A Control Technique for Integration of DG Units to the Electrical Networks

ABSTRACT:

This paper deals with a multi objective control technique for integration of distributed generation (DG) resources to the electrical power network. The proposed strategy provides compensation for active, reactive, and harmonic load current components during connection of DG link to the grid. The dynamic model of the proposed system is first elaborated in the stationary reference frame and then transformed into the synchronous orthogonal reference frame. The transformed variables are used in control of the voltage source converter as the heart of the interfacing system between DG resources and utility grid. By setting an appropriate compensation current references from the sensed load currents in control circuit loop of DG, the active, reactive, and harmonic load current components will be compensated with fast dynamic response, thereby achieving sinusoidal grid currents in phase with load voltages, while required power of the load is more than the maximum injected power of the DG to the grid. In addition, the proposed control method of this paper does not need a phase-locked loop in control circuit and has fast dynamic response in providing active and reactive power components of the grid-connected loads. The effectiveness of the proposed control technique in DG application is demonstrated with injection of maximum available power from the DG to the grid, increased power factor of the utility grid, and reduced total harmonic distortion of grid current through simulation and experimental results under steady-state and dynamic operating conditions.

KEYWORDS:

1.      Digital signal processor

2.      Distributed generation (DG)

3.      Renewable energy sources

4.      Total harmonic distortion (THD)

5.      voltage source converter (VSC)

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. General schematic diagram of the proposed control strategy for DG system.

EXPECTED SIMULATION RESULTS:

Fig. 2. Load voltage, load, grid, and DG currents before and after connection

of DG and before and after connection and disconnection of additional load into

the grid.

Fig. 3. Grid, load, DG currents, and load voltage (a) before and after connection

of additional load and (b) before and after disconnection of additional

load.

Fig. 4. Phase-to-neutral voltage and grid current for phase (a).

Fig. 5. Reference currents track the load current (a) after interconnection of

DG resources and (b) after additional load increment.

Fig. 6. Load voltage, load, grid, and DG currents during connection of DG

link to the unbalanced grid voltage.

CONCLUSION:

A multi objective control algorithm for the grid-connected converter-based DG interface has been proposed and presented in this paper. Flexibility of the proposed DG in both steady-state and transient operations has been verified through simulation and experimental results.

Due to sensitivity of phase-locked loop to noises and distortion, its elimination can bring benefits for robust control against distortions in DG applications. Also, the problems due to synchronization between DG and grid do not exist, and DG link can be connected to the power grid without any current overshoot. One other advantage of proposed control method is its fast dynamic response in tracking reactive power variations; the control loops of active and reactive power are considered independent. By the use of the proposed control method, DG system is introduced as a new alternative for distributed static compensator in distribution network. The results illustrate that, in all conditions, the load voltage and source current are in phase and so, by improvement of power factor at PCC, DG systems can act as power factor corrector devices. The results indicate that proposed DG system can provide required harmonic load currents in all situations. Thus, by reducing THD of source current, it can act as an active filter. The proposed control technique can be used for different types of DG resources as power quality improvement devices in a customer power distribution network.

REFERENCES:

[1] T. Zhou and B. François, “Energy management and power control of a hybrid active wind generator for distributed power generation and grid integration,” IEEE Trans. Ind. Electron., vol. 58, no. 1, pp. 95–104, Jan. 2011.

[2] M. Singh, V. Khadkikar, A. Chandra, and R. K. Varma, “Grid interconnection of renewable energy sources at the distribution level with power quality improvement features,” IEEE Trans. Power Del., vol. 26, no. 1, pp. 307–315, Jan. 2011.

[3] M. F. Akorede, H. Hizam, and E. Pouresmaeil, “Distributed energy resources and benefits to the environment,” Renewable Sustainable Energy Rev., vol. 14, no. 2, pp. 724–734, Feb. 2010.

[4] C. Mozina, “Impact of green power distributed generation,” IEEE Ind. Appl. Mag., vol. 16, no. 4, pp. 55–62, Jun. 2010.

[5] B. Ramachandran, S. K. Srivastava, C. S. Edrington, and D. A. Cartes, “An intelligent auction scheme for smart grid market using a hybrid immune algorithm,” IEEE Trans. Ind. Electron., vol. 58, no. 10, pp. 4603–4611, Oct. 2011.

Fuzzy Controller for Three Phases Induction Motor Drives

ABSTRACT:

Because of the low maintenance and robustness induction motors have many applications in the industries. Most of these applications need fast and smart speed control system. This paper introduces a smart speed control system for induction motor using fuzzy logic controller. Induction motor is modeled in synchronous reference frame in terms of dq form. The speed control of induction motor is the main issue achieves maximum torque and efficiency. Two speed control techniques, Scalar Control and Indirect Field Oriented Control are used to compare the performance of the control system with fuzzy logic controller. Indirect field oriented control technique with fuzzy logic controller provides better speed control of induction motor especially with high dynamic disturbances. The model is carried out using Matlab/Simulink computer package. The simulation results show the superiority of the fuzzy logic controller in controlling three-phase induction motor with indirect field oriented control technique.

KEYWORDS:

1.      Vector control

2.      Fuzzy logic

3.      Induction motor drive

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1. Block diagram of scalar controller for IM.

Fig. 2. Indirect Field Oriented Control of IM.

EXPECTED SIMULATION RESULTS:

Fig. 3. Speed response of scalar and vector control

Fig 4. Torque response of scalar and vector control.

 Fig. 5. Flux response of scalar control.

Fig. 6. Flux response of vector control.

CONCLUSION:

Fuzzy logic controller shows fast control response with three-phase induction motor. Two different control techniques are used with Fuzzy logic controllers which are scalar and field oriented control techniques. Fuzzy logic controller system shows better response with these two techniques. Meanwhile, the scalar controller has a sluggish response than FOC because of the inherent coupling effect in field and torque components. However, the developed fuzzy logic control with FOC shows fast response, smooth performance, and high dynamic response with speed changing and transient conditions.

REFERENCES:

[1] A. Mechernene, M. Zerikat and M. Hachblef, “Fuzzy speed regulation for induction motor associated with field-oriented control”, IJ-STA, volume 2, pp. 804-817, 2008.

[2] Leonhard, W.,” Controlled AC drives, a successful transfer from ideas to industrial practice”, CETTI, pp: 1-12, 1995.

[3] M. Tacao, “Commandes numérique de machines asynchrones par lagique floue”, thése de PHD, Université de Lava- faculté des science et de génie Québec, 1997.

[4] Fitzgerald, A.E. et al., Electric Machinery, 5th Edn, McGraw-Hill, 1990.

[5] Marino, R., S. Peresada and P. Valigi, “Adaptive input-output linearizing control of induction motors”, IEEE Trans. Autom. Cont., 1993.

Power Quality Improvement in Conventional Electronic Load Controller for an Isolated Power Generation

ABSTRACT:

This paper deals with the power quality improvement in a conventional electronic load controller (ELC) used for isolated pico-hydropower generation based on an asynchronous generator (AG). The conventional ELC is based on a six-pulse uncontrolled diode bridge rectifier with a chopper and an auxiliary load. It causes harmonic currents injection resulting distortion in the current and terminal voltage of the generator. The proposed ELC employs a 24-pulse rectifier with 14 diodes and a chopper. A polygon wound autotransformer with reduced kilovolts ampere rating for 24-pulse ac–dc converter is designed and developed for harmonic current reduction to meet the power quality requirements as prescribed by IEEE standard-519. The comparative study of two topologies, conventional ELC (six-pulse bridge-rectifier-based ELC) and proposed ELC (24-pulse bridge-rectifier-based ELC) is carried out in MATLAB using SIMULINK and Power System Block set toolboxes. Experimental validation is carried out for both ELCs for regulating the voltage and frequency of an isolated AG driven by uncontrolled pico-hydro turbine.

KEYWORDS:

1.      Electronic load controller (ELC)

2.       Isolated asynchronous generator (IAG)

3.      Pico-hydro turbine

4.      24-pulse bridge rectifier.

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1. IAG system configuration and control strategy of a chopper switch in

a six-pulse diode bridge ELC.

 EXPECTED SIMULATION RESULTS:

Fig. 2. Simulated transient waveforms of IAG on application and removal of consumer load using six-pulse diode-bridge-rectifier-based ELC.

Fig. 3. Simulated transient waveforms on application and removal of consumer load using 24-pulse rectifier-based ELC.

Fig. 4. Waveforms and harmonic spectra of (a) conventional six-pulse ELC current (i_da ), (b) generator voltage (v_a), and (c) generator current (i_a ) under the zero consumer load conditions.

Fig. 5. Waveforms and harmonic spectra of (a) proposed 24-pulse ELC current (i_da ), (b) generator voltage (v_a ), and (c) generator current (i_a ) under the zero consumer load conditions.

 CONCLUSION:

The proposed ELC has been realized using 24-pulse converter and a chopper. A comparative study of both types of ELCs (6-pulse and 24-pulse configured ELC) has been demonstrated on the basis of simulation using standard software MATLAB and developing a hardware prototype in the laboratory environment. The proposed 24-pulse ELC has given improved performance of voltage and frequency regulation of IAG with negligible harmonic distortion in the generated voltage and current at varying consumer loads.

REFERENCES:

[1] B. Singh, “Induction generator—A prospective,” Electr. Mach. Power Syst., vol. 23, pp. 163–177, 1995.

[2] R. C. Bansal, T. S. Bhatti, and D. P. Kothari, “Bibliography on the application of induction generator in non conventional energy systems,” IEEE Trans. Energy Convers., vol. EC-18, no. 3, pp. 433–439, Sep. 2003.

[3] G. K. Singh, “Self-excited induction generator research—A survey,” Electr. Power Syst. Res., vol. 69, no. 2/3, pp. 107–114, May 2004.

[4] R. C. Bansal, “Three phase isolated asynchronous generators: An overview,” IEEE Trans. Energy Convers., vol. 20, no. 2, pp. 292–299, Jun. 2005.

[5] O. Ojo, O. Omozusi, and A. A. Jimoh, “The operation of an inverter assisted single phase induction generator,” IEEE Trans. Ind. Electron., vol. 47, no. 3, pp. 632–640, Jun. 2000.

A Control Strategy for Unified Power Quality Conditioner

ABSTRACT:

 This paper presents a control strategy for a Unified Power Quality Conditioner. This control strategy is used in three-phase three-wire systems. The UPQC device combines a shunt-active tilter together with a series-active filter in a hack to- back configuration, to simultaneously compensate the supply voltage and the load current. Previous works presented a control strategy for shunt-active filter that guarantees sinusoidal, balanced and minimized source currents even if under unbalanced and / or distorted system voltages, also known as “Sinusoidal Fryze Currents”. Then, this control strategy was extended to develop a dual control strategy for series-active filter. Now, this paper develops the integration principles of shunt current compensation and series voltages compensation, both based on instantaneous active and non-active powers, directly calculated from a-b-c phase voltages and line currents. Simulation results are presented to validate the proposed UPQC control strategy.

KEYWORDS:

1.      Active Filters

2.      Active Power Line Conditioners

3.      Instantaneous Active and Reactive Power

4.      Sinusoidal Fryze Currents

5.      Sinusoidal Fryze Voltages

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1 . General configuration of the Unified Power Quality Conditioner - UPQC.

 EXPECTED SIMULATION RESULTS:

Fig. 2: Load current. current of the shunt active filter and source current.

Fig 3 Supply voltage. compensating voltage and the compensated voltage delivered to the critical load

Fig. 4. DC link voltage signal v_DC and DC voltage regulator signal G_loss

Fig. 5. Source currents, compensated voltages  and the compensated

voltage V_aw together with the source current l

CONCLUSION:

A control strategy for Unified Power Quality Conditioner - the UPQC - is proposed. Simulation results have validated the proposed control strategy, for the use in three-phase three-wire systems. In case of using in three phase four-wire systems, there is the necessity of compensating the neutral current. In this case, three-phase four wire PWM converter is necessary.

The computational efforts to develop the proposed control strategy is reduced, if compared with pq-Theory based controllers, since the α-β-0 transformation is avoided. For three-phase three-wire systems, the performance of the proposed approach is comparable with those based on the pq Theory, without loss of robustness even if operating under distorted and unbalanced system voltage conditions.

Presently, the authors are working on the possibility of extending the proposed control strategy for the use in three phase four-wire systems.

REFERENCES:

[1] S. Fryze. "Wirk-. Blind- und Scheinleistung in elektrischen Stromkainsen mit nicht-sinusfomigen Verlauf von Strom und Spannung." ETZ-Arch. Elektrotech.. vol. 53. 1932, pp. 596-599. 625-627. 700-702.

[2] L. Malesani. L. Rosseto. P. Tenti. "Active Filter for Reactive Power and Harmonics Compensation", IEEE - PESC 1986. pp. 321-330.

[3] Luis F.C. Monteiro, M. Aredes. "A Comparative Analysis among Different Control Strategies for Shunt Active Filters." Proc. (CDROM) of the V INDUSCON - Conferencia de Aplicacoes In dustriais. Salvador. Brazil, July 2002. pp.345-350.

[4] T. Furuhashi, S . Okuma. Y. Uchikawa, "A Study on the Theory of Instantaneous Reactive Power," IEEE Trans. on Industrial Electronics. vol. 37. no. 1. pp. 86-90. Feb. 1990.

[5] L. Rossetto, P. Tenti. "Evaluation of Instantaneous Power Terms in Multi-Phase Systems: Techniques and Application to Power- Conditioning Equipments." ETEP - Eur.. Trans.elect. Po wer Eng . vol. 4. no. 6. pp. 469-475, Nov./Dec. 1994.