1 A New Family of Matrix Converters R. W. Erickson and O. A. Al-Naseem Colorado Power Electronics Center University of Colorado Boulder, CO , USA 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

3 II. Converter Derivation and Operation Basic Configuration of New Matrix Converter Basic converterModular 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 Cell DC capacitor voltage = V When semiconductor devices conduct, switch cell can produce instantaneous voltages v aA 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 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 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 Series 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 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 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 Waveforms Change 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 [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 [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 [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 [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 [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 [7]S. Bernet and R. Teichmann, “The Auxiliary Resonant Commutated Pole Matrix Converter for DC Applications,” IEEE Power Electronics Specialists Conference, 1997.