Improved pulse-width modulation scheme for T-type multilevel inverter

ABSTRACT: 

In recent times, reduced switch count multilevel inverter (RSC-MLI) has become an emerging area of research in power electronic converters. To control these RSC-MLI topologies, various novel modulation schemes are reported. Multi reference is one of such modulation scheme reported for various RSC topologies, such as T-type. However, the performance of this conventional scheme results in high total harmonic distortion (THD) in line voltages, when compared with the conventional level shifted pulse-width modulation scheme. This observation is clearly presented in this study and the reason for its degraded THD performance has been deeply discussed. To alleviate this problem, a modified multi-reference dual-carrier modulation technique with multiple references and two carriers is proposed. To implement this proposed modulation technique, an alternate carrier and modulation signals arrangement with multiple carriers and single reference is also presented. Finally, a comparative THD performance of the proposed and conventional modulation schemes is carried out on a five-level T-type MLI and obtained simulation results are validated experimentally.

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1 Five-level T-type topology

EXPERIMENTAL RESULTS: 

Fig. 2 Performance analysis of multi-reference modulation scheme on five-level T-type configuration with ma = 0.95 and fc = 1500 Hz (a) Phase voltage, line voltage and load current, (b) Respective harmonic spectra, (c) Comparative harmonic performance of conventional multi-reference modulation scheme for five-level T-type MLI and LSPWM for five-level CHB

Fig. 3 Comparison of LSPWM-OPD and multi-reference modulation scheme with ma = 0.95 and fc = 1500 Hz

(a) Conventional multi-reference modulation scheme for a five-level T-type, (b) Comparison of position of carriers in multi-reference modulation in terms of LSPWM-OPD scheme,

(c) Position of carriers in LSPWM-OPD modulation scheme, (d) Phase and line harmonic spectra of LSPWM-OPD for a five-level CHB

Fig. 4 Modified multi-reference dual-carrier modulation scheme for a five-level T-type topology with ma = 0.95 and fc = 1500 Hz (a) Proposed scheme, (b) Carriers of proposed scheme in terms of LSPWM-IPD, (c) Phase voltage, line voltage and load current, (d) Respective harmonic spectra

CONCLUSION:

In this paper, the poor harmonic performance of the conventional multi-reference modulation method for T-type MLI topology is analysed. To address this problem, a modified multi-reference dual-carrier modulation is proposed. The performance of the proposed modulation scheme is identical to LSPWM-IPD technique which is the best PWM technique with lowest THD value available. Further, to implement the proposed PWM scheme, an alternate carrier and modulation signals arrangement is also proposed which can be easily realisable on digital platforms. The performance of the proposed modulation schemes is evaluated with simulation and experimental studies on a five-level T-type MLI topology. The experimental studies are in good agreement with simulation studies and also verify the superior performance of the proposed schemes over conventional modulation schemes. A generalisation of the modified reduced carrier modulation to implement any number of levels for a T-type is presented with the help of a flowchart.

REFERENCES:

[1] Singh, B., Singh, B.N., Chandra, A., et al.: ‘A review of three-phase improved power quality AC–DC converters’, IEEE Trans. Ind. Electron., 2004, 51, (3), pp. 641–660
[2] Franquelo, L.G., Rodriguez, J., Leon, J.I., et al.: ‘The age of multilevel converters arrives’, IEEE Ind. Electron. Mag., 2008, 2, (2), pp. 28–39
[3] Kouro, S., Malinowski, M., Gopakumar, K., Pou, J., Franquelo, L.G., Wu, B., Rodriguez, J., Pérez, M.A., Leon, J.I.: ‘Recent advances and industrial applications of multilevel converters’, IEEE Trans. Ind. Electron., 2010, 57, (8), pp. 2553–2580
[4] Rodriguez, J., Lai, J.-S., Peng, F.Z.: ‘Multilevel inverters: a survey of topologies, controls, and applications’, IEEE Trans. Ind. Electron., 2002, 49, (4), pp. 724–738, doi: 10.1109/TIE.2002.801052
[5] McGrath, B.P., Holmes, D.G.: ‘Multicarrier PWM strategies for multilevel inverters’, IEEE Trans. Ind. Electron., 2002, 49, (4), pp. 858–867

Vector Current Control Derived from Direct Power Control for Grid-Connected Inverters

ABSTRACT:

We propose a vector current control derived from direct power control (VCC-DPC) for a three-phase voltage source inverter (VSI) in the synchronous rotating frame through instantaneous real and reactive powers. The proposed VCC-DPC method has the same control structure as the conventional VCC except for the coordinate transformation, since we obtain the d–q axes currents model of VSI without using Park transformation  and the PLL system. Consequently, the proposed method has the same property as the conventional VCC if the PLL extracts the phase angle of the grid voltage correctly. However, with the consideration of the slow dynamics of the PLL, the proposed method has an enhanced dynamical performance feature compared with the conventional VCC. Moreover, it has another benefit that the reduction of the computational burden could be expected since  there is no Park transformation and the PLL in the controller implementation. We can guarantee that the closed-loop system with the proposed method is exponentially stable in the operating  range. Finally, both simulation and experimental results using a 15-kW-inverter system match the theoretical expectations closely.

KEYWORDS:

1.      Voltage source inverter

2.      Vector current controller

3.      Instantaneous real and reactive powers

4.      Exponentially stable

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1. Block diagram of (a) the standard VCC with PLL; (b) the proposed method without PLL.

EXPERIMENTAL RESULTS:

Fig. 2. Performance of the inverter when the reference of id is changed from 5 A to 10 A at 1:51 s. (a) grid voltage, (b) id, (c) iq. (red-solid line: conventional method; blue-dashed line: proposed method).

Fig. 3. Performance of the inverter when the inverter is connected at 0:51 s and the reference of id is changed to 5 A. (a) grid voltage, (b) real power, (c) reactive power, (d) id, (e) iq, (red-solid line: conventional VCC method; green-solid line: conventional VCC method with faster PLL; blue-dashed line: proposed method)

CONCLUSION:

In this paper, we have introduced a VCC-DPC for three phase VSI with instantaneous real and reactive powers. We obtained the d–q axes currents model of VSI without using Park transformation and the PLL. For fair comparison, we designed a PI controller with feed forward. Thus, the proposed method has the same control structure as the conventional VCC except for the coordinate transformation and PLL. Moreover, the proposed VCC-DPC will reduce the computational burden since there is no Park transformation and as well as the PLL. Simulation results show that the proposed method has the same properties as the conventional VCC when the PLL extracts the correct phase angle of the grid voltage. However, in the case where the slow dynamics of the PLL is activated,   the proposed method has improved dynamical performance in  comparison with the conventional VCC. We have also tested the performance of the proposed method with a 15-kW inverter system. Experimental results show that the proposed method has a robust property for the parameter uncertainness as well. This work is an initial start for the VCC-DPC through the DPC model. In the future, we will design a compensator for the harmonics or unbalanced issues based on this concept.

REFERENCES:

[1] 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.

[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] F. Blaabjerg, Y. Yang, D. Yang, and X. Wang, “Distributed power generation  systems and protection,” Proc. IEEE, vol. 105, no. 7, pp. 1311–1331, 2017.

[4] Q.-C. Zhong, “Power-electronics-enabled autonomous power systems: Architecture and technical routes,” IEEE Trans. Ind. Electron., vol. 64, no. 7, pp. 5907–5918, 2017.

[5] X. Wang, F. Blaabjerg, M. Liserre, Z. Chen, J. He, and Y. Li, “An active damper for stabilizing power-electronics-based AC systems,”  IEEE Trans. Power Electron., vol. 29, no. 7, pp. 3318–3329, 2014.

Three Phase Single Stage Isolated Cuk based PFC Converter

ABSTRACT:

 In this paper, analysis and design of a three phase isolated Cuk based power factor correction (PFC) converter has been proposed. The proposed converter is operated in discontinuous output inductor current mode (DOICM) to achieve PFC at ac input. This avoids the inner current control loop which further eliminates the sensing of current. This makes the system more reliable and robust. The converter requires only one simple voltage control loop for output voltage regulation and all the power switches are driven by the same gate signal which simplifies the gate driver circuit. The detailed operation of the converter and design calculations are presented. And also a small signal model of the converter by using CIECE approach is presented to aid the controller design. The experimental results from a 2-kW laboratory prototype with 208-V line-to-line input voltage, 400-V output voltage are presented to confirm the operation of the proposed converter. An input power factor of 0.999, an input current total harmonic distortion of as low as 4.06% and a high conversion efficiency of 95.1% are achieved from laboratory prototype.

KEYWORDS:

1.      Three phase power factor correction (PFC)

2.      Isolation

3.      Cuk converter

4.      Discontinuous conduction mode (DCM)

5.      AC-DC converters

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. (a) Single phase isolated Cuk PFC converter; (b) Proposed structure of the three phase isolated Cuk converter.

EXPERIMENTAL RESULTS:

Fig. 2. Experimental waveforms at 1kW output power: (a) input voltages of each phase (50V/div); (b) input currents of each phase and output voltage (2.0A/div, 200V/div); (c) input voltage (50V/div) and input current (2.0A/div) of each phase; (d) input current harmonic spectrum.

Fig.3. Experimental waveforms at 1kW output power: (a) input voltage and voltage across capacitor 𝑐1𝑎 (100V/div); (b) output voltage and voltage across capacitor 𝑐2𝑎 (100V/div); (c) one phase transformer primary and secondary currents (5.0A/div each); (d) output currents of each module (5.0A/div); (e) transformer primary voltages of each phase (200V/div); (f) voltage across each switch (200V/div).

Fig. 4. (a) The experimental output voltage (200V/div), output current (2.0A/div) and input current (5.0A/div) for load power disturbance from 0.8 kW to 1.0 kW; (b) The experimental output voltage (100V/div), input voltage (100V/div) and input current (5.0A/div) for phase input voltage disturbance from 100 V to 115 V.

CONCLUSION:

In this paper, a three phase isolated Cuk converter based power factor correction rectifier operating in discontinuous output inductor current mode (DOICM) is presented. Due to the large size input inductor filter, the proposed converter does not require an additional input filter. The steady state operation of the converter and each component design have been given in detail. It is shown that by operating the converter in DOICM, the input currents are sinusoidal and in phase with input voltages. Subsequently, it does not require inner current control loop and eliminates the current sensors which reduces the system cost and increase the reliability. Another advantage is that the converter works with zero current turn off in the output diode which eliminates the reverse recovery losses of diodes. To aid the controller design, detailed small signal model of the converter by using CIECE approach is presented. A simple voltage control loop with only one output voltage sensor is used to regulate the output voltage.

An experimental laboratory prototype of 2 kW is designed and built to confirm the operation of the proposed converter. The experimental results confirms the analysis and operation of the converter. A high efficiency of 95.1% and an input current THD as low as 4.06% are achieved with the developed laboratory prototype.

REFERENCES:

[1] Limits for Harmonic Current Emissions (Equipment Input Current <16A Per Phase), IEC/EN61000-3-2, 1995.

[2] IEEE Recommended Practices and Requirements for Harmonics Control in Electric Power Systems, IEEE Std. 519, 1992.

[3] D. Gauger, T. Froeschle, L. Illingworth and E. Rhyne, "A Three-Phase Off-Line Switching Power Supply with Unity Power Factor and Low TIF," Telecommunications Energy Conference, 1986. INTELEC '86. International, Toronto, Canada, 1986, pp. 115-121.

[4] BREWSTER, R.F., and BARRET, A.H., “Three-phase AC to DC voltage converter with power line harmonic current reduction,” US Patent 4143414, 6th March, 1979.

[5] D. Chapman, D. James and C. J. Tuck, "A high density 48 V 200 A rectifier with power factor correction-an engineering overview," Proceedings of Intelec 93: 15th International Telecommunications Energy Conference, Paris, 1993, vol. 1, pp. 118-125.

A Unidirectional Single-Stage Three-Phase Soft-switched Isolated DC-AC Converter

ABSTRACT:

This paper presents a novel single-stage soft switched high frequency link three-phase DC-AC converter topology. The topology supports unidirectional DC to AC power flow and is targeted for applications like grid integration of photovoltaic sources, fuel cell etc. The high frequency magnetic isolation results in reduction of system volume, weight and cost. Sine-wave pulse width modulation is implemented in DC side converter. Though high frequency switched, DC side converter is soft-switched for most part of the line cycle. The AC side converter active switches are line frequency switched incurring negligible switching loss. The line frequency switching of AC side converter facilitates use of high voltage blocking inherently slow semiconductor devices to generate high voltage AC output. In addition, a cascaded multilevel structure is presented in this paper for direct medium voltage AC grid integration. A detailed circuit analysis considering non-idealities like transformer leakage and switch capacitances, is presented in this paper. A 6kW three phase laboratory prototype is build. The presented simulation and experimental results verify the operation of proposed topologies.

KEYWORDS:

1.      Zero-voltage switching (ZVS)

2.      Pulse width modulation

3.      DC-AC converter

4.      High-frequency transformer (HFT)

5.      Cascaded multilevel inverter

6.      Single-stage

7.      Rectifier-type HFL

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Proposed 3φ single stage HFL topology

Fig. 2. Proposed 3φ cascaded multilevel HFL topology

EXPERIMENTAL RESULTS:

Fig. 3. Output phase voltages- (a) simulation, (b) experimental: [CH1] c phase voltage (100V/div.), [CH2] a phase voltage (100V/div.), [CH3] b phase voltage (100V/div.). Time scale 4ms/div. Output current waveforms- (c) simulation, (d) experimental: [CH1] c phase current (10A/div.), [CH2] a phase current (10A/div.), [CH3] b phase current (10A/div.). Time scale 4ms/div.

CONCLUSION:

In this paper, a single-stage unidirectional 3φ high frequency link inverter topology along with its multilevel configuration is proposed. Proposed topologies have following features. 1) The DC side converter is soft switched (ZVS) for most part of the line cycle without additional snubber circuit.  2) High frequency magnetic isolation improves the system power density and reduces weight and cost. 3) The AC side active switches are line frequency switched incurring negligible switching loss. 4) High voltage blocking slow switches can be used in line frequency switched AC side converter to generate high voltage AC output. 5) The cascaded structure proposed in this paper is targeted for direct medium voltage grid integration and 6) in this scheme the grid end line filter will have high voltage and low current rating resulting in smaller size with reduced conduction loss. The circuit operation of the proposed converters are discussed in detail considering non-idealities like transformer leakage inductance and device capacitances. The presented simulation and experimental results at verify the operation principle and advantages of the proposed converter topologies. The proposed topologies support unidirectional DC to AC power flow and primarily targeted for grid integration of utility scale photovoltaic sources.

REFERENCES:

[1] J. M. Carrasco, L. G. Franquelo, J. T. Bialasiewicz, E. Galv´an, R. C. PortilloGuisado, M. M. Prats, J. I. Le´on, and N. Moreno-Alfonso, “Power-electronic systems for the grid integration of renewable energy sources: A survey,” IEEE Transactions on industrial electronics, vol. 53, no. 4, pp. 1002–1016, 2006.

[2] E. Romero-Cadaval, G. Spagnuolo, L. G. Franquelo, C. A. Ramos-Paja, T. Suntio, and W. M. Xiao, “Grid-connected photovoltaic generation plants: Components and operation,” IEEE Industrial Electronics Magazine, vol. 7, no. 3, pp. 6–20, 2013.

[3] S. Essakiappan, H. S. Krishnamoorthy, P. Enjeti, R. S. Balog, and  S. Ahmed, “Multilevel medium-frequency link inverter for utility scale  photovoltaic integration,” IEEE Transactions on Power Electronics,  vol. 30, no. 7, pp. 3674–3684, 2015.

[4] Y. Shi, R. Li, Y. Xue, and H. Li, “High-frequency-link-based grid tied pv system with small dc-link capacitor and low-frequency ripple free maximum power point tracking,” IEEE Transactions on Power Electronics, vol. 31, no. 1, pp. 328–339, 2016.

[5] K. V. Iyer, R. Baranwal, and N. Mohan, “A high-frequency ac-link single-stage asymmetrical multilevel converter for grid integration of renewable energy systems,” IEEE Transactions on Power Electronics, vol. 32, no. 7, pp. 5087–5108, 2017.

A Fuzzy Logic Based Switching Methodology for a Cascaded H-Bridge Multilevel Inverter

ABSTRACT:

In this paper, a unusual switching technique is implemented using a fuzzy logic approach. The proposed technique simplifies the conventional method by eliminating the traditional logic gate design. The fuzzy logic pulse generator acts as a look-up table as well as a pulse generator. Based on the modulation index as input, controlled membership functions (MFs) and rules of the fuzzy logic controller (FLC) opens various possibilities in producing pulses directly. The proposed technique is evaluated on the cascaded multilevel inverter with symmetric and asymmetric operations using selective harmonic elimination pulse width modulation (SHE-PWM). MFs are designed based on the pre-calculated firing conditions for different modulation index values. The hardware verification is carried out to support the proposed switching technique.

KEYWORDS:

1.      Cascaded H-Bridge Multilevel Inverter (CHBMLI)

2.      Fuzzy Logic Controller (FLC)

3.      Membership Function (MF)

4.      Pulse Width Modulation (PWM)

5.      Selective Harmonic Elimination (SHE)

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. (a) Symmetrical 7-level CHB MLI and (b) Trinary asymmetrical

9-level CHB MLI.

 EXPERIMENTAL RESULTS:

Fig. 2. (a) Output voltage and load current waveforms for 7 level symmetric CHB MLI at mi = 0:3, (b) Output voltage and load current waveforms  for 7 level symmetric CHB MLI at mi = 0:6, (c) Output voltage and load  current waveforms for 7 level symmetric CHB MLI at mi = 0:9, (d) Output voltage and load current waveforms for 9 level asymmetric CHB MLI at  mi = 0:9, (e) THD spectrum of 7 level output voltage waveform at mi =  0.9 for symmetrical CHB MLI, (f) THD profile of symmetrical CHB MLI for both simulation and experimental at different mi values.

CONCLUSION:

An unusual switching approach is introduced for avoiding look-up table and complex logic gate arrangements to generate the gating pulses for the CHB MLI. In the proposed technique, single FLC works as a pulse generating lookup table which provides gate pules without any mediator. Furthermore, the proposed technique is experimentally validated with symmetrical and asymmetrical CHB MLI for seven and nine level configurations respectively. The proposed technique can be extended to n-level inverters and other MLI configurations.

REFERENCES:

[1] L. G. Franquelo, J. Rodriguez, J. I. Leon, S. Kouro, R. Portillo, and M. A. Prats, “The age of multilevel converters arrives,” IEEE industrial electronics magazine, vol. 2, no. 2, 2008.

[2] J. Venkataramanaiah, Y. Suresh, and A. K. Panda, “A review on symmetric, asymmetric, hybrid and single dc sources based multilevel inverter topologies,” Renewable and Sustainable Energy Reviews, vol. 76, pp. 788–812, 2017.

[3] D. G. Holmes and T. A. Lipo, Pulse width modulation for power converters: principles and practice. John Wiley & Sons, 2003, vol. 18.

[4] M. S. Dahidah, G. Konstantinou, and V. G. Agelidis, “A review of multilevel selective harmonic elimination pwm: formulations, solving algorithms, implementation and applications,” IEEE Transactions on Power Electronics, vol. 30, no. 8, pp. 4091–4106, 2015.

[5] B. Ozpineci, L. M. Tolbert, and J. N. Chiasson, “Harmonic optimization of multilevel converters using genetic algorithms,” in Power Electronics Specialists Conference, 2004. PESC 04. 2004 IEEE 35th Annual, vol. 5. IEEE, 2004, pp. 3911–3916.

Fuzzy Logic Based MPPT Control for a PV/Wind Hybrid Energy System

ABSTRACT:

In this paper, we present a modeling and simulation of a standalone hybrid energy system which combines two renewable energy sources, solar and wind, with an intelligent MPPT control based on fuzzy logic to extract the maximum energy produced by the two PV and Wind systems. Moreover, other classical MPPT methods were simulated and evaluated to compare with the FLC method in order to deduce the most efficient in terms of rapidity and oscillations around the  maximum power point, namely Perturb and Observe (P&O),  Incremental Conductance (INC) for the PV system and Hill  Climbing Search (HCS) for the Wind generator. The simulation results show that the fuzzy logic technique has a better performance and more efficient compared to other methods due to its fast response, the good energy efficiency of the PV/Wind system and low oscillations during different weather conditions.

KEYWORDS:

1.      Hybrid energy system

2.      MPPT

3.      Fuzzy Logic Control (FLC)

4.      Wind system

5.      Photovoltaic system

6.      PMSG

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Hybrid energy system architecture.

EXPECTED SIMULATION RESULTS:

Fig. 2. PV generator output power for different MPPT techniques.

Fig. 3. PV generator output voltage for different MPPT techniques.

Fig. 4. Mechanical power of wind turbine for different MPPT techniques.

Fig. 5. Power coefficient (Cp) for different MPPT techniques.

CONCLUSION:

In this work, an intelligent control based on fuzzy logic is developed to improve the performance and reliability of a PV/Wind hybrid energy system, also the implementation of the other conventional MPPT algorithms for compared with the FLC technique. For a best performance analysis of MPPT techniques on the system, the simulations are carried out under different operating conditions. Simulation results show that the fuzzy controller has a better performance because it allows with a fast response and high accuracy to achieve and track the maximum power point than the P&O, INC and HCS methods for the PV and Wind generators respectively.

REFERENCES:

[1] A.V. Pavan Kumar, A.M. Parimi and K. Uma Rao, “Implementation of MPPT control using fuzzy logic in solar-wind hybrid power system,” IEEE International Conference on Signal Processing, Informatics, Communication and Energy Systems (SPICES), India, 19-21 February, 2015.

[2] C. Marisarla and K.R. Kumar, “A hybrid wind and solar energy system with battery energy storage for an isolated system,” International Journal of Engineering and Innovative Technology, vol. 3, n°3, pp. 99-104, ISSN 2277-3754, September 2013.

[3] L. Qin and X. Lu, “Matlab/Simulink-based research on maximum power point tracking of photovoltaic generation,” Physics Procedia, 24, pp.10- 18, 2012.

[4] B. Bendib, F. Krim, H. Belmili, M. F. Almi and S. Boulouma, “Advanced fuzzy MPPT controller for a stand-alone PV system,” Energy Procedia, 50, pp.383-392, 2014.

[5] H. Bounechba, A. Bouzid, K. Nabti and H. Benalla, “Comparison of perturb & observe and fuzzy logic in maximum power point tracker for pv systems,” Energy Procedia, 50, pp.677-684, 2014.