An Improved Torque and Current Pulsation Suppression Method for Railway Traction Drives Under Fluctuating DC-Link Voltage

ABSTRACT:  

For railway traction drives, the active front end usually adopts a single-phase rectifier. However, the dc-link voltage of this single-phase rectifier contains a second-order fluctuating component due to the fluctuation of the instantaneous power at both the ac and dc sides. Fed by the fluctuating dc-link voltage, the traction motor suffers from severe torque and current pulsation. The hardware solution with an additional LC resonant filter is simple, but it will reduce the power density of the system. An alternative solution is to eliminate the beat component in the stator voltage/current through modulation ratio or frequency compensation. However, it is difficult to achieve high performance for the conventional feedforward method. In this paper, an improved closed-loop torque and current pulsation suppression method is proposed, which can eliminate the q-axis current pulsation component in the field-oriented control system through frequency compensation. The torque pulsation suppression is also achieved automatically. Simulation and experimental results show that the proposed scheme can effectively reduce the torque and current pulsation in various operation modes compared with the conventional feedforward method.

KEYWORDS:

1.      Fluctuating dc-link voltage

2.      q-axis current pulsation

3.      Suppression

4.      Torque pulsation

5.      Traction drive

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Circuit schematic of the ac/dc/ac traction drive system.

EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results of two methods in the asynchronous modulation mode. (a) Line voltage of the motor. (b) and (c) Stator current and torque with the conventional method. (d) and (e) Stator current and torque with the proposed method. (f) DC-link voltage of the inverter without and with the proposed method.

(g) Transition waveforms of the stator current without and with the proposed method.

Fig. 3. Spectrum analysis of the simulation results of the two methods in the asynchronous modulation mode. (a)–(c) Stator current without compensation, with the conventional method, and with the proposed method. (d)–(f) Torque without compensation, with the conventional method, and with the proposed method.

Fig. 4. Simulation results of the two methods in the synchronous modulation mode. (a) Line voltage of the motor. (b) and (c) Stator current and torque with the conventional method. (d) (e) Stator current and torque with the proposed method.

Fig. 5. Simulation results of the two methods in the square-wave modulation mode. (a) Line voltage of the motor. (b) and (c) Stator current and torque with the conventional method. (d) and (e) Stator current and torque with the proposed method.

CONCLUSION:

A closed-loop torque and current pulsation suppression method for railway traction drives under fluctuating dc-link voltage is proposed. This method aims to eliminate the q-axis current pulsation component in the FOC system through output frequency compensation. The torque pulsation suppression is achieved on the basis of q-axis current pulsation elimination automatically. A resonant controller is proposed for the closed loop control of q-axis current and dynamic compensation of the output frequency. Different from the conventional feed forward open-loop frequency compensation method, the torque pulsation with the proposed method is suppressed through the elimination of the q-axis current pulsation component rather than the beat component in the output voltage. The effectiveness of the proposed method have been verified by simulation and experiments on traction drives with the inverter operated in asynchronous, synchronous, and square wave modulation modes, respectively. The results have been compared to those with the conventional feed forward frequency compensation method based on fluctuating dc-link voltage detection. Both simulation and experimental results show that the suppression of stator current and torque pulsation are obvious in different modulation modes with the proposed control method using the same dc-link capacitance.

The proposed suppression method can reduce the sensitivity of the system to variations of the grid frequency. However, the fluctuating component in the dc-link voltage will be increased with the proposed method compared with the LC resonant filter solution.

REFERENCES:

[1] R. J. Hill, “Electric railway traction. II. Traction drives with three-phase induction motors,” Power Eng. J., vol. 8, no. 3, pp. 143–152, Jun. 1994.

[2] A. Steimel, “Electric railway traction in Europe,” IEEE Ind. Appl. Mag., vol. 2, no. 6, pp. 6–17, Nov./Dec. 1996.

[3] H. Ouyang, K. Zhang, P. Zhang, Y. Kang, and J. Xiong, “Repetitive compensation of fluctuating DC link voltage for railway traction drives,” IEEE Trans. Power Electron., vol. 26, no. 8, pp. 2160–2171, Aug. 2011.

[4] J. Klima, M. Chomat, and L. Schreier, “Analytical closed-form investigation of PWM inverter induction motor drive performance under DC bus voltage pulsation,” IET Electr. Power Appl., vol. 2, no. 6, pp. 341–352, Nov. 2008.

[5] A. Cheok, S. Kawamoto, T. Matsumoto, and H. Obi, “AC drive with particular reference to traction drives,” in Proc. 4th Int. Conf. Adv. Power Syst. Control, Oper. Manage., 1997, pp. 348–353.

A Direct Maximum Power Point Tracking Method for Single-Phase Grid Connected PV Inverters

ABSTRACT:

 A direct maximum power point tracking (MPPT) method for PV systems has been proposed in this work. This method solves two of the main drawbacks of the Perturb and Observe (P&O) MPPT, namely: i) the tradeoff between the speed and the oscillations in steady-state, ii) the poor effectiveness in dynamic conditions, especially in low irradiance when the measurement of signals becomes more sensitive to noise. The proposed MPPT is designed for single-phase single-stage grid-connected PV inverters and is based on estimating the ripple of the instantaneous PV power and voltage, using a second-order generalized integrator-based quadrature signal generator (SOGI-QSG). We analyzed the global stability of the closed-loop control system and validated the proposed algorithm through simulation and experiments on an inverter test platform according to the EN 50530 standard. The experimental results confirm the performance of the proposed method in terms of both speed and tracking efficiency.

KEYWORDS:

1.      Single stage PV Inverter

2.      Lyapunov Stability

3.      MPPT

4.      P&O

5.      EN 50530 standard

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. System configuration of single-stage single-phase grid-connected PV system.

EXPECTED SIMULATION RESULTS:

Fig. 2. Experimental PV voltage waveforms after startup showing the convergence to MPP with different 𝐾 values.

Fig. 3. Start waveforms comparison for DC link voltage.

Fig. 4. The output PV power under trapezoidal irradiance profile.

Fig. 5. DC link voltage under trapezoidal irradiance profile

Fig. 6. Instantanous efficiency under trapezoidal irradiance profile.

Fig. 7. Experimental start waveforms of PV power for both methods.

Fig. 8. Experimental start waveforms comparison of DC link voltage.

Fig. 9. Experimental results of PV power under trapezoidal irradiance profile.

Fig. 10. Experimental results for DC link voltage under trapezoidal irradiance profile.

Fig. 11. Efficiency under static irradiance for both methods.

Fig. 12. PV power for P&O under dynamic irradiance profile according to EN 50530.

Fig. 13. PV power for the proposed method under dynamic irradiance profile according to EN 50503.

Fig. 14. Efficiency comparison for the both methods from low-to-medium irradiance

Fig. 15. Efficiency comparison for the both methods from medium-to-high irradiance.

CONCLUSION:

This paper has described the design of an effective controller for direct reaching the maximum power point for a single-stage single-phase grid-connected PV inverter. The proposed method has been designed based on the stability analysis using the Lyapunov quadratic function that is formed from the variation of energy stored in the DC link capacitor. From the simulations and experimental results on an advanced test platform and according to the EN 50530 standard, it was confirmed that the proposed method achieves high efficiency in both static and dynamic conditions. Furthermore, the proposed method is very fast to reach the MPP.

 REFERENCES:

[1] T. Kerekes, R. Teodorescu, and U. Borup, “Transformerless Photovoltaic Inverters Connected to the Grid,” APEC 07 - Twenty-Second Annual IEEE Applied Power Electronics Conference and Exposition. pp. 1733– 1737, 2007.

[2] I. S. Kim, M. B. Kim, and M. J. Youn, “New Maximum Power Point Tracker Using Sliding-Mode Observer for Estimation of Solar Array Current in the Grid-Connected Photovoltaic System,” IEEE Transactions on Industrial Electronics, vol. 53, no. 4. pp. 1027–1035, 2006.

[3] J. Selvaraj and N. A. Rahim, “Multilevel Inverter For Grid-Connected PV System Employing Digital PI Controller,” IEEE Transactions on Industrial Electronics, vol. 56, no. 1. pp. 149–158, 2009.

[4] M. Rosu-Hamzescu and S. Oprea, “Practical guide to implementing solar panel MPPT algorithms,” Microchip Technol. Inc, 2013.

[5] D. Sera, R. Teodorescu, J. Hantschel, and M. Knoll, “Optimized Maximum Power Point Tracker for Fast-Changing Environmental Conditions,” IEEE Transactions on Industrial Electronics, vol. 55, no. 7. pp. 2629–2637, 2008.

Simulation and Analysis of Stand-alone Photovoltaic System with Boost Converter using MATLAB/Simulink

ABSTRACT:  

Use of renewable energy and in particular solar energy has brought significant attention over the past decades. Photovoltaic (PV) power generation projects are implemented in very large number in many countries. Many research works are carried out to analyze and validate the performance of PV modules. Implementation of experimental set up for PV based power system with DC-DC converter to validate the performance of the system is not always possible due to practical constraints. Software based simulation model helps to analyze the performance of PV and a common circuit based model which could be used for validating any commercial PV module will be more helpful. Simulation of mathematical model for Photovoltaic (PV) module and DC-DC boost converter is presented in this paper. The model presented in this paper can be used as a generalized PV module to analyze the performance of any commercially available PV modules. I-V characteristics and P-V characteristics of PV module under different temperature and irradiation level can be obtained using the model. The design of DC-DC boost converter is also discussed in detail. Simulation of DC-DC converter is performed and the results are obtained from constant DC supply fed converter and PV fed converter.

KEYWORDS:

1.      DC-DC Boost converter

2.      MATLAB/Simulink

3.      Modeling

4.      Photovoltaic

5.      Simulation

6.      Solar power

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1 Simulink Model of proposed system

 EXPECTED SIMULATION RESULTS:

Fig.2 PWM Pulse generation

Fig. 3(a) Input Voltage of DC-DC Boost Converter

Fig. 4(b) Output Voltage of Boost Converter constant DC input supply

Fig. 5 (c) Output current of Boost Converter constant DC input supply

Fig. 6 (a) Input voltage of PV fed converter

Fig. 7 (b) Output voltage and current waveform of PV fed converter

Fig. 8. Change in irradiation level of PV Module

Fig. 9. Output Voltage and Current waveforms of Boost Converter at

different irradiation level.

CONCLUSION:

A circuit based system model of PV modules helps to analyze the performance of commercial PV modules. A general model of PV module is developed using commonly used blocks in the form of masked subsystem block. I-V and P-V characteristics outputs are generated for MSX 60 PV module under different irradiation and different temperature levels and the model is simulated for GEPVp-200-M Module under various conditions as presented in the data sheet. The results obtained from the simulation shows excellent matching with the characteristics graphs provided in the data sheet of the selected models. Thus, the model can be used to analyze the performance of any commercial PV module. The DC-DC boost converter is also simulated and the results are obtained from the converter with constant DC input supply and by interconnecting the PV module with it. The results shows close match between the output of converter with constant DC input and the PV fed converter. The output voltage and current of the PV fed DC-DC boost converter obtained for change of irradiation levels at constant temperature is also presented.

REFERENCES:

[1] J.A.Gow, C.D.Manning, “ Development of photovoltaic array model for the use in power electronic simulation studies,” IEE Proceedings Electric power applications, Vol. 146, No.2, March,1999.

[2] Jee-Hoon Jung, and S. Ahmed, “Model Construction of Single Crystalline Photovoltaic Panels for Real-time Simulation,” IEEE Energy Conversion Congress & Expo, September 12-16, 2010, Atlanta, USA.

[3] T. F. Elshatter, M. T. Elhagry, E. M. Abou-Elzahab, and A. A. T. Elkousy, “Fuzzy modeling of photovoltaic panel equivalent circuit,” in Proc. Conf. Record 28th IEEE Photovoltaic Spec. Conf., pp. 1656– 1659, 2000.

[4] M. Balzani and A. Reatti, “Neural network based model of a PV array for the optimum performance of PV system,” in Proc. Ph.D. Res. Microelectron. Electron., vol. 2, pp. 123–126, 2005.

[5] S. Sheik Mohammed, ”Modeling and Simulation of Photovoltaic module using MATLAB/Simulink” International Journal of Chemical and Environmental Engineering, 2011

Power Quality Enhancement in Residential Smart Grids through Power Factor Correction Sta

ABSTRACT:

The proliferation of non-linear loads and the increasing penetration of Distributed Energy Resources (DER) in Medium-Voltage (MV) and Low-Voltage (LV) distribution grids, make it more difficult to maintain the power quality levels in residential electrical grids, especially in the case of weak grids. Most household appliances contain a conventional Power Factor Corrector (PFC) rectifier, which maximizes the load Power Factor (PF) but does not contribute to the regulation of the voltage Total Harmonic Distortion (THDV ) in residential electrical grids. This manuscript proposes a modification for PFC controllers by adapting the operation mode depending on the measured THDV . As a result, the PFCs operate either in a low current Total Harmonic Distortion (THDI ) mode or in the conventional resistor emulator mode and contribute to the regulation of the THDV and the PF at the distribution feeders. To prove the concept, the modification is applied to a current sensorless Non-Linear Controller (NLC) applied to a single-phase Boost rectifier. Experimental results show its performance in a PFC front-end stage operating in Continuous Conduction Mode (CCM) connected to the grid with different THDV .

KEYWORDS:

1.      Harmonic distortion

2.      Non-linear carrier control

3.      Power factor correction

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Residential LV grid with household appliances feed through conventional AC/DC stages (without the proposed operation mode selector) and the proposed PQE controller.

EXPECTED SIMULATION RESULTS:

Fig. 2. Experimental results of PQE PFC at 50 Hz. Voltage and current waveforms in a) resistor emulator mode (k = 0), b) sinusoidal current mode (k = 1) and c) measured spectra in both operation modes.

Fig. 3. Experimental results of PQE PFC at 60 Hz. Voltage and current waveforms in a) resistor emulator mode (k = 0), b) sinusoidal current mode (k = 1) and c) measured spectra in both operation modes.

Fig. 4. Experimental results of PQE PFC at 400 Hz. Voltage and current waveforms in a) resistor emulator mode (k = 0), b) sinusoidal current mode (k = 1) and c) measured spectra in both operation modes.

CONCLUSION:

The consequence on the electrical power quality of connecting household appliances to the grid through PFC stages has been assessed considering different THDV scenarios. As has been shown in (17) and (23), there are conditions under which sinusoidal current consumption results in better PF at the PCC than with resistor emulator behavior, commonly assumed to be ideal for PFC stages. A modification of the carrier signal of NLC controllers applied to PFC stages is designed to impress sinusoidal input current despite the input voltage distortion. The line current estimation with no interaction with the power stage implements the NLC with high noise immunity. The digital implementation of the non-linear controller is appropriate to define the carrier and to include additional reduction of the current distortion depending on the application. The PQE controller can be applied to mitigate the effect of nonlinear loads within household appliances on residential electrical grids. The operation mode of the digital controller can be autonomously adjusted through the locally measured THDV , without extra circuitry. The user or a THDV threshold detection selects the convenient behavior (either resistor emulator or pure sinusoidal current). Experimental results obtained with high THDV (above 5 %) confirm the feasibility of the PQE controller in both sinusoidal current and resistive emulator modes.

REFERENCES:

[1] IEEE Std. 519-2014 (Revision of IEEE Std. 519-1992), IEEE Recommended Practice and Requirements for Harmonic Control in ElectricPower Systems, DOI 10.1109/IEEESTD.2014.6826459, pp. 1–29, Jun. 2014.

[2] Y. J. Wang, R. M. O’Connell, and G. Brownfield, “Modeling and prediction of distribution system voltage distortion caused by nonlinear residential loads,” IEEE Trans. Power Del., vol. 16, DOI 10.1109/61.956765, no. 4, pp. 744–751, Oct. 2001.

[3] H. Oraee, “A quantitative approach to estimate the life expectancy of motor insulation systems,” IEEE Trans. Dielectr. Electr. Insul., vol. 7, DOI 10.1109/94.891990, no. 6, pp. 790–796, Dec. 2000.

[4] D. Fabiani and G. C. Montanari, “The effect of voltage distortion on ageing acceleration of insulation systems under partial discharge activity,” IEEE Electr. Insul. Mag., vol. 17, DOI 10.1109/57.925300, no. 3, pp. 24–33, May. 2001.

[5] T. J. Dionise and V. Lorch, “Harmonic filter analysis and redesign for a modern steel facility with two melt furnaces using dedicated capacitor banks,” in IEEE IAS Annual Meeting, vol. 1, DOI 10.1109/IAS.2006.256496, pp. 137–143, Oct. 2006.