Design and Implementation of Asymmetrical Multilevel Inverter With Reduced Components and Low Voltage Stress

 Abstract

Design and Implementation Multilevel inverters with a high device count, low boosting and DC voltage imbalance are all common problems exists in the traditional topologies. In this article, a new single-phase asymmetrical multilevel inverter (MLI) that can generate 33 levels at the output with fewer components and lower total standing voltage (TSV) at the switches is presented. The multiple input sources of the proposed inverter make it suited for the use in renewable energy generating systems which have a variety of DC sources. The stress distribution among the switches is investigated that reduces the use of high rated devices with which overall cost of the inverter gets reduced. The topology can be extended by adding the circuits in series for higher levels. The performance of the inverter is calculated considering a variety of critical parameters such as TSV, cost function (CF), power loss, and efficiency calculations. The MLI is tested under dynamic load conditions with sudden load disturbances with a range of combinational loads and it has been determined to be stable throughout its operation. A detailed comparison is made based on stress across the switches, stress distribution, switches count, DC sources count, gate driver circuits, component count factor, TSV, CF, and other existing topologies using graphical representations and shown to be cost-effective and superior in all aspects. The total harmonic distortion (THD) derived from simulation and experiment complies with IEEE standards. The proposed framework has been developed in MATLAB/Simulink and tested in a laboratory environment with hardware.

Index Terms

Multilevel inverter, maximum blocking voltage (MBV), total standing voltage (TSV), normalised voltage stress (NVS), stress distribution, cost function (CF), total harmonic distortion (THD).

Proposed Diagram:

Figure 1. Proposed 33-Level Mli Topology.

Expected Simulation Results:

Figure 2. Simulation Thd For The Proposed 33-Level Mli.

Figure 3. Simulation Output Of Modulation Index Variation.

Figure 4. Experimental Circuit Of The Proposed 33-Level Mli.

Conclusion

Design and Implementation The proposed new asymmetrical MLI topology that can able to generate 33 voltage levels is implemented with reduced components and less TSV. A detailed stress distribution across the switches is analyzed with which the low voltage rated switches are selected, which decreases the cost and size of the inverter. An extended circuit is designed for higher output voltage levels. The developed MLI is compared with other existing MLI architectures considering several parameters for estimation of its performance and found to be superior. The MLI requires fewer power switches with less DC sources count for the generation of higher output levels. TSVPU of the MLI is 3.31, only 25% of the switches are under maximum stress. Hence the cost of the inverter gets reduced. The comparisons represents that the proposed MLI has low TSV, cost-effective and efficient. As the unequal DC sources and low-rated switches are utilized in this topology, it is feasible for various hybrid energy storage and electric vehicle applications. For evaluating the performance of the MLI, it is tested for dynamically loaded conditions and found to be stable throughout its operation. Both simulation and experimental THD obtained is 2.03% with an efficiency of 95.2%, cost function _ is 3.11 and 3.51 respectively, which is less when compared with other existing topologies. The proposed topology can be extended for the solar PV applications with various ratings of PV panels for the multiple inputs.

References

[1] N. A. Rahim, K. Chaniago, and J. Selvaraj, ``Single-phase seven-level grid- connected inverter for photovoltaic system,'' IEEE Trans. Ind. Electron., vol. 58, no. 6, pp. 2435_2443, Jun. 2011.

[2] M. Alsolami, K. A. Potty, and J. Wang, ``A gallium-nitride-device-based switched capacitor multiport multilevel converter for UPS applications,'' IEEE Trans. Power Electron., vol. 32, no. 9, pp. 6853_6862, Sep. 2017.

[3] K. Bandara, T. Sweet, and J. Ekanayake, ``Photovoltaic applications for off-grid electrification using novel multi-level inverter technology with energy storage,'' Renew. Energy, vol. 37, no. 1, pp. 82_88, Jan. 2012.

[4] M. Hosseinpour, A. Sei_, A. Dejamkhooy, and F. Sedaghati, ``Switch count reduced structure for symmetric bi-directional multilevel inverter based on switch-diode-source cells,'' IET Power Electron., vol. 13, no. 8, pp. 1675_1686, Jun. 2020.

[5] K. V. Iyer and N. Mohan, ``Modulation and commutation of a single stage isolated asymmetrical multilevel converter for the integration of renewables and battery energy storage system in ships,'' IEEE Trans. Transport. Electric., vol. 2, no. 4, pp. 580_596, Dec. 2016.

Hybrid Three-Phase Transformer-Based Multilevel Inverter with Reduced Component Count

 Abstract

This paper proposes a novel three-phase transformer-based multilevel inverter (MLI) topology to maximize the output voltage levels for high-power high-voltage applications while reducing component counts as compared to its transformer-based counterparts. The proposed hybrid topology is formed by connecting a three-level T-type module with full H-bridge cells through single-phase transformers. The T- type module is fixed while the full H-bridge cell can be repeated for enlarging the output voltage levels without increasing the voltage stress on switches. Key features of the proposed topology include low part count, capacitor-free, diode-free, voltage boosting, simple control, and modularity. Within the framework, a simple low-frequency pulse width modulation (LFPWM) switching scheme is used to control the output voltage, and the working principle is detailed for seven-, nine-, and N-level operation. The operability and performance of the proposed topology are numerically verified and experimentally validated at different loads. Moreover, its conversion efficiency is experimentally examined. Finally, a comparative study with existing transformer-based MLI circuits is conducted to prove its key merits.

Keywords

Cascaded-transformer multi level inverter (CTMI), DC-AC converter, hybrid multilevel inverter (MLI), multilevel inverter topology.

Circuit Diagram:

Figure 1. The Circuit Configuration Of The Proposed Transformer Based MLI Topology.

Expected Simulation Results:

Figure 2. Simulation Waveforms Of The Proposed Topology When _ Is 1. (A) Pole Voltage Va0 Synthesizing. (B) Pole Voltages Va0, Vb0, And Vc0. (C) Line Voltages Vab, Vbc, And Vca.

Figure 3. Simulation Waveforms When _ Is 1. (A) Vab, Van, And Ian At Resistive Load. (B) Vab, Van, And Ian At Resistive-Inductive Load.

Figure 4. Simulation Waveforms When _ Is 1.5. (A) Pole Voltage Va0 Synthesizing. (B) Pole Voltages Va0, Vb0, And Vc0. (C) Line Voltages Vab, Vbc, And Vca.

Figure 5. Simulation Waveforms When _ Is 1.5. (A) Vab, Van, And Ian At Resistive Load. (B) Vab, Van, And Ian At Resistive-Inductive Load.

Conclusion

This paper proposes a novel three-phase transformer-based nine-level inverter with a reduced component count, having the key features of being capacitor-, diode-free, and low counts of DC sources, switches, and transformers. The pro- posed circuit can increase the voltage level count to N levels without increasing the voltage stress across the switches, being a promising candidate for high-power high-voltage applications. Further, it has beneficial features of modularity, voltage boosting and simple structure. The working principle of the proposed topology was theoretically demonstrated, numerically verified, and experimentally validated through the in-house setup. Finally, the advantages of the proposed topology, in terms of component counts, are highlighted by a comparative study.

References

[1] P. R. Bana, K. P. Panda, R. T. Naayagi, P. Siano, and G. Panda, ``Recently developed reduced switch multilevel inverter for renewable energy integration and drives application: Topologies, comprehensive analysis and comparative evaluation,'' IEEE Access, vol. 7, pp. 54888_54909, 2019.

[2] M. Vijeh, M. Rezanejad, E. Samadaei, and K. Bertilsson, ``A general review of multilevel inverters based on main submodules: Structural point of view,'' IEEE Trans. Power Electron., vol. 34, no. 10, pp. 9479_9502, Oct. 2019.

[3] M. N. Raju, J. Sreedevi, R. P. Mandi, and K. S. Meera, ``Modular multilevel converters technology: A comprehensive study on its topologies, modelling, control and applications,'' IET Power Electron., vol. 12, no. 2, pp. 149_169, Feb. 2019.

[4] A. Salem, H. Van Khang, K. G. Robbersmyr, M. Norambuena, and J. Rodriguez, ``Voltage source multilevel inverters with reduced device count: Topological review and novel comparative factors,'' IEEE Trans. Power Electron., vol. 36, no. 3, pp. 2720_2747, Mar. 2021.

[5] H. P. Vemuganti, D. Sreenivasarao, S. K. Ganjikunta, H. M. Suryawanshi, and H. Abu-Rub, ``A survey on reduced switch count multilevel inverters,'' IEEE Open J. Ind. Electron. Soc., vol. 2, pp. 80_111, 2021.

Single-Input Quadruple-Boosting Switched-Capacitor Nine-Level Inverter with Self-Balanced Capacitors

 Abstract

This paper suggests a single-input switched-capacitor Nine-level inverter configuration advantaging from quadruple voltage-boosting ability, natural voltage balancing of capacitors, and reduced components per level. Also, the single-source character of the proposed topology makes it cheaper and more compact. The cascaded version of the suggested topology has also been introduced, by which high boosting factors, as well as large number of steps, can be obtained. The proposed topology can effectively supply the resistive-inductive or pure inductive load types. The capacitors' impulsive-charging-current issue has been solved by simple small-inductance-based inductor-diode (L-D) networks. The comparative analysis affirms the fewer device-usage in suggested configuration per equal gain or level count than existed structures, resulting in less size and cost. The usage of Nearest-Level modulation guarantees the low- frequency operation of semiconductors and reduces the switching losses. The comparative analysis and experimental outcomes affirm the competitiveness and accurate functionality of suggested configuration.

Index Terms

Multilevel inverter, number of levels, self-balanced capacitors, switched-capacitor, voltage gain.

Proposed Diagram:

Figure 1. Proposed 9-Level Inverter.

Conclusion

This paper has proposed a basic switched-capacitor 9-level inverter that is extendable to higher levels. The single-source nature, quadruple voltage-boosting ability, capacitors' natural charge-balancing, increased levels per device, and capability of feeding low power factor (resistive-inductive or inductive) load types are the main advantages of the suggested topology. The H-bridge switches tolerate Vo;max, but due to their fundamental-frequency operation, their switching- loss is suppressed. The capacitors' impulse-charging current has been reduced by a small-inductance-based L-D net- work. The output voltage THD of the suggested topology is about 8.5%. The comparative analysis confirms that the suggested topology has higher ratios of a number of levels and gain to devices, which is an important advantage. The efficiency of an implemented laboratory-scale prototype of the suggested topology for Vdc D 30 [V] is about 90.9%, which is acceptable. Two extended versions of the suggested basic topology have been introduced to achieve more levels and voltage-gains. The experimental outcomes validate the proper performance of the suggested switched-capacitor 9-level inverter topology.

References

[1] M. Vijeh, M. Rezanejad, E. Samadaei, and K. Bertilsson, ``A general review of multilevel inverters based on main submodules: Structural point of view,'' IEEE Trans. Power Electron., vol. 34, no. 10, pp. 9479_9502, Oct. 2019.

[2] M. Karimi, P. Kargar, and K. Varesi, ``An extendable asymmetric boost multi-level inverter with self-balanced capacitors,'' Int. J. Circuit Theory Appl., vol. 50, no. 4, pp. 1297_1316, Apr. 2022.

[3] F. Esmaeili and K. Varesi, ``A novel single-phase multi-level inverter topology based on bridge-type connected sources with enhanced number of levels per number of devices,'' J. Energy Manage. Technol., vol. 4, no. 3, pp. 37_47, 2020.

[4] S. Deliri, K. Varesi, and S. Padmanaban, ``An extendable single-input reduced-switch 11-level switched-capacitor inverter with quintuple boosting factor,'' IET Gener., Transmiss. Distrib., to be published.

[5] A. Ashraf Gandomi, K. Varesi, and S. H. Hosseini, ``Control strategy,applied on double flying capacitor multi-cell inverter for increasing number of generated voltage levels,'' IET Power Electron., vol. 8, no. 6, pp. 887_897, Jun. 2015.

Symmetric and Asymmetric Multilevel Inverter Topologies With Reduced Device Count

 Abstract

In this work, two new topologies of single-phase hybrid multilevel inverters for symmetrical and asymmetrical configurations are presented for use in drives and control of electrical machines and the connection of renewable energy sources. The proposed topology uses 2 dc sources, 12 switches,1 flying capacitor, and 3 diodes to generate boosted 13-levels and 17-levels for symmetric and asymmetric configuration, respectively. Self-voltage balancing of its capacitor voltage regardless of load type, load dynamics, or modulation index is a key advantage of the suggested design. The higher performance of proposed topologies in terms of the total number of switches, TSV, THD, switch stress, and dc sources are demonstrated by comparing those with recently published topologies. In addition, a widely employed nearest level control modulation approach is used to provide output voltage levels with low THD. Finally, experiments were undertaken to validate the performance of the suggested topology.

Keywords

Multilevel inverter (MLI), switched-capacitor, nearest level control (NLC), total standing voltage (TSV).

Proposed Diagram:

Figure 1. Proposed SCMLI Topology.

Expected Simulation Results:

Figure 2. Simulation Results For The Symmetrical Topology. Output Voltage, Output Current, Voltage And Current Across Capacitor C1 For (A) Dynamic Change Of R-Load (B) Dynamic Change Of Rl-Load (C) Change In Frequency Of The Reference Sinusoidal Signal (D) Change In Modulation Index (Mi).

Figure 3. Simulation Results For The Asymmetrical Topology. Output Voltage, Output Current, Voltage And Current Across Capacitor C1 For (A) Dynamic Change Of R-Load (B) Dynamic Change Of Rl-Load (C) Change In Frequency Of The Reference Sinusoidal Signal (D) Change In Modulation Index (Mi).

Conclusion

This paper presented a topology for symmetric and asymmetric configuration, which generates 13 and 17 output levels, respectively, with lesser components. TSV and THD are also quite low. Although it used 2 sources, it generates boosted output voltage for both configurations with the help of a flying capacitor. Utilizing the concept of a dc-link capacitor across the sources, the output levels are increased. All the capacitors are self-balanced without the need for extra control circuitry. The static and dynamic stability of a topology is determined by the findings obtained for various load scenarios. In addition, power loss analysis provides insight into the switch kinetics. On the basis of the comparative analysis, it can be determined that the proposed topology provides greater performance compared to other topologies in the literature that have been compared. The architecture is very efficient and well-suited for renewable energy applications such as solar PV systems that are grid-connected.

References

[1] M. Sarebanzadeh, M. A. Hosseinzadeh, C. Garcia, E. Babaei, M. Hosseinpour, A. Sei_, and J. Rodriguez, ``A 15-level switched capacitor multilevel inverter structure with self-balancing capacitor,'' IEEE Trans. Circuits Syst. II, Exp. Briefs, vol. 69, no. 3, pp. 1477_1481, Mar. 2022, doi: 10.1109/TCSII.2021.3123115.

[2] F. Esmaeili, H. R. Koo_gar, and H. Qasemi, ``A novel single-phase multilevel high-gain inverter with low voltage stress,'' IEEE J. Emerg. Sel. Topics Power Electron., vol. 10, no. 5, pp. 6084_6092, Oct. 2022, doi:10.1109/JESTPE.2022.3166233.

[3] M. A. Hosseinzadeh, M. Sarebanzadeh, E. Babaei, M. Rivera, and P. Wheeler, ``A switched-DC source sub-module multilevel inverter topology for renewable energy source applications,'' IEEE Access, vol. 9, pp. 135964_135982, 2021, doi: 10.1109/ACCESS.2021.3115660.

[4] N. Sandeep, ``A 13-level switched-capacitor-based boosting inverter,'' IEEE Trans. Circuits Syst. II, Exp. Briefs, vol. 68, no. 3, pp. 998_1002, Mar. 2021, doi: 10.1109/TCSII.2020.3017338.

[5] Y. Ye, G. Zhang, X. Wang, Y. Yi, and K. W. E. Cheng, ``Self-balanced switched-capacitor thirteen-level inverters with reduced capacitors count,'' IEEE Trans. Ind. Electron., vol. 69, no. 1, pp. 1070_1076, Jan. 2022, doi: 10.1109/TIE.2021.3050378.

Review of Reduced Switch-Count Power Cells for Regenerative Cascaded H-Bridge Motor Drives

 Abstract

Reduced Switch Cascaded H-Bridge (CHB) topology is one of the attractive topologies in high-power medium voltage motor drive applications due to its modularity and scalability. Research in high power regenerative motor drives has gained significant attention with the increasing demand for efficient energy use. In a cascaded H-Bridge (CHB) converter, the regenerative capability can be introduced by replacing diode front end (DFE) with active front end (AFE) topologies. However, this results in a huge increase in the number of power semiconductors, gate drivers, and heat sink size and thus increases the overall size and cost of the regenerative CHB motor drives. To overcome the aforementioned challenges, different power cell designs have been introduced to reduce the switch count, allowing the design of more suitable-sized and more economical drives. This paper comprehensively reviews the reduced switch-count power cell designs, including single-phase and three-phase grid connections. Each reduced switch-count cell design is analyzed, and its advantages and disadvantages are studied in detail. The challenges that arise with each design and the method to address the challenges are discussed.

Keywords

Cascaded H-bridge (CHB), reduced switch-count, control, motor drives, active front end, multilevel converter.

Proposed Diagram:

Figure 1. Multilevel Inverters Classification.

Expected Simulation Results:

Figure 2. Dc-Capacitors And Dc-Link Voltages For Semi-Reduced Cell Shown In [12].

Figure 3. Semi-Reduced Cell Input Current With 50 Hz Input Frequency And 20 Hz Output Frequency As Shown In [12].

Figure 4. Primary Input Current Using Fig. 14 Interconnection As Shown In [12].

Figure 5. Reduced Cell Input Current For 50 Hz Grid Frequency And 20 Hz Output Frequency, As Shown In [67].

Figure 6. Reduced Cell Primary Input Current As Shown In [67].

Figure 7. Input Primary Current As Resulted From [71] Experimental Results.

Conclusion

This paper presented a comprehensive review of the existing single-phase and three-phase reduced switch-count power cell designs for the regenerative Cascaded H-Bridge motor drives applications. Each power cell design is evaluated against the conventional 10-switch regenerative power cell to determine the advantages and disadvantages regarding structure, control, and harmonics present in the system. The key characteristics of the power cells are summarized to identify the requirements and differences between all regenerative power cells presented in this paper. Additionally, a new possible configuration is proposed to reduce the existing three phase reduced switch-count power cell.

References

[1] H. Akagi, ``Multilevel converters: Fundamental circuits and systems,'' Proc. IEEE, vol. 105, no. 11, pp. 2048_2065, Nov. 2017, doi: 10.1109/JPROC.2017.2682105.

[2] S. Ahmad, S. H. Johari, A. Ahmad, and M. F. M. A. Halim, ``Grid connected multilevel inverters for PV application,'' in Proc. IEEE Conf. Energy Convers. (CENCON), Johor Bahru, Malaysia, Oct. 2015, pp. 181_186, doi: 10.1109/CENCON.2015.7409536.

[3] M. Trabelsi, H. Vahedi, and H. Abu-Rub, ``Review on single-DC-source multilevel inverters: Topologies, challenges, industrial applications, and recommendations,'' IEEE Open J. Ind. Electron. Soc., vol. 2, pp. 112_127, 2021, doi: 10.1109/OJIES.2021.3054666.

[4] V. Patel, M. Tinari, C. Buccella, and C. Cecati, ``Analysis on multilevel inverter powertrains for E-transportation,'' in Proc. IEEE 13th Int. Conf. mCompat., Power Electron. Power Eng. (CPE-POWERENG), Sonderborg, Denmark, Apr. 2019, pp. 1_6, doi: 10.1109/CPE.2019.8862373.

[5] J. Rodríguez, J.-S. Lai, and F. Z. Peng, ``Multilevel inverters: A survey of topologies, controls, and applications,'' IEEE Trans. Ind. Electron., vol. 49, no. 4, pp. 724_738, Aug. 2002.

Speed Control of Induction Motor using Scalar Control Technique

 ABSTRACT

This paper presents design and implementation of scalar control of induction motor. This method leads to be able to adjust the speed of the motor by control the frequency and amplitude of the stator voltage of induction motor, the ratio of stator voltage to frequency should be kept constant, which is called as V/F or scalar control of induction motor drive.

Induction Motor

This paper presents a comparative study of open loop and clos loop V/F control induction motor. The V/F control is based on advent of stator voltage derivatives. Simulation is carried out in MATLAB/SIMULINK environment and results are compared for speed control of induction motor.

Keywords
Scalar control (V/F), Induction Motor (IM), Open loop V/F control, closed loop V/F control, PI controller.

Block Diagram:

Fig-1: Block diagram of the open loop V/F control for an IM.

Expected Simulation Results:

Fig-2 Current vs. Time

Fig-3 Torque vs. Time

Fig-4 Current vs. Time

Fig-5 Torque vs. Time

CONCLUSION

Simulation is carried out in MATLAB environment for speed control of induction motor for full load, using PI controller. And the results are checked. From the above experiment and results we concluded that the closed loop V/F control gives better response and better result as compared to open loop V/F control of induction motor.

REFERENCES

[1] B.K. Bose, Power Electronics and AC Drives, Prentice- Hall,’’ NJ,USA, 2002.

[2] I. Boldea, ‘‘Control issues in adjustable speed drives, ’’ IEEE Industrial Electronics Magazine, Vol. 2, No. 3, Sept. 2008, pp. 32 - 50.

[3] A. Munoz-Garcia, T.A. Lipo, D.W. Novotny, ‘‘A new induction motor V/f control method capable of highperformance regulation at low speeds, ’’ Vol. 34, No. 4, July/August 1998, pp. 813 - 821.

[4] H. Akroum, M. Kidouche, A. Aibeche, ‘‘A dSPACE DSP Control Platform for V/F Controlled Induction Motor Drive and Parameters Identification,’’ Lecture Notes in Electrical Engineering (LNEE), vol. 121, pp. 305-312, 2011.

[5] A. Oteafy, J. Chiasson, ‘‘A Study of the Lyapunov Stability of an Open- Loop Induction Machine IEEE Transactions on Control Systems Technology,’’ Vol. 18 , No. 6, Nov. 2010, pp. 1469 – 1476

Droop Control of Parallel Dual-Mode Inverters Used in Micro Grid

Abstract: 

Grid-connected and island control of parallel inverters used in micro grid based on a variety of micro-source were introduced in this paper. Micro-grid in the connected mode should be able to operate automatically with the grid frequency and output high quality electricity in PQ control, and in island mode it can realize load power sharing of the parallel DGs in Droop control [1]. Simultaneously, it should also ensure the stability of the load voltage and frequency in island mode with the droop-based controller which can make the micro-grid smoothly switching between the two operation modes. Finally, simulation of two inverters in the connected mode and island mode was introduced in MATLAB / SIMULINK; the simulation results show the effect of droop control and the load-sharing function. The results also indicate the feasibility and correctness of the control strategy.

Keywords

micro grid; parallel dual-mode inverters; PQ control; droop control

Block Diagram:

FIGURE 1. MICRO-GRID STRUCTURE DIAGRAM.

Expected Simulation Results:

FIGURE 2. THE SIMULATION OF GRID-CONNECTED MODE.

FIGURE 3. THE SIMULATION OF ISLAND MODE.

FIGURE 4. THE VOLTAGE AND CURRENT FROM ISLAND TO

                                         GRID-CONNECTED MODE.

FIGURE 5. INVERTER1 AND INVERTER2 OUTPUT ACTIVE POWER.

FIGURE 6. ACTIVE POWER ABSORBED BY THE LOAD.

CONCLUSION

Micro-grid often operates under two typical modes. Micro-grid in the grid-connected mode can make it run automatically with the grid frequency and output high quality electricity. Furthermore, micro-grid in island mode can realize load power sharing of the parallel distributed power of micro-grid. Meanwhile, it can also ensure the stability of the load voltage and frequency. Moreover, the droop controller [5] can make the micro-grid smooth switching between the two kinds of operation modes. Finally, the simulation results indicated that the phase and magnitude of the load voltage are successfully matched to the grid voltage at the point of transfer from island mode to grid-connected operation without any distortions. Similarly, when the mode returns back, the load voltage can quickly approach its desired voltage without voltage and current rush by using the proposed method and strategy.

REFERENCES

[1] Hu, Shang-Hung., Kuo, Chun-Yi., Lee, Tzung-Lin & Josep M.Guerrero, “Droop-Controlled Inverters with Seamless Transition between Islanding and Grid-Connected Operations,” ECCE, Phoenix, AZ, Sept 2011, pp.2196-2201.

[2] Yang Zhan gang, Wang Cheng Shan, Che Yan Bo, “A Small-scale Micro-grid System with Flexible Modes of Operation,” Automation of Electric Power Systems, vol.33, No.14, July 2009, pp.89-92.

[3] Kanellos,F.D., Tsouchnikas,A.I., & Hatziargyriou, N.D., “Micro-grid simulation during grid-connected and islanded modes of operation,” presented at the Int. Conf. Power Systems Transients (IPST), Montreal, QC, Canada, 2005, Paper IPST05-113.

[4] Chen, C.L. Wang, Y.B. & Lai, J.S., “Design of parallel inverters for smooth mode transfer micro-grid applications,” in Applied Power Electronics Conference and Exposition, 2009 IEEE.APEC 2009, pp. 1288-1294.

[5] Lee, C.T. Jiang, R.P. & Cheng, P.T., “A grid synchronization method for droop controlled distributed energy resources converters,” in Energy Conversion Congress and Exposition, 2011 IEEE. ECCE 2011, pp. 743- 749.

Distributed Generation System Control Strategies in Microgrid Operation

 Abstract:

Control strategies of distributed generation (DG) are investigated for different combination of DG and storage units in a microgrid. This paper develops a detailed photovoltaic (PV) array model with maximum power point tracking (MPPT) control, and presents real and reactive power (PQ) control and droop control for DG system for microgrid operation. In grid-connected mode, PQ control is developed by controlling the active and reactive power output of DGs in accordance with assigned references. In islanded mode, DGs are controlled by droop control. Droop control implements power reallocation between DGs based on predefined droop characteristics whenever load changes or the microgrid is connected/disconnected to the grid, while the microgrid voltage and frequency is maintained at appropriate levels. This paper presents results from a test microgrid system consisting of a voltage source converter (VSC) interfacing with a DG, a PV array with MPPT, and changeable loads. The control strategies are tested via two scenarios: the first one is to switch between grid-connected mode and islanded mode and the second one is to change loads in islanded mode. Through voltage, frequency, and power characteristics in the simulation under such two scenarios, the proposed control strategies can be demonstrated to work properly and effectively.

Keywords:

Distributed generation, PV, Microgrid, Droop control, PQ control.

Schematic Diagram:

Fig. 1. Schematic of the microgrid.

Expected Simulation Results:

Fig. 2. PQ control under grid-connected mode.

Fig. 3. Droop control for switching modes.

Fig. 4. Droop control for varying load.

Conclusion

In this paper a detailed PV model with MPPT, and PQ and droop controllers is developed for inverter interfaced DGs. The use of PQ control ensures that DGs can generate certain power in accordance with real and reactive power references. Droop controller is developed to ensure the quick dynamic frequency response and proper power sharing between DGs when a forced isolation occurs or load changes. Compared to pure V/f control and master-slave control, the proposed control strategies which have the ability to operate without any online signal communication between DGs make the system operation cost-effective and fast respond to load changes. The simulation results obtained shows that the proposed controller is effective in performing real and reactive power tracking, voltage control and power sharingduring both grid-connected mode and islanded mode. To fully represent the complexity of the microgrid, future work will include the development of hierarchical controllers for a microgrid consisting of several DGs and energy storage system. The function of primary controller is to assign optimal power reference to each DG to match load balances and the secondary controllers are designed to control local voltage and frequency.

REFERENCES

Barsali, S., Ceraolo M., Pelacchi, P., and Poli, D. (2002). Control techniques of dispersed generators to improve the continuity of electricity supply. IEEE Conf., Power Engineering Society, vol.2, pp.789-794.

Cai, N., and Mitra J. (2010). A decentralized control architecture for a microgrid with power electronic interfaces. IEEE conf., North American Power Symposium, pp. 1-8.

Chen, X., Wang, Y.H., and Wang, Y.C. (2013). A novel seamless transferring control method for microgrid based on master-slave configuration. IEEE Conf., ECCE Asia, pp. 351-357.

Cho, C. H., Jeon, J.H., Kim, J.Y., Kwon, S., Park, K., and Kim, S. (2011). Active synchronizing control a microgrid. IEEE Trans., Power Electron., vol. 26, no. 12, pp. 3707-3719.

Choi, J.W. and Sul, S.K. (1998). Fast current controller in three-phase AC/DC boost converter using d-q axis crosscoupling. IEEE Trans., Power Electron., vol.13, no.1, pp. 179-185.

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:

Active and reactive power control, fault ride through, MPPT, Photovoltaic system, RTDS Supercapacitor Energy storage

Block Diagram:

Fig.1. Grid connected PV system with energy storage

Expected Simulation Diagram:

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

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

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

                                                                               storage

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

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

Analysis of the Capacitor-Less D-STATCOM for Voltage Profile Improvement in Distribution Network With High PV Penetration

 ABSTRACT

Distributed Energy Resources (DERs) have disrupted the traditional electrical system. Grid connected photovoltaic (PV) systems deliver electric energy closer to the consumer, shifting the paradigm from centralized to distributed generation. The impact of the stochastic PV output power gives rise to potentially rapid voltage fluctuations. Reactive power compensation is needed to regulate the voltage profile to meet the relevant standards. Traditional approaches like switched capacitors cannot provide reactive power that is continuously adjustable at short time scales. This paper examines an alternative distribution static synchronous compensator (D-STATCOM) based on a matrix converter (MC) for the low voltage distribution networks with high PV penetration. This technology can extend service life by using inductors for energy storage. The converter being studied provides ancillary services, including reactive power support; the impact on reliability, operational constraints, and electrical behavior is demonstrated. The contribution of this paper is a detailed analysis and impact study of the capacitor-less D-STATCOM in high PV penetration distribution networks. The significance of this paper is that it studies the behavior of the power electronics converter and its interaction with the power systems without assuming or neglecting details of either. Compensation effects and reliability comparisons between the proposed capacitorless D-STATCOM and the incumbent

D-STATCOM technology are also studied in this paper.

INDEX TERMS

D-STATCOM, voltage profile, reactive power compensation, model predictive control, matrix converter, grid integration, renewable energy sources, high PV penetration, reliability of power electronics.

Block Diagram:

FIGURE 1. Line Drop Compensation Circuit.

Expected Simulation Results:

FIGURE 2. Results from QSTS simulation showing power flow and bus

                                                  voltage without D-STATCOM.

FIGURE 3. Results from QSTS simulation showing power flow and bus

                                                       voltage with D-STATCOM.

FIGURE 4. Impact of D-STATCOM on voltage profile of bus 890 without

                                                      and with high PV penetration.

CONCLUSION

This paper presented a detailed analysis and impact study of the capacitor-less D-STATCOM in high PV penetration distribution networks. This paper answered questions on (1) functional capabilities, (2) impact on the distribution network, (3) converter-level behavior, and (4) reliability of the proposed capacitorless D-STATCOM compared to other incumbent technologies (i.e., SVCs, VSC-based D-STATCOM, and OLTCs). The main contributions of this paper were:

 Impact study of capacitorless D-STATCOM on a distribution network with high PV permeability

 Impact and behavior comparison between capacitorless D-STATCOM and VSC-based D-STATCOM

 Reliability comparison between capacitorless D-STATCOM and VSC-based D-STATCOM

The significance of this paper is that it studies the behavior of the power electronics converter and its interaction with the power systems without assuming or neglecting details of either. In the power system study in this paper, a complete OpenDSS simulation of the IEEE 34 bus distribution test system was used to illustrate the impact of the capacitorless D-STATCOM during high PV penetration. In the power electronics study, the converter-level behavior of the capacitorless D-STATCOM was demonstrated with a 7.5 kVA experimental prototype. The main findings of this paper:

 The capacitorless D-STATCOM provides dynamic support to the distribution network allowing more PV penetration.

 The capacitorless D-STATCOM could precisely control the voltage and perform conservative voltage reduction to reduce losses, thus, improving the efficiency of the low voltage network.

 A distribution network with high PV penetration and a capacitorless D-STATCOM has shown fewer tap changes in mechanical OLTCs. Thus, increasing the service life of already existing distribution network equipment.

 A reliability study of the D-STATCOM technologies has shown that dc-link capacitors are the reliability bottleneck of the incumbent VSC-based D-STATCOM.

 The capacitorless D-STATCOM has the same compensation effects as the VSC-based D-STATCOM without relying on E-caps.

 A fault-tolerant capacitorless D-STATCOM has a 79% longer life than a fault-tolerant VSC-based DSTATCOM.

REFERENCES

[1] H. Anuta, P. Ralon, M. Taylor, and F. L. Camera, Renewable Power Generation Costs in 2019. Abu Dhabi: International Renewable Energy Agency, Jun. 2020.

[2] IEA International Energy Agency, “PVPS 2019: Snapshot of global PV markets,” Accessed: Jun. 2021. [Online]. Available: www.iea-pvps.org

[3] M. Thomson and D. G. Infield, “Impact of widespread photovoltaics generation on distribution systems,” IET Renewable Power Gener., vol. 1, no. 1, pp. 33–40, Mar. 2007.

[4] Y. Ueda, K. Kurokawa, T. Tanabe, K. Kitamura, and H. Sugihara, “Analysis results of output power loss due to the grid voltage rise in grid-connected photovoltaic power generation systems,” IEEE Trans. Ind. Electron., vol. 55, no. 7, pp. 2744–2751, Jun. 2008.

[5] R. Tonkoski, D. Turcotte, and T. H. El-Fouly, “Impact of high PV penetration on voltage profiles in residential neighborhoods,” IEEE Trans. Sustain. Energy, vol. 3, no. 3, pp. 518–527, May 2012.