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Harmonics and Mitigation Techniques through Advanced Control in

Grid-Connected Renewable Energy Sources: A Review
Xiaodong Liang Chowdhury Andalib-Bin-Karim
Senior Member, IEEE Student Member, IEEE
Memorial University of Newfoundland Memorial University of Newfoundland
Department of Electrical and Department of Electrical and
Computer Engineering Computer Engineering
St John’s, NL, Canada St John’s, NL, Canada
xliang@mun.ca cabk60@mun.ca

Abstract–With more renewable energy based distributed electronic devices in these inverters generates harmonics at
generation (DG) units connected to utility power grids, DG`s output. For example, a PV inverter may experience high
deterioration of power quality at the point of common coupling frequency switching during low irradiance level of solar
(PCC) becomes a major concern. There are two types of
harmonics associated with DG units, together they may cause
energy, resulting in an injection of highly distorted current to
excessive harmonic distortion at the PCC. The first type of the distribution network [1]. Such harmonics contain high
harmonics is generated by power electronic devices in DG units frequency harmonic components at multiples of the carrier
such as photovoltaic (PV) systems, which contains high frequency frequency of the inverter. To mitigate such harmonics, the
harmonic components at multiples of the carrier frequency of the grid-tie filters such as LCL or LC filters are used at the output
DG interfacing inverter. Such harmonics are firstly reviewed in of the inverters. These filters can potentially cause a harmonic
this paper, and potential operational effect at the system level due
to LCL or LC filters installed at the inverter output to mitigate
resonance for system operation if not properly designed.
such harmonics are discussed. The second type of harmonics is The second type of harmonics are created by nonlinear local,
generated by other nonlinear local, PCC and utility loads in the PCC and utility loads in the system at multiples of the power
system, which are common type of harmonics at multiples of the grid frequency, 50/60Hz. To ensure good power quality
power grid frequency, 50/60Hz. Harmonic mitigation for such supplied to the consumers, utility companies need to maintain
harmonics achieved through advanced control of the DG harmonics level at the PCC with each consumer within
interfacing inverter operated as a power quality conditioner are
reviewed and summarized. This systematic review can facilitate
acceptable limits as required in grid codes. For example,
better understanding of harmonics associated with renewable according to IEEE Std 519-2014, the recommended harmonic
energy based DG units and provide guidelines on advanced distortion limit of line-to-neutral voltages is that the voltage
control schemes to realize ancillary harmonic compensation total harmonic distortion (VTHD) at the PCC is 8% for the bus
service through DG interfacing inverters. voltage less than or equal to 1 kV, 5% for the bus voltage
between 1 kV and 69 kV, and 2.5% for the bus voltage between
Index Terms – Active filtering, harmonics mitigation, power
69 kV and 161 kV etc [2].
quality, renewable energy based distributed generation, virtual
impedance. It is recognized recently that, in addition to its major power
delivery function, a DG interfacing inverter can be operated as
I. INTRODUCTION a power quality conditioner by providing ancillary harmonic
compensation service without additional costs if the apparent
With more emphasis on power generation in an power volt-ampere (VA) rating of the inverter is sufficient.
environmental friendly way, renewable energy based Since most DG inverters will operate at less than their full
distributed generation (DG) has received great attention in capacity, such ancillary services are technically feasible. A DG
recent years. Among all renewable energy sources, interfacing inverter can improve the system efficiency and
photovoltaic (PV) systems have experienced rapid growth both ensure reliable harmonic compensation through advanced
in residential and commercial sectors due to recent advance- control schemes.
ment of the PV technology and various support programs Due to increasing penetration of renewable energy sources
introduced by governments and utility companies worldwide such as PV systems in today’s power grids, harmonics
to encourage grid-connected PV generation. associated with interfacing inverters and their complicated grid
There are two types of harmonics associated with renewable interaction request in-depth research to be performed in this
energy based DG units. The first type of harmonics is particular area. Some research was conducted in past decades
generated by power electronic devices in renewable energy [3]-[17], VTHD and ITHD (the current total harmonic
sources. For certain types of renewable energy sources such as distortion) or ITDD (the current total demand distortion)
PV systems, the grid connection is achieved through an values were reported in the literature for PV power plants and
interfacing power electronic inverter. The switching of power systems. The typical dominant harmonics were usually

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considered to be the 3rd, 5th, 7th, 11th and 13th harmonics for services through DG interfacing inverters for harmonics from
pulse width modulation (PWM) voltage source inverters nonlinear local, PCC and utility loads.
(VSIs). In the majority of the cases, VTHD values were less The critical aspects of the review include: 1) To facilitate
than 5%, while ITHD values can be anywhere between 1% and better understanding of harmonic characteristics generated by
35%. For example, as reported in [12], the highest VTHD of PV systems, point out issues in harmonic measurement
two PV power plants was observed to be 2.1%, the lowest practice currently in use based on the reported field
VTHD was noted to be 1.5%, and the ITDD values were in the measurement and lab testing results; and 2) To compare
range of 1% - 1.57%. In [15], several different inverters were several existing harmonic mitigation control schemes for DG
tested through experiments, VTHD values were approximately interfacing inverters to provide guideline for future research.
between 1.2% and 5%; while ITHD values were between 2% Based on review results in this paper, a classification of the
and 35%. The conclusion from past research was that the existing control schemes to operate DG interfacing inverters as
VTHD from PV systems was usually within recommended a power quality conditioner is presented in Fig. 1. There are
harmonic distortion limits, however the ITHD may exceed the two main streams of approaches for harmonic mitigation: 1)
limits as mentioned in [15]. virtual impedance based method; and 2) active harmonic
Despite such effort, harmonics generated by PV systems are filtering based method. Both streams will be summarized in
not well understood, and harmonic mitigation techniques for detail in this paper.
renewable energy based DG interfacing inverters remain The paper is arranged as follows: in Section II, harmonics
underdeveloped. Therefore, there is an urgent need to conduct generated by PV systems are reviewed, and the potential
this review to facilitate better understanding of current status operational effect at the system level due to LCL or LC grid-
and provide guidance for future research. There are two major tie filters is discussed; harmonic compensation using virtual
aspects in this paper: 1) understand harmonics generated by impedance based control methods through DG interfacing
PV systems through lab testing and field measurements inverters are reviewed in Section III, and active harmonic
reported in the literature; and 2) review various state-of-art filtering based control methods are presented in Section IV;
control techniques to offer ancillary harmonic compensation and the conclusions are drawn in Section V.

Fig. 1 Classification of the existing control methods for harmonic compensation.

sources, and 2) other nonlinear loads in the system. Although

II. HARMONICS IN RENEWABLE GENERATION SYSTEMS
harmonics from other nonlinear loads have been well
Power electronic interfacing inverters utilized at renewable understood after more than two decades industrial practice [2],
energy based DG units pose harmonics concern at the PCC as characteristic harmonics generated from renewable energy
the penetration of DG units increases. Ad discussed in previous sources remain unclear. In this section, the focus will be to
sections, harmonics at the PCC come from two separate review harmonics generated by PV systems through lab testing
sources: 1) power electronic devices at renewable energy and field measurement results reported in the literature.

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A. Harmonics Generated by PV Systems banks (SC1 and SC2) for voltage support. A set of 1.2 Mvar
PV systems use power electronic inverters to connect with power factor correction capacitors is located close to the 2 MW
the distribution system, and these inverters generate harmonics customer site. The configuration of the studied system is
and inject them to power grids during operation. Harmonic shown in Fig. 2 [12].
characteristics are affected by the system impedance, control With many long lines and capacitors involved, the system
system, and grid-tie filters (LCL or LC filters). Based on IEEE harmonic resonance is analyzed in [12] (Fig. 3). It is found that
std. 929-2000, voltage, voltage flicker, frequency, and for the base case analysis, the harmonic resonance frequencies
distortion are four parameters used to evaluate power quality are located around the 3rd and 25th orders for the 60 Hz
in PV systems [4][5]. The Total Harmonic Distortion (THD) fundamental frequency. The recorded current harmonic
in terms of voltages and currents are the parameters to be spectra through field measurements by Hydro One during June
evaluated from the harmonics aspect [15]. 2012 show a harmonic current spectrum on a day with a high
Several papers have reported harmonics generated by PV 3rd harmonic current content, and some other days without high
systems through lab experiments or field measurements [6]- 3rd harmonics [12].
[17]. The measurement approach provides the data showing It is concluded in [12] that the steady-state VTHDs at the
harmonic characteristics for PV generation, allows to two solar farms and the main feeder were within the harmonic
distinguish critical situations that can affect the grid power distortion limits recommended by IEEE Std. 519. Note this
quality negatively, and offers comparison data for analytical study did not consider harmonics from the rest of the system.
models [15], and thus, this approach had been widely used. It appears that the highest harmonic order measured in [12]
Measurement results were reported as early as 1982 in [6], is 25th, which poses concerns about harmonic measurement
where harmonics characteristics of a single residential PV accuracy. Because at the output of a PWM VSI, characteristic
installation using a line-commutated inverter were recorded harmonics are the multiples of the carrier/switching frequency
from the fundamental current to the 13th harmonic current. In of the inverter [18]-[20], which are usually much higher than
the following decades, the technology had been evolved, 25th order. For example, if the carrier frequency of a two-level
currently the PV interfacing inverter mainly uses various PWM VSI is 2200 Hz, the characteristic harmonic bands will
PWM based VSIs [7], and thus, their associated harmonic be located around 2200 Hz, 4400 Hz, and 6600 Hz etc. A 4400
characteristics have been changed. Hz harmonic band corresponds to the 73rd order harmonic for
A laboratory experiment using a 3 kW rated single-phase a 60 Hz system. However, such higher order harmonics are not
inverter for PV panels was conducted in [10], the active power recorded in [12], and their effect is not included in the VTHD
of the inverter varied between 500 W and 2500 W in steps of and ITHD calculation.
500 W during the experiment, and measurements are taken at In Reference [13], a comprehensive testing is conducted to
each loading point. The recorded VTHD was always within the evaluate harmonics and inter-harmonics generated by PV
recommended IEEE limit, while the recorded ITHD had a inverters. One conclusion is drawn in [13], which matches the
higher value close to 30% at a light load, and approached the authors’ concern about Reference [12] measurement practice
IEEE standard limit with an increased loading. The paper discussed earlier, is that some PV inverters might have strong
concluded that harmonic distortions of the distribution high frequency component emission in low-power modes
network with the PV panels connected were within IEEE and/or at rated and higher power mode. Accordingly, it is
standard limits [10]. In this study, voltage and current suggested that tests of PV inverters include high frequency
harmonic spectra were not measured. range and suitable high frequency distortion indices be used
However, as mentioned in [11], although each inverter [13]. Another interesting discovery in [13] is that the
associated with a set of PV panels may generate harmonics maximum power point tracking control might be a possible
which are within acceptable standard limits recommended by origin of the interharmonic distortion.
IEEE std. 519, the harmonics at the PCC of a large scale A field test of inverters installed in a Brazilian solar farm
connection of many inverters in a realistic solar farm may was conducted in [14]. Measurements were performed on three
exceed these limits [11]. Harmonic distortion level for large different commercial inverters, with 15 kVA rated capacity
scale solar farms should be carefully evaluated. each. High frequency harmonic current distortions may reach
Reference [12] reports field measurements data for two 10 up to 2% of the fundamental frequency current, but high
MW solar farms at a 27.6 kV main feeder. The harmonic data frequency harmonic voltages remain below 0.2% of the
were recorded for several months by the transmission utility, fundamental frequency voltage. Therefore, it is concluded in
Hydro One, at the main feeder and the two solar farms. The [14] that these specific PV inverters are unlikely to cause
feeder consists of a 7.8 km of overhead distribution line and significant problems to the utility. Fig. 4 shows the measured
two small segments of three phase underground cable. Two 10 sample harmonic voltage and current spectra with the
MW solar farms located about 6.2 km away are connected to dominant harmonic frequency located at 16.5 kHz.
this feeder. The feeder is equipped with two 20 Mvar capacitor

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By examining the solar farm set-up in [14], it is found that distortions at the PCC might exceed IEEE recommended
no long distribution lines or cables are involved in the system. harmonic distortion limits.
A long line/cable can potentially cause harmonic resonance Based on review results in this paper, although some field
[18]-[20] at 16.5 kHz frequency. Therefore, the conclusion tests and lab experiments have been conducted, harmonics
drawn in [14] might need to be changed if a long line/cable is generated by PV systems are still not well understood. More
implemented in the system. In the case of resonance, field tests particularly allowing higher order harmonic contents
harmonics at the PCC will be amplified, and harmonic to be included are much needed in the future.

Fig. 2 The electrical single line diagram for the main feeder [12].

transient overvoltage related effect is also reported in [23]. In

this paper we will tightly focus on harmonic resonance aspect.
The possibility that these filters excite harmonic resonance
by interacting with the system impedance is evaluated in
[21][22]. The general configuration of a VSI system is shown
in Fig. 5 (a). A LCL filter with a damping resistor Rd in series
with the capacitor is shown in Fig. 5 (b) [21].
It is concluded in [21] that: 1) the damping resistance Rd has
a significant damping impact on harmonic resonance, an
individual PV inverter could excite harmful resonance if the
passive damping impedance is below 2 Ω; 2) The supply
system impedance is not the dominant factor contributing to
resonance amplification; 3) the number of PVs affects the
Fig. 3 The network harmonic resonance response showing impedance versus resonance magnitude and frequency. Fig. 6 shows the system
the order of harmonics for a base operating case with one 20 Mvar station
capacitor and 1.2 Mvar load capacitor in operation [12]. resonance with different damping resistor R values [21]. In this
figure, the unit for the damping resistor R is Ω, and the
corresponding power loss in W, Ploss, for each damping
resistance is shown. Reference [22] presents a similar effect
using a 6 Ω damping resistor.
The harmonic content at the PCC for a case study (a
residential system with 10 houses) is shown in Fig. 7 [21].
Harmonics amplified at the switching frequency can be
observed, which matches the discussion in previous sections.
(a) (b)
Fig. 4. The sample recorded harmonic current spectrum: (a) high frequency III. HARMONIC COMPENSATION: VIRTUAL IMPEDANCE BASED
harmonic (HFH) voltage at 16.5 kHz; (b) HFH current at 16.5 kHz [14]. CONTROL METHOD
B. Operational Effect Due to a LCL or LC Filter DG grid interfacing inverters can be controlled as virtual
The LCL or LC filters are widely applied in PV inverters to impedance at harmonic frequencies in order to provide
mitigate high frequency harmonics generated by the inverters. ancillary harmonic compensation services. The concept of
The main operational effect at the system level due to such virtual impedance is well summarized in [24]. A virtual
filters is harmonic resonance as reported in [21][22]. The impedance can emulate the effect of a physical impedance
without the need to connect a real component to a system, it

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can be an inductor, a resistor, or a combination of both. Virtual impedance can be realized by modifying the voltage or current
impedance can be either at the fundamental or harmonic reference or the PWM signal through digital control of the
frequencies: 1) at the fundamental frequency, it can be used for inverters according to harmonic compensation requirements
power flow control and grid disturbance ride through; and 2) [24]. Different control schemes based on virtual impedance are
at harmonic frequencies, it can be used for active damping and discussed in this section.
harmonics compensation. To mitigate harmonics, virtual

(a) (b)
Fig. 5 (a) A general configuration of a VSI system [21]; (b) a model of individual PV with a damping resistor Rd at the LCL filter [21].

to realize the 1st and 2nd objectives is that harmonic currents

are absorbed by the DG unit.

Fig. 8 A general system configuration for a grid-connected DG unit [25].

B. Current Control Method (CCM)

Harmonic compensation in a DG unit can be effectively
Fig. 6 The system resonance with different damping resistors in ohm [21]. realized by using the CCM, and most grid-tied DG inverters
use the CCM scheme [25]-[31]. In this method, the DG line
current is controlled according to a modified current reference,
which is achieved based on the harmonic compensation
requirement and available power rating of the inverter.
To realize the 1st objective, PCC voltage harmonic
compensation, the DG unit is controlled to behave like a small
damping resistor at the selected harmonic frequencies, when
viewed from the distribution system level. As a result, more
harmonic currents from non-linear loads will flow to the DG
unit, the grid mainly supplies sinusoidal fundamental current,
Fig. 7 Harmonic contents of secondary PCC voltage with the rated voltage of
therefore, the PCC voltage harmonic distortion is reduced
120 V [21]. [25][26].
In the CCM, the current reference is modified by adding a
Fig. 8 shows a general system configuration for a grid- harmonic current reference term (Iref_h) to the fundamental
connected DG unit. Harmonics compensation objectives can current reference term (Iref_f) derived from the power control
be categorized as follows: 1) PCC voltage harmonics branch as follows:
compensation; 2) local load harmonics compensation; and 3)

 =
 _  +
 _ (1)
DG line current harmonics rejection [25]. The common feature

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1 distortion is reduced to 2.32% VTHD, compared to 7.20%

 _ = −  . ( ().  ) (2)
 VTHD in the local load harmonic compensation mode [25].
Reference [30] provides another case study using the CCM
where Rv is the virtual harmonic damping resistor and the
with the 5th and 7th harmonics compensated, and the PCC
harmonic component of the PCC voltage (VPCC) is extracted
voltage harmonic compensation is shown in Fig. 11. By acting
using a harmonic detector (HD(s)), s is the Laplace operator. Rv
as a low resistance at the selected harmonic frequencies, the
shall be determined according to the PCC harmonic
DG unit absorbs most of the nonlinear load currents as shown
compensation requirement, the DG available rating, and the
in Fig. 14(c). The VTHD at the PCC is 2.5% in this case
consideration of the stability range [25]. The value of Rv will
compared to 10.25% without harmonic compensation [30].
affect the compensation performance. Generally, a smaller Rv
gives better compensation, but tends to reduce the system
stability [3]. The proportional and parallel multiple resonant
controllers (PR controller) at fundamental and harmonic
frequencies are adopted to ensure accurate control of DG line
current [3][27]. The PR controller can achieve very high gain (a)
at resonant frequencies with narrow bandwidth. The desired
bandwidth can be obtained by appropriate tuning of the
integral gain of the controller [28][29].
To realize the 2nd objective, local load harmonics
compensation, the DG unit absorbs harmonic currents from (b)
local nonlinear loads. In this case, the DG and local loads can
be treated as a microgrid, which behaves like a linear
load/source seen from the grid [25]. However, the PCC voltage
distortion may not be reduced.
The block diagram of the CCM for DG single-phase grid- (c)
interfacing inverters is depicted in Fig. 9, where switching
between the 1st and 2nd objectives can be done [26]. Note: the
virtual impedance is only used for the PCC voltage harmonics
compensation mode.
(d)
Fig. 10 PCC harmonic voltage compensation results using the CCM: (a) PCC
voltage, (b) DG current, (c) microgrid current, and (d) grid current [25].

Fig. 11 PCC harmonic voltage compensation results using the CCM (Case 2):
(a) PCC phase voltage, (b) grid current, and 3) DG current [30].
Fig. 9 Block diagram of the CCM for DG single-phase grid-interfacing C. Voltage Control Method (VCM)
inverters [26].
Although VCM-based DG unit is rarely used for harmonic
The performance of PCC voltage harmonic compensation compensation in the literature, it has the potential to be used in
using the CCM is demonstrated in Fig. 10. In the PCC both grid-connected and islanded modes. In an islanded mode,
harmonic compensation mode, with the control of the virtual the CCM is not suitable for harmonic compensation, as it
damping resistor, Rv = 0.5 Ω, the PCC harmonic voltage cannot provide direct voltage support to the load. The VCM,
however, can provide a seamless transition from a grid-

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connected mode to an islanded model. Therefore, the VCM is a and system instability problems associated with high gain value
suitable method to realize harmonic compensation for should be taken into consideration while choosing the value of
microgrids. When multiple DG units are connected to the G [36]. The block diagram of the VCM based harmonic
system, the VCM can utilize the droop control (real power- compensation is depicted in Fig. 12 [26].
frequency (P-f) droop and reactive power-voltage (Q-V) droop) A case study has been conducted for the PCC harmonic
to derive the fundamental voltage reference signal (Vref_f), thus voltage compensation mode using the VCM (Fig. 13). The
facilitating the proper power sharing among DG units [3][25]. gains for the compensation of PCC voltage at the 5th, 7th, and
Droop control is originally used for the synchronous 11th harmonic frequencies are G5 = 12, G7 = 12, and G11 = 5.
generator control. Mechanical power input of a synchronous As the DG impedance at harmonic frequencies is reduced by a
factor of (1 + Gh), the DG unit absorbs most of the nonlinear
generator is adjusted by the governor system based on the grid
load currents as shown in Fig. 13 (d). The VTHD at the PCC
frequency deviation, which is known as P-f static feature of a
is 2.43% in this case compared to 6.72% without harmonic
synchronous generator. The reactive power supply of a
compensation [30].
synchronous generator is regulated by the exciter system
depending on the terminal voltage of the generator. Recently,
due to increasing implementation of renewable energy sources
with DG interfacing inverters, droop control becomes a
common control approach for such inverters. For a small
variation in the bus voltage magnitude (V), the active power (P)
at the bus does not change appreciably; similarly, for a small
variation in the bus phase angle (δ), the reactive power (Q) does
not change appreciably. Such approximation is considered
accurate enough only for a system with a very low R/X ratio,
i.e., with a dominant inductive branch. The assumption of weak
P–V and Q–δ couplings serves as the basis of the P-f and Q-V
droop control. With this assumption, the active power can be
controlled by the frequency, and the reactive power can be
controlled by the voltage magnitude [32]–[35].
The VCM can achieve a reliable PCC harmonic
compensation using a virtual harmonic impedance control
method. A double loop voltage controller is generally
incorporated in the voltage tracking stage, with a proportional- Fig. 12 Block diagram of the VCM based harmonic compensation [26].
resonant controller in the outer loop, to control the filter
capacitor voltage. The voltage reference is modified by adding
a harmonic voltage reference feed forward term [30] as follows:
 =  _  +  _ (3)
_ () = (−). _ () (4)
where, G is the gain value of the feed forward term, VPCC_h is
the harmonic component of the PCC voltage, which is extracted
using a harmonic detector, Vref_h is the DG harmonic voltage.
The equivalent impedance of DG unit at harmonic frequencies,
ZDG_h,eq, can be expressed by
_ , = _ /(1 + ) (5)
(#$)%&''_(

 _ = − (6) Fig. 13 PCC harmonic voltage compensation results using the CCM: (a) PCC
)*+_( voltage, (b) DG current, (c) microgrid current, and (d) grid current [30].

Where, IDG_h is the DG harmonic current, and ZDG_h is the DG The comparison between CCM and VCM is summarized as
harmonic impedance. By controlling the DG harmonic voltage follows [30]:
with a proper selection of the gain value, the equivalent 1) Without harmonic compensation, the current controlled
harmonic impedance of the DG unit can be made lower than DG (CCM) automatically pushes all harmonic currents to
that of the grid side. As a result, the DG unit will absorb more the grid side and causes a polluted PCC, while the voltage
harmonic currents contributed by non-linear loads, and reduce controlled DG (VCM) can share harmonic currents with
voltage harmonic distortion at the PCC. The over modulation the grid based on their respective impedances. Therefore,

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for the conventional control scheme without harmonic Fig. 15 shows the experiment of the transition of a DG unit
compensation, the VCM leads to less voltage harmonic from a grid-connected mode to an islanded mode [38]. Table I
distortion at the PCC than the CCM. provides a summary of different compensation schemes [25].
2) The VCM can conduct a seamless control transition from
a grid-connected mode to an islanded mode, but the CCM
has difficulties in an islanded mode due to its inability to
provide voltage and frequency support.
3) For multiple DG units operation, the CCM works as a
shunt low resistor, and there is no circulating current
among DG units with the CCM. Due to the inductive
nature of the harmonic impedance, there is very limited
harmonic current circulation among DG units with the
VCM. To avoid circulating current issues during
operation, harmonic component extraction without phase
shift is very important for both methods.
Reference [37] proposes a virtual admittance for harmonic
and/or unbalance compensation when multiple inverters
operate in parallel. The proposed method in [37] can be used
for both CCM and VCM.
D. Hybrid Control Method (HCM)
Considering limitations of traditional CCM and VCM, an
innovative control approach, named the Hybrid Control
Method (HCM), has been proposed [38][39]. The advantages
of HCM include: 1) it allows the coordinated closed-loop
control of the fundamental voltage and line harmonic currents Fig. 14 Block diagram of the HCM based harmonic compensation [38].
in the DG unit; 2) local harmonic loads can be compensated
without the harmonic extraction process; and 3) the DG unit can
be switched between a grid-connected mode and an islanded
mode at any time instant without using additional transient
mitigation methods, and smooth transition can be realized
without generating transient currents. In this method, a
resonant controller with the frequency selective nature is
adopted in the current control loop, it has a high gain at the
selected frequencies, which allows accurate control of the filter
capacitor voltage and line current at different frequencies
without noticeable interference [38].
A single loop control structure with three separate parallel
control branches in HCM can be adopted as follows [26]:

-.% = /0 (). (1 – 3 ) +  45/673 (). (
( −
8 ) Fig. 15 Experimental transition performance of single DG unit from grid-
connected mode (HCM with line harmonic current rejection) to islanding
+ 945:76; ().
# (7) mode (VCM). (a) PCC voltage, (b) Filter capacitor voltage, (c) Main grid
current, (d) DG line current [38].
Where, s is the Laplace operator. In Equation (7), the 1st term
TABLE I
realizes the closed loop control of the filter capacitor voltage Different compensation schemes (CCM, VCM, and HCM) [25]
by adopting a fundamental frequency resonant controller in the
control loop; the 2nd term realizes proper regulation of line
harmonic current in a closed loop manner by incorporating
harmonic frequency resonant controllers in the control loop;
while the 3rd term provides necessary damping to the filter
resonance. The HCM based compensation technique can be
used for reliable compensation of both the PCC voltage and
local load current harmonics. The block diagram of the HCM
based harmonic compensation is depicted in Fig. 14 [38].

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IV. HARMONIC COMPENSATION: ACTIVE FILTERING METHOD for converter switching is generated based on the current
In power systems, active power filters (APFs) are mostly control technique.
used to improve power quality and compensate power A. Control based on Reference Generation Techniques
unbalance. APFs can be classified as shunt or series type based The performance of an APF mainly depends on the selection
on the topology used. Shunt APFs are connected at the load of reference generation schemes, which is either in frequency
terminal to mitigate harmonic currents generated by non-linear or time domain. The frequency domain based reference
load, they can also be used for reactive power and unbalanced generation method is an older technology, the Fourier
current compensation. Series APFs are usually connected Transformation of a distorted voltage or current signal is
before the load in series to the ac grid through a matching performed, and harmonic components are extracted to generate
transformer to eliminate voltage harmonics, compensate grid appropriate compensating signals, which requires large
voltage disturbances, and regulate the terminal voltage of the computation time for online applications. The most commonly
load or transmission line [40]. used algorithms for reference generation schemes are time-
In a grid-connected renewable energy based DG unit, the domain-based techniques, they are easy to implement and
interfacing inverter can be operated as an APF to improve the require less computation time. Instantaneous derivation of
power quality. The inverter can be connected in parallel to non- compensating signals can be obtained from measured
linear load as a shunt APF [40]. In addition, a combination of harmonic polluted voltage or current signals [42][43].
shunt and series converters design for a PV system known as a Reference [44] used the instantaneous active and reactive
unified power quality conditioner (UPQC), is proposed in [41], power (p-q) theory based control method for PV system
and a hybrid filter as a combination of a series APF and a shunt inverters serving as APFs. A modified p-q theory based control
passive filter is proposed in [42]. is presented in [43]. Using p-q theory, the reference current is
Reference [40] proposes a multiple functional PV converter, generated such that it ensures to maintain the required real
which operates by supplying active and reactive powers when power (p) and reactive power (q) values for compensating the
the sun is available, and operates as a harmonic and reactive network. Based on the knowledge of the required power to be
power compensator at low irradiation. Fig. 16 shows the compensated and the measured phase voltage value in ‘α-β’
effectiveness of a grid-connected PV system with shunt reference frame, the compensating current in ‘α-β’ reference
controller functionality, where load voltage harmonic spectra frame is computed. An inverse transformation is conducted to
without and with the shunt converter are displayed. obtain the phase current to be injected by the inverter to ensure
required value of p and q for compensation. In this method, zero
sequence component is neglected, so it may not be accurate
when the three phase system is unbalanced [44]. This method
is mainly used to improve power quality in aspects other than
harmonics, such as sudden change in irradiation, fluctuations in
the PCC voltage (voltage sags or swells), or the combination of
multiple disturbances occurring simultaneously [43].
Fig. 16 Load voltage harmonic spectra for distorting load: without shunt The synchronous d-q reference frame based method can also
converter (black), with shunt converter (white) connected to the grid [40].
be applied to control the APF [45]. In this method, the non-
The shunt inverter injects a compensating current out of linear load current is considered as an input signal and can be
phase to the non-linear load current in order to ensure unity transformed from a-b-c to d-q-0 frame by Park’s transform-
load power factor and cancel out harmonic components ation. The phase angle value required for grid synchronization
[40][43]-[45]. The compensating current is produced by can be obtained from the phase locked loop (PLL). In this
comparing the load current with a pre-determined reference method, the reference generation is not affected by voltage
current. An error signal is generated by comparing the required unbalance. Therefore, this method demonstrates a reliable
compensating current with the actual shunt current flowing compensation performance even under unbalanced voltage
through the inverter, which is used to generate appropriate gate conditions [45][46]. A block diagram of this method is depicted
signals for the inverter switching. in Fig. 17. The effectiveness of the method is shown in Fig. 18
The main control objective of an APF is to generate an for the PCC source current before and after active filtering [45].
appropriate compensating current. Different current control Several indirect methods of reference generation are
methods can be applied to track the compensating current to presented in [47]. The main idea of indirect method is to
be injected. There are three critical steps involved: 1) firstly, balance system parameters, such as inductor current or
necessary voltage and current signals must be sensed from capacitor voltage using different types of controllers. The PLL
different locations of the system; 2) secondly, appropriate is suggested to be used for reference generation in some papers
compensating signals are generated; 3) finally, the gate signal for indirect methods.

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Fig. 17 Block diagram of synchronous d-q reference frame based compensation algorithm [45].

(a) (b)
Fig. 18 The PCC source current waveforms: (a) before filtering; (b) after filtering [45].

Fig. 19 Block scheme of DPC with source voltage sensor [49].

diagram of the DPC with a voltage sensor is depicted in Fig. 19

B. Direct Power Control (DPC) Method
[49]. The DPC algorithm is easy to implement as it does not
The DPC method can be successfully applied in an APF require internal control loop of controlled variables, coordinate
based grid connected PV system for harmonic current and transformations or decoupling between active and reactive
reactive power compensation [48]-[50]. In this method, the components of the current. It has excellent performance in
instantaneous values of active power (Ps) and reactive power terms of dynamic response, harmonic and reactive power
(Qs) are computed using the sensed voltage and current signals compensation. The main disadvantage of this method is the
of the source, and then compared with the reference values of dependency of switching frequency, which can be overcome by
active (Pref) and reactive power (Qref) in hysteresis controllers. introducing space vector modulation technique [51]. The
The active power reference should be generated in such a way effectiveness of the DPC method is shown in Fig. 20 [49].
that it maintains a balance between the power supplied by the To obtain appropriate gate signals for switching devices of
source and the filter, and the power consumed by the load. For APFs based on the derived compensating commands, numerous
reference generation purpose, an outer integral proportional current control techniques can be applied [52]-[56]. The current
(IP) controller is incorporated in the system, which also ensures control technique must have good tracking capability of time
the regulation of dc link voltage during steady-state and limits varying reference signal. The PWM control is widely used and
its variability during transient [48][49]. The reference value of also known as linear current control technique. In this
reactive power is set to be zero for a unity power factor. A block

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technique, a modulating signal (with a 50 Hz or 60 Hz [2] IEEE Std 519-2014, “IEEE Recommended Practice and Requirements
for Harmonic Control in Electric Power Systems”, 2014.
frequency) is derived from a current regulator, which is [3] J. He, M. S. Munir, and Y. W. Li, "Opportunities for power quality
compared to a triangular wave (usually with a frequency of improvement through DG-grid interfacing converters," in Proc. IEEE
several kilohertz), to obtain the appropriate pulse signal to Int. Power Electronics Conference, 2010, pp. 1657-1664.
[4] X. Liang, “Emerging power quality challenges due to integration of
control the switching pattern of the inverter. This method is
renewable energy sources”, IEEE Trans. Industry Applications, vol. 53,
easy to implement and requires small response time [52]. Other no. 2, pp. 855-866, 2017.
techniques such as the hysteresis current control technique [5] IEEE Std 929-2000, “IEEE Recommended Practice for Utility Interface
[47][53], the Space Vector Pulse Width Modulation (SVPWM) of Photovoltaic (PV) Systems”, 2000.
[6] G. L. Campen, “An analysis of the harmonics and power factor effects
based current control [46][54], sliding mode control, dead-beat at a utility intertied photovoltaic system”, IEEE Trans. Power Apparatus
control, fuzzy logic based control etc. are reported in the and Systems, Vol. PAS-101, No. 12, pp. 4632-4639, 1982.
literature [55][56]. [7] D. Ronanki, P. H. Sang, V. Sood, and S. S Williamson, “Comparative
assessment of three-phase transformerless grid-connected solar
inverters”, in Proc 2017 IEEE International Conference on Industrial
Technology (ICIT), pp. 66-71, 2017.
[8] D. Cyganski, J. A. Orr, A. K. Chakravorti, A. E. Emanuel, E. M.
Gulachenski, C. E. Root, and R. C. Bellemare, “Current and voltage
harmonic measurements and modeling at the Gardner photovoltaic
project”, IEEE Trans. Power Delivery, Vol. 4, No. 1, pp. 800 – 809,
1989.
[9] A. R. Oliva, and J. C. Balda, “A PV dispersed generator: a power quality
analysis within the IEEE 519”, IEEE Trans. Power Delivery, Vol. 18.
No. 2, pp. 525-530, 2003.
[10] M. A. Awadallah, B. Venkatesh, and B. N. Singh, “Impact of solar panels
on power quality of distribution networks and transformers”, Canadian
Journal of Electrical and Computer Engineering, vol. 38, no. 1, pp. 45-
51, 2015.
[11] R. K. Varma, and M. Salama, “Large-Scale Photovoltaic Solar Power
Integration in Transmission and Distribution Networks”, 2011 IEEE
Power and Energy Society General Meeting, pp. 1-4, 2011.
Fig. 20 Using DPC method - Source voltage, source current, DC side capacitor [12] R. K. Varma, S. A. Rahman, T. Vanderheide, and M. D. N. DANG,
voltage and filter current waveforms, filter switched on [49]. “Harmonic impact of a 20-MW PV solar farm on a utility distribution
network”, IEEE Power and Energy Technology Systems Journal, vol. 3,
V. CONCLUSION no. 3, pp. 89-98, 2016.
[13] R. Langella, A. Testa, J. Meyer, F. Möller, R. Stiegler, and S. Z. Djokic,
In this paper, harmonics generated by PV systems are firstly “Experimental-based evaluation of PV inverter harmonic and
interharmonic distortion due to different operating conditions”, IEEE
reviewed based on field measurements and lab experiments
Trans. Instrumentation and Measurement, vol. 65, no. 10, pp. 2221-
reported in the literature. It is found that industry practice 2233, 2016.
through field measurements did not include high frequency [14] R. Torquato, W. Freitas, G. R. T. Hax, A. R. Donadon, and R. Moya,
harmonics, which poses serious harmonic evaluation concerns. “High frequency harmonic distortions measured in a Brazilian solar
farm”, 2016 17th International Conference on Harmonics and Quality
Characteristic harmonic bands at the PWM VSI output are of Power (ICHQP), pp. 623 – 627, 2016.
located around multiples of the switching frequency of the [15] S. Favuzza, F. Spertino, G. Graditi, and G. Vitale, “Comparison of power
inverter, which corresponds to high frequencies. Therefore, quality impact of different photovoltaic inverters: The viewpoint of the
grid”, in Proc. IEEE International Conference on Industrial Technology
more accurate field measurements and lab testing data for (ICIT), Vol. 1, pp. 542-547, 2004.
harmonics generated by large solar farms and small residential [16] G. Chicco, J. Schlabbach, and F. Spertino, “Characterisation and
and commercial PV panels are needed for future research, and assessment of the harmonic emission of grid-connected photovoltaic
systems”, in Proc. IEEE Russia Power Tech (PowerTech2005), pp. 1-7,
high frequency harmonics must be considered in harmonic 2005.
measurement and evaluation of PV systems. [17] I. T. Papaioannou, M. C. Alexiadis, C. S. Demoulias, D. P. Labridis, and
Various state-of-art control techniques are summarized for a P. S. Dokopoulos, “Modeling and field measurements of photovoltaic
units connected to LV grid. Study of penetration scenarios”, IEEE Trans.
DG interfacing inverter providing ancillary harmonic Power Delivery, Vol. 26. No. 2, pp. 979-987, 2011.
compensation in addition to its major power delivery function. [18] X. Liang, and R. Adedun, “Load harmonics analysis and mitigation”,
Virtual impedance based control methods for grid-connected 48th IEEE Industrial & Commercial Power Systems Conference, pp. 1-
8, 2012.
renewable energy sources show great potential in this area. It is
[19] X. Liang, S.O. Faried, and O. Ilochonwu, "Subsea Cable Applications in
recommended that more advanced virtual impedance based Electrical Submersible Pump Systems", IEEE Trans. Industry
control systems should be developed and explored in the future. Applications, Vol. 46, No. 2, pp. 575-583, 2010.
[20] X. Liang, N. C. Kar, and J. Liu, "Load Filter Design Method for Medium
Voltage Drive Applications in Electrical Submersible Pump Systems",
VI. REFERENCES IEEE Trans. Industry Applications, Vol. 51, No. 3, pp. 2017-2029, 2015.
[1] A. Chidurala, T. K. Saha, N. Mithulananthan, and R. C. Bansal, [21] H. Hu, Q. Shi, Z. He, J. He, and S. Gao, “Potential harmonic resonance
"Harmonic emissions in grid connected PV systems: A case study on a impacts of PV inverter filters on distribution systems”, IEEE Trans.
large scale rooftop PV site," in Proc. IEEE PES General Meeting, Sustainable Energy, vol. 6, no. 1, pp. 151-161, 2015.
Conference & Exposition, 2014, pp. 1-5.

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This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TIA.2018.2823680, IEEE
Transactions on Industry Applications

[22] O. S. Nduka, and B. C. Pal, “Harmonic Domain Modeling of PV System [42] B. Singh, K. A. Haddad, and A. Chandra, "A review of active filters for
for the Assessment of Grid Integration Impact”, IEEE Trans. Sustainable power quality improvement," IEEE Trans. Industrial Electronics, vol.
Energy, vol. 8, no. 3, pp. 1154-1165, 2017. 46, no.5, pp. 960-971, Oct 1999.
[23] T. Kuczek, M. Florkowski, and W. Piasecki, “Transformer switching [43] S. Devassy, and B. Singh, “Modified pq-theory-based control of solar-
with vacuum circuit breaker: case study of PV inverter LC filters impact PV-integrated UPQC-S”, IEEE Trans. Industrial Applications, vol. 53,
on transient overvoltages”, IEEE Trans. Power Delivery, Vol. 31, No. 1, no.5, pp. 5031 - 5040, September/October 2017.
pp. 44-49, 2016. [44] D. H. Pontoriero and P. E. Mercado, "Network compensation with active
[24] S. Munir and Y. W. Li, "Residential distribution system harmonic power filters integrated to PV generation," in Proc. IEEE Porto Power
compensation using PV interfacing inverter," IEEE Trans. Smart Grid, Tech, 2001, pp. 1-6.
vol. 4, no. 2, pp. 816-827, Jun 2013. [45] R. Belaidi, M. Hatti, A. Haddouche, and M. Mghezzi Larafi, "Shunt
[25] Y. W. Li and J. He, "Distribution system harmonic compensation active power filter connected to a photovoltaic array for compensating
methods: An overview of DG-interfacing inverters," IEEE Industrial harmonics and reactive power simultaneously," in Proc. IEEE 4th Int.
Electronics Magazine, vol. 8, no. 4, pp. 18-31, Dec 2014. Conf. Power Engineering, Energy and Electrical Drives, 2013, pp. 1482-
[26] J. He and Y. W. Li, "Generalized microgrid harmonic compensation 1486.
strategies using DG unit interfacing converters," in Proc. IEEE [46] N. Mendalek and K. A. Haddad, "Modeling and nonlinear control of
Industrial Electronics Society Annual Conference, 2012, pp. 3419-3424. shunt active power filter in the synchronous reference frame," in Proc.
[27] J. He, Y. W. Li, X. Wang, and F. Blaabjerg, "An improved current IEEE 9th Int. Conf. Harmonics and Quality of Power, 2000, pp. 30-35.
control scheme for grid-connected DG unit based distribution system [47] Q. Yao and D. G. Holmes, "A simple, novel method for variable-
harmonic compensation," in Proc. IEEE 28th Annual Applied Power hysteresis-band current control of a three phase inverter with constant
Electronics Conference and Exposition, 2013, pp. 986-991. switching frequency," in Proc. IEEE Industry Applications Society 28th
[28] R. Teodorescu, F. Blaabjerg, and M. Liserre, "Proportional-resonant Annual Meeting, 1993, pp. 1122-1129.
controllers. A new breed of controllers suitable for grid-connected [48] A. Chaoui, F. Krim, J. Gaubert, and L. Rambault, "DPC controlled three-
voltage-source converters," in Proc. OPTIM, 2004, pp. 9-14. phase active filter for power quality improvement," Int. Journ. Electrical
[29] F. Blaabjerg, R. Teodorescu, M. Liserre, and A. V. Timbus. "Overview Power & Energy Systems, vol. 30, no. 8, pp. 476-485, Oct 2008.
of control and grid synchronization for distributed power generation [49] A. Chaoui, J. Gaubert, and F. Krim, "Power quality improvement using
systems," IEEE Trans. Industrial Electronics, vol. 53, no. 5, pp. 1398- DPC controlled three-phase shunt active filter," Electric Power Systems
1409, Oct 2006. Research, vol. 80, no. 6, pp. 657-666, Jun 2010.
[30] J. He, Y. W. Li, and M. S. Munir, "A flexible harmonic control approach [50] A. Boukezata, A. Chaoui, J. P. Gaubert, and M. Hachemi, "Improving
through voltage-controlled DG–grid interfacing converters," IEEE the quality of energy in grid connected photovoltaic systems," in Proc.
Trans. Industrial Electronics, vol. 59, no. 1, pp. 444-455, Jan 2012. IEEE 3rd Int. Conf. Systems and Control, 2013, pp. 1122-1126.
[31] N. Pogaku and T.C. Green, “Harmonic mitigation throughout a [51] S. Saidi, R. Abbassi, and S. Chebbi, "Power quality improvement using
distribution system: a distributed-generator based solution,” IEE Proc. VF-DPC-SVM controlled three-phase shunt active filter," in Proc. IEEE
Gener. Transm. Distrib., vol. 153, no. 3, pp. 350- 358, 11 May 2006. 12th Int. Conf. Systems, Signals & Devices, 2015, pp. 1-5.
[32] M. Kosari, and S. H. Hosseinian, “Decentralized reactive power sharing [52] H. A. Kazem, “Harmonic Mitigation Techniques Applied to Power
and frequency restoration in islanded microgrid”, IEEE Trans Power Distribution Networks,” Advances in Power Electronics, vol. 2013, pp.
Systems, Vol. 32, No. 4, pp. 2901-2912, 2017. 1-10, Jan 2013.
[33] S. Bhattacharya, and S. Mishra, “Efficient power sharing approach for [53] R. Sunny and R. Anto, "Harmonics control and performance analysis of
photovoltaic generation based microgrids”, IET Renew. Power Gener., a grid connected photovoltaic system," in Proc. IEEE Int. Conf.
Vol. 10, No. 7, pp. 973–987, 2016. Advanced Computing and Communication Systems, 2013, pp. 1-6.
[34] M. Kallamadi, and V. Sarkar, “Enhanced real-time power balancing of [54] H. Zhang, H. Zhou, J. Ren, W. Liu, S. Ruan, and Y. Gao, "Three-phase
an AC microgrid through transiently coupled droop control”, IET Gener. grid-connected photovoltaic system with SVPWM current controller," in
Transm. Distrib., Vol. 11 Iss. 8, pp. 1933-1942, 2017. Proc. IEEE 6th Int. Power Electronics and Motion Control Conference,
[35] C. Andalib-Bin-Karim, X. Liang, and H. Zhang, “Fuzzy secondary 2009, pp. 2161-2164.
controller based virtual synchronous machine control scheme for [55] M. Hojabri, A. Z. Ahmad, A. Toudeshki, and M. Soheilirad, "An
microgrids”, in Proc. 2017 IEEE Industry Applications Society (IAS) overview on current control techniques for grid connected renewable
Annual Meeting, pp. 1-14, 2017. energy systems," Int. Proceedings Computer Science and Information
[36] M. S. Munir, and Y. W. Li, "Harmonic compensation using residential Technology, vol. 56, pp. 119-126, 2012.
PV interfacing inverter," in Proc. IEEE Industrial Electronics Society [56] X. Liang, and C. Andalib-Bin-Karim, “Harmonic mitigation through
38th Annual Conference, 2012, pp. 5324-5329. advanced control methods in grid-connected renewable energy sources”,
[37] C. Blanco, D. Reigosa, J. C. Vasquez, J. M. Guerrero, and F. Briz, in Proc of 2017 IEEE Industry Applications Society (IAS) Annual
“Virtual admittance loop for voltage harmonic compensation in Meeting, pp. 1-12, 2017.
microgrids”, IEEE Trans Industry Applications, Vol. 52, No. 4, pp. 3348
– 3356, 2016.
[38] J. He and Y. W. Li, "Hybrid voltage and current control approach for Xiaodong Liang (M’06–SM’09) was born in
DG-grid interfacing converters with LCL filters," IEEE Trans. Industrial Lingyuan, China. She received the B.Eng. and
Electronics, vol. 60, no. 5, pp. 1797-1809, May 2013. M.Eng. degrees from Shenyang Polytechnic
[39] J. He, Y. W. Li, and F. Blaabjerg, "Flexible microgrid power quality University, Shenyang, China in 1992 and 1995,
enhancement using adaptive hybrid voltage and current controller," respectively, the M.Sc. degree from the University
IEEE Trans. Industrial Electronics, vol. 61, no. 6, pp. 2784-2794, Jun of Saskatchewan, Saskatoon, Canada in 2004, and
2014. the Ph.D. degree from the University of Alberta,
[40] R. A. Mastromauro, M. Liserre, T. Kerekes, and A. Dell'Aquila, "A Edmonton, Canada in 2013, all in Electrical
single-phase voltage-controlled grid-connected photovoltaic systems Engineering. Her research interests include power
with power quality conditioner functionality," IEEE Trans. Industrial system dynamics, power quality, renewable energy,
Electronics, vol. 56, no. 11, pp. 4436-4444, Nov 2009. and electric machines.
[41] L. B. G. Campanhol, S. A. O. d. Silva, A. A. d. Oliveira, V. D. Bacon, " From 1995 to 1999, she served as a lecturer at Northeastern University,
Single-stage three-phase grid-tied PV system with universal filtering Shenyang, China. From October 2001 to August 2013, she was an Engineer
capability applied to DG systems and AC microgrids", IEEE Trans. with Schlumberger in Edmonton, Canada, and was promoted to be a Principal
Power Electronics, vol. 32, no.12, pp. 9131 - 9142, Dec 2017. Power Systems Engineer with this large oil service company in 2009. After
serving Schlumberger for almost 12 years, from August 2013 to May 2015,
she worked with Washington State University in Vancouver, Washington,

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This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TIA.2018.2823680, IEEE
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United States as an Assistant Professor. In July 2015, she joined Memorial

University of Newfoundland in St. John’s, Canada as an Assistant Professor,
where she’s promoted to be an Associate Professor in September 2018.
Dr. Liang is a registered professional engineer in the province of
Newfoundland and Labrador, Canada.

Chowdhury Andalib-Bin-Karim (S’17) was born

in Chittagong, Bangladesh. He received the B.Sc.
in Electrical and Electronic Engineering degree
from Islamic University of Technology (IUT),
Bangladesh in 2013. His research interests include
power system dynamics, power quality, and
renewable energy grid integration. From 2013 to
2015, he served as a lecturer at Bangladesh
University, Dhaka, Bangladesh. From January
2016 to December 2017, he was a Master’s of
Engineering student at Memorial University of
Newfoundland, St. John’s, Canada.

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