An Ultracapacitor Integrated Power Conditioner for Intermittency Smoothing and Improving Power Quality of Distribution Grid

 ABSTRACT:

Penetration of various types of distributed energy resources (DERs) like solar, wind, and plug-in hybrid electric vehicles (PHEVs) onto the distribution grid is on the rise. There is a corresponding increase in power quality problems and intermittencies on the distribution grid. In order to reduce the intermittencies and improve the power quality of the distribution grid, an ultracapacitor (UCAP) integrated power conditioner is proposed in this paper. UCAP integration gives the power conditioner active power capability, which is useful in tackling the grid intermittencies and in improving the voltage sag and swell compensation. UCAPs have low energy density, high-power density, and fast charge/discharge rates, which are all ideal characteristics for meeting high-power low-energy events like grid intermittencies, sags/swells. In this paper, UCAP is integrated into dc-link of the power conditioner through a bidirectional dc–dc converter that helps in providing a stiff dc-link voltage. The integration helps in providing active/reactive power support, intermittency smoothing, and sag/swell compensation. Design and control of both the dc–ac inverters and the dc–dc converter are discussed. The simulation model of the overall system is developed and compared with the experimental hardware setup.

KEYWORDS:

1.      Active power filter (APF)

2.      Dc–dc converter

3.      D–q control

4.      Digital signal processor (DSP)

5.      Dynamic voltage restorer (DVR)

6.      Energy storage integration

7.       Sag/swell

8.       Ultracapacitors (UCAP)

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. One-line diagram of power conditioner with UCAP energy storage.

EXPECTED SIMULATION RESULTS:

Fig. 2. (a) Source and load rms voltages V_srms and V_Lrms during sag. (b) Source voltages V_sab (blue), V_sbc (red), and V_sca (green) during sag. (c) Injected voltages V_inj2a (blue), V_inj2b (red), and V_inj2c (green) during sag. (d) Load voltages V_Lab (blue), V_Lbc (red), and V_Lca (green) during sag.

Fig. 3. (a) Currents and voltages of dc–dc converter. (b) Active and reactive

power of grid, load, and inverter during voltage sag.

CONCLUSION:

In this paper, the concept of integrating UCAP-based rechargeable energy storage to a power conditioner system to improve the power quality of the distribution grid is presented. With this integration, the DVR portion of the power conditioner will be able to independently compensate voltage sags and swells and the APF portion of the power conditioner will be able to provide active/reactive power support and renewable intermittency smoothing to the distribution grid. UCAP integration through a bidirectional dc–dc converter at the dc-link of the power conditioner is proposed. The control strategy of the series inverter (DVR) is based on inphase compensation and the control strategy of the shunt inverter (APF) is based on id − iq method. Designs of major components in the power stage of the bidirectional dc–dc converter are discussed. Average current mode control is used to regulate the output voltage of the dc–dc converter due to its inherently stable characteristic. A higher level integrated controller that takes decisions based on the system parameters provides inputs to the inverters and dc–dc converter controllers to carry out their control actions. The simulation of the integrated UCAP-PC system which consists of the UCAP, bidirectional dc–dc converter, and the series and shunt inverters is carried out using PSCAD. The simulation of the UCAP-PC system is carried out using PSCAD. Hardware experimental setup of the integrated system is presented and the ability to provide temporary voltage sag compensation and active/reactive power support and renewable intermittency smoothing to the distribution grid is tested. Results from simulation and experiment agree well with each other thereby verifying the concepts introduced in this paper. Similar UCAP based energy storages can be deployed in the future in a microgrid or a low-voltage distribution grid to respond to dynamic changes in the voltage profiles and power profiles on the distribution grid.

REFERENCES:

[1] N. H. Woodley, L. Morgan, and A. Sundaram, “Experience with an inverter-based dynamic voltage restorer,” IEEE Trans. Power Del., vol. 14, no. 3, pp. 1181–1186, Jul. 1999.

[2] J. G. Nielsen, M. Newman, H. Nielsen, and F. Blaabjerg, “Control and testing of a dynamic voltage restorer (DVR) at medium voltage level,” IEEE Trans. Power Electron., vol. 19, no. 3, pp. 806–813, May 2004.

[3] V. Soares, P. Verdelho, and G. D. Marques, “An instantaneous active and reactive current component method for active filters,” IEEE Trans. Power Electron., vol. 15, no. 4, pp. 660–669, Jul. 2000.

[4] H. Akagi, E. H. Watanabe, and M. Aredes, Instantaneous Reactive Power Theory and Applications to Power Conditioning, 1st ed. Hoboken, NJ, USA: Wiley/IEEE Press, 2007.

[5] K. Sahay and B. Dwivedi, “Supercapacitors energy storage system for power quality improvement: An overview,” J. Energy Sources, vol. 10, no. 10, pp. 1–8, 2009.

Design of a multilevel inverter with reactive power Control ability for connecting PV cells to the grid

 ABSTRACT:  

With the increasing use of PV cells in power system, optimal utilization of the equipment is an important issue. In these systems the MPPT controller is used to inject the maximum available power from solar energy. During day time that the active power decreases because of low intensity, the inverter is capable of injecting reactive power up to its nominal capacity and this is a chance for reactive power compensation. In this paper the aim is to propose a control method for injecting the maximum active power and if possible, the reactive power. In addition, a low pass filter is suggested to solve the problem of current fluctuations in case of unbalanced load. Simulation results on a typical system in MATLAB indicate proper performance of the presented method.

KEYWORDS:

1.      NPC inverter

2.      Maximum Power Point Tracking (MPPT)

3.      Photovoltaic cell (PV)

4.      PI current control

5.      Space vector pulse width modulation (SVPWM)

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig1. Studied system for injecting power to the grid and local load

 EXPECTED SIMULATION RESULTS:

Figure2. output active and reactive power of the inverter

Figure3. THD of injected current to the grid in no-load condition

Figure4. Injecting active power in no-load condition and low intensity of light

Figure5. load increase at t=0.5s and its effects on active and reactive power

Figure6. Injected voltage and current to the grid and the effect of inductive load on current

Figure7. Analyzing THD of injected current to the grid in PeL=50kw and PQL=30kvar condition

Figure8. Power increment in two levels: a. at t=0.5s and b. at t=0.7s

Figure9. Output power of inverter and the grid

Figure10. Output voltage and current after using filter and limiter

Figure11. THD of circuit when PeL=50kw and PQL=30kvar and using filter and limiter

CONCLUSION:

In this paper a control strategy is proposed for current control of PV inverter that control s maximum generated active power and reactive power compensation of local load simultaneously .The main idea is to utilize inverter for reactive power injection during active power decrement .using a low pass filter and power limiter in control system , produced oscillations due to unbalanced load is eliminated and inverter works in safe condition simulation results show the proposed method to be viable in controlling inverter

REFERENCES:

 [1] Chung-ChuanHou,Chih-Chung Shih, Po-Tai Cheng,Ahmet M. Hava, Common-Mode Voltage Reduction Pulsewidth

Modulation Techniques for Three-Phase Grid-Connected Converters , IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 28, NO. 4, APRIL 2013

[2] GeorgiosTsengenes, Thomas Nathenas, Georgios Adamidis,” A three-level space vector modulated grid connected inverter with control scheme based on instantaneous power theory", Simulation Modelling Practice and Theory 25 (2012) 134–147

[3] S. Kouro, K. Asfaw, R. Goldman, R. Snow, B. Wu, and J. Rodríguez, NPC Multilevel Multistring Topology for Larg Scale Grid Connected Photovoltaic Systems,2010 2nd IEEE International Symposium on Power Electronics for Distributed Generation Systems

[4] Georgios A. Tsengenes, Georgios A. Adamidis, Study of a Simple Control Strategy for Grid

Connected VSI Using SVPWM and p-q Theory,XIX International Conference on Electrical Machines - ICEM 2010, Rome

[5] César Trujillo Rodríguez, David Velasco de la Fuente, Gabriel Garcerá, Emilio Figueres, and Javier A. Gua can eme Moreno,Reconfigurable Control Scheme for a PV

Full-Soft-Switching High Step-Up Bidirectional Isolated Current-Fed Push-Pull DC-DC Converter for Battery Energy Storage Applications

ABSTRACT:

This paper presents a novel bidirectional current fed push-pull DC-DC converter topology with galvanic isolation. The control algorithm proposed enables full-soft-switching of all transistors in a wide range of input voltage and power with no requirement for snubbers or resonant switching. The converter features an active voltage doubler rectifier controlled by the switching sequence synchronous to that of the input-side switches. As a result, full-soft-switching operation at a fixed switching frequency is achieved. Operation principle for the energy transfer in both directions is described, followed by verification with a 300 W experimental prototype. The converter has considerably higher voltage step-up performance than traditional current-fed converters Experimental results obtained are in good agreement with the theoretical steady-state analysis.

KEYWORDS:

1.      Current-fed dc-dc converter

2.       Bidirectional converter

3.      Soft-switching

4.       ZVS

5.       ZCS

6.      Push-pull converter

7.      Switching control method

8.       Naturally clamped

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Full-soft-swithicng CF push-pull converter proposed.

EXPECTED SIMULATION RESULTS:

Fig. 2. Experimental current and voltage waveforms of the switch S1.1

Fig. 3. Experimental current and voltage waveforms of the switch S1.2.

Fig. 4. Experimental current and voltage waveforms of the switch S4.

CONCLUSION:

A novel bidirectional current-fed push-pull converter with galvanic isolation was introduced. It features full-soft switching operation of all semiconductor components, while its DC voltage gain is higher than in traditional current-fed converters due to the utilization of the circulating energy for the input voltage step-up. As a result, it does not suffer from short intervals of energy transfer from the input side to the output side since at least half of the switching period is dedicated for this. Moreover, it does not require any clamping circuits, since the novel control algorithm features natural clamping of the switches at the current-fed side. Despite a relatively high number of semiconductor components, it shows the peak efficiency of 96.3%, which does not depend on the energy transfer direction for the corresponding operating point. Soft-switching operation with continuous current at the current fed side makes the converter proposed suitable for residential battery energy storage systems. Further research will be directed towards experimental verification of the converter performance with a lithium iron phosphate battery.

REFERENCES:

[1] F. Blaabjerg, and D.M. Ionel, "Renewable Energy Devices and Systems – State-of-the-Art Technology, Research and Development, Challenges and Future Trends," Electric Power Components and Systems, vol.43, no.12, pp.1319-1328, 2015.

[2] C, Heymans, S, B. Walker, S. B. Young, M. Fowler, "Economic analysis of second use electric vehicle batteries for residential energy storage and load-levelling," Energy Policy, vol. 71, pp. 22-30, Aug. 2014.

[3] J. Weniger, T. Tjaden, V. Quaschning, "Sizing of Residential PV Battery Systems," Energy Procedia, vol. 46, pp. 78-87,2014.

[4] S. J. Chiang, K. T. Chang and C. Y. Yen, "Residential photovoltaic energy storage system," IEEE Trans. Ind. Electron., vol. 45, no. 3, pp. 385-394, Jun 1998.

[5] S. X. Chen, H. B. Gooi and M. Q. Wang, "Sizing of Energy Storage for Microgrids," IEEE Trans. Smart Grid, vol. 3, no. 1, pp. 142-151, 2012.

Modeling and Analysis of 3-Phase VSI using SPWM Technique for Grid Connected Solar PV System

ABSTRACT:

Solar energy is one of the most promising Renewable Energy Sources (RES) that can be used to produce electric energy through Photovoltaic (PV) process. The Solar Photovoltaic (SPV) systems which directly supply power to the grid are becoming more popular. A power electronic converter which converts DC power from the PV array to AC power at required voltage and frequency levels is known as Inverter. Generally different Pulse Width Modulation (PWM) techniques have been implemented for grid connected 3-phase Voltage Source Inverter (VSI) system. This paper describes few types of PWM techniques and mathematical model of LC filter circuit is given using state space analysis. Sine-PWM technique is proposed for 3-phase VSI and implemented using the state space model of the LC filter circuit. The simulation is performed in MATLAB/Simulink platform. Simulation results are presented for the inverter and load side to demonstrate the satisfactory performance of the sine-PWM technique.

KEYWORDS:

1.      Pulse width modulation

2.      Solar photovoltaic

3.      Voltage source inverter

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. General Block Diagram of Grid Connected SPV system

EXPECTED SIMULATION RESULTS:

Fig. 2. Carrier wave (V_tri) and Modulating wave (V_sin)

 Fig. 3. Inverter Output line to line Voltages (V_iAB,V_iBC,V_iCA)

Fig. 4. Inverter Output Currents (i_iA,i_iB,i_iC)

Fig. 5. Load line to line voltages (V_LAB, V_LBC, V_LCA)

Fig. 6. Load Phase Currents (i_LA,i_LB,i_LC)

Fig. 7. Inverter output line voltage, Inverter output current, Load line

voltage, Load phase currents

CONCLUSION:

Increasing demand on energy efficiency and power quality issues, grid connected solar PV systems is taking a good place. In this paper SPWM and SVPWM techniques have been discussed for 3-phase grid connected VSI. The LC filter circuit is used in the proposed system. This filter circuit is mathematically modeled by using state space analysis and complete state space equation is obtained. The SPWM technique is implemented and simulated on 3 phases VSI using state space model of the LC filter circuit for grid connected solar PV system. Various simulation results are analyzed and presented on the inverter and load side of the proposed system in order to demonstrate the satisfactory performance of sine-PWM technique for grid connected solar PV system.

 REFERENCES:

[1] J.Y. Lee, and Y.Y. Sun, “A New SPWM Inverter with Minimum Filter Requirement,” International Journal of Electronics, Vol. 64, No. 5, pp. 815-826, 1988.

[2] K. Zhou and D. Wang, “Relationship Between Space-Vector Modulation and Three- Phase Carrier-Based PWM: A Comprehensive Analysis,” IEEE Transactions on Industrial Electronics, Vol. 49, No. 1, pp. 186- 196, February 2002.

[3] A.W. Leedy, and R.M. Nelms, “Harmonic Analysis of a Space Vector PWM Inverter using the Method of Multiple Pulses,” IEEE Transactions on Industrial Electronics, Vol. 4, pp. 1182-1187, July 2006.

[4] A.M. Khambadkone, and J. Holtz, “Current Control in Over-modulation Range for Space Vector Modulation based Vector Controlled Induction Motor Drives,” IEEE Industrial Electronics Society, Vol.2, pp. 1134- 1339, 2000.

[5] E. Hendawi, F. Khater, and A. Shaltout, “Analysis, Simulation and Implementation of Space Vector Pulse Width Modulation Inverter,” International Conference on Application of Electrical Engineering, pp. 124-131, 2010.