18

CHAPTER 2

VIENNA RECTIFIER

Abstract— A synchronous logic control based three-phase boost unity power factor rectifier

unit that works as an interface to ensure high energy efficiency by reducing reactive power

consumption and supply current harmonics, as well as to maintain a constant DC-bus

voltage. This chapter discusses the determination of performance characteristics of Vienna

rectifier topology with the synchronous logic based control. Furthermore this enabled the

design and development of a three-phase active rectifier system that was built and tested with

the inputs and output. This chapter also describes the Vienna Rectifier’s power stage and

phase angle control based synchronous logic technique, with particular emphasis on finding

differences between real prototype results and the simulation results. The design and

experimental performance of a three-phase rectifier with a power output of 3 kW is

presented. The real prototype results confirm with the simulation results.

2.1 Introduction

Many high power equipments derive electrical power from three-phase mains, incorporating

an active three-phase PFC front end can contribute significantly in improving overall power

factor, reducing line pollution, lowering component stresses and reducing component size

(e.g. the filter capacitor). Stationary operational behavior of three-phase/switch/level PWM

rectifier was analyzed [24] for asymmetrical loading of the output voltages. Maximum

admissible load of the neutral point that is capacitive output voltage center point was

calculated.

This topology mentioned known as the VIENNA rectifier and the three-level power structure

19

results in a low blocking voltage stress on the power semiconductors and a small input

inductor value and size. Therefore, Vienna is an ideal choice for the implementation of a

medium power, unity power factor rectifier that also has a high power density.

Three-phase AC to DC diode rectifier with three low-power and low frequency, four-

quadrant switches, with high power factor was presented in [9]. The main features were low

cost, small size, high efficiency and simplicity. The high power factor was achieved with

three active bidirectional switches rated at a small fraction of the total power, and gated at the

line frequency.

Application of power module (IXYS VUM25-E) realizing bridge legs of a three-

phase/switch/level VIENNA rectifier system with low effects on the mains were discussed in

[25]. This can be a step in the modularization direction. The switching losses and on-state

losses of a bridge leg of a rectifier were analyzed to determine the maximum output power.

Three-phase diode bridge and DC/DC boost converter combination yielded a three

phase/switch/level PWM rectifier [26]. Sinusoidal mains current, controlled output voltage

and low blocking voltage stress on the power switches were characterized. Due to high

current rate of rise when the phase transistors are turned on the single phase diode bridges in

center point legs cannot be realized as mains rectifier. Diodes with short forward recovery

time have to be applied to avoid high turn-on losses.

Detailed operation and control of VIENNA rectifiers have been reported by Kolar etal. [22-

26], Mehl etal. [8] and Qiao etal. [37]. Major drawback of the VIENNA topology compared

20

to the full bridge is that it does not allow bi-directional power flow.

The Vienna topology can be implemented with either three switches or six switches. A six

switch Vienna Rectifier (see Fig. 1) was selected to lower conduction losses since the phase

current flows through only one diode in each phase during the switch conduction and

guaranteed to clamp the switch voltage to only half the output voltage.

New controller was proposed with one or two integrators and a reset along with several

comparators and flip/flops in [37]. Control was implemented by sensing either inductor

currents or switching currents without multipliers or input voltage sensors.

Three-phase active rectifier (converter) system was built and tested with the inputs and

output. The results confirmed the theoretical analysis. The rectifier was designed to operate

over a wide line-to-line input voltage range of 160 to 520 Vrms, while delivering a nominal

output power output of 3 kW. For an output power of 3 kW and voltage of 900 Vdc, the input

phase current was about 4.5 Arms.

Design and prototype results of a new forced air cooled, three-phase, six-switch, 3 kW output

power, PWM Vienna Rectifier is presented here. The complete chapter is organized as

follows: Section 2.2 explains design strategy of Vienna Converter. Section 2.3 discusses

details of the converter analysis. The system simulation presented in Section 2.4. The

simulation results, comparison and discussion are presented in Section 2.5. Details on the

experimental performance, such as the input currents and respective harmonics, output

voltage, load current, mid-point voltage and input voltages are given in Section 2.6. The

21

overall converter system performances with the synchronous logic control implementation

are summarized in Section 2.7.

2.2 Design (Example)

After studying the design and experimental investigation of VIENNA rectifier employing a

novel integrated power semiconductor module as detailed in [25], the design example of a

converter was conceived with a Flowchart of the generalized design methodology for VIENNA

rectifier is shown in Figure 2.1.

Flowchart of the generalized design methodology for VIENNA rectifier:

I. Determine the required output power rating (Po), input voltage (Vin)

and required efficiency (η) of the system

II. Select a suitable sinusoidal switching pattern for the Converter

III. Determine the required lead and lag angles to keep the output voltage

constant even under high mains voltage and reduced output load

conditions

IV. Select the suitable Bi-Directional switches (Transistors and Diodes)

based on the type (MOSFET or IGBT), voltage and current for the

specified power Po and voltage

V. Select the boost rectifiers for positive and negative sides based on the

voltage, current and power Po

VI. Calculate the input filter inductance based on the input power Pin =

Po/η and desired per unit impedance

VII. Calculate input filter capacitance based on distortion for the specified

output power Po

VIII. Calculate input power inductance based on the input power and

selected switching frequency

IX. Calculate the output storage capacitance for the specified output

power, required ripple voltage and ride through time requirement

X. Verify input current harmonics at various R, RL (fixed) and RL

(variable) loads

XI. Verify system efficiency at various output power levels with R, RL

(fixed) and RL (variable) loads

XII. Finalize the design

Figure 2.1. Flowchart of the

generalized design

methodology for VIENNA

rectifier

N

Y

Y

N

I

III

IV

VI

V

II

X

XI

XII

VII

VIII

IX

22

VIENNA Rectifier specifications:

Input voltage: uNR = 230 Vrms

Output power: Po = 3 kW

Estimated efficiency (%): η = 93%

The design procedure is as follows:

1. Choose a suitable sinusoidal switching pattern for the Inverter three-phases. Enough lead

angle range accommodated in order to keep the output voltage constant even under high

mains voltage and reduced output load conditions. Control the switches on-time, to

comply with the technical reports IEE 519-1992 and IEC61000-3-2/4.

2. Select the switching frequency of the Bi-Directional switches (Transistors and Diodes)

based on the type (MOSFET or IGBT) and voltage and current for the specified load Po.

The selected switching frequency is 50 kHz.

3. Select the values for the filter components based on the per unit impedance for the given

power level and output ratings. Modify with the feedback of the results.

2.3 Converter Analysis

Figure 2.1(a) shows the proposed three-phase, three-level, high-quality Vienna rectifier.

Figure 2.1(a): - Scheme of the proposed three-phase high-quality rectifier.

23

This scheme is formally topologically similar to the Vienna rectifier the output capacitors are

C1 and C2. Each of the bi-directional switches sR, sS, sT can be built by using one switch

and one diode bridge rectifier or two switches and two diode rectifiers. All these components

are switched in such a manner that the EMI noise and the power losses are reduced and only

smaller magnetics are needed, thus saving cost and improving converter reliability.

Moreover, made sure only the standard high-frequency low-cost powdered iron-core type or

ferrite-core type input inductors are used.

2.4 System Simulation

At nominal output power level, it is possible to keep the output voltage constant for input low

voltage variations by making sure the input current is kept under the limits of the source

capacity. The switches on-time increased which in turn increases the boost effect. It is also

possible to compensate for input over-voltages provided the difference in potential of the

peak source voltage is reasonably lower than the maximum output voltage.

Apart from other benefits, the major benefit of this converter, as compared to simple bridge

rectifier with capacitor, is the input current harmonics reduction. Since this converter is

suitable for medium/high power applications, the harmonic limits described in the technical

report IEC 61000-3-4 as: “Limitation of emission of harmonic currents in low-voltage power

supply systems for equipment with rated current greater than 16 A per phase” are met.

Simulations have been performed in order to verify the input current harmonics at different

load levels while keeping the output voltage constant. Tabulated simulation results by

changing the loads on the output with R, RL and RL variable type and presented in the

following figures. The control strategy has enough lag and lead angle “δ” to keep the output

voltage stable, while keeping constant their sinusoidal PWM switching pattern.

24

2.4.1 Simulation

Figure 2.2 (a): - Vienna Rectifier with PI Controller (Synchronous Logic) (SIMULINK).

Figure 2.2(b): – Vienna Rectifier Main Circuit (SIMULINK).

N

25

Figure 2.2(c): – Vienna Rectifier Voltage controller (SIMULINK).

2.5 Simulation Results

The simulation with resistive loads at nominal conditions presented in Tables 2.1 & 2.2 give

an output voltage of 899 Vdc and current of 3.33 A, and the input current harmonics are

much lower than the required levels as per the statutory requirements. The simulation and its

results are shown in Fig. 2.2(a), (b) & (c), Fig. 2.3 and Fig. 2.4(a) & (b) and also shown in

Table 2.1 and Table 2.2, with Resistive (R) Load. The input current is, iNR = 4.77 A

(corresponding to 3 kW) at 232 Vac input voltage, only 5th, 7th, 11th, 13th, and 17th harmonics

are considered. Third and its multiples are negligible to consider.

26

Figure 2.3: - Simulation results of Input current harmonics at different Resistive loads.

Figure 2.4(a): – Vienna Rectifier Input voltages, Output Capacitor voltages and Center point Voltage.

Figure 2.4(b): – Vienna Rectifier Load current and voltage.

0

0.05

0.1

0.15

0.2

0.25

5th

Harm.

7th

Harm.

11th

Harm.

13th

Harm.

17th

Harm.

19th

Harm.

23rd

Harm.

25th

Harm.

29th

Harm.

100W

200W

400W

600W

800W

1000W

27

Table 2.1: – Vienna Rectifier Simulation Input current and voltage at different Resistive loads.

Input R

Phase V

Input

Phase I

Input Phase

PF

Input R

Phase W

Output

Voltage

Output

Current

Output

Load in W

Efficiency(ƞ)

R Load in %

232 0.66 0.99 152 900 0.33 300 66

232 1.13 0.99 260 900 0.67 600 77

232 2.08 0.99 478 900 1.33 1200 84

232 2.98 0.99 686 900 2.00 1800 87

232 3.87 0.99 889 900 2.67 2400 90

232 4.77 0.99 1096 900 3.33 3000 91

Table 2.2: – Vienna Rectifier Simulation Input current harmonics at different Resistive loads.

Input current harmonics % at different R load levels, R-Phase

Output R

Phase W

5th

Harm.

7th

Harm.

11th

Harm.

13th

Harm.

17th

Harm.

19th

Harm.

23rd

Harm.

25th

Harm.

29th

Harm. THD %

300W 0.066 0.072 0.03 0.035 0.025 0.025 0.016 0.021 0.016 17.87

600W 0.104 0.122 0.033 0.052 0.027 0.025 0.025 0.018 0.021 15.88

1200W 0.091 0.181 0.075 0.034 0.036 0.027 0 0.008 0 7.49

1800W 0.052 0.141 0.095 0.05 0.021 0.023 0.01 0.003 0.005 4.86

2400W 0.221 0.055 0.052 0.034 0.012 0.015 0.018 0 0 6.15

3000W 0.212 0.05 0.063 0.041 0.016 0.005 0.018 0.016 0.002 4.87

300W 10.02 10.93 4.55 5.31 3.79 3.79 2.43 3.19 2.43 17.87

600W 9.20 10.79 2.92 4.60 2.39 2.21 2.21 1.59 1.86 15.88

1200W 4.37 8.70 3.60 1.63 1.73 1.30 0.00 0.38 0.00 7.49

1800W 1.74 4.73 3.19 1.68 0.70 0.77 0.34 0.10 0.17 4.86

2400W 5.72 1.42 1.35 0.88 0.31 0.39 0.47 0.00 0.00 6.15

3000W 4.45 1.05 1.32 0.86 0.34 0.10 0.38 0.34 0.04 4.87

IEC Limit 10.7 7.2 3.1 2 1.2 1.1 0.9 0.8 0.7

28

2.6 Experimental Results

In order to verify the concept, a prototype of a three-phase VIENNA rectifier with proposed

control approach using synchronous logic with line current sensing was built with following

specifications: Input voltage 230 Vac; Output voltage: 900 Vdc and Output power 3 kW.

Figure 2.1(a) shows the VIENNA Rectifier system used in this proto type experiment. The

real proto-type setup is shown in figures 2.5(a), power section and 2.5(b), logic section. The

power supply, some line filters and output load sections are not shown due to space

constraints. The experimental set-up with appropriate components chosen is as follows:

three-phase Input filter inductance, Input filter capacitance; main inductance; Output

Capacitance, Fast Recovery Diodes, the three main bi-directional switches sR, sS and sT are

implemented with two IGBTs in series with two FRDs (Fast Recovery Diodes) in series as

shown in Fig.2.5(c). The output load resistance R is 270 ohm (Three 806 Ohms load coils in

parallel). The switching frequency is 50 kHz. The experimental results are shown in Fig. 2.6,

Input Current waveforms (Ch1 – Ch3) of iNR, iNS, iNT and Input phase Voltage waveform

(Ch4) of uNT when an output Resistive Load of 3 kW applied. Only Input current harmonics

of 5th, 7th, 11th, 13th, 17th, 19th, 23th, 25th and 29th order were considered when output was

loaded with R, RL fixed and RL variable type. Third and its multiples were negligible to

consider.

29

Figure 2.5(a): – Real-Lab prototype set up of the Vienna Rectifier Power section.

Figure 2.5: - (b) Real-Lab prototype set up of the Vienna Rectifier Logic section, c) Bi-directional switch

Ch1: 6 A, Ch2: 6 A, Ch3: 6 A, Ch4: 250 V; Scale: 4.0 ms; Trigger: Ch4 + 90 V

Figure 2.6: – Three-phase Input Current waveforms (Ch1 – Ch3) iNR, iNS, iNT and Input phase Voltage

waveform (Ch4) of uNT when Resistive Load of 3 kW applied on output.

30

Readings have been taken in order to verify the input current harmonics at different load

levels while keeping the output voltage constant. Tabulated readings of current harmonics

and efficiency, by changing the loads on the output with R, RL and RL variable type and

presented in the following Figures 2.7(a), 2.7(c), 2.7(e) and 2.8 respectively. Input current

and voltage measurements at different R, RL and RL variable type are presented in the

following Tables 2.3 & 2.4, Tables 2.5 & 2.6 and Tables 2.7 & 2.8 respectively. The

measured power factor is 0.99 while the output voltage is 900 Vdc. Output Voltages and

current are shown in the following Figures 2.7(b), 2.7(d) and 2.7(f) respectively. Currents are

multiplied by 100 to make them easily readable. The current spectrum shown in Fig. 2.7(a) is

with Resistive (R) Load. The input current is, iNR = 4.68 A (corresponding to 3 kW) at 237

Vac input voltage. Third and its multiples are negligible to consider. The efficiency at rated

power is 91%.

Table 2.3: – Vienna Rectifier Input current and voltage at different Resistive loads.

Input R-Ph.

Voltage

(uNR)

Input R-Ph.

Current

(iNR)

Input R

Ph. PF

Input R

Ph.

Load W

Output

Voltage

(DC)

Output

Current

(DC)

Output

Load

Efficiency

(ƞ) R

Load in %

235 0.63 0.99 146 900 0.11 100 68

237 1.11 0.99 260 900 0.22 200 77

236 2.05 0.99 478 899 0.44 399 83

235 2.95 0.99 685 899 0.67 600 88

236 3.81 0.99 889 898 0.89 800 90

237 4.68 0.99 1097 898 1.11 999 91

31

Table 2.4: – Vienna Rectifier Input current harmonics at different Resistive loads.

Input current harmonics % at different R load levels, R-Phase

Output R

Phase W

5th

Harm.

7th

Harm.

11th

Harm.

13th

Harm.

17th

Harm.

19th

Harm.

23rd

Harm.

25th

Harm.

29th

Harm. THD

300W 0.066 0.072 0.03 0.035 0.025 0.025 0.016 0.021 0.016 18.69

600W 0.104 0.122 0.033 0.052 0.027 0.025 0.025 0.018 0.021 16.18

1200W 0.091 0.181 0.075 0.034 0.036 0.027 0 0.008 0 10.90

1800W 0.052 0.141 0.095 0.05 0.021 0.023 0.01 0.003 0.005 6.36

2400W 0.221 0.055 0.052 0.034 0.012 0.015 0.018 0 0 6.23

3000W 0.212 0.05 0.063 0.041 0.016 0.005 0.018 0.016 0.002 4.96

300W 10.48 11.43 4.76 5.56 3.97 3.97 2.54 3.33 2.54 18.69

600W 9.37 10.99 2.97 4.68 2.43 2.25 2.25 1.62 1.89 16.18

1200W 4.44 8.83 3.66 1.66 1.76 1.32 0.00 0.39 0.00 10.90

1800W 1.76 4.78 3.22 1.69 0.71 0.78 0.34 0.10 0.17 6.36

2400W 5.80 1.44 1.36 0.89 0.31 0.39 0.47 0.00 0.00 6.23

3000W 2.36 0.56 0.70 0.46 0.18 0.06 0.20 0.18 0.02 4.96

IEC Limit 10.7 7.2 3.1 2 1.2 1.1 0.9 0.8 0.7

Figure 2.7(a): - Input current harmonics at different Resistive loads.

0

0.05

0.1

0.15

0.2

0.25

5th

Harm.

7th

Harm.

11th

Harm.

13th

Harm.

17th

Harm.

19th

Harm.

23rd

Harm.

25th

Harm.

29th

Harm.

100W

200W

400W

600W

800W

1000W

32

Figure 2.7(b): – Output Voltage and Current when Resistive Load of 3 kW applied on output.

The current spectrum shown in Fig. 2.7(c) is with Resistive and Inductive (RL) Load with a

fixed power factor. The R-Phase input current is, iNR = 4.82 A (corresponding to 3kW) at

236 Vac input voltage. Third and its multiples are negligible to consider. The efficiency at

rated power is 89%.

Table 2.5: – Vienna Rectifier Input current and voltage at different Resistive and Inductive loads (Fixed PF).

Input R-Ph.

Voltage

(uNR)

Input R-Ph.

Current

(iNR)

Input R

Ph. PF

Input R

Ph.

Load W

Output

Voltage

(DC)

Output

Current

(DC)

Output

Load

Efficiency

(ƞ) R

Load in %

235 0.65 0.99 151 900 0.11 100 66

235 1.14 0.99 266 900 0.22 200 75

237 2.11 0.99 495 899 0.44 400 81

236 3.04 0.99 709 899 0.67 600 85

237 3.92 0.99 920 898 0.89 800 87

236 4.82 0.99 1125 898 1.11 1000 89

-600

-400

-200

0

200

400

600

R-Load

V1 - R

V2 - R

33

Table 2.6: – Vienna Rectifier Input current harmonics at different Resistive and Inductive loads (Fixed PF).

Output R

Phase W

5th

Harm.

7th

Harm.

11th

Harm.

13th

Harm.

17th

Harm.

19th

Harm.

23rd

Harm.

25th

Harm.

29th

Harm. THD

300W 0.069 0.076 0.032 0.037 0.026 0.026 0.017 0.0220 0.017 19.02

600W 0.110 0.129 0.035 0.055 0.029 0.027 0.027 0.019 0.022 16.65

1200W 0.097 0.194 0.080 0.036 0.039 0.029 0.005 0.009 0.005 11.33

1800W 0.056 0.152 0.103 0.054 0.023 0.025 0.011 0.003 0.005 6.67

2400W 0.241 0.060 0.057 0.037 0.013 0.016 0.020 0.005 0.005 6.6

3000W 0.233 0.055 0.069 0.045 0.018 0.006 0.020 0.018 0.002 5.3

300W 10.66 11.63 4.85 5.65 4.04 4.04 2.58 3.39 2.58 19.02

600W 9.64 11.31 3.06 4.82 2.5 2.32 2.32 1.67 1.95 16.65

1200W 4.61 9.17 3.8 1.72 1.82 1.37 0.25 0.41 0.25 11.33

1800W 1.85 5.01 3.38 1.78 0.75 0.82 0.36 0.11 0.18 6.67

2400W 6.14 1.53 1.44 0.94 0.33 0.42 0.5 0.14 0.14 6.6

3000W 4.84 1.14 1.44 0.94 0.37 0.11 0.41 0.37 0.05 5.3

IEC Limit 10.7 7.2 3.1 2 1.2 1.1 0.9 0.8 0.7

Figure 2.7(c): - Input current harmonics with Resistive and Inductive (RL) Load with a fixed rated power factor.

0.000

0.050

0.100

0.150

0.200

0.250

0.300

5th Harm.

7th Harm.

11th Harm.

13th Harm.

17th Harm.

19th Harm.

23rd Harm.

25th Harm.

29th Harm.

100W

200W

400W

600W

800W

1000W

34

Figure 2.7(d): – Output Voltage and Current when Fixed Resistive and Inductive (RL) Load of 3 kW applied on

output.

The current spectrum shown in Fig. 2.7(d) is with Resistive and Inductive (RL) Load with

variable power factor from unity to rated level. The input current is, iNR = 4.80 A

(corresponding to 3 kW) at 236 Vac input voltage, only harmonics 5th, 7th, 11th, 13th, and

17th, are considered. Third and its multiples are negligible to consider. The efficiency at

rated power is 89%.

-600

-400

-200

0

200

400

600

RL-Load (Fixed)

V1 - RL-Fixed

V2 - RL-Fixed

35

Table 2.7: – Vienna Rectifier Input current and voltage at different Resistive and Inductive loads (Variable PF).

Input R-Ph.

Voltage

(uNR)

Input R-Ph.

Current

(iNR)

Input R

Ph. PF

Input R

Ph.

Load W

Output

Voltage

(DC)

Output

Current

(DC)

Output

Load

Efficiency

(ƞ) R

Load in %

235 0.65 0.99 151 900 0.11 100 66

236 1.13 0.99 264 900 0.22 200 76

236 2.09 0.99 488 899 0.44 400 82

237 2.96 0.99 694 899 0.67 600 87

235 3.95 0.99 917 898 0.89 800 87

236 4.80 0.99 1120 898 1.11 1000 89

Table 2.8: – Vienna Rectifier Input current harmonics at different Resistive and Inductive loads (Variable PF).

Input current harmonics % at different RL loads (Variable PF), R-Phase

Output R

Phase W

5th

Harm.

7th

Harm.

11th

Harm.

13th

Harm.

17th

Harm.

19th

Harm.

23rd

Harm.

25th

Harm.

29th

Harm. THD

300W 0.069 0.076 0.032 0.037 0.026 0.026 0.017 0.022 0.017 19.02

600W 0.110 0.129 0.035 0.055 0.029 0.027 0.027 0.019 0.022 16.84

1200W 0.097 0.194 0.080 0.036 0.039 0.029 0.005 0.009 0.005 11.44

1800W 0.052 0.141 0.095 0.05 0.021 0.023 0.01 0.003 0.005 6.34

2400W 0.232 0.057 0.051 0.034 0.012 0.015 0.019 0.005 0.005 6.28

3000W 0.223 0.052 0.061 0.041 0.016 0.005 0.019 0.017 0.002 5.05

300W 10.66 11.63 4.85 5.65 4.04 4.04 2.58 3.39 2.58 19.02

600W 9.76 11.44 3.10 4.88 2.53 2.35 2.35 1.69 1.97 16.84

1200W 4.66 9.27 3.84 1.74 1.84 1.38 0.26 0.41 0.26 11.44

1800W 1.76 4.76 3.21 1.69 0.71 0.78 0.34 0.10 0.17 6.34

2400W 5.87 1.44 1.29 0.86 0.30 0.38 0.48 0.13 0.13 6.28

3000W 4.65 1.08 1.27 0.85 0.33 0.10 0.40 0.35 0.04 5.05

IEC Limit 10.7 7.2 3.1 2 1.2 1.1 0.9 0.8 0.7

36

Figure 2.7(e): - Input current harmonics with Resistive and Inductive (RL) Load with variable rated power

factor from unity to rated.

Figure 2.7(f): – Output Voltage and Current when Variable Resistive and Inductive (RL) Load of 3 kW applied

on output.

Figure 2.8: - Efficiencies with various resistive loads.

0.000

0.050

0.100

0.150

0.200

0.250

0.300

5th Harm.

7th Harm.

11th Harm.

13th Harm.

17th Harm.

19th Harm.

23rd Harm.

25th Harm.

29th Harm.

100W

200W

400W

600W

800W

1000W

-600

-400

-200

0

200

400

600

RL-Load (Variable)

V1 - RL-Variable

V2 - RL-Variable

0

20

40

60

80

100

100 200 400 600 800 1000

ƞ R Load

ƞ RL Fixed

ƞ RL Variable

37

The efficiencies shown in Fig. 2.8 are with Resistive, Resistive and Inductive (RL) Load with

fixed power factor and with variable power factor from unity to rated. Measurements were

tabulated by changing the loads on the output of the setup. The efficiency varied based on the

type of load and also percentage of the load from 66% to 91%.

The various working details of the Vienna Rectifier are shown in Figures 2.9(a) to 2.9(f) at

various important transitional points of all three-phases. So, there are six main transitional

points to review in a cycle. The direction of the current and the power flow are the areas of

importance in understanding the workings of the Vienna Rectifier.

Figure 2.9(a): - Phase S moving to its positive side from negative.

38

Figure 2.9(b): - When Phase R moving to its negative side from positive.

Figure 2.9(c): - When Phase T moving to its positive side from negative.

39

Figure 2.9(d): - Phase S moving to its nagative side from positive.

Figure 2.9(e): - When Phase R moving to its positive side from negative.

40

Figure 2.9(f): - When Phase T moving to its negative side from positive.

Figure 2.10: - Phase T moving to its negative side from positive (a) - Just before (b) - Just after.

41

Details of various switch conditions; voltage and current waveforms are shown in Figures

2.10(a) and 2.10(b), just before and just after phase T moving to its nagative side from

positive side respectively.

2.7 Summary

The proposed three-phase three-switch three-level (VIENNA) rectifier circuit with unity

power factor was investigated and was able to control current distortion that was generally

generated by diode bridge rectifiers and capacitive filter. A new three-phase synchronous

logic control simulations showed that it could produce very low output voltage ripple and

very low input current harmonics with unity power factor. The resulting current harmonics

were below the statutory limits of IEC 61000-3-4 at different load level. It was also possible

to compensate for input over-voltage just by adjusting the control signals to bidirectional

switches.

An experimental prototype system of 3 kW VIENNA rectifier was built to verify the concept.

Near unity power factor was measured in all three-phases. The proposed control logic was

implemented by sensing input voltages, input currents, output currents and output voltage.

The controller was very simple and reliable. The inductance value was reduced and also

small in size when compared to the only passive filter circuit. The experimental results

confirm the designed proto-type circuit’s behavior.