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  2. What is Power quality ? • Definition : “Power quality problem is any power problem manifested in voltage, current, or frequency deviation that results in failure or misoperation of customer equipment”. • Power quality can be simply defined as shown in the interaction diagram: • Harmonics • Waveform Distortion • Voltage Sags • Voltage Swells • Blackouts/Brownouts • Transient • Arc Type • Temporal • Converter Type • Saturation Type • NLL-Analog/Digital Switching • Inrush • Overcurrent • Flickering

  3. Why are we concerned about PQ The Main reasons behind the growing concern about PQ are: • North American industries lose Tens-of-Billions of Dollars every year in downtime due to power quality problems. (Electrical Business Magazine) • Load nonlinearities in rising and is expected to reach 50 to 70% in the year 2005 (Electric Power Research Institute) [Computers, UPS, fax machines, printers, fluorescent lighting, ASD, industrial rectifiers, DC drives, arc welders, etc). • The characteristics of the electric loads have changed. • Harmonics are continuous problem not transient or intermittent.

  4. Power Quality Issue and Problems Power Quality issues can be roughly broken into a number of sub-categories: • Harmonics (sub, super and interharmonics); • Voltage swells, sags, fluctuations, flicker, and transients • Voltage magnitude and frequency deviation, voltage imbalance (3ph sys.) • Hot grounding loops and ground potential rise (GPR)–Safety & Fire Hazards • Monitoring and measurement.

  5. Power Quality PQ Issue Harmonics and NLL issues: • The harmonic issue (waveform distortion) is a top priority to for all equipment manufacturer, users and Electric Utilities (New IEC, ANSI, IEEE Standards).

  6. SYSTEM MODELS Single Line Diagram of Radial Utilization System

  7. Nonlinear Load Models Volt-Ampere (VL – IL) Arc Type Cyclical Load Temporal time-dependent (Cyclical load)

  8. Nonlinear Load Models Volt-Ampere (VL – IL) Industrial Motorized Load Cyclical Motorized Modulated Fanning Effect Converter-Rectifier Modulated

  9. Nonlinear Load Models Volt-Ampere (VL – IL) Limiter Type Switch Mode Power Supply (SMPS) FL-Starter Ballast Nonlinear Magnetic Saturation type

  10. Nonlinear Load Models Volt-Ampere (VL – IL) Adjustable Speed Drive (ASD) Dual Loop Nonlinear

  11. Switched Modulated Power Filters and Capacitor Compensators Dual-Tuned-Arm Filter TAF + Static Capacitor Compensator Tuned-Arm Filter (TAF) Asymmetrical Tuned-Arm Filter (ATAF) C-Type Filter MPF/SPF(Family of Filters – Compensators) Developed by Dr. A. M. Sharaf

  12. Switched Modulated Power Filters and capacitor Compensators Economic Tuned-Arm Power Filter and Capacitor Compensator Scheme (used in S-phase 2 wire loads) • Motorized Inrush Loads • Water Pumps • A/C • Refrigeration • Blower / Fans Switched Capacitor Compensator Scheme (used for on/off Motorized loads)

  13. Novel Dynamic Tracking Controllers (Family of Smart Controllers Developed by Dr. A. M. Sharaf) • The Dynamic Control Strategies are: • Dynamic minimum current ripple tracking • Dynamic minimum current level • Dynamic minimum power tracking • Dynamic minimum effective power ripple tracking • Dynamic minimum RMS source current tracking • Dynamic maximum power factor • Minimum Harmonic ripple content • Minimum reference harmonic ripple content • Electric Power/Energy Savings • Improve Supply PQ by reducing Harmonics and improve power factor and enhance waveforms as close as possible to sine wave

  14. Novel Dynamic Controllers Dynamic Minimum-RMS Current tracking Minimum Harmonic Reference Content

  15. Switching Devices (on/off or PWM) The solid-state switches (S1, S2) are usually (GTO, IGBT/bridge, MOSFET/bridge, SSR, TRIAC) turns “ON” when a pulse g(t) is applied to its control gate terminal by the activation switching circuit. Removing the pulse will turn the solid-state switch “OFF” TS/W=1/fS = (ton + toff) 0<ton<TS/W

  16. Switching Devices – PWM Circuits (1) PWM Circuit (Developed by Dr. C. Diduch) for use with Matlab/Simulink (2) PWM Circuit (Matlab/Simulink/Stateflow-Grundlagen)

  17. Concept of Modulated Power Filters (MPF) The Linear Combination of two Unit Step Functions to describe a Pulse of Amplitude 1 and duration t0. Tune Arm Filter layout

  18. Modulated Tuned Arm Filter (Sym. & Asym.) • Load is either: • Symmetrical Arc Type • SMPS • Adjustable Speed Drives • Asymmetrical Arc-type • Dynamic Controller: • -Min. effec. Power • RMS current tracking • Min. Harmonic Content Single Line Diagram of System and Modulated / PWM Tuned-Arm Filter

  19. Modulated Tuned Arm Filter with (SMPS) Load Without (THD=74%) With (THD=9%)

  20. Modulated Asymmetrical Tuned-Arm Filter Without (THD=42%) With (THD=14%) With (THD=7%) Without (THD=18%) Nonlinear Temporal Load Parameters: R1=R01+R11sin(wr1*t); E1=E01+E11sin(wr2*t); R2=R02+R22sin(wr1*t); E2=E02+E22sin(wr2*t); R2= R1(1+) R01=8 R02=12 R11=2 R22=6 wr1=15 E2= -E1(1+)E01= 46 E02=70 E11=12 E22=35 wr2=5 Dynamic Controller: Dual loop of RMS current tracking and Min. Harmonic Content

  21. A Low-cost Voltage Stabilization and Power Quality Enhancement Scheme for a Small Renewable Wind Energy Scheme Professor Dr. Adel M. Sharaf. P.Eng. UNB-ECE Dept Canada

  22. OUTLINE • Introduction • System Description • Novel PWM Switching Control Scheme • Modulated Power Filter Compensator • Simulation Results • Conclusion

  23. Introduction • Motivation of renewable wind energy • Fossil fuel shortage and its escalating prices • Reducing environmental pollution caused by conventional methods for electricity generation

  24. Introduction • Challenges of the reliability of wind power system • Load excursion • Wind velocity variation • Conventional passive capacitor compensation devices become ineffective

  25. System Description • Self-excited induction generator (SEIG) • Transformers and short feeder • Hybrid loads: linear load and non-linear load • The modulated power filter compensator (MPFC)

  26. Novel PWM Switching Control Scheme

  27. Novel PWM Switching Control Scheme • Multi-loop dynamic error driven • The voltage stabilization loop • The load bus dynamic current tracking loop • The dynamic load power tracking loop • Using proportional, integral plus derivative (PID) control scheme • Simple structure and fast response

  28. Novel PWM Switching Control Scheme • Objective: • To stabilize the voltage under random load and wind speed excursion • Maximize power/energy utilization • The control gains (Kp, Ki) are selected using a guided trial and error method to minimize the objective function, which is the sum of all three basic loops.

  29. The Functional Model of MPFC • The capacitor bank and the RL arm are connected by a 6-pulse diode to block the reverse flow of current. • Capacitor size normally selected as 40%-60% of the non-linear load KVAR capacitor.

  30. Proposed MPFC Scheme and Its Functional Model

  31. Simulation Results • Digital simulation environment: • MATLAB 7.0.1/SIMULINK • Sequence of load excursion: • From 0s to 0.2s: Both Linear Load 200 kVA (50%) and nonlinear Load 200 kVA (50%) connected • From 0.2s to 0.4s: Linear Load 200 kVA(50%) connected only • From 0.4s to 0.6s: No load is connected

  32. System Dynamic Response Without MPFC

  33. System Dynamic Response With MPFC

  34. Error plane of the dynamic error driven controller

  35. Conclusions • The digital simulation results validated that the proposed low cost MPFC scheme is effective in voltage stabilization for both linear and nonlinear electrical load excursions. • The proposed MPFC scheme will be easily integrated in renewable wind energy standalone units in the range from 600kW to 1600kW.

  36. Reference • [1] A.M.Sharaf and Liang Zhao, ‘A Novel Voltage Stabilization Scheme for Standalone Wind Energy Using a Facts Dual Switching Universal Power Stabilization Scheme’, 2005 • [2] M.S. El-Moursi and Adel M. Sharaf, 'Novel STATCOM controller for voltage stabilization of wind energy scheme', Int. J. Global Energy Issues, 2006. • [3] A. M. Sharaf and Guosheng Wang, ‘Wind Energy System Voltage and Energy Enhancement Using Low Cost Dynamic Capacitor Compensation Scheme’, 2004. • [4] A.M. Sharaf and Liang Yang, 'A Novel Efficient Stand-Alone Photovoltaic DC Village Electricity Scheme’, 2005

  37. Reference • [5] Pradeep K. Nadam, Paresk C. Sen, 'Industrial Application of Sliding Mode Control', IEEE/IAS International Conference On Industrial Automation and Control, Proceedings, pp. 275-280, 1995 • [6] Paresk C. Sen, 'Electrical Motor and Control-Past, Present and Future', IEEE Transactions on Industrial Electronics, Vol.37, No.6, pp.562-575, December 1990 • [7] Edward Y.Y. Ho, Paresk C. Sen, 'Control Dynamics of Speed Drive System Using Sliding Mode Controllers with Integral Compensation', IEEE Transactions on Industry Applications, Vol.21, NO.5, pp 883-892, September/October 1991.

  38. A FACTS based Dynamic Capacitor Scheme for Voltage Stabilization and Power Quality Enhancement

  39. Abstract • Power Quality voltage problems in a power system may be either at system frequency or due to transient surges with higher frequency components. • These are called switching-type over-voltages which can be produced during opening or closing a switch and can be severe in certain cases. • The paper presents a low-cost FACTS based dynamic capacitor compensator DCC- scheme for voltage compensation and power quality enhancement. • The FACTS –DCC dynamic compensator is a member of a family of smart power low cost compensators developed by the First Author.

  40. The growing use of nonlinear industrial type or inrush type electric loads can cause a real challenge to power quality for electric utilities around the world, especially in the current era of the unregulated power market where: competition, supply quality, security and reliability are key issues for any economic survival. Power Quality over voltage conditions in a power system may be either at system frequency or due to transient surges with higher frequency components. With EHV transmission systems, lightning is less of a problem because lightning surges rarely reach the impulse withstand voltage of the system equipment, e.g. 400 kV circuit breakers are impulse tested with an impulse 1425 kV , (1 us wave front to peak voltage and 50% of peak voltage). In EHV systems, switching surges thus become relatively more important [1]. Introduction

  41. Cont. / Introduction • The problem of the dynamic switching overvolatges affects also voltage stability of large non linear / motorized loads. It can increase the transmission line losses, and decrease the overall power factor [8]. • Solid state AC controllers are widely Solid state AC controllers are widely used to convert AC power for feeding number of electrical loads such as adjustable speed drives, arc furnaces, power supplies etc. • Some of theses power converter controllers behave as nonlinear loads because they generally draw a non- sinusoidal current from AC sources. • The paper presents a new low cost FACTS based dynamic compensator scheme (DCC) for improving the voltage stability and enhancing power quality for hybrid linear/nonlinear and motorized load.

  42. The System under study Fig.1 (a) depicts the single line diagram of the sample radial 138 kV (L-L) AC Power System.

  43. Fig.1 (b) shows the MATLAB block diagram. MATLAB Sim-Power System Model

  44. The MATLAB Sim-Power System functional model of the hybrid (linear, non linear and motorized) load is shown in Fig.2.

  45. New Dynamic Capacitor Compensator (DCC) scheme comprising a switched power filter

  46. Controller Design Fig.4 shows the proposed novel Tri-loop (PI) Proportional plus Integral, dynamic error driven sinusoidal SPWM switching controller.

  47. Cont. / Controller Design • The Tri-loop dynamic controller is used to stabilize the load bus voltage by regulated pulse width switching of the two IGBT solid state switches. The three regulating key loops are: • Loop 1 – the main loop for the dynamic voltage error using the RMS voltage at the load bus; this loop is to maintain the voltage at the load bus at a reference value by modulating the admittance of the compensator. • Loop 2– the dynamic error is using RMS dynamic load current. This loop is an auxiliary loop to compensate for any sudden electrical load excursions. • Loop 3 – the Harmonic ripple loop is used to provide an effective dynamic tracking control to suppress any sudden current ripples and compensate the AC system power transfer capability even under switching excursions.

  48. The following Figures show the load voltage, current, and active power, reactive power, the active vs. reactive power, and the transmitted power loss; without the proposed low cost FACTS Dynamic Capacitor Compensator (DCC).

  49. The following Figures show the load voltage, current, and active power, reactive power, the active vs. reactive power, with the proposed low cost FACTS Dynamic Capacitor Compensator (DCC).

  50. Conclusions • The paper presents a low cost FACTS Based Capacitor Compensator (DCC) for a radial 138 kV L-L sample test system. Digital simulation and comparison between without and with figures validated the following: • The receiving load bus voltage without the FACTS Based Capacitor Compensator (DCC) was about 0.66 pu when reaching steady state. Using the FACTS (DCC) compensator it is increased to about 0.96 pu (which is acceptable -5% from 1 pu). • The receiving load bus current is increased from 0.36 pu to 0.62 pu with the FACTS Based Capacitor Compensator (DCC). • The received active power at the hybrid load bus is increased from 0.36 pu to 0.95 pu. • The received reactive power at the hybrid load side is decreased from 0.2 pu to -0.5pu. • The receiving end power factor is also increased from 0.832 lag to 0.95 lag. • The transmitted power loss is decreased from 0.042 pu to 0.017 pu (about 40% less).

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