JEECS (Journal of Electrical Engineering and Computer Science.
Vol.
No.
June 2026, pp.
e-ISSN: 2579-5392 p-ISSN: 2528-0260 Harmonic Performance in Hybrid AC-DC Microgrid Connected Bidirectional Converter with LCL Filter Hasti Afianti.
Ahmadi.
Saidah.
Richa Watiasih.
Bambang Purwahyudi Department of Electrical Engineering.
Faculty of Engineering.
Universitas Bhayangkara Surabaya.
Jl.
Ahmad Yani 114.
Surabaya, 60231.
Indonesia Article Info Article history:
Received: 25 February 2026 Revised: 2 May 2026 Accepted: 18 May 2026 Keyword:
AC-DC microgrid Bidirectional converter Grid connected inverter Hybrid LCL filter Abstract This paper presents the harmonic performance of a grid-connected hybrid AC-DC microgrid.
Using solar power as a source in the DC microgrid and the grid in the AC microgrid eliminates the need for energy storage.
Solar power generation is known to be intermittent, requiring a power supply to meet the load demand in the DC microgrid.
Therefore, a converter that can operate as both an inverter and a rectifier is required.
One way to address this issue is to use a bidirectional AC-DC converter (BC).
To perform its function, this converter requires a filter to reduce the switching frequency ripple current injected into the grid.
Among the available options, the LCL filter is widely recognized as the most effective solution for suppressing switching frequency harmonics.
In this study, the performance of the LCL filter will be analyzed through simulations using MATLAB/Simulink.
The results show that the bidirectional AC-DC converter designed with the LCL filter effectively suppresses resonances occurring at the converter output in rectifier or inverter mode.
, the voltage in the AC microgrid remained stable, the THD stayed below 5%, and the system frequency was well maintained.
However, during the standby period, when the power transfer in both the DC and AC microgrids is zero, the THD on the grid remains high, up to 200%.
Corresponding author:
Hasti Afianti, hasti_afianti@ubhara.
DOI: https://doi.
org/10.
54732/jeecs.
This is an open access article under the CCAeBY license.
Introduction Lasseter with his new electricity concept, distribution generators that supply the surrounding load into a subsystem or microgrid of the distribution system makes the starting point of change in the conventional electricity .
Research on microgrid has been growing.
AC microgrids.
DC microgrids, and combination of them was known as hybrid AC-DC microgrids .
, .
On an AC microgrid, there are main buses that use the AC system, as well as on DC microgrids, where the main bus uses the DC system.
In both types of microgrid, both source and load will use the system on the main bus type is described in many researchs .
, .
, .
A hybrid AC-DC microgrid system is the combination of the two.
There are two central buses.
DC bus and AC bus, and they are connected with an interlinking converter as illustrated in Figure 1.
The interlinking converter has a very important role.
This power electronics equipment is expected to be able to flow power from an AC microgrid to a DC microgrid if the power generated by a DC source cannot supply the load power Conversely, if a DC source produces excess power from the DC load requirements, this converter must be able to transfer this excess power to the AC microgrid to be traded.
That is way better use AC-DC bidirectional converter for an interlinking converter.
Even now, many microgrid systems with DER do not use batteries or storage systems .
, .
Power delivered by these converters must be of high quality .
However, the switching actions of semiconductor devices introduce harmonics into the voltage and current waveforms, which are very dangerous for electric power system equipment and must be prevented from entering the network .
, .
Available online: https://ejournal.
id/jeecs | 67 | JEECS (Journal of Electrical Engineering and Computer Science.
Vol.
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June 2026, pp.
e-ISSN: 2579-5392 p-ISSN: 2528-0260 The most effective filter for suppressing of the current harmonics occurring from the switching frequency injected into the grid is the LCL filter, than L filter .
The LCL filter must be designed appropriately to achieve high quality grid currents.
More specifically, the inverter-side inductor plays a key role in reducing the maximum ripple of the inverter output current.
In general, the maximum current ripple decreases as the value of inverter-side inductor increases.
However, increasing inverter-side inductor also makes the filter bulkier and more expensive.
Therefore, a reasonable compromise must be reached between the selected value of inverter-side inductor and the allowable current ripple .
, .
The capacitor.
in the middle branch of the LCL filter provide a low-impedance path for highfrequency ripple currents and help prevent switching harmonics from propagating into the grid.
To limit reactive power injection and avoid resonance issues, it is commonly recommended that the capacitor size in LCL filters should not exceed approximately 5% of the systemAos nominal capacitance .
, .
Comprehensive investigation of the LCL filter component values using conventional mathematical theory can actually increase the stability and THD values of current and voltage .
Using ANN-based MPPT replaces conventional "trial-and-error" algorithms like Perturb and Observe (P&O), significantly reducing voltage ripples and switching-induced noise that contribute to harmonic distortion in grid-tied PV systems, 3-5% THD reduction is typical in optimized designs .
The Crown Porcupine Optimization (CPO) algorithm improves steady-state stability in microgrids by automating the tuning of control parameters to reduce non-linear distortions, thereby reducing THD from double digits to below 4% .
In this paper, the LCL filter in an AC-DC bidirectional converter connected to hybrid AC-DC microgrids was built by Simulink / Matlab.
The built system is connected to a grid without a storage system.
The simulation is carried out by providing power and load changes to prove the control performance compact the LCL filter of the bidirectional converter working properly.
The power changes occur, followed by changes in load.
Section II described the system configuration with the bidirectional converter, followed by the simulation and discussion in Section i.
This section discusses the converter in the standby mode, which has never been done in another paper, and the conclusion in Section IV.
Research Methodology Power Flow in Hybrid AC-DC Microgrid This system is composed of three major components: the DC microgrid, the AC microgrid, and the bidirectional AC-DC converter as an interlinking converter, as presented in Figure 1.
The DC microgrid includes DC sourcesAisuch as photovoltaic (PV) panels and fuel cellsAithat supply power to DC loads.
Meanwhile, the hybrid ACAeDC microgrid is connected to the main utility grid, which serves as the AC power The main grid is expected to provide both real .
and reactive power to the network, supporting operation on both the AC microgrid side and the DC microgrid through the interlinking In this configuration, the grid not only helps maintain overall power balance but also contributes to system stability.
Specifically, the gridAos active and reactive power support voltage and frequency regulation throughout the entire hybrid AC-DC microgrid .
, .
Microgrid Microgrid Interlinking Converter Load Load Figure 1.
Power flow in hybrid AC-DC microgrid Available online: https://ejournal.
id/jeecs | 68 | JEECS (Journal of Electrical Engineering and Computer Science.
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e-ISSN: 2579-5392 p-ISSN: 2528-0260 Case 1.
Oc ycEyayaycIycuycycycayce > Oc ycEyayayaycuycaycc Whare Oc ycEyayaycIycuycycycayce is the combined power generated including solar PV and battery .
, and Oc ycEyayayaycuycaycc is the total power of the DC load and battery in charging state.
In this case, the DC microgrid power generation Oc ycEyayaycIycuycycycayce exceeds load consumption.
The exceed power flows to the AC sub grid through BC, which can be calculated as.
ycEyaAya = Oc ycEyayaycIycuycycycayce Oe Oc ycEyayayaycuycaycc Oe Oc ycEyayayaycuycyc Whare Oc ycEyayayaycuycyc represents the power loss induced by DC/DC converter and line impedance.
In this situation The BC is in inverter mode.
Case 2.
Oc ycEyayaycIycuycycycayce < Oc ycEyayayaycuycaycc Power flow from AC to DC microgrid through BC occurs, as the residual power induced by the difference between Oc ycEyayaycIycuycycycayce and DC load power consumption is negative, ycEyaAya < 0.
In this situation The BC is in rectivier mode.
Case 3.
Oc ycEyayaycIycuycycycayce = Oc ycEyayayaycuycaycc The power is balanced in the DC microgrid and there is no power flow between AC and DC microgrid.
Hence, ycEyaAya = 0.
In grid-tied state.
AC bus voltage/frequency is controlled by utility grid (UG).
BC power flow is determined by the power balance in DC microgrid.
The BC is in standby mode without active power transmission .
2 AC-DC Bidirectional Converter With LCL Filter The interlinking converter connects the DC microgrid with the AC microgrid.
It is implemented using a six-switch .
ix-IGBT) bridge configuration, as illustrated in Figure 2.
The converter receives control inputs from both sides: on the AC side, the controller uses measured grid current and voltage, while on the DC side it uses the DC bus voltage.
By utilizing feedback from both microgrids, the converter can operate bidirectionally functioning either as a rectifier or as an inverter.
This allows it to convert DC power to AC power or AC power to DC power, depending on the instantaneous power requirements and availability on each side of the hybrid microgrid.
Figure 2 illustrates the topology of AC-C bidirectional converter equipped with LCL filter.
The load voltage is denoted as udc , while vdc represents the DC voltage source used to enable bidirectional power Zac Load consist of a resistor and an inductor as a load in AC sub- microgrid .
The filter network consists of L1 Ae Cf Ae L2 forming an LCL structure.
It is well established that, in the lowfrequency range, an LCL filter behaves similarly to a single-inductor filter .
Where the equivalent inductance and resistance are L = L1 L2 Lac Load and R = R1 R2 Rac Load.
Therefore, the low-frequency mathematical model of the LCL filter can be obtained by neglecting the filter capacitor C f .
Figure 2.
Hybrid AC-DC microgrid with bidirectional converter circuit Available online: https://ejournal.
id/jeecs | 69 | JEECS (Journal of Electrical Engineering and Computer Science.
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June 2026, pp.
e-ISSN: 2579-5392 p-ISSN: 2528-0260 Rectifier Mode In rectifier operation, the AC source delivers power through the converter to the DC side.
Using the low-frequency approximation of the LCL filter.
Whare the ex is grid voltage source, and ix is the phase current .
2yuUyco yceycu = yayco cos.
uiyc Oe 3 ) .
2yuUyco ycnycu = yayco cos.
uiyc Oe 3 ) .
Where k = 0, 1, 2 and x = a, b, c respectively, and O is the grid frequency in rad/s.
The per-phase equivalent circuit is given as:
yccycn ya yccycycu ycIycnycu = yceycu Oe ycycu = yceycu Oe .
cycuycA ycycA0 ) .
The converter side phase to neutral voltage ycycuycA and the neutral to ground voltage ycycA0 can be expressed as follows:
ycycuycA = ycyccyca ycIycu yc Where ycIycu is the switching function.
ycycA0 = Oe 3yccyca Ocycu=yca,yca,yca ycIycu 1, ycIycu ycuyccycc ycnyc ycuycu ycaycuycc ycIycu yceycyceycu ycnyc ycuyceyce 0, ycIycu yceycyceycu ycnyc ycuycu ycaycuycc ycIycu ycuyccycc ycnyc ycuyceyce By substituting Equations .
, and .
into equation .
, one can obtain:
yccycn ya ycu ycIycnycu = yceycu Oe ycycu = yceycu Oe ycyccyca .
cIycu Oe Ocycu=yca,yca,yca ycIycu ) ycIycu = { yccyc The DC current can be expressed as a function of three phase current:
ycnyccyca = ycIyca ycnyca ycIyca ycnyca ycIyca ycnyca A group of differential equations can be formulated in matrix form as shown in Equation .
ycIyca Oe 3 Ocycu=yca,yca,yca ycIycu ya yccycyca ycI .
cnyca ] = .
ceyca ] Oe ycyccyca ycIyca Oe 3 Ocycu=yca,yca,yca ycIycu [ ycIyca Oe 3 Ocycu=yca,yca,yca ycIycu ] [ yccyc ] .
ycIyca ] .
cnyca ] Oe yccyca Oe ycnyayccyca ycIyayccyca ycnyca For control design, the three-phase variables in the stationary abc frame are transformed into the synchronous rotating dq frame using the Park transformation.
Applying this transformation to the perphase loop equation, equation 4 becomes:
ya yccycyccyca = .
cIyca ycIyca ccycn ] ycI .
cn ] = [ yce ] [ yc Oeyuiya yuiya ycnycc ] [ ] Oe .
cIycc ] ycyccyca 0 ycnyc yccyc ycn ycIyc ] [ ycc ] Oe ycyccyca Oe ycnyayccyca ycnyc ycIyayccyca Where yceyccyc is the magnitude of the source voltage vector yccyc ya yccycyccyca = 2 .
cIycc .
Inverter Mode In inverter operation, the DC source delivers power to the converter, and the energy flows from the DC side back to the AC side.
Although the direction of power reverses, the electrical path and filter dynamics remain the same.
therefore, the differential equation is obtained by reversing the relative polarity between the converter voltage and the grid voltage in the per-phase loop.
Thus, the per-phase dynamic equation in inverter mode becomes:
yccycnyca ycIyca Oe 3 Ocycu=yca,yca,yca ycIycu yccyc yceyca ycnyca yccycnyca Oc ya ycI .
cnyca ] = ycyccyca ycIyca Oe 3 ycu=yca,yca,yca ycIycu Oe .
ceyca ] .
yccyc yceyca ycnyca yccycnyca .
cIyca Oe 3 Ocycu=yca,yca,yca ycIycu ] [ yccyc ] Available online: https://ejournal.
id/jeecs | 70 | JEECS (Journal of Electrical Engineering and Computer Science.
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June 2026, pp.
e-ISSN: 2579-5392 p-ISSN: 2528-0260 ycnyca yc ycIyca ] .
cnyca ] Oe yccyca ycnyayccyca ycIyayccyca ycnyca Using the Park transformation, one can obtain:
ya yccycyccyca = Oe.
cIyca .
ycIyca ycIycc ccycn ] ycI .
cn ] = ycyccyca .
cI ] [ yc Oeyuiya yuiya ycnycc ] .
cn ] Oe [ yce ] yc ya yccycyccyca = Oe 2 .
cIycc ycn ycIyc ] [ ycc ] Oe ycyccyca ycnyayccyca ycIyayccyca Results and Discussions System modeling is done as shown in Figure 2 and explained in Section 2.
The DC microgrid has one 600-volt DC source, each connected to a fixed 1 kW load, while the power from the DC source will be regulated to determine the system response.
In the AC microgrid, a 4 MW generator with a voltage of 400 V, a frequency of 50 Hz and a transmission with an R/X ratio of 7, is connected to the load to be regulated.
The simulation algorithm is started by setting the power source conditions in the DC microgrid as explained in Figure 5.
During the simulation, two cases are considered: power changes in the DC microgrid and load changes in the AC microgrid.
The simulation is carried out for 2 seconds with a schedule of power and load changes as shown in Figure 3 and Figure 4.
0 ,5 kW 5 kW 5,5 kW 10 kW 1 5 kW Time .
Figure 3.
The schedule of power changes Time .
Figure 4.
The schedule of load changes In this simulation, the analysis was performed at three locations of the hybrid microgrid system: the DC microgrid, the AC microgrid, and the bidirectional converter (BC).
Variations in the DC source power cause corresponding changes in the voltage and current of the DC microgrid.
Figure 6 illustrates the power flow at the DC resource, the DC load, and the power transferred through the BC.
When the DC power is very low or nearly zero .
or example, when the PV source receives no solar irradiatio.
, the BC transfers power from the AC microgrid to meet the DC load demand.
In this condition, the power transferred through the BC becomes negative.
When the DC power matches the DC load demand, the BC does not transfer power.
is indicated by the BC power value being close to zero.
Conversely, when the DC power exceeds the DC load demand .
, when the PV operates under maximum irradiatio.
, the BC power becomes positive, indicating that the DC microgrid is delivering excess power to the AC microgrid.
Figure 7 presents a comparison of the active power at the AC load, the grid, and the power transferred to the DC microgrid.
Variations in the AC microgrid load during the simulation have minimal influence on the power transferred to the DC microgrid.
The transferred power becomes negative when the grid supplies power to the system, while a positive grid power value indicates that the grid is receiving power from the DC microgrid.
The power conditions within the AC microgrid corresponding to these operating states are summarized in Table 1.
The impact of power variations on the DC source can be observed not only within the DC microgrid but also in the AC microgrid.
Based on the DC power changes and the AC load variations shown in Figure 3 and Figure 4, the bidirectional converter operates alternately as a rectifier or an inverter, depending on the system conditions.
Despite these fluctuations in power and load, the voltage in the AC microgrid remains stable and is properly maintained throughout the simulation.
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e-ISSN: 2579-5392 p-ISSN: 2528-0260 Start Read source and load Power in DC Psource = Pload Yes Idc = 0 BC Standby Mode Psource < Pload Idc > 0 Yes Idc < 0 BC Inverter Mode BC Rectifier Mode End Figure 5.
Simulation Algorithm Figure 6.
DC microgrid power Figure 7.
AC sub microgrid active power Table 2 presents the efficiency of the converter operating in both rectifier and inverter modes.
The results demonstrate that the converter can operate with very high efficiency under most conditions.
However, it still encounters challenges in maintaining consistent performance when the AC and DC microgrid power levels are similar, particularly when the power transfer approaches zero.
This limitation is evident from the relatively low efficiency of 65,95% at a DC microgrid power of 5kW, compared to the significantly higher efficiency of 99.
62% achieved at 15 kW.
This issue has not been addressed in previous studies and should be considered an important topic for future research.
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e-ISSN: 2579-5392 p-ISSN: 2528-0260 Table 1.
AC microgrid power
DC Power
(W)
0,5 103
5,5 103
Measureme nt Point
Active
Power / P
(W)
Reactive Power / Q
(VAR)
Source Load
Line
Transfer
Source Load
Line
Transfer
Source Load
Line
Transfer
Source Load
Line
Transfer
Source Load
Line
Transfer
-34,63
-285,3
1,33.
-997,4
-7,63.
-615,7
7,839.
-348,7
-1,68.
Table 2.
Efficiency of bidirectional converter (BC) BC interface power
DC Power
(W)
Efficiency BC Mode
(W)
0,5 103
99,39 %
Rectifier -34,63 52,51 65,95 % Rectifier 5,5 103
97,24 %
Inverter
99,55 %
Inverter
99,62 %
Inverter A different behavior is observed in the current waveform: the AC microgrid current changes not only in magnitude but also in its phase angle relative to the voltage.
In the initial condition shown in Figure 7, both voltage and current remain stable because no power or load variations have yet occurred.
However, the current leads or lags the voltage, indicating that the BC is operating in rectifier mode.
When the power supplied by the DC source is insufficient to meet the DC load demand, additional power is drawn from the AC microgrid.
At 0.
75 s, the DC power increases to a level that matches the load requirements, and the AC microgrid current reduces to nearly zero.
This indicates that no current is flowing through the BC.
At this moment, the BC is not functioning as either a rectifier or an inverter.
Despite this, a phase shift of approximately 90A between the voltage and current is still observed.
Up to 1.
25 s, the power generated in the DC microgrid increases and eventually exceeds the DC load The excess power flows through the BC toward the AC microgrid, causing the phase shift between current and voltage to approach 180A, indicating that the BC has transitioned to inverter mode.
At 1.
6 s, the DC power increases again.
Since the DC load is already fully supplied, the additional surplus power continues to be delivered to the AC microgrid through the BC.
This change affects the magnitude of the current but does not alter the BCAos operating mode.
it remains functioning as an inverter.
The system variations that occur during the simulation also influence the harmonic content, as illustrated in Figure 8 through 11.
The total harmonic distortion (THD) values closely follow the power fluctuations in the DC microgrid, rather than the load variations in the AC microgrid.
Figure 8 presents the THD of the voltage measured at the output of the bidirectional converter (BC), while Figure 9 shows the THD after the voltage has been filtered by the LCL filter.
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e-ISSN: 2579-5392 p-ISSN: 2528-0260 Figure 8.
THD voltage in bidirectional converter side Figure 9.
THD voltage in AC microgrid side Figure 10.
THD current in bidirectional converter side Figure 11.
THD current in AC microgrid side Figure 10 presents the THD of the current measured at the output of the BC.
The figure shows that the current THD increases significantly during periods of power imbalance.
Specifically, between 0.
4 s and 1.
s, the power generated by the DC source is only sufficient to supply the DC load, causing the BC to operate in neither rectifier nor inverter mode.
This operating condition results in substantial harmonic distortion that exceeds the allowable limits.
Even after compensation by the LCL filter, the harmonic content during this interval remains high, as illustrated in Figure 11.
This is a logical event because the fundamental current flowing at that time is close to zero, where this current is a divider of the total current of other orders, this causes a drastic increase in the overall THD value.
Outside of this period, the THD values return to acceptable levels and comply with the required standards.
For further research, real-time testing of this system in more complex environments, such as adding more load models and renewable energy conditions, will bring the system closer to real-world conditions.
Furthermore, research combining bidirectional ac-dc control with artificial intelligence (AI) instruments, as has been done by several researchers .
, .
, will make the system more efficient in terms of overall system performance.
Conclusion In this paper, a hybrid ACAeDC microgrid system was developed using a bidirectional converter (BC) capable of operating in both rectifier and inverter modes.
The system performed effectively, with the BC responding appropriately to power fluctuations within the DC microgridAiwhether due to an increase or decrease in available Throughout these variations, the voltage in the AC microgrid remained stable, the THD stayed below 5%, and the system frequency was well maintained.
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e-ISSN: 2579-5392 p-ISSN: 2528-0260 Load variations in the AC microgrid did not significantly influence the power transferred through the BC.
however, they did affect the power drawn from or supplied to the AC grid.
Although the LCL filter provides strong harmonic attenuation under steady operating conditions, its performance is compromised during transitions in the BCAos operating mode .
rom rectifier to inverter and vice versa, standby mod.
During these transitions, resonance effects can occur within the LCL filter, preventing effective harmonic damping and temporarily increasing the systemAos THD.
Acknowledgement The author gratefully acknowledges the financial support from the Directorate of Research and Community Service.
Ministry of Higher Education.
Science, and Technology of the Republic of Indonesia.
References