1. Explosion-proof issues
Because the environment in which this frequency converter operates contains a lot of explosive gases or dust, it must be sealed and explosion-proof. Therefore, its casing cannot be a regular casing; a standard explosion-proof chamber must be used to house all the components of the frequency converter. An observation window is made on the explosion-proof chamber door to house the display unit, and the start, stop, and speed control buttons are also mounted on the explosion-proof chamber door.
2. Heat dissipation issues
Since all components of the frequency converter are housed in an explosion-proof enclosure where air cannot circulate, heat dissipation becomes a critical issue that needs to be addressed. Here, we employ a novel heat dissipation technology – heat pipe cooling.
(1) Principle of heat pipe technology
A heat pipe is a heat transfer element with extremely high thermal conductivity. It transfers heat through the evaporation and condensation of a working fluid within a fully enclosed vacuum tube. It boasts a series of advantages, including extremely high thermal conductivity, good isothermal properties, adjustable heat transfer area on both the hot and cold sides, long-distance heat transfer capability, and temperature control. Heat exchangers composed of heat pipes offer advantages such as high heat transfer efficiency, compact structure, and low fluid resistance.
(2) Layout of frequency converter
We designed the main circuit as a large unit, installed on the rear wall of a rectangular explosion-proof enclosure. A transition heatsink connects to heat-generating components such as the IGBT module and rectifier module on the rear wall. A slotted heatsink is welded to the outer wall of the explosion-proof enclosure, and the transition heatsink and the slotted heatsink are connected via heat pipes. The heat generated inside the inverter is dissipated through the transition heatsink, heat pipes, and slotted heatsink on the rear wall of the explosion-proof enclosure.
3. Differences in main circuit structure compared to general-purpose frequency converters
(1) The absence of a circuit avoids the unsafe factors caused by electric sparks generated when the relay operates, thus increasing the safety and reliability of the frequency converter.
(2) The purpose of selecting a rectifier capacity that is twice that of a general frequency converter is to withstand the impact of capacitor charging current at the moment the frequency converter is turned on.
(3) Multiple non-inductive capacitors are selected for the filter capacitor. Electrolytic capacitors are large in size and are prone to explosion in high temperature environment, which is unsafe; while non-inductive capacitors are small in size, resistant to high temperature and high pressure, and are very safe to use in such environment.
