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.

An Adaptive Off-Time Controlled DCM Flyback PFC Converter With Unity Power Factor and High Efficiency

ABSTRACT:

Constant duty cycle controlled discontinuous conduction mode (DCM) flyback power factor correction (PFC) converter has the advantage of high power factor (PF) and the disadvantage of low efficiency. While, constant on-time (COT) controlled critical conduction mode (CRM) flyback PFC converter has the exact opposite features, besides its switching frequency varies in a line cycle, and the variation range is very large, which complicates the electromagnetic interference (EMI) design. In order to obtain both benefits of these two control methods, an adaptive off-time (AOT) control technique for DCM flyback PFC converter is proposed in this paper. By utilizing the output voltage and the amplitude of line voltage to adjust the off-time of the main switch, the magnetizing current of transformer exactly operates in CRM when the rectified input voltage gets the peak. Thus, the root-mean-square (RMS) current of the main switch and the diode, as well as the conduction loss can be effectively reduced, and high efficiency can be obtained. The proposed control technique also can achieve theoretical unity PF over universal input voltage range of 90_264VAC. Moreover, its variation range of switching frequency is greatly reduced compared to that of COT control. A 60W prototype has been fabricated and tested in the laboratory and experimental results are presented to verify the effectiveness of the proposed method.

KEYWORDS:

1.      Adaptive control

2.      Flyback converter

3.      Power factor

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

 

 

Figure 1. Block Diagram And Key Waveforms Of Aot Controlled Dcm Flyback Pfc Converter.

 EXPECTED SIMULATION RESULTS:

Figure 2. The Rms Current Of The Main Switch And The Diode Of Flyback Pfc Converter With The Aforementioned Three Control Methods For Different Vin.

Figure 3. The Peak Current Of The Main Switch And The Diode Of Flyback Pfc Converter With The Aforementioned Three Control Methods For Different Vin.

Figure 4. Bode Plot Of Aot Control Loop.

CONCLUSION:

This paper proposes an adaptive off-time controlled DCM flyback PFC converter. According to the output voltage and the amplitude of line voltage, the proposed controller adaptively adjusts the off-time of the main switch, so that the magnetizing current of the transformer can exactly operate in CRM. This operation mode can effectively reduce the conduction loss of the main switch and increase efficiency, and on the other hand, similar with constant duty cycle control, the duty cycle and the switch period of AOT control remains fixed during each line cycle, therefore, theoretical unity PF and sinusoidal input current can be also obtained over universal input voltage range. Moreover, the variation range of the switching frequency of AOT control strategy is greatly narrowed compared to that of COT control, which will bring potential convenience in the input filter design. A 60W experimental prototype has been built to verify the theoretical analysis. Experimental results show the minimal PF of AOT control and constant duty cycle control is 0.994, which is significantly higher the minimal PF 0.92 of COT control, and the highest efficiency of AOT control and COT control is 87.6%, which is obviously higher than the highest efficiency 86.5% of constant duty cycle control.

REFERENCES:

[1] M. M. Jovanovic andY. Jang, ``State-of-the-art, single-phase, active power- factor-correction techniques for high-power applications_An overview,'' IEEE Trans. Ind. Electron., vol. 52, no. 3, pp. 701_708, Jun. 2005.

[2] O. Garcia, J. A. Cobos, R. Prieto, P. Alou, and J. Uceda, ``Single phase power factor correction: A survey,'' IEEE Trans. Power Electron., vol. 18, no. 3, pp. 749_755, May 2003.

[3] C. Qiao, G. Feng, and K. M. Smedley, ``A topology survey of single- stage power factor corrector with a boost type input-current-shaper,'' IEEE Trans. Power Electron., vol. 16, no. 3, pp. 360_368, May 2001.

[4] Z. Chen, P. Davari, and H. Wang, ``Single-phase bridgeless PFC topology derivation and performance benchmarking,'' IEEE Trans. Power Electron., vol. 35, no. 9, pp. 9238_9250, Sep. 2020, doi: 10.1109/tpel.2020.2970005.

[5] H. Luo, J. Xu, D. He, and J. Sha, ``Pulse train control strategy for CCM boost PFC converter with improved dynamic response and unity power factor,'' IEEE Trans. Ind. Electron., vol. 67, no. 12, pp. 10377_10387, Dec. 2020.

Advanced PET Control for Voltage Sags Unbalanced Conditions Using Phase-Independent VSC-Rectification

ABSTRACT:

The power electronic transformer (PET) is an emerging technology that is quickly becoming a key component of the next-to-come power distribution networks (PDNs), due to its versatility on energy management, as well as, the improvement on the quality of the energy. PDNs are characterized by their unbalanced conditions, causing that PETs driven by conventional dq0 controls introduce current distortions on the primary winding of the transformer. Such distortion is evidenced in the 2! oscillations of Vd and Vq acting as harmonic sources. In this sense, this paper proposes a novel control approach for PETs. The key idea behind of this proposal consists of operating each phase independently, which is achieved through the enclosed rectification and the mitigation of the 2! Oscillations in a Dual Active Bridge (DAB) topology. The attained advantages by this control scheme are: (a) balancing of the primary winding currents; (b) unitary power factor; (c) negligible harmonic distortion; and (d) 2! oscillation mitigation on the DC bus.

KEYWORDS:

1.      AC-DC-AC

2.      Power conversion

3.      Power electronic transformer

4.      Dual active bridge

5.      VSC

6.      Unbalanced control

7.       Voltage sags

8.      Unbalanced input voltages.

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

 

Fig. 1. Three-phase VSC rectifier with an unbalanced control

EXPECTED SIMULATION RESULTS:

 

Fig. 2. Simulation for an unbalanced voltage sag during V a g = 1\0_; V b g = 0:5\ 􀀀 120_; V c g = 0:5\120__

.

 

Fig. 3. Simulation for an unbalanced voltage sag during V a g = 1\0_; V b g = 1\ 􀀀 120_; V c g = 0:1\120__

.

 

Fig.4. Simulation for an unbalanced voltage sag during V a g = 0:8\0_; V b

g = 0:6\ 􀀀 133:9_; V c g = 0:6\133:9__

.

 

Fig. 5. Simulation for an unbalanced voltage sag with dq0 control during V a g = 1\0_; V b g = 1\ 􀀀 120_; V c g = 0:1\120__

.

CONCLUSION:

The main contribution of this work consists in a new control structure, which employ a phasorial approach with a single PI control, for PETs working on distribution systems where the operation with unbalanced input voltages is frequently. The capacity of this control of independently generate the modulation variables mabc i with different magnitudes and angles, reach a better performance than other control structures; dq0, for example, to mitigate the problems caused by unbalanced input voltages conditions. Under these input conditions in a PET, the advantages achieve by the proposed control are: (i) balanced AC input currents, (ii) sinusoidal AC input current, and (iii) PF = 1. Furthermore, the control structure is an easy-to-implement and requires no additional components. Finally, in this work, all the advantages mentioned above were validated by using simulation and a lab prototype.

REFERENCES:

[1] H. Chen and D. Divan, “Soft-switching solid-state transformer (s4t),” IEEE Trans. Power Electr., vol. 33, no. 4, pp. 2933–2947, 2018.

[2] H. Chen, A. Prasai, and D. Divan, “Dyna-c: A minimal topology for bidirectional solid-state transformers,” IEEE Trans. Power Electr., vol. 32, no. 2, pp. 995–1005, 2017.

[3] G. Brando, A. Dannier, and A. Del Pizzo, “A simple predictive control technique of power electronic transformers with high dynamic features,” in 5th IET Intern. Conf. on Power Electr., Mach. and Drives, 2010, pp. 1–6.

[4] K. K. Mohapatra and N. Mohan, “Matrix converter fed open-ended power electronic transformer for power system application,” in IEEE PES GM - Conversion and Delivery of Electrical Energy in the 21^st Century, 2008, pp. 1–6.

[5] D. Wang, C. Mao, J. Lu, S. Fan, and F. Peng, “Theory and application of distribution electronic power transformer,” Electric Power Syst. Research, vol. 77, no. 3, pp. 219–226, 2007.