On the Maximum Bandwidth Attainable by Power Factor Correctors with a Standard Compensator

When a power factor corrector (PFC) is designed with a relatively fast output-voltage feedback loop, the static and the dynamic behaviour of the power stage is different to that obtained with a slow output-voltage feedback loop. This is because of the influence of the voltage ripple that is present on the control signal. This voltage ripple generates a parasitic feedback loop, which is different to the desired one (the dc output-voltage feedback loop). The effect of this parasitic feedback loop can be integrated into the power stage model in such a way that a new model for the power stage is obtained. Assuming this model, the only feedback loop is the one corresponding to the dc output voltage, i.e., the desired output-voltage feedback loop. The design of this feedback loop determines the final dynamic behaviour of the PFC, which can be optimized to achieve the maximum bandwidth compatible with compliance with existing regulations regarding the injection of line harmonics and with PFC stability. The main objective of this paper is thus to determine the maximum crossover angular frequency,omega_o, compatible with a desired value of the phase margin, phi_m, and with compliance with EN 61000-3-2 regulations in all possible classes of equipment (A, B, C and D) when a standard compensator (a PI with one additional pole) is used. The results obtained show that the maximum bandwidth attainable by a PFC strongly depends on its class. This maximum bandwidth depends on the power processed by the converter in the case of equipment classified as class A or class B. However, the maximum bandwidth attainable for equipment belonging to class C or to class D does not depend on the power processed and is always higher in the case of class D than in that of class C.