Design of Passive Filter

The passive shunt filter is the filter most commonly used to eliminate current harmonic distortion. In particular, these filters are connected in shunt with a connected load. Fig. 10.3 (a) depicts its electric circuit diagram, whereas Figure 10.3 (b) depicts its hardware setup. An ultimate objective is to mitigate harmonics, produced by nonlinear loads, especially by induction motor drives. Although passive filters offer a low-impedance path to divert all harmonic components of current, they also have the tendency to offer some reactive power to the system. Importantly, the filter is used to serve two objectives: one for filtering purpose and the other for reactive compensation, which ultimately improves the power factor of load circuit. Therefore, the passive shunt LC filter is designed which mitigates 3rd and 5th order harmonics and reduces the overall THD of the line current-voltages. Chosen parameters of the inductor and capacitor of the shunt passive filter are 6 mH and 6.5 mF, respectively.

Simulation Results, Analysis, and Discussion

In this proposed work, the PH A-5850 was used for carrying out PQ analysis at various PCCs. MATLAB simulations were performed and validation was achieved by developing an experimental set-up. For measurements, the PHA was connected in between an autotransformer and a direct online (DOL) starter, using current probes and voltage probes for evaluating harmonics in line current and line voltage, respectively. This investigation was carried out under varying loads on a squirrel cage induction motor (SQIM), namely no-load, half-load, full-load, and under blocked- rotor. Fig. 10.4 (a) illustrates the block diagram of an experimental setup of an SQIM with the PHA. Rating of a three-phase SQIM is 3-HP, 4.5 A. rated voltage 415 V,

FIGURE 10.3 Typical passive filter, (a) Electric circuit diagram, and (b) hardware set-up

FIGURE 10.4 (a) Experimental setup with PHA (b) Experimental setup of TIM with PHA rated speed 1440 rpm and В class insulation. Furthermore, an autotransformer is connected, which is used for varying the supply voltage. The DOL starter is used for starting the three-phase SQIM. Fig. 10.4 (b) depicts the complete hardware setup for a proposed scheme in which red, yellow, and blue probes have been used for measuring harmonics in line current. Similarly, red, yellow, and blue clamps are used for measuring harmonics in line voltage. Current measurement range is 0.1 mA to 1000 A. Also, the PHA is capable measuring harmonics upto the 99th order, with a display of 50 harmonics displayed on one screen.

Analysis of TIM Under No-load Conditions

Under no-load conditions, the output power delivered is zero, i.e., the output work is zero, although the rotor is rotating, as the output torque is zero. Fig. Ю.5 (a) illustrates the minimum current rating of 3.3 A at a working machine at no-load. However, under half-load conditions, as depicted in Fig. 10.5(b), output power delivered to the rotor shaft is half that, compared to rated power. Maximum-rated current of TIM is 4.5 A, with load being adjusted to midway between its minimum and maximum values. Minimum current is 3.3 A in order that half-load current is adjusted to 3.9 A. Fig. 10.5 (c) depicts the full-load conditions at which the power delivered to output is maximal. Similarly, Figure 10.5 (d) exhibits blocked-rotor conditions where the rotor of TIM is blocked with a reduced adjustable voltage, fed using an autotransformer. Note that the reduced voltage is of the order of 95 V.

Harmonic Analysis of TIM in Absence of Harmonic Elimination Technique

Using data collection and its analysis, harmonics analysis was carried out for TIM using the PHA under different load patterns: no-load, half-load, full-load, and blocked-rotor. Fig. 10.6 (a)-(f) illustrates the harmonic analysis using Fast Fourier Transform (FFT) for line voltages V„ V₂, and Vj, and line currents /,, I₂, and / . under no-load conditions. It may be noted that 3rd order and 5th order harmonics are 1.1% and 1.1%, respectively, which are more dominant, without using the filter. Overall, THD is 1.8%. Similarly, for line voltage V₂, 3rd order and 5th order harmonics are 1.2% and 0.8%, respectively, and overall THD is 1.7%. For line voltage V„ 3rd order, and 5th order harmonics are 1.2% and 0.7%, respectively, with overall THD being 1.8%. For line current 3rd order and 5th order harmonics are 2.7% and 2.5%, respectively, with overall THD being 4.4%. For line current /,, 3rd order and 5th order harmonics are 5.2% and 3.7%, respectively; overall THD is 7.2%. For line current I_p 3rd order and 5th order harmonics are 3.5% and 2.0%, respectively, with overall THD being 4.6%.

As shown in Fig. 10.7 under half-load conditions, for line voltage V„ 3rd order and 5th order harmonics are 1.1% and 1.1%, respectively, with overall THD being 1.9%. For line voltage V₂, 3rd order and 5th order harmonics are 1.4% and 1.1%, respectively. Overall THD is 2.1%. For line voltage V₃, 3rd order and 5th order harmonics

FIGURE 10.5 Voltage-current analysis under (a) no-load (b) halt-load (c) full-load (d) blocked-rotor

are 1.2% and 0.7%, respectively; overall THD is 1.8%. Similarly, for line current /,, 3rd order and 5th order harmonics are 2.5% and 1.5%, respectively, with overall THD being 5.3%. For line current I₂, 3rd order and 5th order harmonics are 5.7% and 3.6%, respectively; overall THD is 7.1%. For line current I_}, 3rd order and 5th order harmonics are 3.7% and 4.0%, respectively, with overall THD being 6.6%.

As shown in Fig. 10.8 under full-load conditions, for line voltage V,, 3rd order and 5th order harmonics are 1% and 1.7%, respectively, with overall THD being 2.3%. For line voltage V₂, 3rd order and 5th order harmonics are 1.4% and 1.7%, respectively; overall THD is 2.4%. For line voltage V₃, 3rd order and 5th order harmonics are 1.2% and 0.7%, respectively, with overall THD being 1.7%. For line current /,, 3rd order and 5th order harmonics are 0.5% and 0.3%, respectively; overall THD is 3.9%. For line current I₂, 3rd order and 5th order harmonics are 9% and 2.6%, respectively, with overall THD being 4.8%. For line current /„ 3rd order and 5th order harmonics are 3.6% and 1.1%, respectively; overall THD is 4.9%.

It must be noted that under blocked-rotor load conditions, the rotor of the TIM is blocked with reduced and adjustable voltage applied, using an autotransformer. As shown in Fig. 10.9 under blocked-rotor conditions, the reduced voltage applied is 95 V at 4.5 A maximum current. For line voltage V,, 3rd order and 5th order harmonics are 90.3% and 1.4%, respectively, with overall THD being 90.9%. For line voltage V₂, 3rd order and 5th order harmonics are 97.4% and 2.7%, respectively; overall THD is 97.9%. For line voltage V₃, 3rd order and 5th order harmonics are 78.3% and 1.6%, respectively. For line current I_}, 3rd order and 5th order harmonics are 0.9% and 0.5%, respectively, with overall THD being 1.4%. For line current I₂, 3rd order and 5th order harmonics are 1.4% and 0.2%, respectively; overall THD is 1.3%. For line current /„ 3rd order and 5th order harmonics are 1.1% and 0.3%, respectively, with overall THD being 1.4%.

Harmonic Analysis of TIM Using Passive Filter

The passive shunt filter is the most commonly used filter for mitigating current harmonic distortion. In this chapter, the passive filter has been designed to mitigate 3rd order harmonics, 5th order harmonics, and overall current THD. L and C chosen values are 6 mH and 6.5 mF, respectively.

As shown in Fig. 10.10 under no-load test, for line current /,. it is observed that THD is reduced from 4.4% to 3.3%, using the passive filter. The 3rd order and 5th order harmonics are 2.7% and 2.5%, respectively, and found to be predominant, without using the filter. However, the harmonics are reduced to 1.4% and 2.0%, respectively, by using the passive filter. Similarly, for line current I₂, it is observed that THD is reduced from 7.2% to 6.6%, using the passive filter. The 3rd order and 5th order harmonics are 5.2% and 3.7%, respectively, and are reduced to 4.9% and 3.3%, respectively, using the passive filter. For line current I₃, it is observed that THD decreased from 4.6% to 3.5%, using the passive filter. The 3rd order and 5th order harmonics are 3.5% and 2.0%, respectively and are reduced to 2.5% and 0.9%, respectively, by using the passive filter.

For line current /, under the half-load test, Fig. 10.11 depicts the harmonics values, using the shunt connected passive filter. It is concluded that THD is reduced from 5.3% to 3.3% using the passive filter. The 3rd order and 5th order harmonics are2.5% and 1.5%,respectively,and found to be predominant, without using the filter, and are reduced to 1% and 1.1%, respectively, by using the passive filter. Similarly, for line current /,, THD is reduced from 7.1% to 5.6% using the passive filter. The 3rd order and 5th order harmonics are 5.7% and 3.6%, respectively, without using the filter, whereas the values are reduced to 4.2% and 2.7%, respectively, by using the passive filter. For line current /„ THD is reduced from 6.6% to 4.8% using the passive filter, with the 3rd order and 5th order harmonics being 3.7% and 4.0%, respectively, without using the filter, whereas harmonic level is reduced to 3.4%, using the passive filter.

As shown in Fig. 10.12 under full-load conditions, for line current /,, it is concluded that THD is reduced from 3.9% to 3.1%, using the passive filter. The 3rd order and 5th order harmonics are 0.5% and 0.3%, respectively without using the filter, but decrease to 0.2% and 0.2% when using the passive filter. For line current I₂, it is concluded that THD is reduced from 4.8% to 4.0%, using the passive filter. The 3rd order and 5th order harmonics are 2.9% and 2.6%, respectively, without using the filter, and are reduced to 2.1% and 2.2%, respectively, by using the passive filter. For line current /„ THD is reduced from 3.9% to 3.1% using the passive filter. The 3rd order and 5th order harmonics are 0.5% and 0.3%, respectively, without using the filter, but are reduced to 0.2% and 0.2%, respectively, by using the passive filter.

Fig. 10.13 shows the situation under blocked-rotor load conditions. For line current /,, THD is reduced from 3.9% to 3.1%, using the passive filter. The 3rd order and 5th order harmonics are 0.5% and 0.3%, respectively, without using the filter, but are reduced to 0.2% and 0.2%, respectively, by using the passive filter. For line current I₂, THD is reduced from 1.3% to 1.1%, using the passive filter. The 3rd order and 5th order harmonics are 1.0% and 0.2%, respectively, without using the filter, being reduced to 0.8% and 0.1%, respectively when using the passive filter. For line current /₍, THD is reduced from 1.4% to 0.8%, using the passive filter. The 3rd order and 5th order harmonics are 1.1% and 0.3%, respectively, without using the filter, and decrease to 0.5% and 0.2%, respectively when using the passive filter.

Table 10.1 illustrates THD analysis in current under dynamic conditions of load on TIM in the absence of the passive filter. It reveals that, as the order of load increases on TIM, the level of harmonics decreases and overall THD also decreases. This decrease in harmonics is due to effective implementation of the PWM technique. Table 10.2 illustrates THD analysis in current in the presence of the passive filter. It is clear that the use of the filter has greatly reduced the level of harmonics and overall THD. Table 10.3 shows the comparison of the two modulation techniques in the proposed system. It revealed the overall superiority of DSVPWM over PWM in reducing the level of harmonics in current. DC-offset is the presence of the DC component in AC signals at various PCCs, whereas the level of DC-offset voltage is also found to be reduced, using the DSVPWM technique relative to the PWM technique.

FIGURE 10.13 Harmonic analysis for (a) l_h(b) U and (с) /_; using the passive filter under blocked-rotor test

TABLE 10.1

Analysis of Current THD (Without Passive Filter)

s. No.	Order of Harmonics	At no-load			At '/r-load			At full-load			At blocked-rotor
I.	3rd	2.7	5.2	3.5	2.5	5.7	3.7	0.5	2.9	3.6	0.9	1.0	1.1
2.	5th	2.5	3.7	2	1.5	3.6	4.0	0.3	2.6	1.1	0.5	0.2	0.3
3.	Ithd	4.4	7.2	4.6	5.3	7.1	6.6	3.9	4.8	4.9	1.4	1.3	1.4

TABLE 10.2

Analysis of Current THD (With Passive Filter)

s. No.	Order of Harmonics	At no-load			At half-load			At full-load			At blocked-rotor
1.	3rd	1.4	4.9	2.5	1.0	4.2	3.4	0.2	2.1	2.9	0.7	0.8	0.5
2.	5th	2.0	3.3	0.9	l.l	2.7	2.8	0.2	2.2	0.3	0.2	0.1	0.2
3.	Who	3.3	6.6	3.5	3.3	5.6	4.8	3.1	4.0	3.8	1.0	l.l	0.8

TABLE 10.3

Analysis of THD and DC-offset, Using SPWM and DSVPWM Techniques

s. No.	Order of Harmonics	Using PWM			Using DSVPWM
1.	3rd	1.26	1.08	2.16	0.31	0.45	0.76
2.	5th	0.12	0.07	0.91	0.01	0.05	0.08
3.	^thd	5.27	3.19	5.86	1.44	2.35	2.35
4.	DC-offset voltage	1.426	3.03	4.456	0.8922	0.6975	0.4947

Conclusion

In this chapter, PQ analysis, based on using modulating techniques, is based on ensuring the provision of harmonic-less power to the medical and healthcare sector. The absence of these modulating techniques for controlling TIM drives in healthcare facilities can put the life of patients at risk. The ultimate objective of the proposed systems is to deliver sinusoidal power at constant magnitude. Due to the harmonics present in electric power supply, many complexities involving the harmonics and electro-magnetic interference are produced. Therefore, the proposed systems have attempted to reduce the overall harmonics presented in line current and line voltages at PCC. Harmonic analysis has been carried out for the three-phase SQIM, using the PHA under dynamic loading conditions. It has been revealed that 3rd and 5th harmonics are more dominant. The passive filter has been designed to improve PQ. By implementing the shunt passive filter, 3rd and 5th harmonics have been reduced. Furthermore, PWM and the discrete SVPWM technique are also used to mitigate the current harmonics. Both modulation techniques are coordinated with an AC-DC-AC converter. Observations show that both switching techniques work effectively, although the SVPWM produces better results than the PWM technique. Also, PHA is capable of measuring harmonics up to the 99th order, with a display of 50 harmonics on one screen. There are a number of interesting possible directions for future work based on this research, and these are outlined as follows:

• • Harmonic analysis of the induction motor can be carried out using different techniques.
• • Harmonic mitigation can be performed by using different techniques.

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