In the equation, Oe is the error variation in the chamber temperatureand superheat while ts refers to the sampling time. Practically, the valueof Oe is determined by the dynamic characteristics of chamber tem-perature and superheat obtained from the dynamic experimental re-sults. Fig. 5(a) presents the chamber temperature variation when thecompressor frequency was abrupty changed from 40 Hz to 60Hz (EEV60%, 2.1 kW). The MF range of input variable ee was determined tobe土0.025 °C/s from Eq. (3) because the maximum error variation inthe chamber temperature during a 30-second period was determined tobe土0.75 °C from the dynamic experiment. Fig. 5(b) shows the super-heat vari ation when the opening angle was changed from 70% to 55%(40Hz, 1.8 kW) stepwise. The MF range of input ee was determinedas土0.05 °C/s from Eq. (3).fig. 6 shows the systematically designed MF's explained above forcontrolling a compressor and an EEV.2.3. Simulations and experiments to analyze infuence of MF rangeComputer simulations were performed to confirmn the validity of thedesigned MFs. Table 3 shows the major specifications of the test VSRSfor simulations and experiments. Table 4 presents the testing range ofMFs including the sampling time for simulations and experiments. Thetested ranges inevitably had some influence on the control perfor-mance. The proposed range from the approach described in Section 2.2is denoted as the“criterion" value in this table. In order to analyze theireffects on the control performance, two different range sets were pre-pared.Fig.7 shows the control block diagram used for the simulation toanalyze the effects of the MF range of input and output variables on thecontrol performance and to verify the feasibility of the designed MFs.The ranges of input variable e and error change rate ee were in-vestigated in the simulation. Since ee can be defined as 0e/ts, the