Unbalanced Power Supply Research Articles

Influence of the neutral in the thermal performance of a three-phase induction motor under unbalanced power supply using the finite element approach

In this paper the influence of the neutral in the thermal performance of a three‐phase squirrel cage induction motor fed by asymmetrical supply voltages is studied and analysed. A 2D finite element formulation was used to solve the steady‐state heat transfer problem. The eddy currents in the rotor bars were evaluated using a combined 3D finite element approach with analytical expressions. The numerical solutions are compared with measured experimental results obtained in laboratory tests for two load conditions and two unbalanced power supply situations with and without the neutral wire connected.

DC harmonic distortion minimization of thyristor converters under unbalanced voltage supply using asymmetrical firing angle

Noncharacteristic harmonics of significant magnitude are produced at the output and input terminals of phase-controlled power converters under unbalanced voltage supply conditions. The concept of switching functions has been proposed before to evaluate the harmonics produced by a phase-controlled six-pulse power converter under both balanced and unbalanced power supply conditions. This paper extends the switching-functions approach to establish analytical equations for the DC output voltage harmonics produced by 12-, 18-, and 24-pulse power converters. The problem is approached from the standpoint of symmetrical voltage components. The increase in distortion under unbalance is caused by the appearance of a second harmonic component. A method, based on an asymmetrical firing angle, to cancel the second harmonic at the power converter output under unbalanced voltage supply is also presented. Cancellation of the second harmonic improves power converter DC output voltage quality.

Calculation of harmonic currents in a three-phase convertor with unbalanced power supply conditions

The paper proposes a practical new method for calculating the harmonic currents of a three-phase bridge controlled rectifier under unbalanced supply conditions. Analytical equations for the harmonic currents are derived, taking into account the effects of DC current ripple and overlap angle. The proposed method is based on the frequency domain method and the rectifier switching functions. All the calculations are conducted only by algebraic calculations, and the accuracy is within 1.1% and 2.6% for the DC and AC side harmonics, respectively. The validity of the proposed method is demonstrated by comparison with the results of digital simulation.

A Balanced Power Supply System in a Josephson Package

A balanced power supply system is proposed for Josephson latching logic circuits for lowering ground noise. Computer simulation shows that the effect of noise reduction on the system is very large compared to conventional unbalanced power supply systems. The system is then tested in a package environment, and the noise is found to be less than about ten percent of that for an unbalanced power supply system at high frequency (400 MHz).