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HARMONIC TREATMENT IN INDUSTRIAL POWER SYSTEMS Presented by Stefanos Manias 1 IEEE PESC-02 JUNE 2002 CONTACT INFORMATION Stefanos N. Manias National Technical University of Athens Phone: +3010-7723503 FAX: +3010-7723593 E-mail: [email protected] Mailing Address National Technical University of Athens Department of Electrical and Computer Engineering 9, Iroon Polytechniou Str, 15773 Zografou Athens, Greece 2 IEEE PESC-02 JUNE 2002 PLAN OF PRESENTATION 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 3 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 WHY HARMONIC ANALYSIS ? When a voltage and/or current waveform is distorted, it causes abnormal operating conditions in a power system such as: 4 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 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 switchgear 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 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 6 IEEE PESC-02 Per-phase equivalent circuit of diode rectifier JUNE 2002 INPUT CURRENT OF DIFFERENT NOLINEAR LOADS TYPE OF NONLINEAR LOAD TYPICAL WAREFORM THD% 1.0 80% (high 3rd component) 0.5 0.0 Current 1-φ Uncontrolled Rectifier -0.5 -1.0 0 10 20 30 40 Time (mS) 1.0 0.5 0.0 Current 1-φ Semicontrolled Rectifier Bridge 2nd, 3rd, 4th ,...... harmonic components -0.5 -1.0 0 10 20 30 40 Time (mS) 1.0 0.5 0.0 -0.5 -1.0 7 80% Current 6 –Pulse Rectifier with output voltage filtering and without input reactor filter 0 10 20 30 40 5, 7, 11, ………. Time (mS) IEEE PESC-02 JUNE 2002 1.0 0.5 0.0 40% 5, 7, 11, ……….. Current 6 - Pulse Rectifier with output voltage filtering and with 3% reactor filter or with continues output current -0.5 -1.0 0 10 20 30 40 Time (mS) 1.0 0.5 0.0 Current 6 - Pulse Rectifier with large output inductor 28% 5, 7, 11, ……….. -0.5 0 10 -1.0 20 Time (mS) 30 40 1.0 0.5 0.0 15% 11, 13, ……….. Current 12 - Pulse Rectifier -0.5 0 -1.0 8 10 20 Time (mS) IEEE PESC-02 30 40 JUNE 2002 CURRENT HARMONICS GENERATED BY 6-PULSE CSI CONVERTERS HARMONIC P.U PULSE 1 5 7 11 13 17 19 23 1.00 0.2 0.143 0.09 0.077 0.059 0.053 0.04 CURRENT HARMONICS GENERATED BY 12-PULSE CSI CONVERTERS 9 HARMONIC P.U PULSE IEEE 519 std 1 5 7 11 13 THD 1.00 0.03-0.06 0.02-0.06 0.05-0.09 0.03-0.08 7.5%-14.2% 5.6% 5.6% 2.8% 2.8% 7.0% IEEE PESC-02 JUNE 2002 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 10 IEEE PESC-02 JUNE 2002 Current waveform and its respective spectrum at the inputs of a motor drive system 11 IEEE PESC-02 JUNE 2002 Current waveform and its respective spectrum at the secondary of the distribution transformer ( i.e. at the service entrance) 12 IEEE PESC-02 JUNE 2002 DEFINITIONS f (t) = Fourier Series of a periodic function f (t) = Co Ch cos hωt θ h h 1 1 T Ch A 2h B2h Co o f ( t )dt, T 2 T A h o f ( t ) cos(hωt )dt T 2 T Bh o f ( t ) sin( hωt )dt T (1) (2) (3) (4) h = harmonic order 13 IEEE PESC-02 JUNE 2002 THD υ % Percentage of the Total Harmonic Distortion of a nonsinusoidal voltage waveform Vh2 h 2 THDi % V1 100 Percentage of the Total Harmonic Distortion of a nonsinusoidal current waveform 2 Ih h 2 I1 100 (6) Vh hth harmonic component of the voltage I h hth harmonic component of the current ~ VH RMS value of the voltage distortion 14 (5) IEEE PESC-02 ~2 V h h 2 JUNE 2002 ~ IH RMS value of the current distortion ~ I RMS value of a nonsinusoidal current = h 2 ~ V ~2 Ih ~2 Ih (7) h 1 RMS value of a nonsinusoidal voltage = ~2 Vh (8) h 1 THD υ % HF Drive kVA 100 SC kVA (9) HF Harmonic Factor = 15 h 2 I 2h / I1 h 5 IEEE PESC-02 (10) JUNE 2002 Drive kVA Full load kVA rating of the Drive system SC kVA Short Circuit kVA of the distribution system at the point of connection SINUSOIDAL VOLTAGE NONSINUSOIDAL CURRENT ~~ P V Ii,1 cos φ1 (11) ~~ ~~ Q V Ii,1 sin φ1 , S V I D Distortion VA S2 P 2 Q2 16 IEEE PESC-02 (12) (13) JUNE 2002 ~ ~ ~ D S V 2 Ii,21 V 2 2 2 ~2 Ii,h (14) h 2 P Ii,1 cos φ1 λ True Power Factor S I (15) Distortion Factor Displace ment Factor NONSINUSOIDAL VOLTAGE AND NONSINUSOIDAL CURRENT ~ ~ ~ ~ P Vh Ih cos φ h , Q Vh Ih sin φ h h 1 D Distortion Power 17 h 1 Snm S*nm n m n m IEEE PESC-02 (16) * S S n m (17) n m n m JUNE 2002 S2 P 2 Q 2 D 2 (18) ~ 2~ 2 ~~ 2 ~~ S Vh Ih V1 I1 V1 IH h 1 ~ ~ VH IH 2 2 V~H~I1 2 S12 S2N (19) ~~ S1 Fundamenta l Apparent Power V1 I1 SN Nonfundame ntal Apparent Power ~~ 2 ~ ~ 2 ~ ~ 2 S2N V1 IH VH I1 VH IH 18 IEEE PESC-02 JUNE 2002 ~~ V1 IH Current Distortion Power (20) ~ ~ VH I1 Voltage Distortion Power (21) ~ ~ VH IH Harmonic Apparent Power (22) S2H PH2 N 2H Total Harmonic Active Power Total Harmonic Non Active Power (23) XC Reactance of the capacitor VL-L 2 / VAR 3phase 19 IEEE PESC-02 JUNE 2002 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. 20 IEEE PESC-02 JUNE 2002 EXAMPLE 1 SINUSOIDAL VOLTAGE-NONSINIMUSOIDAL CURRENT A periodic, sinusoidal voltage of instantaneous value v 200 2 sin ωt Is applied to a nonlinear load impedance. The resulting instantaneous current is given by: i 2 20sin ωt 45o 10sin 2ωt 60o 10sin 3ωt 60o Calculate the components P, Q, D of the apparent voltamperes and hence calculate the displacement factor, the distortion factor and the power factor. Solution v 200 2 sin ωt i 2 20sin ωt 45o 10sin 2ωt 60o 10sin 3ωt 60o 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: ~ V 200V ~2 I 202 102 102 6102 A2 21 IEEE PESC-02 JUNE 2002 The apparent voltamperes at the input is therefore given by ~ 2~ 2 S V I 2002 6 102 24 106 VA 2 2 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 ~~ P V I1 cos ψ1 ψ1 = displacement angle between the fundamental of the voltage and the fundamental of the current 200 20 cos 45o 4000 W 2 ~~ Q V I1 sin ψ1 200 20 sin 45o 22 4000 VA 2 IEEE PESC-02 JUNE 2002 ~I ~I ~I ~I 200 10 10 8 10 VA ~ D2 V 2 ~ V2 2 2 1 2 3 2 2 2 2 6 2 ~ ~ P2 Q2 D2 V2 I 2 ~~ ~ P V I1 cos ψ1 I1 PF power factor cos ψ1 ~~ S VI I 1 Displacement factor cos ψ1 0.707 2 I 20 Distortion factor 1 0.817 I 600 Therefore, the power factor is PF 23 1 2 0.577 2 6 IEEE PESC-02 JUNE 2002 EXAMPLE 2 NONSINUSOIDAL VOLTAGE-RL LOAD A periodic, sinusoidal voltage given by v 2 200sin ωt 200sin 5ωt 30o 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 f1 50HZ. ~ Solution. The rms terminal voltage V is given by ~ ~2 ~2 V V1 V5 200 2 200 2 Therefore ~ V 283V Z1 4 j10 Z1 10.8 1 tan 1 10 / 4 68.2o 24 IEEE PESC-02 JUNE 2002 5 51 50 Z5 4 j50 Z5 50 5 tan 1 50 / 4 85.4o The instantaneous load current is given by 200 200 i 2 sin t 68.2o sin 5t 30o 85.4o 50 10.8 ~ The rms load current I is therefore given by ~ 2 ~ 2 ~ 2 ~ 2 ~ 2 V1 V5 I I1 I5 Z1 Z5 18.52 2 4 2 359A 2 25 IEEE PESC-02 JUNE 2002 Apparent voltamperes S at the load terminals in the absence of capacitance is therefore ~ ~ 2 S2 V 2 I 2 28.72 106 VA P Average power In this case is n ~ ~ ~~ ~ ~ P Vn In cos L V1 I1 cos 1 V2 I2 cos 2 ... 1 200 18.52 cos 68.2o 200 4 cos85.4o 1440W The power factor before compensation is therefore PF 26 P S 1440 28.72 10 6 0.27 IEEE PESC-02 JUNE 2002 EXAMPLE 3 NONSINUSOIDAL VOLTAGE AND NONSINIMUSOIDAL CURRENT A periodic, nonsinusoidal voltage with instantaneous value given by The resulting current has an instantaneous value given by i 2 20 sinωt 45 10 sin2ωt 60 10 sin3ωt 60 v 2 200sin ωt 200sin 2ωt - 30o is applied to a nonlinear impedance. o L o o SLR , SLX , SLD of the load apparent voltamperes and compare thee with the classical values PL , QL , DL respectively. Calculate the components Solution. 2 20 sinωt 45 10 sin2ωt 60 10 sin3ωt 60 v 2 200sin ωt 200sin 2ωt - 30o iL o o o 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. 27 IEEE PESC-02 JUNE 2002 The rms voltage and current at the supply are given by ~ V2 2002 2002 8 104 V2 ~2 IL 202 102 102 6 102 A2 ~ and ~ The load apparent voltamperes SL therefore has a value defined in terms V IL ~ ~ 2 S2L V 2 IL2 48 106 VA Instantaneous expressions of the hypothetical currents i R , i X , i D are given by i R 2 20 cos 45o sin t 10 cos 300 sin 2t 30o 2 ~2 ILR 20 cos 45o 10 cos 30o 2 11 10 2 A 2 4 i X 2 20 sin 45o cos ωt 10 sin 300 cos 2ωt 30o 2 10 sin 3t 60 2 ~2 ILX 20 sin 45o 10 sin 30o iD 2 9 10 2 A 2 4 o ~2 ILD 10 2 A 2 28 IEEE PESC-02 JUNE 2002 Note that current components i R , i X contain only those harmonic terms which are common to both voltage and current. These are therefore consistent with the n1 terms. ~ ~ ~ The rms load current components ILR , ILX , ILD are found, as expected to sum ~ to the total rms load current IL ~2 ~2 ~2 ~ 11 9 ILD ILR ILD 10 2 1 6 10 2 IL2 4 4 Components S 2 LR S 2 LX SLR , SLX , SLD of the apparent voltamperes can now be obtained ~ 2 ~ 2 11 2 2 V ILR 10 8 10 4 22 106 VA 4 ~ 2~ 2 9 2 2 V ILX 10 8 10 4 18 106 VA 4 ~ ~2 2 S2LD V 2 ILD 10 2 8 10 4 8 106 VA 29 IEEE PESC-02 JUNE 2002 The component voltamperes are seen to sum to the total apparent voltamperes S2LR S2LX S2LD 106 22 18 8 48106 VA 2 S2L Components PL , QL , DL of SL are found as follows: n ~ ~ 2 PL Vn1 In1 cos ψ n1 1 2 200 20 cos 45 200 10 cos 30 2 100 20 2 10 3 106 2 2 30 3 2 o 2 o 2 106 8 3 4 6 20.8 106 S2LR IEEE PESC-02 JUNE 2002 2 n ~ ~ 2 Q L Vn1 In1 sin ψ n1 1 200 20 sin 45o 200 10 sin 30o 2 10 6 2 2 1 14.6 10 6 S2LX D2L S2L PL2 Q2L 48 20.8 14.6 106 12.6 106 VA 2 S2LD From the possible compensation viewpoint it is interesting to note that SLX and Q L differ by significant amount. SLX 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”. 31 IEEE PESC-02 JUNE 2002 Similarly the definition of active voltamperes SLR 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 SLR and SLX are entirely fictitious and non-physical. The active SLR Is not to be compares in importance with the average power PL which is a real physical property of the circuit. Term SLR Is merely the analytical complement of term SLX voltamperes Term SLX 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. 32 IEEE PESC-02 JUNE 2002 Voltage and current profiles in a commercial building 33 IEEE PESC-02 JUNE 2002 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 1st, 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. 34 IEEE PESC-02 JUNE 2002 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. 35 IEEE PESC-02 JUNE 2002 • 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 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 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. 36 IEEE PESC-02 JUNE 2002 POWER QUALITY STANDARDS – IEEE 519-1992 STANDARDS TABLE I CURRENT DISTORTION LIMITS FOR GENERAL DISTRIBUTION SYSTEMS (120-69000 V) 37 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 4.0 1.5 0.7 12.0 100<1,000 12.0 5.5 5.0 2.0 1.0 15.0 >1,000 15.0 7.0 6.0 2.5 1.4 20.0 Source: IEEE Standard 519-1992. 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 TABLE II LOW VOLTAGE SYSTEM CLASSIFICATION AND DISTORTION LIMITS IEEE 519-1992 STANDARTS Special Applications General System Dedicated System Notch Depth 10% 20% 50% THD (Voltage) 3% 5% 10% Notch Area (AN)* 16,400 22,800 36,500 Source: IEEE Standard 519-1992. 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. 38 IEEE PESC-02 JUNE 2002 TABLE III LIMITS OF THD% IEEE 519-1992 STANDARDS 39 SYSTEM Nominal Voltage Special Application General Systems Dedicated Systems 120-600V 3.0 5.0 8.0 69KV and below - 5.0 - IEEE PESC-02 JUNE 2002 TABLE IV PROPOSED IEC 555-2 CLASS D STANDARDS for power from 50 to 600W 40 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 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. 41 IEEE PESC-02 JUNE 2002 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. 3 MVA 10 b Ib= Base current in Amps (24) Amps 3kVb Zs = System impedance = MVAb= Base MVA, MVA b MVA sc p.u. (25) MVAsc= short circuit MVA at the point of interest VH= Percent individual harmonic voltage distortion = I h h Zs 100 Volts Ib 42 IEEE PESC-02 (26) JUNE 2002 2 Vh 12 THD υ % h 2 100 V1 THD i % 2 2 Ih h 2 I1 100 (27) h = harmonic order Ih 100 IH = Percent individual harmonic distortion = IL (28) Isc = Short Circuit current at the point under consideration. IL = Estimated maximum demand load current Isc MVA sc S.C. Ratio = Short circuit Ratio I L MVA D (29) MVAD = Demand MVA 43 IEEE PESC-02 JUNE 2002 K Factor = Factor useful for transformers design and specifically from transformers that feed Adjustable Speed Drives h h 1 2 Ih IL 2 (30) 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 44 IEEE PESC-02 JUNE 2002 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 A N1 Source inductance A NDR1 Source inductance the sum of inductance s from PCC to the drive (32) ANDR1 : Notch area at the input of the drive 45 IEEE PESC-02 JUNE 2002 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. 46 IEEE PESC-02 JUNE 2002 EXAMPLE OF A SYSTEM ONE LINE DIAGRAM 47 IEEE PESC-02 JUNE 2002 System impedances diagram which can be used to calculate its resonance using PSPICE or SIMULINK programs 48 IEEE PESC-02 JUNE 2002 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) 49 IEEE PESC-02 JUNE 2002 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) 50 IEEE PESC-02 JUNE 2002 3) Basic parallel-active filter for current source in nonlinear loads 51 IEEE PESC-02 JUNE 2002 4) Basic series-active filter for voltage-source in nonlinear loads 52 IEEE PESC-02 JUNE 2002 5) Parallel combination of parallel active and parallel passive 6) Series combination of series active and series passive 53 IEEE PESC-02 JUNE 2002 7) Hybrid of series active and parallel passive 8) Hybrid of parallel active and series passive 54 IEEE PESC-02 JUNE 2002 9) Series combination of parallel-passive and parallel-active 10) Parallel combination of series-passive and series-active 55 IEEE PESC-02 JUNE 2002 11) Combined system of series-active and parallel-active 12) Combined system of parallel-active and series-active 56 IEEE PESC-02 JUNE 2002 A SIMPLE EXAMPLE OF AN INDUSTRIAL POWER DISTRIBUTION SYSTEM 57 IEEE PESC-02 JUNE 2002 HARMONIC LIMITS EVALUATION WHEN POWER-FACTOR-CORRECTION CAPASITORS ARE USED - - As it can be seen from the power distribution circuit the power-factorcorrection 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. Rtot Ltot IS If C VS Ih AC Source Harmonic Load Z in Using the above circuit the following equations hold: 58 IEEE PESC-02 JUNE 2002 2 kVLL X R sys cos tan 1 , MVA sc R 2 kVLL 1 X Xsys sin tan , MVA sc R R sys Xsys R sys α 2 Xsys α 2 (33) (34) α = The turns ratio of the transformer at PCC 2 1000 kVLL R tr R pu kVA tr 2 1000 kVLL X tr X pu kVA tr 59 IEEE PESC-02 (35) (36) JUNE 2002 R tot Rsys R tr (37) X tot Xsys X tr Xc 2 1000 kVcap C (39) kVAR cap 1 ωX c Xc (40) 1 ωC X tot L tot ω 60 (38) (41) X tot 2 πf IEEE PESC-02 (42) JUNE 2002 The impedance Z looking into the system from the load, consists of the in parallel combination of source impedance R jX tot and the tot capacitor impedance Zin R tot jωL tot j / ωC 1 R tot jωL tot j ωC 1 1 ωo L tot , fo ωo C 2πωo (43) (44) The equation for Zin 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 ωo (rad/sec) or f o (HZ) and equating the inductive and capacitive reactances. 61 IEEE PESC-02 JUNE 2002 - 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 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. 62 IEEE PESC-02 JUNE 2002 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 X ratio of system impedance 2.4 R 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: a. 200 KVAR b. 400 KVAR c. 600 KVAR d. 800 KVAR 63 IEEE PESC-02 JUNE 2002 The parallel resonant frequencies for every case of power factor correction is calculated as follows: 20 sintan 250 2.4 1.4769Ω 202 R sys cos tan 12.4 0.6154Ω 250 2 Xsys α 1 20 50 0.4 R sys 0.6154 502 0.000246Ω Xsys 1.4769 502 0.000591Ω 1000 0.42 R tr 0.01 0.00160Ω 1000 1000 0.42 X tr 0.07 0.0112Ω 1000 64 IEEE PESC-02 JUNE 2002 R tot 0.000246 0.0016 0.001846Ω X tot 0.000591 0.0112 0.011791Ω 0.011791 L tot 37.55 10 6 H 2 π 50 Case a: 1000 0.42 Xc 0.8 Ω 200 1 C 3.98 103 F 2 π 50 0.8 fo 1 2 π 37.50 10 6 3.98 103 412.18HZ For 200 KVAR, the harmonic order at which parallel resonance occurs is: h 412.18 50 8.24 65 IEEE PESC-02 JUNE 2002 Case b: 1000 0.42 Xc 0.4 Ω 400 C 7.96 103 F f o 291.45HZ h 5.83 Case c: 1000 0.42 Xc 0.267 Ω 600 C 11.94 103 F f o 237.97HZ h 4.76 66 IEEE PESC-02 JUNE 2002 Case d: 1000 0.42 Xc 0.2 Ω 800 C 15.92 103 F f o 206.08HZ h 4.12 It is clear for the above system that in the 600 KVAR case, there exists a parallel resonant frequency f o close to the 5th harmonic. 67 IEEE PESC-02 JUNE 2002 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 68 IEEE PESC-02 JUNE 2002 - - 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. 69 IEEE PESC-02 JUNE 2002 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: 70 IEEE PESC-02 JUNE 2002 f os 1 1 = Resonant frequency of the series filter (45) 2πLf C 2 2 f 1000 kV 1 2πf X c cap Lf C 2πf os 2 2πf os 2 2π f os 2 kVAR cap (46) The new parallel combination is having resonant frequency when 1 ωo L tot ωo Lf 0 ωo C fo (parallel resonance) 1 1 2πL tot Lf C 2 = resonance frequency of the (47) equivalent distribution circuit Also R tot jωL tot If I h R tot jωL tot ωL f 1 ωC 71 IEEE PESC-02 (48) JUNE 2002 Is I h j ωLf 1 / ωC R tot j ωL tot ωLf 1 ωC Vh Is R tot jωLtot (49) (50) R tot jωL tot jωLf j 1 ωC Zin 1 R tot jωL tot jωLf j ωC R tot jωL tot jωLf 1 ωC 1 R tot j ωL tot ωL f ω C 72 j IEEE PESC-02 (51) JUNE 2002 As it was discussed before Selecting f o 235HZ or 4.7 th harmonic With Lf KVcap= 0.4 , 2 50 1000 0.4 2 π 2352 600 KVARcap= 600 68.45 10 6 H 38.45μH The new parallel combination is having resonant frequency: fo with fo 1 2 π L tot Lf C Ltot 37.55 106 H Lf 38.45 106 H C 11.94 103 F 1 2 π 76 106 11.94 103 h 167.16 / 50 3.43 73 we have 167.16HZ (without Lf was 4.76) IEEE PESC-02 JUNE 2002 The following table shows the variation of Parallel resonant frequency With and without resonant inductor Parallel Resonant f0 74 KVAR C(mF) Without 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 With Lf JUNE 2002 SIMULATED RESULTS USING MATLAB/SIMULINK T1 i - + C motor . + v - 380kw/490rpm V compens Bus Bar (horiz)2 T Ground (input) Gnd + v - 200m cable 4x240 50m cable 4x1 V1 Ground (output)1 - Current Measurement4 i + v - + Voltage Measurement3 voltage Series RLC Branch Scope3 Scope1 + i Source itot Scope2 + i - Scope4 Scope Current Measurement6 Bus Bar (horiz)3 Source1 chock2%5 chock2%3 chock2%1 AC Voltage Source Ground (input)8 Ground (input)4 Ground (input)5 Ground (output) Current Measurement5 i - + + i - Current Measurement3 Bus Bar (horiz)7 AC Current Source7 Bus Bar (horiz)5 AC Current Source4 Series RLC Branch3 Series RLC Branch2 AC Current Source5 AC Current Source8 AC Current Source6 AC Current Source3 Bus Bar (horiz)6 Bus Bar (horiz)4 Ground (input)2 - i Current Measurement1 + Ground (input)3 Bus Bar (horiz)1 AC Current Source1 AC Current Source2 Series RLC Branch1 AC Current Source Bus Bar (horiz) Ground (input)1 75 IEEE PESC-02 JUNE 2002 SIMULINK RESULTS 76 IEEE PESC-02 JUNE 2002 SIMULINK RESULTS 77 IEEE PESC-02 JUNE 2002 ACTIVE FILTERING Parallel type 78 Series type IEEE PESC-02 JUNE 2002 RESULTS OF ACTIVE FILTERING 2500 1500 25 500 20 [% I1] I [A] 30 -500 15 10 -1500 5 -2500 0 0 5 10 15 20 25 Time [ms] 30 35 2 40 5 8 11 14 17 Harmonics 20 23 Input current of a 6-pulse Rectifier driving a DC machine without any input filtering 35% 30% 2500 25% [%I1] I Dynacomp [A] 5000 0 20% 15% 10% -2500 5% -5000 0% 0 10 20 30 40 Time [ms] Input current with Active Filtering 79 IEEE PESC-02 2 5 8 11 14 17 20 23 Harmonics JUNE 2002 1000 14 12 10 [% U1] U [V] 500 0 8 6 4 -500 2 -1000 0 0 5 10 15 20 25 Time [ms] 30 35 40 2 5 8 11 14 17 Harmonics 5 8 11 14 17 Harmonics 20 23 Typical 6-pulse drive voltage waveform 1000 14 12 10 [% U] U [V] 500 0 8 6 4 -500 2 -1000 0 0 5 10 15 20 25 Time [ms] 30 35 40 2 20 23 Voltage source improvement with active filtering 80 IEEE PESC-02 JUNE 2002 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. LF C Equivalent circuit 81 IEEE PESC-02 JUNE 2002 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. 82 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 WAVEFORMS OF THE PARALLEL ACTIVE FILTER Source voltage Load current Source current A. F. output current 83 IEEE PESC-02 JUNE 2002 PARALLEL ACTIVE FILTER EQUATIONS IC GI L G1 0 IS (52) G h 1 ZL VS I LH Z Z ZS L ZS L 1 G 1 G ZL 1 VS 1 G IL I LH ZL 1 G Z ZL ZS S 1 G 1 G If ZL ZS h 1 G h (53) (54) (55) Then the above equations become I C I Lh (56) ISh 1 G I LHh 1 G 84 IEEE PESC-02 VSh 0 ZL (57) JUNE 2002 I Lh I LHh VSh ZL (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 ZL ZS and consequently equations (53) and (55) become IS I LH 1 G (59) 1 G h 1 (60) ZS = Source impedance I LH = Is the equivalent harmonic current source ZL = Equivalent load impedance G = 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. 85 IEEE PESC-02 JUNE 2002 VdC C • The DC bus nominal voltage, VdC, must be greater than or equal to line voltage peak in order to actively control i C . • 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: 2 VdC Vφn t max i Cdt 3 Also LF 0 di φL C max Δv Cmax dt nφV = peak line-neutral voltage CdV = DC voltage of the DC bus of the inverter Lφ i = Line phase current xamCvΔ = maximum acceptable voltage ripple, C i = Phase current of the inverter 86 IEEE PESC-02 JUNE 2002 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 v u , v v and v w and the threephase load currents i Lv , i Lu and i Lw into α-β orthogonal coordinate. vα v β i Lα i Lβ 87 2 1 3 0 1/ 2 2 1 3 0 1/ 2 3/2 3/2 IEEE PESC-02 vu 1/ 2 vv 3 / 2 v w i Lu i Lv 3 / 2 i Lw 1/ 2 JUNE 2002 Then according to p - q theory, the instantaneous real power p L and the instantaneous imaginary (reactive) power q L are calculated. p L v α q v β L vβ i Lα v α i Lβ where 88 pL pL pL ~ pL DC + low frequency comp. + high freq. comp. q L qL q L ~ qL DC + low frequency comp. + high freq. comp. IEEE PESC-02 JUNE 2002 ~ The conventional active power is corresponding to p L, the conventional reactive ~ power to q L and the negative sequence to the 2 f components of p L and q L . The commands of the three-phase compensating currents injected by the shunt active conditioner, iCu , iCv and iCware given by: iCu i Cv i Cw 1 2 1/ 2 3 1 / 2 0 vα 3/2 - vβ 3 / 2 1 v β p v α q p = Instantaneous real power command q = Instantaneous reactive power command 89 IEEE PESC-02 JUNE 2002 Substituting p ~ pL Current Harmonics compensation is achieved ~ q qL p ~ pL Current Harmonics and low frequency variation ~ Components of reactive power compensation q q L qL p pL ~ pL Current Harmonics and low frequency variation Components of active and reactive power compensation q q L ~ qL 90 IEEE PESC-02 JUNE 2002 HARMONIC DETECTION METHODS i) 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. 91 IEEE PESC-02 JUNE 2002 SHUNT ACTIVE FILTER CONTROL a) Shunt active filter control based on voltage detection 92 IEEE PESC-02 JUNE 2002 Using this technique the three-phase voltages, which are detected at the point of installation, are transformed to v d and vq on the dq coordinates. Then two first ~ order high-pass filters of 5HZ in order to extract the ac components vd and ~ vq from v d and vq . 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. iAF K V vh 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 i AF with the actual current of the active filter i AF 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 v i is compared with a high frequency triangular waveform to generate the gate signals for the power semiconductor devices. 93 IEEE PESC-02 JUNE 2002 b) Reference current calculation scheme using source currents (is), load currents (iL) and voltages at the point of installation (vS). 94 IEEE PESC-02 JUNE 2002 3-φ HYBRID ACTIVE-PASSIVE FILTER Compensation of current harmonics and displacement power factor can be achieved simultaneously. 95 IEEE PESC-02 JUNE 2002 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 VCh KISh 96 IEEE PESC-02 JUNE 2002 If the AC mains voltage is pure sinusoidal, then ISh ZF I Lh K ZF ZS THD i ZF I Lh K Z Z F S h 2 IS1 • 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. 97 IEEE PESC-02 JUNE 2002 Displacement power factor correction is achieved by controlling the voltage drop across the passive filter capacitor. VC βVT Displacement power factor control can be achieved since at fundamental frequency the passive filter equivalent impedance is capacitive. 98 IEEE PESC-02 JUNE 2002 HYBRID ACTIVE-PASSIVE FILTER Single-phase equivalent circuit 99 IEEE PESC-02 Single-phase equivalent circuit for 5th Harmonic JUNE 2002 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 vAF K i F5 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 Z5 j5ωL F K0 The active filter presents a negative resistance to the external Circuit, thus improving the Q of the filter. K rF 100 1 rf K j5ωC F VBUS5 0 , IEEE PESC-02 IS5 1 VS5 j5ωL T JUNE 2002 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 v AF K i F5 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. 101 IEEE PESC-02 JUNE 2002 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 102 IEEE PESC-02 JUNE 2002 - The series active filter exhibits high impedance to harmonic current and consequently blocks harmonic current flow from the load to the source. VC Output vol tage of the A.F. KGI S IS ZL I L VS ZS ZL KG ZS ZL KG (61) (62) G = Equivalent transfer function of the detection circuit of harmonic current, including delay time of the control circuit. G1 0 103 , G h 1 IEEE PESC-02 (63) JUNE 2002 K = A gain in pu ohms The voltage distortion of the input AC source VSh is much smaller than the current distortion. K ZL h If and K ZS ZL h (64) Then VC ZLILh VSh IS 0 104 (65) (66) IEEE PESC-02 JUNE 2002 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) 105 IEEE PESC-02 JUNE 2002 SELECTION OF AF’ S FOR SPECIFIC APPLICATION CONSIDERATIONS AF Configuration with higher number of * is more preferred Compensation for Specific Application 106 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 CONCLUSIONS 107 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 REFERENCES [1] [2] [3] [4] [5] [6] 108 RECOMMENDED PRACTICES ON HARMONIC TREATMENT IEEE Std. 519-1992, ΄΄IEEE Recommended Practices and Requirements for Harmonic Control in Electric Power Systems΄΄, 1993. IEC Sub-Committee 77B report, ΄΄Compatibility Levels in Industrial Plants for Low Frequency Conducted Disturbances΄΄, 1990. 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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. IEEE PESC-02 JUNE 2002