Generalized formulation of multilevel selective harmonic elimination PWM: Case I-Non-Equal DC Sources

The paper presents optimal solutions for eliminating harmonics from the output waveform of a multilevel staircase pulse-width modulation (PWM) method with non-equal dc sources. Therefore, the degrees of freedom for specifying the cost function increased without physical changes as compared to the conventional stepped waveform. The paper discusses an efficient hybrid real coded genetic algorithm (HRCGA) that reduces significantly the computational burden resulting in fast convergence. An objective function describing a measure of effectiveness of eliminating selected order of harmonics while controlling the fundamental for any number of levels and for any number of switching angels is derived. It is confirmed that multiple independent sets of solutions exist and the ones that offer better harmonic performance are identified. Different operating points including five- and seven-level inverters are investigated and simulated. Selected experimental results are reported to verify and validate the effectiveness of the proposed method

A Seven-level defined selective harmonic elimination PWM strategy

Selective harmonic elimination pulse-width modulation (SHE-PWM) techniques offer an optimized control approach for a given converter and are therefore suitable for the low switching frequency high-power applications. Optimization techniques can be successfully used to obtain the solutions of the equations defining the SHE-PWM waveform. In this paper, a seven-level multilevel strategy (MSHE-PWM) defined on the line-to-neutral basis and based on a ratio of a variable number of angles distributed over three levels to be able to calculate the transition points is reported. The technique provides eighteen switching transitions for every quarter period in the standard modulation index range. In the overmodulation region, this can be changed in order to increase the gain of the modulator which in turn results in a compromised bandwidth. The switching angles as a function of the modulation index are reported for the standard as well as the overmodulation range. Selected simulation results are presented to verify the effectiveness and feasibility of the proposed method

On abolishing symmetry requirements in the formulation of a five-level selective harmonic elimination pulse-width modulation technique

Selective harmonic elimination pulse width modulation (SHE-PWM) techniques offer a tight control of the harmonic spectrum of a given voltage waveform generated by a power electronic converter along with a low number of switching transitions. These optimal switching transitions can be calculated through Fourier theory, and for a number of years quarter-wave and half-wave symmetries have been assumed when formulating the problem. It was shown recently that symmetry requirements can be relaxed as a constraint. This changes the way the problem is formulated, and different solutions can be found without a compromise. This letter reports solutions to the switching transitions of a five-level SHE-PWM when both the quarter- and half-wave symmetry are abolished. Only the region of high-modulation indices is reported since the low-modulation indices region requires a unipolar waveform to be realized. Selected simulation and experimental results are reported to show the effectiveness of the proposed method

Five-level selective harmonic elimination PWM strategies and multicarrier phase-shifted sinusoidal PWM: A comparison

The multicarrier phase-shifted sinusoidal pulse-width modulation (MPS-SPWM) technique is well-known for its important advantage of offering an increased overall bandwidth as the number of carriers multiplied with their equal frequency directly controls the location of the dominant harmonics. In this paper, a five-level (line-to-neutral) multilevel selective harmonic elimination PWM (MSHE-PWM) strategy based on an equal number of switching transitions when compared against the previously mentioned technique is proposed. It is assumed that the four triangular carriers of the MPS-SPWM method have nine per unit frequency resulting in seventeen switching transitions for every quarter period. Requesting the same number of transitions from the MSHE-PWM allows the control of sixteen non-triplen harmonics. It is confirmed that the proposed MSHE-PWM offers significantly higher converter bandwidth along with higher modulation operating range. Selected results are presented to confirm the effectiveness of the proposed technique

Modified phase-shifted PWM control for flying capacitor multilevel converters

The issue of voltage imbalance remains a challenge for the flying capacitor multilevel converter. The phase-shifted pulsewidth modulation (PS-PWM) method has a certain degree of self-balancing properties. However, the method alone is not sufficient to maintain balanced capacitor voltages in practical applications. The paper proposes a closed-loop modified PS-PWM control method by incorporating a novel balancing algorithm. The algorithm takes advantage of switching redundancies to adjust the switching times of selected switching states and thus maintaining the capacitor voltages balanced without adversely affecting the system's performance. Key techniques of the proposed control method, including selection of switching states, calculation of adjusting times for the selected states, and determination of new switching instants of the modified PS-PWM are described and analyzed. Simulation and experimental results are presented to confirm the feasibility of the proposed method

The future of power electronics/power engineering education: challenges and opportunities

This paper discusses some factors affecting the education sector in the power electronics/power engineering area along with the renewed challenges and opportunities in the light of so many recent R&D developments at system level. It provides an overview of university-based curriculum initiatives and modern methods of instruction encouraging life long learning culture based on problem and project-based learning. The design studio approach currently used at Murdoch University, Perth, Western Australia is outlined. This approach is mapped to the modern attributes of engineering graduates along with Bloom's taxonomic levels of the cognitive domain. It is recognized that the aim should be to achieve learning in the highest possible level of the cognitive domain and the project-based approach is identified as the way forward. Finally, the assessment of students by an industrial panel is also presented as a complementary way to interact with the industry and involve their feedback directly with the educational process

A laboratory-supported power electronics and related technologies undergraduate curriculum for aerospace engineering

Power electronics technologies will play a vital role in the aerospace industry in the years to come and all emerging technologies are already an important part of the industry either at R&D or in many cases production level. It is recognised that aerospace engineering and avionics students need to be aware of these technologies and in a position to work as a team member with development of power electronics technologies addressing specific needs. The paper discusses pioneering initiatives undertaken and the newly introduced course of power electronics and related technologies into the undergraduate aerospace engineering curriculum at the University of Glasgow, UK. The various components of the course are described in detail, along with the laboratory programme, which is based on a ``closed-loop' ' approach for the understanding of the various concepts. The prelaboratory/post-laboratory questions and the course assessment are given. A sample final exam question is also provided to introduce the industry relevance requirement component of the course. The views of the students regarding their experiences, especially in the laboratory environment, are critically discussed

On considering magnetic saturation with maximum torque to current control in interior permanent magnet synchronous motor drives

The influence of magnetic saturation on maximum torque to current controlled interior permanent magnet synchronous motor drives is discussed in this paper. A maximum torque to current condition that takes into account magnetic saturation and determines the optimal d-axis current is derived. For the implementation of the proposed controller, an experimental procedure is used to adjust its parameters, therefore, the knowledge of the exact model is not required. Selected experimental results are presented to verify the theoretical considerations and to confirm the high performance of the suggested controller