Analysis and Performance Improvement of Pole Phase Modulated Induction Motor Drives for Traction Applications

Reddy, B Prathap and K, Siva Kumar (2019) Analysis and Performance Improvement of Pole Phase Modulated Induction Motor Drives for Traction Applications. PhD thesis, Indian institute of technology Hyderabad.

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Abstract

In the present days, transportation is a key factor for country advancement. The rapid urbanization and increased population have led to a sudden rise in travel demand, which results in an increase of gasoline-powered vehicles. These vehicles are causing environmental pollution, global warming by emitting hazardous gases. Moreover, fast enervation, high price of the fossil fuels and necessity of the ecological systems augment the research towards the electric vehicles. In order to select a drive for electric traction applications the key constraints are, enriched torque-speed range with high efficiency, high power handling capability, the volume of the motor and high fault tolerant capability. In high power traction applications, the conventional 3-ϕ induction motors (IM) need to be oversized for meeting the required range of speed and torque, requires higher voltage ratings of power electronic devices for handling the high power and also the output power deteriorates drastically under fault conditions. Over these conventional solutions, the multiphase induction motors (MIM) are finding more and more attention progressively in the industry as well as academia, because of the improved efficiency with lower space harmonics, wider range of speed and torque, the ability to handle high power with reduced voltage ratings of power electronic devices, better torque/power distribution, high fault tolerant capability etc. In order to meet the high torque requirement of traction or propulsion applications, the pole phase modulated induction motor (PPMIM) drive has to operate in high pole and low phase mode. This reduction in number of phases will magnify the magnitude of space harmonics in the air gap. Moreover, the presence of higher time harmonics in the excitation voltage will also affect the harmonics in the air gap magneto-motive force (MMF) and torque ripple. This may create a huge noise and mechanical vibrations which will shorten the lifespan of MIM drive. On the other hand, in high phase and low pole mode of PPMIM drives, the maximum possible DLVU with multiphase space vector pulse width modulation (SVPWM) will come down due to the higher number of phases, which is eventually equal to sine PWM (SPWM). Therefore, there is a necessity to enhance the performance of PPMIM drives as follows, (i) Improved DLVU in low pole and high phase mode with, (ii) reduced torque ripple in high pole and low phase mode. To achieve these two objectives, this work investigates the multilevel inverter schemes with lesser number of active, passive devices with simple PWM control techniques as compared to the conventional multilevel inverter (MLI) configurations. Multi-level inverter (MLI) configurations are proposed for improving the performance of 9-ϕ PPMIM drives by using four DC sources with a ratio of 1:1 and 2:1 in Chapter-2. The proposed MLI configurations are realized by using three 3-ϕ two-level inverters and one 9-ϕ two-level inverter. The proposed 9-ϕ PPMIM drive is are able to operate at 3-phase 12-pole mode and 9-phase 4-pole modes by maintaining the constant slots/pole/phase ratio. This proposed MLI configuration is also able to operate as a 9-ϕ twolevel inverter under fault condition of source or inverter switch faults. Whereas in neutral point clamped (NPC) and flying capacitor (FC) configurations, the complete system has to be shut down during source fault condition. In 3-phase 12-pole mode, the carriers of available identical voltage profile coils (IVPC) are phase shifted by 600 for getting the multilevel voltage across the effective phase as well as for shifting the lower order harmonics to higher order frequencies, which results in better torque ripple profile. Moreover, in 9-phase 4-pole mode, the DC link voltage utilization (DLVU) of proposed MLI configuration is improved by 15.4% with carrier based 3-ϕ SVPWM as compared to conventional SPWM. By maintaining the V/f ratio constant, the proposed MLI fed PPMIM drive facilitates a wide range of torque variations with half of the rated speed in a fault condition. This advantage makes it suitable for traction and electric vehicle applications where reliability and wide range of torque-speed are a major concern. The chapter-3 investigates the alternative MLI configurations for PPMIM drives with reduced resource count with the help of IVPC’s per phase. To achieve this, a 3-level topology is proposed, where the two IVPC’s/phase are configured as two 9-phase star groups which are excited with 9-ϕ 2-level inverters separately with a common DC link. The DC link requirement of the 9-ϕ IM drive is reduced by 6 times as compared with the traditional 3-ϕ IM drive. Similar to Chapter-2, for achieving the better torque ripple profile with proposed topology, a phase shifted carrier SVPWM is used which produces the multilevel voltage across the effective phases. Further to reduce the number of active switches, a 3-switch inverter leg based multilevel inverter (MLI) configuration is proposed for 9-ϕ pole phase modulated induction motor (PPMIM) drives by using split winding concept and dual inverter concepts. The proposed MLI configuration requires only one DC source and 3 switches per phase, whereas the traditional MLI’s required a higher number of DC sources and 4 switches per phase. However, for achieving the 3-level voltage across the effective phase, each 3-switch inverter leg has to be modulated with two non-overlapping phase shifted references, which limits the modulation index (M.I). With this limit on the M.I, to achieve the rated load voltage requirement, a higher DC link voltage is required. So for enhancing the possible M.I of 3- switch inverter leg, in this chapter a phase grouping concept is proposed by using the available 18 IVPC’s of the 9-phase 4-pole IM. In both pole phase combinations of 9-ϕ PPMIM drive, the proposed MLI configuration will generate a 3-level voltage across the effective phase with better harmonic profile, that helps in a reduction of torque ripple. However, with these double-layer integral slot 9-ϕ PPMIM drives two pole phase combinations are possible. As a result, the available variations in speed and torque are limited, whereas the traction application requires wider speed torque variations. The above issue of PPMIM drives can be addressed with the higher number of phases as well higher number of stator slots. Practically, stator core frames with high number of slots (e.g. 90, 120 slots) are used for high power applications (in few hundreds of kW) like drives for high power traction, propulsion and airborne applications. However, the size and weight constraints restrict these MIM drives in the medium and low power applications like Electric vehicles, locomotives etc. Therefore, to achieve the higher number of pole phase combinations with the conventional IM having 36 or 48 slot stator frames, a fractional-slot multilayer winding (FSMLW) is proposed in Chapter 4. This proposed FSMLW will helps in for minimizing the slot dependency on the number of pole-phase combinations in PPM. The generalization of PPM is revised as the number of layers per slot is plays a key role in designing these FSMLW. For validating the proposed FSMLW concept, a 15-ϕ winding is designed with 36 slots, which is capable to run at three different pole-phase combinations, i.e.1: 3: 5 speed ratios which makes it suitable for Electric Vehicles and locomotive applications. These wide variations in speed torque of the proposed 15-ϕ PPMIM drive with FSMLW will give the similar characteristics of the typical 3-gear IC engine. To enhance the performance of this FSW PPMIM drives, a carrier phase shifted sinusoidal pulse width modulation (CPS-SPWM) is used along with phase grouping concept, which is described in Chapter 2 and 3. It is noticed that, the PWM techniques play vital role for enhancing the performance of PPMIM drives. Therefore, it is need to analyze various PWM techniques thoroughly for these applications. To analyze the performance of the FSW 15-ϕ PPMIM drive with different possible carrier phase shifted SVPWM’s (CPS-SVPWM) is discussed in Chapter 5. As discussed earlier in high pole mode, the carriers of the IVPC’s per phase are phase shifted by an appropriate angle to minimize the harmonics in the effective phase voltage, which results in better torque ripple profile. In addition, the detailed comparison of three possible different CPS-SVPWM’s are presented, with their pros and cons for selecting the proper carrier phase shift angle. The 9-phase IM and FSW 15-phase IM models are designed by using the Ansys RMxprt. These RMxprt models are converted to Maxwell FEM models and co-simulated with the proposed MLI’s along with the proposed CPS SVPWM schemes in Simplorer environment. The performance of these 9-phase and 15-phase PPMIM drives in terms of flux line distribution, magnetic flux density, torque-speed response, efficiency and torque ripple profile has been analyzed for 5 hp IM FEM Models by using Ansys Maxwell. The x effectiveness of the all proposed multilevel inverter configurations have been experimentally verified with a laboratory prototype on 5 hp 9-ϕ MIM and 5 hp FSW 15-ϕ MIM drives. The 3- phase inverter boards for PPMIM drives are developed in the laboratory by using IGBTs (G4BC20FD, G4BC20S) along with gate drivers (where PCB is designed in gEDA software). The required DC link voltages are realized by using the BR1010 rectifier circuits and electrolytic capacitors. The gate driver circuits are designed by using the DC voltage regulators (MC7815, MC7805, MC7905), Diode (IN4007), NOT Gates (SN74HC04), Buffer circuits, optocouplers (TLP350) and electrolytic capacitors etc. By using these inverter boards all the proposed MLI configurations and CPS PWM schemes are realized and that are experimentally verified on the 5 hp 9-phase and 15-phase PPMIM models by using the open loop V/f control. The switching frequency has been considered as 2 KHz for all pole-phase combinations. The gating pulses for controlling 15-phase inverter are generated with FPGA SPARTAN-6 (XC6SLX9) board, where the gate pulse logic is implemented with VHDL programming.

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IITH Creators:
IITH CreatorsORCiD
K, Siva KumarUNSPECIFIED
Item Type: Thesis (PhD)
Uncontrolled Keywords: DC link voltage utilization, Induction motor device, Multilevel inverters, FEM analysis, SVPWM, Pole phase-modulation, phase grouping, Carrier phase shifted PWM, Identical voltage profile coils TD1546
Subjects: Electrical Engineering
Divisions: Department of Electrical Engineering
Depositing User: Team Library
Date Deposited: 29 Jul 2019 10:21
Last Modified: 29 Jul 2019 10:21
URI: http://raiith.iith.ac.in/id/eprint/5830
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