2015 IEEE European Modelling Symposium
A New Control Approach for Shunt Hybrid Active Power Filter to Compensate
Harmonics and Dynamic Reactive Power with Grid Interconnection
1
Tuçe Demirdelen, 2Mustafa nci, 3Mehmet Tümay
1,2,3
1
Çukurova University, Balcal,Adana, Turkey
tdemirdelen@cu.edu.tr, 2minci@cu.edu.tr, 3mtumay@cu.edu.tr
PCC[1]. The grid voltages and currents shape non sinusoidal
form that is called harmonic distortion due to these types of
loads. Harmonic distortions can not only increase power
losses, but also reduce the lifetime of equipments. In order to
reduce the current harmonic pollution, passive filter is one of
the traditional solution ineffectively. These filters may cause
unwanted resonance conditions. Their other limitation is
unable to adapt to the changing conditions in the network
and their size. With remarkable process in the speed and
capacity of semiconductor switching devices, active filters
have been studied and put into practical use, because they
have the ability to overcome the disadvantages inherent in
passive filters. These types of filters are more effective in
harmonic compensation and improve performance [2].
However, active power filters have high initial cost, running
cost and required comparatively high power converter
ratings. To overcome the aforementioned disadvantages,
passive and active filters can be combined into a single
device called hybrid active power filters (HAPF). HAPFs
effectively smooth the problems of the passive filter and an
active power filter solution; hence ensure cost effective
harmonic compensation. The passive filter in the system
performs basic filtering action at the dominant harmonic
frequencies, whereas the active filter part mitigates higher
harmonics with precise control methods. This will effectively
reduce the overall size and cost of active filtering. In
addition, no fundamental voltage is applied to the active part.
This results in a great reduction of the voltage rating of the
active power filter part.
Several hybrid APF (HAPF) topologies [2-11,15-17]
constitute active and passive parts in series and/or parallel
have been proposed for reactive power and harmonic current
filtering in [3-11]. The most common topologies are shunt
HAPF (SHAPF) [3-10] consisting of an APF and passive
filter connected in series with each other and series HAPF
[11] which is a combined system of shunt passive filter and
series APF. An extensive overview of the topological
structures is explained in [2].
The controller design is a significant and challenging task
due to its impact on the performance and stability of overall
system. For this reason, numerous control methods such as
pq theory [3-5], fast fourier transform [5], dq theory [6-7],
fuzzy controller [8-9], proportional resonant current
controller [10] are controller methods applied in literature.
Most studies about SHAPF in literature can not achieve
dynamic reactive power compensation [7-9]. Furthermore,
SHAPF can compensate the dynamic reactive power with
Abstract—The grid interconnection of renewable energy source
is a popular issue in the electric utilities. Different types of
converter topology in grid interconnection have been improved
by researchers to improve power quality and efficiency of the
electrical system. The main contribution of this paper is that
shunt hybrid active power filter (SHAPF) with a DC-DC
converter at dc link is to provide interconnection between
renewable source and grid with linear dynamic loads. The
other contribution of this paper is to present a novel control
strategy for reactive power compensation and harmonics
elimination in industrial networks using a hybrid active power
filter as a combination of a three phase, two level voltage
source converter connected in parallel with single tuned LC
passive filter. In proposed control method, reactive power
compensation is achieved successfully with perceptible amount.
Besides, the performance results of harmonic compensation
are satisfactory. Theoretical analyses and simulation results
are obtained from an actual industrial network model in
PSCAD. The simulation results are presented for proposed
system in order to demonstrate that the harmonic
compensation performance meets the IEEE-519 standard.
Keywords-Harmonics, grid interconnection, power quality,
reactive power compensation, shunt hybrid active power filters
(SHAPFs)
I.
INTRODUCTION
By the development of technology, electric utilities and
usage of electric power are increased. The majority part of
energy demand is provided by fossil fuels. However, fossil
fuels are finite resources and will eventually decreased. Due
to this condition, they become too expensive or too
environmentally damaging to retrieve. In the recent years,
renewable energy in power generation has been emerging as
an alternative energy source to mitigate the disadvantages of
fossil fuels. Renewable energy source (RES) integrated at
distribution level is termed as distributed generation (DG).
The utility is concerned due to the high penetration level of
intermittent RES in distribution systems as it may pose a
threat to network in terms of stability, voltage regulation and
power-quality (PQ) issues. Therefore, the DG systems are
required to comply with strict technical and regulatory
frameworks to ensure safe, reliable and efficient operation of
overall network. With the advancement in power electronics
and digital control technology, the DG systems can now be
actively controlled to enhance the system operation with
improved PQ at PCC. However, the intensive use of
nonlinear loads cause several power quality problems at
978-1-5090-0206-1/15 $31.00 © 2015 IEEE
DOI 10.1109/EMS.2015.44
247
constant dc link voltage in [5]. In this article, direct current
controlled pulse width modulation is used. In addition, the dc
link is controlled as both active and reactive current
component. The results are obtained for low voltage level
with compensating small amount of reactive power.
Besides, SHAPF can achieve the dynamic reactive power
compensation with adaptive dc link voltage in [3]. Moreover,
the dc link is controlled as active current component. The
reference dc link voltage may be insufficient to track the new
reference value when the adaptive dc link voltage may be
changed from low level to high level [5]. In addition, when
this dc link is controlled as active current component, an
extra start up precharging control circuit is needed. In the last
article [4], SHAPF can achieve the dynamic reactive power
compensation with adaptive dc link voltage. Also, selective
harmonic compensation is achieved. The dc link is controlled
as both active and reactive current component as in [5]. The
results are obtained for 220 V, 10 kVA system. However,
SHAPF compensates small amount of reactive power.
The growing amount of electric energy generated from
distributed or decentralized energy resources (DER), mainly
of renewables, requires their appropriate grid integration.
Thus, the renewable energy source interfacing with grid is
the major issue in the electric utility side. Different types of
converter topology in grid interconnection have been
improved by researchers to develop power quality and
efficiency of the electrical system [12-13]. This paper
focuses the shunt hybrid active filter interfaces for the
renewable energy source with proposed controller.
On account of the limitations between existing
literatures, the purpose of this paper is the following:
1. To provide interconnection between renewable source
and grid by using shunt hybrid active power filter (SHAPF)
with unidirectional isolated DC-DC converter at dc link.
2. To introduce a new control strategy for reactive power
compensation and harmonics elimination.
3. To adaptively controlled dc link voltage as reactive
current component.
4. To achieve reactive power compensation which is
nearly equal to 99% of load reactive power capacity.
As this paper primarily focuses on the aforesaid four
aspects of the shunt hybrid active power filter.
II.
Figure 1. Proposed Power System
A. Harmonic Current Control
The harmonic control of SHAPF is shown in Figure 2.
The first step is to isolate the harmonic components from the
fundamental component of the grid currents. This is achieved
through dq transformation (1), synchronized with the PCC
voltage vector, and a first order low pass filter with cut off
frequency of 10 Hz. Then the dq inverse transformation (2)
produces the harmonic reference currents in abc referential
frame.
ª
« cosθ p
ªid º
«i » = 2 «− sin θ
«
p
« q»
3«
2
¬«io ¼»
«
¬« 2
PROPOSED SYSTEM AND CONTROLLER
Figure 1 presents the proposed SHAPF system. As can be
seen in Figure 1 inverter unit is connected to the grid through
a LC filter tuned on the vicinity of the 5th harmonic.
As can be seen in Figure 2, the controller of proposed
system consists of four main parts: harmonic reference
generation, reactive current reference generation, dc link
voltage controller, dc-dc converter controller and final
reference compensation current- pwm control block.
The harmonic current control, reactive current control
and dc link control are achieved by indirect current control.
With this control method, any extra start up precharging
control process is not necessary for dc link. In addition,
reactive power compensation is achieved successfully with
perceptible amount. Besides, the harmonic compensation
performance is satisfactory.
ªia _ harmonic _ ref º
»
«
«ib _ harmonic _ ref » =
«ic _ harmonic _ ref »
¼
¬
º
cos(θ p − 2π ) cos(θ p + 2π ) » ªisa º
3
3 »
− sin(θ p − 2π ) − sin(θ p + 2π )» ««isb »»
3
3
» «i »
2
2
» ¬ sc ¼
¼»
2
2
ª
cosθ p
− sin θ p
«
«
2«
cos(θ p − 2π ) − sin(θ p − 2π )
3
3
3«
«
«cos(θ p + 2π ) − sin(θ p + 2π )
3
3
¬«
2º
»
2 » ªi
d _ lpf º
2 »«
»
i
q _ lpf »
2 »«
»
«
2 » ¬io _ lpf ¼
»
2 ¼»
(1)
(2)
B. Reactive Power Control
Dynamic reactive power variations in approximately
20% occurred in load are compensated by inverter side of
SHAPF. In this way, the dynamic reactive power
compensation characteristics of SHAPF firstly provides at
high levels in this article. The system responds to
instantaneous load changes immediately. The reference
248
current provided essential reactive power is produced. In
order to achieve the reactive power compensation of SHAPF,
the reference current having 90° phase difference among the
PCC point should be produced. To produce this reference
current, the output voltage of SHAPF inverter should be
generated in phase with PCC voltage vector. The block
diagram of reactive power control is shown in Figure 2.
The reference currents should be calculated to
compensate reactive power in the system. The reference
currents are generated by the dq method. The first step is to
isolate the fundamental components from the harmonic
components of the grid currents. This is achieved through the
dq transformation (3). The quadrature component of the
source current which is taken from dq transformation is
directly passed through the LPF. Thus, the 50 Hz component
of the source current is generated. Then, this signal is applied
to produce the reactive power compensation current by
inversing dq transformation. However, this reference current
is in quadrature axis. To achieve reactive power
compensation by voltage controlled voltage source SHAPF,
the reference current must be in phase with source voltage.
Thus, the reference current is transformed by using only d
component inverse dq transformation (4).
ªid º
«i » =
« q»
¬«io ¼»
ª
« cos θ p
2«
«− sin θ p
3«
2
«
¬« 2
ª ia _ reactive _ ref
«
«ib _ reactive _ ref
« ic
¬ _ reactive _ ref
º
»
»=
»
¼
º
cos(θ p − 2π ) cos(θ p + 2π ) » ªi sa º
3
3 »
− sin(θ p − 2π ) − sin(θ p + 2π )» ««isb »»
3
3
» «i »
2
2
» ¬ sc ¼
2
2
¼»
ª
− sin θ p
cos θ p
«
«
2«
cos(θ p − 2π ) − sin(θ p − 2π )
3
3
3«
«
«cos(θ p + 2π ) − sin(θ p + 2π )
3
3
¬«
2º
»
2 » ªiq _ fund º
2 »«
0 »»
2 »«
«
»
2 ¬ 0 »¼
»
2 ¼»
(3)
(4)
C. DC Link Voltage Controller
Figure 2 shows the block diagram of the dc link voltage
controller. The first step is to calculate the instantaneous
load reactive power. This is achieved through dq
transformation synchronized with the PCC voltage vector.
Then using the d and q component both three phase grid
voltage and current, the instantaneous load reactive power is
calculated. In next process, the reference dc link voltage is
determined with the equation [3] shown in Figure 2.
Figure 2 illustrates the control of the error signal. The
error signal is controlled by conventional PI controller [6].
Figure 2. Proposed Controller Block Diagram
249
IGBTs are generated through the pulse width modulation
generator whose amplitude and frequency of carrier wave are
± 1 and 20 kHz, respectively. The passive filter part supports
a fixed reactive power which is equal to 10 kVAR. The
reactive power capacity of the nonlinear load is 2 kVAR.
In this section, two mode of operation are discussed in
simulation cases. A renewable energy source (RES) is
connected on the dc link of grid interface SHAPF. The main
aim of proposed approach is to regulate the power at PCC
during: 1) PRES>0 and 2) PRES=0 where PRES is the
power generated from RES. While performing the power
management operation, the SHAPF is actively controlled in
such a way that it always draws/supplies fundamental active
power from/to the grid. Initially, the SHAPF is not connected
to the network. Before time t=0.5 s, the source, load and
SHAPF currents are illustrated in Figure 4 (a).
First mode of operation considers a case where PRES>0,
the SHAPF injects RES active power into grid and also
enhanced the quality of power at PCC. Before time t=1 s,
RES is not connected to the network. The source, SHAPF
and load active power are shown in Figure 5(a). At t=1 s, the
RES connected to the network. The SHAPF starts injecting
active power generated from RES as shown in Figure 5 (b).
Besides, SHAPF compensates harmonics successfully as
shown in Figure 4 (b).
Second mode of operation considers a case when there is
no power generation from RES. The SHAPF is to enhance
the quality of power at PCC. The proposed control method
for dynamic reactive power compensation with adjustable dc
link voltage will be verified by simulations. When the
loading reactive power consumption is greater than provided
by the passive filter part, the inverter side of the SHAPF can
compensate the remainder reactive power of the passive
filter. At time t= 2 s, the 4th load is connected to the system.
The reactive power rating of loads is increased 12 kVAR.
When the loads are connected to the system, the system
gives a dynamic response. Thus, the inverter side is
compensated the reactive power remainded by passive filter
capacity. The source reactive power is nearly equal to zero
shown in Figure 5 (c). The reduced THD of the source
current, while compensating these loads variations, working
balanced supply means in all the cases, sinusoidal current is
drawn from the source shown in Figure 4 (c). SHAPF dc link
voltage is adaptively changed from 160 to 225V shown in
Figure 5 (c). The amount of source side reactive power
remains nearly zero. In 2.5 s, the 5th load is connected to the
system. The reactive power rating of loads is increased 13
kVAR. The inverter side is compensated remainded by
passive filter capacity. The amount of source side reactive
power also remains nearly zero shown in Figure 5 (d).
The dc link voltage of SHAPF is adaptively changed
from 225 to 290V shown in Figure 5 (d). The reduced THD
of the source current, while compensating these loads
variations, working balanced supply means in all the cases,
sinusoidal current is drawn from the source shown in Figure
4 (d).
D. DC DC Converter Controller
Single phase shift (SPS) control method which is the
most widely used is applied for the proposed system. In SPS
control, the cross-connected switch pairs in both full bridges
are switched in turn to generate phase-shifted square waves
with 50% duty ratio to the transformer’s primary and
secondary sides. Only a phase-shift ratio (or angle) D can be
controlled. Through adjusting the phase-shift ratio the
equivalent ac output voltages of full-bridges, the voltage
across the transformer’s leakage inductor will change. Then,
the power flow direction and magnitude can be easily
controlled. An extensive overview of this control method is
explained in [14].
For the proposed system, the power flow is realized
from RES to SHAPF. Thus, dc-dc converter generate
negative phase-shift angle for this power flow direction.
This phase shift angle is controlled by simple PI controller.
This converter only performs when PRES>0 where
PRES is the power generated from RES shown in Figure3.
Figure 3. Unidirectional Isolated DC DC Converter and Power Flow
Direction
E. Final Reference Compensation Current and PWM
Control Block
The final reference current consists of three phase
harmonic reference current signals, three phase reactive
reference current signals and dc link control signals. The
reference signal (In_harmonic_ref + In_reactive_ref +
Vcappi_n) is generated using these signals together. Then,
the reference signals are compared with carrier signal to
generate switching signals shown in in Figure 2.
III.
SIMULATION RESULTS
Simulation
studies
are
carried
out
using
PSCAD/EMTDC. The main purpose of the simulation is to
evaluate the effectiveness and correctness of the control
strategy used in the SHAPF with variations of linear loads.
Parameters used in simulations are given in Table I. In
simulation, the nominal frequency of the power grid is 50 Hz
and the harmonic current source is generated by the three
phase diode rectifier. Also, the dynamic reactive power
changing is generated by linear loads shown in Table II. The
phase to phase grid voltage is selected as 380 V (peak-peak).
Passive filters are tuned at 5th and the control signals of
250
Figure 4. Three phase Source Voltages, Source - SHAPF - Load Currents (a)when SHAPF is not operated, (b) when PRES>0, (c) when PRES=0 and 1
kVAR loads are connected (d ) when PRES=0 and another 1 kVAR loads are connected
Compared the simulation results with dynamic load
changes, the proposed method can:
1) Interconnect between renewable source by using shunt
hybrid active power filter (SHAPF)
2) Provide dynamic reactive power compensation
3) Reduce the THD of source side current
4) Adaptively change the dc link voltage value
TABLE I.
SIMULATION PARAMETERS
Parameters
Line frequency
Filter Capacitor (CF)
Filter Inductance (LF)
Tuned freq. of series filter (ftuned)
Filter Capacitor (CF)
Load Inductances(Lac1)
Switching frequency (fswitching)
Simulation Step Time
DC Link Reference Value
DC link Capacitors
251
Value
380 V
50 Hz
200 μF
2 mH
250 Hz
2.7 mH
20 kHz
40 μs
100-300 V
12 mF
Figure 5. Source - SHAPF - Load Active power and SHAPF DC link voltage when PRES=0, (b) Source - SHAPF - Load Active power and SHAPF DC
link voltage when PRES>0, (c) Source - SHAPF - Load Reactive power and SHAPF DC link voltage when PRES=0 and 1 kVAR loads are connected ,
(d)Source - SHAPF - Load Reactive power and SHAPF DC link voltage when PRES=0 and another 1 kVAR loads are connected
252
TABLE II.
SIMULATION PARAMETERS FOR TESTING LOADING
Inductive Loads
1st Load ( Rload1 Lload1)
2nd Load ( Rload2 Lload2)
3rd Load ( Rload3 Lload3)
4th Load ( Rload4 Lload4)
5th Load ( Rload5 Lload5)
Physical
Value
5
90 mH
10 225 mH
10 225 mH
20 450 mH
20 450 mH
Reactive
Capacity
5kVAR
[3]
Power
[4]
2 kVAR
2 kVAR
[5]
1 kVAR
1 kVAR
[6]
As a result, it is clearly shown that shunt hybrid active
power filter (SHAPF) with a DC-DC converter at dc link
achieves interconnection between renewable source and grid
with linear dynamic loads. Besides, SHAPF using the
proposed method can provide better compensation
performance both harmonic and dynamic reactive power
compensation.
IV.
[7]
[8]
CONCLUSION
[9]
In this paper, SHAPF provides interconnection between
renewable source and grid with linear dynamic loads.
Besides, the novel control scheme for SHAPF is proposed in
order to compensate both harmonic and dynamic reactive
power with adaptive dc link voltage. The main contributions
of this paper are:
-The grid interconnection is supplied by SHAPF for the
renewable energy source.
-To introduce a new control strategy for reactive power
compensation and harmonics elimination.
-To adaptively controlled dc link voltage.
-To achieve reactive power compensation which is nearly
equal to 100% of load reactive power capacity.
The harmonic current control, the dc link control and
reactive current control are achieved by indirect current
control. With this control method, any extra start up
precharging control process is not necessary for dc link. In
addition, reactive power compensation is achieved
successfully with perceptible amount. Besides, the harmonic
compensation performance is satisfactory.
In a conclusion, the SHAPF injects RES active power
into grid and also enhanced the quality of power at PCC.
Simulation results of the three-phase three-wire SHAPF in
dynamic reactive power compensation.
[10]
[11]
[12]
[13]
[14]
[15]
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