Police said unusual wiring, copper pipes and suspicious objects found inside and outside Dan Zethraeus' car led them to believe it contained an explosive device, and they quickly evacuated buildings around the downtown underground parking garage where he had left it.
The security measures were lifted when bomb experts confirmed the device was "some kind of scientific experiment," police spokesman Hans Sinding said.
"It's a prototype of an invention that I'm developing that is meant to solve the vehicle traffic of the future," Zethraeus told The Associated Press by phone.
The idea is for the car to run on a "new type of electric road where you transfer electricity to the car while it's in motion," he said. "I am doing tests right now but I took a day off and drove to Copenhagen. I'm sorry that this was mistaken for something else."
He described his invention as a "device that powers the car with electricity from the road" but declined to give more details, saying the technology wasn't patented yet.
Zethraeus, who works as a project manager and director for Swedish Television, said he would remove the equipment from his car when going on road trips in the future.
Police had closed several busy streets around the Kongens Nytorv square and evacuated dozens of people from nearby buildings.
Denmark's intelligence service has said the country remains under a "serious" terror threat following the publication of newspaper cartoons lampooning the Prophet Muhammad in 2005, an act that offended many Muslims.
Associated Press writers Karl Ritter and Malin Rising in Stockholm contributed to this report.
Copyright 2013 The Associated Press.