Vin Shunt Pdf

MODELLING & SIMULATION OF A SINGLE PHASE SHUNT ACTIVE POWER FILTER NARASIMHA.S.KULKARNI Electrical & Electronics. BVBCET Hubli-31 [email protected] +91-9620153143

Abstract In this paper a single phase shunt active power filter is used for compensating the reactive power and harmonic current and unbalanced load current generated by non linear load in the grid. Here we are using single phase inverter with four IGBT’s. The obtained filter current is forced to follow a reference and this reference current must be difference between the sinusoidal input current in phase with the sinusoidal voltage supplying the load and the load current .For obtaining this reference current a frequency independent method has been used which is simpler than the traditional methods. Simulations results are presented, showing that the proposed model may operate at frequencies ranging from 40 to 65 Hz without parameter adjustment.

1. INTRODUCTION We are in an electronic era, where for almost every other work be it domestic or industrial we need electronic devices which mainly work on electric supply. The major contribution to the industrial sector is been provided by electronic equipments, mainly power electronic devices as they are main components in the control sectors of different processes. These devices impose non linear loads to the ac mains & draw a reactive & harmonic current present in the mains along with active current. This leads to low efficiency, harmful electro magnetic disturbances to other equipments & also heating of the transformers. The importance of power factor correction is also increasing... Handling of load equipments with micro-processor based controllers and power electronic devices, adjustable speed drives and power factor correction equipments all are sensitive to many power disturbances. Hence it is important to curtail these harmonics & disturbances in the supply current, also improve low power factor caused by the nonlinear loads. Most techniques use a current shaper to shape the input current

to sinusoidal waveform. There are several disadvantages in this technique. a. Since the current shaper is in cascade path of the power, it processes all the power & thus requires high current & voltage semiconductor devices thus involves significant power losses. b. It is not convenient to insert a current shaper to existing electronic equipment, as significant redesign would be needed. The other conventional approaches of reducing harmonics by using passive LC filters may result in parallel and series resonance with network impedance, over compensation of reactive power at fundamental frequency and poor flexibility for dynamic compensation of different frequency components. Hence the usage of Active Power Filters which are adjustable and dynamic in nature has gained importance. Active power filters can compensate for several harmonic orders and are not affected by network characteristics, eliminating the risk of resonance between the filter and network impedance and these take up very little space compared to passive power filters. Types of Active power filters based on topology is 1. 2. 3.

Series APF. Shunt APF. Hybrid APF.

Series APF works in series with the non linear loads these may be single or three phase depending on the supply in conjunction with used. These are mainly used to mitigate the voltage unbalance and voltage harmonics. Shunt APF works in parallel with the no linear load. These may be of single or three phase depending on the supply in conjunction with it is used.

Hybrid APF consists of Series APF and Shunt passive filters.

active power filter not only eliminates power line harmonics, but can also improve power factor.

Applications of Active power Filters. 1. To compensate current & voltage harmonics. 2. To compensate reactive power. 3. To regulate terminal voltage. 4. To suppress flickers. 5. To improve voltage balance in three phase Systems. So dealing with the prototype single phase shunt APF, 2.

SHUNT ACTIVE POWER FILTER

Fig. 2 Shunt APF Therefore we use a simple control strategy to control the APF which is described below. 4.

CONTROL STRATEGY

Principle of operation

Fig. 1 Simple block diagram of Shunt APF As shown in Fig 1. It’s a device that connected in parallel & cancels the reactive & harmonic currents from non linear loads. Then we get resulting total current from ac mains is purely sinusoidal. 3.

The filter generates the harmonic currents that are required by the load then the main supply delivers the fundamental current & the harmonics are eliminated from the power lines. The equations required are as given below

iL(t) = i o (t) + i p (t) + i q (t) + i h (t)…(1) Where i o (t) = dc component;

PRINCIPLE OF OPERATION:

The shunt active power filters compensate current harmonics by injecting equal-but-opposite harmonic compensating current. The shunt active power filter operates as a current source injecting the harmonic components generated by the load but phase shifted by 180 degree. The components of harmonic currents contained in the load current are cancelled by the effect of the active filter, and the source current remains Sinusoidal and in phase with the respective phase to neutral Voltage. In the fig. 2 shown below we can come to know that The shunt active power filter is a voltage source inverter controlled as a current source by means of a pulse width modulation signal. Adequate control of

i p (t) = in phase line current; i q (t) = reactive current; i h (t) = harmonic currents; iL

(t)=Io + Ip cos(wt) + Iqsin(wt) + Ip/2 cos (2wt) …. (2)

The only component that the mains should supply is the active current ip(Ip cos(wt)). Using 1. it can be noted that if the active filter supplies the dc component ,the reactive and the harmonic currents for the load, then the mains needs only to supply the active current.this can be easily accomplished by subtracting the active current component ip from the measured load current il iF(t)= iL(t)- ip(t)= iL(t) –IP cos (wt) ….(3)

in equation (3) IP is the magnitude of the in phase current ( which needs to be estimated) & cos (wt) is a sinusoid in phase with the line voltage.

Fig. 5 Final control block implemented. 5. SIMULATIONS Fig. 3 Closed loop diagram for calculating compensating current. 4. MODELLING OF SINGLE PHASE SHUNT APF a. Current controlled voltage source converter model.

Several simulations were run with a grid connected voltage source converter in order to check the performance of the scheme. Fig 4. shows a simulation after using the control scheme. Trace (a) is source voltage with non sinusoidal load current. Trace (b) is the source current after use of APF.

Fig. 4 Single phase VSI. b. Grid. c. Shunt APF control scheme refer to Fig 3.

Trace (a) is source voltage with non sinusoidal load current for 50 Hz.

d. Modeling of load current. e. Final block diagram implemented in MATLAB/SIMULIK software.

Trace (b) is the source voltage and source current after use of APF foor 50 Hz.

The simulation was repeated for 40,50 & 60Hz without any adjustment of the circuit parameters. 6. CONCLUSION Shunt active power filter is advantageous as discussed above. A simple & effective method for calculating the current reference required by a shunt APF was presented. This method allows harmonic elimination & power factor correction in nonlinear loads . Since it can satisfactorily in the range of 40 to 65Hz without any adjustments. These characteristics along with its simplicity, suggest this method is superior to other traditional methods of evaluating the harmonic & reactive currents in a nonlinear loads. Simulation results show that it has a slow transient response this can be advantageous to soften transient phenomena from the mains point of view. Finally , the ability operate under varying frequencies makes this method useful for the dynamic shunt active power filter. ACKNOWLEDGEMENT The author would like to thank Dr. A.B. Raju for his valuable help & guidance in the preparation of this work. REFERENCES [1] J.Sebastian Tepper. Juan W.Dixon, Gustavo Venegas & Luis Moran. “A Simple Frequency Independent Method For calculating the reactive and harmonic current in a non linear load” IEEE trans.Indust.Electronics Vol 43,No.6,pp 647653,Dec.1996 [2]H.Akagi Y.Kanazawa,and A.Nabae, “Instantaneous reactive power compensators comprising switching devices without energy storage ” , ” IEEE trans.Indust.Electronics Vol IA-20,pp. 625630,May/June 1994. [3]Akagi, H.Nabae, A., Atoh, S., “Control Strategy of Active Power Filters Using Multiple Voltage-Source PWM Converters” IEEE Trans. Industry Applications, Vol.1A-22, pp. 460-465, 1986. [4]Emílio F. Couto, Júlio S. Martins, João L. Afonso, “ Simulation results f a shunt active power filter with control based on p-q theory.” [5] “Power electronics handbook” by MUHAMMAD H. RASHID, Fellow IEEE

[6]Dugan,Roger C,Electrical power systems quality,McGraw-Hill,New York,Tokyo,1996