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# Download WC Alexander, “Universal power converter,” US Patent

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ULTRASPARSE AC-LINK CONVERTERS ABSTRACT: Soft-switching ac-link universal power converters, also called partial resonant converters and ac-link buck–boost converters, have received noticeable attention during the last few years. In these converters, each of the inputs and outputs can be dc, single-phase ac, or multiphase ac; therefore, they can be used for dc–dc, dc–ac, ac–dc, or ac–ac power conversion systems. The soft-switching aclink universal power converters are compact, reliable, and expected to offer longer lifetime compared with the other types of converters. However, they require more switches, which make the control process more involved. The sparse ac-link buck– boost converters were proposed to partially solve this problem. The sparse configuration reduces the number of switches from 24 to 20 in a three-phase ac–ac configuration. This paper proposes a modified configuration, which further reduces the number of switches without changing the principles of operation. This converter, which is named ultra sparse ac-link buck–boost converter, reduces the number of switches from 24 to 16, in a three-phase ac-to-ac case, and from 20 to 10, in a dc-to-three phase- ac configuration. The proposed converter is applicable to systems with unidirectional flow of power, such as PV and wind power generation systems. INTRODUCTION: Soft-switching ac-link universal power converter, also called partial resonant aclink converter and ac-link buck–boost converter, was introduced. Different applications of this converter have been studied. This converter has several advantages over the other types of converters. Being universal, the input and output of this converter may be dc, ac, single-phase, or multiphase. This converter is an extension of the dc–dc buck–boost converter. Therefore, unlike matrix converters, it is capable of both stepping up and stepping down the voltage. It can also change the frequency over a wide range. By adding the complementary switches and by modifying the switching scheme, the link inductor, which is the main energy storage element in this converter, can have ac instead of the dc. This approach improves the performance of the converter and significantly increases the utilization of the link inductor. In this converter, the frequency of the link current and voltage is only limited by the characteristics of the switches and the sampling time of the microcontroller. Therefore, the frequency can be very high, which results in compact link and filter components. By placing a small capacitor in parallel with the link inductor, the converter benefits from soft switching. EXISTING SYSTEM: A schematic of the topology, in which the link is formed by a low reactive rating inductor capacitor pair. All power transfer goes through the link inductor in a completely indirect means. Each leg of the converter is made of 2 bidirectional switches, realized by anti-series IGBT/diodes. As shown in this figure, six bidirectional switches interface a link inductor to the output, while another 6 bidirectional switches interface the same link inductor to the input. The converter transfers power entirely through the link inductor. Charging and discharging take place alternately. The frequency of charge/discharge is called the link frequency and is typically much higher than the input/output line frequency. The resulting input and output current pulses have to be precisely modulated such that when filtered, they achieve unity power factor at the input while meeting the output references. Normally, the instantaneous values of the input current commands are in phase or are phase adjusted with respect to the input voltages so as to achieve unity power factor PROPOSED SYSTEM: Despite using unidirectional switches, the sparse ac-link buck–boost converter can support bidirectional power flow. However, there are several applications that do not require bidirectional flow of power. For these applications, the ultrasparse aclink buck–boost converter is proposed in this paper. This converter requires fewer switches than the sparse ac-link buck–boost converter. Therefore, it is more reliable, more compact, less expensive, and less complicated compared to the sparse and the conventional ac-link buck–boost converters. ADVANTAGES: Reduces conduction losses. Reduced number of switches. Zero-voltage turn on of the switches, soft turn off of the switches, alternating link current, short resonating modes, BLOCK DIAGRAM: INTERMEDIATE CROSS OVER SWITCHING CIRCUIT INPUT AC SUPPLY 12V DC BRIDGE RECTIFIER FULL BRIDGE INVERTER DRIVER CIRCUIT RESONANT CIRCUIT RECTIFIER OUTPUT SIDE BRIDGE CONVERTER FILTER 5V DC PIC CONTROLLER WITH BUFFER LOAD TOOLS AND SOFTWARE USED: MPLAB – microcontroller programming. ORCAD – circuit layout. MATLAB/Simulink – Simulation APPLICATIONS: AC drives applications Wind energy applications CONCLUSION: This paper has proposed a novel soft-switching ac-link universal power converter. The proposed converter, named ultrasparse ac-link buck–boost converter, is a modification of the ac-link buck–boost converter. In this converter, the number of switches is reduced from 24 in the original ac–ac configuration to 16. This converter may be used in applications with unidirectional flow of power, where the phase shift between the fundamental component of the unfiltered load current and the voltage is less than 30◦ (displacement power factor higher than 0.87). Despite reducing the number of switches, the proposed converter has all the advantages of the original converter, including zero-voltage turn on of the switches, soft turn off of the switches, alternating link current, short resonating modes, and the possibility of having galvanic isolation with the addition of a single-phase high-frequency transformer REFERENCES: [1] W. C. Alexander, “Universal power converter,” U.S. Patent 2008/ 001 335 1A1, Jan. 17, 2008. [2] M. Amirabadi, H. A. Toliyat, and W. C. Alexander, “Partial resonant AClink converter: A highly reliable variable frequency drive,” in Proc. IEEE IECON, 2012, pp. 1946–1951. [3] M. Amirabadi, A. Balakrishnan, H. A. Toliyat, and W. C. Alexander, “High frequencyAC-link PVinverter,” IEEE Trans. Ind. Electron., vol. 61, no. 1, pp. 281– 291, Jan. 2014. [4] M. Amirabadi, H. A. Toliyat, andW. C. Alexander, “A multi-port AC-link PV inverter with reduced size and weight for stand-alone application,” IEEE Trans. Ind. Appl., vol. 49, no. 5, pp. 2217–2228, Sep./Oct. 2013. [5] M. Amirabadi, “Soft-switching high-frequency ac-link universal power converters with galvanic isolation,” Ph.D. dissertation, Elect. Comput. Eng. Dept., Texas A&M Univ., College Station, TX, USA, 2013