International Journal of Scientific & Engineering Research, Volume 4, Issue 11, November-2013 1523

ISSN 2229-5518

Simplified Matrix Converter Fed Induction Motor Drive

Vinod Battu, Grandhi Ramu

Abstract—Matrix converter (MC) consists of an array of bidirectional switches, which are used to directly connect the power supply to the load without using any dc-link or large energy storage elements. These highly attractive characteristics are the reason for the tremendous interest in this topology. One of the biggest difficulties in the operation of this converter was the commutation of the bidirectional switches. This problem has been solved by introducing intelligent and soft commutation techniques, giving new momentum to research in this area. . The aim of this paper is to propose a scalar matrix converter modulation equivalent to the SVM ones in order to obtain the same electrical characteristics with a simple approach. Then, the proposed symmetrical carrier-based PW M, equivalent to the SVM, is applied to control the induction motor.

Index Terms— Matrix converter,Space vector Modulation, Carrier based SVM, Induction Motor..

——————————  ——————————

1 INTRODUCTION

he matrix converter has several advantages over tradition- al rectifier-inverter type power frequency converters. It provides sinusoidal input and output waveforms, with mini- mal higher order harmonics and no sub harmonics; it has in- herent bi-directional energy flow capability; the input power factor can be fully controlled. Last but not least, it has minimal energy storage requirements, which allows to get rid of bulky

and lifetime- limited energy-storing capacitors.
Fig.1 Matrix coonverter
The matrix converter consists of 9 bi-directional
switches that allow any output phase to be connected to any
input phase. The circuit scheme is shown in Fig.1.The input terminals of the converter are connected to a three phase volt- age-fed system, usually the grid, while the output terminal are connected to a three phase current- fed system, like an induc- tion motor might be. The capacitive filter on the voltage- fed side and the inductive filter on the current- fed side represent- ed in the scheme of Fig.2.1 are intrinsically necessary. Their size is inversely proportional to the matrix converter switching frequency [2]. It is worth noting that due to its inherent bi- directionality and symmetry a dual connection might be also feasible for the matrix converter: a current- fed system at the input and a voltage- fed system at the output
With nine bi-directional switches the matrix converter can
theoretically assume 512 (29) different switching states combi- nations. But not all of them can be usefully employed. Regard- less to the control method used, the choice of the matrix con- verter switching statescombinations (from now on simply ma- trix converter configurations) to be used must comply with two basic rules. Taking into account that the converter is sup- plied by a voltage source and usually feeds an inductive load, the input phases should never be short-circuited and the out- put currents should not be interrupted. From a practical point of view these rules imply that one and only one bi-directional switch per output phase must be switched on at any instant. By this constraint, in a three phase to three phase matrix con- verter 27 are the permitted switching combinations.
One of the biggest difficulties in the operation of this con-
verter was the commutation of the bidirectional switches. This problem has been solved by introducing intelligent and soft commutation techniques, giving new momentum to research in this area.It is therefore relevant to propose simple, but effi- cient modulation schemes like the three phase VSI modula- tion, with the well-known symmetrical carrier-based modula- tion. Thus, an interesting scientific and industrial approach is to propose a symmetrical carrier based modulation to greatly simplify this implementation and its understanding. The aim of this paper is to propose a scalar matrix converter modula- tion equivalent to the SVM ones in order to obtain the same electrical characteristics (same logic state at each time, same constraints, same efficiency…), with a simple approach. Then, the proposed symmetrical carrier-based PWM, equivalent to the SVM, creates, without any additional calculation, the nine logic control signals of the matrix converter switches by using the matrix [M]. This modulation process can be extended to other PWM strategies.

2 INDUCTION MOTOR MODEL

In the control of any power electronics drive system(say a mo- tor), to start with a mathematical model of the plant is required. This mathematical model is required further to design any type of controller to control the process of the plant. The induction motor

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ISSN 2229-5518

Fig.2 Equivalent circuit of induction motor in d -q fram

model is established using a rotating (d, q) field reference (with- out saturation) concept.. The equivalent circuit used for obtaining the mathematical model of the induction motor is shown in the Fig. 2. An induction motor model is then used to predict the volt- age required to drive the flux and torque to the demanded values within a fixed time period[9]. This calculated voltage is then syn- thesized using the space vector modulation. The stator & rotor voltage equations are given by

where usd and usq, urd and urq are the direct axes & quad- rature axes stator and rotor voltages. The squirrel-cage induction motor considered for the simulation study in this paper, has the d and q-axis components of the rotor voltage zero. By superposi- tion, i.e., adding the torques acting on the d-axis and the q-axis of the rotor windings, the instantaneous torque produced in the elec- tromechanical interaction is given by

3 CARRIER BASED SVM

In this part, the basic knowledge of the SVM applied to matrix converter is introduced to highlight the proposed modulation objectives. The well-known matrix converter Space Vector Modulation (SVM) [1]-[4] approach leads to define three vec- tor families:
- First family: 6 rotating vectors (each phase input is connected
to a different phase output).
- Second family: 3 null vectors (free wheeling ie a switches
configuration leading to zero voltage on the load) called Oi
with i = 1, 2 or 3.
- Third family (the remaining ones): 18 active vectors called Aj (with a fixed angular position, and proportional to one input phase-to-phase voltage), where j is an integer between 1 and
18.
Matrix SVM modulations use only the two last families to cre- ate output voltages and input currents [17], [18], as the first one has a vector position varying with the time, which is not useful for building the references with the space vector ap- proach.

The general matrix SVM sequence, shown in Fig. 2, uses four active vectors Ak (among the six vectors nearest to the output voltage reference vector), and one to three null states Ok to complete the PWM period. This specific sequence allows hav- ing only one switching when a vector is changed.
Fig. 3. General SVM sequence for the matrix converter
In classical SVM methods, only the two greatest phase-to- phase input voltages (U1 and U2 in Fig. 2) and also a null voltage (free-wheeling state) are connected to outputs (u, v, w) during a PWM period (T) [19]-[21].
The null vector O2 automatically involves at the output the common potential to U1 and U2, which is in fact the highest input phase potential in absolute value. A particular modula- tion can be defined by only using this null state O2, which generates a discontinuous modulation (DPWM) [19]. This terminology is proposed here, as this specific choice allows blocking one of the three “switching cells” of the matrix con- verter, in the same way as one inverter leg is blocked when using discontinuous PWM in VSI. This particular modulation, presented in Fig. 3, reduces the number of switching and in- creases the converter efficiency compared to the general SVM sequence (Fig.2.).

Fig.4. DPWM SVM sequence for the matrix converter
To generate this DPWM SVM, it is necessary to
- use the two greatest phase-to-phase input voltages to build the output voltages,
- use only the null state connected to the highest input phase potential in absolute value. In the SVM sequence, this particu- lar null state is necessarily positioned in the medium part of the half PWM period.
The aim of the article is to propose a carrier based modulation method to obtain the SVM DPWM sequence, involving less calculation and thereby a simpler solution compared to the classical SVM implementation
As demonstrated in this document, the numbering for sections

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upper case Arabic numerals, then upper case Arabic numerals, separated by periods. Initial paragraphs after the section title are not indented. Only the initial, introductory paragraph has a drop cap.

4 SPEED CONTORL OF INDUCTION MOTOR WITH

MATRIX CONVERTER

An interesting and elegant protection scheme which might be used to prevent output side overvoltages due to hard shut-

5 SIMULATION RESULTS

The carrier based modulation has been implemented and used to control the induction motor. Proposed method has been simulated in MATLAB/Simulink and the simulation model is shown in figure 7. Simulation model of the matrix converter is shown in figure 8.

Matrix Converter

down of the converter was firstly proposed in [29] and more
recently implemented in [30]. The method simply consists in a proper control strategy of the matrix unidirectional switches

b A

A c B B C

Vabc Iabc a

b c

-10

Constant Tm

to be carried out after the emergency stop command has been a C
set and before shutting-down the converter. The control strat- egy basically aims to create the same operating conditions of a
traditional DC-link voltage converter at the shutdown. In tra- ditional DC-link voltage converter (Fig.2.11), when all the switches are turned off, a static free-wheeling path to the mo-

Induction Machine

tor currents is provided by the free-wheeling diodes. Through these paths the magnetic energy stored in the motor can be automatically transferred to the DC- link energy storage ele-
Fig 7. MATLAB/Simulink model of the matrix converter based induction motor control
ments without any over voltages and over currents risk.

From RU

From1 RV

From2 RW

a From3 SU

From5 SV

From4 SW

S4 S5 S6

Fig. 5 Conventional control of Induction motor using DC link

From6 TU

From7 TV

From8 TW

inverter and rectifier.
For the matrix converter, since no static free-wheeling paths 2

are available, such operating condition must be actively im-
posed. The positive and negative DC rails are respectively
substituted by the most positive and most negative input line-

S7 S8

5 6

3 B C A

to-neutral voltage. For each output line current, the unidirec-
tional switches of the matrix that provide a flowing path direct
to and coming from the positive and negative rail respectively, have to be turned on.

Fig 8.MATLAB/Simulink model of the matrix converter.-

180

160

140

120

100

0 0.2 0.4 0.6 0.8

Time 1 1.2 1.4 1.6 1.8 2

Fig. 6 Induction motor control using matrix converter.
Fig. 9 Speed of the induction motor with paper title and editor)

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ISSN 2229-5518

-20

-40

-60

0 0.2 0.4 0.6 0.8

Time 1 1.2 1.4 1.6 1.8 2

3. [3] D. Casadei, G. Grandi, G. Serra, and A. Tani, “Space vector control of matrix converters with unity input power factor and sinusoidal input/output wave- forms,” in Proc. EPE Conf., Brighton, U.K., Sep. 13– 16,
1993, vol. 7, pp. 170–175.
4. [4] S. Hongwu et al., “Implementation of voltage- based commutation in space-vector-modulated matrix converter,” IEEE Trans. Ind. Electron., vol.59, no.1, pp.154-166, Jan. 2012.
5. [5] J.W. Kolar, T. Friedli, J. Rodriguez, P.W. Wheeler, “Review of Three- Phase PWM AC–AC Converter Topologies,” IEEE Trans. Ind. Electron., vol.58, no.11,
Fig. 10 Stator current supplied to the induction motor

400

300

200

100

-100

-200

-300

-400

0 0.02 0.04 0.06 0.08 Time 0.1 0.12 0.14 0.16 0.18 0.2

Fig. 11 Output voltages of the matrix converter

6. CONCLUSIONS

This paper has presented an original carrier-based modulator for matrix converters based on a “virtual matrix converter” concept. This choice limits to four the number of duty cycle calculations. The proposed carrier-based modulator creates the same instantane- ous connexion matrix [S] as the SVM or the RIV (in the DPWM specific case here), but with less calculation and with a more synthesized and systematic approach. Therefore, this modulation is easier to implement com- pared to the previous ones. Speed control of Induction motor using matrix converter is presented in the paper and MATLAB/SIMULINK results are also presented.

7. REFERENCES

1. J. Rodriguez, M. Rivera, J.W. Kolar, P.W. Wheeler, “A Review of Control and Modulation Methods for Ma- trix Converters,” IEEE Trans. Ind. Electron., vol.59, no.1, pp.58-70, Jan. 2012.
2. [2] M. Hamouda, H.F. Blanchette, K. Al-Haddad, F.Fnaiech, “An Efficient DSP-FPGA-Based Real-Time implementation method of SVM algorithms for an in- direct matrix converter,” IEEE Trans. Ind. Electron., vol.58, no.11, pp.5024-5031, Nov. 2011.
pp.4988-5006, Nov. 2011.
6. J.M.P. Martinez, R.B. Llavori, M.J.A. Cabo, and T.B.
Pedersen, "Integrating Data Warehouses with Web
Data: A Survey," IEEE Trans. Knowledge and Data Eng.,
preprint, 21 Dec. 2007,
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