Analytical Calculation of the Residual ZVS Losses of TCM-Operated Single-Phase PFC Rectifiers

Abstract

Triangular-current-mode (TCM) modulation guarantees zero-voltage-switching across the mains cycle in AC-DC power converters, eliminating hard-switching with a minor ≈ 30 % penalty in conduction losses over the conventional continuous current mode (CCM) modulation scheme. TCM-operated converters, however, include a wide variation in both switching frequency and switched current across the mains cycle, complicating an analytical description of the key operating parameters to date. In this work, we derive an analytical description for the semiconductor bridge-leg losses in a TCM AC-DC converter, including the rms current and/or conduction losses, switching frequency, and switching losses. For SiC MOSFETs, we introduce a new loss model for switching losses under zero-voltage-switching, which we call "residual ZVS losses". These losses include the constant Coss losses found in previous literature but must also add, we find, turn-off losses that occur at high switched currents. The existence and modeling of these turn-off losses, which are due to currents flowing through the Miller capacitance and raise the inner gate source voltage to the threshold level and accordingly limit the voltage slew rate, are validated on the IMZA65R027M1H 650 V SiC MOSFET. The complete loss model-and the promise of TCM for high power density and high efficiency-is validated on a 2.2 kW hardware bridge-leg demonstrator, which achieves a peak 99.6 % semiconductor efficiency at full load. The proposed, fully-analytical model predicts bridge-leg losses with only 12 % deviation at the nominal load, accurately including residual ZVS losses across load, modulation index, and external gate resistance.

Analytical Loss Model for Three-Phase 1200V SiC MOSFET Inverter Drive System Utilizing Miller Capacitor-Based dv/dt-Limitation

“…At low turn-off currents and under ZVS, the voltage slew rate dv DS /dt scales with the switched turn-off current I off . At higher switched currents, though, the voltage slope dv DS /dt saturates, replicating the "kink current" I k behavior found in [36]. The kink current is:…”

“…The turn-on transition occurs under ZCS conditions (I on = 0 A) and the measured slew rate is dv DS /dt = 60 V/ns, with the turn-off transitions at I off = 5 A and I off = 40 A achieving voltage slew rates of 6.1 V/ns and 45 V/ns, respectively. We might expect the voltage slew rate to increase by a factor of 8 with an 8× increase in current; instead, we find an increase of 7.4 and encounter the saturation of dv DS /dt under high-current switching conditions that was reported in [36]. For all of the measured turn-on and turn-off transitions in Fig.…”

“…2) Turn-off Loss Model: A detailed turn-off loss model is given in [36], and only a short summary is given here.…”

Hybrid-Mode Adaptive Zero-Voltage Switching for Single-Phase DC–AC Conversion With Paralleled SiC MOSFETs

“…Extensive research has been conducted on soft-switching modulation strategies of DC-AC power converters including critical conduction mode (CrM) [1], triangular current mode (TCM) [2] [3], and discontinuous current mode (DCM) [4].…”

“…This issue is particularly highlighted in the ACtied converters as the output current is naturally sinusoidal thus the switching frequency is supposed to be continuously varying, e.g., 210kHz-500kHz in [2]. Such large variation yields excessive turn-OFF loss [3], as well as core and winding loss of the inductor [10] in high-frequency ranges. In a twolevel topology, this drawback could be alleviated by swapping between bipolar and unipolar modulations [11], between CrM and DCM operations [12], between TCM and DCM [13], or implementing a variable valley current [10] or peak current [8] control to reduce the wide high-frequency range.…”