Pulse Width Modulated Voltage Excitation Research Articles

Investigation and Prediction of High-Frequency Iron Loss in Lamination Steels Driven by Voltage-Source Inverters Using Wide-Bandgap Switches

The availability of wide-bandgap (WBG) power switches makes it possible to excite electric machines with much higher pulsewidth modulation (PWM) switching frequencies. This article experimentally characterizes the magnetic and iron loss properties of lamination steels over a wide range of PWM frequencies and magnetization states excited by a voltage-source inverter using GaN-based WBG switches. With the collected hysteresis loop and iron loss data, a new frequency-interconnected dynamic Jiles-Atherton (J-A) model has been developed explicitly for PWM-induced iron loss analysis. Experiments have been conducted to verify the model prediction accuracy over a broad range of operating conditions. The proposed model has been subsequently integrated with a dynamic hysteresis model devoted to fundamental field iron loss estimation, providing an accurate and efficient tool for total iron loss estimation during PWM voltage excitation using high-frequency WBG devices. This article includes an investigation of the impact of elevated fundamental frequencies and field amplitudes on the total iron loss including comparisons between analytical predictions and experimental test results.

Characterization and Modeling of Soft Magnetic Materials for Improved Estimation of PWM-Induced Iron Loss

This article investigates the iron loss properties of soft magnetic materials under conditions of high excitation frequency and varying premagnetized dc-bias fields (i.e., different magnetization states). Using measured iron loss data collected from the customized test equipment, a modified dynamic Jiles–Atherton model has been developed specifically for the purpose of achieving improved pulsewidth modulation (PWM)-induced iron loss estimation. The accuracy and scalability of the proposed prediction model for different conditions are evaluated including the flux ripple amplitude, excitation frequency, dc-bias field, and symmetry of the triangular waveform. Experimental results have confirmed that the proposed model can accurately predict the dynamic hysteresis loop and corresponding iron loss over a wide range of operating conditions. By introducing a companion iron loss model developed for fundamental and low-order harmonic fields, the total iron loss under inverter PWM voltage excitation is explored. The results show that model parameters derived from a limited number of tests can be used to predict the iron loss in a much broader operating range, which makes it a promising tool for PWM-induced iron loss estimation in new machine designs intended for demanding operating conditions.

Torque Ripple Reduction in Sectored Multi Three-Phase Machines Based on PWM Carrier Phase Shift

The interest in multiphase machines for high power and reliable drives has been growing, and many control algorithms have been proposed to improve their torque performance. This article presents a new approach to the modeling of a multi three-phase drive, aiming at the minimization of the torque ripple introduced by the pulsewidth modulation (PWM) voltage excitation, by the shift of carrier phase angles among different three-phase inverters. The underlying idea is to use standard three-phase converters feeding the individual segment and to apply a phase shift between the PWM carriers. For the torque ripple analyzed in this article, only the interaction between the armature field, resulting from the PWM voltage excitation, and the fundamental component of the permanent-magnet field is considered. The proposed carrier phase-shift angles are obtained for a case study of a sectored triple three-phase synchronous permanent-magnet machine. Analytical, numerical and finite-element analysis results are presented to explain how the carrier shift angles affect the current and torque ripple. Finally, experimental results are presented to validate the model and the control algorithm.

Vibration and acoustic noise emitted by dry-type air-core reactors under PWM voltage excitation

According to coupling way between the magnetic field and the structural order, structure mode is discussed by engaging finite element (FE) method and both natural frequency and modal shape for a dry-type air-core reactor (DAR) are obtained in this paper. On the basis of harmonic response analysis, electromagnetic force under PWM (Pulse Width Modulation) voltage excitation is mapped with the structure mesh, the vibration spectrum is gained and the consequences represents that the whole structure vibration predominates in the radial direction, with less axial vibration. Referring to the test standard of reactor noise, the rules of emitted noise of the DAR are measured and analyzed at chosen switching frequency matches the sample resonant frequency and the methods of active vibration and noise reduction are put forward. Finally, the low acoustic noise emission of a prototype DAR is verified by measurement. At the request of the authors, this article is being retracted effective 30 October 2018.

Mechanical Resonance in Nonoriented Electrical Steels Induced by Magnetostriction Under PWM Voltage Excitation

Acoustic noise in inverter-fed motors can increase if resonance induced by magnetostriction occurs. This paper presents results of measurements of magnetostriction-induced mechanical resonance in nonoriented (NO) steels, commonly used in motor cores, under pulse width modulation (PWM) excitation. The resonant frequency of a strip of NO steels was determined and it was magnetized by PWM voltage waveforms. The PWM switching frequency was chosen to be the same as the sample resonant frequency. The peak-to-peak magnetostriction under PWM excitation was up to 28% higher than that under sinusoidal excitation when an integer multiple of the switching frequency matched the resonant frequency of the sample.

Investigation of power loss in non-oriented electrical steels under pulse width modulated voltage excitation

Power loss of various electrical steels energised by PWM voltage excitation was measured and compared with that under sinusoidal excitation by use of an Epstein tester. The results indicate that total power loss under PWM excitation is the larger. During measurements flux densities varied from 0.5 to 1.7 T and maximum and minimum loss increases occurred at 1.7 and 0.5 T, respectively. The PWM parameters such as the switching frequency and modulation depth were maintained constant at 1.5 kHz and 0.7, respectively. It is assumed that the mechanism of loss increase can be attributed to frequency dependent losses as well as to the flux waveform.

Effects of geometrical factors on iron loss increase in wound toroidal cores energized by pulse width modulated voltage sources

The pulse width modulated (PWM) inverter power supplies have been used increasingly to drive many electromagnetic devices for various purposes. When typical magnetic cores are energized by such voltage waveforms, additional iron losses occur due to distorted flux waveform. Most of these losses are due to an increase in frequency dependent losses. It should be noted that core geometry may also affect total power loss increase under PWM voltage excitation. This is because of a different magnetization process with respect to sinusoidal excitation. The effects of geometrical factors on magnetic properties of wound toroidal cores made of 3% grain oriented electrical steel were investigated. The results indicated that geometrical factors affect an iron loss increase under PWM voltage excitation as well as under sinusoidal excitation. The aspect ratio is particularly important in this regard.

Investigation of power loss in non-oriented electrical steels under pulse width modulated voltage excitation

Power loss of various electrical steels energised by PWM voltage excitation was measured and compared with that under sinusoidal excitation by use of an Epstein tester. The results indicate that total power loss under PWM excitation is the larger. During measurements flux densities varied from 0.5 to 1.7 T and maximum and minimum loss increases occurred at 1.7 and 0.5 T, respectively. The PWM parameters such as the switching frequency and modulation depth were maintained constant at 1.5 kHz and 0.7, respectively. It is assumed that the mechanism of loss increase can be attributed to frequency dependent losses as well as to the flux waveform.

Measurements of power loss distribution in a typical stator core under PWM voltage excitation

The pulse width modulated (PWM) inverter is widely used to feed small induction motors for variable speed and torque control. When a laminated stator core is energised in this way additional iron losses occur due to localised distorted flux. Flux density and power loss distribution under PWM and sinusoidal voltage excitations were measured in a typical induction motor stator core lamination at 1.3 T, 50 Hz by using a computer-aided magnetising system to set up flux distribution as would occur in a practical three-phase stator core. The iron loss increased 15–20% under PWM excitation. The loss increase under PWM excitation in the stator core laminations was 3% lower than in Epstein strips of the same electrical steel under the same conditions showing an effect of the magnetic circuit geometry.

Magnetic properties of 6.5% silicon steel sheets under PWM voltage excitation

Power losses of 6.5% silicon steel sheets under PWM (pulse width modulation) voltage excitation were examined. The PWM wave was composed of a 50 Hz fundamental wave, a 16 kHz carrier frequency wave and some other higher harmonics. It was found that the power losses of the inductor cores were much larger than those of the transformer cores when the cores were driven by a PWM inverter, although such a great difference was not observed under sinusoidal voltage excitation. Power losses of the inductor made of 6.5% silicon steel sheets and conventional grain oriented 3% silicon steel sheets under PWM voltage excitation were also investigated. It was found that the power losses of the inductor made of 6.5% silicon steel sheets were reduced by more than 30% compared to those of the inductor made of grain oriented 3% silicon steel sheets. This was because the grain oriented 3% silicon steel sheets had higher losses at higher harmonics found in the PWM excitation. Therefore, it was clearly shown that 6.5% silicon steel sheet was a suitable material for the inductor under PWM voltage excitation.

Investigation of power loss in wound toroidal cores under PWM excitation

The pulse width modulation (PWM) inverter is widely used when voltage-frequency regulation is required. When laminated cores are energised by PWM voltage supplies additional losses occur due to flux distortion. The iron loss of three types of grain-oriented 3.25% Si-Fe toroidal cores was measured by means of a computer aided system under PWM and sinusoidal voltage excitation at different flux densities. The loss increase under PWM excitation was found to be higher at high flux densities due to higher harmonic distortion. Another important difference between sinusoidal and PWM voltage excitation is a significant difference in the variation of instantaneous energy loss through the magnetising cycle which is also believed to contribute to the additional losses. The losses in the three different geometries were greater under PWM excitation than under sinusoidal voltage and flux.