DIGITAL CONTROL SYSTEM FOR HIGH PRECISION POWER SUPPLIES OF THE NEW BRAZILIAN SYNCHROTRON SOURCE Gabriel O. Brunheira, Jakson P. Bonaldo, João Nilton H. da Rosa, Cleber Rodrigues, José A. Pomilio School of Electrical and Computer Engineering University of Campinas Campinas, São Paulo, Brazil jbonaldo@gmail.com, antenor@dsce.fee.unicamp.br Brazilian Synchrotron Light Laboratory – LNLS Power Electronic Group – ELP Rua Giuseppe Máximo Scolfaro, 10.000 Zip Code 13083-970, P.O. Box 6192 – Campinas – SP - Brazil gabriel.brunheira@lnls.br, joao.rosa@lnls.br, clero@lnls.br Abstract – This paper proposes an architecture of digital current regulator intended to be used to control the power supplies of the new Brazilian synchrotron light source, called Sirius. It is based on a high-precision Digital to Analog Converter and a modern System on Chip device, which has the capability of performing real- time control tasks together with managing and interface tasks. Despite this system will be used to control many kinds of power supplies, it was validated in a 100 W power supply, which was previously developed to be used in the present Synchrotron Light Source. Keywords - Digital Control, High Precision Current Source, DC-DC converter I. INTRODUCTION The Brazilian Synchrotron Light Laboratory (LNLS), located in Campinas-SP, has built and operated the first Synchrotron Light Source in the southern hemisphere and the only one in Latin America [1]. Now it is building a second one, called Sirius, which will be a third generation synchrotron source, with 3GeV energy and very higher brilliance, as well the lowest emittance among not only those in operation, but also in design process [2, 3]. Due to the small size of the electron beam, its orbit must be much more stable, as well the current sources which feed the magnets. The number of these power supplies (PS) will also be much greater than in the current light source, probably more than one thousand units. Thus the use of a digital regulation system is strongly indicated, mainly due to the following advantages [4, 5, 6]: • Lower susceptibility to noise, thermal variations and components aging; • Easier parameter adjusts and higher malleability; • Unique controller hardware for all PS's; • More diagnosis functionalities; • Allows implementation of more complex control strategies. Therefore, it has been decided to apply digital control in all current source families that will be used in Sirius, using, when possible, the same hardware, i.e., the same control and processing board. This strategy was chosen by other particle accelerators with good results [7]. This system will be called Universal Digital Controller (UDC). Usually, the current sources used at LNLS present a precision better than 0.01% in relation to their output range [8, 9, 10] (in this case precision can be understood as a general expression which encompasses resolution, short and long time stability, linearity, etc. This represents an additional difficult for the design of current digital regulators, because their performance is affected by quantization and mathematical noise, accuracy of analog-to- digital converters (ADC) and the resolution of the pulse width modulator (PWM) [11, 12]. Moreover, some models of power supplies will have a high bandwidth, up to 2kHz, what means an additional difficult once the available time for processing will be shorter, the reference values must be updated at this frequency and, mainly, the switching frequency must be enough higher than this value. Many strategies have been proposed in order to obtain PWM with high resolution, as delay line, dithering, dual clock, etc, and each one has its advantages and disadvantages [13]. This work used a Digital Signal Processor (DSP) which has internally a high resolution PWM (HRPWM) based on a delay line. This off-the-shell solution was suitable for this project because of its low cost, size and reliability. Moreover, it saved developments costs and can be combined in the future with other solutions, like dithering, in order to increase PWM resolution even more. This work will discuss the main components of a digital regulation system, as well its characterization and modeling. The proposed system validation was performed with a bipolar current source with rated output of 10A/10V. This PS model is already used at LNLS but with analog regulation. For the tests this analog circuit was exchanged by the digital one. Section II will show the basic modeling of the system in the analog domain. Section III brings considerations about the digital implementation of the regulator, discussing the main performance indicators of the signal acquisition and the digital PWM behavior. Experimental results are shown in section IV and section V presents the conclusions. 978-1-4799-0272-9/13/$31.00 ©2013 IEEE 326