ABSTRACT:
In this paper, a high-frequency ac-link photovoltaic
(PV) inverter is proposed. The proposed inverter overcomes most of the problems
associated with currently available PV inverters. In this inverter, a
single-stage power-conversion unit fulfills all the system requirements, i.e.,
inverting dc voltage to proper ac, stepping up or down the input voltage,
maximum power point tracking, generating low-harmonic ac at the output, and
input/output isolation. This inverter is, in fact, a partial resonant ac-link
converter in which the link is formed by a parallel inductor/capacitor (LC)
pair having alternating current and voltage. Among the significant merits of
the proposed inverter are the zero-voltage turn-on and soft turn-off of the
switches which result in negligible switching losses and minimum voltage stress
on the switches. Hence, the frequency of the link can be as high as permitted
by the switches and the processor. The high frequency of operation makes the
proposed inverter very compact. The other significant advantage of the proposed
inverter is that no bulky electrolytic capacitor exists at the link.
Electrolytic capacitors are cited as the most unreliable component in PV
inverters, and they are responsible for most of the inverters’ failures,
particularly at high temperature. Therefore, substituting dc electrolytic
capacitors with ac LC pairs will significantly increase the reliability
of PV inverters. A 30-kW prototype was fabricated and tested. The principle of
operation and detailed design procedure of the proposed inverter along with the
simulation and experimental results are included in this paper. To evaluate the
long-term performance of the proposed inverter, three of these inverters were
installed at three different commercial facilities in Texas, USA, to support
the PV systems. These inverters have been working for several months now.
KEYWORDS:
1.
Inverters
2.
Photovoltaic
(PV) systems
3.
Zero voltage
switching
SOFTWARE: MATLAB/SIMULINK
CIRCUIT DIAGRAM:
Fig.
1. Proposed PV inverter.
EXPECTED SIMULATION RESULTS:
Fig.
2. PV current and voltage at full power.
Fig.
3. AC-side current and voltage at full power.
Fig.
4. Link voltage at full power.
Fig.
5. Link current at full power.
Fig. 6. Link current and voltage at
full power, using 0.1-μF link capacitance.
Fig.
7. Link current and voltage at 15 kW.
Fig.
8. AC-side current and voltage when the irradiance drops from 850 to
650
w/m2.
Fig.
9. AC-side current and voltage when the temperature changes from
25 ◦C
to 50 ◦C.
Fig.
10. AC-side current and voltage when the AC-side voltage drops to 10%
of
its nominal value (at t = 0.016 s).
Fig.
11. PV current and voltage when the AC-side voltage drops to 10% of its
nominal
value (at t = 0.016 s).
CONCLUSION:
In
this paper, a reliable and compact PV inverter has been proposed. This inverter
is a partial resonant ac-link converter in which the link is formed by an LC
pair having alternating current and voltage. The proposed converter
guarantees the isolation of the input and output. However, if galvanic
isolation is required, the link inductance can be replaced by a singlephase high-frequency
transformer. The elimination of the dc link and low-frequency transformer makes
the proposed inverter more compact and reliable compared with other types of PV
inverters. In this paper, the principle of operation of the proposed converter
along with the detailed design procedure has been presented. The performance of
the proposed converter has been evaluated through both simulation and
experimental results.
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