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International Journal Of Electrical, Electronics And Data Communication, ISSN: 2320-2084 Volume-4, Issue-9, Sep.-2016 RECOGNIZATION AND REDUCTION OF SOURCE CURRENT HARMONICS IN A LOADED SYSTEM USING WAVELET DECOMPOSITION 1 N.HARIHARAVARSHAN, 2R.MELVINA MINNY Electrical and Electronics Department Panimalar Engineering College Chennai, India E-mail: [email protected], [email protected] Abstract- All the electrical equipment connected to the grid must abide by certain indisputable and indubitable regulations regarding grid current harmonics, which will maintain the quality of grid power .The motor drive systems are always equipped with rectifiers, inverters and many other devices for their speed regulation process, this collaboration of inverter and rectifier stay as a conventional setup in today’s world. These inverter that are composed of power switches and reactive components like inductor and capacitor. These reactive components are bulky and increases the system cost, particularly in low cost applications such as electrical home appliances, these equipment are also a cause of producing harmonics into the system this will finally provide a prodigal solution. The home appliances such as air conditioners ,refrigerators, washing machines, electric fans, water pumps etc., use variable speed motor drives (induction motor) in which power electronic technologies have been enabled, these appliances produces harmonics and reactive power. This harmonic current level tends to increase, as the power of the appliances increases, a directly proportional relationship. The continuous increase of such harmonics will seem to be an open ended threat to the system. To mitigate these disturbances active filters with controllers have been employed to reduce the harmonic level in the system. In this paper, an active filter system along with a PI controller which is capable of filtering the harmonic current produced by the loads is proposed with a new prospective of analyzing the distorted wave in detail. Thought mitigation is a process which would seem very mandatory to improve power quality there is a further improvement in this parochial view that is the wave requires contemplation to have a better idea of the amount of energy lost and at which point the loss is more comparatively. So this paper discuss about the wavelet analysis of the deviated wave and make the energy usage in a frugal, wise that is more efficient way than wasting in harmonic distortion. Keywords- Harmonics,Active Filter,PI Controller, Induction Motor, THD,Wavelet Analysis. practical. This keeps the currents out of the supply system. This is the most common type of filtering applied because of economics and because it also tends to correct the load power factor as well as remove the harmonic current. I. INTRODUCTION Harmonics have existed from the earliest days of the industry and were (and still are) caused by the nonlinear magnetizing impedances of transformers, reactors, fluorescent lamp ballasts, induction motors etc. In addition, power electronic devices have become abundant today because of their capabilities for precise process control and energy savings benefits. Harmonic currents caused by nonlinear loads connected to the distribution system are flowing through the system impedances, and in turn distorts the supply voltage. Such loads are increasingly more abundant in all industrial, commercial, and residential installations and their percentage of the total load is growing steadily. Harmonic currents increase the r.m.s. current in electrical systems and deteriorate the supply voltage quality. They stress the electrical network and potentially damage equipment. They may disrupt normal operation of devices and increase the operating costs. Another approach is to apply a series filter that blocks the harmonic currents. This is a parallel-tuned circuit that offers a high impedance to the harmonic current. It is not often used because it is difficult to insulate and the load voltage is very much distorted. The filters are classified as active and passive. B. Passive Filters The passive filters are used in order to protect the system by reducing the harmonic current to enter the power system. The most common type of shunt active filters used in harmonic reduction is the single tuned filter (STF) shown in Fig 1 which is either a low pass or band pass filter. This type of filter is the simplest form to design and less expensive. II. FILTERS A. Filters A filter is an electronic device that can remove specific ranges of frequencies from a signal. A filter could be in shunt or series. The shunt filter works by short-circuiting harmonic currents as close to the source of distortion as Fig 1.Single tuned filter circuit configuration Recognization and Reduction of Source Current Harmonics in a Loaded System Using Wavelet Decomposition 1 International Journal Of Electrical, Electronics And Data Communication, ISSN: 2320-2084 The double tuned filter(DTF) shown in Fig.2 can be used to filter two harmonic source simultaneously.DTF has a few advantages such as only one reactor is subjected to full-line voltage and smaller space needed. Volume-4, Issue-9, Sep.-2016 filter will operate in several modes (balanced or unbalanced), then the injection of mitigation current is complete in order to nullify or compensate the harmonic currents. Injection of this mitigation current gives enhanced power quality. The performance of the shunt active power filter is dependent to a great extent upon the method used for the estimate of reference current. A. Shunt Active Power Filter In the present electrical distribution system, there has been a rapid increase of distorted loads such as power supplies, domestic appliances, rectifier gear and adjustable speed drives (ASD), etc. As the number of these loads rises, harmonic currents generated by these loads may become very significant. These harmonics could lead to a variety of different power system issues including the distorted voltage waveforms, gear overheating, malfunction in system protection, incorrect power flow metering, excessive neutral currents, light flicker etc. They have also decreased efficiency by drawing reactive current component of the distribution network. Fig.2.Double tuned filter circuit configuration C. Active Filters It is made up of OP-Amps, resistors and capacitors shown in Fig.3. Active filters are easy to adjust over a wide frequency range without altering the desired response. High input impedance prevents excessive loading of the driving source, and low input impedance prevents the filter from being affected by the load. In order to overcome these issues active power filters (APFs) has been developed. The voltage source inverter (VSI) based shunt active filter has been used in present and is known as a viable solution. The active filters are used in the condition where the harmonic orders change in terms of magnitude and phase angles. In such conditions it is feasible to the use active elements instead of passive ones in order to provide dynamic compensation. There are three types of configurations; they are: series active filter, shunt active filter and hybrid filter. The control scheme, in which the necessary mitigating currents are determined by sensing line currents only, is easy to implement. The system uses a conventional proportional plus integral (PI) controller for the generation of the reference current. B. Control Schemes The switching pulses of an active filter circuit are generated using two common techniques such as direct current control (current reference) and indirect current control (voltage reference). The direct current control technique is preferred to the shunt active power filter over indirect current control due to fast response and robustness. The direct current control technique is adapted to generate the switching gate pulses along with any one of the controls like hysteresis control and ramp comparison control etc. Fig.3.Active Filter Circuit configuration III. PROPOSED SYSTEM A. Hysteresis Comparison Method In this method, inverter output current is forced to follow the current reference in each phase. Deviation between these two quantities is limited by upper and lower band in a hysteresis loop. If actual current reach the upper limit of the hysteresis band, the inverter leg is switched off so that current decrease reach till the lower band of hysteresis loop where the inverter leg is switched on again and the actual current increase to upper band. The sine wave shape of the reference signal causes inverter switching frequency vary and gives different current ripple in one fundamental inverter period. Three phase shunt active filter is used as a prototype as shown in figure. The shunt active power filter (SAPF) is used to produce mitigation current in opposite phase. Power circuit for SAPF is planned as a MOSFET based three-phase voltage source inverter with DC storage capacitor for better mitigation of non-sinusoidal unbalanced/balanced loads. The active power filter has a control scheme i.e PI controller for DC voltage regulation. The capacitors are planning to limit the DC voltage ripple to a particular value, typically 1 to 2%. In this case the capacitor should be planned for the worst case. Since the shunt active Recognization and Reduction of Source Current Harmonics in a Loaded System Using Wavelet Decomposition 2 International Journal Of Electrical, Electronics And Data Communication, ISSN: 2320-2084 Volume-4, Issue-9, Sep.-2016 C. Block Diagram of the Proposed System Fig.4.Current shape for hysteresis control The hysteresis control tend to give higher distortion due to increase of load current. Hence in order to reduce the distortions in current, ramp comparison method is employed. A ramp comparison method is better in form of lower effect in line current distortion compared with hysteresis control method. The ramp comparison is preferred compared to that of hysteresis method as the main source of distortion is considered from. Fig 6. Block diagram of proposed system The above Fig 6 is the block diagram of linear and non linear load in which the total harmonic distortion value is to be reduced using an input active filter and PI controller at the source end. It includes 2 level 4 pulse PWM current generator to generate the pulses from the PI controller. B. Ramp Comparison Method In this mode of controller, sine wave reference signal produced is added with a triangular signal to create other sinusoidal triangular reference. This reference is then compared with actual current. The point where sinusoidal triangular wave and actual current cross, becomes time when inverter leg is switched. This method causes inverter switching frequency and PWM pulses wide vary and give different current ripples in one inverter period. Ramp comparison method tend to give lower distortion due to increase of load current. This method is better in form of lower effect on line current distortion. The Fig.5, shows the typical ramp comparison method used in the paper. IV. PROPOSED CONTROL ALGORITHM The proposed control algorithm here is the implementation of ramp comparison method in the PI controller for the generation of gate pulses shown below. Fig.7.PI controller block diagram Using ramp comparison method the error current signal ΔiF is generated on comparing with reference current (iF*) and actual filter current (iF). The generated error current signal is manipulated using proportional plus integral controller (PI) and fed to current limiter. Hence, to reduce the error current signal by increasing the controller gain. The block diagram of ramp comparison PWM control is shown in Fig. 4.10.The sine wave reference signal produced is added with a triangular signal to create other sinusoidal triangular reference. This reference is then compared with actual current. The point where sinusoidal triangular wave and actual current cross, becomes time when inverter leg is switched. This Fig.5.Current shape for ramp comparison method. Recognization and Reduction of Source Current Harmonics in a Loaded System Using Wavelet Decomposition 3 International Journal Of Electrical, Electronics And Data Communication, ISSN: 2320-2084 Volume-4, Issue-9, Sep.-2016 method causes inverter switching frequency and PWM pulses wide vary and give different current ripples in one inverter period. The differential equations related to shunt active filter and PI controller are v s Vm sin t is I m sin t ∗ = ∗ − di L F R i F v s mV C dt dV C C m iF dt Fig 8. Simulink diagram for induction motor without active filter and PI Controller From the above equations di 1 vs R iF L F vcs dt 1 dv m * C c dt iF m i F k p ( v c V C ) k i ( v c V C )dt Fig 9. Original distorted current waveform Where, is – source current is* – reference source current iL– load current VC – measured dc link capacitor voltage m - constant In this proposed system, space vector control pulse width modulation (SVPWM) technique is adopted for inverter fed squirrel cage induction motor (SCIM) drive system to achieve the better performance and reduction of harmonic effects. Fig 10. Decomposition of original distorted current waveform Wavelet analysis is preferred over FFT analysis (Fast Fourier Analysis) because wavelet analysis can support varying loads and systems, another reason for applying wavelet transform on the obtained waveform is that it has a control on the uncertainty principle each wavelet that is obtained from the mother wavelet has something about the frequency spectrum of the signal ,last but the most undisputable reason is that it exactly gives the point in the time spectrum where the change is found and the amount of change in that point which is not available feature in FFT . These are the reasons for choosing wavelet analysis over FFT analysis, and wavelet analysis has been applied to the existing current waveform to decompose the original current waveform into child waveform from the mother wavelet. V. SIMULATIONS AND ANALYSIS A.Simulink diagram of induction motor without active filter and PI Controller The Fig.8, is the simulation diagram of the induction motor and a non linear load without active filter and PI-controller. The AC source is rectified into DC source from which ripples are removed using a capacitor bank. Using an inverter circuit the DC source is again converted into AC which is then fed to the induction motor. The inverter and the rectifier circuit is composed of semiconductor devices like MOSFET, diode etc. As it is well known that the semi conductor devices are capable of injecting harmonics into the system, the same happens here and hence these harmonic currents ingress the transmission line through the source. Thus polluting the entire power system. Fig.9, shows the distorted waveform of the current Fig.10, Shows the decomposed form of the original current waveform. These current waveforms have a very high ripple content due to the presence of harmonics. The decomposition from the mother wavelet to child wavelet is shown in fig.11, the exact location of the harmonics in the current waveform is thus clearly examined which will be easier to frame the solutions according to the intensity level. Recognization and Reduction of Source Current Harmonics in a Loaded System Using Wavelet Decomposition 4 International Journal Of Electrical, Electronics And Data Communication, ISSN: 2320-2084 Volume-4, Issue-9, Sep.-2016 The above Fig.13, and Fig.14, is the input voltage waveforms of the system. The magnitude of the input voltage source is 230V. The above waveform is sinusoidal in shape which is given as the input to the system. The nonlinear load that we are considering to build the matlab simulation is an induction motor. The specification considered while constructing the matlab simulation model, is given in the table 1 TABLE 1 Fig 11. Decomposition into mother and child wavelet of distorted current waveform The Fast Fourier Transform Analysis for Induction motor and non linear load without active filter and PI Controller. The total harmonic distortion value is found to be 69.07% shown in the Fig 12 which is found to be a high value. This high value leads to a high pollution into the system because of the harmonic content which can be seen from the FFT analysis spectrum. Fig. 12. Fast Fourier Transform for induction motor without active filter and PI Controller. B. Simulink Diagram of induction motor with active filter and PI Controller Fig 13.Original voltage waveform Fig. 15.Simulink Diagram of Shunt Active Filter used in the harmonic control Shunt active filters are used to eliminate the unwanted harmonics and compensate power factor by injecting equal but opposite harmonic compensation currents. An active power filter acts as a current controlled voltage source inverter connected in parallel with non linear load as shown in Fig 15, is controlled to generate the required compensation currents. Fig 14. Decomposition of original voltage waveform Recognization and Reduction of Source Current Harmonics in a Loaded System Using Wavelet Decomposition 5 International Journal Of Electrical, Electronics And Data Communication, ISSN: 2320-2084 Volume-4, Issue-9, Sep.-2016 Fig.19. Decomposition into mother and child wavelets of original current waveform Fig 16. Simulink diagram of induction motor with active filter and PI controller To reduce the harmonic content in the system, an active filter and a PI controller is implemented at the source end of the system. The speed (rpm) of the induction motor is compared with a reference speed whose error signal is sent to the PI controller. The output of the PI is then given to the PWM pulse generator whose pulses are given as a trigger signal to the MOSFET devices used in the rectifier circuit. By this the performance of the active filter is improved thereby reducing the harmonic content from the system using the Simulink diagram shown in Fig 16. Fig 20. Fast Fourier Transform analysis for induction motor with active filter and PI Controller Wavelet analysis is done for the system and the child wavelet is being derived from the mother wavelet as shown in fig 19. The Fast Fourier Transform Analysis for Induction Motor and non linear load with active filter and PI controller. The total harmonic distortion value is found to be 35.97% as shown in Fig 18. Thus the total harmonic content is found to be reduced to about 60.85%. TABLE 2 Fig 17. Original current waveform CONCLUSION The solid state AC-AC converter system with diode fed R load and induction motor loads are modelled and simulated successfully. The results of simulation with and without active filter in supply side are presented. The simulation results indicate that the harmonics are reduced by about 92.58% by introducing active filter and PI controller in the supply side for only linear load and reduced by about Fig 18. Decomposition of original current waveform Fig 17 and Fig 18 shows the waveforms of the current after the active filter and PI controller has been added in the system. From observing the waveform we can see that the current waveform is found to have reduced in the ripple content compared to the previous case. Recognization and Reduction of Source Current Harmonics in a Loaded System Using Wavelet Decomposition 6 International Journal Of Electrical, Electronics And Data Communication, ISSN: 2320-2084 60.85% by introducing active filter and PI controller for both linear and non linear load. The advantages of this system are that the line drop and line losses are reduced by introducing active filter. The scope of the present work is to reduce the current harmonic THD by using Active filter and PI controller. This proposed control scheme will be very effective in harmonic mitigation. The reduction of current harmonics using two inductor power factor correction circuits will be done in future. REFERENCES [1] [2] [3] [4] Volume-4, Issue-9, Sep.-2016 rejection,’IEEE Trans. Ind. Electron., vol. 56, no. 8, pp. 3117–3127, (Aug. 2009). [5] Pottker.F and Barbi.I, ‘Power factor correction of nonlinear loads employing a single phase active filter: Control strategy, design methodology and experimentation,’ in Proc. 28th Annu. IEEE PESC(1997), pp. 412–417. [6] Mishra.M.K, Linash.P.K, ‘A Control Algorithm for Single Phase Active Power Filter under Non-stiff Sources’, IEEE Trans. Power Electronics, vol. 21, May 2006, pp. 822-825. [7] Aredes. M, Hafner.J&Heumann. K (1997). ‘Three-phase four-wire shunt active filter control strategies’. 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