ABSTRACT:
In this paper, a low-frequency square-wave inverter with
a series-connected pulse width modulation (PWM) inverter is investigated for
high-power applications. The series compensators produce only the desired
harmonic voltages to make the net output voltage sinusoidal with small PWM
switching harmonics only. An open-loop control strategy for the series
compensator is proposed in this paper. This strategy indirectly sets the
compensator dc bus voltage to the desired level. No external dc source or
active power at fundamental frequency is required to control this dc bus voltage.
Different variations of this basic strategy are presented in this paper for
medium voltage applications. Theoretical analysis of this strategy is presented
in this paper with simulation and experimental results.
KEYWORDS:
1.
AC motor
drives
2.
Power
conversion
3.
Power
conversion harmonics.
SOFTWARE: MATLAB/SIMULINK
CIRCUIT DIAGRAM:
CONCLUSION:
In
this paper, an open-loop natural control of voltage source inverter has been
proposed mainly for high-power applications. The main square-wave inverter is
built with high-voltage low switching- frequency semiconductor devices like
integrated gate commutated thyristors (IGCTs). The series compensators are IGBT-based
inverters and operate from relatively low dc bus voltages at high switching
frequencies. The series compensators produce only the desired harmonic voltages
to make the net output voltage sinusoidal. For medium-voltage application,
several compensating PWM inverters are connected in series. Each cell
compensates one particular harmonic only. As the order of harmonics increases,
the required dc bus voltage level drops. This enables to exploit higher
switching frequency for higher order harmonic cell. It has been established
both theoretically and experimentally that the dc bus of the compensators do
not require any external dc source or closed-loop controller for this proposed strategy.
The active power at harmonic frequencies keeps the compensator dc bus voltage
charged. For variable speed drives applications, the magnitude of the
fundamental output voltage should be controlled by regulating the dc bus
voltage of the square-wave inverter. For static synchronous compensator (STATCOM)
applications, the limited variation of this dc bus voltage may also be
required. This can be achieved by drawing small active power at fundamental
frequency from the grid.
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