Control by Emulation: APF Borderline Controller Example

The Borderline Current Mode (BCM) Active Power Factor Controller (APFC) developed in this study applies a capacitor to emulate the inductor of the power stage and hence the capacitor voltage replicates continuously the inductor current. By this, the instantaneous current of the inductor is available to the controller circuitry without actually measuring it at any given instance. The emulating network is synchronized to the real power system by a zero-crossing signal of the (physical) inductor current. The controller does not include a precision analog multiplier (as some APF BCM controllers do) and does not need to sense the input voltage. An interesting and useful attribute of the proposed controller is its ability to be transformed by a simple circuit reconfiguration into a Continuous Current Mode (CCM) APFC controller that also functions without sensing the input voltage. The paper covers the theoretical aspects of the new controllers family, presents a pre-ASIC discrete-circuit implementation, simulation, and experimental results. The pros and cons of the new controller concept are discussed and possible ways for digital implementation of the new controller concept are suggested.