Nkosinathi Gule

Stellenbosch University | SUN · Department of Electrical & Electronic Engineering

In this paper, an adaptive sliding mode observer (ASMO) associated with a phase locked loop (PLL) is assessed for the sensor‐less control of a rotor‐tied doubly‐fed induction generator (RDFIG). In the proposed PLL‐ASMO estimator, the ASMO utilizes the stator current, the stator voltage, and the back electromotive force (EMF) as state variables. The...

The recent increase in both the adoption and size of wind energy conversion systems (WECS) has led to the investigation of new generator topologies. The doubly fed induction generator (DFIG) remains the most popular generator to be employed in WECS due to its variable speed and partially rated converter. Frequent maintenance requirements to their s...

The brushless doubly fed induction machine (BDFIM) is being considered as a possible solution for low-speed wind energy generator applications. It has been proposed as an alternative to the doubly fed induction machine (DFIM) due to its robust rotor structure as well as low operational maintenance requirements. However, due to its complicated contr...

In doubly fed induction generators (DFIGs), the rotor is excited through slip-ring and brush assemblies. These slip-ring and brush assemblies often require frequent routine maintenance, which affects the reliability of the DFIG. Alternatively, a contact-less energy transfer system, such as a rotary transformer, can be utilized in place of the slip...

In this paper, an adaptive sliding mode observer (ASMO) associated with a phase locked loop (PLL) is assessed for the sensor-less control of a rotor-tied doubly-fed induction generator (RDFIG). In the proposed PLL-ASMO estimator, the ASMO utilizes the stator current, the stator voltage and the back electromotive force (EMF) as state variables. The...

Research interest on brushless doubly fed induction machines (BDFMs) is increasing, as they offer higher reliability compared to doubly fed induction generators (DFIGs) in wind turbines. At the moment, BDFMs do not have a definitive structure nor design process, as literature is rife with different approaches to designing BDFMs. In this paper, a co...

In this paper, it is proposed that design evaluations of brushless doubly fed machines (BDFMs) be conducted at unity power factor in the synchronous generating mode, for wind turbine applications. In the build up to this idea, differences in power output at asynchronous, synchronous motoring, and synchronous generating modes are highlighted and dis...

The paper presents a dqmodel used to analyze a brushless doubly fed induction machines' closed loop control ability. A simplified vector control algorithm is proposed by reducing the controllers dependence on cross compensation in the powerwinding current control loop. Simulink is used to show the viability of the controller in operation. It is fou...

The brushless doubly fed induction machine (BDFM) is considered as an alternative to doubly fed induction generators (DFIGs) in wind energy conversion systems. However, BDFMs have a complex machine structure, and their operations are relatively complicated. In this study, the winding function theory is used in the development of a coupled circuit (...

In this study, a sensorless vector control for the rotor‐tied doubly fed induction generator (RDFIG) is proposed in the grid‐connected mode. The proposed sensorless vector control method includes a slip speed/angle estimator which is based on the association of the high‐order sliding mode observer (HOSMO) with a phase‐locked loop (PLL). In addition...

In this paper, a slip speed/position estimator for sensor-less control of rotor-tied DFIG systems is presented. The proposed slip speed/position estimator is based on the association of the phase locked loop and the sliding mode observer. The proposed sliding mode observer (SMO) uses the three-phase stator currents and the back electromotive force...

In this study, a sensorless vector control strategy of a rotor‐tied doubly fed induction generator (RDFIG) system based on the association of the phase‐locked loop (PLL) estimator and the super‐twisting sliding mode observer (STSMO) is proposed and analysed. The proposed sensorless control strategy utilises the stator current and the back‐electromo...

In this paper, a comprehensive analytical design methodology for a single-phase axial rotary transformer (RT) is presented. The proposed procedure is designed to yield the minimum RT volume or size while at the same time offer adequate efficiency. Furthermore, the proposed methodology is used in the design and evaluation of a 1.2-kVA single-phase a...

In this paper, the performance of an LCL filter at lower switching frequencies (<5000 Hz) in a grid-connected three-phase voltage-source converter is analysed. An LCL filter is designed for a switching frequency of 2500 Hz using the conventional LCL filter design procedure. In addition, a comparative study of the designed LCL filter and the L filte...

Rotor-tied doubly fed induction generators (DFIGs) boast of higher efficiencies than conventional DFIGs and may be more suitable for rotary transformer designs. This paper maps out a methodology for designing rotor-tied DFIGs. Following this methodology, a 5.5 kW rotor-tied DFIG was designed and finite element analysis (FEA) was performed with rele...

The steady state operation of a rotor-tied doubly fed induction generator (DFIG) is described in this paper in relation to slip, the electrical and mechanical frequencies. The ratio of the stator power to the input mechanical power of a rotor-tied DFIG relative to slip is illustrated. The transformer model based equivalent circuit of rotor-tied DFI...

In this paper, the rotor side converter control of a wind energy conversion system based on the doubly-fed induction generator is investigated. The proposed control algorithm is based on the voltage-oriented control approach. The control algorithm is aimed at maximum power point tracking. In addition, it allows the wind energy conversion system bas...

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...

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 use...

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 mo...

The paper presents the simulation of a delta modulated Pulse Width Modulation (PWM)-fed Brush DC Equivalent (BDCE) controlled nine phase induction machine drive. The BDCE control method involves the decoupling of the stator current into a torque producing component and a field producing component. The BDCE controlled drive is simulated using both M...

In a brush dc equivalent (BDCE) controlled machine, quasi-square like constant air gap flux density and rotor induced voltage waveforms are utilized. Analytical expressions for calculating the developed power, flux density, stator and rotor copper losses for the BDCE controlled cage rotor multiphase induction machine are developed in this paper. Fr...

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-...

In this paper, a winding function theory based method of predicting the rotor bar and end ring current waveforms of a brush dc equivalent (BDCE) controlled cage rotor multi-phase induction machine is presented. Steady state analytically calculated and FEA results from an arbitrary chosen nine-phase induction machine are given. The analytical method...

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 flu...

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...

Word processed copy. Thesis (M.Sc. (Electrical Engineering))--University of Cape Town, 2006. Includes bibliographical references (leaves 82-88).

ENGLISH ABSTRACT: The multiphase induction machine drive has been under investigation for the last half century. Although it offers several attractive advantages over the conventional three-phase induction machine drive, it is restricted to highly specialised applications. One aspect of the multiphase induction machine drive is the complexity of th...