IEEE Transactions on Industrial Electronics, 2016
This paper presents time-varying and constant
switching frequency based sliding mode control (SMC) methods for three-phase
transformerless dynamic voltage restorers (TDVRs) which employ half-bridge
voltage source inverter (VSI). An equation is derived for the time-varying
switching frequency. However, since the time-varying switching frequency is not
desired in practice, a smoothing operation is applied to the sliding surface
function within a narrow boundary layer with the aim of eliminating the
chattering effect and achieving a constant switching frequency operation. The
control signal obtained from the smoothing operation is compared with a
triangular carrier signal to produce the PWM signals. The feasibility of both
SMC methods has been validated by experimental results obtained from a TDVR
operating under highly distorted grid voltages and voltage sags. The results
obtained from both methods show excellent performance in terms of dynamic
response and low total harmonic distortion (THD) in the load voltage. However,
the constant switching frequency based SMC method not only offers a constant
switching frequency at all times and preserves the inherent advantages of the
SMC, but also leads to smaller THD in the load voltage than that of
time-varying switching frequency based SMC method.
KEYWORDS:
1.
Constant switching frequency
2.
Dynamic voltage restorer
3.
Sliding mode control
4.
Time-varying switching frequency.
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig.
1. Block diagram of three-phase TDVR with the proposed SMC methods. (a)
Time-varying switching frequency based SMC method, (b) Constant switching
frequency based SMC method.
EXPECTED SIMULATION RESULTS:
Fig.2.
Simulated responses of sk v , se k v , and Lk v obtained
by the constant switching frequency based SMC under three-phase-to-ground
fault. (a) sk v , (b) se k v , and (c)Lk v .
Fig. 3.
Simulated responses of vsk , se k v , and Lk v obtained by the
constant switching frequency based SMC under single-phase-to-ground fault. (a)sk v , (b) se k v , and (c)Lk v .
Fig.
4. Simulated responses of sk v , se k v , and Lk v obtained
by the SMC method presented in [15]. (a) sk v , (b) se k v , and
(c) Lk
Fig.
5. Simulated responses of sk v , se k v , and Lk v obtained
by the time-varying switching frequency based SMC. (a) sk v , (b) se
k v , and (c)Lk
v .
Fig.
6. Simulated responses of sk v , se k v , and Lk v obtained
by the constant switching frequency based SMC. (a) sk v , (b) se k v ,
and (c)Lk v .
CONCLUSION:
In
this study, time-varying and constant switching frequency based SMC methods are
presented for three-phase TDVR employing half-bridge VSI. An analytical
equation is derived to compute the time-varying switching frequency. Since, the
time-varying switching frequency is not desired in a real application, a
smoothing operation is applied to the sliding surface function within a narrow
boundary layer with the aim of eliminating the chattering effect and achieving
a constant switching frequency. The control signal obtained from the smoothing
operation is compared with a triangular carrier signal to produce the PWM
signals. It is observed that the smoothing operation results in a constant
switching frequency operation at all times. The feasibility of both SMC methods
has been validated by experimental results obtained from the TDVR operating
under highly distorted grid voltages and voltage sags. The results obtained
from both methods show excellent performance. However, the constant switching
frequency based SMC method not only offers a constant switching frequency at
all times and preserves the inherent advantages of the SMC, but also leads to
smaller THD in the load voltage than that of time-varying switching frequency
based SMC method.
REFERENCES:
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[3] Y.
W. Li, F. Blaabjerg, D. M. Vilathgamuwa, and P. C. Loh, ”Design and comparison
of high performance stationary-frame controllers for DVR implementation,” IEEE
Trans. Power Electron., vol. 22, no. 2, pp. 602-612, Mar. 2007.
[4] H.
Kim, and S. K. Sul, ”Compensation voltage control in dynamic voltage restorers
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