This article introduces the basic principles of traditional hysteresis control methods, deduces the relationship between switching frequency and hysteresis loop width, and analyzes and studies the reasons for the unstable switching frequency under hysteresis control, as well as the impact of switching frequency on control accuracy. On this basis, a constant frequency adaptive hysteresis control is proposed. When deriving the formula for calculating the loop width, the reference current slope is taken into consideration, and the relationship between the inductor current on the grid-connected side during the rising and falling phases and the loop width is expressed in sections, thereby achieving real-time regulation of the loop width to ensure constant switching frequency. Finally, simulation results confirm that using this method can achieve a fixed switching frequency in inverter grid connection, and achieve high tracking accuracy under high-frequency switching.
Medical air system is widely used in hospitals. Parameters such as terminal pressure, terminal pressure drop, terminal flow, water content, and particle concentration can directly decide the quality of medical air system. At present, there is no relevant calibration specification,or method for medical air system in China. This article presents a novel calibration method for medical air system by determining corresponding environmental conditions, calibration standards, location of standards and calculation equations. The calibration results show that the calibration method is scientific and practical for metrological performance evaluation of medical air system.
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