Fully digital control of a three phase UPS by VECON integrated controller

This paper presents a fully digital control technique for voltage-fed three-phase inverters to be used in uninterruptible power supplies. An application-specific digital signal processor (VECON) is used to attain the regulation of the output voltages, which is maintained also in presence of wide load variations. After a short description of the system, attention is focused on VECON´S performances and implemented control algorithm. Even if no transformer is used in the power converter, the line-to-neutral voltages are independently controlled thus allowing supply of single-phase or unbalanced loads. An inner current control loop is implemented to provide limitation of the phase currents in case of short circuit and overload. Each current and voltage is controlled by a digital PI regulator. The overall control takes less than 20 μs. Sinusoidal output voltages and well controlled phase currents are attained, as demonstrated by experimental results coming from a 15 kVA prototype