Mwana Wa Kalaga Mbukani - Academia.edu (original) (raw)
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Papers by Mwana Wa Kalaga Mbukani
2018 International Symposium on Power Electronics, Electrical Drives, Automation and Motion (SPEEDAM), 2018
In the rotor-tied configuration of the doubly-fed induction generator (DFIG), the rotor is connec... more In the rotor-tied configuration of the doubly-fed induction generator (DFIG), the rotor is connected to the grid whilst the stator of the DFIG is connected to the grid through a back-to-back converter. In this paper, the modelling and control algorithm of the stator-side converter of a custom-designed S.S-kW rotor-tied DFIG are presented. Furthermore, the performance of the proposed control algorithm is experimentally evaluated during synchronisation and in sub-synchronous operating conditions.
The doubly-fed induction generator (DFIG) is amongst the most popular wind turbine generator in S... more The doubly-fed induction generator (DFIG) is amongst the most popular wind turbine generator in South Africa. This is partly due to the fact that its backto-back power converters are partially rated. More precisely, they are rated at 30% of the generator rated power. A new DFIG topology has been proposed recently. That is the rotor-tied doubly-fed induction generator (RDFIG). In this topology, the rotor side is connected to the grid while the stator side is connected to the power converter. It has been shown that this topology holds the advantage of higher e ciency compared to the standard DFIG topology. High accuracy in all the measurements is required for the optimum operations of wind energy conversion systems (WECSs). The measurement of the rotor position/speed is amongst the most important measurements when it comes to implement any control system for the WECS. The conventional method of measuring the rotor position/speed is to use an electronic/mechanical sensor (encoder or re...
The need to reduce the world's carbon foot print has led to a signi cant rise in wind energy ... more The need to reduce the world's carbon foot print has led to a signi cant rise in wind energy generation. The doubly-fed induction generator (DFIG) is one of the most popular wind turbine generators partly due to its low rated backto-back converter. A constant DC-link voltage in the doubly-fed induction generator system's back to back converter allows for bidirectional power ow of the rotor power. Hence, e ective control of the DC-link voltage is necessary. The presence of the switching elements in the back-to-back converter creates harmonics in the systems. LCL and L lters are mostly used to mitigate the harmonics. DFIGs are mainly connected to the grid, however, they can be used in stand-alone mode in isolated rural areas, where there are low loads with no grid connection. DFIGs in the stand-alone mode have to be controlled such that they provide voltage and frequency stability at varying load conditions and changing wind speeds. In this thesis, the power control of the gri...
2018 IEEE 9th International Symposium on Sensorless Control for Electrical Drives (SLED), 2018
In this paper, a position/speed sensor-less control strategy of a rotor-tied doubly-fed induction... more In this paper, a position/speed sensor-less control strategy of a rotor-tied doubly-fed induction generator (DFIG) is proposed and its performance is analysed. The proposed sensorless control strategy is based on a slip speed/angle estimation technique. The proposed slip speed/angle estimation technique consists of a sliding mode observer (SMO) associated with a phase locked loop (PLL) estimator. The proposed SMO takes the three-phase stator current as state variable. The proposed PLL estimator includes a simple judgement function which allows the PLL to perform in super-synchronous operating conditions. The performance of the proposed sensor-less control strategy is validated through simulations using a 37.3-kW conventional DFIG connected in rotor-tied configuration and the experimental tests using a 5.5-kW custom-designed rotor-tied DFIG.
IEEE Access
Transformational techniques unifying synthesis of two-state DC-DC converters and analytical synth... more Transformational techniques unifying synthesis of two-state DC-DC converters and analytical synthesis techniques allowing generation of all possible converters meeting a certain criteria already exist. The analysis of a family of converters derived from a single converter cell has also been unified. Current waveforms generated by the family of converters were shown to be related. However, a concept or basic building blocks that facilitate unified synthesis, analysis, prediction of current waveforms and assignment of switch states over a very wide range of DC-DC converters is still lacking. This study will propose three 3-terminal basic building blocks and one 3-terminal filter block. It will be shown that between them, they are sufficient for realizing all non-isolated DC-DC converters excluding those with coupled inductors. The various DC-DC converters fall into those realized through cascade, stacked, stacked plus cascade, interleaved/paralleled or differential connection of the basic building blocks. A systematic approach for evaluating input-output current gains will be presented. Moreover, a basic building block will be shown to have fixed switching states for proper operation. This gives rise to the generation of a unique set of current waveforms at the three terminals irrespective of where a basic building block is embedded. It has been shown that the effort and time needed to design DC-DC converters can be reduced as switching device stresses can be estimated without the need for tedious first principle derivations. INDEX TERMS Basic building blocks, converter cells, current waveforms, non-isolated DC-DC converters, steady-state gains, unified analysis of DC-DC converters, unified synthesis of DC-DC converters.
IEEE Transactions on Industry Applications
IET Electric Power Applications
2018 International Symposium on Power Electronics, Electrical Drives, Automation and Motion (SPEEDAM), 2018
In the rotor-tied configuration of the doubly-fed induction generator (DFIG), the rotor is connec... more In the rotor-tied configuration of the doubly-fed induction generator (DFIG), the rotor is connected to the grid whilst the stator of the DFIG is connected to the grid through a back-to-back converter. In this paper, the modelling and control algorithm of the stator-side converter of a custom-designed S.S-kW rotor-tied DFIG are presented. Furthermore, the performance of the proposed control algorithm is experimentally evaluated during synchronisation and in sub-synchronous operating conditions.
The doubly-fed induction generator (DFIG) is amongst the most popular wind turbine generator in S... more The doubly-fed induction generator (DFIG) is amongst the most popular wind turbine generator in South Africa. This is partly due to the fact that its backto-back power converters are partially rated. More precisely, they are rated at 30% of the generator rated power. A new DFIG topology has been proposed recently. That is the rotor-tied doubly-fed induction generator (RDFIG). In this topology, the rotor side is connected to the grid while the stator side is connected to the power converter. It has been shown that this topology holds the advantage of higher e ciency compared to the standard DFIG topology. High accuracy in all the measurements is required for the optimum operations of wind energy conversion systems (WECSs). The measurement of the rotor position/speed is amongst the most important measurements when it comes to implement any control system for the WECS. The conventional method of measuring the rotor position/speed is to use an electronic/mechanical sensor (encoder or re...
The need to reduce the world's carbon foot print has led to a signi cant rise in wind energy ... more The need to reduce the world's carbon foot print has led to a signi cant rise in wind energy generation. The doubly-fed induction generator (DFIG) is one of the most popular wind turbine generators partly due to its low rated backto-back converter. A constant DC-link voltage in the doubly-fed induction generator system's back to back converter allows for bidirectional power ow of the rotor power. Hence, e ective control of the DC-link voltage is necessary. The presence of the switching elements in the back-to-back converter creates harmonics in the systems. LCL and L lters are mostly used to mitigate the harmonics. DFIGs are mainly connected to the grid, however, they can be used in stand-alone mode in isolated rural areas, where there are low loads with no grid connection. DFIGs in the stand-alone mode have to be controlled such that they provide voltage and frequency stability at varying load conditions and changing wind speeds. In this thesis, the power control of the gri...
2018 IEEE 9th International Symposium on Sensorless Control for Electrical Drives (SLED), 2018
In this paper, a position/speed sensor-less control strategy of a rotor-tied doubly-fed induction... more In this paper, a position/speed sensor-less control strategy of a rotor-tied doubly-fed induction generator (DFIG) is proposed and its performance is analysed. The proposed sensorless control strategy is based on a slip speed/angle estimation technique. The proposed slip speed/angle estimation technique consists of a sliding mode observer (SMO) associated with a phase locked loop (PLL) estimator. The proposed SMO takes the three-phase stator current as state variable. The proposed PLL estimator includes a simple judgement function which allows the PLL to perform in super-synchronous operating conditions. The performance of the proposed sensor-less control strategy is validated through simulations using a 37.3-kW conventional DFIG connected in rotor-tied configuration and the experimental tests using a 5.5-kW custom-designed rotor-tied DFIG.
IEEE Access
Transformational techniques unifying synthesis of two-state DC-DC converters and analytical synth... more Transformational techniques unifying synthesis of two-state DC-DC converters and analytical synthesis techniques allowing generation of all possible converters meeting a certain criteria already exist. The analysis of a family of converters derived from a single converter cell has also been unified. Current waveforms generated by the family of converters were shown to be related. However, a concept or basic building blocks that facilitate unified synthesis, analysis, prediction of current waveforms and assignment of switch states over a very wide range of DC-DC converters is still lacking. This study will propose three 3-terminal basic building blocks and one 3-terminal filter block. It will be shown that between them, they are sufficient for realizing all non-isolated DC-DC converters excluding those with coupled inductors. The various DC-DC converters fall into those realized through cascade, stacked, stacked plus cascade, interleaved/paralleled or differential connection of the basic building blocks. A systematic approach for evaluating input-output current gains will be presented. Moreover, a basic building block will be shown to have fixed switching states for proper operation. This gives rise to the generation of a unique set of current waveforms at the three terminals irrespective of where a basic building block is embedded. It has been shown that the effort and time needed to design DC-DC converters can be reduced as switching device stresses can be estimated without the need for tedious first principle derivations. INDEX TERMS Basic building blocks, converter cells, current waveforms, non-isolated DC-DC converters, steady-state gains, unified analysis of DC-DC converters, unified synthesis of DC-DC converters.
IEEE Transactions on Industry Applications
IET Electric Power Applications