Implementação de modulador para aumento de banda passante de um sistema de condicionamento de energia baseado em um conversor multinível

Abstract

Power quality issues, while critical to the network and/or loads being powered, are not new. Voltage sags and swells, voltage and current unbalances, reactive current circulation and current and voltage distortions are phenomena that impact not only the efficiency of the electrical grid, but also the continuity and compliance of power supply to loads that will suffer from them more or less severely depending on their sensitivity. Such adversities have been widely investigated in the past and their studies remain pertinent in the present. In fact, power quality issues are even more relevant these days due to the installation of inverter-based renewable energy power plants such as large-scale wind and photovoltaics, the popularization of electric vehicles and the vehicle-to-grid (V2G) concept, and the growth of distributed generation, among others. The Unified Power Quality Conditioner (UPQC), although relatively complex, is considered one of the power conditioning devices with both the greatest potential and versatility to overcome these power quality problems. This is because it can mitigate almost all voltage and current related power quality issues when properly designed and operated. In this sense, having as its object of study a UPQC, this work addresses topics such as the design of the LCL filter connecting the system to the grid/load, the control strategies of the electrical variables of interest, and the PWM modulator used when multilevel converter topologies are considered for use in such a power conditioner. In view of this, in particular, a multirate modulation strategy compatible with series and/or parallel multicell converters with interleaved carriers and any number of cells is proposed. Such a modulator takes advantage of the possibility of updating the switch commands in each subcycle of the switching period defined by the interleaving of the carriers instead of doing it only once or twice per cycle as is typical in classical symmetrically sampled modulations (only at the carrier's peak or at its valley) and asymmetrically sampled (at both the carrier's peak and valley), respectively. In addition, it is fully implemented at a software (code) level and has as an important feature the ability to naturally avoid overswitching, i.e., several extra switching pulses per carrier cycle of the semiconductor devices. Thus, experimental results of a UPQC based on two-level three-phase inverters are presented and discussed. Furthermore, proposals for improving the performance of this system regarding its dynamic response and steady state error are analyzed at the theoretical and simulation level for two-level and multilevel three-phase converters. In fact, these solutions include the use of the proposed multirate modulator to allow increasing the power conditioner’s bandwidth, which is possible due to the frequency response characteristics and working principle of the modulator.