Digital control of a rapid capacitor charger with sensor-less voltage feedback

We are reporting on a software implemented HV-sensor for a Digitally Controlled Rapid Capacitor Charger. The new contribution of this paper is to replace a physical voltage sensor with an algorithm that executes in real time in the digital controller for the charger. This avoids the cost, bandwidth limitations and insulation challenges of a conventional HV-sensor. The capacitor charger is controlled by a digital signal controller using a peak current mode control algorithm with adaptive slope compensation as reported in [1]. The peak current mode algorithm uses the analog comparator to detect the peak current and the duty cycle of the inverter at the current peak. Through knowledge of the current waveshape, we can deduct the charge that was transferred during each cycle. This information can be used to predict the voltage of the load capacitor during the charging process. To evaluate the feasibility of this approach, we compare the results from the capacitor voltage prediction algorithm to data obtained with a laboratory grade HV probe.