AC-DC-AC Converter with Induction Machine-modeling and Implementation on Floating Point DSP as a Cost Effective Interface for Renewable Energy Applications M. Jasinski, G. Wrona and M. P. Kazmierkowski Warsaw University of Technology, Institute of Control & Industrial Electronics, ul. Koszykowa 75, 00-662 Warszawa, E-mail Poland, tel. (48) 22 628 06 65. fax (48) 625 66 33, e-mail: mja@isep.pw.edu.pl, wronag@ee.pw.edu.pl, mpk@isep.pw.edu.pl. Abstract- The paper presents advanced vector control system for AC- DC-AC converter operating as grid interface for renewable energy systems. The control method is based on Direct Torque Control with Space Vector Modulation (DTC-SVM) for Machine Side Converter (MSC) and Direct Power Control with Space Vector Modulation (DPC- SVM) for Line Side Converter (LSC). The whole control and protection system has been implemented on cost effective floating point DSP microcontroller TMS320F28335. Simulation and experimental results which illustrate steady state and dynamic properties of the developed system obtained from the 3kW laboratory model are given. INTRODUCTION Recently, in control of power electronic converters new and more complex algorithms require more and more computing power. Also, advances in power semiconductor technology allows to use higher switching frequency. This leads to requirement of high-speed Digital Signal Processors (DSP). One of them is floating point microcontroller TMS320F28335 from Texas Instrument. This system combines sophisticated peripherals which are typical for microcontrollers and high computing power characteristic for DSPs. The main advantage of this DSP controller is ability to operate on floating point numbers without having to use additional libraries [5]. In this paper Direct Torque Control (DTC) for machine side converter and Direct Power Control (DPC) for line side converter are presented. Instead of hysteresis controllers used in the conventional schemes [8] in this work linear PI controllers with Space Vector Modulators (SVM) are implemented [9]. This eliminates the fundamental drawback of hysteresis controllers, a variable switching frequency, and also facilitate their implementations on digital platform. The Direct Power and Torque Control with Space Vector Modulation (DPTC-SVM) algorithm is characterized by simple structure, limited number of transformation, and good operation properties in transient and steady states. In the past works [7,10,12], the DPTC-SVM control algorithm has been implemented on fixed-point DSP/RISC. In this paper we present implementation of this algorithm on floating point microcontroller TMS320F28335. OPERATION OF LINE SIDE CONVERTER – LSC LSC can be described in different coordinate system. Basic scheme of the LSC with AC input choke and output DC side capacitor is shown in Fig. 1a, while Fig. 1b shows it’s single-phase representation. Where, U L is a line voltage space vector, I L is a line current space vector, U P is the LSC input voltage space vector, and U i is a space vector of voltage drop on the input (AC grid side) choke L and it resistance R. The U p voltage is controllable and depends on switching signals pattern and DC-link voltage level. Thanks to control magnitude and phase of the U p voltage, the line current can be controlled by changing the voltage drop on the input choke - U i . Therefore, inductances between grid and AC side of the LSC are indispensable. They create a current source and provide boost feature of the LSC. Through controlling the converter AC side voltage in its phase and amplitude, U p the phase and amplitude of the line current vector I L is controlled indirectly. Further, in Fig. 2 are shown both motoring and regenerating phasor diagrams of LSC. From this figure can be seen that the magnitude of U p is higher during regeneration than in rectifying mode. With assumption of a stiff line power (i.e., U L is a pure Fig. 2. Phasor diagrams of LSC: a,b) non unity power factor operation; c,d) unity power factor operation L L j I ω L I L RI L L j I ω L I L RI L L j I ω L I L RI L L j I ω L I L RI Fig. 1. Line side converter (LSC) topology: a) three phase system; b) single phase equivalent 978-1-4244-6391-6/10/$26.00 ｩ2010 IEEE 620