LC FILTER FOR THREE PHASE INVERTERA Project report submitted by: MUTHURAJ P – 13MQ37 ELDHO JACOB – 13MQ81 Dissertation submitted in partial fulfillment of the requirements for the degree of MASTER OF ENGINEERING Branch: EEE Specialization: POWER ELECTRONICS & DRIVES of PSG COLLEGE OF TECHNOLOGY MARCH - 2014 ELECTRICAL & ELECTRONICS PSG COLLEGE OF TECHNOLOGY (Autonomous Institution) COIMBATORE – 641 004 LC FILTER FOR THREE PHASE INVERTER LC FILTER DESIGN: A low pass LC filter is required at the output terminal of Full Bridge VSI to reduce harmonics generated by the pulsating modulation waveform. While designing LC filter, the cut-off frequency is chosen such that most of the low order harmonics is eliminated. To operate as an ideal voltage source, that means no additional voltage distortion even though under the load variation or a nonlinear load, the output impedance of the inverter must be kept zero. Therefore, the capacitance value should be maximized and the inductance value should be minimized at the selected cut-off frequency of the low-pass filter. Each value of L and C component is determined to minimize the reactive power in these components because the reactive power of L and C will decide the cost of LC filter and it is selected to minimize the cost, then it is common that the filter components are determined at the set of a small capacitance and a large inductance and consequently the output impedance of the inverter is so high. With these design values, the voltage waveform of the inverter output can be sinusoidal under the linear load or steady state condition because the output impedance is zero. But in case of a step change of the load or a nonlinear load, the output voltage waveform will be distorted cause by the slow system response as the output response is non-zero. Figure 1 shows the power circuit of the single phase PWM-VSI with any linear or nonlinear load. The load current flows differently depending on the kind of loads such as linear and nonlinear load. Therefore it is difficult to represent the transfer function of inverter output voltage to load current.The plant composed of L-C low-pass filter satisfies linear property, so it is possible to represent the system which has two inputs of inverter output voltage and load current. T1 T3 T5 T4 T6 T2 C1 n V1 100Vdc C2 Ra 1k Rc 1k FIG 1 n Rb 1k FLOW CHART TO DESIGN A PASSIVE(LC) FILTER START HARMONIC ANALYSIS OF PWM VOLTAGE AND NONLINEAR CURRENT SELECTING CUT-OFF FREQUENCY SELECTING MINIMUM CAPACITANCE BASED ON COST SELECTING CUT-OFF FREQUENCY SELECTING CONTROLLER RESPONSE IS THE CONTROL RESPONSE REALIZABLE? SELECTING CONTROLLER GAINS SATISFING CONTROL RESPONSE ANALYSING OUTPUT VOLTAGE HARMONICS UNDER THE LINEAR AND NON-LINEAR LOAD THD = 5% SELECTING DC LINK VOLTAGE AN CALCULATE INDUCTANCE FIG 2 STOP . Vdc – DC voltage of the inverter Δi Lmax – Current ripple (ripple current can be chosen as 10% .FORMULA USED: (i)To find inductor. Prated – Reactive power rated (reactive power is chosen as 15% of the rated power) Vrated – AC rated voltage .15% of rated current) Fs – Switching frequency (ii)To find capacitor. C=15 ∗Prated 2 ∗2 πf ∗V rated 3 Where. 1 ∗Vdc∗1 8 L= ∗Fs Δi Lmax Where. .5mH INDUCTANCE DESIGN PROCEDURE Several factors need to be considered while designing an inductor. At this current most of the ferrite core shapes does not support the design (computed from the Area Product). Estimation of Losses and Temperature Rise In this application the Inductor has to handle large energy due to the RMS current is 10A maximum. 600V INDUCTANCE VALUE CALCULATED = 4. So we select Iron powder core for this design. Energy Handling Capability of the Inductor (determines the size of the core) 4.DESIGN OF INDUCTOR: FILTER DESIGN: INVERTER LC FILTER SWITCHING FRREQUENCY = 5KHz OUTPUT CURRENT = 10A RMS LINE VOLTAGE = 230V RMS LINE FREQUENCY = 50Hz CAPACITANCE VALUE CALCUALATED = 10uF. Calculate Number of Turn 5. Selection of Copper wire 6. few of which are listed below 1. Frequency of Operation 2. Core Material Selection 3. it can be seen that factors such as flux density. Area Product Ap. From the above. In this applications the inductance value is specified. the window utilization factor. by the equation that may be stated as Follows.The design of the ac inductor requires the calculation of the volt-amp (VA) capability. . Bac. J. all have an influence on the inductor area product. Relationship of. Ap. and the current density. Ku (which defines the maximum space occupied by the copper in the window). Ap. to the Inductor Volt-Amp Capability The volt-amp capability of a core is related to its area product. Temperature Rise The inductance of an iron-core inductor. which is a function of gap dimension. and the shape. with an air gap. size. Desired inductance 2.Fundamental Considerations The design of a linear ac inductor depends upon five related factors: 1 . may be expressed as: Final determination of the air gap requires consideration of the effect of fringing flux. Frequency 4. and location of the winding . the shape of the pole faces. (across inductor) 3. Applied voltage. Operating Flux density which will not saturate the core 5. Pg. Gap loss. Pg The copper loss.Fringing flux decreases the total reluctance of the magnetic path. F. and therefore increases the inductance by a factor. Pcu. to a value greater than that calculated from Equation Where G is winding length of the core Now that the fringing flux. it is necessary to recalculate the number of turns using the fringing flux. Copper loss. F. if the skin effect is minimal. is calculated from core manufacturers' data. Pfe. N(new). Factor F with the new turns. and solve for Bac The losses in an ac inductor are made up of three components: 1. is I2R and is straightforward. has been calculated. Pfe 3. Pcu 2. . is independent of core material strip thickness and permeability. Gap loss. The iron loss. Iron loss. 045 H 300 A/cm2 ef 90 % Iron Powder Material Magnetic G permiability um 1200 H Flux Density Bac 1.68811 67 cm4 .4 J Temp Rise Goal Tr 60 C Calculate Apparent 2 power Pt Pt = VA = VL*IL 2300 A 3 Calculate Area Product AP AP = VA*10^4/ (4.44*Ku*f*Bac*J) 616.4 Tesla I Window Utilisation Ku 0.INDUCTOR DESIGN STEPS 1 Design Spec VL 230 A Inductance L B Line Current IL 10 A C Line Frequency f 50 Hz D Current Density J E Efficiency goal F 0. 3 cm 2844 g Mean Length Turn MLT Iron Area Ac 31.4640422 87 cm 4.573 5.6404 23 mm .064 cm4 Coef Kg 288.50255 9 turns 0.(MPL/um) 2.045 H 0.028 cm2 Window Area Wa 24.4 Select Core Iron Powder Core EI228 core Material Magnetic Path Length MPL 34.8KG + winding weight lg 238.715 Calculate Number of 5 Turns N 6 Inductance Required L Calculate required 7 airgap lg lg = (0.936 cm5 Surface Area At 1078 cm2 Material P P Winding Length G Lamination E 32.4piN2Ac104/L) .7 cm 8.496 cm2 Area product Ap 760. 02 cm2 uOhm/c m uOhm/c 82.8 m 203 .4piAC F10-8) 1.3006997 51 202.96670 27 turns 10 Calculate flux density Bac = VL*10^4/ (4.0333333 33 cm2 Awl=IL/J Select wire from Wire 12 table AW G 14 Calculate Winding Resistance Aw 0.44*N1*Ac*f Bac 1.Calculate Fringing flux 8 F F Calculate New number 9 of turns N1 N1=sqrt(lg*L/0.6451150 76 Tesla Calculate Bare wire 11 area Awl 0. 624748 48 W PL 111.68*B^1.13 R=MLT*N1*uOHm*1 0-6 R 0. 86 16 Calculate Core Loss Pfe =w/k *Wtfe 17 Calculate Gap Loss Pg = Ki*E*lg*f*B2 18 Calculate Total Loss sum of losses .000557*f^1.954452 56 W w/k 1.50224 22 W 14 Calculate Copper Loss PL = IL2 * RL Calculate Watts per 15 kilogram W/K = 0.9230411 8 W Pg 55.5495445 26 Ohms PL 54.3654455 33 Ohm Pfe 0. 826 Calculate Window 21 utilisation 0.1034343 62 watts per cm2 Tr 69.075759 95 Calculate the 20 Temperature rise Tr = 450*psi^0.Calculate surface area watt 19 density psi = PL/At psi 0.1657141 6 watt Ku = N1*Aw/Wa INDUCTOR WINDING DETAILS 210 3 2 20 0 I 1 0 I . Winding no.Inductor Termination Winding Arrangement WINDING DETAILS N o. Terminals No Wire Insulation of gauge between turn SWG winding Layers s 1 I 1&2 200 14 Nil (Varnishing Reqd) 2 I Tapping 3 Core Details : EI 225 210 Remarks . CORE DIMENSIONAL DETAILS . WIRE TABLE . . SIMULATION CIRCUIT: . SIMULATION RESULTS: Without Filter: With Filter: . 2012. Mrs.” Proceedings of Third Biennial National Conference. NCNTE.REFERENCES: [1] Miss.”Design and Simulation of three phase Inverter for grid connected Photovoltic systems. Mini Rajeev . Sangita R Nandurkar . Feb 24-25 .
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