FPGA Implementation of a Fuzzy Controller for Automobile DC-DC Converters Jacobo Alvarez #1 , Alfonso Lago *2 , Andres Nogueiras #3 Carlos Martinez-Peñalver #4 , Jorge Marcos *5 , Jesus Doval #6 , Oscar Lopez #7 # Department of Electronics Technology, University of Vigo Campus Lagoas-Marcosende. 36280-Vigo (Spain) 1,2,3,4,5,6,7 jalvarez, alago, aaugusto, penalver, acevedo, jdoval, olopez@uvigo.es Abstract— The design of synchronous multiphase DC-DC converters for automobile applications is now a very active field, because the automotive industry forecast that future power demands inside a car will oscillate between 2.5 kW and 3.5kW, keeping a dual system of 42/14V batteries. The design of controllers for the optimal behavior of such converters is a very delicate task. In this paper, an optimized fuzzy control algorithm has been developed to control a synchronous multiphase converter of 1.6kW. First, the fuzzy control algorithm is designed and verified, together with a non lineal model of the converter power stage, by means of Matlab and Simulink. Then, the fuzzy controller hardware is developed through Xilinx System Generator for Simulink, and implemented in a Spartan 3 FPGA to achieve a real-time controller. I. INTRODUCTION Actual and future trends in car manufacturing show a rising tendency to install electrical and electronic components that provide great level of security and comfort for the users. For example, positioning systems, powerful sound equipment, conditioned air, thermal steering wheel, etc. All these equipment represents an enormous load increase for the electrical system that cannot be assumed with the present system of 14V. The automotive industry forecast that in the next years, power demands inside a car will oscillate between 2.5 kW and 3.5kW [1]. In addition to the controllers of motors, switches and protections, one of the main new components inside of the car will be one or more DC-DC converters [2]. These converters will be necessary to reduce the 42V from the battery - alternator to the more usual 14V, to supply power to all the systems that initially will not be able to use 42V. The design of synchronous multiphase DC-DC converters allows improvements of the characteristics of high power systems. The automotive industry forecast that future power demands inside a car will oscillate between 2.5 kW and 3.5kW, keeping a dual system of 42/14V batteries. This is the reason why it is possible to consider developing several parallel connected converters [3] [4]. The solution proposed in this paper is based on a multiphase converter of 16 phases, that can be included in a dual power system inside a car with batteries of 42/14V. Employing such a high number of phases minimizes the passive components size in each one, and also the stress level due to lower currents. However, such a high number of phases implies a complex specific control scheme which must allow synchronization between phases, in order to reduce output voltage ripple of the converter and equalize output currents among all the phases. That is why the authors have chosen to develop a digital fuzzy controller to achieve this task. The properties of the fuzzy systems allow to deal with non-linear systems such as the DC-DC converters, as well as to smooth the system response [5] [6] [7]. The high computational load of the fuzzy algorithms force the use of an FPGA implementation, to achieve the desired accuracy in real-time control at the frequency of the PWM signal needed for the DC-DC converter, which will be 200 kHz. To develop all the tasks involved, the authors have used Matlab, Simulink and Xilinx System Generator for Simulink tools. These software suites allow to combine a non linear model of the multiphase DC-DC converter, developed by the authors [8] [9], with the fuzzy controller. This is very important to achieve a good understanding of the real non linear dynamic behavior of the fuzzy controller together with the power circuit, in order to compare the resulting data simulations to find the optimal fuzzy controller. First, the fuzzy algorithm has been designed and tested with the fuzzy toolbox included in Matlab. Then, the fuzzy controller hardware has been developed using the System Generator libraries from Xilinx [10]. These libraries allow to simulate the fuzzy controller hardware in Simulink together with the theoretical converter model, as well as implement it in a Xilinx FPGA. To design a fuzzy controller, the following steps must be followed. First, the feedback variables are selected among all the variables available in the converter, then the membership functions for the inputs and the outputs are designed, and finally the rule base for the fuzzy inference engine is described. II. SPECIFICATIONS The main goal of this work is to develop an optimal real- time fuzzy controller [11] [12] [13] for the DC-DC converter, that can be implemented in a FPGA. To achieve this, there are some considerations that must be taken into account. 237 FPT 2006 0-7803-9729-0/06/$20.00  2006 IEEE