25-10-2016, 12:03 PM
1461048051-ANovelSRFBasedCascadedMultilevelActiveFilterforPowerLineConditioners.pdf (Size: 294.4 KB / Downloads: 5)
Abstract— This paper presents a novel synchronous reference
frame (SRF) controlled five-level cascaded multilevel inverter
based shunt active filter for power line conditioners (PLCs) to
improve the power quality in the distribution system. The SRF
based compensation is developed by sensing load currents only,
which require for harmonics and reactive power compensation
due to non-linear loads. The attempt is to come up with a simple
control strategy. Incidentally it is different from conventional
methods and provides superior performance. The cascaded
multilevel voltage source inverter switching signals are generated
from proposed triangular-periodical current controller; that
gives better dynamic performance under transient and steady
state conditions. The proportional integral (PI) controller is used
to maintain the capacitance voltage of the cascaded inverter
almost constant. The extensive simulation results demonstrate
that the cascaded multilevel inverter based active power filter
using the synchronous reference frame controller effetely
compensates the current harmonics and reactive volt amperes
under both steady state and transient conditions
INTRODUCTION
Nonlinear loads such as diode/thyristor rectifiers, switched
mode power supply (SMPS), welding equipment,
incandescent lighting, and motor drives are degrading power
quality in transmission and distribution grid systems. These
non-linear loads result in harmonic or distortion current and
create reactive power problems [1]. These harmonics induce
malfunctions in sensitive equipment, overvoltage by
resonance, increased heating in the conductors and harmonic
voltage drop across the network impedance that affects power
factor [2]. Traditionally passive filters have been used to
compensate harmonics and reactive power; but passive filters
are large in size; aging and tuning problems exist and can
resonate with the supply impedance. Recently active power
line conditioners (APLC) or active power filters (APF) are
designed for compensating the current-harmonics and reactive
power simultaneously [3].
The controller is the most significant part of the APF topology
and extensive research is being conducted to improve its
control strategy. In 1979, FBD (Fryze-Buchholz-Dpenbrock)
method is used in time domain and real time for compensating
current harmonics [4]. In 1984, H.Akagi [5] introduced instantaneous active and reactive power theory method that is
quite efficient for balanced three-phase loads, being later
worked by Watanabe and Aredes [6] for three-phase four
wires power systems, zero-sequence currents was later
proposed by F.Z.Peng [7]. In 1995, Bhattacharya proposed the
calculation of the d-q components of the instantaneous threephase
currents and this method creates a synchronous
reference frame concept [8]. The SRF method is consists of a
phase locked loop (PLL) circuit and abc-dqo transformation; it
is a simple algorithm and good dynamic responses. The SRF
is ability to compensate harmonics and reactive-power
component from the distortion load currents [9-11].
This paper present a novel synchronous reference frame
controller based cascaded shunt active power filter for the
harmonics and reactive power mitigation of the non-linear
loads. The cascaded H-bridge active filter has been applied for
power quality applications due to increase the number of
voltage levels, low switching losses and higher order of
harmonic elimination. The cascade M-level inverter consists
of (M-1)/2 H-bridges and each bridge has its own separate dc
source [1-2] [11]. The cascaded voltage source inverter
switching signals are generated using proposed triangularperiodical
current controller; it provides better dynamic
performance under both transient and steady state conditions.
The compensation process is based sensing load currents only,
which require current harmonics and reactive power
elimination due to the loads. The PI-controller is used to
maintain the capacitance voltage of the cascaded inverter
constant. The shunt APLC system is validated through
extensive simulation and investigated under steady state and
transient with different non-linear loads.
II. DESIGN OF SHUNT APLC SYSTEM
Cascaded active filter for power line conditioning system is
connected in the distribution network at the PCC through filter
inductances and operates in a closed loop. Three phase active
power filter comprises of 24-power transistors with
freewheeling diodes; each phase consists of two-H-bridges in
cascaded connection and every H-bridge having a dc capacitor.
The shunt APLC system contains a cascaded multilevel
inverter,
CONCLUSIONS
This paper indicates the suitability of cascade multilevel
inverter based active filter for power line conditioning of
distribution networks. The cascaded inverter provides lower
cost, higher performance and higher efficiency than the
traditional PWM-inverter for power line conditioning
applications. The cascaded inverter switching signals are
derived from the proposed triangular-periodical current
modulator that provides good dynamic performance under
both transient and steady state operating conditions. SRF is
employed to extract the fundamental component from the nonlinear
load currents. This controller is developed by sensing
load currents only. This approach is fairly simple to
implement and is different from conventional methods. The
PI-controller maintains the capacitance voltage of the
cascaded inverter nearly constant. The extensive simulation
results demonstrate the performance of the APF under
different non-linear load conditions.