Modelling, Design, Control, and Implementation of a Modified Z-source Integrated PV/Grid/EVDC Charger/Inverter

ABSTRACT:

Solar Energy has been the most popular sources of renewable energy for residential and semi commercial applications. Fluctuations of solar energy harvested due to atmospheric conditions can be mitigated through energy storage systems. Solar energy can also be used to charge electric vehicle batteries to reduce the dependency on the grid. One of the requirements for a converter for such applications is to have a reduced number of conversion stages and provide isolation. Z-source inverter (ZSI) topology is able to remove multiple stages and achieve voltage boost and DC-AC power conversion in a single stage. The use of passive components also presents an opportunity to integrate energy storage systems (ESS) into them. This paper presents modeling, design and operation of a modified Z-source inverter (MZSI) integrated with a split primary isolated battery charger for DC charging of electric vehicles (EV) batteries. Simulation and experimental results have been presented for the proof of concept of the operation of the proposed converter.

KEYWORDS:

  1. Z-source-inverters
  2. Active filter
  3. Energy storage
  4. Photovoltaic (PV) power generation
  5. Quasi-Zsource inverter (qZSI)
  6. Single-phase systems
  7. Transportation electrification
  8. Solar energy
  9. Distributed power generation
  10. Inverter

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 

Fig. 1. Simplified Block Diagram of the System

 EXPECTED SIMULATION RESULTS

 

Fig. 2. Simulation Waveform of the grid current,Ig, DC link voltage,VPN, Capacitor Voltage,VC1, and Battery current,ib for the power balance between the Photovoltaic input power, the AC Grid side and the battery power.

Fig. 3. Simulation Waveform for the power balance between the Photovoltaic input power, the AC Grid side and the battery power.

CONCLUSION:

A modified ZSI topology has been proposed in this paper is an attractive solution for photovoltaic grid connected charging systems. It consist of a single stage photovoltaic grid (PV-Grid) connection and an integrated charger for PV-Grid connected charging or energy storage. This topology can be applied to centralized configuration for charging in semi-commercial locations such as a parking lot of a shopping mall. For residential applications, this idea can be extended to string inverters with the charger side of the string inverter configurations connected in series or parallel for current sharing. The paper proposes a an energy storage topology using Z source converter through symmetrical operation of its impedance network.

REFERENCES:

[1] D. Aggeler, F. Canales, H. Zelaya, D. L. Parra, A. Coccia N. Butcher, and O. Apeldoorn, “Ultra-fast dc-charge infrastructures for ev-mobility and future smart grids,” in Proc. of IEEE PES Innovative Smart Grid Technologies Conference Europe, pp. 1–8, Oct. 2010.

[2] G. Carli and S. S. Williamson, “Technical considerations on power conversion for electric and plug-in hybrid electric vehicle battery charging in photovoltaic installations,” IEEE Trans. on Ind. Electron., vol. 28, no. 12, pp. 5784–5792, 2013.

[3] J. G. Ingersoll and C. A. Perkins, “The 2.1 kw photovoltaic electric vehicle charging station in the city of santa monica, california,” in Proc. of the Twenty Fifth IEEE Photovoltaic Specialists Conference, pp. 1509– 1512, May. 1996.

[4] S. B. Kjaer, J. K. Pedersen, and F. Blaabjerg, “A review of single-phase grid-connected inverters for photovoltaic modules,” IEEE Trans. on Ind. Appl., vol. 41, no. 5, pp. 1292–1306, Sep. 2005.

[5] N. A. Ninad, L. A. C. Lopes, and I. S. Member, “Operation of Single-phase Grid-Connected Inverters with Large DC Bus Voltage Ripple,” Proc. of the IEEE Canada Electrical Power Conference, 2007.

 

 

Reduction of Energy Storage Requirements in Future Smart Grid Using Electric Springs

 

ABSTRACT:

The electric spring is an emerging technology proven to be effective in i) stabilizing smart grid with substantial penetration of intermittent renewable energy sources and ii) enabling load demand to follow power generation. The subtle change from output voltage control to input voltage control of a reactive power controller offers the electric spring new features suitable for future smart grid applications. In this project, the effects of such subtle control change are highlighted, and the use of the electric springs in reducing energy storage requirements in power grid is theoretically proven and practically demonstrated in an experimental setup of a 90 kVApower grid.Unlike traditional Statcom and StaticVar Compensation technologies, the electric spring offers not only reactive power compensation but also automatic power variation in non-critical loads. Such an advantageous feature enables noncritical loads with embedded electric springs to be adaptive to future power grid. Consequently, the load demand can follow power generation, and the energy buffer and therefore energy storage requirements can be reduced.

KEYWORDS:

  1. Distributed power systems
  2. Energy storage
  3. Smart grid
  4. Stability

 SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 

Fig. 1. Experimental setup based on the 90 kVA Smart Grid Hardware Simulation System at the Maurice Hancock Smart Energy Laboratory.

 EXPECTED SIMULATION RESULTS:

Fig. 2. Measured rms power line voltage (vs) and non-critical load voltage (vo)

Fig. 3. Measured average powers of the wind power simulator (PG+PR), battery storage (PS) and non-critical load(P1)

Fig. 4. Measured power (Ps) and energy change (Es) of the battery storage.

Fig. 5. Measured electric spring reactive power (QES), critical load voltage (VR2) and power (P2).

 CONCLUSION:

In this paper, the differences between the output voltage control and the input voltage control of a reactive power controller are highlighted. While energy storage is an effective but expensive means to balance power supply and demand, an analysis and practical confirmation are presented to show that electric springs can reduce energy storage requirements in a power grid. Electric springs allow the non-critical load power to vary with the renewable energy profile. By reducing the instantaneous power imbalance of power supply and demand, electric springs allow the non-critical load demand profile to follow the power generation profile and reduce the energy storage requirements in power grid. This important point has been theoretically proved and practically verified in an experimental setup. Due to the advantageous features such as enabling the load demand to follow the power generation, the reduction of energy storage requirements, the reactive power compensation for voltage regulation, and the possibility of both active and reactive power control [28], electric springs open a door to distributed stability control for future smart grid with substantial penetration of intermittent renewable energy sources.

REFERENCES:

[1] D. Westermann and A. John, “Demand matching wind power generation with wide-area measurement and demand-side management,” IEEE Trans. Energy Convers., vol. 22, no. 1 , pp. 145–149, 2007.

[2] P. Palensky and D. Dietrich, “Demand side management: Demand response, intelligent energy systems, and smart loads,” IEEE Trans. Ind. Inform., vol. 7 , no. 3 , pp. 381–388, 2011.

[3] P. Varaiya, F. Wu, and J. Bialek, “Smart operation of smart grid: Risklimiting dispatch,” Proc. IEEE, vol. 99, no. 1 , pp. 40–57, 2011.

[4] I. Koutsopoulos and L. Tassiulas, “Challenges in demand load control for the smart grid,” IEEE Netw., vol. 25, no. 5 , pp. 16–21, 2011.

[5] A. Mohsenian-Rad, V. W. S. Wong, J. Jatskevich, R. Schober, and A. Leon-Garcia, “Autonomous demand-side management based on gametheoretic energy consumption scheduling for the future smart grid,” IEEE Trans. Smart Grid, vol. 1 , no. 3 , pp. 320–331, 2011.

 

 

Grid-Connected PV Array with Supercapacitor Energy Storage System for Fault Ride Through

ABSTRACT:

A fault ride through, power management and control strategy for grid integrated photovoltaic (PV) system with supercapacitor energy storage system (SCESS) is presented in this paper. During normal operation the SCESS will be used to minimize the short term fluctuation as it has high power density and during fault at the grid side it will be used to store the generated power from the PV array for later use and for fault ride through. To capture the maximum available solar power, Incremental Conductance (IC) method is used for maximum power point tracking (MPPT). An independent P-Q control is implemented to transfer the generated power to the grid using a Voltage source inverter (VSI). The SCESS is connected to the system using a bi-directional buck boost converter. The system model has been developed that consists of PV module, buck converter for MPPT, buck-boost converter to connect the SCESS to the DC link. Three independent controllers are implemented for each power electronics block. The effectiveness of the proposed controller is examined on Real Time Digital Simulator (RTDS) and the results verify the superiority of the proposed approach.

KEYWORDS:

  1. Active and reactive power control
  2. Fault ride through
  3. MPPT
  4. Photovoltaic system
  5. RTDS Supercapacitor
  6. Energy storage

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

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Fig.1. Grid connected PV system with energy storage

 EXPECTED SIMULATION RESULTS:

 image002

Fig.2. Grid voltage after three phase fault is applied

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Fig.3. PV array power PPV with SCESS and with no energy storage

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Fig.4. Grid active power Pg for a three phase fault with and without energy storage

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Fig.5.SCESS power PSC for the applied fault on the grid side

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Fig.6. Grid reactive power Qg during three phase fault

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Fig.7. DC link voltage for the applied fault

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Fig.8. PV array voltage VPV during three phase fault

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Fig.9. MPPT output voltage Vref for the applied fault

CONCLUSION:

This paper presents grid connected PV system with supercapacitor energy storage system (SCESS) for fault ride through and to minimize the power fluctuation. Incremental conductance based MPPT is implemented to track the maximum power from the PV array. The generated DC power is connected to the grid using a buck converter, VSI, buck-boost converter with SCESS. The SCESS which is connected to the DC link controls the DC link voltage by charging and discharging process. A P-Q controller is implemented to transfer the DC link power to the grid. During normal operation the SCESS minimizes the fluctuation caused by change in irradiation and temperature. During a grid fault the power generated from the PV array will be stored in the SCESS. The SCESS supplies both active and reactive power to ride through the fault. RTDS based results have shown the validity of the proposed controller.

REFERENCES:

[1] T. Esram, P.L. Chapman, “Comparison of Photovoltaic Array Maximum Power Point Tracking Techniques,” IEEE Transaction on Energy Conversion, vol.22, no.2, pp.439-449, June 2007

[2] J. M. Enrique, E. Durán, M. Sidrach-de-Cardona, and J. M. Andújar,“Theoretical assessment of the maximum power point tracking efficiency of photovoltaic facilities with different converter topologies,” Sol. Energy, vol. 81, no. 1, pp. 31–38, Jan. 2007.

[3] W. Xiao, N. Ozog, and W. G. Dunford, “Topology study of photovoltaic interface for maximum power point tracking,” IEEE Trans. Ind. Electron., vol. 54, no. 3, pp. 1696–1704, Jun. 2007.

[4] J. L. Agorreta, L. Reinaldos, R. González, M. Borrega, J. Balda, and L. Marroyo, “Fuzzy switching technique applied to PWM boost converter operating in mixed conduction mode for PV systems,” IEEE Trans. Ind. Electron., vol. 56, no. 11, pp. 4363– 4373, Nov. 2009.

[5] A.Schneuwly, “Charge ahead [ultracapacitor technology and applications]”, IET Power Engineering Journal, vol.19, 34-37, 2005.