It is a convertible prototype for the KDF-Wagen developped by Ferdinand Porsche, registration plate: IIIA-37022, see att.
The saloon cars were named V-1 ("Versuchwagen"), the cabriolet V-2. The first V-2 was built at Porsche's home in Stuttgart and was ready in december 1935. Later on the V-2 became an headlight upgrade. The headlights moved from the center of the car into the fenders. This was executed around 1937.
In 1937 a serie of 30 SALOON cars, the W-30, were produced at Daimler-Benz in Sindelfingen. NOT mentioned is that also a convertible was produced.
Because of this I think the pictured convertible was also built and /or upgraded at Porsche`s.