Design and Simulation of three phase Inverter for grid connected Photovoltaic systems

ABSTRACT:

Grid connected photovoltaic (PV) systems feed electricity directly to the electrical network operating parallel to the conventional source. This paper deals with design and simulation of a three phase inverter in MATLAB SIMULINK environment which can be a part of photovoltaic grid connected systems. The converter used is a Voltage source inverter (VSI) which is controlled using synchronous d-q reference frame to inject a controlled current into the grid. Phase lock loop (PLL) is used to lock grid frequency and phase. The design of low pass filter used at the inverter output to remove the high frequency ripple is also discussed and the obtained simulation results are presented.

 

KEYWORDS:

  • VSI Inverter
  • PLL
  • d-q reference frame
  • Grid connected system.

SOFTWARE: MATLAB/SIMULINK

 

BLOCK DIAGRAM:

grid tied pv system

Fig.1 Block diagram of the system

 

EXPECTED SIMULATION RESULTS:

Fig.2 Output frequency obtained from PLL

Fig.3 Sin & Cos wave generated by PLL

Fig.4 Synchronization between reference grid voltage & PLL output voltage

 

Fig.5 Three phase voltage fed by inverter to grid

Fig .6 Average active power fed to grid is 1000 Watt

 

CONCLUSION:

The design of the system is carried out for feeding 1KW power to the grid The Inverter is controlled in order to feed active power to the grid, using synchronous d-q transformation. PLL is used to lock grid frequency and phase. The phase detection part of PLL is properly done by using dq transformation in the three phase system. The FFT analysis of the inverter output current shows that the THD is within limits and the controlled injected current generates three phase balance current which controls power at the output of the transformer. To simulate the actual grid connected PV system, the PV model, dc to dc converter model and the control of the dc to dc converter should be included in place of the battery source.

 

REFERENCES:

  • Soeren Baekhoej, John K Pedersen & Frede Blaabjerg, ―A Review of single phase grid connected inverter for photovoltaic modules,‖ IEEE transaction on Industry Application , Vol. 41,pp. 55 – 68, Sept 2005
  • Milan Pradanovic& Timothy Green, ―Control and filter design of three phase inverter for high power quality grid connection, ― IEEE transactions on Power Electronics,18. pp.1- 8, January 2003
  • C Y Wang,Zhinhong Ye& G.Sinha, ― Output filter design for a grid connected three phase inverter,‖Power electronics Specialist Conference, pp.779-784,PESE 2003
  • Samul Araujo& Fernando Luiz, ― LCL fiter design for grid connected NPC inverters in offshore wind turbins,‖ 7th International conference on Power Electronics, pp. 1133-1138, October 2007.
  • Frede Blaabjerg , Remus Teodorescu and Marco Liserre, ―Overview of control & grid synchronization for distributed power generation systems,‖ IEEE transaction on Industrial Electronics, Vol. 53, pp. 500 – 513,Oct- 2006

 

Control for Grid-Connected and Intentional Islanding Operations of Distributed Power Generation

ABSTRACT:

Intentional islanding describes the condition in which a microgrid or a portion of the power grid, which consists of a load and a distributed generation (DG) system, is isolated from the remainder of the utility system. In this situation, it is important for the microgrid to continue to provide adequate power to the load. Under normal operation, each DG inverter system in the microgrid usually works in constant current control mode in order to provide a preset power to the main grid. When the microgrid is cut off from the main grid, each DG inverter system must detect this islanding situation and must switch to a voltage control mode. In this mode, the microgrid will provide a constant voltage to the local load. This paper describes a control strategy that is used to implement grid-connected and intentional-islanding operations of distributed power generation. This paper proposes an intelligent load-shedding algorithm for intentional islanding and an algorithm of synchronization for grid reconnection.

 

KEYWORDS:

  1. Distributed generation (DG)
  2. Grid-connected operation
  3. Intentional-islanding operation
  4. Islanding detection
  5. Load shedding
  6. Synchronization

 

SOFTWARE: MATLAB/SIMULINK

 

BLOCK DIAGRAM:

grid connected  

Fig. 1. Schematic diagram of the grid connected inverter system.

 

EXPECTED SIMULATION RESULTS:

grid-connected to intentional-islanding operation.

Fig. 2. From grid-connected to intentional-islanding operation.

Synchronization for grid reconnection.
Fig. 3. Synchronization for grid reconnection.

Phase voltage (top) without and (bottom) with the synchronization algorithm.

Fig. 4. Phase voltage (top) without and (bottom) with the synchronization algorithm.


Fig. 5. Phase voltage
Va without the load-shedding algorithm.

Phase voltage Va with the load-shedding algorithm

Fig. 6.Phase voltage Va with the load-shedding algorithm.

CONCLUSION:

 Through this paper, the control, islanding detection, load shedding, and reclosure algorithms have been proposed for the operation of grid-connected and intentional-islanding DGs. A controller was designed with two interface controls: one for grid connected operation and the other for intentional islanding operation. An islanding-detection algorithm, which was responsible for the switch between the two controllers, was presented. The simulation results showed that the detection algorithm can distinguish between islanding events and changes in the loads and can apply the load-shedding algorithms when needed. The reclosure algorithm causes the DG to resynchronize itself with the grid. In addition, it is shown that the response of the proposed control schemes is capable of maintaining the voltages and currents within permissible levels during grid connected and islanding operation modes. The experimental results showed that the proposed control schemes are capable of maintaining the voltages within the standard permissible levels during grid connected and islanding operation modes. In addition, it was shown that the reclosure algorithm causes the DG to resynchronize itself with the grid.

 

REFERENCES:

  • Jayaweera, S. Galloway, G. Burt, and J. R. McDonald, “A sampling approach for intentional islanding of distributed generation,” IEEE Trans. Power Syst., vol. 22, no. 2, pp. 514– 521, May 2007.
  • M. Guerrero, J. C. Vásquez, J. Matas, M. Castilla, and L. García de Vicuña, “Control strategy for flexible microgrid based on parallel lineinteractive UPS systems,” IEEE Trans. Ind. Electron., vol. 56, no. 3, pp. 726–736, Mar. 2009.
  • Fuangfoo, T. Meenual,W.-J. Lee, and C. Chompoo-inwai, “PEA guidelines for impact study and operation of DG for islanding operation,” IEEE Trans. Ind. Appl., vol. 44, no. 5, pp. 1348–1353, Sep./Oct. 2008. 156 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 58, NO. 1, JANUARY 2011
  • Carpaneto, G. Chicco, and A. Prunotto, “Reliability of reconfigurable distribution systems including distributed generation,” in Proc. Int. Conf. PMAPS, 2006, pp. 1–6.
  • IEEE Recommended Practice for Utility Interface of Photovoltaic (PV) Systems, IEEE Std 929-2000, 2000, p. i.