10
Copyright (c) 2009 IEEE. Personal use is permitted. For any other purposes, Permission must be obtained from the IEEE by emailing [email protected]. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Space Vector Modulation for Two-Level Unidirectional PWM Rectifiers Ivo Barbi, Senior Member, IEEE and Flabio Alberto Bardemaker Batista Abstract — This paper presents the concepts for application of space vector modulation to two-level unidirectional PWM rectifiers and a methodology for the use of this modulation is proposed and applied in three different groups of rectifiers. For each group of rectifiers, the converter switching stages are analyzed to determine switch control signals for space vector modulation. One switching sequence is proposed for all rectifiers in order to minimize the number of switch commutations and to reduce the switching losses. Duty cycle functions are determined and the desired switching sequences are performed by a simple PWM modulator with no need to determine the present sector of the vector. For this propose it is necessary only to impose the desired current sectors from input voltage references. In order to validate the proposed modulation techniques, simulation and experimental results are presented for a 20 kW prototype. I. INTRODUCTION There are a great number of topologies of unidirectional PWM rectifiers with power factor correction [1-9]. In cases where bidirectional power flow is not necessary, these converters offer some advantages including a decrease in the number of power switches, natural protection for DC bus short circuits and less processing of energy for the active switches [7-9]. Various methods to implement space vector modulation in unidirectional PWM rectifiers have been proposed, especially for multi-level topologies [10-17]. When the output voltage is lower than the rated voltage of commercial switches, two-level topologies [1-6] become attractive, because they do not need to control middle point voltage, reducing the number of sensors and/or controllers [16-17]. In this study a simple methodology to apply space vector modulation to two-level unidirectional PWM rectifiers, in order to minimize the number of switch commutations as well as reduce converter losses, is proposed. Section II presents some unidirectional PWM two-level rectifiers and in section III the basic steps required in order to apply space vector modulation to these converters, with simulation verification, are described. The proposed application methodology for this modulation technique is based on sub-sector definition, rectifier operation stage analysis and duty cycle determination. Therefore, it is not necessary to identify the present vector sector, but simple to impose the appropriate current sector in phase with line voltages [1]. In section IV, the experimental results are presented and in section V the analysis results and conclusions are discussed. II. TWO-LEVEL UNIDIRECTIONAL PWM RECTIFIERS The three-phase three-switch two-level Y-connected unidirectional PWM rectifier [1-2], shown in Fig. 1, has unity power factor and output voltage regulation. This rectifier uses six diodes and one inner controlled switch per arm. A structure similar to rectifier Y_1 is presented in Fig. 2. In this converter (rectifier Δ_1) the bidirectional switches are connected in Δ [3]. In [4] two unidirectional rectifiers are presented with the bidirectional switches outside the arms of the converter. The rectifier of Fig. 3 has the Y connection (rectifier Y_2) and the rectifier of Fig. 4 uses the switches connected in Δ (rectifier Δ_2). Fig. 1. Unidirectional PWM rectifier Y_1. Fig. 2. Unidirectional PWM rectifier Δ_1. Fig. 3. Unidirectional PWM rectifier Y_2. Authorized licensed use limited to: UNIVERSIDADE FEDERAL DE SANTA CATARINA. Downloaded on November 13, 2009 at 07:49 from IEEE Xplore. Restrictions apply.

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Space Vector Modulation for Two-Level Unidirectional PWM Rectifiers

Ivo Barbi, Senior Member, IEEE and Flabio Alberto Bardemaker Batista Abstract — This paper presents the concepts for application of space vector modulation to two-level unidirectional PWM rectifiers and a methodology for the use of this modulation is proposed and applied in three different groups of rectifiers. For each group of rectifiers, the converter switching stages are analyzed to determine switch control signals for space vector modulation. One switching sequence is proposed for all rectifiers in order to minimize the number of switch commutations and to reduce the switching losses. Duty cycle functions are determined and the desired switching sequences are performed by a simple PWM modulator with no need to determine the present sector of the vector. For this propose it is necessary only to impose the desired current sectors from input voltage references. In order to validate the proposed modulation techniques, simulation and experimental results are presented for a 20 kW prototype.

I. INTRODUCTION

There are a great number of topologies of unidirectional PWM rectifiers with power factor correction [1-9]. In cases where bidirectional power flow is not necessary, these converters offer some advantages including a decrease in the number of power switches, natural protection for DC bus short circuits and less processing of energy for the active switches [7-9].

Various methods to implement space vector modulation in unidirectional PWM rectifiers have been proposed, especially for multi-level topologies [10-17]. When the output voltage is lower than the rated voltage of commercial switches, two-level topologies [1-6] become attractive, because they do not need to control middle point voltage, reducing the number of sensors and/or controllers [16-17].

In this study a simple methodology to apply space vector modulation to two-level unidirectional PWM rectifiers, in order to minimize the number of switch commutations as well as reduce converter losses, is proposed. Section II presents some unidirectional PWM two-level rectifiers and in section III the basic steps required in order to apply space vector modulation to these converters, with simulation verification, are described.

The proposed application methodology for this modulation technique is based on sub-sector definition, rectifier operation stage analysis and duty cycle determination.

Therefore, it is not necessary to identify the present vector sector, but simple to impose the appropriate current sector in phase with line voltages [1].

In section IV, the experimental results are presented and in section V the analysis results and conclusions are discussed.

II. TWO-LEVEL UNIDIRECTIONAL PWM RECTIFIERS

The three-phase three-switch two-level Y-connected unidirectional PWM rectifier [1-2], shown in Fig. 1, has unity power factor and output voltage regulation. This rectifier uses six diodes and one inner controlled switch per arm.

A structure similar to rectifier Y_1 is presented in Fig. 2. In this converter (rectifier Δ_1) the bidirectional switches

are connected in Δ [3]. In [4] two unidirectional rectifiers are presented with the

bidirectional switches outside the arms of the converter. The rectifier of Fig. 3 has the Y connection (rectifier Y_2) and the rectifier of Fig. 4 uses the switches connected in Δ (rectifier Δ_2).

Fig. 1. Unidirectional PWM rectifier Y_1.

Fig. 2. Unidirectional PWM rectifier Δ_1.

Fig. 3. Unidirectional PWM rectifier Y_2.

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Fig. 4. Unidirectional PWM rectifier Δ _2.

Fig. 5. Unidirectional PWM rectifier Bridge_1.

Fig. 6. Unidirectional PWM rectifier Bridge_2.

In Fig. 5 the rectifier Bridge_1 [5] is presented. This structure is derived from the bidirectional rectifier with the additional DC rail diode.

The rectifier Bridge_2, shown in Fig. 6, has the same number of semiconductors as rectifiers Y_2 and Δ_2, with the bidirectional switches in a bridge arrangement [6].

These unidirectional rectifiers may be grouped according to the connections of switches as Y-Connected Rectifiers, Δ-Connected Rectifiers or Bridge-Connected Rectifiers.

Each converter has different characteristics, such as the number of semiconductors, the voltage and current stress of the semiconductors, efficiency, loss distribution and others.

In this study the application of space vector modulation to these topologies is studied. General aspects of the modulation applied to unidirectional rectifiers as the sub-sector definition, the vector sequence and duty cycle functions are presented and specific characteristic for each group are determined.

III. SPACE VECTOR METHODOLOGY

In [1] the space vector modulation is applied to rectifier Y_1. In this section the definitions used for the rectifier Y_1 are adopted for all rectifiers presented.

Fig. 7. Definition of Current Sectors.

Fig. 8. Relation between input voltages vF(t) and rectifier fundamental voltage

component vR(t).

TABLE I AVAILABLE VECTORS.

Vector Point A Point B Point C VAB VBC VCA 0V (0 0 0) A = B = C 0 0 0

1V (1 0 0) P N N O+V 0 OV−

2V (1 1 0) P P N 0 O+V OV−

3V (0 1 0) N P N OV− O+V 0

4V (0 1 1) N P P OV− 0 O+V

5V (0 0 1) N N P 0 OV− O+V

6V (1 0 1) P N P O+V OV− 0

These topologies have six symmetrical operation intervals [2], where six current sectors are defined in one line period: A+, B–, C+, A–, B+ and C–, as shown in Fig. 7. Each sector has an interval of 60º and it is defined by the current that has the greatest value and its respective signal.

From the analysis of the rectifier topologies, seven available vectors are defined as shown in Table I. Non null vectors are represented by the potential of points A, B and C, and the null vector represents the situation where the three points are connected.

In this notation, used for unidirectional converters, the representation of the available vectors does not agree with the switching states, because the potentials of points A, B and C are dependent on the input currents direction.

For unidirectional rectifiers, the definition of the sectors is a little different from the traditional one [18]. In this case, implementation of the available vectors considers phase current direction. Supposing that the currents are in phase with the respective voltages, each phase presents an equivalent circuit with the relation between input voltages vF(t) and the rectifier fundamental voltage component vR(t) being that shown in Fig. 8.

Sub-sectors are defined from the intersection of vector sectors and current sectors, as shown in Fig. 9.

Therefore, space vector representation is carried out in one diagram divided into these sub-sectors, as shown in Fig. 10, where each current sector is divided into two sub-sectors and has four available vectors.

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Fig. 9. Definition of sub-sectors.

Fig. 10. Space vector representation with definition of sub-sectors.

For all groups of rectifiers a specific sector analysis will be described for sector 1 and this can be extended to each of the other sectors considering the adaptation of the direction of input currents [1]. In sector 1, the sub-sectors SS1A and SS1C are considered. In sub-sector SS1A, the highest current is in phase A and this current is positive and vectors 0V , 1V and

2V are used. However, in sub-sector SS1C the highest current is in phase

C. This current is negative and the vectors used are the same as in previous case: 0V , 1V and 2V .

Table II shows the proposed vector sequences in sector 1 and 2 for the different groups of rectifiers. These sequences are the same for all rectifiers and they are dependent on the input currents direction.

In one sector, to update the sequence from one sub-sector to another, the position of the non null vectors needs to be changed.

The same methodology used to apply the space vector modulation technique in [1] was extended to other three-phase two-level unidirectional PWM rectifiers.

This methodology is summarized as:

TABLE II VECTOR SEQUENCES.

Sub-Sector Y - Connected Rectifiers

Δ - Connected Rectifiers

Bridge - ConnectedRectifiers

Signal of I

SS1A 0 2 1 2 0V V V V V 1 2 0 2 1V V V V V 1 2 0 2 1V V V V V +

SS1C 0 1 2 1 0V V V V V 2 1 0 1 2V V V V V 2 1 0 1 2V V V V V −

SS2C 0 3 2 3 0V V V V V 2 3 0 3 2V V V V V 2 3 0 3 2V V V V V −

SS2B 0 2 3 2 0V V V V V 3 2 0 2 3V V V V V 3 2 0 2 3V V V V V + - Identification of current sectors and vector sectors and

definition of sub-sectors; - Analysis of topological stages of the converter and

verification of available vectors in each sub-sector; - Definition of most appropriate logic for the available

command signals and vector sequence; - Determination of intervals for application of vectors and

calculation of duty-cycle functions in sub-sectors; - Implementation of command signals from the PWM

modulator.

A. Space Vector Modulation Applied to Y-Connected Two-Level Rectifiers

The switching stages of rectifier Y_2 are analyzed to apply the space vector modulation to this group of rectifiers.

In sub-sector SS1A, the space vector 1V is performed in the operation stage of Fig. 11a and space vector 2V is performed in the operation stage of Fig. 11b. Therefore, in sub-sector SS1C, the space vector 1V is performed in the operation stage of Fig. 12a and space vector 2V is performed in the operation stage of Fig. 12b.

In both sectors, in order to implement the null vector, the three switches need to be turned on, and the points A, B and C are connected to the point M.

(a) (b)

Fig. 11. Operation stages for rectifier Y_2 in sub-sector SS1A: (a) vector 1V ,

(b) vector 2V .

(a) (b)

Fig. 12. Operation stages for rectifier Y_2 in sub-sector SS1C: (a) vector 1V ,

(b) vector 2V .

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TABLE III CONTROL SIGNALS FOR SUB-SECTORS SS1A AND SS1C.

SUB-SECTOR SS1A SUB-SECTOR SS1C Vector SA1,2 SB1,2 SC1,2 SA1,2 SB1,2 SC1,2 1V (1 0 0) On Off Off Off On On

2V (1 1 0) On On Off Off Off On

0V (0 0 0) On On On On On On

The logic used to determine the command signals considers

that the switches in the arm which processes the highest current are turned on in the respective current sector interval. The proposed control signals for implementing these vectors are those shown in Table III.

The main objective of the logic behind the distribution of the command signals is the minimization of the number of switch commutations and reduction of the switching losses of the converter.

However, the selected switching pattern was chosen so that, in the three phases, the level of the control signal is the same (on) at the beginning and end of the switching period.

For sub-sector SS1A, the proposed vector sequence is 0 2 1 2 0V V V V V , resulting in the drive signals in Fig. 13a. Therefore, the intervals for the commands of the switches are

1,2

1,2 0 2

1,2 0

A S

B

C

T TT T T

T T

== +=

(1)

Using the projections of the vectors on the axes α and β [1] for the respective sectors, the three-phase duty cycles are determined as a function of the Dα and Dβ duty cycles:

1,2

1,2

1,2

1

3 112 23 112 2

A

B

C

D

D D D

D D D

α β

α β

=

= − ⋅ + ⋅

= − ⋅ − ⋅

(2)

For sub-sector SS1C, the proposed vector sequence is 0 1 2 1 0V V V V V , resulting in the drive signals of Fig. 13b. In this case, the intervals for the commands of switches and

the three-phase duty cycles are

1,2 0

1,2 0 1

1,2

A

B

C S

T TT T T

T T

== +=

(3)

1,2

1,2

1,2

3 112 21 2

1

A

B

C

D D D

D DD

α β

β

= − ⋅ − ⋅

= − ⋅=

(4)

(a) (b)

Fig. 13. Drive signals for rectifier Y_2: (a) sub-sector SS1A, (b) sub-sector SS1C.

Fig. 14. Duty cycle for switches SA1 and SA2 in rectifier Y_2.

Extending this analysis to the other sectors, the duty cycle functions for each switch are defined as shown in Fig 14. In this scenario, the duty cycle for switch SA is presented for

0.359dD = and 0.076qD = . Observe that when using the same methodology to a rectifier in the same group (rectifier Y_1 [1]) the same duty cycle function is found.

In the analysis of duty cycle equations, one can verify that the expressions for neighboring sub-sectors are equal in the same current sector. Therefore, it is not necessary to identify the sectors of vectors; only to impose the desired current sectors from the input voltages.

The switch control signals to implement the desired vectors are performed by a simple PWM modulator, through the comparison of duty cycle functions with a triangular waveform.

B. Space Vector Modulation Applied to Δ-Connected Two-Level Rectifiers

For this group of rectifiers the switching stages of rectifier Δ_1 are analyzed to apply the space vector modulation.

In sub-sector SS1A, the space vector 1V is performed in the operation stage of Fig. 15a and space vector 2V is performed in the operation stage of Fig. 15b.

Therefore, in sub-sector SS1C, the space vector 1V is performed in the operation stage of Fig. 16a and space vector

2V is performed in the operation stage of Fig. 16b.

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(a) (b)

Fig. 15. Operation stages for rectifier Δ_1 in sub-sector SS1A: (a) vector 1V ,

(b) vector 2V .

(a) (b)

Fig. 16. Operation stages for rectifier Δ_1in sub-sector SS1C: (a) vector 1V ,

(b) vector 2V .

TABLE IV CONTROL SIGNALS FOR SUB-SECTORS SS1A AND SS1C.

SUB-SECTOR SS1A SUB-SECTOR SS1C Vector SA SB SC SA SB SC 1V (1 0 0) Off Off Off Off On Off

2V (1 1 0) On Off Off Off Off Off

0V (0 0 0) On Off On Off On On

In both sectors, in order to implement the null vector, two of the three switches need to be turned on.

The logic used to determine the command signals considers that the switch in the arm which processes the highest current is turned on in the respective current sector interval.

In this sector interval, one of the other two switches is turned off. The proposed control signals for implementing these vectors are those shown in Table IV.

The selected switching pattern was chosen so that, in the three phases, the level of the control signal is the same (off) at the beginning and end of the switching period.

For sub-sector SS1A, the proposed vector sequence is 1 2 0 2 1V V V V V , resulting in the drive signals in Fig. 17a. Therefore, the intervals for the commands of the switches are

0 2

0

0A

B

C

T T TTT T

= +==

(5)

The three-phase duty cycles are determined as a function of the Dα and Dβ duty cycles:

3 112 2

0

3 112 2

A

B

C

D D D

D

D D D

α β

α β

= − ⋅ + ⋅

=

= − ⋅ − ⋅

(6)

(a) (b)

Fig. 17. Drive signals for rectifier Δ_1: (a) sub-sector SS1A, (b) sub-sector SS1C.

Fig. 18. Duty cycle for switch SA in rectifier Δ_1.

For sub-sector SS1C, the proposed vector sequence is 2 1 0 1 2V V V V V , resulting in the drive signals in Fig. 17b. In

this case, the intervals for the commands of the switches and the three-phase duty cycles are

0 1

0

0A

B

C

TT T T

T T

== +=

(7)

0

1 2

3 112 2

A

B

C

D

D D

D D D

β

α β

=

= − ⋅

= − ⋅ − ⋅

(8)

Extending this analysis to the other sectors, the duty cycle functions for each switch are defined as shown in Fig. 18 for the same values of Fig. 14.

Also for this rectifier, with the analysis of duty cycle equations, it is not necessary to identify the sectors of vectors, only to impose the desired current sectors from the input voltages.

C. Space Vector Modulation Applied to Bridge-Connected Two-Level Rectifiers

To this group of rectifiers, the switching stages of rectifier Bridge_1 are analyzed to apply the space vector modulation.

In sub-sector SS1A, the space vector 1V is performed in the operation stage of Fig. 19a and space vector 2V is performed in the operation stage of Fig. 19b.

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(a) (b)

Fig. 19. Operation stages for rectifier Bridge_1 in sub-sector SS1A: (a)

vector 1V , (b) vector 2V .

(a) (b)

Fig. 20. Operation stages for rectifier Bridge_1 in sub-sector SS1C: (a)

vector 1V , (b) vector 2V .

Therefore, in sub-sector SS1C, the space vector 1V is performed in the operation stage of Fig. 20a and space vector

2V is performed in the operation stage of Fig. 20b. The logic used to determine the command signals considers

that the switches in the arm which processes the highest current is turned off in the respective current sector interval.

In order to implement the null vector, two switches need to be turned on and for non null vectors just one switch is turned on.

The proposed control signals for implementing these vectors are shown in Table V. However, the selected switching pattern was chosen so that, in the three phases, the level of the control signal is the same (off) at the beginning and end of the switching period.

For sub-sector SS1A, the proposed vector sequence is 1 2 0 2 1V V V V V , resulting in the drive signals in Fig. 21a. Therefore, the intervals for the commands of the switches are

1 2 2 2

1 0 2

1 0

0A A B C

B

C

T T T TT T T

T T

= = = == +=

(9)

1 1 2 3

1

1

0

3 112 23 112 2

A B B B

B

C

D D D D

D D D

D D D

α β

α β

= = = =

= − ⋅ + ⋅

= − ⋅ − ⋅

(10)

TABLE V CONTROL SIGNALS FOR SUB-SECTORS SS1A AND SS1C.

SUB-SECTOR SS1A SUB-SECTOR SS1C Vector SA1 SB1 SC1 SA2 SB2 SC2 1V (1 0 0) Off Off Off Off On Off

2V (1 1 0) Off On Off Off Off Off

0V (0 0 0) Off On On On On Off

(a) (b)

Fig. 21. Drive signals for rectifier Bridge_1: (a) sub-sector SS1A, (b) sub-sector SS1C.

Fig. 22. Duty cycle function for switch SA1 in rectifier Bridge_1.

For sub-sector SS1C, the proposed vector sequence is 2 1 0 1 2V V V V V , resulting in the drive signals in Fig. 21b. In

this case, the intervals for the commands of the switches and the three-phase duty cycles are

2 0

2 0 1

2 1 1 1 0

A

B

C A B C

T TT T T

T T T T

== +

= = = = (11)

2

2

2 1 1 1

3 112 21 2

0

A

B

C A B C

D D D

D DD D D D

α β

β

= − ⋅ − ⋅

= − ⋅= = = =

(12)

Extending this analysis to the other sectors, the duty cycle functions for each switch are defined as shown in Fig. 22 for the same values as in Fig. 14.

As in the other rectifiers, from the analysis of the duty cycle equations, it is not necessary to identify the sectors of vectors, only to impose the desired current sectors from the input voltages.

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D. Simulation Results Simulations are realized to verify the proposed modulation

for all rectifiers. The power parameters used in the simulations and in the experimental verification are shown in Table VI.

TABLE VI SPECIFICATIONS USED IN SIMULATIONS AND IN EXPERIMENTATION

Variable Description Value pV Peak line voltage 311 V inV RMS input voltage 220 V oV Output voltage 700 V rf Line frequency 60 Hz oP Output power 20 kW

1 2 3L ,L ,L Rectifier input inductors 2.4 mH oC Output capacitor 4400 μF

sf Switching frequency 10k Hz The input line currents and the duty cycle for one switch are

given in Figs. 23-25, for one rectifier of each group (Y-connected, Δ-connected and Bridge-connected).

Fig. 23. Input line currents and duty cycle for switch SA in Y_2 rectifier (10

A/div; 1 ms/div).

Fig. 24. Input line currents and duty cycle for switch SA in Δ_2 rectifier (10

A/div; 1 ms/div).

Fig. 25. Input line currents and duty cycle for switch SA1 in Bridge_2 rectifier

(10 A/div; 1 ms/div).

TABLE VII RECTIFIER COMPARISON

S Sμ Sp Ps DLF DHF Dμ Dp Rectifier

Y_1 3 0.205 1.013 1.013 6 12 0.034 6.073

Rectifier Y_2 6 0.102 1.013 1.013 0 12 0.051 3.042

Rectifier Δ_1 3 0.247 0.507 0.507 0 18 0.047 4.967

Rectifier Δ_2 6 0.123 0.487 0.487 0 12 0.056 2.546

Rectifier Bridge_1 6 0.123 0.487 0.487 0 7 0.087 3.630

Rectifier Bridge_2 6 0.123 0.487 0.487 0 12 0.051 2.587

In these simulations, duty cycle functions are consistent with the theoretical ones and input line currents have a sinusoidal format.

To evaluate the semiconductors arrangements, performance indices are defined as presented in (13), (14) and (15) [7]. Simulation results show the rectifier performance indices in Table VII.

MAX MAX

OS

Sn Snn

PV I

μ =⋅∑

, MAX MAX

OD

Dn Dnn

PV I

μ =⋅∑

(13)

MEDSnn

SO

Ip

I=∑

, MEDDn

nD

O

Ip

I=∑

(14)

MAX MEDSn Snn

PO

V Is

P

⋅=∑

(15)

where: S is the number of active switches; DLF is the number of low frequency diodes; DHF is the number of high frequency diodes; μS and μD characterize transistor and diode utilization; pS and pD characterize transistor and diode conduction

loses; sP characterizes transistor switching loses.

IV. EXPERIMENTAL RESULTS

The laboratory setup for a 20 kW PWM rectifier is shown in [1], this prototype allows the performance of rectifiers Y_1 and Δ_1. The selected components of the converter, the control strategy and an example of the design procedure are presented in [1] and in [2].

A. Experimental Results for PWM RectifierY_1 Duty cycles for three switches, with a format similar to the

theoretical and simulation duty cycles, are shown in Fig. 26. In analogical measurements 5 V correspond to a duty cycle of 100%.

The input currents in the unidirectional PWM rectifier are given in Fig. 27, where it can be observed that they present a low current distortion (THD40 = 3.16%).

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Fig. 26. Duty cycles for switches A, B and C in rectifier Y_1 (5 V/div; 4

ms/div).

Fig. 27. Input line currents in rectifier Y_1 (20 A/div; 4 ms/div).

Fig. 28. Input voltage reference (2.5 V/div) and current in phase A (20 A/div;

4 ms/div) in rectifier Y_1.

The input current in phase A and the voltage reference for phase A are presented simultaneously in Fig. 28. In this case, the system has a high power factor (0.998).

Fig. 29. Duty cycles for switches A, B and C in rectifier Δ_1 (5 V/div; 4

ms/div).

Fig. 30. Input line currents in rectifier Δ_1 (20 A/div; 4 ms/div).

Fig. 31. Input voltage reference (2.5 V/div) and current in phase A (20 A/div;

4 ms/div) in rectifier Δ_1.

The measured total harmonic distortion of the input voltage is 2.83% and the rectifier efficiency is greater than 95% when operating at above one half of the nominal load.

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B. Experimental Results for PWM RectifierΔ_1 In Fig. 29, the duty cycles for three switches with a format

similar to the theoretical and simulation duty cycles are shown.

The input currents in rectifier Δ_1 are given in Fig. 30, where it can be observed that they present a low current distortion (THD40 = 2.18%).

The input current in phase A and the voltage reference for phase A are presented simultaneously in Fig. 31. The system has a high power factor (0.996) and in this case, the measured total harmonic distortion of the input voltage is 3.08%.

The rectifier efficiency is greater than 96% when operating at above one half of the nominal load.

V. CONCLUSION

A simple methodology to apply the space vector modulation technique was proposed and extended to three different groups of three-phase two-level unidirectional PWM rectifiers. The same steps are used to apply the space vector modulation to all rectifiers.

The proposed vector sequences are the same for all rectifiers because they have the same points of connection at the input (A, B and C) and output (P and N). Therefore, it is necessary to verify the characteristics of the semiconductor arrangements to determine the duty cycle functions.

Rectifiers in the same group use the same duty cycle functions, as verified in simulation and in experimental results. These steps may be used as the starting point for the analysis of new topologies or different semiconductor arrangements.

With this methodology, it is not necessary to determine the sectors of vectors, only to impose the desired current sectors from the input voltage references. The proposed modulation reduces the number of switch commutations and improves the rectifier efficiency.

The simulation and experimental results validated the proposed modulation and the unidirectional rectifiers offer regulated output voltage, high efficiency, high power factor and low input current THD.

In Y-connected rectifiers the number of switches turned on to perform the desired vectors is greater than in the other rectifiers. Δ-connected rectifiers and bridge-connected rectifiers allow the possibility to maintain one switch open for an interval of 60º. Therefore, conduction loses and switching losses are reduced in these topologies.

REFERENCES

[1] F. A. B. Batista and I. Barbi, “Space vector modulation applied to three-phase three-switch two-level unidirectional PWM rectifier,” IEEE Trans. Power Electron. , vol. 22, no. 6, Nov. 2007, pp. 2245-2252.

[2] D. Borgonovo, Y. R. Novaes and I. Barbi, “A three-phase three-switch two-level PWM rectifier,” Proc. of the 34th Annual IEEE Power Electronics Specialists Conference, Acapulco-Mexico, 2003, pp. 1075-1079.

[3] W. Koczara and P. Bialoskorki, “Unity power factor three-phase rectifiers,” 24th Annual IEEE Power Electronics Specialists Conference, PESC '93, Record. 20-24, June 1993, pp. 669-674.

[4] Rong-Jie Tu and Chern-Lin Chen, “A new space-vector-modulated control for a unidirectional three-phase switch-mode rectifier,” IEEE Transactions on Industrial Electronics, vol. 45, no. 2, 1998, pp. 256-262.

[5] J. Yimin; M., Hengchum and F. C. Lee, “Simple High Performance Three-Phase Boost Rectifiers”. 25th Annual IEEE Power Electronics Specialists Conference, PESC '94, Record. 20-25, June 1994, pp. 1158-1163, vol. 2.

[6] J. C. Salmon, “Circuit topologies for PWM boost rectifiers operated from 1-phase and 3-phase AC supplies and using either single or split DC rail voltage outputs”. 10th. Annual Applied Power Electronics Conference and Exposition, APEC '95, Proceedings. 5-9, March 1995, pp. 473-479.

[7] J. W. Kolar and H. Ertl, “Status of the techniques of three-phase rectifier systems with low effects on the mains,” The 21st International Telecommunications Energy Conference, INTELEC '99, June 6-9, 1999.

[8] B. Singh et al.; “A review of Three-Phase Improved Power Quality AC-DC Converters,” IEEE Transactions on Industrial Electronics, vol. 51, no. 3, 2004. pp. 641-660.

[9] T. J. Omedi, R. Barlik, “Three-Phase AC-DC Unidirectional PWM Multiple-Switch Rectifier Topologies – Selected Proprieties and Critical Evaluation”. IEEE International Symposium on Industrial Electronics, ISIE '96, Proceedings. vol. 2, 17-20 June 1996, pp. 784 - 789.

[10] M. Salo and H. Tuusa, “A vector controlled current-source PWM rectifier with a novel current damping method”, IEEE Trans. Power Electron., vol. 15, Issue 3, May 2000, pp. 464-470.

[11] T. Viitanen and H. Tuusa, “Experimental results of vector controlled and vector modulated VIENNA I rectifier,” Record of the 35th IEEE Power Electronics Specialists Conference, vol. 6, June 25-26, 2004, pp. 4637-4643.

[12] R. Greul, S. D. Round and J. W. Kolar, “The Delta-Rectifier: Analysis, Control and Operation”; IEEE Trans. Power Electron., vol. 21, Issue 6, Nov. 2006, pp. 1637-1648.

[13] R. Greul, S. D. Round and J. W. Kolar, “Analysis and Control of a Three-Phase, Unity Power Factor Y-Rectifier”; IEEE Trans. Power Electron., vol. 22, Issue 5, Sept. 2007, pp. 1900-1911.

[14] L. Dalessandro, S. D. Round, U. Drofenik and J. W. Kolar, “Discontinuous Space-Vector Modulation for Three-Level PWM Rectifiers”, IEEE Trans. Power Electron., vol. 23, Issue 2, March 2008, pp. 530-542.

[15] R. Burgos, Rixin Lai, Yunqing Pei, Fei Wang, D. Boroyevich, J. Pou, “Space Vector Modulator for Vienna-Type Rectifiers Based on the Equivalence BetweenTwo- and Three-Level Converters:A Carrier-Based Implementation”. IEEE Trans. Power Electron. , vol. 23, no. 4, July 2008, pp. 1888-1898.

[16] L. Dalessandro, S. D. Round, and J. W. Kolar, “Center-Point Voltage Balancing of Hysteresis Current Controlled Three-Level PWM Rectifiers”, IEEE Trans. Power Electron., vol. 23, Issue 5, Sept. 2008, pp. 2477-2488.

[17] J. Biela, U. Drofenik, F. Krenn, J. Miniboeck and J. W. Kolar, “Three-Phase Y-Rectifier Cyclic 2 Out of 3 DC Output Voltage Balancing Control Method”, IEEE Trans. Power Electron., vol. 24, Issue 1, Jan. 2009, pp. 34-44.

[18] H. W. Van Der Broeck, H. Skudelny and G. V. Stanke, “Analysis and realization of a pulse width modulator based on voltage space vectors,” IEEE Trans. On Industry Applications, vol. 24, 1988, pp. 142-150.

Flabio Alberto Bardemaker Batista was born in

Alegrete, Rio Grande do Sul, Brazil in 1971. He

received the B.S. degree in electrical engineering

from Federal University of Santa Maria, Santa Maria,

Brazil, in 1995 and the M.S. and the Dr. degrees in

electrical engineering from Federal University of

Santa Catarina, Florianopolis, Brazil, in 1996 and

2006 respectively. Currently he is Professor of the Federal Institute of Santa

Catarina. His research interests include power factor correction and digital

control.

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Copyright (c) 2009 IEEE. Personal use is permitted. For any other purposes, Permission must be obtained from the IEEE by emailing [email protected].

This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication.

Ivo Barbi was born in Gaspar, Santa Catarina, Brazil

in 1949. He received the B.S. and M.S. degrees in

electrical engineering from Federal University of

Santa Catarina, Florianópolis, Brazil, in 1973 and

1976 respectively, and the Dr. degree from the

Institut National Polytechnique de Toulouse, France,

in 1979.

He founded the Brazilian Power Electronics Society and the Power

Electronics Institute of the Federal University of Santa Catarina.

Currently he is Professor of the Power Electronics Institute of the Federal

University of Santa Catarina.

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