Combination Analysis and Switching Method of a Cascaded H-Bridge Multilevel Inverter Based on Transformers With the Different Turns Ratio for Increasing the Voltage Level

 ABSTRACT:

This paper analyzes the combination in a cascaded H-bridge multilevel inverter (CHBI) based on transformers with the different turn ratios for increasing the voltage level and proposes the switching method for achieving the output voltage distribution among H-bridge cells (HBCs). The transformers used in this paper are connected to the output of the respective HBCs, and the secondary sides of all the transformers are connected in series for generating the final output voltage. Only one of the transformers, in particular, has a different turn ratio for increasing the output voltage level. In this paper, the possible turn ratio of the special transformer with a different turn ratio is discussed in detail, and a switching method based on the level-shifted switching method for the topology used in this paper is proposed. To verify the effectiveness of the proposed method, a three-phase 21-level CHBI is experimentally tested.

KEYWORDS:

1.      Cascaded H-bridge inverter (CHBI)

2.      Cascaded multilevel

3.      Level-shifted switching method

4.      Multilevel inverter

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Transformer-based CHBI topology used in this paper.

EXPECTED SIMULATION RESULTS

Fig. 2. Simulation results of the proposed switching method with the

balanced voltage distribution at Mi = 1.

Fig. 3. Simulation results of the proposed switching method atMi =1. (a) With and (b) without the balanced voltage and power distributions.

CONCLUSION:

Transformer-based CHBI topology was introduced in this paper. The comparison analysis between topologies was shown in Table XI. The theoretical analysis regarding the selection of the turns ratio of the subtransformer was presented. In addition, a switching method based on the level-shifted switching method with the balanced voltage and power distributions was proposed for the transformer-based CHBI topology. Several requirements related to the decision of switching devices and the design of transformer were suggested.A21-level CHBIwas used to determine the feasibility and effectiveness of the proposed switching method.

When using the proposed switching method, two issues are to be noted: 1) to use the proposed switching method, the configuration of transformer-based CHBI topology should follow that of Table II. It guarantees that the minimum variation (dVx ) of the voltage level is always the same. 2) If the system operates in the wide voltage range (wideMi ), Table VII should be changed as that explained in this paper to guarantee a balanced voltage distribution for Mi range required. Table VI guarantees a balanced voltage distribution for 0.8<Mi < 1. Consequently, this configuration can be applied for the main power supply system generating the ac voltage in grid.

REFERENCES:

[1] J. Rodr´ıguez, S. Bernet, B. Wu, J. O. Pontt, and S. Kouro, “Multilevel voltage-source-converter topologies for industrial medium-voltage drives,” IEEE Trans. Ind. Electron., vol. 54, no. 6, pp. 2930–2945, Dec. 2007.

[2] J. S. Lee and K. B. Lee, “New modulation techniques for a leakage current reduction and a neutral-point voltage balance in transformerless photovoltaic systems using a three-level inverter,” IEEE Trans. Power Electron., vol. 29, no. 4, pp. 1720–1732, Apr. 2014.

[3] C. H. Ng, M. A. Parker, L. Ran, P. J. Tavner, J. R. Bumby, and E. Spooner, “A multilevel modular converter for a large, light weight wind turbine generator,” IEEE Trans. Power Electron., vol. 23, no. 3, pp. 1062–1074, May 2008.

[4] V.Yaramasu and B.Wu, “Predictive control of a three-level boost converter and an NPC inverter for high-power PMSG-based medium voltage wind energy conversion systems,” IEEE Trans. Power Electron., vol. 29, no. 10, pp. 5308–5322, Oct. 2014.

[5] J. Mei, B. Xiao, K. Shen, L. M. Tolbert, and J. Y. Zheng, “Modular multilevel inverter with new modulation method and its application to photovoltaic grid-connected generator,” IEEE Trans. Power Electron., vol. 28, no. 11, pp. 5063–5073, Nov. 2013.

Autonomous Power Management for Interlinked AC-DC Microgrids

ABSTRACT:

The existing power management schemes for interlinked AC-DC microgrids have several operational drawbacks. Some of the existing control schemes are designed with the main objective of sharing power among the interlinked microgrids based on their loading conditions, while other schemes regulate the voltage of the interlinked microgrids without considering the specific loading conditions. However, the existing schemes cannot achieve both objectives efficiently. To address these issues, an autonomous power management scheme is proposed, which explicitly considers the specific loading condition of the DC microgrid before importing power from the interlinked AC microgrid. This strategy enables voltage regulation in the DC microgrid, and also reduces the number of converters in operation. The proposed scheme is fully autonomous while it retains the plug-nplay features for generators and tie-converters. The performance of the proposed control scheme has been validated under different operating scenarios. The results demonstrate the effectiveness of the proposed scheme in managing the power deficit in the DC microgrid efficiently and autonomously while maintaining the better voltage regulation in the DC microgrid.

KEYWORDS:

1.      Autonomous control

2.      Distributed control

3.      Droop control

4.      Hybrid microgrids

5.      Interlinked microgrids

6.      Power management

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Interlinked AC-DC microgrids and their control strategy.

EXPECTED SIMULATION RESULTS

Fig. 2 Scenario 1: Results showing (a) generators and tie-converter power, (b) DC microgrid voltage and (c) tie-converter control signals for four different load operating conditions.

Fig. 3. Scenario 2: Results showing (a) DC microgrid load demand, (b) generators and tie-converter power, (c) DC microgrid voltage and (d) tie-converter control signals at varying solar PV and load operating conditions.

CONCLUSION:

An autonomous power management scheme has been presented for interlinked AC-DC microgrids having different configurations. The proposed scheme manages the power deficit in the DC microgrid efficiently and autonomously. The number of tie-converters in operation has been reduced with the proposed prioritization to avoid unnecessary operational losses. The scheme has demonstrated better voltage regulation in the DC microgrid. The performance and robustness of the proposed scheme have been validated for two different scenarios of the DC microgrid at variable load conditions.

REFERENCES:

[1] J. Rocabert, A. Luna, F. Blaabjerg, and P. Rodr´ıguez, “Control of power converters in AC microgrids,” IEEE Transactions on Power Electronics, vol. 27, no. 11, pp. 4734–4749, Nov. 2012.

[2] M. Liserre, T. Sauter, and J. Y. Hung, “Future energy systems: integrating renewable energy sources into the smart power grid through industrial electronics,” IEEE Industrial Electronics Magazine, vol.4. no. 1, pp. 18–37, Mar. 2010.

[3] M. Tsili and S. Papathanassiou, “A review of grid code technical requirements for wind farms,” IET Renewable Power Generation, vol. 3, no. 3, pp. 308–332, Sep. 2009.

[4] T. Strasser, F. Andr´en, J. Kathan, C. Cecati, C. Buccella, P. Siano, P. Leit˜ao, G. Zhabelova, V. Vyatkin, P. Vrba, and V. Maˇr´ık, “A review of architectures and concepts for intelligence in future electric energy systems,” IEEE Transactions on Industrial Electronics, vol. 62, no. 4,pp. 2424–2438, Apr. 2015.

[5] A. Kwasinski, “Quantitative evaluation of dc microgrids availability: Effects of system architecture and converter topology design choices,” IEEE Transactions on Power Electronics, vol. 26, no. 3, pp. 835–851, Mar. 2011.

Autonomous Power Control and Management Between Standalone DC Microgrids

ABSTRACT:

Renewable integrated DC Microgrids (DCMGs) are gaining popularity by feeding remote locations in qualitative and quantitative manner. Reliability of autonomous DC microgrids (ADCMG) depend on battery capacity and size due to stochastic behavior of renewables. Over charging and discharging scenarios compel the microgrid into insecure zone. Increasing the storage capacity is not an economical solution because of additional maintenance and capital cost. Thus interconnecting neighbor microgrids increases virtual storing and discharging capacity when excess power and deficit scenario arises respectively in any of the DCMG. Control strategy plays vital role in regulating the power within and between microgrids. Power control and management technique is developed based on bus signaling method to govern sources, storages and loads to achieve effective coordination and energy management between microgrids. Proposed scheme is simple and reliable since bus voltages are utilized in shifting the modes without having dedicated communication lines. Proposed scheme is validated through real time simulation of two autonomous DC grids in real time digital simulator (RTDS) and its results are validated by hardware experimentation.

KEYWORDS:

1.      Autonomous DC Microgrid

2.      Bus signaling method

3.      Power control and management scheme

4.      Renewable sources

5.      Real time simulation

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. System architecture for interconnection of two ADCMGs.

EXPECTED SIMULATION RESULTS

Fig. 2. Operating zones of ADCMG1: (a) Bus voltage, (b) Irradiation, (c) PV

output power, (d) Battery terminal voltage, (e) Battery output power, and (f) Load power.

Fig. 3. Operating zones of ADCMG2: (a) Bus voltage, (b) Irradiation, (c) PV

output power, (d) Battery terminal voltage, (e) Battery output power, and (f)

Load power.

Fig. 4. Operation of BDC using PCMS: (a) ADCMG1 voltage, (b) ADCMG2

voltage, (c) Power exported from ADCMG1, (d) Power exported from

ADCMG2, (e) Powers within ADCMG1, and (f) Powers within ADCMG2.

CONCLUSION:

A PCMS is developed based on bus signaling technique for inter DC grid power flow in case of ADCMGs to increase the system reliability and efficient utilization of resources. Two practical DC grid voltages (380V, 48V) are considered for evaluating the performance of developed scheme in simulation. PCMS is explored under normal and extreme scenarios including the over and under loading conditions of ADCMGs, further more with over charging and discharging of battery. It can be observed from above analysis that proposed PCMS is stable, efficient and effective in realizing communication independent control even under dynamic power variations during the power exchange. This statement is also justified with experimental results obtained through prototype model developed in the laboratory with reduced voltage of ADCMG1. Proposed system provides isolation and also enhances system reliability. Application potential of system suits low and medium voltage customers like domestic consumers, data centers, telecommunication systems, etc. in isolated locations where utility connection is not present or feasible.

REFERENCES:

[1] T. Dragicevi, X. Lu, J. C. Vasquez, and J. M.Guerrero, “DC Microgrids – Part II: A Review of Power Architectures, Applications and Standardization Issues,” IEEE Trans. Power Electron., vol. 31, no. 5, pp. 3528–3549, May. 2016.

[2] Q. Yang, L. Jiang, H. Zhao, and H. Zeng, “Autonomous Voltage Regulation and Current Sharing in Islanded Multi-inverter DC Microgrid,” IEEE Trans. Smart Grid, vol. PP, no. 99, pp. 1–1, 2017.

[3] J. Torreglosa, P. Garcia, L. Fernandez, and F. Jurado, “Predictive Control for the Energy Management of a Fuel Cell-Battery-Supercapacitor Tramway,” IEEE Trans. Ind. Informat., vol. 10, no. 1, pp. 276-285, Feb. 2013.

[4] L. Herrera, W. Zhang, and J. Wang, “Stability Analysis and Controller Design of DC Microgrids with Constant Power Loads,” IEEE Trans. Smart Grid, vol. 8, no. 2, pp. 881–888, March. 2017.

[5] D. E. Olivares, A. Mehrizi-sani, A. H. Etemadi, C. A. Cañizares, R. Iravani, M. Kazerani, A. H. Hajimiragha, O. Gomis-bellmunt, M. Saeedifard, R. Palma-behnke, G. A. Jiménez-estévez, and N. D. Hatziargyriou, “Trends in Microgrid Control,” IEEE Trans. Smart Grid, vol. 5, no. 4, pp. 1905–1919, July. 2014.

An Improved DC-Link Voltage Control Strategy for Grid Connected Converters

 ABSTRACT:

This paper presents a robust control strategy to improve dc-link voltage control performances for Grid connected Converters (GcCs). The proposed control strategy is based on an adaptive PI controller and is aimed to ensure fast transient response, low dc-link voltage fluctuations, low grid current THD and good disturbance rejection after sudden changes of the active power drawn by the GcC. The proportional and integral gains of the considered adaptive PI controller are self-tuned so that they are well suited with regard to the operating point of the controlled system and/or its state. Several simulation and experimental results are presented to confirm and validate the effectiveness and feasibility of the proposed dc-link voltage control strategy.

KEYWORDS:

1.      DC-link voltage control

2.      adaptive PI controller

3.      Grid connected Converters

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

 Fig. 1. Commonly used control structure for Grid-connected Converters

 EXPECTED SIMULATION RESULTS

Fig. 2. Simulation results (ξ=0.7, Vdc init=100V, Vdc

*=150, i=0 at t=0s and i=Imax at t=0.5s) (a) Comparison between standard PI control and adaptive PI control  (b) waveform of the selected ωn value for the adaptive PI controller

CONCLUSION:

This paper presented an improved dc-link voltage controller based on an adaptive PI controller with an anti-windup process. The proportional and integral gains of the proposed PI controller are self-tuned so that the following constraints are satisfied: 1) no overshoot after step jumps of the dc-link voltage reference input; 2) fast dynamic response after step jumps of the dc-link voltage reference; 3) fast dynamic response after step jump of the input current i and 4) low grid current THD value during steady state operation. The considered control was experimentally tested on a prototyping platform. The obtained experimental results are quite similar to simulation results and show the effectiveness and reliability of the adopted control strategy.

REFERENCES:

[1] D. Casadei, M. Mengoni, G. Serra, A. Tani, and L. Zarri, “A control scheme with energy saving and dc-link overvoltage rejection for induction motor drives of electric vehicles,” IEEE Trans. Ind. Appl.,vol. 46, no. 4, pp. 1436–1446, Jul./Aug. 2010.

[2] Li, F., Zou, Y.P., Wang, C.Z., Chen, W., Zhang, Y.C., Zhang, J. “Research on AC Electronic Load Based on back to back Single phase PWM Rectifiers,” Applied Power Electronics Conference and Exposition, 2008. APEC 2008. Twenty-Third Annual IEEE. 2008, pp.630-634. 2008.

[3] M. Karimi-Ghartimani, S.A. Khajehoddin, P. Jain, A. Bakhshai, “A systematic approach to dc-bus control design in single phase grid connected renewable converters,” IEEE Trans. Power Electron, vol. 28, no. 7, pp. 3158–3166, July. 2013.

[4] X. Yuan, F. Wang, D. Boroyevich, Y. Li, and R. Burgos, “Dc-link voltage control of a full power converter for wind generator operating in weak-grid systems,” IEEE Trans. Power Electron., vol. 24, no. 9, pp. 2178–2192, Sep. 2009.

[5] C.-S. Lam, W.-H. Choi, M.-C. Wong, and Y.-D. Han, “Adaptive dc link voltage-controlled hybrid active power filters for reactive power compensation,” IEEE Trans. Power Electron., vol. 27, no. 4, pp. 1758– 1772, Apr. 2012.

An f-P/Q Droop Control in Cascaded-Type Microgrid

ABSTRACT:

In cascaded-type microgrid, the synchronization and power balance of distributed generators become two new issues that needs to be addressed urgently. To that end, an f-P/Q droop control is proposed in this letter, and its stability is analyzed as well. This proposed droop control is capable to achieve power balance under both resistive-inductive an resistive-capacitive loads autonomously. Compared with the inverse power factor droop control, an obvious advantage consists in extending the scope of application. Finally, the feasibility of the proposed method is verified by simulation results.

KEYWORDS:

1.      Cascaded-type microgrid

2.      Droop control

3.      Power balance

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Structure of islanded cascaded-type microgrid.

CONTROL  SYSTEM:

Fig. 2. The local control diagram of the i-th DG.

EXPECTED SIMULATION RESULTS

Fig.3. Simulation results of case I. (a) Active power. (b) Reactive power

Fig. 4. Simulation results of case II. (a) Active power. (b) Reactive power.

 CONCLUSION:

A bridge modular switched-capacitor-based multilevel inverter with optimized UFD-SPWM control method is proposed in the paper. The switched-capacitor-based stage can obtain high conversion efficiency and multiple voltage levels. Meanwhile, it functions as an active energy buffer, enhancing the power decoupling ability and conducing to cut the total size of the twice-line energy buffering capacitance. Furthermore, voltage multi-level in DC-link reduces the switching loss of inversion stage because turn-off voltage stress of switches changes with phase of output voltage rather than always suffers from one relatively high DC voltage. Most importantly, the control method of UFD-SPWM, doubling equivalent witching frequency, is employed in the inversion stage for a high quality output waveform with reduced harmonic. In addition, the optimized voltage level phase maximizes the fundamental component in output voltage pulses to reduce harmonic backflow as possible. Hence, the comprehensive system efficiency has been promoted and up to peak value of 97.6%. Finally, two conversion stages are controlled independently for promoting reliability and decreasing complexity. In future work, detailed loss discussion, including theoretic calculation and validation of loss breakdown, will be presented.

REFERENCES:

[1] M. Jun, "A new selective loop bias mapping phase disposition PWM with dynamic voltage balance capability for modular multilevel converter," IEEE Trans. Ind. Electron., vol. 61, no. 2, pp. 798-807, Feb. 2014.

[2] N. Mehdi, and G. Moschopoulos, "A novel single-stage multilevel type full-bridge converter," IEEE Trans. Ind. Electron., vol. 60, no. 1, pp. 31-42, Jan. 2013.

[3] E. Ehsan and N. B. Mariun, "Experimental results of 47-level switchladder multilevel inverter," IEEE Trans. Ind. Electron., vol. 60, no. 11, pp. 4960-4967, Nov. 2013.

[4] J. Lai, “Power conditioning circuit topologies,” IEEE Trans. Ind. Electron., vol. 3, no. 2, pp. 24-34, Jun. 2009.

[5] L. He, C. Cheng, “Flying-Capacitor-Clamped Five-Level Inverter Based on Switched-Capacitor Topology,” IEEE Trans. Ind. Electron., vol. 63, no.12, pp. 7814-7822, Sep. 2016.