A Nested Control Strategy for Single Phase Power Inverter Integrating Renewable Energy Systems in a Microgrid

ABSTRACT:  

In this paper a nested power-current-voltage control scheme is introduced for control of single phase power  inverter, integrating small-scale renewable energy based power generator in a microgrid for both stand-alone and grid-connected modes. The interfacing power electronics converter raises various power quality issues such as current harmonics in injected grid current, fluctuations in voltage across the local loads, voltage harmonics in case of non-linear loads and low output power factor.

The proposed nested proportional resonant current and model predictive voltage controller aims to improve the quality of grid current and local load voltage waveforms in grid-tied mode simultaneously by achieving output power factor near to unity. In stand-alone mode, it strives to enhance the quality of local load voltage waveform. The nested control strategy successfully accomplishes smooth transition from grid-tied to stand-alone mode and vice-versa without any change in the original control structure. The performance of the controller is validated through simulation results.

KEYWORDS:
  1. Microgrid
  2. Stand-alone mode
  3. Grid-connected mode
  4. Voltage harmonics
  5. Current harmonics
  6. Proportional resonant control
  7. Model predictive control

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Block diagram of MPVC scheme

EXPECTED SIMULATION RESULTS:

 Fig. 2(a). Steady state grid voltage, load voltage and grid current waveforms with resistive load

Fig. 3(b). Steady state grid voltage, load voltage and grid current waveforms with non-linear load

Fig. 4. THD values of voltage and current waveforms in grid connected mode

Fig. 5(a). Steady state grid voltage, load voltage and filter current waveforms with resistive load

Fig. 6 (b). Steady state grid voltage and load voltage waveforms with non-linear Load

Fig. 7. THD values of load voltage waveform in stand-alone mode

Fig. 8(a). Transient state grid voltage, load voltage and grid current waveforms with change in active power reference

Fig. 9(b). Transient state grid voltage, load voltage and grid current waveforms with change in reactive power reference

Fig. 10(c). Grid voltage, load voltage and grid current waveforms during voltage Sag

(a) Transfer from stand-alone to grid-tied mode

(b) Transfer from grid-tied to stand-alone mode

Fig.11. Grid voltage, load voltage, filter inductor current, grid current

Waveforms

(a) Transfer from stand-alone to grid-tied mode

(b) Transfer from grid-tied to stand-alone mode

Fig.12. Grid current tracking error waveforms

CONCLUSION:

 

In this paper, a nested proportional resonant current and model predictive voltage controller is introduced for control of single phase VSI integrating a RES based plant in a microgrid. This strategy improves the quality of local load voltage and grid current waveforms with both linear and non linear loads. A non-linear load such as the diode bridge rectifier introduces voltage harmonics, but this scheme is successful in achieving low THD values for inverter local load voltage and grid current simultaneously. Simulation results validates the outstanding performance of the proposed controller in both steady state and transient state operations. A smooth transfer of operation modes from stand-alone to grid-tied and vice versa is also achieved by the nested control scheme without changing the control algorithm.

 REFERENCES:

[1] H. Farhangi, “The path of the smart grid,” IEEE Power and Energy Magazine, vol. 8, no. 1, pp. 18-28, Jan/Feb. 2010.

[2] F. Blaabjerg, Z. Chen, and S. B. Kjaer, “Power electronics as efficient interface in dispersed power generation systems,” IEEE Trans. Power Electron., vol. 19, no. 5, pp. 1184–1194, Sep. 2004.

[3] F. Blaabjerg, R. Teodorescu, M. Liserre, and A. V. Timbus, “Overview of control and grid synchronization for distributed power generation systems,” IEEE Trans. on Ind. Electron., vol. 53, no. 5, pp. 1398–1409,  Oct. 2006.

[4] Q. C. Zhong and T. Hornik, “Cascaded Current–Voltage Control to Improve the Power Quality for a Grid-Connected Inverter With a Local  Load,” IEEE Transactions on Ind. Electron., vol. 60, no. 4, pp. 1344- 1355, April 2013.

[5] Y Zhilei, X Lan and Y Yangguang, “Seamless Transfer of Single-Phase Grid-Interactive Inverters Between Grid-Connected and Stand-Alone  Modes,” IEEE Transactions on Power Electronics, vol. 25, no. 6, pp. 1597-1603, June 2010.

Control of a Three-Phase Hybrid Converter for a PV Charging Station

ABSTRACT:

Hybrid boost converter (HBC) has been proposed to replace a dc/dc boost converter and a dc/ac converter to reduce conversion stages and switching loss. In this paper, control of a three-phase HBC in a PV charging station is designed and tested. This HBC interfaces a PV system, a dc system with hybrid plugin electrical vehicles (HPEVs) and a three-phase ac grid. The control of the HBC is designed to realize maximum power point tracking (MPPT) for PV, dc bus voltage regulation, and ac voltage or reactive power regulation. A test bed with power electronics switching details is built in MATLAB/SimPowersystems for validation. Simulation results demonstrate the feasibility of the designed control architecture. Finally, lab experimental testing is conducted to demonstrate HBC’s control performance.

 

KEYWORDS:

  1. Plug-in hybrid vehicle (PHEV)
  2. Vector Control
  3. Grid-connected Photovoltaic (PV)
  4. Three-phase Hybrid Boost Converter
  5. Maximum Power Point Tracking (MPPT)
  6. Charging Station.

 

SOFTWARE: MATLAB/SIMULINK

 

BLOCK DIAGRAM:

Fig.1 Architecture configurations of a PV charging station. The conventional topology includes a dc/dc converter and a dc/ac VSC. These two converters will be replaced by a three-phase HBC.

 

EXPECTED SIMULATION RESULTS

 

Fig.2 Performance of CC-CV algorithm

Fig.3. Performance of a modified IC-PI MPPT algorithm when solar irradiance variation is applied.

Fig. 4. Performance of the dc voltage control in the vector control. The solid lines represent the system responses when the dc voltage control is enabled. The dashed lines represent the system responses when the dc voltage control is disabled.

Fig. 5. Performance of a proposed vector control to supply or absorb reactive power independently.

Fig. 6. Power management of PV charging station.

Fig. 7. Dst, Md and Mq for case 4.

Fig. 8.  System performance under 70% grid’s voltage drop.

 

CONCLUSION:

Control of three-phase HBC in a PV charging station is proposed in this paper. The three-phase HBC can save switching loss by integration a dc/dc booster and a dc/ac converter converter into a single converter structure. A new control for the three-phase HBC is designed to achieve MPPT, dc voltage regulation and reactive power tracking. The MPPT control utilizes modified incremental conductance-PI based MPPT method. The dc voltage regulation and reactive power tracking are realized using vector control. Five case studies are conducted in computer simulation to demonstrate the performance of MPPT, dc voltage regulator, reactive power tracking and overall power management of the PV charging station. Experimental results verify the operation of the PHEV charging station using HBC topology. The simulation and experimental results demonstrate the effectiveness and robustness of the proposed control for PV charging station to maintain continuous dc power supply using both PV power and ac grid power.

 

REFERENCES:

  • Ehsani, Y. Gao, and A. Emadi, Modern electric, hybrid electric, and fuel cell vehicles: fundamentals, theory, and design. CRC press, 2009.
  • Sikes, T. Gross, Z. Lin, J. Sullivan, T. Cleary, and J. Ward, “Plugin hybrid electric vehicle market introduction study: final report,” Oak Ridge National Laboratory (ORNL), Tech. Rep., 2010.
  • Khaligh and S. Dusmez, “Comprehensive topological analysis of conductive and inductive charging solutions for plug-in electric vehicles,” IEEE Transactions on Vehicular Technology, vol. 61, no. 8, pp. 3475–3489, 2012.
  • Anegawa, “Development of quick charging system for electric vehicle,” Tokyo Electric Power Company, 2010.
  • Musavi, M. Edington, W. Eberle, and W. G. Dunford, “Evaluation and efficiency comparison of front end ac-dc plug-in hybrid charger topologies,” IEEE Transactions on Smart grid, vol. 3, no. 1, pp. 413–421, 2012.

 

A Function Based Maximum Power Point Tracking Method for Photovoltaic Systems

ABSTRACT:

In this paper a novel maximum power point tracking (MPPT) algorithm based on introducing a complex function for photovoltaic systems is proposed. This function is used for determination of the duty cycle of the DC-DC converter in PV systems to track the maximum power point (MPP) in any environment and load condition. It has been suggested based on analyzing the expected behavior of converter controller. The function is formed by a two-dimensional Gaussian function and an Arctangent function. It has been shown that contrary to many algorithms which produce wrong duty-cycles in abrupt irradiance changes, the proposed algorithm is able to behave correctly in these situations. In order to evaluate the performance of method, various simulations and experimental tests have been carried out. The method has been compared with some major MPPT techniques with regard to start-up, steady state and dynamic performance. The results reveal that the proposed method can effectively improve the dynamic performance and steady state performance simultaneously.

 

KEYWORDS:

  1. Gaussian-Arctangent Function Based MPPT
  2. Maximum Power Point Tracking
  3. Photovoltaic Systems
  4. Variable Perturbation Frequency

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Electrical scheme of the system under test.

EXPECTED SIMULATION RESULTS:

 

Fig. 2. Output power of PV for battery load in startup test.

(a)

(b)

(c)

(d)

Fig. 3. The output power and duty cycle in step irradiance change for: (a) VSSINC, (b) LCASF method (c) Fuzzy method and (d) Proposed method.

Fig. 4. Response of algorithms to load change.

(a)

(b)

(c)

(d)

Fig. 5. Response of GAF-VPF algorithm to changes in (a) , (b) , (c) and (d) k.

CONCLUSION:

In this paper a new MPPT algorithm named Gaussian-Arctangent Function-Based (GAF) method was proposed. The method is based on introducing a complex function formed by multiplying a two-dimensional Gaussian function with an Arctangent function. This function is used for generating an adaptive perturbation size. In addition, variable perturbation frequency has been utilized for computing the time of applying the next duty cycle. Simulation results and experimental measurements confirm the attractiveness and superiority of the proposed method with respect to some well-known MPPT methods such as variable step-size Incremental Conductance, load-current adaptive step-size and perturbation frequency (LCASF) and Fuzzy method. The algorithm behaves robustly in case of load variation and measurement noise. The other advantage of proposed method is its simplicity of design. It does not require exact tuning of so many parameters. The only system-dependent constants required for controller setup are open-circuit voltage and short-circuit current and standard condition. Although, the computational cost of proposed method is higher than methods like P&O and Incremental Conductance, it can be easily implemented in low cost micro-controllers. All in all, these features make it well-suited for tracking uncommonly fast irradiance variations like mobile solar applications.

REFERENCES:

[1] Moacyr Aureliano Gomes de Brito, Luigi Galotto, Jr., Leonardo Poltronieri Sampaio, Guilherme de Azevedo e Melo, and Carlos Alberto Canesin, „Evaluation of the Main MPPT Techniques for Photovoltaic Applications”, IEEE Trans. Ind. Electron., vol. 60, no. 3, pp. 1156-1167, March 2013.

[2] C. Hua, J. Lin, and C. Shen, “Implementation of a DSP-controlled photovoltaic system with peak power tracking,” IEEE Trans. Ind. Electron., vol. 45, no. 1, pp. 99–107, Feb. 1998.

[3] A.R Reisi, M.H.Moradi, S.Jamasb, “Classification and comparison of maximum power point tracking techniques for photovoltaic system: A review”, Renewable & Sustainable Energy Reviews, vol. 19, pp. 433-443, March 2013.

[4] Qiang Mei, Mingwei Shan, Liying Liu, and Josep M. Guerrero, “A Novel Improved Variable Step Size Incremental-Resistance MPPT Method for PV Systems”, IEEE Trans. Ind. Electron., vol. 58, no. 6, pp. 2427-2434, June 2011.

[5] N. Femia, G. Petrone, G. Spagnuolo, and M. Vitelli, “Optimization of perturb and observe maximum power point tracking method,” IEEE Trans. Power Electron., vol. 20, no. 4, pp. 963–973, July 2005.