ABSTRACT
This
paper presents variable and fixed switching frequency based hysteresis current
control (HCC) methods for single-phase grid-connected voltage source inverters
(VSI) with LCL filter. The main feature of the proposed HCC methods is that the
reference inverter current is generated through a proportional-resonant (PR)
controller for achieving zero steady-state error in the grid current. The
consequence of using PR controller is eliminating the need for using derivative
operations in generating the reference inverter current. Furthermore, active
damping method is employed to damp the LCL resonance. An equation is derived
for variable switching frequency. Fixed switching frequency operation is
achieved by modulating the hysteresis band. The performance of both HCC methods
has been validated by simulation and experimentally. It is reported that the
proposed HCC methods not only preserve the inherent features of the
conventional HCC methods, but also damp the LCL resonance using an active
damping method and guarantee zero steady-state error in the grid current.
KEYWORDS:
1.
Fixed
switching frequency
2.
Grid-connected
inverter
3.
Hysteresis
current control
4.
Variable
switching frequency.
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig. 1. Single-phase grid-connected
VSI with the proposed HCC methods. (a) Variable switching frequency based HCC,
(b) Fixed switching frequency based HCC.
EXPECTED SIMULATION RESULTS:
Fig. 2. Simulation and experimental
results of , , , and obtained by: (a) the variable switching frequency based
HCC, (b) the fixed switching frequency based HCC. 1 i * ,1damp i2 i2 *2 i i
Fig. 3. Simulation and experimental
results of , , and obtained by: (a) the variable switching frequency based HCC,
(b) the fixed switching frequency based HCC. 2 ig vsw f
CONCLUSION
In this study,
variable and fixed switching frequency based HCC methods are presented for
single-phase grid-connected VSI with LCL filter. Unlike the conventional HCC
methods, the proposed HCC methods employ the reference inverter current
generated with the PR current controller by processing the grid current error.
The use of PR controller ensures zero steady-state error in the grid current
independently from the hysteresis bandwidth. In addition, the need for using
derivative operations in generating the reference inverter current is
eliminated by using PR controller. Also, active damping method is employed to
damp the LCL resonance. A formula is derived for the variable switching
frequency. The fixed switching frequency operation is achieved by modulating
the hysteresis band obtained from the derived variable switching frequency
equation. The performances of both HCC methods are validated by experimental
investigation. These results show excellent performance in terms of dynamic
response, robustness, zero steady-state error, and low THD in the grid current.
Hence, the proposed HCC methods not only preserve the inherent features of the
HCC methods, but also damp the LCL resonance using an active damping method and
guarantee zero steady-state error in the grid current.
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