The PWM Rectifier in Bridge Connection

11.3.5 The PWM Rectifier in Bridge Connection

Figure 11.33a shows the power circuit of the fully controlled FIGURE 11.30 Voltage doubler rectifier: (a) power circuit; (b) equiva-

(b)

(c)

single-phase PWM rectifier in bridge connection, which uses

lent circuit with T 1 on; and (c) equivalent circuit with T 2 on.

four transistors with antiparallel diodes to produce a con- trolled dc voltage v o . Using a bipolar PWM switching strategy, this converter may have two conduction states: (i) Transistors

On the other hand, the equivalent circuit of Fig. 11.30c is T 1 and T 4 in the on-state and T 2 and T 3 in the off-state; valid when transistor T 2 is in the conduction state, resulting in (ii) Transistors T 2 and T 3 in the on-state and T 1 and T 4 in the the following expression for the inductor voltage

off-state.

In this topology, the output voltage v o must be higher than the peak value of the ac source voltage v s , to ensure a proper

di s v L

=L control of the input current. =v s (t ) +V C2 > 0 (11.29)

dt Figure 11.33b shows the equivalent circuit with transistors T 1 and T 4 on. In this case, the inductor voltage is given by

hence, for this condition, the input current i s (t) increases.

di s

Therefore the waveform of the input current can be con-

v L =L

=v s (t ) −V 0 < 0 (11.30)

trolled by switching appropriately transistors T 1 and T 2 in a

dt

similar way as shown in Fig. 11.18a for the single-phase boost Therefore, in this condition a reduction of the inductor current converter. Figure 11.31 shows a block diagram of the control i s is produced. system for the voltage doubler rectifier, which is very similar

Figure 11.33c shows the equivalent circuit with transistors to the control scheme of the boost rectifier. This topology can T 2 and T 3 on. Here, the inductor voltage has the following

present an unbalance in the capacitor voltages V C1 and V C2 , expression

which will affect the quality of the control. This problem is solved by adding to the actual current value i s an offset signal

di s

proportional to the capacitor’s voltage difference.

v L =L

=v s (t ) +V 0 > 0 (11.31)

dt

Figure 11.32 shows the waveform of the input current. The ripple amplitude of this current can be reduced by which means an increase in the instantaneous value of the decreasing the hysteresis width of the controller.

input current i s .

i sref

v oref

FIGURE 11.31 Control system of the voltage doubler rectifier.

200 J. Rodríguez et al.

FIGURE 11.33 Single-phase PWM rectifier in bridge connection: (a) power circuit; (b) equivalent circuit with T 1 and T 4 on; (c) equivalent circuit with T 2 and T 3 on; (d) equivalent circuit with T 1 and T 3 or T 2 and T 4 on; and (e) waveform of the input current during regeneration.

Finally, Fig. 11.33d shows the equivalent circuit with tran- the semiconductor switching frequency and provides a more

sistors T 1 and T 3 or T 2 and T 4 are in the on-state. In this case, defined current spectrum.

the input voltage source is short-circuited through inductor L, Finally, it must be said that one of the most attractive char- which yields

acteristics of the fully controlled PWM converter in bridge connection and the voltage doubler is their regeneration capa- bility. In effect, these rectifiers can deliver power from the load

di s v L =L

=v s (t ) +V 0 > 0 (11.32) dt to the single-phase supply, operating with sinusoidal current and a high power factor of PF > 0.99. Figure 11.33e shows that during regeneration, the input current i s is 180 ◦ out of phase

Equation (11.32) implies that the current value will depend on with respect to the supply voltage v s , which means operation the sign of v s .

with power factor PF ≈ −1 (PF is approximately 1 because of The waveform of the input current i s can be controlled by the small harmonic content in the input current).

appropriately switching transistors T 1 –T 4 or T 2 –T 3 , originat-

ing a similar shape to the one shown in Fig. 11.18a for the single-phase boost rectifier.

11.3.6 Applications of Unity Power Factor

The control strategy for the rectifier is similar to the one

Rectifiers

illustrated in Fig. 11.31, for the voltage doubler topology. The quality of the input current obtained with this rectifier is

11.3.6.1 Boost Rectifier Applications

the same as presented in Fig. 11.32 for the voltage doubler The single-phase boost rectifier has become the most popular configuration.

topology for power factor correction (PFC) in general purpose The input current waveform can be slightly improved if the power supplies. To reduce the costs, the complete control sys- state of Fig. 11.33d is used. This can be done by replacing tem shown in Fig. 11.19 and the gate drive circuit of the power the hysteresis current control with a more complex linear con- transistor have been included in a single integrated circuit (IC), trol plus a three-level PWM modulator. This method reduces like the UC3854 [10] or MC33262, shown in Fig. 11.34.

11 Single-phase Controlled Rectifiers 201

C LOAD

INPUT FIGURE 11.34 Simplified circuit of a power factor corrector with control integrated circuit.

Rectifier

PFC

Output Stage

Dimming Control

FIGURE 11.35 Functional block diagram of electronic ballast with power factor correction.

Today there is increased interest in developing high-

11.3.6.2 Voltage Doubler PWM Rectifier

frequency electronic ballasts to replace the classical electro- The development of low-cost compact motor drive sys- magnetic ballast present in fluorescent lamps. These electronic tems is a very relevant topic, particularly in the low-power ballasts require an ac–dc converter. To satisfy the harmonic range. Figure 11.36 shows a low-cost converter for low-power current injection from electronic equipment and to maintain induction motor drives. In this configuration, a three-phase

a high power quality, a high power factor rectifier can be used, induction motor is fed through the converter from a single- as shown in Fig. 11.35 [11].

phase power supply. Transistors T 1 ,T 2 and capacitors C 1 ,C 2

AC MAINS

FIGURE 11.36 Low-cost induction motor drive.

202 J. Rodríguez et al. constitute the voltage doubler single-phase rectifier, which con- side. This rectifier generates a sinusoidal input current and

trols the dc link voltage and generates sinusoidal input current, controls the charge of the battery [13]. working with close-to-unity power factor [12]. On the other

Perhaps the most typical and widely accepted area of hand, transistors T 3 ,T 4 ,T 5 , and T 6 and capacitors C 1 and C 2 application of high power factor single-phase rectifiers is in constitute the power circuit of an asymmetric inverter that locomotive drives [14]. An essential prerequisite for proper supplies the motor. An important characteristic of the power operation of voltage source three-phase inverter drives in circuit shown in Fig. 11.36 is the capability of regenerating modern locomotives is the use of four-quadrant line-side con- power to the single-phase mains.

verters, which ensure motoring and braking of the drive, with reduced harmonics in the input current. Figure 11.38 shows

a simplified power circuit of a typical drive for a locomotive connected to a single-phase power supply [14], which includes

a high power factor rectifier at the input. Distortion of the input current in the line-commutated recti-

11.3.6.3 PWM Rectifier in Bridge Connection

Finally, Fig. 11.39 shows the main circuit diagram of the fiers with capacitive filtering is particularly critical in the UPS 300 series Shinkansen train [15]. In this application, ac power fed from motor-generator sets. In effect, due to the higher from the overhead catenary is transmitted through a trans- value of the generator impedance, the current distortion can former to single-phase PWM rectifiers, which provide the dc originate an unacceptable distortion on the ac voltage, which voltage for the inverters. The rectifiers are capable of control- affects the behavior of the whole system. For this reason, it is ling the input ac current in an approximate sine waveform very attractive to use rectifiers with low distortion in the input and in phase with the voltage, achieving power factor close to current.

unity on powering and on regenerative braking. Regenerative Figure 11.37 shows the power circuit of a single-phase UPS, braking produces energy savings and an important operational which has a PWM rectifier in bridge connection at the input flexibility.

THY SW THY1 THY2

Output 1f100 V Input 1f100 V

FIGURE 11.37 Single-phase UPS with PWM rectifier.

I dc i s

dc 3

DC - Link

Inverter

Motor

FIGURE 11.38 Typical power circuit of an ac drive for locomotive.

11 Single-phase Controlled Rectifiers 203 OVERHEAD

SMOOTHING CAPACITOR

PWM INVERTER

INDUCTION MOTORS

TRANSFORMER

GTO THYRISTOR

FIGURE 11.39 Main circuit diagram of 300 series Shinkansen locomotives.

Acknowledgment

3. J. Bassett, “New, zero voltage switching, high frequency boost con- The authors gratefully acknowledge the valuable contribution

verter topology for power factor correction,” in Proc. INTELEC’95, of Dr. Rubén Peña, and support provided by the Millennium 1995, pp. 813–820. Science Initiative (ICM) from Mideplan, Chile. 4. R. Streit and D. Tollik, “High efficiency telecom rectifier using

a novel soft-switched boost-based input current shaper,” in Proc. INTELEC’91, 1991, pp. 720–726.

References

5. Y. Jang and M. M. Jovanovic´, “A new, soft-switched, high-power- factor boost converter with IGBTs,” presented at the INTELEC’99,

1. R. Dwyer and D. Mueller, “Selection of transformers for comercial

1999, Paper 8-3.

buildings,” in Proc. of IEEE/IAS 1992 Annual Meeting, U.S.A., Oct 6. M. M. Jovanovic´, “A technique for reducing rectifier reverse- 1992, pp. 1335–1342.

recovery-related losses in high-voltage, high-power boost converters,” 2. D. C. Martins, F. J. M. de Seixas, J. A. Brilhante, and I. Barbi, “A family

in Proc. IEEE APEC’97, 1997, pp. 1000–1007. of dc-to-dc PWM converters using a new ZVS commutation cell,” in

7. D. M. Mitchell, “AC-DC converter having an improved power factor,” Proc. IEEE PESC’93, 1993, pp. 524–530.

U.S. Patent 4 412 277, Oct 25, 1983.

204 J. Rodríguez et al. 8. A. F. de Souza and I. Barbi, “A new ZVS-PWM unity power factor

Transactions on Industry Applications, Vol. 35, No. 1. Jan/Feb 1999, rectifier with reduced conduction losses,” IEEE Trans. Power Electron,

pp. 52–60.

Vol. 10, No. 6, Nov 1995, pp. 746–752. 13. K. Hirachi, H. Yamamoto, T. Matsui, S. Watanabe, and M. Nakaoka, 9. A. F. de Souza and I. Barbi, “A new ZVS semiresonant power factor

“Cost-effective practical developments of high-performance 1kVA rectifier with reduced conduction losses,” IEEE Trans. Ind. Electron,

UPS with new system configurations and their specific control imple- Vol. 46, No. 1, Feb 1999, pp. 82–90.

mentations,” European Conference on Power Electronics EPE 95, 10. P. Todd, “UC3854 controlled power factor correction circuit design,”

Spain 1995, pp. 2035–2040.

Application Note U-134, Unitrode Corp. 14. K. Hückelheim and Ch. Mangold, “Novel 4-quadrant converter con- 11. J. Adams, T. Ribarich, and J. Ribarich, “A new control IC for dimmable

trol method,” European Conference on Power Electronics EPE 89, high-frequency electronic ballast,” IEEE Applied Power Electronics

Germany 1989, pp. 573–576.

Conference APEC’99, USA,1999, pp. 713–719. 15. T. Ohmae and K. Nakamura, “Hitachi’s role in the area of power 12. C. Jacobina, M. Beltrao, E. Cabral, and A. Nogueira, “Induc-

electronics for transportation,” Proc. of the IECON’93. Hawai, Nov tion motor drive system for low-power applications,” IEEE

1993, pp. 714–718.

Three-phase Controlled Rectifiers

Juan W. Dixon, Ph.D.

12.1 Introduction .......................................................................................... 205

Department of Electrical Engineering, Pontificia

12.2 Line-commutated Controlled Rectifiers....................................................... 205

Universidad Católica de Chile 12.2.1 Three-phase Half-wave Rectifier • 12.2.2 Six-pulse or Double Star Rectifier • 12.2.3 Double

Vicuña Mackenna 4860, Star Rectifier with Interphase Connection • 12.2.4 Three-phase Full-wave Rectifier or Graetz Bridge Santiago, Chile

• 12.2.5 Half Controlled Bridge Converter • 12.2.6 Commutation • 12.2.7 Power Factor • 12.2.8 Harmonic Distortion • 12.2.9 Special Configurations for Harmonic Reduction • 12.2.10 Applications of Line-commutated Rectifiers in Machine Drives • 12.2.11 Applications in HVDC Power Transmission • 12.2.12 Dual Converters • 12.2.13 Cycloconverters • 12.2.14 Harmonic Standards and Recommended Practices

12.3 Force-commutated Three-phase Controlled Rectifiers .................................... 225

12.3.1 Basic Topologies and Characteristics • 12.3.2 Operation of the Voltage Source Rectifier • 12.3.3 PWM Phase-to-phase and Phase-to-neutral Voltages • 12.3.4 Control of the DC Link Voltage • 12.3.5 New Technologies and Applications of Force-commutated Rectifiers Further Reading...................................................................................... 246

12.1 Introduction

is measured from the crossing point between the phase supply voltages. At that point, the anode-to-cathode thyristor voltage

Three-phase controlled rectifiers have a wide range of applica- v AK begins to be positive. Figure 12.3 shows that the possi- tions, from small rectifiers to large high voltage direct current ble range for gating delay is between α =0 ◦ and α = 180 ◦ , (HVDC) transmission systems. They are used for electrochem- but because of commutation problems in actual situations, the ical processes, many kinds of motor drives, traction equipment, maximum firing angle is limited to around 160 ◦ . As shown

controlled power supplies and many other applications. From in Fig. 12.4, when the load is resistive, current i d has the the point of view of the commutation process, they can be same waveform of the load voltage. As the load becomes more classified into two important categories: line-commutated con- and more inductive, the current flattens and finally becomes trolled rectifiers (thyristor rectifiers) and force-commutated pulse constant. The thyristor goes to the non-conducting condition width modulated (PWM) rectifiers.

(OFF state) when the following thyristor is switched ON, or the current, tries to reach a negative value.

With the help of Fig. 12.2, the load average voltage can be

12.2 Line-commutated Controlled evaluated, and is given by: Rectifiers