Analysis of Non-ideal Step Down Matrix Converter Based on Circuit DQ Transformation

This paper analyzes non-ideal step down matrix converter (MC) under the control strategy proposed by Venturini [l] using circuit W transformation (CWT) technique [2]. The non-ideal step down MC consists of L. C and switches where L and C act as current and voltage sources, respectively. Closed form solutions for the voltage gain and the input phase angle are obtained from the W transformed equivalent circuit. I. 1"RONflION New type of AC to AC converter so called generalized transformer was proposed by Venturini. This converter can be used to reduce or boost the output voltage simultaneously varying the output frequency and the input power factor. Sinusoidal input and output waveforms can also be produced with this converter using small size reactive components. However such a conversion technique was not used widely because number of practical implementation problems existed such as synchronization, protection, slow switching speed and bidirectional capabilities of the power devices. In recent years the progress of power device and the development of large power integrated circuits have attracted growing interests for the applications of matrix converter (MC) and practical implementations have been considered. However the research about MC is only limited to ideal cases, so far, which contains ideal voltage and current sources and switches. The analysis of practical MC is far beyond that of the ideal MC because of its complexity due to the non-ideal sources such as L and C reactive components. In this paper we obtained the analytic expressions for the voltage gain. input power factor and so on with ease using the circuit W transformation technique (CWT) [2]. Since it converts rotationary circuit variables to stationary ones through partial fractions and equivalent conversion circuits, the cumbersome nine switches of MC are substituted by equivalent ideal transformers and thereby non-ideal step down MC is analyzed using simple circuit theory. Both the analytic expression and digital computer simulation results are compared in the paper. 11. CDQT OF STEP DOWN NINE SWITCH K A. Step Down Nine Switch MC The AC to AC nine switch matrix converter topology was firstly introduced in 1976 and recently improved significantly using generalized high frequency switching strategy. Fig. 1 shows the power circuit of the AC to AC step down nine switch MC. Cyu H. CHO Department of Electronic Engineering Korea Advanced Institute of Science and Technology P.0.Box 150. Chongryang, Seoul 130-650. Korea FAX : (011)-822-960-2103 Fig. 1 Step down nine switch MC (a) ideal (b) non-ideal Venturini's modulation function M for the control of output voltage, frequency and input power factor is given by di = 1 + 24 cos(mmt-(i-l)a). i = 1.2.3. mm = 0 0 a i Adi = 1 + 24 cos(oat+(i-1)a). i = 1.2.3. ma = W O + m i 4 : voltage control variable, 0 I 4 I 0 . 5 al. a2 : forward, reverse power factor control variable 0 I a l . a2 , a1 + a2 = 1, a1 a2 = a, a] + a2 = 1 In this equation, al. a2 and 4 are the variables for the controls of the output voltage and the input displacement factor. Therefore the elementary switches are modeled based on the relations given by O-7803-oO90~/91/07oO-oS25$01 .OO 01991IEEE