Energy Management and Control Strategy of Photovoltaic/Battery Hybrid Distributed Power Generation Systems With an Integrated Three-Port Power Converter

ABSTRACT:

 Photovoltaic (PV)/battery hybrid power units have attracted vast research interests in recent years. For the conventional distributed power generation systems with PV/battery hybrid power units, two independent power converters, including a unidirectional dc–dc converter and a bidirectional converter, are normally required. This paper proposes an energy management and control strategy for the PV/battery hybrid distributed power generation systems with only one integrated three-port power converter. As the integrated bidirectional converter shares power switches with the full-bridge dc–dc converter, the power density and the reliability of the system is enhanced. The corresponding energy management and control strategy are proposed to realize the power balance among three ports in different operating scenarios, which comprehensively takes both the maximumpower point tracking (MPPT) benefit and the battery charging/discharging management into consideration. The simulations are conducted using the Matlab/Simulinksoftware to verify the operation performance of the proposed PV/battery hybrid distributed power generation system with the corresponding control algorithms, where the MPPT control loop, the battery charging/discharging management loop are enabled accordingly in different operating scenarios.

KEYWORDS:

1.      Energy management

2.      Maximum power point tracking

3.      Bidirectional power converter

4.      Photovoltaic/battery hybrid power unit

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 Figure 1. The Proposed Pv/Battery Hybrid Distributed Power Generation System.

 EXPECTED SIMULATION RESULTS:

Figure 2. Pv Characteristic Curves With Irradiance = 1 Kw/M2 (Red) And Irradiance = 0.5 Kw/M2 (Blue) (Temperature = 25◦C).

 Figure 3. Steady State Simulation Results Of Operation Scenario 2. (A) Dc Bus Voltage Vbus; (B) Pv Voltage Vpv; (C) Pv Current Ipv; (D) Pv Referenc Voltage Vref; (E) Battery Charging Current Ib.

 

Figure 4. Steady State Simulation Results Of Operation Scenario 4. (A) Dc Bus Voltage Vbus; (B) Pv Voltage Vpv; (C) Pv Current Ipv; (D) Pv Reference Voltage Vref; (E) Battery Charging Current Ib.

Figure 5. Steady State Simulation Results Of Operation Scenario 5. (A) Dc Bus Voltage Vbus; (B) Pv Voltage Vpv; (C) Pv Current Ipv; (D) Battery Charging Current Ib.

Figure 6. Simulation Results With Irradiance Dropping From 1000 W/M2 To 500 W/M2 At T = 2 S. (A) Dc Bus Voltage Vbus; (B) Pv Voltage Vpv; (C) Pv Current Ipv; (D) Pv Reference Voltage Vref; (E) Battery Charging Current Ib.

 

Figure 7. Simulation Results With Load Power Rising From 8 Kw To 10 Kw At T = 2 S. (A) Dc Bus Voltage Vbus; (B) Pv Voltage Vpv; (C) Pv Current Ipv; (D) Pv Reference Voltage Vref; (E) Battery Charging Current Ib.

 

CONCLUSION:

 An integrated three-port power converter as the interface for the PV/battery hybrid distributed power generation system is proposed. Compared with the conventional system topology containing an independent DC-DC unidirectional conversion stage and a bidirectional conversion stage, the proposed sys- tem has advantages in terms of higher power density and reliability. The phase shift angle of the full bridge and the switch duty cycle are adopted as two control variables to obtain the required DC bus voltage and realize the power balance among three ports. Different operating scenarios of the system under various power conditions are discussed in detail and a comprehensive energy management and control strategy is proposed accordingly. The priority controller can enable one of the control loops in different scenarios to optimize the whole system performance, taking both the MPPT benefit and the battery charging/discharging manage- ment requirements into consideration. The simulation results verify the performance of the proposed PV/battery hybrid distributed power generation system and the feasibility of the control algorithm.

REFERENCES:

[1] 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.

[2] J. M. Carrasco, L. G. Franquelo, J. T. Bialasiewicz, E. Galvan, R. Potillo, M. M. Prats, J. I. Leon, and N. Moreno-Alfonso, ‘‘Power-electronic sys- tems for the grid integration of renewable energy sources: A survey,’’ IEEE Trans. Ind. Electron., vol. 53, no. 4, pp. 1002–1016, Jun. 2006.

[3] BP Statistical Review of World Energy, British Petroleum, London, U.K., Jun. 2018.

[4] J. P. Barton and D. G. Infield, ‘‘Energy storage and its use with inter- mittent renewable energy,’’ IEEE Trans. Energy Convers., vol. 19, no. 2, pp. 441–448, Jun. 2004.

[5] M. S. Whittingham, ‘‘History, evolution, and future status of energy storage,’’ Proc. IEEE, vol. 100, pp. 1518–1534, May 2012.

Control of UPQC Based on Steady State Linear Kalman Filter for Compensation of Power Quality Problems

ABSTRACT:

 A frequency lock loop (FLL) based steady state linear Kalman filter (SSLKF) for unified power quality conditioner (UPQC) control in three-phase systems is introduced. The SSLKF provides a highly accurate and fast estimation of grid frequency and the fundamental components (FCs) of the input signals. The Kalman filter is designed using an optimized filtering technique and intrinsic adaptive bandwidth architecture, and is easily integrated into a multiple model system. Therefore, the Kalman state estimator is fast and simple. The fundamental positive sequence components (FPSCs) of the grid voltages in a UPQC system are estimated via these SSLKF-FLL based filters. The estimation of reference signals for a UPQC controller is based on these FPSCs. Therefore, both active filters of a UPQC can perform one and more functions towards improving power quality in a distribution network. In addition to the SSLKF-FLL based algorithm, a bat optimization algorithm (based on the echolocation phenomenon of bats) is implemented to estimate the value of the proportional integral (PI) controller gains. The bat algorithm has a tendency to automatically zoom into a region where a promising alternative solution occurs, preventing the solution from becoming trapped in a local minima. The complete three-phase UPQC is simulated in the Matlab/Simulink platform and the hardware is tested under various power quality problems.

KEYWORDS:

1.      Damping factor, echo-location

2.      FPSC

3.      Harmonics

4.      ITSE

5.      SSLKF-FLL

6.      Power quality

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 

 

Figure. 1 Configuration of UPQC

EXPECTED SIMULATION RESULTS:

Fig. 2 Dynamic behavior of control algorithm and shunt converter used in UPQC

Fig. 3 Steady state and dynamic response of UPQC with SSLKF-FLL

 CONCLUSION:

 SSLKF based control is conducted for a three-phase UPQC system under a nonlinear load to achieve PQ compensation. SSLKF control is able to identify the FPSCs (in-phase and quadrature) and grid frequency accurately for the UPQC system, providing fast and smooth steady-state and dynamic responses. The combination of FLL with steady state linear Kalman filters demonstrates superior behavior when compared to other types of single phase PLL techniques published in the literature. It shows that the phase angle and amplitude of a distorted waveform can be precisely and rapidly determined via the Kalman filters. The PI controller parameters, which are tuned in this study using BA optimization, seek minimized DC bus voltage variations, even with upset value of current or voltage. After the 20 iterations, the PI controller proportional (Kp) and integral (Ki) gain are obtained as 200.15 and 1.0, respectively, which maintains the DC bus voltage levels at their desired magnitude. The simulation and test results determine the validity of the proposed UPQC algorithm. The proposed UPQC and BA demonstrates the potential for performance enhancement of the system and PQ improvement of the distribution networks. The presented work can be investigated and evaluated in the future with different linear (or a combination of both linear and nonlinear) loads via the same control algorithm. Similarly, soft computing techniques, such as fuzzy control, artificial neural networks, or intelligent control algorithms, can be used for three-phase UPQCs to improve the system’s effectiveness. Renewable energy sources, such as wind and solar power can be integrated with this (or other) topologies of UPQC.

REFERENCES:

[1] H Hafezai, G D Antona, A Dede, et al. Power quality conditioning in LV distribution networks: Results by field demonstration. IEEE Transactions on Smart Grid, 2017, 8(1): 418-427.

[2] B Singh, A Chandra, Kl A Haddad. Power quality: Problems and mitigation techniques. West Sussex: John Wiley and Sons, 2014.

[3] V Kavitha, K Subramanian. Investigation of power quality issues and its solution for distributed power system. Proc. International Conference on Circuit, Power and Computing Technologies (ICCPCT), Kollam, 2017: 1-6.

[4] M H Bollen. Understanding power quality problems: voltage sags and interruptions. New York: Wiley-IEEE Press, 2000.

[5] S S Reddy. Determination of optimal location and size of static VAR compensator in a hybrid wind and solar power system. International Journal of Applied Engineering Research, 2016, 11(23): 11494-11500.

Comparison of Fuzzy and ANFIS Controllers for Asymmetrical 31-Level Cascaded Inverter With Super Imposed Carrier PWM Technique

ABSTRACT:

 The modified topology for an asymmetrical 31-level cascaded inverter is analyzed with less number of DC voltage sources, power diodes, and power electronic knobs. The Super Imposed Carrier Pulse Width Modulation (SIC-PWM) is proposed for a 31-level asymmetrical modified cascaded inverter topology to reduce the Total Harmonic Distortions (THD). The Fuzzy logic controller (FLC) and Adaptive Neuro-Fuzzy Inference System (ANFIS) are suggested for a 31-level asymmetrical modified cascaded inverter topology to control the root mean square (RMS) voltage. These controllers help in maintaining the output voltage constant even when there is a change in input voltage to the inverter. This study aims to compare Fuzzy logic and ANFIS controllers by applying them to the 31-level cascaded inverter. Using both the controllers the inverter is controlled and its performance is compared using a step response tool in MATLAB. The study of the proposed modified 31-level Asymmetrical cascaded inverter is carried out to evaluate the THD without and with Fuzzy logic and ANFIS controller. Using the step response tool, Settling Time, Overshoot, RMS Voltage values, Peak Time, Peak value, and Rise Time were evaluated and compared for Fuzzy and ANFIS controlled 31-level asymmetrical cascaded inverter. The THD value for without a controller is 4.97%, with the fuzzy logic controller is 4.15% and with ANFIS controller is 3.77%. In both MatLab and real-time simulation, total harmonic distortion (THD) is observed to be the almost same and is lower than 5% which is under IEEE standards. The performance of Fuzzy and ANFIS controlled 31-level asymmetrical cascaded inverter is evaluated and compared with the use of MATLAB/Simulink and the same is done with Real-Time simulation using OPAL-RT 5700.

 KEYWORDS:

1.      Asymmetrical cascaded inverter

2.      Super imposed carrier PWM technique

3.      Total harmonic distortion

4.      Adaptive neuro-fuzzy inference system (ANFIS)

5.      Fuzzy logic controller (FLC)

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Figure 1. The fundamental circuit diagram of symmetrical and asymmetrical cascaded inverter.

 EXPECTED SIMULATION RESULTS:

 

Figure 2. Load wide output voltage for 31-level modified asymmetrical inverter.

 

Figure 3. Output Current through load for 31-level modified asymmetrical inverter.

Figure 4. FFT Analysis for output voltage of 31-level modified asymmetrical inverter.

 

Figure 5. Reference and output RMS voltage for 31-level inverter with fuzzy.

Figure 6. Output voltage across load with Fuzzy logic controller.

Figure 7. FFT analysis for 31-level inverter with fuzzy.

Figure 8. Output voltage across load with ANFIS controller.

CONCLUSION:

The proposed modified 31-level Asymmetrical cascaded inverter with and without Fuzzy logic and ANFIS controller is presented in this paper, demonstrating a substantial change in THD percentages and RMS voltage control. The proposed modified 31-level Asymmetrical cascaded inverter with Fuzzy logic and ANFIS controller is designed in MATLAB/ SIMULINK and verified in Real-Time simulation using OPAL-RT 5700. By using Super Imposed Carrier Pulse Width Modulation (SIC-PWM) with and without the controller, the RMS output voltage is controlled and THD is decreased. The performance of step response parameter values is evaluated and compared for Fuzzy and ANFIS controlled 31-level Asymmetrical cascaded inverter. The dynamic conditions were also analyzed for different DC source voltages and variable resistive loads, the RMS output voltage is controlled and maintained constant (i.e., RMS value is 21.98V for Fuzzy and 22.21V for ANFIS). Using the analytical solution for a 31-level cascaded inverter, it has been identified that the THD value for without a controller is 4.97%, with the fuzzy logic controller is 4.15% and with ANFIS controller is 3.77%. As compared to the Fuzzy logic controller, the ANFIS controller gives better performance. i.e., the RMS Voltage is controlled and settled in less settling time.

REFERENCES:

[1] K. K. Gupta, A. Ranjan, P. Bhatnagar, L. K. Sahu, and S. Jain, ``Multilevel inverter topologies with reduced device count: A review,'' IEEE Trans. Power Electron., vol. 31, no. 1, pp. 135_151, Jan. 2016.

[2] W. A. Halim, S. Ganeson, M. Azri, and T. T. Azam, ``Review of multi- level inverter topologies and its applications,'' J. Telecommun., Electron. Comput. Eng., vol. 8, no. 7, pp. 51_56, 2016.

[3] R. A. Krishna and L. P. Suresh, ``A brief review on multilevel inverter topologies,'' in Proc. Int. Conf. Circuit, Power Comput. Technol. (ICCPCT), Mar. 2016, pp. 1_6.

[4] J. Venkataramanaiah, Y. Suresh, and A. K. Panda, ``A review on symmetric, asymmetric, hybrid and single DC sources based multilevel inverter topologies,'' Renew. Sustain. Energy Rev., vol. 76, pp. 788_812, Sep. 2017, doi: 10.1016/j.rser.2017.03.066.

[5] F. Dijkhuizen, ``Multilevel converters: Review, form, function and motivation,'' in Proc. Ever, 2012, p. 7.

A Two-stage Single-phase Grid-connected Solar-PV System with Simplified Power Regulation

ABSTRACT:

 This study focuses on the design and development of a simplified active power regulation scheme for a two-stage single-phase grid-connected solar-PV (SPV) system with maximum power point (MPP) estimation. It aims to formulate and test an improvised new control scheme to estimate the real-time MPP of the PV panel and operate only at either the MPP or on the right-hand side (RHS) of the PV characteristics of the panel. A simple active power regulatory control scheme was formulated to provide frequency control services to a single-phase grid without using an energy storage device. The plant operator provides the reserve fraction as the input for the active power regulation controller. At any time, the reserve fraction is used to determine the magnitude of the reference power to be extracted from the PV panel for injection into the grid. A simple PI controller was used to track the calculated reference power. The different modes of operation of the regulatory scheme are presented in detail. All the above control schemes are integrated and implemented through appropriate switching of the DC-DC converter alone. The DC-AC converter maintains the DC link voltage and unity power factor at the single-phase grid terminals. The proposed control schemes were tested on a 250 Wp solar panel feeding power to a 230 V, 50 Hz single-phase grid through a two-stage converter. The entire scheme was modeled using the Matlab/Simulink platform, and the same was validated by hardware experimentation using Chroma Solar Simulator and NI my RIO controller under varied irradiation, temperature, and reserve fractions. The simulation and hardware results are compared and reported.

 KEYWORDS:

1.      Solar photo voltaic (SPV)

2.      Maximum power point (MPP)

3.      Right hand side (RHS)

4.      Power regulation

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1 Two-stage grid-connected single-phase solar-PV system with control logic

 EXPECTED SIMULATION RESULTS:

 

Fig. 2 Variation in maximum power estimation and grid power under varied irradiation and temperature with zero reserve

 

Fig. 3 Variation in maximum power estimation and grid  power under varied irradiation at constant temperature 25^oC with reserve fraction

Fig. 4 Variation in maximum power estimation and grid power under varied irradiation and temperature with the change in reserve fraction

Fig. 5 Grid injected current corresponding to the various irradiation, temperature, and reserve fraction

 

Fig. 6 Grid voltage in p.u. and grid injected current

 CONCLUSION:

The proposed simplified active power control with reserve fraction over the entire operating range from near-zero to 100 % of the available MPP was tested and reported for various operating conditions. The RHS operating point of the SPV was maintained under all operating conditions with a specified reserve fraction. This was validated by observing the operating voltage of the SPV, along with the results obtained through the solar simulator. Further, the power quality was ensured at the grid terminals in the proposed scheme by maintaining the THD and zero reactive power exchange. The essential findings and results required for supporting the proposed scheme were provided by modeling and simulating a grid-connected 250 Wp solar-PV system. Subsequently, experimental results obtained by implementing a prototype setup with the same specifications in the laboratory helped to validate the effectiveness of the proposed active power regulation scheme.

 REFERENCES:

 [1] N Gelsora, N Gelsorb, T Wangmob, et al. Solar energy on the Tibetan plateau: Atmospheric influences. Solar Energy, 2018, 173: 984-992.

[2] E Lorenzani, G Migliazza, F Immovilli, et al. CSI and CSI7 current source inverters for modular transformerless PV inverters. Chinese Journal of Electrical Engineering, 2019, 5(2): 32-42.

[3] X Zhang, Q Gao, Y Hu, et al. Active power reserve photovoltaic virtual synchronization control technology. Chinese Journal of Electrical Engineering, 2020, 6(2): 1-6.

[4] F Zhang, D Jiang, K Xu, et al. Two-stage transformerless dual-buck PV grid-connected inverters with high efficiency. Chinese Journal of Electrical Engineering, 2018, 4(2): 36-42.

[5] E I Batzelis, S A Papathanassiou. A method for the analytical extraction of the single-diode PV model parameters. IEEE Trans. Sustain. Energy, 2016, 7(2): 504-512.

A Novel Single-Phase Five-Level Transformer-less Photovoltaic (PV) Inverter

 ABSTRACT:

 Multilevel inverters are preferred solutions for photovoltaic (PV) applications because of lower total harmonic distortion (THD), lower switching stress and lower electromagnetic interference (EMI). In order to reduce the leakage current in the single-phase low-power PV inverters, a five-level transformer-less inverter is proposed in this paper. A total of eleven switches are required, while six of them only withstand a quarter of the dc-bus voltage, so the costs for them are low. Another four switches are turned on or off at the power line cycle, the switching losses for them are ignored. In addition, the flying-capacitors (FCs) voltages are only a quarter of the dc-bus voltage, and they are balanced at the switching frequency, which further reduces the system investment. The experimental results based on a 1 kW prototype show that the proposed modulation strategy can balance the FCs voltages at Vdc/4 very well. And the leakage current can be reduced to about 27 mA under both active and reactive operations, which satisfies the VDE 0126-1-1 standard.

 KEYWORDS:

1.      Leakage current

2.      Multilevel inverter

3.      Pulse width modulation

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1. Proposed single-phase five-level inverter topology.

 EXPECTED SIMULATION RESULTS:

 

                                         Fig. 2. Simulation waveforms under asymmetry filter inductance conditions. (a)

L1=1.6 mH and L2=1.44 mH. (a) L1=1.6 mH and L2=1.28 mH.

 

Fig. 3. Waveforms of output voltage VAB, Vout and current iout.

Fig. 4. Waveforms of output voltage VAB and FC voltages VC1, VC2.

Fig. 5. Waveforms of VAN, VBN, VCM and ileakage.

Fig. 6. Waveforms of VAN, VBN and VCM in the positive half cycle.

Fig. 7. Waveforms of VAN, VBN and VCM in the negative half cycle.

 

Fig. 8. Waveforms of VAB, VC1 and iout when θ is 35 degrees.

Fig. 9. Transient experiment in load.

 

CONCLUSION:

In this paper, a single-phase five-level transformer-less inverter and its modulation strategy for the PV systems are proposed. It adopts the symmetrical filter inductor configuration. The difference from the traditional FC-based topologies is that the FCs voltages are controlled at Vdc/4. Through the combination of dc-bus voltage and FCs voltages, the CM voltage is theoretically maintained at a constant value during the whole power frequency of unite grid, and then the leakage current is reduced. The two FCs voltages can be balanced at Vdc/4 automatically at the switching frequency through the selection of the redundant switching states. Finally, the volume and investment cost of the FCs are decreased. The theoretical analysis and experimental verifications are presented. In conclusion, the proposed topology and modulation strategy can ensure a constant CM voltage without any high-frequency components throughout the power frequency cycle. Consequently, the leakage current can be significantly reduced below 300 mA, which meets the specification in the standard VDE-0126-1-1.

REFERENCES:

[1] M. Pahlevani, S. Eren, J. M. Guerrero and P. Jain, “A hybrid estimator for active/reactive power control of single-phase distributed generation systems with energy storage,” IEEE Trans. Power Electron., vol. 31, no. 4, pp. 2919-2936, Apr. 2016.

[2] E. Rebello, D. Watson and M. Rodgers, “Performance analysis of a 10 MW wind farm in providing secondary frequency regulation: experimental aspects,” IEEE Trans. Power Syst, vol. 34, no. 4, pp. 3090-3097, Jul. 2019.

[3] H. Wang, L. Kou, Y. Liu and P. C. Sen, “A seven-switch five-level active-neutral-point-clamped converter and its optimal modulation strategy,” IEEE Trans. Power Electron., vol. 32, no. 7, pp. 5146-5161, Jul. 2017.

[4] X. Guo, X. Zhang, H. Guan, T. Kerekes and F. Blaabjerg, “Three-phase ZVR topology and modulation strategy for transformerless PV system,” IEEE Trans. Power Electron., vol. 34, no. 2, pp. 1017-1021, Feb. 2019.

[5] W. Li, Y. Gu, H. Luo, W. Cui, X. He and C. Xia, “Topology review and derivation methodology of single-phase transformerless photovoltaic inverters for leakage current suppression,” IEEE Trans. Ind. Electron., vol. 62, no. 7, pp. 4537-4551, Jul. 2015.