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In this work, a multi-level 42-sided polygonal space vector structure (SVS) for suppression of lower order harmonics for Open-End Induction Motor(OEIM) drive applications is proposed. The proposed power circuit topology consists of two inverters feeding an OEIM from either side. The main inverter fed with a single DC link providing active power for motoring operation is switched at low switching frequency. The secondary inverter fed with a capacitive supply is switched at high frequency to suppress lower order harmonics upto 39th order, up to the base speed of operation allowing maximum utilization of the DC link. The advantages of lower order harmonic suppression in motor phase voltage, for polygonal space vector structures are combined with multi-level inverter topology. This offers various advantages like multilevel operation with low inverter switching for the main power delivery inverter and harmonic suppression throughout the modulation range. The low switching frequency primary inverter generates low order harmonics. The harmonics are suppressed by the capacitor fed secondary inverter which supplies only reactive power for suppression of lower order harmonics in motor phase voltage. Use of a single DC link facilitates four-quadrant operation of the inverter.

A voltage source inverter generating a polygonal voltage space vector structure (SVS) having 117- concentric 30-sided polygons of different radii are proposed. Modulation using a 30-sided SVS eliminates lower order harmonics till 25th order from motor phase voltage. The proposed scheme combines the advantages of a 30-sided SVS with that of a multilevel inverter. The topology consists of two cascaded five-level inverters feeding from either end of the open-end induction motor stator windings. One of the cascaded five-level inverter is connected to an active dc source and delivers the required active power for the scheme, while the other is capacitor fed and acts as a switched capacitive filter. In this article, nonaligned 30-sided polygons, i.e., regular 30-sided polygons that are not symmetric with respect to $\alpha$ and $\beta$ axis are also considered for inverter operation. The harmonic analysis of such nonaligned 30-sided polygons is investigated in this article. Nearest level switching is employed throughout the modulation range, enabling further reduction of switching loss in the system. Extensive hardware experimentations are carried out to validate the proposed scheme and the results are included in the article.

A 21-concentric 42-sided polygonal space vector structure (SVS) for suppression of lower order harmonics for Open-End Induction Motor drive applications is proposed in this work. The Open-End Induction Motor is fed with primary and secondary inverters from either side. The primary inverter providing active power for motor operation is fed with an active DC link. The primary inverter is switched at low switching frequency to minimize stress on high voltage switching devices. As a result, the primary inverter consists of lower order harmonics in the pole voltage. The secondary inverter is employed only to suppress the harmonics generated by primary inverter and does not contribute any active power for motoring operation. Hence, the secondary inverter can be fed with a capacitive supply balanced at a nominal voltage. The secondary inverter, operating at lower voltages is switched with high frequency to suppress the lower order harmonics upto 39th order in the motor phase voltage. The advantages of polygonal space vector structures are retained throughout the modulation index, by generating 21-concentric layers of 42-sided polygons. This results in lower switching losses in low frequency switching main inverter and low voltage secondary inverter. A single DC link is employed in the power circuit topology to facilitate four-quadrant operation of the inverter. The proposed scheme is tested in MATLAB simulations and laboratory prototype. The simulation and experimental results are presented.

The Induction Motor Drives based on polygonal voltage space vector structures proposed in literature make use of switched-capacitive filtering for the suppression of lower order harmonics in the motor phase voltage. The Open-End Induction Motor (OEIM) drive systems feed the Motor with a primary and secondary inverter from either end. The primary inverter is fed with an active DC link supply, that provides all the active power for motor operation. The harmonics in motor phase voltage generated by primary inverter, are suppressed by employing a secondary inverter fed with a capacitive supply. The superposition of primary and secondary vectors generate reference vectors, that lie on the tips of a regular polygon. This work explains explains the suppression of lower order harmonics by Polygonal Voltage Space Vector Structures, by proposing a method of visualizing the harmonics in the α − β plane. The cancellation of fifth and seventh order harmonics in the reference space vector for a 42- sided Voltage Space Vector Structure will be explained using the proposed method of visualizing the harmonics. The 5th and 7th order harmonics are canceled, as the reference vector spans a 60° duration. The suppression of said harmonics by secondary inverter, results in sixth harmonic reactive power in secondary inverter. A quantitative analysis is carried out for the design of capacitor feeding secondary inverter to maintain a small ripple in secondary inverter, while delivering sixth order power for suppression of harmonics.

The work proposes a new power circuit topology to generate a 42-sided polygonal space vector structure for filtering out the lower order harmonics up to 39th order from motor phase voltage through out the modulation range. In the proposed scheme, the open stator winding of the induction motor is fed with a primary inverter from one end and a secondary inverter from the other end. The primary inverter is fed with a single DC source for suppling the active power for the drive operation. The secondary inverter works as the switched capacitive filter to eliminate the lower order harmonics generated by the primary inverter. The machine phase voltage is devoid of all the lower order harmonics (5th, 7th,....39th) which results in smoother torque profile for motor operation. The proposed scheme also extends the linear modulation range till 99.82%. A unique pulse width modulation technique is used to reduce switching transitions in the primary inverter, causing lower switching losses in the proposed inverter scheme. Also, the proposed scheme is studied extinsively with MATLAB simulation and validated with hardware results.