Improved Particle Swarm Optimization For Photovoltaic System Connected To The Grid With Low Voltage Ride Through Capability

 ABSTRACT:

 Grid connected photovoltaic (PV) system encounters different types of abnormalities during grid faults; the grid side inverter is subjected to three serious problems which are excessive DC link voltage, high AC currents and loss of grid-voltage synchronization. This high DC link voltage may damage the inverter. Also, the voltage sags will force the PV system to be disconnected from the grid according to grid code. This paper presents a novel control strategy of the two-stage three-phase PV system to improve the Low-Voltage Ride-Through (LVRT) capability according to the grid connection requirement. The non-linear control technique using Improved Particle Swarm Optimization (IPSO) of a PV system connected to the grid through an isolated high frequency DCeDC full bridge converter and a three-phase three level neutral point clamped DC-AC converter (3LNPC2) with output power control under severe faults of grid voltage. The paper, also discusses the transient behavior and the performance limit for LVRT by using a DC-Chopper circuit. The model has been implemented in MATLAB/SIMULINK. The proposed control succeeded to track MPP, achieved LVRT requirements and improving the quality of DC link voltage. The paper show

KEYWORDS:

  1. Particle swarm optimization
  2. Maximum power point tracking
  3. PV system
  4. High frequency isolated converter
  5. Low voltage ride through
  6. Grid

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

 

Fig. 1. Block diagram of the PV system connected to the grid.

EXPECTED SIMULATION RESULTS:

Fig. 2. PV module characteristics (a) Current-voltage characteristics (b) power-voltage characteristics.

Fig. 3. Behavior of PV array under normal condition using IPSO.

Fig. 4. DC-link voltage under normal condition using IPSO.

Fig. 5. Behavior of PV array under normal condition using IC.

Fig. 6. DC-link voltage under normal condition using IC.

Fig. 7. Behavior of grid connected inverter system under normal operation.

 

Fig. 8. The grid voltage fault.

Fig. 9. Behavior of PV array under fault condition.

Fig. 10. DC-link voltage under fault condition.

Fig. 11. Behavior of grid connected inverter system under fault condition.

Fig. 12. Behavior of PV array with LVRT capability.

Fig. 13. DC-link voltage during a grid fault with LVRT capability.

Fig. 14. Behavior of grid connected inverter system with LVRT capability.

CONCLUSION:

Based on the existing grid requirements, this paper discussed the potential of a two-stage three-phase grid-connected PV system operating in grid fault condition. The power control method proposed in this paper is effective when the system is under grid fault operation mode. It can be concluded that the future three-phase grid-connected PV systems are ready to be more active and more “smart” in the regulation of power grid.

Non-linear robust control technique using IPSO control is implemented for MPPT of 100.7 kW PV system connected to the grid. Complete control of both active and reactive powers is implemented using Matlab/Simulink with complete simulation under severe faults of grid voltage. The results show superior behavior of the IPSO; it has a faster dynamic response and better steady-state performance than the traditional algorithm; IC method, thus improving the efficiency of the photovoltaic power generation system. The use of full bridge single phase inverter with a high frequency transformer which combines the advantages of 60 Hz technology and transformer- less inverter technology, achieved MPPT requirements with IPSO. Also, this system overcomes the drawbacks of DC-chopper parameters design.

Two loops of control for the utility-connected 3LNPC2 are implemented which improve the performance of inverter and reduces the harmonics in output voltage. This control, also, increases the power injected to the grid and consequently increases the total efficiency of the system. The results show that the DC chopper circuit is capable of reducing the DC-link voltage below threshold values during the fault and protect it from failure or damage. The IPSO is capable of tracking MPP with LVRT capability included.

An anti-wind up conditioned strategy is used in order to improve the quality on the DC link voltage during and after the grid fault. It succeeds to stop accumulation of the integral part during fault, which helps system to follow up pre-faults values rapidly after clearing the fault. Finally, simulated results have demonstrated the feasibility of the IPSO algorithm and capability of MPPT in grid-connected PV systems with LVRT enhancement.

REFERENCES:

[1] Ramdan B.A. Koad, Ahmed. F. Zobaa, Comparison between the conventional methods and PSO based MPPT algorithm for photovoltaic systems, Int. J. Electr. Electron. Sci. Eng. 8 (2014) 619e624.

[2] Ali Reza Reisi, Mohammad Hassan Moradi, Shahriar Jamas, Classification and comparison of maximum power point tracking techniques for photovoltaic system: a review, Renew. Sustain. Energy Rev. 19 (2013) 433e443.

[3] N.H. Saad, A.A. Sattar, A.M. Mansour, Artificial neural controller for maximum power point tracking of photovoltaic system, in: MEPCON’2006 Conference, II, El-MINIA, Egypt, 2006, pp. 562e567.

[4] Raal Mandour I. Elamvazuthi, Optimization of maximum power point tracking (MPPT) of photovoltaic system using artificial intelligence (AI) algorithms, J. Emerg. Trends Comput. Information Sci. 4 (2013) 662e669.

[5] Saeedeh Ahmadi, Shirzad Abdi, Maximum power point tracking of photovoltaic systems using PSO algorithm under partially shaded conditions, in: The 2nd Cired Regional Conference, Tehran, Iran, 14, 2014, pp. 1e7.

Transformer less Inverter with Virtual DC Bus Concept for Cost- Effective Grid-Connected PV Power Systems

 

ABSTRACT:

In order to eliminate the common-mode (CM) leakage current in the transformer less photovoltaic (PV) systems, the concept of the virtual dc bus is proposed in this paper. By connecting the grid neutral line directly to the negative pole of the dc bus, the stray capacitance between the PV panels and the ground is bypassed. As a result, the CM ground leakage current can be suppressed completely. Meanwhile, the virtual dc bus is created to provide the negative voltage level for the negative ac grid current generation. Consequently, the required dc bus voltage is still the same as that of the full-bridge inverter. Based on this concept, a novel transformer less inverter topology is derived, in which the virtual dc bus is realized with the switched capacitor technology. It consists of only five power switches, two capacitors, and a single filter inductor. Therefore, the power electronics cost can be curtailed. This advanced topology can be modulated with the uni polar sinusoidal pulse width modulation (SPWM) and the double frequency SPWM to reduce the output current ripple. As a result, a smaller filter inductor can be used to reduce the size and magnetic losses. The advantageous circuit performances of the proposed transformer less topology are analyzed in detail, with the results verified by a 500-W prototype.

KEYWORDS:

  1. Common mode (CM) current
  2. Photovoltaic (PV) system
  3. Switched capacitor
  4. Transformer less inverter
  5. Unipolar sinusoidal pulse width modulation (SPWM)
  6. Virtual dc bus.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig.1 Proposed topology

EXPECTED SIMULATION RESULTS:

 Fig.2 Output current and grid voltage

Fig.3 Current harmonics distribution

Fig.4 Simulation waveform for reactive power generation

Fig.5 Enlarged figure for current stress on S3

Fig.6 CM current of H5 circuit

Fig.7 Current stress under different capacitor ratio for proposed circuit: (a) C1/C2=1/2; (b) C1/C2=2/1

CONCLUSION:

The concept of the virtual DC bus is proposed to solve the CM current problem for the transformerless grid-connected PV inverter. By connecting the negative pole of the DC bus directly to the grid neutral line, the voltage on the stray PV capacitor is clamped to zero. This eliminates the CM current completely. Meanwhile, a virtual DC bus is created to provide the negative voltage level. The required DC voltage is only half of the half bridge solution, while the performance in eliminating the CM current is better than the full bridge based inverters. Based on this idea, a novel inverter topology is proposed with the virtual DC bus concept by adopting the switched capacitor technology. It consists of only five power switches and a single filter inductor. The proposed topology is especially suitable for the small power single phase applications, where the output current is relatively small so that the extra current stress caused by the switched capacitor does not cause serious reliability problem for the power devices and capacitors. With excellent performance in eliminating the CM current, the virtual DC bus concept provides a promising solution for the transformerless grid-connected PV inverters.

REFERENCES:

[1] Benner, J.P.; Kazmerski, L.; , “Photovoltaics gaining greater visibility,” Spectrum, IEEE , vol.36, no.9, pp.34-42, Sep 1999

[2] Zheng Zhao; Ming Xu; Qiaoliang Chen; Jih-Sheng Lai; Younghoon Cho; , “Derivation of boost-buck converter based high-efficiency robust PV inverter,” Energy Conversion Congress and Exposition (ECCE), 2010 IEEE , vol., no., pp.1479-1484, 12-16 Sept. 2010

[3] Erickson, R.W.; Rogers, A.P.; , “A Microinverter for Building-Integrated Photovoltaics,” Applied Power Electronics Conference and Exposition, 2009. APEC 2009. Twenty-Fourth Annual IEEE , vol., no., pp.911-917, 15-19 Feb. 2009

[4] Kjaer, S.B.; Pedersen, J.K.; Blaabjerg, F.; , “A review of single-phase grid-connected inverters for photovoltaic modules,” Industry Applications, IEEE Transactions on , vol.41, no.5, pp. 1292- 1306, Sept.-Oct. 2005

[5] Koutroulis, E.; Blaabjerg, F.; , “Design optimization of grid-connected PV inverters,” Applied Power Electronics Conference and Exposition (APEC), 2011 Twenty-Sixth Annual IEEE , vol., no., pp.691-698, 6-11 March 2011