EFFECT OF HARMONICS ON DISTRIBUTED GENERATION Dr. Elham Makram Department of Electrical and Computer Engineering Clemson University Clemson, South Carolina 29634-0915 Clemson University Electric Power Research Association DG Conference, Clemson SC March 14, 2002

DG Conference Clemson University March 13-15, 2002 Outline Overview of the effect of nonlinear loads on Power System Harmonics Effect of converter drive and arc furnace Effect of harmonics on power factor Effect of capacitor placement on harmonics Impact of unbalance on harmonics Need for accurate modeling for harmonic analysis Comparison of Time domain and Frequency domain methods Performance analysis of models for nonlinear loads Change in the scenario due to addition of Distributed Generation DG devices and corresponding systems DG Conference Clemson University March 13-15, 2002

DG Conference Clemson University March 13-15, 2002 Effect Of converter drive and arc furnace 2 4 6 8 10 12 14 16 18 20 Current Magnitude (%) TRANS5_49 LINE3 LINE2 LINE1 Line Number 5th 7th 11th 13th 17th 19th 23rd 25th 2 4 6 8 10 12 14 16 18 20 Voltage Magnitude (%) Bus 12 Bus 11 Bus Numbers 5 7 11 13 17 19 23 25 The presence of a 6-pulse converter on the power system causes harmonic currents to flow through the system. Voltage distortion is negligible Arc furnace produces voltage distortion and current distortion; the distortion in voltage being much higher than that in current. As such the AF by itself is more harmful to other customer loads than the converter drive. DG Conference Clemson University March 13-15, 2002

DG Conference Clemson University March 13-15, 2002 Effect Of Harmonics on Power Factor 1 A nonlinear load at a bus causes the power factor at that bus and at buses close to it to drop. 0.95 0.9 Power Factor Linear Load 0.85 AF Load 0.8 0.75 Bus 12 Bus 11 Bus 8 Bus 4 1 Buses 0.9 Placement of power factor improvement capacitors at buses close to the nonlinear load bus worsens the power at the nonlinear load bus, and also at buses close to it. 0.8 Power Factor 0.7 Without capacitor With capacitor 0.6 0.5 0.4 Bus 12 Bus 11 Bus 8 Bus 4 Buses DG Conference Clemson University March 13-15, 2002

DG Conference Clemson University March 13-15, 2002 Effect of Capacitor placement on Harmonics The presence of capacitor banks increases the current and voltage distortion at the nonlinear load bus and the buses close to it. Before capacitor placement After capacitor placement Current Voltage Current Voltage 200 2000 400 2000 100 1000 200 1000 -100 -1000 -200 -1000 -200 -2000 -400 -2000 0.02 0.04 0.06 0.08 0.02 0.04 0.06 0.08 Magnitude in Ampere 0.02 0.04 0.06 0.08 Magnitude in Volt 0.02 0.04 0.06 0.08 Magnitude in Ampere Magnitude in Volt Time (seconds) Time (seconds) Time (seconds) Time (seconds) 250 400 1500 1500 200 300 1000 1000 150 200 100 500 100 500 50 5 10 15 20 25 5 10 15 20 25 5 10 15 20 25 5 10 15 20 25 Harmonic Order Harmonic Order Harmonic Order Harmonic Order DG Conference Clemson University March 13-15, 2002

DG Conference Clemson University March 13-15, 2002 Impact of unbalance on harmonics In addition to characteristic (6n1) harmonics, unbalance introduces uncharacteristic (triplen) harmonics 0.97 0.97 0.96 0.96 0.95 0.95 Unbalance adversely affects the power factor. Comparison is shown between the results obtained using a linear model and those obtained using a nonlinear model for the arc furnace 0.94 0.94 Power Factor Power Factor Nonlinear Model Nonlinear Model Linear Model Linear Model 0.93 0.93 0.92 0.92 0.91 0.91 0.9 0.9 0% 0% 5% 5% 10% 10% 15% 15% 20% 20% 25% 25% Degree of Unbalance Degree of Unbalance DG Conference Clemson University March 13-15, 2002

DG Conference Clemson University March 13-15, 2002 Impact of unbalance on harmonics Degree of unbalance affects harmonics differently, i.e. with an increase in the degree of unbalance, the non-characteristic harmonics increase, whereas the characteristic harmonics show a decrease. The symmetrical component decomposition of individual harmonics helps to give an insight into the behavior of harmonics under varying degrees of unbalance. Unbalance adversely affects the power factor, although if the unbalance is within practical limits, the drop in the power factor is not very significant. Unbalanced conditions render certain models for nonlinear loads, to be inadequate for use. DG Conference Clemson University March 13-15, 2002

DG Conference Clemson University March 13-15, 2002 Comparison of Time domain and Frequency domain methods 14 12 Frequency domain method of harmonic analysis gives pessimistic results, and is not equipped to accurately solve for certain types of harmonic analysis problems. 10 8 Current in line 3 (% magnitude) Time 6 Frequency 4 2 5 7 11 13 17 19 23 25 Harmonic Number 25 20 The DC side load also determines the amount of harmonics injected into the system. There is no provision in the frequency domain method to model this. 15 DC load 1/4 DC load Current Magnitude (%) 1/8 DC load 10 5 5 7 11 13 17 19 23 25 Harmonic Number DG Conference Clemson University March 13-15, 2002

DG Conference Clemson University March 13-15, 2002 Performance analysis of models for nonlinear loads Voltage-Current characteristics for the arc furnace Using a Linear model Using a Nonlinear model 400 200 300 150 200 100 100 50 Voltage (V) Voltage (V) -100 -50 -200 -100 -300 -150 -400 -150 -100 -50 50 100 150 -200 -150 -100 -50 50 100 150 Current (kA) Current (kA) Preserving the nonlinearity of the problem yields a more accurate solution. DG Conference Clemson University March 13-15, 2002

DG Conference Clemson University March 13-15, 2002 Original Picture Traditional Distribution System NONLINEAR LOADS Residential Commercial Industrial DG Conference Clemson University March 13-15, 2002

DG Conference Clemson University March 13-15, 2002 Change in the scenario due to addition of Distributed Generation System would no longer be radial DG devices would have power conditioning sub-systems, which would inject harmonics into the distribution system as well This situation would be different from the case of multiple nonlinear loads DG Conference Clemson University March 13-15, 2002

DG Conference Clemson University March 13-15, 2002 DG devices and corresponding systems to be considered DG device Interconnection Type of system Photovoltaics Microturbines Wind Energy Inverters Converter – Inverter pair Induction generator – Converter - Inverter pair Residential Commercial Industrial DG Conference Clemson University March 13-15, 2002

DG Conference Clemson University March 13-15, 2002 Preliminary results: Impact of a PV System A Typical Residential PV System DG Conference Clemson University March 13-15, 2002

DG Conference Clemson University March 13-15, 2002 Modeling of Residential System Residential system is modeled by considering four typical houses. Loads considered in each house are: Linear Loads (assumed): Incandescent light Refrigerator load Nonlinear Loads: Compact Fluorescent Lights Television Set Heat pump DG Conference Clemson University March 13-15, 2002

DG Conference Clemson University March 13-15, 2002 Cases Studied Case 1: DG as a standalone unit supplying residential loads Case 2: Residential system loads fed by the distribution system only Case 3: Residential loads fed by PV and the distribution system DG Conference Clemson University March 13-15, 2002

DG Conference Clemson University March 13-15, 2002 Results for Case 1 Voltage and current at the load bus 4.82 4.84 4.86 4.88 4.9 -150 -100 -50 50 100 150 Time(seconds) Magnitude (volts) Load voltage waveform 4.83 4.85 4.87 4.89 -60 -40 -20 20 40 60 Magnitude (amperes) Load current waveform 5 10 15 25 30 Harmonic Order Magnitude (%) Frequency Spectrum DG Conference Clemson University March 13-15, 2002

DG Conference Clemson University March 13-15, 2002 Results for Cases 2 & 3 COMPARISON OF LOAD VOLTAGE 1 2 3 4 5 6 7 8 9 10 Magnitude (%) 11 13 15 17 19 21 23 25 Harmonic order Case 2 Case 3 DG Conference Clemson University March 13-15, 2002

DG Conference Clemson University March 13-15, 2002 Results for Cases 2 & 3 COMPARISON OF LOAD CURRENT 50 Case 2 Case 3 45 40 35 30 Magnitude (%) 25 20 15 10 5 3 5 7 9 11 13 15 17 19 21 23 25 Harmonic order DG Conference Clemson University March 13-15, 2002

DG Conference Clemson University March 13-15, 2002 Conclusions Harmonics produced on the load side by the PV system were not significant compared to the high current distortion caused due to the household nonlinear loads. Harmonic distortion injected into the distribution system decreased after connecting the PV system The harmonics picture may change than the way it appears now when number of PV systems connected to the distribution system increase. DG Conference Clemson University March 13-15, 2002

DG Conference Clemson University March 13-15, 2002 Work In Progress Modeling of other types of DG – Micro turbines, Wind Energy Effect of DG on harmonic distortion in case of commercial and industrial systems Impact of varying degrees of penetration of DG Combined effect of different combinations of DG devices DG Conference Clemson University March 13-15, 2002

DG Conference Clemson University March 13-15, 2002 Future Power System Transmission system Load 2 Load 5 Load 1 Solar Energy Fuel cell Microturbine Load 6 Load 3 Load 4 Wind energy Distribution system DG Conference Clemson University March 13-15, 2002