HARMONIC FILTER BASED AC DRIVE: ANALYSIS FOR REACTIVE POWER Anjali Nagar1,
Guide - Siddharth Shankar Mishra2
2Assistant Professor, 12Oriental University Indore
Abstract- In the era of electrical engineering the utilization of power is a basic unconditional factor but meanwhile the utilities are suffered due to the electrical pollution or noise called harmonics. The harmonics are never been generated by the source it is generated by the load or drives. Hence the study of harmonics and the method to minimize the harmonics has been taken into consideration to develop this project work. For Understanding what is important to know about harmonics can be challenging for those without extensive engineering background. Calculations are a major part of design process in all aspects of engineering applications. This laborious and time consuming process can be made really easy by the aid of a high level engineering software like MATLAB.
This project deals with the scope and flexibility of MATLAB for:
1. Calculation of design parameters for L –C components of different branches of a harmonic filter.
2. Graphical analysis of Harmonic Pollution and different Harmonic components.
3. Verification of design using SIMULINK and Power System Toolbox before implementation to check any design error that might cause undesirable results.
1 HARMONIC MITIGATION
TECHNIQUES
For the reduction of harmonics the number of techniques has been develops for the fulfilment and the requirement suggested by the current harmonic standard. Generally these techniques are divided into following main five types,
1. Passive filters for example DC link choke, series and shunt, line reactors and low pass filter.
2. Phase multiplication systems for example 12-pulse, 18-pulse rectifier.
3. Active harmonic compensation systems for example series and parallel.
4. Hybrid systems
5. PWM rectifiers for example step-up, step-down, VSI, CSI.
The intent of these techniques is to make the input current a pure sinusoidal waveform, so as to reduce the overall current THD. In passive filters, the flow of the undesired harmonic currents into the power system can be prevented by the usage of a high series impedance to block them or by diverting them to a low impedance parallel path. Here these kind of methods are representing the basic concept of the series and the shunt passive filters, respectively. Series passive filters can be purely inductive type or LC tuned type. AC line reactor filter and DC link inductor filter are the two purely inductive type filters. AC line reactors offer a considerable magnitude of
inductance that alters the way the current is drawn by the rectifier bridge. They make the current waveform less discontinuous, resulting in lower current harmonics[6]. To maximize the input reactance while minimizing AC voltage drop both AC line reactors and DC link inductance (choke), shown in Fig. 1.3, can be combined. The DC link inductance is electrically present after the diode rectifier and before the DC bus capacitor and it performs very similar to the three phase AC line reactors. Both AC line and DC link inductance insertion methods provide a limited amount of THD reduction that is not sufficient to comply with the IEEE 519 standards.
Fig.1.1 AC line reactor and DC line inductance based passive filtering.
1.1 IGBT Fundamental The Insulated Gate Bipolar Transistor
(IGBT) is basically the active device or also called as minority-carrier device having very high input impedance and also the current carrying capacity of the device is
very high. If the characteristics of these devices have been observed then its bipolar characteristics indicate that it is a voltage controlled device. The similar kind of characteristics has been gettable by making the combine use of power MOSFET and BJT, but instead of that same work has been performed by a single device hence IGBT has been preferable. This IGBT has been well compatible with the n number of application in power electronics such as pulse width modulation, three phase drive system where it is well controlling low noise and it also going to improve the performance of UPS(uninterrupted power supply), SMPS(switching mode power supply), it is also applicable where high switch repetition rate are required. IGBT improves the efficiency of the system and it will improve the performance of the system by reducing the audible noise of the drive. It is also suitable for the resonant mode convertor with low conduction loss and low switching loss.
2LITERATURESURVEY
When the pollution or harmonic distortion concept is going to be discuses then it is found that this is major area where the power quality issue are considered.
According to Clyde Glikar[12] the harmonic distortion always affect some utilities as well as research organization power industries, where harmonics are getting generated by the load and getting reflected towards the source. This results into excessive power requirement and generates the heat. Therefore this paper suggest a use of capacitor bank towards the load so that harmonic distortion can be minimized.
According to B. C. Smith and N. R.
Watson[13] the harmonic distortion can be minimized in Ac as well as DC drives system by adopting the different converter technique. These convertor techniques are used to controlled the harmonic modulation by means of filtering and communication angle. The various 3Ф, 12 pulse convertor are generally used or configure for the large power applications, but while using this kind of convertor V and I sources are considered for the distortion.
The 3 harmonic simulation text of the design system has been discussed by G. Bathurst and N. R. Watson[14][15]
where the demonstrating guideline has been provided through different case study and the different examples of simulation with the practical approach.
The different example of simulation has been provided for harmonic problem.
According to him evaluation has been made in existing software which is used for the analysis of harmonics and develop the new method for harmonic simulation.
The comparative study of fundamental harmonic data and it’s effect over THD and after evaluation available new data has been compared. This is one of the effective methodology for the design of harmonic filter in order to reduced the total harmonic distortion.
3 BASIC THREE PHASE DRIVES
Basically in three phase systems, two pulses of current flows by keeping the phase difference of 600. In line 1, one pulse will get occurs during the voltage difference in between L1 & L2 is at its peak and similarly second pulse will get occurs when the potential difference between L1 & L3 is at its peak value. Fig.
3.1 shows the actual current in input for basic drives.
Fig. 3.1 Actual input current 3.1 Input Current to a Basic Variable Frequency Drive
The n numbers of problems are getting created in the design of electrical system due to high peak current pulses of short duration.
One of the important problem deals with power transformer which are going to feed the drives. Basically the transformer has been design to handle the current which is smooth and sinusoidal. And the current pulses shown in figure are a main cause of extra heating of transformer. Therefore transformer should get design to deal with safely with such current otherwise system will get
collapse due to overheating. Where filtering system is not applied. Then it is required the transformer with current carrying capacity which is exactly double.
Therefore one test has been done for this kind of note, where the input current (RMS) with zero harmonics for a drive and filtering of 107 percent of fundamental current with harmonic filtering system. This test has been performed by using power line with moderately high impedance. If we select low value impedance then difference may be 175 percent. Hence the additional current may be required if we increase the size of all devices and wire switch gear and transformers which will be a cause of increment in installation cost which is a penalty of the harmonic current distortion.
3.2 Distribution of Drive Load and Linear Load
The linear load of a transformer is totally depend upon the load of drive for the same transformer and the transformer should get load by 44 percent of its nominal power when it is going to use the drives with zero harmonic filtering system. This results into the nearly double size requirement of transformer.
The another issue is related with the other equipment interface to transformer. The magnetic field and its strength around a wire is directly proportional to the rate of changes in the direction of the current in the given wire.
When the current pulses are getting change very fast then heavy electrical noise will get develop than normal current. And humming can be recognized in other equipments and fluctuating display on monitor which provides the data which is not reliable. For the operation of electronic equipment which are sensitive.
4 CIRCUIT MODEL DESCRIPTION A 50 Hz, 500 kW load has been feed by a 50 Hz voltage source with the help of an AC-DC-AC converter circuit. The voltage gettable at secondary will be 600V; 50 Hz of the Y-Δ transformer is first rectified with the help six pulse diode bridge. The filtered DC voltage is applied to two-level inverter of IGBT which will be generating 50 Hz. Pulse Width Modulation (PWM) has been used by IGBT inverter with carrier
frequency of 2 kHz. With a sample time of 2 µs. The VL has been regulated at 1 pulse (380 V rms) by a PI voltage regulator using abc_to_dq and dq_to_abc transformations. The initial output of the voltage regulator circuit will be a vector which will contain the 3 modulating signals which is used by the PMW Generator circuit for generating the 6 IGBT pulses. The modulation index will be return by second output.
Three Phase discrete PWM Pulse Generator has been available in the block library of Extras/Discrete Control. The voltage regulator has been built from blocks of the Extras/Measurements and Extras/ Discrete Control libraries.
The current for diode as well as IGBT has been observed with the help of multimeter block. For signal processing observation, signals displayed on Scope block with sampling rate of 2µs has been stored in a variable named Scope one for filter and another scope for without filter circuit.
4.1 Demonstration
Start the simulation. After a transient period of nearly of 50 ms, the given system will go to reach the steady state.
Then voltage waveforms has been observed at DC bus, output of inverter as well as load on Scope one. The harmonics which are generated by the inverter nearer to the multiples of 2 kHz are getting filtered by the LC filter.
As the maximum value of load voltage which is expected is 537 V (380 Vrms). In steady state, then the average value of the modulation index will be m = 0.80 & the average value of the DC voltage will be 778 V. When the simulation process is completed then open the Powergui block & select 'FFT Analysis' where it will display the range of 0 to 1000 Hz frequency spectrum of signals which will store in the scope structure. The FFT will be performed on a 5-cycle window starting at t=0.1-2/50 (last 5 cycles of recording). Select input labeled 'Vab Load’. Click on Display and observe the frequency spectrum of last 5 cycles. Notice harmonics around multiples of the 2 kHz carrier frequency.
Maximum harmonic is 1.4 % of fundamental and THD is 5.35 %.
Now the same system design with all the same parameter but without filter
the compare the result of the THDv and THDi and FFT Analysis .
Fig. 4.1 Designed simulation model without filter in MATLAB 5 WAVE FORM OUTPUT
As per the waveform we get the result of system .In the system when we not use the filter the inverter output waveform of the current and voltage is not sinusoidal and with filter we get the proper sinusoidal waveform of the current and voltage.
Fig. 5.1 Waveform of Vinv, Vab load, Iabc (without Harmonics Filter Power
system)
Fig. 5.2 Waveform of Vinv, Vab load, Iabc (with Harmonics Filter Power
system) 5.1 FFT Analysis
The FFT Analysis of total harmonic distortion are acknowledge the result of harmonics filter system .
When we take the Bar Graph of the without harmonics filter power system the result is
Fig. 5.3 Vab_load –THD =72.15%
Fig. 5.4 Vab_inv THD =72.15%
Fig. 5.5 Iabc THD= 70.79%
When we take the Bar Graph of the with harmonics filter power system the result is
Fig. 5.6 Vab_load THD =5.59%
Fig. 5.7 Vab_inv THD=53.32%
Fig. 5.8 Iabc THD = 4.23%
The result is Without Harmonics Filter power system
Vab_load - THD = 72.15%
Vab_inv - THD = 72.15%
Iabc - THD = 70.79%
The result is With Harmonics Filter power system
Vab_load- THD = 5.59%
Vab_inv- THD = 53.32%
Iabc- THD = 4.23%
6 CONCLUSION & FUTURE SCOPE The use of simulation tools as MATLAB/
Simulink, allows reproducing the behaviour of the power systems in different situations, analysing how the system answers in these situations and choosing the solution that better fit with the particular problem without additional costs. However for the analysis of different harmonic distortion and its reduction the passive filters having different values may be simulated. By performing the simulation we approach the reduction of the values of the voltage as well as current harmonic distortions because of an underground traction system & a steel industry has obtained. Hence the reduction of the distortion by implementing the passive filter has been simulated for mention systems.
As per IEEE 519 standard the major factor for power quality degradation
is Harmonic pollution. Harmonic Filters will reduce the effects of harmonics as well as it will provide reactive power for improvement of power factor. With the help of MATLAB all the parameters of harmonic filter can be design very effectively and easily.
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