A Tranformerless Grid-Connected Photovoltaic

这些都是光伏发电系统吧比较经典的论文,希望可以帮到大家。大概都是零八年以后的IEEE论文,有些方法运用比较经典。

A Tranformerless Grid-Connected Photovoltaic System with Active and Reactive Power Control

Su-Won Lee1, Jae-Hyung Kim2, Seong-Ryong Lee3, Byoung-Kuk Lee2, and Chung-Yuen Won2

1 Center for Advanced IT HRD with closed Industry Cooperation, Sungkyunkwan University, Suwon, 440-746, Korea

2 School of Information and Communication Engineering, Sungkyunkwan University, Suwon, 440-746, Korea 3 School of Electrical and Information Engineering, Kunsan National University, Kunsan, 573-701, Korea

Also, considering the high cost of a solar cell panel, the transformerless type is suitable for the PV system [4],[5].

The conventional grid-connected PV system merely supplies the maximum active power from the PV array to the grid via an inverter. Today, non-linear loads are widely used in residential and office buildings. If the grid-connected PV system is applied to non-linear loads, the power quality is relatively poorer, because of the active power supply by the PV array.

To solve this problem, the grid-connected PV system should not only supply active power to the system via MPPT, but also improve the power quality (low THD and unity power factor). In the grid-connected PV system, which considers the power I. INTRODUCTION

quality, studies on the line frequency transformer type (Fig.

Nowadays, renewable energy resources are receiving

1(a)) are in progress, but studies on the transformerless type

attention as a solution to guarantee energy security and reduce

(Fig. 1(b)) are limited [6]-[10].

greenhouse gases, and large-scale research activity has been carried out in this field. Photovoltaic (PV) energy is becoming one of the most important renewable energy resources, since it is clean, generated on-site, pollution free and inexhaustible [1],[2]. Generally, a PV system is categorized into the stand-alone and grid-connected type. In the global market, a large proportion of PV solar power is supplied by the grid-connected type.

A conventional grid-connected PV system supplies the

(a) DC/AC inverter with transformer. maximum available active power from the PV array to the grid.

Fig. 1 shows the most widely used topologies of the grid-connected PV system. Fig. 1(a) consists of an inverter and a line frequency transformer. Even if this topology is simple, it has the disadvantage of the heavy weight and huge volume, because of the large line frequency transformer. The PV module has a wide operating voltage range, owing to the duration of the irradiance and temperature change. Therefore, the output (b) DC/AC inverter with DC/DC converter. voltage of the inverter is restricted by the minimum PV input Fig. 1. The topologies of PV system DC voltage. The PV system with two conversion stages, with a

In this paper, a transformerless grid-connected photovoltaic DC/DC converter as the first stage and a DC/AC inverter as the

second stage, is shown in Fig. 1(b). Although a non-insulation (PV) system with an active and reactive power control algorithm problem is inherent in Fig. 1(b), it is good for making low cost is proposed. The proposed system operations can be divided into and compact products. However, this topology needs a very sunny mode and night mode. In night mode, it compensates for high efficiency DC/DC converter for the high efficiency PV the reactive power demanded by nonlinear loads. In sunny system. Recently, a study on a non-isolated DC/DC converter mode, it not only supplies active power from the PV array to the with a high efficiency, by the soft switching method, was grid or loads, but also performs power quality control (PQC), to

improve the power factor and reduce the harmonic current. In released [3].

In order to supply the PV system on a global scale, the major order to verify the proposed system, simulation results are issue is the reduction in the cost and size of the inverter system. presented.

Abstract-This paper presents a transformerless grid-connected photovoltaic (PV) system with active and reactive power control. The proposed system operations can be categorized into sunny mode and night mode. In night mode, it compensates for the reactive power demanded by nonlinear loads. In sunny mode, it not only supplies active power from the PV array to the grid or loads, but also performs power quality control (PQC), to improve the power factor and reduce the harmonic current. Simulation results are provided to demonstrate the effectiveness of the proposed system.

这些都是光伏发电系统吧比较经典的论文,希望可以帮到大家。大概都是零八年以后的IEEE论文,有些方法运用比较经典。

II. SYSTEM CONFIGURATION AND CONTROL

Figure 2 shows a schematic diagram of a transformerless type grid-connected PV system. The DC/DC converter is connected between the PV array and DC link capacitor, and controlled so as to track the maximum power point of the PV array.

The PWM inverter is synchronized and connected to the grid. The inverter current (Iinv) should be controlled not only to compensate the reactive current of the grid depending on the load, but also to produce its active current corresponding to the PV output power.

be obtained.

Figure 3 shows the proposed control block diagram. The DC/DC converter performs the maximum power point tracking (MPPT) to extract the maximum possible power from the PV array. The DC-link voltage controller is used to control the voltage loop to produce the dc reference current command (IVdc). The load current and the grid voltage are used in the PQC block to generate the active current component of the load current. Using (2), the required grid current amplitude can be calculated. The load current and required grid current amplitude which is multiplied by sin* t are used to produce the inverter reference current command I*inv. Then, the PWM inverter decides the PWM switching pattern via the PI current controller which have the reference current (I*inv) and the real output current (Iinv) of the inverter as the inputs.

Fig. 2. Schematic diagram of transformerless type grid-connected PV system.

The system currents can be expressed as (1);

ILoad=Iinv±Ig (1) where, '-' means Ppv > PLoad and '+' means Ppv < PLoad. Ppv and PLoad are the active power of the PV arrays and load, respectively.

In sunny mode, the proposed system supplies the active and reactive power to the grid or loads. For unity power factor of the grid, the grid current should be controlled to ensure that it includes only the active current. The active current is defined as the sinusoidal current in phase with the grid voltage. Hence the required grid current amplitude can be expressed as (2).

P

(2)Ig*=Re[ILoad] IVdc=Load IVdc

VgWhere, Re[ILoad] is the active current component of the load

current and IVdc is the output current of the dc-link voltage

controller.

Parameter Value Parameter Value

FsFsw_invFilter capacitor 4.7uF

Boost input

Boost inductor 3.4mH 340uF

capacitor

Fsw_con1KVA Where, Fs is the fundamental frequency, Fsw_con is the switching frequency of Filter inductor

3mH

The required grid current amplitude can be to ensure that the DC/DC converter and Fsw_inv is the switching frequency of inverter.

grid current includes only the active current is as follows. The operation characteristics were analyzed into two modes:

(3) the sunny mode, the night mode. Where Vg is the voltage Iinv*=ILoad Ig*×sin*ωt

waveform of the grid, and Ig, Iinv and Iload are current waveforms

Where, sin* t is an unity sinusoidal waveform in phase with

of the grid, inverter and load, respectively. Also Pg, Ppv and Pload

the grid voltage by phase-lock-loop (PLL).

are the active power waveforms of the grid, PV arrays and load,

respectively. In night mode, the grid active current can be calculated by

Figure 4 shows the simulation results of the conventional

IVdc=0 (equation (2)). Also, if the grid active current is applied to

system in sunny mode where the load changes from no load to

the equation (3), the reference current of the inverter (I*inv) can

1kVA nonlinear load at 0.5sec.

这些都是光伏发电系统吧比较经典的论文,希望可以帮到大家。大概都是零八年以后的IEEE论文,有些方法运用比较经典。

Fig. 4. Simulation results of the conventional system in sunny mode.

Fig. 6. Simulation results of the proposed system in sunny mode.

Fig. 5. FFT results of the conventional system in sunny mode.

Fig. 7. FFT results of the proposed system in sunny mode

Figure 8 shows the simulation results of the proposed system in the night mode. As shown Fig. 8(a), the grid current is sinusoidal waveform, which is in phase with the grid voltage. The grid supplies the active power which is needed to loads and the inverter compensates all the reactive power. Fig. 9 illustrates the FFT results of the grid current, the inverter current and the load current. The THD of the grid current is 2.95%. The power factor of the proposed system is 0.99.

From fig. 4(f), the PV system supplies 100% active power to the grid before the load change at 0.5 sec. However, in case that the load change occurs at 0.5sec, the PV system supplies the active power which is needed to loads and others are supplied to the grid. As shown Fig. 4(b), the grid current (Ig) is bitterly distorted. Fig. 5 illustrates the FFT result of the grid voltage and current, the inverter current and the load current. The total harmonic distortion (THD) of the grid current is 57.2%. The power factor of the conventional system is 0.86.

Figure 6 shows the simulation results of the proposed system in sunny mode where the load changes from no load to 1kVA nonlinear load at 0.5sec. From fig. 6(f), the PV system supplies 100% active power to the grid before the load change at 0.5 sec. However, in case that the load change occurs at 0.5sec, the PV system supplies the active power which is needed to loads and others are supplied to the grid. The load current (ILoad) is bitterly distorted. The grid current (Ig), on the other hand, can be observed to keep a nearly sinusoidal waveform through the compensating operation of the inverter. Fig. 6(a) show the grid voltage and current, showing that the grid current is inverse phase with the grid voltage. As shown Fig. 6(e), the DC-link voltage control maintains the desired level of 380V. Fig. 7 illustrates the FFT results of the grid voltage and current, the inverter current and the load current. The THD of the grid current is 2.54%. The power factor of the proposed system is

0.98.

Fig. 8. Simulation results of the proposed system in night mode.

The improvement in power quality can be observed through the THD analysis displayed in Fig. 7 and Fig. 9 and the THD of

这些都是光伏发电系统吧比较经典的论文,希望可以帮到大家。大概都是零八年以后的IEEE论文,有些方法运用比较经典。

the grid current could be controlled within 3% in spite of a highly distorted load current.

Grid-Connected Photovoltaic System with Active and Reactive Power Control using dq0 Transformation,” in Proc. 39th Annu. Power Electronics Specialists Conference, pp. 1202-1207, Jun. 2008.

[8] F. Delfino, G. B. Denegri, and R. Procopio, “An Integrated Active and

Reactive Power Control Scheme for Grid-Connected Photovoltaic Production System,” in Proc. 39th Annu. Power Electronics Specialists Conference, pp. 1463-1468, Jun. 2008.

[9] T.-F. Wu, C.-L. Shen and H.-S. Nei, “A 1 3W Grid-Connected PV

Inverter with APF Based on Nonlinear Programming and FZPD Algorithm,” in Proc. 34th Annu. Power Electronics Specialists Conference, pp. 546-552, June 2003.

[10] Louis Cheng, Richard Cheung, and K. H. Leung, “Advanced Photovoltaic

Inverter with Additional Active Power Line Conditioning Capability,” in Proc. 28th Annu. Power Electronics Specialists Conference, vol. 1, pp. 279-283, June. 1997.

Fig. 9. FFT results of the proposed system in night mode.

IV. CONCLUSION

In order to supply the PV system world widely, the technical development on low cost and small size is major issue now. Also, considering the high cost solar cell's panel, transformerless type is suitable for the PV system. This paper presents a transformerless grid-connected PV system with active and reactive power control. The proposed system operation is divided by sunny mode and night mode. In night mode, it operates to compensate the reactive power demanded by nonlinear loads. In sunny mode, it not only supplies active power which is developed in the PV array to the grid or loads, but also performs power quality control(PQC) to improve power factor and reduce harmonic current.

ACKNOWLEDGMENT

This work was supported in part by the New & Renewable Energy Development Project (2007-N-PV08-03-0) of the KEMCO.

REFERENCES

[1] G. Grandi, D. Casadei, and C. Rossi, "Direct Coupling of Power Active

Filters with Photovoltaic Generation System with Improved MPPT Capability", in Proc. 2003 IEEE Bologna Power Tech Conference, vol. 2, June, 2003.

[2] Y.-C Kuo, T.-J Liang, and J.-F Chen, “Novel Maximum-Power

-Point-Tracking Controller for Photovoltaic Energy Conversion System,” IEEE Trans. Ind. Electron., vol. 48, no. 3, June. 2001.

[3] J.-H. Lee, J.-H. Kim, C.-Y. Won, S.-J. Jang, Y.-C. Jung, “Soft Switching

Multi-Phase Boost Converter for Photovoltaic System,” in Proc. 13th International Power Electronics and Motion Control Conference, pp. 1924-1928, Sep. 2008.

[4] Yi Huang, Fang Z. Peng, Jin Wang, and Dong-wook Yoo, “A Survey of the

Power Conditioning System for PV Power Generator,” in Proc. 37th Annu. Power Electronics Specialists Conference, pp. 3257-3262, June 2006.

[5] B.-D Min, J.-P Lee, J.-H Kim, D.-W Yoo, and E.-H Song, “A New

Topology with High Efficiency throughout All Load Range for Photovoltaic PCS,” IEEE Trans. Industrial Electronics : Accepted for future publication.

[6] S.H. Ko, S.R. Lee, H. Dehbonei, and C.V. Nayar, “A Grid-Connected

Photovoltaic System with Direct Coupled Power Quality Control," IECON 2006-32nd Annual Conf., pp. 5203-5208, Nov. 2006.

[7] Mateus F. Schonardie, and Denizar C. Martins, “Three-Phasse

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