Analysis of Equivalent Inductance of Three-Phase Induction Motors in the Switching Frequency Range

Abstract

The equivalent inductance of three-phase induction motors is experimentally investigated in this paper, with particular reference to the frequency range from 1 kHz to 20 kHz, typical for the switching frequency in inverter-fed electrical drives. The equivalent inductance is a basic parameter when determining the inverter-motor current distortion introduced by switching modulation, such as rms of current ripple, peak-to-peak current ripple amplitude, total harmonic distortion (THD), and synthesis of the optimal PWM strategy to minimize the THD itself. In case of squirrel-cage rotors, the experimental evidence shows that the equivalent inductance cannot be considered constant in the frequency range up to 20 kHz, and it considerably differs from the value measured at 50 Hz. This frequency-dependent behaviour can be justified mainly by the skin effect in rotor bars affecting the rotor leakage inductance in the considered frequency range. Experimental results are presented for a set of squirrel-cage induction motors with different rated power and one wound-rotor motor in order to emphasize the aforesaid phenomenon. The measurements were carried out by a three-phase sinusoidal generator with the maximum operating frequency of 5 kHz and a voltage source inverter operating in the six-step mode with the frequency up to 20 kHz.

Prediction of DC-Link Voltage Switching Ripple in Three-Phase Four-Leg PWM Inverters

“…For this experiment, a relatively high inductance is required to minimize disruptive AC current ripple on the AC side. However, the effect of frequency-driven inductance variation in induction motors should be taken into account [26]. In this case, inductance at the switching frequency is lower than the value at the fundamental frequency.…”

Applications of Power Electronics

“…The knowledge of motor behavior through proper modeling plays an important role for motor drive system design and control. The frequency-dependent behavior of an induction motor's equivalent inductance and its importance on the output current ripple and total harmonic distortion (THD) is analyzed in [32]. In [33], 3D finite element analysis (FEA) is used to analyze the profile effect of various magnet shapes in axial flux PM motors to obtain higher efficiency.…”

Applications of Power Electronics

“…This special issue with 49 published articles has gained a great deal of attention from both academia and industry, clearly showing the growth in significance of "Applications of Power Electronics" in the current research and development arena. The accepted articles cover broad topics in the field of power electronics, and they are categorized into seven different focus areas: T1: Fault Diagnosis, Reliability and Condition Monitoring [14][15][16][17]; T2: Modeling, Control and Design of Power Electronic Converters [18][19][20][21][22][23][24][25]; T3: Electrical Machines, Drives and Traction Systems [26][27][28][29][30][31][32][33][34]; T4: Distributed Power Generation and e-Grid [35][36][37][38][39][40][41][42][43][44][45][46]; T5: Emerging Power Electronic Technologies (Pulsed Power, Energy Storage, Others) [47][48][49][50][51]; T6: Energy Access and Micro-Grids [52][53][54][55][56]; T7: Wireless Power Transfer Systems…”