Power Quality Improvement of Unbalanced Power System with Distributed Generation Units

Power Quality Improvement of Unbalanced Power System with

Distributed Generation Units

ABSTRACT:

This paper presents a power electronic system for improving the power quality of the unbalanced distributed generation units in three-phase four-wire system. In the system, small renewable power generation units, such as small PV generator, small wind turbines may be configured as single phase generation units. The random nature of renewable power sources may result in significant unbalance in the power network and affect the power quality. An electronic converter system is proposed to correct the system unbalance and harmonics so as to deal with the power quality problems. The operation and control of the converter are described. Simulation results have demonstrated that the system can effectively correct the unbalance and enhance the system power quality.

KEYWORDS:

1.      Component

2.      Distributed generation

3.      Voltage source converter

4.      Power Quality Compensator

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig.1. Instantaneous power relationship in a system and a parallel connected compensator with energy storage system

Fig.2.The connection of VSC in a three-phase four-wire system

EXPECTED SIMULATION RESULTS:

Fig.3. Feeder 1 currents and power

 

Fig.4. Feeder 2 currents and power

Fig.5. Grid currents and power

                      

Fig.6. Compensator currents and power

                     

Fig.7. Grid current fundamental component

CONCLUSION:

This paper presents a study of using a voltage source converter (VSC) based compensator to deal with the unbalance and harmonic distortion issue in the low voltage system with embedded single phase DG units. The VSC performs the functions of an interface for an energy storage system as well. The VSC is connected in parallel with the system to control the energy storage system, correct the system unbalance, remove the harmonic components and minimize the neutral current of the supply system.

REFERENCES:

[1] G..Strbac, “Impact of dispersed generation on distribution systems: a European perspective” Power Engineering Society Winter Meeting, 2002. IEEE, vol. 1, . 2002, pp. 118 –120.

[2] M. Dussart, P. Lauwers, S. Magnus, Y. Laperches, “Connection requirements for dispersed generation: evolutions of existing requirements and need for further standardization” Electricity Distribution, 2001. Part 1: Contributions. CIRED2001, Conference Publication No. 482, © IEE2001

[3] J.A.P. Lopes, “Integration of dispersed generation on distribution networks-impact studies” Power Engineering Society Winter Meeting, 2002. IEEE, vol. 1, 2002, pp. 323 –328.

[4] F. Blaabjerg, Z. Chen, S. B Kjaer, “Power Electronics as Efficient Interface in Dispersed Power Generation Systems”, IEEE Transactions on Power Electronics, vol. 19, Issue: 5, Sept. 2004, pp.1184- 1194.

[5] Z. Chen, “Three Phase Four Wire System Power Redistribution Using A Power Electronic Converter”, Power Engineering Letters, IEEE Power Eng. Rev. October, 2000, pp. 47-49.

Transient Stability Enhancement by DSSC with Fuzzy Supplementary Controller

Transient Stability Enhancement by DSSC with

Fuzzy Supplementary Controller

ABSTRACT

 The distributed flexible alternative current transmission system (D-FACTS) is a recently developed FACTS technology. Distributed Static Series Compensator (DSSC) is one example of DFACTS devices. DSSC functions in the same way as a Static Synchronous Series Compensator (SSSC), but is smaller in size, lower in price, and possesses more capabilities. Likewise, DSSC lies in transmission lines in a distributed manner. In this work, we designed a fuzzy logic controller to use the DSSC for enhancing transient stability in a two-machine, two-area power system. The parameters of the fuzzy logic controller are varied widely by a suitable choice of membership function and parameters in the rule base. Simulation results demonstrate the effectiveness of the fuzzy controller for transient stability enhancement by DSSC.

KEYWORDS

1.      D-FACTS

2.       Simulation model

3.       DSSC

4.       Transient stability Fuzzy logic controller

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1. Simulation model of two-machine system for transient stability study with DSSC.

Fig. 2. D-FACTS deployed on the power line.

Fig. 3. Circuit schematic of a DSSC module.

EXPECTED SIMULATION RESULTS:

Fig. 4. Changing the rotor angle difference (d_theta1_2) when the DSSCs entered the circuit.

             

Fig. 5. Changing the rotor angle difference (d_theta1_2) after the fault with DSSC (without supplementary fuzzy logic damping controller) and without DSSC.

 Fig. 6. Changing the angular speed of the machines after the fault with DSSC (without supplementary fuzzy logic damping controller) and without DSSC.

Fig.7. Rotor angle difference (d_theta1_2) deviation after the fault with FLC and classic controller.

Fig. 8. Machine voltage variation after the fault with FLC and classic controller.

Fig. 9. Rotor angle difference (d_theta1_2) deviation after the fault with FLC and classic damping controller and without damping controller.

Fig. 10. Machine voltage variation after the fault with FLC and classic damping controller and without damping controller.

Fig. 11. Variation of FLC output signal after the fault.

CONCLUSION:

In this study, we introduced a graphical-based simulation model of the DSSC. DSSC was placed in a sample two machine power system to increase transient stability. Simulation studies presented in the paper showed that when the DSSCs were out of service, the rotor angle between the machines (d_theta1_2) increased rapidly and two machines fell out of synchronism after fault clearing. However, when the DSSCs were in circuit, DSSCs stabilized the system even without specific controller. Subsequently, an FLC was added to the main control system of the DSSC in order to improve the transient stability margin of the system. The simulation results show that specific to this case, DSSC can stabilize the system under severe fault. Moreover, a comparative study between the FLC and conventional classic controller shows that the proposed FLC has better performance and influence in transient stability enhancement and oscillation damping

REFERENCES:

[1] Yi Guo, David J. Hil and Youyi Wang, “Global Transient Stability and Voltage Regulation for Power System,” IEEE Transaction On Power System, Vol. 16, No. 4, Nov. 2001.

[2] L. Gyugyi, “Dynamic compensation of ac transmission lines by solid-state synchronous voltage sources,” IEEE Trans. Power Delivery, 19(2), 1994, pp.904-911.

[3] P. Rao, M.L. Crow and Z.Young, “STATCOM control for power system voltage control application,” IEEE Trans. Power Delivery, 15, 2000, pp.1311-1317.

[4] H. Wang and F.Li, “Multivariable sampled regulators for the coordinated control of STATCOM ac and dc voltage,” IEE Proc. Gen. Tran. Dist., 147(2), 2000, pp. 93-98.

[5] A.H.M.A Rahim and M.F.Kandlawala, “Robust STATCOM voltage controller design using loop shaping technique,” Electric Power System Research, 68, 2004, pp.61-74.

Seventeen-Level Inverter Formed by Cascading Flying Capacitor and Floating Capacitor H-Bridges

Seventeen-Level Inverter Formed by Cascading

Flying Capacitor and Floating Capacitor H-Bridges

ABSTRACT:

A multilevel inverter for generating 17 voltage levels using a three-level flying capacitor inverter and cascaded H-bridge modules with floating capacitors has been proposed. Various aspects of the proposed inverter like capacitor voltage balancing have been presented in the present paper. Experimental results are presented to study the performance of the proposed converter. The stability of the capacitor balancing algorithm has been verified both during transients and steady state operation. All the capacitors in this circuit can be balanced instantaneously by using one of the pole voltage combinations. Another advantage of this topology is its ability to generate all the voltages from a single dc-link power supply which enables back-to-back operation of converter. Also, the proposed inverter can be operated at all load power factors and modulation indices. Additional advantage is, if one of the H-bridges fail, the inverter can still be operated at full load with reduced number of levels. This configuration has very low dv/dt and common-mode voltage variation.

KEYWORDS:

1.     Cascaded H-bridge

2.     Flying capacitor

3.     Multilevel inverter

4.     17-level inverter.

                                          

 SOFTWARE: MATLAB/SIMULINK

 CIRCUIT  DIAGRAM:

CONCLUSION:

A new 17-level inverter configuration formed by cascading a three-level flying capacitor and three floating capacitor Hbridges has been proposed for the first time. The voltages of each of the capacitors are controlled instantaneously in few switching cycles at all loads and power factors obtaining high performance output voltages and currents. The proposed configuration uses a single dc link and derives the other voltage levels from it. This enables back-to-back converter operation where power can be drawn and supplied to the grid at prescribed power factor. Also, the proposed 17-level inverter has improved reliability. In case of failure of one of the H-bridges, the inverter can still be operated with reduced number of levels supplying full power to the load. This feature enables it to be used in critical applications like marine propulsion and traction where reliability is of highest concern. Another advantage of the proposed configuration is modularity and symmetry in structure which enables the inverter to be extended to more number of phases like five-phase and six-phase configurations with the same control scheme. The proposed inverter is analyzed and its performance is experimentally verified for various modulation indices and load currents by running a three-phase 3-kW squirrel cage induction motor. The stability of the capacitor balancing algorithm has been tested experimentally by suddenly accelerating the motor at no load and observing the capacitor voltages at various load currents.

REFERENCES:

[1] J. Rodriguez, J.-S. Lai, and F. Z. Peng, “Multilevel inverters: A survey of topologies, controls, and applications,” IEEE Trans. Ind. Appl., vol. 49, no. 4, pp. 724–738, Aug. 2002.

[2] L. G. Franquelo, J. Rodriguez, J. I. Leon, S. Kouro, R. Portillo, and M. A. M. Prats, “The age of multilevel converters arrives,” IEEE Ind. Electron. Mag., vol. 2, no. 2, pp. 28–39, Jun. 2008.

[3] S. Kouro, M. Malinowski, K. Gopakumar, J. Pou, L. G. Franquelo, B.Wu, J. Rodriguez, M. A. Perez, and J. I. Leon, “Recent advances and industrial applications of multilevel converters,” IEEE Trans. Ind. Electron., vol. 57, no. 8, pp. 2553–2580, Aug. 2010.

[4] A. M. Massoud, S. Ahmed, P. N. Enjeti, and B. W.Williams, “Evaluation of a multilevel cascaded-type dynamic voltage restorer employing discontinuous space vector modulation,” IEEE Trans. Ind. Electron., vol. 57, no. 7, pp. 2398–2410, Jul. 2010.

[5] S. Rivera, S. Kouro, B.Wu, S. Alepuz,M. Malinowski, P. Cortes, and J. R. Rodriguez, “Multilevel direct power control—a generalized approach for grid-tied multilevel converter applications,” IEEE Trans. Power Electron., vol. 29, no. 10, pp. 5592–5604, Oct. 2014.

Switching Losses and Harmonic Investigations in Multilevel Inverters

ABSTRACT:

Use of conventional two-level pulse width modulation (PWM) inverters provide less distorted current and voltage but at the cost of higher switching losses due to high switching frequencies. Multilevel inverters are emerging as a viable alternative for high power, medium voltage applications. This paper compares total harmonic distortion and switching losses in conventional two-level inverters with multilevel inverters (three-level and five-level) at different switching frequencies. An optimized switching frequency has been obtained for a lower level of total harmonic distortion and switching losses. Diode-clamped, three-phase topology is considered for study. A sinusoidal PWM technique is used to control the switches of the inverter. Simulation study confirms the reduction in harmonic distortion and switching losses as the number of the levels increases.

KEYWORDS:

1.     Harmonics

2.     Multilevel inverters

3.     Pulse width modulation

4.     Switching losses

5.     Total harmonic distortion.

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

 EXPECTED SIMULATION RESULTS:

CONCLUSION:

A comparative study of THD of the output voltage waveform and switching losses of two-level, three-level and five-level three-phase diode clamped inverters has been presented in this paper using the SPWM technique. It has been observed that both THD and switching losses decrease with the increase in the number of levels in the output voltage. However, with the decrease in carrier frequency, the THD level increases and switching losses reduce proportionately. Figures 10, 12 and 14 can be referred to optimize the switching losses and harmonic contents for operation of an inverter at an optimized switching frequency. The above investigation is made without an output filter. By using suitable filters, the harmonic content can be further reduced.

REFERENCES:

1. F. Z. Peng & J. S. Lai, ‘Multilevel Converters - A new breed of power converters’, IEEE Transaction on Industry Applications, Vol. 32, No. 3, May/June, 1996, pp. 509-517.

2. Jose Rodriguez, J. S. Lai & F. Z. Peng, ‘Multilevel Inverters: A Survey of Topologies, Controls, and Applications’, IEEE Transaction on Industrial Electronics, Vol. 49, No. 4, Aug 2002, pp. 724-738.

3. Mohan Ned, Undeland T.M. & Robbins W.P., ‘Power Electronics: Converters, Applications and Design’, John Wiley and Sons, Second Edition, 2001.

4. G. Bhuvaneswari & Nagaraju, ‘Multilevel Inverters - A Comparative Study’, IETE Journal of Research, Vol. 51, No.2, Mar-Apr 2005, pp. 141-153.

5. B. Kaku, I. Miyashita & S. Sone, ‘Switching Loss Minimized Space Vector PWM Method for IGBT Three-Level Inverter’, IEE Proceedings, Electric Power Applications, Vol. 144, No. 3, May 1997, pp 182-190.

MODIFIED INCREMENTAL CONDUCTANCE ALGORITHM FOR PHOTOVOLTAIC SYSTEM UNDER PARTIAL SHADING CONDITIONS AND LOAD VARIATION

ABSTRACT:

Under partial shading conditions, multiple peaks are observed in the power–voltage (P–V ) characteristic curve of a photovoltaic (PV) array, and the conventional maximum power point tracking (MPPT) algorithms may fail to track the global maximum power point (GMPP). Therefore, this paper proposes a modified incremental conductance (Inc Cond) algorithm that is able to track the GMPP under partial shading conditions and load variation. A novel algorithm is introduced to modulate the duty cycle of the dc–dc converter in order to ensure fast MPPT process. Simulation and hardware implementation are carried out to evaluate the effectiveness of the proposed algorithm under partial shading and load variation. The results show that the proposed algorithm is able to track the GMPP accurately under different types of partial shading conditions, and the response during variation of load and solar irradiation are faster than the conventional Inc Cond algorithm. Hence, the effectiveness of the proposed algorithm under partial shading condition and load variation is validated in this paper.

KEYWORDS:

1.     DC–DC converter

2.     Incremental conductance (Inc Cond)

3.     Maximum power point tracking (MPPT)

4.     Partial shading

5.     Photovoltaic (PV) system.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 EXPECTED SIMULATION RESULTS:

CONCLUSION:

In this paper, a modified Inc Cond algorithm has been used to track the GMPP for the PV array under partial shading conditions and also load variation. A novel algorithm is used to modulate the duty cycle of the converter, and thus, the tracking speed is improved. The simulation and experimental results showed that the proposed algorithm is able to track the GMPP accurately and thus reduces the power losses faced by the conventional algorithm. The experimental results also showed that the proposed algorithm is able to respond rapidly and accurately to the variation in the load and the solar irradiation during partial shading conditions. As a conclusion, the proposed algorithm performed better in tracking the GMPP under partial shading conditions and load variation, as compared with the conventional Inc Cond algorithm.

REFERENCES:

[1] S. Mekhilef, R. Saidur, and A. Safari, “A review on solar energy use in industries,” Renew. Sustain. Energy Rev., vol. 15, no. 4, pp. 1777–1790, May 2011.

[2] S. Mekhilef, A. Safari, W. E. S. Mustaffa, R. Saidur, R. Omar, and M. A. A. Younis, “Solar energy in Malaysia: Current state and prospects,” Renew. Sustain. Energy Rev., vol. 16, no. 1, pp. 386–396, Jan. 2012.

[3] K. H. Solangi, M. R. Islam, R. Saidur, N. A. Rahim, and H. Fayaz, “A review on global solar energy policy,” Renew. Sustain. Energy Rev., vol. 15, no. 4, pp. 2149–2163, May 2011.

[4] T. Esram and P. L. Chapman, “Comparison of photovoltaic array maximum power point tracking techniques,” IEEE Trans. Energy Convers., vol. 22, no. 2, pp. 439–449, Jun. 2007.

[5] M. A. G. de Brito, L. Galotto, L. P. Sampaio, G. de Azevedo e Melo, and C. A. Canesin, “Evaluation of the main MPPT techniques for photovoltaic applications,” IEEE Trans. Ind. Electron., vol. 60, no. 3, pp. 1156–1167, Mar. 2013.