This paper proposes a new concept for the control of voltage-source inverter (VSI)-fed induction machines. The method uses a predictive algorithm and can be split into two parts. The purpose of the first part, i.e., predictive torque control (PTC), is to predict the stator reference flux vector corresponding to the reference torque at the end of the sampling interval. The second part of the method provides accurate tracing of the stator reference flux by selecting either an active or a zero voltage vector. This approach is called immediate flux control (IFC), where two possible variants are suggested. In the first variant, a simple and fast algorithm obtains minimal stator flux error by impressing either an active or a zero voltage vector throughout the entire sampling interval. Consequently, the switching frequency becomes very low, but current and torque ripple are considerable. The second IFC variant generates the stator flux more accurately by applying an active voltage vector only throughout a calculated time slot within a sampling interval, whereas, during the remaining time of the sampling interval, a zero voltage vector is impressed. As a result, higher switching frequency arises, but it is still lower than that with space vector modulation. Both IFC variants, together with PTC, require minimal processing time and were efficiently implemented in a digital signal processor, which controlled a 3-kW induction machine drive. The obtained experimental results confirm the validity of the proposed approach.

This paper presents a low-cost fault-tolerant system for open-phase fault (OPF) in a power-converter-fed permanent-magnet synchronous machine. The proposed fault-tolerant system is based on field orientation control with additional fault tolerance functionality. A current predictive method for OPF detection is presented, together with an estimation of the threshold level for detection. The proposed method is based on the prediction of stator current for the next sampling interval. Furthermore, a new method for postfault operation of the machine is proposed. For optimal performance of the complete drive, a prefiring angle is introduced in order to avoid the temporary generation of negative torque. This improvement increases the average generated postfault electromagnetic torque, and consequently, it reduces the mechanical stress on various machine parts. The proposed fault detection and postfault operation solutions were simulated in MATLAB, and they were also tested on an experimental setup. The results show several advantages of the proposed fault-tolerant solution, like its short fault-detection time, substantial robustness against variation of machine parameters or load fluctuations, and negligible implementation costs, since no hardware modifications are needed. The fault detection algorithm does not require high computing power, and it operates well even during transients.

This paper presents an application of a novel method for the diagnostics of electric and magnetic asymmetries of rotor cage in induction motor (IM) due to broken rotor bars. An increasing anomaly in magnetic field distribution results in degradation of steady-state and dynamic performance of an IM. This degradation can be determined through the analysis of the average duty cycle of the modulated supply voltage. Broken rotor bars would cause torque and speed ripple which is mitigated by an efficient speed-control algorithm. Consequently, specific oscillation in the duty cycle of the modulated stator voltage appears. This effect can be simply detected without additional hardware and therefore provides a correct evaluation of faulty motor performance, which is a very significant part of condition monitoring and diagnostic procedure in modern supervision systems for electrical drives.

This paper presents an implementation of a modified method for direct current control (DCC) in a permanent-magnet synchronous motor (SM). The control is performed using a predictive algorithm in rotor field coordinates due to its simpler implementation. Its task is to minimize the final current error at the end of the sampling interval. Depending on the desired performance, two variants are proposed, yielding either lower switching frequency or lower current ripple. Both variants of DCC, named DCC I and DCC II, have been rearranged for applications in SMs with either surface-mounted permanent magnets or interior (buried) permanent magnets. A comparison with field-oriented control using space-vector modulation and synchronized on/off modulation shows the advantages and drawbacks of the proposed method. Simulations and measurements on a laboratory model with SM having low inductances (thus expecting high ripple) and very high number of poles (high stator supply frequency) confirm the validity of the approach. Additional considerations regarding practical problems, some of which can be found in similar predictive methods, are also presented.

This paper presents a method for the detection of broken rotor bars in an induction motor. After introducing a simplified dynamic model of an induction motor with broken cage bars in a rotor field reference frame which allows for observation of its internal states, a fault detection algorithm is proposed. Two different motor estimation models are used, and the difference between their rotor flux angles is extracted. A particular frequency component in this signal appears only in the case of broken rotor bars. Consequently, the proposed algorithm is robust enough to load oscillations and/or machine temperature change, and also indicates the fault severity. The method has been verified at different operating points by simulations as well as experimentally. The fault detection is reliable even in cases where traditional methods give ambiguous verdicts.

The paper presents a three-phase parallel active power filter without filter current measurement. Only supply grid voltage sensors, filter capacitor voltage sensor and supply line current sensors are used to provide filterpsila proper operation, aiming to reduce reactive power and line current distortion, caused by a non-linear load. Due to filterpsilas inverter-like topology with known parameters in filter branch, the predictive direct current control (DCC) method has been successfully applied, thus obtaining good dynamic response, reducing the commutation frequency of the active power filterpsilas switches and consequently decreasing the filter branch losses.