| 要約: | This thesis proposes a new simplified control strategy for the single phase shunt active
power filter (SAPF) system. The SAPF circuit injects a compensated current comprising
harmonics and reactive current components of load current but with opposite phase at the
point of common coupling (PCC) of the line so that the source current will be free from
harmonic distortion as well as in phase with the source voltage. By using a nonlinear load
equivalent resistance estimation control strategy, the source voltage should see a load as
a near pure resistor. The proposed control strategy features simple configuration and has
only two mathematical division operations. Therefore, the nonlinear load equivalent
resistance can be determined by dividing an average DC load voltage over an average DC
load current. Both quantities are obtained from filtered absolute values of source voltage
and load current respectively. A sinusoidal reference current is obtained by dividing the
source voltage over the calculated equivalent resistance. The feedforward load current
subtracted the sinusoidal reference current to yield a compensated reference current. Next,
the actual compensated current need to be feedback and subtracted by the reference
compensated current at set point to produce an error signal. In order to compensate the
error signal, a proportional (P) and proportional plus integral (PI) controllers are
employed to yield a control signal. Then, the control signal is compared with a 20 kHz
carrier signal to form pulse width modulation (PWM) gating signals that drive Insulated
Gate Bipolar Transistor (IGBT) switches of full bridge voltage source inverter (VSI)
based SAPF configuration. Computer simulation and experimental work were carried out
for verification purpose. As a result, the total harmonics distortion (THD) of source
current after compensation has been attenuated significantly below IEEE Std. 519 and IEC61000-3-2 standards respectively. Besides, the line’s power factor also remarkably
improved to near unity (0.999). Moreover, the SAPF demonstrated a good and fast
dynamic response capability under a sudden change in load and source as well as
instantaneous connection and disconnection with the line. Furthermore, the developed
analog controller circuit is inexpensive and offers easy implementation. On top of that,
the proposed Trapezoidal rule based low pass filter has better performance than
conventional Butterworth and first order RC low pass filters (LPF) in term of dynamic
response and output ripple content.
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