Borislav Jeftenic

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

Gain scheduling control of DC motor drive with field weakening

A new adaptive control system for a DC motor drive with field weakening is proposed. The adaptation mechanism is based on the gain scheduling. A deep knowledge of the phenomena in the drive was necessary to define the scheduled variables that capture the essential nonlinearities of the process considered. However, in practice, to realize the proposed adaptive control system, the only a priori knowledge required is the experimentally determined magnetization curve. Simulation and experimental results indicating high performances of the control system proposed, are presented.

Implementation of Fuzzy Control to Improve Energy Efficiency of Variable Speed Bulk Material Transportation

The paper presents a control strategy for the system of belt conveyors (BCs) with adjustable speed drives based on the principle of optimum energy consumption. Fuzzy logic controller is used in the algorithm for generating the reference speed. 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 BC system with remote control on an open-pit mine. The measurements were performed to verify the proposed concept during the eight months of exploitation. Results of the measurements are presented in the paper.

Speed sensorless direct torque control implementation in a current source inverter fed induction motor drive

In the paper one speed sensorless direct torque control (DTC) implementation in a current source inverter (CSI) fed induction motor drive is proposed. DTC of a CSI fed induction motor drive involves the direct control of the rotor flux linkage and the electromagnetic torque by applying the optimum current switching vectors. For sensorless control of the drive, an improved estimator is applied using stator voltages and currents. The stator current, voltage and resistance are not measured, but determined by a reconstruction from DC link measurements and the inverter switches states. This reduces the count of the sensors in the drive since the inputs for the flux estimator are reconstructed motor voltage and current obtained from the measured DC link values. An EMS offset estimator using simple technique based on the knowing states of the inverter switches compensates the offset of the pure integrator in the flux estimator. The angle of the rotor flux space vector, needed for the switching table, is determined from the referred rotor flux values and motor parameters used in the control algorithm are only the stator resistance and the transient inductance. Experiments are provided to confirm the performance of the proposed control algorithm.

Nonlinear multi-input-multi-output neural network control of DC motor drive with field weakening

A new multi-input-multi-output nonlinear control system, based on a simple and straightforward modification of the internal model control, is proposed. The nonlinear modified internal model control structure is completely defined by the inverse process model and guarantees the offset-free control. A feedforward neural network (NN) inverse model with one hidden layer and a small number of hidden neurons is successfully applied in a real-time control of the nonlinear process considered.

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.

Current source converter topologies for PMSG wind turbine applications

Different current source converter topologies for permanent magnet synchronous generator (PMSG) wind turbine applications are presented and analyzed in the paper. In high-power and medium-voltage range, current source converter has its natural advantages, such as simple topology, compact size, high power capability, excellent short circuit protection, and flexible power flow control. However, it also presents some challenges for control scheme development. In the paper two different approaches are shown. One utilizes phase control thyristors and active filter for harmonics compensation, while other uses PWM controlled SGCTs. By controlling the inverter modulation index at the highest possible level, the proposed control scheme keeps the dc link current at a minimum value with various wind speeds and therefore greatly reduces the converter power loss at lower power levels. Simulation results are given for both control schemes.

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.

A two-motor centre-driven winder drive fed by a five-leg voltage source inverter

Recent research has shown that it is possible to independently control two three-phase induction machines while supplying them via a single five-leg voltage source inverter (VSI). In such a two-motor drive system one phase of each motor is connected to a common inverter leg. Major shortcoming of this topology for general-purpose applications is the need to double the DC bus voltage in order to achieve the same speed control range as with the standard dual three-phase VSI topology. Also, the semiconductors of the common leg have to withstand up to twice the operating current of the other inverter legs. This paper investigates the applicability of this topology for a specific constant-power two-motor drive of winder type, where these drawbacks can be to a large extent avoided. In particular, in two-motor centre-driven winders voltage requirements of two machines are hugely different during normal operation of the drive, so that the need for doubling the DC bus voltage does not take place. The current rating of the common leg does not need to be doubled either. Modelling of the centre-driven winder is summarised first. An appropriate PWM method for a two-motor drive with the common inverter leg is developed next, which allows control over how the available DC bus voltage is allocated to the two motors. Description of the five-leg inverter control scheme is further given. Detailed verification of the two-motor drive configuration is provided by simulating the operation of the centre-driven two-motor winder using the standard three-phase inverter topology and comparing the results with those obtained using the five-leg inverter configuration in conjunction with the developed PWM strategy.

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.