Implications of Discrete vs. Continuously Adjustable Current for Electrically Heated Catalytic Converters

Despite the obvious shift in daily commuting towards electromobility, internal combustion engines (ICEs) still dominate the market, particularly in the transport sector. Their main drawback—cold-start emissions—has driven the development of active control strategies beyond passive exhaust optimizations. An electrically heated catalytic converter (EHC) helps the catalytic converter reach the light-off temperature more quickly through active control; however, it places additional demands on the already strained onboard electrical power distribution network. This paper presents a case study comparing two power supply and control configurations for managing the temperature of the EHC: (i) a smart-switch-based approach using bang-bang control, and (ii) a DC/DC converter with a proportional–integral–derivative (PID) controller. To define key target requirements for a dedicated DC/DC converter suitable for real-world conditions, measurement data such as temperature and electrical power demand were gathered through preliminary pollutant emissions tests performed in a laboratory environment using a programmable bench power supply. For the selected test procedure, engine cold-start emissions using various heater power supply scenarios were reduced by a factor of 6 for Total Hydrocarbons (THC) and by a factor of 5 for Carbon Monoxide (CO). Based on a comparative analysis of power supply parameters, a custom four-leg interleaved Buck converter was developed to meet the target power requirement and to specifically reduce voltage overstress caused by parasitic inductances in the onboard distribution network during rapid load current transients. The efficiency of the proposed DC/DC converter reached 95.8%. Unlike a bang-bang-controlled smart switch, the use of the DC/DC converter reduces both electrical and thermal stress on the vehicle’s cable harness.