Passivity-Based Control Strategy With Improved Robustness for Single-Phase Three-Level T-Type Rectifiers

ABSTRACT:

Three-Level A passivity-based control (PBC) strategy with improved robustness for single-phase three-level rectifiers feeding resistive and constant power loads (CPLs) is proposed. It is shown that the control of the rectifier can be achieved if the damping injection is applied to the grid current only. In this case, the knowledge of load resistance is required in the computation of reference grid current amplitude.

INDUCTANCE

Since the output voltage and load current are dc quantities, the load resistance can b e estimated easily. Then, the amplitude of the reference grid current is calculated from the power balance equation of the rectifier. The transfer function from reference grid current to actual grid current is derived. The derived transfer function is analyzed under variations in the filter inductance.

PBC

The results reveal that the proposed PBC offers strong robustness to variations in the filter inductance when a suitable damping gain is selected. The performances of the proposed PBC strategy under undistorted and distorted grid voltage as well as, variations in inductor are investigated via experimental studies during steady-state and transients caused by the resistive load and CPL changes. In all cases, the output voltage is regulated at the desired value, and grid current tracks its reference.

KEYWORDS:

  1. Passivity-based control
  2. Damping injection
  3. Three-level T-type rectifier
  4. Constant power load

SOFTWARE: MATLAB/SIMULINK

SCHEMATIC DIAGRAM:

Figure 1. Single-Phase Three-Level T-Type Rectifier Feeding Resistive Load And Cpl.

EXPECTED SIMULATION RESULTS:

Figure 2. Waveforms Of Grid-Voltage (Eg), Grid Current (Ig) And Its Reference (I_ G ), Five-Level Voltage (Vxy ), Output Voltage (Vdc ) And Its Reference (V _ Dc ), And Capacitor Voltages (Vc1 And Vc2) Under Undistorted Grid Voltage.

Figure 3. Waveforms Of Grid-Voltage (Eg), Grid Current (Ig) And Its Reference (I_ G ), Output Voltage (Vdc ) And Its Reference (V _ Dc ), And Capacitor Voltages (Vc1 And Vc2) Under Distorted Grid Voltage.

Figure 4. Waveforms Of Grid-Voltage (Eg), Grid Current (Ig) And Its Reference (I_ G ), Output Voltage (Vdc ) And Its Reference (V _ Dc ), And Capacitor Voltages (Vc1 And Vc2) Under Rl D 25: (A) Le < L (Le D 1:6 Mh) And &1 D 1, (B) Le < L (Le D 1:6 Mh) And &1 D 20, (C) Le > L (Le D 2:4 Mh) And &1 D 20.

Figure 5. Waveforms Of Grid-Voltage (Eg), Grid Current (Ig) And Its Reference (I_ G ), Output Voltage (Vdc ) And Its Reference (V _ Dc ), Grid Current Error (X1), Output Voltage Error (X2), And Capacitor Voltages (Vc1 And Vc2) For A Step Change In &1 From 1 To 20 When Le D L.

Figure 6. Waveforms Of Grid-Voltage (Eg), Grid Current (Ig) And Its Reference (I_ G ), Output Voltage (Vdc ) And Its Reference (V _ Dc ), Resistive Load Current (Ir ), And Capacitor Voltages (Vc1 And Vc2) For A Step Change In V _ Dc From 250v To 300v Under Resistive Load R D 25.

Figure 7. Waveforms Of Grid-Voltage (Eg), Grid Current (Ig) And Its Reference (I_ G ), Output Voltage (Vdc ), Resistive Load Current (Ir ), Cpl Current (Icpl), Total Load Current (Il), And Capacitor Voltages (Vc1 And Vc2) For A Step Change In: (A) R From 100 To 50, (B) Cpl From 0.625kw To 1.25kw.

Figure 8. Waveforms Of Grid-Voltage (Eg), Grid Current (Ig) And Its Reference (I_ G ), Output Voltage (Vdc ) And Its Reference (V _ Dc ), Cpl Current (Icpl), And Capacitor Voltages (Vc1 And Vc2) For A Step Change In V _ Dc From 250v To 300v Under Cpl.

CONCLUSION:

This paper presented a robust PBC strategy for single-phase three-level T-type rectifiers feeding resistive and constant power loads. It is pointed out that both dc output voltage and grid current of the rectifier can be controlled if the damping injection is applied to the grid current only. It is shown that the proposed PBC strategy possesses strong robustness to variations in the inductance when the damping gain is selected in accordance with the grid current transfer function magnitude.

DC

The performance of the proposed PBC strategy is investigated by experimental studies during steady-state and transients caused by the load and reference voltage changes under undistorted and distorted grid voltage conditions and variations in inductance. It is shown that the dc output voltage is regulated at its reference value, and grid current tracks its reference in all conditions, particularly under constant power load, which may endanger the stability of the system due to the negative resistance characteristic.

REFERENCES:

[1] M. P. Kazmierkowski, L. G. Franquelo, J. Rodriguez, M. A. Perez, and J. I. Leon, “High-performance motor drives,” IEEE Ind. Electron. Mag., vol. 5, no. 3, pp. 6_26, Sep. 2011.

[2] S. Vazquez, S. M. Lukic, E. Galvan, L. G. Franquelo, and J. M. Carrasco, “Energy storage systems for transport and grid applications,” IEEE Trans. Ind. Electron., vol. 57, no. 12, pp. 3881_3895, Dec. 2010.

[3] F. Blaabjerg, M. Liserre, and K. Ma, “Power electronics converters for wind turbine systems,” IEEE Trans. Ind. Appl., vol. 48, no. 2, pp. 708_719, Mar./Apr. 2012.

[4] X. Liu, P. C. Loh, P. Wang, and F. Blaabjerg, “A direct power conversion topology for grid integration of hybrid AC/DC energy resources,” IEEE Trans. Ind. Electron., vol. 60, no. 12, pp. 5696_5707, Dec. 2013.

[5] G. Wang, G. Konstantinou, C. D. Townsend, J. Pou, S. Vazquez, G. D. Demetriades, and V. G. Agelidis, “A review of power electronics for grid connection of utility-scale battery energy storage systems,” IEEE Trans. Sustain. Energy, vol. 7, no. 4, pp. 1778_1790, Oct. 2016.

Non-Isolated DC-DC Power Converter With High Gain and Inverting Capability Best Electrical Engineering

ABSTRACT:

DC-DC Power As the voltage gain of converter increases with the same ratio, the current gain also increases, this increase in current gains will affect the size of the input and the output capacitor. To reduce the ripple in the input current with simultaneous decreasing the input current ripple, a novel current fed interleaved high gain converter is proposed by utilizing the interleaved front-end structure and Cockcroft Walton (CW)-Voltage Multiplier (VM).

PHOTOVOLTAIC

DC-DC Power The “current fed” term is used because, in proposed circuitry, all the capacitors of CW-VM are energized by a current path via inductors of the interleaved structure. The proposed converter can be applied as an input boost up the stage for low voltage battery energy storage systems, photovoltaic (PV) and fuel cell (FC) based DC-AC applications. The anticipated topology consists of the two low voltage rating switches.

CURRENT

DC-DC Power The main benefits of the anticipated converter configuration are the continuous (ripple free) input current, high voltage gain, reduced switch rating, high reliability, easy control structure and a high percentage of efficiency. The proposed converter’s working principle, mathematical based steady state analysis, and detailed component design are discussed.

CONVERTER

DC-DC Power The parasitic of the components has been considered in the analysis to show the deviation from the ideal cases. A detailed comparison with the other available converters is presented. The experimental results of the 300W prototype are developed to confirm the performance and functionality of the anticipated DC-DC converter.

KEYWORDS:

  1. Non-isolated
  2. Inverting
  3.  Interleaved
  4. High gain
  5. Renewable
  6. Current fed
  7. Voltage multiplier

SOFTWARE: MATLAB/SIMULINK

SCHEMATIC DIAGRAM:

Figure 1. Proposed Inverting High Gain Dc-Dc Converter.

EXPECTED SIMULATION RESULTS:

Figure 2. Input And Output: Voltage And Current Waveforms.

Figure 3. Inductor Voltages And Currents Waveforms.

Figure4. Input And Inductor Current Waveforms.

Figure 5. Switch Voltages And Input Current And Output Voltage Waveforms.

Figure 6. Switch Voltages, Input And Inductor Currents Waveforms.

Figure 7. Diode D1 And D2 Voltages And Inductor Currents Waveforms.

Figure 8. Capacitor Across Capacitor C1 And C2 Waveforms.

Figure 9. Voltage Difference Between Capacitors Waveforms.

CONCLUSION:

DC-DC Power A novel non-isolated current fed interleaved inverting high gain DC-DC power converter is reported for the renewable applications. The reported converter combines the feature of the interleaved fundamental boost converter & diode capacitor stages. The full-wave voltage multiplier arrangement is incorporated to raise the voltage gain by using a very minimal number of devices.

VM

DC-DC Power At the same duty cycle, the proposed converter be able to easily extend to the greater numeral of stages to increase the gain by adding only 1 diode & 1 capacitor for each VM stage increment. The detailed operating modes for CCM & DCM are studied with the help of practical design criterion. The practical and the theoretical voltage gains at the same duty ratios has been validated and they are approximately equal.

DC-DC

DC-DC Power The detailed comparison with the recently proposed other converter has shown that the anticipated converter is further superior over the available converter topologies. The fabricated prototype is tested at 300W and observed conversion is efficiency 93.07% and presented experimental results to confirm the performance and theoretical analysis.

CONTROL

DC-DC Power The closed-loop control, integration with renewable energy systems, soft switching of semiconductors devices and voltage stress minimization of semiconductor devices are the future tasks of the proposed converter.

REFERENCES:

[2] Texas Instruments. TPS63700 Datasheet. (Jun. 2013). [Online]. Available: http://www.ti.com-/lit/ds/symlink/tps-63700.pdf

[3] S.-W. Hong, S.-H. Park, T.-H. Kong, and G.-H. Cho, “Inverting buck-boost DC-DC converter for mobile AMOLED display using real-time self-tuned minimum power-loss tracking (MPLT) scheme with lossless soft-switching for discontinuous conduction mode,” IEEE J. Solid-State Circuits, vol. 50, no. 10, pp. 2380_2393, Oct. 2015.

[4] M. Jabbari, “Resonant inverting-buck converter,” IET Power Electron., vol. 3, no. 4, pp. 571_577, Jul. 2010.

[5] Y. P. Siwakoti, F. Z. Peng, F. Blaabjerg, P. C. Loh, and G. E. Town, “Impedance-source networks for electric power conversion Part I: A topological review,” IEEE Trans. Power Electron., vol. 30, no. 2, pp. 699_716, Feb. 2015.

[6] T.-J. Liang, J.-H. Lee, S.-M. Chen, J.-F. Chen, and L.-S. Yang, “Novel isolated high-step-up DC_DC converter with voltage lift,” IEEE Trans. Ind. Electron., vol. 60, no. 4, pp. 1483_1491, Apr. 2013.

Multi-Mode Operation and Control of a Z-Source Virtual Synchronous Generator in PV Systems Best Electrical Engineering Projects

ABSTRACT:

The increasing penetration of power electronics-based distributed energy resources (DERs) displacing conventional synchronous generators is rapidly changing the dynamics of large-scale power systems. As the result, the electric grid loses inertia, voltage support, and oscillation damping needed to provide ancillary services such as frequency and voltage regulation. This paper presents the multi-mode operation of a Z-source virtual synchronous generator (ZVSG). The converter is a Z-source inverter capable of emulating the virtual inertia to increase its stability margin and track its frequency. The added inertia will protect the system by improving the rate of change of frequency. This converter is also capable of operating under normal and grid fault conditions while providing needed grid ancillary services. In normal operation mode, the ZVSG is working in MPPT mode where the maximum power generated from the PV panels is fed into the grid. During grid faults, a low voltage ride through control method is implemented where the system provides reactive power to reestablish the grid voltage based on the grid codes and requirements. The proposed system operation is successfully validated experimentally in the OPAL-RT real-time simulator.

KEYWORDS:

  1. Impedance-source inverter
  2. Virtual synchronous generator
  3. Photovoltaic (PV) systems
  4. Low voltage ride through

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Figure 1. Proposed ZVSG Converter Equipped With VSG And LVRT Control Algorithms.

EXPECTED SIMULATION RESULTS:

Figure 2. Rocof Curves With Different Amounts Of (A) Inertia (H) And (B) Damping Constant (Dp ).

Figure 3. Comparison In Zvsg Current Increase While (A) The Converter Is Directly Connecte (100(Ma)_3:2_10000 D 3200a) And (B) A Pre-Synchronizing Control Method Is Hired To Decrease The Current Increment (200(Ma)_1_5000 D 1000a).

Figure 4. Multi-Mode Operation Of The Zvsg During (A) Normal Operation (C) Voltage Sage Occurrence At T1 And Switching To Lvrt Mode And (D) Returning To Normal Mode At T2.

CONCLUSION:

This paper studied the multi-mode operation of an impedance-source virtual synchronous generator which is comprised of a single-stage ZSI, equipped with VSG control algorithm and is capable of providing grid ancillary services. Since the PLL may fail to detect the correct angle in case of harmonic distorted voltage, a virtual flux orientation control method is hired which can select the correct angle to be fed to Park transformation. The operation of the system has been tested while transitioning from islanded to grid-connected mode where, to protect the system against inrush current while connecting to the grid, a pre-synchronizing control method is used to minimize the phase difference between grid and converter. In addition, a solution to survive the system against voltage faults is embedded in the system which can regulate the reactive power based on the grid codes. Hence, the control paradigm will switch from MPP generation to LVRT mode after detecting voltage sag in the system. In this method, the peak of the grid current is kept constant during LVRT operation mode and ensures over current protection limit is not violated then. The ZVSG has been implemented in the OPAL-RT real-time digital simulator and its validity have been verified by conducting several case studies. The proposed seamless control frame-work helps to smoothly switch between normal and faulty conditions.

REFERENCES:

[1] K. Jiang, H. Su, H. Lin, K. He, H. Zeng, and Y. Che, “A practical secondary frequency control strategy for virtual synchronous generator,” IEEE Trans. Smart Grid, vol. 11, no. 3, pp. 2734_2736, May 2020.

[2] K. Shi, W. Song, H. Ge, P. Xu, Y. Yang, and F. Blaabjerg, “Transient analysis of microgrids with parallel synchronous generators and virtual synchronous generators,” IEEE Trans. Energy Convers., vol. 35, no. 1, pp. 95_105, Mar. 2020.

[3] J. Chen and T. O’Donnell, “Parameter constraints for virtual synchronous generator considering stability,” IEEE Trans. Power Syst., vol. 34, no. 3, pp. 2479_2481, May 2019.

[4] H. Cheng, Z. Shuai, C. Shen, X. Liu, Z. Li, and Z. J. Shen, “Transient angle stability of paralleled synchronous and virtual synchronous generators in islanded microgrids,” IEEE Trans. Power Electron., vol. 35, no. 8, pp. 8751_8765, Aug. 2020.

[5] H. Nian and Y. Jiao, “Improved virtual synchronous generator control of DFIG to ride-through symmetrical voltage fault,” IEEE Trans. Energy Convers., vol. 35, no. 2, pp. 672_683, Jun. 2020.

Mitigation of Complex Non-Linear Dynamic Effects in Multiple Output Cascaded DC-DC Converters Major Electrical Projects

ABSTRACT:

In the modern world of technology, the cascaded DC-DC converters with multiple output configurations are contributing a dominant part in the DC distribution systems and DC micro-grids. An individual DC-DC converter of any configuration exhibits complex non-linear dynamic behavior resulting in instability. This paper presents a cascaded system with one source boost converter and three load converters including buck, Cuk, and Single-Ended Primary Inductance Converter (SEPIC) that are analyzed for the complex non-linear bifurcation phenomena. An outer voltage feedback loop along with an inner current feedback loop control strategy is used for all the sub-converters in the cascaded system. To explain the complex non-linear dynamic behavior, a discrete mapping model is developed for the proposed cascaded system and the Jacobian matrix’s eigenvalues are evaluated. For the simplification of the analysis, every load converter is regarded as a fixed power load (FPL) under reasonable assumptions such as fixed frequency and input voltage. The eigenvalues of period-1 and period-2 reveal that the source boost converter undergoes period-2 orbit and chaos whereas all the load converters operate in a stable period-1 orbit. The proposed configuration eliminates the period-2 and chaotic behavior from all the load converters and is also validated using simulation in MATLAB/Simulink and experimental results.

KEYWORDS:

  1. Bifurcation
  2.  Chaos
  3. DC-DC power converters
  4. Non-linear dynamical systems

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Figure 1. Block Diagram Of The Proposed Cascaded System.

EXPECTED SIMULATION RESULTS:

Figure 2. Inductor Current Ripple And Output Voltage Ripple Waveforms Of Stable Period-1 Operation For A) Boost Converter At Vs D 35 V B) Buck Converter At Vs D 50 V C) Cuk Converter At Vs D 50 V D)Sepic Converter At Vs D 50 V

Figure 3. Inductor Current Ripple And Output Voltage Ripple Waveforms Of Period-2 Operation For A) Boost Converter At Vs D 25 V B) Buck Converter At Vs D 36 V C) Cuk Converter At Vs D 24 V D) Sepic Converter At Vs D 40 V.

Figure 4. Inductor Current Waveforms Of All The Converters Of The Cascaded System At Vs D 35 V.

Figure 5. Inductor Current Waveforms Of All The Converters Of The Cascaded System At Vs D 25 V.

Figure 6. Inductor Current Waveform Of Source Boost Converter For Step Change In The Input Voltage Verifying Non-Linear Incident Effects.

CONCLUSION:

This paper presents a configuration of the cascaded multiple output DC-DC converters to eliminate complex non-linear dynamic behavior and improve the stability when subjected to varying source voltage. The proposed cascaded DC-DC converter system consists of one source boost converter, one load Buck converter, one load Cuk converter, and a SEPIC converter. All the converters in the proposed system are engaged with a current-mode controller with a compensation network technique in which an outer voltage feedback loop and an inner inductor current feedback loop are used along with an offset divided voltage protection circuit and an RS-latch. The simulation and experimental results reveal that the source boost converter undergoes period-2 orbit and ultimately chaos when the input voltage of the source boost converter is decreased. However, it is verified that all the converters that are acting as a load in the proposed system continue to operate in the stable period-1 orbit and the input voltage of the source boost converter does not affect their stability. The discrete mapping model is developed by considering all the load converters as FPLs because of their stable behavior which also generalizes it for other types of converters. The Jacobian matrix is developed using the data of the discrete mapping model and the eigenvalues are obtained which are close to 1. So, by decreasing the input source voltage, the eigenvalues move out of the unit circle which results in period-2 behavior of the system that severely affects the stability of the whole cascaded converter system. The proposed structure makes load converters in the system insensitive towards input voltage variation which has been demonstrated analytically and using experimental results.

REFERENCES:

[1] C. M. F. S. Reza and D. D.-C. Lu, “Recent progress and future research direction of nonlinear dynamics and bifurcation analysis of grid-connected power converter circuits and systems,” IEEE J. Emerg. Sel. Topics Power Electron., vol. 8, no. 4, pp. 3193_3203, Dec. 2020.

[2] A. Kargarian, J. Mohammadi, J. Guo, S. Chakrabarti, M. Barati, G. Hug, S. Kar, and R. Baldick, “Toward distributed/decentralized DC optimal power _ow implementation in future electric power systems,” IEEE Trans. Smart Grid, vol. 9, no. 4, pp. 2574_2594, Jul. 2018.

[3] J. W.-T. Fan and H. S.-H. Chung, “Bifurcation phenomena and stabilization with compensation ramp in converter with power semiconductor filter,” IEEE Trans. Power Electron., vol. 32, no. 12, pp. 9424_9434, Dec. 2017.

[4] M. Schuck and R. C. N. Pilawa-Podgurski, “Ripple minimization through harmonic elimination in asymmetric interleaved multiphase DC_DC converters,” IEEE Trans. Power Electron., vol. 30, no. 12, pp. 7202_7214, Dec. 2015.

[5] A. Braitor, G. C. Konstantopoulos, and V. Kadirkamanathan, “Stability analysis and nonlinear current-limiting control design for DC micro-grids with CPLs,” IET Smart Grid, vol. 3, no. 3, pp. 355_366, Jun. 2020.

Multifunctional Cascade Control of Voltage-Source Converters Equipped With an LC Filter Major Electrical Projects

ABSTRACT:

This paper proposes a multifunctional cascade controller structure for voltage-source converters. The proposed structure contains a decoupling loop between the outer voltage control loop and the inner current control loop, and operation in either voltage or current control mode is possible. In voltage control mode, the current controller can be made completely transparent. In the case of faults, the proposed structure enables inherent overcurrent protection by a seamless transition from voltage to current control mode, wherein the current controller is fully operational. Seamless transitions between the control modes can also be triggered with an external signal to adapt the converter to different operating conditions. The proposed structure allows for integration of simple, accurate, and flexible overcurrent protection to state-of-the-art single loop voltage controllers without affecting voltage control properties under normal operation. The properties of the proposed controller structure are validated experimentally on a 10-kVA converter system.

KEYWORDS:

  1. Ac-voltage control
  2. Cascade control
  3. Current control
  4. Overcurrent protection
  5. Voltage-source converters

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Block diagram of the experimental setup. CB stands for circuit breaker.

EXPECTED SIMULATION RESULTS:

Fig. 2. Experimental validation of the transparency of the current controller in the proposed cascade controller  structure. The application example controller presented in Section IV is compared with its single-loop counterpart based on the controller proposed in [14]: (left) reference tracking under no load (middle) reference tracking under 1 p.u. resistive and 0.45 p.u. inductive load and (right) disturbance rejection in the form of load change from no load to 1 p.u. resistive and 0.45 p.u. inductive load.

Fig. 3. Experimental transition between control modes with (a) 1 p.u. resistive and 0.45 p.u. inductive load (b) 0.08 p.u. resistive and 0.45 p.u. inductive load. Additionally, reference steps in both control modes are presented. VCM and CCM stand for voltage and current control mode, respectively.

Fig. 4. Experimental emulation of a load fault by connecting a low-resistance load in parallel with the steady-state load. Recovery from the fault, which is triggered by a circuit breaker, is also shown. The fault emulation is shown for the case where the converter is designed to trip in the event of overcurrent (left), for the reference current limitation method proposed in [24] (middle), and for the proposed structure (right).

CONCLUSION:

 This paper presented a multifunctional cascade controller  structure for VSCs. The proposed controller structure allows for operation in either voltage or current control mode. In voltage control mode and under linear operation, the current controller can be made completely transparent. Consequently, the properties of both control modes are purely determined by their corresponding control loops, which can be designed independently of each other. The transitions between control modes are seamless and occur either due to converter overloading, i.e., the controller inherently includes overcurrent protection, or by manually activating the current control mode of the controller. The properties of the proposed cascade controller structure are validated by means of experiments.

REFERENCES:

[1] R. Rosso, X. Wang, M. Liserre, X. Lu, and S. Engelken, “Grid-forming converters: an overview of control approaches and future trends,” in Proc. IEEE ECCE, Detroit, MI, USA, Oct. 2020, pp. 4292–4299.

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

[3] Q. Lei, F. Z. Peng, and S. Yang, “Multiloop control method for high-performance microgrid inverter through load voltage and current decoupling with only output voltage feedback,” IEEE Trans. Power Electron., vol. 26, no. 3, pp. 953–960, Mar. 2011.

[4] F. de Bosio, L. A. de Souza Ribeiro, F. D. Freijedo, M. Pastorelli, and J. M. Guerrero, “Effect of state feedback coupling and system delays on the transient performance of stand-alone VSI with LC output filter,” IEEE Trans. Ind. Electron., vol. 63, no. 8, pp. 4909–4918, Aug. 2016.

[5] P. C. Loh, M. Newman, D. Zmood, and D. Holmes, “A comparative analysis of multiloop voltage regulation strategies for single and threephase UPS systems,” IEEE Trans. Power Electron., vol. 18, no. 5, pp. 1176–1185, Sep. 2003.

Low-Voltage Ride Through Strategy for MMC With Y0/Y0 Arrangement Transformer Under Single-Line-to-Ground Fault Latest 2021 IEEE Power Electronics and Drives Projects, Academic electrical projects

ABSTRACT:

In the offshore wind farm high-voltage direct-current (HVDC) system, the power delivery capability of the onshore modular multilevel converter (MMC) decreases severely under grid fault, which makes the DC-bus voltage increase rapidly and threatens the safe operation of the system. This paper proposes a low-voltage ride through (LVRT) strategy for MMC with Y0/Y0 arrangement transformer under single-line-to-ground (SLG) fault. The influence of different transformer arrangements to the MMC under SLG fault is analyzed. On this basis, a power delivery capability enhanced method is proposed for MMC with Y0/Y0 arrangement transformer to take advantage of its control ability on zero sequence current. In addition, an optimized LVRT strategy based on resonant controller is proposed, which has simple control structure and can ride through the SLG fault without DC chopper. The offshore wind farm MMC-HVDC simulation system is established in PSCAD/EMTDC and simulation studies are conducted to validate the effectiveness of the proposed LVRT strategy.

KEYWORDS:

  1. Modular multilevel converter (MMC)
  2. Grid fault
  3. High-voltage direct-current (HVDC)
  4. Low-voltage ride through (LVRT)

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Figure 1. Block Diagram Of The Conventional Control Strategy Of Mmc Under Slg Fault.

EXPECTED SIMULATION RESULTS:

Figure 2. Simulation Results Of Mmc With Y0/1 Arrangement Transformer Using The Conventional Strategy (P D 935mw).

Figure 3. Simulation Results Of Mmc With Y0/Y0 Arrangement Transformer Using The Conventional Strategy (P D 935mw).

Figure 4. Simulation Results Of Mmc With Y0/Y0 Arrangement Transformer Using The Proposed Strategy (P D 935mw).

Figure 5. Simulation Results Of Mmc With Y0/1 Arrangement Transformer Using The Conventional Strategy (P D

750mw).

Figure 6. Simulation Results Of Mmc With Y0/Y0 Arrangement Transformer Using The Conventional Strategy (P D 750mw).

Figure 7. Simulation Results Of Mmc With Y0/Y0 Arrangement Transformer Using The Proposed Strategy (P D 750mw).

CONCLUSION:

In this paper, the influence of different transformer arrangements to MMC under SLG fault has been analyzed, and an LVRT strategy for MMC with Y0/Y0 arrangement transformer has been proposed. Comparative simulation studies have been conducted under SLG fault. The conclusions can be summarized as follow. (1) Compared with the Y0/1 arrangement transformer, the grid-side zero sequence current can be restrained by using Y0/Y0 arrangement transformer, and the power delivery capability can be enhanced. However, the zero sequence current is transferred to the MMC side. (2) The proposed LVRT strategy can restrain the zero sequence current and enhance the power delivery capability for MMC with Y0/Y0 arrangement transformer effectively. The MMC can ride through SLG fault without DC chopper by using the proposed LVRT strategy when the wind farm works in the full-power mode. (3) The proposed LVRT strategy can work well under different power factors, which means the MMC using the proposed strategy can not only ride through the grid fault,but also provide reactive power support to the grid within its capability when the wind farm doesn’t work in the full-power mode.

REFERENCES:

[1] S. M. Muyeen, R. Takahashi, and J. Tamura, “Operation and control of HVDC-connected offshore wind farm,” IEEE Trans. Sustain. Energy, vol. 1, no. 1, pp. 30_37, Apr. 2010.

[2] R. Shah, J. C. Sánchez, R. Preece, and M. Barnes, “Stability and control of mixed AC-DC systems with VSC-HVDC: A review,” IET Gener. Transm. Distrib., vol. 12, no. 10, pp. 2207_2219, 2018.

[3] X. Zeng, T. Liu, S. Wang, Y. Dong, B. Li, and Z. Chen, “Coordinated control of MMC-HVDC system with offshore wind farm for providing emulated inertia support,” IET Renew. Power Gener., vol. 14, no. 5, pp. 673_683, Apr. 2020.

[4] J. Lyu, X. Cai, M. Amin, and M. Molinas, “Sub-synchronous oscillation mechanism and its suppression in MMC-based HVDC connected wind farms,” IET Gener. Transmiss. Distrib., vol. 12, no. 4, pp. 1021_1029, Feb. 2018.

[5] S. Xue, C. Gu, B. Liu, and B. Fan, “Analysis and protection scheme of station internal AC grounding faults in a bipolar MMC-HVDC system,” IEEE Access, vol. 8, pp. 26536_26548, 2020.

Improved DC-Link Voltage Regulation Strategy for Grid-Connected Converters Academic Projects in Electrical

ABSTRACT:

In this paper, an improved dc-link voltage regulation strategy is proposed for grid-connected converters applied in dc microgrids. For the inner loop of the grid connected converter, a voltage modulated direct power control is employed to obtain two second-order linear time invariant systems, which guarantees that the closed-loop system is globally exponentially stable. For the outer loop, a sliding mode control strategy with a load current sensor is employed to maintain a constant dc-link voltage even in the presence of constant power loads at the dc-side, which adversely affect the system stability. Furthermore, an observer for the dc-link current is designed to remove the dc current sensor at the same time improving the reliability and decreasing the cost. From both simulation and experimental results obtained from a 15-kVA prototype setup, the proposed method is demonstrated to improve the transient performance of the system and has robustness properties to handle parameter mismatches compared with the inputoutput linearization method.

KEYWORDS:

  1. Dc microgrid
  2. Direct power control
  3. Grid connected converter
  4. Observer
  5. Sliding mode control

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Block diagram of the proposed control method (SMC with observer) for a rectifier system in the dc microgrid.

EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results when the dc load is changed from 460 W to 153 W. at 0.05 s and the reactive power is changed from 0 Var to 1 kVar at 0.75 s. (a) Real power; (b) reactive power; (c) is;c line current; (d) dc-link voltage.

Fig. 3. Simulation results when the dc load is changed from 460 W to 153 W at 0.05 s and vs;a has 10% sag. (a) Grid voltage; (b) is;c current; (c) dc-link voltage; (b) real and reactive power.

Fig. 4. Simulation results when the dc load is changed from 460 W to 153 W at 0.05 s and the THD of the grid voltage is 2.2%. (a) Grid voltage; (b) is;c current; (c) dc-link voltage; (b) real and reactive power.

CONCLUSION:

A three-phase PWM rectifier was controlled by the proposed control strategy, which has a dc-link current observer based SMC in the outer loop and a voltage modulated-DPC in the inner loop. The SMC was applied to generate the real power reference in the inner loop in order to make sure the dc link voltage to be within a certain level in the dc microgrids even there exist CPLs. Furthermore, an observer for the dc link current was designed in order to remove the need for a current sensor. Both simulation and experimental results show that the proposed method effectively reduces the overshoot of the dc-link voltage and is robust to parameter mismatch of the capacitance value in the dc-link.

REFERENCES:

[1] J. Liu, X. Lu, and J. Wang, “Resilience analysis of DC microgrids under denial of service threats,” IEEE Trans. Power Syst., vol. 34, no. 4, pp. 3199–3208, July 2019.

[2] F. Blaabjerg, M. Liserre, and K. Ma, “Power electronics converters for wind turbine systems,” IEEE Trans. Ind. Appl., vol. 48, no. 2, pp. 708– 719, 2012.

[3] B. Wei, Y. Gui, A. Marzabal, Trujillo, J. M. Guerrero, and J. C. Vasquez, “Distributed average secondary control for modular UPS systems based microgrids,” IEEE Trans. Power Electron., vol. 34, no. 7, pp. 6922–6936, July 2019.

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

[5] M. Kazmierkowski and L. Malesani, “Current control techniques for three-phase voltage-source PWM converters: a survey,” IEEE Trans. Ind. Electron., vol. 45, no. 5, pp. 691–703, Oct 1998.

Improved Controller and Design Method for Grid -Connected Three -Phase Differential SEPIC Inverter Academic Projects in Electrical

ABSTRACT:

Single-ended primary-inductor converter (SEPIC) based differential inverters (SEPIC-BDI) have received wide concerns in renewable energy applications due to their modularity, galvanic isolation, decreased power stages, continuous input current, and step up/down capability. However, its design still has several challenges related to component design, the existence of complex right half plane (RHP) zeros, and increased sensitivity to component mismatches. In this context, this paper presents an improved control and enhanced design method for the three-phase SEPIC-BDI for grid-tied applications. A generalized static linearization approach (SLA) is proposed to mitigate the low-order harmonics. It practically simplifies the control complexity and decreases the required control loops and sensor circuits. The mismatch between the SEPIC converters in each phase is highly mitigated due to the independent operation of the SLA in each phase and the output dc offset currents are reduced. The proposed enhanced design methodology modifies the SEPIC open-loop transfer function by moving the complex RHP zeros to the left half-plane (LHP). Therefore, a simple proportional-integral (PI) controller effectively maintains converter stability without adding higher-order compensators in the literature. Moreover, a straightforward integrator in the control loop eliminates the negative sequence harmonic component (NSHC) and provides a low computational burden. Simulations and experimental results based on 200V, 1.6 kW, 50 kHz prototype with silicon carbide (SiC) devices are provided to validate the effectiveness of the proposed work. The results show that the proposed controller and design method achieve pure output current waveforms at various operating points of the inverter and dc voltage variations.

KEYWORDS:

  1. Differential inverter
  2. Renewable energy applications
  3. Negative sequence harmonic component
  4. Power converters
  5. Power losses
  6. Single-ended primary-inductor converter (SEPIC)

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Figure 1. Circuit Schematic Of The Isolated Sepic-Bdi.

EXPECTED SIMULATION RESULTS:

Figure 2. Simulation Results Of The Output Voltage And Grid Voltage Of One Sepic At Sepic-Bdi Using Cms.

Figure 3. Simulation Results Of The Output Voltage And Grid Voltage Of One Phase Leg Of Sepic-Bdi Using Proposed Mcms.

CONCLUSION:

An enhanced design methodology and improved controller for three-phase SEPIC-BDI inverter have been proposed for grid-connected renewable energy applications. Additionally, this paper presented a generalized method based on the static linearization approach (SLA) for mitigating the low-order harmonic components, which are usually inherent by differential inverters. The superiority and effectiveness of the proposed controller and SEPIC-BDI inverter system are validated using simulation and experimental results at voltage range (100-120 V) and power range (0.2-1.6 kW). By using the proposed SLA method with the SEPIC-BDI system, the mismatch effects between the different SEPIC converters are alleviated and the DC offset components in the output currents are eliminated. Moreover, by selecting the converter parameters based on the proposed enhanced design methodology, more stable operation can be obtained by moving the complex RHP zeros to the LHP. Therefore, a simple PI controller is needed to maintain converter stability compared to the required nonlinear controllers and high order compensator types in the existing methods in the literature.

REFERENCES:

[1] S. Kouro, J. I. Leon, D. Vinnikov, and L. G. Franquelo, “Grid-connected photovoltaic systems: An overview of recent research and emerging PV converter technology,” IEEE Ind. Electron. Mag., vol. 9, no. 1, pp. 47_61, Mar. 2015.

[2] E. M. Ahmed, E. A. Mohamed, A. Elmelegi, M. Aly, and O. Elbaksawi, “Optimum modiFIed fractional order controller for future electric vehicles and renewable energy-based interconnected power systems,” IEEE Access, vol. 9, pp. 29993_30010, 2021.

[3] M. M. Alhaider, E. M. Ahmed, M. Aly, H. A. Serhan, E. A. Mohamed, and Z. M. Ali, “New temperature-compensated multi-step constant-current charging method for reliable operation of battery energy storage systems,” IEEE Access, vol. 8, pp. 27961_27972, 2020.

[4] M. Aly and H. Rezk, “A differential evolution-based optimized fuzzy logic MPPT method for enhancing the maximum power extraction of proton exchange membrane fuel cells,” IEEE Access, vol. 8, pp. 172219_172232, 2020.

[5] H. D. Paulino, P. J. M. Menegaz, and D. S. L. Simonetti, “A review of the main inverter topologies applied on the integration of renewable energy resources to the grid,” in Proc. XI Brazilian Power Electron. Conf.,Sep. 2011, pp. 963_969.

Four-Level Three-Phase Inverter With Reduced Component Count for Low and Medium Voltage Applications Readymade Electrical Projects

ABSTRACT:

This paper proposes a novel three-phase topology with a reduced component count for low- and medium-voltage systems. It requires three bidirectional switches and twelve unidirectional switches for producing four-level voltages without using flying capacitors or clamping diodes, reducing the size, cost, and losses. Removing flying capacitors and clamping diodes allows it to simplify control algorithms and increase the reliability, efficiency, and lifetime. A modified low-frequency modulation (LFM) scheme is developed and implemented on the proposed topology to produce a staircase voltage with four steps. Further, a level-shifted pulse width modulation (LSPWM) is used to reduce the filter size and increase the output voltage controllability. In this study, a voltage balancing control algorithm is executed to balance the DC-link capacitor voltages. The performance of the proposed topology is numerically demonstrated and experimentally validated on an in-house test setup. Within the framework, the power loss distribution in switches and conversion efficiency of the proposed circuit are studied, and its main features are highlighted through a comparative study.

KEYWORDS:

  1. DC-AC converters
  2. Four-level inverters
  3. Low and medium voltage applications
  4. Multilevel inverters
  5. Three-phase inverters

SOFTWARE: MATLAB/SIMULINK

SCHEMATIC DIAGRAM:

Figure 1. The Proposed Four-Level Topology. (A) Multiple Sources Configuration (Msc), Recommended For Energy Systems, (B) Single Source Configuration (Ssc), Recommended For Industrial Applications.

EXPECTED SIMULATION RESULTS:

Figure 2. Pole Voltages Va0, Vb0, And Vc0 Using Lfm (A) Simulation,

Figure 3. Pole Voltages Va0, Vb0, And Vc0 Using Lspwm (A) Simulation,

Figure 4. Line Voltages Vab, Vbc, And Vca Using Lfm (A) Simulation,

Figure 5. Line Voltages Vab, Vbc, And Vca Using Lspwm (A) Simulation,

Figure 6. Obtained Vab, Van, And Ian When Feeding R-Load (A) Simulation(C) Simulation (Lspwm),

Figure 7. Obtained Vab, Van, And Ian For R-L Load Using Lfm (A) Simulation,

Figure 8. Obtained Vab, Van, And Ian For R-L Load Using Lspwm (A) Simulation,

CONCLUSION:

This paper proposes a novel inverter topology with a reduced component count, being attractive in low- and medium-voltage applications. The proposed circuit generates four voltage levels without requiring flying capacitors or clamping diodes, reducing the size, cost, control complexity of the inverter and enhancing its reliability and lifetime. Several simulation and experimental tests were presented to validate the proposed topology performance at resistive and inductive loads. The proposed inverter was compared with the recently developed four-level topologies to highlight its merits. Moreover, its conversion efficiency was analysed when varying the switching frequency, modulation schemes, and loads.

REFERENCES:

[1] P. Omer, J. Kumar, and B. S. Surjan, “A review on reduced switch count multilevel inverter topologies,” IEEE Access, vol. 8, pp. 22281_22302, 2020.

[2] 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.

[3] 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.

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

[5] 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.

DC-link Voltage Ripple Control of Regenerative CHB Drives for Capacitance Reduction Readymade Electrical Projects

ABSTRACT:

The diode-front-end (DFE) CHB inverters have prevailed in the non-regenerative industry drive domain for high-power medium-voltage applications. The regenerative version of the CHB drives is made possible by adding the extra active-front-end (AFE) rectifier in each power cell, such as a three-phase PWM rectifier. However, due to the instantaneous power unbalance, the dc-link capacitors of the regenerative power cell need to be overdesigned to maintain a stable low ripple dc-link voltage. To reduce the dc-link capacitance, this paper proposes a novel closed-loop voltage ripple controller for the regenerative CHB drive without adding extra sensors. In the proposed method, dc-link voltage ripple amplitude and phase angle are accurately detected with a high-performance adaptive filter. Moreover, a latent instability issue is discussed and is avoided in the proposed controller. The performance of the proposed control strategy is validated experimentally on a seven-level regenerative CHB drive.

KEYWORDS:

  1. Multilevel Drives
  2. DC-Link Capacitor Reduction
  3. Regenerative
  4. Adaptive filtering
  5. Stability

SOFTWARE: MATLAB/SIMULINK

SCHEMATIC DIAGRAM:

Fig. 1 Proposed Capacitor Reduction Control Scheme based on Adaptive Filter

EXPECTED SIMULATION RESULTS:

Fig. 2 Simulation Result with Frequency Varitaion

CONCLUSION:

Due to the unbalanced instantaneous power flow, an oversized dc-link capacitor is required to be designed in each power cell to achieve a low voltage ripple dc-bus in regenerative CHB drives. To reduce the dc-link capacitance while maintaining a low dc-link voltage ripple, this paper proposes a novel closed-loop voltage ripple controller for the regenerative CHB drive without extra sensors. The dc-link voltage ripple amplitude and phase angle are accurately detected with a high-performance adaptive filter under the output frequency variation. Moreover, a latent instability issue is discussed in detail. This issue is then avoided in the proposed voltage ripple controller by setting a suboptimal operation point and a mechanism to retract away from the unstable region. The proposed capacitance reduction strategy is validated on a seven-level regenerative CHB drive showing good stability and performance. It was verified that the dc capacitance can be reduced to 25% of its original design while a 5% dc voltage ripple is allowed. Therefore, the size and cost of the regenerative CHB system can be greatly reduced, while the lifetime and reliability of the motor drive are improved.

REFERENCES:

[1] B. Wu and M. Narimani, High-power converters and AC drives. IEEE-Wiley Press, 2017.

[2] J. Rodriguez, P. W. Hammond, J. Pontt, R. Musalem, P. Lezana and M. J. Escobar, “Operation of a medium-voltage drive under faulty conditions,” in IEEE Transactions on Industrial Electronics, vol. 52, no. 4, pp. 1080-1085, Aug. 2005.

[3] P. W. Hammond, “A new approach to enhance power quality for medium voltage drives,” in IEEE Transaction on Industry Applications, vol. 33, no. 1, pp. 202–208, Feb. 1997.

[4] J. Rodriguez, J. Pontt, N. Becker, and A. Weinstein, “Regenerative drives in the megawatt range for high-performance downhill belt conveyors,” IEEE Transactions on Industry Applications, vol. 38, no. 1, pp. 203–210, 2002.

[5] J. Rodriguez, L. Moran, J. Pontt, J. Espinoza, R. Diaz, and E. Silva, “Operating Experience of Shovel Drives for Mining Applications,” IEEE Transactions on Industry Applications, vol. 40, no. 2, pp. 664–671, 2004.