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When the device is installed far to the receiving end bus and close to the receiving end in case unified power flow controller (UPFC) device is now recognized as one of the most important flexible AC transmission systems (FACTS) device since it can provide various type of compensation, i.e. voltage regulator, phase shifting regulation, impedance compensation and reactive compensation. It has been proved that the mid-point of a transmission line is the optimal location for some FACTS devices or reactive power support and the proof is based on the linear load, which is not valid practically. The validity of the above optimal location of pulse width modulation (PWM) based UPFC device is investigated when the non-linear load model is considered. In this paper, the UPFC as a voltage regulator applied to a linear and non-linear load is modelled and analysed. It was found that the optimum installation position for this device is at the receiving end bus in case of linear load, while it is at the sending end bus in case of non-linear load, where wide range of active power can be controlled. However, the wide range of reactive power can be controlled of non-linear load.