High-Efficiency Two-Stage Three-LevelGrid-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 feedforward 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 Carrier-Based PWM Strategy With the OffsetVoltage Injection for Single-Phase Three-LevelNeutral-Point-Clamped Converters


Single-phase three-level neutral point clamped (NPC) converters are widely applied in high-speed railway electrical traction drive systems.  A significant problem related to the single-phase three-level NPC converters is the fluctuation of the neutral-point voltage. In this paper, a capacitor voltage balancing technique is proposed that injects an offset voltage into the sinusoidal modulating signals of the conventional carrier-based pulse width modulation (CBPWM) method.

Furthermore, when the injected offset voltage is maximized, it cannot only balance the dc-link capacitors voltages, but also reduce switching losses. Theoretical analysis has shown that both methods can control the neutral point voltage effectively, but the neutral point voltage controller in the CBPWM with maximum offset voltage injection (CBPWM-MOVI) has a faster dynamic response.

It was observed that the high-order harmonics frequencies of the line current are centered around the twice switching frequency in the CBPWM with the offset voltage injection (CBPWM-OVI) but are centered around the switching frequency in the CBPWM-MOVI. And also, the CBPWM-MOVI has switching commutations number at least 25% below that of the CBPWM-OVI in one modulating signal period. The performances of the two strategies were verified by simulation and experimental tests.

  1. Carrier-based pulse width modulation (CBPWM),
  2. Neutral-point voltage balancing
  3. Single-phase
  4. The offset voltage injection
  5. Three-level converter



 Fig. 1. Single-phase three-level NPC converter.


Fig. 2. Simulation results of the main voltage us and the line current is .

(a) CBPWM-OVI with k = 0.5. (b) CBPWM-MOVI.

Fig. 3. Simulation results of FFT analysis for frequency spectrum of the line

current is . (a) CBPWM-OVI with k = 0.5. (b) CBPWM-MOVI.

Fig. 4. Simulation results of the input port voltage uab . (a) CBPWM-OVI

with k = 0.5. (b) CBPWM-MOVI.

 Fig. 5. Simulation results of dc-link voltage u1 and u2 . (a) CBPWM-OVI

with k = 0.5. (b) CBPWM-MOVI.

Fig. 6. Simulation results of dc-link voltage error, the modulating signal

and the offset voltage. (A) CBPWM-OVI with k = 0.5. (B) CBPWM-MOVI.

(C) CBPWM-MOVI (partial enlarged view).


 This paper proposes CBPWM strategies in conjunction with an offset voltage injection for a single-phase three-level NPC converter to achieve neutral point voltage control and PWM drive signals generation. The restriction range of the offset voltage is discussed in details. Based on this, this paper presents a CBPWM strategy with the maximum offset voltage injection. The salient features of the proposed CBPWM-OVI and CBPWM-MOVI strategies are as follows:

1) both methods guarantee to achieve voltage balancing, while the CBPWM-MOVI has a faster dynamic response of the neutral point voltage controller than the CBPWMOVI;

2) the high-order harmonics of the line current distribute around at twice switching frequency 2fs in the CBPWMOVI, and the same as the switching frequency in the CBPWM-MOVI;

3) the total number of switching commutations of CBPWMMOVI is 25% below that of the CBPWM-OVI, at least in a modulating signal period;

4) both CBPWM-OVI and CBPWM-MOVI with voltage step compensation can guarantee the maximum voltage level step to be half of the dc-link voltage compared with the existing CBPWM strategy.

Simulation and experimental results verify the validity and feasibility of these conclusions, and the proposed CBWMOVI and CBPWM-MOVI strategies are also desirable for single-phase three-level NPC UPS inverter or solar inverter applications.


[1] R. Hill, “Electric railway traction—Part II. Traction drives with three phase induction motors,” Power Eng. J., vol. 8, no. 3, pp. 143–152, Jun. 1994.

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[5] J. Lai and F. Peng, “Multilevel converters—A new breed of power converters,” IEEE Trans. Ind. Appl., vol. 32, no. 3, pp. 509–517, May/Jun. 1996.

Permanent Magnet Synchronous Generator Based Wind Energy and DG Hybrid System


This paper examines the utilization of changeless magnet synchronous generators (PMSGs) for a breeze vitality transformation framework (WECS) and a diesel motor driven generator (DG hybrid system) set of an independent cross breed framework with a battery vitality stockpiling framework (BESS). For voltage control at the purpose of normal coupling (PCC) and adjusted supply at terminals of DG hybrid system set, a solitary stage D-Q hypothesis based control calculation is connected for the exchanging of voltage source converter (VSC) of BESS and the greatest power point following (MPPT) is accomplished for WECS with a gradual conductance procedure for the exchanging of a dc-dc help converter. Recreation aftereffects of created model of proposed independent mixture framework, which is produced in MATLAB show execution of both the controllers and power quality enhancement of the half breed framework.




Fig. 1 Schematic diagram of Wind-Diesel hybrid configuration


Fig. 2 (a) Characteristics of the system with constant wind speed under varying loads.

Fig. 3 (b) Estimation of supply currents and voltages using control algorithm

Fig.4 (c) dynamic Performance of controller of hybrid system under varying linear loads at 10 m/s wind speed

Fig. 5(a) Characteristics of the system with constant wind speed under varying loads.

Fig. 6(b) Estimation of supply currents and voltages using control algorithm

Fig.7(c) dynamic Performance of controller of hybrid system under varying nonlinear loads at 10 m/s wind speed.

Fig. 8 waveforms and harmonic spectra (a) Phase ‘a’ supply voltage of at PCC (b) Phase ‘a’ supply current under nonlinear unbalanced loads.

Fig. 9 Controllers’ performance under wind speed reduction (11 m/s-8 m/s)

Fig. 10  Controllers’ performance under rise in wind speed (8 m/s-11 m/s)


A 3-φ independent breeze diesel half breed framework utilizing PMSG alongside BESS has been recreated in MATLAB utilizing Simpower framework tool compartments. Different parts have been intended for the cross breed framework and controller’s acceptable execution has been delineated utilizing 1-φ-D-Q hypothesis with SOGI channels for different loads under unique conditions while keeping up consistent voltage at PCC and adjusted source flows of diesel generator and furthermore for music concealment according to rules of IEEE-519-1992 standard. A mechanical sensor less methodology has been utilized for accomplishing MPPT through gradual conductance procedure.


A Single-Phase Cascaded Multilevel Inverter Composed of Four-Level Sub-multilevel Cells


This paper presents a novel cascaded multilevel inverter topology. The series connection of proposed basic cells is the main core of this topology. Different methods to determine the values of DC voltage sources in cells are investigated. Advantages and disadvantages of this topology in comparison with classical topologies are discussed. Symmetric and asymmetric structures of this topology are well analyzed through simulations.


  1. Cascaded multilevel inverter
  2. Single phase



Fig.. 1. General scheme of proposed cascaded multilevel inverter


Fig. 2. Simulation results of two-cell proposed inverter Symmetric design: (a) va (b) Vaal and iout(c) THD Asymmetric design: (d) va (e) Vout and iout(f) THD

Fig.3.The blocking voltage of  switches(a) S11 and S12 (b)S21 and  S22  (c)S31 and S32 (d)S41 and S42 (e) Sa (f) Sb  (g) T1 and T4 (h)  T2 and T3.


In this paper a new structure for multilevel inverters based on series connection of four-level sub-multilevel basic cells is proposed. The H-bridge inverter and additional circuit have been added to the basic form of the proposed inverter in order to generate positive and negative polarities and facilitate the symmetric and asymmetric implementations regarding the values of the dc sources. Different methods are suggested to choose the values of the dc sources and they are appraised by comparison studies with classical cascaded H-bridge inverter. The results of this survey illustrate the fact that the number of switches and the total blocking voltage of the inverter are reduced for the proposed topology compared to the classical ones. Finally, the simulation results on a two-cell inverter with symmetric and asymmetric implementation confirm the proper performance of the proposed topology.


[I] 1. Franquelo, J. Rodriguez, J. Leon, S. Kouro, R. Portillo, and M. EPrlaectst,ro “nT. hMea ga.g, e of multilevel converters arrives,” IEEE Ind. vol. 2, no. 2, pp. 28-39, Jun. 2008.

[2] J. Rodriguez, S. Member, J. Lai, and S. Member, “Multilevel Inverters : A Survey of Topologies , Controls , and Applications,” IEEE Trans. Ind. Electron., vol. 49, no. 4, pp. 724-738,2002.

[3] J. Rodriguez, 1. G. Franquelo, S. Kouro, J. I. Leon, R. C. Portillo, M. A. M. Prats, and M. A. Perez, “Multilevel Converters: An Enabling Technology for High-Power Applications,” Proc. IEEE, vol. 97, no. II, pp. 1786-1817, Nov. 2009.

[4] J.-S. 1. J.-S. Lai and F. Z. P. F. Z. Peng, “Multilevel converters-a new breed of power converters,” lAS ’95. Coif. Rec. 1995 IEEE Ind. Appl. Can! Thirtieth lAS Annu. Meet., vol. 3, no. 3, pp. 509-517,1995.

[5] M. Malinowski, K. Gopakumar, J. Rodriguez, and M. A. Perez, E”Ale cStruorvne.,y on Cascaded Multilevel Inverters,” IEEE Trans. Ind. vol. 57, no. 7, pp. 2197-2206, Jul. 2010.


A Buck & Boost based Grid Connected PV Inverter Maximizing Power Yield from Two PV Arrays in Mismatched Environmental Conditions


A single phase grid connected transformerless photo voltaic (PV) inverter which can operate either in buck or in boost mode, and can extract maximum power simultaneously from two serially connected subarrays while each of the subarray is facing different environmental conditions, is presented in this paper. As the inverter can operate in buck as well as in boost mode depending on the requirement, the constraint on the minimum number of serially connected solar PV modules that is required to form a subarray is greatly reduced. As a result power yield from each of the subarray increases when they are exposed to different environmental conditions. The topological configuration of the inverter and its control strategy are designed so that the high frequency components are not present in the common mode voltage thereby restricting the magnitude of the leakage current associated with the PV arrays within the specified limit. Further, high operating efficiency is achieved throughout its operating range. A detailed analysis of the system leading to the development of its mathematical model is carried out. The viability of the scheme is confirmed by performing detailed simulation studies. A 1.5 kW laboratory prototype is developed, and detailed experimental studies are carried out to corroborate the validity of the scheme.


  1. Grid connection
  2. Single phase
  3. Transformerless
  4. Buck & Boost based PV inverter
  5. Maximum power point
  6. Mismatched environmental condition
  7. Series connected module



Fig. 1. Dual Buck & Boost based Inverter (DBBI)



Fig. 2. Simulated waveform: Variation in (a) ppv1 and ppv2, (b) vpv1 and

vpv2, (c) ipv1 and ipv2 during entire range of operation

Fig.3. Simulated waveform: vg and ig and their magnified views

Fig. 4. Simulated waveform: iL1 and iL2 and their magnified views

Fig. 5. Simulated waveform: vco1 and vco2 and their magnified views


A single phase grid connected transformerless buck and boost based PV inverter which can operate two subarrays at their respective MPP was proposed in this paper. The attractive features of this inverter were i) effect of mismatched environmental conditions on the PV array could be dealt with A single phase grid connected  transformerless buck and boost based PV inverter which can operate two subarrays at their respective MPP was proposed in this paper. The attractive features of this inverter were i) effect of mismatched environmental conditions on the PV array could be dealt with in an effective way, ii) operating efficiency achieved, _euro = 97.02% was high, iii) decoupled control of component converters was possible, iv) simple MPPT algorithm was employed to ensure MPP operation for the component converters, v) leakage current associated with the PV arrays was within the limit mentioned in VDE 0126-1-1. Mathematical analysis of the proposed inverter leading to the development of its small signal model was carried out. The criterion to select the values of the output filter components was presented. The scheme was validated by carrying out detailed simulation studies and subsequently the viability of the scheme was ascertained by carrying out thorough experimental studies on a 1.5 kW prototype of the inverter fabricated for the purpose.


[1] T. Shimizu, O. Hashimoto, and G. Kimura, “A novel high-performance utility-interactive photovoltaic inverter system,” IEEE Trans. Power Electron., vol. 18, no. 2, pp. 704-711, Mar. 2003.

[2] S. V. Araujo, P. Zacharias, and R. Mallwitz, “Highly efficient singlephase transformerless inverters for grid-connected photovoltaic systems,” IEEE Trans. Ind. Electron., vol. 57, no. 9, pp. 3118-3128, Sep. 2010.

[3] B. Ji, J. Wang, and J. Zhao, “High-efficiency single-phase transformerless PV H6 inverter with hybrid modulation method,” IEEE Trans. Ind.Electron., vol. 60, no. 5, pp. 2104-2115, May 2013.

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[5] H. Xiao and S. Xie, “Transformerless split-inductor neutral point clamped three-level PV grid-connected inverter,” IEEE Trans. Power Electron., vol. 27, no. 4, pp. 1799-1808, Apr. 2012.