On the Practical Evaluation of the Switching Loss in the Secondary Side Rectifiers of LLC Converters

Abstract

The switching loss of the secondary side rectifiers in LLC resonant converters can have a noticeable impact on the overall efficiency of the complete power supply and constrain the upper limit of the optimum switching frequencies of the converter. Two are the main contributions to the switching loss in the secondary side rectifiers: on the one hand, the reverse recovery loss (Qrr), most noticeably while operating above the series resonant frequency; and on the other hand, the output capacitance (Coss) hysteresis loss, not previously reported elsewhere, but present in all the operating modes of the converter (under and above the series resonant frequency). In this paper, a new technique is proposed for the measurement of the switching losses in the rectifiers of the LLC and other isolated converters. Moreover, two new circuits are introduced for the isolation and measurement of the Coss hysteresis loss, which can be applied to both high-voltage and low-voltage semiconductor devices. Finally, the analysis is experimentally demonstrated, characterizing the switching loss of the rectifiers in a 3 kW LLC converter (410 V input to 50 V output). Furthermore, the Coss hysteresis loss of several high-voltage and low-voltage devices is experimentally verified in the newly proposed measurement circuits.

Grid and PV Fed Uninterruptible Induction Motor Drive Implementation and Measurements

“…In case of resonant converters, the semiconductors are switched when the voltage drop across the switching element is zero (ZVS: Zero Voltage Switching) or the current flow is zero (ZCS: Zero Current Switching). These switching modes result in soft switching on the semiconductor, so the dynamic power loss on the semiconductor is greatly reduced [5][6][7][8]. The LLC converters used operate in ZVS mode.…”

“…A major advantage of the LLC converter is that in the case of a wide range of varying loads, the switching frequency only needs to be adjusted at a narrow interval, so it can be well controlled at a very low loads, or even without a load. It also has the additional advantage of low EMI noise due to soft turn off [5][6][7][8]. However, it is not always advisable to use The design of the LLC converter and the uninterruptible induction motor drive is presented in Section 2.…”

“…The parameter Lp can be determined by measuring the inductance on the primary winding of the transformer while the secondary side is open. The parameter Lr is similarly measured for a short-circuited secondary coil [6,7]. The appearance of the parameter Lr (resonant inductance) therefore stems from the simplification that can be determined according to Equation (1) [5][6][7][8].…”

“…The parameter Lr is similarly measured for a short-circuited secondary coil [6,7]. The appearance of the parameter Lr (resonant inductance) therefore stems from the simplification that can be determined according to Equation (1) [5][6][7][8].…”

“…The parameter Lp (primary inductance) is also created, which combines the primary leakage inductance and the magnetizing inductance (Equation ( 2)) [5][6][7][8]. A constant direct current (DC) is connected to the input of the LLC converter, which is applied to a single-phase inverter (DC/AC).…”