Pulse Width Modulation Excitation Research Articles

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.

Magnetic properties of 6.5% silicon content non-oriented electrical steel under sine and PWM excitation

The specific total loss of 6.5% silicon content electrical steel, 0.1 mm thick, was measured under sine and pulse width modulation (PWM) excitation conditions. The loss separation is presented in order to assess the effect of high electrical resistivity and the low thickness on the eddy current and excess losses. The hysteresis loss was subdivided into high and low induction and the results were compared to those obtained in 3% SiFe steel. The texture of the samples was measured and discussed relating their effect on the magnetic properties of the material. The results from the texture indicate that its hysteresis loss can be further improved.

Behavior of three-phase induction motors with variable stator coil winding pitch

A pulse-width modulation (PWM) inverter and sinusoidal output voltage supplies feeding four different chorded three-phase induction motors were tested for low-order odd voltage harmonic components and efficiency at different loads. The total harmonic distortion due to the third, fifth, and ninth harmonics was lowest in a motor with 160° coil pitch energized by both sinusoidal and PWM voltages. The efficiencies of the motor with the short-chorded winding were as much as 5% and 16% higher than that of the full-pitched motor under sinusoidal and PWM excitation, respectively, due to harmonic cancellation.

A Novel Approach for Sensorless Control of PM Machines Down to Zero Speed Without Signal Injection or Special PWM Technique

A novel approach is developed in this paper for sensorless control of permanent magnet (PM) machines down to zero speed without signal injection or special pulsewidth modulation (PWM) techniques. Taking advantage of the low inductance in a PM machine, the phase current ripples under a conventional PWM excitation are measured to derive the rotor position and speed. The new approach can also be used to estimate the rotor position at standstill if a minor rotor saliency exists. Neither prior knowledge of machine parameters, nor any special signal injection, is needed for the rotor position detection. Sensorless control of a PM machine based on the proposed scheme has been investigated by comprehensive computer simulations. Experimental results are presented to verify the effectiveness of the approach.

Localised losses in stator laminations of an induction motor under PWM excitation

Electronically generated voltage waveforms have increasingly been used to energise small induction motors for speed and torque control due to low cost. The most popular such waveform is a pulse width modulation (PWM), which is obtained by logically comparing a reference voltage waveform with a carrier wave of different frequency. When a small induction motor is driven by a typical PWM voltage supply, additional power losses occur in its stator core due to a magnetisation process, which is very different to standard sine wave excitation. In this investigation flux density and power loss distribution under PWM and sinusoidal voltage excitations were measured in a small induction motor stator core using a system which set up flux distribution as would occur in a rotating 3-phase stator core. The iron loss increase was between 15 and 20% under PWM excitation. Surprisingly, the increase in iron loss in a typical induction motor stator core lamination was 3% lower than that in Epstein strips of the same electrical indicating an effect of the magnetic circuit geometry as well as the voltage waveform.

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.