A static load model is always equivalent to a constant impedance model. For modelling any other characteristic, you have to define a general load type (TypLod) and, on the Simulation RMS page, switch it to e.g. 100 % dynamic.

A real constant PQ load model can be obtained by setting all voltage and frequency exponents and also the related time constants to zero; you can additionally specify limits for the described characteristic. If the voltage drops below the limit, the load will have a constant impedance characteristic. This is necessary because constant power results in very large currents at very low voltages.