The soft start-up process is started before commencing the charging or discharging operation when the system is first activated. First of all, the voltage and current value of the DC-link and SC module are sensed by the ADC (analog to digital converters) and fed to the DSP controller through isolated sensing circuits.
The supercapacitor charging voltage and current are plotted during the soft-start region. In this case, the five-phase digital soft-start algorithm achieved a steady state response by minimizing the inrush current and peak overshoot voltage at the output.
The soft-start feature is commonly used in PWM (Pulse Width Modulation) controller ICs, which are currently available on the market, such as the UC1526, UC2526, TL594, LM5045, BM1P107FJ, and UC3526. This limits the inrush current and avoids the overshoot voltage at the output during start-up transients.
Therefore, before switching to the normal operation mode, a soft start mode is necessary to prevent circuit from damage. The proposed digital control algorithm introduces five phase of operation as a soft start algorithm before switching to the normal mode of operation.
The proposed five phase digital soft-start algorithm alone can prevent the DAB-IBDC converter at standalone renewable energy storage system from an inrush current and peak overshoot voltages without being supported by any additional hardware circuits.
In first phase, the average low input voltage is initially applied to avoid starting the inrush current, once the output capacitor reaches the minimum charge, the output current increases gradually to threshold level through help of the other phases. A soft start-enabled flag is used to allow a soft-start.