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IEEE PESC-02JUNE 2002 1 HARMONIC TREATMENT IN INDUSTRIAL POWER SYSTEMS Presented by Stefanos Manias

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JUNE 2002IEEE PESC-02 2 CONTACT INFORMATION Stefanos N. Manias National Technical University of Athens Phone: +3010-7723503 FAX: +3010-7723593 E-mail: manias@central.ntua.grmanias@central.ntua.gr Mailing Address National Technical University of Athens Department of Electrical and Computer Engineering 9, Iroon Polytechniou Str, 15773 Zografou Athens, Greece

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JUNE 2002IEEE PESC-02 3 PLAN OF PRESENTATION 1. DEFINITIONS 2. CATEGORIES OF POWER QUALITY VARIATIONS 3. HARMONIC DISTORTION SOURCES IN INDUSTRIAL POWER SYSTEMS 4. EFFECTS OF HARMONICS ON ELECTRICAL EQUIPMENT 5. HARMONIC MEASUREMENTS IN INDUSTRIAL POWER SYSTEMS 6. HARMONIC STANDARDS 7. HARMONIC MITIGATING TECHNIQUES 8. GENERAL PASSIVE AND ACTIVE FILTER DESIGN PROCEDURES 9. DESIGN EXAMPLES 10. CONCLUSIONS

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JUNE 2002IEEE PESC-02 4 WHY HARMONIC ANALYSIS ? When a voltage and/or current waveform is distorted, it causes abnormal operating conditions in a power system such as: Voltage Harmonics can cause additional heating in induction and synchronous motors and generators. Voltage Harmonics with high peak values can weaken insulation in cables, windings, and capacitors. Voltage Harmonics can cause malfunction of different electronic components and circuits that utilize the voltage waveform for synchronization or timing. Current Harmonics in motor windings can create Electromagnetic Interference (EMI).

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JUNE 2002IEEE PESC-02 5 Current Harmonics flowing through cables can cause higher heating over and above the heating that is created from the fundamental component. Current Harmonics flowing through a transformer can cause higher heating over and above the heating that is created by the fundamental component. Current Harmonics flowing through circuit breakers and switch- gear can increase their heating losses. RESONANT CURRENTS which are created by current harmonics and the different filtering topologies of the power system can cause capacitor failures and/or fuse failures in the capacitor or other electrical equipment. False tripping of circuit breakers ad protective relays.

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JUNE 2002IEEE PESC-02 6 a) Current Source nonlinear load Diode rectifier for ac drives, electronic equipment, etc HARMONIC SOURCES Thyristor rectifier for dc drives, heater drives, etc. Per-phase equivalent circuit of thyristor rectifier b) Voltage source nonlinear load Per-phase equivalent circuit of diode rectifier

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JUNE 2002IEEE PESC-02 7 TYPE OF NONLINEAR LOAD TYPICAL WAREFORM THD% 1-φ Uncontrolled Rectifier 80% (high 3 rd component) 1-φ Semicontrolled Rectifier Bridge 2 nd, 3 rd, 4 th,...... harmonic components 6 –Pulse Rectifier with output voltage filtering and without input reactor filter 80% 5, 7, 11, ………. INPUT CURRENT OF DIFFERENT NOLINEAR LOADS

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JUNE 2002IEEE PESC-02 8 6 - Pulse Rectifier with large output inductor 28% 5, 7, 11, ……….. 6 - Pulse Rectifier with output voltage filtering and with 3% reactor filter or with continues output current 40% 5, 7, 11, ……….. 12 - Pulse Rectifier 15% 11, 13, ………..

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JUNE 2002IEEE PESC-02 9 CURRENT HARMONICS GENERATED BY 6-PULSE CSI CONVERTERS HARMONICP.U PULSE 11.00 50.2 70.143 110.09 130.077 170.059 190.053 230.04 CURRENT HARMONICS GENERATED BY 12-PULSE CSI CONVERTERS HARMONICP.U PULSEIEEE 519 std 11.00- 50.03-0.065.6% 70.02-0.065.6% 110.05-0.092.8% 130.03-0.082.8% THD7.5%-14.2%7.0%

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JUNE 2002IEEE PESC-02 10 RECENT CURRENT MEASUREMENTS TAKEN IN AN INDUSTRIAL PLANT WITH 600 KVA, 20 KV/400 V DISTRIBUTION TRANFORMER Current waveform and its respective spectrum at the inputs of a motor drive system

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JUNE 2002IEEE PESC-02 11 Current waveform and its respective spectrum at the inputs of a motor drive system

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JUNE 2002IEEE PESC-02 12 Current waveform and its respective spectrum at the secondary of the distribution transformer ( i.e. at the service entrance)

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JUNE 2002IEEE PESC-02 13 DEFINITIONS f (t) = Fourier Series of a periodic function f (t) = (1) (2) (3) (4) h = harmonic order

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JUNE 2002IEEE PESC-02 14 (5) (6) Percentage of the Total Harmonic Distortion of a nonsinusoidal voltage waveform Percentage of the Total Harmonic Distortion of a nonsinusoidal current waveform harmonic component of the voltage harmonic component of the current RMS value of the voltage distortion

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JUNE 2002IEEE PESC-02 15 (7) (8) (9) (10) RMS value of a nonsinusoidal current = RMS value of a nonsinusoidal voltage = Harmonic Factor = RMS value of the current distortion

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JUNE 2002IEEE PESC-02 16 SINUSOIDAL VOLTAGE NONSINUSOIDAL CURRENT (11) (12) (13) Full load kVA rating of the Drive system Short Circuit kVA of the distribution system at the point of connection

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JUNE 2002IEEE PESC-02 17 (14) (15) NONSINUSOIDAL VOLTAGE AND NONSINUSOIDAL CURRENT (16) (17)

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JUNE 2002IEEE PESC-02 18 (18) (19)

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JUNE 2002IEEE PESC-02 19 (20) (21) (22) (23)

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JUNE 2002IEEE PESC-02 20 Harmonic sequence is the phase rotation relationship with respect to the fundamental component. Positive sequence harmonics ( 4th, 7th, 10th, ……. (6n+1) th ) have the same phase rotation as the fundamental component. These harmonics circulate between the phases. Negative sequence harmonics ( 2nd, 5th, 8th ……… (6n-1) th ) have the opposite phase rotation with respect to the fundamental component. These harmonics circulate between the phases. Zero sequence harmonics ( 3rd, 6th, 9th, ….. (6n-3) th ) do not produce a rotating field. These harmonics circulate between the phase and neutral or ground. These third order or zero sequence harmonics, unlike positive and negative sequence harmonic currents, do not cancel but add up arithmetically at the neutral bus.

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JUNE 2002IEEE PESC-02 21 EXAMPLE 1 A periodic, sinusoidal voltage of instantaneous value Is applied to a nonlinear load impedance. The resulting instantaneous current is given by: Calculate the components P, Q, D of the apparent voltamperes and hence calculate the displacement factor, the distortion factor and the power factor. Solution The presence of the nonlinearity causes frequency components of current (i.e. the second and third harmonic terms) that are not present in the applied voltage. The rms voltage and current at the supply are: SINUSOIDAL VOLTAGE-NONSINIMUSOIDAL CURRENT

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JUNE 2002IEEE PESC-02 22 The apparent voltamperes at the input is therefore given by In this example only the fundamental frequency components are common to both voltage and current. Therefore, the real power P and the apparent power Q are = displacement angle between the fundamental of the voltage and the fundamental of the current

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JUNE 2002IEEE PESC-02 23 Displacement factor Distortion factor Therefore, the power factor is

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JUNE 2002IEEE PESC-02 24 EXAMPLE 2 A periodic, sinusoidal voltage given by is applied to a series, linear, resistance-inductance load of resistance 4Ω and fundamental frequency reactance 10Ω. Calculate the degree of power factor improvement realizable by capacitance Solution. The rms terminal voltage is given by Compensation when Therefore NONSINUSOIDAL VOLTAGE-RL LOAD

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JUNE 2002IEEE PESC-02 25 The instantaneous load current is given by The rms load currentis therefore given by

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JUNE 2002IEEE PESC-02 26 Average powerIn this case is The power factor before compensation is therefore Apparent voltamperesat the load terminals in the absence of capacitance is therefore

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JUNE 2002IEEE PESC-02 27 EXAMPLE 3 A periodic, nonsinusoidal voltage with instantaneous value given by Solution. is applied to a nonlinear impedance. The resulting current has an instantaneous value given by Calculate the componentsof the load apparent voltamperes and compare thee with the classical valuesrespectively. Note that the presence of the load nonlinearity causes a frequency component of load current (I.e. the third harmonic term) that is not present in the supply voltage. NONSINUSOIDAL VOLTAGE AND NONSINIMUSOIDAL CURRENT

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JUNE 2002IEEE PESC-02 28 The rms voltage and current at the supply are given by The load apparent voltamperestherefore has a value defined in termsand Instantaneous expressions of the hypothetical currentsare given by

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JUNE 2002IEEE PESC-02 29 Note that current componentscontain only those harmonic terms which are common to both voltage and current. These are therefore consistent with the terms. The rms load current componentsare found, as expected to sum to the total rms load current Componentsof the apparent voltamperes can now be obtained

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JUNE 2002IEEE PESC-02 30 The component voltamperes are seen to sum to the total apparent voltamperes Componentsofare found as follows:

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JUNE 2002IEEE PESC-02 31 From the possible compensation viewpoint it is interesting to note that anddiffer by significant amount. could be defined as that component of the load apparent voltamperes that Is obtained by the combination of supply voltage harmonics with quadrature Components of corresponding frequency load current harmonics.

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JUNE 2002IEEE PESC-02 32 Similarly the definition of active voltamperescould be given by that component of the load apparent voltamperes that is obtained by the combination of supply voltage harmonics with in-phase components of corresponding frequency load current harmonics. Bothandare entirely fictitious and non-physical. The active voltamperesIs not to be compares in importance with the average power which is a real physical property of the circuit. TermIs merely the analytical complement of term Term the energy-storage reactive voltamperes, is that component of the load apparent voltamperes that can be entirely compensated (for sinusoidal supply voltage) or minimized (for nonsinusoidal supply voltage) by energy-storage methods.

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JUNE 2002IEEE PESC-02 33 Voltage and current profiles in a commercial building

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JUNE 2002IEEE PESC-02 34 HARMONIC STANDARDS International Electrotechnical Commission (IEC) European Standards. - EN 61000-3-2 Harmonic Emissions standards were first published as IEC 55-2 1982 and applied only to household appliances. It was revised and reissued in 1987 and 1995 with the applicability expanded to include all equipment with input current 16A per phase. However, until January 1 st, 2001 a transition period is in effect for all equipment not covered by the standard prior to 1987. - The objective of EN 61000-3-2 (harmonics) is to test the equipment under the conditions that will produce the maximum harmonic amplitudes under normal operating conditions for each harmonic component. To establish limits for similar types of harmonics current distortion, equipment under test must be categorized in one of the following four classes.

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JUNE 2002IEEE PESC-02 35 CLASS-A: Balanced three-phase equipment and all other equipment except that stated in one of the remaining three classes. CLASS-B: Portable electrical tools, which are hand held during normal operation and used for a short time only (few minutes) CLASS-C: Lighting equipment including dimming devices. CLASS-D: Equipment having an input current with special wave shape ( e.g.equipment with off-line capacitor-rectifier AC input circuitry and switch Mode power Supplies) and an active input power 600W. - Additional harmonic current testing, measurement techniques and instrumentation guidelines for these standards are covered in IEC 1000-4-7.

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JUNE 2002IEEE PESC-02 36 IEEE 519-1992 United States Standards on harmonic limits - IEEE limits service entrance harmonics. - The IEEE standard 519-1992 limits the level of harmonics at the customer service entrance or Point of Common Coupling (PCC). - With this approach the costumers current distortion is limited based on relative size of the load and the power suppliers voltage distortion based on the voltage level. IEEE 519 and IEC 1000-3-2 apply different philosophies, which effectively limit harmonics at different locations. IEEE 519 limits harmonics primarily at the service entrance while IEC 1000-3-2 is applied at the terminals of end-user equipment. Therefore, IEC limits will tend to reduce harmonic-related losses in an industrial plant wiring, while IEEE harmonic limits are designed to prevent interactions between neighbors and the power system.

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JUNE 2002IEEE PESC-02 37 POWER QUALITY STANDARDS – IEEE 519-1992 STANDARDS TABLE I CURRENT DISTORTION LIMITS FOR GENERAL DISTRIBUTION SYSTEMS (120-69000 V ) I sc /I L <1111

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JUNE 2002IEEE PESC-02 38 TABLE II LOW VOLTAGE SYSTEM CLASSIFICATION AND DISTORTION LIMITS IEEE 519-1992 STANDARTS Special Applications General System Dedicated System Notch Depth10%20%50% THD (Voltage)3%5%10% Notch Area (A N )* 16,40022,80036,500 Source: IEEE Standard 519-1992. Note: The value A N for another than 480Volt systems should be multiplied by V/480. The notch depth, the total voltage distortion factor (THD) and the notch area limits are specified for line to line voltage. In the above table, special applications include hospitals and airports. A dedicated system is exclusively dedicated to converter load. *In volt-microseconds at rated voltage and current.

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JUNE 2002IEEE PESC-02 39 TABLE III LIMITS OF THD% IEEE 519-1992 STANDARDS SYSTEM Nominal Voltage Special Application General Systems Dedicated Systems 120-600V3.05.08.0 69KV and below-5.0-

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JUNE 2002IEEE PESC-02 40 TABLE IV PROPOSED IEC 555-2 CLASS D STANDARDS for power from 50 to 600W HarmonicRelative limits Milliamps/Watt Absolute Limits Amps 33.42.30 51.91.14 71.00.77 90.50.40 110.350.33 13linear extrapolation 0.15 (15/n)

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JUNE 2002IEEE PESC-02 41 METHODOLOGY FOR COMPUTING DISTORTION Step 1: Compute the individual current harmonic distortion at each dedicated bus using different Software programs (i.e. SIMULINK, SPICE, e.t.c.) or tables that provide the current distortion of nonlinear loads. Step 2: Compute the voltage and current harmonic content at the Point of Common Coupling (PCC) which is located at the input of the industrial power system. - Each individual harmonic current at the PCC is the sum of harmonic current contribution from each dedicated bus. - The load current at PCC is the sum of the load current contribution from each dedicated bus. - The maximum demand load current at PCC can be found by computing the load currents for each branch feeder and multiply by a demand factor to obtain feeder demand. Then the sum of all feeder demands is divided by a diversity factor to obtain the maximum demand load current.

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JUNE 2002IEEE PESC-02 42 Step 3: Choose a base MVA and base KV for the system use the following equations in order to compute individual and total current and voltage harmonic distortions at PCC and any other point within the power system. I b = Base current in Amps = System impedance = MVA b = Base MVA, MVA sc = short circuit MVA at the point of interest V H = Percent individual harmonic voltage distortion = (24) (25) (26)

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JUNE 2002IEEE PESC-02 43 h = harmonic order I H = Percent individual harmonic distortion = I sc = Short Circuit current at the point under consideration. I L = Estimated maximum demand load current S.C. Ratio = Short circuit Ratio MVA D = Demand MVA (27) (28) (29)

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JUNE 2002IEEE PESC-02 44 K Factor = Factor useful for transformers design and specifically from transformers that feed Adjustable Speed Drives ONCE THE SHORT CIRCUIT RATIO IS KNOWN, THE IEEE CURRENT HARMONIC LIMITS CAN BE FOUND AS SPECIFIED IN TABLE I OF THE IEEE 519-1992 POWER QUALITY STANDARDS USING THE ABOVE EQUATIONS VALUES OF IDIVINDUAL AND TOTAL VOLTAGE AND CURRENT HARMONIC DISTORTION CAN BE COMPUTED AND COMPARED WITH THE IEEE LIMITS (30)

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JUNE 2002IEEE PESC-02 45 Step 4: If the analysis is being performed for CSI-type drives then the area of the voltage notch A N should also be computed. - At this point an impedance diagram of the under analysis industrial power system should be available. - The Notch Area A N at the PCC can be calculated as follows. A N = A N1 + A N2 + …………. V. microsec A N1, A N2, …… are the notch areas contribution of the different busses A NDR1 : Notch area at the input of the drive (31) (32)

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JUNE 2002IEEE PESC-02 46 Step 5: Determine preliminary filter design. Step 6: Compute THD v and THD i magnitudes and impedance versus frequency plots with filters added to the system, one at a time. SIMULINK or PSPICE software programs can be used for final adjustments. Step 7: Analyze results and specify final filter design.

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JUNE 2002IEEE PESC-02 47 EXAMPLE OF A SYSTEM ONE LINE DIAGRAM

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JUNE 2002IEEE PESC-02 48 System impedances diagram which can be used to calculate its resonance using PSPICE or SIMULINK programs

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JUNE 2002IEEE PESC-02 49 1) Parallel-passive filter for current-source nonlinear loads TYPES OF FILTERS Harmonic Sinc Low Impedance Cheapest VA ratings = V T (Load Harmonic current + reactive current of the filter)

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JUNE 2002IEEE PESC-02 50 2) Series-passive filter for voltage-source nonlinear loads Harmonic dam High-impedance Cheapest VA ratings = Load current (Fundamental drop across filter + Load Harmonic Voltage)

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JUNE 2002IEEE PESC-02 51 3) Basic parallel-active filter for current source in nonlinear loads

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JUNE 2002IEEE PESC-02 52 4) Basic series-active filter for voltage-source in nonlinear loads

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JUNE 2002IEEE PESC-02 53 5) Parallel combination of parallel active and parallel passive 6) Series combination of series active and series passive

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JUNE 2002IEEE PESC-02 54 7) Hybrid of series active and parallel passive 8) Hybrid of parallel active and series passive

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JUNE 2002IEEE PESC-02 55 9) Series combination of parallel-passive and parallel-active 10) Parallel combination of series-passive and series-active

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JUNE 2002IEEE PESC-02 56 11) Combined system of series-active and parallel-active 12) Combined system of parallel-active and series-active

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JUNE 2002IEEE PESC-02 57 A SIMPLE EXAMPLE OF AN INDUSTRIAL POWER DISTRIBUTION SYSTEM

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JUNE 2002IEEE PESC-02 58 HARMONIC LIMITS EVALUATION WHEN POWER-FACTOR-CORRECTION CAPASITORS ARE USED - As it can be seen from the power distribution circuit the power-factor- correction capacitor bank, which is connected on the 480 Volts bus, can create a parallel resonance between the capacitors and the system source inductance. - The single phase equivalent circuit of the distribution system is shown below. Using the above circuit the following equations hold:

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JUNE 2002IEEE PESC-02 59 = The turns ratio of the transformer at PCC (33) (34) (35) (36)

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JUNE 2002IEEE PESC-02 60 (37) (38) (39) (40) (41) (42)

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JUNE 2002IEEE PESC-02 61 The impedance looking into the system from the load, consists of the parallel combination of source impedance and the capacitor impedance The equation for can be used to determine the equivalent system impedance for different frequencies. The harmonic producing loads can resonate (parallel resonance), the above equivalent circuit. Designating the parallel resonant frequency by (rad/sec) or (HZ) and equating the inductive and capacitive reactances. (43) (44)

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JUNE 2002IEEE PESC-02 62 - Harmonic current components that are close to the parallel resonant frequency are amplified. - Higher order harmonic currents at the PCC are reduced because the capacitors are low impedance at these frequencies. - The figure below shows the effect of adding capacitors on the 480 Volts bus for power factor correction. This figure shows that by adding some typical sizes of power factor correction capacitors will result in the magnification of the 5 th and 7 th harmonic components, which in turns makes it even more difficult to meet the IEEE 519-1992 harmonic current standards. - Power factor correction capacitors should not be used without turning reactors in case the adjustable speed drives are >10% of the plant load.

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JUNE 2002IEEE PESC-02 63 Let us examine an industrial plant with the following data: - Medium voltage = 20KV LL - Low voltage = 0.4 KV LL - Utility three phase short circuit power = 250 MVA - For asymmetrical current, the ratio of system impedance The Transformer is rated: 1000 KVA, 20 KV-400 Y/230 V R pu = 1%, X pu = 7% - The system frequency is: f sys = 50 HZ. - For power factor correction capacitors the following cases are examined: a. 200 KVAR b. 400 KVAR c. 600 KVAR d. 800 KVAR EXAMPLE

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JUNE 2002IEEE PESC-02 64 The parallel resonant frequencies for every case of power factor correction is calculated as follows:

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JUNE 2002IEEE PESC-02 65 Case a: For 200 KVAR, the harmonic order at which parallel resonance occurs is:

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JUNE 2002IEEE PESC-02 66 Case b: Case c:

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JUNE 2002IEEE PESC-02 67 Case d: It is clear for the above system that in the 600 KVAR case, there exists a parallel resonant frequency close to the 5 th harmonic.

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JUNE 2002IEEE PESC-02 68 POWER FACTOR CORRECTION AND HARMONIC TREATMENT USING TUNED FILTERS - Basic configuration of a tuned 3-φ capacitor bank for power factor correction and harmonic treatment. Simple and cheap filter Prevents of current harmonic magnification

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JUNE 2002IEEE PESC-02 69 - IN ORDER TO AVOID HARMONIC MAGNIFICATION WE CHOOSE A TUNED FREQUENCY < FITH HARMONIC (i.e 4.7) - The frequency characteristic of the tuned filter at 4.7 is shown below As it can be seen from the above figure significant reduction of the 5 th harmonic is achieved. Moreover, there is some reduction for all the other harmonic components.

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JUNE 2002IEEE PESC-02 70 The single phase equivalent circuit of the power distribution system with the tuned filter is shown below Using the above circuit the following equations hold:

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JUNE 2002IEEE PESC-02 71 (parallel resonance) = resonance frequency of the equivalent distribution circuit = Resonant frequency of the series filter The new parallel combination is having resonant frequency when Also (45) (46) (47) (48)

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JUNE 2002IEEE PESC-02 72 (49) (50) (51)

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JUNE 2002IEEE PESC-02 73 As it was discussed before Selecting or 4.7 th harmonic With KV cap = 0.4, KVAR cap = 600 The new parallel combination is having resonant frequency: withwe have (without L f was 4.76)

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JUNE 2002IEEE PESC-02 74 The following table shows the variation of Parallel resonant frequency With and without resonant inductor KVARC(mF) Parallel Resonant f 0 Without L f With L f 2003.988.80115.3μH4.08 4007.966.2257.7μH3.66 60011.945.0838.45μH3.43 80015.924.4029.5μH3.08

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JUNE 2002IEEE PESC-02 75 SIMULATED RESULTS USING MATLAB/SIMULINK

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JUNE 2002IEEE PESC-02 76 SIMULINK RESULTS

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JUNE 2002IEEE PESC-02 77 SIMULINK RESULTS

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JUNE 2002IEEE PESC-02 78 ACTIVE FILTERING Parallel typeSeries type

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JUNE 2002IEEE PESC-02 79 RESULTS OF ACTIVE FILTERING Input current of a 6-pulse Rectifier driving a DC machine without any input filtering Input current with Active Filtering

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JUNE 2002IEEE PESC-02 80 Typical 6-pulse drive voltage waveform Voltage source improvement with active filtering

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JUNE 2002IEEE PESC-02 81 SHUNT ACTIVE FILTERS By inserting a parallel active filter in a non-linear load location we can inject a harmonic current component with the same amplitude as that of the load in to the AC system. C Equivalent circuit

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JUNE 2002IEEE PESC-02 82 Low implementation cost. Do not create displacement power factor problems and utility loading. Supply inductance L S, does not affect the harmonic compensation of parallel active filter system. Simple control circuit. Can damp harmonic propagation in a distribution feeder or between two distribution feeders. Easy to connect in parallel a number of active filter modules in order to achieve higher power requirements. Easy protection and inexpensive isolation switchgear. Easy to be installed. Provides immunity from ambient harmonic loads. ADVANTAGES OF THE SHUNT OR PARALLEL ACTIVE FILTER

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JUNE 2002IEEE PESC-02 83 WAVEFORMS OF THE PARALLEL ACTIVE FILTER Source voltage Load current Source current A. F. output current

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JUNE 2002IEEE PESC-02 84 (53) (54) (55) (56) (57) (52) If Then the above equations become PARALLEL ACTIVE FILTER EQUATIONS

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JUNE 2002IEEE PESC-02 85 (58) = Source impedance = Is the equivalent harmonic current source = Equivalent load impedance = equivalent transfer function of the active filter For pure current source type of harmonic source and consequently equations (53) and (55) become (59) (60) Equation (55) is the required condition for the parallel A.F. to cancel the load harmonic current. Only G can be predesign by the A.F. while Z s and Z L are determined by the system. Equation (59) shows that the compensation characteristics of the A.F. are not influenced by the source impedance, Z s. This is a major advantage of the A.F. with respect to the passive ones.

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JUNE 2002IEEE PESC-02 86 The DC bus nominal voltage,, must be greater than or equal to line voltage peak in order to actively control The selection of the interface inductance of the active filter is based on the compromise of keeping the output current ripple of the inverter low and the same time to be able to track the desired source current. The required capacitor value is dictated by the maximum acceptable voltage ripple. A good initial guess of C is: = peak line-neutral voltage = DC voltage of the DC bus of the inverter = Line phase current = maximum acceptable voltage ripple, = Phase current of the inverter Also

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JUNE 2002IEEE PESC-02 87 For identifying the harmonic currents in general the method of computing instantaneous active and reactive power is used. Transformation of the three-phase voltages and and the three- phase load currents and into α-β orthogonal coordinate. P-Q THEORY

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JUNE 2002IEEE PESC-02 88 Then according to theory, the instantaneous real power and the instantaneous imaginary (reactive) power are calculated. where DC + low frequency comp. + high freq. comp.

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JUNE 2002IEEE PESC-02 89 The conventional active power is corresponding to, the conventional reactive power to and the negative sequence to the 2 f components of and. The commands of the three-phase compensating currents injected by the shunt active conditioner,, and are given by: = Instantaneous real power command = Instantaneous reactive power command

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JUNE 2002IEEE PESC-02 90 Current Harmonics compensation is achieved Current Harmonics and low frequency variation Components of reactive power compensation Current Harmonics and low frequency variation Components of active and reactive power compensation Substituting

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JUNE 2002IEEE PESC-02 91 HARMONIC DETECTION METHODS i)Load current detection i AF = i Lh It is suitable for shunt active filters which are installed near one or more non-linear loads. ii) Supply current detection i AF = K S i Sh Is the most basic harmonic detection method for series active filters acting as a voltage source v AF. iii) Voltage detection It is suitable for shunt active filters which are used as Unified Power Quality Conditioners. This type of Active Filter is installed in primary power distribution systems. The Unified Power Quality Conditioner consists of a series and a shunt active filter.

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JUNE 2002IEEE PESC-02 92 SHUNT ACTIVE FILTER CONTROL a) Shunt active filter control based on voltage detection

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JUNE 2002IEEE PESC-02 93 Using this technique the three-phase voltages, which are detected at the point of installation, are transformed to and on the dq coordinates. Then two first order high-pass filters of 5HZ in order to extract the ac components and from and. Next the ac components are applied to the inverse dq transformation circuit, so that the control circuit to provide the three-phase harmonic voltages at the point of installation. Finally, amplifying each harmonic voltage by a gain K v produces each phase current reference. The active filter behaves like a resistor 1/K V ohms to the external circuit for harmonic frequencies without altering the fundamental components. The current control circuit compares the reference current with the actual current of the active filter and amplifies the error by a gain K I. Each phase voltage detected at the point of installation, v is added to each magnified error signal, thus constituting a feed forward compensation in order to improve current controllability. As a result, the current controller yields three-phase voltage references. Then, each reference voltage is compared with a high frequency triangular waveform to generate the gate signals for the power semiconductor devices.

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JUNE 2002IEEE PESC-02 94 b) Reference current calculation scheme using source currents (i s ), load currents (i L ) and voltages at the point of installation (v S ).

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JUNE 2002IEEE PESC-02 95 3-φ HYBRID ACTIVE-PASSIVE FILTER Compensation of current harmonics and displacement power factor can be achieved simultaneously.

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JUNE 2002IEEE PESC-02 96 In the current harmonic compensation mode, the active filter improves the filtering characteristic of the passive filter by imposing a voltage harmonic waveform at its terminals with an amplitude

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JUNE 2002IEEE PESC-02 97 THD i decreases if K increases. The larger the voltage harmonics generated by the active filter a better filter compensation is obtained. A high value of the quality factor defines a large band width of the passive filter, improving the compensation characteristics of the hybrid topology. A low value of the quality factor and/or a large value in the tuned factor increases the required voltage generated by the active filter necessary to keep the same compensation effectiveness, which increases the active filter rated power. If the AC mains voltage is pure sinusoidal, then

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JUNE 2002IEEE PESC-02 98 Displacement power factor correction is achieved by controlling the voltage drop across the passive filter capacitor. Displacement power factor control can be achieved since at fundamental frequency the passive filter equivalent impedance is capacitive.

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JUNE 2002IEEE PESC-02 99 HYBRID ACTIVE-PASSIVE FILTER Single-phase equivalent circuit for 5 th Harmonic

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JUNE 2002IEEE PESC-02 100 This active filter detects the 5 th harmonic current component that flows into the passive filter and amplifies it by a gain K in order to determine its voltage reference which is given by As a result, the active filter acts as a pure resistor of K ohms for the 5 th harmonic voltage and current. The impedance of the hybrid filter at the 5 th harmonic frequency, Z 5 is given by The active filter presents a negative resistance to the external Circuit, thus improving the Q of the filter.

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JUNE 2002IEEE PESC-02 101 CONTROL CIRCUIT The control circuit consists of two parts; a circuit for extracting the 5 th current harmonic component from the passive filter i F and a circuit that adjusts automatically the gain K. The reference voltage for the active filter HARMONIC-EXTRACTING CIRCUIT The extracting circuit detects the three-phase currents that flow into the passive filter using the AC current transformers and then the α-β coordinates are transformed to those on the d-g coordinates by using a unit vector (cos5ωt, sin5ωt) with a rotating frequency of five times as high as the line frequency.

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JUNE 2002IEEE PESC-02 102 SERIES ACTIVE FILTERS By inserting a series Active Filter between the AC source and the load where the harmonic source is existing we can force the source current to become sinusoidal. The technique is based on a principle of harmonic isolation by controlling the output voltage of the series active filter. Equivalent Circuit

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JUNE 2002IEEE PESC-02 103 - The series active filter exhibits high impedance to harmonic current and consequently blocks harmonic current flow from the load to the source. (61) (62) = Equivalent transfer function of the detection circuit of harmonic current, including delay time of the control circuit. (63)

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JUNE 2002IEEE PESC-02 104 = A gain in pu ohms The voltage distortion of the input AC source is much smaller than the current distortion. Ifand Then (64) (65) (66)

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JUNE 2002IEEE PESC-02 105 HYBRID SERIES AND SHUNT ACTIVE FILTER At the Point of Common Coupling provides: Harmonic current isolation between the sub transmission and the distribution system (shunt A.F) Voltage regulation (series A.F) Voltage flicker/imbalance compensation (series A.F)

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JUNE 2002IEEE PESC-02 106 SELECTION OF AF S FOR SPECIFIC APPLICATION CONSIDERATIONS AF Configuration with higher number of * is more preferred Compensation for Specific Application Active Filters Active Series Active Shunt Hybrid of Active Series and Passive Shunt Hybrid of Active Shunt and Active Series Current Harmonics ****** Reactive Power ****** Load Balancing * Neutral Current *** Voltage Harmonics ****** Voltage Regulation ******* Voltage Balancing ****** Voltage Flicker ****** Voltage Sag&Dips *******

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JUNE 2002IEEE PESC-02 107 CONCLUSIONS Solid State Power Control results in harmonic pollution above the tolerable limits. Harmonic Pollution increases industrial plant downtimes and power losses. Harmonic measurements should be made in industrial power systems in order (a) aid in the design of capacitor or filter banks, (b) verify the design and installation of capacitor or filter banks, (c) verify compliance with utility harmonic distortion requirements, and (d) investigate suspected harmonic problems. Computer software programs such as PSPICE and SIMULINK can be used in order to obtain the harmonic behavior of an industrial power plant. The series LC passive filter with resonance frequency at 4.7 is the most popular filter. The disadvantages of the the tuned LC filter is its dynamic response because it cannot predict the load requirements. The most popular Active Filter is the parallel or shunt type. Active Filter technology is slowly used in industrial plants with passive filters as a hybrid filter. These filters can be used locally at the inputs of different nonlinear loads. Active Filter Technology is well developed and many manufactures are fabricating Active filters with large capacities. A large number of Active Filters configurations are available to compensate harmonic current, reactive power, neutral current, unbalance current, and harmonics. The active filters can predict the load requirements and consequently they exhibit very good dynamic response. LC tuned filters can be used at PCC and the same time active filters can be used locally at the input of nonlinear loads.

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JUNE 2002IEEE PESC-02 108 REFERENCES RECOMMENDED PRACTICES ON HARMONIC TREATMENT [1] IEEE Std. 519-1992, ΄΄IEEE Recommended Practices and Requirements for Harmonic Control in Electric Power Systems΄΄, 1993. [2] IEC Sub-Committee 77B report, ΄΄Compatibility Levels in Industrial Plants for Low Frequency Conducted Disturbances΄΄, 1990. [3] IEC Sub-Committee 77A report, ΄΄Disturbances Caused by Equipment Connected to the Public Low-Voltage Supply System Part 2 : Harmonics ΄΄, 1990 (Revised Draft of IEC 555-2). [4] UK Engineering Recommendation G.5/3: ΄΄Limits for Harmonics in the UK Electricity Supply System΄΄, 1976. [5] CIRGE WG 36.05 Report, ΄΄Equipment producing harmonics and Conditions Governing their Connection to the Mains power Supply΄΄, Electra, No. 123, March 1989, pp. 20-37. [6] Australian Standards AS-2279.1-1991, ΄΄Disturbances in mains Supply Networks-Part 2: Limitation of Harmonics Caused by Industrial Equipment΄΄, 1991.

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JUNE 2002IEEE PESC-02 109 DEFINITIONS [7] J. Arriilaga, D.A. Bradley, and P.S. Bodger, ΄΄Power System Harmonics΄΄,New York: Wiley, 1985. [8] N. Shepherd and P. Zand, ΄΄Energy flow and power factor in nonsinusoidal circuits΄΄, Cambridge University Press, 1979. EFFECTS OF HARMONICS [9] J.M. Bowyer, ΄΄Three-Part Harmony: System Interactions Leading to a Divergent Resonant System΄΄, IEEE Trans. on Industry Applications, Vol. 31, No. 6, Nov/Dec 1995, pp. 1341-1349. [10] R.D. Hondenson and P.J. Rose, ΄΄Harmonics: the Effects on power Quality and Transformers΄΄, IEEE Trans. on Industry Applications, Vol. 30, No.3, May/June 1994, pp. 528-532. [11] J.S. Subjak and J. S. McQuilkin, ΄΄Harmonics-Causes, effects, Measurements and Analysis: An Update΄΄, IEEE Trans. on Industry Applications, Vol. 26, No. 6, Nov/Dec 1990, pp. 103-1042. [12] P.Y. Keskar, ΄΄Specification of Variable Frequency Drive Systems to Meet the New IEEE 51 Standard΄΄, IEEE Trans. on Industry Applications, Vol.32, No.2, March/April 1996, pp. 393-402.

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JUNE 2002IEEE PESC-02 110 [13] T.S. Key, ΄΄Cost and Benefits of Harmonic Current Reduction for Switch-Mode Power Supplies in a Commercial Building΄΄, IEEE Trans. on Industry Applications, Vol. 32, No. 5, September/October 1996, pp. 1017-1025. PASSIVE HARMONIC TREATMENT TECHNIQUES [14] M.F. McGranaghan and D.R. Mueller, ΄΄Designing Harmonic Filters for Adjustable-Speed Drives to comply with IEEE-519 Harmonic limits΄΄, IEEE Trans. on Industry Applications, Vol. 35, No 2, March/April 1999, pp. 312-18. [15] F.Z. Peng, ΄΄Harmonic Sources and filtering Approaches΄΄, IEEE Industry Applications Magazine, July/August 2001, pp. 18-25. [16] J.K. Phipps, ΄΄A transfer Function Approach to Harmonic Filter Design΄΄, IEEE Industry Applications Magazine March/April 1997. [17] S.M. Peeran, ΄΄Application, Design, and Specification of Harmonic Filters for Variable frequency Drives΄΄, IEEE Trans. on Industry Applications, Vol. 31, No. 4, July/August 1995, pp. 841-847.

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JUNE 2002IEEE PESC-02 111 [18] J. Lai and T.S. Key, ΄΄Effectiveness of Harmonic Mitigation Equipment for Commercial Office Buildings΄΄, IEEE Trans. on Industry Applications, Vol. 33, No. 4, July/August 1997, pp. 1104-1110. [19] D.E. Rice,΄΄A Detailed Analysis of Six-Pulse Converter harmonic Currents΄΄, IEEE Trans. on Industry Applications, Vol. 30, No. 2, March/April 1994, pp. 294-304. [20] R.L. Almonte and Ashley, ΄΄Harmonics at the Utility Industrial Interface: A Real World Example΄΄, IEEE Trans. on Industry Applications, Vol. 31, No. 6, November/December 1995, pp. 1419-1426. [21] K. A. Puskarich, W.E. Reid and P. S. Hamer, ΄΄Harmonic Experiments with a large load-Commutated inverter drive΄΄, IEEE Trans. on Industry Applications, Vol. 37, No. 1, Jan/Feb. 2001, pp. 129-136. [22] L.S. Czarnecki and O. T. Tan, ΄΄Evaluation and Reduction of Harmonic Distortion Caused by Solid State Voltage Controller of Induction Motors΄΄, IEEE Trans. on Energy Conversion, Vol. 9, No. 3, Sept. 1994, pp. 528-421.

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JUNE 2002IEEE PESC-02 112 [23] R.G. Ellis, ΄΄Harmonic Analysis of Industrial power Systems΄΄, IEEE Trans. on Industry Applications, Vol. 32, No. 2, March/April 1996, pp. 417-421. [24] D. Adrews et al, ΄΄ Harmonic Measurements, Analysis and Power factor Correction in a Modern Steel Manufacturing Facility΄΄, IEEE Trans. on Industry Applications, Vol. 32, No. 3, May/June 196, pp. 617-624. [25] D. Shipp and W. S. Vilcheck, ΄΄Power Quality and Line Considerations for Variable Speed AC Drivers΄΄, IEEE Trans. on Industry Applications, Vol.32, No.2, March/April 1996, pp. 403- 410. [26] J. A Bonner et al, ΄΄Selecting ratings for Capacitors and Reactors In Applications Involving Multiple Single-Tuned Filters΄΄, IEEE Trans. on Power Delivery, Vol. 10, No. 1, Jan. 1995, pp. 547-555. [27] E. J. Currence, J.E Plizga, and H. N. Nelson, ΄΄Harmonic Resonance at a medium-sized Industrial Plant΄΄, IEEE Trans. on Industry Applications, Vol. 31, No. 4, July/August 1995, pp. 682- 690.

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JUNE 2002IEEE PESC-02 113 [28] G. Lemieux, ΄΄Power system harmonic resonance. A document case΄΄, IEEE Trans. on Industry Applications, Vol. 26, No. 3, pp. 483-487, May/June 1990. [29] D. D. Shipp, ΄΄Harmonic Analysis and Suppression for electrical systems΄΄, ΙEEE Trans. on Industry Applications Vol. 15, No. 5, Sept./Oct. 1979. ACTIVE HARMONIC TREATMENT TECHNIQUES [30] H. Akagi, ΄΄New trends in active filters for Power conditioning΄΄, IEEE Trans. on Industry Applications, Vol. 32, Nov/Dec. 1996, pp. 1312-1322. [31] Bhim Singh et al, ΄΄A Review of Active Filters for Power Quality Improvement΄΄, IEEE Trans. on Industrial Electronics, Vol. 46, No. 5, Oct. 1999, pp. 960-971. [32] F. Z. Peng, ΄΄Application Issues of Active Power Filters΄΄, IEEE Industry Applications Magazine, Sep./Oct. 1998, pp. 22-30. [33] S. Bhattacharga et al, ΄΄Active Filter Systems Implementation΄΄, IEEE Industry Applications Magazine, Sep./Oct. 1998, pp. 47-63.

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JUNE 2002IEEE PESC-02 114 [34] S. Bhattacharya et al, ΄΄Hybrid Solutions for improving Passive Filter Performance in high power Applications΄΄, IEEE, Trans. on Industry Applications, Vol. 33, No. 3, May/June 1997, pp. 732-747. [35] H. Akagi, ΄΄Control Strategy and site selection of a shunt active filter for damping of harmonies propagation in power distribution systems ΄΄, IEEE Trans. on Power Delivery, Vol. 12, Jan. 1997, pp.354-363. [36] H. Fujita, T. Yamasaki, and H. Akagi, ΄΄A Hybrid Active Filter for Damping of Harmonic Resonance in Industrial Power Systems΄΄, IEEE Trans. on Power Electronics, Vol. 15, No. 2, March 2000, pp. 215-222. [37] H. Akagi et al, ΄΄ Α shunt Active Filter Based on Voltage Detection for Harmonic Termination of a Radial power Distribution Line΄΄, IEEE Trans. on Industry Applications, Vol. 35, No. 3, May/June 1999, pp. 638-645. [38] D. Rivas et al, ΄΄ A simple control scheme for hybrid Active Power Filter΄΄, IEE PESC-00, pp. 991-996.

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JUNE 2002IEEE PESC-02 115 [39] L. Zhou and Zi Li, ΄΄A Novel Active Power filter Based on the Least compensation Current Control Method΄΄, IEEE Trans. on Power Electronics, Vol. 15, No. 4, July 2000, pp. 655-659. MODELING [40] IEEE Task Force on Modeling and Simulation, ΄΄Modeling and Simulation of the propagation of harmonies in electric power networks, Part I: Concepts, models, and simulation techniques΄΄, IEEE Trans. on Power Delivery, Vol. 11, No. 1, Jan. 1996, pp. 452- 465. [41] IEEE Task Force on Modeling and Simulation ΄΄Modeling and Simulation of the propagation of harmonies in electric power networks, Part II: Sample systems and examples΄΄, IEEE Trans. on Power Delivery, Vol. 11, No. 1, Jan. 1996, pp. 466-474. [42] W. Jewel et al, ΄΄Filtering Dispersed harmonic Sources on Distribution΄΄, IEEE Trans. on Power Delivery, Vol. 15, No. 3, July 2000, pp. 1045-1051. [43] N.K. Madora and A. Kusko, ΄΄Computer-Aided Design and Analysis of Power-Harmonic Filters΄΄ IEEE Trans. on Industry Applications, Vol. 36, No. 2, March/April 2000, pp.604-613.

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