In this paper a three-dimensional non-holonomic integrator (NI) with drift terms is considered. For this type of plant, the question how to obtain desired piecewise constant output functions with minimum norm control inputs is explored. It is shown that this can be achieved by a nonlinear controller that provides simultaneous modulation of both the amplitude and the frequency of the harmonic input vector. The internal states are implicitly forced to follow natural periodic orbits satisfying the non-holonomic constraints of the plant. Global asymptotic stability and high dynamics in the output response are achieved. The problem of singularity at zero initial state is solved by a time optimal control scheme for the internal states. By combining the nonlinear controller and the time-optimal controller using an appropriate switching strategy, a powerful control concept can be established. The torque control of an induction machine is considered as an illustrative example for the application of the control scheme. Experimental results of the closed loop feedback control system are presented.
COBISS.SI-ID: 16326678
The paper presents a new field weakening control scheme for operation of permanent magnet synchronous machine over a wide range of speeds. At the high rotational speed, the stator voltage is limited by the inverter DC bus voltage. In order to control the machine torque above the base speed, the proposed method controls the angle of the stator voltage by the integration of gain scheduled q-axis current error. The stability of the drive is increased by a feedback loop, which compensates dynamic disturbances and smoothers the transition into field weakening. The proposed method can fully utilize the available DC bus voltage. It is robust to the variation of machine parameters. Excellent performance of the proposed method is achieved in operation with and without speed and position sensors.
COBISS.SI-ID: 16458774
This paper reflects a newly developed method for evaluation of iron core quality for resistance spot welding (RSW) transformers. The classical methods for determination of the iron core quality are mostly based on a sinusoidal excitation. The proposed method is based on corresponding excitation by hysteresis controlled current in primary winding under no load operation, whereas consequently the primary current changes between its maximum and minimum value. Therefore, the operation point during the test is defined by the maximum magneto motive force (mmf) of the magnetic circuit. The tested iron core that reaches higher value of the magnetic flux density with the same maximum mmf, has lower average magnetic resistance and it is categorized as a better one, for the discussed RSW application. Furthermore, the value of the input reactive power is considered as an additional indicator for evaluation of the iron core quality. The proposed method is fully verified with numerical computations and laboratory measurements. The main advantage of the proposed method is that no extra equipment is required when testing the RSW systems.
COBISS.SI-ID: 15897110
This paper presents an in-depth comparative analysis of the variable speed drive (VSD) performance between an IEC frame size 90 four-pole three-phase induction motor (IM) and the equal line-start interior permanent magnet synchronous motor (LSIPMSM). Employing measurement data from no-load tests, load tests, and temperature-rise tests of the aforementioned motors and different cage materials as well, the motors' no-load and load characteristics are first examined in detail and then the drives' characteristics are analyzed in open-loop volts per hertz (V/f) control by using the same voltage-source inverter and the aforementioned IM or LSIPMSM in both constant torque and constant power operation. It has been established that particularly the motors' current and power factor characteristics have distinct impact on the consequent VSD performance in terms of loss and efficiency. Furthermore, it has been shown that the lower loss of the LSIPMSM enables a significant increase of the VSD's constant power range.
COBISS.SI-ID: 16458518
This paper deals with the acoustic noise emissions caused by a welding transformer (WT) operating as part of a middle-frequency direct current resistance spot welding system (RSWS). The WT consists of an iron core, one primary winding, and two secondary windings. The primary winding is supplied by the voltage from the input converter while the full-wave diode output rectifier is connected to the two secondary windings in order to generate a direct welding current. In the case study, the alternating current primary voltage is generated in two different ways, by applying a pulse width modulation and two hysteresis controllers. The aim of this paper is to analyze how the voltage generation method influences the acoustic noise emissions caused by the WT. The analysis is based on the values of the supply current, the welding current, and the iron core flux density measured on a 160 kW industrial WT operating as a part of laboratory RSWS where the supply voltage is generated in two different ways. The results presented in the paper show that proper voltage generation method can substantially reduce the acoustic noise emissions caused by a WT.
COBISS.SI-ID: 15840534