ABSTRACT:
Sliding mode control (SMC) is recognized as robust controller
with a high stability in a wide range of operating conditions, although it
suffers from chattering problem. In addition, it cannot be directly applied to
multi switches power converters. In this paper, a high performance and fixed
switching frequency sliding mode controller is proposed for a single-phase
unipolar inverter. The chattering problem of SMC is eliminated by smoothing the
control law in a narrow boundary layer, and a pulse width modulator produces
the fixed frequency switching law for the inverter. The smoothing procedure is based
on limitation of pulse width modulator. Although the smoothed control law
limits the performance of SMC, regulation and dynamic response of the inverter
output voltage are in an acceptable superior range. The performance of the
proposed controller is verified by both simulation and experiments on a
prototype 6-kVA inverter. The experimental results show that the total harmonic
distortion of the output voltage is less than 1.1% and 1.7% at maximum linear
and nonlinear load, respectively. Furthermore, the output dynamic performance
of the inverter strictly conforms the standard IEC62040-3. Moreover, the measured
efficiency of the inverter in the worst condition is better than 95.5%.
KEYWORDS:
1.
Pulse width
modulator
2.
Sliding mode control
3.
Unipolar
single phase inverter
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig.
1. Proposed controller for single-phase inverters with a resonator in voltage
loop.
EXPECTED SIMULATION RESULTS:
Fig.
2. Simulation result. a) Output voltage and current at 6-kW linear load. b) Output
voltage and current at 6-kVA nonlinear load with CF = 2.75
and PF = +0.7.
Fig.
3. Simulation result: transient response of the output voltage for linear
step
load from zero to 100%
.
Fig.
4. Simulation result: transient response of the output voltage for linear
step
load from 100% to zero.
Fig.
5. Experimental result: efficiency of inverter versus output power.
CONCLUSION:
In this paper, a fixed frequency SMC was presented
for a single-phase inverter. The performance of the proposed controller has
been demonstrated by a 6-kVA prototype. Experimental results show that the
inverter is categorized in class1 of the IEC64020-3 standard for output dynamic
performance. The inverter efficiency was measured up to 95.5% in the worst
case.
Since the direct SMC cannot be applied to four
switches unipolar inverter and it also suffers from the chattering problem, a
PWM is employed to generate a fixed frequency switching law. The PWM modulates
the smoothed discontinuous control law which is produced by SMC. To smooth the
control law, the limitation of the PWM was considered.
The simulation and experimental results show that
the load regulation is about 1% at the steady state as well. But, to obtain better
regulation, a resonance compensator was added in the voltage loop. With this
compensator, the load regulation was measured which has been below 0.2%.
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[2]
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[3]
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[4]
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