A Robust Commutation Circuit for Reliable Single- Step Commutation of the Matrix Converter S.A. Nabavi Niaki and R. Iravani Department of ECE, University of Toronto Toronto, ON, M5S 3G4, CANADA nabavi.niaki@utoronto.ca H. Kojori Honeywell Advanced Technology Mississauga, ON L5L 3S6, Canada Abstract—The matrix converter (MC) is an attractive topology for the more electric aircraft because of its high-power density and bidirectional power flow features. One of the challenging issues in MC is the current commutation. The commutation process in a matrix converter (MC) is more complex as compared with that of the traditional AC-DC-AC converter due to the lack of natural free-wheeling paths. Multi-step commutation methods along with various voltage clamp circuits, connected at input and output, have been proposed for the MC. These methods are complex and require accurate real-time information about direction of current and input AC system voltages. Reducing the commutation time and process is a main objective of using MC in aerospace applications where the range of frequency is between 360-800 Hz. This paper presents a robust commutation circuit for reliable single-step commutation of the MC, and demonstrates its feasibility through computer simulations and experimental results obtained from a laboratory scale prototype. I. INTRODUCTION The matrix converter (MC) has attracted significant attentions [1]–[8] due to its features that enable (i) adjustable power factor, (ii) bi-directional power flow, (iii) high-quality waveforms, and (iv) compact design due to the lack of energy storage components. Various multi-step commutation strategies for the MC have been proposed [8], [10] and compared in the technical literature [11],[12]. Among these methods, the 4-step commutation is the most widely accepted one. The main technical issues of the multi-step methods are as follows. (i) The sequence of switch turn on-off is determined by the direction of output current and/or the values of the input-side voltages. The commutating reliability depends on accurate evaluation of the voltage difference of the two involved input phases and the output-side current direction. When the output- side current or the difference of the input voltages is small, the commutation is prone to failure. (ii) Reducing the commutation time enhances the quality of the input and output waveforms [13]. The commutation time can be reduced by reduction of the number of steps from four to two [14] or one [15]. This, hence, increases the commutation algorithm complexity. For the aerospace applications where the range of input- side frequency is between 360-800 Hz, reducing the commutation time is one of the main objectives. This paper introduces a novel single-step commutation circuit for the MC that provides a safe and reliable bidirectional path for the load current during the commutation period and protects the switches against any overvoltage due to the load current interruptions under steady state or fault conditions. This commutation circuit is directly connected across each switch module and does not require an additional clamp circuit. The main advantage of the proposed commutation circuit is that it introduces only a fairly short deadtime delay (in the range of nanoseconds). This single-step delay considerably minimizes the commutation time compared to multi-step commutation methods. The proposed method does not require line current and/or phase voltage measurements. II. MULTI-STEP COMMUTATION PROCESS During the past decades, three kinds of multi-step commutation strategies have been proposed, i.e., 1) current- based commutation (CBC), 2) voltage-based commutation (VBC), and 3) hybrid commutation (HC). The multi-step commutation algorithms require line current and/or phase voltage measurements. CBC and VBC strategies rely on the knowledge of the output-current direction and the relative magnitude of input voltages respectively. However, the directions of output current and the relative magnitudes of the input voltages are difficult to measure, particularly at zero or close to zero crossing instants. The misjudgment of output- current direction in the commutation process leads to an open circuit of the load current and causes overvoltage. If the relative magnitude of the input voltages is misjudged, a short circuit of the input phases can happen. HC strategies rely on information about the relative magnitude of input voltages and the output-current direction. Fig. 1 depicts the 4-step sequence of current commutation from the bidirectional switch S a (AC switch module) to the bidirectional switch S b , when the load current is positive 978-1-4799-2325-0/14/$31.00 ©2014 IEEE 3349