An Improved Beatless Control Method of AC Drives for Railway Traction Converters

ABSTRACT:  

The traction converter consists of a single phase AC-DC rectifier and a three-phase DC-AC inverter. Due to special structural characteristics of single phase rectifier, a fluctuating voltage component with the frequency twice of the grid’s, exists in DC-link voltage. Fed by fluctuating DC-link voltage, a beat phenomenon occurs in traction motor, and harmonic components appear in both stator current and electromagnetic torque, especially when motor operates near the ripple frequency. In this paper, the mechanism and influence of fluctuating voltage are analyzed in detail. Based on modeling analysis of motor and switching function of inverter, a frequency compensation factor is derived in vector control of induction motor. Then an improved frequency compensation control method is proposed to suppress beat phenomenon without LC resonant circuit. Finally the modified scheme is verified by simulation and experiment.

KEYWORDS:

1.      Fluctuating DC voltage

2.      Beat phenomenon

3.      Vector control

4.      Beatless control

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1. FOC with frequency compensation for Induction Motor

 EXPECTED SIMULATION RESULTS:

Fig. 2. Waves of stator current and electromagnetic torque of traction Motor

Fig. 3. FFT of stator current and electromagnetic torque before adding frequency compensation method

Fig. 4. FFT of stator current and electromagnetic torque after adding traditional frequency compensation method

Fig. 5. FFT of stator current and electromagnetic torque after adding improved frequency compensation method

 CONCLUSION:

In high-power traction converters, without LC filter circuit paralleled in DC-link, a fluctuating voltage twice of the grid frequency contains in DC-link voltage. This paper aims at adopting software control method to suppress beat phenomenon in traction motor caused byDC ripple voltage. According to theoretical analysis, DC ripple voltage is influenced by output power of motor, DC-link capacitor and power factor. Then, influences of fluctuating voltage are analyzed in detailed from aspect of switching function and motor model. Based on above analysis, combining with rotor field oriented control of traction motor, the frequency of switching function is modified to suppress beat phenomenon. An improved frequency compensation control method is proposed. Simulation model is built to verify the proposed scheme. Finally, the proposed control method is verified by drag experiment on a dynamometer test platform.

REFERENCES:

[1] J. Klima, M. Chomat, L. Schreier, “Analytical Closed-form Investigation of PWM Inverter Induction Motor Drive Performance under DC Bus Voltage Pulsation,” IET Electric Power Application, Vol. 2, No. 6, pp. 341–352, Nov, 2008.

[2] H. W. van der Broeck and H. C. Skudelny, "Analytical analysis of the harmonic effects of a PWM AC drive," inIEEE Transactions on Power Electronics, vol. 3, no. 2, pp. 216-223, Apr 1988.

[3] K Nakata, T Nakamachi , K Nakamura, “A beatless control of inverter-induction motor system driven by a rippled DC power source,” Electrical Engineering in Japan, Vol.109, No.5, pp.122-131,1989.

[4] Z Salam, C.J. Goodman, “Compensation of fluctuating DC link voltage for traction inverter driver,” Power Electronics and Variable Speed Drives, 1996. Sixth International Conference on (Conf. Publ. No. 429), pp. 390-395, 1996.

[5] S. Kouro, P. Lezana, M. Angulo and J. Rodriguez, "Multicarrier PWM With DC-Link Ripple Feedforward Compensation for Multilevel Inverters," IEEE Transactions on Power Electronics, vol. 23, no. 1, pp. 52- 59, Jan. 2008.

Integrated Photovoltaic and Dynamic Voltage Restorer System Configuration

ABSTRACT:  

This paper presents a new system configuration for integrating a grid-connected photovoltaic (PV) system together with a self-supported dynamic voltage restorer (DVR). The proposed system termed as a “six-port converter,” consists of nine semiconductor switches in total. The proposed configuration retains all the essential features of normal PV and DVR systems while reducing the overall switch count from twelve to nine. In addition, the dual functionality feature significantly enhances the system robustness against severe symmetrical/asymmetrical grid faults and voltage dips. A detailed study on all the possible operational modes of six-port converter is presented. An appropriate control algorithm is developed and the validity of the proposed configuration is verified through extensive simulation as well as experimental studies under different operating conditions.

KEYWORDS:

1.      Bidirectional power flow

2.      Distributed power generation

3.      Photovoltaic (PV) systems

4.      Power quality

5.      Voltage control

SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:

Fig. 1. Proposed integrated PV and DVR system configuration.

EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results: operation of proposed system during health grid mode (PV-VSI: active and DVR-VSI: inactive). (a) Vpcc; (b) PQload; (c) PQgrid; (d) PQpv-VSI; and (e) PQdvr-VSI.

Fig. 3. Simulation results: operation of proposed system during fault mode (PV-VSI: inactive and DVR-VSI: active). (a) Vpcc; (b) Vdvr; (c) Vload; (d) PQload; (e) PQgrid; (f) PQpv-VSI; and (g) PQdvr-VSI.

Fig. 4. Simulation results: operation of proposed system during balance three phase sag mode (PV-VSI: active and DVR-VSI: active). (a) Vpcc; (b) Vdvr-VSI; (c) Vload; (d) PQgrid; (e) PQpv-VSI; and (f) PQdvr-VSI.

Fig. 5. Simulation results: operation of proposed system during unbalanced sag mode (PV-VSI: active and DVR-VSI: active). (a) Vpcc; (b) Vdvr-vsi; (c) Vload; (d) PQgrid; (e) PQpv-VSI; and (f) PQdvr-VSI.

Fig. 6. Simulation results: operation of proposed system during inactive PV plantmode (PV-VSI: active and DVR-VSI: active). (a) Vpcc; (b) Vload; (c) Vdc; (d) PQload; (e) PQdvr-VSI; and (f) PQpv-VSI.

 CONCLUSION:

In this paper, a new system configuration for integrating a conventional grid-connected PV system and self supported DVR is proposed. The proposed configuration not only exhibits all the functionalities of existing PV and DVR system, but also enhances the DVR operating range. It allows DVR to utilize active power of PV plant and thus improves the system robustness against sever grid faults. The proposed configuration can operate in different modes based on the grid condition and PV power generation. The discussed modes are healthy grid mode, fault mode, sag mode, and PV inactive mode. The comprehensive simulation study and experimental validation demonstrate the effectiveness of the proposed configuration and its practical feasibility to perform under different operating conditions. The proposed configuration could be very useful for modern load centers where on-site PV generation and strict voltage regulation are required.

REFERENCES:

[1] R. A. Walling, R. Saint, R. C. Dugan, J. Burke, and L. A. Kojovic, “Summary of distributed resources impact on power delivery systems,” IEEE Trans. Power Del., vol. 23, no. 3, pp. 1636–1644, Jul. 2008.

[2] C. Meza, J. J. Negroni, D. Biel, and F. Guinjoan, “Energy-balance modeling and discrete control for single-phase grid-connected PV central inverters,” IEEE Trans. Ind. Electron., vol. 55, no. 7, pp. 2734–2743, Jul.2008.

[3] T. Shimizu, O. Hashimoto, and G. Kimura, “A novel high-performance utility-interactive photovoltaic inverter system,” IEEE Trans. Power Electron., vol. 18, no. 2, pp. 704–711, Mar. 2003.

[4] S. B. Kjaer, J. K. Pedersen, and F. Blaabjerg, “A review of single-phase grid-connected inverters for photovoltaic modules,” IEEE Trans. Ind.Appl., vol. 41, no. 5, pp. 1292–1306, Sep./Oct. 2005.

[5] T. Esram, J. W. Kimball, P. T. Krein, P. L. Chapman, and P. Midya, m“Dynamic maximum power point tracking of photovoltaic arrays using ripple correlation control,” IEEE Trans. Power Electron., vol. 21, no. 5, pp. 1282–1291, Sep. 2006.

Dynamic Voltage Conditioner, a New Concept for Smart Low-Voltage Distribution System

ABSTRACT

Power Quality (PQ) improvement in distribution level is an increasing concern in modern electrical power systems. One of the main problems in LV networks is related to load voltage stabilization close to the nominal value. Usually this problem is solved by Smart Distribution Transformers, Hybrid Transformers and Solid-state Transformers, but also Dynamic Voltage Conditioner (DVC) can be an innovative and a cost effective solution. The paper introduces a new control method of a single-phase DVC system able to compensate these long duration voltage drifts. For these events, it is mandatory to avoid active power exchanges so,  the controller is designed to work with non-active power only. Operation limits for quadrature voltage injection control is formulated and reference voltage update procedure is proposed to guarantee its continuous operating. DVC performance for main voltage and load variation is examined. Proposed solution is validated with simulation study and experimental laboratory tests. Some simulation and experimental results are illustrated to show the prototype device’s performance.

KEYWORDS:

          Power Quality

          Power conditioning

         Power electronics

        Dynamic Voltage Conditioner DVC

        DVR

        LV Distribution System

        Smart Grid

 SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation - DVC operation limit update procedure under voltage - limits due to : Case 2.b) – (a) grid and minimum grid voltage, (b) PCC and PCC reference voltage, (c) load power factor.

 Fig. 3. Experimental - DVC response to load variation, adding and removing the load – (a),(d) PCC voltage, (b),(e) DVC injected voltage, (c),(f) load current.

CONCLUSION

A new device concept, which goes beyond typical DVR functionalities, is presented. The proposed device is named DVC (Dynamic Voltage Conditioner), it is an active voltage conditioner able to cover both short- and fast-events, as a typical DVR, and long-events (in the grid voltage range from 0.9-1.1 p.u.). So it can perfectly satisfy modern power system DSO requirements. In particular the paper presents only the control strategy that can be adapted during steady state condition (long-events) for a single-phase DVC. Indeed, the steady state condition is not reported in literature and the single phase configuration seems to be the best economic solution for smart grid LV distribution system. The device controller, here introduced for first time, has been designed to operate with non-active power during steady state condition. So, to guarantee DVC continuous working, the paper describes a control method to generate DVC reference voltage considering its limits. Moreover, single-phase design can decrease device initial cost and it is also more compatible with LV distribution and mostly single-phase domestic loads.

Designed control method is verified by MATLAB based simulation and laboratory experimental test bed. Results show that, the device has good performance and it can improve  PQ level of the installed distribution Smart Grid network effectively (mainly in the grid voltage range from 0.9-1.1 p.u.). This is essential for nowadays modern network because the proposed DVC can give flexibility to the system operator in order to move all problematic single-phase loads on a specific phase (where the DVC is installed).

Even if the paper analyzed a single-phase system, all the theoretical analysis on device limits can be extended for three phase system and it will be addressed in future works. It should be noted that, this solution since it injects the compensation voltage in quadrature to line current, creates phase shifting on installed phase voltage so, it can impose voltage unbalance issues to the

supplied three-phase loads. Therefore this device can be used effectively in LV distribution network with single phase loads only.

 REFERENCES:

[1]     “IEEE recommended practice for monitoring electric power quality,” IEEE Std 1159-2009 (Revision of IEEE Std 1159-1995), pp. c1–81, June 2009.

[2]     C. Sankaran, Power quality. CRC press, 2001.

[3]     “IEEE application guide for IEEE std 1547(TM), IEEE standard for interconnecting distributed resources with electric power systems,” IEEE Std 1547.2-2008, pp. 1–217, April 2009.

[4]     E. Standard, “50160,” Voltage characteristics of public distribution systems, 2010.

[5]     H. Farhangi, “The path of the smart grid,” IEEE Power and Energy Magazine, vol. 8, no. 1, pp. 18–28, January 2010.

Investigation on cascade multilevel inverter with symmetric, asymmetric, hybrid and multi-cell configurations

 ABSTRACT:  

In recent past, numerous multilevel architectures came into existence. In this background, cascaded multilevel inverter (CMLI) is the promising structure. This type of multilevel inverters synthesizes a medium voltage output based on a series connection of power cells which use standard low-voltage component configurations. This characteristic allows one to achieve high-quality output voltage and current waveforms. However, when the number of levels increases switching components and the count of dc sources are also increased. This issue became a key motivation for the present paper. The present paper is devoted to investigate different types of CMLI which use less number of switching components and dc sources and finally proposed a new version of Multi-cell based CMLI. In order to verify the proposed topology, MATLAB – simulations and hardware verifications are carried out and results are presented.

KEYWORDS:

1.      Cascade multilevel inverter

2.      Multi-cell

3.      Switching components

4.      High quality output voltages

SOFTWARE: MATLAB/SIMULINK

 INVESTIGATION ON CASCADE MULTILEVEL INVERTER:

Figure 1 (a) CHB multilevel inverter, (b) key waveform for seven-level inverter, (c) CHB multilevel inverter by employing single-phase transformers, (d) simulation verification of seven-level CHB multilevel inverter, (e) FFT spectrum.

Figure 2 (a) Asymmetrical thirteen-level CHB inverter, (b) simulation verification of thirteen-level CHB multilevel inverter, (c) FFT spectrum.

Figure 3 (a) Asymmetrical CHB multilevel inverter, (b) output voltages of each H-bridge module, (c) twenty-seven level output voltage waveform, (d) FFT spectrum.

Figure 4 (a) Asymmetrical CHB multilevel inverter using sub-cells, (b) output voltage of sub-cells, (c) thirty-one level output voltage waveform, (d) FFT spectrum.

Figure 5 (a) Hybrid CHB multilevel inverter, (b) output voltage of each H-bridge and load voltage (nine-level) waveform, (c) FFT spectrum.

Figure 6 (a) Hybrid multilevel inverter using traditional inverter, (b) output voltage waveform, (c) FFT Spectrum.

Figure 7 The proposed multi-cell CMLI.

.

Figure 8 (a) The proposed 25-level asymmetric multi-cell CMLI, (b) key waveforms.

Figure 9 (a) Output voltage of first H-bridge, (b) output voltage of second H-bridge, (c) resultant output voltage with 25-levels, (d) FFT spectrum.

CONCLUSION:

In this paper CMLI with sub-cells is proposed with less number of switches. To highlight the merits of proposed inverter, an in-depth investigation is carried out on symmetric, asymmetric and hybrid multilevel inverters based on CHB topologies. Symmetric configuration has capacity to produce only limited number of levels in output voltage. On the counter side, symmetrical configuration can be operated in asymmetrical mode with different DC sources. However, asymmetrical configurations can produce higher number of output levels and thereby qualitative output waveforms could be generated. Later, hybrid CHB inverters are also introduced, which utilizes single DC source for entire structure. Thus complexity and voltage balancing issues can be reduced. Finally proposed inverter is introduced with less number of switching components and able to produce qualitative output waveforms. To verify the proposed inverter adequate simulation is done with help of MATLAB simulink. Later on, hardware variations are carried out in laboratory. Verifications are quite impressive with greater number of levels in the output voltage and lower harmonic content in FFT spectrums. Spectrums indicate that, low order harmonics are drastically reduced. Thus power quality is significantly enhanced. Thus proposed inverter shows some promising attributes when compared with traditional CHB based architectures.

REFERENCES:

[1] Babaei E, Alilu S, Laali S. A new general topology for cascaded multilevel inverters with reduced number of components based on developed H-bridge. IEEE Trans Ind Electron 2014;61(8):3932–9.

[2] Malinowski Mariusz, Gopakumar K, Rodriguez Jose, Pe´rez Marcelo A. A survey on cascaded multilevel inverters. IEEE Trans Ind Electron 2010;57(7):2197–205.

[3] Wu JC, Wu KD, Jou HL, Xiao ST. Diode-clamped multi-level power converter with a zero-sequence current loop for three-phase three-wire hybrid power filter. Elsevier J Electr Power Syst Res2011;81(2):263–70.

[4] Khoucha Farid, Lagoun Mouna Soumia, Kheloui Abdelaziz, Benbouzid Mohamed El Hachemi. A comparison of symmetrical and asymmetrical three-phase H-bridge multilevel inverter for DTC induction motor drives. IEEE Trans Energy Convers 2011;26(1):64–72.

[5] Ebrahimi J, Babaei E, Gharehpetian GB. A new topology of cascaded multilevel converters with reduced number of components for high-voltage applications. IEEE Trans Power Electron 2011;26(11):3119–30.