Verification of Envelope Tracking Concepts for High Frequency TCM/ZVS in Two-Level AC/DC Converter Applications

Triangular current mode (TCM) enables the benefit of zero voltage switching, but it is accompanied by two significant functional limitations. Initially, it often requires expensive FPGA, ASIC, and/or specialized hardware-based sensing. Secondly, the time delays linked with such sensing and processing can lead to a trade-off between the achievable switching frequency and the precision of the triangular inductor current waveform. This paper delivers the experimental verification of an alternative method where the inductor current envelopes are measured using straightforward analog quasi-peak detectors. The sampling rate needed for these envelopes is in first approximation independent of the applied switching frequency. The control behavior is mainly unaffected by time and signal delays due to the low frequency envelope signals being used, allowing for an affordable standard DSP to implement the proposed method. Importantly, the same control loop can also facilitate continuous conduction mode (CCM) operation, whereby a normal CCM operation at constant switching frequency and a mode with variable switching frequency and constant ripple current can be featured. Using a standard two-level grid-tied inverter configuration as a case study, this paper shows a measurement based verification of the concept of the envelope tracking-based TCM (E-TCM) and CCM (E-CCM) method. A prototype is presented to demonstrate the behavior of an envelope tracking hardware solution, including a measurement-based evaluation of the proposed circuits in operation with a 0.5 kVA, two-level SiC-based converter. This converter, together with its envelope tracking circuit, is capable of operating in TCM at frequencies up to several hundred kHz and can dynamically transition to CCM during operation.