382 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 49, NO. 2, APRIL 2002 Gate Drive Level Intelligence and Current Sensing for Matrix Converter Current Commutation Patrick W. Wheeler, Member, IEEE, Jon C. Clare, Member, IEEE, Lee Empringham, Member, IEEE, Michael Bland, Member, IEEE, and Maurice Apap Abstract—This paper is concerned with the process of current commutation in matrix converters. The mechanisms involved in the commutation process are described and practical waveforms are presented. A novel commutation strategy is described that uses gate drive level intelligence in the form of a field-programmable gate array. Current direction is determined using device voltages and, therefore, the measurement problems associated with all other commutation methods are overcome. Practical results from an 18-kW matrix converter induction motor drive are presented. Index Terms—Current commutation, direct ac-to-ac converters, matrix converters. I. INTRODUCTION T HE matrix converter offers an all-silicon solution for ac-to-ac power conversion. A three-phase to three-phase matrix converter consists of an array of nine bidirectional switches arranged so that any of the output lines of the con- verter can be connected to any of the input lines (Fig. 1). A line filter is included to circulate the high-frequency switching harmonics. The switches are modulated in such a way as to generate the desired output waveform [1]. The matrix converter has many advantages over traditional topologies. It is inherently bidirectional and can regenerate en- ergy back to the utility. It draws sinusoidal input current and, depending on the modulation technique, can be arranged that unity displacement factor is seen at the supply side irrespective of the type of load [2]. The converter size has the potential to be considerably smaller than conventional technologies since there are no large capacitors or inductors to store energy. The matrix converter seems to be an ideal topology to utilize developing technologies such as high-temperature silicon car- bide devices. These devices operate at around 300 C [3] so the lack of electrolytic capacitors would be a significant advantage. Traditional inverter-based converter circuits include natural freewheel paths that allow straightforward commutation of the load current from one device to another. This is achieved by inserting a short dead time during the transition between switching devices while the load current freewheels through the appropriate diode. However, in the matrix converter circuit there are no natural freewheel paths, and this causes extra Manuscript received April 20, 2001; revised September 11, 2001. Abstract published on the Internet January 9, 2002. This work was supported by the U.S. Army Research Laboratories under Grant 96300732 and by the Engineering and Physical Sciences Research Council, U.K., under Grant GR/N08438. The authors are with the Power Electronics, Machines and Control Group, School of Electrical and Electronic Engineering, University of Nottingham, Nottingham, NG7 2RD, U.K. (e-mail: pat.wheeler@nottingham.ac.uk). Publisher Item Identifier S 0278-0046(02)02884-8. Fig. 1. Matrix converter circuit. difficulties when commutating the current between switches [4]. There have been a number of proposed solutions to this current commutation issue [4]–[7], but they all have limita- tions in their practical implementation. These commutation techniques rely on the accurate measurement of the either output current [4], [5] or the input voltage [6], [7], with any inaccuracies, especially at relatively low magnitudes, leading to commutation failure. This paper describes a new two-step semi-soft commutation technique which addresses many of the implementation difficulties found in the existing techniques. II. CURRENT COMMUTATION The phenomena associated with the current commutation process can be experimentally examined, modeled, and simu- lated. The characteristics of each commutation depend on the direction of the output current and the relative magnitudes of the input voltages at the instant of commutation. This paper considers the commutation process in detail and assesses the switching energy losses in matrix converters arising from the proposed method of current commutation. Other current-based commutation techniques can be similarly analyzed. Reliable current commutation between switches in matrix converters is more difficult to achieve than in conventional voltage-source inverters since there are no natural freewheel paths. The commutation has to be actively controlled at all times with respect to two basic rules [4]. It is important that no two bidirectional switches are switched on at any one time. This would result in line-to-line short circuits and the destruction of the converter due to the large resulting currents. Also, the 0278-0046/02$17.00 © 2002 IEEE