This paper presents a soft start-up strategy of pulse-density-modulated series-resonant converter for induction heating application. The pulse-density modulation (PDM) technique is widely used in converters based on voltage-source series-resonant inverters (SRIs) to control the output current or power. However, during a start-up process, PDM has some disadvantages both in inrush current limiting and providing a zero-voltage switching operation of SRI transistors. In the paper, different PDM techniques are considered and basic moments of PDM using within the start-up process are analyzed. A new soft start-up strategy of PDM converter for induction heating application is proposed. The main features of the proposed strategy include an interleaved or a stepped PDM control, an initial combination of PDM at the beginning of the start-up process, and an operating algorithm during the start-up process. The proposed strategy was verified by a 2.5 kW experimental setup of the pulse-density-modulated interleaved converter with an operating frequency from 50 kHz up to 100 kHz. Experimental results confirm the effectiveness of the proposed start-up strategy and show that the maximum current amplitude within start-up processes exceeds the maximum steady-state current amplitude by no more than 30%.
A problem of electrical and radioelectronic equipment’s high energy pulse disturbance immunity is considered in the paper, in particular against microsecond high voltage disturbances (MHVD) in the power mains. It is showed causes of MHVD with amplitude up to 4 kV and even higher. A review of various protection methods against MHVD is carried out and it is shown that the use of a two-terminal network (TTN) with a significantly nonlinear current-voltage characteristic: varistors, suppressors and gas arrestors is the most effective. The report analyzes the operation principle of these two-poles and shows that the typical inclusion of such a device directly at the equipment’s input is not effective enough for cases where the high-frequency impedance of the mains is low. An L-circuit for connecting the TTN together with an LR link is proposed, and results of computer simulation with the aid of PSPICE showed that such a scheme reduces the MHVD amplitude on the network input of the equipment by 1.5 times comparing with the typical inclusion of such a device even under a low impedance of the mains Adding the low-pass filter to the L-circuit allows to reduce the MHVD amplitude by 40 and more times comparing with the typical inclusion of the TTN. References 8, figures 6.
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