Power Management in PV-Battery-HydroBased Standalone Microgrid

ABSTRACT:

This paper proposes a high-efficiency two stage three-level grid-connected photovoltaic inverter. This work deals with the frequency regulation, voltage regulation, power management and load levelling of solar photovoltaic (PV)-battery-hydro based microgrid (MG). In this MG, the battery capacity is reduced as compared to a system, where the battery is directly connected to the DC bus of the voltage source converter (VSC). A bidirectional DC–DC converter connects the battery to the DC bus and it controls the charging and discharging current of the battery. It also regulates the DC bus voltage of VSC, frequency and voltage of MG. The proposed system manages the power flow of different sources like hydro and solar PV array. However, the load levelling is managed through the battery. The battery with VSC absorbs the sudden load changes, resulting in rapid regulation of DC link voltage, frequency and voltage of MG. Therefore, the system voltage and frequency regulation allows the active power balance along with the auxiliary services such as reactive power support, source current harmonics mitigation and voltage harmonics reduction at the point of common interconnection. The experimental results under various steady state and dynamic conditions, exhibit the excellent performance of the proposed system and validate the design and control of proposed MG.

 SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:

Fig. 1 Microgrid Topology and MPPT Control (a) Proposed PV-battery-hydro MG,

EXPECTED SIMULATION RESULTS:

Fig. 2 Dynamic performance of PV-battery-hydro based MG following by solar irradiance change (a) vsab, isc, iLc and ivscc, (b) Vdc, Ipv, Vb and Ib, (c) vsab, isa, iLa and ivsca, (d) Vdc, Ipv, Vb and Ib

Fig.3 Dynamic performance of hydro-battery-PV based MG under load perturbation (a) vsab, isc, Ipv and ivscc, (b) Vdc, Ipv, Vb and Ib, (c) vsab, isc, Ipv and ivscc, (d) Vdc, Ipv, and Vb

 CONCLUSION: 

In the proposed MG, an integration of hydro with the battery, compensates the intermittent nature of PV array. The proposed system uses the hydro, solar PV and battery energy to feed the voltage (Vdc), solar array current (Ipv), battery voltage (Vb) and battery current (Ib). When the load is increased, the load demand exceeds the hydro generated power, since SEIG operates in constant power mode condition. This system has the capability to adjust the dynamical power sharing among the different RES depending on the availability of renewable energy and load demand. A bidirectional converter controller has been successful to maintain DC-link voltage and the battery charging and discharging currents. Experimental results have validated the design and control of the proposed system and the feasibility of it for rural area electrification.

REFERENCES:

[1] Ellabban, O., Abu-Rub, H., Blaabjerg, F.: ‘Renewable energy resources: current status, future prospects and technology’, Renew. Sustain. Energy Rev.,2014, 39, pp. 748–764

[2] Bull, S.R.: ‘Renewable energy today and tomorrow’, Proc. IEEE, 2001, 89, (8), pp. 1216–1226

[3] Malik, S.M., Ai, X., Sun, Y., et al.: ‘Voltage and frequency control strategies of hybrid AC/DC microgrid: a review’, IET Renew. Power Gener., 2017, 11, (2), pp. 303–313

[4] Kusakana, K.: ‘Optimal scheduled power flow for distributed photovoltaic/ wind/diesel generators with battery storage system’, IET Renew. Power Gener., 2015, 9, (8), pp. 916–924

[5] Askarzadeh, A.: ‘Solution for sizing a PV/diesel HPGS for isolated sites’, IET Renew. Power Gener., 2017, 11, (1), pp. 143–151

High-Efficiency Two-Stage Three-LevelGrid-Connected Photovoltaic Inverter

ABSTRACT:

This paper proposes a high-efficiency two stage three-level grid-connected photovoltaic inverter. The proposed two-stage inverter comprises a three-level step up converter and a three-level inverter. The three-level step up  converter not only improves the power-conversion efficiency by lowering the voltage stress but also guarantees the balancing of the dc-link capacitor voltages using a simple control algorithm; it also enables the proposed inverter to satisfy the VDE 0126-1-1 standard of leakage current. The three-level inverter minimizes the overall power losses with zero reverse-recovery loss. Furthermore, it reduces harmonic distortion, the voltage ratings of the semiconductor device, and the electromagnetic interference by using a three-level circuit configuration; it also enables the use of small and low cost filters. To control the grid current effectively, we have used a feed-forward nominal voltage compensator with a mode selector; this compensator improves the control environment by presetting the operating point. The proposed high-efficiency two-stage three-level grid-connected photovoltaic inverter overcomes the low  efficiency problem of conventional two-stage inverters, and it provides high power quality with maximum efficiency of 97.4%. Using a 3-kW prototype of the inverter, we have evaluated the performance of the model and proved its feasibility.

KEYWORDS:

  1. Transformerless
  2. Multilevel
  3. Dc-ac power conversion
  4. Single-phase

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Proposed high-efficiency two-stage three-level grid-connected PV inverter circuit diagram.

EXPECTED SIMULATION RESULTS:

 Fig.2. Simulation results for the leakage current of the proposed twostage

inverter.

Fig.3. Simulation results for the leakage current using a conventional three-level step-up converter of Fig. 2(b) as dc-dc power conversion stage of two-stage inverter.

CONCLUSION: 

A high-efficiency two-stage three-level grid-connected PV inverter and control system are introduced. Also, a theoretical analysis is provided along with the experimental results. By using the novel circuit configuration, the proposed two-stage inverter performs power conversion with low leakage current and high efficiency; in dc-dc power conversion stage, the connection of midpoints of capacitors enables the proposed two-stage inverter to limit the leakage current below 300mA; in dc-ac power conversion stage, the overall power losses are minimized by eliminating the reverse-recovery problems of the MOSFET body diodes. Besides, the proposed inverter with three voltage levels reduces the power losses, harmonic components, voltage ratings, and EMI; it also enables using small and low cost filters. For the control system, the feedforward nominal voltage compensator also improves the control environment by presetting the operating point. This developed control algorithm makes the proposed inverter feasible. Thus, the proposed high-efficiency two-stage three-level grid connected PV inverter provides high power quality with high power-conversion efficiency. By using a 3-kW prototype, this experiment has verified that the proposed inverter has high efficiency, and the developed control system is suitable for the proposed inverter.

REFERENCES:

[1] B.K. Bose, “Global energy acenario and impact of power electronics in 21st century,” IEEE Transactions on Industrial Electronics, vol. 60, no. 7, pp. 2638-2651, July. 2013.

[2] Y. Zhou, D. C. Gong, B. Huang, and B. A. Peters, “The impacts of carbon tariff on green supply chain design,” IEEE Transactions on Automation Science and Engineering, July. 2015. Available: DOI: 10.1109/TASE.2015.2445316

[3] Y. Wang, X. Lin, and M. Pedram, “A near-optimal model-based control algorithm for households equipped with residential photovoltaic power generation and energy storage systems,” IEEE Transactions on Sustainable Energy, vol. 7, no. 1, pp. 77-86, Jan. 2016.

[4] Y. W. Cho, W. J. Cha, J. M. Kwon, and B. H. Kwon, “Improved  single-phase transformerless inverter with high power density and high efficiency for grid-connected photovoltaic systems,” IET Renewable Power Generation, vol. 10, no. 2, pp. 166-174, Feb. 2016.

[5] A. Shayestehfard, S. Mekhilef, and H. Mokhlis, “IZDPWMBased feedforward controller for grid-connected inverters under unbalanced and distorted conditions,” IEEE Trans. Ind. Electron., vol. 64, no. 1, pp. 14-21, Jan. 2017.

A Three-Phase Symmetrical DC-Link Multilevel Inverter with Reduced Number of DC Sources

ABSTRACT:

This paper presents a novel three-phase DC-link multilevel inverter topology with reduced number of input DC power supplies. The proposed inverter consists of series-connected half-bridge modules to generate the multilevel waveform and a simple H-bridge module, acting as a polarity generator. The inverter output voltage is transferred to the load through a three-phase transformer, which facilitates a galvanic isolation between the inverter and the load. The proposed topology features many advantages when compared with the conventional multilevel inverters proposed in the literatures. These features include scalability, simple control, reduced number of DC voltage sources and less devices count. A simple sinusoidal pulse-width modulation technique is employed to control the proposed inverter. The performance of the inverter is evaluated under different loading conditions and a comparison with some existing topologies is also presented. The feasibility and effectiveness of the proposed inverter are confirmed through simulation and experimental studies using a scaled down low-voltage laboratory prototype.

 KEYWORDS:

  1. Hybrid multilevel inverter
  2. DC-link inverter
  3. half-bridge module
  4. symmetric DC voltage supply

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1 The proposed three-phase CMLI with two half-bridge cells per phase leg

 EXPECTED SIMULATION RESULTS:

 Fig. 2 Simulation results of the output line voltages and line currents for (a) load of nearly 0.8–lagging power factor and (b) load of nearly unity power factor

Fig. 3 Simulation results for a dynamic change in the load from nearly unity PF (100.31∠4.49°Ω) to 0.8 lagging PF (127.13∠38.13°Ω): (a) level generator output voltage, (b) polarity generator output voltage (phase voltage) and (c) line voltage and line current


Fig. 4 Simulation results for a dynamic change in the load magnitude with the same PF: (a) Line voltage, (b) Line current

Fig. 5 Simulation results for a dynamic change in the load from nearly 0.9 lagging PF (108.01∠22.21°Ω) to 0.7 lagging PF (142.88∠45.58°Ω): (a) level generator output voltage, (b) polarity generator output voltage (phase voltage) and (c) line voltage and line current

Fig. 6 Simulation results for carrier frequency of 8 kHz: (a) line voltages and currents, (b) line current THD, (c) line voltage THD

CONCLUSION

This paper presents a new symmetrical multilevel inverter topology with two different stages. The proposed inverter requires less power electronic devices and features modularity, hence simple structure, less cost, and high scalability. The number of input DC-supplies for the proposed topology is found to be nearly 67% less than the similar symmetric half-bridge topologies, which is a great achievement for industrial applications. This phenomenon will reduce the complexity of DC voltage management. As being a symmetric structure, all the switching devices experience same voltage stress, which is a very important factor for high voltage applications. The feasibility of the proposed inverter is confirmed through simulation and experimental analysis for different operating conditions.

REFERENCES:

[1] L. G. Franquelo, J. Rodriguez, J. I. Leon, S. Kouro, R. Portillo, and M. A. Prats, “The age of multilevel converters arrives,” IEEE Ind. Electron. magazine, vol. 2, pp. 28-39, 2008.

[2] A. Nabae, I. Takahashi, and H. Akagi, “A new neutral-point-clamped PWM inverter,” IEEE Trans. Ind. Appl., pp. 518-523, 1981.

[3] S. Kouro, M. Malinowski, K. Gopakumar, J. Pou, L. G. Franquelo, B. Wu, et al., “Recent advances and industrial applications of multilevel converters,” IEEE Trans. Ind. Electron., vol. 57, pp. 2553-2580, 2010.

[4] J. Rodriguez, J.-S. Lai, and F. Z. Peng, “Multilevel inverters: a survey of topologies, controls, and applications,” IEEE Trans. Ind. Electron., vol. 49, pp. 724-738, 2002.

[5] B. Xiao, L. Hang, J. Mei, C. Riley, L. M. Tolbert, and B. Ozpineci, “Modular cascaded H-bridge multilevel PV inverter with distributed MPPT for grid-connected applications,” IEEE Trans. Ind. Appl., vol. 51, pp. 1722-1731, 2015.

Varying Phase Angle Control In Isolated Bidirectional DC–DC Converter For Integrating Battery Storage And Solar PV System In Standalone Mode

ABSTRACT:

This study proposes a varying phase angle control (VPAC) in isolated bidirectional dc–dc converter (IBDC) for integrating battery storage unit to a DC link in a standalone solar photovoltaic (PV) system. The IBDC is capable of power transfer using high step up/down ratio between DC link and battery. The VPAC control proposed in this study effectively manage the power flow control between the battery storage unit and the solar PV fed DC link by continuously varying the phase angle between high voltage and low voltage (LV) bridge voltage of the IBDC. The solar PV system is incorporated with the maximum power point tracking using DC–DC converter. In order to control the voltage across the AC load a voltage source inverter is used. The study also presents the design aspects of the IBDC converter for the application considered. The performance of the proposed power flow control strategy has been studied through PSCAD/EMTDC simulation and validated using LPC 2148 ARM processor.

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1 Block diagram for proposed standalone system

(a) Generalised block diagram, (b) Mode 1 operation, (c) Mode 2 operation, (d) Mode 3 operation

EXPECTED SIMULATION RESULTS:

 

 Fig. 2 Simulation results of IBDC

(a) Battery current during change in mode 1 to mode 2, (b) Battery current during change in mode 2 to mode 1, (c) Solar PV power, load power and battery power during change in mode 1 to mode 2, (d) Solar PV power, load power and battery power during change in mode 2 to mode 1

 CONCLUSION: 

The proposed variable phase angle control of IBDC converter balances the power flow between the solar PV system, battery storage unit and AC load in all the modes. The VPAC algorithm ensures that the, (i) solar PV system delivers maximum demanded power corresponding to the load and battery gets charged/ discharged through the available excess/short power. The governing mathematical formulation of problem reveals the dependency of average battery current on phase angle between the voltages of LV and HV side of the IBDC converter and hence provides a strategy to control the power flow. The analysis presented can be used to design the passive components and switches of the IBDC. From the obtained results, the performance of the proposed VPAC has been established with smooth transition of power flow between the PV fed DC link and the battery through the IBDC converter. The maximum power is extracted from the solar PV and AC load voltage is controlled in all the modes.

REFERENCES:

[1] Bull, S.R.: ‘Renewable energy today and tomorrow’, Proc. IEEE, 2001, 89, (8), pp. 1216–1226

[2] Solodovnik, E.V., Liu, S., Dougal, R.A.: ‘Power controller design for maximum power tracking in solar installations’, IEEE Trans. Power Electron., 2004, 19, (5), pp. 1295–1304

[3] Kuo, Y.-C., Liang, T.-J., Chen, J.-F.: ‘Novel maximum-power-point tracking controller for photovoltaic energy conversion system’, IEEE Trans. Ind. Electron., 2001, 48, (3), pp. 594–601

[4] Koutroulis, E., Kalaitzakis, K., Voulgaris, N.C.: ‘Development of a microcontroller-based, photovoltaic maximum power point tracking control system’, IEEE Trans. Power Electron., 2001, 16, (1), pp. 46–54

 

Single-phase solar PV system with battery and exchange of power in grid-connected and standalone modes

ABSTRACT:

A grid tied photovoltaic (PV) power conversion topology is presented in this study with a novel scheme of resynchronization to the grid. This scheme serves the purpose of supplying continuous power to the load along with feeding power to the grid. The control approach helps in mitigation of harmonics and improving the power quality while extracting the optimum power from the PV array. Depending on the availability of grid voltage, the proposed configuration is controlled using three approaches, defined as grid current control, Point of Common Coupling (PCC) voltage control and intentional islanding with re-synchronisation. A simple proportional integral controller manages the grid current, load voltage, battery current and DC Direct Current (DC) link voltage within these modes. Moreover, a control scheme for quick and smooth transitions among the modes is described. The robustness of the system under erratic behaviour of solar insolation, load power and disturbances in grid supply makes it a suitable choice for a residential application. The control, design and simulation results are presented to demonstrate the satisfactory operation of the proposed system.

SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:

 Fig. 1 Proposed system topology

 EXPECTED SIMULATION RESULTS:

Fig. 2 Performance of the system under grid isolation

  • GCC to PVC, (b) Harmonic spectrum of grid current (ig), (c) Harmonic spectrum of load voltage (vL)

 Fig. 3 Performance of the system under grid reconnection

(a) Mode change from PVC to IIRS, (b) Grid voltage (vg) vs. load voltage (vL) during

intentional islanding

Fig. 4 Performance of the system for insolation change from 1000 W/m2

to 500/m2

CONCLUSION: 

The proposed scheme has combined the solar PV power generating unit to single-phase grid with a unique feature of resynchronization of grid to the system after overcoming the grid failures. The ability of the system to generate maximum power for varying insolation, feeding active power to the grid as well as load and store/extract power to/from the battery has been validated by the dynamic performance. This helps in increasing the efficiency of the system. The scheme has utilised minimum number of switches resulting in lower switching losses. The VSC has the ability to diminish the switching harmonics in grid current and load voltages resulting in <5% THD as demanded by the IEEE 519 standard. The system has ability to re-synchronise with the grid within five cycles of grid voltage for any phase difference. This helps in achieving the fast time response of the system, thus making it a suitable choice for residential applications. The obtained results have authenticated the robustness and feasibility of the proposed system under various disturbances.

REFERENCES:

[1] Zheng, H., Li, S., Bao, K., et al.: ‘Comparative study of maximum power point tracking control strategies for solar PV systems’. IEEE Conf. on Transmission, Distribution and Exposition, May 2012, pp. 1–8

[2] Weihang, Y., Jianhui, W., Wenzhong, G., et al.: ‘A MPPT algorithm based on extremum seeking with variable gain for microinverters in microgrid’. IEEE Conf. on Control (CCC), July 2015, pp. 7939–7944

[3] Zhang, Q., Hu, C., Chen, L., et al.: ‘A center point iteration MPPT method with application on the frequency-modulated LLC microinverter’, IEEE Trans. Power Electron., 2014, 29, (3), pp. 1262–1274

[4] Li, Q., Wolfs, P.: ‘A review of the single phase photovoltaic module integrated converter topologies with three different DC link configurations’, IEEE Trans. Power Electron., 2008, 23, (3), pp. 1320–1333

[5] Gloire, N., Lei, D., Xiaozhong, L., et al.: ‘Single phase grid-connected PV inverter applying a boost coupled inductor’. IEEE Conf. on Transportation Electrification (ITEC Asia-Pacific), August–September 2014, pp. 1–5

Novel High Performance Stand Alone Solar PV System with High Gain, High Efficiency DC-DC Converter Power Stages

ABSTRACT:  

This paper proposes a novel 3- stand-alone solar PV system configuration that uses high gain, high efficiency (96%) dc-dc converters both in the forward power stage as well as the bidirectional battery interface. The high voltage gain converters enable the use of low voltage PV and battery sources. This results in minimization of partial shading and parasitic capacitance effects on the PV source. Series connection of a large number of battery modules is obviated, preventing the overcharging and deep discharging issues that reduce the battery life. Also, the proposed configuration facilitates “required power tracking (RPT)” of the PV source as per the load requirements eliminating the use of expensive and ‘difficult to manage’ dump loads. High performance inverter operation is achieved through abc to dq reference frame transformation, which helps in generating precise information about the load’s active power component for RPT, regulation of ac output voltage and minimization of control complexity. Inverter output voltage is regulated by controlling the modulation index of sinusoidal pulse width modulation, resulting in a stable and reliable system operation. The active power demand is controlled by regulating the dc link voltage. All the analytical, simulation and experimental results of this work are presented.

 KEYWORDS:

  1. Power conversion
  2. Pulse width modulation converters
  3. Power conditioning, Inverters
  4. Three-phase electric power
  5. Power control
  6. Photovoltaic cells
  7. Energy conversion
  8. Solar power generation
  9. High gain DC-DC Converter
  10. MPPT

 SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 

 

Fig. 1. Simplified block diagram of a two stage stand alone PV system

 EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results of the proposed system during the sequence of events considered

Fig.3 Dynamic response of the dc link: (a) An effective load (Reff) connected across the dc link; (b) Response to step change in effective load (200W to 400W); (c) Response to step change in reference dc link voltage, * Vdc from 250V to 400V.

 CONCLUSION:

 This paper has described and implemented a novel 3- solar PV inverter system for stand-alone applications. Considering that high PV side voltage leads to several drawbacks, a low voltage PV source is used in the system. The limitation of low voltage PV source is overcome by using a special high voltage gain front end dc-dc converter capable of operating at high efficiency and MPPT. The proposed scheme is particularly conducive to long battery life by as it ensures no battery overcharge or deep discharge. For this purpose, the   conventional MPPT scheme is replaced by RPT, which ensures only the required power is tracked from the PV source. This prevents the drawing of excess power from the PV source and the use and management of expensive ‘dump’ loads. Not only the main power stage, but the battery interfacing bi-directional stage also supports high voltage gain with high efficiency. Due to the use of special high gain, high efficiency converters in the power stage, the overall efficiency of the system is 94%. Preliminary investigations have yielded encouraging results. The capacity of the proposed control strategy can be enhanced for high power operation by interfacing other renewable sources (fuel cell stack, wind etc.) to the dc link of the proposed system without significantly altering the control strategy. In spite of the good performance of the proposed system, as verified through several simulation and experimental results, there are some limitations too, as listed below:

  1. The high gain, high efficiency dc-dc converters used in the proposed system may be difficult to design for high power levels.
  2. In the proposed system, battery is interfaced with the high voltage (400V) dc link requiring a high voltage gain, high efficiency dc-dc converter. Battery interfacing to the low voltage (40V) dc bus should be explored.
  3. The proposed system uses a large number of sensors, which may increase the cost and complexity. All these issues are being currently investigated and the findings will be reported in a future paper.

REFERENCES:

[1] S.R. Bhat, A. Pittet and B.S. Sonde, “Performance optimization of induction motor-pump system using photovoltaic energy source,” IEEE Transactions on Industry Applications, vol. IA- 23, no. 6, pp. 995–1000, Nov. 1987.

[2] S. Duryea, S. Islam and W. Lawrence, “A battery management system for stand alone photovoltaic energy systems,” 34th IEEE IAS Annual Meeting, vol. 4, pp. 2649-2654, Phoenix, AZ , 3rd – 7th Oct., 1999.

[3] M. Uzunoglu, O. C. Onar, and M. S. Alam, “Modeling, control and simulation of a PV/FC/UC based hybrid power generation system for stand-alone applications” Renewable Energy, vol. 34, no. 3, pp. 509-520, Mar. 2009.

[4] R. M. Cuzner and G. Venkataramanan, “The status of dc microgrid protection,” IEEE Industry Applications Society Annual  Meeting, pp. 1-8, 5th-9th Oct. 2008

[5] P. Sharma and V. Agarwal, “Exact maximum power point tracking of grid-connected partially shaded PV source using current compensation concept,” IEEE Transactions on Power Electronics, vol. 29, no. 9, pp. 4684-4692, Sep. 2014.

Control and Implementation of a Standalone Solar Photo-Voltaic Hybrid System

ABSTRACT:  

A control algorithm for a standalone solar photovoltaic (PV)-diesel-battery hybrid system is implemented in this paper. The proposed system deals with the intermittent nature of the energy generated by the PV array and it also provides power quality improvement. The PV array is integrated through a DC-DC boost converter and controlled using a maximum power point tracking (MPPT) algorithm to obtain the maximum power under varying operating conditions. The battery energy storage system (BESS) is integrated to the diesel engine generator (DG) set for the coordinated load management and power flow within the system. The admittance based control algorithm is used for load balancing, harmonics elimination and reactive power compensation under three phase four-wire linear and nonlinear loads. A four-leg voltage source converter (VSC) with BESS also provides neutral current compensation. The performance of proposed standalone hybrid system is studied under different loading conditions experimentally on a developed prototype of the system.

KEYWORDS:

  1. Admittance based control algorithm
  2. BESS
  3. DG set
  4. Four-leg VSC
  5. Neutral current compensation
  6. Power quality
  7. Solar photovoltaic array
  8. Standalone system

 SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Schematic diagram of the proposed system

 EXPECTED SIMULATION RESULTS:

Fig. 2. Performance of proposed system under unbalance nonlinear load

CONCLUSION:

 The admittance based control technique has been used for a PV-diesel-battery hybrid system for an uninterrupted power supply and power quality improvement. The incremental based MPPT algorithm has delivered maximum solar array power under varying conditions of temperature and insolation radiation. The technique has been demonstrated to eliminate harmonics, load balancing and to provide neutral current compensation by incorporating four-leg VSC in the system. The PCC voltage and frequency have been maintained constant. Satisfactory performance of the system has been observed through test results obtained for steady state and dynamic conditions under both linear/nonlinear loads.

REFERENCES:

[1] Z. Jiang, “Power Management of Hybrid Photovoltaic-Fuel Cell Power Systems”, Proc. of IEEE Power Engg. Society General Meeting, Montreal Quebec, Canada, 2006.

[2] A. Naik, R.Y. Udaykumar and V. Kole, “Power management of a hybrid PEMFC-PV and Ultra capacitor for stand-alone and grid connected applications”, Proc. of IEEE Int. Conf. Power Electron. Drives and Energy Sys. (PEDES), 2012, pp. 1-5.

[3] J. Philip, C. Jain, , K. Kant, B. Singh, S. Mishra, A. Chandra and K. Al- Haddad “Control and implementation of a standalone solar photo-voltaic hybrid system”, Proc. of IEEE Industry Applications Society Annual Meeting, Addison, TX, 18- 22 Oct. 2015, pp.1-8.

[4] J. Philip, B. Singh and S. Mishra, “Design and operation for a standalone DG-SPV-BES microgrid system”, Proc. of 6thIEEE Power India Int. Conf. (PIICON), Delhi, 5-7 Dec, 2014, pp.1-6.

 

A Unified Control Strategy for Three-phase Inverter in Distributed Generation

ABSTRACT:  

This paper presents a unified control strategy that enables both islanded and grid-tied operation of three-phase inverter in distributed generation (DG), with no need for switching between two corresponding controllers or critical islanding detection. The proposed control strategy composes of an inner inductor current loop, and a novel voltage loop in the synchronous reference frame (SRF). The inverter is regulated as a current source just by the inner inductor current loop in grid-tied operation, and the voltage controller is automatically activated to regulate the load voltage upon the occurrence of islanding. Furthermore, the waveforms of the grid current in grid-tied mode and the load voltage in islanding mode are distorted under nonlinear local load with the conventional strategy. And this issue is addressed by proposing a unified load current feed forward in the paper. Additionally, the paper presents the detailed analysis and the parameter design of the control strategy. Finally, the effectiveness of the proposed control strategy is validated by the simulation and experimental results.

KEYWORDS:

  1. Distributed generation
  2. Three-phase inverter
  3. Islanding
  4. Unified control
  5. Seamless transfer
  6. Load current

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

 Fig. 1 Schematic diagram of the distributed generzation based on the proposed control strategy.

 EXPECTED SIMULATION RESULTS:

Fig. 2 Bode plot of the transfer function from load current to grid current with

and without the load current feedforward, when DG operates in grid-tied

mode.

Fig. 3 Simulation waveforms of load voltage vCa, grid current iga and inductor

current iLa when DG is in grid-tied mode under condition of the step down of

the grid current reference from 9A to 5A with: (a) conventional voltage mode

control, and (b) proposed unified control strategy.

Fig. 4 Simulation waveforms of load voltage vCa, grid current iga and inductor

current iLa when DG is transferred from grid-tied mode to islanded mode with:

(a) conventional hybrid voltage and current mode control, and (b) proposed

unified control strategy.

 CONCLUSION:

 A unified control strategy is proposed for three-phase inverter in DG to operate in both islanded and grid-tied mode, with no need for switching between two different control architectures or critical islanding detection. A novel voltage controller is presented. It is inactivated in grid-tied mode, and the DG operates as a current source with fast dynamic performance. Upon the utility outage, the voltage controller can automatically be activated to regulate the load voltage. Moreover, a novel load current feedforward is proposed, and it can improve the waveform quality of both the grid current in grid-tied mode and the load voltage in islanded mode. The proposed unified control strategy is verified by the simulation and experimental results.

 REFERENCES:

[1] R. C. Dugan and T. E. McDermott, “Distributed generation,” IEEE Ind. Appl. Mag., vol. 8, no. 2, pp. 19-25, Mar./Apr. 2002.

[2] R. H. Lasseter, “Microgrids and distributed generation,” J. Energy Eng., vol. 133, no. 3, pp. 144-149, Sep. 2007.

[3] C. Mozina, “Impact of Green Power Distributed Generation,” IEEE Ind. Appl. Mag., vol. 16, no. 4, pp. 55-62, Jul./Aug. 2010.

[4] IEEE Recommended Practice for Utility Interface of Photovoltaic(PV) Systems, IEEE Standard 929-2000, 2000.

[5] IEEE Standard for Interconnecting Distributed Resources with Electric Power Systems, IEEE Standard 1547-2003, 2003.

Single-Phase Solar PV System with Battery And Exchange of Power In Grid-Connected And Standalone Modes

ABSTRACT:  

A grid tied photovoltaic (PV) power conversion topology is presented in this study with a novel scheme of resynchronization to the grid. This scheme serves the purpose of supplying continuous power to the load along with feeding power to the grid. The control approach helps in mitigation of harmonics and improving the power quality while extracting the optimum power from the PV array. Depending on the availability of grid voltage, the proposed configuration is controlled using three approaches, defined as grid current control, Point of Common Coupling (PCC) voltage control and intentional islanding with re-synchronisation. A simple proportional integral controller manages the grid current, load voltage, battery current and DC Direct Current (DC) link voltage within these modes. Moreover, a control scheme for quick and smooth transitions among the modes is described. The robustness of the system under erratic behaviour of solar insolation, load power and disturbances in grid supply makes it a suitable choice for a residential application. The control, design and simulation results are presented to demonstrate the satisfactory operation of the proposed system.

 SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:

 Fig. 1 Proposed system topology

 EXPECTED SIMULATION RESULTS:

Fig. 2 Performance of the system under grid isolation

(a) GCC to PVC, (b) Harmonic spectrum of grid current (ig), (c) Harmonic spectrum of load voltage (vL)

Fig. 3Performance of the system under grid reconnection

(a) Mode change from PVC to IIRS, (b) Grid voltage (vg) vs. load voltage (vL) during

intentional islanding

 Fig. 4 Performance of the system for insolation change from 1000 W/m2

to 500/m2

 CONCLUSION:

The proposed scheme has combined the solar PV power generating unit to single-phase grid with a unique feature of resynchronization of grid to the system after overcoming the grid failures. The ability of the system to generate maximum power for varying insolation, feeding active power to the grid as well as load and store/extract power to/from the battery has been validated by the dynamic performance. This helps in increasing the efficiency of the system. The scheme has utilised minimum number of switches resulting in lower switching losses. The VSC has the ability to diminish the switching harmonics in grid current and load voltages resulting in <5% THD as demanded by the IEEE 519 standard. The system has ability to re-synchronise with the grid within five cycles of grid voltage for any phase difference. This helps in achieving the fast time response of the system, thus making it a suitable choice for residential applications. The obtained results have authenticated the robustness and feasibility of the proposed system under various disturbances.

REFERENCES:

[1] Zheng, H., Li, S., Bao, K., et al.: ‘Comparative study of maximum power point tracking control strategies for solar PV systems’. IEEE Conf. on Transmission, Distribution and Exposition, May 2012, pp. 1–8

[2] Weihang, Y., Jianhui, W., Wenzhong, G., et al.: ‘A MPPT algorithm based on extremum seeking with variable gain for microinverters in microgrid’. IEEE Conf. on Control (CCC), July 2015, pp. 7939–7944

[3] Zhang, Q., Hu, C., Chen, L., et al.: ‘A center point iteration MPPT method with application on the frequency-modulated LLC microinverter’, IEEE Trans. Power Electron., 2014, 29, (3), pp. 1262–1274

[4] Li, Q., Wolfs, P.: ‘A review of the single phase photovoltaic module integrated converter topologies with three different DC link configurations’, IEEE Trans. Power Electron., 2008, 23, (3), pp. 1320–1333

[5] Gloire, N., Lei, D., Xiaozhong, L., et al.: ‘Single phase grid-connected PV inverter applying a boost coupled inductor’. IEEE Conf. on Transportation  Electrification (ITEC Asia-Pacific), August–September 2014, pp. 1–5

 

 

 

Hybrid Modulation Concept for Five-Level Active-Neutral-Point-Clamped Converter

ABSTRACT:  

In this letter, a hybrid modulation concept consisting of three-level space vector modulation (3L-SVM) and phase-shifted pulse width modulation (PS-PWM) is proposed for five-level active neutral- point-clamped (5L-ANPC) converter. Under this concept, a simpler 3L-SVM plus PS-PWM scheme is applied to realize 5L modulation, instead of using complex 5L-SVM. The control of neutral voltage, flying capacitor voltage, and the improved dc voltage utilization are all implemented. With the help of the proposed concept,   well-developed 3L-SVM schemes can be directly applied to the 5L-ANPC converter, which significantly simplify the gating signal generation. This concept can also be applied to other hybrid clamped 5L converters with two dc-link capacitors. It provides a unique solution, which utilize lower level SVM scheme to control higher level multilevel converters.

KEYWORDS:

  1. Five-level active-neutral-point-clamped (5LANPC)
  2. Multilevel converter
  3. Phase-shifted pulse width modulation (PS-PWM)
  4. Space vector modulation (SVM)

 SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

 

Fig. 1 Single-phase circuit of a 5L-ANPC converter.

 EXPECTED SIMULATION RESULTS:

 

Fig. 2. Waveforms of modulation wave Vma , phase voltage vphase , line–line voltage vl l , three-phase current, two dc-link capacitor voltage, and three-phase FC voltage of 5L-ANPC converter with proposed hybrid modulation concept: (a) M = 0.23. (b) M = 1.15. (c) Neutral voltage and FC voltage control.

 

Fig. 3. Comparison waveforms of modulation wave Vma , phase voltage vphase , line–line voltage vl l , three-phase current, two dc-link capacitor voltage, and three-phase FC voltage of 5L-ANPC converter with PS-PWM in [5]: (a) M = 0.23. (b) M = 1.15. (c) Neutral voltage and FC voltage control.

 CONCLUSION:

 In this letter, a new hybrid modulation concept is proposed for 5L-ANPC converters. Instead of using 5L-SVM, it applies 3L-SVM plus PS-PWM to modulate the 5L-ANPC converters. With the proposed concept, the control of neutral voltage, FC voltage, and the increased voltage utilization are all realized.  Well-developed 3L-SVM schemes can be applied directly to simplify the modulation process. The simulation and experiment have proved the effectiveness of the modulation scheme. Although this modulation concept is developed for 5L-ANPC converter, it can also be applied to other hybrid 5L converters with two dc-link capacitors [13]. By dividing these converters into two cells, 3L-SWM can be applied to their 3L converter cells, while both cells are together modulated by PS-PWM using the modulation waves derived from 3L-SVM. The proposed concept provides a unique solution which utilize lower level SVM scheme to modulation higher level multilevel converters at desired performance.

REFERENCES:

[1] S. Kouro, J. Rodriguez, B. Wu, S. Bernet, and M. Perez, “Powering the future of industry: High-power adjustable speed drive topologies,” IEEE Ind. Appl. Mag., vol. 18, no. 4, pp. 26–39, Jul./Aug. 2012.

[2] P. Barbosa, P. Steimer, J. Steinke, M. Winkelnkemper, and N. Celanovic, “Active-neutral-point-clamped (ANPC) multilevel converter technology,” in Proc. Power Electron. Appl. Eur. Conf., 2005, pp. 1–10.

[3] J. Li, Z. Pan, and R. Burgos, “A new control scheme of five-level active NPC converters for common mode voltage mitigation in medium voltage drives,” in Proc. IEEE Energy Convers. Congr. Expo., 2014, pp. 234–241.

[4] R. T. Hamid, S. Danny, M. M. Kashem, and C. Phil, “Novel modulation  and control strategy for five-level ANPC converter with unbalanced DC voltage applied to a single-phase grid connected PV system,” in Proc.  IEEE Ind. Appl. Soc. Annu. Meet., 2013, pp. 1–8.

[5] K. Wang, L. Xu, Z. Zheng, and Y. Li, “Capacitor voltage balancing of a five-level ANPC converter using phase-shifted PWM,” IEEE Trans. Power  Electron., vol. 30, no. 3, pp. 1147–1156, Mar. 2015.