ABSTRACT:
Transformer-less photovoltaic (PV)
inverters are more widely adopted due to high efficiency, low cost and light weight,
etc. However, H5, HERIC, etc. transformer-less PV inverters do not have the bidirectional
capability for solar energy storage system in the future. With topology
derivation history reviewed from rectifier to inverter, the essence of bidirectional
rectifier/inverter is revealed to find a reverse power flow approach. Therefore,
this paper proposes an advanced bidirectional technique for a selected H6
inverter topology with only modulation strategy modified, while the others
remain the same. For the H6 circuitry in both rectifier and inverter modes,
excellent three level DM voltage feature is achieved, while leakage current issue
is eliminated at the same time with improved modulation method. Simulations and
experimental results verify the proposed single phase bidirectional H6
rectifier/inverter technique.
KEYWORDS:
1. H6 inverter
2. Rectifier
3. Improved modulation
4. Bidirectional power flow
5. Leakage
current
SOFTWARE: MATLAB/SIMULINK
CIRCUIT DIAGRAM:
Figure
1 Selected H6 inverter
(a)
Ac
grid voltage, ac current, DM voltage and CM voltage in rectifier mode
(b) Switching pulses S1&S4, S2&S3, S5, S6 in rectifier
mode
(c)
Expanded switching pulses S1&S4, S2&S3, S5, S6 in rectifier mode
(d) Ac grid voltage, ac current, DM voltage and CM voltage in
inverter mode
(e) Switching pulses S1&S4, S2&S3, S5, S6 in inverter mode
(f)
Expanded switching pulses S1&S4, S2&S3, S5, S6 in inverter mode
Figure
2 Bidirectional H6 rectifier/inverter modulation method simulation Results
(a) Current stress
(b) Voltage stress
Figure 3 H6 rectifier device stress
CONCLUSION:
Aiming solar
energy storage system, this paper improves a grid-tied single phase H6 PV
inverter from unidirectional power flow to bidirectional power flow. A unified
hybrid modulation method is proposed for both rectifier and inverter modes. The
main advantages of the proposed solution can be summarized as:
1) Compared with
the traditional hybrid modulation method for power rejection to grid only, a
simple modification in the switching patterns is just needed for solar energy
storage system with H6 type topology.
2) Battery
storage is adopted for emergency usage in small solar energy storage system.
Therefore, a slight cost of efficiency decreases in rectifier mode due to the
partly used body diodes is acceptable, and the excellent DM/CM voltage features
of the H6 circuitry in both rectifier and inverter modes are totally achieved.
3) The improved
hybrid modulation method would be easily modified and applied to other H6 and
similar topologies.
REFERENCES:
[1] R. Teodorescu, M. Liserre, and P.
Rodriguez, Grid converters for photovoltaic and wind power systems. Hoboken,
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[2] Rik W. De Doncker. Power Electronics
– key enabling technology for a CO2 neutral electrical energy supply.
Available: http://www.ifeec.tw/rik.html
[3] Generators connected to the
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anwendungsregel-2011-08.html.
[4] T. Kerekes, R. Teodorescu, P.
Rodriguez, G. Vazquez, and E. Aldabas, "A
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[5] R. Bojoi, L. R. Limongi, D. Roiu,
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