Improved DC-Link Voltage Regulation Strategy for Grid-Connected Converters

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

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

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

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.

 

An Improved Bipolar Voltage Boost AC Voltage Controller With Reduced Switching Transistors

ABSTRACT:

Single-stage power conversion with simple circuit arrangement is one of the attractive features of direct bipolar voltage ac-ac converters. This increases their potency in various applications that require voltage and frequency regulation. The grid voltage compensators, direct variable speed ac-ac drives, and induction heating systems require inverting and non-inverting operation of the input voltage. Their size, cost, and circuit complexity directly depend on the number of switching transistors, as the operation of each transistor requires the use of one gate drive circuit (GDC) and one isolated dc power supply (IDCPS). The size and cost of GDC and IDCPS are much larger than that of switching transistors. The use of fewer switching transistors also ensures low conversion losses and simplifies the switching schemes. Therefore, this research proposes a new ac-ac converter that is realized as a bipolar boost ac voltage controller having a low count of switching transistors. The suggested topology also eliminates the shoot-through of the input source or output filtering capacitor. The characteristics of the proposed circuit are explored through simulation results obtained through the Simulink platform. The confirmation of the simulation results is validated through the laboratory prototype.

KEYWORDS:

1.      AC converter

2.      Bipolar voltage

3.      Grid voltage compensator

4.      Induction heating system

5.      Shoot through

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

 

Figure 1. Existing Power Converting Topologies Reported In (A) [13] And (B) [20].

EXPECTED SIMULATION RESULTS:

 

 

Figure 2. Instantaneous Power Losses Of Low-Frequency (A) Diodes And (B) Diode-Mosfet Pairs.

 

Figure 3. Simulated Waveforms: (A) & (B) Input-Output Voltage; (C) & (D) High-Frequency Switching Voltage; (E) To (J) Low-Frequency Switching Voltage.

Figure 4. Simulated Waveforms: (A) & (C) Output And Input Currents With A Resistive Load; (B) & (D) Output And Input Currents With An Inductive Load.

 

 

Figure 5. Practically Recorded Waveforms: (A) & (B) Input-Output Voltage; (C) & (D) High-Frequency Switching Voltage; (E) To (J) Low-Frequency Switching Voltage.

CONCLUSION:

This research is focused on the analysis and development of a new direct ac-ac power converting topology that may be applied in applications having variable bipolar voltage boost characteristics. The suggested circuit may be operated to have a non-inverted and inverted output with voltage boost characteristics. The regulation in the output bipolar voltage is ensured through the PWM control. The developed topology has eliminated the use of two switching transistors. This reduction has eliminated the requirement of two GDC and IDCPS circuits. This achievement not only simplifies the switching schemes but also reduces the overall size and cost of the power converting topology. The size, cost, and losses of the GDS and IDCPS are larger than that of the switching transistor. The performance evaluation of the developed topology is compared with the existing circuits. The comparison of the simulated results with the practical results validates the effectiveness of the developed topology.

REFERENCES:

[1] O. C. D. S. Filho, B. R. D. Almeida, D. D. S. O. Júnior, and T. R. F. Neto, ``High-frequency isolatedAC_DC_AC interleaved converter for power quality applications,'' IEEE Trans. Ind. Appl., vol. 54, no. 5, pp. 4594_4602, Sep. 2018.

[2] D.-C. Lee and Y.-S. Kim, ``Control of single-phase-to-three-phase AC/DC/ACPWMconverters for induction motor drives,'' IEEE Trans. Ind. Electron., vol. 54, no. 2, pp. 797_804, Apr. 2007.

[3] P. Alemi, Y.-C. Jeung, and D.-C. Lee, ``DC-link capacitance minimization in T-type three-level AC/DC/AC PWM converters,'' IEEE Trans. Ind. Electron., vol. 62, no. 3, pp. 1382_1391, Mar. 2015.

[4] N. Ashraf, G. Abbas, R. Abbassi, and H. Jerbi, ``Power quality analysis of the output voltage of AC voltage and frequency controllers realized with various voltage control techniques,'' Appl. Sci., vol. 11, no. 2, p. 538, Jan. 2021.

[5] H. Qin and J. W. Kimball, ``Solid-state transformer architecture using AC_AC dual-active-bridge converter,'' IEEE Trans. Ind. Electron., vol. 60, no. 9, pp. 3720_3730, Sep. 2013, doi: 10.1109/TIE.2012.2204710.