Abstract
Single-phase and three-phase AC-AC converters are employed in variable speed drive, induction heating systems, and grid voltage compensation. They are direct frequency and voltage controllers having no intermediate power conversion stage. The frequency controllers govern the output frequency (low or high) in discrete steps as per the requirements. The voltage controllers only regulate the RMS value of the output voltage. The output voltage regulation is achieved on the basis of the various voltage control techniques such as phase-angle, on-off cycle, and pulse-width modulation (PWM) control. The power quality of the output voltage is directly linked with its control techniques. Voltage controllers implemented with a simple control technique have large harmonics in their output voltage. Different control techniques have various harmonics profiles in the spectrum of the output voltage. Traditionally, the evaluation of power quality concerns is based on the simulation platform. The validity of the simulated values depends on the selection of the period of a waveform. Any deficiency in the selection of the period leads to incorrect results. A mathematical analytical approach can tackle this issue. This becomes important to analytically analyze the harmonious contents generated by various switching control algorithms for the output voltage so that these results can be successfully used for power quality analysis and filtering of harmonics components through various harmonics suppression techniques. Therefore, this research is focused on the analytical computation of the harmonics coefficients in the output voltage realized through the various voltage and frequency control techniques. The mathematically computed results are validated with the simulation and experimental results.
Highlights
The application of pulse selective approach (PSA) to compute the harmonic contents of non-sinusoidal current and voltage waveforms of AC-AC voltage controllers is presented in the coming sections
The power quality of the output voltage can be explored by computing the harmonics analytically through a pulse selective approach
The on-off cycle control is another voltage control technique used to govern the load voltage’s RMS value. This control scheme is employed at a low switching frequency that results in the generation of low-frequency harmonics
Summary
Power quality is one of the major concerns in today’s modern power system. In traditional generation and distribution systems, the issue of low power quality is meaningless as the connected load is linear such as incandescent lamps and heating load. That includes the use of auto-transformers, transformer tap-changing mechanisms, and variable resistance. These power control mechanisms are inefficient and are replaced with switching converters nowadays. The power electronic converters are plying a vital role in the development of modern-day life by converting one form of electric power into another form. The converted output in the power conversion process is not always in the pure form and includes unwanted components called harmonics. The nature of unwanted harmonics deteriorating the power quality should be known before employing different harmonics mitigation and compensation methods. This research focuses on the mathematical computation of the harmonic components analytically and the validation of mathematically computed results through simulation and experimental results
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