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**HARMONIC TREATMENT IN INDUSTRIAL POWER SYSTEMS**

Presented by Stefanos Manias IEEE PESC-02 JUNE 2002

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CONTACT INFORMATION Stefanos N. Manias National Technical University of Athens Phone: FAX: Mailing Address Department of Electrical and Computer Engineering 9, Iroon Polytechniou Str, Zografou Athens, Greece IEEE PESC-02 JUNE 2002

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**PLAN OF PRESENTATION DEFINITIONS**

CATEGORIES OF POWER QUALITY VARIATIONS HARMONIC DISTORTION SOURCES IN INDUSTRIAL POWER SYSTEMS EFFECTS OF HARMONICS ON ELECTRICAL EQUIPMENT HARMONIC MEASUREMENTS IN INDUSTRIAL POWER SYSTEMS HARMONIC STANDARDS HARMONIC MITIGATING TECHNIQUES GENERAL PASSIVE AND ACTIVE FILTER DESIGN PROCEDURES DESIGN EXAMPLES CONCLUSIONS IEEE PESC-02 JUNE 2002

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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). IEEE PESC-02 JUNE 2002

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**False tripping of circuit breakers ad protective relays.**

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. IEEE PESC-02 JUNE 2002

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**HARMONIC SOURCES a) Current Source nonlinear load**

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

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**INPUT CURRENT OF DIFFERENT**

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

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**with large output inductor**

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

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**CURRENT HARMONICS GENERATED BY 6-PULSE CSI CONVERTERS**

P.U PULSE 1 1.00 5 0.2 7 0.143 11 0.09 13 0.077 17 0.059 19 0.053 23 0.04 CURRENT HARMONICS GENERATED BY 12-PULSE CSI CONVERTERS HARMONIC P.U PULSE IEEE 519 std 1 1.00 - 5 5.6% 7 11 2.8% 13 THD 7.5%-14.2% 7.0% IEEE PESC-02 JUNE 2002

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**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 IEEE PESC-02 JUNE 2002

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**Current waveform and its respective spectrum**

at the inputs of a motor drive system IEEE PESC-02 JUNE 2002

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**Current waveform and its respective spectrum**

at the secondary of the distribution transformer ( i.e. at the service entrance) IEEE PESC-02 JUNE 2002

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**DEFINITIONS f (t) = Fourier Series of a periodic function f (t) =**

(1) (2) (3) (4) h = harmonic order IEEE PESC-02 JUNE 2002

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**Percentage of the Total Harmonic Distortion of a nonsinusoidal voltage waveform**

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

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**Harmonic Factor = (7) (8) (9) (10) RMS value of the current distortion**

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

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**SINUSOIDAL VOLTAGE NONSINUSOIDAL CURRENT**

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

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**NONSINUSOIDAL VOLTAGE AND NONSINUSOIDAL CURRENT**

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

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

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

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**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. IEEE PESC-02 JUNE 2002

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EXAMPLE 1 SINUSOIDAL VOLTAGE-NONSINIMUSOIDAL CURRENT 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: IEEE PESC-02 JUNE 2002

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**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 IEEE PESC-02 JUNE 2002

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**Therefore, the power factor is**

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

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**EXAMPLE 2 Solution. The rms terminal voltage is given by**

NONSINUSOIDAL VOLTAGE-RL LOAD 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 Compensation when Solution. The rms terminal voltage is given by Therefore IEEE PESC-02 JUNE 2002

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**The instantaneous load current is given by**

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

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**at the load terminals in the absence of capacitance is therefore**

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

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EXAMPLE 3 NONSINUSOIDAL VOLTAGE AND NONSINIMUSOIDAL CURRENT A periodic, nonsinusoidal voltage with instantaneous value given by is applied to a nonlinear impedance. The resulting current has an instantaneous value given by Calculate the components of the load apparent voltamperes and compare thee with the classical values respectively. Solution. 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. IEEE PESC-02 JUNE 2002

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**The rms voltage and current at the supply are given by**

The load apparent voltamperes therefore has a value defined in terms and Instantaneous expressions of the hypothetical currents are given by IEEE PESC-02 JUNE 2002

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**Note that current components contain only those harmonic terms which **

are common to both voltage and current. These are therefore consistent with the terms. The rms load current components are found, as expected to sum to the total rms load current Components of the apparent voltamperes can now be obtained IEEE PESC-02 JUNE 2002

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**The component voltamperes are seen to sum to the total apparent voltamperes**

Components of are found as follows: IEEE PESC-02 JUNE 2002

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**differ by significant amount.**

From the possible compensation viewpoint it is interesting to note that and differ 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”. IEEE PESC-02 JUNE 2002

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**Similarly the definition of active voltamperes could 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”. Both and are entirely fictitious and non-physical. The active voltamperes Is not to be compares in importance with the average power which is a real physical property of the circuit. Term Is merely the analytical complement of term al the energy-storage reactive voltamperes, is that component Term of the load apparent voltamperes that can be entirely compensated (for sinusoidal supply voltage) or minimized (for nonsinusoidal supply voltage) by energy-storage methods. IEEE PESC-02 JUNE 2002

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**Voltage and current profiles in a**

commercial building IEEE PESC-02 JUNE 2002

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HARMONIC STANDARDS International Electrotechnical Commission (IEC) European Standards. - EN Harmonic Emissions standards were first published as IEC 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 A per phase. However, until January 1st, 2001 a transition period is in effect for all equipment not covered by the standard prior to 1987. - The objective of EN (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. IEEE PESC-02 JUNE 2002

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**except that stated in one of the remaining three classes. **

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 IEEE PESC-02 JUNE 2002

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**IEEE limits service entrance harmonics. **

IEEE United States Standards on harmonic limits IEEE limits service entrance harmonics. The IEEE standard limits the level of harmonics at the customer service entrance or Point of Common Coupling (PCC). With this approach the costumer’s current distortion is limited based on relative size of the load and the power supplier’s voltage distortion based on the voltage level. IEEE 519 and IEC apply different philosophies, which effectively limit harmonics at different locations. IEEE 519 limits harmonics primarily at the service entrance while IEC 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. IEEE PESC-02 JUNE 2002

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**POWER QUALITY STANDARDS –**

IEEE STANDARDS TABLE I CURRENT DISTORTION LIMITS FOR GENERAL DISTRIBUTION SYSTEMS ( V) Isc/IL <11 11<h<17 17<h<23 23<h<35 35<h TDD <20* 4.0 2.0 1.5 0.6 0.3 5.0 20<50 7.0 3.5 2.5 1.0 0.5 8.0 50<100 10.0 4.5 0.7 12.0 100<1,000 5.5 15.0 >1,000 6.0 1.4 20.0 Source: IEEE Standard Note: Even harmonics are limited to 25 percent of the odd harmonic limits above. Current distortions that result in a direct current offset; for example, half wave converters are not allowed. Table I is for 6-pulse rectifiers. For converters higher than 6 pulse, the limits for characteristic harmonics are increased by a factor o f q/6 , where q is the pule number, provided that the amplitudes of noncharacteristic harmonics are less than 25 percent. *All power generation equipment is limited to these values of current distortion, regardless of actual ISC/IL. Where ISC = Maximum short circuit at PCC. And IL = Average Maximum demand load current (fundamental frequency component at PCC). IEEE PESC-02 JUNE 2002

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**LOW VOLTAGE SYSTEM CLASSIFICATION AND DISTORTION LIMITS**

TABLE II LOW VOLTAGE SYSTEM CLASSIFICATION AND DISTORTION LIMITS IEEE STANDARTS Special Applications General System Dedicated System Notch Depth 10% 20% 50% THD (Voltage) 3% 5% Notch Area (AN)* 16,400 22,800 36,500 Source: IEEE Standard Note: The value AN 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. IEEE PESC-02 JUNE 2002

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**SYSTEM Nominal Voltage**

TABLE III LIMITS OF THD% IEEE STANDARDS SYSTEM Nominal Voltage Special Application General Systems Dedicated Systems V 3.0 5.0 8.0 69KV and below - IEEE PESC-02 JUNE 2002

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**Harmonic Relative limits Milliamps/Watt Absolute Limits Amps 3 3.4**

TABLE IV PROPOSED IEC CLASS D STANDARDS for power from 50 to 600W Harmonic Relative limits Milliamps/Watt Absolute Limits Amps 3 3.4 2.30 5 1.9 1.14 7 1.0 0.77 9 0.5 0.40 11 0.35 0.33 13 linear extrapolation 0.15 (15/n) IEEE PESC-02 JUNE 2002

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**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. IEEE PESC-02 JUNE 2002

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**Ib= Base current in Amps**

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. Ib= Base current in Amps (24) (25) = System impedance = MVAb= Base MVA, MVAsc= short circuit MVA at the point of interest VH= Percent individual harmonic voltage distortion = (26) IEEE PESC-02 JUNE 2002

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**IH = Percent individual harmonic distortion =**

(27) h = harmonic order (28) IH = Percent individual harmonic distortion = Isc = Short Circuit current at the point under consideration. IL = Estimated maximum demand load current S.C. Ratio = Short circuit Ratio (29) MVAD = Demand MVA IEEE PESC-02 JUNE 2002

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**K Factor = Factor useful for transformers design and **

specifically from transformers that feed Adjustable Speed Drives (30) ONCE THE SHORT CIRCUIT RATIO IS KNOWN, THE IEEE CURRENT HARMONIC LIMITS CAN BE FOUND AS SPECIFIED IN TABLE I OF THE IEEE 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 IEEE PESC-02 JUNE 2002

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**The Notch Area AN at the PCC can be calculated as follows.**

Step 4: If the analysis is being performed for CSI-type drives then the area of the voltage notch AN should also be computed. At this point an impedance diagram of the under analysis industrial power system should be available. The Notch Area AN at the PCC can be calculated as follows. AN = AN1 + AN2 + …………. V . microsec (31) AN1 , AN2 , …… are the notch areas contribution of the different busses (32) ANDR1 : Notch area at the input of the drive IEEE PESC-02 JUNE 2002

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**Step 5: Determine preliminary filter design.**

Step 6: Compute THDv and THDi 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. IEEE PESC-02 JUNE 2002

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**EXAMPLE OF A SYSTEM ONE LINE**

DIAGRAM IEEE PESC-02 JUNE 2002

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

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

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**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) IEEE PESC-02 JUNE 2002

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**3) Basic parallel-active filter for current source in nonlinear loads**

IEEE PESC-02 JUNE 2002

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**4) Basic series-active filter for voltage-source in nonlinear loads**

IEEE PESC-02 JUNE 2002

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**5) Parallel combination of parallel active and parallel passive**

6) Series combination of series active and series passive IEEE PESC-02 JUNE 2002

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**7) Hybrid of series active and parallel passive**

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

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**9) Series combination of parallel-passive and parallel-active**

10) Parallel combination of series-passive and series-active IEEE PESC-02 JUNE 2002

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**11) Combined system of series-active and parallel-active**

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

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**A SIMPLE EXAMPLE OF AN INDUSTRIAL POWER DISTRIBUTION SYSTEM**

IEEE PESC-02 JUNE 2002

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**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: IEEE PESC-02 JUNE 2002

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**= The turns ratio of the transformer at PCC**

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

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

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The impedance looking into the system from the load, consists of the parallel combination of source impedance and the capacitor impedance (43) (44) 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. IEEE PESC-02 JUNE 2002

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**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 5th and 7th harmonic components, which in turns makes it even more difficult to meet the IEEE 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. IEEE PESC-02 JUNE 2002

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**The Transformer is rated:**

EXAMPLE Let us examine an industrial plant with the following data: Medium voltage = 20KVLL Low voltage = 0.4 KVLL 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 Rpu = 1%, Xpu = 7% - The system frequency is: fsys = 50 HZ. - For power factor correction capacitors the following cases are examined: 200 KVAR 400 KVAR 600 KVAR 800 KVAR IEEE PESC-02 JUNE 2002

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

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

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

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

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**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 IEEE PESC-02 JUNE 2002

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**The frequency characteristic of the tuned filter at 4.7 is shown below**

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 5th harmonic is achieved. Moreover, there is some reduction for all the other harmonic components. IEEE PESC-02 JUNE 2002

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**Using the above circuit the following equations hold:**

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: IEEE PESC-02 JUNE 2002

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**= Resonant frequency of the series filter**

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

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

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**As it was discussed before Selecting**

or 4.7 th harmonic As it was discussed before Selecting With KVcap= 0.4 , KVARcap= 600 The new parallel combination is having resonant frequency: with we have (without Lf was 4.76) IEEE PESC-02 JUNE 2002

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**The following table shows the variation of Parallel resonant frequency **

With and without resonant inductor KVAR C(mF) Parallel Resonant f0 Without Lf With Lf 200 3.98 8.80 115.3μH 4.08 400 7.96 6.22 57.7μH 3.66 600 11.94 5.08 38.45μH 3.43 800 15.92 4.40 29.5μH 3.08 IEEE PESC-02 JUNE 2002

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**SIMULATED RESULTS USING**

MATLAB/SIMULINK IEEE PESC-02 JUNE 2002

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SIMULINK RESULTS IEEE PESC-02 JUNE 2002

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SIMULINK RESULTS IEEE PESC-02 JUNE 2002

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ACTIVE FILTERING Parallel type Series type IEEE PESC-02 JUNE 2002

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**RESULTS OF ACTIVE FILTERING**

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

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**Typical 6-pulse drive voltage waveform**

Voltage source improvement with active filtering IEEE PESC-02 JUNE 2002

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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 IEEE PESC-02 JUNE 2002

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**ADVANTAGES OF THE SHUNT OR PARALLEL**

ACTIVE FILTER Low implementation cost. Do not create displacement power factor problems and utility loading. Supply inductance LS, 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. IEEE PESC-02 JUNE 2002

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**WAVEFORMS OF THE PARALLEL ACTIVE FILTER**

Source voltage Load current Source current A. F. output current IEEE PESC-02 JUNE 2002

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**PARALLEL ACTIVE FILTER EQUATIONS**

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

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**For pure current source type of harmonic source**

(58) 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 Zs and ZL are determined by the system. For pure current source type of harmonic source and consequently equations (53) and (55) become (59) (60) = Source impedance = Is the equivalent harmonic current source = Equivalent load impedance = equivalent transfer function of the active filter Equation (59) shows that the compensation characteristics of the A.F. are not influenced by the source impedance, Zs. This is a major advantage of the A.F. with respect to the passive ones. IEEE PESC-02 JUNE 2002

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**= peak line-neutral voltage**

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: Also = 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 IEEE PESC-02 JUNE 2002

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P-Q THEORY 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. IEEE PESC-02 JUNE 2002

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**DC + low frequency comp. + high freq. comp.**

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

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**= Instantaneous real power command**

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 IEEE PESC-02 JUNE 2002

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**Substituting 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 IEEE PESC-02 JUNE 2002

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**HARMONIC DETECTION METHODS**

Load current detection iAF= iLh It is suitable for shunt active filters which are installed near one or more non-linear loads. ii) Supply current detection iAF= KS iSh Is the most basic harmonic detection method for series active filters acting as a voltage source vAF. 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. IEEE PESC-02 JUNE 2002

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**SHUNT ACTIVE FILTER CONTROL**

a) Shunt active filter control based on voltage detection IEEE PESC-02 JUNE 2002

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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 Kv produces each phase current reference. The active filter behaves like a resistor 1/KV 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 KI . 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. IEEE PESC-02 JUNE 2002

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b) Reference current calculation scheme using source currents (is), load currents (iL) and voltages at the point of installation (vS). IEEE PESC-02 JUNE 2002

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**3-φ HYBRID ACTIVE-PASSIVE FILTER**

Compensation of current harmonics and displacement power factor can be achieved simultaneously. IEEE PESC-02 JUNE 2002

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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 IEEE PESC-02 JUNE 2002

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**THDi decreases if K increases. **

If the AC mains voltage is pure sinusoidal, then THDi 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. IEEE PESC-02 JUNE 2002

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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. IEEE PESC-02 JUNE 2002

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**Single-phase equivalent circuit**

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

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**The active filter presents a negative resistance to the external **

This active filter detects the 5th 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 5th harmonic voltage and current. The impedance of the hybrid filter at the 5th harmonic frequency, Z5 is given by The active filter presents a negative resistance to the external Circuit, thus improving the Q of the filter. IEEE PESC-02 JUNE 2002

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**HARMONIC-EXTRACTING CIRCUIT**

CONTROL CIRCUIT The control circuit consists of two parts; a circuit for extracting the 5th current harmonic component from the passive filter iF 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. IEEE PESC-02 JUNE 2002

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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 IEEE PESC-02 JUNE 2002

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- 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) IEEE PESC-02 JUNE 2002

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

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**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) IEEE PESC-02 JUNE 2002

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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 IEEE PESC-02 JUNE 2002

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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. IEEE PESC-02 JUNE 2002

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**RECOMMENDED PRACTICES ON HARMONIC TREATMENT**

REFERENCES RECOMMENDED PRACTICES ON HARMONIC TREATMENT [1] IEEE Std , ΄΄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 Report, ΄΄Equipment producing harmonics and Conditions Governing their Connection to the Mains power Supply΄΄, Electra, No. 123, March 1989, pp [6] Australian Standards AS , ΄΄Disturbances in mains Supply Networks-Part 2: Limitation of Harmonics Caused by Industrial Equipment΄΄, 1991. IEEE PESC-02 JUNE 2002

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**DEFINITIONS EFFECTS OF HARMONICS**

[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 [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 [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 [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 IEEE PESC-02 JUNE 2002

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**PASSIVE HARMONIC TREATMENT TECHNIQUES**

[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 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 [15] F.Z. Peng, ΄΄Harmonic Sources and filtering Approaches΄΄, IEEE Industry Applications Magazine, July/August 2001, pp [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 IEEE PESC-02 JUNE 2002

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[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 [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 [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 [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 [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 IEEE PESC-02 JUNE 2002

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[23] R.G. Ellis, ΄΄Harmonic Analysis of Industrial power Systems΄΄, IEEE Trans. on Industry Applications, Vol. 32, No. 2, March/April 1996, pp [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 [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 [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 [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 IEEE PESC-02 JUNE 2002

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**ACTIVE HARMONIC TREATMENT TECHNIQUES**

[28] G. Lemieux, ΄΄Power system harmonic resonance. A document case΄΄, IEEE Trans. on Industry Applications, Vol. 26, No. 3, pp , 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 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 [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 [32] F. Z. Peng, ΄΄Application Issues of Active Power Filters΄΄, IEEE Industry Applications Magazine, Sep./Oct. 1998, pp [33] S. Bhattacharga et al, ΄΄Active Filter Systems Implementation΄΄, IEEE Industry Applications Magazine, Sep./Oct. 1998, pp IEEE PESC-02 JUNE 2002

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[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 [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 [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 [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 [38] D. Rivas et al, ΄΄ A simple control scheme for hybrid Active Power Filter΄΄, IEE PESC-00, pp IEEE PESC-02 JUNE 2002

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[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 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 [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 [42] W. Jewel et al, ΄΄Filtering Dispersed harmonic Sources on Distribution΄΄, IEEE Trans. on Power Delivery, Vol. 15, No. 3, July 2000, pp [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 IEEE PESC-02 JUNE 2002

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