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

ABSTRACT:

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). 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. 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. 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:

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. 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. 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. 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

 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

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 _xed power load (FPL) under reasonable assumptions such as _xed 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

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

 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.