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

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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.
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.
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
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.
 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,
 MPLAB – microcontroller programming.
 ORCAD – circuit layout.
 MATLAB/Simulink – Simulation
 AC drives applications
 Wind energy applications
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
[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