novel hybrid neutral point clamped inverter for single

INTERNATIONAL JOURNAL of RENEWABLE ENERGY RESEARCH K. Geetha and B. V. Sreenivasappa, Vol.11, No.2, June, 2021

Novel Hybrid Neutral Point Clamped Inverter for Single-Phase Grid-Tied Transformerless Inverter

K. Geetha *‡, B. V. Sreenivasappa**

* Center for Research in Power Electronics, Presidency University, Bangalore, Karnataka, India

** Center for Research in Power Electronics, Presidency University, Bangalore, Karnataka, India ([email protected], [email protected])

‡ Geetha K, Center for Research in Power Electronics, Presidency University, Bangalore, Karnataka, India Tel: +91 9535622776,

[email protected]

Received: 26.04.2021 Accepted:20.05.2021

Abstract- The grid-tied inverter is one of the fast-evolving technology in the present era that aims to support the centralized power generation system with a distributed power generation system. The use of renewable energy resources makes it popular due to its easy availability. The issues associated with grid-tied inverter are its size and cost. To reduce the size and cost of the inverter it is desirable to replace the conventional inverter with a transformerless inverter. The absence of an isolation transformer leads to leakage current flow between the grid and the photovoltaic cell. This paper presents a discussion on the neutral point clamped inverter used in the grid-tied inverter system that aims to reduce the leakage current with the help of a novel hybrid neutral point clamping that provides an additional freewheeling path. It is observed that the proposed topology ensures good common mode differential mode characteristics by keeping the leakage current down to 7.2 mA rms and clamping the common-mode voltage effectively to zero volts. A current THD of 0.19 % and a European efficiency of 96.52 % is achieved.

Keywords grid-tied, single-phase, neutral point clamp, leakage current.

1. Introduction

The increase in energy demand and the destruction of fossil fuels are causing concerns about the use of renewable energy resources. In [1] and [2] authors reported a method to integrate energy harvested from different renewable energy resources for optimal energy needs. Solar power is one of the available renewable energy resources that is used to meet the increased demand in the power sector because it is abundant in nature [3-4] and does not pollute the environment. Photovoltaic cells are already in use for domestic purposes, where the power generated is used by the producer. Nowadays, the generated power is also fed into the grid to use photovoltaic cells efficiently in the distributed power generation system. The issues of the grid-tied inverter system that needs to be addressed are the size and weight of the inverter. This is primarily due to the line transformer used to provide isolation between photovoltaic cells and the grid. This could be resolved by using an inverter that doesn't require a transformer known as a transformerless grid-tied inverter. When the transformer is removed, due to lack of isolation, the leakage current that flows from the grid to the photovoltaic cells must be addressed. Various techniques are proposed in the literature to reduce the leakage current present in the grid-tied inverter. The leakage current analysis shows that it can be

reduced either by keeping the common-mode voltage constant or by isolating the alternate current (AC) side from the direct current (DC) side of the circuit during the freewheeling period or by using the common ground technique. All of these techniques use an inverter that can be broadly categorized as full-bridge (FB) and multilevel inverters. The full-bridge inverter can produce a two-level or three-level output based on the modulation technique used, like unipolar sine pulse width modulation (SPWM), bipolar SPWM, and hybrid SPWM [5]. Bipolar SPWM produces two-level output with constant common-mode voltage but requires high filtering. Unipolar and Hybrid SPWM techniques are more efficient and require less filtering, but the leakage current needs to be further reduced in these techniques. Various types of full-bridge inverters are proposed that reduce leakage current either by making common-mode voltage constant or by introducing additional switches that decouple the AC side from the DC side of the inverter [6]. H5 inverter proposed in [7] uses the DC bypass technique that decouples the photovoltaic (PV) module from the inverter during the freewheeling mode. But due to the junction capacitance, there would be high-frequency ripples in the leakage current that can be removed using another switch suggested in [8] known as optimised or improved H5 (oH5) inverter. oH5 inverter considerably reduces the ripples but still, improvements are


731

required in the topology to maintain the leakage current to a lower level. H6 [9] and full-bridge DC (FBDC) bypass inverter presented in [10] uses an additional switch over H5 topology that disconnects the PV module from the AC side. Compared to H6, full-bridge bypass topology has improved differential and common mode characteristics. The highly efficient reliable inverter concept (Heric) proposed in [11] uses the AC bypass technique that keeps the freewheeling current at the AC side filter and avoids flow towards the PV module. Due to nonideality, the inverter may not decouple effectively which could lead to switching of common-mode voltage between 0 to Vpv/2 and also high-frequency ripples in the leakage current.

The harmonic content is another issue that needs to be controlled to a standard level along with the leakage current. It is, therefore, necessary to include certain techniques that could control the harmonic content of the inverter output. Here comes the use of a multi-level inverter in which more than three levels are present. Consequently, it requires less filtering than a full-bridge inverter, reduces filtering costs and also voltage stress on power devices. In particular, there are three types of multilevel inverters, a diode clamped or a neutral point clamped inverter, a flying capacitor type inverter and a cascaded half-bridge inverter. The flying capacitor type inverter requires a large flying capacitor. Whereas the cascaded bridge inverter requires different DC bus voltages to produce multilevel output. Neutral point clamped (NPC) inverters are therefore simple compared to the other two types of multilevel inverters.

A basic half-bridge and full-bridge neutral point clamped inverters are presented in [12]. These are also known as diode clamped inverter. The idea in the NPC inverter is, it clamps the common-mode voltage to a constant value by using a clamping switch. As the common-mode voltage is always constant the leakage current becomes zero. Total harmonic distortion depends on the number of levels at the output. Hence, it can be reduced by increasing the number of diode networks, thereby increasing the number of levels at the output end. In [13] an NPC inverter is proposed, in that a capacitor divider is added to guarantee the non-generation of leakage current. A low leakage current five-level multilevel inverter is proposed in [14]. In this topology, a dc-link capacitor with a rated voltage of quarter the input voltage applied that significantly reduces the cost of the capacitor. This topology effectively reduces leakage current and provides good common mode as well as differential mode characteristics. A three-level T-type topology is presented in [15] that has no diodes in the conduction path hence yields low loss. A new active neutral point clamped topology is presented in [16]. Here the efficiency is increased by introducing silicon carbide (SIC) metal-oxide semiconductor field-effect transistor (MOSFET) and it gives less harmonic distortion. A shoot-through problem is addressed by separating the bridge leg with the NPC circuit and the filter with the help of four switches and two diodes [17]. A non-isolated inverter with a full-bridge configuration (NIIFBC) is presented in [18]. This topology also reduces the shoot through that occurs when all the switches are turned ON. Another non-isolated full-bridge NPC inverter from [19] designed to reduce the effect of junction capacitance that occurs when the switch is turned off,

and hence reduces the high-frequency ripple in the leakage current. To achieve a high efficiency a family of NPC topology is proposed in [20] with the introduction of two basic NP and PN switching cells. A typical PNNPC structure reduces the leakage current by clamping the common-mode voltage to zero. In the PNNPC inverter, the insulated gate bipolar junction transistors (IGBT) are replaced with super junction metal oxide semiconductor field-effect transistor (SJ-MOSFET) that gains the advantage of PNNPC structure and MOSFETs thereby improving the efficiency [21], the topology is referred as MNPC. Along with leakage current, and harmonic content one has to concentrate power flow management and power quality which is essential for optimal usage of energy harvested and converted in the distributed power generation system [22]. This paper proposes a hybrid technique used to provide an additional freewheeling path for the PNNPC topology that helps in removing the high-frequency fluctuation in the leakage current and also keeps common-mode voltage constant to zero volts. The results are compared with well-known full-bridge topologies such as H5,

a

b

c

Fig. 1. a. Proposed Topology-1 b. Topology-2 c. Gating Signal


732

oH5, H6, FBDC bypass, Heric and also with MNPC which is an advanced version of PNNPC.

The paper is organized as follows: Section 2 presents a description of the proposed topology; Section 3 includes power loss calculation for IGBT and MOSFET; Section 4 describes simulation results and comparison; Section 5 presents the conclusion.

2. Proposed Topologies

The neutral point clamped grid-tied inverter helps to keep the common-mode voltage constant that retains leakage current to a lower level, and the AC side decoupling technique helps in disconnecting the inverter from the grid side during freewheeling mode and provides low leakage current and also good efficiency as the number of active power devices during freewheeling mode are reduced. Even though NPC topologies theoretically keep the common-mode voltage constant, practically it is observed that the leakage current is varying in some topologies. Hence a novel hybrid neutral point clamping technique is presented in this paper, wherein the conventional NPC structure, an AC decoupling technique presented in [23] is introduced to disconnect the filter from the inverter. This hybrid technique provides an additional path for the flow of freewheeling current for maintaining the common-mode voltage constant in all the modes. Fig. 1a shows one such novel hybrid NPC topology (Topology-1) built by using the PNNPC inverter proposed in [20]. It consists of a full-bridge made up of eight switches S1-S8. An AC decoupling network made up of six diodes D1-D6 and a switch S9. This inverter is controlled by a hybrid sine pulse width modulation technique as shown in Fig. 1c. The switching losses are higher in IGBT compared to silicon (Si) MOSFET devices. Further, both conduction and switching losses are considerably reduced in SIC MOSFET devices [24]. SIC MOSFET are also popular for compactness, increased operating switching frequency that reduces the passive components required to filter the inverter output before feeding it to the grid. Hence to gain the advantage of SIC MOSFET all IGBTs in Topology-1 are replaced with SIC MOSFET devices as shown in Fig. 1b (Topology-2). Eq. (1) and Eq. (2) are used to find the differential mode and common mode voltages of the inverter. The inverter has a four-mode profile. Mode-1 is a positive active mode. Mode-2 is a positive freewheeling mode. Mode-3 is a negative active mode and Mode-4 is a negative freewheeling mode.

𝑉"# = 𝑉%& = 𝑉%' − 𝑉&'(1)

𝑉-# =𝑉%' + 𝑉&'

2 (2)

2.1. Mode-1: Positive active mode:

The current path of the inverter in mode-1 is as shown in Fig. 2a. Here the switches S1, S2, S5 and S6 are turned ON as per the gating signal shown in Fig. 1c. S3, S4, S7, S8 and S9 are turned OFF. Hence the current direction is from VPV-S1-S2-VG-S5-S6-VPV. We can observe that 𝑉%' = +𝑉01& 𝑉&' = 0.

𝑉"# = 𝑉%& = 𝑉%' − 𝑉&' = +𝑉01 − 0 = +𝑉01(3)

𝑉-# =𝑉%' + 𝑉&'

2 =𝑉01 + 02 =

𝑉012 (4)

2.2. Mode-2: Positive freewheeling mode:

The current path of the inverter in mode-2 is as shown in Fig. 2b. Here the switches S2, S5, S7, S8 and S9 are turned ON as per the gating signal shown in Fig. 1c. S1, S3, S4 and S6 are turned OFF. This forms two freewheeling current paths. i. VG-

a

b

c

d

Fig. 2. a. Mode-1 b. Mode-2 c. Mode-3 d. Mode-4

Table 1. Switching States Mode S1 S2 S3 S4 S5 S6 S7 S8 S9

1 ON OFF OFF OFF ON ON OFF OFF OFF

2 OFF OFF OFF OFF ON OFF ON ON ON

3 OFF ON ON ON OFF OFF OFF OFF OFF

4 OFF ON ON ON OFF OFF ON ON ON


733

D1-S9-D6-VG ii. VG-S5-S7-S8-S2-VG. And the voltages are given by 𝑉%' = +167

8 & 𝑉&'9 +

1678

𝑉"# = 𝑉%& = 𝑉%' − 𝑉&' =𝑉012 −

𝑉012 = 0(5)

𝑉-# =𝑉%' + 𝑉&'

2 =𝑉012 + 𝑉0122 =

𝑉012 (6)

2.3. Mode-3: Negative active mode:

The current path of the inverter in mode-3 is as shown in Fig. 2c. Here the switches S1, S2, S5, S6 S7, S8 and S9 are turned OFF as per the gating signal shown in Fig. 1c. S3 and S4 are turned ON. Hence the current direction is from VPV-S4-VG-S3-VPV. Hence 𝑉%' = 0 & 𝑉&'9𝑉01.

𝑉"# = 𝑉%& = 𝑉%' − 𝑉&' = 0 − 𝑉01 = −𝑉01(7)

𝑉-# =𝑉%' + 𝑉&'

2 =0 + 𝑉012 =

𝑉012 (8)

Mode-4: Negative freewheeling mode:

The current path of the inverter in mode-4 is as shown in Fig. 2d. Here the switches S2, S5, S7, S8 and S9 are turned ON as per the gating signal shown in Fig. 1c. S1, S3, S4 and S6 are turned OFF. This forms two freewheeling current paths. i. VG-D5-S9-D2-VG ii. VG-S2-S8-S7-S5-VG. And the voltages are given by 𝑉%' = +167

8 & 𝑉&'9 +

1678

.

𝑉"# = 𝑉%& = 𝑉%' − 𝑉&' =1678− 167

8= 0(9)

𝑉-# = 1?@A1B@8

=767C A767C8

= 1678(10)

During mode-2 and mode-4, the hybrid clamping and AC decoupling techniques give better leakage current performance due to the existence of an additional freewheeling path. And also forces the common voltage to clamps at zero volts. This mechanism helps in achieving better common mode, differential mode voltage characteristics reduces the leakage current significantly compared to the reference topology i.e. PNNPC and MNPC. Table 1 lists the switching status of all the switches in the four modes of operation of the inverter.

𝑃-#E = 𝐼#8 𝑅HI8#JK(11)

𝑃-#L = 𝐼#8 𝑅HI M14 −

2𝑀3𝜋P(12)

𝑃-QR&SE = 𝐼#𝑉T𝑀4 +𝐼#

8 𝑅UV2𝑀3𝜋 (13)

𝑃-QR&SL = 𝐼#𝑉T M1𝜋 −

𝑀4P+𝐼#8 𝑅UV M

14 −

2𝑀3𝜋P(14)

𝑃-" = 𝐼#𝑉W𝑀4 +𝐼#

8 𝑅XY2𝑀3𝜋 (15)

𝑃Z[ = \𝐸^_ +𝐸^WW`𝑓Z[(16)

3. Power loss calculation

The detailed analysis of power loss calculation through datasheets are explained in [25] [26] are used to find the efficiency of the inverter. The conduction losses of high frequency and low-frequency MOSFET IGBT and diode are given by Eq. (11) to (15) while switching losses of MOSFET and IGBT can be calculated by using Eq. (16). Calculation of Eon and Eoff for MOSFET is performed with the help of equations given in [26]. To verify and compare the efficiency

Table 2. Device analysis Parameters H5 oH5 H6 FBDC Heric PNNPC MNPC Topology-2

Total Power Devices

IGBT 5 6 6 6 6 8 0 0 MOSFET 0 0 0 0 0 0 7 9 DIODE 0 0 0 2 0 0 4 6

Voltage Stress VPV 6 4 6 4 6 2 3 3 0.5VPV 0 2 0 2 0 6 4 6

Conduction Loss VG>0 IGBT 3 4 4 4 3 4 0 0

MOSFET 0 0 0 0 0 0 4 4

VG<0 IGBT 3 4 4 4 3 2 0 0 MOSFET 0 0 0 0 0 0 2 2

Switching Loss IGBT 2 3 2 2 1 2 0 0 MOSFET 0 0 0 0 0 0 2 2

Table 3. Simulation Parameters Power rating Pi 1kW Grid voltage VG 230V Grid Frequency fG 50Hz Switching frequency fsw 20kHz

PV Voltage VPV 400V Split capacitor C1, C2 560µf Filter inductors L1, Lg 4mH, 4mH, Filter Capacitor Cf 1µf Parasitic Capacitor

CPV1, CPV2 0.1µf

MOSFET SCT2750NY Diode C3D04060A


734

of the proposed topology with other topologies, all the referred topologies efficiency are calculated using SIC MOSFET. Fig. 3k. Shows variation in the efficiency at different load condition in H5, oH5, H6, Heric, FBDC, PNNPC, MNPC,

proposed Topology-2. The curves of H6, MNPC, PNNPC and Heric, H5 are overlapping with each other due to small variation in the efficiency. The experimental results may slightly different from the calculated values. From the graph,

a b c

d e f

g h i

j k

Fig. 3. Common Mode voltage and leakage current of a. H5, b. oH5, c. H6, d.FBDC, e. Heric, f. PNNPC, g. MNPC h. Topology-1 and 2, i. Differential mode characetrics, j. VG and IG of Topology-1 and 2, k Efficinciecy of inverter at dodifferent load condition.

Fig. 4. Voltage stress on Switches of Proposed Topology-1 and Topology- 2

Table 4. Comparison of Topologies Parameters H5 oH5 H6 FBDC Heric PNNPC MNPC Topology-2

Icm mA * 2.8 1 NA 0.7 5.6 13.28 13.27 NA Efficiency % * NA NA 96.3 97.4 NA 96.53 97.28 NA

Current THD % * NA NA NA NA NA 1.6 1.6 0.19 Icm mA p-p $ 282 281 294 50 275 68 47 31 Icm mArms $ 15.3 14.5 15.5 7.5 14.7 8.19 7.5 7.2

Vcm V $ 0 to Vpv Vpv/4 to Vpv/2 0-Vpv/2 0-Vpv/2 0-Vpv 0 0 0 Efficiency % # 97.8 96.9 97.7 97.63 97.88 97.7 97.7 96.52

*from References $ Simulation # calculation


735

it can be noted that the proposed topology-2 has less efficiency compared to others due to the increase in the number of devices added for improving common mode characteristics and is found to be 96.52%.

4. Simulation Results and Comparison

The proposed topologies are simulated in MatLab Simulink. Table 3 lists the simulation parameter for a 1kW single-phase grid-tied inverter. An LCL filter design presented in [27] is used to filter the high-frequency component present in the output of an inverter. To verify the results, topologies from the literature are simulated in MATLAB Simulink in the same environment. Fig. 4 shows the common mode characteristics of referred topologies. Fig. 4i. shows differential mode characteristics and Fig. 4j. shows grid voltage and current at unity power factor. From Fig. 4 and Table. 4 it can be noted that in H5 and Heric inverter the common-mode voltage (Vcm) fluctuates between 0 to VPV, in H6, FBDC is swinging between 0 to 0.5Vpv. and in improved H5 inverter the magnitude of the variation is reduced. In the PNNPC inverter even though common-mode voltage is approximately zero we can notice small variation at zero crossings which are absent in MNPC and Topology-2. Further Table. 4 also lists the leakage current obtained in these inverters. From both Fig. 4 and Table. 4 it can also be observed that the leakage current in the proposed topology is at the lower end compared to the other topologies. Hence, the proposed inverter gives good differential mode and common mode characteristics. The voltage stress on all nine switches are plotted and is as shown in Fig. 5. The voltage stress on switches S1, S2, S5, S6, S7 and S8 is 50% of the input voltage, on switches S3, S4 is varying between 50% of the input to the maximum input voltage i.e. 400V and on switch S9 it is the maximum input voltage. This indicates that the switches with lower ratings can be utilised for the design of the proposed inverter.

5. Conclusion

This paper presented a novel hybrid neutral point clamped grid-tied inverter. In the proposed inverter, a basic PNNPC inverter is improvised by inserting a hybrid cell at the filter side to disconnect the inverter from the filter by using the AC bypass technique. Hence it successfully removes the high-frequency component present in the PNNPC inverter leakage current and common-mode voltage. The peak to peak leakage current is found to be 31 mA and rms value is 7.2 mA which is within the standard acceptable range of 300mA P-P and 30 mA rms. the common-mode voltage is constant over the simulation period and is clamped to zero volts successfully. The hybrid SPWM technique is adapted which gives good differential mode and common mode characteristics. The simulation results show that leakage current is lesser than the standards. The efficiency of the inverter is 96.52%, as compared to reference topologies it is at the lower side due to the increase in the number of switches in the freewheeling path. But the reduction in leakage current makes these topologies superior as compared to PNNPC. Hence, these can be used in a single-phase grid-tied inverter where the reduction of leakage current is prominent.

References

[1] F. Ayadi, I. Colak, I. Garip and H. I. Bulbul, "Impacts of Renewable Energy Resources in Smart Grid," 8th International Conference on Smart Grid (icSmartGrid), Paris, France, pp. 183-188, 2020.

[2] S. S. Dash, "Tutorial 1: Opportunities and challenges of integrating renewable energy sources in smart," IEEE 6th International Conference on Renewable Energy Research and Applications (ICRERA), San Diego, CA, USA, pp. 19-23, 2017.

[3] Mazidi, G. N. Baltas, M. Eliassi and P. Rodríguez, "A Model for Flexibility Analysis of RESS with Electric Energy Storage and Reserve," 7th International Conference on Renewable Energy Research and Applications (ICRERA), Paris, France, pp. 1004-1009, 2018.

[4] N. Campagna, M. Caruso, V. Castiglia, R. Miceli and F. Viola, "Energy Management Concepts for the Evolution of Smart Grids," 8th International Conference on Smart Grid (icSmartGrid), Paris, France, pp. 208-213, 2020.

[5] R. S. Lai and K. D. T. Ngo, "A PWM method for reduction of switching loss in a full-bridge inverter," Proceedings of 1994 IEEE Applied Power Electronics Conference and Exposition - ASPEC'94, pp. 122-127 vol.1, 1994.

[6] M. N. H. Khan, M. Forouzesh, Y. P. Siwakoti, L. Li, T. Kerekes, and F. Blaabjerg, “Transformerless Inverter Topologies for Single-Phase Photovoltaic Systems: A Comparative Review,” IEEE J. Emerg. Sel. Top. Power Electron., vol. 8, no. 1, pp. 805–835, 2020.

[7] M. Victor, F. Greizer, S. Bremicker and U. Hübler, "Method of converting a direct current voltage from a source of direct current voltage, more specifically from a photovoltaic source of direct current voltage, into a alternating current voltage". U.S. Patent Patent 7,411,802, 2008.

[8] H. Xiao, S. Xie, Y. Chen and R. Huang, "An optimized transformerless photovoltaic grid-connected inverter," IEEE Trans. Ind. Electron, vol. 58, no. 5, pp. 1887-1895, 2011.

[9] R. Gonzalez, J. Lopez, P. Sanchis, E. Gubia, A. Ursua and L. Marroyo, "High-efficiency transformerless single-phase photovoltaic inverter," 12th International Power Electronics and Motion Control Conference, Portoroz, 2006.

[10] R. Gonzalez, J. Lopez, P. Sanchis and L. Marroyo, "Transformerless inverter for single-phase photovoltaic systems," IEEE Transactions on Power Electronics, vol. 22, no. 2, pp. 693-697, Mar 2007.

[11] H. Schmidt, S. Christoph and J. Ketterer, "Current inverter for direct/alternating currents, has direct and alternating connections with an intermediate power store, a bridge circuit, rectifier diodes and a inductive choke". German Patent Patent DE10, 2003.


736

[12] M. Calais, J. Myrzik, T. Spooner, and V. G. Agelidis, “Inverters for single-phase grid connected photovoltaic systems - An overview,” PESC Rec. - IEEE Annu. Power Electron. Spec. Conf., vol. 4, no. 5, pp. 1995–2000, 2002.

[13] R. González, E. Gubía, J. López, and L. Marroyo, “Transformerless single-phase multilevel-based photovoltaic inverter,” IEEE Trans. Ind. Electron., vol. 55, no. 7, pp. 2694–2702, 2008.

[14] X. Zhu et al., "Leakage Current Suppression of Single-Phase Five-Level Inverter for Transformer-less PV System," IEEE Transactions on Industrial Electronics., pp. 1-1, 2020.

[15] Y. Wang, W. W. Shi, N. Xie, and C. M. Wang, “Diode-free T-type three-level neutral-point-clamped inverter for low-voltage renewable energy system,” IEEE Trans. Ind. Electron., vol. 61, no. 11, pp. 6168–6174, 2014,

[16] E. Gurpinar, D. De, A. Castellazzi, D. Barater, G. Buticchi, and G. Franceschini, “Performance analysis of SiC MOSFET based 3-level ANPC grid-connected inverter with novel modulation scheme,” 2014 IEEE 15th Work. Control Model. Power Electron. COMPEL 2014, pp. 1–7, 2014.

[17] L. Zhou, F. Gao, G. Shen, and M. Chen, “Highly reliable transformerless neutral point clamped inverter with separated inductors,” ECCE 2016 - IEEE Energy Convers. Congr. Expo. Proc., Milwaukee, WI, USA, pp. 1–6, 2016.

[18] C. Anandababu and B. G. Fernandes, “Neutral Point Clamped MOSFET Inverter with Full-Bridge Configuration for Nonisolated Grid-Tied Photovoltaic System,” IEEE J. Emerg. Sel. Top. Power Electron., vol. 5, no. 1, pp. 445–457, 2017.

[19] C. Anandababu and B. G. Fernandes, “Leakage current generation in view of circuit topology of non-isolated full-bridge neutral point clamped grid-tied photovoltaic inverters,” IET Power Electron., vol. 9, no. 8, pp. 1571–1580, 2016.

[20] L. Zhang, K. Sun, L. Feng, H. Wu, and Y. Xing, “A family of neutral point clamped full-bridge topologies for transformerless photovoltaic grid-tied inverters,” IEEE Trans. Power Electron., vol. 28, no. 2, pp. 730–739, 2013.

[21] A. Syed, T. K. Sandipamu, and F. T. K. Suan, “High-efficiency neutral-point-clamped transformerless MOSFET inverter for photovoltaic applications,” IET Power Electron., vol. 11, no. 2, pp. 246–252, 2018,

[22] D. Motyka, M. Kajanová and P. Braciník, "The Impact of Embedded Generation on Distribution Grid Operation," 7th International Conference on Renewable Energy Research and Applications (ICRERA), Paris, France, pp. 360-364, 2018.

[23] S. Hu, C. Li, W. Li, X. He, and F. Cao, “Enhanced HERIC based transformerless inverter with hybrid clamping cell for leakage current elimination,” IEEE Energy Conversion Congress and Exposition, ECCE, pp. 5337–5341, 2015.

[24] A. Acquaviva, A. Rodionov, A. Kersten, T. Thiringer and Y. Liu, "Analytical Conduction Loss Calculation of a MOSFET Three-Phase Inverter Accounting for the Reverse Conduction and the Blanking Time," in IEEE Transactions on Industrial Electronics, vol. 68, no. 8, pp. 6682-6691, Aug. 2021.

[25] Baifeng Chen, Bin Gu, Lanhua Zhang, Zaka Ullah Zahid, Jih-Sheng Lai, Zhiling Liao, Ruixiang Hao, “A high-efficiency MOSFET transformerless inverter for nonisolated microinverter applications,” IEEE Trans. Power Electron., vol. 30, no. 7, pp. 3610–3622, 2015.

[26] D. Graovac and M. Pürschel, “MOSFET Power Losses Calculation Using the Data- Sheet Parameters,” July, pp. 1–23, 2006.

[27] J. Sedo and S. Kascak, “Design of output LCL filter and control of single-phase inverter for grid-connected system,” Electr. Eng., vol. 99, no. 4, pp. 1217–1232, 2017.

novel hybrid neutral point clamped inverter for single

Documents