aThree-Phase Transformerless Shunt Active Power Filter with Reduced Switch Count for Harmonic Compensation in Grid-Connected Applications


Shunt active power filter is the preeminent solution against nonlinear loads, current harmonics and power quality problems. APF topologies for harmonic compensation use numerous high-power rating components and are therefore disadvantageous. Hybrid topologies combining low-power rating APF with passive filters are used to reduce the power rating of voltage source inverter. Hybrid APF topologies for high-power rating systems use a transformer with large numbers of passive components. In this paper, a novel four-switch two-leg VSI topology for a three-phase SAPF is proposed for reducing the system cost and size. The proposed topology comprises a two-arm bridge structure, four switches, coupling inductors, and sets of LC PFs. The third leg of the three-phase VSI is removed by eliminating the set of power switching devices, thereby directly connecting the phase with the negative terminals of the dc-link capacitor. The proposed topology enhances the harmonic compensation capability and provides complete reactive power compensation compared with conventional APF topologies. The new experimental prototype is tested in the laboratory to verify the results in terms of total harmonic distortion, balanced supply current, and harmonic compensation, following the IEEE-519 standard.


  1. Harmonics
  2. hybrid topology
  3. nonlinear load
  4. power quality (PQ)
  5. Transformerless inverter
  6. Grid-connected system



Fig. 1. Proposed transformerless APF system


 Fig. 2. Steady state operation of the proposed SAPF a) Utility voltage (THDv=4%) b) Utility current (THDi=4.1%) c) Load current (THDi=30.1%) d) Compensating filter current.

Fig. 3. a) DC voltage (50V/div). b) Filter current (100A/div) at filter switched ON (t=0.15).

Fig. 4. Starting performance of the proposed SAPF. a) Utility voltage (THDv=4%) b) Utility current (THDi=4.1%) c) Load current (THDi=30.1%) d) Compensating current at switched ON.

Fig. 5. a) On-state and Off-state APF operations. b) Zoom image of utility line current (𝒊𝑺𝒂𝒃𝒄) at 5th and 7th order harmonics.

Fig. 6. Dynamic performance with the R-L load step-change waveforms of the proposed SAPF.


In this paper, a novel three-phase reduced switch count and transformer-less APF circuit, operating with the function of active filtering and enhanced reactive power compensation. The main point of the proposed APF circuit topology, which uses a two-leg bridge structure and only four IGBT power devices in the three-phase power converter. Compared with the other existing topologies, the elimination of the transformer and minimum active and passive component contributes to a significant reduction in the manufacturing cost, volumetric size and weight. The proposed APF system is more robust, efficient and stable to improve the feasibility and harmonic propagation of the power distribution system. A detail analysis of the both the active filter inverter and passive filter, including the reactive power capability and filtering characteristics has been presented. The series LC tuned PF at the 5th and 7th order harmonic frequencies improves the harmonic mitigation performance. However, the series ac coupling inductors can overcome the fixed reactive power compensation caused by the defined value of the LC filter. The control algorithm can ensure the regulated sinusoidal voltage, phase amplitude, and low THD in the power distribution system, along with dc-link voltage control. The experimental and simulation results have verified the feasibility of the proposed APF topology and its excellent performance in terms of both transient and steady states responses to compensate selectively either the reactive power compensation, as well as in damping out the current harmonic distortion. Furthermore, the proposed APF system based on transformerless and power switching device reduced count configuration could be used in extensive applications, such as the grid-connected power converters, grid interfaced distributed energy sources, and so on.


[1] S. D. Swain, P. K. Ray, and K. B. Mohanty, “Improvement of Power Quality Using a Robust Hybrid Series Active Power Filter,” IEEE Transactions on Power Electronics, vol. 32, pp. 3490-3498, 2017.

[2] A. Javadi, A. Hamadi, L. Woodward, and K. Al-Haddad, “Experimental Investigation on a Hybrid Series Active Power Compensator to Improve Power Quality of Typical Households,” IEEE Transactions on Industrial Electronics, vol. 63, pp. 4849-4859, 2016.

[3] W. U. Tareen, S. Mekhilef, M. Seyedmahmoudian, and B. Horan, “Active power filter (APF) for mitigation of power quality issues in grid integration of wind and photovoltaic energy conversion system,” Renewable and Sustainable Energy Reviews, vol. 70, pp. 635-655, 4// 2017.

[4] J. Solanki, N. Fröhleke, and J. Böcker, “Implementation of Hybrid Filter for 12-Pulse Thyristor Rectifier Supplying High-Current Variable-Voltage DC Load,” IEEE Transactions on Industrial Electronics, vol. 62, pp. 4691-4701, 2015.

[5] L. Asiminoaei, C. Lascu, F. Blaabjerg, and I. Boldea, “Performance Improvement of Shunt Active Power Filter With Dual Parallel Topology,” IEEE Transactions on Power Electronics, vol. 22, pp. 247-259, 2007.

A Modified Three-Phase Four-Wire UPQC Topology With Reduced DC-Link Voltage Rating



The unified power quality conditioner (UPQC) is a custom power device, which mitigates voltage and current-related PQ issues in the power distribution systems. In this paper, a UPQC topology for applications with non-stiff source is proposed. The proposed topology enables UPQC to have a reduced dc-link voltage without compromising its compensation capability. This proposed topology also helps to match the dc-link voltage requirement of the shunt and series active filters of the UPQC. The topology uses a capacitor in series with the interfacing inductor of the shunt active filter, and the system neutral is connected to the negative terminal of the dc-link voltage to avoid the requirement of the fourth leg in the voltage source inverter (VSI) of the shunt active filter. The average switching frequency of the switches in the VSI also reduces, consequently the switching losses in the inverters reduce. Detailed design aspects of the series capacitor and VSI parameters have been discussed in the paper. A simulation study of the proposed topology has been carried out using PSCAD simulator, and the results are presented. Experimental studies are carried out on three-phase UPQC prototype to verify the proposed topology.


  1. Average switching frequency
  2. Dc-link voltage
  3. Hybrid topology
  4. Non-stiff source
  5. Unified power quality conditioner (UPQC)



Fig. 1. Equivalent circuit of proposed VSI topology for UPQC compensated system (modified topology).



Fig. 2. Simulation results before compensation (a) load currents (b) terminal voltages.

Fig. 3. Simulation results using conventional topology. (a) DC capacitor voltages (top and bottom). (b) Source currents after compensation. (c) Voltage across the interfacing inductor in phase-a of the shunt active filter. (d) Shunt active filter currents. (e) Terminal voltages with sag, DVR-injected voltages, and load voltages after compensation.


Fig. 4. Simulation results with modified topology. (a) Voltage across series capacitor and load voltage in phase-a. (b) Inverter output voltage in leg-a of shunt active filter. (c) DC and fundamental values of voltage across series capacitor and inverter output voltage.

Fig. 5. Simulation results using modified topology. (a) DC capacitor voltages. (b) Source currents after compensation. (c) Voltage across the interfacing inductor in phase-a of the shunt active filter. (d) Shunt active filter currents. (e) Terminal voltages with sag, DVR injected voltages, and load voltages after compensation.


A modified UPQC topology for three-phase four-wire system has been proposed in this paper, which has the capability to compensate the load at a lower dc-link voltage under nonstiff source. Design of the filter parameters for the series and shunt active filters is explained in detail. The proposed method is validated through simulation and experimental studies in a three-phase distribution system with neutral-clamped UPQC topology (conventional). The proposed modified topology gives the advantages of both the conventional neutral-clamped topology and the four-leg topology. Detailed comparative studies are made for the conventional and modified topologies. From the study, it is found that the modified topology has less average switching frequency, less THDs in the source currents, and load voltages with reduced dc-link voltage as compared to the conventional UPQC topology.


[1] M. Bollen, Understanding Power Quality Problems: Voltage Sags and Interruptions. New York: IEEE Press, 1999.

[2] S. V. R. Kumar and S. S. Nagaraju, “Simulation of DSTATCOM and DVR in power systems,” ARPN J. Eng. Appl. Sci., vol. 2, no. 3, pp. 7–13, Jun. 2007.

[3] B. T. Ooi, J. C. Salmon, J. W. Dixon, and A. B. Kulkarni, “A three phase controlled-current PWM converter with leading power factor,” IEEE Trans. Ind. Appl., vol. IA-23, no. 1, pp. 78–84, Jan. 1987.

[4] Y. Ye, M. Kazerani, and V. Quintana, “Modeling, control and implementation of three-phase PWM converters,” IEEE Trans. Power Electron., vol. 18, no. 3, pp. 857–864, May 2003.

[5] R. Gupta, A. Ghosh, and A. Joshi, “Multiband hysteresis modulation and switching characterization for sliding-mode-controlled cascaded multilevel inverter,” IEEE Trans. Ind. Electron., vol. 57, no. 7, pp. 2344–2353, Jul. 2010.