Study of Control Strategies for Shunt Active Power Filter for Harmonics Suppression


Excessive use of nonlinear and time changing devices results in harmonic currents in the secondary distribution system. The suppression of harmonics is a main issue and one of the practical ways to compensate harmonics is shunt active power filter (SAPF). The core part of the SAPF is control techniques used for reference current generation. This paper presents a comprehensive study of three control strategies namely instantaneous reactive power (p – q) theory.


synchronous reference frame (SRF) theory and instantaneous active and reactive current (id – iq) component method for SAPF in a three phase three wire distribution system. These three control methods aims to pay harmonics, reactive power and load unbalance under sinusoidal balanced supply voltage conditions. Simulation results present a relative investigation of three control techniques based on current THD and load unbalance.


  1. Harmonics
  2. Hysteresis band current control (HBCC)
  3. Id – iq method
  4. Nonlinear loads
  5. P – q theory
  6. Shunt active power filter
  7. SRF theory



Fig. 1. SAPF connected to distribution grid


Fig. 2. Simulation results of SAPF with p-q theory under nonlinear balanced

load (a) Source voltage (b) Load current (c) Source current after filtering

(d) Compensation current.

Fig. 3. Simulation results of SAPF with id-iq method under nonlinear

balanced load (a) Source current after filtering (b) Compensation current

Fig. 4. Simulation results of SAPF with id-iq method under nonlinear

unbalanced load (a) Source voltage (b) Load current (c) Source current

after filtering (d) Compensation current.

Fig. 5. Dynamic performance of SAPF during load change with id-iq method

Load current (b) Source current (c) Compensation current.

Fig. 6. (a) Source voltage (V) and load current (A) (b) Source voltage (V)

and source current (A) (c) Compensation current (d) Reactive power

demand of the load (e) Reactive power supplied by the SAPF (f)

Reactive power supplied by the source.


 The harmonic distortions exist in the distribution system due to the massive use of power electronic based nonlinear loads. Harmonic distortions can result in serious problems such as increase in current, reactive VAs, VAs, power factor reduction and increase in losses. The SAPF with three control strategies viz. p-q theory, SRF theory and id-iq method has been studied in this paper.


The simulation has been carried out for different load scenarios and the THD, percentage of individual dominant harmonics has also observed. From the simulation analysis, it is observed that the SAPF giving quite reasonably good performance in compensating harmonics, reactive power and load unbalance. Among the three control techniques, it is noticed that the id-iq method gives reasonably better performance in terms of current THD.


[1] S. Rahmani, N. Mendalek, and K. Al-Haddad, “Experimental design of a nonlinear control technique for three-phase shunt active power filter,” IEEE Trans. Ind. Electron, vol. 57, no. 10, pp. 3364-3375, Oct. 2010.

[2] IEEE Recommended Practice and Requirements for Harmonic Control in Electric Power Systems – Redline,” IEEE Std 519-2014 (Revision of IEEE Std 519-1992) – Redline , pp.1-213, June 11 2014.

[3] S. Senini and P. J. Wolfs, “Hybrid active filter for harmonically unbalanced three phase three wire railway traction loads,” IEEE Trans. Power Electron., vol. 15, no. 4, pp. 702–710, Jul. 2000.

[4] S. Rahmani, K. Al-Haddad, H. Y. Kanaan, and B. Singh,

“Implementation and simulation of a modified PWM with two current control techniques applied to a single-phase shunt hybrid power filter,” Proc. Inst. Elect. Eng. Electr. Power Appl., vol. 153, no. 3, pp. 317–326, May 2006.

[5] B. Singh, K. Al-Haddad, and A. Chandra, “A review of active filters for power quality improvement,” IEEE Trans. Ind. Electron, vol. 46, no. 5, pp. 960-971, Oct 1999.

Harmonic Mitigation by SRF Theory Based Active Power Filter using Adaptive Hysteresis Control


Power quality is an all-encompassing concept for a multitude of individual types of power system disturbances. The presence of harmonics in power supply network poses a severe  power quality problem that results in greater power losses in the distribution system, interference problems in communication systems and, sometimes, in operation failures of electronic equipment. Shunt active power filters are employed to suppress the current harmonics and reduce the total harmonic distortion (THD).

The voltage source inverter (VSI) is the core of an active power filter. The hysteresis current control is a method of controlling the VSI. Hysteresis control can be either of fixed band type or adaptive band type. In this paper, Synchronous Reference Frame (SRF) theory is implemented for the generation of reference current signals for the controller. This paper investigates the effectiveness of the proposed model in harmonics currents mitigation by simulating a model of a three-phase three wire shunt active power filter based on adaptive hysteresis current control and SRF theory. Simulation results indicate that the proposed active power filter can restrain harmonics of electrical source current effectively

  1. Synchronous reference frame theory
  2. Adaptive hysteresis control
  3. Harmonic mitigation
  4. Shunt active filter
  5. Voltage source inverter



Fig. 1. Reference Current Generation Block



 Fig. 2. Nonlinear Load Currents

Fig. 3. Compensating APF Currents

Fig.4.Source currents after compensation

Fig.5. Harmonic analysis of source current with Adaptive Hysteresis Band


 In the adaptive band hysteresis control, the switching  frequency is nearly constant with respect to the system parameters and defined switching frequency. However, at low switching frequency case, the tracking is not as good as the one in high switching frequency. Obviously, a decrease in switching frequency results in an increase in the hysteresis bandwidth that causes the free operation of current error in a  wider range.

This higher low-frequency error, in turn, will lead to higher low order harmonics in the source current, and hence higher THD. Based on the above facts, the switching frequency should be kept as high as possible for better performances of adaptive band hysteresis current control.

The developed model has the following advantages:

  • Simplification of the power conversion circuit can be achieved.
  • (ii) Under the developed model, the performance of control strategy can be effectively examined without long simulation run time and convergence problem.

[I] L. A Moran, J. W. Dixon, “Active Filters”, Chapter 33 in “Power Electronics Handbook”, Academic Press, August 200 I, pp. 829-841.

[2] IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems, IEEE Standard 519-1992, 1993

[3] Singh, 8.; Chandra, A; AI-Haddad K. “Computer-Aided Modeling and Simulation of Active Power Filters”, Electric Power Components and Systems, 27: 11, 1227 -1241,1999

[4] L. Moran, 1. Dixon, J. Espinoza, R. Wallace “Using Active Power Filters to Improve Power Quality”, 5th Brasilian Power Electronics Conference, COBEP’99, 19-23 September 1999, pp 501-511.

[5] Massoud, AM. ; Finney, SJ.; Williams, B.W. “Review of harmonic current extraction techniques for an active power filter”, 11th International Conference on Harmonics and Quality of Power, pp 154 – 159,12-15 Sept. 2004

A Multilevel Inverter Structure based on Combination of Switched-Capacitors and DC Sources


This paper presents a switched-capacitor multilevel inverter (SCMLI) combined with multiple asymmetric DC sources. The main advantage of proposed inverter with similar cascaded MLIs is reducing the number of isolated DC sources and replacing them with capacitors. A self-balanced asymmetrical charging pattern is introduced in order to boost the voltage and create more voltage levels. Number of circuit components such as active switches, diodes, capacitors, drivers and DC sources reduces in proposed structure.

This multi-stage hybrid MLI increases the total voltage of used DC sources by multiple charging of the capacitors stage by stage. A bipolar output voltage can be inherently achieved in this structure without using single phase H-bridge inverter which was used in traditional SCMLIs to generate negative voltage levels. This eliminates requirements of high voltage rating elements to achieve negative voltage levels. A 55-level step-up output voltage (27 positive levels, a zero level and 27 negative levels) are achieved by a 3-stage system which uses only 3 asymmetrical DC sources (with amplitude of 1Vin, 2Vin and 3Vin) and 7 capacitors (self-balanced as multiples of 1Vin). MATLAB/SIMULINK simulation results and experimental tests are given to validate the performance of proposed circuit.

  1. Multi-level inverter
  2. Switched-capacitor
  3. Bipolar converter
  4. Asymmetrical
  5. Self-balancing



Fig (1) Three stage structure of the proposed inverter



 Fig (2) Waveform of the output voltage in (a) 50Hz and pure resistive load (b)

the inset graphs of voltage and current

 Fig (3) waveform of the output voltage in 50Hz with resistive-inductive load

 Fig (4) Capacitor’s voltage in 50Hz (a) middle stage (b) last stage


 In this paper, a multilevel inverter based on combination of multiple DC sources and switched-capacitors is presented. Unlike traditional converters which used H-bridge cell to produce negative voltage that the switches should withstand maximum output AC voltage, the suggested structure has the ability of generating bipolar voltage (positive, zero and negative), inherently. Operating principle of the proposed SCMLI in charging and discharging is carried out.

Also, evaluation of reliability has been done and because of high number of redundancy, there has been many alternative switching states which help the proposed structure operate correctly even in fault conditions. For confirming the superiority than others, a comprehensive comparison in case of number of devices and efficiency is carried out and shows that the proposed topology has better performance than others. For validating the performance, simulation and experimental results are brought under introduced offline PWM control method.


[1] L. G. Franquelo, J. Rodriguez, J. I. Leon, S. Kouro, R. Portillo, and M. A. M. Prats, “The age of multilevel converters arrives,” IEEE Trans. Ind. Electron. Mag., vol. 2, no. 2, pp. 28–39, June, 2008.

[2] M. Saeedifard, P. M. Barbosa and P. K. Steimer,”Operation and Control of a Hybrid seven Level Converter,” IEEE Trans. Power Electron., vol. 27, no.2, pp. 652–660, February, 2012.

[3] A. Nami. “A New Multilevel Converter Configuration for High Power High Quality Application,” PhD Thesis, Queensland University of Technology, 2010.

[4] V. Dargahi, A. K. Sadigh, M. Abarzadeh, S. Eskandari and K. Corzine, “A new family of modular multilevel converter based on modified flying capacitor multicell converters IEEE Trans. Power Electron., vol. 30, no.

1, pp. 138-147, January, 2015.

[5] I. López, S. Ceballos, J. Pou, J. Zaragoza, J. Andreu, I. Kortabarria and V. G. Agelidis,” Modulation strategy for multiphase Neutral-Point Clamped converters,” IEEE Trans. Power Electron., vol. 31, no. 2, pp. 928–941, March, 2015.

A Highly Efficient and Reliable Inverter Configuration Based Cascaded Multi-Level Inverter for PV Systems


This paper presents an improved Cascaded Multi-Level Inverter (CMLI) based on a highly efficient and reliable configuration for the minimization of the leakage current. Apart from a reduced switch count, the proposed scheme has additional features of low switching and conduction losses. The proposed topology with the given PWM technique reduces the high-frequency voltage transitions in the terminal and common-mode voltages. Avoiding high-frequency voltage transitions achieves the minimization of the leakage current and reduction in the size of EMI filters. Furthermore, the extension of the proposed CMLI along with the PWM technique for 2m+1 levels is also presented, where m represents the number of Photo Voltaic (PV) sources.

The proposed PWM technique requires only a single carrier wave for all 2m+1 levels of operation. The Total Harmonic Distortion (THD) of the grid current for the proposed CMLI meets the requirements of IEEE 1547 standard. A comparison of the proposed CMLI with the existing PV Multi-Level Inverter (MLI) topologies is also presented in the paper. Complete details of the analysis of PV terminal and common-mode voltages of the proposed CMLI using switching function concept, simulations, and experimental results are presented in the paper.

  1. Cascaded multi-level inverter
  2. Leakage current
  3. Common-mode voltage
  4. Terminal voltage




Fig. 1. Proposed five-level grid-connected CMLI with PV and parasitic elements.



Fig. 2. Simulation results of proposed five-level CMLI showing the waveforms of : (a) output voltage vuv; (b) grid current iac; (c) terminal voltage vxg; (d) terminal voltage vyg; (e) terminal voltage vzg; (f) leakage current ileak; (g) common-mode voltage vcm.

Fig. 3. Proposed five-level CMLI integrated with MPPT. The subplots give waveforms of : (a) voltage VPV1; (b) voltage VPV2; (c) current IPV1; (d) current IPV2; (e) power PPV1; (f) power PPV2; (g) resultant modulation index ma; (h) output power POUT; (i) modified reference wave vref_modified; (j) inverter output voltage vab.


 In this paper, an improved five-level CMLI with low switch count for the minimization of leakage current in a transformerless PV system is proposed. The proposed CMLI minimizes the leakage current by eliminating the high-frequency transitions in the terminal and common-mode voltages. The proposed topology also has reduced conduction and switching losses which makes it possible to operate the CMLI at high switching frequency.

Furthermore, the solution for generalized 2m+1 levels CMLI is also presented in the paper. The given PWM technique requires only one carrier wave for the generation of 2m+1 levels. The operation, analysis of terminal and common-mode voltages for the CMLI is also presented in the paper. The simulation and experimental results validate the analysis carried out in this paper. The MPPT algorithm is also integrated with the proposed five-level CMLI to extract the maximum power from the PV panels. The proposed CMLI is also compared with the other existing MLI topologies in Table V to show its advantages.


[1] Y. Tang, W. Yao, P.C. Loh and F. Blaabjerg, “Highly Reliable Transformerless Photovoltaic Inverters With Leakage Current and Pulsating Power Elimination,” IEEE Trans. Ind. Elect., vol. 63, no. 2, pp. 1016-1026, Feb. 2016.

[2] W. Li, Y. Gu, H. Luo, W. Cui, X. He and C. Xia, “Topology Review and Derivation Methodology of Single-Phase Transformerless Photovoltaic Inverters for Leakage Current Suppression,” IEEE Trans. Ind. Elect., vol. 62, no. 7, pp. 4537-4551, July 2015.

[3] J. Ji, W. Wu, Y. He, Z. Lin, F. Blaabjerg and H. S. H. Chung, “A Simple Differential Mode EMI Suppressor for the LLCL-Filter-Based Single-Phase Grid-Tied Transformerless Inverter,” IEEE Trans. Ind. Elect., vol. 62, no. 7, pp. 4141-4147, July 2015.

[4] Y. Bae and R.Y.Kim, “Suppression of Common-Mode Voltage Using a Multicentral Photovoltaic Inverter Topology With Synchronized PWM,” IEEE Trans. Ind. Elect., vol. 61, no. 9, pp. 4722-4733, Sept. 2014.

[5] N. Vazquez, M. Rosas, C. Hernandez, E. Vazquez and F. J. Perez-Pinal, “A New Common-Mode Transformerless Photovoltaic Inverter,” IEEE Trans. Ind. Elect., vol. 62, no. 10, pp. 6381-6391, Oct. 2015.

PMSG Based Wind Energy Generation System:Energy Maximization and its Control


This paper deals with the energy maximization and control analysis for the permanent magnet synchronous generator (PMSG) based wind energy generation system (WEGS). The system consists of a wind turbine, a three-phase IGBT based rectifier on the generator side and a three-phase IGBT based inverter on the grid side converter system. The pitch angle control by perturbation and observation (P&O) algorithm for obtaining maximum power point tracking (MPPT).

MPPT is most effective under, cold weather, cloudy or hazy days. A designed control technique is proposed for the MPPT mechanism of the system. This paper will explore in detail about the control analysis for both the generator and grid side converter system. Further, it will also discuss about the pitch angle control for the wind turbine in order to obtain maximum power for the complete wind energy generation system. The proposed WEGS for maximization of power is modelled, designed and simulated using MATLAB R2014b Simulink with its power system toolbox and discrete step solver incorporated in the simulation tool.


  1. Maximum power point tracking (MPPT)
  2. Permanent magnet synchronous generator (PMSG)
  3. Pitch angle control (PAC)
  4. Wind energy generation system (WEG)



Fig. 1. Control issue in PMSG based wind turbine system



Fig.2. Wind speed (15 m/s).

Fig.3. Pitch angle ( 26 Degree).

Fig.4. Active power output (1.49 MW).

Fig.5. Stator voltage of PMSG (per unit).

Fig.6. Stator current of PMSG (per unit).

Fig.7. Wind speed (m/s).

Fig.8. Pitch control.

Fig.9. Electrical torque of PMSG.

Fig.10. Wind turbine power with pitch control.


This paper has briefly discussed about the energy maximization and control analysis for the PMSG based wind energy generation system. The paper also explored in detail about the different control algorithm for both the machine and grid side converter system and has used VSC control for our proposed mechanism. A brief discussion on the pitch angle control for the wind turbine has been described which aims to obtain maximum power for the complete wind energy generation system.

A designed control technique named as (P&O) has also been proposed for the MPPT mechanism of the system whose results has been validated using MATLAB R2014b Simulink. As discussed before the presented technique includes maximum power point tracking module, pitch angle control and average model for machine side and grid side converters. Also, the integrated control system controls the generator speed, DC-link voltage and active power along with the above-mentioned factors.


[1] M. Benadja and A. Chandra, “A new MPPT algorithm for PMSG based grid connected wind energy system with power quality improvement features”, IEEE Fifth Power India Conference, Murthal, pp. 1-6, 2012.

[2] S. Sharma and B. Singh, “An autonomous wind energy conversion system with permanent magnet synchronous generator”, International Conference on Energy, Automation and Signal, Bhubaneswar, Odisha, pp. 1-6, 2011.

[3] M. Singh and A. Chandra, “Power maximization and voltage sag/swell ride-through capability of PMSG based variable speed wind energy conversion system”,34th Annual Conference of IEEE Industrial Electronics, Orlando, FL, pp. 2206-2211, 2008.

[4] T. Tafticht, K. Agbossou, A. Cheriti and M. L. Doumbia, “Output Power Maximization of a Permanent Magnet Synchronous Generator Based Stand-alone Wind Turbine”,IEEE International Symposium on Industrial Electronics, Montreal, pp. 2412-2416, 2006.

[5] N. A. Orlando, M. Liserre, R. A. Mastromauro and A. D. Aquila, “A Survey of Control Issues in PMSG-Based Small Wind-Turbine Systems”, IEEE Transactions on Industrial Informatics, vol. 9, no. 3, pp. 1211-1221, Aug. 2013.

Power Management in PV-Battery-HydroBased Standalone Microgrid


This paper proposes a high-efficiency two stage three-level grid-connected photovoltaic inverter. that work deals with the frequency regulation, voltage regulation, power management and load levelling of solar photovoltaic (PV)-battery-hydro based microgrid (MG). In this MG, the battery capacity is reduced as compared to a system, where the battery is directly connected to the DC bus of the voltage source converter (VSC). A bidirectional DC–DC converter connects the battery to the DC bus and it controls the charging and discharging current of the battery. It also regulates the DC bus voltage of VSC, frequency and voltage of MG.

The proposed system manages the power flow of different sources like hydro and solar PV array. However, the load levelling is managed through the battery. Battery with VSC absorbs the sudden load changes, resulting in rapid regulation of DC link voltage, frequency and voltage of MG. Therefore, the system voltage and frequency regulation allows the active power balance along with the auxiliary services such as reactive power support, source current harmonics mitigation and voltage harmonics reduction at the point of common interconnection. Experimental results under various steady state and dynamic conditions, exhibit the excellent performance of the proposed system and validate the design and control of proposed MG.



Fig. 1 Microgrid Topology and MPPT Control (a) Proposed PV-battery-hydro MG,


Fig. 2 Dynamic performance of PV-battery-hydro based MG following by solar irradiance change (a) vsab, isc, iLc and ivscc, (b) Vdc, Ipv, Vb and Ib, (c) vsab, isa, iLa and ivsca, (d) Vdc, Ipv, Vb and Ib

Fig.3 Dynamic performance of hydro-battery-PV based MG under load perturbation (a) vsab, isc, Ipv and ivscc, (b) Vdc, Ipv, Vb and Ib, (c) vsab, isc, Ipv and ivscc, (d) Vdc, Ipv, and Vb


In the proposed MG, an integration of hydro with the battery, compensates the intermittent nature of PV array. The proposed system uses the hydro, solar PV and battery energy to feed the voltage (Vdc), solar array current (Ipv), battery voltage (Vb) and battery current (Ib). When the load is increased, the load demand exceeds the hydro generated power, since SEIG operates in constant power mode condition.

This system has the capability to adjust the dynamical power sharing among the different RES depending on the availability of renewable energy and load demand. A bidirectional converter controller has been successful to maintain DC-link voltage and the battery charging and discharging currents. Experimental results have validated the design and control of the proposed system and the feasibility of it for rural area electrification.


[1] Ellabban, O., Abu-Rub, H., Blaabjerg, F.: ‘Renewable energy resources: current status, future prospects and technology’, Renew. Sustain. Energy Rev.,2014, 39, pp. 748–764

[2] Bull, S.R.: ‘Renewable energy today and tomorrow’, Proc. IEEE, 2001, 89, (8), pp. 1216–1226

[3] Malik, S.M., Ai, X., Sun, Y., et al.: ‘Voltage and frequency control strategies of hybrid AC/DC microgrid: a review’, IET Renew. Power Gener., 2017, 11, (2), pp. 303–313

[4] Kusakana, K.: ‘Optimal scheduled power flow for distributed photovoltaic/ wind/diesel generators with battery storage system’, IET Renew. Power Gener., 2015, 9, (8), pp. 916–924

[5] Askarzadeh, A.: ‘Solution for sizing a PV/diesel HPGS for isolated sites’, IET Renew. Power Gener., 2017, 11, (1), pp. 143–151

High-Efficiency Two-Stage Three-Level Grid-Connected Photovoltaic Inverter


This paper proposes a high-efficiency two stage three-level grid-connected photovoltaic inverter. The proposed two-stage inverter comprises a three-level step up converter and a three-level inverter. The three-level step up  converter not only improves the power-conversion efficiency by lowering the voltage stress but also guarantees the balancing of the dc-link capacitor voltages using a simple control algorithm; it also enables the proposed inverter to satisfy the VDE 0126-1-1 standard of leakage current. The three-level inverter minimizes the overall power losses with zero reverse-recovery loss.

Furthermore, it reduces harmonic distortion, the voltage ratings of the semiconductor device, and the electromagnetic interference by using a three-level circuit configuration; it also enables the use of small and low cost filters. To control the grid current effectively, we have used a feed-forward nominal voltage compensator with a mode selector; this compensator improves the control environment by presetting the operating point. The proposed high-efficiency two-stage three-level grid-connected photovoltaic inverter overcomes the low  efficiency problem of conventional two-stage inverters, and it provides high power quality with maximum efficiency of 97.4%. Using a 3-kW prototype of the inverter, we have evaluated the performance of the model and proved its feasibility.


  1. Transformerless
  2. Multilevel
  3. Dc-ac power conversion
  4. Single-phase



Fig. 1. Proposed high-efficiency two-stage three-level grid-connected PV inverter circuit diagram.


 Fig.2. Simulation results for the leakage current of the proposed twostage


Fig.3. Simulation results for the leakage current using a conventional three-level step-up converter of Fig. 2(b) as dc-dc power conversion stage of two-stage inverter.


A high-efficiency two-stage three-level grid-connected PV inverter and control system are introduced. Also, a theoretical analysis is provided along with the experimental results. By using the novel circuit configuration, the proposed two-stage inverter performs power conversion with low leakage current and high efficiency; in dc-dc power conversion stage, the connection of midpoints of capacitors enables the proposed two-stage inverter to limit the leakage current below 300mA; in dc-ac power conversion stage, the overall power losses are minimized by eliminating the reverse-recovery problems of the MOSFET body diodes. Besides, the proposed inverter with three voltage levels reduces the power losses, harmonic components, voltage ratings, and EMI; it also enables using small and low cost filters.

For the control system, the feed forward nominal voltage compensator also improves the control environment by presetting the operating point. This developed control algorithm makes the proposed inverter feasible. Thus, the proposed high-efficiency two-stage three-level grid connected PV inverter provides high power quality with high power-conversion efficiency. By using a 3-kW prototype, this experiment has verified that the proposed inverter has high efficiency, and the developed control system is suitable for the proposed inverter.


[1] B.K. Bose, “Global energy acenario and impact of power electronics in 21st century,” IEEE Transactions on Industrial Electronics, vol. 60, no. 7, pp. 2638-2651, July. 2013.

[2] Y. Zhou, D. C. Gong, B. Huang, and B. A. Peters, “The impacts of carbon tariff on green supply chain design,” IEEE Transactions on Automation Science and Engineering, July. 2015. Available: DOI: 10.1109/TASE.2015.2445316

[3] Y. Wang, X. Lin, and M. Pedram, “A near-optimal model-based control algorithm for households equipped with residential photovoltaic power generation and energy storage systems,” IEEE Transactions on Sustainable Energy, vol. 7, no. 1, pp. 77-86, Jan. 2016.

[4] Y. W. Cho, W. J. Cha, J. M. Kwon, and B. H. Kwon, “Improved  single-phase transformerless inverter with high power density and high efficiency for grid-connected photovoltaic systems,” IET Renewable Power Generation, vol. 10, no. 2, pp. 166-174, Feb. 2016.

[5] A. Shayestehfard, S. Mekhilef, and H. Mokhlis, “IZDPWMBased feedforward controller for grid-connected inverters under unbalanced and distorted conditions,” IEEE Trans. Ind. Electron., vol. 64, no. 1, pp. 14-21, Jan. 2017.

A Three-Phase Symmetrical DC-Link Multilevel Inverter with Reduced Number of DC Sources


This paper presents a novel three-phase DC-link multilevel inverter topology with reduced number of input DC power supplies. The proposed inverter consists of series-connected half-bridge modules to generate the multilevel waveform and a simple H-bridge module, acting as a polarity generator. The inverter output voltage is transferred to the load through a three-phase transformer, which facilitates a galvanic isolation between the inverter and the load. The proposed topology features many advantages when compared with the conventional multilevel inverters proposed in the literatures.

These features include scalability, simple control, reduced number of DC voltage sources and less devices count. A simple sinusoidal pulse-width modulation technique is employed to control the proposed inverter. The performance of the inverter is evaluated under different loading conditions and a comparison with some existing topologies is also presented. The feasibility and effectiveness of the proposed inverter are confirmed through simulation and experimental studies using a scaled down low-voltage laboratory prototype.

  1. Hybrid multilevel inverter
  2. DC-link inverter
  3. half-bridge module
  4. symmetric DC voltage supply



Fig. 1 The proposed three-phase CMLI with two half-bridge cells per phase leg


 Fig. 2 Simulation results of the output line voltages and line currents for (a) load of nearly 0.8–lagging power factor and (b) load of nearly unity power factor

Fig. 3 Simulation results for a dynamic change in the load from nearly unity PF (100.31∠4.49°Ω) to 0.8 lagging PF (127.13∠38.13°Ω): (a) level generator output voltage, (b) polarity generator output voltage (phase voltage) and (c) line voltage and line current

Fig. 4 Simulation results for a dynamic change in the load magnitude with the same PF: (a) Line voltage, (b) Line current

Fig. 5 Simulation results for a dynamic change in the load from nearly 0.9 lagging PF (108.01∠22.21°Ω) to 0.7 lagging PF (142.88∠45.58°Ω): (a) level generator output voltage, (b) polarity generator output voltage (phase voltage) and (c) line voltage and line current

Fig. 6 Simulation results for carrier frequency of 8 kHz: (a) line voltages and currents, (b) line current THD, (c) line voltage THD


This paper presents a new symmetrical multilevel inverter topology with two different stages. The proposed inverter requires less power electronic devices and features modularity, hence simple structure, less cost, and high scalability. The number of input DC-supplies for the proposed topology is found to be nearly 67% less than the similar symmetric half-bridge topologies, which is a great achievement for industrial applications.

This phenomenon will reduce the complexity of DC voltage management. As being a symmetric structure, all the switching devices experience same voltage stress, which is a very important factor for high voltage applications. The feasibility of the proposed inverter is confirmed through simulation and experimental analysis for different operating conditions.


[1] L. G. Franquelo, J. Rodriguez, J. I. Leon, S. Kouro, R. Portillo, and M. A. Prats, “The age of multilevel converters arrives,” IEEE Ind. Electron. magazine, vol. 2, pp. 28-39, 2008.

[2] A. Nabae, I. Takahashi, and H. Akagi, “A new neutral-point-clamped PWM inverter,” IEEE Trans. Ind. Appl., pp. 518-523, 1981.

[3] S. Kouro, M. Malinowski, K. Gopakumar, J. Pou, L. G. Franquelo, B. Wu, et al., “Recent advances and industrial applications of multilevel converters,” IEEE Trans. Ind. Electron., vol. 57, pp. 2553-2580, 2010.

[4] J. Rodriguez, J.-S. Lai, and F. Z. Peng, “Multilevel inverters: a survey of topologies, controls, and applications,” IEEE Trans. Ind. Electron., vol. 49, pp. 724-738, 2002.

[5] B. Xiao, L. Hang, J. Mei, C. Riley, L. M. Tolbert, and B. Ozpineci, “Modular cascaded H-bridge multilevel PV inverter with distributed MPPT for grid-connected applications,” IEEE Trans. Ind. Appl., vol. 51, pp. 1722-1731, 2015.

Varying Phase Angle Control In Isolated Bidirectional DC–DC Converter For Integrating Battery Storage And Solar PV System In Standalone Mode


This study proposes a varying phase angle control (VPAC) in isolated bidirectional dc–dc converter (IBDC) for integrating battery storage unit to a DC link in a standalone solar photovoltaic (PV) system. The IBDC is capable of power transfer using high step up/down ratio between DC link and battery.  VPAC control proposed in this study effectively manage the power flow control between the battery storage unit and the solar PV fed DC link by continuously varying the phase angle between high voltage and low voltage (LV) bridge voltage of the IBDC.

Solar PV system is include with the maximum power point tracking using DC–DC converter. In order to control the voltage across the AC load a voltage source inverter is used. The study also presents the design form of the IBDC converter for the application considered. The performance of the proposed power flow control design has been studied through PSCAD/EMTDC simulation and validated using LPC 2148 ARM processor.



Fig. 1 Block diagram for proposed standalone system

(a) Generalised block diagram, (b) Mode 1 operation, (c) Mode 2 operation, (d) Mode 3 operation



 Fig. 2 Simulation results of IBDC

(a) Battery current during change in mode 1 to mode 2, (b) Battery current during change in mode 2 to mode 1, (c) Solar PV power, load power and battery power during change in mode 1 to mode 2, (d) Solar PV power, load power and battery power during change in mode 2 to mode 1


The proposed variable phase angle control of IBDC converter balances the power flow between the solar PV system, battery storage unit and AC load in all the modes.  VPAC algorithm ensures that the, (i) solar PV system delivers maximum demanded power corresponding to the load and battery gets charged/ discharged through the available excess/short power.

Governing mathematical formulation of problem reveals the need of average battery current on phase angle between the voltages of LV and HV side of the IBDC converter and hence provides a strategy to control the power flow.

Analysis presented can be used to method the passive components and switches of the IBDC. From the obtained results, the performance of the proposed VPAC has been established with smooth transition of power flow between the PV fed DC link and the battery through the IBDC converter. The maximum power is essence from the solar PV and AC load voltage is controlled in all the modes.


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Single-phase solar PV system with battery and exchange of power in grid-connected and standalone modes


A grid tied photovoltaic (PV) power conversion topology is presented in this study with a novel scheme of resynchronization to the grid. This scheme serves the purpose of supplying continuous power to the load along with feeding power to the grid. The control approach helps in mitigation of harmonics and improving the power quality while extracting the optimum power from the PV array. Depending on the availability of grid voltage, the proposed configuration is controlled using three approaches, defined as grid current control, Point of Common Coupling (PCC) voltage control and intentional islanding with re-synchronisation.

A simple proportional integral controller manages the grid current, load voltage, battery current and DC Direct Current (DC) link voltage within these modes. Moreover, a control scheme for quick and smooth transitions among the modes is described. The robustness of the system under erratic behaviour of solar insolation, load power and disturbances in grid supply makes it a suitable choice for a residential application. The control, design and simulation results are presented to demonstrate the satisfactory operation of the proposed system.



 Fig. 1 Proposed system topology


Fig. 2 Performance of the system under grid isolation

GCC to PVC, (b) Harmonic spectrum of grid current (ig), (c) Harmonic spectrum of load voltage (vL)

 Fig. 3 Performance of the system under grid reconnection

(a) Mode change from PVC to IIRS, (b) Grid voltage (vg) vs. load voltage (vL) during

intentional islanding

Fig. 4 Performance of the system for insolation change from 1000 W/m2

to 500/m2


The proposed scheme has combined the solar PV power generating unit to single-phase grid with a unique feature of resynchronization of grid to the system after overcoming the grid failures. The ability of the system to generate maximum power for varying insolation, feeding active power to the grid as well as load and store/extract power to/from the battery has been validated by the dynamic performance. This helps in increasing the efficiency of the system.

The scheme has utilised minimum number of switches resulting in lower switching losses. The VSC has the ability to diminish the switching harmonics in grid current and load voltages resulting in <5% THD as demanded by the IEEE 519 standard. The system has ability to re-synchronise with the grid within five cycles of grid voltage for any phase difference. This helps in achieving the fast time response of the system, thus making it a suitable choice for residential applications. The obtained results have authenticated the robustness and feasibility of the proposed system under various disturbances.


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