Implementation of a DC Power System with PV Grid-Connection and Active Power Filtering

ABSTRACT:  

The objective of this paper is to develop a DC power supply system with photovoltaic (PV) grid-connection and active power filtering. The proposed power supply system consists of an input stage and an output stage. In the input stage, a dc/dc converter incorporated with the perturbation-and-observation method can draw the maximum power from the PV source, which can be delivered to the output stage. On the other hand, grid connection or active power filtering, depending on the power of photovoltaic; will be implemented by a dc/ac inverter in the output stage. Two microcontrollers are adopted in the proposed system, of which one is to implement the MPPT algorithm, the other is used to determine the operation modes, which can be grid connection mode, direct supply mode or active power filtering mode. Finally, the experimental results are measured to verify the proposed algorithms and feasibility of the system.

 KEYWORDS:

  1. 12 Pulse AClDC Converter
  2. Phase Controller
  3. Autotransformer

 SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 image001

Fig. 1 Block diagram of the proposed DC power system

EXPECTED SIMULATION RESULTS:

 image002

 Fig. 2 The Pin, V1 and i1 waveforms of the MPPT Algorithm

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(V1: 100 V/div,i1: 2 A/div, Pin: 200 W/div, time: 10 s/div)

Fig. 3 Experimental results of the MPPT function of the boost converter operate under input voltage change (150V→200V→150V).

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(Vac: 100 V/div,iC : 5 A/div, time: 10 ms/div)

(a)

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(Vac: 100 V/div,iC : 5 A/div, time: 10 ms/div)

(b)

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(Vac: 100 V/div,iC : 5 A/div, time: 10 ms/div)

Fig. 4 The AC voltage Vac and output current io waveforms while output power is (a) 1kW, (b) 500W and (c) 250W.

 image007

(iL : 5 A/div, time: 10 ms/div)

Fig. 5 The load current waveform with Rn=50Ω.

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Fig. 6 Comparison the measured harmonic amount of grid voltage and current with Europe harmonic standard IEC 1000-3-2 Class A before compensation

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Fig. 7 Comparison the measured harmonic amount of grid voltage and current with Europe harmonic standard IEC 1000-3-2 Class A after compensation

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(Vac : 200 V/div,iS : 10 A/div, iC : 5 A/div time: 10 ms/div)

Fig. 8 The measured results of AC voltage Vac, AC current is and compensated current ic of the system operate under the active power filtering mode.

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(a)

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(b)

(Vac : 200 V/div,iac : 10 A/div, iC : 5 A/div, time: 20 ms/div)

Fig. 9 The load variations of the proposed power system operates under active power filtering mode (a) heavy load → light load, and (b) light load →heavy load.

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(VS : 100 V/div,VC1 : 300 V/div, i1 : 5 A/div, iC : 2 A/div, Pin : 500 W/div )

Fig. 10 The operational mode switching of the proposed r system.

CONCLUSION:

A DC power system with PV grid-connection and active power filtering has been presented in this paper, in which a DC/DC converter is firstly used to promote the output voltage of PV array and achieve the MPP. The proposed system can automate switching among the grid connection mode, direct supply mode or active power filtering mode according to the output power of PV array. In addition, two microcontrollers are used to act as system controllers, in which can except implement complicate calculation and PWM output, it can also reduce the hardware complication and cost to improve the reliability and feasibility of system. The experimental results have verified the feasibility and flexibility of the proposed system.

REFERENCES:

[1] A. Lohner, T. Meyer and A. Nagel,“A New Panel- Integratable Inverter Concept for Grid-Connected Photovoltaic System,”IEEE International Symposium on Industrial Electronics, Vol. 2, June 1996, pp. 827-831.

[2] U. Herrmann, H. G. Langer, H. van der Broeck,“Low Cost DC to AC Converter for Photovoltaic Power Conversion in Residential Applications,”Proceedings of the IEEE PESC, June 1993, pp. 588-594.

[3] J. H. R. Enslin, M. S. Wolf, D. B. Snyman and W. Sweiges,“Integrated Photovoltaic Maximum Power Point Tracking Converter,”IEEE Trans. On Industrial Electronics, Vol. 44, No. 6, 1997, pp. 769-773.

[4] S. J. Chiang, K. T. Chang and C. Y. Yen,“Residential Photovoltaic Energy Storage System,” IEEE Trans. on Industrial Electronics, Vol. 45, No. 3, 1998, pp. 385-394.

[5] S. Sopitpan, P. Changmoang and S. Panyakeow,“PV Systems With/without Grid Back-up for Housing Applications,”Proceedings of the IEEE Photovoltaic Specialists Conference, 2000, pp. 1687-1690.

Analysis of 12 Pulse Phase Control AC/DC Converter

ABSTRACT:

 In this paper, the unbalanced current in the 12- pulse phase control AC/DC converters was studied. The 12- pulse A-Y type AClDC converter will keep a balanced voltage with 30″ phase shifted at the low coupling coefficient condition. But an unbalanced current will be obtained in the 12-pulse autotransformer phase shift AClDC converter at the low coupling coefficient condition. The theoretical phasor analysis of the unbalanced current was presented and a feedback controller was designed to overcome this problem. Finally, a 3 kW 12-pulse autotransformer phase shifted AClDC converter was implemented to demonstrate the theoretical analysis.

KEYWORDS:

  1. 12 Pulse AClDC Converter
  2. Phase Controller
  3. Autotransformer

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

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Fig. 1. Conventional 12-pulse AClDC converter.

(a) A-Y isolated transformer.

(b) Autotransformer phase shifted.

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Fig. 2. 12-pulse phase control A-Y connected AC/DC converter.

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Fig. 3. I;!-pulse phase control autotransformer connected AC/DC converter.

 EXPECTED SIMULATION RESULTS:

 image010

 

Fig. 4 The output current io, and io, of 12-pulse phase control A-Y

typ: transformer ACDC converter with K=0.96 and a = 30″

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Fig 5 The output current io, and io, of 12-pulse autotransformer

phase shift ACDC converter with K=0.96 and a = 30″.

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Fig. 6 The output current of 12-pulse autotransformer connected

AC/DC converter with the controller

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Fig. 7 Experimental results for a resistive load without controller

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Fig. 8 Experimental results for a resistive load with controller

CONCLUSION:

 In this paper, the 12-pulse phase control ACDC converters with A-Y type and autotransformer type are analyzed and studied. The theoretical analysis is presented and the computer simulation results are performed. The 12- pulse A-Y type ACDC converter can function well under any firing condition. However, a serious unbalanced circulation current exists in the autotransformer connected ACDC converter at the non-unity coupling coefficient conditions. Finally, a 3 kW 12-pulse autotransformer phase controlled ACDC converter was implemented to demonstrate the theoretical analysis.

 REFERENCES:

 

  1. S. Choi, A. Jouanne, P. Enjeti and 1. Pitel, “New Polyphase Transformer Arrangements with Reduced kVA Capacities for Harmonic Current Reduction in Rectifier Type Utility Interface,“ IEEE PESC, 1995.

 

  1. S. Choi, P. N. Enjeti, H. Lee and I. J. Pitel, “A New Active Interphase Reactor for 12-Pulse Rectifiers Provides Clean Power Utility Interface,” IEEE IAS, pp.2468-2474, 1995.

 

  1. G. Oliver, G. E. April, E. Ngandui and C. Guimaraes, “Novel Transformer Connection to Improve Current Sharing on High Current DC Rectifier,” IEEE IAS, pp.986-962, 1993.

 

  1. S. Miyairi, etc.al, “New Method for Reducing Harmonic Involved in Input and Output of Rectifier with Interphase Transformer,” IEEE Trans. On Industry Applications, Vol. IA-22, No.5, pp.790- 797, SepIOct, 1986.

 

  1. A .R. Prasad, P. D. Ziogas, and S. Manias, “An Active Power Factor Correction Technique for Three-phase Diode Rectifier,” IEEE Trans. on Power Electronics, Vo1.6, No.1, pp.83-92, 1991