ABSTRACT:
In this paper, an improved dc-link voltage
regulation strategy is proposed for grid-connected converters applied in dc
microgrids. For the inner loop of the grid connected converter, a voltage
modulated direct power control is employed to obtain two second-order linear
time invariant systems, which guarantees that the closed-loop system is
globally exponentially stable. For the outer loop, a sliding mode control
strategy with a load current sensor is employed to maintain a constant dc-link
voltage even in the presence of constant power loads at the dc-side, which
adversely affect the system stability. Furthermore, an observer for the dc-link
current is designed to remove the dc current sensor at the same time improving
the reliability and decreasing the cost. From both simulation and experimental results
obtained from a 15-kVA prototype setup, the proposed method is demonstrated to
improve the transient performance of the system and has robustness properties to
handle parameter mismatches compared with the inputoutput linearization method.
KEYWORDS:
1.
Dc microgrid
2.
Direct power
control
3.
Grid connected
converter
4.
Observer
5.
Sliding mode
control
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig.
1. Block diagram of the proposed control method (SMC with observer) for a
rectifier system in the dc microgrid.
EXPECTED SIMULATION RESULTS:
Fig.
2. Simulation results when the dc load is changed from 460 W to 153 W. at 0.05
s and the reactive power is changed from 0 Var to 1 kVar at 0.75 s. (a) Real
power; (b) reactive power; (c) is;c line current; (d) dc-link voltage.
Fig.
3. Simulation results when the dc load is changed from 460 W to 153 W at 0.05 s
and vs;a has 10% sag. (a) Grid voltage; (b) is;c current; (c) dc-link voltage;
(b) real and reactive power.
Fig.
4. Simulation results when the dc load is changed from 460 W to 153 W at 0.05 s
and the THD of the grid voltage is 2.2%. (a) Grid voltage; (b) is;c current;
(c) dc-link voltage; (b) real and reactive power.
CONCLUSION:
A
three-phase PWM rectifier was controlled by the proposed control strategy,
which has a dc-link current observer based SMC in the outer loop and a voltage
modulated-DPC in the inner loop. The SMC was applied to generate the real power
reference in the inner loop in order to make sure the dc link voltage to be
within a certain level in the dc microgrids even there exist CPLs. Furthermore,
an observer for the dc link current was designed in order to remove the need
for a current sensor. Both simulation and experimental results show that the
proposed method effectively reduces the overshoot of the dc-link voltage and is
robust to parameter mismatch of the capacitance value in the dc-link.
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