Inductor Current Envelope Based TCM/ZVS Operation of a High Switching Frequency Single-Phase AC/DC Converter

For many power converter topologies, triangular current mode (TCM) operation can offer zero voltage switching at the expense of slightly higher conduction losses but with two important practical limitations. Firstly, implementing TCM often requires a costly FPGA or an application specific integrated circuit and/or custom hardware-based sensing. Secondly, the reaction and propagation delays of such sensing and signal processing can introduce a trade-off between the achievable switching frequency and achievable precision of the controlled triangular inductor current waveform. This paper proposes an alternative approach whereby the positive and negative envelopes of the inductor current are captured using simple analog quasi-peak detectors. The sampling rate needed for the envelopes can be far slower than the switching frequency yet precise TCM operation with zero voltage switching can be ensured by means of an appropriate control scheme easily implemented using a comparatively cheap digital signal processor. Advantageously, the same control loop can also enable continuous conduction mode operation. Using a common two-level grid-tied-inverter topology as an example, this paper details the principle of the proposed envelope tracking based TCM (E-TCM) method and provides a simulation based evaluation of control error and bandwidth compared to zero-current-crossing-detection based TCM and a hysteresis based TCM. Different current sensing techniques such as hall sensors and current shunt resistors were taken into account and the simulated sensing circuitry is based on verified measurement data. With realistic signal sensing and processing delays considered, the proposed E-TCM exhibits more than 5x less distortion on the reverse current used for ZVS in the highest switching frequency regions.