High-Efficiency Asymmetric Forward-Flyback Converter for Wide Output Power Range

ABSTRACT

 This paper proposes an asymmetric forward-flyback dc-dc converter that has high power-conversion efficiency ηe over a wide output power range. To solve the problem of ringing in the voltage of the rectifier diodes and the problem of duty loss in the conventional asymmetric half-bridge (AHB) converter, the proposed converter uses a voltage doubler structure with a forward inductor Lf in the second stage, instead of using the transformer leakage inductance, to control output current. Lf resonates with the capacitors in the voltage doubler to achieve a zero-voltage turn-on of switches and a zero-current turn-off of diodes for a wide output power range. The proposed converter could operate at a wider input voltage range than the other AHB converters. ηe was measured as 95.9% at output power PO = 100 W and as 90% at PO = 10 W, when the converter was operated at input voltage 390 V, output voltage 142 V, and switching frequency 100 kHz.

KEYWORDS

1.      DC-DC power conversion

2.      Resonance

3.      Stress

4.      Transformer windings

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Circuit structure of the proposed converter.

EXPECTED SIMULATION RESULTS

Fig. 2. Voltage and current waveforms of switches of the proposed converter

at (a) PO = 100 W and (b) PO = 10 W.

Fig. 3. Voltage and current waveforms of D1 and D2 at PO = 100 W: (a) the proposed converter, (b) the conventional AHB converter, and (c) the converter of [20].

CONCLUSION

The proposed asymmetric forward-flyback dc-dc converter had high power conversion efficiency ηe for a wide range of output power PO. The problems of voltage ringing and duty loss in the conventional AHB converter was solved by adopting a forward inductor Lf in the voltage doubler circuit of the secondary stage. The proposed converter used an unbalanced secondary turns of transformer which allowed it to operate for a much wider range of input voltage than the other converter [20] that uses a voltage doubler structure in the secondary stage. The proposed converter also reduced the voltage stress on switches and the current stress on diodes significantly compared to the dual resonant converter (the converter of [24]). The proposed converter had ηe ≥ 90% for 10 ≤ PO ≤ 100 W at VIN = 390 V, VO = 142 V, and fS = 100 kHz (the highest ηe = 95.9%, at PO = 100 W), and could operate at 330 ≤ VIN ≤ 440 V. The proposed asymmetric forward-flyback dc-dc converter is a good candidate for developing a step-down dc-dc converter for applications that require high power-conversion efficiency over wide ranges of input voltage and output power.

REFERENCES:

[1] J. B. Lio, M. S. Lin, D. Y. Chen, and W. S. Feng, “Single-switch soft-switching flyback converter,” Electron. Letter, vol. 32, no. 16, pp. 1429-1430, Aug. 1996.

[2] A. Abramovitz, C. S. Liao, and K. Smedley, “State-Plane analysis of regenerative snubber for flyback converters,” IEEE Trans. Power Electron., vol. 28, no. 11, pp. 5323-5332, Nov. 2013.

[3] L. Huber, and M. M. Jovanovic, “Evaluation of flyback topologies for notebook AC/DC adapter/charger applications,” in Proc. High Freq. Power Conversion Conf., 1995, pp. 284-294.

[4] S. Du, F. Zhu, and P. Qian, “Primary side control circuit of a flyback converter for HBLED,” in Proc. 2nd IEEE Int. Symp. Power Electron. Distrib. Generation Syst., 2010, pp. 339-342.

[5] E. S. Kim, B. G. Chung, S. H. Jang, M. G. Choi, and M. H. Kye, “A study of novel flyback converter with very low power consumption at the standby operation mode,” in Proc. IEEE Appl. Power Electron. Conf., 2010, pp. 1833-1837

An Adaptive Proportional Resonant Controller forSingle Phase PV Grid Connected Inverter Based onBand-Pass Filter Technique

ABSTRACT:  

This paper presents an adaptive proportional resonant (PR) controller for single phase grid connected inverter that adapts its control parameters to grid impedance variations. Forth order band bass filter is designed and then integrated with the adaptive scheme for on-line detection of any variations in the resonance frequency. The estimated frequency is then processed by statistical signal processing operation to identify the variations in the grid impedance. For the on–line tuning of the PR parameters, a look-up table technique is utilized and its parameters are linked with the estimated impedance values. Simulation results based on MATLAB environment clearly verify the effectiveness of the proposed control scheme for 2 kW grid connected inverter system.

KEYWORDS:

1.      Adaptive Proportional Resonant Controller

2.      Grid Impedance Estimation

3.      LCL Filter

4.      Look-up Table

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1. Block diagram of the proposed adaptive PR controller.

 EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation result of emulated grid voltage.

Fig.3. FFT analysis of grid current. (a) APR controller. (b).PR controller.

Fig. 4. Online adaptation of the APR control parameters.

Fig. 5. Grid voltage and current waveforms under changeable grid

impedance with the proposed control strategy.

CONCLUSION:

A new control strategy based on an adaptive proportional resonant (APR) controller has been developed and successfully tested on a simulated 2 kW single phase grid tide PV inverter. A fourth order Sallen-Key bandpass filter tailored to the system to capture the harmonic components around the resonant frequency has been implemented. Statistic signal processing technique was employed in order to provide the controller with signals corresponded to the changeable grid impedance. A considerable low level of current total harmonic distortion (THD) is achieved in comparison with conventional PR controller and compliance with IEEE929-Standard has been demonstrated.

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 Industrial Electronics Magazine, vol. 9, pp. 47-61, 2015.

[2] "IEEE Recommended Practice for Utility Interface of Photovoltaic (PV) Systems," in IEEE Std 929-2000, ed, 2000.

[3] "IEEE Draft Application Guide for IEEE Standard 1547, Interconnecting Distributed Resources With Electric Power Systems," in IEEE Unapproved Draft Std P1547.2/D11, Sept 2008, ed, 2008, p. 1.

[4] H. M. El-Deeb, A. Elserougi, A. S. Abdel-Khalik, S. Ahmed, and A. M. Massoud, "An adaptive PR controller for inverter-based distribution generation with active damped LCL filter," in 2013 7th IEEE GCC Conference and Exhibition (GCC), 2013, pp. 462-467.

[5] W. L. Chen and J. S. Lin, "One-Dimensional Optimization for Proportional-Resonant Controller Design Against the Change in Source Impedance and Solar Irradiation in PV Systems," IEEE Transactions on Industrial Electronics, vol. 61, pp. 1845-1854, 2014.

Standalone Operation of Modified Seven-LevelPacked U-Cell (MPUC) Single-Phase Inverter

ABSTRACT:  

In this paper the standalone operation of the modified seven-level Packed U-Cell (MPUC) inverter is presented and analyzed. The MPUC inverter has two DC sources and six switches, which generate seven voltage levels at the output. Compared to cascaded H-bridge and neutral point clamp multilevel inverters, the MPUC inverter generates a higher number of voltage levels using fewer components. The experimental results of the MPUC prototype validate the appropriate operation of the multilevel inverter dealing with various load types including motor, linear, and nonlinear ones. The design considerations, including output AC voltage RMS value, switching frequency, and switch voltage rating, as well as the harmonic analysis of the output voltage waveform, are taken into account to prove the advantages of the introduced multilevel inverter.

KEYWORDS:

1.      Multilevel inverter

2.      Packed u-cell

3.      Power quality

4.      Multicarrier PWM

5.      Renewable energy conversion

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Figure 1. Single-phase seven-level MPUC inverter in standalone mode of operation

EXPECTED SIMULATION RESULTS:

Figure 2. Seven-level MPUC inverter output voltage and current with DC source voltages. Ch₁: V₁,

Ch₂: V₂, Ch₃: V_ab, Ch₄: i_l.

Figure 3. One cycle of output voltage and gate pulses of MPUC inverter switches. Ch₁: V_ab, Ch₂: T₁

gate pulses, Ch₃: T₂ gate pulses, Ch₄: T₃ gate pulses

Figure 4. MPUC inverter switches’ voltage ratings. Ch₁: V_ab, Ch₂: T₁ voltage, Ch₃: T₂ voltage, Ch₄:

T₃ voltage. and nonlinear). The step-by-step process for connecting loads is depicted in Figure 7, which show

Fig.5. Test results when a nonlinear load is connected to the MPUC inverter.Ch₁  :V_ab  :Ch₄ :i_l.

Figure 6. Output voltage and current waveform of MPUC inverter when different loads are added

step by step. Ch₁: V_ab, Ch₄: i_l. (A) Transient state when nonlinear load is added to the RL load (left)

and after a while a motor load is added to the system (right); (B) steady state when a nonlinear load is

added to the RL load (left) and after a while a motor load is added to the system (right).

Figure 7. Voltage and current waveform of MPUC inverter with RMS calculation for 120 V system.

CONCLUSION:

In this paper a reconfigured PUC inverter topology has been presented and studied experimentally. The proposed MPUC inverter can generate a seven-level voltage waveform at the output with low harmonic contents. The associated switching algorithm has been designed and implemented on the introduced MPUC topology with reduced switching frequency aspect. Switches’ frequencies and ratings have been investigated experimentally to validate the good dynamic performance of the proposed topology. Moreover, the comparison of MPUC to the CHB multilevel inverter showed other advantages of the proposed multilevel inverter topology, including fewer components, a lower manufacturing price, and a smaller package due to reduced filter size.

Author Contributions: All authors contributed equally to the work presented in this paper.

Funding: This research received no external funding.

Conflicts of Interest: The authors declare no conflict of interest.

REFERENCES:

1. Bose, B.K. Multi-Level Converters; Multidisciplinary Digital Publishing Institute: Basel, Switzerland, 2015.

2. Mobarrez, M.; Bhattacharya, S.; Fregosi, D. Implementation of distributed power balancing strategy with a layer of supervision in a low-voltage DC microgrid. In Proceedings of the 2017 IEEE Applied Power Electronics Conference and Exposition (APEC), Tampa, FL, USA, 26–30 March 2017; pp. 1248–1254.

3. Franquelo, L.G.; Rodriguez, J.; Leon, J.I.; Kouro, S.; Portillo, R.; Prats, M.A.M. The age of multilevel converters arrives. IEEE Ind. Electron. Mag. 2008, 2, 28–39. [CrossRef]

4. Malinowski, M.; Gopakumar, K.; Rodriguez, J.; Perez, M.A. A survey on cascaded multilevel inverters. IEEE Trans. Ind. Electron. 2010, 57, 2197–2206. [CrossRef]

5. Nabae, A.; Takahashi, I.; Akagi, H. A new neutral-point-clamped PWM inverter. IEEE Trans. Ind. Appl. 1981,5, 518–523. [CrossRef]

Single Stage PV Array Fed Speed Sensorless Vector Control of Induction Motor Drive for Water Pumping

 ABSTRACT:  

 This paper deals with a single stage solar powered speed sensorless vector controlled induction motor drive for water pumping system, which is superior to conventional motor drive. The speed is estimated through estimated stator flux. The proposed system includes solar photovoltaic (PV) array, a three-phase voltage source inverter (VSI) and a motor-pump assembly. An incremental conductance (InC) based MPPT (Maximum Power Point Tracking) algorithm is used to harness maximum power from a PV array. The smooth starting of the motor is attained by vector control of an induction motor. The desired configuration is designed and simulated in MATLAB/Simulink platform and the design, modeling and control of the system, are validated on an experimental prototype developed in the laboratory.

KEYWORDS:

1.      Speed Sensorless Control

2.      Stator Field-Oriented Vector Control

3.      Photovoltaic (PV)

4.      InC MPPT Algorithm

5.      Induction Motor Drive (IMD)

6.      Water Pump

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. PV fed induction motor drive configuration

 EXPECTED SIMULATION RESULTS:

Fig. 2. Starting and MPPT of PV array at 1000 W/m²

Fig. 3. Intermediate signals during starting at 1000 W/m²

(a)

(b)

Fig. 4. Simulation results during starting at 1000 W/m² (a) Proposed drive (b) Waveforms showing sensed speed and estimated speed

Fig. 5. SPV array performance during decrease in insolation from 1000 W/m² to 500 W/m²

(a)

 (b)

Fig. 6. Dynamic performance during irradiance decrement from 1000 W/m² to 500 W/m² (a) Proposed drive (b) Waveforms showing sensed speed and estimated speed

Fig. 7. PV array performance on increasing insolation from 500 W/m² to 1000 W/m²

(a)

(b)

Fig. 8. Dynamic performance during irradiance decrement from 500 W/m² to 1000 W/m² (a) Proposed drive (b) Waveforms showing sensed speed and estimated speed

CONCLUSION:

A single stage solar PV array fed speed sensorless vector-controlled induction motor drive has been operated subjected to different conditions and the steady state and dynamic behaviors have been found quite satisfactory and suitable for water pumping. The torque and stator flux, have been controlled independently. The motor is started smoothly. The reference speed is generated by DC link voltage controller controlling the voltage at DC link along with the speed estimated by the feed-forward term incorporating the pump affinity law. The power of PV array is maintained at maximum power point at the time of change in irradiance. This is achieved by using incremental-conductance based MPPT algorithm. The speed PI controller has been used to control the q-axis current of the motor. Smooth operation of IMD is achieved with desired torque profile for wide range of speed control. Simulation results have displayed that the controller behavior is found satisfactory under steady state and dynamic conditions of insolation change. The suitability of the drive is also verified by experimental results under various conditions and has been found quite apt for water pumping.

REFERENCES:

[1] R. Foster, M. Ghassemi and M. Cota, Solar energy: Renewable energy and the environment, CRC Press, Taylor and francis Group, Inc. 2010.

[2] M. Kolhe, J. C. Joshi and D. P. Kothari, “Performance analysis of a directly coupled photovoltaic water-pumping system”, IEEE Trans. on Energy Convers., vol. 19, no. 3, pp. 613-618, Sept. 2004.

[3] J. V. M. Caracas, G. D. C. Farias, L. F. M. Teixeira and L. A. D. S. Ribeiro, “Implementation of a high-efficiency, high-lifetime, and low-cost converter for an autonomous photovoltaic water pumping system”, IEEE Trans. Ind. Appl., vol. 50, no. 1, pp. 631-641, Jan.-Feb. 2014.

[4] R. Kumar and B. Singh, “ Buck-boost converter fed BLDC motor for solar PV array based water pumping, ” IEEE Int. Conf. Power Electron. Drives and Energy Sys. (PEDES), 2014.

[5] Zhang Songbai, Zheng Xu, Youchun Li and Yixin Ni, “Optimization of MPPT step size in stand-alone solar pumping systems,” IEEE Power Eng. Society Gen. Meeting, June 2006.