ABSTRACT:
In a dc distribution system, where multiple power sources
supply a common bus, current sharing is an important issue. When renewable
energy resources are considered, such as photovoltaic (PV), dc/dc converters
are needed to decouple the source voltage, which can vary due to operating
conditions and maximum power point tracking (MPPT), from the dc bus voltage. Since
different sources may have different power delivery capacities that may vary with
time, coordination of the interface to the bus is of paramount importance to
ensure reliable system operation. Further, since these sources are most likely
distributed throughout\ the system, distributed controls are needed to ensure a
robust and fault tolerant control system. This paper presents a model
predictive control-based MPPT and model predictive control-based droop current
regulator to interface PV in smart dc distribution systems. Back-to-back dc/dc
converters control both the input current from the PV module and the droop
characteristic of the output current injected into the distribution bus. The
predictive controller speeds up both of the control loops, since it predicts
and corrects error before the switching signal is applied to the respective
converter.
KEYWORDS:
1.
DC microgrid
2.
Droop control
3.
Maximum power
point tracking (MPPT)
4.
Model
predictive control (MPC)
5.
Photovoltaic
(PV)
6.
Photovoltaic
systems
SOFTWARE: MATLAB/SIMULINK
CIRCUIT DIAGRAM:
Fig.
1. Multiple-sourced dc distribution system with central storage.
EXPECTED SIMULATION RESULTS:
Fig.
2. Ideal bus voltage and load power as system impedance increases and loads are
interrupted to prevent voltage collapse. (a) Bus voltage decreases in response
to increased system impedance at t1 to reach the operating
point on the new P–V curve at t2 . The new bus voltage
is below the UVP limit, so control action cause load to be shed, moving to a
new operating point on the same P–V curve at t3 with a
higher bus voltage. (b) Load power in the system changes as point-of-load
converters are turned OFF to reduce total system load when the bus voltage
drops below the UVP.
Fig.
3. Response of dc bus voltage to step changes in the power drained by
load.
Fig.
4. Response of dc bus voltage and output power to imbalanced input
PV
sources
. Fig.
5. Response validation of dc bus voltage to step changes in the power
drained
by load.
Fig.
6. Response validation of dc bus voltage and output power to imbalanced
input
PV sources.
Fig.
7. Response of dc bus voltage and output power to the input PV sources
of
Fig. 7.
CONCLUSION:
High
efficiency and easy interconnection of renewable energy sources increase
interests in dc distribution systems. This paper examined autonomous local
controllers in a single-bus dc microgrid system for MPP tracked PV sources. An
improved MPPT technique for dc distribution system is introduced by predicting
the error at next sampling time using MPC. The proposed predictive MPPT
technique is compared to commonly used P&O method to show the benefits and
improvements in the speed and efficiency of the MPPT. The results show that the
MPP is tracked much faster by using the MPC technique than P&O method.
In a smart dc distribution system for microgrid
community, parallel dc/dc converters are used to interconnect the sources, load,
and storage systems. Equal current sharing between the parallel dc/dc
converters and low voltage regulation is required. The proposed droop MPC can
achieve these two objectives. The proposed droop control improved the
efficiency of the dc distribution system because of the nature of MPC, which
predicts the error one step in horizon before applying the switching signal. The
effectiveness of the proposed MPPT-MPC and droop MPC is verified through
detailed simulation of case studies. Implementation of the MPPT-MPC and droop
MPC using dSPACE DS1103 validates the simulation results.
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