the operation of the excavator. The development of systems for measuring the volume flow of material and their application on excavators makes it possible for the measurement results to be used not only for statistical analysis, but also to develop algorithms for control of excavators. The location where the measurement system is installed complicates the use of its measurement results. Specifically, the information on the instantaneous production which the control system receives from the measurement system is delayed by the amount of time it takes the excavated material to travel from the bucket wheel to the location where its volume is measured (one of the conveyors on the excavator). In this work we will present the algorithm for control of a bucket wheel excavator according to the criterion of desired capacity, where the results of the system for measuring volume flow are used as feedback information on the capacity. The results of measurements performed on the terrain verify the control strategy, which is developed and tested based on mathematical model of bucket wheel excavator presented in the paper.

Drives and control system for paper-board cross cutter

Cross cutter for paper or board is a facility that produces sheets of the desired length from a reel of web coming from the paper or board production line. Reliable operation, high speed of the web during cutting, and high accuracy of the sheet dimensions are common requirements. Mechanical assemblies of many existing machines are in good condition, offering possible extension of the service life, provided that drives and control system are modernized. The paper presents the characteristics and requirements of basic subsystems of the paper-board cross cutter from the control system perspective. Drag-link mechanism which provides the variation of the instantaneous speed of the cutter blades, necessary for proper operation of the cutter is described and analyzed. Experimental results obtained on a real, commercial paper-board cross cutter are presented in the paper. The results show that high accuracy of the sheet length can be achieved.

Universal control block for paper machine drives

Different methods for coordinated motion of the paper or board machine sections were used, mainly depending on the production date. Present solutions are based on individual sectional AC or DC drives as parts of the network control system. The drives are integrated in the control and supervision system with the application of a high performance communication protocol, usually PROFIBUS, Ethernet or DeviceNet. Quality of control system of any paper machine is ensured and the software development procedure is kept straightforward with the use of the universal control block presented in this paper. The generalized structure of the proposed control block is suitable for application on different sections found in paper or board machines, with adequate parametrization. The performance of the block is tested on the dry-end of machine, where the definite amount of sheet tension is required by the technological process. The tension force saliently couples the adjacent drives, which can compromise the performance of the drives, and even lead to unstable operation. The proposed control system structure achieves stable operation of drives coupled through the material, with the possibility to control the sheet tension force.

Improved efficiency of bucket wheel excavator operation with advances in the control algorithm

Open pit mines with a continuous excavation use bucket wheel excavator as basic mining machine in the process of soft and medium-hard materials excavation. Excavators are being constructed today with a daily production capacity greater than 200,000 m3 due to constantly growing demand for greater quantities of excavated material. The analysis of the technology for excavating massifs, as well as the structure and geometry of excavators, has led to the most applied solutions for control of excavators being through automatic operation: ns/cosβ and P=const. Due to the non-homogenous structure of material and the inconsistent and unpredictable geometry of the excavated block, aforementioned methods do not provide the necessary efficiency for the operation of the excavator. Considering disadvantages of existing control strategies, a new control strategy is proposed in the paper which provides maximum efficiency of excavator operation according to the designed capacity. Advances made in the developed algorithm improve time, capacitive and overall energy efficiency of its operation. Results of measurements performed on the terrain verify the developed control strategy.

Controlled multi-motor crawler travel drives on open pit mining machines

Travel drive on open pit mine machines is multi-motor drive, consisting of two, four, six or more motors. This drive is the most demanding drive on the open pit mining machines. The single drives are cross-coupled through terrain, which is rugged and inhomogeneous, making the quasi-stiff mechanical coupling. This is the reason why the relation of coupling between the individual drives permanently changes during motion, in an unpredictable way. During the driving along the curved path, it is necessary to provide significantly different speeds for individual motors. Special problem is the fact that lean on the ground is achieved through crawler tread, which introduces significant gaps in the transmission system. The required uniform load distribution between individual motors is provided by the control system.