Nkosinathi Gule

Optimal ratio of field to torque phases in multi-phase induction machines using special phase current waveforms

This paper presents a simple criterion to calculate the optimal ratio of field to torque phases in a concentrated winding multi-phase induction machine using special phase current waveforms. The method is validated through finite element analysis. It is shown that with higher stator phase numbers, up to 66 - 80 % of the rotor winding is active at a time as fewer field phases are utilised. An almost constant square like air gap flux density and rotor induced voltage waveforms are produced when using the special stator current waveforms.

Multiphase Cage-Rotor Induction-Machine Drive With Direct Implementation of Brush DC Operation

In this paper, a multiphase induction-machine drive utilizing the brush-dc-machine operation principle is presented and implemented on a cage-rotor multiphase induction machine. The results from measurements prove that the proposed brush dc control method for multiphase induction-machine drives produces remarkable results in the subbase and flux-weakening-speed regions of the drive. Also, results show that the drive systems efficiency compares well with that of a standard three-phase drive system. The method can be used for any high-phase-number cage or wound-rotor induction machine.

Optimal design methodology of a three phase rotary transformer for doubly fed induction generator application

Rotary transformers can be used to provide magnetic coupling to the rotor circuit of a doubly fed induction generator. This topology eliminates the need for slip ring and brush assemblies thus reducing the maintenance required. This paper presents an analytical method for determining an optimal design of a rotary transformer. The methodology is used to design a 3 kVA three phase transformer which is validated using a FEM simulation package. Also, a study of suitability in terms of size at different power levels is conducted.

Multi-phase cage rotor induction machine drive with direct implementation of brush DC operation

In this paper, a multi-phase induction machine drive utilising the brush dc machine operation principle is presented and implemented on a cage rotor multi-phase induction machine. The results from measurements prove that the proposed brush dc control method for multi-phase induction machine drives produces remarkable results in the sub-base and flux weakening speed regions of the drive. It is found that a lower number of number of field phases can be used for better use of the inverter current capability and for better current density distribution. Also, results show that the drive systems efficiency compares well with that of a standard three phase drive system. The method can be used for any high-phase-number cage or wound rotor induction machines.

Design and evaluation of a 1.2 kVA single phase rotary transformer

The doubly fed induction generator (DFIG) is the most popular choice for wind energy generation systems. The cost and difficulty incurred in the maintenance of the slip rings has led to the development of the brushless DFIG. Amongst other design options, the brushless DFIG can be realized through the use of rotary transformers (RTs). Due to the low operating frequency of the rotor currents, a RT used in place of slip rings in a conventional DFIG configuration, can be bulky. However, by utilizing a rotor tied to the grid DFIG system configuration, the RTs operating frequency can be increased to the grids frequency. In this paper a single phase 1.2 kVA RT is designed, using a previously proposed optimal design method, and developed. Three of these RTs can be used in place of the slip rings in DFIGs. Remarkable measurement results as well as simulation results are also presented.

Brush-DC equivalent control based delta modulation for a PWM inverter-fed nine phase induction machine drive

A recently developed control method for multiphase induction machine drives termed the Brush-DC Equivalent control has presented a simpler control strategy that does not use any complex transformations. It has been implemented using a hysteresis current controller and in this paper, a delta modulated current control technique is presented. Delta modulation is proposed in to replace hysteresis control because hysteresis control uses a varying switching frequency which makes harmonic filtering and protection of the inverter difficult. A constant switching delta modulation scheme eliminates these challenges. It has inherent harmonic filtering giving better performance in terms of current and torque ripples. A Brush-DC controlled nine-phase cage rotor induction machine drive is used to investigate the implementation of the delta modulated current controller. The drive is simulated using Matlab/Simulink to determine its performance when stator voltages are used as feedback to the filter in the delta modulator.

The BDCE equivalent control method for multiphase induction machine

The concept behind the brush dc equivalent (BDCE) control method for multiphase induction machine is described in this paper. The BDCE concept is developed from the dc machine operation. A method for calculating the air-gap flux density is given in this paper. Calculated and finite element analysis (FEA) evaluated flux density waveforms for a nine-phase induction machine are provided. Also, a comparison of analytically calculated and measured torque of the machine is given.