1

A New Family of Matrix Converters

R. W. Erickson and O. A. Al-NaseemColorado Power Electronics Center

University of ColoradoBoulder, CO 80309-0425, USA

rwe@colorado.edu

Abstract—A new family of matrix converters is introduced, that employs relatively simple voltage-clamped buses and can generate multilevel voltage waveforms of arbitrary magnitude and frequency. The basic configuration includes a nine-cell matrix that uses four-quadrant switch cells. Each four-quadrant switch cell resembles a full-bridge inverter and can assume three voltage levels during conduction. Semiconductor devices in a switch cell are clamped to a known constant dc voltage of a capacitor.

Control of the input and output voltage waveforms of the proposed converter can be achieved through space vector modulation. Simulation results show how the converter can operate with any input and output voltages, currents, frequencies, and power factors while maintaining constant dc voltages across all switch cell capacitors.

2

Comparison of conventional matrix converter with proposed new family of

converters

Conventionalmatrix converter

Proposed newmatrix converters

Voltage conversionratio Vout/Vin

Buck only:Vout ≤ 0.866Vin

Buck–boost:0 ≤ Vout < ∞

Switch commutation Coordinatio n of4-quadrant switches

Simpl etransisto r +freewheelin g diode

B us ba r structure Complex Modularand simple

Multileve l operation No Possible

Utility-sidefil te r elements

A C capacitors Inductive

Machine-sidefil te r elements

Inductive Inductive

3

II. Converter Derivation and OperationBasic Configuration of New Matrix Converter

abcABCn

NiaibiciAiBiC

Three-phaseac system 1Three-phaseac system 2Basic converter

Q1 Q2Q3 Q4D1D2D3D4aAaAModular switch cell

Symbol

Realization

• Converter contains a matrix of switch cells

• Switch cells include dc capacitors

• Input and output ports include inductive elements

4

Operation of Switch CellQ1 Q2Q3 Q4D1D2D3D4aA• DC capacitor voltage = V

• When semiconductor devices conduct, switch cell can produce instantaneous voltages vaA of +V, 0, or –V

• Switch cell can block voltages of magnitude less than or equal to V

• Diodes clamp maximum transistor voltage to V

• Break-before-make operation: it is allowed to turn off all transistors in the converter; diodes are able to provide a conducting path for inductor currents

• Modular switch cells lead to modular bus structure: simple H-bridges

5

Branch connections

abcABCn

NiaibiciAiBiC

Three-phaseac system 1Three-phaseac system 2• To avoid interrupting the input

and output inductor currents, five of the nine branches of the matrix must conduct at any instant

• 81 valid combinations of conducting branches

• At rated voltage: two-level operation

• At low voltage: three-level operation is possible

6

Example

Phase APhase BPhase C Phase aPhase bPhase c-240V+-240V+VAB = 0VVab = 0VVbc = 0VVca = 0VVBC = 0VVCA = 0V-240V+Phase APhase BPhase C Phase aPhase bPhase c0VVab = 0VVbc = 240VVca = -240VVAB = 0VVBC = 0VVCA = 0V-240V+Phase APhase BPhase C Phase aPhase bPhase c+240V-VAB = 0VVCA = 0VVab = 0VVca = -480VVbc = 480VVBC = 0V

(a)(b)(c)

Branch AaBranch Cc

UTILITY SIDE MACHINE SIDE• Three valid choices of switching combinations, for V = 240 V and all for the same choice of conducting branches

• In each case, the four nonconducting branches block voltages less than or equal to 240 V

• When a line-to-line voltage of 2V = 480 V is produced at one side of the switch matrix, then the voltages at the other side must be zero

• Number of valid switching combinations: 19683

7

Increasing the number of levels

abcABCn

Niaibic iAiBiC

Three-phaseac system 1Three-phaseac system 2Series connection of switch cells

For this example—

At rated voltage: three-level operation

At low voltage: five-level operation is possible

Sharing of voltage stress: semiconductor blocking voltages are reduced by factor of two

8

III. Control

dq

• Derived space-vector control algorithm for proposed new converters

• Showed that dc capacitor voltages can be controlled

• Developed extensive computer program to verify operation of control algorithms

Space vectors of basic converter

9

Space Vector Control

(0,√3Vcap) (1.5Vcap, 0.5√3Vcap)d-axisq-axis(0,0)V1V2φV060°d2V2d1V1d0V0

Space vector control can be applied to the proposed new converters

10

Simulated Waveforms:Basic converter in a wind power application

Space vector control algorithm

Utility side:

60 Hz, 240 V, p.f. = 1

Generator side:

25 Hz, 240 V, p.f. = 1

Smooth waveforms: line currents

PWM waveforms: line-line voltages

Operating point #1

11

Simulated Waveforms

Regulation of capacitor voltages within switch cells

—Dashed lines show nominal voltages ± 12%

Operating point #1

12

Simulated Waveforms

Switching states of each cell

Operating point #1

13

Spectrum, utility-side voltage

Operating point #1

Harmonic order

Low switching frequency of 1 kHz

Utility frequency = 60 Hz

Harmonics are sidebands of switching frequency

14

Spectrum, utility-side voltage

Operating point #1

Harmonic order

Switching frequency increased to 20 kHz

Utility frequency = 60 Hz

15

Simulated WaveformsChange of operating point

Utility side:

60 Hz, 240 V, p.f. = 0.5

Generator side:

6.25 Hz, 60 V, p.f. = 1

Smooth waveforms: line currents

PWM waveforms: line-line voltages

Operating point #2

16

Simulated Waveforms

Regulation of capacitor voltages is maintained at nonunity power factor

Operating point #2

17

IV. Conclusions

• Introduction of a new family of matrix converters, that are fundamentally different from the traditional matrix converter

• New converters can both increase and decrease the voltage amplitude and can operate with arbitrary power factors

• Extension to multilevel switching can be attained with device voltages locally clamped to dc capacitor voltages

• Demonstration of space vector modulation to control the input and output voltage waveforms

• It is also demonstrated that the controller can stabilize the dc voltages of the capacitors

• Operation of the basic version of the new family of matrix converters has been confirmed.

18

References

[1] A. Nabae, I. Takahashi, and H. Akagi, “A New Neutral-Point Clamped PWM Inverter,” IEEE Trans. Industry Applications, vol. IA-17, No. 5, Sept./Oct. 1981, pp. 518-523.

[2] P. Bhagwat and V. Stefanovic, “Generalized Structure of a Multilevel PWM Inverter,” IEEE Transactions on Industry Applications, vol. IA-19, no. 6, Nov./Dec. 1983, pp. 1057-1069.

[3] F. Z. Peng and J. S. Lai, “A Multilevel Voltage-Source Inverter with Separate DC Sources,” Proceedings IEEE Industry Applications Society Annual Meeting, 1995, pp. 2541-2548.

[4] O. A. Al-Naseem, “Modeling and Space Vector Control of a Novel Multilevel Matrix Converter for Variable-Speed Wind Power Generators,” Ph.D. thesis, University of Colorado, April 2001.

[5] A. Alesina and M. Venturini, “Analysis and Design of Optimum Amplitude Nine-Switch Direct AC-AC Converters,” IEEE Transactions on Power Electronics, vol. 4, no. 1, January 1989.

[6] L. Huber and D. Borojevic, “Space Vector Modulated Three-Phase to Three-Phase Matrix Converter with Input Power Factor Correction,” IEEE Transactions on Industry Applications, vol. 31, no. 6, Nov./Dec. 1995.

[7] S. Bernet and R. Teichmann, “The Auxiliary Resonant Commutated Pole Matrix Converter for DC Applications,” IEEE Power Electronics Specialists Conference, 1997.