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.

High-Efficiency MOSFET Transformerless Inverter for Non-isolated Microinverter Applications


State-of-the-art low-power-level metal–oxide–semiconductor field-effect transistor (MOSFET)-based transformerless photovoltaic (PV) inverters can achieve high efficiency by using latest super junction MOSFETs. However, these MOSFET-based inverter topologies suffer from one or more of these drawbacks: MOSFET failure risk from body diode reverse recovery, increased conduction losses due to more devices, or low magnetics utilization. By splitting the conventional MOSFET based phase leg with an optimized inductor, this paper proposes a novel MOSFET-based phase leg configuration to minimize these drawbacks. Based on the proposed phase leg configuration, a high efficiency single-phase MOSFET transformerless inverter is presented for the PV microinverter applications. The pulsewidth modulation (PWM) modulation and circuit operation principle are then described. The common-mode and differential-mode voltage model is then presented and analyzed for circuit design. Experimental results of a 250Whardware prototype are shown to demonstrate the merits of the proposed transformerless inverter on non-isolated two-stage PV microinverter application.

 KEYWORDS: Microinverter, MOSFET inverters, photovoltaic (PV) inverter, transformerless inverter.




Fig. 1. Two-stage nonisolated PV microinverter.



Fig. 2. Proposed transformerless inverter topology with (a) separated magnetic and (b) integrated magnetics.



Fig. 3. Output voltage and current waveforms.


Fig. 4. PWM gate signals waveforms.


Fig. 5. Inverter splitting inductor current waveform.


Fig. 6. Waveforms of voltage between grid ground and DC ground (VEG ).


This paper proposes a MOSFET transformerless inverter with a novel MOSFET-based phase leg, which achieves:

1) high efficiency by using super junction MOSFETs and SiC diodes;

2) minimized risks from the MOSFET phase leg by splitting the MOSFET phase leg with optimized inductor and minimizing the di/dt from MOSFET body diode reverse recovery;

3) high magnetics utilization compared with previous high efficiency MOSFET transformerless inverters in [21], [22], [25], which only have 50% magnetics utilization.

The proposed transformerless inverter has no dead-time requirement, simple PWM modulation for implementation, and minimized high-frequency CMissue. A 250Whardware prototype has been designed, fabricated, and tested in two-stage nonisolated microinverter application. Experimental results demonstrate that the proposed MOSFET transformerless inverter achieves 99.01% peak efficiency at full load condition and 98.8% CEC efficiency and also achieves around 98% magnetic utilization. Due to the advantages of high efficiency, low CM voltage, and improved magnetic utilization, the proposed topology is attractive for two-stage nonisolated PV microinverter applications and transformerless string inverter applications.


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[2] S. B. Kjaer, J. K. Pedersen, and F. Blaabjerg, “A review of singlephase grid-connected inverters for photovoltaic modules,” IEEE Trans. Ind. Appl., vol. 41, no. 5, p. 1292, Sep. 2005.

[3] Q. Li and P. Wolfs, “A review of the single phase photovoltaic module integrated converter topologies with three different dc link configurations,” IEEE Trans. Power Electron., vol. 23, no. 3, pp. 1320–1333, May 2008.

[4] Y. Xue, L. Chang, S. B. Kjaer, J. Bordonau, and T. Shimizu, “Topologies of single-phase inverters for small distributed power generators: An overview,” IEEE Trans. Power Electron., vol. 19, no. 5, pp. 1305–1314, 2004.

[5] W. Yu, J. S. Lai, H. Qian, and C. Hutchens, “High-efficiency MOSFET inverter with H6-type configuration for photovoltaic non-isolated AC-module applications,” IEEE Trans. Power Electron., vol. 56, no. 4, pp. 1253–1260, Apr. 2011.