9th International Conference on Power Electronics and Motion Control - EPE-PEMC 2000 Košice 5 - 6 THE STEADY STATES ANALYSIS OF THE DOUBLY-FED INDUCTION MOTOR (DFIM) WITH MATRIX CONVERTER E. Chekhet, V. Sobolev, I. Shapoval Institute of Electrodynamics of the Ukrainian National Academy of Sciences, Prospect Pobedy 56, 03680, Kiev, Ukraine tel./fax: (+38 044) 446 92 66; e-mail: chk@ied.kiev.ua Abstract. Doubly-fed induction motor (DFIM) in conjunction with AC-AC matrix converter is investigated. “Venturini” control algorithm for matrix converter is used. Steady states analysis of the DFIM with matrix converter is carried out. MC input current harmonic content is analysed. Modified MC control algorithm is proposed. Keywords: Matrix converters, Converter control, Analysis, Doubly-fed induction motor, Pulse-width modulation 1. INTRODUCTION In some technological applications such as centrifugal pumps, Fans, wind generators desired control performance can be achieved using restricted speed regulation range (less than 20-25 %). Doubly fed induction machine (DFIM) has been found as an attractive solution for these applications. DFIM allows to get control effect using bi-directional rotor power converter whose power is proportional to required slip range. The progress in power semiconductor devices and microprocessor technique renewed interest to direct frequency conversion, especially to matrix converter (MC) [1,2,6]. The MC has a number of advantages over conventional configuration rectifier-inverter. Matrix converter requires no large reactive components, as there is no DC link. The requirement for reactive components is therefore restricted to small input filter. It makes the matrix converter an all silicon solution to ac-ac power conversion. In combination with the PWM it guarantees higher control resolution, reduction of the switching frequency and requires less reactive elements. The MC also draws sinusoidal input current after the filtering of switching frequency harmonic. Most control algorithms also allow the input displacement factor to be set at unity or controllable. General schematic diagram of the DFIM-matrix converter system is shown in Fig. 1. [5]. In this paper the implementation of MC with PWM in DFIM is analyzed. 2. ANALYSIS OF CONVENTIONAL MC PWM ALGORITHM One of the PWM control algorithms for MC was proposed by M.Venturini [1]. The sense of proposition consists in the alternate switching input MC phases to output load phases during time intervals, which durations sinusoidally change. As the result the average voltage in each load phase is defined as follows: l l l μ U U 3 1 a ⋅ = ∑ = (1) where l μ are on-time ratios (ratio of the time interval duration of connection each input phase l to load phase to carrier frequency PWM period). The law of the l μ changes is defined by the expression             − − + = 3 π 2 1) ( t ω qF 1 3 1 μ m m l l (2) where q is depth of modulation, F m is modulating function with angular frequency ω m =ω i- ±ω o , ω i and ω o are angular frequencies of the ac mains voltages and fundamental output voltage harmonic respectively. Proposed algorithm has disadvantage related to output/input voltage ratio which maximum value is equal to 0,5. The alternative to the proposed algorithm could be vector PWM (VPWM) algorithm, where output/input voltage ratio achieves value 2 3 [3,4]. The principle of VPWM is that the averaged output voltage is formed during each PWM cycle using four stationary output space vectors [3]. Their selection depends on phase of the averaged output vector with respect to the input instantaneous current phase. Thus, the condition of VPWM realisation is the necessity of tracing ac mains voltages. If MC is in the rotor of DFIM then “Venturini” algorithm is a more simple solution as it requires no tracing ac mains voltages. The output MC frequency is equal to difference of control frequency by nine bi-directional MC switches and ac mains frequency. Therefore, in order to get slip frequency it is sufficient to keep up the control frequency equal to sum of ac mains and slip frequencies. There are three different states only in comparison with five in MC with VPWM. The sequence of the states is determined and it requires no additional expenses on hardware and software to optimize MC switches commutation. Košice Slovak Republic 2000