Fig. 3

Candidates for f_char/dischar models: The function f_char/dischar models the relationship of VPP SoC versus its charging and discharging capabilities (see also Fig. 1). Tested in this paper are the performance of 5 different promising candidates. The first candidate, does not take this relationship into account. The second model bounds the SoC, so that only 20% to 80% of the VPP SoC can be used. The third model uses simply a linear, the fourth a concave and the fifth a non-concave piece-wise linear relationship. The fifth model is most precicse, however, the resulting VPP optimization problem turns into a mixed-integer one