Basic Theory & Key Technologies Of Intrinsically Safe Switching Converters

Direct current power supplies applied in the flammable and explosive conditions must meet the requirements of anti-explosive. As the optimal means, intrinsically safe switching power supplies will be of promise in the future. Thus, it is nessecery to investigate the basic theory and key techniques of intrinsically safe switching converters.A new large-power safe-barrier with controlled output current is proposed. A fast protection circuit is designed to cut off the source power when the output short-circuit occurs. To overcome the difficulty of Boost converters to realize intrinsic safety, an improved structure of Boost converter is presented. A novel capacitor short citcuit spark energy releasing circuit is invented to further improve the output power of intrinsically safe switching converters.It is pointed out that there are three operation modes for Boost converters and Buck-Boost converters, i.e., the Complete Inductor Supplying Mode (CISM), the Incomplete Inductor Supplying with Continuous Conduction Mode (IISM-CCM) and the Incomplete Inductor Supplying with Discontinuous Conduction Mode (IISM-DCM). The critical conditions and the maximum output voltage ripple within the whole working range of a converter are obtained. It is concluded that the minimum inductance to guarantee the maximum output ripple voltage to be the lowest is the critical inductance of CISM and IISM in case of the lowest input voltage and the minimum load resistance. It is also found that the lowest output voltage ripple is independent of the inductance.The maximum output short-circuit discharged energy of a converter in the whole operating range is deduced. It is found that the maximum output short-circuit discharged energy relates to not only the output voltage and the capacitance but also the switching frenquency and the energy stored in the inductor. It is discovered that the ignition ability is affacted by the load and that the published ignation curve for simple capacitive circuit is not suitable for switching converters. To solve above problem, a new non-explosive output intrinsic safety criterion for switching converters based on modeling the output short-circuit discharging behaviour as a simple capacitive circuit is suggested, which is verified by the experiment results on IEC standard spark ignation apparatus.The maximum current through the inductor of a switching converter is deduced. It is discovered that although the current through the inductor of a switching converter is much lower than the corresponding value on the published ignition curve, ignition still occurs. It is also found that the ignition ability is stenghfened as the output capacitance becoming larger. To solve above problem, a new non-explosive intrinsic safety criterion for switching converters is suggested based on an equivalent resistance analysis approach, in which, the inductor disconnected discharging behavior of a switching converter is modeled as an equivalent simple inductive circuit with an equivalent resistance during the inductor disconnected instant. The proposed method is verified by the experiment results on IEC standard spark ignation apparatus.The approach to design an intrinsically safe switching converter is proposed. The design regions of inductance and capacitance to meet both requirements of electric performance and intrinsically safety are deduced. The influence of switching frequency on design is discussed. The minimum switching frequency of the output intrinsically safe switching converters and totally intrinsic safty switching converters are deduced, respectively.