Patent ID: 6476588
Filing Date: 2002-11-05
Classification: H02M

Abstract:
A method for operating the voltage transformer, which comprises:measuring an input voltage and an output voltage of a transformer having: an input side having a voltage input carrying the input voltage; an output side having a voltage output carrying the output voltage; a capacitor disposed on the output side and providing the output voltage; a coil having a coil current; a controllable switching element connected to the coil for controlling current flowing through the coil, the switching element having switching times for setting a voltage ratio; and a control unit having: an input side connected to the voltage input and to the voltage output; and an output side connected to the switching element for controlling the switching times of the switching element as a function of the input voltage and the output voltage, for setting the voltage ratio, and for preventing an excessive rise in the coil current; calculating the switching times of the switching element as a function of the input voltage and the output voltage; driving the switching element alternately into conductive and non-conductive states in accordance with the calculated switching times for achieving a desired voltage ratio of the voltage transformer and to prevent an excessive rise in the coil current; periodically switching the switching element into the conductive and non-conductive states with a prescribed switching period; switching the switching element into the conductive state at a start of each switching period for a prescribed initial time interval to bridge the capacitor; calculating the initial time interval as a function of a maximum permissible coil current, an inductance of the coil, and the input voltage of the voltage transformer; switching the switching element into the non-conductive state in each switching period after expiration of the initial time interval, at least for a prescribed subsequent time interval, to extinguish the coil current; calculating the subsequent time interval as a function of the maximum permissible coil current, the inductance of the coil, the input voltage, and the output voltage; additionally switching the switching element into the non-conductive state in each switching period after expiration of the subsequent time interval, until the end of the switching period, for an additional time interval, to set the desired voltage ratio; and calculating the additional time interval as a function of a capacitance of the capacitor, the maximum permissible coil current, the initial time interval, and the subsequent time interval.