Voltage Control of Multiphase Cage Induction Generators at a Speed Varying over a Wide Range

Abstract

The subject of this publication is a method of controlling the DC voltage of a PWM rectifier supplied by a multiphase cage induction generator with the number of stator phases greater than three operating in a wide range of driving speeds. Voltage regulation is performed by changing the frequency and amplitude of the stator voltages with simultaneous switching of the phase sequence of these voltages. The step change of the voltage sequence is made in the designated ranges of the generator speed, which enables the stabilization of the output voltage in a wide range from the minimum speed of about 25% of the rated speed. Such sequence switching changes the number of pole pairs produced by the winding for each supply sequence. The difference compared to multi-speed induction machines is that, in the presented solution, there is only one winding, not a few, which enables good use of the machine’s magnetic core in the same dimensions as for the three-phase machine of a similar power. Steady-state characteristics and dynamic operation were obtained using laboratory measurements of a standalone nine-phase induction generator. The automatic control system maintained the output voltage at the set level, regardless of the generator load and driving power.

Field-Oriented Control of a Nine-Phase Cage Induction Generator with Large Speed Changes and Variable Load

“…The general structure of the automatic DC voltage control system is shown in Figure 1, where field-oriented vector control was used instead of scalar control, as in [1]. In this paper, the physical basis of the voltage regulation of multiphase cage induction generators is presented.…”

“…This paper presents a vector control method for field-oriented multiphase squirrel-cage induction generators driven at a variable speed. The presented method is a continuation and extension of the method presented in [1], where scalar generator control was used. The presented system is a variant of the stator-converter-controlled induction generator (SCCIG) with a squirrel-cage rotor.…”

“…It can be used in low-power wind or water power plants operating at variable speed. There are SCCIG systems with a three-phase generator and a diode rectifier [2] or a PWM rectifier [1,3,4]. In multiphase systems, double three-phase windings with a mutual phase shift by an electrical angle of 30 • [5][6][7][8][9] are most often used, as well as multiphase symmetrical windings with the following number of phases: nine [1], twelve [5], or six [10].…”

“…There are SCCIG systems with a three-phase generator and a diode rectifier [2] or a PWM rectifier [1,3,4]. In multiphase systems, double three-phase windings with a mutual phase shift by an electrical angle of 30 • [5][6][7][8][9] are most often used, as well as multiphase symmetrical windings with the following number of phases: nine [1], twelve [5], or six [10]. The generators can operate as self-excited with a capacitor bank connected to the stator winding [2], or pre-excited by an external source with a capacitor connected to the terminals of the DC output circuit [1,2,5,6,11].…”

“…In multiphase systems, double three-phase windings with a mutual phase shift by an electrical angle of 30 • [5][6][7][8][9] are most often used, as well as multiphase symmetrical windings with the following number of phases: nine [1], twelve [5], or six [10]. The generators can operate as self-excited with a capacitor bank connected to the stator winding [2], or pre-excited by an external source with a capacitor connected to the terminals of the DC output circuit [1,2,5,6,11]. The latter solution provides greater control possibilities, because in the case of a back-to-back converter connecting the generator with the network [3,5,6,8,9,12,13], the C DC intermediate capacitor receives a direct pre-charge.…”