Research Paper
Volume : 5 | Issue : 8 | Special Issue August-2016 • ISSN No 2277 - 8179
Engineering
KEYWORDS: Active filter; feed forward control;
Active Power Filter On Feed-Forward Control
analogue device; voltage control; electric current
control.
Jisha R C
PG Student, Electrical and electronics Department,Calicut University
Mr.Prajith J M
Assistant Professor, Electrical and electronics Department,Calicut University
ABSTRACT
is paper proposed a feed forward control strategy for a active power filter. e feed forward controller and the
current controller are designrd based on the state space averaging model and the voltage controller is designed based on the power
model.Since the grid voltage may generatebig impulsive impulsive current during system start up the feed forward controller effectievely
reduces the effect of perturbing grid voltage and DC voltage on controlled current to improve the dynamic performance of system.e
reference current for grid current control is direct obtained from the DCvoltage control loop ,which simplifies the control algorithms.e
detectionof load current and inverter output current are cancelled. e control circuit is realized with analogue device and the experimental
results demonstrate the validity of the proposed control strategy.
I. INTRODUCTION
With the development of power electronic technology and its wide
application in industry,the pollution of power grid becomes more
and more serious.Because the traditional passive filter has following
shortcomings,such as unideal filtering effect,emerging syntony with
power grid easily,it is gradually replaced by active power filter.
e fundamental principle of active power filter is to produce
harmonic currents or voltages which is in the opposite direction of
load harmonic current or voltages but equalto its amplitude in order
to eliminate harmful harmonics in power grid.It requires that the
control of active power filter has better traceability and property for
real time. Detection algorithm which bases on instantaneous
reactive power but the algorithm is relatively complex although the
experience mode decomposition method reduces the complexity of
detection algorithm in a certain extend the calculation is still
relatievely large.On the search method of current tracking
control,although adopting hysteresis loop control can obtain good
dynamic tracking function.,there are shortcomings of low control
precision and switching frequency variations.e dead beat control
quickly predict the change trend of harmonic current and it is easy to
implemented by computer, it has much dependence on the
prediction model. Because of the complex algorithm ,the prediction
period will be increased, and it causes larger prediction error,
ultimately affecting the compensation effect .
Figure. 1 Schematic diagram of single-phrase active power
filter
LiF(t) = 2[d(t)-1]uc(t) + uS(t)
Cůc(t)=[1-2d(t)]iF(t)
Where d(t) is duty cycle.
III. CONTROL STRATEGIES
A.CURRENT LOOP CONTROL
Equation 1 shows the relation of DC voltage uC(t) controlled as Uc, the
filter current can be written as
LïF(t)=2UCd(t)-uc(t)+US(t)
In order to decrease impact current generated in grid voltage system
start-up,this document proposes a feed forward control strategy of
active power filter. is strategy is based on the method of current
loop as the inner loop and voltage loop as the outer loop, and
measuring current between grid current and inverters DC side
voltages. is strategy introduces the voltage feed forward
compensation to eliminate the effect on grid voltage and DC voltage
to output current.
(1)
(2)
Fig (2) shows the current control block diagram.In the figure is*(t) is
the grid control reference signal and Gcc(s) is the current controller.
Here feed forward controller is introduced to eliminate the effect of
grid voltage and DC voltage. Transfer function can be written as,
GF(s)=
(3)
is controller using the traditional PI algorithm:
II. MATHEMATICAL MODELLING OF SYSTEM
Fig 1 is a circuit diagram of single phase active power filter
.iL(t),iS(t),IF(t) are load current, grid current and filter current
respectievely. US(t) and UC(t) are grid voltage and DC voltage
respectievely.L represents filtering inductance. e dynamic
mathematical model of the system for:
GCC(s)=
(4)
Figure. 2 Current Control Loop
IJSR - INTERNATIONAL JOURNAL OF SCIENTIFIC RESEARCH
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Research Paper
Volume : 5 | Issue : 8 | Special Issue August-2016 • ISSN No 2277 - 8179
Design of current controller parameters:
Transfer function is written as
Go(s) =
(5)
Is*(t) is a periodic quantity
By equation 5 the characteristic equation of current loop is:
∆(s)=LS2+2UC(KPOs+KIO)
(6)
ω1 =m2Πfu =
m≥3
(7)
where,
KiO=
(8)
Fig(5)
2ξ1ω1=
(9)
Critical damping design of control loop when ξ=1, en
Kpo=
Fig(6) and (7) shows the dynamic response waveform of active power
filter without introducing feed forward control and with feed
forward control respectievely.
(10)
B. VOLTAGE LOOP CONTROL
is paper based on the energy balance theory, measures the inverter
DC voltage.e control is shown in figure(3). e working principle
of voltage loop is that the DC capacitor voltage Uc(t) is lower than
that of the set point Uc*(t),when active power filtering is started. is*(t)
is relatievely higher.
Fig(6)
Figure 3 DC voltage control loop of inverter
Gcu(s)=Kp1+
(11)
IV. Experimental Result
Figure (4) shows the waveformbefore connecting active power filter,
there we can see that grid current with serious distortion
Fig(7)
V CONCLUSIONS
is paper introduces a low cost a.ctive power filter and it uses
harmonic and reactive power compensation at the same time.e
introduction of active power filter with feed forward control reduce
grid voltage and DC voltage on the effect of controlled
current.Another advantages of this circuitis it is the circuit without
complex mathematical operation and it is using the simplified
control algorithms
Fig(4)
ACKNOWLEDGMENT
I would like to thank my project guide Mr. Prajith J M from
Electronics and Electrical Department and all the people who
provided me with the facilities being required and conductive
conditions for my PG project.
Figure(5) shows the waveform of grid current with active power filter
References
It shows that before filtering the total distortion rate of grid current
is 61.8%,and after connecting active power filter it is reduced to 2.7%
2
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Research Paper
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