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.

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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.

Analysis and Implementation of a Novel Bidirectional DC–DC Converter

ABSTRACT:  

A novel bidirectional dc–dc converter is presented in this paper. The circuit configuration of the proposed converter is very simple. The proposed converter employs a coupled inductor with same winding turns in the primary and secondary sides. In step-up mode, the primary and secondary windings of the coupled inductor are operated in parallel charge and series discharge to achieve high step-up voltage gain. In step-down mode, the primary and secondary windings of the coupled inductor are operated in series charge and parallel discharge to achieve high step-down voltage gain. Thus, the proposed converter has higher step-up and step-down voltage gains than the conventional bidirectional dc–dc boost/buck converter. Under same electric specifications for the proposed converter and the conventional bidirectional boost/buck converter, the average value of the switch current in the proposed converter is less than the conventional bidirectional boost/buck converter. The operating principle and steady-state analysis are discussed in detail. Finally, a 14/42-V prototype circuit is implemented to verify the performance for the automobile dual-battery system.

KEYWORDS:

1.      Bidirectional dc–dc converter

2.      Coupled inductor

SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:

Fig. 1. Proposed bidirectional dc–dc converter.

 EXPECTED SIMULATION RESULTS:

Fig. 2. Some experimental waveforms of the proposed converter in step-up

mode. (a) i_L1, i_L2, and i_L, (b) i_S1, i_S2, and i_S3. (c) v_DS1, v_DS2, and v_DS3.

Fig. 3. Dynamic response of the proposed converter in step-up mode for the

output power variation between 20 and 200 W.

Fig. 4. Some experimental waveforms of the proposed converter in step down

mode. (a) i_LL, i_L1, and i_L2, (b) i_S3, i_S1, and i_S2. (c) v_DS3, v_DS1, and v_DS2.

Fig. 5. Dynamic response of the proposed converter in step-down mode for

the output power variation between 20 and 200 W.

CONCLUSION:

This paper researches a novel bidirectional dc–dc converter. The circuit configuration of the proposed converter is very simple. The proposed converter has higher step-up and step-down voltage gains and lower average value of the switch current than the conventional bidirectional boost/buck converter. From the experimental results, it is see that the experimental waveforms agree with the operating principle and steady-state analysis. At full-load condition, the measured efficiency is 92.7% in stepup mode and is 93.7% in step-down mode. Also, the measured efficiency is around 92.7%–96.2% in step-up mode and is around 93.7%–96.7% in step-down mode, which are higher than the conventional bidirectional boost/buck converter.

REFERENCES:

[1] M. B. Camara, H. Gualous, F. Gustin, A. Berthon, and B. Dakyo, “DC/DC converter design for supercapacitor and battery power management in hybrid vehicle applications—Polynomial control strategy,” IEEE Trans. Ind. Electron., vol. 57, no. 2, pp. 587–597, Feb. 2010.

[2] T. Bhattacharya, V. S. Giri, K. Mathew, and L. Umanand, “Multiphase bidirectional flyback converter topology for hybrid electric vehicles,” IEEE Trans. Ind. Electron., vol. 56, no. 1, pp. 78–84, Jan. 2009.

[3] Z. Amjadi and S. S. Williamson, “A novel control technique for a switched-capacitor-converter-based hybrid electric vehicle energy storage system,” IEEE Trans. Ind. Electron., vol. 57, no. 3, pp. 926–934, Mar. 2010.

[4] F. Z. Peng, F. Zhang, and Z. Qian, “A magnetic-less dc–dc converter for dual-voltage automotive systems,” IEEE Trans. Ind. Appl., vol. 39, no. 2, pp. 511–518, Mar./Apr. 2003.

[5] A. Nasiri, Z. Nie, S. B. Bekiarov, and A. Emadi, “An on-line UPS system with power factor correction and electric isolation using BIFRED converter,” IEEE Trans. Ind. Electron., vol. 55, no. 2, pp. 722–730, Feb. 2008.