POWER MITIGATION ASSIGNMENT-21. For linear load:

Fig 1: 3 phase rectifier feeding a linear loadThe Fig 1 shows a 3 phase rectifier feeding a linear load made up of a resistor. The circuit is mainly designed for a 220V AC input. The 3phase AC input is rectified using a bridge rectifier having 3 legs. The AC input is first given to a 3 phase VI measurement block to get the instantaneous voltages and currents. These instantaneous active and reactive powers (P and Q) are obtained by using the P-Q transformation block. The linear load is made up of a resistive load of 10k. The output is also connected to a 1k resistive load. Generally, the THD of a balanced load is comparatively improved as the neutral current is always zero. Hence the use of neutral conductors should be reduced in order to obtain a improved power factor by reducing the load imbalances. Thus, this reduces the THD in the circuit.The simulation was carried out and the below results were observed.Input Voltage: 220V, 50Hz

Fig 2a: For an AC input voltage of 220V, 50HzFor an AC input voltage of 220V-50Hz, the observed voltage is 300V. This is due to the internal inductance of 16.58mH and resistance of 0.8929.

Fig 2b.1: Input current in phase A

Fig 2b.2: Input current in phaseB

Fig 2b.3: Input current in phaseCThe Fig 2b.1, Fig 2b.2 and Fig 2b.3 shows the input current from the 3 phases A, B and C is found to be 0.02A. The THD is calculated with respect to the input currents.

Fig 3.1: Output voltage from the linear load phase A

Fig 3.2: Output voltage from the linear load phase B

Fig 3.3: Output voltage from linear load phase C

Fig 4: Output voltage from the rectifier circuitThe Fig 4 shows the output voltage from the 3 phase rectifier. The output so obtained is a pulsating DC voltage having a value of 300V. The pulsating output voltage can be further improved by the addition of capacitors at the load end.

Fig 5: Active and reactive powersThe Fig 5 shows the active and reactive power obtained in the circuit. The active power is the useful power that is transmitted from the source to the load. The reactive power does not contribute to any useful power but it keeps circulating between the phases. The active power therefore has a value of 100V and the reactive power is 50V peak-to-peak. The power factor of the circuit can be improved cancelling the reactive power to zero.

Fig 6: Current from the VI measurement block (Iabc)The Fig 6.shows the current Iabc from the VI measurement block. All the 3 phase currents are sinusoidal and have a peak current value of 0.22A.Fig 7: Total Harmonic Distortion analysis of currents across Phase A, Phase B and Phase CThe Fig 7 shows the Total Harmonic Distortion (THD) spectrum of the currents flowing through the 3 phases. For a fundamental frequency of 50Hz and with the number of cycles considered is 2, the THD is found to be around 4.60%.2. For non-linear load:

Fig 8: 3 phase rectifier feeding a non-linear loadThe Fig 8 shows a 3 phase rectifier feeding a non-linear load made up of a resistor. The circuit is mainly designed for a 220V AC input. The 3phase AC input is rectified using a bridge rectifier having 3 legs. The AC input is first given to a 3 phase VI measurement block to get the instantaneous voltages and currents. These instantaneous active and reactive powers (P and Q) are obtained by using the P-Q transformation block. The non-linear load is made up of an asynchronous machine. The THD of a non-linear load is high compared to that of a linear load. This can be proved seeing the waveforms obtained from the simulation.

Fig 9.a: For an AC input voltage of 220V, 50HzFor an input of 220V, 50Hz the output obtained from the 3phase source is distorted due to the load being non-linear.

Fig 9b.1: Input current in phase A

Fig 9b.2: Input current in phase B

Fig 9b.3: Input current in phase CThe Fig 2b.1, Fig 2b.2 and Fig 2b.3 shows the input current from the 3 phases A, B and C is found to be 22A. The THD is calculated with respect to the input currents.

Fig 10: Output voltage from non-linear loadFig 3, shows the output voltage from the asynchronous machine.

Fig 11: Output voltage from the rectifier circuitFig 11 shows the output voltage from the 3 phase rectifier circuit. The output from the rectifier is seen to be distorted and has a large number of ripples. The output from the rectifier has a magnitude almost equal to 10V.

Fig 11: Active and reactive powersFig 11 shows the active and reactive powers from the circuit. the active power is found to be around 500W and the reactive power is found to be nearly equal to 10W.

Fig 12: Current from the VI measurement block (Iabc)The Fig 12.shows the current Iabc from the VI measurement block. it can be seen that all the 3 phase currents do not have the same magnitude. This is due to the non-linear load.

Fig 13: Total Harmonic Distortion analysis of currents across Phase A, Phase B and Phase CThe Fig 13 shows the Total Harmonic Distortion (THD) spectrum of the currents flowing through the 3 phases. For a fundamental frequency of 60Hz and with the number of cycles considered is 2, the THD is found to be around 28.75%.

INFERENCESSeeing the above obtained graphs and THD spectrum it can thereby be verified that, the THD of a linear load is comparatively less than the THD obtained from a linear load.Thus balanced loads are preferred in order to reduce the THD. If the THD is reduces the power factor is also improved. Improved power factor implies the power factor being close to unity. This thereby will improve the overall efficiency of the system.