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

Lovemore Gunda, Nkosinathi Gule
2015 2015 IEEE International Conference on Industrial Technology (ICIT)  
A considerable amount of research has been done on the control of induction machines since the introduction of the power electronic inverter. The use of power electronic inverters has also opened the way for the design of multiphase induction machines. The current rating of the power electronic components used in multiphase inverters is lower than those used in three-phase inverters. On the machine side, the multiphase machines have higher power and torque density than their three-phase
more » ... arts. The control of these multiphase induction machines poses a challenge for the designer of the drive system. Scalar control, direct torque control and vector control methods work well in three-phase machines. However, the analysis of vector based techniques becomes complex as the number of phases increases and new methods are being proposed to reduce the complexity of implementing machine control. The Brush-DC Equivalent (BDCE) control method was proposed to simplify the design of controllers. This method does not include complex coordinate transformations like are used in vector-based techniques. The BDCE control method is derived from the control of separately excited brush-DC machines utilising compensating windings. The induction machine controlled using the BDCE method is designed such that the phases of the machine act alternately in rime as torqueproducing or field-producing phases. This is achieved by supplying the induction machine windings with specially designed trapezoidal stator current waveforms. The BDCE control method enables decoupled control of flux and torque without complex coordinate transformations. The method can be implemented for high phase-number multiphase induction machines without added complexity. In this thesis, the BDCE control method implementing a delta modulated current controller which generates pulse width modulated signals for the power electronic inverter is presented. The delta modulation technique is proposed because it gives good inverter performance characteristics and reduces torque and current ripples. It also reduces total current harmonic distortions through the use of a fixed switching frequency. The BDCE controlled drive is simulated using Matlab/Simulink. The simulation results suggest that delta modulation gives lower current and torque ripples with attenuated low order voltage harmonics. Practical evaluation of the drive is done using the delta modulated current controller to validate the simulation results. An alternative delta modulation scheme in which the reference current signal is integrated before being fed to the forward comparator is proposed, designed and tested. The alternative delta modulation scheme produces the required trapezoidal stator currents and allows decoupled control of the field and torque currents. The results of the practical evaluation compare Stellenbosch University ii well with the simulation results and show that a delta modulated current controller can be used in the drive. Better results are expected if stator voltages are fed back to the modulator to estimate the reference signal. Stellenbosch University Stellenbosch University iv verwag indien die stator spannings teruggevoer word na die modulator om 'n beter verwysings sein af te skat. Stellenbosch University v Acknowledgements The author is highly indebted to Dr N Gule, the project supervisor for his continuous support and guidance during the whole research period. He was a source of academic, moral and emotional support during the highly challenging research period. Many thanks also go to:  The Stellenbosch University Electrical and Electronic Engineering department for the departmental bursary that funded this research.  The Electrical machines laboratory team of technicians for setting up the work benches to enable the progress of practical tests.  Mr David Groenewald for his continued support in electronic equipment set up and the inverter board repairs.  God Jehovah Almighty for giving power to the author to progress with the research under His guidance and protection. Stellenbosch University vi "The absence of complex analytical formulas often makes easier the concentration for the physical understanding of problems, for more lively observation and better understanding of the substance, than when the electric phenomena are viewed through the clouds of mathematical symbols." Sir J.J.
doi:10.1109/icit.2015.7125171 dblp:conf/icit2/GundaG15 fatcat:m6wec7xfybbprp2qzt3kbcw67u