IEEE Transactions on Power Delivery, 2015
ABSTRACT:
This paper presents a new multilevel cascaded-type
dynamic voltage restorer (MCDVR) with fault current limiting function. This
topology can operate in two operational modes: 1) compensation mode for voltage
fluctuations and unbalances, and 2) short-circuit current limiting mode. The
current limiting function of the MCDVR is performed by activating anti-parallel
thyristors during the short-circuit fault, and deactivating them during normal
operation. The mathematical model of the MCDVR system is also established in
this paper. The control scheme design and optimal parameter selection are outlined
based on the detailed theoretical analysis of the converter. The transient
states of the MCDVR in both the compensation mode and current-limiting mode are
also analyzed. Simulation results based on the PSCAD/EMTDC software and
experimental results on a laboratory setup help to validate the proposed
topology and the theoretical analysis.
KEYWORDS:
1.
Dynamic
voltage restorer (DVR)
2.
Multilevel
inverters
3.
Fault current
limiter
4.
Voltage
restoration
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig.
1. Schematic diagram of the proposed MCDVR.
Fig.
2. Simulation results of the MCDVR system. Top to bottom: (a) the supply
voltage Us, (b) the load voltage UL, (c) the secondary voltage Udvr,
(d) the load current IL, and (e) the dc-link voltage.
Fig.
3. Forward switching simulations of the MCDVR system, top to bottom: (a) the
load current IL, (b) the current Iscr in the thyristor’s path,
(c) the output current Idvr of the VSI, (d) the dc-link voltage Udc,
and (e) the timing sequence
Fig.
4. Backward switching simulations of the MCDVR system, top to bottom: (a) the
load current IL, (b) the current Iscr in the thyristor’s path,
(c) the output current Idvr of the VSI, (d) the dc-link voltage Udc,
and (e) the timing sequence.
CONCLUSION:
Cascaded
multilevel inverters have been applied in the industry as a cost-effective
means of series sag compensation. However, a large current will be induced into
the VSI through a series transformer during faults, and this is harmful to the
VSI and the other equipment in the grid. In this paper, the MCDVR was proposed
to deal with voltage sags and short-circuit current faults. The MCDVR has not
only the advantages of the H-bridge cascade inverter, but also reduces the
secondary side current in the preliminary period of the fault. A mathematical
model of this system was also established in this paper. A careful analysis of
the transient state verified the feasibility of the proposed MCDVR. Based on
the theoretical analysis, PSCAD/EMTDC simulations and the experimental results,
we can conclude the following:
1) The H-bridge
cascade inverter can be adopted to reduce the series transformation ratio and
the secondary current during the preliminary period of the fault.
2) The transient
state of the MCDVR system was introduced in great detail.
3)
The proposed control method can limit fault current with two cycle. The
consistencies between the simulation results and experimental results help to
verify the proposed topology and theoretical analysis.
REFERENCES:
[1]
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[2]
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[3]
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