Aleksandar B. Nikolic

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.

Improvements in Direct Torque Control of Induction Motor Supplied by CSI

Improvements in direct torque control of induction motor supplied by current source inverter are proposed in the paper. The flux estimator uses simple integrator and its error is compensated by EMF offset estimator. The stator current and voltage, used for EMF calculation, are determined by a reconstruction from DC link measurements, known characteristics of the inverter semiconductors and the current states of the inverter switches. The rectifier is controlled by a PI current controller as inner control loop of rotor flux controller. The rectifier current reference is resolved from the torque and rotor flux references in the similar way as in the standard vector control scheme to obtain fast DC link current response at all speeds. For the torque control, improved current switching-vector table is used, without hysteresis control that produces higher torque ripples. Simulation and experimental results are provided to confirm the performance of the proposed control algorithm

DTC of a CSI-fed induction motor with DC link based adaptive estimator

Direct torque control (DTC) of a current source inverter (CSI) fed induction motor is proposed in the paper. The main contribution of the paper is a flux estimator with only two inputs (the current and the voltage measured from DC link) and a modified integrator with an adaptive compensation. The stator current, voltage and resistance are determined by a reconstruction from DC link measurements, known characteristics of the inverter semiconductors and the current states of the inverter switches. The rectifier is controlled by a PI current controller. The rectifier current reference is resolved from the torque and the rotor flux references in the similar way as in the standard vector control scheme to obtain fast DC link current response at all speeds. For the torque control, the optimal current switching-vector table is used. Simulation and experimental results are provided to confirm the performance of the proposed control algorithm. Some of these results are compared with those obtained with the vector control method of the same drive.

Importance of continuous monitoring and control of auxiliary power consumption in thermal power plants

The paper presents the conceptual solution on the basis of which a system for continuous monitoring and control of auxiliary power consumption is defined in the four most important thermal power plants within the Electric Power Industry of Serbia (TENT A and B, TE Kostolac A and B). A unique system of measuring of auxiliary power consumption at the level of EPS is established in order to perform the appropriate measurement in the following phases, whose data would be archived for the purpose of further analyzes of energy balances. The results of these measurements should be used to define the concrete measures for auxiliary power consumption reduction in power plants, which, in addition to improving energy efficiency, would directly affect the cost reduction.

Indirect model predictive control strategies with input filter resonance mitigation for a matrix converter operating at fixed switching frequency

This paper proposes two indirect model predictive control techniques with input filter resonance mitigation operating at fixed switching frequency. These techniques address the main issues of the implementation of model predictive control in a direct matrix converter, namely the high computational cost, the adequate selection of weighting factors and the variable switching frequency which could produce resonances in the input filter. The techniques are based on the fictitious dc-link concept, which has been used in the past for the classical modulation and control techniques of the direct matrix converter. Simulated results confirm the feasibility of the proposal demonstrating that it is an alternative to classical predictive control strategies for the direct matrix converter.

Wireless Sensor Network based monitoring system for high power transformers

Industrial Wireless Sensor Network (WSN) used for supervising of high power transformer cooling system is presented in the paper. Due to the fact that in the thermal power plant where industrial prototype is installed is very noisy environment, a lot of problems should be solved in order to obtain high reliability and accuracy of the system. Results of the analysis presented in paper are obtained from the real thermal power plant where WSN system control cooling systems of 100MVA and 210MVA generator power transformers.

Different control schemes for current source converters in wind applications

Different current source converter topologies for 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 three different approaches are shown. One utilizes phase control thyristors and active filter for harmonics compensation, while other uses PWM controlled SGCTs. Finally, the third solution presents direct torque control and virtual-flux based direct power control (DPTC). Simulation results are given for all presented control schemes and some features of each control are emphasized.

Fixed-point DSP Algorithm for Flux Estimation in DTC IM Drive

A precise and simple for implementation DSP algorithm for flux estimation in direct torque controlled induction motor drive is presented. The main goal is to avoid using complex mathematical functions (square root and arc tan) and/or look-up tables for calculating flux amplitude and position. Complete algorithm, written in C, is at first analyzed in a simulation model and the final performance is examined on an Intels 80C196KC20 microcontroller. Comparison to the standard functions in respect to the accuracy, execution time and implementation simplicity shows accurate performance needed for flux control in direct torque controlled drives