To verify the performance of the proposed control strategy, a MATLAB®–SIMULINK® prototype of the rectifier is developed. A sinusoidal PWM (SPWM) voltage source inverter, which is a very popular topology in industry, is used as the DC/AC inverter for the intended rectifier–inverter AC motor drive topology (see Figure 4.39).
To illustrate the design feasibility of the proposed converter, a prototype with the following specifications is chosen:
1. Input line-to-line voltage 220 V.
2. DC-link reference voltage 370 V.
3. Input inductance 5 mH.
4. Rated output power 1 kW.
AMATLAB®–SIMULINK®model for the proposed rectifier–inverter structure is developed to perform the digital simulation. Figure 4.40 shows the converter input phase current waveform and its harmonic spectrum at rated output power operation. The same waveform for a conventional converter is shown in Figure 4.41.
vsa
AC/DC converter AC/DC inverter
D5
FIGURE 4.39 Complete diagram of the proposed UPF AC drive.
0.24 0.26 0.28 0.3 Time (s)
0.32 0.34 0.36 0.38 5 Magnitude based on Base peak—parameter
1 0 2 3 4
FIGURE 4.40 Input current and spectral composition of the proposed scheme at rated load.
5 Magnitude based on Base peak—parameter
6
FIGURE 4.41 Input current and spectral composition of a typical commercial converter.
Before improvement, the THD of the rectifier input current was found to be 91.5% and the input PF was 0.72. After improvement, the input current THD was 3.8% and the input PF was 0.999. Thus, with the proposed reference compensation current strategy, the harmonics are effectively reduced and the PF is dramatically increased.
In order to show the performance of the converter under varying load conditions, it is operated below and above its rated value. The converter input phase current waveform and its harmonic spectrum at 50% rated output power are shown in Figure 4.42. The converter input PF is found to be 0.996 and the input current THD is 4.0%.
The converter input phase current waveform and its harmonic spectrum at 150% rated output power are shown in Figure 4.43. The converter input PF is found to be 0.999 and the input current THD is 3.7%. It is evident that the proposed control strategy has a good adapt-ability to different load conditions. This strategy can also be used for rectifiers operating at various rated power levels.
Figure 4.44 illustrates the input phase currents and DC-link voltage waveforms when the converter output power demand changes instantaneously from 50% to 100% of its rated value due to load disturbance. The load change was initiated at 0.26 s where the converter was in steady state. One can clearly see that the converter exhibits a good response to the
5 Magnitude based on Base peak—parameter
6
FIGURE 4.42 Input current and spectral composition of the proposed scheme at 50% rated load.
5 Magnitude based on Base peak—parameter
6
FIGURE 4.43 Input current and spectral composition of the proposed scheme at 150% rated load.
Implementing Power Factor Correction in AC/DC Converters 133
5
0
Input current (A)
–5 0.24 0.26 0.28 0.3
Time (s)
0.32 0.34 0.36 0.38 100 0.24 200 300
DC link voltage (V)
400 500
0.26 0.28 0.3 Time (s)
0.32 0.34 0.36 0.38
FIGURE 4.44 Converter response due to load change.
sudden load variation. From this figure, it can be seen that this proposed control technique has a good adaptability to load variation.
4.6.5 Experimental Results
The control system is implemented using a single-board dSPACE 1102 microprocessor and is developed under the integrated development of MATLAB®–SIMULINK®RTW provided by The Math Works. A 1-kW hardware prototype of the rectifier–inverter structure as shown in Figure 4.39 was constructed and its performance was observed.
The rectifier input current and voltage waveforms before and after improvements are shown in Figures 4.45 and 4.46, respectively. The fluke-43 spectrum analyzer with online numerical value illustration is used to monitor the waveforms. The input PF is shown online at the upper right-hand side of Figures 4.45 and 4.46. Prior to improvement, the input current THD and PF were 91.5% and 0.72, respectively.
The proposed scheme is able to improve the input current THD to 3.8% and the input PF to 0.99. There is a remarkable improvement in PF and THD. The experimental results are iden-tical to the MATLAB® predicted ones calculated based on the waveforms in Figures 4.40 and 4.41. Figures 4.47 and 4.48 show the experimental input current fast-Fourier trans-form (FFT) spectrum for a typical conventional converter and the proposed converter, respectively.
Power
0.51 kW 0.72 PF
1.00 DPF 50.0 Hz 0.71 kVA
0.49 kVAR Full
100 V
10 A
Back Screen 1
0 0
FIGURE 4.45 Input voltage and current of a typical conventional converter.
Power
0.51 kW 0.99 PF
1.00 DPF 50.1 Hz 0.51 kVA
0.01 kVAR Fundamental
100 V
10 A
Back Screen 1
0 0
FIGURE 4.46 Input voltage and current of the proposed prototype.
At 50% rated output power, the converter input PF is found to be 0.99 and the input current THD has increased to 4.0%, as shown in Figure 4.49. At 150% rated output power, the converter input PF is found to be 0.99 and the input current THD is reduced to 3.7%
(see Figure 4.50).
Figure 4.51 shows the DC-link voltage waveforms when the converter output power demand changes instantaneously from 50% to 100% of its rated value responding to load disturbance. One can see that with the proposed control strategy, the converter exhibits a good response to sudden load variation.
To investigate the effect of input inductance, this was varied as well. Under 3 and 7 mH input inductances, the converter input currents and voltages are shown in Figures 4.52 and 4.53, respectively. These results illustrate that the proposed converter with bidirectional switches coupled with the proposed strategy overcomes most of the shortcomings of the conventional converters such as change of input PF due to output power, input inductance, and load torque variations.
Harmonics
91.5 THD% f 1
50.00 Hz 4.15 A 100% f 0°
5.64 rmsA 17.7 KF
Back Screen 3
100
%f 50
0 1 5 9 13 17 21 25 29 33 37 41 45 49
FIGURE 4.47 Input current FFT of a typical conventional converter.
Implementing Power Factor Correction in AC/DC Converters 135
Harmonics
3.8 THD% f 1
50.08 Hz 3.93 A 100% f 0°
3.93 rmsA 1.2 KF
Back Screen 2
100
%f 50
0 1 5 9 13 17 21 25 29 33 37 41 45 49
FIGURE 4.48 Input current FFT of the proposed prototype conventional converter.
Harmonics
4.0 THD% f 1
50.00 Hz 1.97 A 100% f 0°
1.97 rmsA 2.0 KF
Back Screen 5
100
%f 50
0 1 5 9 13 17 21 25 29 33 37 41 45 49
FIGURE 4.49 Input current FFT of the proposed prototype at 50% rated load.
Harmonics
3.7 THD% f
1 50.08 Hz
5.86 A 100% f 0°
5.86 rmsA 1.1 KF
Back Screen 7
100
%f 50
0 1 5 9 13 17 21 25 29 33 37 41 45 49
FIGURE 4.50 Input current FFT of the proposed prototype at 150% rated load.
500
400
300
DC link voltage (V) 200
1000.6 0.62 0.64
Time (s)
0.66 0.68
FIGURE 4.51 Converter response to a sudden load change in DC-link voltage.
Power
0.51 kW 0.99 PF
1.00 DPF 49.9 Hz 0.51 kVA
0.01 kVAR Fundamental
100 V
10 A
Back Screen 1
0 0
FIGURE 4.52 Converter input current and voltage for 3 mH input inductance.
Power
0.51 kW 1.00 PF
1.00 DPF 50.1 Hz 0.51 kVA
0.01 kVAR Fundamental
100 V
10 A
Back Screen 1
0 0
FIGURE 4.53 Converter input current and voltage for 7 mH input inductance.
Implementing Power Factor Correction in AC/DC Converters 137
Homework
4.1. A P/O self-lift Luo-converter (see Figure 6.4 in Chapter 6) is used to imple-ment PFC in a single-phase diode rectifier with R−C load. The AC supply voltage is 200 V/60 Hz and the required output voltage is 400 V. The switch-ing frequency is 2.4 kHz. Determine the duty cycle k in a half supply period (8.33 ms). Other component values for reference are R= 100 Ω, L1= L2= 10, and C= C1= CO= 20 μF.
4.2. A P/O super-lift Luo-converter (see Figure 7.1 in Chapter 7) is used to imple-ment PFC in a single-phase diode rectifier with R−C load. The AC supply voltage is 200 V/60 Hz and the required output voltage is 600 V. The switch-ing frequency is 3.6 kHz. Determine the duty cycle k in a half supply period (8.33 ms). Other component values for reference are R= 100 Ω, L1= L2= 10, and C= C1= CO= 20 μF.
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