In SiC inverter-fed motor drives, fast-switched power devices escalate the reflected wave phenomenon, causing overvoltage oscillations at the motor terminals with shorter cable lengths between the inverter and motor. Likewise, overvoltage oscillations manifest at motor neutral point due to the reflection of inverter common-mode voltage through the machine windings. Despite extensive research on motor terminal overvoltage mitigation, the motor neutral point overvoltage remains insufficiently addressed in the literature, although it can have a more detrimental impact on the machine winding insulation especially if the high switching frequency of SiC inverters aligns with the machine antiresonance frequency. This paper evaluates the effectiveness of three passive filter designs (R, RC, and C filter) connected between the motor neutral point and grounded frame for neutral point overvoltage mitigation. The paper provides mathematical design guidelines for the parameter selection of the three filters while assesses their performance in mitigating the motor neutral point overvoltage. An experimental evaluation using a 2.2kW SiC-based motor drive setup is presented, demonstrating the effectiveness of the three filter designs to eliminate the motor neutral point overvoltage while highlighting the pros and cons of each filter design.

Commitment to decarbonization and pursuit of sustainable energy goals have accelerated the utilization of renewable energy resources where the electrical grid would have to transmit massive amounts of carbon-free power via the high-voltage network along transmission corridors operating at or nearing capacity. Constructing new transmission lines is significantly challenging due to regulatory restraints and public opposition. Alternatively, expansion of existing transmission corridors can be accomplished by converting the HVAC system into HVDC system. This paper employs a 9-pulse line-commutated converter (LCC) to transform the commonly adopted double circuit HVAC into a six-wire bipolar HVDC transmission system. Compared to equivalently rated 6- and 12-pulse LCCs, the 9-pulse LCC topology reduces the size of converter station by employing fewer thyristor valves. The principle of operation and mathematical analysis of the 9-pulse LCC are explained in this paper. The implementation of 6-wire HVDC transmission system using 9-pulse LCCs is presented and validated using MATLAB simulations for 100kV, 960MW system. A quantitative comparison between 9-pulse LCC-based HVDC system and 6- and 12-pulse counterparts is also provided to highlight the pros and cons of the suggested system.

Partial discharge (PD) is a prime cause of premature failure of inverter-fed motor winding insulation. With the emergence of fast-switching wide-bandgap silicon-carbide (SiC) power devices, random-wound motors are more vulnerable to highly repetitive PDs due to the high-frequency steep-fronted switching transitions that result in overvoltage oscillations at the motor terminals and non-uniform voltage distribution within the motor winding turns. This paper investigates the impact of the applied PWM voltage waveforms on the PD behavior in SiC-based inverter-fed motor drives, including two-level and three-level PWM waveforms. The electric field distribution inside insulation defects (air cavities) is analysed for the PWM voltage waveforms to theoretically predict the number and phase of probable PD events within the fundamental cycle. An experimental PD measurement setup is used to validate the theoretical analysis by applying the PWM voltage waveforms, that are generated by SiC-based power converters, on a typical turn-to-turn motor winding insulation system created by a twisted pair of enamelled magnet wire. Phase-resolved PD patterns are generated to assess the PD behavior against the PWM characteristics of each voltage waveform and the associated overvoltage pattern when power cables are used to emulate the voltage reflections in cable-fed motor drives.

The emergence of silicon carbide (SiC) power devices is considered an enabling technology toward more efficient and compact motor drives. This returns to the primary advantages of the SiC power devices, that result from their fast switching speed and elevated temperature capabilities. However, the high voltage slew rate (dv/dt) associated with the fast switching transitions has been a concern for SiC-based motor drives with interconnection power cables due to potential motor overvoltage that can degrade the winding insulation and cause premature failure. This paper proposes a quasi-three-level PWM scheme to combat the motor overvoltage oscillations in cable-fed drives with open-winding configurations. The proposed scheme reshapes the PWM voltage pulses at the inverter side to counterbalance the voltage reflections across the cable, resulting in alleviated motor overvoltage within tolerable insulation design level. The proposed scheme is conceptually illustrated in this paper and applied to dual three-phase SiC inverter for open-winding motor drives. The performance of the motor drive system under the proposed modulation scheme is verified through simulation and experimentation.

Machines with modular structure significantly simplify the manufacturing process, particularly the stator winding, and highly increase the slot fill factor. The non-overlapping concentrated winding, or single tooth winding, is the most compatible winding layout with segmented structure. This technology is well-established for permanent magnet family machines. However, their incompetence to produce a sinusoidal MMF distribution provides a key challenge to apply single tooth winding to induction machines. This paper introduces a new single tooth winding layout for a single-phase induction motor with segmented stator. The proposed winding layout is based on dual two-phase windings shifted in space by 450 electrical degrees to completely cancel out both the third and fifth order harmonics. The proposed winding entails 8 slots per pole pair. Although the number of active conductors in the proposed winding is higher than a conventional distributed winding layout to produce the same MMF magnitude, the significant reduction in the end turn copper and the increase in the slot fill factor compensate this copper volume increase while maintain approximately the same machine volume, which introduces it as a promising candidate in high frequency motor applications. A prototype machine is used for experimental verification.

The interest in multiphase drives has been steadily growing during the last decade due to the promising potentials offered by multiphase machines over conventional three-phase counterpart. In this context, six-phase induction machines are preferably used in many diversified high-power applications. Generally, thanks to its improved flux distribution, the asymmetrical six-phase winding topology fed from two three-phase voltage source inverters (VSIs) is commonly employed with isolated neutral points to prevent the flow of zero sequence currents and to limit the number of current controllers to four instead of five when neutral points are connected. In this paper, an innovative design of a six-phase dc-ac inverter is proposed for such type of six-phase ac machines based on the single-ended primary-inductance converter (SEPIC) topology. The proposed topology employs only four active-legs with eight switches with the same output voltage magnitudes as in conventional VSIs and without the mandatory dead-time between switches in the same-leg. Also, it naturally delivers a pure sinusoidal waveform at the output stage. The principle of operation of the proposed inverter topology is investigated in details and assessed through a detailed simulation study of an open-loop control system.

Transformer-less photovoltaic (PV) inverters are the major functional units of modern grid-connected PV energy production systems. In general, two power conversion stages are required when low-voltage unregulated photovoltaic (PV) output is conditioned to generate AC power. In this paper, the boost inverter topology that achieves both boosting and inversion functions in a single stage is used as a building block to develop a three phase grid connected PV system which offers high conversion efficiency, low-cost and compactness. The proposed system employs a modified modulation scheme for the three phase boost inverter to control both active and reactive power injected to the grid. This modified modulation scheme enhances the boosting capability of the boost inverter and improves the THD of the grid injected current. Moreover, it reduces the voltage stress on the capacitors and switching devices. Analysis and simulation results are presented to confirm the advantages and efficiency of the proposed modulation technique.