A sampling algorithm for digitally controlled boost PFC converters

Abstract

Digital control of a boost power factor correction (PFC) converter requires sampling of the input current. As the input current contains a considerable amount of switching ripple and high frequency switching noise, the choice of the sampliig instant is very important.To avoid aliasing without employing a (very) high sampling frequency, the sampling is synchronized with the pulse width modulation (PWM). Sampling algorithms employing this technique successfully reject the input current ripple but are not immune to the high frequency switching noise present on all sampled signals. Therefore, a new sampling algorithm, intended for center-based or symmetric PWM, is deduced with as most important features: switching noise immunity, straighfforwardness, accurate measurement of the averaged input current and the need for only few processor cycles. The operating principle, design issues and a theoretical study of the input current error induced by the sampling algorithm due to sampling instant timing errors are derived. All theoretical results are validated experimentally by using a digitally controlled boost PFC converter switching at 50kHz.

DC-bus voltage controllers for a three-phase voltage-source inverter for distributed generation

“…The output of the current controller is added to the output of the duty-ratio feed-forward. The duty-ratio feed-forward branch is added to obtain a better disturbance rejection [19]. The result of this summation is the input of the PWM modulator which outputs the switching-signals for the inverter.…”

Sample correction for digitally controlled boost PFC converters operating in both CCM and DCM

“…As a result of this switching during a line period, the converter dynamics change abrubtly [3], [5], yielding input current distortion. If digital control is applied, sampling of the input current is usually necessary [6]- [10], although some attempts are made to control a boost PFC converter without instantaneous measurement of the input current [11]. In the case of input current sampling, another source of input current distortion in MCM is posed by the sampling algorithm.…”

“…In the case of input current sampling, another source of input current distortion in MCM is posed by the sampling algorithm. After all, the sampling algorithm is only designed to produce samples of the averaged input current in CCM [7], [9], [10]. In this paper, the conditions for MCM operation are determined and the input current distortion caused by the sampling algorithm, is analysed, yielding a correction factor to compensate for the error on the input current samples.…”

“…Therefore, the sampling frequency is often chosen equal to the switching frequency. As the input current waveform is now represented by one sample each switching cycle, it is very important to choose the right sampling instant [10]. This instant is commonly chosen in the middle of the rising edge of the input current waveform.…”

“…This instant is commonly chosen in the middle of the rising edge of the input current waveform. This algorithm is called rising edge sampling (RES) [7], [9], [10]. …”